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Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

An engineer reviews the operational status of router R1 connected to a shared multiaccess Ethernet segment:

text
R1# show ip ospf interface GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is up
Internet Address 10.10.10.1/24, Area 0
Process ID 10, Router ID 10.10.10.1, Network Type BROADCAST, Cost: 1
State DROTHER, Priority 0
Designated Router (ID) 10.10.10.3, Interface address 10.10.10.3
Backup Designated Router (ID) 10.10.10.2, Interface address 10.10.10.2

If both the Designated Router (DR) and Backup Designated Router (BDR) suffer a simultaneous hardware failure, which role will router R1 transition to on this broadcast segment?

  1. R1 will remain in the DROTHER state and will not participate in the election for DR or BDR.Answer
  2. B
    R1 will immediately assume the Designated Router (DR) role because it is the only remaining router on the segment.
  3. C
    R1 will become the Backup Designated Router (BDR) first before being promoted to Designated Router (DR).
  4. D
    R1 will automatically convert its network type to Point-to-Point to re-establish neighbor adjacencies.

Answer

R1 will remain in the DROTHER state and will not participate in the election for DR or BDR.
In OSPFv2 multiaccess networks, setting an interface priority to 0 disqualifies the router from participating in the DR/BDR election process. Even if both the active DR and BDR fail, a router with a priority of 0 will stay in the DROTHER state and will never assume the DR or BDR role.

Step-by-Step Solution

1
Inspect the interface priority value in the CLI snippet.
The interface priority on GigabitEthernet0/1 is set to 0 (`Priority 0`).
OSPF interface priority determines eligibility in DR/BDR elections.
2
Evaluate the OSPF DR/BDR election rules for priority 0.
A priority of 0 means the router is ineligible to become either DR or BDR.
Setting the priority to 0 is the administrative mechanism used to isolate a router from taking on DR or BDR election responsibilities.
3
Determine the operational state following DR and BDR failures.
R1 remains in the DROTHER state indefinitely until an eligible router (priority > 0) joins the segment.
Even if DR and BDR fail simultaneously, an ineligible router cannot be promoted.

Key Concept

OSPF Interface Priority 0 Election Exclusion
Estimated Time:1m 0s
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Topics

OSPFv2 Network Types and DR/BDR Selection

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