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Re: Transparent vs Routed Firewall
From: Chris Brenton <cbrenton () chrisbrenton org>
Date: Thu, 04 Feb 2010 17:17:30 -0500

Greets Alex,

On Wed, 2010-02-03 at 19:19 +0200, Alex wrote:

I'm in the task of setting up a Cisco ASA to protect some internal
servers. I was thinking of configuring it to be transparent (aka layer
2, bridged etc.) rather than routed (aka layer 3).

I dig transparent when it is internal. Less impact on the existing
infrastructure, you don't have to resubnet, no new DHCP scopes, etc.
etc. You are far less likely to bork the network if you go with a
transparent implementation during an internal installation.

With that said, I assume you don't need NAT or VPN termination? If you
do, you might want to reconsider.

The reason I was thinking of going the transparent way is
that it "feels" more like a firewall to me,

A heavy rock "feels" like it should fall faster than a lighter one, that
does not make the statement correct. ;-)

From a security perspective, transparent gains you squat. In fact I
would argue it is _less_ secure as you loose the ability to leverage
routing as one of your security layers. I've head folks say it
"stealths" the firewall, but that is completely false. A little work
with tcptraceroute or a similar tool and you can easily figure out
exactly where the firewall is sitting, what rules are in play, etc. 

So based on the info you provided I would consider transparent for its
ease of deployment, not for any type of security gain.


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