Linux router with 2 WAN, 1LAN, iproute2

Hi,

I would like to build a linux router using Ubuntu 11.4 which i have installed on a pc with 3 ethernet interfaces which are assigned like so:

eth0 - LAN -> IP: 192.168.3.1

eth1 - WAN1 -> IP: 192.168.2.146

eth2 - WAN2 -> IP: 91.212.254.117

I want my router to use both WAN connections and when one of them goes down to keep working unintererupted on the other one.

For the purpose of testing my setup i am using the internet on the router itself, trying to ping the gateways on each WAN. This is my setup:

Now for my problem...

I start by pinging some IP in the internet. I check the route to that ip

ip route get 8.8.8.8

...and discover it's going out through eth2. I unplug the cable from eth2 and the ping keeps getting replys. Checking the route again reveals that the route is nou going through eth1 which is just fine. I put back the cable into eth2 and unplug it from eth1. Route switches back to eth2. Problem is that when i put the cable back into eth1 i start getting erros ( destination host not found ) and it takes verry long for it to start getting replys again. Also if i unplug the cable from eth2 while pinging eth2 gw and then plug it back again it just works seemlesly but if i do the same with eth1 i have to wait a lot of time for the thing to start getting replys again and first i get some destination host not found errors. This dosn't happen with eth2. So how can i make my router work propperly and track down the problem ?