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Community Member

Wireless links backed up with ISDN

Any help would be appreciated. We are trying to link two buildings using wireless. This is not a problem. However we also need some form of backup. The idea is to use ISDN as a backup. The scenario would be that the wireless was plugged into one ethernet port of a router and the local LAN into the other, with an ISDN module inserted in the router. The problem arises if the link goes down, but the ethernet the Accesspoint is connected too, remains up. The router would then not dial the remote site. Is there any way to configure a router so that when the wireless link goes down the router would see the route go down and dial using the ISDN.

Community Member

Re: Wireless links backed up with ISDN

Get a copy of the excellent book "High Availability Networking with Cisco".

While it doesn't deal with wireless specifically, it does spend a lot of time talking about backing up Frame Relay with ISDN, which has a similar issue of the basic link being up even if there's no traffic being passed. The book has great example configs and explains each step of the process.

Cisco Employee

Re: Wireless links backed up with ISDN

Easiest way as the ethernet will not go down even if the radio link fails is to running a routing protocol like ospf and use dialer watch to activate the isdn when needed

Normally I configure a loop back on the router at either end then the end that dials up the back up link set it to watch the route of the loopback interface on the remote end when it can no longer see this route in the routing table it will dial up

Here is a link on how to do dialer watch


Here is a good link that discusses the various backup methods

Community Member

Re: Wireless links backed up with ISDN


I will try this out, It seems good in theory.

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