Re: IP forwarding?

[Alexandros Papadopoulos <apapadop@alumni.cmu.edu>]

On Wednesday 30 March 2005 10:28, Jason Lim wrote:
<snip>
> I basically have 2 networks, each with 32 IPs.
>
> Say the first network is 1.2.3.1-32
> and the second network is 5.6.7.1-32
>
> Is there a way to make it so requests for 1.2.3.1 go to 5.6.7.1, and
> 1.2.3.2 go to 5.6.7.2, so basically map 1.2.3.1-32 to go to
> 5.6.7.1-32?

So you need the following:

* The gateway that will receive packets destined to 1.2.3.0/32 to have a 
route to the 5.6.7.0/32 network.
* The gateway running iptables rules that will forward any request to 
1.2.3.[1-32] to 5.6.7.[1-32] and of course fiddle with the source 
address of reply packets to make it work.

The former is pretty simple, route add blah blah. The latter can be done 
with iptables as described here: 
http://www.linuxsecurity.com/resource_files/firewalls/IPTables-Tutorial/iptables-tutorial.html#DNATTARGET

I'm not sure if you can use DNAT rules for subnets, or you need to do it 
on a host-by-host basis. Worst case scenario, you'd end up with 32 
rules.

Are you sure you can't get around this with updated DNS records?

-A