300-410 Question 56
Single answerA network engineer is configuring OSPF between two routers, R1 and R2. Both routers are directly connected, but the neighbor relationship is failing to establish. The engineer notices the following configurations:
R1:
- Interface Gig0/0: IP address 192.168.1.1/24
- OSPF authentication: MD5 with key 'cisco123'
R2:
- Interface Gig0/0: IP address 192.168.1.2/24
- OSPF authentication: MD5 with key 'Cisco123'
What is the most likely reason the OSPF neighbor relationship is failing?
- A
The IP addresses on R1 and R2 are in different subnets.
- B
The OSPF authentication key is mismatched between R1 and R2.
- C
OSPF authentication is not supported on Gigabit interfaces.
- D
R1 and R2 are configured with different OSPF process IDs.
Show answer and explanation
Correct answer: B
Explanation
In OSPF, authentication keys must match exactly, including case-sensitivity, for a neighbor relationship to form. In this scenario, the mismatch in the MD5 authentication keys ('cisco123' vs. 'Cisco123') is the root cause of the problem.
- A. Incorrect.
The IP addresses 192.168.1.1/24 and 192.168.1.2/24 are in the same subnet, so this is not the issue.
- B. Correct.
OSPF authentication keys are case-sensitive. In this case, 'cisco123' on R1 and 'Cisco123' on R2 are different, which will prevent the neighbor relationship from being established.
- C. Incorrect.
OSPF authentication is supported on Gigabit interfaces, so this is not the issue.
- D. Incorrect.
OSPF process IDs do not need to match between routers for a neighbor relationship to form, so this is not the issue.