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OT: Advice on network setup

Hi All,

This isn't really specifically a firewall question, although I do plan
on running a firewall on this machine.  I've been given the task of
installing a firewall router in a data-centre that will sit in front of
a bunch of co located machines.  The information I have from the data
centre for our cabinet is:

network address:
first usable: 
last usable:  
broadcast address:

Having not really studied this stuff since about 1999 (and not really
doing all that well on the exam), I'm hoping somebody can reassure me
about what I'm doing.  At the moment, the connection from the data-centre
comes straight into a hub inside our cabinet with the co located hosts 
connected to it.  What we are thinking is that we put our machine
between the data-centre connection and the hub like this:

                datacentre gateway (

                                |    (
                             |     | firewall / router
                                |    (???.???.???.???)
                          |    hub    |  
                                |         ( -- 239)
                        |   |   |   |   |
                        co located hosts

So all traffic goes through the firewall router on it's way in and out.
There's a couple of things I'm not sure of.

        - On the firewall, do I set it's external IP to
        (the network address)?  Or do I have to give it one of the
        usable addresses?

        - On the firewall, what will I set the internal IP to?  It
          doesn't matter right?

        - I set the firewall's gateway to

        - On the co located hosts, I set the gateway to the internal IP
          I assigned to my firewall, correct?

        - I've only every setup a firewall gateway using SNAT and DNAT
          for an office LAN with only one real IP, in this case, I don't
          need it, do I?

        - Is there any other advice anyone can give me on this setup?
          I'm mostly concerned about how to assign IPs and route
          traffic.  Especially the external and internal IP for the

Thanks in advance,



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