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Re: Help! posted 09/14/2001
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It is very likely that what is causing this behavior is the subnet of 
the ISDN being advertised/redistributed from IGRP back into OSPF.  In 
particular when the ppp session is setup, a /32 route for the IP of the 
other end of the connection is put into the route table.  When the 
connection is broken the /32 route is withdrawn.  IGRP sees a route 
update and redistributes into OSPF.  OSPF generates an external LSA and 
needs to bring up the ISDN circuit so the LSA can be transmitted and the 
database kept in sync.

There are two good ways to resolve this issue.  You can filter the 
redistribution to prevent the subnet of the ISDN from being redistributed 
(probably the more common of the solutions) or you can configure the ISDN 
interface so ppp does not insert the /32 route.

There have been quite a few threads on this subject and a search of the 
archives might be helpful in finding more details.


Rick  Burts, CCSI   CCIE 4615        burts@xxxxxxxxxxxxxx
Mentor Technologies                  240-568-6500  ext  6652
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On Fri, 14 Sep 2001, Fear, Russell H wrote:

> Can anyone in the group help me with thhe following problem.
> I have an ospf router which is redistributing igrp into area 0. It also has
> an isdn back-up as a demand circuit so that if the main connection to area 0
> dies, the isn kicks in and routes are still available. The problem is that
> the LSAs caused by the re-distribution bring up the link continually. If I
> block these, I block routing updates. I cant make the area a stub or an nssa
> because it is area 0 and has two other areas hanging off it.
> Am I missing something obvious ? It's been driving me mad. Help please .
> Russell
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