[ale] Routing with 2 Internet connections

[Joe Knapka]

Nick Travis <wormfishin at gmail.com> writes:

> I have a firewall setup with 2 interfaces on the internet, Everything
> is working fine for eth1, but when a request comes in on eth2, it's
> being routed back out eth1.  How can I set the routes up so everything
> goes back out the same interface it came in on?

I don't believe you can do this without some rather involved
router-fu.

Your default route tells the machine which interface to send any
packet for which it doesn't know a more-specific route for. In your
case, you could set up either interface as the default, but there
isn't a simple way to say, "If this packet is related to a packet that
came in on eth1, send it out on eth1". The trick is, how do you define
"related to a packet that came in on eth1"?

If you're only worried about traffic from some particular range
of addresses, you can manually add specific routes for those
addresses through whichever gateway you need to use. But that
doesn't sound like what you want.

You may find the Linux Advance Routing and Traffic Control HOWTO
an interesting read, at <URL: http://lartc.org>.

Cheers,

-- Joe

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