[ILUG] Routing question - I think :-)

[John Reilly]

On Tue, 2004-04-20 at 13:12, 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 could try the following..

Given hosts A and B as follows
	Host A:
	public address a.a.a.a   on dev eth0
	private address x.x.x.x  on dev eth1

	Host B:
	public address b.b.b.b   on dev eth0
	private address x.x.x.y  on dev eth1


On host A:
route add -host b.b.b.b gw x.x.x.y dev eth1

On host B:
route add -host a.a.a.a gw x.x.x.x dev eth1


You didn't say whether the two public IPs are on the same network.  If
this is the case, I think you'll need to change the metrics so that the
route over the private network takes preference, but I can't really
comment on this, not having done it. 

Rgds,
John


-- 
John Reilly <jr at inconspicuous.org>