From: William Chen (kwchen@netvigator.com)
Date: Thu Mar 25 2004 - 13:57:15 GMT-3
Hi PM,
What I think about the disadvantage of OSPF DM is that, it will blindly
bring up the ISDN. There maybe some links (that will not be backup by the
ISDN) go down, and it will also cause the ISDN to dial. However, by using
dialer watch, you can always decide what is the true case you want to use
the ISDN.
Moreover, I don't think there is an incompatible of these two features,
so I think they can be used together without any problems.
1. Dialer Watch will be used to trigger the call. (You can deny the OSPF
from interesting packets, if you don't want the changes in OSPF database to
trigger the call).
2. OSPF DM will be used to prevent the ISDN from stand up always.
Best Regards,
William Chen
----- Original Message -----
From: "Packet Man" <ccie2b@hotmail.com>
To: <jphillips@ufcwdrugtrust.org>; <ccielab@groupstudy.com>
Sent: Friday, March 26, 2004 12:01 AM
Subject: RE: OSPF Demand circuit and Backup
> Hey Joseph,
>
> I see what you're saying but once the primary link goes down, doesn't that
> trigger ospf to flood lsa's out all it's interfaces so that all routers
can
> sync their lsa databases?
>
> And, once all lsa databases are in sync, don't all routers then know that
> the former primary link isn't available and therefore when the spf process
> is run, any paths that previously used the primary link will now use the
> ISDN link instead?
>
> And, if that's true, doesn't that mean that Dialer Watch isn't needed? Or,
> put another way, wouldn't configuring Dialer Watch, in addtion to OSPF
> demand circuit be reduntant?
>
> If this isn't true, can you describe a scenario where both Dialer Watch
and
> OSPF demand circuit over the same isdn link would be needed?
>
> Thanks, pm
>
>
> >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 07:44:06 -0800
> >
> >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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