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+Network Working Group C. Kalt
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+Request for Comments: 2810 April 2000
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+Updates: 1459
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+Category: Informational
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+ Internet Relay Chat: Architecture
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+Status of this Memo
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+ This memo provides information for the Internet community. It does
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+ not specify an Internet standard of any kind. Distribution of this
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+ memo is unlimited.
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+
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+Copyright Notice
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+
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+ Copyright (C) The Internet Society (2000). All Rights Reserved.
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+
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+Abstract
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+
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+ The IRC (Internet Relay Chat) protocol is for use with text based
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+ conferencing. It has been developed since 1989 when it was originally
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+ implemented as a mean for users on a BBS to chat amongst themselves.
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+
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+ First formally documented in May 1993 by RFC 1459 [IRC], the protocol
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+ has kept evolving. This document is an update describing the
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+ architecture of the current IRC protocol and the role of its
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+ different components. Other documents describe in detail the
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+ protocol used between the various components defined here.
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+
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+Table of Contents
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+
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+ 1. Introduction ............................................... 2
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+ 2. Components ................................................. 2
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+ 2.1 Servers ................................................ 2
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+ 2.2 Clients ................................................ 3
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+ 2.2.1 User Clients ...................................... 3
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+ 2.2.2 Service Clients ................................... 3
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+ 3. Architecture ............................................... 3
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+ 4. IRC Protocol Services ...................................... 4
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+ 4.1 Client Locator ......................................... 4
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+ 4.2 Message Relaying ....................................... 4
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+ 4.3 Channel Hosting And Management ......................... 4
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+ 5. IRC Concepts ............................................... 4
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+ 5.1 One-To-One Communication ............................... 5
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+ 5.2 One-To-Many ............................................ 5
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+ 5.2.1 To A Channel ...................................... 5
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+ 5.2.2 To A Host/Server Mask ............................. 6
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+Kalt Informational [Page 1]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
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+
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+
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+ 5.2.3 To A List ......................................... 6
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+ 5.3 One-To-All ............................................. 6
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+ 5.3.1 Client-to-Client .................................. 6
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+ 5.3.2 Client-to-Server .................................. 7
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+ 5.3.3 Server-to-Server .................................. 7
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+ 6. Current Problems ........................................... 7
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+ 6.1 Scalability ............................................ 7
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+ 6.2 Reliability ............................................ 7
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+ 6.3 Network Congestion ..................................... 7
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+ 6.4 Privacy ................................................ 8
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+ 7. Security Considerations .................................... 8
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+ 8. Current Support And Availability ........................... 8
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+ 9. Acknowledgements ........................................... 8
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+ 10. References ................................................ 8
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+ 11. Author's Address .......................................... 9
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+ 12. Full Copyright Statement .................................. 10
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+
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+1. Introduction
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+
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+ The IRC (Internet Relay Chat) protocol has been designed over a
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+ number of years for use with text based conferencing. This document
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+ describes its current architecture.
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+
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+ The IRC Protocol is based on the client-server model, and is well
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+ suited to running on many machines in a distributed fashion. A
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+ typical setup involves a single process (the server) forming a
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+ central point for clients (or other servers) to connect to,
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+ performing the required message delivery/multiplexing and other
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+ functions.
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+
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+ This distributed model, which requires each server to have a copy
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+ of the global state information, is still the most flagrant problem
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+ of the protocol as it is a serious handicap, which limits the maximum
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+ size a network can reach. If the existing networks have been able to
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+ keep growing at an incredible pace, we must thank hardware
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+ manufacturers for giving us ever more powerful systems.
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+
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+2. Components
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+
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+ The following paragraphs define the basic components of the IRC
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+ protocol.
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+
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+2.1 Servers
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+
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+ The server forms the backbone of IRC as it is the only component
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+ of the protocol which is able to link all the other components
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+ together: it provides a point to which clients may connect to talk to
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+
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+
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+Kalt Informational [Page 2]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
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+
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+
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+ each other [IRC-CLIENT], and a point for other servers to connect to
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+ [IRC-SERVER]. The server is also responsible for providing the basic
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+ services defined by the IRC protocol.
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+
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+2.2 Clients
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+
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+ A client is anything connecting to a server that is not another
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+ server. There are two types of clients which both serve a different
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+ purpose.
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+
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+2.2.1 User Clients
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+
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+ User clients are generally programs providing a text based
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+ interface that is used to communicate interactively via IRC. This
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+ particular type of clients is often referred as "users".
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+
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+2.2.2 Service Clients
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+
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+ Unlike users, service clients are not intended to be used manually
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+ nor for talking. They have a more limited access to the chat
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+ functions of the protocol, while optionally having access to more
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+ private data from the servers.
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+
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+ Services are typically automatons used to provide some kind of
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+ service (not necessarily related to IRC itself) to users. An example
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+ is a service collecting statistics about the origin of users
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+ connected on the IRC network.
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+
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+3. Architecture
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+
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+ An IRC network is defined by a group of servers connected to each
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+ other. A single server forms the simplest IRC network.
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+
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+ The only network configuration allowed for IRC servers is that of
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+ a spanning tree where each server acts as a central node for the rest
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+ of the network it sees.
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+
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+ 1--\
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+ A D---4
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+ 2--/ \ /
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+ B----C
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+ / \
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+ 3 E
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+ Servers: A, B, C, D, E Clients: 1, 2, 3, 4
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+
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+ [ Fig. 1. Sample small IRC network ]
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+
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+
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+Kalt Informational [Page 3]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
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+
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+
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+ The IRC protocol provides no mean for two clients to directly
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+ communicate. All communication between clients is relayed by the
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+ server(s).
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+
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+4. IRC Protocol Services
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+
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+ This section describes the services offered by the IRC protocol. The
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+ combination of these services allow real-time conferencing.
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+
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+4.1 Client Locator
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+
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+ To be able to exchange messages, two clients must be able to locate
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+ each other.
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+
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+ Upon connecting to a server, a client registers using a label which
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+ is then used by other servers and clients to know where the client is
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+ located. Servers are responsible for keeping track of all the labels
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+ being used.
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+
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+4.2 Message Relaying
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+
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+ The IRC protocol provides no mean for two clients to directly
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+ communicate. All communication between clients is relayed by the
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+ server(s).
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+
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+4.3 Channel Hosting And Management
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+
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+ A channel is a named group of one or more users which will all
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+ receive messages addressed to that channel. A channel is
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+ characterized by its name and current members, it also has a set of
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+ properties which can be manipulated by (some of) its members.
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+
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+ Channels provide a mean for a message to be sent to several clients.
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+ Servers host channels, providing the necessary message multiplexing.
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+ Servers are also responsible for managing channels by keeping track
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+ of the channel members. The exact role of servers is defined in
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+ "Internet Relay Chat: Channel Management" [IRC-CHAN].
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+
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+5. IRC Concepts
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+
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+ This section is devoted to describing the actual concepts behind the
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+ organization of the IRC protocol and how different classes of
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+ messages are delivered.
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+
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+
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+Kalt Informational [Page 4]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
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+
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+
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+5.1 One-To-One Communication
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+
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+ Communication on a one-to-one basis is usually performed by clients,
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+ since most server-server traffic is not a result of servers talking
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+ only to each other. To provide a means for clients to talk to each
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+ other, it is REQUIRED that all servers be able to send a message in
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+ exactly one direction along the spanning tree in order to reach any
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+ client. Thus the path of a message being delivered is the shortest
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+ path between any two points on the spanning tree.
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+
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+ The following examples all refer to Figure 1 above.
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+
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+ Example 1: A message between clients 1 and 2 is only seen by server
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+ A, which sends it straight to client 2.
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+
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+ Example 2: A message between clients 1 and 3 is seen by servers A &
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+ B, and client 3. No other clients or servers are allowed see the
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+ message.
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+
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+ Example 3: A message between clients 2 and 4 is seen by servers A, B,
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+ C & D and client 4 only.
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+
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+5.2 One-To-Many
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+
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+ The main goal of IRC is to provide a forum which allows easy and
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+ efficient conferencing (one to many conversations). IRC offers
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+ several means to achieve this, each serving its own purpose.
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+
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+5.2.1 To A Channel
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+
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+ In IRC the channel has a role equivalent to that of the multicast
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+ group; their existence is dynamic and the actual conversation carried
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+ out on a channel MUST only be sent to servers which are supporting
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+ users on a given channel. Moreover, the message SHALL only be sent
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+ once to every local link as each server is responsible to fan the
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+ original message to ensure that it will reach all the recipients.
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+
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+ The following examples all refer to Figure 2.
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+
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+ Example 4: Any channel with 1 client in it. Messages to the channel
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+ go to the server and then nowhere else.
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+
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+ Example 5: 2 clients in a channel. All messages traverse a path as if
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+ they were private messages between the two clients outside a
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+ channel.
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+
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+
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+
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+
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+
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+
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+Kalt Informational [Page 5]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
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+
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+
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+ Example 6: Clients 1, 2 and 3 in a channel. All messages to the
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+ channel are sent to all clients and only those servers which must
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+ be traversed by the message if it were a private message to a
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+ single client. If client 1 sends a message, it goes back to
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+ client 2 and then via server B to client 3.
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+
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+5.2.2 To A Host/Server Mask
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+
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+ To provide with some mechanism to send messages to a large body of
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+ related users, host and server mask messages are available. These
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+ messages are sent to users whose host or server information match
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+ that of the mask. The messages are only sent to locations where
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+ users are, in a fashion similar to that of channels.
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+
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+5.2.3 To A List
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+
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+ The least efficient style of one-to-many conversation is through
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+ clients talking to a 'list' of targets (client, channel, mask). How
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+ this is done is almost self explanatory: the client gives a list of
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+ destinations to which the message is to be delivered and the server
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+ breaks it up and dispatches a separate copy of the message to each
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+ given destination.
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+
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+ This is not as efficient as using a channel since the destination
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+ list MAY be broken up and the dispatch sent without checking to make
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+ sure duplicates aren't sent down each path.
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+
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+5.3 One-To-All
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+
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+ The one-to-all type of message is better described as a broadcast
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+ message, sent to all clients or servers or both. On a large network
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+ of users and servers, a single message can result in a lot of traffic
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+ being sent over the network in an effort to reach all of the desired
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+ destinations.
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+
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+ For some class of messages, there is no option but to broadcast it to
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+ all servers so that the state information held by each server is
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+ consistent between servers.
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+
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+5.3.1 Client-to-Client
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+
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+ There is no class of message which, from a single message, results in
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+ a message being sent to every other client.
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+
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+
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+
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+
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+
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+Kalt Informational [Page 6]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
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+
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+
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+5.3.2 Client-to-Server
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+
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+ Most of the commands which result in a change of state information
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+ (such as channel membership, channel mode, user status, etc.) MUST be
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+ sent to all servers by default, and this distribution SHALL NOT be
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+ changed by the client.
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+
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+5.3.3 Server-to-Server
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+
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+ While most messages between servers are distributed to all 'other'
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+ servers, this is only required for any message that affects a user,
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+ channel or server. Since these are the basic items found in IRC,
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+ nearly all messages originating from a server are broadcast to all
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+ other connected servers.
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+
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+6. Current Problems
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+
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+ There are a number of recognized problems with this protocol, this
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+ section only addresses the problems related to the architecture of
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+ the protocol.
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+
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+6.1 Scalability
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+
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+ It is widely recognized that this protocol does not scale
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+ sufficiently well when used in a large arena. The main problem comes
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+ from the requirement that all servers know about all other servers,
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+ clients and channels and that information regarding them be updated
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+ as soon as it changes.
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+
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+6.2 Reliability
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+
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+ As the only network configuration allowed for IRC servers is that of
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+ a spanning tree, each link between two servers is an obvious and
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+ quite serious point of failure. This particular issue is addressed
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+ more in detail in "Internet Relay Chat: Server Protocol" [IRC-
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+ SERVER].
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+
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+6.3 Network Congestion
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+
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+ Another problem related to the scalability and reliability issues, as
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+ well as the spanning tree architecture, is that the protocol and
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+ architecture for IRC are extremely vulnerable to network congestions.
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+ This problem is endemic, and should be solved for the next
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+ generation: if congestion and high traffic volume cause a link
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+ between two servers to fail, not only this failure generates more
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+ network traffic, but the reconnection (eventually elsewhere) of two
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+ servers also generates more traffic.
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+
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+
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+
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+
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+Kalt Informational [Page 7]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
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+
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+
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+ In an attempt to minimize the impact of these problems, it is
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+ strongly RECOMMENDED that servers do not automatically try to
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+ reconnect too fast, in order to avoid aggravating the situation.
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+
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+6.4 Privacy
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+
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+ Besides not scaling well, the fact that servers need to know all
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+ information about other entities, the issue of privacy is also a
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+ concern. This is in particular true for channels, as the related
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+ information is quite a lot more revealing than whether a user is
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+ online or not.
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+
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+7. Security Considerations
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+
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+ Asides from the privacy concerns mentioned in section 6.4 (Privacy),
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+ security is believed to be irrelevant to this document.
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+
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+8. Current Support And Availability
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+
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+ Mailing lists for IRC related discussion:
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+ General discussion: ircd-users@irc.org
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+ Protocol development: ircd-dev@irc.org
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+
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+ Software implementations:
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+ ftp://ftp.irc.org/irc/server
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+ ftp://ftp.funet.fi/pub/unix/irc
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+ ftp://coombs.anu.edu.au/pub/irc
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+
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+ Newsgroup: alt.irc
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+
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+9. Acknowledgements
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+
|
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+ Parts of this document were copied from the RFC 1459 [IRC] which
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+ first formally documented the IRC Protocol. It has also benefited
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+ from many rounds of review and comments. In particular, the
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+ following people have made significant contributions to this
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+ document:
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+
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+ Matthew Green, Michael Neumayer, Volker Paulsen, Kurt Roeckx, Vesa
|
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436
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+ Ruokonen, Magnus Tjernstrom, Stefan Zehl.
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+Kalt Informational [Page 8]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
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+
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+
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+10. References
|
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+
|
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|
+ [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
|
|
456
|
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
|
|
457
|
+
|
|
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|
+ [IRC] Oikarinen, J. and D. Reed, "Internet Relay Chat
|
|
459
|
+ Protocol", RFC 1459, May 1993.
|
|
460
|
+
|
|
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|
+ [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
|
|
462
|
+ 2812, April 2000.
|
|
463
|
+
|
|
464
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+ [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
|
|
465
|
+ 2813, April 2000.
|
|
466
|
+
|
|
467
|
+ [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
|
|
468
|
+ 2811, April 2000.
|
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469
|
+
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+11. Author's Address
|
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471
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+
|
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472
|
+ Christophe Kalt
|
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|
+ 99 Teaneck Rd, Apt #117
|
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+ Ridgefield Park, NJ 07660
|
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|
+ USA
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+
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|
+ EMail: kalt@stealth.net
|
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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504
|
+Kalt Informational [Page 9]
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+
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+RFC 2810 Internet Relay Chat: Architecture April 2000
|
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|
+
|
|
508
|
+
|
|
509
|
+12. Full Copyright Statement
|
|
510
|
+
|
|
511
|
+ Copyright (C) The Internet Society (2000). All Rights Reserved.
|
|
512
|
+
|
|
513
|
+ This document and translations of it may be copied and furnished to
|
|
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|
+ others, and derivative works that comment on or otherwise explain it
|
|
515
|
+ or assist in its implementation may be prepared, copied, published
|
|
516
|
+ and distributed, in whole or in part, without restriction of any
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|
517
|
+ kind, provided that the above copyright notice and this paragraph are
|
|
518
|
+ included on all such copies and derivative works. However, this
|
|
519
|
+ document itself may not be modified in any way, such as by removing
|
|
520
|
+ the copyright notice or references to the Internet Society or other
|
|
521
|
+ Internet organizations, except as needed for the purpose of
|
|
522
|
+ developing Internet standards in which case the procedures for
|
|
523
|
+ copyrights defined in the Internet Standards process must be
|
|
524
|
+ followed, or as required to translate it into languages other than
|
|
525
|
+ English.
|
|
526
|
+
|
|
527
|
+ The limited permissions granted above are perpetual and will not be
|
|
528
|
+ revoked by the Internet Society or its successors or assigns.
|
|
529
|
+
|
|
530
|
+ This document and the information contained herein is provided on an
|
|
531
|
+ "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
|
|
532
|
+ TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
|
|
533
|
+ BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
|
|
534
|
+ HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
|
|
535
|
+ MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
|
|
536
|
+
|
|
537
|
+Acknowledgement
|
|
538
|
+
|
|
539
|
+ Funding for the RFC Editor function is currently provided by the
|
|
540
|
+ Internet Society.
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|
541
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+Kalt Informational [Page 10]
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+
|