kunt

rfc2813.txt (56681B)

---

 
 
 
 
 
 
 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.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 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
 
 
 
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          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.
 
 
 
 
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 2.2 Clients
 
    For each client, all servers MUST have the following information: a
    netwide unique identifier (whose format depends on the type of
    client) and the server to which the client is connected.
 
 2.2.1 Users
 
    Each user is distinguished from other users by a unique nickname
    having a maximum length of nine (9) characters.  See the protocol
    grammar rules (section 3.3.1) for what may and may not be used in a
    nickname.  In addition to the nickname, all servers MUST have the
    following information about all users: the name of the host that the
    user is running on, the username of the user on that host, and the
    server to which the client is connected.
 
 2.2.2 Services
 
    Each service is distinguished from other services by a service name
    composed of a nickname and a server name.  The nickname has a maximum
    length of nine (9) characters.  See the protocol grammar rules
    (section 3.3.1) for what may and may not be used in a nickname.  The
    server name used to compose the service name is the name of the
    server to which the service is connected.  In addition to this
    service name all servers MUST know the service type.
 
    Services differ from users by the format of their identifier, but
    more importantly services and users don't have the same type of
    access to the server: services can request part or all of the global
    state information that a server maintains, but have a more restricted
    set of commands available to them (See "IRC Client Protocol" [IRC-
    CLIENT] for details on which) and are not allowed to join channels.
    Finally services are not usually subject to the "Flood control"
    mechanism described in section 5.8.
 
 2.3 Channels
 
    Alike services, channels have a scope [IRC-CHAN] and are not
    necessarily known to all servers.  When a channel existence is known
    to a server, the server MUST keep track of the channel members, as
    well as the channel modes.
 
 
 
 
 
 
 
 
 
 
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 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 received MUST be dropped.  Dropping a link
    in such circumstances is a little excessive but necessary to maintain
    the integrity of the network and to prevent future problems.  Another
    common error condition is that the prefix found in the server's
    internal database identifies a different source (typically a source
    registered from a different link than from which the message
    arrived).  If the message was received from a server link and the
    prefix identifies a client, a KILL message MUST be issued for the
    client and sent to all servers.  In other cases, the link from which
    the message arrived SHOULD be dropped for clients, and MUST be
    dropped for servers.  In all cases, the message MUST be discarded.
 
    The command MUST either be a valid IRC command or a three (3) digit
    number represented in ASCII text.
 
    IRC messages are always lines of characters terminated with a CR-LF
    (Carriage Return - Line Feed) pair, and these messages SHALL NOT
    exceed 512 characters in length, counting all characters including
    the trailing CR-LF. Thus, there are 510 characters maximum allowed
    for the command and its parameters.  There is no provision for
    continuation message lines.  See section 5 for more details about
    current implementations.
 
 3.3.1 Message format in Augmented BNF
 
    The protocol messages must be extracted from the contiguous stream of
    octets.  The current solution is to designate two characters, CR and
    LF, as message separators.  Empty messages are silently ignored,
    which permits use of the sequence CR-LF between messages without
    extra problems.
 
    The extracted message is parsed into the components <prefix>,
    <command> and list of parameters (<params>).
 
    The Augmented BNF representation for this is found in "IRC Client
    Protocol" [IRC-CLIENT].
 
    The extended prefix (["!" user "@" host ]) MUST NOT be used in server
    to server communications and is only intended for server to client
    messages in order to provide clients with more useful information
    about who a message is from without the need for additional queries.
 
 
 
 
 
 
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 3.4 Numeric replies
 
    Most of the messages sent to the server generate a reply of some
    sort.  The most common reply is the numeric reply, used for both
    errors and normal replies.  The numeric reply MUST be sent as one
    message consisting of the sender prefix, the three digit numeric, and
    the target of the reply.  A numeric reply is not allowed to originate
    from a client; any such messages received by a server are silently
    dropped. In all other respects, a numeric reply is just like a normal
    message, except that the keyword is made up of 3 numeric digits
    rather than a string of letters.  A list of different replies is
    supplied in "IRC Client Protocol" [IRC-CLIENT].
 
 4. Message Details
 
    All the messages recognized by the IRC server and client are
    described in the IRC Client Protocol specification.
 
    Where the reply ERR_NOSUCHSERVER is returned, it means that the
    target of the message could not be found.  The server MUST NOT send
    any other replies after this error for that command.
 
    The server to which a client is connected is required to parse the
    complete message, returning any appropriate errors.  If the server
    encounters a fatal error while parsing a message, an error MUST be
    sent back to the client and the parsing terminated.  A fatal error
    may follow from incorrect command, a destination which is otherwise
    unknown to the server (server, client or channel names fit this
    category), not enough parameters or incorrect privileges.
 
    If a full set of parameters is presented, then each MUST be checked
    for validity and appropriate responses sent back to the client.  In
    the case of messages which use parameter lists using the comma as an
    item separator, a reply MUST be sent for each item.
 
    In the examples below, some messages appear using the full format:
 
    :Name COMMAND parameter list
 
    Such examples represent a message from "Name" in transit between
    servers, where it is essential to include the name of the original
    sender of the message so remote servers may send back a reply along
    the correct path.
 
    The message details for client to server communication are described
    in the "IRC Client Protocol" [IRC-CLIENT].  Some sections in the
    following pages apply to some of these messages, they are additions
    to the message specifications which are only relevant to server to
 
 
 
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    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
 
 
 
 
 
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    "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.
 
 
 
 
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    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.
 
 
 
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    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.
 
 
 
 
 
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    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.
 
 
 
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    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
 
 
 
 
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    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.
 
 
 
 
 
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    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.
 
 
 
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 RFC 2813          Internet Relay Chat: Server Protocol        April 2000
 
 
 4.2.3 Mode message
 
    The MODE message is a dual-purpose command in IRC.  It allows both
    usernames and channels to have their mode changed.
 
    When parsing MODE messages, it is RECOMMENDED that the entire message
    be parsed first, and then the changes which resulted passed on.
 
    It is REQUIRED that servers are able to change channel modes so that
    "channel creator" and "channel operators" may be created.
 
 5. Implementation details
 
    A the time of writing, the only current implementation of this
    protocol is the IRC server, version 2.10. Earlier versions may
    implement some or all of the commands described by this document with
    NOTICE messages replacing many of the numeric replies. Unfortunately,
    due to backward compatibility requirements, the implementation of
    some parts of this document varies with what is laid out.  One
    notable difference is:
 
         * recognition that any LF or CR anywhere in a message marks
           the end of that message (instead of requiring CR-LF);
 
    The rest of this section deals with issues that are mostly of
    importance to those who wish to implement a server but some parts
    also apply directly to clients as well.
 
 5.1 Connection 'Liveness'
 
    To detect when a connection has died or become unresponsive, the
    server MUST poll each of its connections.  The PING command (See "IRC
    Client Protocol" [IRC-CLIENT]) is used if the server doesn't get a
    response from its peer in a given amount of time.
 
    If a connection doesn't respond in time, its connection is closed
    using the appropriate procedures.
 
 5.2 Accepting a client to server connection
 
 5.2.1 Users
 
    When a server successfully registers a new user connection, it is
    REQUIRED to send to the user unambiguous messages stating: the user
    identifiers upon which it was registered (RPL_WELCOME), the server
    name and version (RPL_YOURHOST), the server birth information
    (RPL_CREATED), available user and channel modes (RPL_MYINFO), and it
    MAY send any introductory messages which may be deemed appropriate.
 
 
 
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 RFC 2813          Internet Relay Chat: Server Protocol        April 2000
 
 
    In particular the server SHALL send the current user/service/server
    count (as per the LUSER reply) and finally the MOTD (if any, as per
    the MOTD reply).
 
    After dealing with registration, the server MUST then send out to
    other servers the new user's nickname (NICK message), other
    information as supplied by itself (USER message) and as the server
    could discover (from DNS servers).  The server MUST NOT send this
    information out with a pair of NICK and USER messages as defined in
    "IRC Client Protocol" [IRC-CLIENT], but MUST instead take advantage
    of the extended NICK message defined in section 4.1.3.
 
 5.2.2 Services
 
    Upon successfully registering a new service connection, the server is
    subject to the same kind of REQUIREMENTS as for a user.  Services
    being somewhat different, only the following replies are sent:
    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).
 
 
 
 
 
 
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 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.
 
 
 
 
 
 
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    By passing the state information about servers first, any collisions
    with servers that already exist occur before nickname collisions
    caused by a second server introducing a particular nickname.  Due to
    the IRC network only being able to exist as an acyclic graph, it may
    be possible that the network has already reconnected in another
    location.  In this event, the place where the server collision occurs
    indicates where the net needs to split.
 
 5.4 Terminating server-client connections
 
    When a client connection unexpectedly closes, a QUIT message is
    generated on behalf of the client by the server to which the client
    was connected.  No other message is to be generated or used.
 
 5.5 Terminating server-server connections
 
    If a server-server connection is closed, either via a SQUIT command
    or "natural" causes, the rest of the connected IRC network MUST have
    its information updated by the server which detected the closure.
    The terminating server then sends a list of SQUITs (one for each
    server behind that connection).  (See Section 4.1.6 (SQUIT)).
 
 5.6 Tracking nickname changes
 
    All IRC servers are REQUIRED to keep a history of recent nickname
    changes.  This is important to allow the server to have a chance of
    keeping in touch of things when nick-change race conditions occur
    with commands manipulating them.  Messages which MUST trace nick
    changes are:
 
            * KILL (the nick being disconnected)
 
            * MODE (+/- o,v on channels)
 
            * KICK (the nick being removed from channel)
 
       No other commands need to check nick changes.
 
    In the above cases, the server is required to first check for the
    existence of the nickname, then check its history to see who that
    nick now belongs to (if anyone!).  This reduces the chances of race
    conditions but they can still occur with the server ending up
    affecting the wrong client.  When performing a change trace for an
    above command it is RECOMMENDED that a time range be given and
    entries which are too old ignored.
 
 
 
 
 
 
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    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.
 
 
 
 
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 5.9 Non-blocking lookups
 
    In a real-time environment, it is essential that a server process
    does as little waiting as possible so that all the clients are
    serviced fairly.  Obviously this requires non-blocking IO on all
    network read/write operations.  For normal server connections, this
    was not difficult, but there are other support operations that may
    cause the server to block (such as disk reads).  Where possible, such
    activity SHOULD be performed with a short timeout.
 
 5.9.1 Hostname (DNS) lookups
 
    Using the standard resolver libraries from Berkeley and others has
    meant large delays in some cases where replies have timed out.  To
    avoid this, a separate set of DNS routines were written for the
    current implementation.  Routines were setup for non-blocking IO
    operations with local cache, and then polled from within the main
    server IO loop.
 
 5.9.2 Username (Ident) lookups
 
    Although there are numerous ident libraries (implementing the
    "Identification Protocol" [IDENT]) for use and inclusion into other
    programs, these caused problems since they operated in a synchronous
    manner and resulted in frequent delays.  Again the solution was to
    write a set of routines which would cooperate with the rest of the
    server and work using non-blocking IO.
 
 6. Current problems
 
    There are a number of recognized problems with this protocol, all of
    which are hoped to be solved sometime in the near future during its
    rewrite.  Currently, work is underway to find working solutions to
    these problems.
 
 6.1 Scalability
 
    It is widely recognized that this protocol does not scale
    sufficiently well when used in a large arena.  The main problem comes
    from the requirement that all servers know about all other servers
    and clients and that information regarding them be updated as soon as
    it changes.  It is also desirable to keep the number of servers low
    so that the path length between any two points is kept minimal and
    the spanning tree as strongly branched as possible.
 
 
 
 
 
 
 
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 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.
 
 
 
 
 
 
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    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.
 
 
 
 
 
 
 
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 RFC 2813          Internet Relay Chat: Server Protocol        April 2000
 
 
 8. Current support and availability
 
       Mailing lists for IRC related discussion:
         General discussion: ircd-users@irc.org
         Protocol development: ircd-dev@irc.org
 
       Software implementations:
         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.
 
 
 
 
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 RFC 2813          Internet Relay Chat: Server Protocol        April 2000
 
 
    [DEFLATE]    Deutsch, P., "DEFLATE Compressed Data Format
                 Specification version 1.3", RFC 1951, May 1996.
 
    [GZIP]       Deutsch, P., "GZIP file format specification version
                 4.3", RFC 1952, May 1996.
 
    [IDENT]      St. Johns, M., "The Identification Protocol", RFC 1413,
                 February 1993.
 
    [TLS]        Dierks, T. and C. Allen, "The TLS Protocol", RFC 2246,
                 January 1999.
 
 11. Author's Address
 
    Christophe Kalt
    99 Teaneck Rd, Apt #117
    Ridgefield Park, NJ 07660
    USA
 
    EMail: kalt@stealth.net
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 RFC 2813          Internet Relay Chat: Server Protocol        April 2000
 
 
 12.  Full Copyright Statement
 
    Copyright (C) The Internet Society (2000).  All Rights Reserved.
 
    This document and translations of it may be copied and furnished to
    others, and derivative works that comment on or otherwise explain it
    or assist in its implementation may be prepared, copied, published
    and distributed, in whole or in part, without restriction of any
    kind, provided that the above copyright notice and this paragraph are
    included on all such copies and derivative works.  However, this
    document itself may not be modified in any way, such as by removing
    the copyright notice or references to the Internet Society or other
    Internet organizations, except as needed for the purpose of
    developing Internet standards in which case the procedures for
    copyrights defined in the Internet Standards process must be
    followed, or as required to translate it into languages other than
    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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