350-401 Question 430
Single answerA network engineer is configuring OSPF authentication between two routers (RouterA and RouterB) to ensure secure neighbor relationships. RouterA has been configured with the following commands:
interface GigabitEthernet0/1 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 SecureKey123
On RouterB, the engineer applies the following commands:
interface GigabitEthernet0/1 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 SecureKey321
After completing the configuration, the OSPF neighbor relationship does not form. What is the most likely reason for this issue?
- A
The hello and dead timers on RouterA and RouterB do not match.
- B
The OSPF process IDs on RouterA and RouterB are different.
- C
The MD5 authentication keys on RouterA and RouterB do not match.
- D
The OSPF network types on RouterA and RouterB are mismatched.
Show answer and explanation
Correct answer: C
Explanation
To establish an OSPF neighbor relationship with MD5 authentication, both routers must use the same authentication key (password) and key ID. In this case, the MD5 keys configured on RouterA ('SecureKey123') and RouterB ('SecureKey321') do not match, resulting in the failure of the OSPF neighbor relationship. This highlights the importance of ensuring consistent authentication configurations when securing OSPF.
- A. Incorrect.
While mismatched hello and dead timers can prevent OSPF neighbor relationships, the issue described here points to authentication because the configuration specifically involves message-digest authentication.
- B. Incorrect.
The OSPF process ID is locally significant and does not need to match between routers to form a neighbor relationship.
- C. Correct.
For OSPF MD5 authentication to work, the authentication keys must match on both routers. In this scenario, 'SecureKey123' on RouterA does not match 'SecureKey321' on RouterB, causing the neighbor relationship to fail.
- D. Incorrect.
Mismatched OSPF network types (e.g., broadcast vs. point-to-point) can prevent neighbor relationships, but the question explicitly mentions authentication as the focus.