OSPF priority in run time

Unanswered Question
Jun 4th, 2007

Hi All,

If the OSPF priority were to be changed on links in run-time, with the

following timers in sec

1) Hello-interval 1

2) Dead-interval 4

3) Wait-interval 4

4) Retransmit 5

How much time will the change from current DR / BDR elections result in?

Which timer will these changes be dependent on? Will there be a change in DR & BDR without reset of OSPF process after a period of time?

The changes are performed on broadcast media interfaces with Dot1q


Given that OSPF priority change might result in DR & BDR elections, will the

flow of traffic be affected with this change?



I have this problem too.
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sundar.palaniappan Mon, 06/04/2007 - 17:01


Priority is carried in hello packets and therefore hello interval is the relevant one. Changing the priority will not affect the status of existing DR/BDR and it will only influence the DR/BDR election when one of them goes down or the OSPF process is restarted. In other words if the current DR/BDR has a lower priority than another router in which set the priority to be the highest it wouldn't automatically cause a new DR election. If you restart the OSPF process to influence a DR election then that naturally would affect the flow of traffic.



Richard Burts Mon, 06/04/2007 - 17:51


We should be careful in stating that changing the OSPF priority will only influence the DR/BDR election when one of them goes down. If priority is increased or is decreased (to a non-zero value) then your statement is quite correct. But if the OSPF priority is set to zero, and if the router is currently DR or BDR then the router immediately withdraws and forces a new election.



bvsnarayana03 Tue, 06/05/2007 - 07:16

Priority is a parameter specific to an interface. It doesnt mean that changing the priority will affect the traffic flow. Its the Cost on interface that affects traffic flow.

Coming to DR & BDR re-election, it wont happen until an existing DR goes offline whether you change the priority to less or 0.

Another way is to clear the OSPF process of DR.

Is there a real need for changing the Hello parameters, as this would require to be done on all router in n/w. This would also lead to heavy transfer of LSA database. Dont prefer doing this until u hv a small network.

schinnappolla Thu, 06/07/2007 - 09:30

Thanks. This is the exact details i was looking for. This really helps.




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