Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

second backup doesn't come up

I have a 3640 router with a serial link and two backups. The first backup is ISDN and the second backup is PSTN. I have defined the static routes with administrative distance "200" for isdn and "250" for the PSTN backup. When the serial line goes down the interesting traffic brings the ISDN link "up" and everything works fine. But when there is a problem with the ISDN link (show isdn status--->layer 1 "down") the router attempts the ISDN link, of course it doesn't come up and the router never tries the PSTN backup. The PSTN backup works only when I "shut" the BRI interface. What shall I configure in order to make router attempt automatically the PSTN backup when the ISDN link is not available.



Re: second backup doesn't come up

We cannot backup a DDR interface since it remains up/up(spoofing), basically your setup requires that the BRI backs up the serial & the async backs up the BRI. When your ISDN layer1 is DEACTIVATED you still see the BRI interface in UP & UP(Spoofing) state....thus the router keeps calling out on that interface.

A "shut" will make it admin down/ down so IOS will go to the next best way.

Thanks, Mak.


Re: second backup doesn't come up

As you have discovered, you cannot use dial on demand to back up a dial on demand link. However, you can use dialer watch or BGP to do the job. See the white paper "Using BGP to Trigger Multiple Levels of Dial Backup on Cisco Routers" on my web site. The changes required to take the same approach with dialer watch (which was not available when I originally wrote the paper) are left as an exercise for the student. There are more details in Chapter 5 of my book "High Availability Networking with Cisco."

Good luck and have fun!

Vincent C Jones

New Member

Re: second backup doesn't come up


I have a same trouble but I donnt know why.

I use ISDN link as backup line for leased line using Dialer-watch beetwen 2 sites. When I do shutting down serial then ISDN came up but I still see interface is up/line protocol is up (spoofing). I can not ping to remote site (ISDN's remote IP address) and other network. Otherwise, my OSPF still update well, I can see full routing table but can not ping to any network .

Note: Full permit by access-list for interesting traffic is applied

Does any one know that ?


Re: second backup doesn't come up

Your ISDN comes up, the OSPF updates area OK, and you get a full routing table. So it could be that your ping is getting through, but the response isn't. Are you sure the routes at the remote site are updating to use the ISDN? Can you ping the IP address of the remote router's ISDN?

Kevin Dorrell


CreatePlease login to create content