Where OSPF elects a DR/BDR: Which OSPF network types perform Designated Router (DR) and Backup Designated Router (BDR) elections?

Introduction / Context:OSPF uses DR/BDR elections to reduce adjacencies on multiaccess media. Not all network types perform elections; understanding where they occur is key for design and troubleshooting adjacencies.

Given Data / Assumptions:

• (1) Broadcast
• (2) Point-to-point
• (3) NBMA (Non-Broadcast Multi-Access)
• (4) NBMA point-to-point (not an election scenario)

Concept / Approach:

DR/BDR is used on multiaccess segments: Broadcast Ethernet and NBMA networks (e.g., Frame Relay multipoint). Point-to-point links have only two neighbors, so elections are unnecessary and not performed.

Step-by-Step Solution:

Verification / Alternative check:

On Ethernet (broadcast), show ip ospf interface shows DR/BDR. On serial point-to-point links, no such election occurs; neighbors form full adjacency directly.

Why Other Options Are Wrong:

Including point-to-point introduces a type where DR/BDR is not used.

'All of the above' incorrectly assumes elections everywhere.

Common Pitfalls:

Confusing Frame Relay point-to-point subinterfaces (no election) with multipoint (election); assuming passive interfaces affect DR/BDR—passive controls hellos, not election rules.

Final Answer:

1 and 3