From: Guy Farber (gfarber@xxxxxxxxx)
Date: Sat Jun 02 2001 - 12:57:27 GMT-3
Hi Bob,
When you use isdn to backup a serial line running ospf, obviously want the
isdn up when the serial is down. Ospf has to refresh LSAs every 30 minutes
or they age out (by default) of the database. What demand-circuit does for
you is automatically sets them no to age. It brings up the isdn circuit only
when it has an LSA change.
What I don't understand is why use backup interface here...
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Bob Chahal
Sent: Sat, June 02, 2001 4:50 PM
To: ccielab@groupstudy.com
Subject: ISDN/OSPF Demand Circuit
I just want to get this clear.
If you configure an ospf isdn demand circuit as a backup to a serial
interface, the LSA do not age so that's not problem. But why configure ISDN
as a demand circuit? Why not just configure it as part of the OSPF domain
and when the interface goes down the circuit will just come and form an
adjacency with the other end and synchronise it's ospf database etc etc.
Some practice lab solutions configure the ISDN with ip ospf network
demand-circuit and then configure backup int bri0 under the serial
interface. All interfaces on the isdn routers are configured as part of the
ospf domain but I think this works fine without the demand-circuit config.
Interesting traffic permits all ip and the only other thing is that only one
end of the isdn circuit actually initiates the call.
I think I'll lab all this out again but I'd be interested to hear what
people might think.
Thanks
Bob
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