An IRCd, short for Internet Relay Chat daemon, is server software that implements the IRC protocol, enabling people to talk to each other via the Internet (exchanging textual messages in real time). It is distinct from an IRC bot that connects outbound to an IRC channel.
The server listens to connections from IRC clients on a set of TCP ports. When the server is part of an IRC network, it also keeps one or more established connections to other servers/daemons.
The term ircd originally referred to only one single piece of software, but it eventually became a generic reference to any implementation of an IRC daemon. However, the original version is still distributed under the same name, and this article discusses both uses.
History
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The original IRCd was known as 'ircd', and was authored by Jarkko Oikarinen (WiZ on IRC) in 1988. He received help from a number of others, such as Markku Savela (msa on IRC), who helped with the 2.2+msa release, etc.
In its first revisions, IRC did not have many features that are taken for granted today, such as named channels and channel operators. Channels were numbered – channel 4 and channel 57, for example – and the channel topic described the kind of conversation that took place in the channel. One holdover of this is that joining channel 0 causes a client to leave all the channels it is presently on: "CHANNEL 0" being the original command to leave the current channel.
The first major change to IRC, in version 2.5, was to add named channels – "+channels". "+channels" were later replaced with "#channels" in version 2.7, numeric channels were removed entirely and channel bans (mode +b) were implemented.
Around version 2.7, there was a small but notable dispute, which led to ircu – the Undernet fork of ircd.
irc2.8 added "&channels" (those that exist only on the current server, rather than the entire network) and "!channels" (those that are theoretically safe from suffering from the many ways that a user could exploit a channel by "riding a netsplit"), and is the baseline release from which nearly all current implementations are derived.
Around 2.8 came the concept of nick and channel delay, a system designed to help curb abusive practices such as takeovers and split riding. This was not agreed on by the majority of modern IRC (EFnet, DALnet, Undernet, etc.) – and thus, 2.8 was forked into a number of different daemons using an opposing theory known as TS – or time stamping, which stored a unique time stamp with each channel or nickname on the network to decide which was the 'correct' one to keep.
Time stamping itself has been revised several times to fix various issues in its design. The latest versions of such protocols are:
- the TS6 protocol, which is used by EFnet, and Hybrid and Ratbox based servers amongst others
- the P10 protocol, which is used by Undernet and ircu based servers.
While the client-to-server protocols are at least functionally similar, server-to-server protocols differ widely (TS5, P10, and ND/CD server protocols are incompatible), making it very difficult to "link" two separate implementations of the IRC server. Some "bridge" servers do exist, to allow linking of, for example, 2.10 servers to TS5 servers, but these are often accompanied with restrictions of which parts of each protocol may be used, and are not widely deployed.
Significant releases based on 2.8 included:
- 2.8.21+CS, developed by Chris Behrens (Comstud)
- 2.8+th, Taner Halicioglu's patchset, which later became
- Hybrid IRCd, originally developed by Jon Lusky (Rodder) and Diane Bruce (Dianora) as 2.8/hybrid, later joined by a large development team.
- 2.9, 2.10, 2.11, ... continue the development of the original codebase,
The original code base continued to be developed mainly for use on the IRCnet network. New server-to-server protocols were introduced in version 2.10, released in 1998, and in 2.11, first released in 2004, and current . This daemon is used by IRCnet and it can be found at http://www.irc.org/ftp/irc/server/ The original ircd is free software, licensed under the GNU General Public License. This development line produced the 4 IRC RFCs released after RFC 1459, which document this server protocol exclusively.
2.8.21+CS and Hybrid IRCd continue to be used on EFnet, with ircd-ratbox (an offshoot of ircd-hybrid) being the most popular.
Sidestream versions
thumb|right|Diagram of derivations and relations for common IRCd implementations.
More recently, several irc daemons were written from scratch, such as ithildin, InspIRCd, csircd (also written by Chris Behrens), ConferenceRoom, Microsoft Exchange Chat Service, WeIRCd, or IRCPlus/IRCXPro.
These attempts have met with mixed success, and large doses of skepticism from the existing IRC development community. With each new IRCd, a slightly different version of the IRC protocol is used, and many IRC clients and bots are forced to compromise on features or vary their implementation based on the server to which they are connected. These are often implemented for the purpose of improving usability, security, separation of powers, or ease of integration with services. Possibly one of the most common and visible differences is the inclusion or exclusion of the half-op channel operator status (which is not a requirement of the RFCs).
Features
Ports
The officially assigned port numbers are 194 ("irc"), 529 ("irc-serv"), and 994 ("ircs"). However, these ports are in the privileged range (0–1024), which on a Unix-like system means that the daemon would historically have to have superuser privileges in order to open them. For various security reasons this used to be undesirable.
The common ports for an IRCd process are 6665 to 6669, with 6667 being the historical default. These ports can be opened by a non-superuser process, and they became widely used.
Connections
Running a large IRC server, one that has more than a few thousand simultaneous users, requires keeping a very large number of TCP connections open for long periods. Very few ircds are multithreaded as nearly every action needs to access (at least read and possibly modify) the global state.
The result is that the best platforms for ircds are those that offer efficient mechanisms for handling huge numbers of connections in a single thread. Linux offers this ability in the form of epoll, in kernel series newer than 2.4.x. FreeBSD (since 4.1) and OpenBSD (since 2.9) offers kqueue. Solaris has had /dev/poll since version 7, and from version 10 onwards has IOCP (I/O Completion Ports). Windows has supported IOCP since Windows NT 3.5. The difference made by these new interfaces can be dramatic. IRCU developers have mentioned increases in the practical capacity per server from 10,000 users to 20,000 users.
TLS (Transport Layer Security)
Some IRCd support Transport Layer Security, or TLS, for those who don't, it is still possible to use SSL via Stunnel. The unofficial, but most often used port for TLS IRCd connections is 6697. More recently, as a security enhancement and usability enhancement, various client and server authors have begun drafting a standard known as the STARTTLS standard which allows for TLS and plain text connections to co-exist on the same TCP port.
IPv4 and IPv6
IRC daemons support IPv4, and some also support IPv6. In general, the difference between IPv6 and IPv4 connections to IRC is purely academic and the service operates in much the same manner through either protocol.
Clustering
Large IRC networks consist of multiple servers for horizontal scaling purposes. There are several IRC protocol extensions for these purposes.
IRCX
IRCX (Internet Relay Chat eXtensions) is an extension to the IRC protocol developed by Microsoft.<br/>
P10
The P10 protocol is an extension to the Internet Relay Chat protocol for server to server communications developed by the Undernet Coder Committee to use in their ircu server software. It is similar in purpose to IRCX and EFnet TS5/TS6 protocols and implements nick and channel timestamping for handling nick collisions and netsplit channel riding, respectively. Other IRCd's that utilize this protocol extension include beware ircd.
TS6
The TS6 protocol is an extension to the Internet Relay Chat protocol for server to server communications developed initially by the developers of ircd-ratbox. It has been extended by various IRC software and has the feature that proper implementations of TS6 can link to each other by using feature negotiation—even if features are disparate.
Configuration
Jupe
Juping a server, a channel, or a nickname refers to the practice of blocking said channel or nickname on the server or network or said server on the network. One possible explanation of how this term came about is that it is named after the oper named Jupiter, who gained control of the nickname NickServ on EFnet. EFnet does not offer services such as NickServ; Jupiter gained control of the nickname as he (among other operators) did not believe nicknames should be owned. Today, EFnet opers jupe nicknames that are used as services on other networks.
A nickname or server jupe takes advantage of the fact that certain identifiers are unique; by using an identifier, one acquires an exclusive lock that prevents other users from making use of it.
Officially sanctioned jupes may also utilize services or server configuration options to enforce the jupe, such as when a compromised server is juped to prevent it from harming the network.
In practice IRC operators now use jupe configurations to administratively make channel or nicknames unavailable. A channel jupe refers to a server specific ban of a channel, which means that a specific channel cannot be joined when connected to a certain server, but other servers may allow a user to join the channel. This is a way of banning access to problematic channels.
O-line
An O-line (frequently also spelled as O:line; on IRCds that support local operators, the O-lines of those are called o:lines with a lower-case O), shortened from Operator Line and derived from the line-based configuration file of the original IRCd, is a line of code in an IRC daemon configuration file that determines which users can become an IRC operator and which permissions they get upon doing so. The name comes from the prefix used for the line in the original IRCd, a capital O. The O-line specifies the username, password, operator flags, and hostmask restrictions for a particular operator. A server may have many O-lines depending on the administrative needs of the server and network.
Operator flags are used to describe the permissions an operator is granted. While some IRC operators may be in charge of network routing, others may be in charge of network abuse, making their need for certain permissions different.