DUAL ISP Config for Cisco 2500

[vlpresher]

My neighbor is installing a wireless connection to backup his leased line T1 circuit. The radio link will be connected to a SOHO6 firewall in the OPT port for the dual ISP connection. Is there any special config for the router to be able to route to the wireless link when the leased line is down?

[kmarrero]

The easiest way is to set up two different default gateways and put a higher metric of "200" on the one that is going to the wireless ISP. This way the gateway to the leased line will always have a lower metric and will be used. Once the leased line is no longer available, then the other gateway will be used.

EXAMPLE:

ip route 0.0.0.0 0.0.0.0 x.x.x.x (x.x.x.x. is the next hop of the leased line connection)

ip route 0.0.0.0 0.0.0.0 y.y.y.y 200 (y.y.y.y is the next hop of the wireless connection)

[vcjones]

Keep in mind if you choose to use this approach (which assumes that the leased line T1 will go down at the link layer whenever it fails, a good assumption for a point-to-point T1, not a good assumption with a frame relay or ATM T1), that incoming traffic such as to a web server your friend is hosting, will not get redirected through the alternate route, and any transactions or transfers in progress will fail because your outside IP address will change when you switch links. Ditto when the T1 returns to life and your traffic switches back to the T1.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com