- A
The 'area range' command is configured with the 'not-advertise' keyword, suppressing the summary.
The 'not-advertise' keyword explicitly prevents the summary route from being advertised, which would cause the routes to be missing.
- B
The summary route is being filtered by a distribute-list on the receiving router.
Why wrong: A distribute-list could filter the summary, but the question asks for the most likely explanation given the configuration of 'area range'.
- C
The component routes are not present in the OSPF database.
Why wrong: 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.
- D
The summary route is being advertised with a metric that is too high.
Why wrong: 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.
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."
300-410 Route Summarization Practice Question
This 300-410 practice question tests your understanding of route summarization. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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).
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
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.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Route Summarization — This question tests Route Summarization — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: 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).
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Same concept, more angles
1 more ways 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.
Last reviewed: Jun 18, 2026
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