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 RFC1459 [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 RFC1459 [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, RFC2119, March 1997.

[IRC] Oikarinen, J. and D. Reed, "Internet Relay Chat
Protocol", RFC1459, 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.

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