GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc2813

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.

Abstract

 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.

Kalt Informational [Page 1] 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
          5.3.1.1  Compressed server to server links ............  18
          5.3.1.2  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

Kalt Informational [Page 2] 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-
 CHAN]).

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
 name.
 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.

Kalt Informational [Page 3] 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.

Kalt Informational [Page 4] 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.

Kalt Informational [Page 5] 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.

Kalt Informational [Page 6] 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

Kalt Informational [Page 7] 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
 communication.

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

Kalt Informational [Page 8] RFC 2813 Internet Relay Chat: Server Protocol April 2000

 "P").  See sections 5.3.1.1 (Compressed server to server links) and
 5.3.1.2 (Anti abuse protections) respectively for more information on
 these options.
 Numeric Replies:
         ERR_NEEDMOREPARAMS              ERR_ALREADYREGISTRED
 Example:
      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
 network.
 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
 server.
 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.

Kalt Informational [Page 9] 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:
         ERR_ALREADYREGISTRED
 Example:
 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
                                 csd.bu.edu.

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:
 NICK, USER and MODE [IRC-CLIENT].
 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.

Kalt Informational [Page 10] 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).
 Examples:
 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
                                 syrk

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

Kalt Informational [Page 11] RFC 2813 Internet Relay Chat: Server Protocol April 2000

 Numeric Replies:
         ERR_ALREADYREGISTRED            ERR_NEEDMOREPARAMS
         ERR_ERRONEUSNICKNAME
         RPL_YOURESERVICE                RPL_YOURHOST
         RPL_MYINFO
 Example:

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
 connected:
    <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
 error.
 Numeric Replies:
         None.

Kalt Informational [Page 12] RFC 2813 Internet Relay Chat: Server Protocol April 2000

 Examples:
 :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
 appropriate.
 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

Kalt Informational [Page 13] RFC 2813 Internet Relay Chat: Server Protocol April 2000

 section 5.7 (Tracking recently used nicknames) for more information
 on this procedure.
 Numeric replies:
         ERR_NOPRIVILEGES                ERR_NOSUCHSERVER
         ERR_NEEDMOREPARAMS
 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 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.

Kalt Informational [Page 14] 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:
         ERR_NEEDMOREPARAMS              ERR_BANNEDFROMCHAN
         ERR_INVITEONLYCHAN              ERR_BADCHANNELKEY
         ERR_CHANNELISFULL               ERR_BADCHANMASK
         ERR_NOSUCHCHANNEL               ERR_TOOMANYCHANNELS
         ERR_TOOMANYTARGETS              ERR_UNAVAILRESOURCE
         RPL_TOPIC
 Examples:
 :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:
         ERR_NEEDMOREPARAMS              ERR_NOSUCHCHANNEL
         ERR_ALREADYREGISTRED
 Examples:
 :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
                                 privilege.

Kalt Informational [Page 15] 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.

Kalt Informational [Page 16] 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:
 RPL_YOURESERVICE, RPL_YOURHOST, RPL_MYINFO.
 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).

Kalt Informational [Page 17] RFC 2813 Internet Relay Chat: Server Protocol April 2000

5.3.1.1 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].

5.3.1.2 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.

Kalt Informational [Page 18] 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.

Kalt Informational [Page 19] 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
 time.
 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.

Kalt Informational [Page 20] 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.

Kalt Informational [Page 21] 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
 clients.

Kalt Informational [Page 22] 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
 disrupted.

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
    mechanisms.
 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.

Kalt Informational [Page 23] 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:
      ftp://ftp.irc.org/irc/server
      ftp://ftp.funet.fi/pub/unix/irc
      ftp://coombs.anu.edu.au/pub/irc
    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
 document:
 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.

Kalt Informational [Page 24] 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
 USA
 EMail: kalt@stealth.net

Kalt Informational [Page 25] 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
 English.
 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
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Kalt Informational [Page 26]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2813.txt · Last modified: 2000/04/27 21:34 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki