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200-101 · Question #137

Refer to the exhibit. What can be concluded from the output of the debug command?

The correct answer is C. The OSPF router connected to interface Serial0/1 has NOT formed a neighbor relationship with the Border router.. OSPF debug output reveals when hello packets are transmitted on an interface but no neighbor adjacency advances beyond the initial state, indicating a failed neighbor relationship.

Implement a Scalable OSPF Based Solution

Question

Refer to the exhibit. What can be concluded from the output of the debug command?

Options

  • AThe output represents normal OSPF operation.
  • BThe interfaces of two OSPF routers connected to the Border router are in the same subnet.
  • CThe OSPF router connected to interface Serial0/1 has NOT formed a neighbor relationship with the Border router.
  • DA router is connected to interface Serial0/3 of the Border router. The OSPF router ID of the connected router is the IP address of the connected interface.

How the community answered

(44 responses)
  • A
    5% (2)
  • B
    9% (4)
  • C
    68% (30)
  • D
    18% (8)

Why each option

OSPF debug output reveals when hello packets are transmitted on an interface but no neighbor adjacency advances beyond the initial state, indicating a failed neighbor relationship.

AThe output represents normal OSPF operation.

The debug output contains indicators of a failed or missing adjacency, which is not normal OSPF operation - normal operation shows neighbors reaching the FULL state with stable adjacency.

BThe interfaces of two OSPF routers connected to the Border router are in the same subnet.

Two interfaces being in the same subnet is a misconfiguration that produces specific error messages about duplicate subnets or mismatched areas, not the neighbor-failure pattern shown in this debug output.

CThe OSPF router connected to interface Serial0/1 has NOT formed a neighbor relationship with the Border router.Correct

OSPF debug commands such as 'debug ip ospf adj' show hello packet transmission and neighbor state transitions. When the output shows hellos being sent on Serial0/1 with no corresponding neighbor progressing to FULL state - typically indicated by repeated INIT or DOWN entries - it confirms that the adjacent router on that interface has not formed a neighbor relationship with the Border router.

DA router is connected to interface Serial0/3 of the Border router. The OSPF router ID of the connected router is the IP address of the connected interface.

The OSPF router ID defaults to the highest loopback IP or highest active interface IP, but the debug output showing a missing neighbor relationship on Serial0/3 does not provide sufficient information to confirm that the neighbor's router ID equals its connected interface address.

Concept tested: OSPF neighbor adjacency failure diagnosis via debug output

Source: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13695-ospf-ne.html

Topics

#OSPF#neighbor relationship#debug output#adjacency troubleshooting

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