                             Server Hide Reference

   $Id: serverhide.txt,v 1.2 2003/08/14 07:51:10 stu Exp $

   Copyright (c) 2001 by ircd-hybrid team

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   Due to pressures from abusers, the Hybrid developers have created a set of
   options to limit what users can and cannot do on the server. Each option
   can be enabled or disabled at runtime.

   This document describes the Hybrid 7 implementation of the server hiding
   ideas originated by (and credited to) numerous people.

     * LINKS as a file: This option is always enabled. It will generate a
       file at a certain interval, defined by the links_delay in ircd.conf,
       that contains the current LINKS data. This data is sent to users
       whenever a LINKS is requested. Opers will always see the current
       server structure.

       The file that the LINKS data is stored in is by default etc/links.txt.

       The benefits of this are that transient splits will not be seen by
       users issuing LINKS commands, and if a server is split, users can
       still see what other servers are normally available.

     * Flattened LINKS: This option forces every server to look as if it is
       connected to the local server. Users will see a flat LINKS tree.

       The benefit to using LINKS flattening is that users cannot get
       information on how servers are routed.

       The flatten_links in the serverhide {} block in the ircd.conf controls
       this feature.

       As a side effect, all netsplit quit messages will appear to originate
       from the local server.

       +--------------------------------------------------------------------+
       | Flattened LINKS is needed for any network that uses the hidden hub |
       | option. See below for more details.                                |
       +--------------------------------------------------------------------+

        

     * Hidden server option: This option will hide the server from a
       flattened LINKS list on other servers. Opers will of course see the
       true routing of the network.

       This is controlled by the hidden option in ircd.conf.

       +--------------------------------------------------------------------+
       | Technically, this code is a hack. With this option enabled, the    |
       | server will prepend '(H) ' to the server info field when           |
       | connecting to other servers. Other servers must understand that    |
       | the (H) means hidden.                                              |
       +--------------------------------------------------------------------+

     * The allow_hidden option is needed to allow servers to use the hidden
       server option described above.

     * The hide_servers option forces the server to not be shown when a user
       issues WHOIS and other commands which may show what server a user is
       on.

       Local user counts, as normally displayed in LUSERS, USERS, and the 255
       numeric, will be shown with the same values as the global counts.
       Displaying it this way will help protect servers and avoid breaking
       scripts that depend on the 265 and 266 numerics on connect.

       To be effective, this option must be used network wide.

     * The disable_remote_commands option takes care of most of the remaining
       issues. These include, for example, ADMIN some.hub.server, VERSION
       someuser, and similar commands. A server with this option enabled will
       only prevent local users from issuing remote commands. Remote users
       will not be affected.

       Remote WHOIS is not blocked. It is, however, restricted to only
       querying WHOIS nick nick. The ircd will disregard the server parameter
       and always use queried nick.

     * All server modes appear to originate from the server you are using.
       This feature is not tunable; and opers also do not see the real server
       setting the mode.

   Each item is briefly described in the serverhide {} block in ircd.conf.

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                             Questions and Answers

&channels and remote WHOIS

   I brought this up a short while ago; and there are some holes in server
   hide at the present time with local channels. The issue I raised, if a
   user is known to be in a local channel, issuing WHOIS servera nick, WHOIS
   serverb nick, etc. until the local channel is seen in the WHOIS data does
   not exist. With disable_remote_commands enabled, the WHOIS is still sent
   (in order to see idle time and the away message) but the server queried
   will always be the server the user is on. The user can never use remote
   WHOIS to determine the server a user is on.

   If an abuser knows that a user is on a specific &channel, they could still
   connect to each server until they find the server showing the user in the
   local channel in a local WHOIS. The disable_local_channels option has been
   created to handle this risk.

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Using Non-QS Compliant Hubs

   The flattened LINKS option will, as a side effect, display all user QUIT's
   due to network splits in the following format:

   :user QUIT :*.net *.split

   This works extremely well as long as all servers on your network are
   compliant with the QS capability, which sends a single SQUIT to the
   network when a server (or tree of servers) splits. All quit messages are
   generated on the local server. Certain older servers do not have this
   ability, and as such will generate their own quit messages for users who
   left because of the split. This can cause leaks in the hub server names
   and the structure of the network.

   A quick example is the following network structure:

   servA(Hyb7) --- hubA(nonQS) --- servB(not-important)

   When servB splits from hubA, hubA will generate a QUIT command for every
   user on servB (and anything behind servB). Since the QUIT message was not
   created on your server, with server hiding enabled, the QUIT message will
   contain the real server names.

   The only way to prevent this leak on a network is to only use hubs
   supporting the QS capability. Hybrid 6, Hybrid 7, and csircd all are
   currently running daemons that support QS. Hybrid 5 and 2.8.21+CSr servers
   do not support QS, and will leak server names (and therefore routing
   information) on splits.

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                                     Index

   XXX - Fill me in with other questions and possible issues
