OSPF non broadcast network

Unanswered Question
Sep 11th, 2007

If an OSPF (NBMA) network is set to nonbroadcast, does this mean that:

a) DR and BDR Will occur

B) DR and BDR will no occur

C) all routers must be fully meshed

D) neighbor command is required for adjacencies

E) adjacencies will be auto detected

My answers are A and D

those are the correct answers right?

because DR and BDR will occur but it depends on the neighbor command and you can manually select the DR by setting the priority on a specific interface..

I have this problem too.
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Kevin Dorrell Tue, 09/11/2007 - 23:12

That is correct.

The neighbor command is required for for adjacencies because broadcasts are assumed not to not work (implicit in the name). In fact, the neighbor command is only necessary on one side of the connection. This seems to be done usually at the hub end, but I have never fully understood if there are any valid argumants for preferring the neighbor statement at one end or the other. If you configure the neighbor statement at both ends, the startup can be a bit bumpy.

If you have a hub-and-spoke topology (which is quite usual), then set your priorities so that the hub becomes the DR. Even better, set the priority on the spokes to 0 so they cannot become DR.

If you have a BDR, then it should also have full connectivity to all the spokes as well as to the DR.

Kevin Dorrell



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