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Re: Transparent vs Routed Firewall
From: John Morrison <john.morrison101 () googlemail com>
Date: Sat, 6 Feb 2010 17:17:20 +0000

Chris has the right idea. Transparent does make it easier if you have
a single un-routed network. Personally I would chop the network up and
put each group of devices in a separate network. You should group your
devices so that all those that do not require any security between
them are on the same layer 3 network. You can then route and firewall
between networks as you require.

As Chris points out transparent mode avoids having to rejig your IP
address space. I would say, that if it is urgent, use it only as a
temporary measure until you can change your IP addressing.

Remember that with the firewall in transparent mode it must be between
the two layer 2 networks that you want to protect from each other. The
traffic MUST still be forced through the firewall for it to do its
job. You cannot just put it in to a switch and expect it to protect
devices on that switch from each other.

On 4 February 2010 22:17, Chris Brenton <cbrenton () chrisbrenton org> wrote:
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.

HTH,
Chris
--
www.chrisbrenton.org


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In this guide we examine the importance of Apache-SSL and who needs an SSL certificate.  We look at how SSL works, how 
it benefits your company and how your customers can tell if a site is secure. You will find out how to test, purchase, 
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