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Versions: 00 RFC 2811

Internet Draft                                                   C. Kalt
Expires: 22 Dec 1999                                         22 Jun 1999

                Internet Relay Chat: Channel Management
                       draft-kalt-irc-chan-00.txt

Status of this Memo

      This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
   working documents as Internet Drafts.

      Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

      The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

      The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119
   [KEYWORDS].

Abstract

      One of the most notable characteristics of the IRC (Internet Relay
   Chat) protocol is to allow for users to be grouped in forums, called
   channels, providing a mean for multiple users to communicate
   together.

      There was originally a unique type of channels, but with the
   years, new types appeared either as a response to a need, or for
   experimental purposes.

      This document specifies how channels, their characteristics and
   properties are managed by IRC servers.








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                  Table of Contents

   1.  Introduction ...............................................   3

   2.  Channel Characteristics ....................................   3
      2.1  Namespace ..............................................   3
      2.2  Channel Scope ..........................................   3
      2.3  Channel Properties .....................................   4
      2.4  Privileged Channel Members .............................   4
         2.4.1  Channel Operators .................................   5
         2.4.2  Channel Creator ...................................   5

   3.  Channel lifetime ...........................................   5
      3.1  Standard channels ......................................   5
      3.2  Safe Channels ..........................................   6

   4.  Channel Modes ..............................................   8
      4.1  Member Status ..........................................   8
         4.1.1  "Channel Creator" Status ..........................   8
         4.1.2  Channel Operator Status ...........................   8
         4.1.3  Voice Privilege ...................................   8
      4.2  Channel Flags ..........................................   9
         4.2.1  Anonymous Flag ....................................   9
         4.2.2  Invite Only Flag ..................................   9
         4.2.3  Moderated Channel Flag ............................   9
         4.2.4  No Messages To Channel From Clients On The Outside    9
         4.2.5  Quiet Channel .....................................  10
         4.2.6  Private and Secret Channels .......................  10
         4.2.7  Server Reop Flag ..................................  10
         4.2.8  Topic .............................................  11
         4.2.9  User Limit ........................................  11
         4.2.10  Channel Key ......................................  11
      4.3  Channel Access Control .................................  11
         4.3.1  Channel Ban and Exception .........................  11
         4.3.2  Channel Invitation ................................  12

   5.  Current Implementations ....................................  13
      5.1  Tracking Recently Used Channels ........................  13
      5.2  Safe Channels ..........................................  13
         5.2.1  Channel Identifier ................................  13
         5.2.2  Channel Delay .....................................  14
         5.2.3  Abuse Window ......................................  14
         5.2.4  Preserving Sanity In The Name Space ...............  14
         5.2.5  Server Reop Mechanism .............................  14

   6.  Current problems ...........................................  15
      6.1  Labels .................................................  16
         6.1.1  Channel Delay .....................................  16



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         6.1.2  Safe Channels .....................................  16
      6.2  Mode Propagation Delays ................................  16
      6.3  Collisions And Channel Modes ...........................  16
      6.4  Resource Exhaustion ....................................  17

   7.  Security Considerations ....................................  17
      7.1  Access Control .........................................  17
      7.2  Channel Privacy ........................................  18

   8.  Current support and availability ...........................  18

   9.  Acknowledgements ...........................................  18

   10.  References ................................................  18

   11.  Author's Address ..........................................  19



































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1. Introduction

      This document defines in detail on how channels are managed by the
   IRC servers and will be mostly useful to people working on
   implementing an IRC server.

      While the concepts defined here are an important part of IRC, they
   remain non essential for implementing clients.  While the trend seems
   to be towards more and more complex and "intelligent" clients which
   are able to take advantage of knowing the internal workings of
   channels to provide the users with a more friendly interface, simple
   clients can be implemented without reading this document.

      Many of the concepts defined here were designed with the IRC
   architecture [IRC-ARCH] in mind and mostly make sense in this
   context.  However, many others could be applied to other
   architectures in order to provide forums for a conferencing system.

      Finally, it is to be noted that IRC users may find some of the
   following sections of interest, in particular sections 2 (Channel
   Characteristics) and 4 (Channel Modes).

2. Channel Characteristics

      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, properties and current members.

2.1 Namespace

      Channels names are strings (beginning with a '&', '#', '+' or '!'
   character) of length up to fifty (50) characters.  Channel names are
   case insensitive.

      Apart from the the requirement that the first character being
   either '&', '#', '+' or '!' (hereafter called "channel prefix"). The
   only restriction on a channel name is that it SHALL NOT contain any
   spaces (' '), a control G (^G or ASCII 7), a comma (',' which is used
   as a list item separator by the protocol).  Also, a column (':') is
   used as a delimiter for the channel mask.  The exact syntax of a
   channel name is defined in "IRC Server Protocol" [IRC-SERVER].

      The use of different prefixes effectively creates four (4)
   distinct namespaces for channel names.  This is important because of
   the protocol limitations regarding namespaces (in general).  See
   section 6.1 (Labels) for more details on these limitations.

2.2 Channel Scope



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      A channel entity is known by one or more servers on the IRC
   network.  A user can only become member of a channel known by the
   server to which the user is directly connected.  The list of servers
   which know of the existence of a particular channel MUST be a
   contiguous part of the IRC network, in order for the messages
   addressed to the channel to be sent to all the channel members.

      Channels with '&' as prefix are local to the server where they are
   created.

      Other channels are known to one (1) or more servers that are
   connected to the network, depending on the channel mask:

         If there is no channel mask, then the channel is known to all
      the servers.

         If there is a channel mask, then the channel MUST only be known
      to servers which has a local user on the channel, and to its
      neighbours if the mask matches both the local and neighbouring
      server names.  Since other servers have absolutely no knowledge of
      the existence of such a channel, the area formed by the servers
      having a name matching the mask has to be contiguous for the
      channel to be known by all these servers.  Channel masks are best
      used in conjunction with server hostmasking [IRC-SERVER].

2.3 Channel Properties

      Each channel has its own properties, which are defined by channel
   modes.  Channel modes can be manipulated by the channel members.  The
   modes affect the way servers manage the channels.

      Channels with '+' as prefix do not support channel modes.  This
   means that all the modes are unset, with the exception of the 't'
   channel flag which is set.

2.4 Privileged Channel Members

      In order for the channel members to keep some control over a
   channel, and some kind of sanity, some channel members are
   privileged.  Only these members are allowed to perform the following
   actions on the channel:

           INVITE  - Invite a client to an invite-only channel (mode +i)
           KICK    - Eject a client from the channel
           MODE    - Change the channel's mode, as well as
                     members' privileges
           PRIVMSG - Sending messages to the channel (mode +n, +m, +v)
           TOPIC   - Change the channel topic in a mode +t channel



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2.4.1 Channel Operators

      The channel operators (also referred to as a "chop" or "chanop")
   on a given channel are considered to 'own' that channel.  Ownership
   of a channel is shared among channel operators.

      Channel operators are identified by the '@' symbol next to their
   nickname whenever it is associated with a channel (i.e. replies to
   the NAMES, WHO and WHOIS commands).

      Since channels starting with the character '+' as prefix do not
   support channel modes, no member can therefore have the status of
   channel operator.

2.4.2 Channel Creator

      A user who creates a channel with the character '!' as prefix is
   identified as the "channel creator".  Upon creation of the channel,
   this user is also given channel operator status.

      In recognition of this status, the channel creators are endowed
   with the ability to toggle certain modes of the channel which channel
   operators may not manipulate.

      A "channel creator" can be distinguished from a channel operator
   by issuing the proper MODE command.  See the "IRC Client Protocol"
   [IRC-CLIENT] for more information on this topic.

3. Channel lifetime

      In regard to the lifetime of a channel, there are typically two
   groups of channels: standard channels which prefix is either '&', '#'
   or '+', and "safe channels" which prefix is '!'.

3.1 Standard channels

      These channels are created implicitly when the first user joins
   it, and cease to exist when the last user leaves it.  While the
   channel exists, any client can reference the channel using the name
   of the channel.

      The user creating a channel automatically becomes channel operator
   with the notable exception of channels which name is prefixed by the
   character '+', see section 4 (Channel modes).  See section 2.4.1
   (Channel Operators) for more details on this title.

      In order to avoid the creation of duplicate channels (typically
   when the IRC network becomes disjoint because of a split between two



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   servers), channel names SHOULD NOT be allowed to be reused by a user
   if a channel operator (See Section 2.4.1 (Channel Operators)) has
   recently left the channel because of a network split.  If this
   happens, the channel name is temporarely unavailable.  The duration
   while a channel remains unavailable should be tuned on a per IRC
   network basis.  It is important to note that this prevents local
   users from creating a channel using the same name, but does not
   prevent the channel to be recreated by a remote user. The latter
   typically happens when the IRC network rejoins.  Obviously, this
   mechanism only makes sense for channels which name begins with the
   character '#', but MAY be used for channels which name begins with
   the character '+'.  This mechanism is commonly known as "Channel
   Delay".

3.2 Safe Channels

      Unlike other channels, "safe channels" are not implicitly created.
   A user wishing to create such a channel MUST request the creation by
   sending a special JOIN command to the server in which the channel
   identifier (then unknown) is replaced by the character '!'.  The
   creation process for this type of channel is strictly controlled.
   The user only chooses part of the channel name (known as the channel
   "short name"), the server automatically prepends the user provided
   name with a channel identifier consisting of five (5) characters.
   The channel name resulting from the combination of these two elements
   is unique, making the channel safe from abuses based on network
   splits.

      The user who creates such a channel automatically becomes "channel
   creator".  See section 2.4.2 (Channel Creator) for more details on
   this title.

      A server MUST NOT allow the creation of a new channel if another
   channel with the same short name exists; or if another channel with
   the same short name existed recently AND any of its member(s) left
   because of a network split.  Such channel ceases to exits after last
   user leaves AND no other member recently left the channel because of
   a network split.

      Unlike the mechanism described in section 5.2.2 (Channel Delay),
   in this case, channel names do not become unavailable: these channels
   may continue to exist after the last user left.  Only the user
   creating the channel becomes "channel creator", users joining an
   existing empty channel do not automatically become "channel creator"
   nor "channel operator".

      To ensure the uniqueness of the channel names, the channel
   identifier created by the server MUST follow specific rules.  For



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   more details on this, see section 5.2.1 (Channel Identifier).


















































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4. Channel Modes

      The various modes available for channels are as follows:

           O - give "channel creator" status;
           o - give/take channel operator privilege;
           v - give/take the voice privilege;

           a - toggle the anonymous channel flag;
           i - toggle the invite-only channel flag;
           m - toggle the moderated channel;
           n - toggle the no messages to channel from clients on the
               outside;
           q - toggle the quiet channel flag;
           p - toggle the private channel flag;
           s - toggle the secret channel flag;
           r - toggle the server reop channel flag;
           t - toggle the topic settable by channel operator only flag;

           k - set/remove the channel key (password);
           l - set/remove the user limit to channel;

           b - set/remove ban mask to keep users out;
           e - set/remove an exception mask to override a ban mask;
           I - set/remove an invitation mask to automatically override
               the invite-only flag;

      Unless mentionned otherwise below, all these modes can be
   manipulated by "channel operators" by using the MODE command defined
   in "IRC Client Protocol" [IRC-CLIENT].

4.1 Member Status

      The modes in this category take a channel member nickname as
   argument and affect the privileges given to this user.

4.1.1 "Channel Creator" Status

      The mode 'O' is only used in conjunction with "safe channels" and
   SHALL NOT be manipulated by users.  Servers use it to give the user
   creating the channel the status of "channel creator".

4.1.2 Channel Operator Status

      The mode 'o' is used to toggle the operator status of a channel
   member.

4.1.3 Voice Privilege



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      The mode 'v' is used to give and take voice privilege to/from a
   channel member.  Users with this privilege can talk on moderated
   channels.  (See section 4.2.3 (Moderated Channel Flag)).

4.2 Channel Flags

      The modes in this category are used to define properties which
   affects how channels operate.

4.2.1 Anonymous Flag

      The channel flag 'a' defines an anonymous channel.  This means
   that when a message sent to the channel is sent by the server to
   users, and the origin is a user, then it MUST be masked.  To mask the
   message, the origin is changed to "anonymous!anonymous@anonymous."
   (e.g. a user with the nickname "anonymous", the username "anonymous"
   and from a host called "anonymous.").  Because of this, servers MUST
   forbid users from using the nickname "anonymous".

      On channels with the character '&' as prefix, this flag MAY be
   toggled by channel operators, but on channels with the character '!'
   as prefix, this flag can be set (but SHALL NOT be unset) by the
   "channel creator" only.  This flag is MUST NOT be made available on
   other types of channels.

      Replies to the WHOIS, WHO and NAMES commands MUST NOT reveal the
   presence of other users on channels for which the anonymous flag is
   set.

4.2.2 Invite Only Flag

      When the channel flag 'i' is set, new members are only accepted if
   they have been invited by a channel operator.  This flags also
   restricts the usage of the INVITE command (See "IRC Client Protocol"
   [IRC-CLIENT]) to channel operators.

4.2.3 Moderated Channel Flag

      The channel flag 'm' is used to control who may speak on a
   channel.  When it is set, only channel operators, and members who
   have been given the voice privilege may send messages to the channel.

      This flag only affects users.

4.2.4 No Messages To Channel From Clients On The Outside

      When the channel flag 'n' is set, only channel members MAY send
   messages to the channel.



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      This flag only affects users.

4.2.5 Quiet Channel

      The channel flag 'q' is for use by servers only.  When set, it
   restricts the type of data sent to users about the channel
   operations: other user joins, parts and nick changes are not sent.
   From a user's point of view, the channel only contain one user.

      This is typically used to create special local channels on which
   the server sends notices related to its operations.  This was used as
   a more efficient and flexible way to replace the user mode 's'
   defined in RFC 1459 [IRC].

4.2.6 Private and Secret Channels

      The channel flag 'p' is used to mark a channel "private" and the
   channel flag 's' to mark a channel "secret".  Both properties are
   similar and conceal the existance of the channel from other users.

      This means that there is no way of getting this channel's name
   from the server without being a member.  In other words, these
   channels MUST be omitted from replies to queries like the WHOIS
   command.

      When a channel is "secret", in addition to the restriction above,
   the server will act as if the channel does not exist for queries like
   the TOPIC, LIST, NAMES commands.  Note that there is one exception to
   this rule: servers will correctly reply to the MODE command.
   Finally, secret channels are not accounted for in the reply to the
   LUSERS command (See "Internet Relay Chat: Client Protocol" [IRC-
   CLIENT]) when the <mask> parameter is specified.

      The channel flags 'p' and 's' MUST NOT both be set at the same
   time.  If a MODE message originating from a server sets the flag 'p'
   and the flag 's' is already set for the channel, the change is
   silently ignored.  This should only happen during a split healing
   phase (mentionned in the "IRC Server Protocol" document [IRC-
   SERVER]).

4.2.7 Server Reop Flag

      The channel flag 'r' is only available on channels which name
   begins with the character '!' and MAY only be toggled by the "channel
   creator".

      This flag is used to prevent a channel from having no channel
   operator for an extended period of time.  When this flag is set, any



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   channel that has lost all its channel operators for longer than the
   "reop delay" period triggers a mechanism in servers to reop some or
   all of the channel inhabitants.  This mechanism is described more in
   detail in section 5.2.4 (Channel Reop Mechanism).

4.2.8 Topic

      The channel flag 't' is used to restrict the usage of the TOPIC
   command to channel operators.

4.2.9 User Limit

      A user limit may be set on channels by using the channel flag 'l'.
   When the limit is reached, servers MUST forbid their local users to
   join the channel.

      It is to be noted that the value of the limit MUST only be made
   available to the channel members in the reply sent by the server to a
   MODE query.

4.2.10 Channel Key

      When a channel key is set (by using the mode 'k'), servers MUST
   reject their local users request to join the channel unless the key
   is given.

      It is to be noted that the value of the limit MUST only be made
   available to the channel members in the reply sent by the server to a
   MODE query.

4.3 Channel Access Control

      The last category of modes is used to control access to the
   channel, they take a mask as argument.

      In order to reduce the size of the global database for control
   access modes set for channels, servers MAY put a maximum limit on the
   number of such modes set for a particular channel.  If such
   restriction is imposed, it MUST only affect user requests.  The limit
   SHOULD be homogenous on a per IRC network basis.

4.3.1 Channel Ban and Exception

      When a user requests to join a channel, his local server checks if
   the user's address matches any of the ban masks set for the channel.
   If a match is found, the user request is denied unless the address
   also matches an exception mask set for the channel.




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      Servers MUST NOT allow a channel member who is banned from the
   channel to speak on the channel, unless this member is a channel
   operator or has voice privilege. (See Section 4.1.3 (Voice
   Privilege)).

      A user who is banned from a channel and who carries an invitation
   sent by a channel operator is allowed to join the channel.

4.3.2 Channel Invitation

      For channels which have the invite-only flag set (See Section
   4.2.2 (Invite Only Flag)), users whose address matches an invitation
   mask set for the channel are allowed to join the channel without any
   invitation.





































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5. Current Implementations

      The only current implementation of these rules as part of the IRC
   protocol is the IRC server, version 2.10.

      The rest of this section deals with issues that are mostly of
   importance to those who wish to implement a server but some parts may
   also be of interest for client writers.

5.1 Tracking Recently Used Channels

      This mechanism is commonly known as "Channel Delay" and generally
   only applies to channels which names is prefixed with the character
   '#' (See Section 3.1 "Standard channels").

      When a network split occurs, servers SHOULD keep track of which
   channels lost a "channel operator" as the result of the break.  These
   channels are then in a special state which lasts for a certain period
   of time.  In this particular state, the channels cannot cease to
   exist.  If all the channel members leave the channel, the channel
   becomes unavailable: the server local clients cannot join the channel
   as long as it is empty.

      Once a channel is unavailable, it will become available again
   either because a remote user has joined the channel (most likely
   because the network is healing), or because the delay period has
   expired (in which case the channel ceases to exist and may be re-
   created).

      The duration for which a channel death is delayed SHOULD be set
   considering many factors among which are the size (user wise) of the
   IRC network, and the usual duration of network splits.  It SHOULD be
   uniform on all servers for a given IRC network.

5.2 Safe Channels

      This document introduces the notion of "safe channels".  These
   channels have a name prefixed with the character '!' and great effort
   is made to avoid collisions in this name space.  Collisions are not
   impossible, however they are very unlikely.

5.2.1 Channel Identifier

      The channel identifier is a function of the time.  The current
   time (as defined under UNIX by the number of seconds elapsed since
   00:00:00 GMT, January 1, 1970) is converted in a string of five (5)
   characters using the following base:
   ``ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890'' (each character has a



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   decimal value starting from 0 for 'A' to 35 for '0').

      The channel identifier therefore has a periodicity of 36^5 seconds
   (about 700 days).

5.2.2 Channel Delay

      These channels MUST be subject to the "channel delay" mechanism
   described in section 5.1 (Channel Delay).  However, the mechanism is
   slightly adapted to fit better.

      Servers MUST keep track of all such channels which lose members as
   the result of a network split, no matter whether the user is a
   "channel operator" or not.

      However, these channels do NOT ever become unavailable, it is
   always possible to join them even when they are empty.

5.2.3 Abuse Window

      Because the periodicity is so long, attacks on a particular
   channel (name) may only occur once in a very long while.  However,
   with luck and patience, it is still possible for a user to cause a
   channel collision.  In order to avoid this, servers MUST "look in the
   future" and keep a list of channel names which identifier is about to
   be used (in the coming few days for example). Such list should remain
   small, not be a burden for servers to maintain and be used to avoid
   channel collisions by preventing the re-creation of such channel for
   a longer period of time than channel delay does.

      Eventually a server MAY choose to extend this procedure to forbid
   creation of channels with the same shortname only (then ignoring the
   channel identifier).

5.2.4 Preserving Sanity In The Name Space

      The combination of the mechanisms described in sections 5.2.2 and
   5.2.3 makes it quite difficult for a user to create a channel
   collision. However, another type of abuse consists of creating many
   channels having the same shortname, but different identifiers.  To
   prevent this from happenning, servers MUST forbid the creation of a
   new channel which has the same shortname of a channel currently
   existing.

5.2.5 Server Reop Mechanism

      When a channel has been opless for longer than the "reop delay"
   period and has the channel flag 'r' set (See Section 4.2.7 (Server



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   Reop Flag)), IRC servers are responsible for giving the channel
   operator status randomly to some of the members.

      The exact logic used for this mechanism by the current
   implementation is described below.  It is to be noted that servers
   MAY use a different logic, but that it is strongly RECOMMENDED that
   all servers use the same logic on a particular IRC network to
   maintain coherence as well as fairness.  For the same reason, the
   "reop delay" SHOULD be uniform on all servers for a given IRC
   network.  As for the "channel delay", the value of the "reop delay"
   SHOULD be set considering many factors among which are the size (user
   wise) of the IRC network, and the usual duration of network splits.

      a) the reop mechanism is triggered after a random time following
         the expiration of the "reop delay".  This should limit the
          eventuality of the mechanism being triggered at the same time
         (for the same channel) on two separate servers.

      b) If the channel is small (five (5) users or less), and the
         "channel delay" for this channel has expired,
            Then reop all channel members if at least one member is
            local to the server.

      c) If the channel is small (five (5) users or less), and the
         "channel delay" for this channel has expired, and the "reop
         delay" has expired for longer than its value,
            Then reop all channel members.

      d) For other cases, reop at most one member on the channel, based
         on some method build into the server. If you don't reop a
         member, the method should be such that another server will
         probably op someone. The method SHOULD be the same over the
         whole network. A good heuristic could be just random reop.
         (The current implementation actually tries to choose a member
          local to the server who has not been idle for too long,
          eventually postponing action, therefore letting other servers
          have a chance to find a "not too idle" member.  This is over
          complicated due to the fact that servers only know the "idle"
          time of their local users)

6. Current problems

      There are a number of recognized problems with the way IRC
   channels are managed.  Some of these can be directly attributed to
   the rules defined in this document, while others are the result of
   the underlying "IRC Server Protocol" [IRC-SERVER].  Although derived
   from RFC 1459 [IRC], this document introduces several novelties in an
   attempt to solve some of the known problems.



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6.1 Labels

      This document defines one of the many labels used by the IRC
   protocol.  Although there are several distinct namespaces (based on
   the channel name prefix), duplicates inside each of these are not
   allowed.  Currently, it is possible for users on different servers to
   pick the label which may result in collisions (with the exception of
   channels known to only one server where they can be averted).

6.1.1 Channel Delay

      The channel delay mechanism described in section 5.1 (Tracking
   Recently Used Channels) and used for channels prefixed with the
   character '#' is a simple attempt at preventing collisions from
   happenning.  Experience has shown that, under normal circumstances,
   it is very efficient; however, it obviously has severe limitations
   keeping it from being an adequate solution to the problem discussed
   here.

6.1.2 Safe Channels

      "Safe channels" described in section 3.2 (Safe Channels) are a
   better way to prevent collisions from happenning as it prevents users
   from having total control over the label they choose.  The obvious
   drawback for such labels is that they are not user friendly.
   However, it is fairly trivial for a client program to improve on
   this.

6.2 Mode Propagation Delays

      Because of network delays induced by the network, and because each
   server on the path is REQUIRED to check the validity of mode changes
   (e.g. user exists and has the right privileges), it is not unusual
   for a MODE message to only affect part of the network, often creating
   a discrepancy between servers on the current state of a channel.

      While this may seem easy to fix (by having only the original
   server check the validity of mode changes), it was decided not to do
   so for various reasons.  One concern is that servers cannot trust
   each other, and that a misbehaving servers can easily be detected.
   This way of doing so also stops wave effects on channels which are
   out of synch when mode changes are issued from different directions.

6.3 Collisions And Channel Modes

      The "Internet Relay Chat: Server Protocol" document [IRC-SERVER]
   describes how channel data is exchanged when two servers connect to
   each other.  Channel collisions (either legitimate or not) are



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   treated as inclusive events, meaning that the resulting channel has
   for members all the users who are members of the channel on either
   server prior to the connection.

      Similarly, each server sends the channel modes to the other one.
   Therefore, each server also receives these channel modes.  There are
   three types of modes for a given channel: flags, masks, and data.
   The first two types are easy to deal with as they are either set or
   unset.  If such a mode is set on one server, it MUST be set on the
   other server as a result of the connection.

      As topics are not sent as part of this exchange, they are not a
   problem.  However, channel modes 'l' and 'k' are exchanged, and if
   they are set on both servers prior to the connection, there is no
   mechanism to decide which of the two values takes precedence.  It is
   left up to the users to fix the resulting discrepancy.

6.4 Resource Exhaustion

      The mode based on masks defined in section 4.3 make the IRC
   servers (and network) vulnerable to a simple abuse of the system: a
   single channel operator can set as many different masks as possible
   on a particular channel.  This can easily cause the server to waste
   memory, as well as network bandwidth (since the info is propagated to
   other servers).  For this reason it is RECOMMENDED that a limit be
   put on the number of such masks per channels as mentionned in section
   4.3.

      Moreover, more complex mechanisms MAY be used to avoid having
   redundant masks set for the same channel.

7. Security Considerations

7.1 Access Control

      One of the main ways to control access to a channel is to use
   masks which are based on the username and hostname of the user
   connections.  This mechanism can only be efficient and safe if the
   IRC servers have an accurate way of authenticating user connections,
   and if users cannot easily get around it.  While it is in theory
   possible to implement such a strict authentication mechanism, most
   IRC networks (especially public networks) do not have anything like
   this in place and provide little guaranty about the accuracy of the
   username and hostname for a particular client connection.

      Another way to control access is to use a channel key, but since
   this key is sent in plaintext, it is vulnerable to traditional man in
   the middle attacks.



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7.2 Channel Privacy

      Because channel collisions are treated as inclusive events (See
   Section 6.3), it is possible for users to join a channel overriding
   its access control settings.  This method has long been used by
   individuals to "take over" channels by "illegitimately" gaining
   channel operator status on the channel.  It is to be noted that the
   same method can be used to find out the exact list of members of a
   channel, as well as to eventually receive some of the messages sent
   to the channel.

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 follow¬°
   ing 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] "Key words for use in RFCs to Indicate Requirement Levels",
   Network Working Group RFC 2119, S. Bradner, March 1997.

[IRC] "Internet Relay Chat Protocol", Network Working Group RFC 1459,
   J. Oikarinen & D. Reed, May 1993

[IRC-ARCH] "Internet Relay Chat: Architecture",
   Work In Progress: draft-kalt-irc-arch-xx.txt




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[IRC-CLIENT] "Internet Relay Chat: Client Protocol",
   Work In Progress: draft-kalt-irc-client-xx.txt

[IRC-SERVER] "Internet Relay Chat: Server Protocol",
   Work In Progress: draft-kalt-irc-server-xx.txt


11. Author's Address


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

     Email: kalt@stealth.net



































Kalt                                                           [Page 20]


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