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New Member

876 Configuring dial backup

We are trying to configure a Cisco 876 router to dial out via the ISDN S/T port as the primary interface. If the primary interface is disconnected for whatever reason we would like the analogue/modem connection to automatic kick in as backup through the AUX interface. Currently both the the ISDN and modem connections dial at the same time which we don't want.

I have attached a tech-support file which contains our configuration and IOS version. Is it possible to configure this router to use the ISDN to be the main connection and the analogue service to only kick in when the ISDN goes down? Appreciate any assistance.


Re: 876 Configuring dial backup

Setup an Async interface for the aux port and make sure to configure the flaoting static route for this interface. For configuring AUX port

New Member

Re: 876 Configuring dial backup

Thanks for your reply. But I cannot see how backup been activiated on the BRI interface so that that the AUX interfce kick in when BRI link fails.


Re: 876 Configuring dial backup

Normally it is done with route Administrative Distance and timeout.

There are two routes to the same destination, one with low AD (e.g. 110), which is preferred, and one with high AD, manually set to e.g. 250.

When route with the lower AD goes down, traffic starts to route over route with AD250, next hop of which is backup interface. When primary link comes back up, traffic is routed over the new link, and connection on backup link times out, since there are no packets flowing.

Hope this helps.