Nathan Davis wrote:

>After thinking about this for awhile, I was wonding if I really need to
>use two *real* ip addresses on the firewall machine.  Or even if there's
>a way to set up a default route to an interface with no ip address
>assigned.  Another option might be to have the cisco (and possibly the
>firewall too) obtain an ip address via dhcp (I don't know how the other
>end might take this, though), or assign the interface connecting the
>firewall to the Cisco a "fake" address.
>

If you want an interface w/ no IP I'd suggest getting the Linux bridging 
stuff.
The idea would be to have 3 NIC's actually.  One external (Router -> FW 
NIC), One for internal NAT'd addresses (any traffic can be forwarded 
through the firewall to internal hosts), the other would be a bridged 
interface to a DMZ (allows you to filter ports but doesn't need an IP).
    There are other ways to set this up also but this is the only way I 
can think of at the moment to get a firewall without using one of your 
addresses.  Unless of course you just forward all your traffic through 
the firewall.  If you want a dedicated address for a specific server 
instead of all your DNS entries going ot the firewall, the firewall can 
be multi-homed (multiple addresses/NIC).

I could probably think of a few more ways to get it done but couldn't 
tell you the "best" way without a bit more info.

sim