ISP selection in a multihomed linux box

[ajra]

Hello Fellows!

I would like ask for some help regarding this scenario (see figure below).

Basically I would like the LAN host to be able to access both ISPs.For that I would like
to set the LAN GATEWAY to mark the traffic destined to ISP1 with 1 and the traffic going to ISP2 with
a MARK 2.

Im using a single cable between the LAN GATEWAY and the multihomed box and vlans so ISP1 traffic should
flow through vlan101 and ISP2 traffic through vlan102.

What i dont know is what kind of discriminant I could use to tell the LAN GATEWAY (by using iptables) that the traffic is either targeted to ISP1 or 2.

Im using iptables 1.3.6 and Ubuntu 7.09. NAT is also working as i can reach both isps gateways

1.1.1.1/24 2.2.2.1/24
ISP1 ISP2
| |
|eth1=1.1.1.2/24 |eth2=2.2.2.2/24
---------------------------------
| MULTIHOMED |
| LINUX BOX |
---------------------------------eth0
| .1 |.1
vlan101 vlan102
192.168.101.0/24 192.168.102.0/24
| |
|.2 |.2
--------------------------------eth0
| LAN GATEWAY |
| LINUX |
| |
--------------------------------
|eth1 192.168.0.1
|
|
LAN HOST 192.168.0.2

Thanks for any help... I could clarify further if i wasnt clear enough..

ant

[rossonieri#1]

hi,

i dont exactly know whether this rule going to work :
simply drop vlan102 outgoing to isp1 and vice versa in OUTPUT chain

or
you can SNAT vlan1 to isp1 interface and vice versa.

HTH.