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Re: MAC address spoofing - conflict?
From: "Michael Dieroff" <michael () bluescreenit co uk>
Date: Mon, 21 Aug 2006 17:13:56 +0100

Hi Lubos,

Think of layer 2 delivery as an "if it matches my address I will read it" - This means if both stations have the same layer 2 (MAC) address both will read the comm's. As the message escalates up the stack, the IP address will need to match too though!!!

So this means, both stations get the comm's.

Hope this helps!


Regards,

Mike


----- Original Message ----- From: "Lubos Kolouch" <lubos.kolouch () gmail com>
To: <pen-test () securityfocus com>
Sent: Monday, August 21, 2006 9:22 AM
Subject: 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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