DR and BDR election
- The router with the highest priority becomes the DR; second highest becomes the BDR. If there is a tie in priority, Whichever router has the highest Router ID will become the DR.
- By default router priority will be same.We can change it if we need it
- Default priority on Cisco routers is 1.If we set Router priority is O, that router will not participate in DR/BDR election
- In FrameRelay (NBMA -non broadcast multi access) network ,HUB Must be elected as DR .We can do this by changing router priority
To change the priority on an interface:
Router(config)#Interface fa 0/0
Router(config-if)# ip ospf priority 125
OSPF routers will form adjacencies with the DR and BDR. If a change occurs to a link, the update is forwarded only to the DR, which then forwards it to all other routers. This greatly reduces the flooding of LSAs.
Note: The DR election process is not preemptive .Thus, if a router with a higher priority is added to the network, it will not automatically supplant an existing DR. We need to clear OSPF process for another DR/BDR election,which is not good in a production enviroment
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