hardMultiple ChoiceObjective-mapped
OSPF Inter-Area Summarization Troubleshooting: area range Command
An engineer configures route summarization in OSPF using the 'area range' command. After configuration, some routes are missing from the routing table of other routers. Which is the most likely explanation?
Quick Answer
The answer is the 'area range' command configured with the 'not-advertise' keyword, which suppresses the summary route entirely. In OSPF, the 'area range' command creates a Type 3 LSA to advertise a summarized prefix into other areas, but adding the 'not-advertise' option explicitly blocks that LSA from being generated, causing the missing routes. On the Cisco CCNP ENARSI 300-410 exam, this question tests your understanding of OSPF inter-area summarization troubleshooting, often appearing as a scenario where routes vanish after configuration. A common trap is assuming the default behavior always advertises; while the default is 'advertise', misconfiguring the keyword or creating a summary that is more specific than the component routes can also cause rejection by receiving routers. Memory tip: think "not-advertise = no Type 3 LSA out the door."
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'area range' command is configured with the 'not-advertise' keyword, suppressing the summary.
The 'area range' command in OSPF creates a summary route that is advertised as a Type 3 LSA. However, if the 'not-advertise' keyword is used, the summary route is suppressed. Additionally, if the summary route is more specific than the component routes, it may be rejected by the receiving router due to OSPF's route selection rules. Another edge case is that the summary route may be created but the component routes are still advertised individually if the 'advertise' keyword is not explicitly used (default is advertise).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The 'area range' command is configured with the 'not-advertise' keyword, suppressing the summary.
Why this is correct
The 'not-advertise' keyword explicitly prevents the summary route from being advertised, which would cause the routes to be missing.
- ✗
The summary route is being filtered by a distribute-list on the receiving router.
Why it's wrong here
A distribute-list could filter the summary, but the question asks for the most likely explanation given the configuration of 'area range'.
- ✗
The component routes are not present in the OSPF database.
Why it's wrong here
If component routes are not present, the summary cannot be created, but the question states that some routes are missing, implying the summary is created.
- ✗
The summary route is being advertised with a metric that is too high.
Why it's wrong here
A high metric would not cause the route to be missing; it would still be present in the routing table if it is the best path.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Same concept, more angles
1 more way this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Drag and drop the steps to configure OSPF inter-area summarization on an ABR into the correct order, from first to last.
medium- ✓ A.Enter OSPF router configuration mode
- ✓ B.Specify the area containing the routes to summarize
- ✓ C.Apply the area range command with prefix and mask
- ✓ D.Verify the summary route in the OSPF database
- ✓ E.Check the routing table for the summary route
Why A: First, enter OSPF configuration mode for the process. Then, configure the area where the routes originate. Next, apply the range command to summarize prefixes into that area. After that, verify the summary route is present in the routing table. Finally, check that the summary is advertised to neighboring areas.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.