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Dial backup for multiple PVCs

I have a Cisco 2620 router with 26 PVCs connected to a frame cloud. I need to configure the edge routers to dial over the AUX port to the 2620 when their link goes down. I'm using OSPF as a routing protocol, all serial connections have their own IP addresses, the 2620 is the only router with a loopback address. The edge routers are 1720's with a WIC-1ENET card, so they have two connected subnets. When the dialer fires up, I need to limit connectivity through the AUX port to one subnet, and just a few hosts at that.

Again, the edge will initiate the dial, and it needs to provide route information to the 2620. I don't care if the 1720 advertizes both subnets, because I can limit egress traffic to a single subnet through an access list.

Should I pre-address the dialer interface, set it as unnumbered to FastEthernet0 or create a loopback for it?

Any good configurations or suggestions out there?

Thanks in advance!


Re: Dial backup for multiple PVCs

Often times complex configuration issues are best addressed in an interactive session with one of our trained technical assistance engineers. While other forum users may be able to help, it’s often difficult to do so for this type of issue.

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If anyone else in the forum has some advice, please reply to this thread.

Thank you for posting.


Re: Dial backup for multiple PVCs

Dial backup using the AUX port can work well, although the performance is limited by the modem link (and on older routers, by the maximum data rate of the aux port. Recovery is also a bit time consuming, as it typically takes 30-60 seconds for the modems to dial, negotiate, and train before communications can begin.

There are sample configurations here on CCO and a white paper on the topic on my web site ( explaining a sample configuration of 2500 dialing a 4700, AUX to AUX. There are also some examples in my book High Availability Networking with Cisco, but again using different router models, so you will have to adjust the syntax.

Bottom line... been there, done that. It works well as long as you set proper expectations. Good luck and have fun!

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