RFC 2810

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.

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

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RFC 2810 Internet Relay Chat: Architecture April 2000

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

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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 ]

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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.

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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.

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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.

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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.

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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.

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RFC 2810 Internet Relay Chat: Architecture April 2000

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

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12. Full Copyright Statement

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.

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