I have two network cards, eth0, and eth1. Each interface has an IP address with the option of having a default gateway, but at present only eth0's gateway is set up as the default route.

I have applications that can launch using -iface ethX. They work fine when using eth0, but not eth1, unless I remove my default route for eth0 and add eth1 as the default route or add a static route to that interface.

My question is this: How can I make it so that I can have two default routes, with eth1's default route only being used when packets flow in or out of eth1?

Is this possible?

Thanks in advance!

If configuring from the command line then you can specify a default route for each interface using route add and specifying the interface with dev. If you want to configure from the GUI then please tell us which distro and desktop you are using.

Also, read here: http://www.linuxjournal.com/article/7291

On RHEL4 and RHEL5 systems, this is the way to make sure routing for multi-homed systems is working as you'd expect.

To have 2 default gateways you have to configure iproute version 2, I wrote a how to here. http://soad1982.blogspot.com/2010/02...-on-linux.html

This got me really close! Here's the problem I'm having now..

eth0 is 192.168.1.15 which is also part of my default network, with 192.168.1.1 being my default route. this works fine.

ppp0 is an outside provider, that sometimes gives me the same IP as what I have on eth0. sometimes I get a different IP for ppp0, but is still within the same subnet as eth0.

when adding the following rule, to try and make any packets seen from 192.168.1.15 on dev ppp0, it still routes out through eth0:

ip rule add from 192.168.1.15 dev ppp0 table ppp0 pref 100
ip route add default via 192.168.1.15 dev ppp0 table ppp0

what am I doing wrong that it won't let me route packets out through dev ppp0 with the same IP as eth0 or an IP within the same subnet as eth0? I suppose the easy answer is to change my default network on eth0, which does work with the following rules, as long as it doesn't match what is on eth0:

ip rule add from 192.168.1.15 table ppp0 pref 100
ip route add default via 192.168.1.15 dev ppp0 table ppp0

...but as soon as I add:

ip rule add from 192.168.1.15 dev ppp0 table ppp0 pref 100
ip route add default via 192.168.1.15 dev ppp0 table ppp0

it will not route properly. I've tried using 192.168.1.15/32, 192.168.1.0/24 but not having any luck.

Thanks in advance.