Multiple Internet sources

[Ian Melnick <dazed@vonsteuben.cps.k12.il.us>]

Hello all,


I have two Internet sources, and a NIC for each. I want to ensure that
data coming in on one NIC doesn't travel out through the gateway of the
other.

I'm asking this question because last week I noticed that when I put two
NICs in the same machine on the same network, only one NIC did the work.
There were two "default" destinations listed when you do `route`, and the
first NIC in there with a "default" destination was always the one that
handled everything. The issue was solved by sharing multiple IP's on the
same interface and eliminating extra "default" listings from the route
table. But there was a third NIC in there on a different subnet that
still was unusable until I removed its "default" entry in the route
table. Routing through that third interface was unnecessary, but now
it's a different story.

With two separate Internet sources, with two completely different
gateways, etc, I don't think I can smush all this into one NIC---can I?

And if I can't, how can I ensure that traffic coming in via one
interface leaves via that same interface, via its defined gateway? I need
to eliminate this issue where one interface ends up being dominant even
when it's on a completely different network.

Would this be something I'd have to set up thru iptables, or is there
just some fancy routing trick?


Thanks in advance!