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DR/BDR election

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

A DR/BDR election is the OSPF selection process that chooses a designated router and backup designated router on a broadcast segment.

On an OSPF broadcast segment, routers elect a designated router (DR) and backup designated router (BDR) to reduce unnecessary adjacency and LSA-exchange traffic. The election occurs in the 2-Way neighbor state, and it is held separately on each segment rather than once per area. section 18.3.2

Verifying a changed election

After R2 G0/1 is configured with ip ospf priority 100, resetting the OSPF process allows the displayed roles to change: R4 becomes DR and R2 becomes BDR.

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes
Explains election scope, neighbor states, priority configuration, verification, and process reset, without detailing selection-order rules.
Examples
Uses six-router traffic counts, neighbor tables, priority configuration, and a point-to-point conversion.
What it assumes
Assumes OSPF-enabled interfaces, router neighbors, and shared network segments; distinguishes broadcast from point-to-point behavior.
What you can do after
Operate/configure OSPF interfaces and diagnose DR, BDR, and DROther roles with Cisco show commands.
How it connects
Connects OSPF network types with neighbor discovery, OSPF adjacency states, LSA exchange, and interface priority.
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Related concepts

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