You can do policy routing, i.e., have multiple routing tables, and select the routing table to use based on your source address (in general other fields, but not relevant here). Note that the table numbers shown below are arbitrarily chosen.
I do not know how to do policy routing using
route from the
net-tools package. It's long deprecated anyway. Use
ip from the
You'll also need to have policy routing enabled in your kernel. The major distributions do this by default if I am not mistaken.
Start from a clean state, if appropriate:
# Assumes that previous configuration properly set address and route scopes
ip route flush all proto static scope global
Then add the tables for each interface.
ip route add 10.0.0.3/24 dev eth0 table 5000
ip route add default via 10.0.0.254 dev eth0 table 5000
ip route add 10.0.1.1/24 dev eth1 table 5001
ip route add default via 10.0.1.26 dev eth1 table 5001
One then sets up routing rules:
ip rule add from 10.0.0.3 table 5000
ip rule add from 10.0.1.1 table 5001
The last step is to configure the default gateway for when you are the initiator, so to speak.
If you want to only use
eth0 as the default gateway, then just do something like this:
ip route add default via 10.0.0.254 dev eth0
Note that there is no table specified, so it defaults to main. Using
eth1 is left as an exercise to the reader.
If you want to load-balance between the two, can do multipath routes using
ip route add default nexthop via 10.0.0.254 dev eth0 weight 1 nexthop via 10.0.1.26 dev eth1 weight 1
As for question two, no Linux does create a default route automatically. If there is no local route for your traffic, you'll get a
EDIT: Note that none of the above should be taken to imply that IP is stateful, that it has anything to do with connections, or even an inherent notion of a flow. It merely means that we assume that a flow has always the same endpoints, and that we bind a flow to gateway depending on our source address. This is simply necessary because many gateways (esp. in the context of residential ISPs) do reverse path filtering.