DR , BDR problem in OSPF?

Answered Question

Please have a look below

R4#sh ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

1.1.1.1 1 FULL/DR 00:00:39 172.26.22.1 FastEthernet0/0

3.3.3.3 1 2WAY/DROTHER 00:00:38 172.26.22.3 FastEthernet0/0

2.2.2.2 1 FULL/BDR 00:00:35 172.26.22.2 FastEthernet0/0

I am confused. According to my knowledge the 1.1.1.1 should not be DR as it has the lowest ID. According to above 3.3.3.3 should be the DR.

But why it is like this?

I have this problem too.
0 votes
Correct Answer by royalblues about 9 years 8 months ago

Imran,

Whenever OSPF starts on the LAN, it always checks for an existing DR/BDR and accepts it if it finds one.

The only time it does an election is when it cannot find a DR and a BDR. it is at this time it uses the parameters like the router id & priority to decide the DR/BDR.

In your case the router 1.1.1.1 must have come online first and hence become the DR.

The second router to come online was 2.2.2.2 and it did find the DR for the LAN. Hence this became the BDR.

If you happen to restart all the routers and assuming all of them come online at the same time, you should see 3.3.3.3 becoming the DR.

HTH, rate if it does

Narayan

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Correct Answer
royalblues Sat, 03/31/2007 - 04:46

Imran,

Whenever OSPF starts on the LAN, it always checks for an existing DR/BDR and accepts it if it finds one.

The only time it does an election is when it cannot find a DR and a BDR. it is at this time it uses the parameters like the router id & priority to decide the DR/BDR.

In your case the router 1.1.1.1 must have come online first and hence become the DR.

The second router to come online was 2.2.2.2 and it did find the DR for the LAN. Hence this became the BDR.

If you happen to restart all the routers and assuming all of them come online at the same time, you should see 3.3.3.3 becoming the DR.

HTH, rate if it does

Narayan

flashsplash Mon, 04/02/2007 - 05:02

also keep the priority of the interfaces in mind. And what kind of Network are u using?

ciao flash

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