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 From:  "Chris Bagnall" <m0n0wall at minotaur dot cc>
 To:  <m0n0wall at lists dot m0n0 dot ch>
 Subject:  RE: [m0n0wall] m0n0 stops accepting new connections
 Date:  Wed, 1 Sep 2004 08:39:54 +0100
> Curiously, before the virus-laden ports were shut down, the 
> firewall showed several blocked packets originating from the 
> LAN and outgoing to the internet on TCP port 445.  I have NOT 
> blocked that port outgoing.  Is it blocked by the default 
> rule perhaps?  I wish I had kept the logs, because now those 
> blocks aren't showing.

To the best of my knowledge it isn't blocked by default. Perhaps m0n0 blocks
NetBIOS to itself by default since it knows it doesn't use it for anything

Your problem sounds very much like the NAT table is filling up with these
brief connection attempts that don't close themselves properly. What I tend
to do is to define 3 rules on all my interfaces to block netbios silently.
The ports to block are 135, 137-139 and 445. I've gone with TCP/UDP, but I
think it's only 139 that actually uses UDP, the rest are TCP. 

That'll prevent m0n0 from wasting CPU cycles logging the damn things and
will also prevent m0n0 from creating NAT entries for them.  Hopefully
that'll solve your problem. The only downside here is if you have 2 LAN
interfaces (perhaps a wireless?) and you want to allow netbios between them.
In that circumstance, you'd want to use the "not" option in the destination.

In all honesty the best approach would be to disconnect the offending users
at the switch and wait for them to complain. When they do, inform them of
the deplorable state of affairs and give 'em a CD with a removal tool.
They're freely available online for most common viruses. That'd do both you
and the offending users a favour (since at the moment they run the risk of
infecting others on the LAN interface).


C.M. Bagnall, Partner, Minotaur
Tel: (07010) 710715   Mobile: (07811) 332969
ICQ: 13350579   AIM: MinotaurUK   MSN: minotauruk at hotmail dot com   Y!:
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