diff options
Diffstat (limited to 'docs/rfc')
| -rw-r--r-- | docs/rfc/rfc1035.txt | 3078 | ||||
| -rw-r--r-- | docs/rfc/rfc1413.txt | 452 | ||||
| -rw-r--r-- | docs/rfc/rfc1459.txt | 3644 |
3 files changed, 7171 insertions, 3 deletions
diff --git a/docs/rfc/rfc1035.txt b/docs/rfc/rfc1035.txt index 007e3c028..b1a9bf5a9 100644 --- a/docs/rfc/rfc1035.txt +++ b/docs/rfc/rfc1035.txt @@ -1 +1,3077 @@ -Network Working Group P. Mockapetris
Request for Comments: 1035 ISI
November 1987
Obsoletes: RFCs 882, 883, 973
DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION
1. STATUS OF THIS MEMO
This RFC describes the details of the domain system and protocol, and
assumes that the reader is familiar with the concepts discussed in a
companion RFC, "Domain Names - Concepts and Facilities" [RFC-1034].
The domain system is a mixture of functions and data types which are an
official protocol and functions and data types which are still
experimental. Since the domain system is intentionally extensible, new
data types and experimental behavior should always be expected in parts
of the system beyond the official protocol. The official protocol parts
include standard queries, responses and the Internet class RR data
formats (e.g., host addresses). Since the previous RFC set, several
definitions have changed, so some previous definitions are obsolete.
Experimental or obsolete features are clearly marked in these RFCs, and
such information should be used with caution.
The reader is especially cautioned not to depend on the values which
appear in examples to be current or complete, since their purpose is
primarily pedagogical. Distribution of this memo is unlimited.
Table of Contents
1. STATUS OF THIS MEMO 1
2. INTRODUCTION 3
2.1. Overview 3
2.2. Common configurations 4
2.3. Conventions 7
2.3.1. Preferred name syntax 7
2.3.2. Data Transmission Order 8
2.3.3. Character Case 9
2.3.4. Size limits 10
3. DOMAIN NAME SPACE AND RR DEFINITIONS 10
3.1. Name space definitions 10
3.2. RR definitions 11
3.2.1. Format 11
3.2.2. TYPE values 12
3.2.3. QTYPE values 12
3.2.4. CLASS values 13
Mockapetris [Page 1]
RFC 1035 Domain Implementation and Specification November 1987
3.2.5. QCLASS values 13
3.3. Standard RRs 13
3.3.1. CNAME RDATA format 14
3.3.2. HINFO RDATA format 14
3.3.3. MB RDATA format (EXPERIMENTAL) 14
3.3.4. MD RDATA format (Obsolete) 15
3.3.5. MF RDATA format (Obsolete) 15
3.3.6. MG RDATA format (EXPERIMENTAL) 16
3.3.7. MINFO RDATA format (EXPERIMENTAL) 16
3.3.8. MR RDATA format (EXPERIMENTAL) 17
3.3.9. MX RDATA format 17
3.3.10. NULL RDATA format (EXPERIMENTAL) 17
3.3.11. NS RDATA format 18
3.3.12. PTR RDATA format 18
3.3.13. SOA RDATA format 19
3.3.14. TXT RDATA format 20
3.4. ARPA Internet specific RRs 20
3.4.1. A RDATA format 20
3.4.2. WKS RDATA format 21
3.5. IN-ADDR.ARPA domain 22
3.6. Defining new types, classes, and special namespaces 24
4. MESSAGES 25
4.1. Format 25
4.1.1. Header section format 26
4.1.2. Question section format 28
4.1.3. Resource record format 29
4.1.4. Message compression 30
4.2. Transport 32
4.2.1. UDP usage 32
4.2.2. TCP usage 32
5. MASTER FILES 33
5.1. Format 33
5.2. Use of master files to define zones 35
5.3. Master file example 36
6. NAME SERVER IMPLEMENTATION 37
6.1. Architecture 37
6.1.1. Control 37
6.1.2. Database 37
6.1.3. Time 39
6.2. Standard query processing 39
6.3. Zone refresh and reload processing 39
6.4. Inverse queries (Optional) 40
6.4.1. The contents of inverse queries and responses 40
6.4.2. Inverse query and response example 41
6.4.3. Inverse query processing 42
Mockapetris [Page 2]
RFC 1035 Domain Implementation and Specification November 1987
6.5. Completion queries and responses 42
7. RESOLVER IMPLEMENTATION 43
7.1. Transforming a user request into a query 43
7.2. Sending the queries 44
7.3. Processing responses 46
7.4. Using the cache 47
8. MAIL SUPPORT 47
8.1. Mail exchange binding 48
8.2. Mailbox binding (Experimental) 48
9. REFERENCES and BIBLIOGRAPHY 50
Index 54
2. INTRODUCTION
2.1. Overview
The goal of domain names is to provide a mechanism for naming resources
in such a way that the names are usable in different hosts, networks,
protocol families, internets, and administrative organizations.
From the user's point of view, domain names are useful as arguments to a
local agent, called a resolver, which retrieves information associated
with the domain name. Thus a user might ask for the host address or
mail information associated with a particular domain name. To enable
the user to request a particular type of information, an appropriate
query type is passed to the resolver with the domain name. To the user,
the domain tree is a single information space; the resolver is
responsible for hiding the distribution of data among name servers from
the user.
From the resolver's point of view, the database that makes up the domain
space is distributed among various name servers. Different parts of the
domain space are stored in different name servers, although a particular
data item will be stored redundantly in two or more name servers. The
resolver starts with knowledge of at least one name server. When the
resolver processes a user query it asks a known name server for the
information; in return, the resolver either receives the desired
information or a referral to another name server. Using these
referrals, resolvers learn the identities and contents of other name
servers. Resolvers are responsible for dealing with the distribution of
the domain space and dealing with the effects of name server failure by
consulting redundant databases in other servers.
Name servers manage two kinds of data. The first kind of data held in
sets called zones; each zone is the complete database for a particular
"pruned" subtree of the domain space. This data is called
authoritative. A name server periodically checks to make sure that its
zones are up to date, and if not, obtains a new copy of updated zones
Mockapetris [Page 3]
RFC 1035 Domain Implementation and Specification November 1987
from master files stored locally or in another name server. The second
kind of data is cached data which was acquired by a local resolver.
This data may be incomplete, but improves the performance of the
retrieval process when non-local data is repeatedly accessed. Cached
data is eventually discarded by a timeout mechanism.
This functional structure isolates the problems of user interface,
failure recovery, and distribution in the resolvers and isolates the
database update and refresh problems in the name servers.
2.2. Common configurations
A host can participate in the domain name system in a number of ways,
depending on whether the host runs programs that retrieve information
from the domain system, name servers that answer queries from other
hosts, or various combinations of both functions. The simplest, and
perhaps most typical, configuration is shown below:
Local Host | Foreign
|
+---------+ +----------+ | +--------+
| | user queries | |queries | | |
| User |-------------->| |---------|->|Foreign |
| Program | | Resolver | | | Name |
| |<--------------| |<--------|--| Server |
| | user responses| |responses| | |
+---------+ +----------+ | +--------+
| A |
cache additions | | references |
V | |
+----------+ |
| cache | |
+----------+ |
User programs interact with the domain name space through resolvers; the
format of user queries and user responses is specific to the host and
its operating system. User queries will typically be operating system
calls, and the resolver and its cache will be part of the host operating
system. Less capable hosts may choose to implement the resolver as a
subroutine to be linked in with every program that needs its services.
Resolvers answer user queries with information they acquire via queries
to foreign name servers and the local cache.
Note that the resolver may have to make several queries to several
different foreign name servers to answer a particular user query, and
hence the resolution of a user query may involve several network
accesses and an arbitrary amount of time. The queries to foreign name
servers and the corresponding responses have a standard format described
Mockapetris [Page 4]
RFC 1035 Domain Implementation and Specification November 1987
in this memo, and may be datagrams.
Depending on its capabilities, a name server could be a stand alone
program on a dedicated machine or a process or processes on a large
timeshared host. A simple configuration might be:
Local Host | Foreign
|
+---------+ |
/ /| |
+---------+ | +----------+ | +--------+
| | | | |responses| | |
| | | | Name |---------|->|Foreign |
| Master |-------------->| Server | | |Resolver|
| files | | | |<--------|--| |
| |/ | | queries | +--------+
+---------+ +----------+ |
Here a primary name server acquires information about one or more zones
by reading master files from its local file system, and answers queries
about those zones that arrive from foreign resolvers.
The DNS requires that all zones be redundantly supported by more than
one name server. Designated secondary servers can acquire zones and
check for updates from the primary server using the zone transfer
protocol of the DNS. This configuration is shown below:
Local Host | Foreign
|
+---------+ |
/ /| |
+---------+ | +----------+ | +--------+
| | | | |responses| | |
| | | | Name |---------|->|Foreign |
| Master |-------------->| Server | | |Resolver|
| files | | | |<--------|--| |
| |/ | | queries | +--------+
+---------+ +----------+ |
A |maintenance | +--------+
| +------------|->| |
| queries | |Foreign |
| | | Name |
+------------------|--| Server |
maintenance responses | +--------+
In this configuration, the name server periodically establishes a
virtual circuit to a foreign name server to acquire a copy of a zone or
to check that an existing copy has not changed. The messages sent for
Mockapetris [Page 5]
RFC 1035 Domain Implementation and Specification November 1987
these maintenance activities follow the same form as queries and
responses, but the message sequences are somewhat different.
The information flow in a host that supports all aspects of the domain
name system is shown below:
Local Host | Foreign
|
+---------+ +----------+ | +--------+
| | user queries | |queries | | |
| User |-------------->| |---------|->|Foreign |
| Program | | Resolver | | | Name |
| |<--------------| |<--------|--| Server |
| | user responses| |responses| | |
+---------+ +----------+ | +--------+
| A |
cache additions | | references |
V | |
+----------+ |
| Shared | |
| database | |
+----------+ |
A | |
+---------+ refreshes | | references |
/ /| | V |
+---------+ | +----------+ | +--------+
| | | | |responses| | |
| | | | Name |---------|->|Foreign |
| Master |-------------->| Server | | |Resolver|
| files | | | |<--------|--| |
| |/ | | queries | +--------+
+---------+ +----------+ |
A |maintenance | +--------+
| +------------|->| |
| queries | |Foreign |
| | | Name |
+------------------|--| Server |
maintenance responses | +--------+
The shared database holds domain space data for the local name server
and resolver. The contents of the shared database will typically be a
mixture of authoritative data maintained by the periodic refresh
operations of the name server and cached data from previous resolver
requests. The structure of the domain data and the necessity for
synchronization between name servers and resolvers imply the general
characteristics of this database, but the actual format is up to the
local implementor.
Mockapetris [Page 6]
RFC 1035 Domain Implementation and Specification November 1987
Information flow can also be tailored so that a group of hosts act
together to optimize activities. Sometimes this is done to offload less
capable hosts so that they do not have to implement a full resolver.
This can be appropriate for PCs or hosts which want to minimize the
amount of new network code which is required. This scheme can also
allow a group of hosts can share a small number of caches rather than
maintaining a large number of separate caches, on the premise that the
centralized caches will have a higher hit ratio. In either case,
resolvers are replaced with stub resolvers which act as front ends to
resolvers located in a recursive server in one or more name servers
known to perform that service:
Local Hosts | Foreign
|
+---------+ |
| | responses |
| Stub |<--------------------+ |
| Resolver| | |
| |----------------+ | |
+---------+ recursive | | |
queries | | |
V | |
+---------+ recursive +----------+ | +--------+
| | queries | |queries | | |
| Stub |-------------->| Recursive|---------|->|Foreign |
| Resolver| | Server | | | Name |
| |<--------------| |<--------|--| Server |
+---------+ responses | |responses| | |
+----------+ | +--------+
| Central | |
| cache | |
+----------+ |
In any case, note that domain components are always replicated for
reliability whenever possible.
2.3. Conventions
The domain system has several conventions dealing with low-level, but
fundamental, issues. While the implementor is free to violate these
conventions WITHIN HIS OWN SYSTEM, he must observe these conventions in
ALL behavior observed from other hosts.
2.3.1. Preferred name syntax
The DNS specifications attempt to be as general as possible in the rules
for constructing domain names. The idea is that the name of any
existing object can be expressed as a domain name with minimal changes.
Mockapetris [Page 7]
RFC 1035 Domain Implementation and Specification November 1987
However, when assigning a domain name for an object, the prudent user
will select a name which satisfies both the rules of the domain system
and any existing rules for the object, whether these rules are published
or implied by existing programs.
For example, when naming a mail domain, the user should satisfy both the
rules of this memo and those in RFC-822. When creating a new host name,
the old rules for HOSTS.TXT should be followed. This avoids problems
when old software is converted to use domain names.
The following syntax will result in fewer problems with many
applications that use domain names (e.g., mail, TELNET).
<domain> ::= <subdomain> | " "
<subdomain> ::= <label> | <subdomain> "." <label>
<label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]
<ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str>
<let-dig-hyp> ::= <let-dig> | "-"
<let-dig> ::= <letter> | <digit>
<letter> ::= any one of the 52 alphabetic characters A through Z in
upper case and a through z in lower case
<digit> ::= any one of the ten digits 0 through 9
Note that while upper and lower case letters are allowed in domain
names, no significance is attached to the case. That is, two names with
the same spelling but different case are to be treated as if identical.
The labels must follow the rules for ARPANET host names. They must
start with a letter, end with a letter or digit, and have as interior
characters only letters, digits, and hyphen. There are also some
restrictions on the length. Labels must be 63 characters or less.
For example, the following strings identify hosts in the Internet:
A.ISI.EDU XX.LCS.MIT.EDU SRI-NIC.ARPA
2.3.2. Data Transmission Order
The order of transmission of the header and data described in this
document is resolved to the octet level. Whenever a diagram shows a
Mockapetris [Page 8]
RFC 1035 Domain Implementation and Specification November 1987
group of octets, the order of transmission of those octets is the normal
order in which they are read in English. For example, in the following
diagram, the octets are transmitted in the order they are numbered.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Whenever an octet represents a numeric quantity, the left most bit in
the diagram is the high order or most significant bit. That is, the bit
labeled 0 is the most significant bit. For example, the following
diagram represents the value 170 (decimal).
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1 0 1 0 1 0 1 0|
+-+-+-+-+-+-+-+-+
Similarly, whenever a multi-octet field represents a numeric quantity
the left most bit of the whole field is the most significant bit. When
a multi-octet quantity is transmitted the most significant octet is
transmitted first.
2.3.3. Character Case
For all parts of the DNS that are part of the official protocol, all
comparisons between character strings (e.g., labels, domain names, etc.)
are done in a case-insensitive manner. At present, this rule is in
force throughout the domain system without exception. However, future
additions beyond current usage may need to use the full binary octet
capabilities in names, so attempts to store domain names in 7-bit ASCII
or use of special bytes to terminate labels, etc., should be avoided.
When data enters the domain system, its original case should be
preserved whenever possible. In certain circumstances this cannot be
done. For example, if two RRs are stored in a database, one at x.y and
one at X.Y, they are actually stored at the same place in the database,
and hence only one casing would be preserved. The basic rule is that
case can be discarded only when data is used to define structure in a
database, and two names are identical when compared in a case
insensitive manner.
Mockapetris [Page 9]
RFC 1035 Domain Implementation and Specification November 1987
Loss of case sensitive data must be minimized. Thus while data for x.y
and X.Y may both be stored under a single location x.y or X.Y, data for
a.x and B.X would never be stored under A.x, A.X, b.x, or b.X. In
general, this preserves the case of the first label of a domain name,
but forces standardization of interior node labels.
Systems administrators who enter data into the domain database should
take care to represent the data they supply to the domain system in a
case-consistent manner if their system is case-sensitive. The data
distribution system in the domain system will ensure that consistent
representations are preserved.
2.3.4. Size limits
Various objects and parameters in the DNS have size limits. They are
listed below. Some could be easily changed, others are more
fundamental.
labels 63 octets or less
names 255 octets or less
TTL positive values of a signed 32 bit number.
UDP messages 512 octets or less
3. DOMAIN NAME SPACE AND RR DEFINITIONS
3.1. Name space definitions
Domain names in messages are expressed in terms of a sequence of labels.
Each label is represented as a one octet length field followed by that
number of octets. Since every domain name ends with the null label of
the root, a domain name is terminated by a length byte of zero. The
high order two bits of every length octet must be zero, and the
remaining six bits of the length field limit the label to 63 octets or
less.
To simplify implementations, the total length of a domain name (i.e.,
label octets and label length octets) is restricted to 255 octets or
less.
Although labels can contain any 8 bit values in octets that make up a
label, it is strongly recommended that labels follow the preferred
syntax described elsewhere in this memo, which is compatible with
existing host naming conventions. Name servers and resolvers must
compare labels in a case-insensitive manner (i.e., A=a), assuming ASCII
with zero parity. Non-alphabetic codes must match exactly.
Mockapetris [Page 10]
RFC 1035 Domain Implementation and Specification November 1987
3.2. RR definitions
3.2.1. Format
All RRs have the same top level format shown below:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
/ /
/ NAME /
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| CLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TTL |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| RDLENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
/ RDATA /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
NAME an owner name, i.e., the name of the node to which this
resource record pertains.
TYPE two octets containing one of the RR TYPE codes.
CLASS two octets containing one of the RR CLASS codes.
TTL a 32 bit signed integer that specifies the time interval
that the resource record may be cached before the source
of the information should again be consulted. Zero
values are interpreted to mean that the RR can only be
used for the transaction in progress, and should not be
cached. For example, SOA records are always distributed
with a zero TTL to prohibit caching. Zero values can
also be used for extremely volatile data.
RDLENGTH an unsigned 16 bit integer that specifies the length in
octets of the RDATA field.
Mockapetris [Page 11]
RFC 1035 Domain Implementation and Specification November 1987
RDATA a variable length string of octets that describes the
resource. The format of this information varies
according to the TYPE and CLASS of the resource record.
3.2.2. TYPE values
TYPE fields are used in resource records. Note that these types are a
subset of QTYPEs.
TYPE value and meaning
A 1 a host address
NS 2 an authoritative name server
MD 3 a mail destination (Obsolete - use MX)
MF 4 a mail forwarder (Obsolete - use MX)
CNAME 5 the canonical name for an alias
SOA 6 marks the start of a zone of authority
MB 7 a mailbox domain name (EXPERIMENTAL)
MG 8 a mail group member (EXPERIMENTAL)
MR 9 a mail rename domain name (EXPERIMENTAL)
NULL 10 a null RR (EXPERIMENTAL)
WKS 11 a well known service description
PTR 12 a domain name pointer
HINFO 13 host information
MINFO 14 mailbox or mail list information
MX 15 mail exchange
TXT 16 text strings
3.2.3. QTYPE values
QTYPE fields appear in the question part of a query. QTYPES are a
superset of TYPEs, hence all TYPEs are valid QTYPEs. In addition, the
following QTYPEs are defined:
Mockapetris [Page 12]
RFC 1035 Domain Implementation and Specification November 1987
AXFR 252 A request for a transfer of an entire zone
MAILB 253 A request for mailbox-related records (MB, MG or MR)
MAILA 254 A request for mail agent RRs (Obsolete - see MX)
* 255 A request for all records
3.2.4. CLASS values
CLASS fields appear in resource records. The following CLASS mnemonics
and values are defined:
IN 1 the Internet
CS 2 the CSNET class (Obsolete - used only for examples in
some obsolete RFCs)
CH 3 the CHAOS class
HS 4 Hesiod [Dyer 87]
3.2.5. QCLASS values
QCLASS fields appear in the question section of a query. QCLASS values
are a superset of CLASS values; every CLASS is a valid QCLASS. In
addition to CLASS values, the following QCLASSes are defined:
* 255 any class
3.3. Standard RRs
The following RR definitions are expected to occur, at least
potentially, in all classes. In particular, NS, SOA, CNAME, and PTR
will be used in all classes, and have the same format in all classes.
Because their RDATA format is known, all domain names in the RDATA
section of these RRs may be compressed.
<domain-name> is a domain name represented as a series of labels, and
terminated by a label with zero length. <character-string> is a single
length octet followed by that number of characters. <character-string>
is treated as binary information, and can be up to 256 characters in
length (including the length octet).
Mockapetris [Page 13]
RFC 1035 Domain Implementation and Specification November 1987
3.3.1. CNAME RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ CNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
CNAME A <domain-name> which specifies the canonical or primary
name for the owner. The owner name is an alias.
CNAME RRs cause no additional section processing, but name servers may
choose to restart the query at the canonical name in certain cases. See
the description of name server logic in [RFC-1034] for details.
3.3.2. HINFO RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ CPU /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ OS /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
CPU A <character-string> which specifies the CPU type.
OS A <character-string> which specifies the operating
system type.
Standard values for CPU and OS can be found in [RFC-1010].
HINFO records are used to acquire general information about a host. The
main use is for protocols such as FTP that can use special procedures
when talking between machines or operating systems of the same type.
3.3.3. MB RDATA format (EXPERIMENTAL)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ MADNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
MADNAME A <domain-name> which specifies a host which has the
specified mailbox.
Mockapetris [Page 14]
RFC 1035 Domain Implementation and Specification November 1987
MB records cause additional section processing which looks up an A type
RRs corresponding to MADNAME.
3.3.4. MD RDATA format (Obsolete)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ MADNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
MADNAME A <domain-name> which specifies a host which has a mail
agent for the domain which should be able to deliver
mail for the domain.
MD records cause additional section processing which looks up an A type
record corresponding to MADNAME.
MD is obsolete. See the definition of MX and [RFC-974] for details of
the new scheme. The recommended policy for dealing with MD RRs found in
a master file is to reject them, or to convert them to MX RRs with a
preference of 0.
3.3.5. MF RDATA format (Obsolete)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ MADNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
MADNAME A <domain-name> which specifies a host which has a mail
agent for the domain which will accept mail for
forwarding to the domain.
MF records cause additional section processing which looks up an A type
record corresponding to MADNAME.
MF is obsolete. See the definition of MX and [RFC-974] for details ofw
the new scheme. The recommended policy for dealing with MD RRs found in
a master file is to reject them, or to convert them to MX RRs with a
preference of 10.
Mockapetris [Page 15]
RFC 1035 Domain Implementation and Specification November 1987
3.3.6. MG RDATA format (EXPERIMENTAL)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ MGMNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
MGMNAME A <domain-name> which specifies a mailbox which is a
member of the mail group specified by the domain name.
MG records cause no additional section processing.
3.3.7. MINFO RDATA format (EXPERIMENTAL)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ RMAILBX /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ EMAILBX /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
RMAILBX A <domain-name> which specifies a mailbox which is
responsible for the mailing list or mailbox. If this
domain name names the root, the owner of the MINFO RR is
responsible for itself. Note that many existing mailing
lists use a mailbox X-request for the RMAILBX field of
mailing list X, e.g., Msgroup-request for Msgroup. This
field provides a more general mechanism.
EMAILBX A <domain-name> which specifies a mailbox which is to
receive error messages related to the mailing list or
mailbox specified by the owner of the MINFO RR (similar
to the ERRORS-TO: field which has been proposed). If
this domain name names the root, errors should be
returned to the sender of the message.
MINFO records cause no additional section processing. Although these
records can be associated with a simple mailbox, they are usually used
with a mailing list.
Mockapetris [Page 16]
RFC 1035 Domain Implementation and Specification November 1987
3.3.8. MR RDATA format (EXPERIMENTAL)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ NEWNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
NEWNAME A <domain-name> which specifies a mailbox which is the
proper rename of the specified mailbox.
MR records cause no additional section processing. The main use for MR
is as a forwarding entry for a user who has moved to a different
mailbox.
3.3.9. MX RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| PREFERENCE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ EXCHANGE /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
PREFERENCE A 16 bit integer which specifies the preference given to
this RR among others at the same owner. Lower values
are preferred.
EXCHANGE A <domain-name> which specifies a host willing to act as
a mail exchange for the owner name.
MX records cause type A additional section processing for the host
specified by EXCHANGE. The use of MX RRs is explained in detail in
[RFC-974].
3.3.10. NULL RDATA format (EXPERIMENTAL)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ <anything> /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Anything at all may be in the RDATA field so long as it is 65535 octets
or less.
Mockapetris [Page 17]
RFC 1035 Domain Implementation and Specification November 1987
NULL records cause no additional section processing. NULL RRs are not
allowed in master files. NULLs are used as placeholders in some
experimental extensions of the DNS.
3.3.11. NS RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ NSDNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
NSDNAME A <domain-name> which specifies a host which should be
authoritative for the specified class and domain.
NS records cause both the usual additional section processing to locate
a type A record, and, when used in a referral, a special search of the
zone in which they reside for glue information.
The NS RR states that the named host should be expected to have a zone
starting at owner name of the specified class. Note that the class may
not indicate the protocol family which should be used to communicate
with the host, although it is typically a strong hint. For example,
hosts which are name servers for either Internet (IN) or Hesiod (HS)
class information are normally queried using IN class protocols.
3.3.12. PTR RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ PTRDNAME /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
PTRDNAME A <domain-name> which points to some location in the
domain name space.
PTR records cause no additional section processing. These RRs are used
in special domains to point to some other location in the domain space.
These records are simple data, and don't imply any special processing
similar to that performed by CNAME, which identifies aliases. See the
description of the IN-ADDR.ARPA domain for an example.
Mockapetris [Page 18]
RFC 1035 Domain Implementation and Specification November 1987
3.3.13. SOA RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ MNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ RNAME /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SERIAL |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| REFRESH |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| RETRY |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| EXPIRE |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| MINIMUM |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
MNAME The <domain-name> of the name server that was the
original or primary source of data for this zone.
RNAME A <domain-name> which specifies the mailbox of the
person responsible for this zone.
SERIAL The unsigned 32 bit version number of the original copy
of the zone. Zone transfers preserve this value. This
value wraps and should be compared using sequence space
arithmetic.
REFRESH A 32 bit time interval before the zone should be
refreshed.
RETRY A 32 bit time interval that should elapse before a
failed refresh should be retried.
EXPIRE A 32 bit time value that specifies the upper limit on
the time interval that can elapse before the zone is no
longer authoritative.
Mockapetris [Page 19]
RFC 1035 Domain Implementation and Specification November 1987
MINIMUM The unsigned 32 bit minimum TTL field that should be
exported with any RR from this zone.
SOA records cause no additional section processing.
All times are in units of seconds.
Most of these fields are pertinent only for name server maintenance
operations. However, MINIMUM is used in all query operations that
retrieve RRs from a zone. Whenever a RR is sent in a response to a
query, the TTL field is set to the maximum of the TTL field from the RR
and the MINIMUM field in the appropriate SOA. Thus MINIMUM is a lower
bound on the TTL field for all RRs in a zone. Note that this use of
MINIMUM should occur when the RRs are copied into the response and not
when the zone is loaded from a master file or via a zone transfer. The
reason for this provison is to allow future dynamic update facilities to
change the SOA RR with known semantics.
3.3.14. TXT RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ TXT-DATA /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
TXT-DATA One or more <character-string>s.
TXT RRs are used to hold descriptive text. The semantics of the text
depends on the domain where it is found.
3.4. Internet specific RRs
3.4.1. A RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
ADDRESS A 32 bit Internet address.
Hosts that have multiple Internet addresses will have multiple A
records.
Mockapetris [Page 20]
RFC 1035 Domain Implementation and Specification November 1987
A records cause no additional section processing. The RDATA section of
an A line in a master file is an Internet address expressed as four
decimal numbers separated by dots without any imbedded spaces (e.g.,
"10.2.0.52" or "192.0.5.6").
3.4.2. WKS RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ADDRESS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| PROTOCOL | |
+--+--+--+--+--+--+--+--+ |
| |
/ <BIT MAP> /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
ADDRESS An 32 bit Internet address
PROTOCOL An 8 bit IP protocol number
<BIT MAP> A variable length bit map. The bit map must be a
multiple of 8 bits long.
The WKS record is used to describe the well known services supported by
a particular protocol on a particular internet address. The PROTOCOL
field specifies an IP protocol number, and the bit map has one bit per
port of the specified protocol. The first bit corresponds to port 0,
the second to port 1, etc. If the bit map does not include a bit for a
protocol of interest, that bit is assumed zero. The appropriate values
and mnemonics for ports and protocols are specified in [RFC-1010].
For example, if PROTOCOL=TCP (6), the 26th bit corresponds to TCP port
25 (SMTP). If this bit is set, a SMTP server should be listening on TCP
port 25; if zero, SMTP service is not supported on the specified
address.
The purpose of WKS RRs is to provide availability information for
servers for TCP and UDP. If a server supports both TCP and UDP, or has
multiple Internet addresses, then multiple WKS RRs are used.
WKS RRs cause no additional section processing.
In master files, both ports and protocols are expressed using mnemonics
or decimal numbers.
Mockapetris [Page 21]
RFC 1035 Domain Implementation and Specification November 1987
3.5. IN-ADDR.ARPA domain
The Internet uses a special domain to support gateway location and
Internet address to host mapping. Other classes may employ a similar
strategy in other domains. The intent of this domain is to provide a
guaranteed method to perform host address to host name mapping, and to
facilitate queries to locate all gateways on a particular network in the
Internet.
Note that both of these services are similar to functions that could be
performed by inverse queries; the difference is that this part of the
domain name space is structured according to address, and hence can
guarantee that the appropriate data can be located without an exhaustive
search of the domain space.
The domain begins at IN-ADDR.ARPA and has a substructure which follows
the Internet addressing structure.
Domain names in the IN-ADDR.ARPA domain are defined to have up to four
labels in addition to the IN-ADDR.ARPA suffix. Each label represents
one octet of an Internet address, and is expressed as a character string
for a decimal value in the range 0-255 (with leading zeros omitted
except in the case of a zero octet which is represented by a single
zero).
Host addresses are represented by domain names that have all four labels
specified. Thus data for Internet address 10.2.0.52 is located at
domain name 52.0.2.10.IN-ADDR.ARPA. The reversal, though awkward to
read, allows zones to be delegated which are exactly one network of
address space. For example, 10.IN-ADDR.ARPA can be a zone containing
data for the ARPANET, while 26.IN-ADDR.ARPA can be a separate zone for
MILNET. Address nodes are used to hold pointers to primary host names
in the normal domain space.
Network numbers correspond to some non-terminal nodes at various depths
in the IN-ADDR.ARPA domain, since Internet network numbers are either 1,
2, or 3 octets. Network nodes are used to hold pointers to the primary
host names of gateways attached to that network. Since a gateway is, by
definition, on more than one network, it will typically have two or more
network nodes which point at it. Gateways will also have host level
pointers at their fully qualified addresses.
Both the gateway pointers at network nodes and the normal host pointers
at full address nodes use the PTR RR to point back to the primary domain
names of the corresponding hosts.
For example, the IN-ADDR.ARPA domain will contain information about the
ISI gateway between net 10 and 26, an MIT gateway from net 10 to MIT's
Mockapetris [Page 22]
RFC 1035 Domain Implementation and Specification November 1987
net 18, and hosts A.ISI.EDU and MULTICS.MIT.EDU. Assuming that ISI
gateway has addresses 10.2.0.22 and 26.0.0.103, and a name MILNET-
GW.ISI.EDU, and the MIT gateway has addresses 10.0.0.77 and 18.10.0.4
and a name GW.LCS.MIT.EDU, the domain database would contain:
10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
18.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
26.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
22.0.2.10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
103.0.0.26.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
77.0.0.10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
4.0.10.18.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
103.0.3.26.IN-ADDR.ARPA. PTR A.ISI.EDU.
6.0.0.10.IN-ADDR.ARPA. PTR MULTICS.MIT.EDU.
Thus a program which wanted to locate gateways on net 10 would originate
a query of the form QTYPE=PTR, QCLASS=IN, QNAME=10.IN-ADDR.ARPA. It
would receive two RRs in response:
10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
The program could then originate QTYPE=A, QCLASS=IN queries for MILNET-
GW.ISI.EDU. and GW.LCS.MIT.EDU. to discover the Internet addresses of
these gateways.
A resolver which wanted to find the host name corresponding to Internet
host address 10.0.0.6 would pursue a query of the form QTYPE=PTR,
QCLASS=IN, QNAME=6.0.0.10.IN-ADDR.ARPA, and would receive:
6.0.0.10.IN-ADDR.ARPA. PTR MULTICS.MIT.EDU.
Several cautions apply to the use of these services:
- Since the IN-ADDR.ARPA special domain and the normal domain
for a particular host or gateway will be in different zones,
the possibility exists that that the data may be inconsistent.
- Gateways will often have two names in separate domains, only
one of which can be primary.
- Systems that use the domain database to initialize their
routing tables must start with enough gateway information to
guarantee that they can access the appropriate name server.
- The gateway data only reflects the existence of a gateway in a
manner equivalent to the current HOSTS.TXT file. It doesn't
replace the dynamic availability information from GGP or EGP.
Mockapetris [Page 23]
RFC 1035 Domain Implementation and Specification November 1987
3.6. Defining new types, classes, and special namespaces
The previously defined types and classes are the ones in use as of the
date of this memo. New definitions should be expected. This section
makes some recommendations to designers considering additions to the
existing facilities. The mailing list NAMEDROPPERS@SRI-NIC.ARPA is the
forum where general discussion of design issues takes place.
In general, a new type is appropriate when new information is to be
added to the database about an existing object, or we need new data
formats for some totally new object. Designers should attempt to define
types and their RDATA formats that are generally applicable to all
classes, and which avoid duplication of information. New classes are
appropriate when the DNS is to be used for a new protocol, etc which
requires new class-specific data formats, or when a copy of the existing
name space is desired, but a separate management domain is necessary.
New types and classes need mnemonics for master files; the format of the
master files requires that the mnemonics for type and class be disjoint.
TYPE and CLASS values must be a proper subset of QTYPEs and QCLASSes
respectively.
The present system uses multiple RRs to represent multiple values of a
type rather than storing multiple values in the RDATA section of a
single RR. This is less efficient for most applications, but does keep
RRs shorter. The multiple RRs assumption is incorporated in some
experimental work on dynamic update methods.
The present system attempts to minimize the duplication of data in the
database in order to insure consistency. Thus, in order to find the
address of the host for a mail exchange, you map the mail domain name to
a host name, then the host name to addresses, rather than a direct
mapping to host address. This approach is preferred because it avoids
the opportunity for inconsistency.
In defining a new type of data, multiple RR types should not be used to
create an ordering between entries or express different formats for
equivalent bindings, instead this information should be carried in the
body of the RR and a single type used. This policy avoids problems with
caching multiple types and defining QTYPEs to match multiple types.
For example, the original form of mail exchange binding used two RR
types one to represent a "closer" exchange (MD) and one to represent a
"less close" exchange (MF). The difficulty is that the presence of one
RR type in a cache doesn't convey any information about the other
because the query which acquired the cached information might have used
a QTYPE of MF, MD, or MAILA (which matched both). The redesigned
Mockapetris [Page 24]
RFC 1035 Domain Implementation and Specification November 1987
service used a single type (MX) with a "preference" value in the RDATA
section which can order different RRs. However, if any MX RRs are found
in the cache, then all should be there.
4. MESSAGES
4.1. Format
All communications inside of the domain protocol are carried in a single
format called a message. The top level format of message is divided
into 5 sections (some of which are empty in certain cases) shown below:
+---------------------+
| Header |
+---------------------+
| Question | the question for the name server
+---------------------+
| Answer | RRs answering the question
+---------------------+
| Authority | RRs pointing toward an authority
+---------------------+
| Additional | RRs holding additional information
+---------------------+
The header section is always present. The header includes fields that
specify which of the remaining sections are present, and also specify
whether the message is a query or a response, a standard query or some
other opcode, etc.
The names of the sections after the header are derived from their use in
standard queries. The question section contains fields that describe a
question to a name server. These fields are a query type (QTYPE), a
query class (QCLASS), and a query domain name (QNAME). The last three
sections have the same format: a possibly empty list of concatenated
resource records (RRs). The answer section contains RRs that answer the
question; the authority section contains RRs that point toward an
authoritative name server; the additional records section contains RRs
which relate to the query, but are not strictly answers for the
question.
Mockapetris [Page 25]
RFC 1035 Domain Implementation and Specification November 1987
4.1.1. Header section format
The header contains the following fields:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode |AA|TC|RD|RA| Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QDCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ANCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| NSCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ARCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
ID A 16 bit identifier assigned by the program that
generates any kind of query. This identifier is copied
the corresponding reply and can be used by the requester
to match up replies to outstanding queries.
QR A one bit field that specifies whether this message is a
query (0), or a response (1).
OPCODE A four bit field that specifies kind of query in this
message. This value is set by the originator of a query
and copied into the response. The values are:
0 a standard query (QUERY)
1 an inverse query (IQUERY)
2 a server status request (STATUS)
3-15 reserved for future use
AA Authoritative Answer - this bit is valid in responses,
and specifies that the responding name server is an
authority for the domain name in question section.
Note that the contents of the answer section may have
multiple owner names because of aliases. The AA bit
Mockapetris [Page 26]
RFC 1035 Domain Implementation and Specification November 1987
corresponds to the name which matches the query name, or
the first owner name in the answer section.
TC TrunCation - specifies that this message was truncated
due to length greater than that permitted on the
transmission channel.
RD Recursion Desired - this bit may be set in a query and
is copied into the response. If RD is set, it directs
the name server to pursue the query recursively.
Recursive query support is optional.
RA Recursion Available - this be is set or cleared in a
response, and denotes whether recursive query support is
available in the name server.
Z Reserved for future use. Must be zero in all queries
and responses.
RCODE Response code - this 4 bit field is set as part of
responses. The values have the following
interpretation:
0 No error condition
1 Format error - The name server was
unable to interpret the query.
2 Server failure - The name server was
unable to process this query due to a
problem with the name server.
3 Name Error - Meaningful only for
responses from an authoritative name
server, this code signifies that the
domain name referenced in the query does
not exist.
4 Not Implemented - The name server does
not support the requested kind of query.
5 Refused - The name server refuses to
perform the specified operation for
policy reasons. For example, a name
server may not wish to provide the
information to the particular requester,
or a name server may not wish to perform
a particular operation (e.g., zone
Mockapetris [Page 27]
RFC 1035 Domain Implementation and Specification November 1987
transfer) for particular data.
6-15 Reserved for future use.
QDCOUNT an unsigned 16 bit integer specifying the number of
entries in the question section.
ANCOUNT an unsigned 16 bit integer specifying the number of
resource records in the answer section.
NSCOUNT an unsigned 16 bit integer specifying the number of name
server resource records in the authority records
section.
ARCOUNT an unsigned 16 bit integer specifying the number of
resource records in the additional records section.
4.1.2. Question section format
The question section is used to carry the "question" in most queries,
i.e., the parameters that define what is being asked. The section
contains QDCOUNT (usually 1) entries, each of the following format:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
/ QNAME /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QTYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QCLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
QNAME a domain name represented as a sequence of labels, where
each label consists of a length octet followed by that
number of octets. The domain name terminates with the
zero length octet for the null label of the root. Note
that this field may be an odd number of octets; no
padding is used.
QTYPE a two octet code which specifies the type of the query.
The values for this field include all codes valid for a
TYPE field, together with some more general codes which
can match more than one type of RR.
Mockapetris [Page 28]
RFC 1035 Domain Implementation and Specification November 1987
QCLASS a two octet code that specifies the class of the query.
For example, the QCLASS field is IN for the Internet.
4.1.3. Resource record format
The answer, authority, and additional sections all share the same
format: a variable number of resource records, where the number of
records is specified in the corresponding count field in the header.
Each resource record has the following format:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
/ /
/ NAME /
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| CLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TTL |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| RDLENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
/ RDATA /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
NAME a domain name to which this resource record pertains.
TYPE two octets containing one of the RR type codes. This
field specifies the meaning of the data in the RDATA
field.
CLASS two octets which specify the class of the data in the
RDATA field.
TTL a 32 bit unsigned integer that specifies the time
interval (in seconds) that the resource record may be
cached before it should be discarded. Zero values are
interpreted to mean that the RR can only be used for the
transaction in progress, and should not be cached.
Mockapetris [Page 29]
RFC 1035 Domain Implementation and Specification November 1987
RDLENGTH an unsigned 16 bit integer that specifies the length in
octets of the RDATA field.
RDATA a variable length string of octets that describes the
resource. The format of this information varies
according to the TYPE and CLASS of the resource record.
For example, the if the TYPE is A and the CLASS is IN,
the RDATA field is a 4 octet ARPA Internet address.
4.1.4. Message compression
In order to reduce the size of messages, the domain system utilizes a
compression scheme which eliminates the repetition of domain names in a
message. In this scheme, an entire domain name or a list of labels at
the end of a domain name is replaced with a pointer to a prior occurance
of the same name.
The pointer takes the form of a two octet sequence:
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| 1 1| OFFSET |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The first two bits are ones. This allows a pointer to be distinguished
from a label, since the label must begin with two zero bits because
labels are restricted to 63 octets or less. (The 10 and 01 combinations
are reserved for future use.) The OFFSET field specifies an offset from
the start of the message (i.e., the first octet of the ID field in the
domain header). A zero offset specifies the first byte of the ID field,
etc.
The compression scheme allows a domain name in a message to be
represented as either:
- a sequence of labels ending in a zero octet
- a pointer
- a sequence of labels ending with a pointer
Pointers can only be used for occurances of a domain name where the
format is not class specific. If this were not the case, a name server
or resolver would be required to know the format of all RRs it handled.
As yet, there are no such cases, but they may occur in future RDATA
formats.
If a domain name is contained in a part of the message subject to a
length field (such as the RDATA section of an RR), and compression is
Mockapetris [Page 30]
RFC 1035 Domain Implementation and Specification November 1987
used, the length of the compressed name is used in the length
calculation, rather than the length of the expanded name.
Programs are free to avoid using pointers in messages they generate,
although this will reduce datagram capacity, and may cause truncation.
However all programs are required to understand arriving messages that
contain pointers.
For example, a datagram might need to use the domain names F.ISI.ARPA,
FOO.F.ISI.ARPA, ARPA, and the root. Ignoring the other fields of the
message, these domain names might be represented as:
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
20 | 1 | F |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
22 | 3 | I |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
24 | S | I |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
26 | 4 | A |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
28 | R | P |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
30 | A | 0 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
40 | 3 | F |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
42 | O | O |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
44 | 1 1| 20 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
64 | 1 1| 26 |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
92 | 0 | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The domain name for F.ISI.ARPA is shown at offset 20. The domain name
FOO.F.ISI.ARPA is shown at offset 40; this definition uses a pointer to
concatenate a label for FOO to the previously defined F.ISI.ARPA. The
domain name ARPA is defined at offset 64 using a pointer to the ARPA
component of the name F.ISI.ARPA at 20; note that this pointer relies on
ARPA being the last label in the string at 20. The root domain name is
Mockapetris [Page 31]
RFC 1035 Domain Implementation and Specification November 1987
defined by a single octet of zeros at 92; the root domain name has no
labels.
4.2. Transport
The DNS assumes that messages will be transmitted as datagrams or in a
byte stream carried by a virtual circuit. While virtual circuits can be
used for any DNS activity, datagrams are preferred for queries due to
their lower overhead and better performance. Zone refresh activities
must use virtual circuits because of the need for reliable transfer.
The Internet supports name server access using TCP [RFC-793] on server
port 53 (decimal) as well as datagram access using UDP [RFC-768] on UDP
port 53 (decimal).
4.2.1. UDP usage
Messages sent using UDP user server port 53 (decimal).
Messages carried by UDP are restricted to 512 bytes (not counting the IP
or UDP headers). Longer messages are truncated and the TC bit is set in
the header.
UDP is not acceptable for zone transfers, but is the recommended method
for standard queries in the Internet. Queries sent using UDP may be
lost, and hence a retransmission strategy is required. Queries or their
responses may be reordered by the network, or by processing in name
servers, so resolvers should not depend on them being returned in order.
The optimal UDP retransmission policy will vary with performance of the
Internet and the needs of the client, but the following are recommended:
- The client should try other servers and server addresses
before repeating a query to a specific address of a server.
- The retransmission interval should be based on prior
statistics if possible. Too aggressive retransmission can
easily slow responses for the community at large. Depending
on how well connected the client is to its expected servers,
the minimum retransmission interval should be 2-5 seconds.
More suggestions on server selection and retransmission policy can be
found in the resolver section of this memo.
4.2.2. TCP usage
Messages sent over TCP connections use server port 53 (decimal). The
message is prefixed with a two byte length field which gives the message
Mockapetris [Page 32]
RFC 1035 Domain Implementation and Specification November 1987
length, excluding the two byte length field. This length field allows
the low-level processing to assemble a complete message before beginning
to parse it.
Several connection management policies are recommended:
- The server should not block other activities waiting for TCP
data.
- The server should support multiple connections.
- The server should assume that the client will initiate
connection closing, and should delay closing its end of the
connection until all outstanding client requests have been
satisfied.
- If the server needs to close a dormant connection to reclaim
resources, it should wait until the connection has been idle
for a period on the order of two minutes. In particular, the
server should allow the SOA and AXFR request sequence (which
begins a refresh operation) to be made on a single connection.
Since the server would be unable to answer queries anyway, a
unilateral close or reset may be used instead of a graceful
close.
5. MASTER FILES
Master files are text files that contain RRs in text form. Since the
contents of a zone can be expressed in the form of a list of RRs a
master file is most often used to define a zone, though it can be used
to list a cache's contents. Hence, this section first discusses the
format of RRs in a master file, and then the special considerations when
a master file is used to create a zone in some name server.
5.1. Format
The format of these files is a sequence of entries. Entries are
predominantly line-oriented, though parentheses can be used to continue
a list of items across a line boundary, and text literals can contain
CRLF within the text. Any combination of tabs and spaces act as a
delimiter between the separate items that make up an entry. The end of
any line in the master file can end with a comment. The comment starts
with a ";" (semicolon).
The following entries are defined:
<blank>[<comment>]
Mockapetris [Page 33]
RFC 1035 Domain Implementation and Specification November 1987
$ORIGIN <domain-name> [<comment>]
$INCLUDE <file-name> [<domain-name>] [<comment>]
<domain-name><rr> [<comment>]
<blank><rr> [<comment>]
Blank lines, with or without comments, are allowed anywhere in the file.
Two control entries are defined: $ORIGIN and $INCLUDE. $ORIGIN is
followed by a domain name, and resets the current origin for relative
domain names to the stated name. $INCLUDE inserts the named file into
the current file, and may optionally specify a domain name that sets the
relative domain name origin for the included file. $INCLUDE may also
have a comment. Note that a $INCLUDE entry never changes the relative
origin of the parent file, regardless of changes to the relative origin
made within the included file.
The last two forms represent RRs. If an entry for an RR begins with a
blank, then the RR is assumed to be owned by the last stated owner. If
an RR entry begins with a <domain-name>, then the owner name is reset.
<rr> contents take one of the following forms:
[<TTL>] [<class>] <type> <RDATA>
[<class>] [<TTL>] <type> <RDATA>
The RR begins with optional TTL and class fields, followed by a type and
RDATA field appropriate to the type and class. Class and type use the
standard mnemonics, TTL is a decimal integer. Omitted class and TTL
values are default to the last explicitly stated values. Since type and
class mnemonics are disjoint, the parse is unique. (Note that this
order is different from the order used in examples and the order used in
the actual RRs; the given order allows easier parsing and defaulting.)
<domain-name>s make up a large share of the data in the master file.
The labels in the domain name are expressed as character strings and
separated by dots. Quoting conventions allow arbitrary characters to be
stored in domain names. Domain names that end in a dot are called
absolute, and are taken as complete. Domain names which do not end in a
dot are called relative; the actual domain name is the concatenation of
the relative part with an origin specified in a $ORIGIN, $INCLUDE, or as
an argument to the master file loading routine. A relative name is an
error when no origin is available.
Mockapetris [Page 34]
RFC 1035 Domain Implementation and Specification November 1987
<character-string> is expressed in one or two ways: as a contiguous set
of characters without interior spaces, or as a string beginning with a "
and ending with a ". Inside a " delimited string any character can
occur, except for a " itself, which must be quoted using \ (back slash).
Because these files are text files several special encodings are
necessary to allow arbitrary data to be loaded. In particular:
of the root.
@ A free standing @ is used to denote the current origin.
\X where X is any character other than a digit (0-9), is
used to quote that character so that its special meaning
does not apply. For example, "\." can be used to place
a dot character in a label.
\DDD where each D is a digit is the octet corresponding to
the decimal number described by DDD. The resulting
octet is assumed to be text and is not checked for
special meaning.
( ) Parentheses are used to group data that crosses a line
boundary. In effect, line terminations are not
recognized within parentheses.
; Semicolon is used to start a comment; the remainder of
the line is ignored.
5.2. Use of master files to define zones
When a master file is used to load a zone, the operation should be
suppressed if any errors are encountered in the master file. The
rationale for this is that a single error can have widespread
consequences. For example, suppose that the RRs defining a delegation
have syntax errors; then the server will return authoritative name
errors for all names in the subzone (except in the case where the
subzone is also present on the server).
Several other validity checks that should be performed in addition to
insuring that the file is syntactically correct:
1. All RRs in the file should have the same class.
2. Exactly one SOA RR should be present at the top of the zone.
3. If delegations are present and glue information is required,
it should be present.
Mockapetris [Page 35]
RFC 1035 Domain Implementation and Specification November 1987
4. Information present outside of the authoritative nodes in the
zone should be glue information, rather than the result of an
origin or similar error.
5.3. Master file example
The following is an example file which might be used to define the
ISI.EDU zone.and is loaded with an origin of ISI.EDU:
@ IN SOA VENERA Action\.domains (
20 ; SERIAL
7200 ; REFRESH
600 ; RETRY
3600000; EXPIRE
60) ; MINIMUM
NS A.ISI.EDU.
NS VENERA
NS VAXA
MX 10 VENERA
MX 20 VAXA
A A 26.3.0.103
VENERA A 10.1.0.52
A 128.9.0.32
VAXA A 10.2.0.27
A 128.9.0.33
$INCLUDE <SUBSYS>ISI-MAILBOXES.TXT
Where the file <SUBSYS>ISI-MAILBOXES.TXT is:
MOE MB A.ISI.EDU.
LARRY MB A.ISI.EDU.
CURLEY MB A.ISI.EDU.
STOOGES MG MOE
MG LARRY
MG CURLEY
Note the use of the \ character in the SOA RR to specify the responsible
person mailbox "Action.domains@E.ISI.EDU".
Mockapetris [Page 36]
RFC 1035 Domain Implementation and Specification November 1987
6. NAME SERVER IMPLEMENTATION
6.1. Architecture
The optimal structure for the name server will depend on the host
operating system and whether the name server is integrated with resolver
operations, either by supporting recursive service, or by sharing its
database with a resolver. This section discusses implementation
considerations for a name server which shares a database with a
resolver, but most of these concerns are present in any name server.
6.1.1. Control
A name server must employ multiple concurrent activities, whether they
are implemented as separate tasks in the host's OS or multiplexing
inside a single name server program. It is simply not acceptable for a
name server to block the service of UDP requests while it waits for TCP
data for refreshing or query activities. Similarly, a name server
should not attempt to provide recursive service without processing such
requests in parallel, though it may choose to serialize requests from a
single client, or to regard identical requests from the same client as
duplicates. A name server should not substantially delay requests while
it reloads a zone from master files or while it incorporates a newly
refreshed zone into its database.
6.1.2. Database
While name server implementations are free to use any internal data
structures they choose, the suggested structure consists of three major
parts:
- A "catalog" data structure which lists the zones available to
this server, and a "pointer" to the zone data structure. The
main purpose of this structure is to find the nearest ancestor
zone, if any, for arriving standard queries.
- Separate data structures for each of the zones held by the
name server.
- A data structure for cached data. (or perhaps separate caches
for different classes)
All of these data structures can be implemented an identical tree
structure format, with different data chained off the nodes in different
parts: in the catalog the data is pointers to zones, while in the zone
and cache data structures, the data will be RRs. In designing the tree
framework the designer should recognize that query processing will need
to traverse the tree using case-insensitive label comparisons; and that
Mockapetris [Page 37]
RFC 1035 Domain Implementation and Specification November 1987
in real data, a few nodes have a very high branching factor (100-1000 or
more), but the vast majority have a very low branching factor (0-1).
One way to solve the case problem is to store the labels for each node
in two pieces: a standardized-case representation of the label where all
ASCII characters are in a single case, together with a bit mask that
denotes which characters are actually of a different case. The
branching factor diversity can be handled using a simple linked list for
a node until the branching factor exceeds some threshold, and
transitioning to a hash structure after the threshold is exceeded. In
any case, hash structures used to store tree sections must insure that
hash functions and procedures preserve the casing conventions of the
DNS.
The use of separate structures for the different parts of the database
is motivated by several factors:
- The catalog structure can be an almost static structure that
need change only when the system administrator changes the
zones supported by the server. This structure can also be
used to store parameters used to control refreshing
activities.
- The individual data structures for zones allow a zone to be
replaced simply by changing a pointer in the catalog. Zone
refresh operations can build a new structure and, when
complete, splice it into the database via a simple pointer
replacement. It is very important that when a zone is
refreshed, queries should not use old and new data
simultaneously.
- With the proper search procedures, authoritative data in zones
will always "hide", and hence take precedence over, cached
data.
- Errors in zone definitions that cause overlapping zones, etc.,
may cause erroneous responses to queries, but problem
determination is simplified, and the contents of one "bad"
zone can't corrupt another.
- Since the cache is most frequently updated, it is most
vulnerable to corruption during system restarts. It can also
become full of expired RR data. In either case, it can easily
be discarded without disturbing zone data.
A major aspect of database design is selecting a structure which allows
the name server to deal with crashes of the name server's host. State
information which a name server should save across system crashes
Mockapetris [Page 38]
RFC 1035 Domain Implementation and Specification November 1987
includes the catalog structure (including the state of refreshing for
each zone) and the zone data itself.
6.1.3. Time
Both the TTL data for RRs and the timing data for refreshing activities
depends on 32 bit timers in units of seconds. Inside the database,
refresh timers and TTLs for cached data conceptually "count down", while
data in the zone stays with constant TTLs.
A recommended implementation strategy is to store time in two ways: as
a relative increment and as an absolute time. One way to do this is to
use positive 32 bit numbers for one type and negative numbers for the
other. The RRs in zones use relative times; the refresh timers and
cache data use absolute times. Absolute numbers are taken with respect
to some known origin and converted to relative values when placed in the
response to a query. When an absolute TTL is negative after conversion
to relative, then the data is expired and should be ignored.
6.2. Standard query processing
The major algorithm for standard query processing is presented in
[RFC-1034].
When processing queries with QCLASS=*, or some other QCLASS which
matches multiple classes, the response should never be authoritative
unless the server can guarantee that the response covers all classes.
When composing a response, RRs which are to be inserted in the
additional section, but duplicate RRs in the answer or authority
sections, may be omitted from the additional section.
When a response is so long that truncation is required, the truncation
should start at the end of the response and work forward in the
datagram. Thus if there is any data for the authority section, the
answer section is guaranteed to be unique.
The MINIMUM value in the SOA should be used to set a floor on the TTL of
data distributed from a zone. This floor function should be done when
the data is copied into a response. This will allow future dynamic
update protocols to change the SOA MINIMUM field without ambiguous
semantics.
6.3. Zone refresh and reload processing
In spite of a server's best efforts, it may be unable to load zone data
from a master file due to syntax errors, etc., or be unable to refresh a
zone within the its expiration parameter. In this case, the name server
Mockapetris [Page 39]
RFC 1035 Domain Implementation and Specification November 1987
should answer queries as if it were not supposed to possess the zone.
If a master is sending a zone out via AXFR, and a new version is created
during the transfer, the master should continue to send the old version
if possible. In any case, it should never send part of one version and
part of another. If completion is not possible, the master should reset
the connection on which the zone transfer is taking place.
6.4. Inverse queries (Optional)
Inverse queries are an optional part of the DNS. Name servers are not
required to support any form of inverse queries. If a name server
receives an inverse query that it does not support, it returns an error
response with the "Not Implemented" error set in the header. While
inverse query support is optional, all name servers must be at least
able to return the error response.
6.4.1. The contents of inverse queries and responses Inverse
queries reverse the mappings performed by standard query operations;
while a standard query maps a domain name to a resource, an inverse
query maps a resource to a domain name. For example, a standard query
might bind a domain name to a host address; the corresponding inverse
query binds the host address to a domain name.
Inverse queries take the form of a single RR in the answer section of
the message, with an empty question section. The owner name of the
query RR and its TTL are not significant. The response carries
questions in the question section which identify all names possessing
the query RR WHICH THE NAME SERVER KNOWS. Since no name server knows
about all of the domain name space, the response can never be assumed to
be complete. Thus inverse queries are primarily useful for database
management and debugging activities. Inverse queries are NOT an
acceptable method of mapping host addresses to host names; use the IN-
ADDR.ARPA domain instead.
Where possible, name servers should provide case-insensitive comparisons
for inverse queries. Thus an inverse query asking for an MX RR of
"Venera.isi.edu" should get the same response as a query for
"VENERA.ISI.EDU"; an inverse query for HINFO RR "IBM-PC UNIX" should
produce the same result as an inverse query for "IBM-pc unix". However,
this cannot be guaranteed because name servers may possess RRs that
contain character strings but the name server does not know that the
data is character.
When a name server processes an inverse query, it either returns:
1. zero, one, or multiple domain names for the specified
resource as QNAMEs in the question section
Mockapetris [Page 40]
RFC 1035 Domain Implementation and Specification November 1987
2. an error code indicating that the name server doesn't support
inverse mapping of the specified resource type.
When the response to an inverse query contains one or more QNAMEs, the
owner name and TTL of the RR in the answer section which defines the
inverse query is modified to exactly match an RR found at the first
QNAME.
RRs returned in the inverse queries cannot be cached using the same
mechanism as is used for the replies to standard queries. One reason
for this is that a name might have multiple RRs of the same type, and
only one would appear. For example, an inverse query for a single
address of a multiply homed host might create the impression that only
one address existed.
6.4.2. Inverse query and response example The overall structure
of an inverse query for retrieving the domain name that corresponds to
Internet address 10.1.0.52 is shown below:
+-----------------------------------------+
Header | OPCODE=IQUERY, ID=997 |
+-----------------------------------------+
Question | <empty> |
+-----------------------------------------+
Answer | <anyname> A IN 10.1.0.52 |
+-----------------------------------------+
Authority | <empty> |
+-----------------------------------------+
Additional | <empty> |
+-----------------------------------------+
This query asks for a question whose answer is the Internet style
address 10.1.0.52. Since the owner name is not known, any domain name
can be used as a placeholder (and is ignored). A single octet of zero,
signifying the root, is usually used because it minimizes the length of
the message. The TTL of the RR is not significant. The response to
this query might be:
Mockapetris [Page 41]
RFC 1035 Domain Implementation and Specification November 1987
+-----------------------------------------+
Header | OPCODE=RESPONSE, ID=997 |
+-----------------------------------------+
Question |QTYPE=A, QCLASS=IN, QNAME=VENERA.ISI.EDU |
+-----------------------------------------+
Answer | VENERA.ISI.EDU A IN 10.1.0.52 |
+-----------------------------------------+
Authority | <empty> |
+-----------------------------------------+
Additional | <empty> |
+-----------------------------------------+
Note that the QTYPE in a response to an inverse query is the same as the
TYPE field in the answer section of the inverse query. Responses to
inverse queries may contain multiple questions when the inverse is not
unique. If the question section in the response is not empty, then the
RR in the answer section is modified to correspond to be an exact copy
of an RR at the first QNAME.
6.4.3. Inverse query processing
Name servers that support inverse queries can support these operations
through exhaustive searches of their databases, but this becomes
impractical as the size of the database increases. An alternative
approach is to invert the database according to the search key.
For name servers that support multiple zones and a large amount of data,
the recommended approach is separate inversions for each zone. When a
particular zone is changed during a refresh, only its inversions need to
be redone.
Support for transfer of this type of inversion may be included in future
versions of the domain system, but is not supported in this version.
6.5. Completion queries and responses
The optional completion services described in RFC-882 and RFC-883 have
been deleted. Redesigned services may become available in the future.
Mockapetris [Page 42]
RFC 1035 Domain Implementation and Specification November 1987
7. RESOLVER IMPLEMENTATION
The top levels of the recommended resolver algorithm are discussed in
[RFC-1034]. This section discusses implementation details assuming the
database structure suggested in the name server implementation section
of this memo.
7.1. Transforming a user request into a query
The first step a resolver takes is to transform the client's request,
stated in a format suitable to the local OS, into a search specification
for RRs at a specific name which match a specific QTYPE and QCLASS.
Where possible, the QTYPE and QCLASS should correspond to a single type
and a single class, because this makes the use of cached data much
simpler. The reason for this is that the presence of data of one type
in a cache doesn't confirm the existence or non-existence of data of
other types, hence the only way to be sure is to consult an
authoritative source. If QCLASS=* is used, then authoritative answers
won't be available.
Since a resolver must be able to multiplex multiple requests if it is to
perform its function efficiently, each pending request is usually
represented in some block of state information. This state block will
typically contain:
- A timestamp indicating the time the request began.
The timestamp is used to decide whether RRs in the database
can be used or are out of date. This timestamp uses the
absolute time format previously discussed for RR storage in
zones and caches. Note that when an RRs TTL indicates a
relative time, the RR must be timely, since it is part of a
zone. When the RR has an absolute time, it is part of a
cache, and the TTL of the RR is compared against the timestamp
for the start of the request.
Note that using the timestamp is superior to using a current
time, since it allows RRs with TTLs of zero to be entered in
the cache in the usual manner, but still used by the current
request, even after intervals of many seconds due to system
load, query retransmission timeouts, etc.
- Some sort of parameters to limit the amount of work which will
be performed for this request.
The amount of work which a resolver will do in response to a
client request must be limited to guard against errors in the
database, such as circular CNAME references, and operational
problems, such as network partition which prevents the
Mockapetris [Page 43]
RFC 1035 Domain Implementation and Specification November 1987
resolver from accessing the name servers it needs. While
local limits on the number of times a resolver will retransmit
a particular query to a particular name server address are
essential, the resolver should have a global per-request
counter to limit work on a single request. The counter should
be set to some initial value and decremented whenever the
resolver performs any action (retransmission timeout,
retransmission, etc.) If the counter passes zero, the request
is terminated with a temporary error.
Note that if the resolver structure allows one request to
start others in parallel, such as when the need to access a
name server for one request causes a parallel resolve for the
name server's addresses, the spawned request should be started
with a lower counter. This prevents circular references in
the database from starting a chain reaction of resolver
activity.
- The SLIST data structure discussed in [RFC-1034].
This structure keeps track of the state of a request if it
must wait for answers from foreign name servers.
7.2. Sending the queries
As described in [RFC-1034], the basic task of the resolver is to
formulate a query which will answer the client's request and direct that
query to name servers which can provide the information. The resolver
will usually only have very strong hints about which servers to ask, in
the form of NS RRs, and may have to revise the query, in response to
CNAMEs, or revise the set of name servers the resolver is asking, in
response to delegation responses which point the resolver to name
servers closer to the desired information. In addition to the
information requested by the client, the resolver may have to call upon
its own services to determine the address of name servers it wishes to
contact.
In any case, the model used in this memo assumes that the resolver is
multiplexing attention between multiple requests, some from the client,
and some internally generated. Each request is represented by some
state information, and the desired behavior is that the resolver
transmit queries to name servers in a way that maximizes the probability
that the request is answered, minimizes the time that the request takes,
and avoids excessive transmissions. The key algorithm uses the state
information of the request to select the next name server address to
query, and also computes a timeout which will cause the next action
should a response not arrive. The next action will usually be a
transmission to some other server, but may be a temporary error to the
Mockapetris [Page 44]
RFC 1035 Domain Implementation and Specification November 1987
client.
The resolver always starts with a list of server names to query (SLIST).
This list will be all NS RRs which correspond to the nearest ancestor
zone that the resolver knows about. To avoid startup problems, the
resolver should have a set of default servers which it will ask should
it have no current NS RRs which are appropriate. The resolver then adds
to SLIST all of the known addresses for the name servers, and may start
parallel requests to acquire the addresses of the servers when the
resolver has the name, but no addresses, for the name servers.
To complete initialization of SLIST, the resolver attaches whatever
history information it has to the each address in SLIST. This will
usually consist of some sort of weighted averages for the response time
of the address, and the batting average of the address (i.e., how often
the address responded at all to the request). Note that this
information should be kept on a per address basis, rather than on a per
name server basis, because the response time and batting average of a
particular server may vary considerably from address to address. Note
also that this information is actually specific to a resolver address /
server address pair, so a resolver with multiple addresses may wish to
keep separate histories for each of its addresses. Part of this step
must deal with addresses which have no such history; in this case an
expected round trip time of 5-10 seconds should be the worst case, with
lower estimates for the same local network, etc.
Note that whenever a delegation is followed, the resolver algorithm
reinitializes SLIST.
The information establishes a partial ranking of the available name
server addresses. Each time an address is chosen and the state should
be altered to prevent its selection again until all other addresses have
been tried. The timeout for each transmission should be 50-100% greater
than the average predicted value to allow for variance in response.
Some fine points:
- The resolver may encounter a situation where no addresses are
available for any of the name servers named in SLIST, and
where the servers in the list are precisely those which would
normally be used to look up their own addresses. This
situation typically occurs when the glue address RRs have a
smaller TTL than the NS RRs marking delegation, or when the
resolver caches the result of a NS search. The resolver
should detect this condition and restart the search at the
next ancestor zone, or alternatively at the root.
Mockapetris [Page 45]
RFC 1035 Domain Implementation and Specification November 1987
- If a resolver gets a server error or other bizarre response
from a name server, it should remove it from SLIST, and may
wish to schedule an immediate transmission to the next
candidate server address.
7.3. Processing responses
The first step in processing arriving response datagrams is to parse the
response. This procedure should include:
- Check the header for reasonableness. Discard datagrams which
are queries when responses are expected.
- Parse the sections of the message, and insure that all RRs are
correctly formatted.
- As an optional step, check the TTLs of arriving data looking
for RRs with excessively long TTLs. If a RR has an
excessively long TTL, say greater than 1 week, either discard
the whole response, or limit all TTLs in the response to 1
week.
The next step is to match the response to a current resolver request.
The recommended strategy is to do a preliminary matching using the ID
field in the domain header, and then to verify that the question section
corresponds to the information currently desired. This requires that
the transmission algorithm devote several bits of the domain ID field to
a request identifier of some sort. This step has several fine points:
- Some name servers send their responses from different
addresses than the one used to receive the query. That is, a
resolver cannot rely that a response will come from the same
address which it sent the corresponding query to. This name
server bug is typically encountered in UNIX systems.
- If the resolver retransmits a particular request to a name
server it should be able to use a response from any of the
transmissions. However, if it is using the response to sample
the round trip time to access the name server, it must be able
to determine which transmission matches the response (and keep
transmission times for each outgoing message), or only
calculate round trip times based on initial transmissions.
- A name server will occasionally not have a current copy of a
zone which it should have according to some NS RRs. The
resolver should simply remove the name server from the current
SLIST, and continue.
Mockapetris [Page 46]
RFC 1035 Domain Implementation and Specification November 1987
7.4. Using the cache
In general, we expect a resolver to cache all data which it receives in
responses since it may be useful in answering future client requests.
However, there are several types of data which should not be cached:
- When several RRs of the same type are available for a
particular owner name, the resolver should either cache them
all or none at all. When a response is truncated, and a
resolver doesn't know whether it has a complete set, it should
not cache a possibly partial set of RRs.
- Cached data should never be used in preference to
authoritative data, so if caching would cause this to happen
the data should not be cached.
- The results of an inverse query should not be cached.
- The results of standard queries where the QNAME contains "*"
labels if the data might be used to construct wildcards. The
reason is that the cache does not necessarily contain existing
RRs or zone boundary information which is necessary to
restrict the application of the wildcard RRs.
- RR data in responses of dubious reliability. When a resolver
receives unsolicited responses or RR data other than that
requested, it should discard it without caching it. The basic
implication is that all sanity checks on a packet should be
performed before any of it is cached.
In a similar vein, when a resolver has a set of RRs for some name in a
response, and wants to cache the RRs, it should check its cache for
already existing RRs. Depending on the circumstances, either the data
in the response or the cache is preferred, but the two should never be
combined. If the data in the response is from authoritative data in the
answer section, it is always preferred.
8. MAIL SUPPORT
The domain system defines a standard for mapping mailboxes into domain
names, and two methods for using the mailbox information to derive mail
routing information. The first method is called mail exchange binding
and the other method is mailbox binding. The mailbox encoding standard
and mail exchange binding are part of the DNS official protocol, and are
the recommended method for mail routing in the Internet. Mailbox
binding is an experimental feature which is still under development and
subject to change.
Mockapetris [Page 47]
RFC 1035 Domain Implementation and Specification November 1987
The mailbox encoding standard assumes a mailbox name of the form
"<local-part>@<mail-domain>". While the syntax allowed in each of these
sections varies substantially between the various mail internets, the
preferred syntax for the ARPA Internet is given in [RFC-822].
The DNS encodes the <local-part> as a single label, and encodes the
<mail-domain> as a domain name. The single label from the <local-part>
is prefaced to the domain name from <mail-domain> to form the domain
name corresponding to the mailbox. Thus the mailbox HOSTMASTER@SRI-
NIC.ARPA is mapped into the domain name HOSTMASTER.SRI-NIC.ARPA. If the
<local-part> contains dots or other special characters, its
representation in a master file will require the use of backslash
quoting to ensure that the domain name is properly encoded. For
example, the mailbox Action.domains@ISI.EDU would be represented as
Action\.domains.ISI.EDU.
8.1. Mail exchange binding
Mail exchange binding uses the <mail-domain> part of a mailbox
specification to determine where mail should be sent. The <local-part>
is not even consulted. [RFC-974] specifies this method in detail, and
should be consulted before attempting to use mail exchange support.
One of the advantages of this method is that it decouples mail
destination naming from the hosts used to support mail service, at the
cost of another layer of indirection in the lookup function. However,
the addition layer should eliminate the need for complicated "%", "!",
etc encodings in <local-part>.
The essence of the method is that the <mail-domain> is used as a domain
name to locate type MX RRs which list hosts willing to accept mail for
<mail-domain>, together with preference values which rank the hosts
according to an order specified by the administrators for <mail-domain>.
In this memo, the <mail-domain> ISI.EDU is used in examples, together
with the hosts VENERA.ISI.EDU and VAXA.ISI.EDU as mail exchanges for
ISI.EDU. If a mailer had a message for Mockapetris@ISI.EDU, it would
route it by looking up MX RRs for ISI.EDU. The MX RRs at ISI.EDU name
VENERA.ISI.EDU and VAXA.ISI.EDU, and type A queries can find the host
addresses.
8.2. Mailbox binding (Experimental)
In mailbox binding, the mailer uses the entire mail destination
specification to construct a domain name. The encoded domain name for
the mailbox is used as the QNAME field in a QTYPE=MAILB query.
Several outcomes are possible for this query:
Mockapetris [Page 48]
RFC 1035 Domain Implementation and Specification November 1987
1. The query can return a name error indicating that the mailbox
does not exist as a domain name.
In the long term, this would indicate that the specified
mailbox doesn't exist. However, until the use of mailbox
binding is universal, this error condition should be
interpreted to mean that the organization identified by the
global part does not support mailbox binding. The
appropriate procedure is to revert to exchange binding at
this point.
2. The query can return a Mail Rename (MR) RR.
The MR RR carries new mailbox specification in its RDATA
field. The mailer should replace the old mailbox with the
new one and retry the operation.
3. The query can return a MB RR.
The MB RR carries a domain name for a host in its RDATA
field. The mailer should deliver the message to that host
via whatever protocol is applicable, e.g., b,SMTP.
4. The query can return one or more Mail Group (MG) RRs.
This condition means that the mailbox was actually a mailing
list or mail group, rather than a single mailbox. Each MG RR
has a RDATA field that identifies a mailbox that is a member
of the group. The mailer should deliver a copy of the
message to each member.
5. The query can return a MB RR as well as one or more MG RRs.
This condition means the the mailbox was actually a mailing
list. The mailer can either deliver the message to the host
specified by the MB RR, which will in turn do the delivery to
all members, or the mailer can use the MG RRs to do the
expansion itself.
In any of these cases, the response may include a Mail Information
(MINFO) RR. This RR is usually associated with a mail group, but is
legal with a MB. The MINFO RR identifies two mailboxes. One of these
identifies a responsible person for the original mailbox name. This
mailbox should be used for requests to be added to a mail group, etc.
The second mailbox name in the MINFO RR identifies a mailbox that should
receive error messages for mail failures. This is particularly
appropriate for mailing lists when errors in member names should be
reported to a person other than the one who sends a message to the list.
Mockapetris [Page 49]
RFC 1035 Domain Implementation and Specification November 1987
New fields may be added to this RR in the future.
9. REFERENCES and BIBLIOGRAPHY
[Dyer 87] S. Dyer, F. Hsu, "Hesiod", Project Athena
Technical Plan - Name Service, April 1987, version 1.9.
Describes the fundamentals of the Hesiod name service.
[IEN-116] J. Postel, "Internet Name Server", IEN-116,
USC/Information Sciences Institute, August 1979.
A name service obsoleted by the Domain Name System, but
still in use.
[Quarterman 86] J. Quarterman, and J. Hoskins, "Notable Computer Networks",
Communications of the ACM, October 1986, volume 29, number
10.
[RFC-742] K. Harrenstien, "NAME/FINGER", RFC-742, Network
Information Center, SRI International, December 1977.
[RFC-768] J. Postel, "User Datagram Protocol", RFC-768,
USC/Information Sciences Institute, August 1980.
[RFC-793] J. Postel, "Transmission Control Protocol", RFC-793,
USC/Information Sciences Institute, September 1981.
[RFC-799] D. Mills, "Internet Name Domains", RFC-799, COMSAT,
September 1981.
Suggests introduction of a hierarchy in place of a flat
name space for the Internet.
[RFC-805] J. Postel, "Computer Mail Meeting Notes", RFC-805,
USC/Information Sciences Institute, February 1982.
[RFC-810] E. Feinler, K. Harrenstien, Z. Su, and V. White, "DOD
Internet Host Table Specification", RFC-810, Network
Information Center, SRI International, March 1982.
Obsolete. See RFC-952.
[RFC-811] K. Harrenstien, V. White, and E. Feinler, "Hostnames
Server", RFC-811, Network Information Center, SRI
International, March 1982.
Mockapetris [Page 50]
RFC 1035 Domain Implementation and Specification November 1987
Obsolete. See RFC-953.
[RFC-812] K. Harrenstien, and V. White, "NICNAME/WHOIS", RFC-812,
Network Information Center, SRI International, March
1982.
[RFC-819] Z. Su, and J. Postel, "The Domain Naming Convention for
Internet User Applications", RFC-819, Network
Information Center, SRI International, August 1982.
Early thoughts on the design of the domain system.
Current implementation is completely different.
[RFC-821] J. Postel, "Simple Mail Transfer Protocol", RFC-821,
USC/Information Sciences Institute, August 1980.
[RFC-830] Z. Su, "A Distributed System for Internet Name Service",
RFC-830, Network Information Center, SRI International,
October 1982.
Early thoughts on the design of the domain system.
Current implementation is completely different.
[RFC-882] P. Mockapetris, "Domain names - Concepts and
Facilities," RFC-882, USC/Information Sciences
Institute, November 1983.
Superceeded by this memo.
[RFC-883] P. Mockapetris, "Domain names - Implementation and
Specification," RFC-883, USC/Information Sciences
Institute, November 1983.
Superceeded by this memo.
[RFC-920] J. Postel and J. Reynolds, "Domain Requirements",
RFC-920, USC/Information Sciences Institute,
October 1984.
Explains the naming scheme for top level domains.
[RFC-952] K. Harrenstien, M. Stahl, E. Feinler, "DoD Internet Host
Table Specification", RFC-952, SRI, October 1985.
Specifies the format of HOSTS.TXT, the host/address
table replaced by the DNS.
Mockapetris [Page 51]
RFC 1035 Domain Implementation and Specification November 1987
[RFC-953] K. Harrenstien, M. Stahl, E. Feinler, "HOSTNAME Server",
RFC-953, SRI, October 1985.
This RFC contains the official specification of the
hostname server protocol, which is obsoleted by the DNS.
This TCP based protocol accesses information stored in
the RFC-952 format, and is used to obtain copies of the
host table.
[RFC-973] P. Mockapetris, "Domain System Changes and
Observations", RFC-973, USC/Information Sciences
Institute, January 1986.
Describes changes to RFC-882 and RFC-883 and reasons for
them.
[RFC-974] C. Partridge, "Mail routing and the domain system",
RFC-974, CSNET CIC BBN Labs, January 1986.
Describes the transition from HOSTS.TXT based mail
addressing to the more powerful MX system used with the
domain system.
[RFC-1001] NetBIOS Working Group, "Protocol standard for a NetBIOS
service on a TCP/UDP transport: Concepts and Methods",
RFC-1001, March 1987.
This RFC and RFC-1002 are a preliminary design for
NETBIOS on top of TCP/IP which proposes to base NetBIOS
name service on top of the DNS.
[RFC-1002] NetBIOS Working Group, "Protocol standard for a NetBIOS
service on a TCP/UDP transport: Detailed
Specifications", RFC-1002, March 1987.
[RFC-1010] J. Reynolds, and J. Postel, "Assigned Numbers", RFC-1010,
USC/Information Sciences Institute, May 1987.
Contains socket numbers and mnemonics for host names,
operating systems, etc.
[RFC-1031] W. Lazear, "MILNET Name Domain Transition", RFC-1031,
November 1987.
Describes a plan for converting the MILNET to the DNS.
[RFC-1032] M. Stahl, "Establishing a Domain - Guidelines for
Administrators", RFC-1032, November 1987.
Mockapetris [Page 52]
RFC 1035 Domain Implementation and Specification November 1987
Describes the registration policies used by the NIC to
administer the top level domains and delegate subzones.
[RFC-1033] M. Lottor, "Domain Administrators Operations Guide",
RFC-1033, November 1987.
A cookbook for domain administrators.
[Solomon 82] M. Solomon, L. Landweber, and D. Neuhengen, "The CSNET
Name Server", Computer Networks, vol 6, nr 3, July 1982.
Describes a name service for CSNET which is independent
from the DNS and DNS use in the CSNET.
Mockapetris [Page 53]
RFC 1035 Domain Implementation and Specification November 1987
Index
* 13
; 33, 35
<character-string> 35
<domain-name> 34
@ 35
\ 35
A 12
Byte order 8
CH 13
Character case 9
CLASS 11
CNAME 12
Completion 42
CS 13
Hesiod 13
HINFO 12
HS 13
IN 13
IN-ADDR.ARPA domain 22
Inverse queries 40
Mailbox names 47
MB 12
MD 12
MF 12
MG 12
MINFO 12
MINIMUM 20
MR 12
MX 12
NS 12
NULL 12
Port numbers 32
Primary server 5
PTR 12, 18
Mockapetris [Page 54]
RFC 1035 Domain Implementation and Specification November 1987
QCLASS 13
QTYPE 12
RDATA 12
RDLENGTH 11
Secondary server 5
SOA 12
Stub resolvers 7
TCP 32
TXT 12
TYPE 11
UDP 32
WKS 12
Mockapetris [Page 55]
\ No newline at end of file +Network Working Group P. Mockapetris +Request for Comments: 1035 ISI + November 1987 +Obsoletes: RFCs 882, 883, 973 + + DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION + + +1. STATUS OF THIS MEMO + +This RFC describes the details of the domain system and protocol, and +assumes that the reader is familiar with the concepts discussed in a +companion RFC, "Domain Names - Concepts and Facilities" [RFC-1034]. + +The domain system is a mixture of functions and data types which are an +official protocol and functions and data types which are still +experimental. Since the domain system is intentionally extensible, new +data types and experimental behavior should always be expected in parts +of the system beyond the official protocol. The official protocol parts +include standard queries, responses and the Internet class RR data +formats (e.g., host addresses). Since the previous RFC set, several +definitions have changed, so some previous definitions are obsolete. + +Experimental or obsolete features are clearly marked in these RFCs, and +such information should be used with caution. + +The reader is especially cautioned not to depend on the values which +appear in examples to be current or complete, since their purpose is +primarily pedagogical. Distribution of this memo is unlimited. + + Table of Contents + + 1. STATUS OF THIS MEMO 1 + 2. INTRODUCTION 3 + 2.1. Overview 3 + 2.2. Common configurations 4 + 2.3. Conventions 7 + 2.3.1. Preferred name syntax 7 + 2.3.2. Data Transmission Order 8 + 2.3.3. Character Case 9 + 2.3.4. Size limits 10 + 3. DOMAIN NAME SPACE AND RR DEFINITIONS 10 + 3.1. Name space definitions 10 + 3.2. RR definitions 11 + 3.2.1. Format 11 + 3.2.2. TYPE values 12 + 3.2.3. QTYPE values 12 + 3.2.4. CLASS values 13 + + + +Mockapetris [Page 1] + +RFC 1035 Domain Implementation and Specification November 1987 + + + 3.2.5. QCLASS values 13 + 3.3. Standard RRs 13 + 3.3.1. CNAME RDATA format 14 + 3.3.2. HINFO RDATA format 14 + 3.3.3. MB RDATA format (EXPERIMENTAL) 14 + 3.3.4. MD RDATA format (Obsolete) 15 + 3.3.5. MF RDATA format (Obsolete) 15 + 3.3.6. MG RDATA format (EXPERIMENTAL) 16 + 3.3.7. MINFO RDATA format (EXPERIMENTAL) 16 + 3.3.8. MR RDATA format (EXPERIMENTAL) 17 + 3.3.9. MX RDATA format 17 + 3.3.10. NULL RDATA format (EXPERIMENTAL) 17 + 3.3.11. NS RDATA format 18 + 3.3.12. PTR RDATA format 18 + 3.3.13. SOA RDATA format 19 + 3.3.14. TXT RDATA format 20 + 3.4. ARPA Internet specific RRs 20 + 3.4.1. A RDATA format 20 + 3.4.2. WKS RDATA format 21 + 3.5. IN-ADDR.ARPA domain 22 + 3.6. Defining new types, classes, and special namespaces 24 + 4. MESSAGES 25 + 4.1. Format 25 + 4.1.1. Header section format 26 + 4.1.2. Question section format 28 + 4.1.3. Resource record format 29 + 4.1.4. Message compression 30 + 4.2. Transport 32 + 4.2.1. UDP usage 32 + 4.2.2. TCP usage 32 + 5. MASTER FILES 33 + 5.1. Format 33 + 5.2. Use of master files to define zones 35 + 5.3. Master file example 36 + 6. NAME SERVER IMPLEMENTATION 37 + 6.1. Architecture 37 + 6.1.1. Control 37 + 6.1.2. Database 37 + 6.1.3. Time 39 + 6.2. Standard query processing 39 + 6.3. Zone refresh and reload processing 39 + 6.4. Inverse queries (Optional) 40 + 6.4.1. The contents of inverse queries and responses 40 + 6.4.2. Inverse query and response example 41 + 6.4.3. Inverse query processing 42 + + + + + + +Mockapetris [Page 2] + +RFC 1035 Domain Implementation and Specification November 1987 + + + 6.5. Completion queries and responses 42 + 7. RESOLVER IMPLEMENTATION 43 + 7.1. Transforming a user request into a query 43 + 7.2. Sending the queries 44 + 7.3. Processing responses 46 + 7.4. Using the cache 47 + 8. MAIL SUPPORT 47 + 8.1. Mail exchange binding 48 + 8.2. Mailbox binding (Experimental) 48 + 9. REFERENCES and BIBLIOGRAPHY 50 + Index 54 + +2. INTRODUCTION + +2.1. Overview + +The goal of domain names is to provide a mechanism for naming resources +in such a way that the names are usable in different hosts, networks, +protocol families, internets, and administrative organizations. + +From the user's point of view, domain names are useful as arguments to a +local agent, called a resolver, which retrieves information associated +with the domain name. Thus a user might ask for the host address or +mail information associated with a particular domain name. To enable +the user to request a particular type of information, an appropriate +query type is passed to the resolver with the domain name. To the user, +the domain tree is a single information space; the resolver is +responsible for hiding the distribution of data among name servers from +the user. + +From the resolver's point of view, the database that makes up the domain +space is distributed among various name servers. Different parts of the +domain space are stored in different name servers, although a particular +data item will be stored redundantly in two or more name servers. The +resolver starts with knowledge of at least one name server. When the +resolver processes a user query it asks a known name server for the +information; in return, the resolver either receives the desired +information or a referral to another name server. Using these +referrals, resolvers learn the identities and contents of other name +servers. Resolvers are responsible for dealing with the distribution of +the domain space and dealing with the effects of name server failure by +consulting redundant databases in other servers. + +Name servers manage two kinds of data. The first kind of data held in +sets called zones; each zone is the complete database for a particular +"pruned" subtree of the domain space. This data is called +authoritative. A name server periodically checks to make sure that its +zones are up to date, and if not, obtains a new copy of updated zones + + + +Mockapetris [Page 3] + +RFC 1035 Domain Implementation and Specification November 1987 + + +from master files stored locally or in another name server. The second +kind of data is cached data which was acquired by a local resolver. +This data may be incomplete, but improves the performance of the +retrieval process when non-local data is repeatedly accessed. Cached +data is eventually discarded by a timeout mechanism. + +This functional structure isolates the problems of user interface, +failure recovery, and distribution in the resolvers and isolates the +database update and refresh problems in the name servers. + +2.2. Common configurations + +A host can participate in the domain name system in a number of ways, +depending on whether the host runs programs that retrieve information +from the domain system, name servers that answer queries from other +hosts, or various combinations of both functions. The simplest, and +perhaps most typical, configuration is shown below: + + Local Host | Foreign + | + +---------+ +----------+ | +--------+ + | | user queries | |queries | | | + | User |-------------->| |---------|->|Foreign | + | Program | | Resolver | | | Name | + | |<--------------| |<--------|--| Server | + | | user responses| |responses| | | + +---------+ +----------+ | +--------+ + | A | + cache additions | | references | + V | | + +----------+ | + | cache | | + +----------+ | + +User programs interact with the domain name space through resolvers; the +format of user queries and user responses is specific to the host and +its operating system. User queries will typically be operating system +calls, and the resolver and its cache will be part of the host operating +system. Less capable hosts may choose to implement the resolver as a +subroutine to be linked in with every program that needs its services. +Resolvers answer user queries with information they acquire via queries +to foreign name servers and the local cache. + +Note that the resolver may have to make several queries to several +different foreign name servers to answer a particular user query, and +hence the resolution of a user query may involve several network +accesses and an arbitrary amount of time. The queries to foreign name +servers and the corresponding responses have a standard format described + + + +Mockapetris [Page 4] + +RFC 1035 Domain Implementation and Specification November 1987 + + +in this memo, and may be datagrams. + +Depending on its capabilities, a name server could be a stand alone +program on a dedicated machine or a process or processes on a large +timeshared host. A simple configuration might be: + + Local Host | Foreign + | + +---------+ | + / /| | + +---------+ | +----------+ | +--------+ + | | | | |responses| | | + | | | | Name |---------|->|Foreign | + | Master |-------------->| Server | | |Resolver| + | files | | | |<--------|--| | + | |/ | | queries | +--------+ + +---------+ +----------+ | + +Here a primary name server acquires information about one or more zones +by reading master files from its local file system, and answers queries +about those zones that arrive from foreign resolvers. + +The DNS requires that all zones be redundantly supported by more than +one name server. Designated secondary servers can acquire zones and +check for updates from the primary server using the zone transfer +protocol of the DNS. This configuration is shown below: + + Local Host | Foreign + | + +---------+ | + / /| | + +---------+ | +----------+ | +--------+ + | | | | |responses| | | + | | | | Name |---------|->|Foreign | + | Master |-------------->| Server | | |Resolver| + | files | | | |<--------|--| | + | |/ | | queries | +--------+ + +---------+ +----------+ | + A |maintenance | +--------+ + | +------------|->| | + | queries | |Foreign | + | | | Name | + +------------------|--| Server | + maintenance responses | +--------+ + +In this configuration, the name server periodically establishes a +virtual circuit to a foreign name server to acquire a copy of a zone or +to check that an existing copy has not changed. The messages sent for + + + +Mockapetris [Page 5] + +RFC 1035 Domain Implementation and Specification November 1987 + + +these maintenance activities follow the same form as queries and +responses, but the message sequences are somewhat different. + +The information flow in a host that supports all aspects of the domain +name system is shown below: + + Local Host | Foreign + | + +---------+ +----------+ | +--------+ + | | user queries | |queries | | | + | User |-------------->| |---------|->|Foreign | + | Program | | Resolver | | | Name | + | |<--------------| |<--------|--| Server | + | | user responses| |responses| | | + +---------+ +----------+ | +--------+ + | A | + cache additions | | references | + V | | + +----------+ | + | Shared | | + | database | | + +----------+ | + A | | + +---------+ refreshes | | references | + / /| | V | + +---------+ | +----------+ | +--------+ + | | | | |responses| | | + | | | | Name |---------|->|Foreign | + | Master |-------------->| Server | | |Resolver| + | files | | | |<--------|--| | + | |/ | | queries | +--------+ + +---------+ +----------+ | + A |maintenance | +--------+ + | +------------|->| | + | queries | |Foreign | + | | | Name | + +------------------|--| Server | + maintenance responses | +--------+ + +The shared database holds domain space data for the local name server +and resolver. The contents of the shared database will typically be a +mixture of authoritative data maintained by the periodic refresh +operations of the name server and cached data from previous resolver +requests. The structure of the domain data and the necessity for +synchronization between name servers and resolvers imply the general +characteristics of this database, but the actual format is up to the +local implementor. + + + + +Mockapetris [Page 6] + +RFC 1035 Domain Implementation and Specification November 1987 + + +Information flow can also be tailored so that a group of hosts act +together to optimize activities. Sometimes this is done to offload less +capable hosts so that they do not have to implement a full resolver. +This can be appropriate for PCs or hosts which want to minimize the +amount of new network code which is required. This scheme can also +allow a group of hosts can share a small number of caches rather than +maintaining a large number of separate caches, on the premise that the +centralized caches will have a higher hit ratio. In either case, +resolvers are replaced with stub resolvers which act as front ends to +resolvers located in a recursive server in one or more name servers +known to perform that service: + + Local Hosts | Foreign + | + +---------+ | + | | responses | + | Stub |<--------------------+ | + | Resolver| | | + | |----------------+ | | + +---------+ recursive | | | + queries | | | + V | | + +---------+ recursive +----------+ | +--------+ + | | queries | |queries | | | + | Stub |-------------->| Recursive|---------|->|Foreign | + | Resolver| | Server | | | Name | + | |<--------------| |<--------|--| Server | + +---------+ responses | |responses| | | + +----------+ | +--------+ + | Central | | + | cache | | + +----------+ | + +In any case, note that domain components are always replicated for +reliability whenever possible. + +2.3. Conventions + +The domain system has several conventions dealing with low-level, but +fundamental, issues. While the implementor is free to violate these +conventions WITHIN HIS OWN SYSTEM, he must observe these conventions in +ALL behavior observed from other hosts. + +2.3.1. Preferred name syntax + +The DNS specifications attempt to be as general as possible in the rules +for constructing domain names. The idea is that the name of any +existing object can be expressed as a domain name with minimal changes. + + + +Mockapetris [Page 7] + +RFC 1035 Domain Implementation and Specification November 1987 + + +However, when assigning a domain name for an object, the prudent user +will select a name which satisfies both the rules of the domain system +and any existing rules for the object, whether these rules are published +or implied by existing programs. + +For example, when naming a mail domain, the user should satisfy both the +rules of this memo and those in RFC-822. When creating a new host name, +the old rules for HOSTS.TXT should be followed. This avoids problems +when old software is converted to use domain names. + +The following syntax will result in fewer problems with many + +applications that use domain names (e.g., mail, TELNET). + +<domain> ::= <subdomain> | " " + +<subdomain> ::= <label> | <subdomain> "." <label> + +<label> ::= <letter> [ [ <ldh-str> ] <let-dig> ] + +<ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str> + +<let-dig-hyp> ::= <let-dig> | "-" + +<let-dig> ::= <letter> | <digit> + +<letter> ::= any one of the 52 alphabetic characters A through Z in +upper case and a through z in lower case + +<digit> ::= any one of the ten digits 0 through 9 + +Note that while upper and lower case letters are allowed in domain +names, no significance is attached to the case. That is, two names with +the same spelling but different case are to be treated as if identical. + +The labels must follow the rules for ARPANET host names. They must +start with a letter, end with a letter or digit, and have as interior +characters only letters, digits, and hyphen. There are also some +restrictions on the length. Labels must be 63 characters or less. + +For example, the following strings identify hosts in the Internet: + +A.ISI.EDU XX.LCS.MIT.EDU SRI-NIC.ARPA + +2.3.2. Data Transmission Order + +The order of transmission of the header and data described in this +document is resolved to the octet level. Whenever a diagram shows a + + + +Mockapetris [Page 8] + +RFC 1035 Domain Implementation and Specification November 1987 + + +group of octets, the order of transmission of those octets is the normal +order in which they are read in English. For example, in the following +diagram, the octets are transmitted in the order they are numbered. + + 0 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 1 | 2 | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 3 | 4 | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 5 | 6 | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +Whenever an octet represents a numeric quantity, the left most bit in +the diagram is the high order or most significant bit. That is, the bit +labeled 0 is the most significant bit. For example, the following +diagram represents the value 170 (decimal). + + 0 1 2 3 4 5 6 7 + +-+-+-+-+-+-+-+-+ + |1 0 1 0 1 0 1 0| + +-+-+-+-+-+-+-+-+ + +Similarly, whenever a multi-octet field represents a numeric quantity +the left most bit of the whole field is the most significant bit. When +a multi-octet quantity is transmitted the most significant octet is +transmitted first. + +2.3.3. Character Case + +For all parts of the DNS that are part of the official protocol, all +comparisons between character strings (e.g., labels, domain names, etc.) +are done in a case-insensitive manner. At present, this rule is in +force throughout the domain system without exception. However, future +additions beyond current usage may need to use the full binary octet +capabilities in names, so attempts to store domain names in 7-bit ASCII +or use of special bytes to terminate labels, etc., should be avoided. + +When data enters the domain system, its original case should be +preserved whenever possible. In certain circumstances this cannot be +done. For example, if two RRs are stored in a database, one at x.y and +one at X.Y, they are actually stored at the same place in the database, +and hence only one casing would be preserved. The basic rule is that +case can be discarded only when data is used to define structure in a +database, and two names are identical when compared in a case +insensitive manner. + + + + +Mockapetris [Page 9] + +RFC 1035 Domain Implementation and Specification November 1987 + + +Loss of case sensitive data must be minimized. Thus while data for x.y +and X.Y may both be stored under a single location x.y or X.Y, data for +a.x and B.X would never be stored under A.x, A.X, b.x, or b.X. In +general, this preserves the case of the first label of a domain name, +but forces standardization of interior node labels. + +Systems administrators who enter data into the domain database should +take care to represent the data they supply to the domain system in a +case-consistent manner if their system is case-sensitive. The data +distribution system in the domain system will ensure that consistent +representations are preserved. + +2.3.4. Size limits + +Various objects and parameters in the DNS have size limits. They are +listed below. Some could be easily changed, others are more +fundamental. + +labels 63 octets or less + +names 255 octets or less + +TTL positive values of a signed 32 bit number. + +UDP messages 512 octets or less + +3. DOMAIN NAME SPACE AND RR DEFINITIONS + +3.1. Name space definitions + +Domain names in messages are expressed in terms of a sequence of labels. +Each label is represented as a one octet length field followed by that +number of octets. Since every domain name ends with the null label of +the root, a domain name is terminated by a length byte of zero. The +high order two bits of every length octet must be zero, and the +remaining six bits of the length field limit the label to 63 octets or +less. + +To simplify implementations, the total length of a domain name (i.e., +label octets and label length octets) is restricted to 255 octets or +less. + +Although labels can contain any 8 bit values in octets that make up a +label, it is strongly recommended that labels follow the preferred +syntax described elsewhere in this memo, which is compatible with +existing host naming conventions. Name servers and resolvers must +compare labels in a case-insensitive manner (i.e., A=a), assuming ASCII +with zero parity. Non-alphabetic codes must match exactly. + + + +Mockapetris [Page 10] + +RFC 1035 Domain Implementation and Specification November 1987 + + +3.2. RR definitions + +3.2.1. Format + +All RRs have the same top level format shown below: + + 1 1 1 1 1 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | | + / / + / NAME / + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | TYPE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | CLASS | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | TTL | + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | RDLENGTH | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--| + / RDATA / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + + +where: + +NAME an owner name, i.e., the name of the node to which this + resource record pertains. + +TYPE two octets containing one of the RR TYPE codes. + +CLASS two octets containing one of the RR CLASS codes. + +TTL a 32 bit signed integer that specifies the time interval + that the resource record may be cached before the source + of the information should again be consulted. Zero + values are interpreted to mean that the RR can only be + used for the transaction in progress, and should not be + cached. For example, SOA records are always distributed + with a zero TTL to prohibit caching. Zero values can + also be used for extremely volatile data. + +RDLENGTH an unsigned 16 bit integer that specifies the length in + octets of the RDATA field. + + + +Mockapetris [Page 11] + +RFC 1035 Domain Implementation and Specification November 1987 + + +RDATA a variable length string of octets that describes the + resource. The format of this information varies + according to the TYPE and CLASS of the resource record. + +3.2.2. TYPE values + +TYPE fields are used in resource records. Note that these types are a +subset of QTYPEs. + +TYPE value and meaning + +A 1 a host address + +NS 2 an authoritative name server + +MD 3 a mail destination (Obsolete - use MX) + +MF 4 a mail forwarder (Obsolete - use MX) + +CNAME 5 the canonical name for an alias + +SOA 6 marks the start of a zone of authority + +MB 7 a mailbox domain name (EXPERIMENTAL) + +MG 8 a mail group member (EXPERIMENTAL) + +MR 9 a mail rename domain name (EXPERIMENTAL) + +NULL 10 a null RR (EXPERIMENTAL) + +WKS 11 a well known service description + +PTR 12 a domain name pointer + +HINFO 13 host information + +MINFO 14 mailbox or mail list information + +MX 15 mail exchange + +TXT 16 text strings + +3.2.3. QTYPE values + +QTYPE fields appear in the question part of a query. QTYPES are a +superset of TYPEs, hence all TYPEs are valid QTYPEs. In addition, the +following QTYPEs are defined: + + + +Mockapetris [Page 12] + +RFC 1035 Domain Implementation and Specification November 1987 + + +AXFR 252 A request for a transfer of an entire zone + +MAILB 253 A request for mailbox-related records (MB, MG or MR) + +MAILA 254 A request for mail agent RRs (Obsolete - see MX) + +* 255 A request for all records + +3.2.4. CLASS values + +CLASS fields appear in resource records. The following CLASS mnemonics +and values are defined: + +IN 1 the Internet + +CS 2 the CSNET class (Obsolete - used only for examples in + some obsolete RFCs) + +CH 3 the CHAOS class + +HS 4 Hesiod [Dyer 87] + +3.2.5. QCLASS values + +QCLASS fields appear in the question section of a query. QCLASS values +are a superset of CLASS values; every CLASS is a valid QCLASS. In +addition to CLASS values, the following QCLASSes are defined: + +* 255 any class + +3.3. Standard RRs + +The following RR definitions are expected to occur, at least +potentially, in all classes. In particular, NS, SOA, CNAME, and PTR +will be used in all classes, and have the same format in all classes. +Because their RDATA format is known, all domain names in the RDATA +section of these RRs may be compressed. + +<domain-name> is a domain name represented as a series of labels, and +terminated by a label with zero length. <character-string> is a single +length octet followed by that number of characters. <character-string> +is treated as binary information, and can be up to 256 characters in +length (including the length octet). + + + + + + + + +Mockapetris [Page 13] + +RFC 1035 Domain Implementation and Specification November 1987 + + +3.3.1. CNAME RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / CNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +CNAME A <domain-name> which specifies the canonical or primary + name for the owner. The owner name is an alias. + +CNAME RRs cause no additional section processing, but name servers may +choose to restart the query at the canonical name in certain cases. See +the description of name server logic in [RFC-1034] for details. + +3.3.2. HINFO RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / CPU / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / OS / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +CPU A <character-string> which specifies the CPU type. + +OS A <character-string> which specifies the operating + system type. + +Standard values for CPU and OS can be found in [RFC-1010]. + +HINFO records are used to acquire general information about a host. The +main use is for protocols such as FTP that can use special procedures +when talking between machines or operating systems of the same type. + +3.3.3. MB RDATA format (EXPERIMENTAL) + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / MADNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +MADNAME A <domain-name> which specifies a host which has the + specified mailbox. + + + +Mockapetris [Page 14] + +RFC 1035 Domain Implementation and Specification November 1987 + + +MB records cause additional section processing which looks up an A type +RRs corresponding to MADNAME. + +3.3.4. MD RDATA format (Obsolete) + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / MADNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +MADNAME A <domain-name> which specifies a host which has a mail + agent for the domain which should be able to deliver + mail for the domain. + +MD records cause additional section processing which looks up an A type +record corresponding to MADNAME. + +MD is obsolete. See the definition of MX and [RFC-974] for details of +the new scheme. The recommended policy for dealing with MD RRs found in +a master file is to reject them, or to convert them to MX RRs with a +preference of 0. + +3.3.5. MF RDATA format (Obsolete) + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / MADNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +MADNAME A <domain-name> which specifies a host which has a mail + agent for the domain which will accept mail for + forwarding to the domain. + +MF records cause additional section processing which looks up an A type +record corresponding to MADNAME. + +MF is obsolete. See the definition of MX and [RFC-974] for details ofw +the new scheme. The recommended policy for dealing with MD RRs found in +a master file is to reject them, or to convert them to MX RRs with a +preference of 10. + + + + + + + +Mockapetris [Page 15] + +RFC 1035 Domain Implementation and Specification November 1987 + + +3.3.6. MG RDATA format (EXPERIMENTAL) + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / MGMNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +MGMNAME A <domain-name> which specifies a mailbox which is a + member of the mail group specified by the domain name. + +MG records cause no additional section processing. + +3.3.7. MINFO RDATA format (EXPERIMENTAL) + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / RMAILBX / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / EMAILBX / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +RMAILBX A <domain-name> which specifies a mailbox which is + responsible for the mailing list or mailbox. If this + domain name names the root, the owner of the MINFO RR is + responsible for itself. Note that many existing mailing + lists use a mailbox X-request for the RMAILBX field of + mailing list X, e.g., Msgroup-request for Msgroup. This + field provides a more general mechanism. + + +EMAILBX A <domain-name> which specifies a mailbox which is to + receive error messages related to the mailing list or + mailbox specified by the owner of the MINFO RR (similar + to the ERRORS-TO: field which has been proposed). If + this domain name names the root, errors should be + returned to the sender of the message. + +MINFO records cause no additional section processing. Although these +records can be associated with a simple mailbox, they are usually used +with a mailing list. + + + + + + + + +Mockapetris [Page 16] + +RFC 1035 Domain Implementation and Specification November 1987 + + +3.3.8. MR RDATA format (EXPERIMENTAL) + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / NEWNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +NEWNAME A <domain-name> which specifies a mailbox which is the + proper rename of the specified mailbox. + +MR records cause no additional section processing. The main use for MR +is as a forwarding entry for a user who has moved to a different +mailbox. + +3.3.9. MX RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | PREFERENCE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / EXCHANGE / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +PREFERENCE A 16 bit integer which specifies the preference given to + this RR among others at the same owner. Lower values + are preferred. + +EXCHANGE A <domain-name> which specifies a host willing to act as + a mail exchange for the owner name. + +MX records cause type A additional section processing for the host +specified by EXCHANGE. The use of MX RRs is explained in detail in +[RFC-974]. + +3.3.10. NULL RDATA format (EXPERIMENTAL) + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / <anything> / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +Anything at all may be in the RDATA field so long as it is 65535 octets +or less. + + + + +Mockapetris [Page 17] + +RFC 1035 Domain Implementation and Specification November 1987 + + +NULL records cause no additional section processing. NULL RRs are not +allowed in master files. NULLs are used as placeholders in some +experimental extensions of the DNS. + +3.3.11. NS RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / NSDNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +NSDNAME A <domain-name> which specifies a host which should be + authoritative for the specified class and domain. + +NS records cause both the usual additional section processing to locate +a type A record, and, when used in a referral, a special search of the +zone in which they reside for glue information. + +The NS RR states that the named host should be expected to have a zone +starting at owner name of the specified class. Note that the class may +not indicate the protocol family which should be used to communicate +with the host, although it is typically a strong hint. For example, +hosts which are name servers for either Internet (IN) or Hesiod (HS) +class information are normally queried using IN class protocols. + +3.3.12. PTR RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / PTRDNAME / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +PTRDNAME A <domain-name> which points to some location in the + domain name space. + +PTR records cause no additional section processing. These RRs are used +in special domains to point to some other location in the domain space. +These records are simple data, and don't imply any special processing +similar to that performed by CNAME, which identifies aliases. See the +description of the IN-ADDR.ARPA domain for an example. + + + + + + + + +Mockapetris [Page 18] + +RFC 1035 Domain Implementation and Specification November 1987 + + +3.3.13. SOA RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / MNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / RNAME / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | SERIAL | + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | REFRESH | + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | RETRY | + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | EXPIRE | + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | MINIMUM | + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +MNAME The <domain-name> of the name server that was the + original or primary source of data for this zone. + +RNAME A <domain-name> which specifies the mailbox of the + person responsible for this zone. + +SERIAL The unsigned 32 bit version number of the original copy + of the zone. Zone transfers preserve this value. This + value wraps and should be compared using sequence space + arithmetic. + +REFRESH A 32 bit time interval before the zone should be + refreshed. + +RETRY A 32 bit time interval that should elapse before a + failed refresh should be retried. + +EXPIRE A 32 bit time value that specifies the upper limit on + the time interval that can elapse before the zone is no + longer authoritative. + + + + + +Mockapetris [Page 19] + +RFC 1035 Domain Implementation and Specification November 1987 + + +MINIMUM The unsigned 32 bit minimum TTL field that should be + exported with any RR from this zone. + +SOA records cause no additional section processing. + +All times are in units of seconds. + +Most of these fields are pertinent only for name server maintenance +operations. However, MINIMUM is used in all query operations that +retrieve RRs from a zone. Whenever a RR is sent in a response to a +query, the TTL field is set to the maximum of the TTL field from the RR +and the MINIMUM field in the appropriate SOA. Thus MINIMUM is a lower +bound on the TTL field for all RRs in a zone. Note that this use of +MINIMUM should occur when the RRs are copied into the response and not +when the zone is loaded from a master file or via a zone transfer. The +reason for this provison is to allow future dynamic update facilities to +change the SOA RR with known semantics. + + +3.3.14. TXT RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / TXT-DATA / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +TXT-DATA One or more <character-string>s. + +TXT RRs are used to hold descriptive text. The semantics of the text +depends on the domain where it is found. + +3.4. Internet specific RRs + +3.4.1. A RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | ADDRESS | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +ADDRESS A 32 bit Internet address. + +Hosts that have multiple Internet addresses will have multiple A +records. + + + + + +Mockapetris [Page 20] + +RFC 1035 Domain Implementation and Specification November 1987 + + +A records cause no additional section processing. The RDATA section of +an A line in a master file is an Internet address expressed as four +decimal numbers separated by dots without any imbedded spaces (e.g., +"10.2.0.52" or "192.0.5.6"). + +3.4.2. WKS RDATA format + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | ADDRESS | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | PROTOCOL | | + +--+--+--+--+--+--+--+--+ | + | | + / <BIT MAP> / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +ADDRESS An 32 bit Internet address + +PROTOCOL An 8 bit IP protocol number + +<BIT MAP> A variable length bit map. The bit map must be a + multiple of 8 bits long. + +The WKS record is used to describe the well known services supported by +a particular protocol on a particular internet address. The PROTOCOL +field specifies an IP protocol number, and the bit map has one bit per +port of the specified protocol. The first bit corresponds to port 0, +the second to port 1, etc. If the bit map does not include a bit for a +protocol of interest, that bit is assumed zero. The appropriate values +and mnemonics for ports and protocols are specified in [RFC-1010]. + +For example, if PROTOCOL=TCP (6), the 26th bit corresponds to TCP port +25 (SMTP). If this bit is set, a SMTP server should be listening on TCP +port 25; if zero, SMTP service is not supported on the specified +address. + +The purpose of WKS RRs is to provide availability information for +servers for TCP and UDP. If a server supports both TCP and UDP, or has +multiple Internet addresses, then multiple WKS RRs are used. + +WKS RRs cause no additional section processing. + +In master files, both ports and protocols are expressed using mnemonics +or decimal numbers. + + + + +Mockapetris [Page 21] + +RFC 1035 Domain Implementation and Specification November 1987 + + +3.5. IN-ADDR.ARPA domain + +The Internet uses a special domain to support gateway location and +Internet address to host mapping. Other classes may employ a similar +strategy in other domains. The intent of this domain is to provide a +guaranteed method to perform host address to host name mapping, and to +facilitate queries to locate all gateways on a particular network in the +Internet. + +Note that both of these services are similar to functions that could be +performed by inverse queries; the difference is that this part of the +domain name space is structured according to address, and hence can +guarantee that the appropriate data can be located without an exhaustive +search of the domain space. + +The domain begins at IN-ADDR.ARPA and has a substructure which follows +the Internet addressing structure. + +Domain names in the IN-ADDR.ARPA domain are defined to have up to four +labels in addition to the IN-ADDR.ARPA suffix. Each label represents +one octet of an Internet address, and is expressed as a character string +for a decimal value in the range 0-255 (with leading zeros omitted +except in the case of a zero octet which is represented by a single +zero). + +Host addresses are represented by domain names that have all four labels +specified. Thus data for Internet address 10.2.0.52 is located at +domain name 52.0.2.10.IN-ADDR.ARPA. The reversal, though awkward to +read, allows zones to be delegated which are exactly one network of +address space. For example, 10.IN-ADDR.ARPA can be a zone containing +data for the ARPANET, while 26.IN-ADDR.ARPA can be a separate zone for +MILNET. Address nodes are used to hold pointers to primary host names +in the normal domain space. + +Network numbers correspond to some non-terminal nodes at various depths +in the IN-ADDR.ARPA domain, since Internet network numbers are either 1, +2, or 3 octets. Network nodes are used to hold pointers to the primary +host names of gateways attached to that network. Since a gateway is, by +definition, on more than one network, it will typically have two or more +network nodes which point at it. Gateways will also have host level +pointers at their fully qualified addresses. + +Both the gateway pointers at network nodes and the normal host pointers +at full address nodes use the PTR RR to point back to the primary domain +names of the corresponding hosts. + +For example, the IN-ADDR.ARPA domain will contain information about the +ISI gateway between net 10 and 26, an MIT gateway from net 10 to MIT's + + + +Mockapetris [Page 22] + +RFC 1035 Domain Implementation and Specification November 1987 + + +net 18, and hosts A.ISI.EDU and MULTICS.MIT.EDU. Assuming that ISI +gateway has addresses 10.2.0.22 and 26.0.0.103, and a name MILNET- +GW.ISI.EDU, and the MIT gateway has addresses 10.0.0.77 and 18.10.0.4 +and a name GW.LCS.MIT.EDU, the domain database would contain: + + 10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU. + 10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU. + 18.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU. + 26.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU. + 22.0.2.10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU. + 103.0.0.26.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU. + 77.0.0.10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU. + 4.0.10.18.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU. + 103.0.3.26.IN-ADDR.ARPA. PTR A.ISI.EDU. + 6.0.0.10.IN-ADDR.ARPA. PTR MULTICS.MIT.EDU. + +Thus a program which wanted to locate gateways on net 10 would originate +a query of the form QTYPE=PTR, QCLASS=IN, QNAME=10.IN-ADDR.ARPA. It +would receive two RRs in response: + + 10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU. + 10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU. + +The program could then originate QTYPE=A, QCLASS=IN queries for MILNET- +GW.ISI.EDU. and GW.LCS.MIT.EDU. to discover the Internet addresses of +these gateways. + +A resolver which wanted to find the host name corresponding to Internet +host address 10.0.0.6 would pursue a query of the form QTYPE=PTR, +QCLASS=IN, QNAME=6.0.0.10.IN-ADDR.ARPA, and would receive: + + 6.0.0.10.IN-ADDR.ARPA. PTR MULTICS.MIT.EDU. + +Several cautions apply to the use of these services: + - Since the IN-ADDR.ARPA special domain and the normal domain + for a particular host or gateway will be in different zones, + the possibility exists that that the data may be inconsistent. + + - Gateways will often have two names in separate domains, only + one of which can be primary. + + - Systems that use the domain database to initialize their + routing tables must start with enough gateway information to + guarantee that they can access the appropriate name server. + + - The gateway data only reflects the existence of a gateway in a + manner equivalent to the current HOSTS.TXT file. It doesn't + replace the dynamic availability information from GGP or EGP. + + + +Mockapetris [Page 23] + +RFC 1035 Domain Implementation and Specification November 1987 + + +3.6. Defining new types, classes, and special namespaces + +The previously defined types and classes are the ones in use as of the +date of this memo. New definitions should be expected. This section +makes some recommendations to designers considering additions to the +existing facilities. The mailing list NAMEDROPPERS@SRI-NIC.ARPA is the +forum where general discussion of design issues takes place. + +In general, a new type is appropriate when new information is to be +added to the database about an existing object, or we need new data +formats for some totally new object. Designers should attempt to define +types and their RDATA formats that are generally applicable to all +classes, and which avoid duplication of information. New classes are +appropriate when the DNS is to be used for a new protocol, etc which +requires new class-specific data formats, or when a copy of the existing +name space is desired, but a separate management domain is necessary. + +New types and classes need mnemonics for master files; the format of the +master files requires that the mnemonics for type and class be disjoint. + +TYPE and CLASS values must be a proper subset of QTYPEs and QCLASSes +respectively. + +The present system uses multiple RRs to represent multiple values of a +type rather than storing multiple values in the RDATA section of a +single RR. This is less efficient for most applications, but does keep +RRs shorter. The multiple RRs assumption is incorporated in some +experimental work on dynamic update methods. + +The present system attempts to minimize the duplication of data in the +database in order to insure consistency. Thus, in order to find the +address of the host for a mail exchange, you map the mail domain name to +a host name, then the host name to addresses, rather than a direct +mapping to host address. This approach is preferred because it avoids +the opportunity for inconsistency. + +In defining a new type of data, multiple RR types should not be used to +create an ordering between entries or express different formats for +equivalent bindings, instead this information should be carried in the +body of the RR and a single type used. This policy avoids problems with +caching multiple types and defining QTYPEs to match multiple types. + +For example, the original form of mail exchange binding used two RR +types one to represent a "closer" exchange (MD) and one to represent a +"less close" exchange (MF). The difficulty is that the presence of one +RR type in a cache doesn't convey any information about the other +because the query which acquired the cached information might have used +a QTYPE of MF, MD, or MAILA (which matched both). The redesigned + + + +Mockapetris [Page 24] + +RFC 1035 Domain Implementation and Specification November 1987 + + +service used a single type (MX) with a "preference" value in the RDATA +section which can order different RRs. However, if any MX RRs are found +in the cache, then all should be there. + +4. MESSAGES + +4.1. Format + +All communications inside of the domain protocol are carried in a single +format called a message. The top level format of message is divided +into 5 sections (some of which are empty in certain cases) shown below: + + +---------------------+ + | Header | + +---------------------+ + | Question | the question for the name server + +---------------------+ + | Answer | RRs answering the question + +---------------------+ + | Authority | RRs pointing toward an authority + +---------------------+ + | Additional | RRs holding additional information + +---------------------+ + +The header section is always present. The header includes fields that +specify which of the remaining sections are present, and also specify +whether the message is a query or a response, a standard query or some +other opcode, etc. + +The names of the sections after the header are derived from their use in +standard queries. The question section contains fields that describe a +question to a name server. These fields are a query type (QTYPE), a +query class (QCLASS), and a query domain name (QNAME). The last three +sections have the same format: a possibly empty list of concatenated +resource records (RRs). The answer section contains RRs that answer the +question; the authority section contains RRs that point toward an +authoritative name server; the additional records section contains RRs +which relate to the query, but are not strictly answers for the +question. + + + + + + + + + + + + +Mockapetris [Page 25] + +RFC 1035 Domain Implementation and Specification November 1987 + + +4.1.1. Header section format + +The header contains the following fields: + + 1 1 1 1 1 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | ID | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + |QR| Opcode |AA|TC|RD|RA| Z | RCODE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | QDCOUNT | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | ANCOUNT | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | NSCOUNT | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | ARCOUNT | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +ID A 16 bit identifier assigned by the program that + generates any kind of query. This identifier is copied + the corresponding reply and can be used by the requester + to match up replies to outstanding queries. + +QR A one bit field that specifies whether this message is a + query (0), or a response (1). + +OPCODE A four bit field that specifies kind of query in this + message. This value is set by the originator of a query + and copied into the response. The values are: + + 0 a standard query (QUERY) + + 1 an inverse query (IQUERY) + + 2 a server status request (STATUS) + + 3-15 reserved for future use + +AA Authoritative Answer - this bit is valid in responses, + and specifies that the responding name server is an + authority for the domain name in question section. + + Note that the contents of the answer section may have + multiple owner names because of aliases. The AA bit + + + +Mockapetris [Page 26] + +RFC 1035 Domain Implementation and Specification November 1987 + + + corresponds to the name which matches the query name, or + the first owner name in the answer section. + +TC TrunCation - specifies that this message was truncated + due to length greater than that permitted on the + transmission channel. + +RD Recursion Desired - this bit may be set in a query and + is copied into the response. If RD is set, it directs + the name server to pursue the query recursively. + Recursive query support is optional. + +RA Recursion Available - this be is set or cleared in a + response, and denotes whether recursive query support is + available in the name server. + +Z Reserved for future use. Must be zero in all queries + and responses. + +RCODE Response code - this 4 bit field is set as part of + responses. The values have the following + interpretation: + + 0 No error condition + + 1 Format error - The name server was + unable to interpret the query. + + 2 Server failure - The name server was + unable to process this query due to a + problem with the name server. + + 3 Name Error - Meaningful only for + responses from an authoritative name + server, this code signifies that the + domain name referenced in the query does + not exist. + + 4 Not Implemented - The name server does + not support the requested kind of query. + + 5 Refused - The name server refuses to + perform the specified operation for + policy reasons. For example, a name + server may not wish to provide the + information to the particular requester, + or a name server may not wish to perform + a particular operation (e.g., zone + + + +Mockapetris [Page 27] + +RFC 1035 Domain Implementation and Specification November 1987 + + + transfer) for particular data. + + 6-15 Reserved for future use. + +QDCOUNT an unsigned 16 bit integer specifying the number of + entries in the question section. + +ANCOUNT an unsigned 16 bit integer specifying the number of + resource records in the answer section. + +NSCOUNT an unsigned 16 bit integer specifying the number of name + server resource records in the authority records + section. + +ARCOUNT an unsigned 16 bit integer specifying the number of + resource records in the additional records section. + +4.1.2. Question section format + +The question section is used to carry the "question" in most queries, +i.e., the parameters that define what is being asked. The section +contains QDCOUNT (usually 1) entries, each of the following format: + + 1 1 1 1 1 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | | + / QNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | QTYPE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | QCLASS | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +QNAME a domain name represented as a sequence of labels, where + each label consists of a length octet followed by that + number of octets. The domain name terminates with the + zero length octet for the null label of the root. Note + that this field may be an odd number of octets; no + padding is used. + +QTYPE a two octet code which specifies the type of the query. + The values for this field include all codes valid for a + TYPE field, together with some more general codes which + can match more than one type of RR. + + + +Mockapetris [Page 28] + +RFC 1035 Domain Implementation and Specification November 1987 + + +QCLASS a two octet code that specifies the class of the query. + For example, the QCLASS field is IN for the Internet. + +4.1.3. Resource record format + +The answer, authority, and additional sections all share the same +format: a variable number of resource records, where the number of +records is specified in the corresponding count field in the header. +Each resource record has the following format: + 1 1 1 1 1 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | | + / / + / NAME / + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | TYPE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | CLASS | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | TTL | + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | RDLENGTH | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--| + / RDATA / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +where: + +NAME a domain name to which this resource record pertains. + +TYPE two octets containing one of the RR type codes. This + field specifies the meaning of the data in the RDATA + field. + +CLASS two octets which specify the class of the data in the + RDATA field. + +TTL a 32 bit unsigned integer that specifies the time + interval (in seconds) that the resource record may be + cached before it should be discarded. Zero values are + interpreted to mean that the RR can only be used for the + transaction in progress, and should not be cached. + + + + + +Mockapetris [Page 29] + +RFC 1035 Domain Implementation and Specification November 1987 + + +RDLENGTH an unsigned 16 bit integer that specifies the length in + octets of the RDATA field. + +RDATA a variable length string of octets that describes the + resource. The format of this information varies + according to the TYPE and CLASS of the resource record. + For example, the if the TYPE is A and the CLASS is IN, + the RDATA field is a 4 octet ARPA Internet address. + +4.1.4. Message compression + +In order to reduce the size of messages, the domain system utilizes a +compression scheme which eliminates the repetition of domain names in a +message. In this scheme, an entire domain name or a list of labels at +the end of a domain name is replaced with a pointer to a prior occurance +of the same name. + +The pointer takes the form of a two octet sequence: + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | 1 1| OFFSET | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +The first two bits are ones. This allows a pointer to be distinguished +from a label, since the label must begin with two zero bits because +labels are restricted to 63 octets or less. (The 10 and 01 combinations +are reserved for future use.) The OFFSET field specifies an offset from +the start of the message (i.e., the first octet of the ID field in the +domain header). A zero offset specifies the first byte of the ID field, +etc. + +The compression scheme allows a domain name in a message to be +represented as either: + + - a sequence of labels ending in a zero octet + + - a pointer + + - a sequence of labels ending with a pointer + +Pointers can only be used for occurances of a domain name where the +format is not class specific. If this were not the case, a name server +or resolver would be required to know the format of all RRs it handled. +As yet, there are no such cases, but they may occur in future RDATA +formats. + +If a domain name is contained in a part of the message subject to a +length field (such as the RDATA section of an RR), and compression is + + + +Mockapetris [Page 30] + +RFC 1035 Domain Implementation and Specification November 1987 + + +used, the length of the compressed name is used in the length +calculation, rather than the length of the expanded name. + +Programs are free to avoid using pointers in messages they generate, +although this will reduce datagram capacity, and may cause truncation. +However all programs are required to understand arriving messages that +contain pointers. + +For example, a datagram might need to use the domain names F.ISI.ARPA, +FOO.F.ISI.ARPA, ARPA, and the root. Ignoring the other fields of the +message, these domain names might be represented as: + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 20 | 1 | F | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 22 | 3 | I | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 24 | S | I | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 26 | 4 | A | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 28 | R | P | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 30 | A | 0 | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 40 | 3 | F | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 42 | O | O | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 44 | 1 1| 20 | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 64 | 1 1| 26 | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + 92 | 0 | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + +The domain name for F.ISI.ARPA is shown at offset 20. The domain name +FOO.F.ISI.ARPA is shown at offset 40; this definition uses a pointer to +concatenate a label for FOO to the previously defined F.ISI.ARPA. The +domain name ARPA is defined at offset 64 using a pointer to the ARPA +component of the name F.ISI.ARPA at 20; note that this pointer relies on +ARPA being the last label in the string at 20. The root domain name is + + + +Mockapetris [Page 31] + +RFC 1035 Domain Implementation and Specification November 1987 + + +defined by a single octet of zeros at 92; the root domain name has no +labels. + +4.2. Transport + +The DNS assumes that messages will be transmitted as datagrams or in a +byte stream carried by a virtual circuit. While virtual circuits can be +used for any DNS activity, datagrams are preferred for queries due to +their lower overhead and better performance. Zone refresh activities +must use virtual circuits because of the need for reliable transfer. + +The Internet supports name server access using TCP [RFC-793] on server +port 53 (decimal) as well as datagram access using UDP [RFC-768] on UDP +port 53 (decimal). + +4.2.1. UDP usage + +Messages sent using UDP user server port 53 (decimal). + +Messages carried by UDP are restricted to 512 bytes (not counting the IP +or UDP headers). Longer messages are truncated and the TC bit is set in +the header. + +UDP is not acceptable for zone transfers, but is the recommended method +for standard queries in the Internet. Queries sent using UDP may be +lost, and hence a retransmission strategy is required. Queries or their +responses may be reordered by the network, or by processing in name +servers, so resolvers should not depend on them being returned in order. + +The optimal UDP retransmission policy will vary with performance of the +Internet and the needs of the client, but the following are recommended: + + - The client should try other servers and server addresses + before repeating a query to a specific address of a server. + + - The retransmission interval should be based on prior + statistics if possible. Too aggressive retransmission can + easily slow responses for the community at large. Depending + on how well connected the client is to its expected servers, + the minimum retransmission interval should be 2-5 seconds. + +More suggestions on server selection and retransmission policy can be +found in the resolver section of this memo. + +4.2.2. TCP usage + +Messages sent over TCP connections use server port 53 (decimal). The +message is prefixed with a two byte length field which gives the message + + + +Mockapetris [Page 32] + +RFC 1035 Domain Implementation and Specification November 1987 + + +length, excluding the two byte length field. This length field allows +the low-level processing to assemble a complete message before beginning +to parse it. + +Several connection management policies are recommended: + + - The server should not block other activities waiting for TCP + data. + + - The server should support multiple connections. + + - The server should assume that the client will initiate + connection closing, and should delay closing its end of the + connection until all outstanding client requests have been + satisfied. + + - If the server needs to close a dormant connection to reclaim + resources, it should wait until the connection has been idle + for a period on the order of two minutes. In particular, the + server should allow the SOA and AXFR request sequence (which + begins a refresh operation) to be made on a single connection. + Since the server would be unable to answer queries anyway, a + unilateral close or reset may be used instead of a graceful + close. + +5. MASTER FILES + +Master files are text files that contain RRs in text form. Since the +contents of a zone can be expressed in the form of a list of RRs a +master file is most often used to define a zone, though it can be used +to list a cache's contents. Hence, this section first discusses the +format of RRs in a master file, and then the special considerations when +a master file is used to create a zone in some name server. + +5.1. Format + +The format of these files is a sequence of entries. Entries are +predominantly line-oriented, though parentheses can be used to continue +a list of items across a line boundary, and text literals can contain +CRLF within the text. Any combination of tabs and spaces act as a +delimiter between the separate items that make up an entry. The end of +any line in the master file can end with a comment. The comment starts +with a ";" (semicolon). + +The following entries are defined: + + <blank>[<comment>] + + + + +Mockapetris [Page 33] + +RFC 1035 Domain Implementation and Specification November 1987 + + + $ORIGIN <domain-name> [<comment>] + + $INCLUDE <file-name> [<domain-name>] [<comment>] + + <domain-name><rr> [<comment>] + + <blank><rr> [<comment>] + +Blank lines, with or without comments, are allowed anywhere in the file. + +Two control entries are defined: $ORIGIN and $INCLUDE. $ORIGIN is +followed by a domain name, and resets the current origin for relative +domain names to the stated name. $INCLUDE inserts the named file into +the current file, and may optionally specify a domain name that sets the +relative domain name origin for the included file. $INCLUDE may also +have a comment. Note that a $INCLUDE entry never changes the relative +origin of the parent file, regardless of changes to the relative origin +made within the included file. + +The last two forms represent RRs. If an entry for an RR begins with a +blank, then the RR is assumed to be owned by the last stated owner. If +an RR entry begins with a <domain-name>, then the owner name is reset. + +<rr> contents take one of the following forms: + + [<TTL>] [<class>] <type> <RDATA> + + [<class>] [<TTL>] <type> <RDATA> + +The RR begins with optional TTL and class fields, followed by a type and +RDATA field appropriate to the type and class. Class and type use the +standard mnemonics, TTL is a decimal integer. Omitted class and TTL +values are default to the last explicitly stated values. Since type and +class mnemonics are disjoint, the parse is unique. (Note that this +order is different from the order used in examples and the order used in +the actual RRs; the given order allows easier parsing and defaulting.) + +<domain-name>s make up a large share of the data in the master file. +The labels in the domain name are expressed as character strings and +separated by dots. Quoting conventions allow arbitrary characters to be +stored in domain names. Domain names that end in a dot are called +absolute, and are taken as complete. Domain names which do not end in a +dot are called relative; the actual domain name is the concatenation of +the relative part with an origin specified in a $ORIGIN, $INCLUDE, or as +an argument to the master file loading routine. A relative name is an +error when no origin is available. + + + + + +Mockapetris [Page 34] + +RFC 1035 Domain Implementation and Specification November 1987 + + +<character-string> is expressed in one or two ways: as a contiguous set +of characters without interior spaces, or as a string beginning with a " +and ending with a ". Inside a " delimited string any character can +occur, except for a " itself, which must be quoted using \ (back slash). + +Because these files are text files several special encodings are +necessary to allow arbitrary data to be loaded. In particular: + + of the root. + +@ A free standing @ is used to denote the current origin. + +\X where X is any character other than a digit (0-9), is + used to quote that character so that its special meaning + does not apply. For example, "\." can be used to place + a dot character in a label. + +\DDD where each D is a digit is the octet corresponding to + the decimal number described by DDD. The resulting + octet is assumed to be text and is not checked for + special meaning. + +( ) Parentheses are used to group data that crosses a line + boundary. In effect, line terminations are not + recognized within parentheses. + +; Semicolon is used to start a comment; the remainder of + the line is ignored. + +5.2. Use of master files to define zones + +When a master file is used to load a zone, the operation should be +suppressed if any errors are encountered in the master file. The +rationale for this is that a single error can have widespread +consequences. For example, suppose that the RRs defining a delegation +have syntax errors; then the server will return authoritative name +errors for all names in the subzone (except in the case where the +subzone is also present on the server). + +Several other validity checks that should be performed in addition to +insuring that the file is syntactically correct: + + 1. All RRs in the file should have the same class. + + 2. Exactly one SOA RR should be present at the top of the zone. + + 3. If delegations are present and glue information is required, + it should be present. + + + +Mockapetris [Page 35] + +RFC 1035 Domain Implementation and Specification November 1987 + + + 4. Information present outside of the authoritative nodes in the + zone should be glue information, rather than the result of an + origin or similar error. + +5.3. Master file example + +The following is an example file which might be used to define the +ISI.EDU zone.and is loaded with an origin of ISI.EDU: + +@ IN SOA VENERA Action\.domains ( + 20 ; SERIAL + 7200 ; REFRESH + 600 ; RETRY + 3600000; EXPIRE + 60) ; MINIMUM + + NS A.ISI.EDU. + NS VENERA + NS VAXA + MX 10 VENERA + MX 20 VAXA + +A A 26.3.0.103 + +VENERA A 10.1.0.52 + A 128.9.0.32 + +VAXA A 10.2.0.27 + A 128.9.0.33 + + +$INCLUDE <SUBSYS>ISI-MAILBOXES.TXT + +Where the file <SUBSYS>ISI-MAILBOXES.TXT is: + + MOE MB A.ISI.EDU. + LARRY MB A.ISI.EDU. + CURLEY MB A.ISI.EDU. + STOOGES MG MOE + MG LARRY + MG CURLEY + +Note the use of the \ character in the SOA RR to specify the responsible +person mailbox "Action.domains@E.ISI.EDU". + + + + + + + +Mockapetris [Page 36] + +RFC 1035 Domain Implementation and Specification November 1987 + + +6. NAME SERVER IMPLEMENTATION + +6.1. Architecture + +The optimal structure for the name server will depend on the host +operating system and whether the name server is integrated with resolver +operations, either by supporting recursive service, or by sharing its +database with a resolver. This section discusses implementation +considerations for a name server which shares a database with a +resolver, but most of these concerns are present in any name server. + +6.1.1. Control + +A name server must employ multiple concurrent activities, whether they +are implemented as separate tasks in the host's OS or multiplexing +inside a single name server program. It is simply not acceptable for a +name server to block the service of UDP requests while it waits for TCP +data for refreshing or query activities. Similarly, a name server +should not attempt to provide recursive service without processing such +requests in parallel, though it may choose to serialize requests from a +single client, or to regard identical requests from the same client as +duplicates. A name server should not substantially delay requests while +it reloads a zone from master files or while it incorporates a newly +refreshed zone into its database. + +6.1.2. Database + +While name server implementations are free to use any internal data +structures they choose, the suggested structure consists of three major +parts: + + - A "catalog" data structure which lists the zones available to + this server, and a "pointer" to the zone data structure. The + main purpose of this structure is to find the nearest ancestor + zone, if any, for arriving standard queries. + + - Separate data structures for each of the zones held by the + name server. + + - A data structure for cached data. (or perhaps separate caches + for different classes) + +All of these data structures can be implemented an identical tree +structure format, with different data chained off the nodes in different +parts: in the catalog the data is pointers to zones, while in the zone +and cache data structures, the data will be RRs. In designing the tree +framework the designer should recognize that query processing will need +to traverse the tree using case-insensitive label comparisons; and that + + + +Mockapetris [Page 37] + +RFC 1035 Domain Implementation and Specification November 1987 + + +in real data, a few nodes have a very high branching factor (100-1000 or +more), but the vast majority have a very low branching factor (0-1). + +One way to solve the case problem is to store the labels for each node +in two pieces: a standardized-case representation of the label where all +ASCII characters are in a single case, together with a bit mask that +denotes which characters are actually of a different case. The +branching factor diversity can be handled using a simple linked list for +a node until the branching factor exceeds some threshold, and +transitioning to a hash structure after the threshold is exceeded. In +any case, hash structures used to store tree sections must insure that +hash functions and procedures preserve the casing conventions of the +DNS. + +The use of separate structures for the different parts of the database +is motivated by several factors: + + - The catalog structure can be an almost static structure that + need change only when the system administrator changes the + zones supported by the server. This structure can also be + used to store parameters used to control refreshing + activities. + + - The individual data structures for zones allow a zone to be + replaced simply by changing a pointer in the catalog. Zone + refresh operations can build a new structure and, when + complete, splice it into the database via a simple pointer + replacement. It is very important that when a zone is + refreshed, queries should not use old and new data + simultaneously. + + - With the proper search procedures, authoritative data in zones + will always "hide", and hence take precedence over, cached + data. + + - Errors in zone definitions that cause overlapping zones, etc., + may cause erroneous responses to queries, but problem + determination is simplified, and the contents of one "bad" + zone can't corrupt another. + + - Since the cache is most frequently updated, it is most + vulnerable to corruption during system restarts. It can also + become full of expired RR data. In either case, it can easily + be discarded without disturbing zone data. + +A major aspect of database design is selecting a structure which allows +the name server to deal with crashes of the name server's host. State +information which a name server should save across system crashes + + + +Mockapetris [Page 38] + +RFC 1035 Domain Implementation and Specification November 1987 + + +includes the catalog structure (including the state of refreshing for +each zone) and the zone data itself. + +6.1.3. Time + +Both the TTL data for RRs and the timing data for refreshing activities +depends on 32 bit timers in units of seconds. Inside the database, +refresh timers and TTLs for cached data conceptually "count down", while +data in the zone stays with constant TTLs. + +A recommended implementation strategy is to store time in two ways: as +a relative increment and as an absolute time. One way to do this is to +use positive 32 bit numbers for one type and negative numbers for the +other. The RRs in zones use relative times; the refresh timers and +cache data use absolute times. Absolute numbers are taken with respect +to some known origin and converted to relative values when placed in the +response to a query. When an absolute TTL is negative after conversion +to relative, then the data is expired and should be ignored. + +6.2. Standard query processing + +The major algorithm for standard query processing is presented in +[RFC-1034]. + +When processing queries with QCLASS=*, or some other QCLASS which +matches multiple classes, the response should never be authoritative +unless the server can guarantee that the response covers all classes. + +When composing a response, RRs which are to be inserted in the +additional section, but duplicate RRs in the answer or authority +sections, may be omitted from the additional section. + +When a response is so long that truncation is required, the truncation +should start at the end of the response and work forward in the +datagram. Thus if there is any data for the authority section, the +answer section is guaranteed to be unique. + +The MINIMUM value in the SOA should be used to set a floor on the TTL of +data distributed from a zone. This floor function should be done when +the data is copied into a response. This will allow future dynamic +update protocols to change the SOA MINIMUM field without ambiguous +semantics. + +6.3. Zone refresh and reload processing + +In spite of a server's best efforts, it may be unable to load zone data +from a master file due to syntax errors, etc., or be unable to refresh a +zone within the its expiration parameter. In this case, the name server + + + +Mockapetris [Page 39] + +RFC 1035 Domain Implementation and Specification November 1987 + + +should answer queries as if it were not supposed to possess the zone. + +If a master is sending a zone out via AXFR, and a new version is created +during the transfer, the master should continue to send the old version +if possible. In any case, it should never send part of one version and +part of another. If completion is not possible, the master should reset +the connection on which the zone transfer is taking place. + +6.4. Inverse queries (Optional) + +Inverse queries are an optional part of the DNS. Name servers are not +required to support any form of inverse queries. If a name server +receives an inverse query that it does not support, it returns an error +response with the "Not Implemented" error set in the header. While +inverse query support is optional, all name servers must be at least +able to return the error response. + +6.4.1. The contents of inverse queries and responses Inverse +queries reverse the mappings performed by standard query operations; +while a standard query maps a domain name to a resource, an inverse +query maps a resource to a domain name. For example, a standard query +might bind a domain name to a host address; the corresponding inverse +query binds the host address to a domain name. + +Inverse queries take the form of a single RR in the answer section of +the message, with an empty question section. The owner name of the +query RR and its TTL are not significant. The response carries +questions in the question section which identify all names possessing +the query RR WHICH THE NAME SERVER KNOWS. Since no name server knows +about all of the domain name space, the response can never be assumed to +be complete. Thus inverse queries are primarily useful for database +management and debugging activities. Inverse queries are NOT an +acceptable method of mapping host addresses to host names; use the IN- +ADDR.ARPA domain instead. + +Where possible, name servers should provide case-insensitive comparisons +for inverse queries. Thus an inverse query asking for an MX RR of +"Venera.isi.edu" should get the same response as a query for +"VENERA.ISI.EDU"; an inverse query for HINFO RR "IBM-PC UNIX" should +produce the same result as an inverse query for "IBM-pc unix". However, +this cannot be guaranteed because name servers may possess RRs that +contain character strings but the name server does not know that the +data is character. + +When a name server processes an inverse query, it either returns: + + 1. zero, one, or multiple domain names for the specified + resource as QNAMEs in the question section + + + +Mockapetris [Page 40] + +RFC 1035 Domain Implementation and Specification November 1987 + + + 2. an error code indicating that the name server doesn't support + inverse mapping of the specified resource type. + +When the response to an inverse query contains one or more QNAMEs, the +owner name and TTL of the RR in the answer section which defines the +inverse query is modified to exactly match an RR found at the first +QNAME. + +RRs returned in the inverse queries cannot be cached using the same +mechanism as is used for the replies to standard queries. One reason +for this is that a name might have multiple RRs of the same type, and +only one would appear. For example, an inverse query for a single +address of a multiply homed host might create the impression that only +one address existed. + +6.4.2. Inverse query and response example The overall structure +of an inverse query for retrieving the domain name that corresponds to +Internet address 10.1.0.52 is shown below: + + +-----------------------------------------+ + Header | OPCODE=IQUERY, ID=997 | + +-----------------------------------------+ + Question | <empty> | + +-----------------------------------------+ + Answer | <anyname> A IN 10.1.0.52 | + +-----------------------------------------+ + Authority | <empty> | + +-----------------------------------------+ + Additional | <empty> | + +-----------------------------------------+ + +This query asks for a question whose answer is the Internet style +address 10.1.0.52. Since the owner name is not known, any domain name +can be used as a placeholder (and is ignored). A single octet of zero, +signifying the root, is usually used because it minimizes the length of +the message. The TTL of the RR is not significant. The response to +this query might be: + + + + + + + + + + + + + + +Mockapetris [Page 41] + +RFC 1035 Domain Implementation and Specification November 1987 + + + +-----------------------------------------+ + Header | OPCODE=RESPONSE, ID=997 | + +-----------------------------------------+ + Question |QTYPE=A, QCLASS=IN, QNAME=VENERA.ISI.EDU | + +-----------------------------------------+ + Answer | VENERA.ISI.EDU A IN 10.1.0.52 | + +-----------------------------------------+ + Authority | <empty> | + +-----------------------------------------+ + Additional | <empty> | + +-----------------------------------------+ + +Note that the QTYPE in a response to an inverse query is the same as the +TYPE field in the answer section of the inverse query. Responses to +inverse queries may contain multiple questions when the inverse is not +unique. If the question section in the response is not empty, then the +RR in the answer section is modified to correspond to be an exact copy +of an RR at the first QNAME. + +6.4.3. Inverse query processing + +Name servers that support inverse queries can support these operations +through exhaustive searches of their databases, but this becomes +impractical as the size of the database increases. An alternative +approach is to invert the database according to the search key. + +For name servers that support multiple zones and a large amount of data, +the recommended approach is separate inversions for each zone. When a +particular zone is changed during a refresh, only its inversions need to +be redone. + +Support for transfer of this type of inversion may be included in future +versions of the domain system, but is not supported in this version. + +6.5. Completion queries and responses + +The optional completion services described in RFC-882 and RFC-883 have +been deleted. Redesigned services may become available in the future. + + + + + + + + + + + + + +Mockapetris [Page 42] + +RFC 1035 Domain Implementation and Specification November 1987 + + +7. RESOLVER IMPLEMENTATION + +The top levels of the recommended resolver algorithm are discussed in +[RFC-1034]. This section discusses implementation details assuming the +database structure suggested in the name server implementation section +of this memo. + +7.1. Transforming a user request into a query + +The first step a resolver takes is to transform the client's request, +stated in a format suitable to the local OS, into a search specification +for RRs at a specific name which match a specific QTYPE and QCLASS. +Where possible, the QTYPE and QCLASS should correspond to a single type +and a single class, because this makes the use of cached data much +simpler. The reason for this is that the presence of data of one type +in a cache doesn't confirm the existence or non-existence of data of +other types, hence the only way to be sure is to consult an +authoritative source. If QCLASS=* is used, then authoritative answers +won't be available. + +Since a resolver must be able to multiplex multiple requests if it is to +perform its function efficiently, each pending request is usually +represented in some block of state information. This state block will +typically contain: + + - A timestamp indicating the time the request began. + The timestamp is used to decide whether RRs in the database + can be used or are out of date. This timestamp uses the + absolute time format previously discussed for RR storage in + zones and caches. Note that when an RRs TTL indicates a + relative time, the RR must be timely, since it is part of a + zone. When the RR has an absolute time, it is part of a + cache, and the TTL of the RR is compared against the timestamp + for the start of the request. + + Note that using the timestamp is superior to using a current + time, since it allows RRs with TTLs of zero to be entered in + the cache in the usual manner, but still used by the current + request, even after intervals of many seconds due to system + load, query retransmission timeouts, etc. + + - Some sort of parameters to limit the amount of work which will + be performed for this request. + + The amount of work which a resolver will do in response to a + client request must be limited to guard against errors in the + database, such as circular CNAME references, and operational + problems, such as network partition which prevents the + + + +Mockapetris [Page 43] + +RFC 1035 Domain Implementation and Specification November 1987 + + + resolver from accessing the name servers it needs. While + local limits on the number of times a resolver will retransmit + a particular query to a particular name server address are + essential, the resolver should have a global per-request + counter to limit work on a single request. The counter should + be set to some initial value and decremented whenever the + resolver performs any action (retransmission timeout, + retransmission, etc.) If the counter passes zero, the request + is terminated with a temporary error. + + Note that if the resolver structure allows one request to + start others in parallel, such as when the need to access a + name server for one request causes a parallel resolve for the + name server's addresses, the spawned request should be started + with a lower counter. This prevents circular references in + the database from starting a chain reaction of resolver + activity. + + - The SLIST data structure discussed in [RFC-1034]. + + This structure keeps track of the state of a request if it + must wait for answers from foreign name servers. + +7.2. Sending the queries + +As described in [RFC-1034], the basic task of the resolver is to +formulate a query which will answer the client's request and direct that +query to name servers which can provide the information. The resolver +will usually only have very strong hints about which servers to ask, in +the form of NS RRs, and may have to revise the query, in response to +CNAMEs, or revise the set of name servers the resolver is asking, in +response to delegation responses which point the resolver to name +servers closer to the desired information. In addition to the +information requested by the client, the resolver may have to call upon +its own services to determine the address of name servers it wishes to +contact. + +In any case, the model used in this memo assumes that the resolver is +multiplexing attention between multiple requests, some from the client, +and some internally generated. Each request is represented by some +state information, and the desired behavior is that the resolver +transmit queries to name servers in a way that maximizes the probability +that the request is answered, minimizes the time that the request takes, +and avoids excessive transmissions. The key algorithm uses the state +information of the request to select the next name server address to +query, and also computes a timeout which will cause the next action +should a response not arrive. The next action will usually be a +transmission to some other server, but may be a temporary error to the + + + +Mockapetris [Page 44] + +RFC 1035 Domain Implementation and Specification November 1987 + + +client. + +The resolver always starts with a list of server names to query (SLIST). +This list will be all NS RRs which correspond to the nearest ancestor +zone that the resolver knows about. To avoid startup problems, the +resolver should have a set of default servers which it will ask should +it have no current NS RRs which are appropriate. The resolver then adds +to SLIST all of the known addresses for the name servers, and may start +parallel requests to acquire the addresses of the servers when the +resolver has the name, but no addresses, for the name servers. + +To complete initialization of SLIST, the resolver attaches whatever +history information it has to the each address in SLIST. This will +usually consist of some sort of weighted averages for the response time +of the address, and the batting average of the address (i.e., how often +the address responded at all to the request). Note that this +information should be kept on a per address basis, rather than on a per +name server basis, because the response time and batting average of a +particular server may vary considerably from address to address. Note +also that this information is actually specific to a resolver address / +server address pair, so a resolver with multiple addresses may wish to +keep separate histories for each of its addresses. Part of this step +must deal with addresses which have no such history; in this case an +expected round trip time of 5-10 seconds should be the worst case, with +lower estimates for the same local network, etc. + +Note that whenever a delegation is followed, the resolver algorithm +reinitializes SLIST. + +The information establishes a partial ranking of the available name +server addresses. Each time an address is chosen and the state should +be altered to prevent its selection again until all other addresses have +been tried. The timeout for each transmission should be 50-100% greater +than the average predicted value to allow for variance in response. + +Some fine points: + + - The resolver may encounter a situation where no addresses are + available for any of the name servers named in SLIST, and + where the servers in the list are precisely those which would + normally be used to look up their own addresses. This + situation typically occurs when the glue address RRs have a + smaller TTL than the NS RRs marking delegation, or when the + resolver caches the result of a NS search. The resolver + should detect this condition and restart the search at the + next ancestor zone, or alternatively at the root. + + + + + +Mockapetris [Page 45] + +RFC 1035 Domain Implementation and Specification November 1987 + + + - If a resolver gets a server error or other bizarre response + from a name server, it should remove it from SLIST, and may + wish to schedule an immediate transmission to the next + candidate server address. + +7.3. Processing responses + +The first step in processing arriving response datagrams is to parse the +response. This procedure should include: + + - Check the header for reasonableness. Discard datagrams which + are queries when responses are expected. + + - Parse the sections of the message, and insure that all RRs are + correctly formatted. + + - As an optional step, check the TTLs of arriving data looking + for RRs with excessively long TTLs. If a RR has an + excessively long TTL, say greater than 1 week, either discard + the whole response, or limit all TTLs in the response to 1 + week. + +The next step is to match the response to a current resolver request. +The recommended strategy is to do a preliminary matching using the ID +field in the domain header, and then to verify that the question section +corresponds to the information currently desired. This requires that +the transmission algorithm devote several bits of the domain ID field to +a request identifier of some sort. This step has several fine points: + + - Some name servers send their responses from different + addresses than the one used to receive the query. That is, a + resolver cannot rely that a response will come from the same + address which it sent the corresponding query to. This name + server bug is typically encountered in UNIX systems. + + - If the resolver retransmits a particular request to a name + server it should be able to use a response from any of the + transmissions. However, if it is using the response to sample + the round trip time to access the name server, it must be able + to determine which transmission matches the response (and keep + transmission times for each outgoing message), or only + calculate round trip times based on initial transmissions. + + - A name server will occasionally not have a current copy of a + zone which it should have according to some NS RRs. The + resolver should simply remove the name server from the current + SLIST, and continue. + + + + +Mockapetris [Page 46] + +RFC 1035 Domain Implementation and Specification November 1987 + + +7.4. Using the cache + +In general, we expect a resolver to cache all data which it receives in +responses since it may be useful in answering future client requests. +However, there are several types of data which should not be cached: + + - When several RRs of the same type are available for a + particular owner name, the resolver should either cache them + all or none at all. When a response is truncated, and a + resolver doesn't know whether it has a complete set, it should + not cache a possibly partial set of RRs. + + - Cached data should never be used in preference to + authoritative data, so if caching would cause this to happen + the data should not be cached. + + - The results of an inverse query should not be cached. + + - The results of standard queries where the QNAME contains "*" + labels if the data might be used to construct wildcards. The + reason is that the cache does not necessarily contain existing + RRs or zone boundary information which is necessary to + restrict the application of the wildcard RRs. + + - RR data in responses of dubious reliability. When a resolver + receives unsolicited responses or RR data other than that + requested, it should discard it without caching it. The basic + implication is that all sanity checks on a packet should be + performed before any of it is cached. + +In a similar vein, when a resolver has a set of RRs for some name in a +response, and wants to cache the RRs, it should check its cache for +already existing RRs. Depending on the circumstances, either the data +in the response or the cache is preferred, but the two should never be +combined. If the data in the response is from authoritative data in the +answer section, it is always preferred. + +8. MAIL SUPPORT + +The domain system defines a standard for mapping mailboxes into domain +names, and two methods for using the mailbox information to derive mail +routing information. The first method is called mail exchange binding +and the other method is mailbox binding. The mailbox encoding standard +and mail exchange binding are part of the DNS official protocol, and are +the recommended method for mail routing in the Internet. Mailbox +binding is an experimental feature which is still under development and +subject to change. + + + + +Mockapetris [Page 47] + +RFC 1035 Domain Implementation and Specification November 1987 + + +The mailbox encoding standard assumes a mailbox name of the form +"<local-part>@<mail-domain>". While the syntax allowed in each of these +sections varies substantially between the various mail internets, the +preferred syntax for the ARPA Internet is given in [RFC-822]. + +The DNS encodes the <local-part> as a single label, and encodes the +<mail-domain> as a domain name. The single label from the <local-part> +is prefaced to the domain name from <mail-domain> to form the domain +name corresponding to the mailbox. Thus the mailbox HOSTMASTER@SRI- +NIC.ARPA is mapped into the domain name HOSTMASTER.SRI-NIC.ARPA. If the +<local-part> contains dots or other special characters, its +representation in a master file will require the use of backslash +quoting to ensure that the domain name is properly encoded. For +example, the mailbox Action.domains@ISI.EDU would be represented as +Action\.domains.ISI.EDU. + +8.1. Mail exchange binding + +Mail exchange binding uses the <mail-domain> part of a mailbox +specification to determine where mail should be sent. The <local-part> +is not even consulted. [RFC-974] specifies this method in detail, and +should be consulted before attempting to use mail exchange support. + +One of the advantages of this method is that it decouples mail +destination naming from the hosts used to support mail service, at the +cost of another layer of indirection in the lookup function. However, +the addition layer should eliminate the need for complicated "%", "!", +etc encodings in <local-part>. + +The essence of the method is that the <mail-domain> is used as a domain +name to locate type MX RRs which list hosts willing to accept mail for +<mail-domain>, together with preference values which rank the hosts +according to an order specified by the administrators for <mail-domain>. + +In this memo, the <mail-domain> ISI.EDU is used in examples, together +with the hosts VENERA.ISI.EDU and VAXA.ISI.EDU as mail exchanges for +ISI.EDU. If a mailer had a message for Mockapetris@ISI.EDU, it would +route it by looking up MX RRs for ISI.EDU. The MX RRs at ISI.EDU name +VENERA.ISI.EDU and VAXA.ISI.EDU, and type A queries can find the host +addresses. + +8.2. Mailbox binding (Experimental) + +In mailbox binding, the mailer uses the entire mail destination +specification to construct a domain name. The encoded domain name for +the mailbox is used as the QNAME field in a QTYPE=MAILB query. + +Several outcomes are possible for this query: + + + +Mockapetris [Page 48] + +RFC 1035 Domain Implementation and Specification November 1987 + + + 1. The query can return a name error indicating that the mailbox + does not exist as a domain name. + + In the long term, this would indicate that the specified + mailbox doesn't exist. However, until the use of mailbox + binding is universal, this error condition should be + interpreted to mean that the organization identified by the + global part does not support mailbox binding. The + appropriate procedure is to revert to exchange binding at + this point. + + 2. The query can return a Mail Rename (MR) RR. + + The MR RR carries new mailbox specification in its RDATA + field. The mailer should replace the old mailbox with the + new one and retry the operation. + + 3. The query can return a MB RR. + + The MB RR carries a domain name for a host in its RDATA + field. The mailer should deliver the message to that host + via whatever protocol is applicable, e.g., b,SMTP. + + 4. The query can return one or more Mail Group (MG) RRs. + + This condition means that the mailbox was actually a mailing + list or mail group, rather than a single mailbox. Each MG RR + has a RDATA field that identifies a mailbox that is a member + of the group. The mailer should deliver a copy of the + message to each member. + + 5. The query can return a MB RR as well as one or more MG RRs. + + This condition means the the mailbox was actually a mailing + list. The mailer can either deliver the message to the host + specified by the MB RR, which will in turn do the delivery to + all members, or the mailer can use the MG RRs to do the + expansion itself. + +In any of these cases, the response may include a Mail Information +(MINFO) RR. This RR is usually associated with a mail group, but is +legal with a MB. The MINFO RR identifies two mailboxes. One of these +identifies a responsible person for the original mailbox name. This +mailbox should be used for requests to be added to a mail group, etc. +The second mailbox name in the MINFO RR identifies a mailbox that should +receive error messages for mail failures. This is particularly +appropriate for mailing lists when errors in member names should be +reported to a person other than the one who sends a message to the list. + + + +Mockapetris [Page 49] + +RFC 1035 Domain Implementation and Specification November 1987 + + +New fields may be added to this RR in the future. + + +9. REFERENCES and BIBLIOGRAPHY + +[Dyer 87] S. Dyer, F. Hsu, "Hesiod", Project Athena + Technical Plan - Name Service, April 1987, version 1.9. + + Describes the fundamentals of the Hesiod name service. + +[IEN-116] J. Postel, "Internet Name Server", IEN-116, + USC/Information Sciences Institute, August 1979. + + A name service obsoleted by the Domain Name System, but + still in use. + +[Quarterman 86] J. Quarterman, and J. Hoskins, "Notable Computer Networks", + Communications of the ACM, October 1986, volume 29, number + 10. + +[RFC-742] K. Harrenstien, "NAME/FINGER", RFC-742, Network + Information Center, SRI International, December 1977. + +[RFC-768] J. Postel, "User Datagram Protocol", RFC-768, + USC/Information Sciences Institute, August 1980. + +[RFC-793] J. Postel, "Transmission Control Protocol", RFC-793, + USC/Information Sciences Institute, September 1981. + +[RFC-799] D. Mills, "Internet Name Domains", RFC-799, COMSAT, + September 1981. + + Suggests introduction of a hierarchy in place of a flat + name space for the Internet. + +[RFC-805] J. Postel, "Computer Mail Meeting Notes", RFC-805, + USC/Information Sciences Institute, February 1982. + +[RFC-810] E. Feinler, K. Harrenstien, Z. Su, and V. White, "DOD + Internet Host Table Specification", RFC-810, Network + Information Center, SRI International, March 1982. + + Obsolete. See RFC-952. + +[RFC-811] K. Harrenstien, V. White, and E. Feinler, "Hostnames + Server", RFC-811, Network Information Center, SRI + International, March 1982. + + + + +Mockapetris [Page 50] + +RFC 1035 Domain Implementation and Specification November 1987 + + + Obsolete. See RFC-953. + +[RFC-812] K. Harrenstien, and V. White, "NICNAME/WHOIS", RFC-812, + Network Information Center, SRI International, March + 1982. + +[RFC-819] Z. Su, and J. Postel, "The Domain Naming Convention for + Internet User Applications", RFC-819, Network + Information Center, SRI International, August 1982. + + Early thoughts on the design of the domain system. + Current implementation is completely different. + +[RFC-821] J. Postel, "Simple Mail Transfer Protocol", RFC-821, + USC/Information Sciences Institute, August 1980. + +[RFC-830] Z. Su, "A Distributed System for Internet Name Service", + RFC-830, Network Information Center, SRI International, + October 1982. + + Early thoughts on the design of the domain system. + Current implementation is completely different. + +[RFC-882] P. Mockapetris, "Domain names - Concepts and + Facilities," RFC-882, USC/Information Sciences + Institute, November 1983. + + Superceeded by this memo. + +[RFC-883] P. Mockapetris, "Domain names - Implementation and + Specification," RFC-883, USC/Information Sciences + Institute, November 1983. + + Superceeded by this memo. + +[RFC-920] J. Postel and J. Reynolds, "Domain Requirements", + RFC-920, USC/Information Sciences Institute, + October 1984. + + Explains the naming scheme for top level domains. + +[RFC-952] K. Harrenstien, M. Stahl, E. Feinler, "DoD Internet Host + Table Specification", RFC-952, SRI, October 1985. + + Specifies the format of HOSTS.TXT, the host/address + table replaced by the DNS. + + + + + +Mockapetris [Page 51] + +RFC 1035 Domain Implementation and Specification November 1987 + + +[RFC-953] K. Harrenstien, M. Stahl, E. Feinler, "HOSTNAME Server", + RFC-953, SRI, October 1985. + + This RFC contains the official specification of the + hostname server protocol, which is obsoleted by the DNS. + This TCP based protocol accesses information stored in + the RFC-952 format, and is used to obtain copies of the + host table. + +[RFC-973] P. Mockapetris, "Domain System Changes and + Observations", RFC-973, USC/Information Sciences + Institute, January 1986. + + Describes changes to RFC-882 and RFC-883 and reasons for + them. + +[RFC-974] C. Partridge, "Mail routing and the domain system", + RFC-974, CSNET CIC BBN Labs, January 1986. + + Describes the transition from HOSTS.TXT based mail + addressing to the more powerful MX system used with the + domain system. + +[RFC-1001] NetBIOS Working Group, "Protocol standard for a NetBIOS + service on a TCP/UDP transport: Concepts and Methods", + RFC-1001, March 1987. + + This RFC and RFC-1002 are a preliminary design for + NETBIOS on top of TCP/IP which proposes to base NetBIOS + name service on top of the DNS. + +[RFC-1002] NetBIOS Working Group, "Protocol standard for a NetBIOS + service on a TCP/UDP transport: Detailed + Specifications", RFC-1002, March 1987. + +[RFC-1010] J. Reynolds, and J. Postel, "Assigned Numbers", RFC-1010, + USC/Information Sciences Institute, May 1987. + + Contains socket numbers and mnemonics for host names, + operating systems, etc. + +[RFC-1031] W. Lazear, "MILNET Name Domain Transition", RFC-1031, + November 1987. + + Describes a plan for converting the MILNET to the DNS. + +[RFC-1032] M. Stahl, "Establishing a Domain - Guidelines for + Administrators", RFC-1032, November 1987. + + + +Mockapetris [Page 52] + +RFC 1035 Domain Implementation and Specification November 1987 + + + Describes the registration policies used by the NIC to + administer the top level domains and delegate subzones. + +[RFC-1033] M. Lottor, "Domain Administrators Operations Guide", + RFC-1033, November 1987. + + A cookbook for domain administrators. + +[Solomon 82] M. Solomon, L. Landweber, and D. Neuhengen, "The CSNET + Name Server", Computer Networks, vol 6, nr 3, July 1982. + + Describes a name service for CSNET which is independent + from the DNS and DNS use in the CSNET. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Mockapetris [Page 53] + +RFC 1035 Domain Implementation and Specification November 1987 + + +Index + + * 13 + + ; 33, 35 + + <character-string> 35 + <domain-name> 34 + + @ 35 + + \ 35 + + A 12 + + Byte order 8 + + CH 13 + Character case 9 + CLASS 11 + CNAME 12 + Completion 42 + CS 13 + + Hesiod 13 + HINFO 12 + HS 13 + + IN 13 + IN-ADDR.ARPA domain 22 + Inverse queries 40 + + Mailbox names 47 + MB 12 + MD 12 + MF 12 + MG 12 + MINFO 12 + MINIMUM 20 + MR 12 + MX 12 + + NS 12 + NULL 12 + + Port numbers 32 + Primary server 5 + PTR 12, 18 + + + +Mockapetris [Page 54] + +RFC 1035 Domain Implementation and Specification November 1987 + + + QCLASS 13 + QTYPE 12 + + RDATA 12 + RDLENGTH 11 + + Secondary server 5 + SOA 12 + Stub resolvers 7 + + TCP 32 + TXT 12 + TYPE 11 + + UDP 32 + + WKS 12 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Mockapetris [Page 55] + diff --git a/docs/rfc/rfc1413.txt b/docs/rfc/rfc1413.txt index e175dcece..17ede58a2 100644 --- a/docs/rfc/rfc1413.txt +++ b/docs/rfc/rfc1413.txt @@ -1 +1,451 @@ -
Network Working Group M. St. Johns
Request for Comments: 1413 US Department of Defense
Obsoletes: 931 February 1993
Identification Protocol
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet
community, and requests discussion and suggestions for improvements.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
Distribution of this memo is unlimited.
1. INTRODUCTION
The Identification Protocol (a.k.a., "ident", a.k.a., "the Ident
Protocol") provides a means to determine the identity of a user of a
particular TCP connection. Given a TCP port number pair, it returns
a character string which identifies the owner of that connection on
the server's system.
The Identification Protocol was formerly called the Authentication
Server Protocol. It has been renamed to better reflect its function.
This document is a product of the TCP Client Identity Protocol
Working Group of the Internet Engineering Task Force (IETF).
2. OVERVIEW
This is a connection based application on TCP. A server listens for
TCP connections on TCP port 113 (decimal). Once a connection is
established, the server reads a line of data which specifies the
connection of interest. If it exists, the system dependent user
identifier of the connection of interest is sent as the reply. The
server may then either shut the connection down or it may continue to
read/respond to multiple queries.
The server should close the connection down after a configurable
amount of time with no queries - a 60-180 second idle timeout is
recommended. The client may close the connection down at any time;
however to allow for network delays the client should wait at least
30 seconds (or longer) after a query before abandoning the query and
closing the connection.
St. Johns [Page 1]
RFC 1413 Identification Protocol February 1993
3. RESTRICTIONS
Queries are permitted only for fully specified connections. The
query contains the local/foreign port pair -- the local/foreign
address pair used to fully specify the connection is taken from the
local and foreign address of query connection. This means a user on
address A may only query the server on address B about connections
between A and B.
4. QUERY/RESPONSE FORMAT
The server accepts simple text query requests of the form:
<port-on-server> , <port-on-client>
where <port-on-server> is the TCP port (decimal) on the target (where
the "ident" server is running) system, and <port-on-client> is the
TCP port (decimal) on the source (client) system.
N.B - If a client on host A wants to ask a server on host B about a
connection specified locally (on the client's machine) as 23, 6191
(an inbound TELNET connection), the client must actually ask about
6191, 23 - which is how the connection would be specified on host B.
For example:
6191, 23
The response is of the form
<port-on-server> , <port-on-client> : <resp-type> : <add-info>
where <port-on-server>,<port-on-client> are the same pair as the
query, <resp-type> is a keyword identifying the type of response, and
<add-info> is context dependent.
The information returned is that associated with the fully specified
TCP connection identified by <server-address>, <client-address>,
<port-on-server>, <port-on-client>, where <server-address> and
<client-address> are the local and foreign IP addresses of the
querying connection -- i.e., the TCP connection to the Identification
Protocol Server. (<port-on-server> and <port-on-client> are taken
from the query.)
For example:
6193, 23 : USERID : UNIX : stjohns
6195, 23 : ERROR : NO-USER
St. Johns [Page 2]
RFC 1413 Identification Protocol February 1993
5. RESPONSE TYPES
A response can be one of two types:
USERID
In this case, <add-info> is a string consisting of an
operating system name (with an optional character set
identifier), followed by ":", followed by an
identification string.
The character set (if present) is separated from the
operating system name by ",". The character set
identifier is used to indicate the character set of the
identification string. The character set identifier,
if omitted, defaults to "US-ASCII" (see below).
Permitted operating system names and character set
names are specified in RFC 1340, "Assigned Numbers" or
its successors.
In addition to those operating system and character set
names specified in "Assigned Numbers" there is one
special case operating system identifier - "OTHER".
Unless "OTHER" is specified as the operating system
type, the server is expected to return the "normal"
user identification of the owner of this connection.
"Normal" in this context may be taken to mean a string
of characters which uniquely identifies the connection
owner such as a user identifier assigned by the system
administrator and used by such user as a mail
identifier, or as the "user" part of a user/password
pair used to gain access to system resources. When an
operating system is specified (e.g., anything but
"OTHER"), the user identifier is expected to be in a
more or less immediately useful form - e.g., something
that could be used as an argument to "finger" or as a
mail address.
"OTHER" indicates the identifier is an unformatted
character string consisting of printable characters in
the specified character set. "OTHER" should be
specified if the user identifier does not meet the
constraints of the previous paragraph. Sending an
encrypted audit token, or returning other non-userid
information about a user (such as the real name and
phone number of a user from a UNIX passwd file) are
St. Johns [Page 3]
RFC 1413 Identification Protocol February 1993
both examples of when "OTHER" should be used.
Returned user identifiers are expected to be printable
in the character set indicated.
The identifier is an unformatted octet string - - all
octets are permissible EXCEPT octal 000 (NUL), 012 (LF)
and 015 (CR). N.B. - space characters (040) following the
colon separator ARE part of the identifier string and
may not be ignored. A response string is still
terminated normally by a CR/LF. N.B. A string may be
printable, but is not *necessarily* printable.
ERROR
For some reason the port owner could not be determined, <add-info>
tells why. The following are the permitted values of <add-info> and
their meanings:
INVALID-PORT
Either the local or foreign port was improperly
specified. This should be returned if either or
both of the port ids were out of range (TCP port
numbers are from 1-65535), negative integers, reals or
in any fashion not recognized as a non-negative
integer.
NO-USER
The connection specified by the port pair is not
currently in use or currently not owned by an
identifiable entity.
HIDDEN-USER
The server was able to identify the user of this
port, but the information was not returned at the
request of the user.
UNKNOWN-ERROR
Can't determine connection owner; reason unknown.
Any error not covered above should return this
error code value. Optionally, this code MAY be
returned in lieu of any other specific error code
if, for example, the server desires to hide
information implied by the return of that error
St. Johns [Page 4]
RFC 1413 Identification Protocol February 1993
code, or for any other reason. If a server
implements such a feature, it MUST be configurable
and it MUST default to returning the proper error
message.
Other values may eventually be specified and defined in future
revisions to this document. If an implementer has a need to specify
a non-standard error code, that code must begin with "X".
In addition, the server is allowed to drop the query connection
without responding. Any premature close (i.e., one where the client
does not receive the EOL, whether graceful or an abort should be
considered to have the same meaning as "ERROR : UNKNOWN-ERROR".
FORMAL SYNTAX
<request> ::= <port-pair> <EOL>
<port-pair> ::= <integer> "," <integer>
<reply> ::= <reply-text> <EOL>
<EOL> ::= "015 012" ; CR-LF End of Line Indicator
<reply-text> ::= <error-reply> | <ident-reply>
<error-reply> ::= <port-pair> ":" "ERROR" ":" <error-type>
<ident-reply> ::= <port-pair> ":" "USERID" ":" <opsys-field>
":" <user-id>
<error-type> ::= "INVALID-PORT" | "NO-USER" | "UNKNOWN-ERROR"
| "HIDDEN-USER" | <error-token>
<opsys-field> ::= <opsys> [ "," <charset>]
<opsys> ::= "OTHER" | "UNIX" | <token> ...etc.
; (See "Assigned Numbers")
<charset> ::= "US-ASCII" | ...etc.
; (See "Assigned Numbers")
<user-id> ::= <octet-string>
<token> ::= 1*64<token-characters> ; 1-64 characters
<error-token> ::= "X"1*63<token-characters>
; 2-64 chars beginning w/X
St. Johns [Page 5]
RFC 1413 Identification Protocol February 1993
<integer> ::= 1*5<digit> ; 1-5 digits.
<digit> ::= "0" | "1" ... "8" | "9" ; 0-9
<token-characters> ::=
<Any of these ASCII characters: a-z, A-Z,
- (dash), .!@#$%^&*()_=+.,<>/?"'~`{}[]; >
; upper and lowercase a-z plus
; printables minus the colon ":"
; character.
<octet-string> ::= 1*512<octet-characters>
<octet-characters> ::=
<any octet from 00 to 377 (octal) except for
ASCII NUL (000), CR (015) and LF (012)>
Notes on Syntax:
1) To promote interoperability among variant
implementations, with respect to white space the above
syntax is understood to embody the "be conservative in
what you send and be liberal in what you accept"
philosophy. Clients and servers should not generate
unnecessary white space (space and tab characters) but
should accept white space anywhere except within a
token. In parsing responses, white space may occur
anywhere, except within a token. Specifically, any
amount of white space is permitted at the beginning or
end of a line both for queries and responses. This
does not apply for responses that contain a user ID
because everything after the colon after the operating
system type until the terminating CR/LF is taken as
part of the user ID. The terminating CR/LF is NOT
considered part of the user ID.
2) The above notwithstanding, servers should restrict the
amount of inter-token white space they send to the
smallest amount reasonable or useful. Clients should
feel free to abort a connection if they receive 1000
characters without receiving an <EOL>.
3) The 512 character limit on user IDs and the 64
character limit on tokens should be understood to mean
as follows: a) No new token (i.e., OPSYS or ERROR-TYPE)
token will be defined that has a length greater than 64
and b) a server SHOULD NOT send more than 512 octets of
user ID and a client MUST accept at least 512 octets of
St. Johns [Page 6]
RFC 1413 Identification Protocol February 1993
user ID. Because of this limitation, a server MUST
return the most significant portion of the user ID in
the first 512 octets.
4) The character sets and character set identifiers should
map directly to those defined in or referenced by RFC 1340,
"Assigned Numbers" or its successors. Character set
identifiers only apply to the user identification field
- all other fields will be defined in and must be sent
as US-ASCII.
5) Although <user-id> is defined as an <octet-string>
above, it must follow the format and character set
constraints implied by the <opsys-field>; see the
discussion above.
6) The character set provides context for the client to
print or store the returned user identification string.
If the client does not recognize or implement the
returned character set, it should handle the returned
identification string as OCTET, but should in addition
store or report the character set. An OCTET string
should be printed, stored or handled in hex notation
(0-9a-f) in addition to any other representation the
client implements - this provides a standard
representation among differing implementations.
6. Security Considerations
The information returned by this protocol is at most as trustworthy
as the host providing it OR the organization operating the host. For
example, a PC in an open lab has few if any controls on it to prevent
a user from having this protocol return any identifier the user
wants. Likewise, if the host has been compromised the information
returned may be completely erroneous and misleading.
The Identification Protocol is not intended as an authorization or
access control protocol. At best, it provides some additional
auditing information with respect to TCP connections. At worst, it
can provide misleading, incorrect, or maliciously incorrect
information.
The use of the information returned by this protocol for other than
auditing is strongly discouraged. Specifically, using Identification
Protocol information to make access control decisions - either as the
primary method (i.e., no other checks) or as an adjunct to other
methods may result in a weakening of normal host security.
St. Johns [Page 7]
RFC 1413 Identification Protocol February 1993
An Identification server may reveal information about users,
entities, objects or processes which might normally be considered
private. An Identification server provides service which is a rough
analog of the CallerID services provided by some phone companies and
many of the same privacy considerations and arguments that apply to
the CallerID service apply to Identification. If you wouldn't run a
"finger" server due to privacy considerations you may not want to run
this protocol.
7. ACKNOWLEDGEMENTS
Acknowledgement is given to Dan Bernstein who is primarily
responsible for renewing interest in this protocol and for pointing
out some annoying errors in RFC 931.
References
[1] St. Johns, M., "Authentication Server", RFC 931, TPSC, January
1985.
[2] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1340,
USC/Information Sciences Institute, July 1992.
Author's Address
Michael C. St. Johns
DARPA/CSTO
3701 N. Fairfax Dr
Arlington, VA 22203
Phone: (703) 696-2271
EMail: stjohns@DARPA.MIL
St. Johns [Page 8]
\ No newline at end of file + + + + + + +Network Working Group M. St. Johns +Request for Comments: 1413 US Department of Defense +Obsoletes: 931 February 1993 + + + Identification Protocol + +Status of this Memo + + This RFC specifies an IAB standards track protocol for the Internet + community, and requests discussion and suggestions for improvements. + Please refer to the current edition of the "IAB Official Protocol + Standards" for the standardization state and status of this protocol. + Distribution of this memo is unlimited. + +1. INTRODUCTION + + The Identification Protocol (a.k.a., "ident", a.k.a., "the Ident + Protocol") provides a means to determine the identity of a user of a + particular TCP connection. Given a TCP port number pair, it returns + a character string which identifies the owner of that connection on + the server's system. + + The Identification Protocol was formerly called the Authentication + Server Protocol. It has been renamed to better reflect its function. + This document is a product of the TCP Client Identity Protocol + Working Group of the Internet Engineering Task Force (IETF). + +2. OVERVIEW + + This is a connection based application on TCP. A server listens for + TCP connections on TCP port 113 (decimal). Once a connection is + established, the server reads a line of data which specifies the + connection of interest. If it exists, the system dependent user + identifier of the connection of interest is sent as the reply. The + server may then either shut the connection down or it may continue to + read/respond to multiple queries. + + The server should close the connection down after a configurable + amount of time with no queries - a 60-180 second idle timeout is + recommended. The client may close the connection down at any time; + however to allow for network delays the client should wait at least + 30 seconds (or longer) after a query before abandoning the query and + closing the connection. + + + + + + + +St. Johns [Page 1] + +RFC 1413 Identification Protocol February 1993 + + +3. RESTRICTIONS + + Queries are permitted only for fully specified connections. The + query contains the local/foreign port pair -- the local/foreign + address pair used to fully specify the connection is taken from the + local and foreign address of query connection. This means a user on + address A may only query the server on address B about connections + between A and B. + +4. QUERY/RESPONSE FORMAT + + The server accepts simple text query requests of the form: + + <port-on-server> , <port-on-client> + + where <port-on-server> is the TCP port (decimal) on the target (where + the "ident" server is running) system, and <port-on-client> is the + TCP port (decimal) on the source (client) system. + + N.B - If a client on host A wants to ask a server on host B about a + connection specified locally (on the client's machine) as 23, 6191 + (an inbound TELNET connection), the client must actually ask about + 6191, 23 - which is how the connection would be specified on host B. + + For example: + + 6191, 23 + + The response is of the form + + <port-on-server> , <port-on-client> : <resp-type> : <add-info> + + where <port-on-server>,<port-on-client> are the same pair as the + query, <resp-type> is a keyword identifying the type of response, and + <add-info> is context dependent. + + The information returned is that associated with the fully specified + TCP connection identified by <server-address>, <client-address>, + <port-on-server>, <port-on-client>, where <server-address> and + <client-address> are the local and foreign IP addresses of the + querying connection -- i.e., the TCP connection to the Identification + Protocol Server. (<port-on-server> and <port-on-client> are taken + from the query.) + + For example: + + 6193, 23 : USERID : UNIX : stjohns + 6195, 23 : ERROR : NO-USER + + + +St. Johns [Page 2] + +RFC 1413 Identification Protocol February 1993 + + +5. RESPONSE TYPES + +A response can be one of two types: + +USERID + + In this case, <add-info> is a string consisting of an + operating system name (with an optional character set + identifier), followed by ":", followed by an + identification string. + + The character set (if present) is separated from the + operating system name by ",". The character set + identifier is used to indicate the character set of the + identification string. The character set identifier, + if omitted, defaults to "US-ASCII" (see below). + + Permitted operating system names and character set + names are specified in RFC 1340, "Assigned Numbers" or + its successors. + + In addition to those operating system and character set + names specified in "Assigned Numbers" there is one + special case operating system identifier - "OTHER". + + Unless "OTHER" is specified as the operating system + type, the server is expected to return the "normal" + user identification of the owner of this connection. + "Normal" in this context may be taken to mean a string + of characters which uniquely identifies the connection + owner such as a user identifier assigned by the system + administrator and used by such user as a mail + identifier, or as the "user" part of a user/password + pair used to gain access to system resources. When an + operating system is specified (e.g., anything but + "OTHER"), the user identifier is expected to be in a + more or less immediately useful form - e.g., something + that could be used as an argument to "finger" or as a + mail address. + + "OTHER" indicates the identifier is an unformatted + character string consisting of printable characters in + the specified character set. "OTHER" should be + specified if the user identifier does not meet the + constraints of the previous paragraph. Sending an + encrypted audit token, or returning other non-userid + information about a user (such as the real name and + phone number of a user from a UNIX passwd file) are + + + +St. Johns [Page 3] + +RFC 1413 Identification Protocol February 1993 + + + both examples of when "OTHER" should be used. + + Returned user identifiers are expected to be printable + in the character set indicated. + + The identifier is an unformatted octet string - - all + octets are permissible EXCEPT octal 000 (NUL), 012 (LF) + and 015 (CR). N.B. - space characters (040) following the + colon separator ARE part of the identifier string and + may not be ignored. A response string is still + terminated normally by a CR/LF. N.B. A string may be + printable, but is not *necessarily* printable. + +ERROR + + For some reason the port owner could not be determined, <add-info> + tells why. The following are the permitted values of <add-info> and + their meanings: + + INVALID-PORT + + Either the local or foreign port was improperly + specified. This should be returned if either or + both of the port ids were out of range (TCP port + numbers are from 1-65535), negative integers, reals or + in any fashion not recognized as a non-negative + integer. + + NO-USER + + The connection specified by the port pair is not + currently in use or currently not owned by an + identifiable entity. + + HIDDEN-USER + + The server was able to identify the user of this + port, but the information was not returned at the + request of the user. + + UNKNOWN-ERROR + + Can't determine connection owner; reason unknown. + Any error not covered above should return this + error code value. Optionally, this code MAY be + returned in lieu of any other specific error code + if, for example, the server desires to hide + information implied by the return of that error + + + +St. Johns [Page 4] + +RFC 1413 Identification Protocol February 1993 + + + code, or for any other reason. If a server + implements such a feature, it MUST be configurable + and it MUST default to returning the proper error + message. + + Other values may eventually be specified and defined in future + revisions to this document. If an implementer has a need to specify + a non-standard error code, that code must begin with "X". + + In addition, the server is allowed to drop the query connection + without responding. Any premature close (i.e., one where the client + does not receive the EOL, whether graceful or an abort should be + considered to have the same meaning as "ERROR : UNKNOWN-ERROR". + +FORMAL SYNTAX + + <request> ::= <port-pair> <EOL> + + <port-pair> ::= <integer> "," <integer> + + <reply> ::= <reply-text> <EOL> + + <EOL> ::= "015 012" ; CR-LF End of Line Indicator + + <reply-text> ::= <error-reply> | <ident-reply> + + <error-reply> ::= <port-pair> ":" "ERROR" ":" <error-type> + + <ident-reply> ::= <port-pair> ":" "USERID" ":" <opsys-field> + ":" <user-id> + + <error-type> ::= "INVALID-PORT" | "NO-USER" | "UNKNOWN-ERROR" + | "HIDDEN-USER" | <error-token> + + <opsys-field> ::= <opsys> [ "," <charset>] + + <opsys> ::= "OTHER" | "UNIX" | <token> ...etc. + ; (See "Assigned Numbers") + + <charset> ::= "US-ASCII" | ...etc. + ; (See "Assigned Numbers") + + <user-id> ::= <octet-string> + + <token> ::= 1*64<token-characters> ; 1-64 characters + + <error-token> ::= "X"1*63<token-characters> + ; 2-64 chars beginning w/X + + + +St. Johns [Page 5] + +RFC 1413 Identification Protocol February 1993 + + + <integer> ::= 1*5<digit> ; 1-5 digits. + + <digit> ::= "0" | "1" ... "8" | "9" ; 0-9 + + <token-characters> ::= + <Any of these ASCII characters: a-z, A-Z, + - (dash), .!@#$%^&*()_=+.,<>/?"'~`{}[]; > + ; upper and lowercase a-z plus + ; printables minus the colon ":" + ; character. + + <octet-string> ::= 1*512<octet-characters> + + <octet-characters> ::= + <any octet from 00 to 377 (octal) except for + ASCII NUL (000), CR (015) and LF (012)> + +Notes on Syntax: + + 1) To promote interoperability among variant + implementations, with respect to white space the above + syntax is understood to embody the "be conservative in + what you send and be liberal in what you accept" + philosophy. Clients and servers should not generate + unnecessary white space (space and tab characters) but + should accept white space anywhere except within a + token. In parsing responses, white space may occur + anywhere, except within a token. Specifically, any + amount of white space is permitted at the beginning or + end of a line both for queries and responses. This + does not apply for responses that contain a user ID + because everything after the colon after the operating + system type until the terminating CR/LF is taken as + part of the user ID. The terminating CR/LF is NOT + considered part of the user ID. + + 2) The above notwithstanding, servers should restrict the + amount of inter-token white space they send to the + smallest amount reasonable or useful. Clients should + feel free to abort a connection if they receive 1000 + characters without receiving an <EOL>. + + 3) The 512 character limit on user IDs and the 64 + character limit on tokens should be understood to mean + as follows: a) No new token (i.e., OPSYS or ERROR-TYPE) + token will be defined that has a length greater than 64 + and b) a server SHOULD NOT send more than 512 octets of + user ID and a client MUST accept at least 512 octets of + + + +St. Johns [Page 6] + +RFC 1413 Identification Protocol February 1993 + + + user ID. Because of this limitation, a server MUST + return the most significant portion of the user ID in + the first 512 octets. + + 4) The character sets and character set identifiers should + map directly to those defined in or referenced by RFC 1340, + "Assigned Numbers" or its successors. Character set + identifiers only apply to the user identification field + - all other fields will be defined in and must be sent + as US-ASCII. + + 5) Although <user-id> is defined as an <octet-string> + above, it must follow the format and character set + constraints implied by the <opsys-field>; see the + discussion above. + + 6) The character set provides context for the client to + print or store the returned user identification string. + If the client does not recognize or implement the + returned character set, it should handle the returned + identification string as OCTET, but should in addition + store or report the character set. An OCTET string + should be printed, stored or handled in hex notation + (0-9a-f) in addition to any other representation the + client implements - this provides a standard + representation among differing implementations. + +6. Security Considerations + + The information returned by this protocol is at most as trustworthy + as the host providing it OR the organization operating the host. For + example, a PC in an open lab has few if any controls on it to prevent + a user from having this protocol return any identifier the user + wants. Likewise, if the host has been compromised the information + returned may be completely erroneous and misleading. + + The Identification Protocol is not intended as an authorization or + access control protocol. At best, it provides some additional + auditing information with respect to TCP connections. At worst, it + can provide misleading, incorrect, or maliciously incorrect + information. + + The use of the information returned by this protocol for other than + auditing is strongly discouraged. Specifically, using Identification + Protocol information to make access control decisions - either as the + primary method (i.e., no other checks) or as an adjunct to other + methods may result in a weakening of normal host security. + + + + +St. Johns [Page 7] + +RFC 1413 Identification Protocol February 1993 + + + An Identification server may reveal information about users, + entities, objects or processes which might normally be considered + private. An Identification server provides service which is a rough + analog of the CallerID services provided by some phone companies and + many of the same privacy considerations and arguments that apply to + the CallerID service apply to Identification. If you wouldn't run a + "finger" server due to privacy considerations you may not want to run + this protocol. + +7. ACKNOWLEDGEMENTS + + Acknowledgement is given to Dan Bernstein who is primarily + responsible for renewing interest in this protocol and for pointing + out some annoying errors in RFC 931. + +References + + [1] St. Johns, M., "Authentication Server", RFC 931, TPSC, January + 1985. + + [2] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1340, + USC/Information Sciences Institute, July 1992. + +Author's Address + + Michael C. St. Johns + DARPA/CSTO + 3701 N. Fairfax Dr + Arlington, VA 22203 + + Phone: (703) 696-2271 + EMail: stjohns@DARPA.MIL + + + + + + + + + + + + + + + + + + + +St. Johns [Page 8] +
\ No newline at end of file diff --git a/docs/rfc/rfc1459.txt b/docs/rfc/rfc1459.txt index c93005377..09fbf34f7 100644 --- a/docs/rfc/rfc1459.txt +++ b/docs/rfc/rfc1459.txt @@ -1 +1,3643 @@ -
Network Working Group J. Oikarinen
Request for Comments: 1459 D. Reed
May 1993
Internet Relay Chat Protocol
Status of This Memo
This memo defines an Experimental Protocol for the Internet
community. Discussion and suggestions for improvement are requested.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
Distribution of this memo is unlimited.
Abstract
The IRC protocol was developed over the last 4 years since it was
first implemented as a means for users on a BBS to chat amongst
themselves. Now it supports a world-wide network of servers and
clients, and is stringing to cope with growth. Over the past 2 years,
the average number of users connected to the main IRC network has
grown by a factor of 10.
The IRC protocol is a text-based protocol, with the simplest client
being any socket program capable of connecting to the server.
Table of Contents
1. INTRODUCTION ............................................... 4
1.1 Servers ................................................ 4
1.2 Clients ................................................ 5
1.2.1 Operators .......................................... 5
1.3 Channels ................................................ 5
1.3.1 Channel Operators .................................... 6
2. THE IRC SPECIFICATION ....................................... 7
2.1 Overview ................................................ 7
2.2 Character codes ......................................... 7
2.3 Messages ................................................ 7
2.3.1 Message format in 'pseudo' BNF .................... 8
2.4 Numeric replies ......................................... 10
3. IRC Concepts ................................................ 10
3.1 One-to-one communication ................................ 10
3.2 One-to-many ............................................. 11
3.2.1 To a list .......................................... 11
3.2.2 To a group (channel) ............................... 11
3.2.3 To a host/server mask .............................. 12
3.3 One to all .............................................. 12
Oikarinen & Reed [Page 1]
RFC 1459 Internet Relay Chat Protocol May 1993
3.3.1 Client to Client ................................... 12
3.3.2 Clients to Server .................................. 12
3.3.3 Server to Server ................................... 12
4. MESSAGE DETAILS ............................................. 13
4.1 Connection Registration ................................. 13
4.1.1 Password message ................................... 14
4.1.2 Nickname message ................................... 14
4.1.3 User message ....................................... 15
4.1.4 Server message ..................................... 16
4.1.5 Operator message ................................... 17
4.1.6 Quit message ....................................... 17
4.1.7 Server Quit message ................................ 18
4.2 Channel operations ...................................... 19
4.2.1 Join message ....................................... 19
4.2.2 Part message ....................................... 20
4.2.3 Mode message ....................................... 21
4.2.3.1 Channel modes ................................. 21
4.2.3.2 User modes .................................... 22
4.2.4 Topic message ...................................... 23
4.2.5 Names message ...................................... 24
4.2.6 List message ....................................... 24
4.2.7 Invite message ..................................... 25
4.2.8 Kick message ....................................... 25
4.3 Server queries and commands ............................. 26
4.3.1 Version message .................................... 26
4.3.2 Stats message ...................................... 27
4.3.3 Links message ...................................... 28
4.3.4 Time message ....................................... 29
4.3.5 Connect message .................................... 29
4.3.6 Trace message ...................................... 30
4.3.7 Admin message ...................................... 31
4.3.8 Info message ....................................... 31
4.4 Sending messages ........................................ 32
4.4.1 Private messages ................................... 32
4.4.2 Notice messages .................................... 33
4.5 User-based queries ...................................... 33
4.5.1 Who query .......................................... 33
4.5.2 Whois query ........................................ 34
4.5.3 Whowas message ..................................... 35
4.6 Miscellaneous messages .................................. 35
4.6.1 Kill message ....................................... 36
4.6.2 Ping message ....................................... 37
4.6.3 Pong message ....................................... 37
4.6.4 Error message ...................................... 38
5. OPTIONAL MESSAGES ........................................... 38
5.1 Away message ............................................ 38
5.2 Rehash command .......................................... 39
5.3 Restart command ......................................... 39
Oikarinen & Reed [Page 2]
RFC 1459 Internet Relay Chat Protocol May 1993
5.4 Summon message .......................................... 40
5.5 Users message ........................................... 40
5.6 Operwall command ........................................ 41
5.7 Userhost message ........................................ 42
5.8 Ison message ............................................ 42
6. REPLIES ..................................................... 43
6.1 Error Replies ........................................... 43
6.2 Command responses ....................................... 48
6.3 Reserved numerics ....................................... 56
7. Client and server authentication ............................ 56
8. Current Implementations Details ............................. 56
8.1 Network protocol: TCP ................................... 57
8.1.1 Support of Unix sockets ............................ 57
8.2 Command Parsing ......................................... 57
8.3 Message delivery ........................................ 57
8.4 Connection 'Liveness' ................................... 58
8.5 Establishing a server-client connection ................. 58
8.6 Establishing a server-server connection ................. 58
8.6.1 State information exchange when connecting ......... 59
8.7 Terminating server-client connections ................... 59
8.8 Terminating server-server connections ................... 59
8.9 Tracking nickname changes ............................... 60
8.10 Flood control of clients ............................... 60
8.11 Non-blocking lookups ................................... 61
8.11.1 Hostname (DNS) lookups ............................ 61
8.11.2 Username (Ident) lookups .......................... 61
8.12 Configuration file ..................................... 61
8.12.1 Allowing clients to connect ....................... 62
8.12.2 Operators ......................................... 62
8.12.3 Allowing servers to connect ....................... 62
8.12.4 Administrivia ..................................... 63
8.13 Channel membership ..................................... 63
9. Current problems ............................................ 63
9.1 Scalability ............................................. 63
9.2 Labels .................................................. 63
9.2.1 Nicknames .......................................... 63
9.2.2 Channels ........................................... 64
9.2.3 Servers ............................................ 64
9.3 Algorithms .............................................. 64
10. Support and availability ................................... 64
11. Security Considerations .................................... 65
12. Authors' Addresses ......................................... 65
Oikarinen & Reed [Page 3]
RFC 1459 Internet Relay Chat Protocol May 1993
1. INTRODUCTION
The IRC (Internet Relay Chat) protocol has been designed over a
number of years for use with text based conferencing. This document
describes the current IRC protocol.
The IRC protocol has been developed on systems using the TCP/IP
network protocol, although there is no requirement that this remain
the only sphere in which it operates.
IRC itself is a teleconferencing system, which (through the use of
the client-server model) is well-suited to running on many machines
in a distributed fashion. A typical setup involves a single process
(the server) forming a central point for clients (or other servers)
to connect to, performing the required message delivery/multiplexing
and other functions.
1.1 Servers
The server forms the backbone of IRC, providing a point to which
clients may connect to to talk to each other, and a point for other
servers to connect to, forming an IRC network. The only network
configuration allowed for IRC servers is that of a spanning tree [see
Fig. 1] where each server acts as a central node for the rest of the
net it sees.
[ Server 15 ] [ Server 13 ] [ Server 14]
/ \ /
/ \ /
[ Server 11 ] ------ [ Server 1 ] [ Server 12]
/ \ /
/ \ /
[ Server 2 ] [ Server 3 ]
/ \ \
/ \ \
[ Server 4 ] [ Server 5 ] [ Server 6 ]
/ | \ /
/ | \ /
/ | \____ /
/ | \ /
[ Server 7 ] [ Server 8 ] [ Server 9 ] [ Server 10 ]
:
[ etc. ]
:
[ Fig. 1. Format of IRC server network ]
Oikarinen & Reed [Page 4]
RFC 1459 Internet Relay Chat Protocol May 1993
1.2 Clients
A client is anything connecting to a server that is not another
server. Each client is distinguished from other clients by a unique
nickname having a maximum length of nine (9) characters. See the
protocol grammar rules for what may and may not be used in a
nickname. In addition to the nickname, all servers must have the
following information about all clients: the real name of the host
that the client is running on, the username of the client on that
host, and the server to which the client is connected.
1.2.1 Operators
To allow a reasonable amount of order to be kept within the IRC
network, a special class of clients (operators) is allowed to perform
general maintenance functions on the network. Although the powers
granted to an operator can be considered as 'dangerous', they are
nonetheless required. Operators should be able to perform basic
network tasks such as disconnecting and reconnecting servers as
needed to prevent long-term use of bad network routing. In
recognition of this need, the protocol discussed herein provides for
operators only to be able to perform such functions. See sections
4.1.7 (SQUIT) and 4.3.5 (CONNECT).
A more controversial power of operators is the ability to remove a
user from the connected network by 'force', i.e. operators are able
to close the connection between any client and server. The
justification for this is delicate since its abuse is both
destructive and annoying. For further details on this type of
action, see section 4.6.1 (KILL).
1.3 Channels
A channel is a named group of one or more clients which will all
receive messages addressed to that channel. The channel is created
implicitly when the first client joins it, and the channel ceases to
exist when the last client leaves it. While channel exists, any
client can reference the channel using the name of the channel.
Channels names are strings (beginning with a '&' or '#' character) of
length up to 200 characters. Apart from the the requirement that the
first character being either '&' or '#'; the only restriction on a
channel name is that it may not contain any spaces (' '), a control G
(^G or ASCII 7), or a comma (',' which is used as a list item
separator by the protocol).
There are two types of channels allowed by this protocol. One is a
distributed channel which is known to all the servers that are
Oikarinen & Reed [Page 5]
RFC 1459 Internet Relay Chat Protocol May 1993
connected to the network. These channels are marked by the first
character being a only clients on the server where it exists may join
it. These are distinguished by a leading '&' character. On top of
these two types, there are the various channel modes available to
alter the characteristics of individual channels. See section 4.2.3
(MODE command) for more details on this.
To create a new channel or become part of an existing channel, a user
is required to JOIN the channel. If the channel doesn't exist prior
to joining, the channel is created and the creating user becomes a
channel operator. If the channel already exists, whether or not your
request to JOIN that channel is honoured depends on the current modes
of the channel. For example, if the channel is invite-only, (+i),
then you may only join if invited. As part of the protocol, a user
may be a part of several channels at once, but a limit of ten (10)
channels is recommended as being ample for both experienced and
novice users. See section 8.13 for more information on this.
If the IRC network becomes disjoint because of a split between two
servers, the channel on each side is only composed of those clients
which are connected to servers on the respective sides of the split,
possibly ceasing to exist on one side of the split. When the split
is healed, the connecting servers announce to each other who they
think is in each channel and the mode of that channel. If the
channel exists on both sides, the JOINs and MODEs are interpreted in
an inclusive manner so that both sides of the new connection will
agree about which clients are in the channel and what modes the
channel has.
1.3.1 Channel Operators
The channel operator (also referred to as a "chop" or "chanop") on a
given channel is considered to 'own' that channel. In recognition of
this status, channel operators are endowed with certain powers which
enable them to keep control and some sort of sanity in their channel.
As an owner of a channel, a channel operator is not required to have
reasons for their actions, although if their actions are generally
antisocial or otherwise abusive, it might be reasonable to ask an IRC
operator to intervene, or for the usersjust leave and go elsewhere
and form their own channel.
The commands which may only be used by channel operators are:
KICK - Eject a client from the channel
MODE - Change the channel's mode
INVITE - Invite a client to an invite-only channel (mode +i)
TOPIC - Change the channel topic in a mode +t channel
Oikarinen & Reed [Page 6]
RFC 1459 Internet Relay Chat Protocol May 1993
A channel operator is identified by the '@' symbol next to their
nickname whenever it is associated with a channel (ie replies to the
NAMES, WHO and WHOIS commands).
2. The IRC Specification
2.1 Overview
The protocol as described herein is for use both with server to
server and client to server connections. There are, however, more
restrictions on client connections (which are considered to be
untrustworthy) than on server connections.
2.2 Character codes
No specific character set is specified. The protocol is based on a a
set of codes which are composed of eight (8) bits, making up an
octet. Each message may be composed of any number of these octets;
however, some octet values are used for control codes which act as
message delimiters.
Regardless of being an 8-bit protocol, the delimiters and keywords
are such that protocol is mostly usable from USASCII terminal and a
telnet connection.
Because of IRC's scandanavian origin, the characters {}| are
considered to be the lower case equivalents of the characters []\,
respectively. This is a critical issue when determining the
equivalence of two nicknames.
2.3 Messages
Servers and clients send eachother messages which may or may not
generate a reply. If the message contains a valid command, as
described in later sections, the client should expect a reply as
specified but it is not advised to wait forever for the reply; client
to server and server to server communication is essentially
asynchronous in nature.
Each IRC message may consist of up to three main parts: the prefix
(optional), the command, and the command parameters (of which there
may be up to 15). The prefix, command, and all parameters are
separated by one (or more) ASCII space character(s) (0x20).
The presence of a prefix is indicated with a single leading ASCII
colon character (':', 0x3b), which must be the first character of the
message itself. There must be no gap (whitespace) between the colon
and the prefix. The prefix is used by servers to indicate the true
Oikarinen & Reed [Page 7]
RFC 1459 Internet Relay Chat Protocol May 1993
origin of the message. If the prefix is missing from the message, it
is assumed to have originated from the connection from which it was
received. Clients should not use prefix when sending a message from
themselves; if they use a prefix, the only valid prefix is the
registered nickname associated with the client. If the source
identified by the prefix cannot be found from the server's internal
database, or if the source is registered from a different link than
from which the message arrived, the server must ignore the message
silently.
The command must either be a valid IRC command or a three (3) digit
number represented in ASCII text.
IRC messages are always lines of characters terminated with a CR-LF
(Carriage Return - Line Feed) pair, and these messages shall not
exceed 512 characters in length, counting all characters including
the trailing CR-LF. Thus, there are 510 characters maximum allowed
for the command and its parameters. There is no provision for
continuation message lines. See section 7 for more details about
current implementations.
2.3.1 Message format in 'pseudo' BNF
The protocol messages must be extracted from the contiguous stream of
octets. The current solution is to designate two characters, CR and
LF, as message separators. Empty messages are silently ignored,
which permits use of the sequence CR-LF between messages
without extra problems.
The extracted message is parsed into the components <prefix>,
<command> and list of parameters matched either by <middle> or
<trailing> components.
The BNF representation for this is:
<message> ::= [':' <prefix> <SPACE> ] <command> <params> <crlf>
<prefix> ::= <servername> | <nick> [ '!' <user> ] [ '@' <host> ]
<command> ::= <letter> { <letter> } | <number> <number> <number>
<SPACE> ::= ' ' { ' ' }
<params> ::= <SPACE> [ ':' <trailing> | <middle> <params> ]
<middle> ::= <Any *non-empty* sequence of octets not including SPACE
or NUL or CR or LF, the first of which may not be ':'>
<trailing> ::= <Any, possibly *empty*, sequence of octets not including
NUL or CR or LF>
<crlf> ::= CR LF
Oikarinen & Reed [Page 8]
RFC 1459 Internet Relay Chat Protocol May 1993
NOTES:
1) <SPACE> is consists only of SPACE character(s) (0x20).
Specially notice that TABULATION, and all other control
characters are considered NON-WHITE-SPACE.
2) After extracting the parameter list, all parameters are equal,
whether matched by <middle> or <trailing>. <Trailing> is just
a syntactic trick to allow SPACE within parameter.
3) The fact that CR and LF cannot appear in parameter strings is
just artifact of the message framing. This might change later.
4) The NUL character is not special in message framing, and
basically could end up inside a parameter, but as it would
cause extra complexities in normal C string handling. Therefore
NUL is not allowed within messages.
5) The last parameter may be an empty string.
6) Use of the extended prefix (['!' <user> ] ['@' <host> ]) must
not be used in server to server communications and is only
intended for server to client messages in order to provide
clients with more useful information about who a message is
from without the need for additional queries.
Most protocol messages specify additional semantics and syntax for
the extracted parameter strings dictated by their position in the
list. For example, many server commands will assume that the first
parameter after the command is the list of targets, which can be
described with:
<target> ::= <to> [ "," <target> ]
<to> ::= <channel> | <user> '@' <servername> | <nick> | <mask>
<channel> ::= ('#' | '&') <chstring>
<servername> ::= <host>
<host> ::= see RFC 952 [DNS:4] for details on allowed hostnames
<nick> ::= <letter> { <letter> | <number> | <special> }
<mask> ::= ('#' | '$') <chstring>
<chstring> ::= <any 8bit code except SPACE, BELL, NUL, CR, LF and
comma (',')>
Other parameter syntaxes are:
<user> ::= <nonwhite> { <nonwhite> }
<letter> ::= 'a' ... 'z' | 'A' ... 'Z'
<number> ::= '0' ... '9'
<special> ::= '-' | '[' | ']' | '\' | '`' | '^' | '{' | '}'
Oikarinen & Reed [Page 9]
RFC 1459 Internet Relay Chat Protocol May 1993
<nonwhite> ::= <any 8bit code except SPACE (0x20), NUL (0x0), CR
(0xd), and LF (0xa)>
2.4 Numeric replies
Most of the messages sent to the server generate a reply of some
sort. The most common reply is the numeric reply, used for both
errors and normal replies. The numeric reply must be sent as one
message consisting of the sender prefix, the three digit numeric, and
the target of the reply. A numeric reply is not allowed to originate
from a client; any such messages received by a server are silently
dropped. In all other respects, a numeric reply is just like a normal
message, except that the keyword is made up of 3 numeric digits
rather than a string of letters. A list of different replies is
supplied in section 6.
3. IRC Concepts.
This section is devoted to describing the actual concepts behind the
organization of the IRC protocol and how the current
implementations deliver different classes of messages.
1--\
A D---4
2--/ \ /
B----C
/ \
3 E
Servers: A, B, C, D, E Clients: 1, 2, 3, 4
[ Fig. 2. Sample small IRC network ]
3.1 One-to-one communication
Communication on a one-to-one basis is usually only performed by
clients, since most server-server traffic is not a result of servers
talking only to each other. To provide a secure means for clients to
talk to each other, it is required that all servers be able to send a
message in exactly one direction along the spanning tree in order to
reach any client. The path of a message being delivered is the
shortest path between any two points on the spanning tree.
The following examples all refer to Figure 2 above.
Oikarinen & Reed [Page 10]
RFC 1459 Internet Relay Chat Protocol May 1993
Example 1:
A message between clients 1 and 2 is only seen by server A, which
sends it straight to client 2.
Example 2:
A message between clients 1 and 3 is seen by servers A & B, and
client 3. No other clients or servers are allowed see the message.
Example 3:
A message between clients 2 and 4 is seen by servers A, B, C & D
and client 4 only.
3.2 One-to-many
The main goal of IRC is to provide a forum which allows easy and
efficient conferencing (one to many conversations). IRC offers
several means to achieve this, each serving its own purpose.
3.2.1 To a list
The least efficient style of one-to-many conversation is through
clients talking to a 'list' of users. How this is done is almost
self explanatory: the client gives a list of destinations to which
the message is to be delivered and the server breaks it up and
dispatches a separate copy of the message to each given destination.
This isn't as efficient as using a group since the destination list
is broken up and the dispatch sent without checking to make sure
duplicates aren't sent down each path.
3.2.2 To a group (channel)
In IRC the channel has a role equivalent to that of the multicast
group; their existence is dynamic (coming and going as people join
and leave channels) and the actual conversation carried out on a
channel is only sent to servers which are supporting users on a given
channel. If there are multiple users on a server in the same
channel, the message text is sent only once to that server and then
sent to each client on the channel. This action is then repeated for
each client-server combination until the original message has fanned
out and reached each member of the channel.
The following examples all refer to Figure 2.
Example 4:
Any channel with 1 client in it. Messages to the channel go to the
server and then nowhere else.
Oikarinen & Reed [Page 11]
RFC 1459 Internet Relay Chat Protocol May 1993
Example 5:
2 clients in a channel. All messages traverse a path as if they
were private messages between the two clients outside a channel.
Example 6:
Clients 1, 2 and 3 in a channel. All messages to the channel are
sent to all clients and only those servers which must be traversed
by the message if it were a private message to a single client. If
client 1 sends a message, it goes back to client 2 and then via
server B to client 3.
3.2.3 To a host/server mask
To provide IRC operators with some mechanism to send messages to a
large body of related users, host and server mask messages are
provided. These messages are sent to users whose host or server
information match that of the mask. The messages are only sent to
locations where users are, in a fashion similar to that of channels.
3.3 One-to-all
The one-to-all type of message is better described as a broadcast
message, sent to all clients or servers or both. On a large network
of users and servers, a single message can result in a lot of traffic
being sent over the network in an effort to reach all of the desired
destinations.
For some messages, there is no option but to broadcast it to all
servers so that the state information held by each server is
reasonably consistent between servers.
3.3.1 Client-to-Client
There is no class of message which, from a single message, results in
a message being sent to every other client.
3.3.2 Client-to-Server
Most of the commands which result in a change of state information
(such as channel membership, channel mode, user status, etc) must be
sent to all servers by default, and this distribution may not be
changed by the client.
3.3.3 Server-to-Server.
While most messages between servers are distributed to all 'other'
servers, this is only required for any message that affects either a
user, channel or server. Since these are the basic items found in
Oikarinen & Reed [Page 12]
RFC 1459 Internet Relay Chat Protocol May 1993
IRC, nearly all messages originating from a server are broadcast to
all other connected servers.
4. Message details
On the following pages are descriptions of each message recognized by
the IRC server and client. All commands described in this section
must be implemented by any server for this protocol.
Where the reply ERR_NOSUCHSERVER is listed, it means that the
<server> parameter could not be found. The server must not send any
other replies after this for that command.
The server to which a client is connected is required to parse the
complete message, returning any appropriate errors. If the server
encounters a fatal error while parsing a message, an error must be
sent back to the client and the parsing terminated. A fatal error
may be considered to be incorrect command, a destination which is
otherwise unknown to the server (server, nick or channel names fit
this category), not enough parameters or incorrect privileges.
If a full set of parameters is presented, then each must be checked
for validity and appropriate responses sent back to the client. In
the case of messages which use parameter lists using the comma as an
item separator, a reply must be sent for each item.
In the examples below, some messages appear using the full format:
:Name COMMAND parameter list
Such examples represent a message from "Name" in transit between
servers, where it is essential to include the name of the original
sender of the message so remote servers may send back a reply along
the correct path.
4.1 Connection Registration
The commands described here are used to register a connection with an
IRC server as either a user or a server as well as correctly
disconnect.
A "PASS" command is not required for either client or server
connection to be registered, but it must precede the server message
or the latter of the NICK/USER combination. It is strongly
recommended that all server connections have a password in order to
give some level of security to the actual connections. The
recommended order for a client to register is as follows:
Oikarinen & Reed [Page 13]
RFC 1459 Internet Relay Chat Protocol May 1993
1. Pass message
2. Nick message
3. User message
4.1.1 Password message
Command: PASS
Parameters: <password>
The PASS command is used to set a 'connection password'. The
password can and must be set before any attempt to register the
connection is made. Currently this requires that clients send a PASS
command before sending the NICK/USER combination and servers *must*
send a PASS command before any SERVER command. The password supplied
must match the one contained in the C/N lines (for servers) or I
lines (for clients). It is possible to send multiple PASS commands
before registering but only the last one sent is used for
verification and it may not be changed once registered. Numeric
Replies:
ERR_NEEDMOREPARAMS ERR_ALREADYREGISTRED
Example:
PASS secretpasswordhere
4.1.2 Nick message
Command: NICK
Parameters: <nickname> [ <hopcount> ]
NICK message is used to give user a nickname or change the previous
one. The <hopcount> parameter is only used by servers to indicate
how far away a nick is from its home server. A local connection has
a hopcount of 0. If supplied by a client, it must be ignored.
If a NICK message arrives at a server which already knows about an
identical nickname for another client, a nickname collision occurs.
As a result of a nickname collision, all instances of the nickname
are removed from the server's database, and a KILL command is issued
to remove the nickname from all other server's database. If the NICK
message causing the collision was a nickname change, then the
original (old) nick must be removed as well.
If the server recieves an identical NICK from a client which is
directly connected, it may issue an ERR_NICKCOLLISION to the local
client, drop the NICK command, and not generate any kills.
Oikarinen & Reed [Page 14]
RFC 1459 Internet Relay Chat Protocol May 1993
Numeric Replies:
ERR_NONICKNAMEGIVEN ERR_ERRONEUSNICKNAME
ERR_NICKNAMEINUSE ERR_NICKCOLLISION
Example:
NICK Wiz ; Introducing new nick "Wiz".
:WiZ NICK Kilroy ; WiZ changed his nickname to Kilroy.
4.1.3 User message
Command: USER
Parameters: <username> <hostname> <servername> <realname>
The USER message is used at the beginning of connection to specify
the username, hostname, servername and realname of s new user. It is
also used in communication between servers to indicate new user
arriving on IRC, since only after both USER and NICK have been
received from a client does a user become registered.
Between servers USER must to be prefixed with client's NICKname.
Note that hostname and servername are normally ignored by the IRC
server when the USER command comes from a directly connected client
(for security reasons), but they are used in server to server
communication. This means that a NICK must always be sent to a
remote server when a new user is being introduced to the rest of the
network before the accompanying USER is sent.
It must be noted that realname parameter must be the last parameter,
because it may contain space characters and must be prefixed with a
colon (':') to make sure this is recognised as such.
Since it is easy for a client to lie about its username by relying
solely on the USER message, the use of an "Identity Server" is
recommended. If the host which a user connects from has such a
server enabled the username is set to that as in the reply from the
"Identity Server".
Numeric Replies:
ERR_NEEDMOREPARAMS ERR_ALREADYREGISTRED
Examples:
USER guest tolmoon tolsun :Ronnie Reagan
Oikarinen & Reed [Page 15]
RFC 1459 Internet Relay Chat Protocol May 1993
; User registering themselves with a
username of "guest" and real name
"Ronnie Reagan".
:testnick USER guest tolmoon tolsun :Ronnie Reagan
; message between servers with the
nickname for which the USER command
belongs to
4.1.4 Server message
Command: SERVER
Parameters: <servername> <hopcount> <info>
The server message is used to tell a server that the other end of a
new connection is a server. This message is also used to pass server
data over whole net. When a new server is connected to net,
information about it be broadcast to the whole network. <hopcount>
is used to give all servers some internal information on how far away
all servers are. With a full server list, it would be possible to
construct a map of the entire server tree, but hostmasks prevent this
from being done.
The SERVER message must only be accepted from either (a) a connection
which is yet to be registered and is attempting to register as a
server, or (b) an existing connection to another server, in which
case the SERVER message is introducing a new server behind that
server.
Most errors that occur with the receipt of a SERVER command result in
the connection being terminated by the destination host (target
SERVER). Error replies are usually sent using the "ERROR" command
rather than the numeric since the ERROR command has several useful
properties which make it useful here.
If a SERVER message is parsed and attempts to introduce a server
which is already known to the receiving server, the connection from
which that message must be closed (following the correct procedures),
since a duplicate route to a server has formed and the acyclic nature
of the IRC tree broken.
Numeric Replies:
ERR_ALREADYREGISTRED
Example:
Oikarinen & Reed [Page 16]
RFC 1459 Internet Relay Chat Protocol May 1993
SERVER test.oulu.fi 1 :[tolsun.oulu.fi] Experimental server
; New server test.oulu.fi introducing
itself and attempting to register. The
name in []'s is the hostname for the
host running test.oulu.fi.
:tolsun.oulu.fi SERVER csd.bu.edu 5 :BU Central Server
; Server tolsun.oulu.fi is our uplink
for csd.bu.edu which is 5 hops away.
4.1.5 Oper
Command: OPER
Parameters: <user> <password>
OPER message is used by a normal user to obtain operator privileges.
The combination of <user> and <password> are required to gain
Operator privileges.
If the client sending the OPER command supplies the correct password
for the given user, the server then informs the rest of the network
of the new operator by issuing a "MODE +o" for the clients nickname.
The OPER message is client-server only.
Numeric Replies:
ERR_NEEDMOREPARAMS RPL_YOUREOPER
ERR_NOOPERHOST ERR_PASSWDMISMATCH
Example:
OPER foo bar ; Attempt to register as an operator
using a username of "foo" and "bar" as
the password.
4.1.6 Quit
Command: QUIT
Parameters: [<Quit message>]
A client session is ended with a quit message. The server must close
the connection to a client which sends a QUIT message. If a "Quit
Message" is given, this will be sent instead of the default message,
the nickname.
When netsplits (disconnecting of two servers) occur, the quit message
Oikarinen & Reed [Page 17]
RFC 1459 Internet Relay Chat Protocol May 1993
is composed of the names of two servers involved, separated by a
space. The first name is that of the server which is still connected
and the second name is that of the server that has become
disconnected.
If, for some other reason, a client connection is closed without the
client issuing a QUIT command (e.g. client dies and EOF occurs
on socket), the server is required to fill in the quit message with
some sort of message reflecting the nature of the event which
caused it to happen.
Numeric Replies:
None.
Examples:
QUIT :Gone to have lunch ; Preferred message format.
4.1.7 Server quit message
Command: SQUIT
Parameters: <server> <comment>
The SQUIT message is needed to tell about quitting or dead servers.
If a server wishes to break the connection to another server it must
send a SQUIT message to the other server, using the the name of the
other server as the server parameter, which then closes its
connection to the quitting server.
This command is also available operators to help keep a network of
IRC servers connected in an orderly fashion. Operators may also
issue an SQUIT message for a remote server connection. In this case,
the SQUIT must be parsed by each server inbetween the operator and
the remote server, updating the view of the network held by each
server as explained below.
The <comment> should be supplied by all operators who execute a SQUIT
for a remote server (that is not connected to the server they are
currently on) so that other operators are aware for the reason of
this action. The <comment> is also filled in by servers which may
place an error or similar message here.
Both of the servers which are on either side of the connection being
closed are required to to send out a SQUIT message (to all its other
server connections) for all other servers which are considered to be
behind that link.
Oikarinen & Reed [Page 18]
RFC 1459 Internet Relay Chat Protocol May 1993
Similarly, a QUIT message must be sent to the other connected servers
rest of the network on behalf of all clients behind that link. In
addition to this, all channel members of a channel which lost a
member due to the split must be sent a QUIT message.
If a server connection is terminated prematurely (e.g. the server on
the other end of the link died), the server which detects
this disconnection is required to inform the rest of the network
that the connection has closed and fill in the comment field
with something appropriate.
Numeric replies:
ERR_NOPRIVILEGES ERR_NOSUCHSERVER
Example:
SQUIT tolsun.oulu.fi :Bad Link ? ; the server link tolson.oulu.fi has
been terminated because of "Bad Link".
:Trillian SQUIT cm22.eng.umd.edu :Server out of control
; message from Trillian to disconnect
"cm22.eng.umd.edu" from the net
because "Server out of control".
4.2 Channel operations
This group of messages is concerned with manipulating channels, their
properties (channel modes), and their contents (typically clients).
In implementing these, a number of race conditions are inevitable
when clients at opposing ends of a network send commands which will
ultimately clash. It is also required that servers keep a nickname
history to ensure that wherever a <nick> parameter is given, the
server check its history in case it has recently been changed.
4.2.1 Join message
Command: JOIN
Parameters: <channel>{,<channel>} [<key>{,<key>}]
The JOIN command is used by client to start listening a specific
channel. Whether or not a client is allowed to join a channel is
checked only by the server the client is connected to; all other
servers automatically add the user to the channel when it is received
from other servers. The conditions which affect this are as follows:
1. the user must be invited if the channel is invite-only;
Oikarinen & Reed [Page 19]
RFC 1459 Internet Relay Chat Protocol May 1993
2. the user's nick/username/hostname must not match any
active bans;
3. the correct key (password) must be given if it is set.
These are discussed in more detail under the MODE command (see
section 4.2.3 for more details).
Once a user has joined a channel, they receive notice about all
commands their server receives which affect the channel. This
includes MODE, KICK, PART, QUIT and of course PRIVMSG/NOTICE. The
JOIN command needs to be broadcast to all servers so that each server
knows where to find the users who are on the channel. This allows
optimal delivery of PRIVMSG/NOTICE messages to the channel.
If a JOIN is successful, the user is then sent the channel's topic
(using RPL_TOPIC) and the list of users who are on the channel (using
RPL_NAMREPLY), which must include the user joining.
Numeric Replies:
ERR_NEEDMOREPARAMS ERR_BANNEDFROMCHAN
ERR_INVITEONLYCHAN ERR_BADCHANNELKEY
ERR_CHANNELISFULL ERR_BADCHANMASK
ERR_NOSUCHCHANNEL ERR_TOOMANYCHANNELS
RPL_TOPIC
Examples:
JOIN #foobar ; join channel #foobar.
JOIN &foo fubar ; join channel &foo using key "fubar".
JOIN #foo,&bar fubar ; join channel #foo using key "fubar"
and &bar using no key.
JOIN #foo,#bar fubar,foobar ; join channel #foo using key "fubar".
and channel #bar using key "foobar".
JOIN #foo,#bar ; join channels #foo and #bar.
:WiZ JOIN #Twilight_zone ; JOIN message from WiZ
4.2.2 Part message
Command: PART
Parameters: <channel>{,<channel>}
Oikarinen & Reed [Page 20]
RFC 1459 Internet Relay Chat Protocol May 1993
The PART message causes the client sending the message to be removed
from the list of active users for all given channels listed in the
parameter string.
Numeric Replies:
ERR_NEEDMOREPARAMS ERR_NOSUCHCHANNEL
ERR_NOTONCHANNEL
Examples:
PART #twilight_zone ; leave channel "#twilight_zone"
PART #oz-ops,&group5 ; leave both channels "&group5" and
"#oz-ops".
4.2.3 Mode message
Command: MODE
The MODE command is a dual-purpose command in IRC. It allows both
usernames and channels to have their mode changed. The rationale for
this choice is that one day nicknames will be obsolete and the
equivalent property will be the channel.
When parsing MODE messages, it is recommended that the entire message
be parsed first and then the changes which resulted then passed on.
4.2.3.1 Channel modes
Parameters: <channel> {[+|-]|o|p|s|i|t|n|b|v} [<limit>] [<user>]
[<ban mask>]
The MODE command is provided so that channel operators may change the
characteristics of `their' channel. It is also required that servers
be able to change channel modes so that channel operators may be
created.
The various modes available for channels are as follows:
o - give/take channel operator privileges;
p - private channel flag;
s - secret channel flag;
i - invite-only channel flag;
t - topic settable by channel operator only flag;
n - no messages to channel from clients on the outside;
m - moderated channel;
l - set the user limit to channel;
Oikarinen & Reed [Page 21]
RFC 1459 Internet Relay Chat Protocol May 1993
b - set a ban mask to keep users out;
v - give/take the ability to speak on a moderated channel;
k - set a channel key (password).
When using the 'o' and 'b' options, a restriction on a total of three
per mode command has been imposed. That is, any combination of 'o'
and
4.2.3.2 User modes
Parameters: <nickname> {[+|-]|i|w|s|o}
The user MODEs are typically changes which affect either how the
client is seen by others or what 'extra' messages the client is sent.
A user MODE command may only be accepted if both the sender of the
message and the nickname given as a parameter are both the same.
The available modes are as follows:
i - marks a users as invisible;
s - marks a user for receipt of server notices;
w - user receives wallops;
o - operator flag.
Additional modes may be available later on.
If a user attempts to make themselves an operator using the "+o"
flag, the attempt should be ignored. There is no restriction,
however, on anyone `deopping' themselves (using "-o"). Numeric
Replies:
ERR_NEEDMOREPARAMS RPL_CHANNELMODEIS
ERR_CHANOPRIVSNEEDED ERR_NOSUCHNICK
ERR_NOTONCHANNEL ERR_KEYSET
RPL_BANLIST RPL_ENDOFBANLIST
ERR_UNKNOWNMODE ERR_NOSUCHCHANNEL
ERR_USERSDONTMATCH RPL_UMODEIS
ERR_UMODEUNKNOWNFLAG
Examples:
Use of Channel Modes:
MODE #Finnish +im ; Makes #Finnish channel moderated and
'invite-only'.
MODE #Finnish +o Kilroy ; Gives 'chanop' privileges to Kilroy on
Oikarinen & Reed [Page 22]
RFC 1459 Internet Relay Chat Protocol May 1993
channel #Finnish.
MODE #Finnish +v Wiz ; Allow WiZ to speak on #Finnish.
MODE #Fins -s ; Removes 'secret' flag from channel
#Fins.
MODE #42 +k oulu ; Set the channel key to "oulu".
MODE #eu-opers +l 10 ; Set the limit for the number of users
on channel to 10.
MODE &oulu +b ; list ban masks set for channel.
MODE &oulu +b *!*@* ; prevent all users from joining.
MODE &oulu +b *!*@*.edu ; prevent any user from a hostname
matching *.edu from joining.
Use of user Modes:
:MODE WiZ -w ; turns reception of WALLOPS messages
off for WiZ.
:Angel MODE Angel +i ; Message from Angel to make themselves
invisible.
MODE WiZ -o ; WiZ 'deopping' (removing operator
status). The plain reverse of this
command ("MODE WiZ +o") must not be
allowed from users since would bypass
the OPER command.
4.2.4 Topic message
Command: TOPIC
Parameters: <channel> [<topic>]
The TOPIC message is used to change or view the topic of a channel.
The topic for channel <channel> is returned if there is no <topic>
given. If the <topic> parameter is present, the topic for that
channel will be changed, if the channel modes permit this action.
Numeric Replies:
ERR_NEEDMOREPARAMS ERR_NOTONCHANNEL
RPL_NOTOPIC RPL_TOPIC
ERR_CHANOPRIVSNEEDED
Oikarinen & Reed [Page 23]
RFC 1459 Internet Relay Chat Protocol May 1993
Examples:
:Wiz TOPIC #test :New topic ;User Wiz setting the topic.
TOPIC #test :another topic ;set the topic on #test to "another
topic".
TOPIC #test ; check the topic for #test.
4.2.5 Names message
Command: NAMES
Parameters: [<channel>{,<channel>}]
By using the NAMES command, a user can list all nicknames that are
visible to them on any channel that they can see. Channel names
which they can see are those which aren't private (+p) or secret (+s)
or those which they are actually on. The <channel> parameter
specifies which channel(s) to return information about if valid.
There is no error reply for bad channel names.
If no <channel> parameter is given, a list of all channels and their
occupants is returned. At the end of this list, a list of users who
are visible but either not on any channel or not on a visible channel
are listed as being on `channel' "*".
Numerics:
RPL_NAMREPLY RPL_ENDOFNAMES
Examples:
NAMES #twilight_zone,#42 ; list visible users on #twilight_zone
and #42 if the channels are visible to
you.
NAMES ; list all visible channels and users
4.2.6 List message
Command: LIST
Parameters: [<channel>{,<channel>} [<server>]]
The list message is used to list channels and their topics. If the
<channel> parameter is used, only the status of that channel
is displayed. Private channels are listed (without their
topics) as channel "Prv" unless the client generating the query is
actually on that channel. Likewise, secret channels are not listed
Oikarinen & Reed [Page 24]
RFC 1459 Internet Relay Chat Protocol May 1993
at all unless the client is a member of the channel in question.
Numeric Replies:
ERR_NOSUCHSERVER RPL_LISTSTART
RPL_LIST RPL_LISTEND
Examples:
LIST ; List all channels.
LIST #twilight_zone,#42 ; List channels #twilight_zone and #42
4.2.7 Invite message
Command: INVITE
Parameters: <nickname> <channel>
The INVITE message is used to invite users to a channel. The
parameter <nickname> is the nickname of the person to be invited to
the target channel <channel>. There is no requirement that the
channel the target user is being invited to must exist or be a valid
channel. To invite a user to a channel which is invite only (MODE
+i), the client sending the invite must be recognised as being a
channel operator on the given channel.
Numeric Replies:
ERR_NEEDMOREPARAMS ERR_NOSUCHNICK
ERR_NOTONCHANNEL ERR_USERONCHANNEL
ERR_CHANOPRIVSNEEDED
RPL_INVITING RPL_AWAY
Examples:
:Angel INVITE Wiz #Dust ; User Angel inviting WiZ to channel
#Dust
INVITE Wiz #Twilight_Zone ; Command to invite WiZ to
#Twilight_zone
4.2.8 Kick command
Command: KICK
Parameters: <channel> <user> [<comment>]
The KICK command can be used to forcibly remove a user from a
channel. It 'kicks them out' of the channel (forced PART).
Oikarinen & Reed [Page 25]
RFC 1459 Internet Relay Chat Protocol May 1993
Only a channel operator may kick another user out of a channel.
Each server that receives a KICK message checks that it is valid
(ie the sender is actually a channel operator) before removing
the victim from the channel.
Numeric Replies:
ERR_NEEDMOREPARAMS ERR_NOSUCHCHANNEL
ERR_BADCHANMASK ERR_CHANOPRIVSNEEDED
ERR_NOTONCHANNEL
Examples:
KICK &Melbourne Matthew ; Kick Matthew from &Melbourne
KICK #Finnish John :Speaking English
; Kick John from #Finnish using
"Speaking English" as the reason
(comment).
:WiZ KICK #Finnish John ; KICK message from WiZ to remove John
from channel #Finnish
NOTE:
It is possible to extend the KICK command parameters to the
following:
<channel>{,<channel>} <user>{,<user>} [<comment>]
4.3 Server queries and commands
The server query group of commands has been designed to return
information about any server which is connected to the network. All
servers connected must respond to these queries and respond
correctly. Any invalid response (or lack thereof) must be considered
a sign of a broken server and it must be disconnected/disabled as
soon as possible until the situation is remedied.
In these queries, where a parameter appears as "<server>", it will
usually mean it can be a nickname or a server or a wildcard name of
some sort. For each parameter, however, only one query and set of
replies is to be generated.
4.3.1 Version message
Command: VERSION
Parameters: [<server>]
Oikarinen & Reed [Page 26]
RFC 1459 Internet Relay Chat Protocol May 1993
The VERSION message is used to query the version of the server
program. An optional parameter <server> is used to query the version
of the server program which a client is not directly connected to.
Numeric Replies:
ERR_NOSUCHSERVER RPL_VERSION
Examples:
:Wiz VERSION *.se ; message from Wiz to check the version
of a server matching "*.se"
VERSION tolsun.oulu.fi ; check the version of server
"tolsun.oulu.fi".
4.3.2 Stats message
Command: STATS
Parameters: [<query> [<server>]]
The stats message is used to query statistics of certain server. If
<server> parameter is omitted, only the end of stats reply is sent
back. The implementation of this command is highly dependent on the
server which replies, although the server must be able to supply
information as described by the queries below (or similar).
A query may be given by any single letter which is only checked by
the destination server (if given as the <server> parameter) and is
otherwise passed on by intermediate servers, ignored and unaltered.
The following queries are those found in the current IRC
implementation and provide a large portion of the setup information
for that server. Although these may not be supported in the same way
by other versions, all servers should be able to supply a valid reply
to a STATS query which is consistent with the reply formats currently
used and the purpose of the query.
The currently supported queries are:
c - returns a list of servers which the server may connect
to or allow connections from;
h - returns a list of servers which are either forced to be
treated as leaves or allowed to act as hubs;
i - returns a list of hosts which the server allows a client
to connect from;
k - returns a list of banned username/hostname combinations
for that server;
l - returns a list of the server's connections, showing how
Oikarinen & Reed [Page 27]
RFC 1459 Internet Relay Chat Protocol May 1993
long each connection has been established and the traffic
over that connection in bytes and messages for each
direction;
m - returns a list of commands supported by the server and
the usage count for each if the usage count is non zero;
o - returns a list of hosts from which normal clients may
become operators;
y - show Y (Class) lines from server's configuration file;
u - returns a string showing how long the server has been up.
Numeric Replies:
ERR_NOSUCHSERVER
RPL_STATSCLINE RPL_STATSNLINE
RPL_STATSILINE RPL_STATSKLINE
RPL_STATSQLINE RPL_STATSLLINE
RPL_STATSLINKINFO RPL_STATSUPTIME
RPL_STATSCOMMANDS RPL_STATSOLINE
RPL_STATSHLINE RPL_ENDOFSTATS
Examples:
STATS m ; check the command usage for the server
you are connected to
:Wiz STATS c eff.org ; request by WiZ for C/N line
information from server eff.org
4.3.3 Links message
Command: LINKS
Parameters: [[<remote server>] <server mask>]
With LINKS, a user can list all servers which are known by the server
answering the query. The returned list of servers must match the
mask, or if no mask is given, the full list is returned.
If <remote server> is given in addition to <server mask>, the LINKS
command is forwarded to the first server found that matches that name
(if any), and that server is then required to answer the query.
Numeric Replies:
ERR_NOSUCHSERVER
RPL_LINKS RPL_ENDOFLINKS
Examples:
Oikarinen & Reed [Page 28]
RFC 1459 Internet Relay Chat Protocol May 1993
LINKS *.au ; list all servers which have a name
that matches *.au;
:WiZ LINKS *.bu.edu *.edu ; LINKS message from WiZ to the first
server matching *.edu for a list of
servers matching *.bu.edu.
4.3.4 Time message
Command: TIME
Parameters: [<server>]
The time message is used to query local time from the specified
server. If the server parameter is not given, the server handling the
command must reply to the query.
Numeric Replies:
ERR_NOSUCHSERVER RPL_TIME
Examples:
TIME tolsun.oulu.fi ; check the time on the server
"tolson.oulu.fi"
Angel TIME *.au ; user angel checking the time on a
server matching "*.au"
4.3.5 Connect message
Command: CONNECT
Parameters: <target server> [<port> [<remote server>]]
The CONNECT command can be used to force a server to try to establish
a new connection to another server immediately. CONNECT is a
privileged command and is to be available only to IRC Operators. If
a remote server is given then the CONNECT attempt is made by that
server to <target server> and <port>.
Numeric Replies:
ERR_NOSUCHSERVER ERR_NOPRIVILEGES
ERR_NEEDMOREPARAMS
Examples:
CONNECT tolsun.oulu.fi ; Attempt to connect a server to
tolsun.oulu.fi
Oikarinen & Reed [Page 29]
RFC 1459 Internet Relay Chat Protocol May 1993
:WiZ CONNECT eff.org 6667 csd.bu.edu
; CONNECT attempt by WiZ to get servers
eff.org and csd.bu.edu connected on port
6667.
4.3.6 Trace message
Command: TRACE
Parameters: [<server>]
TRACE command is used to find the route to specific server. Each
server that processes this message must tell the sender about it by
sending a reply indicating it is a pass-through link, forming a chain
of replies similar to that gained from using "traceroute". After
sending this reply back, it must then send the TRACE message to the
next server until given server is reached. If the <server> parameter
is omitted, it is recommended that TRACE command send a message to
the sender telling which servers the current server has direct
connection to.
If the destination given by "<server>" is an actual server, then the
destination server is required to report all servers and users which
are connected to it, although only operators are permitted to see
users present. If the destination given by <server> is a nickname,
they only a reply for that nickname is given.
Numeric Replies:
ERR_NOSUCHSERVER
If the TRACE message is destined for another server, all intermediate
servers must return a RPL_TRACELINK reply to indicate that the TRACE
passed through it and where its going next.
RPL_TRACELINK
A TRACE reply may be composed of any number of the following numeric
replies.
RPL_TRACECONNECTING RPL_TRACEHANDSHAKE
RPL_TRACEUNKNOWN RPL_TRACEOPERATOR
RPL_TRACEUSER RPL_TRACESERVER
RPL_TRACESERVICE RPL_TRACENEWTYPE
RPL_TRACECLASS
Examples:
TRACE *.oulu.fi ; TRACE to a server matching *.oulu.fi
Oikarinen & Reed [Page 30]
RFC 1459 Internet Relay Chat Protocol May 1993
:WiZ TRACE AngelDust ; TRACE issued by WiZ to nick AngelDust
4.3.7 Admin command
Command: ADMIN
Parameters: [<server>]
The admin message is used to find the name of the administrator of
the given server, or current server if <server> parameter is omitted.
Each server must have the ability to forward ADMIN messages to other
servers.
Numeric Replies:
ERR_NOSUCHSERVER
RPL_ADMINME RPL_ADMINLOC1
RPL_ADMINLOC2 RPL_ADMINEMAIL
Examples:
ADMIN tolsun.oulu.fi ; request an ADMIN reply from
tolsun.oulu.fi
:WiZ ADMIN *.edu ; ADMIN request from WiZ for first
server found to match *.edu.
4.3.8 Info command
Command: INFO
Parameters: [<server>]
The INFO command is required to return information which describes
the server: its version, when it was compiled, the patchlevel, when
it was started, and any other miscellaneous information which may be
considered to be relevant.
Numeric Replies:
ERR_NOSUCHSERVER
RPL_INFO RPL_ENDOFINFO
Examples:
INFO csd.bu.edu ; request an INFO reply from
csd.bu.edu
:Avalon INFO *.fi ; INFO request from Avalon for first
server found to match *.fi.
Oikarinen & Reed [Page 31]
RFC 1459 Internet Relay Chat Protocol May 1993
INFO Angel ; request info from the server that
Angel is connected to.
4.4 Sending messages
The main purpose of the IRC protocol is to provide a base for clients
to communicate with each other. PRIVMSG and NOTICE are the only
messages available which actually perform delivery of a text message
from one client to another - the rest just make it possible and try
to ensure it happens in a reliable and structured manner.
4.4.1 Private messages
Command: PRIVMSG
Parameters: <receiver>{,<receiver>} <text to be sent>
PRIVMSG is used to send private messages between users. <receiver>
is the nickname of the receiver of the message. <receiver> can also
be a list of names or channels separated with commas.
The <receiver> parameter may also me a host mask (#mask) or server
mask ($mask). In both cases the server will only send the PRIVMSG
to those who have a server or host matching the mask. The mask must
have at least 1 (one) "." in it and no wildcards following the
last ".". This requirement exists to prevent people sending messages
to "#*" or "$*", which would broadcast to all users; from
experience, this is abused more than used responsibly and properly.
Wildcards are the '*' and '?' characters. This extension to
the PRIVMSG command is only available to Operators.
Numeric Replies:
ERR_NORECIPIENT ERR_NOTEXTTOSEND
ERR_CANNOTSENDTOCHAN ERR_NOTOPLEVEL
ERR_WILDTOPLEVEL ERR_TOOMANYTARGETS
ERR_NOSUCHNICK
RPL_AWAY
Examples:
:Angel PRIVMSG Wiz :Hello are you receiving this message ?
; Message from Angel to Wiz.
PRIVMSG Angel :yes I'm receiving it !receiving it !'u>(768u+1n) .br ;
Message to Angel.
PRIVMSG jto@tolsun.oulu.fi :Hello !
; Message to a client on server
Oikarinen & Reed [Page 32]
RFC 1459 Internet Relay Chat Protocol May 1993
tolsun.oulu.fi with username of "jto".
PRIVMSG $*.fi :Server tolsun.oulu.fi rebooting.
; Message to everyone on a server which
has a name matching *.fi.
PRIVMSG #*.edu :NSFNet is undergoing work, expect interruptions
; Message to all users who come from a
host which has a name matching *.edu.
4.4.2 Notice
Command: NOTICE
Parameters: <nickname> <text>
The NOTICE message is used similarly to PRIVMSG. The difference
between NOTICE and PRIVMSG is that automatic replies must never be
sent in response to a NOTICE message. This rule applies to servers
too - they must not send any error reply back to the client on
receipt of a notice. The object of this rule is to avoid loops
between a client automatically sending something in response to
something it received. This is typically used by automatons (clients
with either an AI or other interactive program controlling their
actions) which are always seen to be replying lest they end up in a
loop with another automaton.
See PRIVMSG for more details on replies and examples.
4.5 User based queries
User queries are a group of commands which are primarily concerned
with finding details on a particular user or group users. When using
wildcards with any of these commands, if they match, they will only
return information on users who are 'visible' to you. The visibility
of a user is determined as a combination of the user's mode and the
common set of channels you are both on.
4.5.1 Who query
Command: WHO
Parameters: [<name> [<o>]]
The WHO message is used by a client to generate a query which returns
a list of information which 'matches' the <name> parameter given by
the client. In the absence of the <name> parameter, all visible
(users who aren't invisible (user mode +i) and who don't have a
common channel with the requesting client) are listed. The same
result can be achieved by using a <name> of "0" or any wildcard which
Oikarinen & Reed [Page 33]
RFC 1459 Internet Relay Chat Protocol May 1993
will end up matching every entry possible.
The <name> passed to WHO is matched against users' host, server, real
name and nickname if the channel <name> cannot be found.
If the "o" parameter is passed only operators are returned according
to the name mask supplied.
Numeric Replies:
ERR_NOSUCHSERVER
RPL_WHOREPLY RPL_ENDOFWHO
Examples:
WHO *.fi ; List all users who match against
"*.fi".
WHO jto* o ; List all users with a match against
"jto*" if they are an operator.
4.5.2 Whois query
Command: WHOIS
Parameters: [<server>] <nickmask>[,<nickmask>[,...]]
This message is used to query information about particular user. The
server will answer this message with several numeric messages
indicating different statuses of each user which matches the nickmask
(if you are entitled to see them). If no wildcard is present in the
<nickmask>, any information about that nick which you are allowed to
see is presented. A comma (',') separated list of nicknames may be
given.
The latter version sends the query to a specific server. It is
useful if you want to know how long the user in question has been
idle as only local server (ie. the server the user is directly
connected to) knows that information, while everything else is
globally known.
Numeric Replies:
ERR_NOSUCHSERVER ERR_NONICKNAMEGIVEN
RPL_WHOISUSER RPL_WHOISCHANNELS
RPL_WHOISCHANNELS RPL_WHOISSERVER
RPL_AWAY RPL_WHOISOPERATOR
RPL_WHOISIDLE ERR_NOSUCHNICK
RPL_ENDOFWHOIS
Oikarinen & Reed [Page 34]
RFC 1459 Internet Relay Chat Protocol May 1993
Examples:
WHOIS wiz ; return available user information
about nick WiZ
WHOIS eff.org trillian ; ask server eff.org for user
information about trillian
4.5.3 Whowas
Command: WHOWAS
Parameters: <nickname> [<count> [<server>]]
Whowas asks for information about a nickname which no longer exists.
This may either be due to a nickname change or the user leaving IRC.
In response to this query, the server searches through its nickname
history, looking for any nicks which are lexically the same (no wild
card matching here). The history is searched backward, returning the
most recent entry first. If there are multiple entries, up to
<count> replies will be returned (or all of them if no <count>
parameter is given). If a non-positive number is passed as being
<count>, then a full search is done.
Numeric Replies:
ERR_NONICKNAMEGIVEN ERR_WASNOSUCHNICK
RPL_WHOWASUSER RPL_WHOISSERVER
RPL_ENDOFWHOWAS
Examples:
WHOWAS Wiz ; return all information in the nick
history about nick "WiZ";
WHOWAS Mermaid 9 ; return at most, the 9 most recent
entries in the nick history for
"Mermaid";
WHOWAS Trillian 1 *.edu ; return the most recent history for
"Trillian" from the first server found
to match "*.edu".
4.6 Miscellaneous messages
Messages in this category do not fit into any of the above categories
but are nonetheless still a part of and required by the protocol.
Oikarinen & Reed [Page 35]
RFC 1459 Internet Relay Chat Protocol May 1993
4.6.1 Kill message
Command: KILL
Parameters: <nickname> <comment>
The KILL message is used to cause a client-server connection to be
closed by the server which has the actual connection. KILL is used
by servers when they encounter a duplicate entry in the list of valid
nicknames and is used to remove both entries. It is also available
to operators.
Clients which have automatic reconnect algorithms effectively make
this command useless since the disconnection is only brief. It does
however break the flow of data and can be used to stop large amounts
of being abused, any user may elect to receive KILL messages
generated for others to keep an 'eye' on would be trouble spots.
In an arena where nicknames are required to be globally unique at all
times, KILL messages are sent whenever 'duplicates' are detected
(that is an attempt to register two users with the same nickname) in
the hope that both of them will disappear and only 1 reappear.
The comment given must reflect the actual reason for the KILL. For
server-generated KILLs it usually is made up of details concerning
the origins of the two conflicting nicknames. For users it is left
up to them to provide an adequate reason to satisfy others who see
it. To prevent/discourage fake KILLs from being generated to hide
the identify of the KILLer, the comment also shows a 'kill-path'
which is updated by each server it passes through, each prepending
its name to the path.
Numeric Replies:
ERR_NOPRIVILEGES ERR_NEEDMOREPARAMS
ERR_NOSUCHNICK ERR_CANTKILLSERVER
KILL David (csd.bu.edu <- tolsun.oulu.fi)
; Nickname collision between csd.bu.edu
and tolson.oulu.fi
NOTE:
It is recommended that only Operators be allowed to kill other users
with KILL message. In an ideal world not even operators would need
to do this and it would be left to servers to deal with.
Oikarinen & Reed [Page 36]
RFC 1459 Internet Relay Chat Protocol May 1993
4.6.2 Ping message
Command: PING
Parameters: <server1> [<server2>]
The PING message is used to test the presence of an active client at
the other end of the connection. A PING message is sent at regular
intervals if no other activity detected coming from a connection. If
a connection fails to respond to a PING command within a set amount
of time, that connection is closed.
Any client which receives a PING message must respond to <server1>
(server which sent the PING message out) as quickly as possible with
an appropriate PONG message to indicate it is still there and alive.
Servers should not respond to PING commands but rely on PINGs from
the other end of the connection to indicate the connection is alive.
If the <server2> parameter is specified, the PING message gets
forwarded there.
Numeric Replies:
ERR_NOORIGIN ERR_NOSUCHSERVER
Examples:
PING tolsun.oulu.fi ; server sending a PING message to
another server to indicate it is still
alive.
PING WiZ ; PING message being sent to nick WiZ
4.6.3 Pong message
Command: PONG
Parameters: <daemon> [<daemon2>]
PONG message is a reply to ping message. If parameter <daemon2> is
given this message must be forwarded to given daemon. The <daemon>
parameter is the name of the daemon who has responded to PING message
and generated this message.
Numeric Replies:
ERR_NOORIGIN ERR_NOSUCHSERVER
Examples:
PONG csd.bu.edu tolsun.oulu.fi ; PONG message from csd.bu.edu to
Oikarinen & Reed [Page 37]
RFC 1459 Internet Relay Chat Protocol May 1993
tolsun.oulu.fi
4.6.4 Error
Command: ERROR
Parameters: <error message>
The ERROR command is for use by servers when reporting a serious or
fatal error to its operators. It may also be sent from one server to
another but must not be accepted from any normal unknown clients.
An ERROR message is for use for reporting errors which occur with a
server-to-server link only. An ERROR message is sent to the server
at the other end (which sends it to all of its connected operators)
and to all operators currently connected. It is not to be passed
onto any other servers by a server if it is received from a server.
When a server sends a received ERROR message to its operators, the
message should be encapsulated inside a NOTICE message, indicating
that the client was not responsible for the error.
Numerics:
None.
Examples:
ERROR :Server *.fi already exists; ERROR message to the other server
which caused this error.
NOTICE WiZ :ERROR from csd.bu.edu -- Server *.fi already exists
; Same ERROR message as above but sent
to user WiZ on the other server.
5. OPTIONALS
This section describes OPTIONAL messages. They are not required in a
working server implementation of the protocol described herein. In
the absence of the option, an error reply message must be generated
or an unknown command error. If the message is destined for another
server to answer then it must be passed on (elementary parsing
required) The allocated numerics for this are listed with the
messages below.
5.1 Away
Command: AWAY
Parameters: [message]
Oikarinen & Reed [Page 38]
RFC 1459 Internet Relay Chat Protocol May 1993
With the AWAY message, clients can set an automatic reply string for
any PRIVMSG commands directed at them (not to a channel they are on).
The automatic reply is sent by the server to client sending the
PRIVMSG command. The only replying server is the one to which the
sending client is connected to.
The AWAY message is used either with one parameter (to set an AWAY
message) or with no parameters (to remove the AWAY message).
Numeric Replies:
RPL_UNAWAY RPL_NOWAWAY
Examples:
AWAY :Gone to lunch. Back in 5 ; set away message to "Gone to lunch.
Back in 5".
:WiZ AWAY ; unmark WiZ as being away.
5.2 Rehash message
Command: REHASH
Parameters: None
The rehash message can be used by the operator to force the server to
re-read and process its configuration file.
Numeric Replies:
RPL_REHASHING ERR_NOPRIVILEGES
Examples:
REHASH ; message from client with operator
status to server asking it to reread its
configuration file.
5.3 Restart message
Command: RESTART
Parameters: None
The restart message can only be used by an operator to force a server
restart itself. This message is optional since it may be viewed as a
risk to allow arbitrary people to connect to a server as an operator
and execute this command, causing (at least) a disruption to service.
Oikarinen & Reed [Page 39]
RFC 1459 Internet Relay Chat Protocol May 1993
The RESTART command must always be fully processed by the server to
which the sending client is connected and not be passed onto other
connected servers.
Numeric Replies:
ERR_NOPRIVILEGES
Examples:
RESTART ; no parameters required.
5.4 Summon message
Command: SUMMON
Parameters: <user> [<server>]
The SUMMON command can be used to give users who are on a host
running an IRC server a message asking them to please join IRC. This
message is only sent if the target server (a) has SUMMON enabled, (b)
the user is logged in and (c) the server process can write to the
user's tty (or similar).
If no <server> parameter is given it tries to summon <user> from the
server the client is connected to is assumed as the target.
If summon is not enabled in a server, it must return the
ERR_SUMMONDISABLED numeric and pass the summon message onwards.
Numeric Replies:
ERR_NORECIPIENT ERR_FILEERROR
ERR_NOLOGIN ERR_NOSUCHSERVER
RPL_SUMMONING
Examples:
SUMMON jto ; summon user jto on the server's host
SUMMON jto tolsun.oulu.fi ; summon user jto on the host which a
server named "tolsun.oulu.fi" is
running.
5.5 Users
Command: USERS
Parameters: [<server>]
Oikarinen & Reed [Page 40]
RFC 1459 Internet Relay Chat Protocol May 1993
The USERS command returns a list of users logged into the server in a
similar format to who(1), rusers(1) and finger(1). Some people
may disable this command on their server for security related
reasons. If disabled, the correct numeric must be returned to
indicate this.
Numeric Replies:
ERR_NOSUCHSERVER ERR_FILEERROR
RPL_USERSSTART RPL_USERS
RPL_NOUSERS RPL_ENDOFUSERS
ERR_USERSDISABLED
Disabled Reply:
ERR_USERSDISABLED
Examples:
USERS eff.org ; request a list of users logged in on
server eff.org
:John USERS tolsun.oulu.fi ; request from John for a list of users
logged in on server tolsun.oulu.fi
5.6 Operwall message
Command: WALLOPS
Parameters: Text to be sent to all operators currently online
Sends a message to all operators currently online. After
implementing WALLOPS as a user command it was found that it was
often and commonly abused as a means of sending a message to a lot
of people (much similar to WALL). Due to this it is recommended
that the current implementation of WALLOPS be used as an
example by allowing and recognising only servers as the senders of
WALLOPS.
Numeric Replies:
ERR_NEEDMOREPARAMS
Examples:
:csd.bu.edu WALLOPS :Connect '*.uiuc.edu 6667' from Joshua; WALLOPS
message from csd.bu.edu announcing a
CONNECT message it received and acted
upon from Joshua.
Oikarinen & Reed [Page 41]
RFC 1459 Internet Relay Chat Protocol May 1993
5.7 Userhost message
Command: USERHOST
Parameters: <nickname>{<space><nickname>}
The USERHOST command takes a list of up to 5 nicknames, each
separated by a space character and returns a list of information
about each nickname that it found. The returned list has each reply
separated by a space.
Numeric Replies:
RPL_USERHOST ERR_NEEDMOREPARAMS
Examples:
USERHOST Wiz Michael Marty p ;USERHOST request for information on
nicks "Wiz", "Michael", "Marty" and "p"
5.8 Ison message
Command: ISON
Parameters: <nickname>{<space><nickname>}
The ISON command was implemented to provide a quick and efficient
means to get a response about whether a given nickname was currently
on IRC. ISON only takes one (1) parameter: a space-separated list of
nicks. For each nickname in the list that is present, the server
adds that to its reply string. Thus the reply string may return
empty (none of the given nicks are present), an exact copy of the
parameter string (all of them present) or as any other subset of the
set of nicks given in the parameter. The only limit on the number
of nicks that may be checked is that the combined length must not be
too large as to cause the server to chop it off so it fits in 512
characters.
ISON is only be processed by the server local to the client sending
the command and thus not passed onto other servers for further
processing.
Numeric Replies:
RPL_ISON ERR_NEEDMOREPARAMS
Examples:
ISON phone trillian WiZ jarlek Avalon Angel Monstah
; Sample ISON request for 7 nicks.
Oikarinen & Reed [Page 42]
RFC 1459 Internet Relay Chat Protocol May 1993
6. REPLIES
The following is a list of numeric replies which are generated in
response to the commands given above. Each numeric is given with its
number, name and reply string.
6.1 Error Replies.
401 ERR_NOSUCHNICK
"<nickname> :No such nick/channel"
- Used to indicate the nickname parameter supplied to a
command is currently unused.
402 ERR_NOSUCHSERVER
"<server name> :No such server"
- Used to indicate the server name given currently
doesn't exist.
403 ERR_NOSUCHCHANNEL
"<channel name> :No such channel"
- Used to indicate the given channel name is invalid.
404 ERR_CANNOTSENDTOCHAN
"<channel name> :Cannot send to channel"
- Sent to a user who is either (a) not on a channel
which is mode +n or (b) not a chanop (or mode +v) on
a channel which has mode +m set and is trying to send
a PRIVMSG message to that channel.
405 ERR_TOOMANYCHANNELS
"<channel name> :You have joined too many \
channels"
- Sent to a user when they have joined the maximum
number of allowed channels and they try to join
another channel.
406 ERR_WASNOSUCHNICK
"<nickname> :There was no such nickname"
- Returned by WHOWAS to indicate there is no history
information for that nickname.
407 ERR_TOOMANYTARGETS
"<target> :Duplicate recipients. No message \
Oikarinen & Reed [Page 43]
RFC 1459 Internet Relay Chat Protocol May 1993
delivered"
- Returned to a client which is attempting to send a
PRIVMSG/NOTICE using the user@host destination format
and for a user@host which has several occurrences.
409 ERR_NOORIGIN
":No origin specified"
- PING or PONG message missing the originator parameter
which is required since these commands must work
without valid prefixes.
411 ERR_NORECIPIENT
":No recipient given (<command>)"
412 ERR_NOTEXTTOSEND
":No text to send"
413 ERR_NOTOPLEVEL
"<mask> :No toplevel domain specified"
414 ERR_WILDTOPLEVEL
"<mask> :Wildcard in toplevel domain"
- 412 - 414 are returned by PRIVMSG to indicate that
the message wasn't delivered for some reason.
ERR_NOTOPLEVEL and ERR_WILDTOPLEVEL are errors that
are returned when an invalid use of
"PRIVMSG $<server>" or "PRIVMSG #<host>" is attempted.
421 ERR_UNKNOWNCOMMAND
"<command> :Unknown command"
- Returned to a registered client to indicate that the
command sent is unknown by the server.
422 ERR_NOMOTD
":MOTD File is missing"
- Server's MOTD file could not be opened by the server.
423 ERR_NOADMININFO
"<server> :No administrative info available"
- Returned by a server in response to an ADMIN message
when there is an error in finding the appropriate
information.
424 ERR_FILEERROR
":File error doing <file op> on <file>"
Oikarinen & Reed [Page 44]
RFC 1459 Internet Relay Chat Protocol May 1993
- Generic error message used to report a failed file
operation during the processing of a message.
431 ERR_NONICKNAMEGIVEN
":No nickname given"
- Returned when a nickname parameter expected for a
command and isn't found.
432 ERR_ERRONEUSNICKNAME
"<nick> :Erroneus nickname"
- Returned after receiving a NICK message which contains
characters which do not fall in the defined set. See
section x.x.x for details on valid nicknames.
433 ERR_NICKNAMEINUSE
"<nick> :Nickname is already in use"
- Returned when a NICK message is processed that results
in an attempt to change to a currently existing
nickname.
436 ERR_NICKCOLLISION
"<nick> :Nickname collision KILL"
- Returned by a server to a client when it detects a
nickname collision (registered of a NICK that
already exists by another server).
441 ERR_USERNOTINCHANNEL
"<nick> <channel> :They aren't on that channel"
- Returned by the server to indicate that the target
user of the command is not on the given channel.
442 ERR_NOTONCHANNEL
"<channel> :You're not on that channel"
- Returned by the server whenever a client tries to
perform a channel effecting command for which the
client isn't a member.
443 ERR_USERONCHANNEL
"<user> <channel> :is already on channel"
- Returned when a client tries to invite a user to a
channel they are already on.
Oikarinen & Reed [Page 45]
RFC 1459 Internet Relay Chat Protocol May 1993
444 ERR_NOLOGIN
"<user> :User not logged in"
- Returned by the summon after a SUMMON command for a
user was unable to be performed since they were not
logged in.
445 ERR_SUMMONDISABLED
":SUMMON has been disabled"
- Returned as a response to the SUMMON command. Must be
returned by any server which does not implement it.
446 ERR_USERSDISABLED
":USERS has been disabled"
- Returned as a response to the USERS command. Must be
returned by any server which does not implement it.
451 ERR_NOTREGISTERED
":You have not registered"
- Returned by the server to indicate that the client
must be registered before the server will allow it
to be parsed in detail.
461 ERR_NEEDMOREPARAMS
"<command> :Not enough parameters"
- Returned by the server by numerous commands to
indicate to the client that it didn't supply enough
parameters.
462 ERR_ALREADYREGISTRED
":You may not reregister"
- Returned by the server to any link which tries to
change part of the registered details (such as
password or user details from second USER message).
463 ERR_NOPERMFORHOST
":Your host isn't among the privileged"
- Returned to a client which attempts to register with
a server which does not been setup to allow
connections from the host the attempted connection
is tried.
Oikarinen & Reed [Page 46]
RFC 1459 Internet Relay Chat Protocol May 1993
464 ERR_PASSWDMISMATCH
":Password incorrect"
- Returned to indicate a failed attempt at registering
a connection for which a password was required and
was either not given or incorrect.
465 ERR_YOUREBANNEDCREEP
":You are banned from this server"
- Returned after an attempt to connect and register
yourself with a server which has been setup to
explicitly deny connections to you.
467 ERR_KEYSET
"<channel> :Channel key already set"
471 ERR_CHANNELISFULL
"<channel> :Cannot join channel (+l)"
472 ERR_UNKNOWNMODE
"<char> :is unknown mode char to me"
473 ERR_INVITEONLYCHAN
"<channel> :Cannot join channel (+i)"
474 ERR_BANNEDFROMCHAN
"<channel> :Cannot join channel (+b)"
475 ERR_BADCHANNELKEY
"<channel> :Cannot join channel (+k)"
481 ERR_NOPRIVILEGES
":Permission Denied- You're not an IRC operator"
- Any command requiring operator privileges to operate
must return this error to indicate the attempt was
unsuccessful.
482 ERR_CHANOPRIVSNEEDED
"<channel> :You're not channel operator"
- Any command requiring 'chanop' privileges (such as
MODE messages) must return this error if the client
making the attempt is not a chanop on the specified
channel.
483 ERR_CANTKILLSERVER
":You cant kill a server!"
- Any attempts to use the KILL command on a server
are to be refused and this error returned directly
to the client.
Oikarinen & Reed [Page 47]
RFC 1459 Internet Relay Chat Protocol May 1993
491 ERR_NOOPERHOST
":No O-lines for your host"
- If a client sends an OPER message and the server has
not been configured to allow connections from the
client's host as an operator, this error must be
returned.
501 ERR_UMODEUNKNOWNFLAG
":Unknown MODE flag"
- Returned by the server to indicate that a MODE
message was sent with a nickname parameter and that
the a mode flag sent was not recognized.
502 ERR_USERSDONTMATCH
":Cant change mode for other users"
- Error sent to any user trying to view or change the
user mode for a user other than themselves.
6.2 Command responses.
300 RPL_NONE
Dummy reply number. Not used.
302 RPL_USERHOST
":[<reply>{<space><reply>}]"
- Reply format used by USERHOST to list replies to
the query list. The reply string is composed as
follows:
<reply> ::= <nick>['*'] '=' <'+'|'-'><hostname>
The '*' indicates whether the client has registered
as an Operator. The '-' or '+' characters represent
whether the client has set an AWAY message or not
respectively.
303 RPL_ISON
":[<nick> {<space><nick>}]"
- Reply format used by ISON to list replies to the
query list.
301 RPL_AWAY
"<nick> :<away message>"
Oikarinen & Reed [Page 48]
RFC 1459 Internet Relay Chat Protocol May 1993
305 RPL_UNAWAY
":You are no longer marked as being away"
306 RPL_NOWAWAY
":You have been marked as being away"
- These replies are used with the AWAY command (if
allowed). RPL_AWAY is sent to any client sending a
PRIVMSG to a client which is away. RPL_AWAY is only
sent by the server to which the client is connected.
Replies RPL_UNAWAY and RPL_NOWAWAY are sent when the
client removes and sets an AWAY message.
311 RPL_WHOISUSER
"<nick> <user> <host> * :<real name>"
312 RPL_WHOISSERVER
"<nick> <server> :<server info>"
313 RPL_WHOISOPERATOR
"<nick> :is an IRC operator"
317 RPL_WHOISIDLE
"<nick> <integer> :seconds idle"
318 RPL_ENDOFWHOIS
"<nick> :End of /WHOIS list"
319 RPL_WHOISCHANNELS
"<nick> :{[@|+]<channel><space>}"
- Replies 311 - 313, 317 - 319 are all replies
generated in response to a WHOIS message. Given that
there are enough parameters present, the answering
server must either formulate a reply out of the above
numerics (if the query nick is found) or return an
error reply. The '*' in RPL_WHOISUSER is there as
the literal character and not as a wild card. For
each reply set, only RPL_WHOISCHANNELS may appear
more than once (for long lists of channel names).
The '@' and '+' characters next to the channel name
indicate whether a client is a channel operator or
has been granted permission to speak on a moderated
channel. The RPL_ENDOFWHOIS reply is used to mark
the end of processing a WHOIS message.
314 RPL_WHOWASUSER
"<nick> <user> <host> * :<real name>"
369 RPL_ENDOFWHOWAS
"<nick> :End of WHOWAS"
- When replying to a WHOWAS message, a server must use
the replies RPL_WHOWASUSER, RPL_WHOISSERVER or
ERR_WASNOSUCHNICK for each nickname in the presented
Oikarinen & Reed [Page 49]
RFC 1459 Internet Relay Chat Protocol May 1993
list. At the end of all reply batches, there must
be RPL_ENDOFWHOWAS (even if there was only one reply
and it was an error).
321 RPL_LISTSTART
"Channel :Users Name"
322 RPL_LIST
"<channel> <# visible> :<topic>"
323 RPL_LISTEND
":End of /LIST"
- Replies RPL_LISTSTART, RPL_LIST, RPL_LISTEND mark
the start, actual replies with data and end of the
server's response to a LIST command. If there are
no channels available to return, only the start
and end reply must be sent.
324 RPL_CHANNELMODEIS
"<channel> <mode> <mode params>"
331 RPL_NOTOPIC
"<channel> :No topic is set"
332 RPL_TOPIC
"<channel> :<topic>"
- When sending a TOPIC message to determine the
channel topic, one of two replies is sent. If
the topic is set, RPL_TOPIC is sent back else
RPL_NOTOPIC.
341 RPL_INVITING
"<channel> <nick>"
- Returned by the server to indicate that the
attempted INVITE message was successful and is
being passed onto the end client.
342 RPL_SUMMONING
"<user> :Summoning user to IRC"
- Returned by a server answering a SUMMON message to
indicate that it is summoning that user.
351 RPL_VERSION
"<version>.<debuglevel> <server> :<comments>"
- Reply by the server showing its version details.
The <version> is the version of the software being
Oikarinen & Reed [Page 50]
RFC 1459 Internet Relay Chat Protocol May 1993
used (including any patchlevel revisions) and the
<debuglevel> is used to indicate if the server is
running in "debug mode".
The "comments" field may contain any comments about
the version or further version details.
352 RPL_WHOREPLY
"<channel> <user> <host> <server> <nick> \
<H|G>[*][@|+] :<hopcount> <real name>"
315 RPL_ENDOFWHO
"<name> :End of /WHO list"
- The RPL_WHOREPLY and RPL_ENDOFWHO pair are used
to answer a WHO message. The RPL_WHOREPLY is only
sent if there is an appropriate match to the WHO
query. If there is a list of parameters supplied
with a WHO message, a RPL_ENDOFWHO must be sent
after processing each list item with <name> being
the item.
353 RPL_NAMREPLY
"<channel> :[[@|+]<nick> [[@|+]<nick> [...]]]"
366 RPL_ENDOFNAMES
"<channel> :End of /NAMES list"
- To reply to a NAMES message, a reply pair consisting
of RPL_NAMREPLY and RPL_ENDOFNAMES is sent by the
server back to the client. If there is no channel
found as in the query, then only RPL_ENDOFNAMES is
returned. The exception to this is when a NAMES
message is sent with no parameters and all visible
channels and contents are sent back in a series of
RPL_NAMEREPLY messages with a RPL_ENDOFNAMES to mark
the end.
364 RPL_LINKS
"<mask> <server> :<hopcount> <server info>"
365 RPL_ENDOFLINKS
"<mask> :End of /LINKS list"
- In replying to the LINKS message, a server must send
replies back using the RPL_LINKS numeric and mark the
end of the list using an RPL_ENDOFLINKS reply.
367 RPL_BANLIST
"<channel> <banid>"
368 RPL_ENDOFBANLIST
Oikarinen & Reed [Page 51]
RFC 1459 Internet Relay Chat Protocol May 1993
"<channel> :End of channel ban list"
- When listing the active 'bans' for a given channel,
a server is required to send the list back using the
RPL_BANLIST and RPL_ENDOFBANLIST messages. A separate
RPL_BANLIST is sent for each active banid. After the
banids have been listed (or if none present) a
RPL_ENDOFBANLIST must be sent.
371 RPL_INFO
":<string>"
374 RPL_ENDOFINFO
":End of /INFO list"
- A server responding to an INFO message is required to
send all its 'info' in a series of RPL_INFO messages
with a RPL_ENDOFINFO reply to indicate the end of the
replies.
375 RPL_MOTDSTART
":- <server> Message of the day - "
372 RPL_MOTD
":- <text>"
376 RPL_ENDOFMOTD
":End of /MOTD command"
- When responding to the MOTD message and the MOTD file
is found, the file is displayed line by line, with
each line no longer than 80 characters, using
RPL_MOTD format replies. These should be surrounded
by a RPL_MOTDSTART (before the RPL_MOTDs) and an
RPL_ENDOFMOTD (after).
381 RPL_YOUREOPER
":You are now an IRC operator"
- RPL_YOUREOPER is sent back to a client which has
just successfully issued an OPER message and gained
operator status.
382 RPL_REHASHING
"<config file> :Rehashing"
- If the REHASH option is used and an operator sends
a REHASH message, an RPL_REHASHING is sent back to
the operator.
391 RPL_TIME
Oikarinen & Reed [Page 52]
RFC 1459 Internet Relay Chat Protocol May 1993
"<server> :<string showing server's local time>"
- When replying to the TIME message, a server must send
the reply using the RPL_TIME format above. The string
showing the time need only contain the correct day and
time there. There is no further requirement for the
time string.
392 RPL_USERSSTART
":UserID Terminal Host"
393 RPL_USERS
":%-8s %-9s %-8s"
394 RPL_ENDOFUSERS
":End of users"
395 RPL_NOUSERS
":Nobody logged in"
- If the USERS message is handled by a server, the
replies RPL_USERSTART, RPL_USERS, RPL_ENDOFUSERS and
RPL_NOUSERS are used. RPL_USERSSTART must be sent
first, following by either a sequence of RPL_USERS
or a single RPL_NOUSER. Following this is
RPL_ENDOFUSERS.
200 RPL_TRACELINK
"Link <version & debug level> <destination> \
<next server>"
201 RPL_TRACECONNECTING
"Try. <class> <server>"
202 RPL_TRACEHANDSHAKE
"H.S. <class> <server>"
203 RPL_TRACEUNKNOWN
"???? <class> [<client IP address in dot form>]"
204 RPL_TRACEOPERATOR
"Oper <class> <nick>"
205 RPL_TRACEUSER
"User <class> <nick>"
206 RPL_TRACESERVER
"Serv <class> <int>S <int>C <server> \
<nick!user|*!*>@<host|server>"
208 RPL_TRACENEWTYPE
"<newtype> 0 <client name>"
261 RPL_TRACELOG
"File <logfile> <debug level>"
- The RPL_TRACE* are all returned by the server in
response to the TRACE message. How many are
returned is dependent on the the TRACE message and
Oikarinen & Reed [Page 53]
RFC 1459 Internet Relay Chat Protocol May 1993
whether it was sent by an operator or not. There
is no predefined order for which occurs first.
Replies RPL_TRACEUNKNOWN, RPL_TRACECONNECTING and
RPL_TRACEHANDSHAKE are all used for connections
which have not been fully established and are either
unknown, still attempting to connect or in the
process of completing the 'server handshake'.
RPL_TRACELINK is sent by any server which handles
a TRACE message and has to pass it on to another
server. The list of RPL_TRACELINKs sent in
response to a TRACE command traversing the IRC
network should reflect the actual connectivity of
the servers themselves along that path.
RPL_TRACENEWTYPE is to be used for any connection
which does not fit in the other categories but is
being displayed anyway.
211 RPL_STATSLINKINFO
"<linkname> <sendq> <sent messages> \
<sent bytes> <received messages> \
<received bytes> <time open>"
212 RPL_STATSCOMMANDS
"<command> <count>"
213 RPL_STATSCLINE
"C <host> * <name> <port> <class>"
214 RPL_STATSNLINE
"N <host> * <name> <port> <class>"
215 RPL_STATSILINE
"I <host> * <host> <port> <class>"
216 RPL_STATSKLINE
"K <host> * <username> <port> <class>"
218 RPL_STATSYLINE
"Y <class> <ping frequency> <connect \
frequency> <max sendq>"
219 RPL_ENDOFSTATS
"<stats letter> :End of /STATS report"
241 RPL_STATSLLINE
"L <hostmask> * <servername> <maxdepth>"
242 RPL_STATSUPTIME
":Server Up %d days %d:%02d:%02d"
243 RPL_STATSOLINE
"O <hostmask> * <name>"
244 RPL_STATSHLINE
"H <hostmask> * <servername>"
221 RPL_UMODEIS
"<user mode string>"
Oikarinen & Reed [Page 54]
RFC 1459 Internet Relay Chat Protocol May 1993
- To answer a query about a client's own mode,
RPL_UMODEIS is sent back.
251 RPL_LUSERCLIENT
":There are <integer> users and <integer> \
invisible on <integer> servers"
252 RPL_LUSEROP
"<integer> :operator(s) online"
253 RPL_LUSERUNKNOWN
"<integer> :unknown connection(s)"
254 RPL_LUSERCHANNELS
"<integer> :channels formed"
255 RPL_LUSERME
":I have <integer> clients and <integer> \
servers"
- In processing an LUSERS message, the server
sends a set of replies from RPL_LUSERCLIENT,
RPL_LUSEROP, RPL_USERUNKNOWN,
RPL_LUSERCHANNELS and RPL_LUSERME. When
replying, a server must send back
RPL_LUSERCLIENT and RPL_LUSERME. The other
replies are only sent back if a non-zero count
is found for them.
256 RPL_ADMINME
"<server> :Administrative info"
257 RPL_ADMINLOC1
":<admin info>"
258 RPL_ADMINLOC2
":<admin info>"
259 RPL_ADMINEMAIL
":<admin info>"
- When replying to an ADMIN message, a server
is expected to use replies RLP_ADMINME
through to RPL_ADMINEMAIL and provide a text
message with each. For RPL_ADMINLOC1 a
description of what city, state and country
the server is in is expected, followed by
details of the university and department
(RPL_ADMINLOC2) and finally the administrative
contact for the server (an email address here
is required) in RPL_ADMINEMAIL.
Oikarinen & Reed [Page 55]
RFC 1459 Internet Relay Chat Protocol May 1993
6.3 Reserved numerics.
These numerics are not described above since they fall into one of
the following categories:
1. no longer in use;
2. reserved for future planned use;
3. in current use but are part of a non-generic 'feature' of
the current IRC server.
209 RPL_TRACECLASS 217 RPL_STATSQLINE
231 RPL_SERVICEINFO 232 RPL_ENDOFSERVICES
233 RPL_SERVICE 234 RPL_SERVLIST
235 RPL_SERVLISTEND
316 RPL_WHOISCHANOP 361 RPL_KILLDONE
362 RPL_CLOSING 363 RPL_CLOSEEND
373 RPL_INFOSTART 384 RPL_MYPORTIS
466 ERR_YOUWILLBEBANNED 476 ERR_BADCHANMASK
492 ERR_NOSERVICEHOST
7. Client and server authentication
Clients and servers are both subject to the same level of
authentication. For both, an IP number to hostname lookup (and
reverse check on this) is performed for all connections made to the
server. Both connections are then subject to a password check (if
there is a password set for that connection). These checks are
possible on all connections although the password check is only
commonly used with servers.
An additional check that is becoming of more and more common is that
of the username responsible for making the connection. Finding the
username of the other end of the connection typically involves
connecting to an authentication server such as IDENT as described in
RFC 1413.
Given that without passwords it is not easy to reliably determine who
is on the other end of a network connection, use of passwords is
strongly recommended on inter-server connections in addition to any
other measures such as using an ident server.
8. Current implementations
The only current implementation of this protocol is the IRC server,
version 2.8. Earlier versions may implement some or all of the
commands described by this document with NOTICE messages replacing
Oikarinen & Reed [Page 56]
RFC 1459 Internet Relay Chat Protocol May 1993
many of the numeric replies. Unfortunately, due to backward
compatibility requirements, the implementation of some parts of this
document varies with what is laid out. On notable difference is:
* recognition that any LF or CR anywhere in a message marks the
end of that message (instead of requiring CR-LF);
The rest of this section deals with issues that are mostly of
importance to those who wish to implement a server but some parts
also apply directly to clients as well.
8.1 Network protocol: TCP - why it is best used here.
IRC has been implemented on top of TCP since TCP supplies a reliable
network protocol which is well suited to this scale of conferencing.
The use of multicast IP is an alternative, but it is not widely
available or supported at the present time.
8.1.1 Support of Unix sockets
Given that Unix domain sockets allow listen/connect operations, the
current implementation can be configured to listen and accept both
client and server connections on a Unix domain socket. These are
recognized as sockets where the hostname starts with a '/'.
When providing any information about the connections on a Unix domain
socket, the server is required to supplant the actual hostname in
place of the pathname unless the actual socket name is being asked
for.
8.2 Command Parsing
To provide useful 'non-buffered' network IO for clients and servers,
each connection is given its own private 'input buffer' in which the
results of the most recent read and parsing are kept. A buffer size
of 512 bytes is used so as to hold 1 full message, although, this
will usually hold several commands. The private buffer is parsed
after every read operation for valid messages. When dealing with
multiple messages from one client in the buffer, care should be taken
in case one happens to cause the client to be 'removed'.
8.3 Message delivery
It is common to find network links saturated or hosts to which you
are sending data unable to send data. Although Unix typically
handles this through the TCP window and internal buffers, the server
often has large amounts of data to send (especially when a new
server-server link forms) and the small buffers provided in the
Oikarinen & Reed [Page 57]
RFC 1459 Internet Relay Chat Protocol May 1993
kernel are not enough for the outgoing queue. To alleviate this
problem, a "send queue" is used as a FIFO queue for data to be sent.
A typical "send queue" may grow to 200 Kbytes on a large IRC network
with a slow network connection when a new server connects.
When polling its connections, a server will first read and parse all
incoming data, queuing any data to be sent out. When all available
input is processed, the queued data is sent. This reduces the number
of write() system calls and helps TCP make bigger packets.
8.4 Connection 'Liveness'
To detect when a connection has died or become unresponsive, the
server must ping each of its connections that it doesn't get a
response from in a given amount of time.
If a connection doesn't respond in time, its connection is closed
using the appropriate procedures. A connection is also dropped if
its sendq grows beyond the maximum allowed, because it is better to
close a slow connection than have a server process block.
8.5 Establishing a server to client connection
Upon connecting to an IRC server, a client is sent the MOTD (if
present) as well as the current user/server count (as per the LUSER
command). The server is also required to give an unambiguous message
to the client which states its name and version as well as any other
introductory messages which may be deemed appropriate.
After dealing with this, the server must then send out the new user's
nickname and other information as supplied by itself (USER command)
and as the server could discover (from DNS/authentication servers).
The server must send this information out with NICK first followed by
USER.
8.6 Establishing a server-server connection.
The process of establishing of a server-to-server connection is
fraught with danger since there are many possible areas where
problems can occur - the least of which are race conditions.
After a server has received a connection following by a PASS/SERVER
pair which were recognised as being valid, the server should then
reply with its own PASS/SERVER information for that connection as
well as all of the other state information it knows about as
described below.
When the initiating server receives a PASS/SERVER pair, it too then
Oikarinen & Reed [Page 58]
RFC 1459 Internet Relay Chat Protocol May 1993
checks that the server responding is authenticated properly before
accepting the connection to be that server.
8.6.1 Server exchange of state information when connecting
The order of state information being exchanged between servers is
essential. The required order is as follows:
* all known other servers;
* all known user information;
* all known channel information.
Information regarding servers is sent via extra SERVER messages, user
information with NICK/USER/MODE/JOIN messages and channels with MODE
messages.
NOTE: channel topics are *NOT* exchanged here because the TOPIC
command overwrites any old topic information, so at best, the two
sides of the connection would exchange topics.
By passing the state information about servers first, any collisions
with servers that already exist occur before nickname collisions due
to a second server introducing a particular nickname. Due to the IRC
network only being able to exist as an acyclic graph, it may be
possible that the network has already reconnected in another
location, the place where the collision occurs indicating where the
net needs to split.
8.7 Terminating server-client connections
When a client connection closes, a QUIT message is generated on
behalf of the client by the server to which the client connected. No
other message is to be generated or used.
8.8 Terminating server-server connections
If a server-server connection is closed, either via a remotely
generated SQUIT or 'natural' causes, the rest of the connected IRC
network must have its information updated with by the server which
detected the closure. The server then sends a list of SQUITs (one
for each server behind that connection) and a list of QUITs (again,
one for each client behind that connection).
Oikarinen & Reed [Page 59]
RFC 1459 Internet Relay Chat Protocol May 1993
8.9 Tracking nickname changes
All IRC servers are required to keep a history of recent nickname
changes. This is required to allow the server to have a chance of
keeping in touch of things when nick-change race conditions occur
with commands which manipulate them. Commands which must trace nick
changes are:
* KILL (the nick being killed)
* MODE (+/- o,v)
* KICK (the nick being kicked)
No other commands are to have nick changes checked for.
In the above cases, the server is required to first check for the
existence of the nickname, then check its history to see who that
nick currently belongs to (if anyone!). This reduces the chances of
race conditions but they can still occur with the server ending up
affecting the wrong client. When performing a change trace for an
above command it is recommended that a time range be given and
entries which are too old ignored.
For a reasonable history, a server should be able to keep previous
nickname for every client it knows about if they all decided to
change. This size is limited by other factors (such as memory, etc).
8.10 Flood control of clients
With a large network of interconnected IRC servers, it is quite easy
for any single client attached to the network to supply a continuous
stream of messages that result in not only flooding the network, but
also degrading the level of service provided to others. Rather than
require every 'victim' to be provide their own protection, flood
protection was written into the server and is applied to all clients
except services. The current algorithm is as follows:
* check to see if client's `message timer' is less than
current time (set to be equal if it is);
* read any data present from the client;
* while the timer is less than ten seconds ahead of the current
time, parse any present messages and penalize the client by
2 seconds for each message;
which in essence means that the client may send 1 message every 2
Oikarinen & Reed [Page 60]
RFC 1459 Internet Relay Chat Protocol May 1993
seconds without being adversely affected.
8.11 Non-blocking lookups
In a real-time environment, it is essential that a server process do
as little waiting as possible so that all the clients are serviced
fairly. Obviously this requires non-blocking IO on all network
read/write operations. For normal server connections, this was not
difficult, but there are other support operations that may cause the
server to block (such as disk reads). Where possible, such activity
should be performed with a short timeout.
8.11.1 Hostname (DNS) lookups
Using the standard resolver libraries from Berkeley and others has
meant large delays in some cases where replies have timed out. To
avoid this, a separate set of DNS routines were written which were
setup for non-blocking IO operations and then polled from within the
main server IO loop.
8.11.2 Username (Ident) lookups
Although there are numerous ident libraries for use and inclusion
into other programs, these caused problems since they operated in a
synchronous manner and resulted in frequent delays. Again the
solution was to write a set of routines which would cooperate with
the rest of the server and work using non-blocking IO.
8.12 Configuration File
To provide a flexible way of setting up and running the server, it is
recommended that a configuration file be used which contains
instructions to the server on the following:
* which hosts to accept client connections from;
* which hosts to allow to connect as servers;
* which hosts to connect to (both actively and
passively);
* information about where the server is (university,
city/state, company are examples of this);
* who is responsible for the server and an email address
at which they can be contacted;
* hostnames and passwords for clients which wish to be given
Oikarinen & Reed [Page 61]
RFC 1459 Internet Relay Chat Protocol May 1993
access to restricted operator commands.
In specifying hostnames, both domain names and use of the 'dot'
notation (127.0.0.1) should both be accepted. It must be possible to
specify the password to be used/accepted for all outgoing and
incoming connections (although the only outgoing connections are
those to other servers).
The above list is the minimum requirement for any server which wishes
to make a connection with another server. Other items which may be
of use are:
* specifying which servers other server may introduce;
* how deep a server branch is allowed to become;
* hours during which clients may connect.
8.12.1 Allowing clients to connect
A server should use some sort of 'access control list' (either in the
configuration file or elsewhere) that is read at startup and used to
decide what hosts clients may use to connect to it.
Both 'deny' and 'allow' should be implemented to provide the required
flexibility for host access control.
8.12.2 Operators
The granting of operator privileges to a disruptive person can have
dire consequences for the well-being of the IRC net in general due to
the powers given to them. Thus, the acquisition of such powers
should not be very easy. The current setup requires two 'passwords'
to be used although one of them is usually easy guessed. Storage of
oper passwords in configuration files is preferable to hard coding
them in and should be stored in a crypted format (ie using crypt(3)
from Unix) to prevent easy theft.
8.12.3 Allowing servers to connect
The interconnection of server is not a trivial matter: a bad
connection can have a large impact on the usefulness of IRC. Thus,
each server should have a list of servers to which it may connect and
which servers may connect to it. Under no circumstances should a
server allow an arbitrary host to connect as a server. In addition
to which servers may and may not connect, the configuration file
should also store the password and other characteristics of that
link.
Oikarinen & Reed [Page 62]
RFC 1459 Internet Relay Chat Protocol May 1993
8.12.4 Administrivia
To provide accurate and valid replies to the ADMIN command (see
section 4.3.7), the server should find the relevant details in the
configuration.
8.13 Channel membership
The current server allows any registered local user to join upto 10
different channels. There is no limit imposed on non-local users so
that the server remains (reasonably) consistant with all others on a
channel membership basis
9. Current problems
There are a number of recognized problems with this protocol, all of
which hope to be solved sometime in the near future during its
rewrite. Currently, work is underway to find working solutions to
these problems.
9.1 Scalability
It is widely recognized that this protocol does not scale
sufficiently well when used in a large arena. The main problem comes
from the requirement that all servers know about all other servers
and users and that information regarding them be updated as soon as
it changes. It is also desirable to keep the number of servers low
so that the path length between any two points is kept minimal and
the spanning tree as strongly branched as possible.
9.2 Labels
The current IRC protocol has 3 types of labels: the nickname, the
channel name and the server name. Each of the three types has its
own domain and no duplicates are allowed inside that domain.
Currently, it is possible for users to pick the label for any of the
three, resulting in collisions. It is widely recognized that this
needs reworking, with a plan for unique names for channels and nicks
that don't collide being desirable as well as a solution allowing a
cyclic tree.
9.2.1 Nicknames
The idea of the nickname on IRC is very convenient for users to use
when talking to each other outside of a channel, but there is only a
finite nickname space and being what they are, its not uncommon for
several people to want to use the same nick. If a nickname is chosen
by two people using this protocol, either one will not succeed or
Oikarinen & Reed [Page 63]
RFC 1459 Internet Relay Chat Protocol May 1993
both will removed by use of KILL (4.6.1).
9.2.2 Channels
The current channel layout requires that all servers know about all
channels, their inhabitants and properties. Besides not scaling
well, the issue of privacy is also a concern. A collision of
channels is treated as an inclusive event (both people who create the
new channel are considered to be members of it) rather than an
exclusive one such as used to solve nickname collisions.
9.2.3 Servers
Although the number of servers is usually small relative to the
number of users and channels, they two currently required to be known
globally, either each one separately or hidden behind a mask.
9.3 Algorithms
In some places within the server code, it has not been possible to
avoid N^2 algorithms such as checking the channel list of a set
of clients.
In current server versions, there are no database consistency checks,
each server assumes that a neighbouring server is correct. This
opens the door to large problems if a connecting server is buggy or
otherwise tries to introduce contradictions to the existing net.
Currently, because of the lack of unique internal and global labels,
there are a multitude of race conditions that exist. These race
conditions generally arise from the problem of it taking time for
messages to traverse and effect the IRC network. Even by changing to
unique labels, there are problems with channel-related commands being
disrupted.
10. Current support and availability
Mailing lists for IRC related discussion:
Future protocol: ircd-three-request@eff.org
General discussion: operlist-request@eff.org
Software implemenations
cs.bu.edu:/irc
nic.funet.fi:/pub/irc
coombs.anu.edu.au:/pub/irc
Newsgroup: alt.irc
Oikarinen & Reed [Page 64]
RFC 1459 Internet Relay Chat Protocol May 1993
Security Considerations
Security issues are discussed in sections 4.1, 4.1.1, 4.1.3, 5.5, and
7.
12. Authors' Addresses
Jarkko Oikarinen
Tuirantie 17 as 9
90500 OULU
FINLAND
Email: jto@tolsun.oulu.fi
Darren Reed
4 Pateman Street
Watsonia, Victoria 3087
Australia
Email: avalon@coombs.anu.edu.au
Oikarinen & Reed [Page 65]
\ No newline at end of file + + + + + + +Network Working Group J. Oikarinen +Request for Comments: 1459 D. Reed + May 1993 + + + Internet Relay Chat Protocol + +Status of This Memo + + This memo defines an Experimental Protocol for the Internet + community. Discussion and suggestions for improvement are requested. + Please refer to the current edition of the "IAB Official Protocol + Standards" for the standardization state and status of this protocol. + Distribution of this memo is unlimited. + +Abstract + + The IRC protocol was developed over the last 4 years since it was + first implemented as a means for users on a BBS to chat amongst + themselves. Now it supports a world-wide network of servers and + clients, and is stringing to cope with growth. Over the past 2 years, + the average number of users connected to the main IRC network has + grown by a factor of 10. + + The IRC protocol is a text-based protocol, with the simplest client + being any socket program capable of connecting to the server. + +Table of Contents + + 1. INTRODUCTION ............................................... 4 + 1.1 Servers ................................................ 4 + 1.2 Clients ................................................ 5 + 1.2.1 Operators .......................................... 5 + 1.3 Channels ................................................ 5 + 1.3.1 Channel Operators .................................... 6 + 2. THE IRC SPECIFICATION ....................................... 7 + 2.1 Overview ................................................ 7 + 2.2 Character codes ......................................... 7 + 2.3 Messages ................................................ 7 + 2.3.1 Message format in 'pseudo' BNF .................... 8 + 2.4 Numeric replies ......................................... 10 + 3. IRC Concepts ................................................ 10 + 3.1 One-to-one communication ................................ 10 + 3.2 One-to-many ............................................. 11 + 3.2.1 To a list .......................................... 11 + 3.2.2 To a group (channel) ............................... 11 + 3.2.3 To a host/server mask .............................. 12 + 3.3 One to all .............................................. 12 + + + +Oikarinen & Reed [Page 1] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + 3.3.1 Client to Client ................................... 12 + 3.3.2 Clients to Server .................................. 12 + 3.3.3 Server to Server ................................... 12 + 4. MESSAGE DETAILS ............................................. 13 + 4.1 Connection Registration ................................. 13 + 4.1.1 Password message ................................... 14 + 4.1.2 Nickname message ................................... 14 + 4.1.3 User message ....................................... 15 + 4.1.4 Server message ..................................... 16 + 4.1.5 Operator message ................................... 17 + 4.1.6 Quit message ....................................... 17 + 4.1.7 Server Quit message ................................ 18 + 4.2 Channel operations ...................................... 19 + 4.2.1 Join message ....................................... 19 + 4.2.2 Part message ....................................... 20 + 4.2.3 Mode message ....................................... 21 + 4.2.3.1 Channel modes ................................. 21 + 4.2.3.2 User modes .................................... 22 + 4.2.4 Topic message ...................................... 23 + 4.2.5 Names message ...................................... 24 + 4.2.6 List message ....................................... 24 + 4.2.7 Invite message ..................................... 25 + 4.2.8 Kick message ....................................... 25 + 4.3 Server queries and commands ............................. 26 + 4.3.1 Version message .................................... 26 + 4.3.2 Stats message ...................................... 27 + 4.3.3 Links message ...................................... 28 + 4.3.4 Time message ....................................... 29 + 4.3.5 Connect message .................................... 29 + 4.3.6 Trace message ...................................... 30 + 4.3.7 Admin message ...................................... 31 + 4.3.8 Info message ....................................... 31 + 4.4 Sending messages ........................................ 32 + 4.4.1 Private messages ................................... 32 + 4.4.2 Notice messages .................................... 33 + 4.5 User-based queries ...................................... 33 + 4.5.1 Who query .......................................... 33 + 4.5.2 Whois query ........................................ 34 + 4.5.3 Whowas message ..................................... 35 + 4.6 Miscellaneous messages .................................. 35 + 4.6.1 Kill message ....................................... 36 + 4.6.2 Ping message ....................................... 37 + 4.6.3 Pong message ....................................... 37 + 4.6.4 Error message ...................................... 38 + 5. OPTIONAL MESSAGES ........................................... 38 + 5.1 Away message ............................................ 38 + 5.2 Rehash command .......................................... 39 + 5.3 Restart command ......................................... 39 + + + +Oikarinen & Reed [Page 2] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + 5.4 Summon message .......................................... 40 + 5.5 Users message ........................................... 40 + 5.6 Operwall command ........................................ 41 + 5.7 Userhost message ........................................ 42 + 5.8 Ison message ............................................ 42 + 6. REPLIES ..................................................... 43 + 6.1 Error Replies ........................................... 43 + 6.2 Command responses ....................................... 48 + 6.3 Reserved numerics ....................................... 56 + 7. Client and server authentication ............................ 56 + 8. Current Implementations Details ............................. 56 + 8.1 Network protocol: TCP ................................... 57 + 8.1.1 Support of Unix sockets ............................ 57 + 8.2 Command Parsing ......................................... 57 + 8.3 Message delivery ........................................ 57 + 8.4 Connection 'Liveness' ................................... 58 + 8.5 Establishing a server-client connection ................. 58 + 8.6 Establishing a server-server connection ................. 58 + 8.6.1 State information exchange when connecting ......... 59 + 8.7 Terminating server-client connections ................... 59 + 8.8 Terminating server-server connections ................... 59 + 8.9 Tracking nickname changes ............................... 60 + 8.10 Flood control of clients ............................... 60 + 8.11 Non-blocking lookups ................................... 61 + 8.11.1 Hostname (DNS) lookups ............................ 61 + 8.11.2 Username (Ident) lookups .......................... 61 + 8.12 Configuration file ..................................... 61 + 8.12.1 Allowing clients to connect ....................... 62 + 8.12.2 Operators ......................................... 62 + 8.12.3 Allowing servers to connect ....................... 62 + 8.12.4 Administrivia ..................................... 63 + 8.13 Channel membership ..................................... 63 + 9. Current problems ............................................ 63 + 9.1 Scalability ............................................. 63 + 9.2 Labels .................................................. 63 + 9.2.1 Nicknames .......................................... 63 + 9.2.2 Channels ........................................... 64 + 9.2.3 Servers ............................................ 64 + 9.3 Algorithms .............................................. 64 + 10. Support and availability ................................... 64 + 11. Security Considerations .................................... 65 + 12. Authors' Addresses ......................................... 65 + + + + + + + + + +Oikarinen & Reed [Page 3] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +1. INTRODUCTION + + The IRC (Internet Relay Chat) protocol has been designed over a + number of years for use with text based conferencing. This document + describes the current IRC protocol. + + The IRC protocol has been developed on systems using the TCP/IP + network protocol, although there is no requirement that this remain + the only sphere in which it operates. + + IRC itself is a teleconferencing system, which (through the use of + the client-server model) is well-suited to running on many machines + in a distributed fashion. A typical setup involves a single process + (the server) forming a central point for clients (or other servers) + to connect to, performing the required message delivery/multiplexing + and other functions. + +1.1 Servers + + The server forms the backbone of IRC, providing a point to which + clients may connect to to talk to each other, and a point for other + servers to connect to, forming an IRC network. The only network + configuration allowed for IRC servers is that of a spanning tree [see + Fig. 1] where each server acts as a central node for the rest of the + net it sees. + + + [ Server 15 ] [ Server 13 ] [ Server 14] + / \ / + / \ / + [ Server 11 ] ------ [ Server 1 ] [ Server 12] + / \ / + / \ / + [ Server 2 ] [ Server 3 ] + / \ \ + / \ \ + [ Server 4 ] [ Server 5 ] [ Server 6 ] + / | \ / + / | \ / + / | \____ / + / | \ / + [ Server 7 ] [ Server 8 ] [ Server 9 ] [ Server 10 ] + + : + [ etc. ] + : + + [ Fig. 1. Format of IRC server network ] + + + +Oikarinen & Reed [Page 4] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +1.2 Clients + + A client is anything connecting to a server that is not another + server. Each client is distinguished from other clients by a unique + nickname having a maximum length of nine (9) characters. See the + protocol grammar rules for what may and may not be used in a + nickname. In addition to the nickname, all servers must have the + following information about all clients: the real name of the host + that the client is running on, the username of the client on that + host, and the server to which the client is connected. + +1.2.1 Operators + + To allow a reasonable amount of order to be kept within the IRC + network, a special class of clients (operators) is allowed to perform + general maintenance functions on the network. Although the powers + granted to an operator can be considered as 'dangerous', they are + nonetheless required. Operators should be able to perform basic + network tasks such as disconnecting and reconnecting servers as + needed to prevent long-term use of bad network routing. In + recognition of this need, the protocol discussed herein provides for + operators only to be able to perform such functions. See sections + 4.1.7 (SQUIT) and 4.3.5 (CONNECT). + + A more controversial power of operators is the ability to remove a + user from the connected network by 'force', i.e. operators are able + to close the connection between any client and server. The + justification for this is delicate since its abuse is both + destructive and annoying. For further details on this type of + action, see section 4.6.1 (KILL). + +1.3 Channels + + A channel is a named group of one or more clients which will all + receive messages addressed to that channel. The channel is created + implicitly when the first client joins it, and the channel ceases to + exist when the last client leaves it. While channel exists, any + client can reference the channel using the name of the channel. + + Channels names are strings (beginning with a '&' or '#' character) of + length up to 200 characters. Apart from the the requirement that the + first character being either '&' or '#'; the only restriction on a + channel name is that it may not contain any spaces (' '), a control G + (^G or ASCII 7), or a comma (',' which is used as a list item + separator by the protocol). + + There are two types of channels allowed by this protocol. One is a + distributed channel which is known to all the servers that are + + + +Oikarinen & Reed [Page 5] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + connected to the network. These channels are marked by the first + character being a only clients on the server where it exists may join + it. These are distinguished by a leading '&' character. On top of + these two types, there are the various channel modes available to + alter the characteristics of individual channels. See section 4.2.3 + (MODE command) for more details on this. + + To create a new channel or become part of an existing channel, a user + is required to JOIN the channel. If the channel doesn't exist prior + to joining, the channel is created and the creating user becomes a + channel operator. If the channel already exists, whether or not your + request to JOIN that channel is honoured depends on the current modes + of the channel. For example, if the channel is invite-only, (+i), + then you may only join if invited. As part of the protocol, a user + may be a part of several channels at once, but a limit of ten (10) + channels is recommended as being ample for both experienced and + novice users. See section 8.13 for more information on this. + + If the IRC network becomes disjoint because of a split between two + servers, the channel on each side is only composed of those clients + which are connected to servers on the respective sides of the split, + possibly ceasing to exist on one side of the split. When the split + is healed, the connecting servers announce to each other who they + think is in each channel and the mode of that channel. If the + channel exists on both sides, the JOINs and MODEs are interpreted in + an inclusive manner so that both sides of the new connection will + agree about which clients are in the channel and what modes the + channel has. + +1.3.1 Channel Operators + + The channel operator (also referred to as a "chop" or "chanop") on a + given channel is considered to 'own' that channel. In recognition of + this status, channel operators are endowed with certain powers which + enable them to keep control and some sort of sanity in their channel. + As an owner of a channel, a channel operator is not required to have + reasons for their actions, although if their actions are generally + antisocial or otherwise abusive, it might be reasonable to ask an IRC + operator to intervene, or for the usersjust leave and go elsewhere + and form their own channel. + + The commands which may only be used by channel operators are: + + KICK - Eject a client from the channel + MODE - Change the channel's mode + INVITE - Invite a client to an invite-only channel (mode +i) + TOPIC - Change the channel topic in a mode +t channel + + + + +Oikarinen & Reed [Page 6] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + A channel operator is identified by the '@' symbol next to their + nickname whenever it is associated with a channel (ie replies to the + NAMES, WHO and WHOIS commands). + +2. The IRC Specification + +2.1 Overview + + The protocol as described herein is for use both with server to + server and client to server connections. There are, however, more + restrictions on client connections (which are considered to be + untrustworthy) than on server connections. + +2.2 Character codes + + No specific character set is specified. The protocol is based on a a + set of codes which are composed of eight (8) bits, making up an + octet. Each message may be composed of any number of these octets; + however, some octet values are used for control codes which act as + message delimiters. + + Regardless of being an 8-bit protocol, the delimiters and keywords + are such that protocol is mostly usable from USASCII terminal and a + telnet connection. + + Because of IRC's scandanavian origin, the characters {}| are + considered to be the lower case equivalents of the characters []\, + respectively. This is a critical issue when determining the + equivalence of two nicknames. + +2.3 Messages + + Servers and clients send eachother messages which may or may not + generate a reply. If the message contains a valid command, as + described in later sections, the client should expect a reply as + specified but it is not advised to wait forever for the reply; client + to server and server to server communication is essentially + asynchronous in nature. + + Each IRC message may consist of up to three main parts: the prefix + (optional), the command, and the command parameters (of which there + may be up to 15). The prefix, command, and all parameters are + separated by one (or more) ASCII space character(s) (0x20). + + The presence of a prefix is indicated with a single leading ASCII + colon character (':', 0x3b), which must be the first character of the + message itself. There must be no gap (whitespace) between the colon + and the prefix. The prefix is used by servers to indicate the true + + + +Oikarinen & Reed [Page 7] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + origin of the message. If the prefix is missing from the message, it + is assumed to have originated from the connection from which it was + received. Clients should not use prefix when sending a message from + themselves; if they use a prefix, the only valid prefix is the + registered nickname associated with the client. If the source + identified by the prefix cannot be found from the server's internal + database, or if the source is registered from a different link than + from which the message arrived, the server must ignore the message + silently. + + The command must either be a valid IRC command or a three (3) digit + number represented in ASCII text. + + IRC messages are always lines of characters terminated with a CR-LF + (Carriage Return - Line Feed) pair, and these messages shall not + exceed 512 characters in length, counting all characters including + the trailing CR-LF. Thus, there are 510 characters maximum allowed + for the command and its parameters. There is no provision for + continuation message lines. See section 7 for more details about + current implementations. + +2.3.1 Message format in 'pseudo' BNF + + The protocol messages must be extracted from the contiguous stream of + octets. The current solution is to designate two characters, CR and + LF, as message separators. Empty messages are silently ignored, + which permits use of the sequence CR-LF between messages + without extra problems. + + The extracted message is parsed into the components <prefix>, + <command> and list of parameters matched either by <middle> or + <trailing> components. + + The BNF representation for this is: + + +<message> ::= [':' <prefix> <SPACE> ] <command> <params> <crlf> +<prefix> ::= <servername> | <nick> [ '!' <user> ] [ '@' <host> ] +<command> ::= <letter> { <letter> } | <number> <number> <number> +<SPACE> ::= ' ' { ' ' } +<params> ::= <SPACE> [ ':' <trailing> | <middle> <params> ] + +<middle> ::= <Any *non-empty* sequence of octets not including SPACE + or NUL or CR or LF, the first of which may not be ':'> +<trailing> ::= <Any, possibly *empty*, sequence of octets not including + NUL or CR or LF> + +<crlf> ::= CR LF + + + +Oikarinen & Reed [Page 8] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +NOTES: + + 1) <SPACE> is consists only of SPACE character(s) (0x20). + Specially notice that TABULATION, and all other control + characters are considered NON-WHITE-SPACE. + + 2) After extracting the parameter list, all parameters are equal, + whether matched by <middle> or <trailing>. <Trailing> is just + a syntactic trick to allow SPACE within parameter. + + 3) The fact that CR and LF cannot appear in parameter strings is + just artifact of the message framing. This might change later. + + 4) The NUL character is not special in message framing, and + basically could end up inside a parameter, but as it would + cause extra complexities in normal C string handling. Therefore + NUL is not allowed within messages. + + 5) The last parameter may be an empty string. + + 6) Use of the extended prefix (['!' <user> ] ['@' <host> ]) must + not be used in server to server communications and is only + intended for server to client messages in order to provide + clients with more useful information about who a message is + from without the need for additional queries. + + Most protocol messages specify additional semantics and syntax for + the extracted parameter strings dictated by their position in the + list. For example, many server commands will assume that the first + parameter after the command is the list of targets, which can be + described with: + + <target> ::= <to> [ "," <target> ] + <to> ::= <channel> | <user> '@' <servername> | <nick> | <mask> + <channel> ::= ('#' | '&') <chstring> + <servername> ::= <host> + <host> ::= see RFC 952 [DNS:4] for details on allowed hostnames + <nick> ::= <letter> { <letter> | <number> | <special> } + <mask> ::= ('#' | '$') <chstring> + <chstring> ::= <any 8bit code except SPACE, BELL, NUL, CR, LF and + comma (',')> + + Other parameter syntaxes are: + + <user> ::= <nonwhite> { <nonwhite> } + <letter> ::= 'a' ... 'z' | 'A' ... 'Z' + <number> ::= '0' ... '9' + <special> ::= '-' | '[' | ']' | '\' | '`' | '^' | '{' | '}' + + + +Oikarinen & Reed [Page 9] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + <nonwhite> ::= <any 8bit code except SPACE (0x20), NUL (0x0), CR + (0xd), and LF (0xa)> + +2.4 Numeric replies + + Most of the messages sent to the server generate a reply of some + sort. The most common reply is the numeric reply, used for both + errors and normal replies. The numeric reply must be sent as one + message consisting of the sender prefix, the three digit numeric, and + the target of the reply. A numeric reply is not allowed to originate + from a client; any such messages received by a server are silently + dropped. In all other respects, a numeric reply is just like a normal + message, except that the keyword is made up of 3 numeric digits + rather than a string of letters. A list of different replies is + supplied in section 6. + +3. IRC Concepts. + + This section is devoted to describing the actual concepts behind the + organization of the IRC protocol and how the current + implementations deliver different classes of messages. + + + + 1--\ + A D---4 + 2--/ \ / + B----C + / \ + 3 E + + Servers: A, B, C, D, E Clients: 1, 2, 3, 4 + + [ Fig. 2. Sample small IRC network ] + +3.1 One-to-one communication + + Communication on a one-to-one basis is usually only performed by + clients, since most server-server traffic is not a result of servers + talking only to each other. To provide a secure means for clients to + talk to each other, it is required that all servers be able to send a + message in exactly one direction along the spanning tree in order to + reach any client. The path of a message being delivered is the + shortest path between any two points on the spanning tree. + + The following examples all refer to Figure 2 above. + + + + + +Oikarinen & Reed [Page 10] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +Example 1: + A message between clients 1 and 2 is only seen by server A, which + sends it straight to client 2. + +Example 2: + A message between clients 1 and 3 is seen by servers A & B, and + client 3. No other clients or servers are allowed see the message. + +Example 3: + A message between clients 2 and 4 is seen by servers A, B, C & D + and client 4 only. + +3.2 One-to-many + + The main goal of IRC is to provide a forum which allows easy and + efficient conferencing (one to many conversations). IRC offers + several means to achieve this, each serving its own purpose. + +3.2.1 To a list + + The least efficient style of one-to-many conversation is through + clients talking to a 'list' of users. How this is done is almost + self explanatory: the client gives a list of destinations to which + the message is to be delivered and the server breaks it up and + dispatches a separate copy of the message to each given destination. + This isn't as efficient as using a group since the destination list + is broken up and the dispatch sent without checking to make sure + duplicates aren't sent down each path. + +3.2.2 To a group (channel) + + In IRC the channel has a role equivalent to that of the multicast + group; their existence is dynamic (coming and going as people join + and leave channels) and the actual conversation carried out on a + channel is only sent to servers which are supporting users on a given + channel. If there are multiple users on a server in the same + channel, the message text is sent only once to that server and then + sent to each client on the channel. This action is then repeated for + each client-server combination until the original message has fanned + out and reached each member of the channel. + + The following examples all refer to Figure 2. + +Example 4: + Any channel with 1 client in it. Messages to the channel go to the + server and then nowhere else. + + + + + +Oikarinen & Reed [Page 11] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +Example 5: + 2 clients in a channel. All messages traverse a path as if they + were private messages between the two clients outside a channel. + +Example 6: + Clients 1, 2 and 3 in a channel. All messages to the channel are + sent to all clients and only those servers which must be traversed + by the message if it were a private message to a single client. If + client 1 sends a message, it goes back to client 2 and then via + server B to client 3. + +3.2.3 To a host/server mask + + To provide IRC operators with some mechanism to send messages to a + large body of related users, host and server mask messages are + provided. These messages are sent to users whose host or server + information match that of the mask. The messages are only sent to + locations where users are, in a fashion similar to that of channels. + +3.3 One-to-all + + The one-to-all type of message is better described as a broadcast + message, sent to all clients or servers or both. On a large network + of users and servers, a single message can result in a lot of traffic + being sent over the network in an effort to reach all of the desired + destinations. + + For some messages, there is no option but to broadcast it to all + servers so that the state information held by each server is + reasonably consistent between servers. + +3.3.1 Client-to-Client + + There is no class of message which, from a single message, results in + a message being sent to every other client. + +3.3.2 Client-to-Server + + Most of the commands which result in a change of state information + (such as channel membership, channel mode, user status, etc) must be + sent to all servers by default, and this distribution may not be + changed by the client. + +3.3.3 Server-to-Server. + + While most messages between servers are distributed to all 'other' + servers, this is only required for any message that affects either a + user, channel or server. Since these are the basic items found in + + + +Oikarinen & Reed [Page 12] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + IRC, nearly all messages originating from a server are broadcast to + all other connected servers. + +4. Message details + + On the following pages are descriptions of each message recognized by + the IRC server and client. All commands described in this section + must be implemented by any server for this protocol. + + Where the reply ERR_NOSUCHSERVER is listed, it means that the + <server> parameter could not be found. The server must not send any + other replies after this for that command. + + The server to which a client is connected is required to parse the + complete message, returning any appropriate errors. If the server + encounters a fatal error while parsing a message, an error must be + sent back to the client and the parsing terminated. A fatal error + may be considered to be incorrect command, a destination which is + otherwise unknown to the server (server, nick or channel names fit + this category), not enough parameters or incorrect privileges. + + If a full set of parameters is presented, then each must be checked + for validity and appropriate responses sent back to the client. In + the case of messages which use parameter lists using the comma as an + item separator, a reply must be sent for each item. + + In the examples below, some messages appear using the full format: + + :Name COMMAND parameter list + + Such examples represent a message from "Name" in transit between + servers, where it is essential to include the name of the original + sender of the message so remote servers may send back a reply along + the correct path. + +4.1 Connection Registration + + The commands described here are used to register a connection with an + IRC server as either a user or a server as well as correctly + disconnect. + + A "PASS" command is not required for either client or server + connection to be registered, but it must precede the server message + or the latter of the NICK/USER combination. It is strongly + recommended that all server connections have a password in order to + give some level of security to the actual connections. The + recommended order for a client to register is as follows: + + + + +Oikarinen & Reed [Page 13] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + 1. Pass message + 2. Nick message + 3. User message + +4.1.1 Password message + + + Command: PASS + Parameters: <password> + + The PASS command is used to set a 'connection password'. The + password can and must be set before any attempt to register the + connection is made. Currently this requires that clients send a PASS + command before sending the NICK/USER combination and servers *must* + send a PASS command before any SERVER command. The password supplied + must match the one contained in the C/N lines (for servers) or I + lines (for clients). It is possible to send multiple PASS commands + before registering but only the last one sent is used for + verification and it may not be changed once registered. Numeric + Replies: + + ERR_NEEDMOREPARAMS ERR_ALREADYREGISTRED + + Example: + + PASS secretpasswordhere + +4.1.2 Nick message + + Command: NICK + Parameters: <nickname> [ <hopcount> ] + + NICK message is used to give user a nickname or change the previous + one. The <hopcount> parameter is only used by servers to indicate + how far away a nick is from its home server. A local connection has + a hopcount of 0. If supplied by a client, it must be ignored. + + If a NICK message arrives at a server which already knows about an + identical nickname for another client, a nickname collision occurs. + As a result of a nickname collision, all instances of the nickname + are removed from the server's database, and a KILL command is issued + to remove the nickname from all other server's database. If the NICK + message causing the collision was a nickname change, then the + original (old) nick must be removed as well. + + If the server recieves an identical NICK from a client which is + directly connected, it may issue an ERR_NICKCOLLISION to the local + client, drop the NICK command, and not generate any kills. + + + +Oikarinen & Reed [Page 14] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + Numeric Replies: + + ERR_NONICKNAMEGIVEN ERR_ERRONEUSNICKNAME + ERR_NICKNAMEINUSE ERR_NICKCOLLISION + + Example: + + NICK Wiz ; Introducing new nick "Wiz". + + :WiZ NICK Kilroy ; WiZ changed his nickname to Kilroy. + +4.1.3 User message + + Command: USER + Parameters: <username> <hostname> <servername> <realname> + + The USER message is used at the beginning of connection to specify + the username, hostname, servername and realname of s new user. It is + also used in communication between servers to indicate new user + arriving on IRC, since only after both USER and NICK have been + received from a client does a user become registered. + + Between servers USER must to be prefixed with client's NICKname. + Note that hostname and servername are normally ignored by the IRC + server when the USER command comes from a directly connected client + (for security reasons), but they are used in server to server + communication. This means that a NICK must always be sent to a + remote server when a new user is being introduced to the rest of the + network before the accompanying USER is sent. + + It must be noted that realname parameter must be the last parameter, + because it may contain space characters and must be prefixed with a + colon (':') to make sure this is recognised as such. + + Since it is easy for a client to lie about its username by relying + solely on the USER message, the use of an "Identity Server" is + recommended. If the host which a user connects from has such a + server enabled the username is set to that as in the reply from the + "Identity Server". + + Numeric Replies: + + ERR_NEEDMOREPARAMS ERR_ALREADYREGISTRED + + Examples: + + + USER guest tolmoon tolsun :Ronnie Reagan + + + +Oikarinen & Reed [Page 15] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + ; User registering themselves with a + username of "guest" and real name + "Ronnie Reagan". + + + :testnick USER guest tolmoon tolsun :Ronnie Reagan + ; message between servers with the + nickname for which the USER command + belongs to + +4.1.4 Server message + + Command: SERVER + Parameters: <servername> <hopcount> <info> + + The server message is used to tell a server that the other end of a + new connection is a server. This message is also used to pass server + data over whole net. When a new server is connected to net, + information about it be broadcast to the whole network. <hopcount> + is used to give all servers some internal information on how far away + all servers are. With a full server list, it would be possible to + construct a map of the entire server tree, but hostmasks prevent this + from being done. + + The SERVER message must only be accepted from either (a) a connection + which is yet to be registered and is attempting to register as a + server, or (b) an existing connection to another server, in which + case the SERVER message is introducing a new server behind that + server. + + Most errors that occur with the receipt of a SERVER command result in + the connection being terminated by the destination host (target + SERVER). Error replies are usually sent using the "ERROR" command + rather than the numeric since the ERROR command has several useful + properties which make it useful here. + + If a SERVER message is parsed and attempts to introduce a server + which is already known to the receiving server, the connection from + which that message must be closed (following the correct procedures), + since a duplicate route to a server has formed and the acyclic nature + of the IRC tree broken. + + Numeric Replies: + + ERR_ALREADYREGISTRED + + Example: + + + + +Oikarinen & Reed [Page 16] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +SERVER test.oulu.fi 1 :[tolsun.oulu.fi] Experimental server + ; New server test.oulu.fi introducing + itself and attempting to register. The + name in []'s is the hostname for the + host running test.oulu.fi. + + +:tolsun.oulu.fi SERVER csd.bu.edu 5 :BU Central Server + ; Server tolsun.oulu.fi is our uplink + for csd.bu.edu which is 5 hops away. + +4.1.5 Oper + + Command: OPER + Parameters: <user> <password> + + OPER message is used by a normal user to obtain operator privileges. + The combination of <user> and <password> are required to gain + Operator privileges. + + If the client sending the OPER command supplies the correct password + for the given user, the server then informs the rest of the network + of the new operator by issuing a "MODE +o" for the clients nickname. + + The OPER message is client-server only. + + Numeric Replies: + + ERR_NEEDMOREPARAMS RPL_YOUREOPER + ERR_NOOPERHOST ERR_PASSWDMISMATCH + + Example: + + OPER foo bar ; Attempt to register as an operator + using a username of "foo" and "bar" as + the password. + +4.1.6 Quit + + Command: QUIT + Parameters: [<Quit message>] + + A client session is ended with a quit message. The server must close + the connection to a client which sends a QUIT message. If a "Quit + Message" is given, this will be sent instead of the default message, + the nickname. + + When netsplits (disconnecting of two servers) occur, the quit message + + + +Oikarinen & Reed [Page 17] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + is composed of the names of two servers involved, separated by a + space. The first name is that of the server which is still connected + and the second name is that of the server that has become + disconnected. + + If, for some other reason, a client connection is closed without the + client issuing a QUIT command (e.g. client dies and EOF occurs + on socket), the server is required to fill in the quit message with + some sort of message reflecting the nature of the event which + caused it to happen. + + Numeric Replies: + + None. + + Examples: + + QUIT :Gone to have lunch ; Preferred message format. + +4.1.7 Server quit message + + Command: SQUIT + Parameters: <server> <comment> + + The SQUIT message is needed to tell about quitting or dead servers. + If a server wishes to break the connection to another server it must + send a SQUIT message to the other server, using the the name of the + other server as the server parameter, which then closes its + connection to the quitting server. + + This command is also available operators to help keep a network of + IRC servers connected in an orderly fashion. Operators may also + issue an SQUIT message for a remote server connection. In this case, + the SQUIT must be parsed by each server inbetween the operator and + the remote server, updating the view of the network held by each + server as explained below. + + The <comment> should be supplied by all operators who execute a SQUIT + for a remote server (that is not connected to the server they are + currently on) so that other operators are aware for the reason of + this action. The <comment> is also filled in by servers which may + place an error or similar message here. + + Both of the servers which are on either side of the connection being + closed are required to to send out a SQUIT message (to all its other + server connections) for all other servers which are considered to be + behind that link. + + + + +Oikarinen & Reed [Page 18] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + Similarly, a QUIT message must be sent to the other connected servers + rest of the network on behalf of all clients behind that link. In + addition to this, all channel members of a channel which lost a + member due to the split must be sent a QUIT message. + + If a server connection is terminated prematurely (e.g. the server on + the other end of the link died), the server which detects + this disconnection is required to inform the rest of the network + that the connection has closed and fill in the comment field + with something appropriate. + + Numeric replies: + + ERR_NOPRIVILEGES ERR_NOSUCHSERVER + + Example: + + SQUIT tolsun.oulu.fi :Bad Link ? ; the server link tolson.oulu.fi has + been terminated because of "Bad Link". + + :Trillian SQUIT cm22.eng.umd.edu :Server out of control + ; message from Trillian to disconnect + "cm22.eng.umd.edu" from the net + because "Server out of control". + +4.2 Channel operations + + This group of messages is concerned with manipulating channels, their + properties (channel modes), and their contents (typically clients). + In implementing these, a number of race conditions are inevitable + when clients at opposing ends of a network send commands which will + ultimately clash. It is also required that servers keep a nickname + history to ensure that wherever a <nick> parameter is given, the + server check its history in case it has recently been changed. + +4.2.1 Join message + + Command: JOIN + Parameters: <channel>{,<channel>} [<key>{,<key>}] + + The JOIN command is used by client to start listening a specific + channel. Whether or not a client is allowed to join a channel is + checked only by the server the client is connected to; all other + servers automatically add the user to the channel when it is received + from other servers. The conditions which affect this are as follows: + + 1. the user must be invited if the channel is invite-only; + + + + +Oikarinen & Reed [Page 19] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + 2. the user's nick/username/hostname must not match any + active bans; + + 3. the correct key (password) must be given if it is set. + + These are discussed in more detail under the MODE command (see + section 4.2.3 for more details). + + Once a user has joined a channel, they receive notice about all + commands their server receives which affect the channel. This + includes MODE, KICK, PART, QUIT and of course PRIVMSG/NOTICE. The + JOIN command needs to be broadcast to all servers so that each server + knows where to find the users who are on the channel. This allows + optimal delivery of PRIVMSG/NOTICE messages to the channel. + + If a JOIN is successful, the user is then sent the channel's topic + (using RPL_TOPIC) and the list of users who are on the channel (using + RPL_NAMREPLY), which must include the user joining. + + Numeric Replies: + + ERR_NEEDMOREPARAMS ERR_BANNEDFROMCHAN + ERR_INVITEONLYCHAN ERR_BADCHANNELKEY + ERR_CHANNELISFULL ERR_BADCHANMASK + ERR_NOSUCHCHANNEL ERR_TOOMANYCHANNELS + RPL_TOPIC + + Examples: + + JOIN #foobar ; join channel #foobar. + + JOIN &foo fubar ; join channel &foo using key "fubar". + + JOIN #foo,&bar fubar ; join channel #foo using key "fubar" + and &bar using no key. + + JOIN #foo,#bar fubar,foobar ; join channel #foo using key "fubar". + and channel #bar using key "foobar". + + JOIN #foo,#bar ; join channels #foo and #bar. + + :WiZ JOIN #Twilight_zone ; JOIN message from WiZ + +4.2.2 Part message + + Command: PART + Parameters: <channel>{,<channel>} + + + + +Oikarinen & Reed [Page 20] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + The PART message causes the client sending the message to be removed + from the list of active users for all given channels listed in the + parameter string. + + Numeric Replies: + + ERR_NEEDMOREPARAMS ERR_NOSUCHCHANNEL + ERR_NOTONCHANNEL + + Examples: + + PART #twilight_zone ; leave channel "#twilight_zone" + + PART #oz-ops,&group5 ; leave both channels "&group5" and + "#oz-ops". + +4.2.3 Mode message + + Command: MODE + + The MODE command is a dual-purpose command in IRC. It allows both + usernames and channels to have their mode changed. The rationale for + this choice is that one day nicknames will be obsolete and the + equivalent property will be the channel. + + When parsing MODE messages, it is recommended that the entire message + be parsed first and then the changes which resulted then passed on. + +4.2.3.1 Channel modes + + Parameters: <channel> {[+|-]|o|p|s|i|t|n|b|v} [<limit>] [<user>] + [<ban mask>] + + The MODE command is provided so that channel operators may change the + characteristics of `their' channel. It is also required that servers + be able to change channel modes so that channel operators may be + created. + + The various modes available for channels are as follows: + + o - give/take channel operator privileges; + p - private channel flag; + s - secret channel flag; + i - invite-only channel flag; + t - topic settable by channel operator only flag; + n - no messages to channel from clients on the outside; + m - moderated channel; + l - set the user limit to channel; + + + +Oikarinen & Reed [Page 21] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + b - set a ban mask to keep users out; + v - give/take the ability to speak on a moderated channel; + k - set a channel key (password). + + When using the 'o' and 'b' options, a restriction on a total of three + per mode command has been imposed. That is, any combination of 'o' + and + +4.2.3.2 User modes + + Parameters: <nickname> {[+|-]|i|w|s|o} + + The user MODEs are typically changes which affect either how the + client is seen by others or what 'extra' messages the client is sent. + A user MODE command may only be accepted if both the sender of the + message and the nickname given as a parameter are both the same. + + The available modes are as follows: + + i - marks a users as invisible; + s - marks a user for receipt of server notices; + w - user receives wallops; + o - operator flag. + + Additional modes may be available later on. + + If a user attempts to make themselves an operator using the "+o" + flag, the attempt should be ignored. There is no restriction, + however, on anyone `deopping' themselves (using "-o"). Numeric + Replies: + + ERR_NEEDMOREPARAMS RPL_CHANNELMODEIS + ERR_CHANOPRIVSNEEDED ERR_NOSUCHNICK + ERR_NOTONCHANNEL ERR_KEYSET + RPL_BANLIST RPL_ENDOFBANLIST + ERR_UNKNOWNMODE ERR_NOSUCHCHANNEL + + ERR_USERSDONTMATCH RPL_UMODEIS + ERR_UMODEUNKNOWNFLAG + + Examples: + + Use of Channel Modes: + +MODE #Finnish +im ; Makes #Finnish channel moderated and + 'invite-only'. + +MODE #Finnish +o Kilroy ; Gives 'chanop' privileges to Kilroy on + + + +Oikarinen & Reed [Page 22] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + channel #Finnish. + +MODE #Finnish +v Wiz ; Allow WiZ to speak on #Finnish. + +MODE #Fins -s ; Removes 'secret' flag from channel + #Fins. + +MODE #42 +k oulu ; Set the channel key to "oulu". + +MODE #eu-opers +l 10 ; Set the limit for the number of users + on channel to 10. + +MODE &oulu +b ; list ban masks set for channel. + +MODE &oulu +b *!*@* ; prevent all users from joining. + +MODE &oulu +b *!*@*.edu ; prevent any user from a hostname + matching *.edu from joining. + + Use of user Modes: + +:MODE WiZ -w ; turns reception of WALLOPS messages + off for WiZ. + +:Angel MODE Angel +i ; Message from Angel to make themselves + invisible. + +MODE WiZ -o ; WiZ 'deopping' (removing operator + status). The plain reverse of this + command ("MODE WiZ +o") must not be + allowed from users since would bypass + the OPER command. + +4.2.4 Topic message + + Command: TOPIC + Parameters: <channel> [<topic>] + + The TOPIC message is used to change or view the topic of a channel. + The topic for channel <channel> is returned if there is no <topic> + given. If the <topic> parameter is present, the topic for that + channel will be changed, if the channel modes permit this action. + + Numeric Replies: + + ERR_NEEDMOREPARAMS ERR_NOTONCHANNEL + RPL_NOTOPIC RPL_TOPIC + ERR_CHANOPRIVSNEEDED + + + +Oikarinen & Reed [Page 23] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + Examples: + + :Wiz TOPIC #test :New topic ;User Wiz setting the topic. + + TOPIC #test :another topic ;set the topic on #test to "another + topic". + + TOPIC #test ; check the topic for #test. + +4.2.5 Names message + + Command: NAMES + Parameters: [<channel>{,<channel>}] + + By using the NAMES command, a user can list all nicknames that are + visible to them on any channel that they can see. Channel names + which they can see are those which aren't private (+p) or secret (+s) + or those which they are actually on. The <channel> parameter + specifies which channel(s) to return information about if valid. + There is no error reply for bad channel names. + + If no <channel> parameter is given, a list of all channels and their + occupants is returned. At the end of this list, a list of users who + are visible but either not on any channel or not on a visible channel + are listed as being on `channel' "*". + + Numerics: + + RPL_NAMREPLY RPL_ENDOFNAMES + + Examples: + + NAMES #twilight_zone,#42 ; list visible users on #twilight_zone + and #42 if the channels are visible to + you. + + NAMES ; list all visible channels and users + +4.2.6 List message + + Command: LIST + Parameters: [<channel>{,<channel>} [<server>]] + + The list message is used to list channels and their topics. If the + <channel> parameter is used, only the status of that channel + is displayed. Private channels are listed (without their + topics) as channel "Prv" unless the client generating the query is + actually on that channel. Likewise, secret channels are not listed + + + +Oikarinen & Reed [Page 24] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + at all unless the client is a member of the channel in question. + + Numeric Replies: + + ERR_NOSUCHSERVER RPL_LISTSTART + RPL_LIST RPL_LISTEND + + Examples: + + LIST ; List all channels. + + LIST #twilight_zone,#42 ; List channels #twilight_zone and #42 + +4.2.7 Invite message + + Command: INVITE + Parameters: <nickname> <channel> + + The INVITE message is used to invite users to a channel. The + parameter <nickname> is the nickname of the person to be invited to + the target channel <channel>. There is no requirement that the + channel the target user is being invited to must exist or be a valid + channel. To invite a user to a channel which is invite only (MODE + +i), the client sending the invite must be recognised as being a + channel operator on the given channel. + + Numeric Replies: + + ERR_NEEDMOREPARAMS ERR_NOSUCHNICK + ERR_NOTONCHANNEL ERR_USERONCHANNEL + ERR_CHANOPRIVSNEEDED + RPL_INVITING RPL_AWAY + + Examples: + + :Angel INVITE Wiz #Dust ; User Angel inviting WiZ to channel + #Dust + + INVITE Wiz #Twilight_Zone ; Command to invite WiZ to + #Twilight_zone + +4.2.8 Kick command + + Command: KICK + Parameters: <channel> <user> [<comment>] + + The KICK command can be used to forcibly remove a user from a + channel. It 'kicks them out' of the channel (forced PART). + + + +Oikarinen & Reed [Page 25] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + Only a channel operator may kick another user out of a channel. + Each server that receives a KICK message checks that it is valid + (ie the sender is actually a channel operator) before removing + the victim from the channel. + + Numeric Replies: + + ERR_NEEDMOREPARAMS ERR_NOSUCHCHANNEL + ERR_BADCHANMASK ERR_CHANOPRIVSNEEDED + ERR_NOTONCHANNEL + + Examples: + +KICK &Melbourne Matthew ; Kick Matthew from &Melbourne + +KICK #Finnish John :Speaking English + ; Kick John from #Finnish using + "Speaking English" as the reason + (comment). + +:WiZ KICK #Finnish John ; KICK message from WiZ to remove John + from channel #Finnish + +NOTE: + It is possible to extend the KICK command parameters to the +following: + +<channel>{,<channel>} <user>{,<user>} [<comment>] + +4.3 Server queries and commands + + The server query group of commands has been designed to return + information about any server which is connected to the network. All + servers connected must respond to these queries and respond + correctly. Any invalid response (or lack thereof) must be considered + a sign of a broken server and it must be disconnected/disabled as + soon as possible until the situation is remedied. + + In these queries, where a parameter appears as "<server>", it will + usually mean it can be a nickname or a server or a wildcard name of + some sort. For each parameter, however, only one query and set of + replies is to be generated. + +4.3.1 Version message + + Command: VERSION + Parameters: [<server>] + + + + +Oikarinen & Reed [Page 26] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + The VERSION message is used to query the version of the server + program. An optional parameter <server> is used to query the version + of the server program which a client is not directly connected to. + + Numeric Replies: + + ERR_NOSUCHSERVER RPL_VERSION + + Examples: + + :Wiz VERSION *.se ; message from Wiz to check the version + of a server matching "*.se" + + VERSION tolsun.oulu.fi ; check the version of server + "tolsun.oulu.fi". + +4.3.2 Stats message + + Command: STATS + Parameters: [<query> [<server>]] + + The stats message is used to query statistics of certain server. If + <server> parameter is omitted, only the end of stats reply is sent + back. The implementation of this command is highly dependent on the + server which replies, although the server must be able to supply + information as described by the queries below (or similar). + + A query may be given by any single letter which is only checked by + the destination server (if given as the <server> parameter) and is + otherwise passed on by intermediate servers, ignored and unaltered. + The following queries are those found in the current IRC + implementation and provide a large portion of the setup information + for that server. Although these may not be supported in the same way + by other versions, all servers should be able to supply a valid reply + to a STATS query which is consistent with the reply formats currently + used and the purpose of the query. + + The currently supported queries are: + + c - returns a list of servers which the server may connect + to or allow connections from; + h - returns a list of servers which are either forced to be + treated as leaves or allowed to act as hubs; + i - returns a list of hosts which the server allows a client + to connect from; + k - returns a list of banned username/hostname combinations + for that server; + l - returns a list of the server's connections, showing how + + + +Oikarinen & Reed [Page 27] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + long each connection has been established and the traffic + over that connection in bytes and messages for each + direction; + m - returns a list of commands supported by the server and + the usage count for each if the usage count is non zero; + o - returns a list of hosts from which normal clients may + become operators; + y - show Y (Class) lines from server's configuration file; + u - returns a string showing how long the server has been up. + + Numeric Replies: + + ERR_NOSUCHSERVER + RPL_STATSCLINE RPL_STATSNLINE + RPL_STATSILINE RPL_STATSKLINE + RPL_STATSQLINE RPL_STATSLLINE + RPL_STATSLINKINFO RPL_STATSUPTIME + RPL_STATSCOMMANDS RPL_STATSOLINE + RPL_STATSHLINE RPL_ENDOFSTATS + + Examples: + +STATS m ; check the command usage for the server + you are connected to + +:Wiz STATS c eff.org ; request by WiZ for C/N line + information from server eff.org + +4.3.3 Links message + + Command: LINKS + Parameters: [[<remote server>] <server mask>] + + With LINKS, a user can list all servers which are known by the server + answering the query. The returned list of servers must match the + mask, or if no mask is given, the full list is returned. + + If <remote server> is given in addition to <server mask>, the LINKS + command is forwarded to the first server found that matches that name + (if any), and that server is then required to answer the query. + + Numeric Replies: + + ERR_NOSUCHSERVER + RPL_LINKS RPL_ENDOFLINKS + + Examples: + + + + +Oikarinen & Reed [Page 28] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +LINKS *.au ; list all servers which have a name + that matches *.au; + +:WiZ LINKS *.bu.edu *.edu ; LINKS message from WiZ to the first + server matching *.edu for a list of + servers matching *.bu.edu. + +4.3.4 Time message + + Command: TIME + Parameters: [<server>] + + The time message is used to query local time from the specified + server. If the server parameter is not given, the server handling the + command must reply to the query. + + Numeric Replies: + + ERR_NOSUCHSERVER RPL_TIME + + Examples: + + TIME tolsun.oulu.fi ; check the time on the server + "tolson.oulu.fi" + + Angel TIME *.au ; user angel checking the time on a + server matching "*.au" + +4.3.5 Connect message + + Command: CONNECT + Parameters: <target server> [<port> [<remote server>]] + + The CONNECT command can be used to force a server to try to establish + a new connection to another server immediately. CONNECT is a + privileged command and is to be available only to IRC Operators. If + a remote server is given then the CONNECT attempt is made by that + server to <target server> and <port>. + + Numeric Replies: + + ERR_NOSUCHSERVER ERR_NOPRIVILEGES + ERR_NEEDMOREPARAMS + + Examples: + +CONNECT tolsun.oulu.fi ; Attempt to connect a server to + tolsun.oulu.fi + + + +Oikarinen & Reed [Page 29] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +:WiZ CONNECT eff.org 6667 csd.bu.edu + ; CONNECT attempt by WiZ to get servers + eff.org and csd.bu.edu connected on port + 6667. + +4.3.6 Trace message + + Command: TRACE + Parameters: [<server>] + + TRACE command is used to find the route to specific server. Each + server that processes this message must tell the sender about it by + sending a reply indicating it is a pass-through link, forming a chain + of replies similar to that gained from using "traceroute". After + sending this reply back, it must then send the TRACE message to the + next server until given server is reached. If the <server> parameter + is omitted, it is recommended that TRACE command send a message to + the sender telling which servers the current server has direct + connection to. + + If the destination given by "<server>" is an actual server, then the + destination server is required to report all servers and users which + are connected to it, although only operators are permitted to see + users present. If the destination given by <server> is a nickname, + they only a reply for that nickname is given. + + Numeric Replies: + + ERR_NOSUCHSERVER + + If the TRACE message is destined for another server, all intermediate + servers must return a RPL_TRACELINK reply to indicate that the TRACE + passed through it and where its going next. + + RPL_TRACELINK + A TRACE reply may be composed of any number of the following numeric + replies. + + RPL_TRACECONNECTING RPL_TRACEHANDSHAKE + RPL_TRACEUNKNOWN RPL_TRACEOPERATOR + RPL_TRACEUSER RPL_TRACESERVER + RPL_TRACESERVICE RPL_TRACENEWTYPE + RPL_TRACECLASS + + Examples: + +TRACE *.oulu.fi ; TRACE to a server matching *.oulu.fi + + + + +Oikarinen & Reed [Page 30] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +:WiZ TRACE AngelDust ; TRACE issued by WiZ to nick AngelDust + +4.3.7 Admin command + + Command: ADMIN + Parameters: [<server>] + + The admin message is used to find the name of the administrator of + the given server, or current server if <server> parameter is omitted. + Each server must have the ability to forward ADMIN messages to other + servers. + + Numeric Replies: + + ERR_NOSUCHSERVER + RPL_ADMINME RPL_ADMINLOC1 + RPL_ADMINLOC2 RPL_ADMINEMAIL + + Examples: + + ADMIN tolsun.oulu.fi ; request an ADMIN reply from + tolsun.oulu.fi + + :WiZ ADMIN *.edu ; ADMIN request from WiZ for first + server found to match *.edu. + +4.3.8 Info command + + Command: INFO + Parameters: [<server>] + + The INFO command is required to return information which describes + the server: its version, when it was compiled, the patchlevel, when + it was started, and any other miscellaneous information which may be + considered to be relevant. + + Numeric Replies: + + ERR_NOSUCHSERVER + RPL_INFO RPL_ENDOFINFO + + Examples: + + INFO csd.bu.edu ; request an INFO reply from + csd.bu.edu + + :Avalon INFO *.fi ; INFO request from Avalon for first + server found to match *.fi. + + + +Oikarinen & Reed [Page 31] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + INFO Angel ; request info from the server that + Angel is connected to. + +4.4 Sending messages + + The main purpose of the IRC protocol is to provide a base for clients + to communicate with each other. PRIVMSG and NOTICE are the only + messages available which actually perform delivery of a text message + from one client to another - the rest just make it possible and try + to ensure it happens in a reliable and structured manner. + +4.4.1 Private messages + + Command: PRIVMSG + Parameters: <receiver>{,<receiver>} <text to be sent> + + PRIVMSG is used to send private messages between users. <receiver> + is the nickname of the receiver of the message. <receiver> can also + be a list of names or channels separated with commas. + + The <receiver> parameter may also me a host mask (#mask) or server + mask ($mask). In both cases the server will only send the PRIVMSG + to those who have a server or host matching the mask. The mask must + have at least 1 (one) "." in it and no wildcards following the + last ".". This requirement exists to prevent people sending messages + to "#*" or "$*", which would broadcast to all users; from + experience, this is abused more than used responsibly and properly. + Wildcards are the '*' and '?' characters. This extension to + the PRIVMSG command is only available to Operators. + + Numeric Replies: + + ERR_NORECIPIENT ERR_NOTEXTTOSEND + ERR_CANNOTSENDTOCHAN ERR_NOTOPLEVEL + ERR_WILDTOPLEVEL ERR_TOOMANYTARGETS + ERR_NOSUCHNICK + RPL_AWAY + + Examples: + +:Angel PRIVMSG Wiz :Hello are you receiving this message ? + ; Message from Angel to Wiz. + +PRIVMSG Angel :yes I'm receiving it !receiving it !'u>(768u+1n) .br ; + Message to Angel. + +PRIVMSG jto@tolsun.oulu.fi :Hello ! + ; Message to a client on server + + + +Oikarinen & Reed [Page 32] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + tolsun.oulu.fi with username of "jto". + +PRIVMSG $*.fi :Server tolsun.oulu.fi rebooting. + ; Message to everyone on a server which + has a name matching *.fi. + +PRIVMSG #*.edu :NSFNet is undergoing work, expect interruptions + ; Message to all users who come from a + host which has a name matching *.edu. + +4.4.2 Notice + + Command: NOTICE + Parameters: <nickname> <text> + + The NOTICE message is used similarly to PRIVMSG. The difference + between NOTICE and PRIVMSG is that automatic replies must never be + sent in response to a NOTICE message. This rule applies to servers + too - they must not send any error reply back to the client on + receipt of a notice. The object of this rule is to avoid loops + between a client automatically sending something in response to + something it received. This is typically used by automatons (clients + with either an AI or other interactive program controlling their + actions) which are always seen to be replying lest they end up in a + loop with another automaton. + + See PRIVMSG for more details on replies and examples. + +4.5 User based queries + + User queries are a group of commands which are primarily concerned + with finding details on a particular user or group users. When using + wildcards with any of these commands, if they match, they will only + return information on users who are 'visible' to you. The visibility + of a user is determined as a combination of the user's mode and the + common set of channels you are both on. + +4.5.1 Who query + + Command: WHO + Parameters: [<name> [<o>]] + + The WHO message is used by a client to generate a query which returns + a list of information which 'matches' the <name> parameter given by + the client. In the absence of the <name> parameter, all visible + (users who aren't invisible (user mode +i) and who don't have a + common channel with the requesting client) are listed. The same + result can be achieved by using a <name> of "0" or any wildcard which + + + +Oikarinen & Reed [Page 33] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + will end up matching every entry possible. + + The <name> passed to WHO is matched against users' host, server, real + name and nickname if the channel <name> cannot be found. + + If the "o" parameter is passed only operators are returned according + to the name mask supplied. + + Numeric Replies: + + ERR_NOSUCHSERVER + RPL_WHOREPLY RPL_ENDOFWHO + + Examples: + + WHO *.fi ; List all users who match against + "*.fi". + + WHO jto* o ; List all users with a match against + "jto*" if they are an operator. + +4.5.2 Whois query + + Command: WHOIS + Parameters: [<server>] <nickmask>[,<nickmask>[,...]] + + This message is used to query information about particular user. The + server will answer this message with several numeric messages + indicating different statuses of each user which matches the nickmask + (if you are entitled to see them). If no wildcard is present in the + <nickmask>, any information about that nick which you are allowed to + see is presented. A comma (',') separated list of nicknames may be + given. + + The latter version sends the query to a specific server. It is + useful if you want to know how long the user in question has been + idle as only local server (ie. the server the user is directly + connected to) knows that information, while everything else is + globally known. + + Numeric Replies: + + ERR_NOSUCHSERVER ERR_NONICKNAMEGIVEN + RPL_WHOISUSER RPL_WHOISCHANNELS + RPL_WHOISCHANNELS RPL_WHOISSERVER + RPL_AWAY RPL_WHOISOPERATOR + RPL_WHOISIDLE ERR_NOSUCHNICK + RPL_ENDOFWHOIS + + + +Oikarinen & Reed [Page 34] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + Examples: + + WHOIS wiz ; return available user information + about nick WiZ + + WHOIS eff.org trillian ; ask server eff.org for user + information about trillian + +4.5.3 Whowas + + Command: WHOWAS + Parameters: <nickname> [<count> [<server>]] + + Whowas asks for information about a nickname which no longer exists. + This may either be due to a nickname change or the user leaving IRC. + In response to this query, the server searches through its nickname + history, looking for any nicks which are lexically the same (no wild + card matching here). The history is searched backward, returning the + most recent entry first. If there are multiple entries, up to + <count> replies will be returned (or all of them if no <count> + parameter is given). If a non-positive number is passed as being + <count>, then a full search is done. + + Numeric Replies: + + ERR_NONICKNAMEGIVEN ERR_WASNOSUCHNICK + RPL_WHOWASUSER RPL_WHOISSERVER + RPL_ENDOFWHOWAS + + Examples: + + WHOWAS Wiz ; return all information in the nick + history about nick "WiZ"; + + WHOWAS Mermaid 9 ; return at most, the 9 most recent + entries in the nick history for + "Mermaid"; + + WHOWAS Trillian 1 *.edu ; return the most recent history for + "Trillian" from the first server found + to match "*.edu". + +4.6 Miscellaneous messages + + Messages in this category do not fit into any of the above categories + but are nonetheless still a part of and required by the protocol. + + + + + +Oikarinen & Reed [Page 35] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +4.6.1 Kill message + + Command: KILL + Parameters: <nickname> <comment> + + The KILL message is used to cause a client-server connection to be + closed by the server which has the actual connection. KILL is used + by servers when they encounter a duplicate entry in the list of valid + nicknames and is used to remove both entries. It is also available + to operators. + + Clients which have automatic reconnect algorithms effectively make + this command useless since the disconnection is only brief. It does + however break the flow of data and can be used to stop large amounts + of being abused, any user may elect to receive KILL messages + generated for others to keep an 'eye' on would be trouble spots. + + In an arena where nicknames are required to be globally unique at all + times, KILL messages are sent whenever 'duplicates' are detected + (that is an attempt to register two users with the same nickname) in + the hope that both of them will disappear and only 1 reappear. + + The comment given must reflect the actual reason for the KILL. For + server-generated KILLs it usually is made up of details concerning + the origins of the two conflicting nicknames. For users it is left + up to them to provide an adequate reason to satisfy others who see + it. To prevent/discourage fake KILLs from being generated to hide + the identify of the KILLer, the comment also shows a 'kill-path' + which is updated by each server it passes through, each prepending + its name to the path. + + Numeric Replies: + + ERR_NOPRIVILEGES ERR_NEEDMOREPARAMS + ERR_NOSUCHNICK ERR_CANTKILLSERVER + + + KILL David (csd.bu.edu <- tolsun.oulu.fi) + ; Nickname collision between csd.bu.edu + and tolson.oulu.fi + + + NOTE: + It is recommended that only Operators be allowed to kill other users + with KILL message. In an ideal world not even operators would need + to do this and it would be left to servers to deal with. + + + + + +Oikarinen & Reed [Page 36] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +4.6.2 Ping message + + Command: PING + Parameters: <server1> [<server2>] + + The PING message is used to test the presence of an active client at + the other end of the connection. A PING message is sent at regular + intervals if no other activity detected coming from a connection. If + a connection fails to respond to a PING command within a set amount + of time, that connection is closed. + + Any client which receives a PING message must respond to <server1> + (server which sent the PING message out) as quickly as possible with + an appropriate PONG message to indicate it is still there and alive. + Servers should not respond to PING commands but rely on PINGs from + the other end of the connection to indicate the connection is alive. + If the <server2> parameter is specified, the PING message gets + forwarded there. + + Numeric Replies: + + ERR_NOORIGIN ERR_NOSUCHSERVER + + Examples: + + PING tolsun.oulu.fi ; server sending a PING message to + another server to indicate it is still + alive. + + PING WiZ ; PING message being sent to nick WiZ + +4.6.3 Pong message + + Command: PONG + Parameters: <daemon> [<daemon2>] + + PONG message is a reply to ping message. If parameter <daemon2> is + given this message must be forwarded to given daemon. The <daemon> + parameter is the name of the daemon who has responded to PING message + and generated this message. + + Numeric Replies: + + ERR_NOORIGIN ERR_NOSUCHSERVER + + Examples: + + PONG csd.bu.edu tolsun.oulu.fi ; PONG message from csd.bu.edu to + + + +Oikarinen & Reed [Page 37] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + tolsun.oulu.fi + +4.6.4 Error + + Command: ERROR + Parameters: <error message> + + The ERROR command is for use by servers when reporting a serious or + fatal error to its operators. It may also be sent from one server to + another but must not be accepted from any normal unknown clients. + + An ERROR message is for use for reporting errors which occur with a + server-to-server link only. An ERROR message is sent to the server + at the other end (which sends it to all of its connected operators) + and to all operators currently connected. It is not to be passed + onto any other servers by a server if it is received from a server. + + When a server sends a received ERROR message to its operators, the + message should be encapsulated inside a NOTICE message, indicating + that the client was not responsible for the error. + + Numerics: + + None. + + Examples: + + ERROR :Server *.fi already exists; ERROR message to the other server + which caused this error. + + NOTICE WiZ :ERROR from csd.bu.edu -- Server *.fi already exists + ; Same ERROR message as above but sent + to user WiZ on the other server. + +5. OPTIONALS + + This section describes OPTIONAL messages. They are not required in a + working server implementation of the protocol described herein. In + the absence of the option, an error reply message must be generated + or an unknown command error. If the message is destined for another + server to answer then it must be passed on (elementary parsing + required) The allocated numerics for this are listed with the + messages below. + +5.1 Away + + Command: AWAY + Parameters: [message] + + + +Oikarinen & Reed [Page 38] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + With the AWAY message, clients can set an automatic reply string for + any PRIVMSG commands directed at them (not to a channel they are on). + The automatic reply is sent by the server to client sending the + PRIVMSG command. The only replying server is the one to which the + sending client is connected to. + + The AWAY message is used either with one parameter (to set an AWAY + message) or with no parameters (to remove the AWAY message). + + Numeric Replies: + + RPL_UNAWAY RPL_NOWAWAY + + Examples: + + AWAY :Gone to lunch. Back in 5 ; set away message to "Gone to lunch. + Back in 5". + + :WiZ AWAY ; unmark WiZ as being away. + + +5.2 Rehash message + + Command: REHASH + Parameters: None + + The rehash message can be used by the operator to force the server to + re-read and process its configuration file. + + Numeric Replies: + + RPL_REHASHING ERR_NOPRIVILEGES + +Examples: + +REHASH ; message from client with operator + status to server asking it to reread its + configuration file. + +5.3 Restart message + + Command: RESTART + Parameters: None + + The restart message can only be used by an operator to force a server + restart itself. This message is optional since it may be viewed as a + risk to allow arbitrary people to connect to a server as an operator + and execute this command, causing (at least) a disruption to service. + + + +Oikarinen & Reed [Page 39] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + The RESTART command must always be fully processed by the server to + which the sending client is connected and not be passed onto other + connected servers. + + Numeric Replies: + + ERR_NOPRIVILEGES + + Examples: + + RESTART ; no parameters required. + +5.4 Summon message + + Command: SUMMON + Parameters: <user> [<server>] + + The SUMMON command can be used to give users who are on a host + running an IRC server a message asking them to please join IRC. This + message is only sent if the target server (a) has SUMMON enabled, (b) + the user is logged in and (c) the server process can write to the + user's tty (or similar). + + If no <server> parameter is given it tries to summon <user> from the + server the client is connected to is assumed as the target. + + If summon is not enabled in a server, it must return the + ERR_SUMMONDISABLED numeric and pass the summon message onwards. + + Numeric Replies: + + ERR_NORECIPIENT ERR_FILEERROR + ERR_NOLOGIN ERR_NOSUCHSERVER + RPL_SUMMONING + + Examples: + + SUMMON jto ; summon user jto on the server's host + + SUMMON jto tolsun.oulu.fi ; summon user jto on the host which a + server named "tolsun.oulu.fi" is + running. + + +5.5 Users + + Command: USERS + Parameters: [<server>] + + + +Oikarinen & Reed [Page 40] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + The USERS command returns a list of users logged into the server in a + similar format to who(1), rusers(1) and finger(1). Some people + may disable this command on their server for security related + reasons. If disabled, the correct numeric must be returned to + indicate this. + + Numeric Replies: + + ERR_NOSUCHSERVER ERR_FILEERROR + RPL_USERSSTART RPL_USERS + RPL_NOUSERS RPL_ENDOFUSERS + ERR_USERSDISABLED + + Disabled Reply: + + ERR_USERSDISABLED + + Examples: + +USERS eff.org ; request a list of users logged in on + server eff.org + +:John USERS tolsun.oulu.fi ; request from John for a list of users + logged in on server tolsun.oulu.fi + +5.6 Operwall message + + Command: WALLOPS + Parameters: Text to be sent to all operators currently online + + Sends a message to all operators currently online. After + implementing WALLOPS as a user command it was found that it was + often and commonly abused as a means of sending a message to a lot + of people (much similar to WALL). Due to this it is recommended + that the current implementation of WALLOPS be used as an + example by allowing and recognising only servers as the senders of + WALLOPS. + + Numeric Replies: + + ERR_NEEDMOREPARAMS + + Examples: + + :csd.bu.edu WALLOPS :Connect '*.uiuc.edu 6667' from Joshua; WALLOPS + message from csd.bu.edu announcing a + CONNECT message it received and acted + upon from Joshua. + + + +Oikarinen & Reed [Page 41] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +5.7 Userhost message + + Command: USERHOST + Parameters: <nickname>{<space><nickname>} + + The USERHOST command takes a list of up to 5 nicknames, each + separated by a space character and returns a list of information + about each nickname that it found. The returned list has each reply + separated by a space. + + Numeric Replies: + + RPL_USERHOST ERR_NEEDMOREPARAMS + + Examples: + + USERHOST Wiz Michael Marty p ;USERHOST request for information on + nicks "Wiz", "Michael", "Marty" and "p" + +5.8 Ison message + + Command: ISON + Parameters: <nickname>{<space><nickname>} + + The ISON command was implemented to provide a quick and efficient + means to get a response about whether a given nickname was currently + on IRC. ISON only takes one (1) parameter: a space-separated list of + nicks. For each nickname in the list that is present, the server + adds that to its reply string. Thus the reply string may return + empty (none of the given nicks are present), an exact copy of the + parameter string (all of them present) or as any other subset of the + set of nicks given in the parameter. The only limit on the number + of nicks that may be checked is that the combined length must not be + too large as to cause the server to chop it off so it fits in 512 + characters. + + ISON is only be processed by the server local to the client sending + the command and thus not passed onto other servers for further + processing. + + Numeric Replies: + + RPL_ISON ERR_NEEDMOREPARAMS + + Examples: + + ISON phone trillian WiZ jarlek Avalon Angel Monstah + ; Sample ISON request for 7 nicks. + + + +Oikarinen & Reed [Page 42] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +6. REPLIES + + The following is a list of numeric replies which are generated in + response to the commands given above. Each numeric is given with its + number, name and reply string. + +6.1 Error Replies. + + 401 ERR_NOSUCHNICK + "<nickname> :No such nick/channel" + + - Used to indicate the nickname parameter supplied to a + command is currently unused. + + 402 ERR_NOSUCHSERVER + "<server name> :No such server" + + - Used to indicate the server name given currently + doesn't exist. + + 403 ERR_NOSUCHCHANNEL + "<channel name> :No such channel" + + - Used to indicate the given channel name is invalid. + + 404 ERR_CANNOTSENDTOCHAN + "<channel name> :Cannot send to channel" + + - Sent to a user who is either (a) not on a channel + which is mode +n or (b) not a chanop (or mode +v) on + a channel which has mode +m set and is trying to send + a PRIVMSG message to that channel. + + 405 ERR_TOOMANYCHANNELS + "<channel name> :You have joined too many \ + channels" + - Sent to a user when they have joined the maximum + number of allowed channels and they try to join + another channel. + + 406 ERR_WASNOSUCHNICK + "<nickname> :There was no such nickname" + + - Returned by WHOWAS to indicate there is no history + information for that nickname. + + 407 ERR_TOOMANYTARGETS + "<target> :Duplicate recipients. No message \ + + + +Oikarinen & Reed [Page 43] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + delivered" + + - Returned to a client which is attempting to send a + PRIVMSG/NOTICE using the user@host destination format + and for a user@host which has several occurrences. + + 409 ERR_NOORIGIN + ":No origin specified" + + - PING or PONG message missing the originator parameter + which is required since these commands must work + without valid prefixes. + + 411 ERR_NORECIPIENT + ":No recipient given (<command>)" + 412 ERR_NOTEXTTOSEND + ":No text to send" + 413 ERR_NOTOPLEVEL + "<mask> :No toplevel domain specified" + 414 ERR_WILDTOPLEVEL + "<mask> :Wildcard in toplevel domain" + + - 412 - 414 are returned by PRIVMSG to indicate that + the message wasn't delivered for some reason. + ERR_NOTOPLEVEL and ERR_WILDTOPLEVEL are errors that + are returned when an invalid use of + "PRIVMSG $<server>" or "PRIVMSG #<host>" is attempted. + + 421 ERR_UNKNOWNCOMMAND + "<command> :Unknown command" + + - Returned to a registered client to indicate that the + command sent is unknown by the server. + + 422 ERR_NOMOTD + ":MOTD File is missing" + + - Server's MOTD file could not be opened by the server. + + 423 ERR_NOADMININFO + "<server> :No administrative info available" + + - Returned by a server in response to an ADMIN message + when there is an error in finding the appropriate + information. + + 424 ERR_FILEERROR + ":File error doing <file op> on <file>" + + + +Oikarinen & Reed [Page 44] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + - Generic error message used to report a failed file + operation during the processing of a message. + + 431 ERR_NONICKNAMEGIVEN + ":No nickname given" + + - Returned when a nickname parameter expected for a + command and isn't found. + + 432 ERR_ERRONEUSNICKNAME + "<nick> :Erroneus nickname" + + - Returned after receiving a NICK message which contains + characters which do not fall in the defined set. See + section x.x.x for details on valid nicknames. + + 433 ERR_NICKNAMEINUSE + "<nick> :Nickname is already in use" + + - Returned when a NICK message is processed that results + in an attempt to change to a currently existing + nickname. + + 436 ERR_NICKCOLLISION + "<nick> :Nickname collision KILL" + + - Returned by a server to a client when it detects a + nickname collision (registered of a NICK that + already exists by another server). + + 441 ERR_USERNOTINCHANNEL + "<nick> <channel> :They aren't on that channel" + + - Returned by the server to indicate that the target + user of the command is not on the given channel. + + 442 ERR_NOTONCHANNEL + "<channel> :You're not on that channel" + + - Returned by the server whenever a client tries to + perform a channel effecting command for which the + client isn't a member. + + 443 ERR_USERONCHANNEL + "<user> <channel> :is already on channel" + + - Returned when a client tries to invite a user to a + channel they are already on. + + + +Oikarinen & Reed [Page 45] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + 444 ERR_NOLOGIN + "<user> :User not logged in" + + - Returned by the summon after a SUMMON command for a + user was unable to be performed since they were not + logged in. + + 445 ERR_SUMMONDISABLED + ":SUMMON has been disabled" + + - Returned as a response to the SUMMON command. Must be + returned by any server which does not implement it. + + 446 ERR_USERSDISABLED + ":USERS has been disabled" + + - Returned as a response to the USERS command. Must be + returned by any server which does not implement it. + + 451 ERR_NOTREGISTERED + ":You have not registered" + + - Returned by the server to indicate that the client + must be registered before the server will allow it + to be parsed in detail. + + 461 ERR_NEEDMOREPARAMS + "<command> :Not enough parameters" + + - Returned by the server by numerous commands to + indicate to the client that it didn't supply enough + parameters. + + 462 ERR_ALREADYREGISTRED + ":You may not reregister" + + - Returned by the server to any link which tries to + change part of the registered details (such as + password or user details from second USER message). + + + 463 ERR_NOPERMFORHOST + ":Your host isn't among the privileged" + + - Returned to a client which attempts to register with + a server which does not been setup to allow + connections from the host the attempted connection + is tried. + + + +Oikarinen & Reed [Page 46] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + 464 ERR_PASSWDMISMATCH + ":Password incorrect" + + - Returned to indicate a failed attempt at registering + a connection for which a password was required and + was either not given or incorrect. + + 465 ERR_YOUREBANNEDCREEP + ":You are banned from this server" + + - Returned after an attempt to connect and register + yourself with a server which has been setup to + explicitly deny connections to you. + + 467 ERR_KEYSET + "<channel> :Channel key already set" + 471 ERR_CHANNELISFULL + "<channel> :Cannot join channel (+l)" + 472 ERR_UNKNOWNMODE + "<char> :is unknown mode char to me" + 473 ERR_INVITEONLYCHAN + "<channel> :Cannot join channel (+i)" + 474 ERR_BANNEDFROMCHAN + "<channel> :Cannot join channel (+b)" + 475 ERR_BADCHANNELKEY + "<channel> :Cannot join channel (+k)" + 481 ERR_NOPRIVILEGES + ":Permission Denied- You're not an IRC operator" + + - Any command requiring operator privileges to operate + must return this error to indicate the attempt was + unsuccessful. + + 482 ERR_CHANOPRIVSNEEDED + "<channel> :You're not channel operator" + + - Any command requiring 'chanop' privileges (such as + MODE messages) must return this error if the client + making the attempt is not a chanop on the specified + channel. + + 483 ERR_CANTKILLSERVER + ":You cant kill a server!" + + - Any attempts to use the KILL command on a server + are to be refused and this error returned directly + to the client. + + + + +Oikarinen & Reed [Page 47] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + 491 ERR_NOOPERHOST + ":No O-lines for your host" + + - If a client sends an OPER message and the server has + not been configured to allow connections from the + client's host as an operator, this error must be + returned. + + 501 ERR_UMODEUNKNOWNFLAG + ":Unknown MODE flag" + + - Returned by the server to indicate that a MODE + message was sent with a nickname parameter and that + the a mode flag sent was not recognized. + + 502 ERR_USERSDONTMATCH + ":Cant change mode for other users" + + - Error sent to any user trying to view or change the + user mode for a user other than themselves. + +6.2 Command responses. + + 300 RPL_NONE + Dummy reply number. Not used. + + 302 RPL_USERHOST + ":[<reply>{<space><reply>}]" + + - Reply format used by USERHOST to list replies to + the query list. The reply string is composed as + follows: + + <reply> ::= <nick>['*'] '=' <'+'|'-'><hostname> + + The '*' indicates whether the client has registered + as an Operator. The '-' or '+' characters represent + whether the client has set an AWAY message or not + respectively. + + 303 RPL_ISON + ":[<nick> {<space><nick>}]" + + - Reply format used by ISON to list replies to the + query list. + + 301 RPL_AWAY + "<nick> :<away message>" + + + +Oikarinen & Reed [Page 48] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + 305 RPL_UNAWAY + ":You are no longer marked as being away" + 306 RPL_NOWAWAY + ":You have been marked as being away" + + - These replies are used with the AWAY command (if + allowed). RPL_AWAY is sent to any client sending a + PRIVMSG to a client which is away. RPL_AWAY is only + sent by the server to which the client is connected. + Replies RPL_UNAWAY and RPL_NOWAWAY are sent when the + client removes and sets an AWAY message. + + 311 RPL_WHOISUSER + "<nick> <user> <host> * :<real name>" + 312 RPL_WHOISSERVER + "<nick> <server> :<server info>" + 313 RPL_WHOISOPERATOR + "<nick> :is an IRC operator" + 317 RPL_WHOISIDLE + "<nick> <integer> :seconds idle" + 318 RPL_ENDOFWHOIS + "<nick> :End of /WHOIS list" + 319 RPL_WHOISCHANNELS + "<nick> :{[@|+]<channel><space>}" + + - Replies 311 - 313, 317 - 319 are all replies + generated in response to a WHOIS message. Given that + there are enough parameters present, the answering + server must either formulate a reply out of the above + numerics (if the query nick is found) or return an + error reply. The '*' in RPL_WHOISUSER is there as + the literal character and not as a wild card. For + each reply set, only RPL_WHOISCHANNELS may appear + more than once (for long lists of channel names). + The '@' and '+' characters next to the channel name + indicate whether a client is a channel operator or + has been granted permission to speak on a moderated + channel. The RPL_ENDOFWHOIS reply is used to mark + the end of processing a WHOIS message. + + 314 RPL_WHOWASUSER + "<nick> <user> <host> * :<real name>" + 369 RPL_ENDOFWHOWAS + "<nick> :End of WHOWAS" + + - When replying to a WHOWAS message, a server must use + the replies RPL_WHOWASUSER, RPL_WHOISSERVER or + ERR_WASNOSUCHNICK for each nickname in the presented + + + +Oikarinen & Reed [Page 49] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + list. At the end of all reply batches, there must + be RPL_ENDOFWHOWAS (even if there was only one reply + and it was an error). + + 321 RPL_LISTSTART + "Channel :Users Name" + 322 RPL_LIST + "<channel> <# visible> :<topic>" + 323 RPL_LISTEND + ":End of /LIST" + + - Replies RPL_LISTSTART, RPL_LIST, RPL_LISTEND mark + the start, actual replies with data and end of the + server's response to a LIST command. If there are + no channels available to return, only the start + and end reply must be sent. + + 324 RPL_CHANNELMODEIS + "<channel> <mode> <mode params>" + + 331 RPL_NOTOPIC + "<channel> :No topic is set" + 332 RPL_TOPIC + "<channel> :<topic>" + + - When sending a TOPIC message to determine the + channel topic, one of two replies is sent. If + the topic is set, RPL_TOPIC is sent back else + RPL_NOTOPIC. + + 341 RPL_INVITING + "<channel> <nick>" + + - Returned by the server to indicate that the + attempted INVITE message was successful and is + being passed onto the end client. + + 342 RPL_SUMMONING + "<user> :Summoning user to IRC" + + - Returned by a server answering a SUMMON message to + indicate that it is summoning that user. + + 351 RPL_VERSION + "<version>.<debuglevel> <server> :<comments>" + + - Reply by the server showing its version details. + The <version> is the version of the software being + + + +Oikarinen & Reed [Page 50] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + used (including any patchlevel revisions) and the + <debuglevel> is used to indicate if the server is + running in "debug mode". + + The "comments" field may contain any comments about + the version or further version details. + + 352 RPL_WHOREPLY + "<channel> <user> <host> <server> <nick> \ + <H|G>[*][@|+] :<hopcount> <real name>" + 315 RPL_ENDOFWHO + "<name> :End of /WHO list" + + - The RPL_WHOREPLY and RPL_ENDOFWHO pair are used + to answer a WHO message. The RPL_WHOREPLY is only + sent if there is an appropriate match to the WHO + query. If there is a list of parameters supplied + with a WHO message, a RPL_ENDOFWHO must be sent + after processing each list item with <name> being + the item. + + 353 RPL_NAMREPLY + "<channel> :[[@|+]<nick> [[@|+]<nick> [...]]]" + 366 RPL_ENDOFNAMES + "<channel> :End of /NAMES list" + + - To reply to a NAMES message, a reply pair consisting + of RPL_NAMREPLY and RPL_ENDOFNAMES is sent by the + server back to the client. If there is no channel + found as in the query, then only RPL_ENDOFNAMES is + returned. The exception to this is when a NAMES + message is sent with no parameters and all visible + channels and contents are sent back in a series of + RPL_NAMEREPLY messages with a RPL_ENDOFNAMES to mark + the end. + + 364 RPL_LINKS + "<mask> <server> :<hopcount> <server info>" + 365 RPL_ENDOFLINKS + "<mask> :End of /LINKS list" + + - In replying to the LINKS message, a server must send + replies back using the RPL_LINKS numeric and mark the + end of the list using an RPL_ENDOFLINKS reply. + + 367 RPL_BANLIST + "<channel> <banid>" + 368 RPL_ENDOFBANLIST + + + +Oikarinen & Reed [Page 51] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + "<channel> :End of channel ban list" + + - When listing the active 'bans' for a given channel, + a server is required to send the list back using the + RPL_BANLIST and RPL_ENDOFBANLIST messages. A separate + RPL_BANLIST is sent for each active banid. After the + banids have been listed (or if none present) a + RPL_ENDOFBANLIST must be sent. + + 371 RPL_INFO + ":<string>" + 374 RPL_ENDOFINFO + ":End of /INFO list" + + - A server responding to an INFO message is required to + send all its 'info' in a series of RPL_INFO messages + with a RPL_ENDOFINFO reply to indicate the end of the + replies. + + 375 RPL_MOTDSTART + ":- <server> Message of the day - " + 372 RPL_MOTD + ":- <text>" + 376 RPL_ENDOFMOTD + ":End of /MOTD command" + + - When responding to the MOTD message and the MOTD file + is found, the file is displayed line by line, with + each line no longer than 80 characters, using + RPL_MOTD format replies. These should be surrounded + by a RPL_MOTDSTART (before the RPL_MOTDs) and an + RPL_ENDOFMOTD (after). + + 381 RPL_YOUREOPER + ":You are now an IRC operator" + + - RPL_YOUREOPER is sent back to a client which has + just successfully issued an OPER message and gained + operator status. + + 382 RPL_REHASHING + "<config file> :Rehashing" + + - If the REHASH option is used and an operator sends + a REHASH message, an RPL_REHASHING is sent back to + the operator. + + 391 RPL_TIME + + + +Oikarinen & Reed [Page 52] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + "<server> :<string showing server's local time>" + + - When replying to the TIME message, a server must send + the reply using the RPL_TIME format above. The string + showing the time need only contain the correct day and + time there. There is no further requirement for the + time string. + + 392 RPL_USERSSTART + ":UserID Terminal Host" + 393 RPL_USERS + ":%-8s %-9s %-8s" + 394 RPL_ENDOFUSERS + ":End of users" + 395 RPL_NOUSERS + ":Nobody logged in" + + - If the USERS message is handled by a server, the + replies RPL_USERSTART, RPL_USERS, RPL_ENDOFUSERS and + RPL_NOUSERS are used. RPL_USERSSTART must be sent + first, following by either a sequence of RPL_USERS + or a single RPL_NOUSER. Following this is + RPL_ENDOFUSERS. + + 200 RPL_TRACELINK + "Link <version & debug level> <destination> \ + <next server>" + 201 RPL_TRACECONNECTING + "Try. <class> <server>" + 202 RPL_TRACEHANDSHAKE + "H.S. <class> <server>" + 203 RPL_TRACEUNKNOWN + "???? <class> [<client IP address in dot form>]" + 204 RPL_TRACEOPERATOR + "Oper <class> <nick>" + 205 RPL_TRACEUSER + "User <class> <nick>" + 206 RPL_TRACESERVER + "Serv <class> <int>S <int>C <server> \ + <nick!user|*!*>@<host|server>" + 208 RPL_TRACENEWTYPE + "<newtype> 0 <client name>" + 261 RPL_TRACELOG + "File <logfile> <debug level>" + + - The RPL_TRACE* are all returned by the server in + response to the TRACE message. How many are + returned is dependent on the the TRACE message and + + + +Oikarinen & Reed [Page 53] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + whether it was sent by an operator or not. There + is no predefined order for which occurs first. + Replies RPL_TRACEUNKNOWN, RPL_TRACECONNECTING and + RPL_TRACEHANDSHAKE are all used for connections + which have not been fully established and are either + unknown, still attempting to connect or in the + process of completing the 'server handshake'. + RPL_TRACELINK is sent by any server which handles + a TRACE message and has to pass it on to another + server. The list of RPL_TRACELINKs sent in + response to a TRACE command traversing the IRC + network should reflect the actual connectivity of + the servers themselves along that path. + RPL_TRACENEWTYPE is to be used for any connection + which does not fit in the other categories but is + being displayed anyway. + + 211 RPL_STATSLINKINFO + "<linkname> <sendq> <sent messages> \ + <sent bytes> <received messages> \ + <received bytes> <time open>" + 212 RPL_STATSCOMMANDS + "<command> <count>" + 213 RPL_STATSCLINE + "C <host> * <name> <port> <class>" + 214 RPL_STATSNLINE + "N <host> * <name> <port> <class>" + 215 RPL_STATSILINE + "I <host> * <host> <port> <class>" + 216 RPL_STATSKLINE + "K <host> * <username> <port> <class>" + 218 RPL_STATSYLINE + "Y <class> <ping frequency> <connect \ + frequency> <max sendq>" + 219 RPL_ENDOFSTATS + "<stats letter> :End of /STATS report" + 241 RPL_STATSLLINE + "L <hostmask> * <servername> <maxdepth>" + 242 RPL_STATSUPTIME + ":Server Up %d days %d:%02d:%02d" + 243 RPL_STATSOLINE + "O <hostmask> * <name>" + 244 RPL_STATSHLINE + "H <hostmask> * <servername>" + + 221 RPL_UMODEIS + "<user mode string>" + + + + +Oikarinen & Reed [Page 54] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + - To answer a query about a client's own mode, + RPL_UMODEIS is sent back. + + 251 RPL_LUSERCLIENT + ":There are <integer> users and <integer> \ + invisible on <integer> servers" + 252 RPL_LUSEROP + "<integer> :operator(s) online" + 253 RPL_LUSERUNKNOWN + "<integer> :unknown connection(s)" + 254 RPL_LUSERCHANNELS + "<integer> :channels formed" + 255 RPL_LUSERME + ":I have <integer> clients and <integer> \ + servers" + + - In processing an LUSERS message, the server + sends a set of replies from RPL_LUSERCLIENT, + RPL_LUSEROP, RPL_USERUNKNOWN, + RPL_LUSERCHANNELS and RPL_LUSERME. When + replying, a server must send back + RPL_LUSERCLIENT and RPL_LUSERME. The other + replies are only sent back if a non-zero count + is found for them. + + 256 RPL_ADMINME + "<server> :Administrative info" + 257 RPL_ADMINLOC1 + ":<admin info>" + 258 RPL_ADMINLOC2 + ":<admin info>" + 259 RPL_ADMINEMAIL + ":<admin info>" + + - When replying to an ADMIN message, a server + is expected to use replies RLP_ADMINME + through to RPL_ADMINEMAIL and provide a text + message with each. For RPL_ADMINLOC1 a + description of what city, state and country + the server is in is expected, followed by + details of the university and department + (RPL_ADMINLOC2) and finally the administrative + contact for the server (an email address here + is required) in RPL_ADMINEMAIL. + + + + + + + +Oikarinen & Reed [Page 55] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +6.3 Reserved numerics. + + These numerics are not described above since they fall into one of + the following categories: + + 1. no longer in use; + + 2. reserved for future planned use; + + 3. in current use but are part of a non-generic 'feature' of + the current IRC server. + + 209 RPL_TRACECLASS 217 RPL_STATSQLINE + 231 RPL_SERVICEINFO 232 RPL_ENDOFSERVICES + 233 RPL_SERVICE 234 RPL_SERVLIST + 235 RPL_SERVLISTEND + 316 RPL_WHOISCHANOP 361 RPL_KILLDONE + 362 RPL_CLOSING 363 RPL_CLOSEEND + 373 RPL_INFOSTART 384 RPL_MYPORTIS + 466 ERR_YOUWILLBEBANNED 476 ERR_BADCHANMASK + 492 ERR_NOSERVICEHOST + +7. Client and server authentication + + Clients and servers are both subject to the same level of + authentication. For both, an IP number to hostname lookup (and + reverse check on this) is performed for all connections made to the + server. Both connections are then subject to a password check (if + there is a password set for that connection). These checks are + possible on all connections although the password check is only + commonly used with servers. + + An additional check that is becoming of more and more common is that + of the username responsible for making the connection. Finding the + username of the other end of the connection typically involves + connecting to an authentication server such as IDENT as described in + RFC 1413. + + Given that without passwords it is not easy to reliably determine who + is on the other end of a network connection, use of passwords is + strongly recommended on inter-server connections in addition to any + other measures such as using an ident server. + +8. Current implementations + + The only current implementation of this protocol is the IRC server, + version 2.8. Earlier versions may implement some or all of the + commands described by this document with NOTICE messages replacing + + + +Oikarinen & Reed [Page 56] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + many of the numeric replies. Unfortunately, due to backward + compatibility requirements, the implementation of some parts of this + document varies with what is laid out. On notable difference is: + + * recognition that any LF or CR anywhere in a message marks the + end of that message (instead of requiring CR-LF); + + The rest of this section deals with issues that are mostly of + importance to those who wish to implement a server but some parts + also apply directly to clients as well. + +8.1 Network protocol: TCP - why it is best used here. + + IRC has been implemented on top of TCP since TCP supplies a reliable + network protocol which is well suited to this scale of conferencing. + The use of multicast IP is an alternative, but it is not widely + available or supported at the present time. + +8.1.1 Support of Unix sockets + + Given that Unix domain sockets allow listen/connect operations, the + current implementation can be configured to listen and accept both + client and server connections on a Unix domain socket. These are + recognized as sockets where the hostname starts with a '/'. + + When providing any information about the connections on a Unix domain + socket, the server is required to supplant the actual hostname in + place of the pathname unless the actual socket name is being asked + for. + +8.2 Command Parsing + + To provide useful 'non-buffered' network IO for clients and servers, + each connection is given its own private 'input buffer' in which the + results of the most recent read and parsing are kept. A buffer size + of 512 bytes is used so as to hold 1 full message, although, this + will usually hold several commands. The private buffer is parsed + after every read operation for valid messages. When dealing with + multiple messages from one client in the buffer, care should be taken + in case one happens to cause the client to be 'removed'. + +8.3 Message delivery + + It is common to find network links saturated or hosts to which you + are sending data unable to send data. Although Unix typically + handles this through the TCP window and internal buffers, the server + often has large amounts of data to send (especially when a new + server-server link forms) and the small buffers provided in the + + + +Oikarinen & Reed [Page 57] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + kernel are not enough for the outgoing queue. To alleviate this + problem, a "send queue" is used as a FIFO queue for data to be sent. + A typical "send queue" may grow to 200 Kbytes on a large IRC network + with a slow network connection when a new server connects. + + When polling its connections, a server will first read and parse all + incoming data, queuing any data to be sent out. When all available + input is processed, the queued data is sent. This reduces the number + of write() system calls and helps TCP make bigger packets. + +8.4 Connection 'Liveness' + + To detect when a connection has died or become unresponsive, the + server must ping each of its connections that it doesn't get a + response from in a given amount of time. + + If a connection doesn't respond in time, its connection is closed + using the appropriate procedures. A connection is also dropped if + its sendq grows beyond the maximum allowed, because it is better to + close a slow connection than have a server process block. + +8.5 Establishing a server to client connection + + Upon connecting to an IRC server, a client is sent the MOTD (if + present) as well as the current user/server count (as per the LUSER + command). The server is also required to give an unambiguous message + to the client which states its name and version as well as any other + introductory messages which may be deemed appropriate. + + After dealing with this, the server must then send out the new user's + nickname and other information as supplied by itself (USER command) + and as the server could discover (from DNS/authentication servers). + The server must send this information out with NICK first followed by + USER. + +8.6 Establishing a server-server connection. + + The process of establishing of a server-to-server connection is + fraught with danger since there are many possible areas where + problems can occur - the least of which are race conditions. + + After a server has received a connection following by a PASS/SERVER + pair which were recognised as being valid, the server should then + reply with its own PASS/SERVER information for that connection as + well as all of the other state information it knows about as + described below. + + When the initiating server receives a PASS/SERVER pair, it too then + + + +Oikarinen & Reed [Page 58] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + checks that the server responding is authenticated properly before + accepting the connection to be that server. + +8.6.1 Server exchange of state information when connecting + + The order of state information being exchanged between servers is + essential. The required order is as follows: + + * all known other servers; + + * all known user information; + + * all known channel information. + + Information regarding servers is sent via extra SERVER messages, user + information with NICK/USER/MODE/JOIN messages and channels with MODE + messages. + + NOTE: channel topics are *NOT* exchanged here because the TOPIC + command overwrites any old topic information, so at best, the two + sides of the connection would exchange topics. + + By passing the state information about servers first, any collisions + with servers that already exist occur before nickname collisions due + to a second server introducing a particular nickname. Due to the IRC + network only being able to exist as an acyclic graph, it may be + possible that the network has already reconnected in another + location, the place where the collision occurs indicating where the + net needs to split. + +8.7 Terminating server-client connections + + When a client connection closes, a QUIT message is generated on + behalf of the client by the server to which the client connected. No + other message is to be generated or used. + +8.8 Terminating server-server connections + + If a server-server connection is closed, either via a remotely + generated SQUIT or 'natural' causes, the rest of the connected IRC + network must have its information updated with by the server which + detected the closure. The server then sends a list of SQUITs (one + for each server behind that connection) and a list of QUITs (again, + one for each client behind that connection). + + + + + + + +Oikarinen & Reed [Page 59] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +8.9 Tracking nickname changes + + All IRC servers are required to keep a history of recent nickname + changes. This is required to allow the server to have a chance of + keeping in touch of things when nick-change race conditions occur + with commands which manipulate them. Commands which must trace nick + changes are: + + * KILL (the nick being killed) + + * MODE (+/- o,v) + + * KICK (the nick being kicked) + + No other commands are to have nick changes checked for. + + In the above cases, the server is required to first check for the + existence of the nickname, then check its history to see who that + nick currently belongs to (if anyone!). This reduces the chances of + race conditions but they can still occur with the server ending up + affecting the wrong client. When performing a change trace for an + above command it is recommended that a time range be given and + entries which are too old ignored. + + For a reasonable history, a server should be able to keep previous + nickname for every client it knows about if they all decided to + change. This size is limited by other factors (such as memory, etc). + +8.10 Flood control of clients + + With a large network of interconnected IRC servers, it is quite easy + for any single client attached to the network to supply a continuous + stream of messages that result in not only flooding the network, but + also degrading the level of service provided to others. Rather than + require every 'victim' to be provide their own protection, flood + protection was written into the server and is applied to all clients + except services. The current algorithm is as follows: + + * check to see if client's `message timer' is less than + current time (set to be equal if it is); + + * read any data present from the client; + + * while the timer is less than ten seconds ahead of the current + time, parse any present messages and penalize the client by + 2 seconds for each message; + + which in essence means that the client may send 1 message every 2 + + + +Oikarinen & Reed [Page 60] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + seconds without being adversely affected. + +8.11 Non-blocking lookups + + In a real-time environment, it is essential that a server process do + as little waiting as possible so that all the clients are serviced + fairly. Obviously this requires non-blocking IO on all network + read/write operations. For normal server connections, this was not + difficult, but there are other support operations that may cause the + server to block (such as disk reads). Where possible, such activity + should be performed with a short timeout. + +8.11.1 Hostname (DNS) lookups + + Using the standard resolver libraries from Berkeley and others has + meant large delays in some cases where replies have timed out. To + avoid this, a separate set of DNS routines were written which were + setup for non-blocking IO operations and then polled from within the + main server IO loop. + +8.11.2 Username (Ident) lookups + + Although there are numerous ident libraries for use and inclusion + into other programs, these caused problems since they operated in a + synchronous manner and resulted in frequent delays. Again the + solution was to write a set of routines which would cooperate with + the rest of the server and work using non-blocking IO. + +8.12 Configuration File + + To provide a flexible way of setting up and running the server, it is + recommended that a configuration file be used which contains + instructions to the server on the following: + + * which hosts to accept client connections from; + + * which hosts to allow to connect as servers; + + * which hosts to connect to (both actively and + passively); + + * information about where the server is (university, + city/state, company are examples of this); + + * who is responsible for the server and an email address + at which they can be contacted; + + * hostnames and passwords for clients which wish to be given + + + +Oikarinen & Reed [Page 61] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + access to restricted operator commands. + + In specifying hostnames, both domain names and use of the 'dot' + notation (127.0.0.1) should both be accepted. It must be possible to + specify the password to be used/accepted for all outgoing and + incoming connections (although the only outgoing connections are + those to other servers). + + The above list is the minimum requirement for any server which wishes + to make a connection with another server. Other items which may be + of use are: + + * specifying which servers other server may introduce; + + * how deep a server branch is allowed to become; + + * hours during which clients may connect. + +8.12.1 Allowing clients to connect + + A server should use some sort of 'access control list' (either in the + configuration file or elsewhere) that is read at startup and used to + decide what hosts clients may use to connect to it. + + Both 'deny' and 'allow' should be implemented to provide the required + flexibility for host access control. + +8.12.2 Operators + + The granting of operator privileges to a disruptive person can have + dire consequences for the well-being of the IRC net in general due to + the powers given to them. Thus, the acquisition of such powers + should not be very easy. The current setup requires two 'passwords' + to be used although one of them is usually easy guessed. Storage of + oper passwords in configuration files is preferable to hard coding + them in and should be stored in a crypted format (ie using crypt(3) + from Unix) to prevent easy theft. + +8.12.3 Allowing servers to connect + + The interconnection of server is not a trivial matter: a bad + connection can have a large impact on the usefulness of IRC. Thus, + each server should have a list of servers to which it may connect and + which servers may connect to it. Under no circumstances should a + server allow an arbitrary host to connect as a server. In addition + to which servers may and may not connect, the configuration file + should also store the password and other characteristics of that + link. + + + +Oikarinen & Reed [Page 62] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +8.12.4 Administrivia + + To provide accurate and valid replies to the ADMIN command (see + section 4.3.7), the server should find the relevant details in the + configuration. + +8.13 Channel membership + + The current server allows any registered local user to join upto 10 + different channels. There is no limit imposed on non-local users so + that the server remains (reasonably) consistant with all others on a + channel membership basis + +9. Current problems + + There are a number of recognized problems with this protocol, all of + which hope to be solved sometime in the near future during its + rewrite. Currently, work is underway to find working solutions to + these problems. + +9.1 Scalability + + It is widely recognized that this protocol does not scale + sufficiently well when used in a large arena. The main problem comes + from the requirement that all servers know about all other servers + and users and that information regarding them be updated as soon as + it changes. It is also desirable to keep the number of servers low + so that the path length between any two points is kept minimal and + the spanning tree as strongly branched as possible. + +9.2 Labels + + The current IRC protocol has 3 types of labels: the nickname, the + channel name and the server name. Each of the three types has its + own domain and no duplicates are allowed inside that domain. + Currently, it is possible for users to pick the label for any of the + three, resulting in collisions. It is widely recognized that this + needs reworking, with a plan for unique names for channels and nicks + that don't collide being desirable as well as a solution allowing a + cyclic tree. + +9.2.1 Nicknames + + The idea of the nickname on IRC is very convenient for users to use + when talking to each other outside of a channel, but there is only a + finite nickname space and being what they are, its not uncommon for + several people to want to use the same nick. If a nickname is chosen + by two people using this protocol, either one will not succeed or + + + +Oikarinen & Reed [Page 63] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + + both will removed by use of KILL (4.6.1). + +9.2.2 Channels + + The current channel layout requires that all servers know about all + channels, their inhabitants and properties. Besides not scaling + well, the issue of privacy is also a concern. A collision of + channels is treated as an inclusive event (both people who create the + new channel are considered to be members of it) rather than an + exclusive one such as used to solve nickname collisions. + +9.2.3 Servers + + Although the number of servers is usually small relative to the + number of users and channels, they two currently required to be known + globally, either each one separately or hidden behind a mask. + +9.3 Algorithms + + In some places within the server code, it has not been possible to + avoid N^2 algorithms such as checking the channel list of a set + of clients. + + In current server versions, there are no database consistency checks, + each server assumes that a neighbouring server is correct. This + opens the door to large problems if a connecting server is buggy or + otherwise tries to introduce contradictions to the existing net. + + Currently, because of the lack of unique internal and global labels, + there are a multitude of race conditions that exist. These race + conditions generally arise from the problem of it taking time for + messages to traverse and effect the IRC network. Even by changing to + unique labels, there are problems with channel-related commands being + disrupted. + +10. Current support and availability + + Mailing lists for IRC related discussion: + Future protocol: ircd-three-request@eff.org + General discussion: operlist-request@eff.org + + Software implemenations + cs.bu.edu:/irc + nic.funet.fi:/pub/irc + coombs.anu.edu.au:/pub/irc + + Newsgroup: alt.irc + + + + +Oikarinen & Reed [Page 64] + +RFC 1459 Internet Relay Chat Protocol May 1993 + + +Security Considerations + + Security issues are discussed in sections 4.1, 4.1.1, 4.1.3, 5.5, and + 7. + +12. Authors' Addresses + + Jarkko Oikarinen + Tuirantie 17 as 9 + 90500 OULU + FINLAND + + Email: jto@tolsun.oulu.fi + + + Darren Reed + 4 Pateman Street + Watsonia, Victoria 3087 + Australia + + Email: avalon@coombs.anu.edu.au + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Oikarinen & Reed [Page 65] +
\ No newline at end of file |