How to test ISDN Backup periodically - HELP

[gross.bauer]

Hello,

has anybody an idea how to test a ISDN backup connection on a cisco router?

There is a cisco router at a remote site connected to the main office via leased line over a serial interface. For backup the router uses a ISDN bri interface with a dialer profile in the case that the leased line is down.

During normal operating I want to test the ISDN backup connection whether it is functioning or not.

Who knows how to do this via a perl script or something else?

thx in advance

[tepatel]

We need to take a look on "how is the backup configured?"..using floating static route, using dialer-watch or using backup command..

Pl. post the running config here..

If you are using the "dialer-watch" then its very easy to test the connection, Just block the watched route on the advertised router..

[gross.bauer]

The backup is confiured via dialer interface and we are using dialer watch also. The routing protocol is OSPF.

But the problem is, that we want to test the ISDN connection periodically and automatically via a script or something else without bringing down the leased line. We often have had the problem that the ISDN backup is not functioning because the telephone provider had problems with the telephone line. But we notice this only in the case of a backup and then it is to late.

[mljohnson]

You could write a script that

- telnets to the remote via the leased line

- pings an address/subnet that is directly connected to the profile

- confirm that the DDR link comes up

- tear the link down manually

- disconnect

If you are using the "backup interface" command for backup, you would have to remove this command. What might be better is to use Dialer Watch or floating static routes for your backup solution, rather than the "backup interface" command.

[gross.bauer]

We know how to test it, but we want to do it periodically and automatically without bringing down the leased line. Because we often have had the problem that the ISDN backup is not functioning because the telephone provider had problems with the telephone line. But we notice this only in the case of a backup and then it is to late.

The backup is confiured via dialer interface and we are using dialer watch also. The routing protocol is OSPF.

For which parameter or value would you ask with the script?

interface status?

ping reponses?

Later we want to evaluate it automatically.

The problem with bringing up the backup interface in normal operation (leased line is up) is, that ospf learns a new route and recalculates the ospf database, and during this time you can not reach the router and sessions will be terminated (also the session of the remote site).

[mljohnson]

I would test on ping response; the interface may come up (even momentarily) even if there is still connectivity issues (you really want to test the ISDN, PPP and IP layers).

If the leased line has preference over the ISDN line, this may help in reducing OSPF churning.

[gross.bauer]

hello, first if all thx for your reply.

I don't have to test all the layers, my lastest idea is to test only the signalling on the d-channel. When a router (may be a new router) at the main office calls the remote router without any authentication method the call will be rejected, in this case the router at the main office will get some status messages. Because the remote router responses with a call rejected, I know that the isdn connection is functioning. i think, I don't have to test the b-channels. Because when the signalling is functioning the isdn connection is ok.

what do you think about this idea?