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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.

Abstract

   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



Oikarinen & Reed                                                [Page 1]

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 4.2.3.1 Channel modes ................................. 21 4.2.3.2 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 Oikarinen & Reed [Page 2]
RFC 1459 Internet Relay Chat Protocol May 1993 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 Oikarinen & Reed [Page 3]
RFC 1459 Internet Relay Chat Protocol May 1993 1. INTRODUCTION 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 ] Oikarinen & Reed [Page 4]
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 Oikarinen & Reed [Page 5]
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 Oikarinen & Reed [Page 6]
RFC 1459 Internet Relay Chat Protocol May 1993 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 Oikarinen & Reed [Page 7]
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 silently. 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 Oikarinen & Reed [Page 8]
RFC 1459 Internet Relay Chat Protocol May 1993 NOTES: 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> ::= '-' | '[' | ']' | '\' | '`' | '^' | '{' | '}' Oikarinen & Reed [Page 9]
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. 1--\ A D---4 2--/ \ / B----C / \ 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. Oikarinen & Reed [Page 10]
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. Oikarinen & Reed [Page 11]
RFC 1459 Internet Relay Chat Protocol May 1993 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 destinations. 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 Oikarinen & Reed [Page 12]
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 disconnect. 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: Oikarinen & Reed [Page 13]
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 Replies: ERR_NEEDMOREPARAMS ERR_ALREADYREGISTRED Example: 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. Oikarinen & Reed [Page 14]
RFC 1459 Internet Relay Chat Protocol May 1993 Numeric Replies: ERR_NONICKNAMEGIVEN ERR_ERRONEUSNICKNAME ERR_NICKNAMEINUSE ERR_NICKCOLLISION Example: 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: ERR_NEEDMOREPARAMS ERR_ALREADYREGISTRED Examples: USER guest tolmoon tolsun :Ronnie Reagan Oikarinen & Reed [Page 15]
RFC 1459 Internet Relay Chat Protocol May 1993 ; 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 server. 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: ERR_ALREADYREGISTRED Example: Oikarinen & Reed [Page 16]
RFC 1459 Internet Relay Chat Protocol May 1993 SERVER test.oulu.fi 1 :[tolsun.oulu.fi] Experimental server ; New server test.oulu.fi introducing itself and attempting to register. The name in []'s is the hostname for the host running test.oulu.fi. :tolsun.oulu.fi SERVER csd.bu.edu 5 :BU Central Server ; Server tolsun.oulu.fi is our uplink for csd.bu.edu 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: ERR_NEEDMOREPARAMS RPL_YOUREOPER ERR_NOOPERHOST ERR_PASSWDMISMATCH Example: 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 Oikarinen & Reed [Page 17]
RFC 1459 Internet Relay Chat Protocol May 1993 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 disconnected. 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: None. Examples: 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. Oikarinen & Reed [Page 18]
RFC 1459 Internet Relay Chat Protocol May 1993 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: ERR_NOPRIVILEGES ERR_NOSUCHSERVER Example: SQUIT tolsun.oulu.fi :Bad Link ? ; the server link tolson.oulu.fi has been terminated because of "Bad Link". :Trillian SQUIT cm22.eng.umd.edu :Server out of control ; message from Trillian to disconnect "cm22.eng.umd.edu" from the net because "Server out of control". 4.2 Channel operations This group of messages is concerned with manipulating channels, their properties (channel modes), and their contents (typically 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; Oikarinen & Reed [Page 19]
RFC 1459 Internet Relay Chat Protocol May 1993 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: ERR_NEEDMOREPARAMS ERR_BANNEDFROMCHAN ERR_INVITEONLYCHAN ERR_BADCHANNELKEY ERR_CHANNELISFULL ERR_BADCHANMASK ERR_NOSUCHCHANNEL ERR_TOOMANYCHANNELS RPL_TOPIC Examples: 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>} Oikarinen & Reed [Page 20]
RFC 1459 Internet Relay Chat Protocol May 1993 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: ERR_NEEDMOREPARAMS ERR_NOSUCHCHANNEL ERR_NOTONCHANNEL Examples: PART #twilight_zone ; leave channel "#twilight_zone" PART #oz-ops,&group5 ; leave both channels "&group5" and "#oz-ops". 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. 4.2.3.1 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 created. 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; Oikarinen & Reed [Page 21]
RFC 1459 Internet Relay Chat Protocol May 1993 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' and 4.2.3.2 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 Replies: ERR_NEEDMOREPARAMS RPL_CHANNELMODEIS ERR_CHANOPRIVSNEEDED ERR_NOSUCHNICK ERR_NOTONCHANNEL ERR_KEYSET RPL_BANLIST RPL_ENDOFBANLIST ERR_UNKNOWNMODE ERR_NOSUCHCHANNEL ERR_USERSDONTMATCH RPL_UMODEIS ERR_UMODEUNKNOWNFLAG Examples: Use of Channel Modes: MODE #Finnish +im ; Makes #Finnish channel moderated and 'invite-only'. MODE #Finnish +o Kilroy ; Gives 'chanop' privileges to Kilroy on Oikarinen & Reed [Page 22]
RFC 1459 Internet Relay Chat Protocol May 1993 channel #Finnish. MODE #Finnish +v Wiz ; Allow WiZ to speak on #Finnish. MODE #Fins -s ; Removes 'secret' flag from channel #Fins. 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 invisible. 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: ERR_NEEDMOREPARAMS ERR_NOTONCHANNEL RPL_NOTOPIC RPL_TOPIC ERR_CHANOPRIVSNEEDED Oikarinen & Reed [Page 23]
RFC 1459 Internet Relay Chat Protocol May 1993 Examples: :Wiz TOPIC #test :New topic ;User Wiz setting the topic. TOPIC #test :another topic ;set the topic on #test to "another topic". 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' "*". Numerics: RPL_NAMREPLY RPL_ENDOFNAMES Examples: NAMES #twilight_zone,#42 ; list visible users on #twilight_zone and #42 if the channels are visible to you. 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 Oikarinen & Reed [Page 24]
RFC 1459 Internet Relay Chat Protocol May 1993 at all unless the client is a member of the channel in question. Numeric Replies: ERR_NOSUCHSERVER RPL_LISTSTART RPL_LIST RPL_LISTEND Examples: 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: ERR_NEEDMOREPARAMS ERR_NOSUCHNICK ERR_NOTONCHANNEL ERR_USERONCHANNEL ERR_CHANOPRIVSNEEDED RPL_INVITING RPL_AWAY Examples: :Angel INVITE Wiz #Dust ; User Angel inviting WiZ to channel #Dust INVITE Wiz #Twilight_Zone ; Command to invite WiZ to #Twilight_zone 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). Oikarinen & Reed [Page 25]
RFC 1459 Internet Relay Chat Protocol May 1993 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: ERR_NEEDMOREPARAMS ERR_NOSUCHCHANNEL ERR_BADCHANMASK ERR_CHANOPRIVSNEEDED ERR_NOTONCHANNEL Examples: KICK &Melbourne Matthew ; Kick Matthew from &Melbourne KICK #Finnish John :Speaking English ; Kick John from #Finnish using "Speaking English" as the reason (comment). :WiZ KICK #Finnish John ; KICK message from WiZ to remove John from channel #Finnish NOTE: It is possible to extend the KICK command parameters to the following: <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>] Oikarinen & Reed [Page 26]
RFC 1459 Internet Relay Chat Protocol May 1993
RFC 1459 Internet Relay Chat Protocol May 1993 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 Oikarinen & Reed [Page 60]
RFC 1459 Internet Relay Chat Protocol May 1993 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 passively); * 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 Oikarinen & Reed [Page 61]
RFC 1459 Internet Relay Chat Protocol May 1993 access to restricted operator commands. In specifying hostnames, both domain names and use of the 'dot' notation (127.0.0.1) 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 link. Oikarinen & Reed [Page 62]
RFC 1459 Internet Relay Chat Protocol May 1993 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 configuration. 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 Oikarinen & Reed [Page 63]
RFC 1459 Internet Relay Chat Protocol May 1993 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 disrupted. 10. Current support and availability Mailing lists for IRC related discussion: Future protocol: ircd-three-request@eff.org General discussion: operlist-request@eff.org Software implemenations cs.bu.edu:/irc nic.funet.fi:/pub/irc coombs.anu.edu.au:/pub/irc Newsgroup: alt.irc Oikarinen & Reed [Page 64]
RFC 1459 Internet Relay Chat Protocol May 1993 Security Considerations Security issues are discussed in sections 4.1, 4.1.1, 4.1.3, 5.5, and 7



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