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Server Hide Reference
$Id$
Copyright (c) 2001-2014 ircd-hybrid development team
----------------------------------------------------------------------
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 ircd-hybrid 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 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, 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 reference.conf.
----------------------------------------------------------------------
Using Non-QS Compliant Hubs
The flattened LINKS option will, as a side effect, display all user QUITs
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 (and above) 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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