350-401 Question 396
Single answerA network engineer is configuring OSPF authentication between two routers, RouterA and RouterB. After enabling MD5 authentication on both routers, the OSPF neighbor relationship fails to establish. Upon reviewing the configurations, the engineer finds the following:
RouterA Configuration: interface GigabitEthernet0/0 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 cisco123
RouterB Configuration: interface GigabitEthernet0/0 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 cisco321
What is the most likely cause of the issue?
- A
The OSPF process ID does not match between RouterA and RouterB.
- B
The MD5 keys configured on RouterA and RouterB do not match.
- C
The OSPF router IDs are not unique between RouterA and RouterB.
- D
The OSPF authentication type is not supported on the interface.
Show answer and explanation
Correct answer: B
Explanation
For OSPF authentication to succeed, the MD5 keys (passwords) configured on both routers must match exactly. In this scenario, RouterA uses 'cisco123', while RouterB uses 'cisco321', leading to a failure in establishing the OSPF neighbor relationship. Ensuring consistent authentication configurations on both routers resolves the issue.
- A. Incorrect.
OSPF process IDs are locally significant and do not need to match between routers for a neighbor relationship to form.
- B. Correct.
The MD5 keys must match exactly on both routers for OSPF authentication to succeed. In this case, the keys ('cisco123' and 'cisco321') are different, causing the neighbor relationship to fail.
- C. Incorrect.
OSPF router IDs must be unique, but mismatched router IDs do not directly cause authentication-related neighbor formation issues.
- D. Incorrect.
MD5 authentication is a supported and commonly used OSPF authentication type. The issue here is not related to the authentication type being unsupported.