The IRC RFC (1459)
     Network Working Group J. Oikarinen
     Request for Comments: 1459 D. Reed
     May 1993
     Internet Relay Chat Protocol
     Status of This Memo
     This memo defines an Experimental Protocol for the Internet
     community. Discussion and suggestions for improvement are requested.
     Please refer to the current edition of the "IAB Official Protocol
     Standards" for the standardization state and status of this protocol.
     Distribution of this memo is unlimited.
     The IRC protocol was developed over the last 4 years since it was
     first implemented as a means for users on a BBS to chat amongst
     themselves. Now it supports a world-wide network of servers and
     clients, and is stringing to cope with growth. Over the past 2 years,
     the average number of users connected to the main IRC network has
     grown by a factor of 10.
     The IRC protocol is a text-based protocol, with the simplest client
     being any socket program capable of connecting to the server.
     Table of Contents
     1. INTRODUCTION ............................................... 4
     1.1 Servers ................................................ 4
     1.2 Clients ................................................ 5
     1.2.1 Operators .......................................... 5
     1.3 Channels ................................................ 5
     1.3.1 Channel Operators .................................... 6
     2. THE IRC SPECIFICATION ....................................... 7
     2.1 Overview ................................................ 7
     2.2 Character codes ......................................... 7
     2.3 Messages ................................................ 7
     2.3.1 Message format in 'pseudo' BNF .................... 8
     2.4 Numeric replies ......................................... 10
     3. IRC Concepts ................................................ 10
     3.1 One-to-one communication ................................ 10
     3.2 One-to-many ............................................. 11
     3.2.1 To a list .......................................... 11
     3.2.2 To a group (channel) ............................... 11
     3.2.3 To a host/server mask .............................. 12
     3.3 One to all .............................................. 12
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     RFC 1459 Internet Relay Chat Protocol May 1993
     3.3.1 Client to Client ................................... 12
     3.3.2 Clients to Server .................................. 12
     3.3.3 Server to Server ................................... 12
     4. MESSAGE DETAILS ............................................. 13
     4.1 Connection Registration ................................. 13
     4.1.1 Password message ................................... 14
     4.1.2 Nickname message ................................... 14
     4.1.3 User message ....................................... 15
     4.1.4 Server message ..................................... 16
     4.1.5 Operator message ................................... 17
     4.1.6 Quit message ....................................... 17
     4.1.7 Server Quit message ................................ 18
     4.2 Channel operations ...................................... 19
     4.2.1 Join message ....................................... 19
     4.2.2 Part message ....................................... 20
     4.2.3 Mode message ....................................... 21 Channel modes ................................. 21 User modes .................................... 22
     4.2.4 Topic message ...................................... 23
     4.2.5 Names message ...................................... 24
     4.2.6 List message ....................................... 24
     4.2.7 Invite message ..................................... 25
     4.2.8 Kick message ....................................... 25
     4.3 Server queries and commands ............................. 26
     4.3.1 Version message .................................... 26
     4.3.2 Stats message ...................................... 27
     4.3.3 Links message ...................................... 28
     4.3.4 Time message ....................................... 29
     4.3.5 Connect message .................................... 29
     4.3.6 Trace message ...................................... 30
     4.3.7 Admin message ...................................... 31
     4.3.8 Info message ....................................... 31
     4.4 Sending messages ........................................ 32
     4.4.1 Private messages ................................... 32
     4.4.2 Notice messages .................................... 33
     4.5 User-based queries ...................................... 33
     4.5.1 Who query .......................................... 33
     4.5.2 Whois query ........................................ 34
     4.5.3 Whowas message ..................................... 35
     4.6 Miscellaneous messages .................................. 35
     4.6.1 Kill message ....................................... 36
     4.6.2 Ping message ....................................... 37
     4.6.3 Pong message ....................................... 37
     4.6.4 Error message ...................................... 38
     5. OPTIONAL MESSAGES ........................................... 38
     5.1 Away message ............................................ 38
     5.2 Rehash command .......................................... 39
     5.3 Restart command ......................................... 39
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     5.4 Summon message .......................................... 40
     5.5 Users message ........................................... 40
     5.6 Operwall command ........................................ 41
     5.7 Userhost message ........................................ 42
     5.8 Ison message ............................................ 42
     6. REPLIES ..................................................... 43
     6.1 Error Replies ........................................... 43
     6.2 Command responses ....................................... 48
     6.3 Reserved numerics ....................................... 56
     7. Client and server authentication ............................ 56
     8. Current Implementations Details ............................. 56
     8.1 Network protocol: TCP ................................... 57
     8.1.1 Support of Unix sockets ............................ 57
     8.2 Command Parsing ......................................... 57
     8.3 Message delivery ........................................ 57
     8.4 Connection 'Liveness' ................................... 58
     8.5 Establishing a server-client connection ................. 58
     8.6 Establishing a server-server connection ................. 58
     8.6.1 State information exchange when connecting ......... 59
     8.7 Terminating server-client connections ................... 59
     8.8 Terminating server-server connections ................... 59
     8.9 Tracking nickname changes ............................... 60
     8.10 Flood control of clients ............................... 60
     8.11 Non-blocking lookups ................................... 61
     8.11.1 Hostname (DNS) lookups ............................ 61
     8.11.2 Username (Ident) lookups .......................... 61
     8.12 Configuration file ..................................... 61
     8.12.1 Allowing clients to connect ....................... 62
     8.12.2 Operators ......................................... 62
     8.12.3 Allowing servers to connect ....................... 62
     8.12.4 Administrivia ..................................... 63
     8.13 Channel membership ..................................... 63
     9. Current problems ............................................ 63
     9.1 Scalability ............................................. 63
     9.2 Labels .................................................. 63
     9.2.1 Nicknames .......................................... 63
     9.2.2 Channels ........................................... 64
     9.2.3 Servers ............................................ 64
     9.3 Algorithms .............................................. 64
     10. Support and availability ................................... 64
     11. Security Considerations .................................... 65
     12. Authors' Addresses ......................................... 65
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     RFC 1459 Internet Relay Chat Protocol May 1993
     The IRC (Internet Relay Chat) protocol has been designed over a
     number of years for use with text based conferencing. This document
     describes the current IRC protocol.
     The IRC protocol has been developed on systems using the TCP/IP
     network protocol, although there is no requirement that this remain
     the only sphere in which it operates.
     IRC itself is a teleconferencing system, which (through the use of
     the client-server model) is well-suited to running on many machines
     in a distributed fashion. A typical setup involves a single process
     (the server) forming a central point for clients (or other servers)
     to connect to, performing the required message delivery/multiplexing
     and other functions.
     1.1 Servers
     The server forms the backbone of IRC, providing a point to which
     clients may connect to to talk to each other, and a point for other
     servers to connect to, forming an IRC network. The only network
     configuration allowed for IRC servers is that of a spanning tree [see
     Fig. 1] where each server acts as a central node for the rest of the
     net it sees.
     [ Server 15 ] [ Server 13 ] [ Server 14]
     / \ /
     / \ /
     [ Server 11 ] ------ [ Server 1 ] [ Server 12]
     / \ /
     / \ /
     [ Server 2 ] [ Server 3 ]
     / \ \
     / \ \
     [ Server 4 ] [ Server 5 ] [ Server 6 ]
     / | \ /
     / | \ /
     / | \____ /
     / | \ /
     [ Server 7 ] [ Server 8 ] [ Server 9 ] [ Server 10 ]
     [ etc. ]
     [ Fig. 1. Format of IRC server network ]
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     RFC 1459 Internet Relay Chat Protocol May 1993
     1.2 Clients
     A client is anything connecting to a server that is not another
     server. Each client is distinguished from other clients by a unique
     nickname having a maximum length of nine (9) characters. See the
     protocol grammar rules 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 clients: the real name of the host
     that the client is running on, the username of the client on that
     host, and the server to which the client is connected.
     1.2.1 Operators
     To allow a reasonable amount of order to be kept within the IRC
     network, a special class of clients (operators) is allowed to perform
     general maintenance functions on the network. Although the powers
     granted to an operator can be considered as 'dangerous', they are
     nonetheless required. Operators should be able to perform basic
     network tasks such as disconnecting and reconnecting servers as
     needed to prevent long-term use of bad network routing. In
     recognition of this need, the protocol discussed herein provides for
     operators only to be able to perform such functions. See sections
     4.1.7 (SQUIT) and 4.3.5 (CONNECT).
     A more controversial power of operators is the ability to remove a
     user from the connected network by 'force', i.e. operators are able
     to close the connection between any client and server. The
     justification for this is delicate since its abuse is both
     destructive and annoying. For further details on this type of
     action, see section 4.6.1 (KILL).
     1.3 Channels
     A channel is a named group of one or more clients which will all
     receive messages addressed to that channel. The channel is created
     implicitly when the first client joins it, and the channel ceases to
     exist when the last client leaves it. While channel exists, any
     client can reference the channel using the name of the channel.
     Channels names are strings (beginning with a '&' or '#' character) of
     length up to 200 characters. Apart from the the requirement that the
     first character being either '&' or '#'; the only restriction on a
     channel name is that it may not contain any spaces (' '), a control G
     (^G or ASCII 7), or a comma (',' which is used as a list item
     separator by the protocol).
     There are two types of channels allowed by this protocol. One is a
     distributed channel which is known to all the servers that are
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     RFC 1459 Internet Relay Chat Protocol May 1993
     connected to the network. These channels are marked by the first
     character being a only clients on the server where it exists may join
     it. These are distinguished by a leading '&' character. On top of
     these two types, there are the various channel modes available to
     alter the characteristics of individual channels. See section 4.2.3
     (MODE command) for more details on this.
     To create a new channel or become part of an existing channel, a user
     is required to JOIN the channel. If the channel doesn't exist prior
     to joining, the channel is created and the creating user becomes a
     channel operator. If the channel already exists, whether or not your
     request to JOIN that channel is honoured depends on the current modes
     of the channel. For example, if the channel is invite-only, (+i),
     then you may only join if invited. As part of the protocol, a user
     may be a part of several channels at once, but a limit of ten (10)
     channels is recommended as being ample for both experienced and
     novice users. See section 8.13 for more information on this.
     If the IRC network becomes disjoint because of a split between two
     servers, the channel on each side is only composed of those clients
     which are connected to servers on the respective sides of the split,
     possibly ceasing to exist on one side of the split. When the split
     is healed, the connecting servers announce to each other who they
     think is in each channel and the mode of that channel. If the
     channel exists on both sides, the JOINs and MODEs are interpreted in
     an inclusive manner so that both sides of the new connection will
     agree about which clients are in the channel and what modes the
     channel has.
     1.3.1 Channel Operators
     The channel operator (also referred to as a "chop" or "chanop") on a
     given channel is considered to 'own' that channel. In recognition of
     this status, channel operators are endowed with certain powers which
     enable them to keep control and some sort of sanity in their channel.
     As an owner of a channel, a channel operator is not required to have
     reasons for their actions, although if their actions are generally
     antisocial or otherwise abusive, it might be reasonable to ask an IRC
     operator to intervene, or for the usersjust leave and go elsewhere
     and form their own channel.
     The commands which may only be used by channel operators are:
     KICK - Eject a client from the channel
     MODE - Change the channel's mode
     INVITE - Invite a client to an invite-only channel (mode +i)
     TOPIC - Change the channel topic in a mode +t channel
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     A channel operator is identified by the '@' symbol next to their
     nickname whenever it is associated with a channel (ie replies to the
     NAMES, WHO and WHOIS commands).
     2. The IRC Specification
     2.1 Overview
     The protocol as described herein is for use both with server to
     server and client to server connections. There are, however, more
     restrictions on client connections (which are considered to be
     untrustworthy) than on server connections.
     2.2 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 USASCII terminal and a
     telnet connection.
     Because of IRC's scandanavian 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.
     2.3 Messages
     Servers and clients send eachother messages which may or may not
     generate a reply. If the message contains a valid command, as
     described in later sections, the client should expect a reply as
     specified but it is not advised to wait forever for the reply; client
     to server and server to server communication is essentially
     asynchronous in nature.
     Each IRC message may consist of up to three main parts: the prefix
     (optional), the command, and the command parameters (of which there
     may be up to 15). The prefix, command, and all parameters are
     separated by one (or more) ASCII space character(s) (0x20).
     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
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     RFC 1459 Internet Relay Chat Protocol May 1993
     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 prefix when sending a message from
     themselves; if they use a prefix, the only valid prefix is the
     registered nickname associated with the client. If the source
     identified by the prefix cannot be found from the server's internal
     database, or if the source is registered from a different link than
     from which the message arrived, the server must ignore the message
     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 7 for more details about
     current implementations.
     2.3.1 Message format in 'pseudo' 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 matched either by <middle> or
     <trailing> components.
     The BNF representation for this is:
     <message> ::= [':' <prefix> <SPACE> ] <command> <params>      <crlf>
     <prefix> ::= <servername> | <nick> [ '!' <user> ]      [ '@' <host> ]
     <command> ::= <letter> { <letter> } | <number> <number>      <number>
     <SPACE> ::= ' ' { ' ' }
     <params> ::= <SPACE> [ ':' <trailing> | <middle> <params>      ]
     <middle> ::= <Any *non-empty* sequence of octets not including SPACE
     or NUL or CR or LF, the first of which may not be ':'>
     <trailing> ::= <Any, possibly *empty*, sequence of octets not including
     NUL or CR or LF>
     <crlf> ::= CR LF
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     1) <SPACE> is consists only of SPACE character(s) (0x20).
     Specially notice that TABULATION, and all other control
     characters are considered NON-WHITE-SPACE.
     2) After extracting the parameter list, all parameters are equal,
     whether matched by <middle> or <trailing>. <Trailing> is      just
     a syntactic trick to allow SPACE within parameter.
     3) The fact that CR and LF cannot appear in parameter strings is
     just artifact of the message framing. This might change later.
     4) The NUL character is not special in message framing, and
     basically could end up inside a parameter, but as it would
     cause extra complexities in normal C string handling. Therefore
     NUL is not allowed within messages.
     5) The last parameter may be an empty string.
     6) Use of 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.
     Most protocol messages specify additional semantics and syntax for
     the extracted parameter strings dictated by their position in the
     list. For example, many server commands will assume that the first
     parameter after the command is the list of targets, which can be
     described with:
     <target> ::= <to> [ "," <target> ]
     <to> ::= <channel> | <user> '@' <servername> | <nick>      | <mask>
     <channel> ::= ('#' | '&') <chstring>
     <servername> ::= <host>
     <host> ::= see RFC 952 [DNS:4] for details on allowed hostnames
     <nick> ::= <letter> { <letter> | <number> | <special>      }
     <mask> ::= ('#' | '$') <chstring>
     <chstring> ::= <any 8bit code except SPACE, BELL, NUL, CR, LF and
     comma (',')>
     Other parameter syntaxes are:
     <user> ::= <nonwhite> { <nonwhite> }
     <letter> ::= 'a' ... 'z' | 'A' ... 'Z'
     <number> ::= '0' ... '9'
     <special> ::= '-' | '[' | ']' | '\' | '`' | '^' | '{' | '}'
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     RFC 1459 Internet Relay Chat Protocol May 1993
     <nonwhite> ::= <any 8bit code except SPACE (0x20), NUL (0x0), CR
     (0xd), and LF (0xa)>
     2.4 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 section 6.
     3. IRC Concepts.
     This section is devoted to describing the actual concepts behind the
     organization of the IRC protocol and how the current
     implementations deliver different classes of messages.
     A D---4
     2--/ \ /
     / \
     3 E
     Servers: A, B, C, D, E Clients: 1, 2, 3, 4
     [ Fig. 2. Sample small IRC network ]
     3.1 One-to-one communication
     Communication on a one-to-one basis is usually only performed by
     clients, since most server-server traffic is not a result of servers
     talking only to each other. To provide a secure means for clients to
     talk to each other, it is required that all servers be able to send a
     message in exactly one direction along the spanning tree in order to
     reach any client. The path of a message being delivered is the
     shortest path between any two points on the spanning tree.
     The following examples all refer to Figure 2 above.
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     RFC 1459 Internet Relay Chat Protocol May 1993
     Example 1:
     A message between clients 1 and 2 is only seen by server A, which
     sends it straight to client 2.
     Example 2:
     A message between clients 1 and 3 is seen by servers A & B, and
     client 3. No other clients or servers are allowed see the message.
     Example 3:
     A message between clients 2 and 4 is seen by servers A, B, C & D
     and client 4 only.
     3.2 One-to-many
     The main goal of IRC is to provide a forum which allows easy and
     efficient conferencing (one to many conversations). IRC offers
     several means to achieve this, each serving its own purpose.
     3.2.1 To a list
     The least efficient style of one-to-many conversation is through
     clients talking to a 'list' of users. How this is done is almost
     self explanatory: the client gives a list of destinations to which
     the message is to be delivered and the server breaks it up and
     dispatches a separate copy of the message to each given destination.
     This isn't as efficient as using a group since the destination list
     is broken up and the dispatch sent without checking to make sure
     duplicates aren't sent down each path.
     3.2.2 To a group (channel)
     In IRC the channel has a role equivalent to that of the multicast
     group; their existence is dynamic (coming and going as people join
     and leave channels) and the actual conversation carried out on a
     channel is only sent to servers which are supporting users on a given
     channel. If there are multiple users on a server in the same
     channel, the message text is sent only once to that server and then
     sent to each client on the channel. This action is then repeated for
     each client-server combination until the original message has fanned
     out and reached each member of the channel.
     The following examples all refer to Figure 2.
     Example 4:
     Any channel with 1 client in it. Messages to the channel go to the
     server and then nowhere else.
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     Example 5:
     2 clients in a channel. All messages traverse a path as if they
     were private messages between the two clients outside a channel.
     Example 6:
     Clients 1, 2 and 3 in a channel. All messages to the channel are
     sent to all clients and only those servers which must be traversed
     by the message if it were a private message to a single client. If
     client 1 sends a message, it goes back to client 2 and then via
     server B to client 3.
     3.2.3 To a host/server mask
     To provide IRC operators with some mechanism to send messages to a
     large body of related users, host and server mask messages are
     provided. These messages are sent to users whose host or server
     information match that of the mask. The messages are only sent to
     locations where users are, in a fashion similar to that of channels.
     3.3 One-to-all
     The one-to-all type of message is better described as a broadcast
     message, sent to all clients or servers or both. On a large network
     of users and servers, a single message can result in a lot of traffic
     being sent over the network in an effort to reach all of the desired
     For some messages, there is no option but to broadcast it to all
     servers so that the state information held by each server is
     reasonably consistent between servers.
     3.3.1 Client-to-Client
     There is no class of message which, from a single message, results in
     a message being sent to every other client.
     3.3.2 Client-to-Server
     Most of the commands which result in a change of state information
     (such as channel membership, channel mode, user status, etc) must be
     sent to all servers by default, and this distribution may not be
     changed by the client.
     3.3.3 Server-to-Server.
     While most messages between servers are distributed to all 'other'
     servers, this is only required for any message that affects either a
     user, channel or server. Since these are the basic items found in
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     RFC 1459 Internet Relay Chat Protocol May 1993
     IRC, nearly all messages originating from a server are broadcast to
     all other connected servers.
     4. Message details
     On the following pages are descriptions of each message recognized by
     the IRC server and client. All commands described in this section
     must be implemented by any server for this protocol.
     Where the reply ERR_NOSUCHSERVER is listed, it means that the
     <server> parameter could not be found. The server must not send any
     other replies after this 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 be considered to be incorrect command, a destination which is
     otherwise unknown to the server (server, nick 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.
     4.1 Connection Registration
     The commands described here are used to register a connection with an
     IRC server as either a user or a server as well as correctly
     A "PASS" command is not required for either client or server
     connection to be registered, but it must precede the server message
     or the latter of the NICK/USER combination. It is strongly
     recommended that all server connections have a password in order to
     give some level of security to the actual connections. The
     recommended order for a client to register is as follows:
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     RFC 1459 Internet Relay Chat Protocol May 1993
     1. Pass message
     2. Nick message
     3. User message
     4.1.1 Password message
     Command: PASS
     Parameters: <password>
     The PASS command is used to set a 'connection password'. The
     password can and must be set before any attempt to register the
     connection is made. Currently this requires that clients send a PASS
     command before sending the NICK/USER combination and servers *must*
     send a PASS command before any SERVER command. The password supplied
     must match the one contained in the C/N lines (for servers) or I
     lines (for clients). It is possible to send multiple PASS commands
     before registering but only the last one sent is used for
     verification and it may not be changed once registered. Numeric
     PASS secretpasswordhere
     4.1.2 Nick message
     Command: NICK
     Parameters: <nickname> [ <hopcount> ]
     NICK message is used to give user a nickname or change the previous
     one. The <hopcount> parameter is only used by servers to indicate
     how far away a nick is from its home server. A local connection has
     a hopcount of 0. If supplied by a client, it must be ignored.
     If a NICK message arrives at a server which already knows about an
     identical nickname for another client, a nickname collision occurs.
     As a result of a nickname collision, all instances of the nickname
     are removed from the server's database, and a KILL command is issued
     to remove the nickname from all other server's database. If the NICK
     message causing the collision was a nickname change, then the
     original (old) nick must be removed as well.
     If the server recieves an identical NICK from a client which is
     directly connected, it may issue an ERR_NICKCOLLISION to the local
     client, drop the NICK command, and not generate any kills.
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     Numeric Replies:
     NICK Wiz ; Introducing new nick "Wiz".
     :WiZ NICK Kilroy ; WiZ changed his nickname to Kilroy.
     4.1.3 User message
     Command: USER
     Parameters: <username> <hostname> <servername> <realname>
     The USER message is used at the beginning of connection to specify
     the username, hostname, servername and realname of s new user. It is
     also used in communication between servers to indicate new user
     arriving on IRC, since only after both USER and NICK have been
     received from a client does a user become registered.
     Between servers USER must to be prefixed with client's NICKname.
     Note that hostname and servername are normally ignored by the IRC
     server when the USER command comes from a directly connected client
     (for security reasons), but they are used in server to server
     communication. This means that a NICK must always be sent to a
     remote server when a new user is being introduced to the rest of the
     network before the accompanying USER is sent.
     It must be noted that realname parameter must be the last parameter,
     because it may contain space characters and must be prefixed with a
     colon (':') to make sure this is recognised as such.
     Since it is easy for a client to lie about its username by relying
     solely on the USER message, the use of an "Identity Server" is
     recommended. If the host which a user connects from has such a
     server enabled the username is set to that as in the reply from the
     "Identity Server".
     Numeric Replies:
     USER guest tolmoon tolsun :Ronnie Reagan
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     ; User registering themselves with a
     username of "guest" and real name
     "Ronnie Reagan".
     :testnick USER guest tolmoon tolsun :Ronnie Reagan
     ; message between servers with the
     nickname for which the USER command
     belongs to
     4.1.4 Server message
     Command: SERVER
     Parameters: <servername> <hopcount> <info>
     The server message is used to tell a server that the other end of a
     new connection is a server. This message is also used to pass server
     data over whole net. When a new server is connected to net,
     information about it be broadcast to the whole network. <hopcount>
     is used to give all servers some internal information on how far away
     all servers are. 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 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
     Most errors that occur with the receipt of a SERVER command result in
     the connection being terminated by the destination host (target
     SERVER). Error replies are usually sent using the "ERROR" command
     rather than the numeric since the ERROR command has several useful
     properties which make it useful here.
     If a SERVER message is parsed and attempts to introduce a server
     which is already known to the receiving server, the connection from
     which that message must be closed (following the correct procedures),
     since a duplicate route to a server has formed and the acyclic nature
     of the IRC tree broken.
     Numeric Replies:
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     SERVER 1 :[] Experimental server
     ; New server introducing
     itself and attempting to register. The
     name in []'s is the hostname for the
     host running
  SERVER 5 :BU Central Server
     ; Server is our uplink
     for which is 5 hops away.
     4.1.5 Oper
     Command: OPER
     Parameters: <user> <password>
     OPER message is used by a normal user to obtain operator privileges.
     The combination of <user> and <password> are required to gain
     Operator privileges.
     If the client sending the OPER command supplies the correct password
     for the given user, the server then informs the rest of the network
     of the new operator by issuing a "MODE +o" for the clients nickname.
     The OPER message is client-server only.
     Numeric Replies:
     OPER foo bar ; Attempt to register as an operator
     using a username of "foo" and "bar" as
     the password.
     4.1.6 Quit
     Command: QUIT
     Parameters: [<Quit message>]
     A client session is ended 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.
     When netsplits (disconnecting of two servers) occur, the quit message
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     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 that of the server that has become
     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.
     Numeric Replies:
     QUIT :Gone to have lunch ; Preferred message format.
     4.1.7 Server quit message
     Command: SQUIT
     Parameters: <server> <comment>
     The SQUIT message is needed to tell 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 the name of the
     other server as the server parameter, which then closes its
     connection to the quitting server.
     This command is also available operators to help keep a network of
     IRC servers connected in an orderly fashion. Operators may also
     issue an SQUIT message for a remote server connection. In this case,
     the SQUIT must be parsed by each server inbetween the operator and
     the remote server, updating the view of the network held by each
     server as explained below.
     The <comment> should be supplied by all operators who execute a SQUIT
     for a remote server (that is not connected to the server they are
     currently on) so that other operators are aware for the reason of
     this action. The <comment> is also filled in by servers which may
     place an error or similar message here.
     Both of the servers which are on either side of the connection being
     closed are required to to send out a SQUIT message (to all its other
     server connections) for all other servers which are considered to be
     behind that link.
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     Similarly, a QUIT message must be sent to the other connected servers
     rest of the network on behalf of all clients behind that 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.
     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.
     Numeric replies:
     SQUIT :Bad Link ? ; the server link has
     been terminated because of "Bad Link".
     :Trillian SQUIT :Server out of control
     ; message from Trillian to disconnect
     "" 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 clients).
     In implementing these, a number of race conditions are inevitable
     when clients 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>{,<channel>} [<key>{,<key>}]
     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 server the client is connected to; all other
     servers automatically add the user to the channel when it is received
     from other servers. The conditions which affect this are as follows:
     1. the user must be invited if the channel is invite-only;
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     2. the user's nick/username/hostname must not match any
     active bans;
     3. the correct key (password) must be given if it is set.
     These are discussed in more detail under the MODE command (see
     section 4.2.3 for more details).
     Once a user has joined a channel, they receive notice about all
     commands their server receives which affect the channel. This
     includes MODE, KICK, PART, QUIT and of course PRIVMSG/NOTICE. The
     JOIN command needs to 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/NOTICE messages to the channel.
     If a JOIN is successful, the user is then sent the channel's topic
     (using RPL_TOPIC) and the list of users who are on the channel (using
     RPL_NAMREPLY), which must include the user joining.
     Numeric Replies:
     JOIN #foobar ; join channel #foobar.
     JOIN &foo fubar ; join channel &foo using key "fubar".
     JOIN #foo,&bar fubar ; join channel #foo using key "fubar"
     and &bar using no key.
     JOIN #foo,#bar fubar,foobar ; join channel #foo using key "fubar".
     and channel #bar using key "foobar".
     JOIN #foo,#bar ; join channels #foo and #bar.
     :WiZ JOIN #Twilight_zone ; JOIN message from WiZ
     4.2.2 Part message
     Command: PART
     Parameters: <channel>{,<channel>}
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     The PART message causes the client sending the message to be removed
     from the list of active users for all given channels listed in the
     parameter string.
     Numeric Replies:
     PART #twilight_zone ; leave channel "#twilight_zone"
     PART #oz-ops,&group5 ; leave both channels "&group5" and
     4.2.3 Mode message
     Command: MODE
     The MODE command is a dual-purpose command in IRC. It allows both
     usernames and channels to have their mode changed. The rationale for
     this choice is that one day nicknames will be obsolete and the
     equivalent property will be the channel.
     When parsing MODE messages, it is recommended that the entire message
     be parsed first and then the changes which resulted then passed on.
  Channel modes
     Parameters: <channel> {[+|-]|o|p|s|i|t|n|b|v} [<limit>] [<user>]
     [<ban mask>]
     The MODE command is provided so that channel operators may change the
     characteristics of `their' channel. It is also required that servers
     be able to change channel modes so that channel operators may be
     The various modes available for channels are as follows:
     o - give/take channel operator privileges;
     p - private channel flag;
     s - secret channel flag;
     i - invite-only channel flag;
     t - topic settable by channel operator only flag;
     n - no messages to channel from clients on the outside;
     m - moderated channel;
     l - set the user limit to channel;
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     b - set a ban mask to keep users out;
     v - give/take the ability to speak on a moderated channel;
     k - set a channel key (password).
     When using the 'o' and 'b' options, a restriction on a total of three
     per mode command has been imposed. That is, any combination of 'o'
  User modes
     Parameters: <nickname> {[+|-]|i|w|s|o}
     The user MODEs are typically changes which affect either how the
     client is seen by others or what 'extra' messages the client is sent.
     A user MODE command may only be accepted if both the sender of the
     message and the nickname given as a parameter are both the same.
     The available modes are as follows:
     i - marks a users as invisible;
     s - marks a user for receipt of server notices;
     w - user receives wallops;
     o - operator flag.
     Additional modes may be available later on.
     If a user attempts to make themselves an operator using the "+o"
     flag, the attempt should be ignored. There is no restriction,
     however, on anyone `deopping' themselves (using "-o"). Numeric
     Use of Channel Modes:
     MODE #Finnish +im ; Makes #Finnish channel moderated and
     MODE #Finnish +o Kilroy ; Gives 'chanop' privileges to Kilroy on
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     channel #Finnish.
     MODE #Finnish +v Wiz ; Allow WiZ to speak on #Finnish.
     MODE #Fins -s ; Removes 'secret' flag from channel
     MODE #42 +k oulu ; Set the channel key to "oulu".
     MODE #eu-opers +l 10 ; Set the limit for the number of users
     on channel to 10.
     MODE &oulu +b ; list ban masks set for channel.
     MODE &oulu +b *!*@* ; prevent all users from joining.
     MODE &oulu +b *!*@*.edu ; prevent any user from a hostname
     matching *.edu from joining.
     Use of user Modes:
     :MODE WiZ -w ; turns reception of WALLOPS messages
     off for WiZ.
     :Angel MODE Angel +i ; Message from Angel to make themselves
     MODE WiZ -o ; WiZ 'deopping' (removing operator
     status). The plain reverse of this
     command ("MODE WiZ +o") must not be
     allowed from users since would bypass
     the OPER command.
     4.2.4 Topic message
     Command: TOPIC
     Parameters: <channel> [<topic>]
     The TOPIC message is used to change or view the topic of a channel.
     The topic for channel <channel> is returned if there is no <topic>
     given. If the <topic> parameter is present, the topic for that
     channel will be changed, if the channel modes permit this action.
     Numeric Replies:
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     :Wiz TOPIC #test :New topic ;User Wiz setting the topic.
     TOPIC #test :another topic ;set the topic on #test to "another
     TOPIC #test ; check the topic for #test.
     4.2.5 Names message
     Command: NAMES
     Parameters: [<channel>{,<channel>}]
     By using the NAMES command, a user can list all nicknames that are
     visible to them on any channel that they can see. Channel names
     which they can see are those which aren't private (+p) or secret (+s)
     or those which they are actually on. The <channel> parameter
     specifies which channel(s) to return information about if valid.
     There is no error reply for bad channel names.
     If no <channel> parameter is given, a list of all channels and their
     occupants is returned. At the end of this list, a list of users who
     are visible but either not on any channel or not on a visible channel
     are listed as being on `channel' "*".
     NAMES #twilight_zone,#42 ; list visible users on #twilight_zone
     and #42 if the channels are visible to
     NAMES ; list all visible channels and users
     4.2.6 List message
     Command: LIST
     Parameters: [<channel>{,<channel>} [<server>]]
     The list message is used to list channels and their topics. If the
     <channel> parameter is used, only the status of that channel
     is displayed. Private channels are listed (without their
     topics) as channel "Prv" unless the client generating the query is
     actually on that channel. Likewise, secret channels are not listed
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     at all unless the client is a member of the channel in question.
     Numeric Replies:
     LIST ; List all channels.
     LIST #twilight_zone,#42 ; List channels #twilight_zone and #42
     4.2.7 Invite message
     Command: INVITE
     Parameters: <nickname> <channel>
     The INVITE message is used to invite users to a channel. The
     parameter <nickname> is the nickname of the person to be invited to
     the target channel <channel>. There is no requirement that the
     channel the target user is being invited to must exist or be a valid
     channel. To invite a user to a channel which is invite only (MODE
     +i), the client sending the invite must be recognised as being a
     channel operator on the given channel.
     Numeric Replies:
     :Angel INVITE Wiz #Dust ; User Angel inviting WiZ to channel
     INVITE Wiz #Twilight_Zone ; Command to invite WiZ to
     4.2.8 Kick command
     Command: KICK
     Parameters: <channel> <user> [<comment>]
     The KICK command can be used to forcibly remove a user from a
     channel. It 'kicks them out' of the channel (forced PART).
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     Only a channel operator may kick another user out of a channel.
     Each server that receives a KICK message checks that it is valid
     (ie the sender is actually a channel operator) before removing
     the victim from the channel.
     Numeric Replies:
     KICK &Melbourne Matthew ; Kick Matthew from &Melbourne
     KICK #Finnish John :Speaking English
     ; Kick John from #Finnish using
     "Speaking English" as the reason
     :WiZ KICK #Finnish John ; KICK message from WiZ to remove John
     from channel #Finnish
     It is possible to extend the KICK command parameters to the
     <channel>{,<channel>} <user>{,<user>} [<comment>]
     4.3 Server queries and commands
     The server query group of commands has been designed to return
     information about any server which is connected to the network. All
     servers connected must respond to these queries and respond
     correctly. Any invalid response (or lack thereof) must be considered
     a sign of a broken server and it must be disconnected/disabled as
     soon as possible until the situation is remedied.
     In these queries, where a parameter appears as "<server>", it will
     usually mean it can be a nickname or a server or a wildcard name of
     some sort. For each parameter, however, only one query and set of
     replies is to be generated.
     4.3.1 Version message
     Command: VERSION
     Parameters: [<server>]
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     The VERSION message is used to query the version of the server
     program. An optional parameter <server> is used to query the version
     of the server program which a client is not directly connected to.
     Numeric Replies:
     :Wiz VERSION *.se ; message from Wiz to check the version
     of a server matching "*.se"
     VERSION ; check the version of server
     4.3.2 Stats message
     Command: STATS
     Parameters: [<query> [<server>]]
     The stats message is used to query statistics of certain server. If
     <server> parameter is omitted, only the end of stats reply is sent
     back. The implementation of this command is highly dependent on the
     server which replies, although the server must be able to supply
     information as described by the queries below (or similar).
     A query may be given by any single letter which is only checked by
     the destination server (if given as the <server> parameter) and is
     otherwise passed on by intermediate servers, ignored and unaltered.
     The following queries are those found in the current IRC
     implementation and provide a large portion of the setup information
     for that server. Although these may not be supported in the same way
     by other versions, all servers should be able to supply a valid reply
     to a STATS query which is consistent with the reply formats currently
     used and the purpose of the query.
     The currently supported queries are:
     c - returns a list of servers which the server may connect
     to or allow connections from;
     h - returns a list of servers which are either forced to be
     treated as leaves or allowed to act as hubs;
     i - returns a list of hosts which the server allows a client
     to connect from;
     k - returns a list of banned username/hostname combinations
     for that server;
     l - returns a list of the server's connections, showing how
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     long each connection has been established and the traffic
     over that connection in bytes and messages for each
     m - returns a list of commands supported by the server and
     the usage count for each if the usage count is non zero;
     o - returns a list of hosts from which normal clients may
     become operators;
     y - show Y (Class) lines from server's configuration file;
     u - returns a string showing how long the server has been up.
     Numeric Replies:
     STATS m ; check the command usage for the server
     you are connected to
     :Wiz STATS c ; request by WiZ for C/N line
     information from server
     4.3.3 Links message
     Command: LINKS
     Parameters: [[<remote server>] <server mask>]
     With LINKS, a user can list all servers which are known by the server
     answering the query. The returned list of servers must match the
     mask, or if no mask is given, the full list is returned.
     If <remote server> is given in addition to <server mask>, the      LINKS
     command is forwarded to the first server found that matches that name
     (if any), and that server is then required to answer the query.
     Numeric Replies:
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     LINKS *.au ; list all servers which have a name
     that matches *.au;
     :WiZ LINKS * *.edu ; LINKS message from WiZ to the first
     server matching *.edu for a list of
     servers matching *
     4.3.4 Time message
     Command: TIME
     Parameters: [<server>]
     The time message is used to query local time from the specified
     server. If the server parameter is not given, the server handling the
     command must reply to the query.
     Numeric Replies:
     TIME ; check the time on the server
     Angel TIME *.au ; user angel checking the time on a
     server matching "*.au"
     4.3.5 Connect message
     Command: CONNECT
     Parameters: <target server> [<port> [<remote server>]]
     The CONNECT command can be used to force a server to try to establish
     a new connection to another server immediately. CONNECT is a
     privileged command and is to be available only to IRC Operators. If
     a remote server is given then the CONNECT attempt is made by that
     server to <target server> and <port>.
     Numeric Replies:
     CONNECT ; Attempt to connect a server to
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     :WiZ CONNECT 6667
     ; CONNECT attempt by WiZ to get servers and connected on port
     4.3.6 Trace message
     Command: TRACE
     Parameters: [<server>]
     TRACE command is used to find the route to specific server. Each
     server that processes this message must tell the sender about it by
     sending a reply indicating it is a pass-through link, forming a chain
     of replies similar to that gained from using "traceroute". After
     sending this reply back, it must then send the TRACE message to the
     next server until given server is reached. If the <server> parameter
     is omitted, it is recommended that TRACE command send a message to
     the sender telling which servers the current server has direct
     connection to.
     If the destination given by "<server>" is an actual server, then the
     destination server is required to report all servers and users which
     are connected to it, although only operators are permitted to see
     users present. If the destination given by <server> is a nickname,
     they only a reply for that nickname is given.
     Numeric Replies:
     If the TRACE message is destined for another server, all intermediate
     servers must return a RPL_TRACELINK reply to indicate that the TRACE
     passed through it and where its going next.
     A TRACE reply may be composed of any number of the following numeric
     TRACE * ; TRACE to a server matching *
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     :WiZ TRACE AngelDust ; TRACE issued by WiZ to nick AngelDust
     4.3.7 Admin command
     Command: ADMIN
     Parameters: [<server>]
     The admin message is used to find the name of the administrator of
     the given server, or current server if <server> parameter is omitted.
     Each server must have the ability to forward ADMIN messages to other
     Numeric Replies:
     ADMIN ; request an ADMIN reply from
     :WiZ ADMIN *.edu ; ADMIN request from WiZ for first
     server found to match *.edu.
     4.3.8 Info command
     Command: INFO
     Parameters: [<server>]
     The INFO command is required to return information which describes
     the server: its version, when it was compiled, the patchlevel, when
     it was started, and any other miscellaneous information which may be
     considered to be relevant.
     Numeric Replies:
     INFO ; request an INFO reply from
     :Avalon INFO *.fi ; INFO request from Avalon for first
     server found to match *.fi.
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     INFO Angel ; request info from the server that
     Angel is connected to.
     4.4 Sending messages
     The main purpose of the IRC protocol is to provide a base for clients
     to communicate with each other. PRIVMSG and NOTICE are the only
     messages available which actually perform delivery of a text message
     from one client to another - the rest just make it possible and try
     to ensure it happens in a reliable and structured manner.
     4.4.1 Private messages
     Command: PRIVMSG
     Parameters: <receiver>{,<receiver>} <text to be sent>
     PRIVMSG is used to send private messages between users. <receiver>
     is the nickname of the receiver of the message. <receiver> can also
     be a list of names or channels separated with commas.
     The <receiver> parameter may also me a host mask (#mask) or server
     mask ($mask). In both cases the server will only send the PRIVMSG
     to those who have a server or host matching the mask. The mask must
     have at least 1 (one) "." in it and no wildcards following the
     last ".". This requirement exists to prevent people sending messages
     to "#*" or "$*", which would broadcast to all users; from
     experience, this is abused more than used responsibly and properly.
     Wildcards are the '*' and '?' characters. This extension to
     the PRIVMSG command is only available to Operators.
     Numeric Replies:
     :Angel PRIVMSG Wiz :Hello are you receiving this message ?
     ; Message from Angel to Wiz.
     PRIVMSG Angel :yes I'm receiving it !receiving it !'u>(768u+1n) .br ;
     Message to Angel.
     PRIVMSG :Hello !
     ; Message to a client on server
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  with username of "jto".
     PRIVMSG $*.fi :Server rebooting.
     ; Message to everyone on a server which
     has a name matching *.fi.
     PRIVMSG #*.edu :NSFNet is undergoing work, expect interruptions
     ; Message to all users who come from a
     host which has a name matching *.edu.
     4.4.2 Notice
     Command: NOTICE
     Parameters: <nickname> <text>
     The NOTICE message is used similarly to PRIVMSG. The difference
     between NOTICE and PRIVMSG is that automatic replies must never be
     sent in response to a NOTICE message. This rule applies to servers
     too - they must not send any error reply back to the client on
     receipt of a notice. The object of this rule is to avoid loops
     between a client automatically sending something in response to
     something it received. This is typically used by automatons (clients
     with either an AI or other interactive program controlling their
     actions) which are always seen to be replying lest they end up in a
     loop with another automaton.
     See PRIVMSG for more details on replies and examples.
     4.5 User based queries
     User queries are a group of commands which are primarily concerned
     with finding details on a particular user or group users. When using
     wildcards with any of these commands, if they match, they will only
     return information on users who are 'visible' to you. The visibility
     of a user is determined as a combination of the user's mode and the
     common set of channels you are both on.
     4.5.1 Who query
     Command: WHO
     Parameters: [<name> [<o>]]
     The WHO message is used by a client to generate a query which returns
     a list of information which 'matches' the <name> parameter given by
     the client. In the absence of the <name> parameter, all visible
     (users who aren't invisible (user mode +i) and who don't have a
     common channel with the requesting client) are listed. The same
     result can be achieved by using a <name> of "0" or any wildcard which
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     will end up matching every entry possible.
     The <name> passed to WHO is matched against users' host, server, real
     name and nickname if the channel <name> cannot be found.
     If the "o" parameter is passed only operators are returned according
     to the name mask supplied.
     Numeric Replies:
     WHO *.fi ; List all users who match against
     WHO jto* o ; List all users with a match against
     "jto*" if they are an operator.
     4.5.2 Whois query
     Command: WHOIS
     Parameters: [<server>] <nickmask>[,<nickmask>[,...]]
     This message is used to query information about particular user. The
     server will answer this message with several numeric messages
     indicating different statuses of each user which matches the nickmask
     (if you are entitled to see them). If no wildcard is present in the
     <nickmask>, any information about that nick which you are allowed to
     see is presented. A comma (',') separated list of nicknames may be
     The latter version sends the query to a specific server. It is
     useful if you want to know how long the user in question has been
     idle as only local server (ie. the server the user is directly
     connected to) knows that information, while everything else is
     globally known.
     Numeric Replies:
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     WHOIS wiz ; return available user information
     about nick WiZ
     WHOIS trillian ; ask server for user
     information about trillian
     4.5.3 Whowas
     Command: WHOWAS
     Parameters: <nickname> [<count> [<server>]]
     Whowas asks for information about a nickname which no longer exists.
     This may either be due to a nickname change or the user leaving IRC.
     In response to this query, the server searches through its nickname
     history, looking for any nicks which are lexically the same (no wild
     card matching here). The history is searched backward, returning the
     most recent entry first. If there are multiple entries, up to
     <count> replies will be returned (or all of them if no <count>
     parameter is given). If a non-positive number is passed as being
     <count>, then a full search is done.
     Numeric Replies:
     WHOWAS Wiz ; return all information in the nick
     history about nick "WiZ";
     WHOWAS Mermaid 9 ; return at most, the 9 most recent
     entries in the nick history for
     WHOWAS Trillian 1 *.edu ; return the most recent history for
     "Trillian" from the first server found
     to match "*.edu".
     4.6 Miscellaneous messages
     Messages in this category do not fit into any of the above categories
     but are nonetheless still a part of and required by the protocol.
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     4.6.1 Kill message
     Command: KILL
     Parameters: <nickname> <comment>
     The KILL message is used to cause a client-server connection to be
     closed by the server which has the actual connection. KILL is used
     by servers when they encounter a duplicate entry in the list of valid
     nicknames and is used to remove both entries. It is also available
     to operators.
     Clients which have automatic reconnect algorithms effectively make
     this command useless since the disconnection is only brief. It does
     however break the flow of data and can be used to stop large amounts
     of being abused, any user may elect to receive KILL messages
     generated for others to keep an 'eye' on would be trouble spots.
     In an arena where nicknames are required to be globally unique at all
     times, KILL messages are sent whenever 'duplicates' are detected
     (that is an attempt to register two users with the same nickname) in
     the hope that both of them will disappear and only 1 reappear.
     The comment given must reflect the actual reason for the KILL. For
     server-generated KILLs it usually is made up of details concerning
     the origins of the two conflicting nicknames. For users it is left
     up to them to provide an adequate reason to satisfy others who see
     it. To prevent/discourage fake KILLs from being generated to hide
     the identify of the KILLer, the comment also shows a 'kill-path'
     which is updated by each server it passes through, each prepending
     its name to the path.
     Numeric Replies:
     KILL David ( <-
     ; Nickname collision between
     It is recommended that only Operators be allowed to kill other users
     with KILL message. In an ideal world not even operators would need
     to do this and it would be left to servers to deal with.
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     4.6.2 Ping message
     Command: PING
     Parameters: <server1> [<server2>]
     The PING message is used to test the presence of an active client at
     the other end of the connection. A PING message is sent at regular
     intervals if no other activity detected coming from a connection. If
     a connection fails to respond to a PING command within a set amount
     of time, that connection is closed.
     Any client which receives a PING message must respond to <server1>
     (server which sent the PING message out) as quickly as possible with
     an appropriate PONG message to indicate it is still there and alive.
     Servers should not respond to PING commands but rely on PINGs from
     the other end of the connection to indicate the connection is alive.
     If the <server2> parameter is specified, the PING message gets
     forwarded there.
     Numeric Replies:
     PING ; server sending a PING message to
     another server to indicate it is still
     PING WiZ ; PING message being sent to nick WiZ
     4.6.3 Pong message
     Command: PONG
     Parameters: <daemon> [<daemon2>]
     PONG message is a reply to ping message. If parameter <daemon2> is
     given this message must be forwarded to given daemon. The <daemon>
     parameter is the name of the daemon who has responded to PING message
     and generated this message.
     Numeric Replies:
     PONG ; PONG message from to
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     4.6.4 Error
     Command: ERROR
     Parameters: <error message>
     The ERROR command is for use by servers when reporting a serious or
     fatal error to its operators. It may also be sent from one server to
     another but must not be accepted from any normal unknown clients.
     An ERROR message is for use for reporting errors which occur with a
     server-to-server link only. An ERROR message is sent to the server
     at the other end (which sends it to all of its connected operators)
     and to all operators currently connected. It is not to be passed
     onto any other servers by a server if it is received from a server.
     When a server sends a received ERROR message to its operators, the
     message should be encapsulated inside a NOTICE message, indicating
     that the client was not responsible for the error.
     ERROR :Server *.fi already exists; ERROR message to the other server
     which caused this error.
     NOTICE WiZ :ERROR from -- Server *.fi already exists
     ; Same ERROR message as above but sent
     to user WiZ on the other server.
     This section describes OPTIONAL messages. They are not required in a
     working server implementation of the protocol described herein. In
     the absence of the option, an error reply message must be generated
     or an unknown command error. If the message is destined for another
     server to answer then it must be passed on (elementary parsing
     required) The allocated numerics for this are listed with the
     messages below.
     5.1 Away
     Command: AWAY
     Parameters: [message]
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     With the AWAY message, clients can set an automatic reply string for
     any PRIVMSG commands directed at them (not to a channel they are on).
     The automatic reply is sent by the server to client sending the
     PRIVMSG command. The only replying server is the one to which the
     sending client is connected to.
     The AWAY message is used either with one parameter (to set an AWAY
     message) or with no parameters (to remove the AWAY message).
     Numeric Replies:
     AWAY :Gone to lunch. Back in 5 ; set away message to "Gone to lunch.
     Back in 5".
     :WiZ AWAY ; unmark WiZ as being away.
     5.2 Rehash message
     Command: REHASH
     Parameters: None
     The rehash message can be used by the operator to force the server to
     re-read and process its configuration file.
     Numeric Replies:
     REHASH ; message from client with operator
     status to server asking it to reread its
     configuration file.
     5.3 Restart message
     Command: RESTART
     Parameters: None
     The restart message can only be used by an operator to force a server
     restart itself. This message is optional since it may be viewed as a
     risk to allow arbitrary people to connect to a server as an operator
     and execute this command, causing (at least) a disruption to service.
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     The RESTART command must always be fully processed by the server to
     which the sending client is connected and not be passed onto other
     connected servers.
     Numeric Replies:
     RESTART ; no parameters required.
     5.4 Summon message
     Command: SUMMON
     Parameters: <user> [<server>]
     The SUMMON command can be used to give users who are on a host
     running an IRC server a message asking them to please join IRC. This
     message is only sent if the target server (a) has SUMMON enabled, (b)
     the user is logged in and (c) the server process can write to the
     user's tty (or similar).
     If no <server> parameter is given it tries to summon <user> from      the
     server the client is connected to is assumed as the target.
     If summon is not enabled in a server, it must return the
     ERR_SUMMONDISABLED numeric and pass the summon message onwards.
     Numeric Replies:
     SUMMON jto ; summon user jto on the server's host
     SUMMON jto ; summon user jto on the host which a
     server named "" is
     5.5 Users
     Command: USERS
     Parameters: [<server>]
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     The USERS command returns a list of users logged into the server in a
     similar format to who(1), rusers(1) and finger(1). Some people
     may disable this command on their server for security related
     reasons. If disabled, the correct numeric must be returned to
     indicate this.
     Numeric Replies:
     Disabled Reply:
     USERS ; request a list of users logged in on
     :John USERS ; request from John for a list of users
     logged in on server
     5.6 Operwall message
     Command: WALLOPS
     Parameters: Text to be sent to all operators currently online
     Sends a message to all operators currently online. After
     implementing WALLOPS as a user command it was found that it was
     often and commonly abused as a means of sending a message to a lot
     of people (much similar to WALL). Due to this it is recommended
     that the current implementation of WALLOPS be used as an
     example by allowing and recognising only servers as the senders of
     Numeric Replies:
  WALLOPS :Connect '* 6667' from Joshua; WALLOPS
     message from announcing a
     CONNECT message it received and acted
     upon from Joshua.
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     5.7 Userhost message
     Command: USERHOST
     Parameters: <nickname>{<space><nickname>}
     The USERHOST command takes a list of up to 5 nicknames, each
     separated by a space character and returns a list of information
     about each nickname that it found. The returned list has each reply
     separated by a space.
     Numeric Replies:
     USERHOST Wiz Michael Marty p ;USERHOST request for information on
     nicks "Wiz", "Michael", "Marty" and "p"
     5.8 Ison message
     Command: ISON
     Parameters: <nickname>{<space><nickname>}
     The ISON command was implemented to provide a quick and efficient
     means to get a response about whether a given nickname was currently
     on IRC. ISON only takes one (1) parameter: a space-separated list of
     nicks. For each nickname in the list that is present, the server
     adds that to its reply string. Thus the reply string may return
     empty (none of the given nicks are present), an exact copy of the
     parameter string (all of them present) or as any other subset of the
     set of nicks given in the parameter. The only limit on the number
     of nicks that may be checked is that the combined length must not be
     too large as to cause the server to chop it off so it fits in 512
     ISON is only be processed by the server local to the client sending
     the command and thus not passed onto other servers for further
     Numeric Replies:
     ISON phone trillian WiZ jarlek Avalon Angel Monstah
     ; Sample ISON request for 7 nicks.
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     6. REPLIES
     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.
     "<nickname> :No such nick/channel"
     - Used to indicate the nickname parameter supplied to a
     command is currently unused.
     "<server name> :No such server"
     - Used to indicate the server name given currently
     doesn't exist.
     "<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.
     "<nickname> :There was no such nickname"
     - Returned by WHOWAS to indicate there is no history
     information for that nickname.
     "<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.
     ":No origin specified"
     - PING or PONG message missing the originator parameter
     which is required since these commands must work
     without valid prefixes.
     ":No recipient given (<command>)"
     ":No text to send"
     "<mask> :No toplevel domain specified"
     "<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.
     "<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.
     "<server> :No administrative info available"
     - Returned by a server in response to an ADMIN message
     when there is an error in finding the appropriate
     ":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.
     "<nick> :Nickname is already in use"
     - Returned when a NICK message is processed that results
     in an attempt to change to a currently existing
     "<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.
     "<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.
     "<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.
     ":SUMMON has been disabled"
     - Returned as a response to the SUMMON command. Must be
     returned by any server which does not implement it.
     ":USERS has been disabled"
     - Returned as a response to the USERS command. Must be
     returned by any server which does not implement it.
     ":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.
     "<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).
     ":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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     ":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"
     "<channel> :Cannot join channel (+l)"
     "<char> :is unknown mode char to me"
     "<channel> :Cannot join channel (+i)"
     "<channel> :Cannot join channel (+b)"
     "<channel> :Cannot join channel (+k)"
     ":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
     ":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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     ":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.
     ":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.
     - 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.
     "<nick> <user> <host> * :<real name>"
     "<nick> <server> :<server info>"
     "<nick> :is an IRC operator"
     "<nick> <integer> :seconds idle"
     "<nick> :End of /WHOIS list"
     "<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.
     "<nick> <user> <host> * :<real name>"
     "<nick> :End of WHOWAS"
     - When replying to a WHOWAS message, a server must use
     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).
     "Channel :Users Name"
     322 RPL_LIST
     "<channel> <# visible> :<topic>"
     323 RPL_LISTEND
     ":End of /LIST"
     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.
     "<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
     "<channel> <nick>"
     - Returned by the server to indicate that the
     attempted INVITE message was successful and is
     being passed onto the end client.
     "<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.
     "<channel> <user> <host> <server> <nick> \
     <H|G>[*][@|+] :<hopcount> <real name>"
     "<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.
     "<channel> :[[@|+]<nick> [[@|+]<nick> [...]]]"
     "<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>"
     "<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>"
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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
     ":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
     ":- <server> Message of the day - "
     372 RPL_MOTD
     ":- <text>"
     ":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).
     ":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.
     "<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.
     ":UserID Terminal Host"
     393 RPL_USERS
     ":%-8s %-9s %-8s"
     ":End of users"
     395 RPL_NOUSERS
     ":Nobody logged in"
     - If the USERS message is handled by a server, the
     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
     "Link <version & debug level> <destination> \
     <next server>"
     "Try. <class> <server>"
     "H.S. <class> <server>"
     "???? <class> [<client IP address in dot form>]"
     "Oper <class> <nick>"
     "User <class> <nick>"
     "Serv <class> <int>S <int>C <server> \
     "<newtype> 0 <client name>"
     "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.
     "<linkname> <sendq> <sent messages> \
     <sent bytes> <received messages> \
     <received bytes> <time open>"
     "<command> <count>"
     "C <host> * <name> <port> <class>"
     "N <host> * <name> <port> <class>"
     "I <host> * <host> <port> <class>"
     "K <host> * <username> <port> <class>"
     "Y <class> <ping frequency> <connect \
     frequency> <max sendq>"
     "<stats letter> :End of /STATS report"
     "L <hostmask> * <servername> <maxdepth>"
     ":Server Up %d days %d:%02d:%02d"
     "O <hostmask> * <name>"
     "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.
     ":There are <integer> users and <integer> \
     invisible on <integer> servers"
     252 RPL_LUSEROP
     "<integer> :operator(s) online"
     "<integer> :unknown connection(s)"
     "<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,
     replying, a server must send back
     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>"
     ":<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.
     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
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