network gateway with a foreign IP address

[John Cornelius]

Claude Jones wrote:
> The problem:
> Company has switched over to FIOS and I have to move behind a 
> router
> I will be behind a 10.0.0.1 LAN on a Cisco Router
> I will be configured with an outside address, let's say 
> 70.xxx.xxx.120 for argument's sake
> Traffic to that address from the outside will be routed to my box 
> inside the network by the Cisco
> I need to tell the box/outside NIC that its gateway is 10.0.0.1 
> even though it's not an address within the IP/subnet that the 
> NIC is configured for
>
> There are reasons for this
> Before you say it can't be done, google my subject line and 
> you'll find this nice howto for Debian
> http://siddhesh.in/foreign-gateway.php
> I'm wondering if I need to pursue the route in that howto, or 
> whether I can configure this with the system-config-network GUI 
> in Fedora -- I see there's a 'Route' tab in there, but I've 
> never used it
>   

I gather that it's simply a case of you moving from direct connection to 
the Internet to a connection that's behind your Cisco router. I further 
presume that the (nominal) 70.x.x.120 address belongs to the Cisco. In 
that case you probably don't want to do what you propose.

Your box should be set up on the internal LAN subnet in the normal way. 
All of the interesting configuration should be done on the Cisco router 
by setting up source and destination NAT so that internet traffic on 
specific ports addressed to the Cisco are routed to your box and 
responses are automatically routed back through the Cisco to their 
destination.

Trying to deal with this issue from inside the LAN rather than in the 
router will most likely lead to frustration since whatever you do will 
be fragile and probably break often if it works at all.

John Cornelius
Cardiff by the Sea, CA, USA