How DR/BDR gets elected in
OSPF:

The
purpose of having a DR and BDR is to reduce the amount of network traffic
generated by OSPF, as only the DR and BDR exchange full routing information,
while other routers only exchange minimal information. This helps ensure the
stability and efficiency of the OSPF network.

The
DR is responsible for managing the flow of routing information between routers
in that segment, and for maintaining the integrity of the routing information.

The
BDR acts as a backup for the DR, taking over if the DR fails or becomes
unavailable.

Election Process:

The
following steps outline the election process:

·        — The router with the highest priority becomes the DR. (Default
priority is 1)

·        — Router with second highest priority becomes BDR.

·      —   If same priority, the router with the highest Router ID is elected as the DR.

Below Diagram all
router has Same priority then router with Highest RID will become DR

Router
c will become DR because it has highest Loopback IP and Router B will be BDR

 

What is Router ID:

The
router ID (RID) is 32-bit unique identifier assigned to each router in an OSPF
network.

It
is used by OSPF to identify the router in the network and to distinguish it
from other routers.

is
either assigned manually by the network administrator or automatically
generated by the router

The
RID is usually assigned using the highest IP address assigned to the router,
either on a physical interface or a loopback interface

 

Commands to manual configure Router ID:

 

Points to be Noted:

·        – If priority is “0” then router can’t be elected as a DR and BDR.

·         –DR/BDR election process is non-preemptive means once router
selected as a DR

   and if new router comes with higher priority ospf DR/BDR
election will not happen

·            Till we manually clear ospf process by using below command.

#clear ip ospf process

·        
We can check DR/BD status by using “#show ip ospf neighbor”
command