show ip ospf neighbor question

Unanswered Question
Oct 3rd, 2007

The output of show ip ospf neighbor shows two lines. The state of one neighbor is Full/-. The state of the other neighbor is Full/BDR. Can one assume from this output that the router on which the command was issued is the DR? Or is there something else that I am missing?

I have this problem too.
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Kevin Dorrell Wed, 10/03/2007 - 12:43

These must be two different network segments.

For the neighbor which is Full/-, it means that the network segment is point-to-point (or effectively so), so there is no DR and BDR on that network segment.

For the neighbor which is Full/BDR, this is a broadcast network. There is a DR and a BDR, and the neighbor is the BDR. There seem to be only two routers on the segment, so by implcation we must be the DR, although this should be checked.

If there was another router on the segment that was neither DR nor BDR, then it would show up as DRother.

Kevin Dorrell

Luxembourg

orenjohnson Wed, 10/03/2007 - 13:06

Kevin,

Thanks for the response. It helps a lot. So the Full/- indicates a point to point connection (I don't recall that in any of my readings or in the output from Cisco's website about the command). From what you're saying, I guess the states for a multi-point connection could only be Full/DR, Full/DBR and Full/Drother. Man, there is just too much material. No wonder, they're breaking it into two tests. Thanks again.

Kevin Dorrell Wed, 10/03/2007 - 22:38

Yes, OSPF is a particular struggle because there is so much of it. But with any subject, I find that every now and then there is a light bulb that suddenly lights up, and a whole bunch of stuff falls into place. I suppose that shows a deficiency in some of the teaching material - that it states the facts OK, but doesn't address people's misconceptions.

For me, a big breakthrough happened when I realised that OSPF is only link-state within each area. Each area has a link-state database that is shared by all the routers participating in the area. Then these areas are joined up by border routers which pass routes (and not link states) from area to area. Anyway, that was my particular light bulb.

Good luck with the studies.

Kevin Dorrell

Luxembourg

paul.matthews Thu, 10/04/2007 - 00:48

Kevin is right about lightbulbs! I have had a few of those over the years

You *will* get a moment when something just clicks, followed by about 15 other clicks as other things suddenly make sense. You may even feel the odd Doh! moment as something you previously struggled with becomes blindingly obvious.

BTW Doyle is good for understanding OSPF.

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