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RE: rogue IP address
From: "Burton M. Strauss III" <BStrauss () acm org>
Date: Tue, 6 May 2003 16:05:12 -0500

A much better link for MAC lookup is


since the IEEE is the body that manages the assignments, they're the most

Be aware that you can spoof the MAC address.   Values beginning 02:xx:xx
(mask 0x02, really) are what's supposed to be used, but if the OS allows you
to set it, you can usually set it to ANYTHING.

This might be relevant if somebody has put up a rogue wireless router/access
point and used the spoofing capability to try and hide it.  If they are
trying to hide it, you're going to have to look for cabinets and boxes which
are plugged into the outlets...

Also, the name that the database will show you isn't always the name you
know.  Sometimes it's the chipset vendor or the oem or the name on the box.
Those are all legal, it's just a matter of who does the paperwork (and who
burns the bits into what).

Still, if they've pieced the rogue together from outdated parts it will
sometimes stand out - gee, what's the ABC Corp. box doing on the network, we
haven't used anybody but XYZ, Corp in five years... tell you exactly what
piece of kit to go snooping for.


-----Original Message-----
From: Erik ! [mailto:viking0069 () hotmail com]
Sent: Monday, May 05, 2003 7:00 PM
To: jharris () rallycentral us; security-basics () securityfocus com
Cc: dondon () pacbell net
Subject: Re: rogue IP address

Yea, if you have the MAC address you're money.

IF you have this, then you can start tracking down what type of NIC your
rogue IP is bound to ... and by deduction MAYBE even the box's hardware.

We used this trick once for a dup IP issue we had on a tier-one ISP's class
B network.

Here's how you do it:

1. Use this link to correlate the MAC address with a manufacturer:


The first three sets of numbers in the MAC address represent the vendor
code. At this site, do your search e.g. 00c095

MAC Address
   prefix         Vendor
   00C095       Zynx Network Appliance box

2. Now match the type of NICs you use to the type of boxes you put them in
(this works best if your company hardware is running the rogue IP address).

Zynx is the brand of NICs we used in our Nokia firewalls. So in this case I
knew that issue was limited to a select number of firewall boxes and we
eventually fixed the dup IP issue.

You don't always get a cut and dry answer, but it does provide an extra step
you can use to troubleshoot.

The alternative may be to have your network guys trace the MAC address to a
*working* switch port. We know how long of a turnaround time that can be ;)

Of course, you need the MAC address here 8)


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