200-301 Question 331
Single answerYou are tasked with configuring OSPFv2 in a single-area network for a small organization. The network consists of three routers (R1, R2, and R3) connected to a single common subnet (192.168.1.0/24). After configuring OSPF on all three routers, you verify that R1 and R2 have established an OSPF adjacency, but R3 is not forming an adjacency with either R1 or R2. Upon reviewing the configuration on R3, you find the following:
router ospf 1
network 192.168.2.0 0.0.0.255 area 0
What is the most likely cause of the issue?
- A
The OSPF area on R3 is configured incorrectly.
- B
R3 is using an incorrect subnet mask in the OSPF network statement.
- C
The OSPF process ID on R3 does not match R1 and R2.
- D
R3 has not been configured with an OSPF router ID.
Show answer and explanation
Correct answer: A
Explanation
In single-area OSPFv2, all routers need to advertise their interfaces in the correct area and match the actual subnet used on the shared network. R3 is advertising the wrong network (192.168.2.0/24 instead of 192.168.1.0/24), which prevents it from forming adjacencies with R1 and R2. Correcting the network statement on R3 to network 192.168.1.0 0.0.0.255 area 0 will resolve the issue.
- A. Correct.
Correct. R3 is advertising the network 192.168.2.0/24 in OSPF, which does not match the actual subnet (192.168.1.0/24) on the shared interface. This mismatch prevents adjacency formation.
- B. Incorrect.
Incorrect. The subnet mask in the network statement is correct (0.0.0.255 corresponds to /24), but the network address is wrong.
- C. Incorrect.
Incorrect. OSPF process IDs do not need to match across routers for adjacency formation. This is not the issue here.
- D. Incorrect.
Incorrect. While an OSPF router ID is important, OSPF will automatically assign one if not manually configured. The lack of a manual router ID would not prevent adjacency formation in this scenario.