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Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

An administrator is reviewing the following Cisco IOS command output from router HQ-R3, which is connected to a shared Ethernet LAN segment alongside other OSPFv2 routers:

HQ-R3# show ip ospf interface GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.1.3/24, Area 0
Process ID 1, Router ID 10.3.3.3, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 10.4.4.4, Interface address 192.168.1.4
Backup Designated Router (ID) 10.2.2.2, Interface address 192.168.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

If both the current Designated Router (10.4.4.4) and Backup Designated Router (10.2.2.2) fail simultaneously, which statement correctly describes the operational outcome for HQ-R3 during the resulting election?

  1. HQ-R3 will remain in the DROTHER state and is ineligible to become either the DR or BDR because its configured interface priority is zero.Answer
  2. B
    HQ-R3 will automatically become the new Designated Router if its Router ID of 10.3.3.3 is higher than all remaining active routers.
  3. C
    HQ-R3 will temporarily become the Backup Designated Router while neighboring routers wait for the 40-second Wait timer to expire.
  4. D
    HQ-R3 will initiate a point-to-point adjacency fallback mechanism and bypass the DR/BDR election entirely.

Answer

HQ-R3 will remain in the DROTHER state and is ineligible to become either the DR or BDR because its configured interface priority is zero.
In OSPFv2 broadcast multi-access networks, an interface configured with an OSPF priority of 0 (`ip ospf priority 0`) is explicitly excluded from DR/BDR elections. Regardless of failures of the current DR and BDR or the numerical value of HQ-R3's Router ID (10.3.3.3), HQ-R3 will always remain in the DROTHER state.

Step-by-Step Solution

1
Examine the interface command output for HQ-R3.
The output indicates `Priority 0` and current state `DROTHER` on interface GigabitEthernet0/0.
Interface priority dictates eligibility and precedence in OSPF DR/BDR elections.
2
Evaluate the effect of Priority 0 on OSPF elections.
An OSPF interface priority of 0 completely disqualifies the router interface from being elected as Designated Router (DR) or Backup Designated Router (BDR).
This is a key administrative control mechanism to prevent specific routers (such as lower-capacity branch routers) from assuming DR responsibilities.
3
Determine the outcome when active DR and BDR fail.
Even if all other routers fail or have lower Router IDs, HQ-R3 will never transition out of the DROTHER state.
Priority 0 strictly overrides Router ID tie-breaking rules.

Key Concept

OSPFv2 Interface Priority 0 Election Exclusion
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Topics

OSPFv2 Network Types and DR/BDR Selection

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