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New Member

Unstable Isdn-backup


One of our customers have a 2610 with two briinterfaces in use for isdn-backup, and a dialer interface. I have two problems: first the bri calls up the backup router at the isp (thats us) all the time, without the leased line beeing down. Second: On of the bri only connects one channel.

The second problem I can live with, but the first I need help to sort out, It gives the customer a high telephone bill:) Kristine

New Member

Re: Unstable Isdn-backup

Hi Kristine,

Is their a Dynamic routing protocol running on the routers? If so, it may be a misconfiguration. Under the routing protocol process, the dialer interface for the BRI port has to be designated as "passive interface".

e.g EIGRP will bring up the BRI every 60 secs because of hello packets on multipoint circuits, with BW less than or equal to T1. i.e BRI, FR

For the channels, under the BRI port, use "dialer load-threshold" command to specify a load at which the second BRI channel is activated.



New Member

Re: Unstable Isdn-backup

Thanks for answering. If I put passive interface under the dialer interface, wouldn't that result in non-functioning routing if the leased line goes down, how will the customers net be annonced in eigrp?

And, the treshold already have value 1 because I wanted to be sure that wasn't the problem. Kristine

New Member

Re: Unstable Isdn-backup

If you are running a dynamic routing protocol you need to apply the passive interface command under the routing PROCESS not the interface. You then apply a floating static route with a higher admin distance than the protocols default value. The network shoud be advertised by entering it under the routing process

In this case Internal EIGRP default distance is 90 therefore configure a floating static route with a value of say 120

Here are a couple of links to try:

Don't forget the ppp multilink command for the BRI !! Forgot to mention that before.


New Member

Re: Unstable Isdn-backup

Thanks a lot, I'll read them, and hopefully solve the problem. Kristine

New Member

Re: Unstable Isdn-backup


As an alternative, you can deny the Eigrp broadcast traffic in the dialer list(interseting traffic which triggers a call on the BRI) and permit all the other ip traffic.

hope that helps,


New Member

Re: Unstable Isdn-backup

Run a "debug dialer" to find out what is keeping it up and block that. If possible add the "backup interface" command under your wan, if it is a point-to-point type interface.