The IP Masquerade HOWTO is among the better ones, describing what you need 
to do for this. 
http://www.linux.org/docs/ldp/howto/IP-Masquerade-HOWTO/index.html

This area changed pretty dramaticly between the 2.2.X kernel and the 2.4.X 
kernel. Much way easier under 2.4.X.

Bob.

On 2002.01.11 08:28 Wes Bateman wrote:
> Andrew:
> 
> Everything, of course, depends on exactly what you're trying to do.  I
> can't see where you'd need an additional router.  The cable "modem" is
> really a router, of sorts (well more router than modem anyway :) ).
> 
> What many people do, and I'm guessing is what you're attempting, is build
> a private network behind the linux firewall.  You'll need two NICs (at
> least) in your Linux box.  One you'd connect directly to the cable modem
> and the other you'd connect to your hub.  You'd configure your Linux box
> with your static public IP or to use DHCP to obtain it from your cable
> provider (is @home still what cox is using there?) on the interface
> connected to the cable modem.  On the interface connected to the hub,
> configure a static address.  You'll probably want to use a reserved
> private address space like 192.168.1.0/24.  The address you give your
> Linux box on that "private" interface will become the gateway address for
> your internal boxes.
> 
> This whole thing assumes that you have only one public address that the
> cable company gives you, and you want to share it with all your internal
> network.
> 
> You'll then want to use iptables or ipchains to build your firewall
> rules.  Additionaly, for the sharing of a single public IP described
> above, you'll want to enable masquerading.  How to do this is pretty well
> documented and you can search for documents on the web.  If you need
> additional help with it, shoot me an email off list and I'll help you
> with
> specific rules need be.
> 
> Again though, everything depends on what you're trying to accomplish :)
> 
> Good luck,
> 
> Wes
> 
> On Thu, 10 Jan 2002, Bruner, Andrew wrote:
> 
> >
> > I'm getting Cox@home and plan on using a Linux box as a firewall. Do I
> need
> > to also configure it as a router? Should I just go out and buy a
> router? Do
> > I need a router at all? I have an 8 port hub that I was planning on
> using in
> > conjunction with the Linux box as a firewall. Will that work?
> > Thanks for any comments.
> > -Andrew
> 
> 
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-- 
Robert A. Klahn
rklahn@acm.org

"Hope has two beautiful daughters: Anger and Courage. Anger at the way
things are, and Courage to struggle to create things as they should be." -
St. Augustine