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RE: rogue IP address
From: "Burton M. Strauss III" <BStrauss () acm org>
Date: Thu, 1 May 2003 17:39:54 -0500

Sometimes, the alert from the LAN management software can be enough - if it
shows the MAC addresses involved.  For example, if it's a D-Link MAC
address - see the OUI list at the IEEE - and all you have are 3Com NICs,
well, the hardware probably won't look like any of your other machines
either and may stand out to a visual audit (that's IT speak for walking
around being nosy poking you head into cubicles and offices looking for
hardware you don't recognize).


Program the switch to drop that IP address - see who screams.  If the switch
won't do it for you, you may have to get brutish here - build a transparent
filtering bridge and drop the packets that way.

Try using tcpdump to see if you can sniff the packet streams and run
something like strings on it.  It may give you login names etc. that you

tcpdump -w x.raw -c50
strings x.raw | grep USER
strings x.raw | grep PASS   (Since people use their mail address for
anonymous ftp)


(This one is a real PITA, but it works - I've done it successfully)  On the
weekend, unplug each of your backbone switch segments, one at a time and see
when the rogue drops off the network.  Then follow it down to (ultimately) a
single LAN segment and thence to a specific physical port.  Remove said box
and ransom it back at the cost of an agreement to play nice in the future.

If you can't do those, here's a sneaky way that sometimes works - build your
own Linux box and give it that address and MAC address.  Put it on the
network backbone, so everybody sees it as "real close".  It should cause
various routing tables and switches to prefer your box and thus disable the
rogue.  See who screams.


-----Original Message-----
From: dondon () pacbell net [mailto:dondon () pacbell net]
Sent: Wednesday, April 30, 2003 5:40 PM
To: security-basics () securityfocus com
Subject: rogue IP address

Someone on our network assigned an IP address to their own system without
my knowledge.  Using LANguard network scanner, the best I can tell is that
it's a Linux box.  The port-to-IP mapping table on our Asante switch
doesn't see to work correctly.

Any suggestions on tracing down that system that is associated with the IP
is appreciated!


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