[Snort-users] ARP mangling:
trankin at ...2080...
Tue May 22 15:06:59 EDT 2001
I used another NetMon in tandem with Snort and there are no actual ARP's for
the 212.250.18 net address. It appears that some software component/function
is rewriting the 'sender protocol address' and 'target protocol address'
fields of the ARP_RARP broadcast frame so that false IP data is written to
the log. Therefore, legitimate ARP's are being incorrectly interpreted
and/or appended to the Snort log file. The layer 3 info for ARP replies is
similarly mutated although the layer 2 info is legitimate. I have tested
this on several independent networks and the results are identical. The
problem is either a software issue ('libpcap' or 'snort') or related to how
the 'libpcap' s/w interacts with my NIC (AMD PCNET PCI 100bTX). Note: this
only happens for ARP traffic.
From: Phil Wood [mailto:cpw at ...440...]
Sent: Tuesday, May 22, 2001 2:46 PM
To: Terry Rankin
Cc: snort-users at lists.sourceforge.net
Subject: Re: [Snort-users] ARP mangling:
On Tue, May 22, 2001 at 01:35:59PM -0400, Terry Rankin wrote:
> I've been using Snort v1.7 on NT4 successfully for a few weeks on several
> networks with only one problem - all layer 3 info in ARP requests/replies
> appears to be getting mangled between reception and logging. The symptoms
> are as follows:
> 1. the target IP of the ARP request is always 184.108.40.206.
> 2. the sending IP of the ARP request varies, but about 75% claim to be
> 220.127.116.11. To date, the last two octets are always 217.0.
> 3. no 'actual' ARP request layer 3 info is ever recorded to the log file
> just the butchered info.
> 4. the ARP replies contain genuine layer 2 addresses.
What is you network configuration. ARP only applies to layer 2 (same link
layer). So, the stuff below, indicates you have a bunch of weird machines
on the same link as you all wanting to know about network 212.250.18.
What are the machines with the layer 2 addresses?
Can you get a tcpdump of this stuff?
> ARP who-has 18.104.22.168 tell 22.214.171.124.
> ARP who-has 126.96.36.199 tell 188.8.131.52
> ARP who-has 184.108.40.206 tell 220.127.116.11
> 05/21-12:15:05.144373 ARP reply 18.104.22.168 is-at 0:10:5A:XX:YY:ZZ.
> I've searched the obvious places for answers without any joy. I would be
> extremely grateful for further information.
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Phil Wood, cpw at ...440...
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