From: Joseph D. Phillips (jphillips@ufcwdrugtrust.org)
Date: Thu Mar 25 2004 - 13:26:56 GMT-3
Seeing's believing. Try just using demand-circuit and see if you can ping everything you want.
Can I get a witness from some of the big brainiac CCIE's here, please? :)
Scott? Brian1? Brian2?
-----Original Message-----
From: Chris Fontes [mailto:cfontes@atrion.net]
Sent: Thursday, March 25, 2004 08:20
To: Joseph D. Phillips; Group Study (E-mail)
Subject: RE: OSPF Demand circuit and Backup
Hi all
Not sure I agree with your whole explanation Joseph.
OSPF demand circuit does keep the link from flapping, but once there is a
topology change the link will come up, ospf will converge and routing will
take place over the link. It will provide reachability.
With dialer watch you only need a dialer map statement for the specific
network(s) that are being watched with the dialer watch-list not for each
network that would be lost if the primary connection goes down (ie if your
learning 6 routes over your primary link, you could just watch one of them
with dialer watch). If the network drops from the routing table, dialer
watch will bring the ISDN link up, ospf will converge and routing will take
place over the link.
Each method would provide the same results.
Packet Man I can't think of any reason why you would cofigure both at the
same time. Its two different methods that provide the same results.
Chris
-----Original Message-----
From: Joseph D. Phillips [mailto:jphillips@ufcwdrugtrust.org]
Sent: Thursday, March 25, 2004 10:44 AM
To: Group Study (E-mail)
Subject: OSPF Demand circuit and Backup
Dialer watch and OSPF demand-circuit accomplish two different purposes.
OSPF demand only keeps the BRI link from flapping after the BRI's IP network
is defined under the OSPF router process.
By itself, it does not provide any reachability to any networks.
If you want a true backup of a frame-relay network, you'd need dialer-watch,
and you'd have to create a dialer map statement for each network which would
be lost if the primary connection goes down.
-----Original Message-----
From: Packet Man [mailto:ccie2b@hotmail.com]
Sent: Thursday, March 25, 2004 07:12
To: ccielab@groupstudy.com
Subject: OSPF Demand circuit and Backup
Hi all,
When an ISDN circuit is configured as an OSPF demand-circuit to backup
another OSPF link in the same area, should and can any other backup method
such as Dialer Watch also be configured on the same ISDN link?
My sense is that there's no need to configure any other backup method and
doing so would only complicate things and lead to unexpected results.
Here's what I believes happens in such a situation (without 2nd method
configured).
Primary link goes down.
This causes ospf to see a topology change has occurred.
OSPF floods lsa over all links including ISDN circuit which brings up ISDN
circuit.
OSPF updates the route table to reflect new topology.
Now, user traffic that would have used the primary link now uses the ISDN
link.
Is this simplified chain of events correct? Are there other significant
things that occur that we should be aware of?
Thanks in advance, pm
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