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Versions: 00 01 RFC 2813

Internet Draft                                                   C. Kalt
Expires: 22 Jan 2000                                         22 Jul 1999

                  Internet Relay Chat: Server Protocol

Status of this Memo

      This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
   working documents as Internet Drafts.

      Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

      The list of current Internet-Drafts can be accessed at

      The list of Internet-Draft Shadow Directories can be accessed at

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   this document are to be interpreted as described in RFC 2119


      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                                                            [Page 1]

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                  Table of Contents

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

   2.  Global database ............................................   3
      2.1  Servers ................................................   3
      2.2  Clients ................................................   3
         2.2.1  Users .............................................   3
         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 ........................................   6

   4.  Message Details ............................................   8
      4.1  Connection Registration ................................   8
         4.1.1  Password message ..................................   8
         4.1.2  Server message ....................................   9
         4.1.3  Nick ..............................................  11
         4.1.4  Service message ...................................  11
         4.1.5  Quit ..............................................  12
         4.1.6  Server quit message ...............................  13
      4.2  Channel operations .....................................  15
         4.2.1  Join message ......................................  15
         4.2.2  Njoin message .....................................  16
         4.2.3  Mode message ......................................  16

   5.  Implementation details  ....................................  17
      5.1  Connection 'Liveness' ..................................  17
      5.2  Accepting a client to server connection ................  17
         5.2.1  Users .............................................  17
         5.2.2  Services ..........................................  18
      5.3  Establishing a server-server connection. ...............  18
         5.3.1  Link options ......................................  18
    Compressed server to server links ............  18
    Anti abuse protections .......................  18
         5.3.2  State information exchange when connecting ........  19
      5.4  Terminating server-client connections ..................  19
      5.5  Terminating server-server connections ..................  19
      5.6  Tracking nickname changes ..............................  20
      5.7  Tracking recently used nicknames .......................  20
      5.8  Flood control of clients ...............................  21
      5.9  Non-blocking lookups ...................................  21
         5.9.1  Hostname (DNS) lookups ............................  21

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         5.9.2  Username (Ident) lookups ..........................  22

   6.  Current problems ...........................................  23
      6.1  Scalability ............................................  23
      6.2  Labels .................................................  23
         6.2.1  Nicknames .........................................  23
         6.2.2  Channels ..........................................  23
         6.2.3  Servers ...........................................  24
      6.3  Algorithms .............................................  24

   7.  Security Considerations ....................................  24
      7.1  Authentication .........................................  24
      7.2  Integrity ..............................................  25

   8.  Current support and availability ...........................  25

   9.  Acknowledgements ...........................................  25

   10.  References ................................................  25

   11.  Author's Address ..........................................  26

Kalt                                                            [Page 3]

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1. Introduction

      This document is intended for people working on implementing an
   IRC server but will also be useful to anyone implementing an IRC

      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

      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 followin 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

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   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 the global
   state information that a server maintains, but are not allowed to
   join channels and have a more restricted set of commands available to
   them (See "IRC Client Protocol" [IRC-CLIENT] for details on which).
   Finally services are not usually subject to the "Flood control"
   mechanism described in section 5.8.

2.3 Channels

      Alike services, channels have a scope [IRC-CHAN] and are not
   necessarily known to all servers.  When a channel existence is known
   to a server, the server MUST keep track of the channel members, as
   well as the channel modes.

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3. The IRC Server Specification

3.1 Overview

      The protocol as described herein is for use with server to server
   connections.  For client to server connections, see the IRC Client
   Protocol specification.

      There are, however, more restrictions on client connections (which
   are considered to be untrustworthy) than on server connections.

3.2 Character codes

      No specific character set is specified. The protocol is based on a
   a set of codes which are composed of eight (8) bits, making up an
   octet.  Each message may be composed of any number of these octets;
   however, some octet values are used for control codes which act as
   message delimiters.

      Regardless of being an 8-bit protocol, the delimiters and keywords
   are such that protocol is mostly usable from US-ASCII terminal and a
   telnet connection.

      Because of IRC's Scandinavian origin, the characters {}|^ are
   considered to be the lower case equivalents of the characters []\~,
   respectively. This is a critical issue when determining the
   equivalence of two nicknames, or channel names.

3.3 Messages

      Servers and clients send each other messages which may or may not
   generate a reply.  Most communication between servers do not generate
   any reply, as servers mostly perform routing tasks for the clients.

      Each IRC message may consist of up to three main parts: the prefix
   (OPTIONAL), the command, and the command parameters (maximum of
   fifteen (15)).  The prefix, command, and all parameters are separated
   by one ASCII space character (0x20) each.

      The presence of a prefix is indicated with a single leading ASCII
   colon character (':', 0x3b), which MUST be the first character of the
   message itself.  There MUST be NO gap (whitespace) between the colon
   and the prefix.  The prefix is used by servers to indicate the true
   origin of the message.  If the prefix is missing from the message, it
   is assumed to have originated from the connection from which it was
   received.  Clients SHOULD not use a prefix when sending a message
   from themselves; if they use one, the only valid prefix is the
   registered nickname associated with the client.

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      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 receveived MUST be dropped.  Dropping a
   link in such circumstances is a little excessive but necessary to
   maintain the integrity of the network and prevent future problems.
      Another common error condition is that the prefix is 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

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      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].

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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.  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>]

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      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) charac¡
   ters, and up to fourteen (14) characters.  The first four (4) charac¡
   ters 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 dependant and should describe the soft¡
   ware version number.

      The <flags> parameter is a string of up to one hundred (100) char¡
   acters.  It is composed of two substrings separated by the character
   ``|'' (%x7C).  If present, the first substring SHOULD be the name of
   the implementation.  The second substring is implementation depen¡
   dant.  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 charac¡
   ter ``P'').  See sections (Compressed server to server links)
   and (Anti abuse protections) respectively for more informa¡
   tion on these options.

   Numeric Replies:



        PASS moresecretpassword 0210010000 IRC|aBgH$ Z

4.1.2 Server message

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

      The SERVER command is used to register a new server. A new connec¡
   tion 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

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   connected to net, information about it be broadcast to the whole net¡

      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 connec¡
   tion which is yet to be registered and is attempting to register as a
   server, or (b) an existing connection to another server, in which
   case the SERVER message is introducing a new server behind that

      Most errors that occur with the receipt of a SERVER command result
   in the connection being terminated by the destination host (target
   SERVER).  Because of the severity of such event, error replies are
   usually sent using the "ERROR" command rather than a numeric.

      If a SERVER message is parsed and it attempts to introduce a
   server which is already known to the receiving server, the connec¡
   tion, 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 condi¡
   tions, the connection from which the already known server has regis¡
   tered 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 iso¡
   lated, with one of the two servers connected to each partition there¡
   fore making it impossible for the two parts to unite.

   Numeric Replies:



Kalt                                                           [Page 11]

Internet Draft    Internet Relay Chat: Server Protocol       22 Jul 1999

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 tol¡
                                sun.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,

      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).


NICK syrk 5 kalt millennium.stealth.net 34 +i :Christophe Kalt
                                ; New user with nickname "syrk", user¡
                                name "kalt", connected from host "mil¡
                                lennium.stealth.net" to server "34"
                                ("csd.bu.edu" according to the previous

: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

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   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 (unregis¡
   tered, or registered) connections.  However, it MUST be used between
   servers to notify other servers of new services joining the IRC net¡

      The <servertoken> is used to identify the server to which the ser¡
   vice is connected.  (See section 4.1.2 for more information on server

      The <hopcount> parameter is used by servers to indicate how far
   away a service is from its home server.  A local connection has a
   hopcount of 0.  The hopcount value is incremented by each passed

      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 knowl¡
   edge of the service, the network path between that server and the
   server on which the service is connected MUST be composed of servers
   whose names all match the mask.  Plain ``*'' is used when no restric¡
   tion is wished.

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

   Numeric Replies:

           RPL_YOURESERVICE                RPL_YOURHOST


SERVICE dict@irc.fr 9 *.fr 0 1 :French Dictionnary
                                ; New service called "dict@irc.fr" reg¡
                                istered 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

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   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 discon¡
   nected or that of the server to which the leaving client was con¡

         <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 for¡
   mat described above.

      If, for some other reason, a client connection is closed without
   the client issuing a QUIT command (e.g. client dies and EOF occurs on
   socket), the server is REQUIRED to fill in the quit message with some
   sort of message reflecting the nature of the event which caused it to
   happen.  Typically, this is done by reporting a system specific

   Numeric Replies:



: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

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   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 addi¡
   tion to this, all channel members of a channel which lost a member
   due to the "split" MUST be sent a QUIT message.  Messages to channel
   members are generated by each client's local server.

      If a server connection is terminated prematurely (e.g. the server
   on the other end of the link died), the server which detects this
   disconnection is REQUIRED to inform the rest of the network that the
   connection has closed and fill in the comment field with something

      When a client is removed as the result of a SQUIT messsage, 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:



SQUIT tolsun.oulu.fi :Bad Link ?
                                ; the server link tolson.oulu.fi has
                                been terminated because of "Bad Link".

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: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 com¡
   mand 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 chan¡

   Numeric Replies:



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: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 succes¡
   sion of JOIN, this message SHOULD be used instead as it is more effi¡
   cient.  The prefix "@@" indicates that the user is the "channel cre¡
   ator", the character "@" alone indicates a "channel operator", and
   the character '+' indicates that the user has the voice privilege.

   Numeric Replies:



:ircd.stealth.net NJOIN #Twilight_zone :@WiZ,+syrk,avalon
                                ; NJOIN message from ircd.stealth.net
                                announcing users joining the #Twi¡
                                light_zone channel: WiZ with channel
                                operator status, syrk with voice privi¡
                                lege 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 mes¡
   sage be parsed first, and then the changes which resulted then passed

      It is REQUIRED that servers are able to change channel modes so
   that "channel creator" and "channel operators" may be created.

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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 imple¡
   ment some or all of the commands described by this document with
   NOTICE messages replacing many of the numeric replies.  Unfortu¡
   nately, due to backward compatibility requirements, the implementa¡
   tion 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).

      After dealing with registration, the server MUST then send out to
   other servers the new user's nickname (NICK message), other informa¡
   tion as supplied by itself (USER message) and as the server could
   discover (from DNS servers).  The server MUST NOT send this informa¡
   tion 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.

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5.2.2 Services

      Upon successfully registering a new service connection, the server
   is subject to the same kind of REQUIREMENTS as for a user.  Services
   being somewhat different, only the following replies are sent:

      After dealing with this, the server MUST then send out to other
   servers (SERVICE message) the new service's nickname and other infor¡
   mation 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 prob¡
   lems 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 con¡
   nection 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 docu¡
   ment) but a particular link MAY set specific options using the PASS
   message (See Section 4.1.1). 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 mes¡
   sage.  If both servers request compression and both servers are able
   to initialize the two compressed streams, then the remainder of the
   communication is to be compressed.  If any server fails to initialize
   the stream, it will send an uncompressed ERROR message to its peer
   and close the connection.

      The data format used for the compression is described by RFC 1950
   [ZLIB], RFC 1951 [DEFLATE] and RFC 1952 [GZIP]. Anti abuse protections

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      Most servers implement various kinds of protections against possi¡
   ble 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 colli¡
   sions with servers that already exist occur before nickname colli¡
   sions 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 colli¡
   sion occurs indicating 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

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   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 affect¡
   ing 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

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   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 con¡
   tinuous stream of messages that result in not only flooding the net¡
   work, but also degrading the level of service provided to others.
   Rather than require every 'victim' to be provide their own protec¡
   tion, flood protection was written into the server and is applied to
   all clients except services.  The current algorithm is as follows:

           * check to see if client's `message timer' is less than
   current time (set to be equal if it is);

           * read any data present from the client;

           * while the timer is less than ten seconds ahead of the
             current time, parse any present messages and penalize the
             client by 2 seconds for each message;

        * additionnal 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 1 message every 2
   seconds without being adversely affected.  Services MAY also be sub¡
   ject 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 ser¡
   viced 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 cur¡
   rent implementation.  Routines were setup for non-blocking IO opera¡
   tions with local cache, and then polled from within the main server
   IO loop.

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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.

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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 suffi¡
   ciently 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 recog¡
   nized that this needs reworking, with a plan for unique names for
   nicks that don't collide being desirable as well as a solution allow¡
   ing 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, its not uncom¡
   mon 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 suc¡
   ceed or both will removed by use of KILL (4.6.1).

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 chan¡
   nels is treated as an inclusive event (people from both nets on chan¡
   nel 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

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   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

      In current server versions, there are only few database consis¡
   tency checks, most of the time each server assumes that a neighbour¡
   ing server is correct.  This opens the door to large problems if a
   connecting server is buggy or otherwise tries to introduce contradic¡
   tions 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 chang¡
   ing to unique labels, there are problems with channel-related com¡
   mands being disrupted.

7. Security Considerations

7.1 Authentication

      Servers only have two means of authenticating incoming connec¡
   tions: 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 mecha¡

      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

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   provide better means to safely authenticate users, the current proto¡
   col offers enough to be able to easily plug-in external authentica¡
   tion 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 Proto¡
   col" [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:

        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 follow¡
   ing 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] "Key words for use in RFCs to Indicate Requirement Levels",
   Network Working Group RFC 2119, S. Bradner, March 1997.

[ABNF]  "Augmented BNF for Syntax Specifications: ABNF",
   Network Working Group RFC 2234, D. Crocker, P. Overell, November 1997

[IRC] "Internet Relay Chat Protocol", Network Working Group RFC 1459,
   J. Oikarinen & D. Reed, May 1993

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[IRC-ARCH] "Internet Relay Chat: Architecture",
   Work In Progress: draft-kalt-irc-arch-xx.txt

[IRC-CLIENT] "Internet Relay Chat: Client Protocol",
   Work In Progress: draft-kalt-irc-client-xx.txt

[IRC-CHAN] "Internet Relay Chat: Channel Management",
   Work In Progress: draft-kalt-irc-chan-xx-txt

[ZLIB] "ZLIB Compressed Data Format Specification version 3.3",
   Network Working Group RFC 1950, P. Deutsch & J-L. Gailly, May 1996.

[DEFLATE] "DEFLATE Compressed Data Format Specification version 1.3",
   Network Working Group RFC 1951, P. Deutsch, May 1996.

[GZIP] "GZIP file format specification version 4.3",
   Network Working Group RFC 1952, P. Deutsch, May 1996

[IDENT] "The Identification Protocol", Network Working Group RFC 1413,
   M. St. Johns, February 1993.

[TLS] "The TLS Protocol", Network Working Group RFC 2246, T. Dierks,
   C. Allen, January 1999

11. Author's Address

     Christophe Kalt
     99 Teaneck Rd, Apt #117
     Ridgefield Park, NJ 07660

     Email: kalt@stealth.net

Kalt                                                           [Page 27]

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