OSPF DR/BDR Election explained

Lessons Discussion
1

This topic is to discuss the following lesson:

2

Really helpful series of posts on OSPF. Thank you!

3

Thanks for this lesson, very helpful! :slight_smile:

4

Wonderful explanation!! The best I’ve found on the web. CCNA books are not so clear!
Thanks!

5

Thanks Davide, glad to hear you like it!

6

simply awesome!!! Thanks a lot…

7

One of the best explanations I have ever come across. You make things seem easy. I haven’t started configurations of OSPF yet but I get it

8

Hi!
Can you explain to me please, where I can use DROTHER and examples of its use?
Than you!
P.S. Sorry for my bad English! )

9

Hi Rene,

Just to let you know that on the multi-segment picture, the networks don’t match with the output below.

On the right side, you should change to 192.168.23.0/24.

Not a big ideal, just to avoid confusing more distracted people :slight_smile:

AF

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Basically only the DR and BDR are important, all other routers are DROTHERS. In case the DR and/or BDR fails one of the currently DROTHERS might become DR/BDR.

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you are the best.thanks for useful lesson

12

Hello,

Thank you very much for explanation. I don’t actually know what DR and BDR do and why should we use them in OSPF protocol. I’d appreciate it if you explain that as well.

13

Hi Mey,

I explained why we need a DR / BDR in this tutorial:

Rene

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Hi, Rene,

In your examples, such as the first one, the output of command

Nancy#show ip ospf neighbor
shows both the 2 "Interface"s as “FastEthernet0/0”
Is the interface a interface on Nancy? Or a interface on the neighbor?

In the 2nd example (2 multi-accesssegments), the output of command

Donna#show ip ospf neighbor
shows 2 "Interface"s as FastEthernet1/0 and FastEthernet0/0.
but there is no interface FastEthernet1/0 in that diagram. Would please
update that diagram?

Thanks

15

I think I have figured out that the “Interface” is the interface on this router instead of the one on the neighbor router. Please confirm. Thanks!

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Hi Chang Shong C,

The first example is correct. We have a multi-access network so you can have multiple OSPF neighbors on one interface.

The 2nd example with the diagram had an error…I just fixed the interface number, thanks for letting me know!

Rene

17

Excellent!

18

Hello,

I don’t have "#clear ip ospf process " this command on my router simulator. It only has clear ip options and no “ospf” option. Any workaround?

thanks

19

That is strange. What simulator do you use? This is a very common command and if OSPF is supported, it should be included.

20

I am using Cisco Packet Tracer 5.3.0.0088

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