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RE: MAC address spoofing - conflict?
From: "Upadhyaya, Vijay" <vupadhyaya () ipolicynetworks com>
Date: Wed, 23 Aug 2006 23:25:48 -0700

Hi, 
According to RFC, the last ARP reply will be kept by the server for the 
same IP address for which host was arping, if its a different IP address and a same MAC address still its not a 
problem, since this could be  classic Proxy ARP. More over 2 Machines with Same MAC can be detected by todays 
intelligent switches which has MAC binding to the ports. 
Hope this helps.
Regards,
Vijay

-----Original Message-----
From: Sebastian Zdrojewski [mailto:en3py () itvc net] 
Sent: Monday, August 21, 2006 11:05 AM
To: 'Lubos Kolouch'; pen-test () securityfocus com
Subject: R: MAC address spoofing - conflict?

At layer 2 all frames should be sent to the port(s) where the MAC address is announced. At layer 3, the NICs will 
accept the packets directed to their IP address and discard the others.

Don't you agree?

En3pY

-----Messaggio originale-----
Da: Lubos Kolouch [mailto:lubos.kolouch () gmail com] 
Inviato: lunedì 21 agosto 2006 10.23
A: pen-test () securityfocus com
Oggetto: Re: MAC address spoofing - conflict?

Yes, but what will happen then? Data will be sent to that MAC address.

If it is switched network, I can imagine the switch will maybe send it
to the correct port from which the response came?

If there is a hub though, the packet will be delivered to which network
card?

Lubos Kolouch

Cedric Blancher píše v Čt 17. 08. 2006 v 08:56 +0200:
Le mercredi 16 août 2006 à 10:26 +0200, Lubos Kolouch a écrit :
I think it does matter. Because there will be more than host replying to
ARP broadcasts and the question is what will happen.

Nope it does not matter, because you won't have multiple answers...

ARP asks for an _IP_ address, not a MAC one. Therefore, if MAC addresses
are identical, but IP addresses are different, an ARP request for one
given IP address will get one answer only. In the end, you will end up
with two entries in ARP cache with the same MAC address, but there's not
problem out there.

And if, in case of some wierd and unexplained behaviour (aka awful bug),
both hosts were replying, they would reply with the same MAC address to
the same request, so you would not have problem either.

Le jeudi 17 août 2006 à 01:03 +0000, penetrationtestmail () gmail com a
écrit : 
And if anyone knows the exact answer, that would be most helpful ;)

The exact answer is: you can seamless spoof MAC addresses on WLAN as
long as you use a different IP address than spoofed host, so you don't
have TCP RST problems and stuff like this. Tested in lab and real life
for pentests.

It's a classical technic (among others[1]) for bypassing some cheap, but
still widespread, WLAN captive portal that only track authenticated
clients with their MAC address.


[1] http://sid.rstack.org/pres/0602_ESW_CaptiveBypass.pdf


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