Routing through two networks

[Jonathan]

Hi all,

I'm trying to achieve something which, on the surface, seems quite
simple but I can't for the life of me figure out a decent way of doing
it.

I have a server which lives within two networks - we'll say 193.0.0.0/24
and 217.0.0.0/24 for simplicity. One of these networks is US peered and
the other isn't and due to this, the bandwidth charges are that much
less for the non-peered allocation.

All I'm trying to do is ensure that any traffic that comes in for
193.0.0.250 routes back out through 193.0.0.1 and anything that comes in
for 217.0.0.250 routes back out through 217.0.0.1 keeping bandwidth
charges to a minimum.

The machine is running 4.8-STABLE and has 2 NICs, though I'm currently
only wired for one. The router (which I don't have access to) appears to
be the same physical router for both IPs.

Any assistance would be muchly appreciated.

Regards,

Jonathan

P.S. Apologies if this is an obvious question, I've been staring at too
many man pages today!