backup interface issues

[ken.vance]

Hi, we are using IOS 12.1(15) on 1700 series routers which use the backup interface command to back up serial links. All works ok, except the isdn calls do not drop when the serial link comes back into service. Can anyone point me in the right direction? We have numerous devices on differnet networks exhibiting this same behaviour.

[Richard Burts]

Ken

With the backup interface functionality it puts the ISDN into a special state where it will not make nor answer calls. In my experience the ISDN usually goes back into that special state when the primary interface becomes available again. Are you using the backup delay command - it might impact returning the ISDN to normal state. Or are you using the backup load command - it might also have an impact.

In fact it would be easier for us to see what the issue might be if you would post the configuration for a serial interface using backup and for the ISDN which is backing up the serial interface.

HTH

Rick

[ken.vance]

Hi, our standard serial i/f config:

interface Serial0

bandwidth 64

backup delay 5 60

backup interface BRI0

ip address xxx.xxx.xxx.xxx yyy.yyy.yyy.yyy

down-when-looped

Pretty basic....when I say the ISDN stays up, if the fault goes undiscovered, it can be for days at a time. We are thinking along the lines of some type of IOS bug, as all the routers are identical, running same IOS version, but in totally seperate, different networks. The only other items in common is they all use eigrp.

[ken.vance]

Just in case it helps, the IOS version string is as follows:

IOS (tm) C1700 Software (C1700-Y-M), Version 12.1(18), RELEASE SOFTWARE (fc1) on all but one, the odd one out being :

IOS (tm) C1700 Software (C1700-Y-M), Version 12.1(15), RELEASE SOFTWARE (fc1) on all but one, the odd

[Richard Burts]

Ken

Thanks for posting the additional information. I agree that the serial interface config is pretty basic and I do not see anything that looks problematic. I notice that you are using the backup delay command. While it should work I think it would be worth removing the backup delay command on one of the routers and testing to see if the behavior changes.

Would you post the config of the ISDN from one of these routers. I do not expect to find much but would like to eliminate any possibility of problem there.

I gather from the original post that this same behavior is observed on most of the routers. Are there any of the routers that do right and terminate the ISDN when the serial comes back into service? Has this always been the case or did it work correctly at some point in time and then change?

HTH

Rick