[Snort-users] firewalling snort machine

Salisko, Rick SaliskoR at ...1594...
Mon Feb 25 05:24:04 EST 2002

-----Original Message-----
From: Erek Adams [mailto:erek at ...577...]
Sent: Friday, February 22, 2002 1:08 PM
To: Salisko, Rick
Cc: 'McCammon, Keith'; Basil Saragoza; snort-users at lists.sourceforge.net
Subject: RE: [Snort-users] firewalling snort machine

On Fri, 22 Feb 2002, Salisko, Rick wrote:

> I have tried to get around a similar problem in the past by setting the
> default gateway of the sensor to the firewall external interface, which, of
> course, is set to deny all such packets. Each time a packet (scan or
> otherwise) is directed to the sensor ip address, any response it sends is
> sent to the firewall, which reports it as a packet forwarding attack.
> Other than opening the sensor to a DOS type attack, can anybody see any
> other blatant holes in this technique ?

*puts on his Devil's Advocate hat*

Ok....  Lessee...

*  Depends on how your firewall responds.  RST or Drop?


*  If your firewall is ever 0wned, then so is your sensor.  But at that point,
who cares--You're hosed.

sensor's is disposable... (no other links, so no other connections to exploit, half-an-hour to rebuild) 

*  Extra load on firewall.  Using a R/O cable and 2 nics, you don't have to
worry about even firewalling the box.

I get more traffic from Code Red then I get from this configuration

*  Single point of failure.  If the firewall goes, so does your sensor.  But
that could also be a moot point.

no, the sensor is still active - I'm not sure I see the connection....

*  You only see what the firewall passes.  You don't see what's hitting the
DMZ/Outside.  And if you think your users can't get around your firewall....

Actually, the sensor lets me see everything, because it's on the outside. I have separate sensors on DMZs....

*  Do you trust your firewall admins?  (Many companies they aren't the same as
the IDS folks.)

I also admin the firewalls............

Erek Adams

All good points, but I think I've considered most possibilities.... (famous last words...)

Thanks for your response

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