From: HP-France,ex2 ("SANCHEZ-MONGE,ANTONIO)
Date: Thu Mar 25 2004 - 16:28:37 GMT-3
Hi Packet Man,
The metric of the path is the cost addition, so it does not only depend on
the local cost (unless both main and backup link go to the same device).
If the metrics are the same, both paths will be installed in the routing
table.
Load balancing will be then the responsibility of the switching engine, and
vary depending on whether you use CEF (and how you configure it), fast
switching, MLS, process switching...
Cheers,
Ato.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Packet Man
Sent: jueves, 25 de marzo de 2004 18:19
To: jphillips@ufcwdrugtrust.org; ccielab@groupstudy.com
Subject: RE: OSPF Demand circuit and Backup & Load Balancing
Hi all,
Just another twist on this topic.
Assume that the primary link is up and the ISDN link is configured as OSPF
demand-circuit and that both have the same cost.
In this instance, would ospf load balance over the 2 links? Why yes or no?
>From: "Joseph D. Phillips" <jphillips@ufcwdrugtrust.org>
>Reply-To: "Joseph D. Phillips" <jphillips@ufcwdrugtrust.org>
>To: "Group Study (E-mail)" <ccielab@groupstudy.com>
>Subject: OSPF Demand circuit and Backup
>Date: Thu, 25 Mar 2004 08:26:56 -0800
>
>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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