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Redundant Backup Link Using ISDN -Configuration Help

I got two Branch Offices(B & C) conencted to our Central Office (A) using dedicated lease line. These two branch offices connect to our Central Office for a database application hosted at our Central Office.

Here is the cUrrent IP addressing setup for all the links:

Site A


Ethernet -

Serial(links to site B) -

Serial(links to site C) -

Site B


Ethernet -

Serial(link to site A) -

Site C


Ethernet -

Serial (Link to site A) -

Since these two sites operate 24 hours and are quite critical sites, I want to setup a redundant link so that site B dial to site C using ISDN if the link from site B to site A is down or vice versa.

Im new to ISDN and am just requesting if someone could help me with the configuration of all the routers at the above three sites using the above IP address. We are using HDLC for the serial links protocol.

Hope someone helps

Cisco Employee

Re: Redundant Backup Link Using ISDN -Configuration Help

There are many ways to design a backup using isdn line. You just need to choose a method which suits bests to your network. Here is the link which will help you decide that

All 3 methods for backup has adv. and disadv. That link also has sample configs for each with troubleshooting information too. Good Luck

Community Member

Re: Redundant Backup Link Using ISDN -Configuration Help

Thanks. This will give me a start

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