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Difficulty: MediumRouting Concepts and Dynamic Routing Protocols

A network technician adds a new Layer 3 switch to a multi-access Ethernet network segment running OSPF Area 00. The operational Designated Router (DR) on the segment has a Router ID of 10.1.1.110.1.1.1 and an OSPF priority of 11. The new switch is configured with an OSPF priority of 255255 and a Router ID of 10.1.1.25410.1.1.254. What will happen to the DR role on this network segment immediately after the new switch establishes adjacency?

  1. The operational Designated Router retains the DR role because OSPF DR elections are non-preemptive.Answer
  2. B
    The new switch immediately preempts and takes over as the Designated Router due to its higher priority setting of 255255.
  3. C
    The two switches share the Designated Router role by performing active-active load balancing across the segment.
  4. D
    The existing Designated Router relinquishes its role and forces a complete OSPF neighbor adjacency reset across all switches.

Answer

The operational Designated Router retains the DR role because OSPF DR elections are non-preemptive.
In OSPF multi-access broadcast networks, Designated Router (DR) and Backup Designated Router (BDR) elections are non-preemptive. Once a router assumes the DR role, it maintains that role until its OSPF process is reset, the interface goes down, or the router reboots. Adding a router with a higher priority (such as 255) will not displace an active DR.

Step-by-Step Solution

1
Identify the dynamic routing protocol and election state
The network segment uses OSPF in a multi-access broadcast topology with an established DR.
OSPF elects a Designated Router (DR) and Backup Designated Router (BDR) to minimize LSA flooding on broadcast networks.
2
Evaluate the impact of introducing a router with a higher priority value (255255)
The new router has a higher priority than the current DR (11), but the current DR is already active.
OSPF DR/BDR election logic is explicitly non-preemptive to prevent constant network churn and routing recalculations whenever routers boot up or restart.
3
Determine the resulting DR status
The current DR remains DR. The new router may become BDR (if eligible and BDR is vacant) or a DROTHER.
A re-election for DR only occurs if the existing DR router process fails, the interface goes down, or the OSPF process is manually cleared.

Key Concept

OSPF Designated Router (DR) Non-Preemptive Election Logic
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Topics

Routing Concepts and Dynamic Routing Protocols

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