[c-nsp] External Firewall

[Dean Smith]

"(3) I wanted to setup what I described in my original message, with the 
firewall performing only stateful inspection functions, and allowing the 
router to perform packet switching functions without interference from 
the firewall once the session is operating."

By definition "stateful" inspection requires the firewall to see all the
packets...to verify that they are indeed part of an agreed connection etc...

So scenario 3 is a nonsense. 

If you could offload the connection once it was setup (in a sort of MLS
style way) - it would no longer be stateful inspection. As the "packet
forwarder" is no longer verifying the "state" at all.


The 7200 can do stateful inspection (via CBAC / Firewall IOS) but you'd need
to give more info about the Processor (NPE), Throughput (inc Pkt sizes,
protocols etc) and any other features you have running for a view on whether
it would cope. (and that would only be an opinion then)

Dean

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Sridhar Ayengar
Sent: 24 March 2008 19:12
To: Fred Reimer
Cc: Cisco NSPs
Subject: Re: [c-nsp] External Firewall

Fred Reimer wrote:
> Why, exactly?  Performance of the firewall?

Yes.  I have two identical networks setup for one company in two 
different locations.  One has a Cisco router (said 7200) talking 
upstream to a big WAN pipe and downstream to two gigabit ethernet 
networks.  The second location has the same WAN and LAN configuration, 
WAN line distance and quality measurement numbers, etc.  The only 
difference it is a BSD PC.  The Cisco performs noticeably and measurably 
better in latency and throughput.  Neither is running firewall code.

Now, the BSD PC has gobs more processor horsepower, memory- and 
bus-bandwidth.  Why should the Cisco outperform it?

To find out, I wanted to set up a selection of scenarios in the lab. 
(1) I wanted to try setting up the firewall between the "internal" 
gigabit network and the 7200.  (2) I then wanted to setup the firewall 
between the WAN interface and the router to see how that performs.  (3) 
I wanted to setup what I described in my original message, with the 
firewall performing only stateful inspection functions, and allowing the 
router to perform packet switching functions without interference from 
the firewall once the session is operating.

As far as I can see, the advantage of (1) is that traffic heading to the 
"external" gigabit LAN wouldn't come across the firewall PC.  However, 
the disadvantage would be that traffic between the two LANs would have 
to pass through it.  That might be unacceptable.

The advantage of (2) might be that traffic between the "internal" and 
"external" LANs wouldn't come near the firewall PC.  Also, the WAN pipe 
may not require the throughput advantage of the Cisco.  (It may indeed, 
but it might not be as sensitive.)  However, this does add a couple 
dozen ms to the latency of the upstream connection.

As far as I can tell, (3) would be the best of both worlds, but I, for 
the life of me, can't figure out if there's a way to set a network up 
like that.

Any ideas?

Peace...  Sridhar