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Re: peer neighbor route., posted 11/10/2003
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When redistribution into OSPF is taking place on one of the routers on one
end of the link and the ip subnet of the link is included under the ospf
process, using this command stop the isdn link from flapping.

I don't remember all the details but the way I understand it is that without
this command, when the isdn link comes up (from interesting traffic for
example), ospf will install a new /32 route in the route table.  When the
link goes down, ospf removes the route, But when the /32 route is removed
that means there's been a topology change.  OSPF, being a routing protocol,
must, of course, notify all it's neighbors of the topology change and send
out a new LSA to do this.  And, this new LSA has to, of course, reach the
other side of the isdn link so ospf brings up the link.  Once the link is up
that /32 route is again installed in the route table only to go away again
after the link goes back down.  And, so the cycle repeats.

To stop this cycle, the no peer neighbor command prevents the /32 route from
being installed in the route table in the first place.

I forget the roll that redistribution plays in this scenario, but I know
that this is explained very well in the book, Troubleshooting IP Routing
Protocols in the section on flapping isdn links (or using the ip ospf demand
circuit command).

----- Original Message ----- 
From: "Casey, Paul (6822)" <Paul.Casey@xxxxxx>
To: <ccielab@xxxxxxxxxxxxxx>
Sent: Monday, November 10, 2003 2:39 PM
Subject: peer neighbor route.,

> Hello,
> I am been looking this peer neighbor route command used under PPP.
> Can someone explain to me what this command is actually for,
> Yes, I have read that you can remove  the /32 host routes it installs from
> the far side of the link,
> used for ISDN typing the no form of the command.
> but what is the purpose of this command when its turned on.
> ex: Why would I want to use this command in the first place - or more to
> point what can I not do without it,..? What do I need /32 host routes for.
> Anyone got an example.
> Cisco website is vague of this stuff. or maybe its just the links I can
> are vague.
> Any help appreciated.
> Kind regards.
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