[ILUG] Routing question - I think :-)

[Nick Murtagh]

Niall O Broin wrote:
> We have two servers which are hosted in a colo facility. One (A) is currently 
> the primary mail server for a number of domains. I want to make the other (B) 
> the secondary server for these domains. Both servers have two LAN 
> connections, the second being used for an RFC1918 private network. I would 
> like to figure out a way of getting traffic to go from server A to server B 
> over the private LAN so that email which lands on B (which will be mostly 
> spam, sadly) and is thence forwarded to A travels over the private LAN (where 
> bandwidth is not chargeable). Is there any way of doing this, given that the 
> public addresses of A are not bound to the private network's NIC?

You need to force B to always relay to the IP of A on the private LAN.
In postfix you could do this with an entry in the transport table:

   domain.name smtp:private.ipaddress.of.B

There's probably a way to do this globally too.