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RE: ARP spoofing attacks
From: Ranjeet Shetye <ranjeet.shetye2 () zultys com>
Date: Thu, 15 Apr 2004 16:36:30 -0700


hi Amit,

There is no real preventive solution, but you can address this issue by
continuous monitoring. Since you are concerned with only one IP device,
i.e. your router, it is simple work.

You could use arpwatch (http://www-nrg.ee.lbl.gov/) to track changes in
IP-to-Mac address pairings. Arpwatch can also use sendmail to email you
the changes. Arpwatch will catch changes in ANY Mac-IP pairing, which is
not meaningful for DHCP-allocated IP ranges. Hence, the "-n" flag will
help you narrow the scope of the hosts you want to track.

1. start up arpwatch
2. "ping" the server and verify that the mac address on the server's NIC
matches the mac address that your arp table is showing
3. let arpwatch catch any changes and notify you.
4. ???
5. profit!!

( sorry, been reading too much /. i guess! :) )

I believe that the freebsd kernel has a similar tracking mechanism built
into it (but no sendmail, kernel uses printk to notify user).

Also, the "arping" utility will let you ping neighbours at the layer 2
level i.e. specify the mac address directly, and also bypass the arp
table since this is a layer 2 ping.

HTH,
Ranjeet.

On Wed, 2004-04-14 at 16:47, David Gillett wrote:
  The short, sharp, general answer is that you can't.
Layer two security measures are going to see a packet
(it happens to be an ARP reply) from the miscreant's 
port, but since its source MAC address is what they 
expect, they'll let it through.  Layer three measures
won't see it either, because it's a unicast within the 
same vlan/subnet and so never needs to hit a layer 3
device.

  About all you can do proactively, if this is a serious
concern, is add a static ARP table entry to every host 
so they never need to send out an ARP request for the
gateway.

David Gillett


-----Original Message-----
From: Amit Agrawal [mailto:csu02103 () cse iitd ernet in]
Sent: Tuesday, April 13, 2004 9:22 PM
To: security-basics () securityfocus com
Subject: ARP spoofing attacks



Hi
 I have a question...How do u secure
 against ARP spoofing attacks...If
 not the whole subnet...I want to be
 sure that no one spoofs the IP of
 my gateway.
 
Amit


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-- 

Ranjeet Shetye
Senior Software Engineer
Zultys Technologies
Ranjeet dot Shetye2 at Zultys dot com
http://www.zultys.com/
 
The views, opinions, and judgements expressed in this message are solely
those of the author. The message contents have not been reviewed or
approved by Zultys.



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any course! All of our class sizes are guaranteed to be 10 students or less 
to facilitate one-on-one interaction with one of our expert instructors. 
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of an Ethical Hacker to better assess the security of your organization. 
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