This what I used a couple years ago to set up our IP masquerade (or IPMASQ)
server, a form of NAT.

http://tldp.org/HOWTO/IP-Masquerade-HOWTO/

I'm running it on RHEL_3, 2.4 kernel.  The server is triple NIC'd and has
one interface to the public LAN and two interfaces to private LANs
(192.168.x.x) where we have all our compute and file servers.  The
IPMASQ server allows me to get software updates from the web but
they're invisible to the outside world.  The HOWTO does have a section
on configuring for a 2.6 kernel.

- Larry

Mark Van Crombrugge wrote on 4/15/2008 8:00 AM:
> I would like to activate NAT (Network Address Translation)on my SL v5.1 
> which is used as a router (2 NIC).
> But after searching the web, all I can find are general theoretical 
> articles, not how to set this up for real.
> 
> Many thanks!
> Mark


-- 
P. Larry Nelson (217-244-9855) | Systems/Network Administrator
461 Loomis Lab                 | High Energy Physics Group
1110 W. Green St., Urbana, IL  | Physics Dept., Univ. of Ill.
MailTo:[log in to unmask]        | http://www.roadkill.com/lnelson/
-------------------------------------------------------------------
  "Information without accountability is just noise."  - P.L. Nelson