350-501 Question #156: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. While troubleshooting the OSPF adjacency between routers R1 and R2 an engineer noticed that both routers are stuck in the EXCHANGE/EXSTART state. What should the engineer fix to solve the ongoing issue?

Options

• Amatch IPv4 addresses
• Bmatch OSPF areas
• Cmatch OSPF network types
• Dmatch MTU values

Explanation

OSPF routers stuck in the EXCHANGE/EXSTART state indicate an issue during the database synchronization process, often caused by a mismatch in the Maximum Transmission Unit (MTU) values between the directly connected interfaces.

Common mistakes.

• A. An IPv4 address mismatch would prevent the OSPF adjacency from reaching the INIT state, as hello packets would not be processed correctly by the neighboring router.
• B. An OSPF area mismatch would typically prevent adjacency formation beyond the INIT or Two-Way state, as area IDs are exchanged in hello packets and must match for full adjacency.
• C. An OSPF network type mismatch can lead to issues with DR/BDR election or neighbor discovery, but it doesn't specifically cause the adjacency to halt in the EXCHANGE/EXSTART state due to packet exchange failure like an MTU mismatch does.

Concept tested. OSPF adjacency states and troubleshooting MTU mismatch

Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13689-18.html

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