Re: Public / private IP addresses

[Alan Chandler <alan@chandlerfamily.org.uk>]

On Monday 29 December 2003 11:43, Antony Gelberg wrote:
> Hi all,
>
> I've dealt with quite a few LANs over the years.  I'd like to try
> something that I never have done before...
>
> I work with ADSL providers who allocate 5 public IP addresses (sometimes
> 1) to a connection.  If I have a LAN of, say, 20 workstations, I can use
> NAT, and give them private addresses - no problem.
>
> I usually have an ADSL router / modem, hooked up to a Linux box
> configured as a bridging firewall, which connects to a switch.
>
> But if they wanted to run a public email server as well, clearly that
> needs a public IP address.  Fine, but how does the routing aspect work?
> Do I need to ditch the bridging configuration on the firewall and
> reconfigure it as a router with 3 NICs?  One connected to the WAN, one
> to the private LAN switch, and one to the public server(s) switch?

There is ANOTHER way - one that I use.  My router allows port forwarding.  In 
other words a mail connection request on port 25 (SMTP) is forwarded by the 
router from its WAN side IP address to a designated IP address on the Lan 
side (10.0.10.100 in by case).  I can do the same on other ports as well - so 
for instance to make the web site available externally I forward port 80 to 
the same machine. 

-- 
Alan Chandler
alan@chandlerfamily.org.uk