Re: Using NAT to relay traffic

[Grant Taylor <gtaylor@riverviewtech.net>]

The problem that you are having when you port forward traffic from Box A to Box B is that the returning traffic comes directly from Box B to the client that sent the traffic in the first place thus you have an incorrect communications path.  Ironically I just had to work on a situation sort of similar to this one.  What I did in my situation to accomplish this was to DNAT the traffic destined to Box A over to Box B, like you have done.  You also need to SNAT the traffic leaving Box A on it's way Box B to be from Box A's IP so that when Box B replies it will reply back to Box A which will in turn reply back to the client system.  Thus you no longer have a triangle of client to Box a to Box B to client but rather client to Box A to Box B to Box A to client.  Let me know what your network config looks like if you would like me to come up with some iptables rules for you.

Reference my replies to "HELP! Transparent Proxy using bridging 2.6.9 and REDIRECT on	different subnet" thread for an example or email me and I'll try to provide more help.



Grant. . . .

Jared Cook wrote:
> I have two servers on two different networks.  I am running a service on 
> box A that I am transitioning to box B.  While I wait on DNS to 
> propagate, I would like to do some iptables magic to send traffic from 
> box A to box B using NAT.  For instance, when pop3 email users connect 
> to box A, I would like box A to send the request to box B 
> transparantly.  Is this possible?  I have had success doing port 
> forwarding to the local machine, but when I specify box B as the "--to", 
> it doesn't work.  Any help would be greatly appreciated.
> 
> Thanks,
> Jared
>