OSPF DR Election

Unanswered Question
May 22nd, 2009
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I have two test routers:


RouterA:

int lo1

ip address 100.100.100.100


RouterB:

int lo1

ip address 192.168.3.1


Router A is becoming the DR every time. I know that I can set the priority, but I also thought that the election was based off of the highest RID on the segment. These are both in area 0, so I don't understand why the lower address is winning the election.


Thanks,


John

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Jon Marshall Fri, 05/22/2009 - 08:20
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John


Once the DR has been elected a router with a higher RID will not preempt. It really depends on which router boots up quicker.


Have you tried shutting the interfaces down, turning on ospf debugging and then bringing them back up.


Jon

John Blakley Fri, 05/22/2009 - 08:30
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Jon,


I rebooted both routers at the same time, and it always elects the lower address. I shut both interfaces and debugged ospf adjacencies, and when I shut the interfaces down, it says that it's remembering the old DR. Why would it say that it's remember the old DR if it's not going to give back control when the old DR comes back online? Either way, in theory, I thought the higher RID would win the election?


Thanks,

John

illusion_rox Sun, 05/24/2009 - 19:27
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Dear Francisco,


I have tried it and made sure that routers are not reloaded but when the actual DR comes up with highest router id, it didnt regained its status of DR ? why is that so ? i can see in debug R1 and R2 saying that remembering old dr, but when i bring back the DR, they doesnt choose it to be DR !!


Kindly explain it

Jon Marshall Fri, 05/22/2009 - 08:41
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"Either way, in theory, I thought the higher RID would win the election?"


Yes it does or more specifically the loopback interface with the highest IP address and if there is no loopback interface the physical interface with the highest IP address assuming you haven't manually set the RID with the "ip ospf router-id x.x.x.x" command.


A lot of it is down to timing when the routers reboot. The first router to be active checks for neighbor's and if there aren't any will elect itself the DR. It's quite a common occurence to see a DR that does not have the highest IP.


Jon

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