Refer to the exhibit. The OSPF neighborship fails between two routers. What is the cause of this issue?

Question

Options

• AThe OSPF router ID is missing on this router.
• BThe OSPF process is stopped on the neighbor router.
• CThere is an MTU mismatch between the two routers.
• DThe OSPF router ID is missing on the neighbor router.

• A
  9% (3)
• B
  17% (6)
• C
  71% (25)
• D
  3% (1)

Explanation

OSPF Neighborship Failure Due to MTU Mismatch

When OSPF neighbors are stuck in the EXSTART/EXCHANGE state, this is the classic indicator of an MTU mismatch - the routers cannot successfully exchange Database Description (DBD) packets because one router's packets exceed the neighbor's maximum transmission unit size, causing the adjacency to fail. MTU mismatch is one of the most common OSPF neighborship issues and would appear in the exhibit as neighbors failing to progress beyond EXSTART.

Why the distractors are wrong:

• A & D (Router ID missing): OSPF will automatically generate a Router ID from the highest loopback or active interface IP; a missing manual Router ID won't prevent neighbor formation on its own.
• B (OSPF process stopped): If the OSPF process were stopped on the neighbor, you would see no neighbor entry at all in the neighbor table, rather than a failed/stuck adjacency.

Memory Tip: Remember "EXSTART = MTU mismatch" - if neighbors are stuck in EXSTART/EXCHANGE, think MTU first. You can resolve this with the ip ospf mtu-ignore command on the interface, or by matching the MTU values on both sides.

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