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RFC 1459


Internet Relay Chat Protocol

Part 3 of 3, p. 43 to 65
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   The following is a list of numeric replies which are generated in
   response to the commands given above.  Each numeric is given with its
   number, name and reply string.

6.1 Error Replies.

        401     ERR_NOSUCHNICK
                        "<nickname> :No such nick/channel"

                - Used to indicate the nickname parameter supplied to a
                  command is currently unused.

        402     ERR_NOSUCHSERVER
                        "<server name> :No such server"

                - Used to indicate the server name given currently
                  doesn't exist.

        403     ERR_NOSUCHCHANNEL
                        "<channel name> :No such channel"

                - Used to indicate the given channel name is invalid.

                        "<channel name> :Cannot send to channel"

                - Sent to a user who is either (a) not on a channel
                  which is mode +n or (b) not a chanop (or mode +v) on
                  a channel which has mode +m set and is trying to send
                  a PRIVMSG message to that channel.

                        "<channel name> :You have joined too many \
                - Sent to a user when they have joined the maximum
                  number of allowed channels and they try to join
                  another channel.

        406     ERR_WASNOSUCHNICK
                        "<nickname> :There was no such nickname"

                - Returned by WHOWAS to indicate there is no history
                  information for that nickname.

        407     ERR_TOOMANYTARGETS
                        "<target> :Duplicate recipients. No message \

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                - Returned to a client which is attempting to send a
                  PRIVMSG/NOTICE using the user@host destination format
                  and for a user@host which has several occurrences.

        409     ERR_NOORIGIN
                        ":No origin specified"

                - PING or PONG message missing the originator parameter
                  which is required since these commands must work
                  without valid prefixes.

        411     ERR_NORECIPIENT
                        ":No recipient given (<command>)"
        412     ERR_NOTEXTTOSEND
                        ":No text to send"
        413     ERR_NOTOPLEVEL
                        "<mask> :No toplevel domain specified"
        414     ERR_WILDTOPLEVEL
                        "<mask> :Wildcard in toplevel domain"

                - 412 - 414 are returned by PRIVMSG to indicate that
                  the message wasn't delivered for some reason.
                  ERR_NOTOPLEVEL and ERR_WILDTOPLEVEL are errors that
                  are returned when an invalid use of
                  "PRIVMSG $<server>" or "PRIVMSG #<host>" is attempted.

        421     ERR_UNKNOWNCOMMAND
                        "<command> :Unknown command"

                - Returned to a registered client to indicate that the
                  command sent is unknown by the server.

        422     ERR_NOMOTD
                        ":MOTD File is missing"

                - Server's MOTD file could not be opened by the server.

        423     ERR_NOADMININFO
                        "<server> :No administrative info available"

                - Returned by a server in response to an ADMIN message
                  when there is an error in finding the appropriate

        424     ERR_FILEERROR
                ":File error doing <file op> on <file>"

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                - Generic error message used to report a failed file
                  operation during the processing of a message.

                        ":No nickname given"

                - Returned when a nickname parameter expected for a
                  command and isn't found.

                        "<nick> :Erroneus nickname"

                - Returned after receiving a NICK message which contains
                  characters which do not fall in the defined set.  See
                  section x.x.x for details on valid nicknames.

        433     ERR_NICKNAMEINUSE
                        "<nick> :Nickname is already in use"

                - Returned when a NICK message is processed that results
                  in an attempt to change to a currently existing

        436     ERR_NICKCOLLISION
                        "<nick> :Nickname collision KILL"

                - Returned by a server to a client when it detects a
                  nickname collision (registered of a NICK that
                  already exists by another server).

                        "<nick> <channel> :They aren't on that channel"

                - Returned by the server to indicate that the target
                  user of the command is not on the given channel.

        442     ERR_NOTONCHANNEL
                        "<channel> :You're not on that channel"

                - Returned by the server whenever a client tries to
                  perform a channel effecting command for which the
                  client isn't a member.

        443     ERR_USERONCHANNEL
                        "<user> <channel> :is already on channel"

                - Returned when a client tries to invite a user to a
                  channel they are already on.

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        444     ERR_NOLOGIN
                        "<user> :User not logged in"

                - Returned by the summon after a SUMMON command for a
                  user was unable to be performed since they were not
                  logged in.

        445     ERR_SUMMONDISABLED
                        ":SUMMON has been disabled"

                - Returned as a response to the SUMMON command.  Must be
                  returned by any server which does not implement it.

        446     ERR_USERSDISABLED
                        ":USERS has been disabled"

                - Returned as a response to the USERS command.  Must be
                  returned by any server which does not implement it.

        451     ERR_NOTREGISTERED
                        ":You have not registered"

                - Returned by the server to indicate that the client
                  must be registered before the server will allow it
                  to be parsed in detail.

        461     ERR_NEEDMOREPARAMS
                        "<command> :Not enough parameters"

                - Returned by the server by numerous commands to
                  indicate to the client that it didn't supply enough

                        ":You may not reregister"

                - Returned by the server to any link which tries to
                  change part of the registered details (such as
                  password or user details from second USER message).

        463     ERR_NOPERMFORHOST
                        ":Your host isn't among the privileged"

                - Returned to a client which attempts to register with
                  a server which does not been setup to allow
                  connections from the host the attempted connection
                  is tried.

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        464     ERR_PASSWDMISMATCH
                        ":Password incorrect"

                - Returned to indicate a failed attempt at registering
                  a connection for which a password was required and
                  was either not given or incorrect.

                        ":You are banned from this server"

                - Returned after an attempt to connect and register
                  yourself with a server which has been setup to
                  explicitly deny connections to you.

        467     ERR_KEYSET
                        "<channel> :Channel key already set"
        471     ERR_CHANNELISFULL
                        "<channel> :Cannot join channel (+l)"
        472     ERR_UNKNOWNMODE
                        "<char> :is unknown mode char to me"
        473     ERR_INVITEONLYCHAN
                        "<channel> :Cannot join channel (+i)"
        474     ERR_BANNEDFROMCHAN
                        "<channel> :Cannot join channel (+b)"
        475     ERR_BADCHANNELKEY
                        "<channel> :Cannot join channel (+k)"
        481     ERR_NOPRIVILEGES
                        ":Permission Denied- You're not an IRC operator"

                - Any command requiring operator privileges to operate
                  must return this error to indicate the attempt was

                        "<channel> :You're not channel operator"

                - Any command requiring 'chanop' privileges (such as
                  MODE messages) must return this error if the client
                  making the attempt is not a chanop on the specified

        483     ERR_CANTKILLSERVER
                        ":You cant kill a server!"

                - Any attempts to use the KILL command on a server
                  are to be refused and this error returned directly
                  to the client.

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        491     ERR_NOOPERHOST
                        ":No O-lines for your host"

                - If a client sends an OPER message and the server has
                  not been configured to allow connections from the
                  client's host as an operator, this error must be

                        ":Unknown MODE flag"

                - Returned by the server to indicate that a MODE
                  message was sent with a nickname parameter and that
                  the a mode flag sent was not recognized.

        502     ERR_USERSDONTMATCH
                        ":Cant change mode for other users"

                - Error sent to any user trying to view or change the
                  user mode for a user other than themselves.

6.2 Command responses.

        300     RPL_NONE
                        Dummy reply number. Not used.

        302     RPL_USERHOST

                - Reply format used by USERHOST to list replies to
                  the query list.  The reply string is composed as

                  <reply> ::= <nick>['*'] '=' <'+'|'-'><hostname>

                  The '*' indicates whether the client has registered
                  as an Operator.  The '-' or '+' characters represent
                  whether the client has set an AWAY message or not

        303     RPL_ISON
                        ":[<nick> {<space><nick>}]"

                - Reply format used by ISON to list replies to the
                  query list.

        301     RPL_AWAY
                        "<nick> :<away message>"

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        305     RPL_UNAWAY
                        ":You are no longer marked as being away"
        306     RPL_NOWAWAY
                        ":You have been marked as being away"

                - These replies are used with the AWAY command (if
                  allowed).  RPL_AWAY is sent to any client sending a
                  PRIVMSG to a client which is away.  RPL_AWAY is only
                  sent by the server to which the client is connected.
                  Replies RPL_UNAWAY and RPL_NOWAWAY are sent when the
                  client removes and sets an AWAY message.

        311     RPL_WHOISUSER
                        "<nick> <user> <host> * :<real name>"
        312     RPL_WHOISSERVER
                        "<nick> <server> :<server info>"
        313     RPL_WHOISOPERATOR
                        "<nick> :is an IRC operator"
        317     RPL_WHOISIDLE
                        "<nick> <integer> :seconds idle"
        318     RPL_ENDOFWHOIS
                        "<nick> :End of /WHOIS list"
        319     RPL_WHOISCHANNELS
                        "<nick> :{[@|+]<channel><space>}"

                - Replies 311 - 313, 317 - 319 are all replies
                  generated in response to a WHOIS message.  Given that
                  there are enough parameters present, the answering
                  server must either formulate a reply out of the above
                  numerics (if the query nick is found) or return an
                  error reply.  The '*' in RPL_WHOISUSER is there as
                  the literal character and not as a wild card.  For
                  each reply set, only RPL_WHOISCHANNELS may appear
                  more than once (for long lists of channel names).
                  The '@' and '+' characters next to the channel name
                  indicate whether a client is a channel operator or
                  has been granted permission to speak on a moderated
                  channel.  The RPL_ENDOFWHOIS reply is used to mark
                  the end of processing a WHOIS message.

        314     RPL_WHOWASUSER
                        "<nick> <user> <host> * :<real name>"
        369     RPL_ENDOFWHOWAS
                        "<nick> :End of WHOWAS"

                - When replying to a WHOWAS message, a server must use
                  the replies RPL_WHOWASUSER, RPL_WHOISSERVER or
                  ERR_WASNOSUCHNICK for each nickname in the presented

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                  list.  At the end of all reply batches, there must
                  be RPL_ENDOFWHOWAS (even if there was only one reply
                  and it was an error).

        321     RPL_LISTSTART
                        "Channel :Users  Name"
        322     RPL_LIST
                        "<channel> <# visible> :<topic>"
        323     RPL_LISTEND
                        ":End of /LIST"

                - Replies RPL_LISTSTART, RPL_LIST, RPL_LISTEND mark
                  the start, actual replies with data and end of the
                  server's response to a LIST command.  If there are
                  no channels available to return, only the start
                  and end reply must be sent.

        324     RPL_CHANNELMODEIS
                        "<channel> <mode> <mode params>"

        331     RPL_NOTOPIC
                        "<channel> :No topic is set"
        332     RPL_TOPIC
                        "<channel> :<topic>"

                - When sending a TOPIC message to determine the
                  channel topic, one of two replies is sent.  If
                  the topic is set, RPL_TOPIC is sent back else

        341     RPL_INVITING
                        "<channel> <nick>"

                - Returned by the server to indicate that the
                  attempted INVITE message was successful and is
                  being passed onto the end client.

        342     RPL_SUMMONING
                        "<user> :Summoning user to IRC"

                - Returned by a server answering a SUMMON message to
                  indicate that it is summoning that user.

        351     RPL_VERSION
                        "<version>.<debuglevel> <server> :<comments>"

                - Reply by the server showing its version details.
                  The <version> is the version of the software being

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                  used (including any patchlevel revisions) and the
                  <debuglevel> is used to indicate if the server is
                  running in "debug mode".

                  The "comments" field may contain any comments about
                  the version or further version details.

        352     RPL_WHOREPLY
                        "<channel> <user> <host> <server> <nick> \
                         <H|G>[*][@|+] :<hopcount> <real name>"
        315     RPL_ENDOFWHO
                        "<name> :End of /WHO list"

                - The RPL_WHOREPLY and RPL_ENDOFWHO pair are used
                  to answer a WHO message.  The RPL_WHOREPLY is only
                  sent if there is an appropriate match to the WHO
                  query.  If there is a list of parameters supplied
                  with a WHO message, a RPL_ENDOFWHO must be sent
                  after processing each list item with <name> being
                  the item.

        353     RPL_NAMREPLY
                        "<channel> :[[@|+]<nick> [[@|+]<nick> [...]]]"
        366     RPL_ENDOFNAMES
                        "<channel> :End of /NAMES list"

                - To reply to a NAMES message, a reply pair consisting
                  of RPL_NAMREPLY and RPL_ENDOFNAMES is sent by the
                  server back to the client.  If there is no channel
                  found as in the query, then only RPL_ENDOFNAMES is
                  returned.  The exception to this is when a NAMES
                  message is sent with no parameters and all visible
                  channels and contents are sent back in a series of
                  RPL_NAMEREPLY messages with a RPL_ENDOFNAMES to mark
                  the end.

        364     RPL_LINKS
                        "<mask> <server> :<hopcount> <server info>"
        365     RPL_ENDOFLINKS
                        "<mask> :End of /LINKS list"

                - In replying to the LINKS message, a server must send
                  replies back using the RPL_LINKS numeric and mark the
                  end of the list using an RPL_ENDOFLINKS reply.

        367     RPL_BANLIST
                        "<channel> <banid>"
        368     RPL_ENDOFBANLIST

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                        "<channel> :End of channel ban list"

                - When listing the active 'bans' for a given channel,
                  a server is required to send the list back using the
                  RPL_BANLIST and RPL_ENDOFBANLIST messages.  A separate
                  RPL_BANLIST is sent for each active banid.  After the
                  banids have been listed (or if none present) a
                  RPL_ENDOFBANLIST must be sent.

        371     RPL_INFO
        374     RPL_ENDOFINFO
                        ":End of /INFO list"

                - A server responding to an INFO message is required to
                  send all its 'info' in a series of RPL_INFO messages
                  with a RPL_ENDOFINFO reply to indicate the end of the

        375     RPL_MOTDSTART
                        ":- <server> Message of the day - "
        372     RPL_MOTD
                        ":- <text>"
        376     RPL_ENDOFMOTD
                        ":End of /MOTD command"

                - When responding to the MOTD message and the MOTD file
                  is found, the file is displayed line by line, with
                  each line no longer than 80 characters, using
                  RPL_MOTD format replies.  These should be surrounded
                  by a RPL_MOTDSTART (before the RPL_MOTDs) and an
                  RPL_ENDOFMOTD (after).

        381     RPL_YOUREOPER
                        ":You are now an IRC operator"

                - RPL_YOUREOPER is sent back to a client which has
                  just successfully issued an OPER message and gained
                  operator status.

        382     RPL_REHASHING
                        "<config file> :Rehashing"

                - If the REHASH option is used and an operator sends
                  a REHASH message, an RPL_REHASHING is sent back to
                  the operator.

        391     RPL_TIME

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                        "<server> :<string showing server's local time>"

                - When replying to the TIME message, a server must send
                  the reply using the RPL_TIME format above.  The string
                  showing the time need only contain the correct day and
                  time there.  There is no further requirement for the
                  time string.

        392     RPL_USERSSTART
                        ":UserID   Terminal  Host"
        393     RPL_USERS
                        ":%-8s %-9s %-8s"
        394     RPL_ENDOFUSERS
                        ":End of users"
        395     RPL_NOUSERS
                        ":Nobody logged in"

                - If the USERS message is handled by a server, the
                  replies RPL_USERSTART, RPL_USERS, RPL_ENDOFUSERS and
                  RPL_NOUSERS are used.  RPL_USERSSTART must be sent
                  first, following by either a sequence of RPL_USERS
                  or a single RPL_NOUSER.  Following this is

        200     RPL_TRACELINK
                        "Link <version & debug level> <destination> \
                         <next server>"
                        "Try. <class> <server>"
        202     RPL_TRACEHANDSHAKE
                        "H.S. <class> <server>"
        203     RPL_TRACEUNKNOWN
                        "???? <class> [<client IP address in dot form>]"
        204     RPL_TRACEOPERATOR
                        "Oper <class> <nick>"
        205     RPL_TRACEUSER
                        "User <class> <nick>"
        206     RPL_TRACESERVER
                        "Serv <class> <int>S <int>C <server> \
        208     RPL_TRACENEWTYPE
                        "<newtype> 0 <client name>"
        261     RPL_TRACELOG
                        "File <logfile> <debug level>"

                - The RPL_TRACE* are all returned by the server in
                  response to the TRACE message.  How many are
                  returned is dependent on the the TRACE message and

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                  whether it was sent by an operator or not.  There
                  is no predefined order for which occurs first.
                  RPL_TRACEHANDSHAKE are all used for connections
                  which have not been fully established and are either
                  unknown, still attempting to connect or in the
                  process of completing the 'server handshake'.
                  RPL_TRACELINK is sent by any server which handles
                  a TRACE message and has to pass it on to another
                  server.  The list of RPL_TRACELINKs sent in
                  response to a TRACE command traversing the IRC
                  network should reflect the actual connectivity of
                  the servers themselves along that path.
                  RPL_TRACENEWTYPE is to be used for any connection
                  which does not fit in the other categories but is
                  being displayed anyway.

        211     RPL_STATSLINKINFO
                        "<linkname> <sendq> <sent messages> \
                         <sent bytes> <received messages> \
                         <received bytes> <time open>"
        212     RPL_STATSCOMMANDS
                        "<command> <count>"
        213     RPL_STATSCLINE
                        "C <host> * <name> <port> <class>"
        214     RPL_STATSNLINE
                        "N <host> * <name> <port> <class>"
        215     RPL_STATSILINE
                        "I <host> * <host> <port> <class>"
        216     RPL_STATSKLINE
                        "K <host> * <username> <port> <class>"
        218     RPL_STATSYLINE
                        "Y <class> <ping frequency> <connect \
                         frequency> <max sendq>"
        219     RPL_ENDOFSTATS
                        "<stats letter> :End of /STATS report"
        241     RPL_STATSLLINE
                        "L <hostmask> * <servername> <maxdepth>"
        242     RPL_STATSUPTIME
                        ":Server Up %d days %d:%02d:%02d"
        243     RPL_STATSOLINE
                        "O <hostmask> * <name>"
        244     RPL_STATSHLINE
                        "H <hostmask> * <servername>"

        221     RPL_UMODEIS
                        "<user mode string>"

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                        - To answer a query about a client's own mode,
                          RPL_UMODEIS is sent back.

        251     RPL_LUSERCLIENT
                        ":There are <integer> users and <integer> \
                         invisible on <integer> servers"
        252     RPL_LUSEROP
                        "<integer> :operator(s) online"
        253     RPL_LUSERUNKNOWN
                        "<integer> :unknown connection(s)"
        254     RPL_LUSERCHANNELS
                        "<integer> :channels formed"
        255     RPL_LUSERME
                        ":I have <integer> clients and <integer> \

                        - In processing an LUSERS message, the server
                          sends a set of replies from RPL_LUSERCLIENT,
                          RPL_LUSEROP, RPL_USERUNKNOWN,
                          RPL_LUSERCHANNELS and RPL_LUSERME.  When
                          replying, a server must send back
                          RPL_LUSERCLIENT and RPL_LUSERME.  The other
                          replies are only sent back if a non-zero count
                          is found for them.

        256     RPL_ADMINME
                        "<server> :Administrative info"
        257     RPL_ADMINLOC1
                        ":<admin info>"
        258     RPL_ADMINLOC2
                        ":<admin info>"
        259     RPL_ADMINEMAIL
                        ":<admin info>"

                        - When replying to an ADMIN message, a server
                          is expected to use replies RLP_ADMINME
                          through to RPL_ADMINEMAIL and provide a text
                          message with each.  For RPL_ADMINLOC1 a
                          description of what city, state and country
                          the server is in is expected, followed by
                          details of the university and department
                          (RPL_ADMINLOC2) and finally the administrative
                          contact for the server (an email address here
                          is required) in RPL_ADMINEMAIL.

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6.3 Reserved numerics.

   These numerics are not described above since they fall into one of
   the following categories:

        1. no longer in use;

        2. reserved for future planned use;

        3. in current use but are part of a non-generic 'feature' of
           the current IRC server.

        209     RPL_TRACECLASS          217     RPL_STATSQLINE
        231     RPL_SERVICEINFO         232     RPL_ENDOFSERVICES
        233     RPL_SERVICE             234     RPL_SERVLIST
        235     RPL_SERVLISTEND
        316     RPL_WHOISCHANOP         361     RPL_KILLDONE
        362     RPL_CLOSING             363     RPL_CLOSEEND
        373     RPL_INFOSTART           384     RPL_MYPORTIS
        492     ERR_NOSERVICEHOST

7. Client and server authentication

   Clients and servers are both subject to the same level of
   authentication.  For both, an IP number to hostname lookup (and
   reverse check on this) is performed for all connections made to the
   server.  Both connections are then subject to a password check (if
   there is a password set for that connection).  These checks are
   possible on all connections although the password check is only
   commonly used with servers.

   An additional check that is becoming of more and more common is that
   of the username responsible for making the connection.  Finding the
   username of the other end of the connection typically involves
   connecting to an authentication server such as IDENT as described in
   RFC 1413.

   Given that without passwords it is not easy to reliably determine who
   is on the other end of a network connection, use of passwords is
   strongly recommended on inter-server connections in addition to any
   other measures such as using an ident server.

8. Current implementations

   The only current implementation of this protocol is the IRC server,
   version 2.8. Earlier versions may implement some or all of the
   commands described by this document with NOTICE messages replacing

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   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.  On 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.

8.1 Network protocol: TCP - why it is best used here.

   IRC has been implemented on top of TCP since TCP supplies a reliable
   network protocol which is well suited to this scale of conferencing.
   The use of multicast IP is an alternative, but it is not widely
   available or supported at the present time.

8.1.1 Support of Unix sockets

   Given that Unix domain sockets allow listen/connect operations, the
   current implementation can be configured to listen and accept both
   client and server connections on a Unix domain socket.  These are
   recognized as sockets where the hostname starts with a '/'.

   When providing any information about the connections on a Unix domain
   socket, the server is required to supplant the actual hostname in
   place of the pathname unless the actual socket name is being asked

8.2 Command Parsing

   To provide useful 'non-buffered' network IO for clients and servers,
   each connection is given its own private 'input buffer' in which the
   results of the most recent read and parsing are kept.  A buffer size
   of 512 bytes is used so as to hold 1 full message, although, this
   will usually hold several commands.  The private buffer is parsed
   after every read operation for valid messages.  When dealing with
   multiple messages from one client in the buffer, care should be taken
   in case one happens to cause the client to be 'removed'.

8.3 Message delivery

   It is common to find network links saturated or hosts to which you
   are sending data unable to send data.  Although Unix typically
   handles this through the TCP window and internal buffers, the server
   often has large amounts of data to send (especially when a new
   server-server link forms) and the small buffers provided in the

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   kernel are not enough for the outgoing queue.  To alleviate this
   problem, a "send queue" is used as a FIFO queue for data to be sent.
   A typical "send queue" may grow to 200 Kbytes on a large IRC network
   with a slow network connection when a new server connects.

   When polling its connections, a server will first read and parse all
   incoming data, queuing any data to be sent out. When all available
   input is processed, the queued data is sent. This reduces the number
   of write() system calls and helps TCP make bigger packets.

8.4 Connection 'Liveness'

   To detect when a connection has died or become unresponsive, the
   server must ping each of its connections that it doesn't get a
   response from in a given amount of time.

   If a connection doesn't respond in time, its connection is closed
   using the appropriate procedures.  A connection is also dropped if
   its sendq grows beyond the maximum allowed, because it is better to
   close a slow connection than have a server process block.

8.5 Establishing a server to client connection

   Upon connecting to an IRC server, a client is sent the MOTD (if
   present) as well as the current user/server count (as per the LUSER
   command).  The server is also required to give an unambiguous message
   to the client which states its name and version as well as any other
   introductory messages which may be deemed appropriate.

   After dealing with this, the server must then send out the new user's
   nickname and other information as supplied by itself (USER command)
   and as the server could discover (from DNS/authentication servers).
   The server must send this information out with NICK first followed by

8.6 Establishing a server-server connection.

   The process of establishing of 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 recognised 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

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   checks that the server responding is authenticated properly before
   accepting the connection to be that server.

8.6.1 Server exchange of state information when connecting

   The order of state information being exchanged between servers is
   essential.  The required order is as follows:

        * all known other servers;

        * all known user information;

        * all known channel information.

   Information regarding servers is sent via extra SERVER messages, user
   information with NICK/USER/MODE/JOIN messages and channels with MODE

   NOTE: channel topics are *NOT* exchanged here because the TOPIC
   command overwrites any old topic information, so at best, the two
   sides of the connection would exchange topics.

   By passing the state information about servers first, any collisions
   with servers that already exist occur before nickname collisions due
   to 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, the place where the collision occurs indicating where the
   net needs to split.

8.7 Terminating server-client connections

   When a client connection closes, a QUIT message is generated on
   behalf of the client by the server to which the client connected.  No
   other message is to be generated or used.

8.8 Terminating server-server connections

   If a server-server connection is closed, either via a remotely
   generated SQUIT or 'natural' causes, the rest of the connected IRC
   network must have its information updated with by the server which
   detected the closure.  The server then sends a list of SQUITs (one
   for each server behind that connection) and a list of QUITs (again,
   one for each client behind that connection).

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8.9 Tracking nickname changes

   All IRC servers are required to keep a history of recent nickname
   changes.  This is required to allow the server to have a chance of
   keeping in touch of things when nick-change race conditions occur
   with commands which manipulate them.  Commands which must trace nick
   changes are:

        * KILL (the nick being killed)

        * MODE (+/- o,v)

        * KICK (the nick being kicked)

   No other commands are to have nick changes checked for.

   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 currently belongs to (if anyone!).  This reduces the chances of
   race conditions but they can still occur with the server ending up
   affecting the wrong client.  When performing a change trace for an
   above command it is recommended that a time range be given and
   entries which are too old ignored.

   For a reasonable history, a server should be able to keep previous
   nickname for every client it knows about if they all decided to
   change.  This size is limited by other factors (such as memory, etc).

8.10 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 be 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 seconds ahead of the current
          time, parse any present messages and penalize the client by
          2 seconds for each message;

   which in essence means that the client may send 1 message every 2

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   seconds without being adversely affected.

8.11 Non-blocking lookups

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

8.11.1 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 which were
   setup for non-blocking IO operations and then polled from within the
   main server IO loop.

8.11.2 Username (Ident) lookups

   Although there are numerous ident libraries 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.

8.12 Configuration File

   To provide a flexible way of setting up and running the server, it is
   recommended that a configuration file be used which contains
   instructions to the server on the following:

        * which hosts to accept client connections from;

        * which hosts to allow to connect as servers;

        * which hosts to connect to (both actively and

        * information about where the server is (university,
          city/state, company are examples of this);

        * who is responsible for the server and an email address
          at which they can be contacted;

        * hostnames and passwords for clients which wish to be given

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          access to restricted operator commands.

   In specifying hostnames, both domain names and use of the 'dot'
   notation ( should both be accepted.  It must be possible to
   specify the password to be used/accepted for all outgoing and
   incoming connections (although the only outgoing connections are
   those to other servers).

   The above list is the minimum requirement for any server which wishes
   to make a connection with another server.  Other items which may be
   of use are:

        * specifying which servers other server may introduce;

        * how deep a server branch is allowed to become;

        * hours during which clients may connect.

8.12.1 Allowing clients to connect

   A server should use some sort of 'access control list' (either in the
   configuration file or elsewhere) that is read at startup and used to
   decide what hosts clients may use to connect to it.

   Both 'deny' and 'allow' should be implemented to provide the required
   flexibility for host access control.

8.12.2 Operators

   The granting of operator privileges to a disruptive person can have
   dire consequences for the well-being of the IRC net in general due to
   the powers given to them.  Thus, the acquisition of such powers
   should not be very easy.  The current setup requires two 'passwords'
   to be used although one of them is usually easy guessed.  Storage of
   oper passwords in configuration files is preferable to hard coding
   them in and should be stored in a crypted format (ie using crypt(3)
   from Unix) to prevent easy theft.

8.12.3 Allowing servers to connect

   The interconnection of server is not a trivial matter: a bad
   connection can have a large impact on the usefulness of IRC.  Thus,
   each server should have a list of servers to which it may connect and
   which servers may connect to it.  Under no circumstances should a
   server allow an arbitrary host to connect as a server.  In addition
   to which servers may and may not connect, the configuration file
   should also store the password and other characteristics of that

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8.12.4 Administrivia

   To provide accurate and valid replies to the ADMIN command (see
   section 4.3.7), the server should find the relevant details in the

8.13 Channel membership

   The current server allows any registered local user to join upto 10
   different channels.  There is no limit imposed on non-local users so
   that the server remains (reasonably) consistant with all others on a
   channel membership basis

9. Current problems

   There are a number of recognized problems with this protocol, all  of
   which  hope to be solved sometime in the near future during its
   rewrite.  Currently, work is underway to find working solutions to
   these problems.

9.1 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 users 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.

9.2 Labels

   The current IRC protocol has 3 types of labels: the nickname, the
   channel name and the server name.  Each of the three 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
   three, resulting in collisions.  It is widely recognized that this
   needs reworking, with a plan for unique names for channels and nicks
   that don't collide being desirable as well as a solution allowing a
   cyclic tree.

9.2.1 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 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

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   both will removed by use of KILL (4.6.1).

9.2.2 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 (both people who create the
   new channel are considered to be members of it) rather than an
   exclusive one such as used to solve nickname collisions.

9.2.3 Servers

   Although the number of servers is usually small relative to the
   number of users and channels, they two currently required to be known
   globally, either each one separately or hidden behind a mask.

9.3 Algorithms

   In some places within the server code, it has not  been  possible  to
   avoid  N^2  algorithms  such  as  checking  the channel list of a set
   of clients.

   In current server versions, there are no database consistency checks,
   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

10. Current support and availability

           Mailing lists for IRC related discussion:
                Future protocol:
                General discussion:

           Software implemenations

           Newsgroup: alt.irc

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Security Considerations

   Security issues are discussed in sections 4.1, 4.1.1, 4.1.3, 5.5, and

12. Authors' Addresses

   Jarkko Oikarinen
   Tuirantie 17 as 9
   90500 OULU


   Darren Reed
   4 Pateman Street
   Watsonia, Victoria 3087