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OSPF preemtive

I was just wondering if there is a way to set OSPF up so it does the DR/BDR election in a preemtive way.

To be read: If a higher priority router (or higher router ID if priority are all the same) come online, can it force a DR/BDR re-election at all?


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Re: OSPF preemtive


I am not aware of any way to do that in OSPF. The protocol was designed for the election to be non-preemptive to improve the stability of relationships in the protocol and to reduce the number of times that routers on the segment would have to go through the process of forming neighbor adjacencies.



Community Member

Re: OSPF preemtive


I hav face the same problem in our network.

We have two Core switch holding the DR/BDR role and during maintenance the BDR have take over by a third network element (service server with OSPF enable) which is not desirable to be neither DR/BRD.

I never heard any method can be use to make the cisco route become preemptive.

Re: OSPF preemtive


From the OSPF RFC 2328 section 7.3:

"In general, when a router's interface to a network first becomes functional, it checks to see whether there is currently a Designated Router for

the network. If there is, it accepts that Designated Router, regardless of its Router Priority. (This makes it harder to predict the identity of the Designated Router, but ensures that the Designated Router changes less often. See below.) "

So DR/BDR election has been standardized to be non preemptive. So the Cisco implementation is RFC conforming. In case a router should NOT become DR or BDR you have to set its priority to 0.

RFC 2328, Section 9.4 Electing the Designated Router:

"(Routers having Router Priority of 0 are ineligible to become Designated Router.)"

Hope this helps! PLease rate all posts.

Regards, Martin

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