comp.os.linux.networking

Hi,
I have the following configuration with 2 PC :

+------+ eth0 eth0 +------+
| PC1 +---------/--------+ PC2 | eth2
| | | +---------------(Device, IP3)
| +---------/--------+ |
+------+ eth1 eth1 +------+

I want to send IP packets to the device (with IP3 address) from PC1 and
using PC2 as a gateway. I have configured PC2 as a gateway for eth0 ->
eth2 and eth1 -> eth2.

But how can I set routes on PC1 ?
What I want is in fact redundancy between eth0 and eth1 :
Connecting to IP3 from PC1 use the link eth0<->eth0 if this link is up
and use the link eth1<->eth1 if eth0<->eth0 is down ?

I think I have to use ip route + nexthop but it's not very clear.
Someone can help me ?