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ISDN BRI dialbackup problems on 2516

I have a small shop here and use a 2516 to connect to an upstream Internet provider via a T1 and have an ISDN BRI dialbackup line using a Motorola NT1D. I know all are old units, but they work well, mostly.

A 2516 has two high speed serial ports and an ISDN BRI S/T port.

The problem is that from time to time, the dial backup doesn't work. From the logs, nothing seems out of place when I drop the T1 to test the dial backup. The BRI0 and it's :1 & :2 flip states, the layer 2 flips states, the Virtual-Access1 flips states and I see I am connected to the dedicated GW at my upstream ISP. All looks normal.

But once in a while, it doesn't pass traffic. It appears to be up and functioning with no unusual messages, but after 25-30 seconds, the dialups drop and re-connect, still with no traffic being passed. Pings from the ethernet and from the console fail.

This condition is 'fixed' by power cycling the NT1. Then the dial up connection will pass traffic like it should.

Is this a common problem? Or do I have an old NT1 that is just acting up or not able to correct itself?

I have two identical routers and both have done it at one time or another. Otherwise I am happy with these units and am not in a hurry to replace them.


Lyle Giese

LCR Computer Services, Inc.

New Member

Re: ISDN BRI dialbackup problems on 2516

Are you meeting the timeout on your ISDN call ? Are you meeting your ISP's timeout ?

By power cycling the NT1, your router is making a new call, going through the authentication phase and re-establishing IP.

If it happens again, try to clear your ISDN interface. If the call comes up, it will prove your NT1 hasn't locked up.

Do some debugging to see if the call gracefully disconnects or see if you get a "clear cause" which can explain any issues with your carrier


New Member

Re: ISDN BRI dialbackup problems on 2516

Timeouts?? Not sure what you mean here.

I have static IP's on all interfaces on my router. I have a class C net assigned by my ISP and they have a backup route in their routers to push my traffic to the ISDN when the T1 is down.

I will do more checking and some debugging when it locks up again.

I am also hoping for some other to let me know if this is a common problem or I have another unusual problem.



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