300-410 ENARSI: Implementing Cisco Enterprise Advanced Routing and ServicesDemo

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QuestionQ377

Layer 3 Technologies

Refer to the exhibit.

Question Image

An OSPF neighbor relationship between R2 and R3 is stuck in the EXCHANGE/EXSTART state. The neighbor relationship between R1 and R2 is established. The network engineer can ping from R2 to R3 and vice versa, but the neighbor relationship remains down. Which action resolves the issue?

  • A Administrative “shut then no shut” both router interfaces.
  • B Enable OSPF on the interface, which is required.
  • C Restore the Layer 2/Layer 3 connectivity issue in the ISP network.
  • D Match MTU on both router interfaces or ignore MTU.
Explanation

An OSPF adjacency stuck in EXSTART or EXCHANGE commonly indicates an MTU mismatch. OSPF Database Description packets carry the interface MTU, and a router rejects packets whose advertised MTU does not match its interface setting unless MTU checking is disabled. Matching the MTU on both ends of the R2-R3 link, or configuring OSPF to ignore the MTU value, allows the adjacency to form.

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