Spanning Multiple DSLs

Noticing that I wasn’t the only person wanting to take advantage of multiple IP gateways on my system, I thought I’d post our findings. This is the result of many headaches on the part of myself and my colleague Mr. Mirotchnick.

Our equipment–and this Answer–are arranged thusly:
– 2 Cisco DSL modems each connected to separate ISPs, First_ISP and Second_ISP
– A Cisco 24-port unmanaged switch, though any switch or no switch at all will do.
– A RHEL9 linux box (kernel 2.6.5-1.358) but any Linux above kernel 2.6 should be OK.

There is no reason you need the switch in your setup though, since you can just as easily have PCI DSL modems in your gateway or have external modems connect directly to your NICs; our office setup, however, requires it for reasons not relevant here.

If you have directly-connected modems you will need to adjust the numbers here to reflect that, since a directly-connected DSL modem won’t have a LAN IP address–you would have to replace and by their WAN equivalents. To keep the Tylenol bill down, you would also need static IP addressing from your ISP



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