RE: mac duplication

["Dom De Vitto" <dom () DeVitto com>]

The easiest way to get what you want is to:
1) For every *other* box on that LAN (including gateways) send rarp
reply to that box's MAC saying the server has a MAC of broadcast
(ff-ff-ff-ff-ff-ff).
2) for every *other* box on that LAN (including gatways) send an rarp
reply to the server, saying that the other box has a broadcast MAC.

repeat 1 & 2 every 5 seconds.
Now traffic from any box on that LAN, and the gateways on that LAN
will be broadcast to all boxes (including yours).
In effect you have made the LAN behave like a hub.

It's important that you don't send a spoofed rarp reply to the actual
real machine, as this will get logged.

This kind of 'rarp storm' attack can cause trouble with *your*
switchport, as you're spoofing MACs, so it looks like your port has
all the machines on it :-(

Try getting a copy of 'sterm' as this does various kinds of spoofing
to enable connections from a to b, but as if the connections are coming
from c. cute.

Dom
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Dom De Vitto                                       Tel. 07855 805 271
http://www.devitto.com                         mailto:dom () devitto com
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-----Original Message-----
From: Jimi Thompson [mailto:jimit () myrealbox com] 
Sent: Sunday, December 14, 2003 12:34 AM
To: vuln-dev () securityfocus com
Subject: Re: mac duplication

Dev,

You seem to need some clarification about how Ethernet actually works.  
I'm going to try to toss out a 50,000 foot view.  Anyone can feel free to
add to this or correct me. Host names map to IP addresses via DNS.  
IP address map to MAC addresses via router tables.  Just as your IP address
has to be unique in order to be routable, so does your MAC 
address.   MAC addresses are purchased in blocks by the people who make 
network devices and blown on to what amount to EPROMS and attached to
network cards, switch ports, etc. 

No two ethernet cards on the planet should have the same MAC address
(emphasis on SHOULD because I've run into cards with duplicated MAC's and
you won't believe the havoc this wreaks).  This is used as a physical layer
address by things like ARP.
If you want to sniff traffic to a particular machine, get yourself a hub
(NOT a switch) and plug the switch into the uplink on the hub and your
sniffer and sniff-ee into the hub ports.

This will A) let you see everything and B)   not cause any serious 
problems for your switch.  I hope that no one was using the machine you were
trying to sniff because chances are you are causing a DOS situation by
duplicating the MAC address.

Jimi

Dev wrote:

> hi ppl, please redirect me to a different mailing list if this is not the
appropriate list to post to.
> I did the following experiment:
>
> I have a switched ethernet network in my university.
> I wanted to capture packets meant for a certain machine on a different 
> port of a Dlink switch. I thought that arp poisoning would be too noisy 
> - arpwatch can catch it, & its too bulky for the MITM machine (in case 
> we are poisoning a heavily loaded server
 machine.)
> & So i duplicated the mac of the victim machine on my own machine. 
>
> What i saw was this:
>
> ping packet drop rate for any of the two machines from a third machine
varied from 40 to almost 80 %. Also say telnet sessions to any of the two
machines (which had now the same mac addresses) worked with notable 4-5
second lockups. 
> Further i could not ping the other machine from one of the duplicated 
> machines. (the last one is okay - it makes a lot of sense)
>
> My premise is that the problem in connectivity is coming becoz the OS does
not fall back to half duplex mode when two machines take up the same mac
address??
> can anyone plz tell me about the behaviour. How do i set up mac duplication
in that case so that i can sniff data. 
> I dont want to hurt network performance. & so dont want to do mac flooding.
Anyways i m not even sure the switches we have here would resort to
broadcast mode in case of mac flooding.
> Last but not the least its my second message to the list, & people were
really helpful in discussing about my queries in my first message.
> Mailing lists rock..
>
> Devrat
>
>
>