Thank you for posting the configuration file. I have looked at it and see that in this configuration file all the BRI interfaces are shut down. Obviously in a shutdown state the BRI will not work.
While your original post seems to describe configuring backup interface to use the ISDN I do not find any backup interface configured in this configuration file. Can you clarify the situation?
One note that may help: if you do configure backup interface and point it at the BRI then it puts the BRI into a special state and in that state the BRI can not make a call and can not answer a call unless the primary interface is in a protocol down state and is not shut down (it requires a real failure of the interface).
Thank you for posting the additional information. I find that the BRI interface file which shows the configuration steps and the steps to test are especially helpful.
As I pointed out in my earlier post when you configure backup-interface pointing to the BRI interface it puts it into the special state of standby. This is exactly what your output shows. As I also pointed out when the BRI is in standby doing a shutdown of the primary interface will not activate the backup. When you issue the shutdown command the IOS assumes that you want the interface down and will not activate the backup. To activate the backup you need to produce a failure of the primary interface. You can unplug the interface, configure the interface to change the encapsulation of one end, configure the other end with no keepalive, or anything that will produce a failure of the interface on your router and the BRI should activate. But shutdown will not activate and this is the normal behavior of IOS.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...