300-440 Question 29
Single answerA network administrator is troubleshooting an OSPF network where manual summarization was configured on an Area Border Router (ABR) between Area 0 and Area 1. However, hosts in Area 1 are unable to reach specific subnets in Area 0. What could be the most likely cause of the issue?
- A
The summary route does not cover all the subnets in Area 0.
- B
OSPF does not support manual summarization on ABRs.
- C
The summarized routes are missing from the ABR's LSDB (Link-State Database).
- D
Manual summarization is only supported on stub areas in OSPF.
Show answer and explanation
Correct answer: A
Explanation
When manual summarization is configured on an ABR, it is essential that the summary route accurately encompasses all the subnets in the area being summarized. If the summary route is too narrow and does not include all subnets, traffic destined for those excluded subnets will fail to route properly, resulting in connectivity issues.
- A. Correct.
If the summary route does not cover all the subnets in Area 0, traffic destined for the uncovered subnets will be dropped, leading to connectivity issues.
- B. Incorrect.
OSPF does support manual summarization on ABRs, so this is incorrect.
- C. Incorrect.
If the summarized routes were missing from the ABR's LSDB, the ABR would not advertise the summary route at all, which is a different issue. However, the LSDB is likely correct since the issue is about specific subnets.
- D. Incorrect.
Manual summarization is not limited to stub areas in OSPF; it is supported on ABRs for any area type, so this is incorrect.