200-301 Question 334
Select 4A network engineer is configuring OSPF on two routers, R1 and R2, within the same area. Despite matching configurations, the OSPF neighbor adjacency is not forming between the two routers. Which of the following could be the cause of this issue?
- A
The IP addresses of the routers' interfaces are in different subnets.
- B
The OSPF hello timers do not match between R1 and R2.
- C
The OSPF process IDs configured on R1 and R2 are different.
- D
The OSPF area IDs configured on R1 and R2 are mismatched.
- E
The OSPF authentication credentials do not match between R1 and R2.
Show answer and explanation
Correct answers: A, B, D, E
Explanation
OSPF neighbor adjacencies require specific parameters to match between routers, such as subnet configuration, hello/dead timers, area IDs, and authentication credentials. Process IDs, however, are locally significant and do not affect neighbor relationships. Understanding these requirements is crucial for troubleshooting OSPF adjacency issues.
- A. Correct.
Correct. OSPF requires that the IP addresses of connected interfaces be in the same subnet for neighbor adjacencies to form. Different subnets would prevent adjacency formation.
- B. Correct.
Correct. OSPF hello and dead timers must match between neighbors. A mismatch in these timers will prevent the establishment of OSPF neighbor adjacencies.
- C. Incorrect.
Incorrect. OSPF process IDs are locally significant and do not need to match between routers for adjacency to form.
- D. Correct.
Correct. OSPF area IDs must match between neighbors for adjacency to form. Mismatched area IDs will prevent the routers from establishing a neighbor relationship.
- E. Correct.
Correct. OSPF authentication credentials, if configured, must match between neighbors. A mismatch in authentication settings will prevent adjacency formation.