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The nospoof patch was adapted from the nospoof5 patch in use on Undernet
servers. It should NOT be needed unless you're running ircd on a really
old OS which doesn't have a patch against TCP spoofing. Note that this
patch should be applied BEFORE running ./configure -- this is very
important, and the usual cause of any problems encountered.
When a client connects to the server, they are sent a PING with a random
number (please do not confuse this with a CTCP PING -- they're very
different things). Until the client responds with a PONG and the correct
random number, it is not registered with the server and cannot do
anything.
Please note that this does break the RFC. However, it has been tested
with most popular clients and is in common use on large IRC networks
currently. The only reported client to have problems is Homer (for
the Macintosh).
To cater for possibly broken clients, a message is also sent to clients
on connect of the form:
*** If your client freezes here, type /QUOTE PONG 12345678 or /PONG 12345678
Because of this, it is a good idea to increase the allowed timeout on
connections since the user might have to manually PONG the server with
the ugly number (although hopefully they only need to cut'n'paste).
If the client PONGs with the wrong number, another message is sent to
the client directing the user what to type. In addition, if the
connection does end up timing out due to no PONG, a message is sent to
the user explaining the client may not be compatible, and lists where
compatible clients for all the major platforms can be found.
The random number sequence is based on an md5 series. I didn't write it.
Someone else did. It's included because many have a dud random() in their
libc (this applies to more people than you think). It is seeded on a
#define value in config.h - YOU MUST CHANGE THIS FROM THE DEFAULT OR YOU
CAN STILL BE SPOOFED. If you still find that you get spoofed, try
changing this value again and recompiling.
KNOWN BUGS:
- There is a known bug whereby the host provided by the client's
USER sequence is not checked for validity until after the PONG
reply (and registration takes place). This allows a form of
"spoofing" to take place, with the client showing under /whois
lookups with a fake hostname. At this stage the client can't
actually issue commands to the server though, and the hostmask
is corrected to what it should be upon the PONG being received
(and the client properly registered).
- The random number generator isn't 64-bit clean. On 64-bit
machines, a 64-bit random number is generated, but I'm not
convinced all 64-bits are random. At least 32 bits are
however, so this isn't a problem.
- Andrew (earthpig@yoyo.cc.monash.edu.au)
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