RFC 2813 (rfc2813) - Internet Relay Chat: Server Protocol
Description: RFC 2813 - Internet Relay Chat: Server Protocol

# RFC 2813 (RFC2813)

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### RFC 2813 - Internet Relay Chat: Server Protocol

    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.

    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

             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.

    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.

    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.

       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.

    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

       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

       "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.

       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.

       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.

       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.

       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

       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.

       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.

    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.

       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).

    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.

       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.

       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.

    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.

    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.

       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.

    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.

       [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

    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.

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