A network engineer is troubleshooting an OSPF adjacency failure between two directly connected routers, R1 and R2. Both routers are configured with the same OSPF process ID and area. The engineer verifies that the interfaces are up and IP connectivity exists. Which configuration mismatch is most likely causing the adjacency to fail?
Trap 1: MTU mismatch between the interfaces
MTU mismatch causes OSPF packets to be silently dropped, but the adjacency may still reach the EXCHANGE state before failing.
Trap 2: Passive interface configuration on one router
Passive interface prevents sending hellos, so the neighbor would not be discovered at all.
Trap 3: Area ID mismatch on the interfaces
Area ID mismatch would result in a different area and the adjacency would not form due to area mismatch.
- A
MTU mismatch between the interfaces
Why wrong: MTU mismatch causes OSPF packets to be silently dropped, but the adjacency may still reach the EXCHANGE state before failing.
- B
Passive interface configuration on one router
Why wrong: Passive interface prevents sending hellos, so the neighbor would not be discovered at all.
- C
Area ID mismatch on the interfaces
Why wrong: Area ID mismatch would result in a different area and the adjacency would not form due to area mismatch.
- D
OSPF network type mismatch between the interfaces
Network type mismatch (e.g., broadcast vs. point-to-point) causes the routers to disagree on DR/BDR election and hello behavior, preventing adjacency.