full-disclosure - Re: hiding routers

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Date: Thu, 19 Apr 2007 13:43:50 -0400
From: "Maxime Ducharme" <mducharme@...ergeneration.com>
To: "'Kristian Hermansen'" <kristian.hermansen@...il.com>,
	<full-disclosure@...ts.grok.org.uk>
Subject: Re: hiding routers

Hello Kristian

I did some implementation of "transparent firewalls"
on Linux.

Usually it wasnt a router, but was placed at the entry
point of networks just after the router.

ebtables on Linux can explains how it is done :
http://ebtables.sourceforge.net/

The firewalls didnt have any IP addresses and were
acting as bridges with filtering capabilities.

I cannot tell if it is common setup, but it was alot
harder to "find" the firewall, almost impossible if
you arent on the same IP segment. This box would not touch
TTL field like you describe below.

These configurations currently work perfectly, I would
recommend it. it wont "breaks tcp/ip and error conditions"
if you understand and configure ebtables correctly.

Hope that helps

Maxime Ducharme

-----Message d'origine-----
De : full-disclosure-bounces@...ts.grok.org.uk
[mailto:full-disclosure-bounces@...ts.grok.org.uk] De la part de Kristian
Hermansen
Envoyé : 18 avril 2007 04:25
À : full-disclosure@...ts.grok.org.uk
Objet : [Full-disclosure] hiding routers

I brought this question up on another mailing list, but didn't get any
good answers...

How common is it that a router does not decrement the TTL of packets,
such that it is unable to be identified using traceroute?  Choosing
not to decrement the TTL causes the next router to appear as the hop,
but the current router to remain hidden.  How does one commonly
identify such hidden routers in an automated fashion?  And is it
policy for any organizations to actually do this, or only with certain
packet types?

The responses I got were along the lines of "don't do that, it breaks
tcp/ip and error conditions".  However, I am still interested in how
likely an organization is to try something like this for both
legitimate and illegitimate purposes.
-- 
Kristian Hermansen

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_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/