Cisco 1721 SDSL primary with ISDN backup


I have a client with a SDSL primary line and they are looking at some sort of redundancy in the case of SDSL failure.  We've tried convincing them to go with a adsl backup but they're set on the isdn backup option.

They have a old cisco 1721 router that used to be used for an ISDN connection and want us to setup the Cisco 1721 with an sdsl wic as primary and have the isdn connection as a backup.  And as the isdn will just be a pay per use service it would need to only dial if necessary.

So, I'm just wondering what would be my best option to trigger the isdn to dial if the sdsl interface goes down.  I've used PBR before with failover E1 connections.  Would that be an option here or is there a more simple option?

This question is pretty easy but is extremely urgent as they're hoping to put something in place this weekend so I'm going to go with 500 big ones!

Thanks in advance.

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PBR is the best option.
This is best for connectivity.
Other options you can loose connectivity even though the interface is still up,
then the backup interface will not dial.

i_campbellAuthor Commented:
Thanks for that.  Can you have a prb config that will only dial the isdn line if necessary?  We need to avoid the pay as you go call charges so only want the isdn line to dial in a failover scenario.


backup delay 30 10
This will dial the link after 30 sec of inactivity on the primary
and return to the primary after it has been up for 10 sec


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