Router Packet Filtering and Firewalls

From: Geoff Shatz (geoff.shatz@pchelps.com)
Date: 01/29/03

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    Date: 29 Jan 2003 22:54:57 -0000
From: Geoff Shatz <geoff.shatz@pchelps.com>
To: security-basics@securityfocus.com
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    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

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