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Using ISDN from both ends of leased Line


Is it possible to configure ISDN as a backup form both ends of a leased line.

For Example Router A , to router B a leased line is established and is working ok. Router A has a ISDN-PRI connection and Router B has BRI connection. Normally when link goes down Router B waits for a "delay" and then triggers ISDN as a backup to leasedline and gets connected to Router A. ( backup delay 10 10 , and backup interface bri 0/0). Now if router B fails to start a ISDN connection to router A , can I make Rouer A to start a connection to Router B. after certain delay of say 15/20 seconds. Only thing both shoud not try to trigger ISDN connection simultaneously.

Any link on

Thanx in advance


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Re: Using ISDN from both ends of leased Line


In general it does not work well to configure backup on both ends of the leased line. One of the issues is that backup-interface puts the backup interface in a special state where it will not initiate a call and will not answer a call. So if you configure router B with a 10 second delay and configure router A with 15 second delay then when router B delay expires and it attempts to call router A will still be in the state where it will not answer calls.

You might get around this restriction by configuring dialer profiles and pointing the backup interface to the dialer interface rather than to the BRI. But if you do that you will get a call from B to A at 10 seconds and then get a call from A to B at 15 seconds. I am not aware of anything that will have A call B only if B has not called A.

In general I believe it is best practice to configure backup interface on only one end of the connection. You might also consider some alternative methods of establishing backup capabilities such as floating static routes or dialer watch.



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