OSPF Nei Election

Answered Question
Mar 15th, 2009

Once a nei election has been completed and a DR/BDR have been assigned, what is the correct way to change the DR without taking down the devices that are the DR and BDR?

I was doing a lab and delayed in enabling the e0 int on the router that should have been the DR(Loopback w/ highest IP). Once I enabled the e0 int, the election was done and of course the router that should be the DR was not.

I tried to change the priority to 3 and clear the ip ospf process ut this did not work. I am doing this in a lab, but if this where a real world example, running around unplugging/reloading routers would not be the best thing to do.

Is there a way to force a re-election and change the DR?

I have looked online and through the BSCI books and could not find another solution.

Thanks in advance

I have this problem too.
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Correct Answer by Richard Burts about 7 years 9 months ago

Todd

I have found a way to deal with the situation when a router has become DR that is not the one that you want to be DR. On the router that is currently DR change its OSPF priority on the interface to zero. The router continues to process OSPF but it immediately relinquishes its role as DR, allowing an election to take place. You can then set the priority back to its normal value if you do not want to keep it at zero. I have tested this and it works well.

It is my impression that this would be slightly less impact than clearing the OSPF process on the router. But either changing the priority to zero or clearing the OSPF process would be less impact than shutting interfaces or rebooting routers.

HTH

Rick

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echelon360 Sun, 03/15/2009 - 15:46

There is no pre-emption with the neighbor election. Hence you can set a higher priority but it doesn't guarantee that the router with that highest priority becomes the DR. (unless all routers initialize their process at the same time)

Usually setting the priority to "0" is a better approach to taking routers out of the DR/BDR election.

alternatively, you might want to utilize the "max-metric router-lsa" on the router that you do not want to be used as primary path via OSPF.

Harold Ritter Sun, 03/15/2009 - 16:26

Todd,

There is no preemption for the DR/BDR election. Try doing a "clear ip ospf process" on the router that is currently the DR after changing the priority on the router you want to become the DR. This should cause an election and the router with the highest priority should then win.

Regards

Regards

Correct Answer
Richard Burts Sun, 03/15/2009 - 18:43

Todd

I have found a way to deal with the situation when a router has become DR that is not the one that you want to be DR. On the router that is currently DR change its OSPF priority on the interface to zero. The router continues to process OSPF but it immediately relinquishes its role as DR, allowing an election to take place. You can then set the priority back to its normal value if you do not want to keep it at zero. I have tested this and it works well.

It is my impression that this would be slightly less impact than clearing the OSPF process on the router. But either changing the priority to zero or clearing the OSPF process would be less impact than shutting interfaces or rebooting routers.

HTH

Rick

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