Two internet connections

Hi guys, I posted about this problem before, got no reply, but I did stumble upon this link: http://linux-ip.net/html/adv-multi-internet.html Scroll down to "10.4.2. Inbound traffic Using Multiple Connections to the Internet" to see what I'm on about. My problem is similar, except the one interface is the internal network, and gets internet from a nat firewall connecting to adsl, and forwarding port 25 to the mail server. It looks like so: eth0: static IP connected to router/leased line - 196.5.10.15 (for arguments' sake eth1: 192.168.16.4 default gateway is 192.168.16.5 Connections are coming in via the adsl (which is around 8 times faster than the leased line) and I'm trying to get the least line to act as a backup line. According to the above link, what I have to do translates roughly into: ip route add nat via 192.168.16.5 BUT, the ext_IP_of_firewall in this case is dynamic (using dyndns to get connections to the right IP. Sow how do I do this with a dynamic IP? Or let's break this down further. How do I force connections that come in via eth0 to be answered via eth0, and similarly connections coming in via eth1 to be answered via eth1, regardless of gateway? Could I setup two gateways, one for each interface, and force them not to mix connections? Thanks -- Kind Regards Hans du Plooy SagacIT (Pty) Ltd hansdp at sagacit dot com