OSPF DR and BDR

[chid_1989]

Hi,

Assuming i have three routers R1,R2 and R3 sharing a LAN. If i give "ip ospf priority 0" in two of these routers ( say R2 and R3 ) and the router R1 which is the DR for the segment now, fails, what will happen. Since there is no BDR, no router will transition to DR. Since no BDR will loose its state, there will be no new election for BDR. Is this a loophole in OSPF?

Thanks

Chidambaram

[Richard Burts]

I am not sure that loophole is the correct term for it. But you are correct that one of the implications of setting priority zero for OSPF on all routers on the segment except for one does create a potential problem if that one router develops a problem. This is something that you have to set, and you should consider carefully the implications of setting it in this way. If you do set it, and if the problem does develop, then do not blame OSPF. This is not a failure of the routing protocol but is an operational action that you took.

HTH

Rick

[chid_1989]

Thanks Richard,

Just in case, i use this config for hub and spoke topology wont it cause a problem? When OSPF runs on frame relay, I may want routers to never become DR or BDR except one router. This only initially led to the doubt.

Thanks

Chidambaram

[Alessio Andreoli]

If you do not want DR/BDR election do  NOT use  ip ospf priority 0, you need to use ip ospf network point-to-point command below the interface configuration.

Be careful anyway, because to avoid DR/BDR election needs a good design behind that.

HTH

Alessio

[Richard Burts]

As I said in my response, using priority 0 is a choice that you make. You should evaluate the plus side (managing which router will become DR) and also the negative side (if the one router goes down then the segment does not form adjacencies). If the plus out weighs the negative then you go ahead and do it. But if the negative out weighs the plus then you do not do it.

And it also occurs to me that in the particular scenario that you mention it is not much of a problem to use priority 0 on all the spoke routers. When you think about it, if the hub router goes down then how will the spoles communicate?

HTH

Rick