300-420 Question 77
Select 2An enterprise network is designed with OSPF as the routing protocol. The network architect has enabled Graceful Restart (GR) to ensure minimal disruption during planned router restarts. During a routine maintenance window, one of the OSPF routers undergoes a restart. While analyzing the network behavior, the architect notices that some OSPF neighbors did not maintain their adjacency during the restart. Which of the following could be reasons for this behavior?
- A
The OSPF neighbors do not support Graceful Restart capability.
- B
The restarting router did not send a Graceful Restart (LSA) message before restarting.
- C
The OSPF neighbors detected a topology change during the restart.
- D
The restarting router was configured with incorrect Graceful Restart timers.
- E
The restarting router is using a different OSPF area than its neighbors.
Show answer and explanation
Correct answers: A, C
Explanation
Graceful Restart in OSPF allows a router to restart without causing adjacency loss, provided its neighbors support the capability and no topology changes are detected. If neighbors lack this capability or detect a topology change during the restart, they will terminate the Graceful Restart process to prevent routing inconsistencies. Thus, the correct answers are the lack of Graceful Restart support by neighbors and topology changes detected during the process.
- A. Correct.
If the OSPF neighbors do not support Graceful Restart capability, they will not maintain adjacency during the restart and will treat the restarting router as down.
- B. Incorrect.
Graceful Restart does not rely on a specific 'Graceful Restart (LSA)' message; instead, it uses signaling mechanisms through OSPF Hello packets and LSA exchange. This option is incorrect.
- C. Correct.
If the OSPF neighbors detect a topology change during the restart, they will terminate the Graceful Restart process and re-establish adjacency to ensure routing consistency.
- D. Incorrect.
Incorrect Graceful Restart timers on the restarting router would not directly cause adjacency loss. Instead, it could result in other issues such as premature or delayed recovery, making this option incorrect.
- E. Incorrect.
The OSPF area configuration mismatch would prevent adjacency formation entirely, not just during a restart. This option is unrelated to the Graceful Restart process.