Hub and Spoke network with ISDN backup

[Geddy99]

Hello...

I've got a hub and spoke network with a Cisco 3700 series router at the hub. This 3700 has a 4-ISDN BRI interface card in it.

This network has 30 remote spoke, or stub, networks attaching back to the hub via point-to-point T1 lines. All of these remote sites also have ISDN lines for backup.

If one of the T1's should go down, we'd like the ISDN at that site to dial up and connect into the 3700 at the hub site.

Now, the 3700 has 4 ISDN lines - each one going into 1 of the ISDN BRI interfaces. So, how can I make it so that when a remote site goes down, that site can dial and hit any of the 4 ISDN BRI's on the 3700?

In other words, remote site A goes down, dials into the 3700, and grabs a connection on ISDN BRI 1. Then, remote B goes down and it tries to grab a connection on ISDN BRI 1, but that's busy so it will automatically roll to ISDN BRI 2.

Would I need to specify a dialer interface for each remote site that I have and do this for each of the four ISDN BRI interfaces on the 3700, or is there an easier way?

Thanks...

 

[Twinmoon]

I think you can have one dialer profile for each remote site. The profile will have 4 dialer strings(the phone # it will call...) And your BRI will need to be members of this profile. Also, your HUB will need to be configured with an appropriate profile so it can receive calls from all of the remote sites. Alternately, your hub will need many profiles and your BRI interfaces will need to be members of all of them. You will also need floating static routes on all of your remote sites. You might also need to define interesting traffic.

From your t1 connections, enter the command
(config-if)#backup interface [interface]
(config-if)#backup delay # #
—The first number is how many seconds to wait after the maiin interface(T1) went down before bringing up the backup. The second # is how many seconds to wait before tearing the backup down.---

I’ve probably missed a few things but this should set you in the right direction.