Multiple IPs to 2 interfaces problem with default route

[Patrick Chemla <patrick.chemla@perfaction.net>]

Hi,

I have set up a Fedora 11 NAT server to NAT outgoing traffic to 2 
interfaces to 2 ISPs.

My internal interface is eth0, the 2 external interfaces are eth1 for 
ISP1 and eth2 for ISP2, each one with a pool of IP addresses.

I wrote a script who create for each internal server the corresponding 
NAT fonction :

interface= outgoing interface for the wanted ISP
public_ip= public IP address affected to this server on the ISP network
server_ip= internal server local ip address

/sbin/iptables -t nat -A PREROUTING -p tcp -i $interface -s 
$public_ip/32 -j DNAT --to-destination $server_ip
/sbin/iptables -t nat -A POSTROUTING -s $server_ip/32 -j SNAT -o 
$interface --to-source $public_ip

It works very fine with one interface, but when I try to activate the 
second interface, I think I get a problem with the default route.

When I started the interfaces, eth1 got a public IP and a default 
gateway. This default gateway is the default gateway for all the server. 
eth2 has his own public IP, own gateway.

I tried to remove the default gateway, thinking the route will be 
according to the NAT setup, but no more packet can get out of the server.

But I need to split packets to interfaces eth1 and eth2 according to the 
public IP of the internal server, not according to a default route 
always pointing to eth1.

How can I set up these routes?

Patrick