RFC 2810 (RFC2810)

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                  RFC 2810 - Internet Relay Chat: Architecture

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 Network Working Group                                           C. Kalt
 Request for Comments: 2810                                   April 2000
 Updates: 1459
 Category: Informational

                    Internet Relay Chat: Architecture

 Status of this Memo

    This memo provides information for the Internet community.  It does
    not specify an Internet standard of any kind.  Distribution of this
    memo is unlimited.

 Copyright Notice

    Copyright (C) The Internet Society (2000).  All Rights Reserved.

 Abstract

    The IRC (Internet Relay Chat) protocol is for use with text based
    conferencing. It has been developed since 1989 when it was originally
    implemented as a mean for users on a BBS to chat amongst themselves.

    First formally documented in May 1993 by RFC 1459 [IRC], the protocol
    has kept evolving. This document is an update describing the
    architecture of the current IRC protocol and the role of its
    different components.  Other documents describe in detail the
    protocol used between the various components defined here.

 Table of Contents

    1.  Introduction ...............................................   2
    2.  Components .................................................   2
       2.1  Servers ................................................   2
       2.2  Clients ................................................   3
          2.2.1  User Clients ......................................   3
          2.2.2  Service Clients ...................................   3
    3.  Architecture ...............................................   3
    4.  IRC Protocol Services ......................................   4
       4.1  Client Locator .........................................   4
       4.2  Message Relaying .......................................   4
       4.3  Channel Hosting And Management .........................   4
    5.  IRC Concepts ...............................................   4
       5.1  One-To-One Communication ...............................   5
       5.2  One-To-Many ............................................   5
          5.2.1  To A Channel ......................................   5
          5.2.2  To A Host/Server Mask .............................   6

          5.2.3  To A List .........................................   6
       5.3  One-To-All .............................................   6
          5.3.1  Client-to-Client ..................................   6
          5.3.2  Client-to-Server ..................................   7
          5.3.3  Server-to-Server ..................................   7
    6.  Current Problems ...........................................   7
       6.1  Scalability ............................................   7
       6.2  Reliability ............................................   7
       6.3  Network Congestion .....................................   7
       6.4  Privacy ................................................   8
    7.  Security Considerations ....................................   8
    8.  Current Support And Availability ...........................   8
    9.  Acknowledgements ...........................................   8
    10.  References ................................................   8
    11.  Author's Address ..........................................   9
    12.  Full Copyright Statement ..................................  10

 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 its current architecture.

    The IRC Protocol is based on the client-server model, and 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.

    This distributed model, which requires each server to have a copy
    of the global state information, is still the most flagrant problem
    of the protocol as it is a serious handicap, which limits the maximum
    size a network can reach.  If the existing networks have been able to
    keep growing at an incredible pace, we must thank hardware
    manufacturers for giving us ever more powerful systems.

 2. Components

    The following paragraphs define the basic components of the IRC
    protocol.

 2.1 Servers

    The server forms the backbone of IRC as it is the only component
    of the protocol which is able to link all the other components
    together: it provides a point to which clients may connect to talk to

    each other [IRC-CLIENT], and a point for other servers to connect to
    [IRC-SERVER].  The server is also responsible for providing the basic
    services defined by the IRC protocol.

 2.2 Clients

    A client is anything connecting to a server that is not another
    server.  There are two types of clients which both serve a different
    purpose.

 2.2.1 User Clients

    User clients are generally programs providing a text based
    interface that is used to communicate interactively via IRC.  This
    particular type of clients is often referred as "users".

 2.2.2 Service Clients

    Unlike users, service clients are not intended to be used manually
    nor for talking.  They have a more limited access to the chat
    functions of the protocol, while optionally having access to more
    private data from the servers.

    Services are typically automatons used to provide some kind of
    service (not necessarily related to IRC itself) to users.  An example
    is a service collecting statistics about the origin of users
    connected on the IRC network.

 3. Architecture

    An IRC network is defined by a group of servers connected to each
    other.  A single server forms the simplest IRC network.

    The only network configuration allowed for IRC servers is that of
    a spanning tree where each server acts as a central node for the rest
    of the network it sees.

                        1--\
                            A        D---4
                        2--/ \      /
                              B----C
                             /      \
                            3        E

    Servers: A, B, C, D, E         Clients: 1, 2, 3, 4

                     [ Fig. 1. Sample small IRC network ]

    The IRC protocol provides no mean for two clients to directly
    communicate.  All communication between clients is relayed by the
    server(s).

 4. IRC Protocol Services

    This section describes the services offered by the IRC protocol.  The
    combination of these services allow real-time conferencing.

 4.1 Client Locator

    To be able to exchange messages, two clients must be able to locate
    each other.

    Upon connecting to a server, a client registers using a label which
    is then used by other servers and clients to know where the client is
    located.  Servers are responsible for keeping track of all the labels
    being used.

 4.2 Message Relaying

    The IRC protocol provides no mean for two clients to directly
    communicate.  All communication between clients is relayed by the
    server(s).

 4.3 Channel Hosting And Management

    A channel is a named group of one or more users which will all
    receive messages addressed to that channel.  A channel is
    characterized by its name and current members, it also has a set of
    properties which can be manipulated by (some of) its members.

    Channels provide a mean for a message to be sent to several clients.
    Servers host channels, providing the necessary message multiplexing.
    Servers are also responsible for managing channels by keeping track
    of the channel members.  The exact role of servers is defined in
    "Internet Relay Chat: Channel Management" [IRC-CHAN].

 5. IRC Concepts

    This section is devoted to describing the actual concepts behind the
    organization of the IRC protocol and how different classes of
    messages are delivered.

 5.1 One-To-One Communication

    Communication on a one-to-one basis is usually performed by clients,
    since most server-server traffic is not a result of servers talking
    only to each other.  To provide a 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.  Thus 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 1 above.

    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.

 5.2 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.

 5.2.1 To A Channel

    In IRC the channel has a role equivalent to that of the multicast
    group; their existence is dynamic and the actual conversation carried
    out on a channel MUST only be sent to servers which are supporting
    users on a given channel.  Moreover, the message SHALL only be sent
    once to every local link as each server is responsible to fan the
    original message to ensure that it will reach all the recipients.

    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.

    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.

 5.2.2 To A Host/Server Mask

    To provide with some mechanism to send messages to a large body of
    related users, host and server mask messages are available.  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.

 5.2.3 To A List

    The least efficient style of one-to-many conversation is through
    clients talking to a 'list' of targets (client, channel, mask).  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 is not as efficient as using a channel since the destination
    list MAY be broken up and the dispatch sent without checking to make
    sure duplicates aren't sent down each path.

 5.3 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 class of messages, there is no option but to broadcast it to
    all servers so that the state information held by each server is
    consistent between servers.

 5.3.1 Client-to-Client

    There is no class of message which, from a single message, results in
    a message being sent to every other client.

 5.3.2 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 SHALL NOT be
    changed by the client.

 5.3.3 Server-to-Server

    While most messages between servers are distributed to all 'other'
    servers, this is only required for any message that affects a user,
    channel or server.  Since these are the basic items found in IRC,
    nearly all messages originating from a server are broadcast to all
    other connected servers.

 6. Current Problems

    There are a number of recognized problems with this protocol, this
    section only addresses the problems related to the architecture of
    the protocol.

 6.1 Scalability

    It is widely recognized that this protocol does not scale
    sufficiently well when used in a large arena.  The main problem comes
    from the requirement that all servers know about all other servers,
    clients and channels and that information regarding them be updated
    as soon as it changes.

 6.2 Reliability

    As the only network configuration allowed for IRC servers is that of
    a spanning tree, each link between two servers is an obvious and
    quite serious point of failure.  This particular issue is addressed
    more in detail in "Internet Relay Chat: Server Protocol" [IRC-
    SERVER].

 6.3 Network Congestion

    Another problem related to the scalability and reliability issues, as
    well as the spanning tree architecture, is that the protocol and
    architecture for IRC are extremely vulnerable to network congestions.
    This problem is endemic, and should be solved for the next
    generation: if congestion and high traffic volume cause a link
    between two servers to fail, not only this failure generates more
    network traffic, but the reconnection (eventually elsewhere) of two
    servers also generates more traffic.

    In an attempt to minimize the impact of these problems, it is
    strongly RECOMMENDED that servers do not automatically try to
    reconnect too fast, in order to avoid aggravating the situation.

 6.4 Privacy

    Besides not scaling well, the fact that servers need to know all
    information about other entities, the issue of privacy is also a
    concern. This is in particular true for channels, as the related
    information is quite a lot more revealing than whether a user is
    online or not.

 7. Security Considerations

    Asides from the privacy concerns mentioned in section 6.4 (Privacy),
    security is believed to be irrelevant to this document.

 8. Current Support And Availability

         Mailing lists for IRC related discussion:
           General discussion: ircd-users@irc.org
           Protocol development: ircd-dev@irc.org

         Software implementations:
           ftp://ftp.irc.org/irc/server
           ftp://ftp.funet.fi/pub/unix/irc
           ftp://coombs.anu.edu.au/pub/irc

         Newsgroup: alt.irc

 9. Acknowledgements

    Parts of this document were copied from the RFC 1459 [IRC] which
    first formally documented the IRC Protocol.  It has also benefited
    from many rounds of review and comments.  In particular, the
    following people have made significant contributions to this
    document:

    Matthew Green, Michael Neumayer, Volker Paulsen, Kurt Roeckx, Vesa
    Ruokonen, Magnus Tjernstrom, Stefan Zehl.

 10. References

    [KEYWORDS]   Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

    [IRC]        Oikarinen, J. and D. Reed, "Internet Relay Chat
                 Protocol", RFC 1459, May 1993.

    [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
                 2812, April 2000.

    [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
                 2813, April 2000.

    [IRC-CHAN]   Kalt, C., "Internet Relay Chat: Channel Management", RFC
                 2811, April 2000.

 11. Author's Address

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

    EMail: kalt@stealth.net

 12.  Full Copyright Statement

    Copyright (C) The Internet Society (2000).  All Rights Reserved.

    This document and translations of it may be copied and furnished to
    others, and derivative works that comment on or otherwise explain it
    or assist in its implementation may be prepared, copied, published
    and distributed, in whole or in part, without restriction of any
    kind, provided that the above copyright notice and this paragraph are
    included on all such copies and derivative works.  However, this
    document itself may not be modified in any way, such as by removing
    the copyright notice or references to the Internet Society or other
    Internet organizations, except as needed for the purpose of
    developing Internet standards in which case the procedures for
    copyrights defined in the Internet Standards process must be
    followed, or as required to translate it into languages other than
    English.

    The limited permissions granted above are perpetual and will not be
    revoked by the Internet Society or its successors or assigns.

    This document and the information contained herein is provided on an
    "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
    TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
    BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
    HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
    MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

 Acknowledgement

    Funding for the RFC Editor function is currently provided by the
    Internet Society.


    

 Comments about this RFC:                                                        
                                                                                 
   * RFC 2810: Hi, Here goes the text in section 5.2.1 : "The following          
     examples all... by AkA (6/2/2007)                                           

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