ISDN Backup on Static Routes.

[ron-tan]

Hi all,

Is there a way to backup frame relay links via ISDN with purely static routes configured and no dynamic routing protocol present ?

The link to be backed up and the ISDN connection is in 2 separate boxes so backup interfaces is out of the question. Understand that ISDN backup can only work if there are dynamic routing protocol configured, so what are my options ?

Thanks.

[Erick Bergquist]

Hi,

You could run HSRP between both routers. Have the router with the frame relay connection as primary router. The ISDN router as standby. Use the HSRP interface tracking feature to track the frame interface and when it goes down adjust the priorities so the standby/ISDN router has a higher priority when frame interface is down.

Users default gateways would be set to the HSRP address.

On the frame relay interface, you can also configure Frame Relay End-To-End keepalives (FREEK) which will bring the frame interface down when the end-to-end keepalives aren't received. This will make the HSRP failover to the ISDN router more reliable. Without FREEK, your frame relay interface could still be up but the remote end may not be reachable. In that case, the primary router would still be active for HSRP.

Erick

[svermill]

I think the first suggestion was a much better than the one I am about to make, but if HSRP isn't an option for whatever reason, this MAY work. You could build a floating static route out of your FR box pointing towards your ISDN box. Set the ISDN box up for Dial on Demand Routing. In this way, the ISDN box will only get traffic if the preferred route out the FR box isn't available. The reason I say MAY work is because I don't know if your topology will allow you to completely isolate your ISDN box in this way. Just a thought.

[ron-tan]

Thanks guys for the tips. The problem with the entire setup is that the FR is connected to my carrier's router which we are not allowed to touch and in turn connected via serial back to back to our router which has the ISDN module. Both routers are defined via static and I can't be tracking the serial link on the ISDN router as that will only be backing up the back-to-back link. I can't do either float or dialer watch as there are static route are in placed.

I've ran out of ideas and am presently exploring tunneling with dynamic instead.

Any ideas still ?

[jailbird]

Nothing easier. Simply set up a static route to the same destination via the external device with a hop count of 15.

When your normal route is unavailable it will automatically have a hop count of 16 and your ISDN link will become usable.