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Manually configuring the DR and BDR and the switchover between the DR and BDR

Latest reply: Dec 31, 2018 11:08:10 2023 5 7 0 0

Hello, everyone!

This post is about manually configuring the DR and BDR and the switchover between the DR and BDR. Please see below.


The DR needs to process real-time change information on the entire network and takes the responsibility of the leader in the entire OSPF network. Therefore, the DR needs strong performance. One possibility is not excluded: A low-end router on the network may become a DR during DR election because its IP address is large. As a result, the router becomes the bottleneck of the entire network performance. You can manually control the election to specify who will become the DR and who will become the BDR.

You can use either of the following methods.

1. Specify the DR and BDR by controlling the router ID of each router.

Each OSPF router selects a DR or BDR based on its router ID. The router with the highest router ID is elected as the DR. In this case, you can manually specify the router ID of each router to control the election. As shown in the preceding figure, the DR and BDR are changed to R4 and R3 respectively, and R1 and R2 become DRother.

Router1(config)#int lo 0
Router1(config-if)#ip add
Router1(config-if)#router ospf 100
Router2(config)#int lo 0
Router2(config-if)#ip add
Router2(config)#router ospf 200
Router3(config)#int lo 0
Router3(config-if)#ip add
Router3(config)#router ospf 300
Router4(config)#int lo 0
Router4(config-if)#ip add
Router4(config)#router ospf 400

As shown in the preceding figure, the network has been converged, and the DR and BDR have been selected. If the router IDs of the routers are changed, they will not be re-elected, which will cause network instability. Therefore, after modifying the configuration, you need to manually restart the OSPF process.

Clear ip ospf pro

Run the following command - show ip ospf neighbor to check whether the configuration takes effect.

2. Change the router priority to control the DR and BDR election.

During the election of a router, the router ID and priority need to be compared. The default priority is 1. Therefore, by default, only the router ID is compared. However, you can manually change the priority to control the election. The method is as follows.

For example, in the preceding figure, R3 is the DR, R1 is the BDR, and others are DRother.

Run the following command in interface mode. The default value is 1. The larger the value, the smaller the value.

R3(config-if)#ip ospf priority 100
R1(config-if)#ip ospf priority 80

The priority range is 0-255. When the priority of a router is 0, the router will not participate in the election.

If the DR BDR has been produced, the default value will not change after you modify the priority and the option that affects the DRBDR. If you need to run the clear ip ospf process command, the system will prompt YES or NO. In this case, the default value is NO.

This would be all on manually configuring the DR and BDR and the switchover between the DR and BDR. Thanks for reading this post!

  • x
  • convention:

Created Dec 29, 2018 05:47:23

A given router can have some interfaces that are designated (DR) and others that are backup designated (BDR), and others that are non-designated. If no router is a DR or a BDR on a given subnet, the BDR is first elected, and then a second election is held for the DR.
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  • x
  • convention:

Created Dec 29, 2018 05:47:56

Router4(config-if)#ip add How do you understand this sentence?
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  • x
  • convention:

Created Dec 29, 2018 08:08:46

In some cases, the automatic configuration can meet the requirements.
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  • x
  • convention:

Created Dec 30, 2018 01:40:57

Great help, I thought the DR and BDR don't need a configuration but it seems does.
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  • x
  • convention:

Created Dec 31, 2018 11:08:10

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  • x
  • convention:


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