RE: Blocking IM via DNS

["d'Ambly, Jeff" <jdambly () monster com>]

Well there are a couple of ways to do this

1) block port 5190, however this no longer works, if it fails on 5190 it
tries every other available port
2) put your users on a proxy and block login.oscar.aol.com
3) create an outbound access-list on your wan interfaces or make it inbound
on you ethernet
       access-list deny ip any host 205.188.7.176
access-list deny ip any host 205.188.3.160
access-list deny ip any host 205.188.3.176
access-list deny ip any host 205.188.5.204
access-list deny ip any host 205.188.5.208
access-list deny ip any host 205.188.7.164
access-list deny ip any host 205.188.7.168
access-list deny ip any host 205.188.7.172
4) router there traffic to null0
ip route 205.188.7.176 255.255.255.255 null0
ip route 205.188.3.160 255.255.255.255 null0
ip route 205.188.3.176 255.255.255.255 null0
ip route 205.188.5.204 255.255.255.255 null0
ip route 205.188.5.208 255.255.255.255 null0
ip route 205.188.7.164 255.255.255.255 null0
ip route 205.188.7.168 255.255.255.255 null0
ip route 205.188.7.172 255.255.255.255 null0


If this where me I would go with the access-list, and I would put it on our
firewall, this why I could use but no one else, they don't call it
privileged mode for nothing ;-)



   --  Jeff d'Ambly
Network Engineer
http://www.monster.com
--------------------------------
Stay the patient course.
Of little worth is your ire.
The network is up.

-----Original Message-----
From: Simeon Johnston [mailto:simeonuj () eetc com]
Sent: Thursday, August 30, 2001 12:45 PM
To: IPTables; ipchains; firewall wizards; FOCUS-LINUX
Subject: Blocking IM via DNS

I have asked this before and have blocked AIM and others but am
wondering if there is an easier way?
In iptables (I think you can do this) I could block by URL.  But that is
another rule and DNS lookup that the FW has to do.
Why not change those addresses on the internal DNS to point to something
bogus?  Like login.oscar.aol.com for AIM would point to a bogus internal
address.
Would this work?  That way the ports wouldn't matter.  I would just need
to find out what URL the IM is looking for.

Is this possible?  IIRC all the IM need to login to some server.  So
blocking that server would be fairly easy w/ a false DNS lookup.  That
way I don't have to continually lookup the new ips of the URL and
blocking the ports (which is impossible for some IM) would be unnecessary.
And one of them uses the nntp protocols for communication.  We use news
servers so I can't block that.

Any input?
BTW, we have complete control over the internal DNS and lookups go to
that computer.

sim
_______________________________________________
firewall-wizards mailing list
firewall-wizards () nfr com
http://list.nfr.com/mailman/listinfo/firewall-wizards