[ILUG] IP address manipulation and routing

[Niall O Broin]

I'm working on a project which is being converted from SCO using 
Informix to Linux using MySQL.
For reasons which are not germane to this discussion, this box makes 
connections to two other systems and each other system must see 
connections coming from a separate IP.

On the SCO box, this is done by having two NICs, each with the 
appropriate IP address, and setting up routes to the other systems with 
a 'dev' specifier so that the traffic arrives at the external system 
with the appropriate IP.

This is of course achievable in exactly the same way on Linux, but I 
was wondering could it be achieved with one NIC? The reason for this is 
that the boxes have two NICs, but I'd like to use one in each box 
(redundant pair) to be used for a crossover cable which will do nothing 
but carry MySQL replication traffic and heartbeat. The boxes are 
PE2850s which I presume could have another NIC installed (they're 2U, 
and there are slot covers there, so I presume a PCI riser is installed. 
I'd be well pissed with Dell if it were an optional extra. But the box 
isn't mine, and I haven't had its top off yet) but that to me just adds 
another POF which I'd prefer top avoid, if there's a software solution.

One thought is to use route commands and specify  dev eth0:1  (or 
whatever) but I don't know if that's allowed in a dev specifier. 
Another thought is that this is presumably achievable with iptables 
somehow, but I am not anything like an iptables whiz.




Niall