350-401 Question 428
Single answerA network engineer is configuring OSPF between two routers. The OSPF neighbor relationship is not forming, and the logs show an authentication failure. The engineer verified that both routers are using the same key-string for authentication. Which of the following could be the cause of the issue?
- A
The authentication type is mismatched between the two routers.
- B
The OSPF process IDs do not match on the two routers.
- C
The OSPF area numbers do not match between the two routers.
- D
The MTU settings on the interfaces are mismatched.
Show answer and explanation
Correct answer: A
Explanation
In OSPF, both the key-string and the authentication type must match between neighbors for the relationship to establish. A mismatch in authentication type, such as one router using plaintext and the other using MD5, will result in an authentication failure. The process ID and MTU settings do not directly impact authentication. Additionally, while area numbers must match for adjacency, they do not cause an authentication failure.
- A. Correct.
If the authentication type (e.g., MD5 or plaintext) is mismatched between the two routers, the neighbor relationship will fail to establish, even if the key-strings match.
- B. Incorrect.
The OSPF process IDs do not need to match between routers for an OSPF neighbor relationship to form. This is not a valid reason for the failure.
- C. Incorrect.
While the area numbers must match for OSPF adjacency to form, this would not specifically cause an 'authentication failure' message in the logs.
- D. Incorrect.
MTU mismatches can cause OSPF adjacency issues, but they are unrelated to authentication failures.