Dynamic routing on a firewall

["Dawes, Rogan (ZA - Johannesburg)" <rdawes () deloitte co za>]

Hi,

I just wanted to pick the list's brain with regards to dynamic routing on a
firewall.

Is it a good idea to allow a firewall to participate in dynamic routing? My
first thoughts are that it sounds like a really dangerous thing  - you
certainly don't want to have routes changing so that a DMZ moves from one
interface to a different one, for instance.

But if the routing can be controlled so that traffic always goes through the
right interface (but possibly to a different upstream router), that should
be OK, I would think.

What mechanisms do the various firewalls (mostly interested in Pix and FW-1)
have to sanity-check routing updates that they receive?

A (simplistic) scenario that could illustrate my concerns:

You have a firewall controlling access to third parties (competitors) which
provide services to your company. Each party is in their own DMZ. You have
dynamic routing enabled on the firewall, since there are two redundant
routers for each party in each parties DMZ, and you need to be able to fail
over from one to the other.

Party A sends a routing update to say that party B is now reachable via
Party A's networks. Any packets that you try to send to party B end up going
to Party A, where they can be captured, etc.

Leaving out the question of how A gets the packets to B eventually, to
complete the connection, is this a realistic scenario? How can one protect
against something like this, using the abovementioned firewalls, if one
still chooses to use dynamic routing?

Rogan
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