ISDN with multiple connection to HSRP routers

Unanswered Question
Oct 21st, 2009


I got a question related to ISDN connecting three routers.

My topology is the following:






R1 and R2 are on HSRP (R1 is master) so that the Ethernet work as only one. Since ISDN interface cannot be used for HSRP I will have the ISDN interfaces as "independent" interfaces where the information will be routed according to the routing table.

When there is traffic from R1 or R2 to R3 should not be a problem to bring up the line. The problem is that in most of the cases it will be R3 who is dialling.

So, my question is, how can I configure R3 to decide where to dial depending on the HSRP active router? Is it possible?

If not, my idea was to call (via dialer map) R1, and if it does not answer, call R2. How can I do that? I've looked in the documentation available but I have not been able to find any helpful information…

Thank you!



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Paolo Bevilacqua Wed, 10/21/2009 - 06:41

You cannot decide where to dial based on HSRP.

Seems to me you should use a different design based on routing, not HSRP.

fvalpondi Wed, 10/21/2009 - 06:49

Thanks for your answer.

You have confirmed what I had thought. Now my other question.

Just discard now HSRP and suppose only R1,R2 and R3.

If R3 tries to dial to R1, and R1 does not answer because it's down, how can I make R3 to dial to R2?

If had thought two different dialer maps with two different numbers (one for each router). But it does not work for different IP addresses....or that is what I understood...

thanks again!

Paolo Bevilacqua Wed, 10/21/2009 - 07:11

Just use multiple dialer strings in dialer interface.

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fvalpondi Wed, 10/21/2009 - 23:00


thanks for the info.

I've looked for information, but I did not find how I have to configure a dialer interface to dial to a second number if the first number does not answer.... :-(

Is there any special command?



fvalpondi Thu, 10/22/2009 - 22:47

Thank you all! I will try it today and I'll inform you about the results :-)


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