Question : Using 2 gateways, static routes in modem

Hi all,

I have a network on the ip range of 172.29.37.x (mask is 255255255.0) accessing the net thru a adsl modem at 172.29.37.233 and this all works fine.

I now have a system which means we have a second adsl connection set up specifically for it. Apparently we need to set up some static routes so that when the machines ask for certain ip ranges we get directed thru this second gateway (it's on the 10.4.48.0/24 range, the gateway is 10.4.48.1)

I have entered static routes into my normal gateway but none of the lan machine can ping the new second gateway.

I think i must be missing something. Can someone help me work this out or direct me to a good resource?

Answer : Using 2 gateways, static routes in modem

I think that here is your problem:

You send some (ping) packets from your PC 172.29.37.100 to 10.4.48.1. Because the destination is not in your LAN the packets start to go to your default GW (172.29.37.233). There they are routed to your new GW 10.4.48.1.

The new GW 10.4.48.1 receives the ping packet and replies to IP 172.29.37.100. However it does not have any route to that destination other than default route (which is not your GW!). So reply packets never reach your LAN.

The solution is to add a route on the NEW GW: net  172.29.37.0/24 gw 10.4.48.10


(Only) If this is not possible you could do NAT so the traffic will go like:
You send some (ping) packets from your PC 172.29.37.100 to 10.4.48.1. Because the destination is not in your LAN the packets start to go to your default GW (172.29.37.233). There they are routed to your new GW 10.4.48.1 and source address is changed to 10.4.48.10.

The new GW 10.4.48.1 receives the ping packet and replies to IP 10.4.48.10 (with which it is directly connected to and knows the route). You GW receives the replies and knows that the initial source of the connection is machine 172.29.37.100 and forwards the packets there.