RFC 2813

Network Working Group                                           C. Kalt

Request for Comments: 2813                                   April 2000

Updates: 1459

Category: Informational

                  Internet Relay Chat: Server Protocol

Status of this Memo

   This memo provides information for the Internet community.  It does

   not specify an Internet standard of any kind.  Distribution of this

   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.


   While based on the client-server model, the IRC (Internet Relay Chat)

   protocol allows servers to connect to each other effectively forming

   a network.

   This document defines the protocol used by servers to talk to each

   other.  It was originally a superset of the client protocol but has

   evolved differently.

   First formally documented in May 1993 as part of RFC 1459 [IRC], most

   of the changes brought since then can be found in this document as

   development was focused on making the protocol scale better.  Better

   scalability has allowed existing world-wide networks to keep growing

   and reach sizes which defy the old specification.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

Table of Contents

   1.  Introduction ...............................................   3

   2.  Global database ............................................   3

      2.1  Servers ................................................   3

      2.2  Clients ................................................   4

         2.2.1  Users .............................................   4

         2.2.2  Services ..........................................   4

      2.3  Channels ...............................................   4

   3.  The IRC Server Specification ...............................   5

      3.1  Overview ...............................................   5

      3.2  Character codes ........................................   5

      3.3  Messages ...............................................   5

         3.3.1  Message format in Augmented BNF ...................   6

      3.4  Numeric replies ........................................   7

   4.  Message Details ............................................   7

      4.1  Connection Registration ................................   8

         4.1.1  Password message ..................................   8

         4.1.2  Server message ....................................   9

         4.1.3  Nick ..............................................  10

         4.1.4  Service message ...................................  11

         4.1.5  Quit ..............................................  12

         4.1.6  Server quit message ...............................  13

      4.2  Channel operations .....................................  14

         4.2.1  Join message ......................................  14

         4.2.2  Njoin message .....................................  15

         4.2.3  Mode message ......................................  16

   5.  Implementation details  ....................................  16

      5.1  Connection 'Liveness' ..................................  16

      5.2  Accepting a client to server connection ................  16

         5.2.1  Users .............................................  16

         5.2.2  Services ..........................................  17

      5.3  Establishing a server-server connection. ...............  17

         5.3.1  Link options ......................................  17

    Compressed server to server links ............  18

    Anti abuse protections .......................  18

         5.3.2  State information exchange when connecting ........  18

      5.4  Terminating server-client connections ..................  19

      5.5  Terminating server-server connections ..................  19

      5.6  Tracking nickname changes ..............................  19

      5.7  Tracking recently used nicknames .......................  20

      5.8  Flood control of clients ...............................  20

      5.9  Non-blocking lookups ...................................  21

         5.9.1  Hostname (DNS) lookups ............................  21

         5.9.2  Username (Ident) lookups ..........................  21

   6.  Current problems ...........................................  21

      6.1  Scalability ............................................  21

      6.2  Labels .................................................  22

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

         6.2.1  Nicknames .........................................  22

         6.2.2  Channels ..........................................  22

         6.2.3  Servers ...........................................  22

      6.3  Algorithms .............................................  22

   7.  Security Considerations ....................................  23

      7.1  Authentication .........................................  23

      7.2  Integrity ..............................................  23

   8.  Current support and availability ...........................  24

   9.  Acknowledgements ...........................................  24

   10.  References ................................................  24

   11.  Author's Address ..........................................  25

   12. Full Copyright Statement ...................................  26

1. Introduction

   This document is intended for people working on implementing an IRC

   server but will also be useful to anyone implementing an IRC service.

   Servers provide the three basic services required for realtime

   conferencing defined by the "Internet Relay Chat: Architecture"

   [IRC-ARCH]: client locator (via the client protocol [IRC-CLIENT]),

   message relaying (via the server protocol defined in this document)

   and channel hosting and management (following specific rules [IRC-


2. Global database

   Although the IRC Protocol defines a fairly distributed model, each

   server maintains a "global state database" about the whole IRC

   network.  This database is, in theory, identical on all servers.

2.1 Servers

   Servers are uniquely identified by their name which has a maximum

   length of sixty three (63) characters.  See the protocol grammar

   rules (section 3.3.1) for what may and may not be used in a server


   Each server is typically known by all other servers, however it is

   possible to define a "hostmask" to group servers together according

   to their name.  Inside the hostmasked area, all the servers have a

   name which matches the hostmask, and any other server with a name

   matching the hostmask SHALL NOT be connected to the IRC network

   outside the hostmasked area.  Servers which are outside the area have

   no knowledge of the individual servers present inside the area,

   instead they are presented with a virtual server which has the

   hostmask for name.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

2.2 Clients

   For each client, all servers MUST have the following information: a

   netwide unique identifier (whose format depends on the type of

   client) and the server to which the client is connected.

2.2.1 Users

   Each user is distinguished from other users by a unique nickname

   having a maximum length of nine (9) characters.  See the protocol

   grammar rules (section 3.3.1) 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 users: the name of the host that the

   user is running on, the username of the user on that host, and the

   server to which the client is connected.

2.2.2 Services

   Each service is distinguished from other services by a service name

   composed of a nickname and a server name.  The nickname has a maximum

   length of nine (9) characters.  See the protocol grammar rules

   (section 3.3.1) for what may and may not be used in a nickname.  The

   server name used to compose the service name is the name of the

   server to which the service is connected.  In addition to this

   service name all servers MUST know the service type.

   Services differ from users by the format of their identifier, but

   more importantly services and users don't have the same type of

   access to the server: services can request part or all of the global

   state information that a server maintains, but have a more restricted

   set of commands available to them (See "IRC Client Protocol" [IRC-

   CLIENT] for details on which) and are not allowed to join channels.

   Finally services are not usually subject to the "Flood control"

   mechanism described in section 5.8.

2.3 Channels

   Alike services, channels have a scope [IRC-CHAN] and are not

   necessarily known to all servers.  When a channel existence is known

   to a server, the server MUST keep track of the channel members, as

   well as the channel modes.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

3. The IRC Server Specification

3.1 Overview

   The protocol as described herein is for use with server to server

   connections.  For client to server connections, see the IRC Client

   Protocol specification.

   There are, however, more restrictions on client connections (which

   are considered to be untrustworthy) than on server connections.

3.2 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 US-ASCII terminal and a

   telnet connection.

   Because of IRC's Scandinavian 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, or channel names.

3.3 Messages

   Servers and clients send each other messages which may or may not

   generate a reply.  Most communication between servers do not generate

   any reply, as servers mostly perform routing tasks for the clients.

   Each IRC message may consist of up to three main parts: the prefix

   (OPTIONAL), the command, and the command parameters (maximum of

   fifteen (15)).  The prefix, command, and all parameters are separated

   by one ASCII space character (0x20) each.

   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 a prefix when sending a message

   from themselves; if they use one, the only valid prefix is the

   registered nickname associated with the client.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   When a server receives a message, it MUST identify its source using

   the (eventually assumed) prefix.  If the prefix cannot be found in

   the server's internal database, it MUST be discarded, and if the

   prefix indicates the message comes from an (unknown) server, the link

   from which the message was received MUST be dropped.  Dropping a link

   in such circumstances is a little excessive but necessary to maintain

   the integrity of the network and to prevent future problems.  Another

   common error condition is that the prefix found in the server's

   internal database identifies a different source (typically a source

   registered from a different link than from which the message

   arrived).  If the message was received from a server link and the

   prefix identifies a client, a KILL message MUST be issued for the

   client and sent to all servers.  In other cases, the link from which

   the message arrived SHOULD be dropped for clients, and MUST be

   dropped for servers.  In all cases, the message MUST be discarded.

   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 5 for more details about

   current implementations.

3.3.1 Message format in Augmented 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 (<params>).

   The Augmented BNF representation for this is found in "IRC Client

   Protocol" [IRC-CLIENT].

   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.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

3.4 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 "IRC Client Protocol" [IRC-CLIENT].

4. Message Details

   All the messages recognized by the IRC server and client are

   described in the IRC Client Protocol specification.

   Where the reply ERR_NOSUCHSERVER is returned, it means that the

   target of the message could not be found.  The server MUST NOT send

   any other replies after this error 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 follow from incorrect command, a destination which is otherwise

   unknown to the server (server, client 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.

   The message details for client to server communication are described

   in the "IRC Client Protocol" [IRC-CLIENT].  Some sections in the

   following pages apply to some of these messages, they are additions

   to the message specifications which are only relevant to server to

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   server communication, or to the server implementation.  The messages

   which are introduced here are only used for server to server


4.1 Connection Registration

   The commands described here are used to register a connection with

   another IRC server.

4.1.1 Password message

      Command: PASS

   Parameters: <password> <version> <flags> [<options>]

   The PASS command is used to set a 'connection password'.  The

   password MUST be set before any attempt to register the connection is

   made.  Currently this means that servers MUST send a PASS command

   before any SERVER command.  Only one (1) PASS command SHALL be

   accepted from a connection.

   The last three (3) parameters MUST be ignored if received from a

   client (e.g. a user or a service).  They are only relevant when

   received from a server.

   The <version> parameter is a string of at least four (4) characters,

   and up to fourteen (14) characters.  The first four (4) characters

   MUST be digits and indicate the protocol version known by the server

   issuing the message.  The protocol described by this document is

   version 2.10 which is encoded as "0210".  The remaining OPTIONAL

   characters are implementation dependent and should describe the

   software version number.

   The <flags> parameter is a string of up to one hundred (100)

   characters.  It is composed of two substrings separated by the

   character "|" (%x7C).  If present, the first substring MUST be the

   name of the implementation.  The reference implementation (See

   Section 8, "Current support and availability") uses the string "IRC".

   If a different implementation is written, which needs an identifier,

   then that identifier should be registered through publication of an

   RFC. The second substring is implementation dependent.  Both

   substrings are OPTIONAL, but the character "|" is REQUIRED.  The

   character "|" MUST NOT appear in either substring.

   Finally, the last parameter, <options>, is used for link options.

   The only options defined by the protocol are link compression (using

   the character "Z"), and an abuse protection flag (using the character

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   "P").  See sections (Compressed server to server links) and (Anti abuse protections) respectively for more information on

   these options.

   Numeric Replies:



        PASS moresecretpassword 0210010000 IRC|aBgH$ Z

4.1.2 Server message

      Command: SERVER

   Parameters: <servername> <hopcount> <token> <info>

   The SERVER command is used to register a new server. A new connection

   introduces itself as a server to its peer.  This message is also used

   to pass server data over whole net.  When a new server is connected

   to net, information about it MUST be broadcasted to the whole


   The <info> parameter may contain space characters.

   <hopcount> is used to give all servers some internal information on

   how far away each server is.  Local peers have a value of 0, and each

   passed server increments the value.  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 <token> parameter is an unsigned number used by servers as an

   identifier.  This identifier is subsequently used to reference a

   server in the NICK and SERVICE messages sent between servers.  Server

   tokens only have a meaning for the point-to-point peering they are

   used and MUST be unique for that connection.  They are not global.

   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


   Most errors that occur with the receipt of a SERVER command result in

   the connection being terminated by the destination host (target

   SERVER).  Because of the severity of such event, error replies are

   usually sent using the "ERROR" command rather than a numeric.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   If a SERVER message is parsed and it attempts to introduce a server

   which is already known to the receiving server, the connection, from

   which that message arrived, MUST be closed (following the correct

   procedures), since a duplicate route to a server has been formed and

   the acyclic nature of the IRC tree breaks.  In some conditions, the

   connection from which the already known server has registered MAY be

   closed instead.  It should be noted that this kind of error can also

   be the result of a second running server, problem which cannot be

   fixed within the protocol and typically requires human intervention.

   This type of problem is particularly insidious, as it can quite

   easily result in part of the IRC network to be isolated, with one of

   the two servers connected to each partition therefore making it

   impossible for the two parts to unite.

   Numeric Replies:



   SERVER test.oulu.fi 1 1 :Experimental server ; New server

                                   test.oulu.fi introducing itself and

                                   attempting to register.

   :tolsun.oulu.fi SERVER csd.bu.edu 5 34 :BU Central Server ; Server

                                   tolsun.oulu.fi is our uplink for

                                   csd.bu.edu which is 5 hops away.  The

                                   token "34" will be used by

                                   tolsun.oulu.fi when introducing new

                                   users or services connected to


4.1.3 Nick

      Command: NICK

   Parameters: <nickname> <hopcount> <username> <host> <servertoken>

               <umode> <realname>

   This form of the NICK message MUST NOT be allowed from user

   connections. However, it MUST be used instead of the NICK/USER pair

   to notify other servers of new users joining the IRC network.

   This message is really the combination of three distinct messages:


   The <hopcount> parameter is used by servers to indicate how far away

   a user is from its home server.  A local connection has a hopcount of

   0.  The hopcount value is incremented by each passed server.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   The <servertoken> parameter replaces the <servername> parameter of

   the USER (See section 4.1.2 for more information on server tokens).


   NICK syrk 5 kalt millennium.stealth.net 34 +i :Christophe Kalt ; New

                                   user with nickname "syrk", username

                                   "kalt", connected from host

                                   "millennium.stealth.net" to server

                                   "34" ("csd.bu.edu" according to the

                                   previous example).

   :krys NICK syrk                 ; The other form of the NICK message,

                                   as defined in "IRC Client Protocol"

                                   [IRC-CLIENT] and used between

                                   servers: krys changed his nickname to


4.1.4 Service message

      Command: SERVICE

   Parameters: <servicename> <servertoken> <distribution> <type>

                <hopcount> <info>

   The SERVICE command is used to introduce a new service.  This form of

   the SERVICE message SHOULD NOT be allowed from client (unregistered,

   or registered) connections.  However, it MUST be used between servers

   to notify other servers of new services joining the IRC network.

   The <servertoken> is used to identify the server to which the service

   is connected.  (See section 4.1.2 for more information on server


   The <hopcount> parameter is used by servers to indicate how far away

   a service is from its home server.  A local connection has a hopcount

   of 0.  The hopcount value is incremented by each passed server.

   The <distribution> parameter is used to specify the visibility of a

   service.  The service may only be known to servers which have a name

   matching the distribution.  For a matching server to have knowledge

   of the service, the network path between that server and the server

   to which the service is connected MUST be composed of servers whose

   names all match the mask.  Plain "*" is used when no restriction is


   The <type> parameter is currently reserved for future usage.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   Numeric Replies:



           RPL_YOURESERVICE                RPL_YOURHOST



SERVICE dict@irc.fr 9 *.fr 0 1 :French Dictionary r" registered on

                                   server "9" is being announced to

                                   another server.  This service will

                                   only be available on servers whose

                                   name matches "*.fr".

4.1.5 Quit

      Command: QUIT

   Parameters: [<Quit Message>]

   A client session ends 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 or service name.

   When "netsplit" (See Section 4.1.6) occur, the "Quit Message" 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 either that of the server which has become

   disconnected or that of the server to which the leaving client was


      <Quit Message> =  ":" servername SPACE servername

   Because the "Quit Message" has a special meaning for "netsplits",

   servers SHOULD NOT allow a client to use a <Quit Message> in the

   format described above.

   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.  Typically, this is done by reporting a system specific


   Numeric Replies:


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RFC 2813          Internet Relay Chat: Server Protocol        April 2000


   :WiZ QUIT :Gone to have lunch   ; Preferred message format.

4.1.6 Server quit message

      Command: SQUIT

   Parameters: <server> <comment>

   The SQUIT message has two distinct uses.

   The first one (described in "Internet Relay Chat: Client Protocol"

   [IRC-CLIENT]) allows operators to break a local or remote server

   link.  This form of the message is also eventually used by servers to

   break a remote server link.

   The second use of this message is needed to inform other servers when

   a "network split" (also known as "netsplit") occurs, in other words

   to inform other servers 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 name of the other server as

   the server parameter, which then closes its connection to the

   quitting server.

   The <comment> is filled in by servers which SHOULD place an error or

   similar message here.

   Both of the servers which are on either side of the connection being

   closed are REQUIRED to send out a SQUIT message (to all its other

   server connections) for all other servers which are considered to be

   behind that link.

   Similarly, a QUIT message MAY be sent to the other still connected

   servers on behalf of all clients behind that quitting 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.  Messages to

   channel members are generated by each client's local server.

   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


   When a client is removed as the result of a SQUIT message, the server

   SHOULD add the nickname to the list of temporarily unavailable

   nicknames in an attempt to prevent future nickname collisions. See

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   section 5.7 (Tracking recently used nicknames) for more information

   on this procedure.

   Numeric replies:




   SQUIT tolsun.oulu.fi :Bad Link ?  ; the server link tolson.oulu.fi

                                   has been terminated because of "Bad


   :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 users).  In

   implementing these, a number of race conditions are inevitable when

   users 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>[ %x7 <modes> ]

               *( "," <channel>[ %x7 <modes> ] )

   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 local server the client is connected to; all

   other servers automatically add the user to the channel when the

   command is received from other servers.

   Optionally, the user status (channel modes 'O', 'o', and 'v') on the

   channel may be appended to the channel name using a control G (^G or

   ASCII 7) as separator.  Such data MUST be ignored if the message

   wasn't received from a server.  This format MUST NOT be sent to

   clients, it can only be used between servers and SHOULD be avoided.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   The JOIN command MUST 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 and NOTICE messages to the channel.

   Numeric Replies:








   :WiZ JOIN #Twilight_zone        ; JOIN message from WiZ

4.2.2 Njoin message

      Command: NJOIN

   Parameters: <channel> [ "@@" / "@" ] [ "+" ] <nickname>

                         *( "," [ "@@" / "@" ] [ "+" ] <nickname> )

   The NJOIN message is used between servers only.  If such a message is

   received from a client, it MUST be ignored.  It is used when two

   servers connect to each other to exchange the list of channel members

   for each channel.

   Even though the same function can be performed by using a succession

   of JOIN, this message SHOULD be used instead as it is more efficient.

   The prefix "@@" indicates that the user is the "channel creator", the

   character "@" alone indicates a "channel operator", and the character

   '+' indicates that the user has the voice privilege.

   Numeric Replies:




   :ircd.stealth.net NJOIN #Twilight_zone :@WiZ,+syrk,avalon ; NJOIN

                                   message from ircd.stealth.net

                                   announcing users joining the

                                   #Twilight_zone channel: WiZ with

                                   channel operator status, syrk with

                                   voice privilege and avalon with no


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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

4.2.3 Mode message

   The MODE message is a dual-purpose command in IRC.  It allows both

   usernames and channels to have their mode changed.

   When parsing MODE messages, it is RECOMMENDED that the entire message

   be parsed first, and then the changes which resulted passed on.

   It is REQUIRED that servers are able to change channel modes so that

   "channel creator" and "channel operators" may be created.

5. Implementation details

   A the time of writing, the only current implementation of this

   protocol is the IRC server, version 2.10. Earlier versions may

   implement some or all of the commands described by this document with

   NOTICE messages replacing 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.  One

   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.

5.1 Connection 'Liveness'

   To detect when a connection has died or become unresponsive, the

   server MUST poll each of its connections.  The PING command (See "IRC

   Client Protocol" [IRC-CLIENT]) is used if the server doesn't get a

   response from its peer in a given amount of time.

   If a connection doesn't respond in time, its connection is closed

   using the appropriate procedures.

5.2 Accepting a client to server connection

5.2.1 Users

   When a server successfully registers a new user connection, it is

   REQUIRED to send to the user unambiguous messages stating: the user

   identifiers upon which it was registered (RPL_WELCOME), the server

   name and version (RPL_YOURHOST), the server birth information

   (RPL_CREATED), available user and channel modes (RPL_MYINFO), and it

   MAY send any introductory messages which may be deemed appropriate.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   In particular the server SHALL send the current user/service/server

   count (as per the LUSER reply) and finally the MOTD (if any, as per

   the MOTD reply).

   After dealing with registration, the server MUST then send out to

   other servers the new user's nickname (NICK message), other

   information as supplied by itself (USER message) and as the server

   could discover (from DNS servers).  The server MUST NOT send this

   information out with a pair of NICK and USER messages as defined in

   "IRC Client Protocol" [IRC-CLIENT], but MUST instead take advantage

   of the extended NICK message defined in section 4.1.3.

5.2.2 Services

   Upon successfully registering a new service connection, the server is

   subject to the same kind of REQUIREMENTS as for a user.  Services

   being somewhat different, only the following replies are sent:


   After dealing with this, the server MUST then send out to other

   servers (SERVICE message) the new service's nickname and other

   information as supplied by the service (SERVICE message) and as the

   server could discover (from DNS servers).

5.3 Establishing a server-server connection.

   The process of establishing 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 recognized 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

   checks that the server responding is authenticated properly before

   accepting the connection to be that server.

5.3.1 Link options

   Server links are based on a common protocol (defined by this

   document) but a particular link MAY set specific options using the

   PASS message (See Section 4.1.1).

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000 Compressed server to server links

   If a server wishes to establish a compressed link with its peer, it

   MUST set the 'Z' flag in the options parameter to the PASS message.

   If both servers request compression and both servers are able to

   initialize the two compressed streams, then the remainder of the

   communication is to be compressed.  If any server fails to initialize

   the stream, it will send an uncompressed ERROR message to its peer

   and close the connection.

   The data format used for the compression is described by RFC 1950

   [ZLIB], RFC 1951 [DEFLATE] and RFC 1952 [GZIP]. Anti abuse protections

   Most servers implement various kinds of protections against possible

   abusive behaviours from non trusted parties (typically users).  On

   some networks, such protections are indispensable, on others they are

   superfluous.  To require that all servers implement and enable such

   features on a particular network, the 'P' flag is used when two

   servers connect.  If this flag is present, it means that the server

   protections are enabled, and that the server REQUIRES all its server

   links to enable them as well.

   Commonly found protections are described in sections 5.7 (Tracking

   recently used nicknames) and 5.8 (Flood control of clients).

5.3.2 State information exchange when connecting

   The order of state information being exchanged between servers is

   essential.  The REQUIRED order is as follows:

           * all known servers;

           * all known client information;

           * all known channel information.

   Information regarding servers is sent via extra SERVER messages,

   client information with NICK and SERVICE messages and channels with

   NJOIN/MODE messages.

   NOTE: channel topics SHOULD NOT be exchanged here because the TOPIC

   command overwrites any old topic information, so at best, the two

   sides of the connection would exchange topics.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   By passing the state information about servers first, any collisions

   with servers that already exist occur before nickname collisions

   caused by 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.  In this event, the place where the server collision occurs

   indicates where the net needs to split.

5.4 Terminating server-client connections

   When a client connection unexpectedly closes, a QUIT message is

   generated on behalf of the client by the server to which the client

   was connected.  No other message is to be generated or used.

5.5 Terminating server-server connections

   If a server-server connection is closed, either via a SQUIT command

   or "natural" causes, the rest of the connected IRC network MUST have

   its information updated by the server which detected the closure.

   The terminating server then sends a list of SQUITs (one for each

   server behind that connection).  (See Section 4.1.6 (SQUIT)).

5.6 Tracking nickname changes

   All IRC servers are REQUIRED to keep a history of recent nickname

   changes.  This is important to allow the server to have a chance of

   keeping in touch of things when nick-change race conditions occur

   with commands manipulating them.  Messages which MUST trace nick

   changes are:

           * KILL (the nick being disconnected)

           * MODE (+/- o,v on channels)

           * KICK (the nick being removed from channel)

      No other commands need to check nick changes.

   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 now 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.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   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).

5.7 Tracking recently used nicknames

   This mechanism is commonly known as "Nickname Delay", it has been

   proven to significantly reduce the number of nickname collisions

   resulting from "network splits"/reconnections as well as abuse.

   In addition of keeping track of nickname changes, servers SHOULD keep

   track of nicknames which were recently used and were released as the

   result of a "network split" or a KILL message.  These nicknames are

   then unavailable to the server local clients and cannot be re-used

   (even though they are not currently in use) for a certain period of


   The duration for which a nickname remains unavailable SHOULD be set

   considering many factors among which are the size (user wise) of the

   IRC network, and the usual duration of "network splits".  It SHOULD

   be uniform on all servers for a given IRC network.

5.8 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 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 (10) seconds ahead of the current

     time, parse any present messages and penalize the client by two (2)

     seconds for each message;

   * additional penalties MAY be used for specific commands which

     generate a lot of traffic across the network.

   This in essence means that the client may send one (1) message every

   two (2) seconds without being adversely affected.  Services MAY also

   be subject to this mechanism.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

5.9 Non-blocking lookups

   In a real-time environment, it is essential that a server process

   does 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.

5.9.1 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 for the

   current implementation.  Routines were setup for non-blocking IO

   operations with local cache, and then polled from within the main

   server IO loop.

5.9.2 Username (Ident) lookups

   Although there are numerous ident libraries (implementing the

   "Identification Protocol" [IDENT]) 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.

6. Current problems

   There are a number of recognized problems with this protocol, all of

   which are hoped to be solved sometime in the near future during its

   rewrite.  Currently, work is underway to find working solutions to

   these problems.

6.1 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 clients 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.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

6.2 Labels

   The current IRC protocol has 4 types of labels: the nickname, the

   channel name, the server name and the service name.  Each of the four

   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 first three, resulting in collisions.  It is widely

   recognized that this needs reworking, with a plan for unique names

   for nicks that don't collide being desirable as well as a solution

   allowing a cyclic tree.

6.2.1 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, it's 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

   both will be removed by use of KILL (See Section 3.7.1 of "IRC Client

   Protocol" [IRC-CLIENT]).

6.2.2 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 (people from both nets on

   channel with common name are considered to be members of it) rather

   than an exclusive one such as used to solve nickname collisions.

   This protocol defines "Safe Channels" which are very unlikely to be

   the subject of a channel collision.  Other channel types are kept for

   backward compatibility.

6.2.3 Servers

   Although the number of servers is usually small relative to the

   number of users and channels, they too are currently REQUIRED to be

   known globally, either each one separately or hidden behind a mask.

6.3 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


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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   In current server versions, there are only few database consistency

   checks, most of the time 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


7. Security Considerations

7.1 Authentication

   Servers only have two means of authenticating incoming connections:

   plain text password, and DNS lookups.  While these methods are weak

   and widely recognized as unsafe, their combination has proven to be

   sufficient in the past:

    * public networks typically allow user connections with only few

      restrictions, without requiring accurate authentication.

    * private networks which operate in a controlled environment often

      use home-grown authentication mechanisms not available on the

      internet: reliable ident servers [IDENT], or other proprietary


   The same comments apply to the authentication of IRC Operators.

   It should also be noted that while there has been no real demand over

   the years for stronger authentication, and no real effort to provide

   better means to safely authenticate users, the current protocol

   offers enough to be able to easily plug-in external authentication

   methods based on the information that a client can submit to the

   server upon connection: nickname, username, password.

7.2 Integrity

   Since the PASS and OPER messages of the IRC protocol are sent in

   clear text, a stream layer encryption mechanism (like "The TLS

   Protocol" [TLS]) could be used to protect these transactions.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

8. Current support and availability

      Mailing lists for IRC related discussion:

        General discussion: ircd-users@irc.org

        Protocol development: ircd-dev@irc.org

      Software implementations:




      Newsgroup: alt.irc

9. Acknowledgements

   Parts of this document were copied from the RFC 1459 [IRC] which

   first formally documented the IRC Protocol.  It has also benefited

   from many rounds of review and comments.  In particular, the

   following people have made significant contributions to this


   Matthew Green, Michael Neumayer, Volker Paulsen, Kurt Roeckx, Vesa

   Ruokonen, Magnus Tjernstrom, Stefan Zehl.

10. References

   [KEYWORDS]   Bradner, S., "Key words for use in RFCs to Indicate

                Requirement Levels", BCP 14, RFC 2119, March 1997.

   [ABNF]       Crocker, D. and P. Overell, "Augmented BNF for Syntax

                Specifications: ABNF", RFC 2234, November 1997.

   [IRC]        Oikarinen, J. and D. Reed, "Internet Relay Chat

                Protocol", RFC 1459, May 1993.

   [IRC-ARCH]   Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,

                April 2000.

   [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC

                2812, April 2000.

   [IRC-CHAN]   Kalt, C., "Internet Relay Chat: Channel Management", RFC

                2811, April 2000.

   [ZLIB]       Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data

                Format Specification version 3.3", RFC 1950, May 1996.

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

   [DEFLATE]    Deutsch, P., "DEFLATE Compressed Data Format

                Specification version 1.3", RFC 1951, May 1996.

   [GZIP]       Deutsch, P., "GZIP file format specification version

                4.3", RFC 1952, May 1996.

   [IDENT]      St. Johns, M., "The Identification Protocol", RFC 1413,

                February 1993.

   [TLS]        Dierks, T. and C. Allen, "The TLS Protocol", RFC 2246,

                January 1999.

11. Author's Address

   Christophe Kalt

   99 Teaneck Rd, Apt #117

   Ridgefield Park, NJ 07660


   EMail: kalt@stealth.net

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RFC 2813          Internet Relay Chat: Server Protocol        April 2000

12.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to

   others, and derivative works that comment on or otherwise explain it

   or assist in its implementation may be prepared, copied, published

   and distributed, in whole or in part, without restriction of any

   kind, provided that the above copyright notice and this paragraph are

   included on all such copies and derivative works.  However, this

   document itself may not be modified in any way, such as by removing

   the copyright notice or references to the Internet Society or other

   Internet organizations, except as needed for the purpose of

   developing Internet standards in which case the procedures for

   copyrights defined in the Internet Standards process must be

   followed, or as required to translate it into languages other than


   The limited permissions granted above are perpetual and will not be

   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an







   Funding for the RFC Editor function is currently provided by the

   Internet Society.

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