RFC 1459
Internet Relay Chat Protocol
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
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
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
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 ]
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
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
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
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
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> ::= '-' | '[' | ']' | '\' | '`' | '^' | '{' | '}'
<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.
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.
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
IRC, nearly all messages originating from a server are broadcast to all other connected servers.
(page 13 continued on part 2)
