[asterisk-users] 2 NICs; Asterisk receives on eth1 and replies on eth0

[RR]

Two different things I think.

For redundancy, if you're using RHEL4U2 or later, you can bond your
ethernet channels and configure any of the 6 modes AA, AP, ALB etc.
you'll get NIC redundancy. Anyone of the NICs die, the other one takes
over the MAC and the IP of the failed NIC and the system is always
accessible on that same IP. That should solve your problem.

Now with the original question,

The original question wasn't redundancy, it was physical separation of
traffic flow between the two NICs, which has a side-benefit of
redundancy but not really since if eth0 dies, no SIP Service!

This is not necessarily a limitation of asterisk but a routing thing.
If you do a "netstat -r", it'll show you eth0 before eth1, which is
what the network stack will then use to send your packets over no
matter where it's coming from if both NICs are on the same subnet. You
may have to either create a manual entry in the routing table. Will
have think about it more in terms of what the exact table would look
like but if you have a different gateway for your internal traffic,
having a static route for that along with some netmask manipulation
might sort your problems.

But like other people have suggested, you're MUCH better off by having
a different subnet for your 2nd NIC. IF you can't, then just bond your
NICs and set them to mode 6 where the OS will load balance your tx/rx
traffic between the two NICs and you'll still only have one address
that you can assign to the DMZ.

Hope this helps.
\R