ISDN backup as a fail over for a T1 connection

[cschuette]

I have two remote locations, one with a 3600 router and one with a 2600 router, that I am in the process of connecting together via a full T1. I would like to use the existing ISDN connection as the fail over backup if the T1 ever went down. Could someone help me to figure out how I would go about setting this up. In the end, I need the ISDN connection to be in an idle standby status until the router detects the T1 connection has gone down, then initiate the call to the other location and keep the connection up until the T1 becomes live again. Also, is it possible to group 6 ISDN channels into 1 link to be used for this backup link. Any help would be greatly appreciated.

[rlcarr]

Here is a link that should help you with some configuration examples,

http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Internetworking:ISDN&s=Implementation_and_Configuration

You have some options on the backup,

Standby mode = you define "interesting traffic" so if the T1 fails the ISDN only comes up with specific traffic. This keeps your ISDN charges low, especially if it isn't a 24x7 shop. Although, if your T1 is flapping, it will cause the ISDN to flap also due to false positives that the primary link is restored.

Route Watch = you define a specific route to watch for. so if the route disappears from the route table it will automatically dial up. This solves the flapping issue, however, your ISDN is dialed up regardless of if you have user traffic on the line. ( you could also apply Time Based Access-lists to limit the connection times).

To bundle the ISDN channels together you just need to use a virtual dialer interface and enable PPP multilink.

Happy Routing,

~rlc

CCNP, CCDA, CNE