You didn't really frame your question - but let's give it a shot.
You received a bunch of answers about how to find out MAC<->IP pairings
in your broadcast domain (I assume you're interested in learning
MAC-to-IP pairings on the same L2 your machine is located). Some
suggested arping, some arpwatch, etc. The easiest way? Sniff.
Say host A on your net is trying to communicate with host B. Host A
needs to know the MAC address for host B (or the MAC address for the
default gateway, if B not located on the same L2/L3 network). So he will
send out an ARP request. ARP replies are no good for you - those are
unicast to the host asking. But hey, a host ARPing for a other host
sends a broadcast - including *his* IP address. And the MAC is obviously
his MAC. And you do get broadcast. So, listen to ARP requests, and
sooner or later (when a host tries to communicate with other and doesn't
know his MAC, or when its refreshing its ARP cache), you will learn all
MAC-to-IP pairs. Even if the host never tries to contact hosts on his
same L2/L3 network, it has to ARP for the default gw MAC. This is the
answer to your original question.
About 100 machines using the same MAC address: two possibilities, out of
the top of my mind. Either the MAC belongs to a router on the same L2
network, which is doing proxy-arp for those machines (machines that
aren't really located on your L2 network), or those machines are, again,
in another network, and the host answering ARP requests for them is a
firewall - which would then filter/NAT/rate-limit/do whatever he has to
do with the packet before forwarding it to the real host.
Other things to keep in mind: pairing between MAC/IP can change - while
both HSRP and VRRP use a virtual MAC address, shared between all routers
on the same HSRP/VRRP group (and hence, no changes on the MAC address if
one of them takes over a failed one), GLBP (AFAIR) can reply to
different ARP requests with different MAC addresses. Also check for MS
MNLB. CheckPoint firewalls used to use multicast MAC addresses for
firewalls in a cluster configuration.
Good luck
Dario
-----Original Message-----
From: kukulkan [mailto:ismandya@sains.com.my]
Sent: Tuesday, October 25, 2005 8:45 PM
To: Chris Moody
Cc: Glyn Geoghegan; pen-test@securityfocus.com
Subject: Re: mac to ip address tools
yeah. There are about 500-600 machines in this place, I say
this because
these are the registered machines. What about those not registered?
there is one thing that bother them is that when we tried to
use arp it
seems that they are about 100 machines with the same mac address.
Wonder could this be the the machines here have been poisoned?
Chris Moody wrote:
The biggest problem with your question lies in topology
restrictions.
Unless you have a host system in the broadcast domain (aka
subnet) of
the host ip in question, all your arp responses will be that of the
gateway enroute to the end host.
You'll get -very- skewed results if you're trying to map say...1000
machines (most of which live on different subnets) and see
nothing but
the MAC of your router as the resolved address.
For something enterprise wide, you will need to look at scripting a
arp cache harvesting mechanism. This can report back the
REAL mac to
ip mapping for the host system.
Contact me offline for more information on how to accomplish this.
-Chris
Glyn Geoghegan wrote:
arp -a
-- G l y n G e o g h e g a n
On 25 Oct 2005, at 10:48, kukulkan wrote:
Hi list,
Need help. Is there any open source tools linux or windows, that
when given a MAC address, the list(s) of IP address can
be obtained?
kukulkan
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