Router Packet Filtering and Firewalls

[Geoff Shatz <geoff.shatz () pchelps com>]

I am trying to confirm my thoughts regarding the use of router packet 
filtering in addition to having a firewall behind the router but first a 
little background...

Years ago when we first connected our firm to the Internet we did not have 
a firewall but used packet filtering on the router to protect our 
perimeter.

As time progressed and security became a much greater issue for everyone 
in IT we moved forward an installed a firewall between our router and the 
LAN. I was managing our router at that time and kept the initial packet 
filters in place as I figured two layers of security were better than one.

A few years ago we were forced to switch ISP's and our new ISP managed the 
router they supplied to us. They supplied the router with no ACL's applied 
to either interface which as I understand it with Cisco IOS creates an 
implicit permit for both inbound and outbound.

After contacting technical support I was told none of their customers use 
packet filtering at the router level and that's what a firewall was for.
I had a small battle with them but they finally relented and configured 
the router the way I asked them to.

We just had a second circuit installed and I had to go through the same 
routine with them and the end result was the same.

Am I missing something here? Is it not better to have both packet 
filtering applied on the router and a firewall behind it? Is there 
something inherently wrong with this or is this just a case of our ISP not 
really giving a damn about security and on top of it being lazy? Any 
comments would be appreciated.

-Geoff