Question 1,502 of 2,152

Route Summarization →hardMultiple ChoiceObjective-mapped

300-410 Route Summarization Practice Question

This 300-410 practice question tests your understanding of route summarization. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

A network engineer is troubleshooting a redistribution issue between EIGRP and OSPF. Router R1 redistributes EIGRP routes into OSPF. The engineer configured a summary route 10.0.0.0/8 using the 'summary-address' command under the OSPF process. After the configuration, OSPF neighbors lose connectivity to the 10.1.0.0/16 subnet, which is one of the component routes. What is the most likely cause?

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.

Question 1hardmultiple choice

Review the full OSPF breakdown →

A
The summary-address command on R1 is configured with the 'tag' keyword, causing the summary to be ignored by other routers.
Why wrong: Incorrect. The tag keyword does not cause the summary to be ignored; it is used for route tagging.
B
The summary route 10.0.0.0/8 is not being generated because the component routes are not all present in the OSPF database.
Correct. In OSPF, the summary-address command generates a summary only if at least one component route exists in the OSPF database. If the component route is missing due to redistribution issues, the summary may not be generated, and the specific routes may be suppressed.
C
The OSPF neighbor relationship is down due to a mismatch in area IDs.
Why wrong: Incorrect. The symptom is specific to one subnet; neighbor relationships are likely up.
D
The engineer forgot to configure the 'network' command for the summary route under OSPF.
Why wrong: Incorrect. The summary-address command does not require a network statement; it is applied to redistributed routes.

Full breakdown with real-world context →

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 summary route 10.0.0.0/8 is not being generated because the component routes are not all present in the OSPF database.

The issue is that the summary-address command in OSPF can suppress the advertisement of more specific routes, but if the summary route is not installed due to a missing component or metric issue, it can cause a routing black hole.

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 summary-address command on R1 is configured with the 'tag' keyword, causing the summary to be ignored by other routers.
Why it's wrong here
Incorrect. The tag keyword does not cause the summary to be ignored; it is used for route tagging.
✓
The summary route 10.0.0.0/8 is not being generated because the component routes are not all present in the OSPF database.
Why this is correct
Correct. In OSPF, the summary-address command generates a summary only if at least one component route exists in the OSPF database. If the component route is missing due to redistribution issues, the summary may not be generated, and the specific routes may be suppressed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The OSPF neighbor relationship is down due to a mismatch in area IDs.
Why it's wrong here
Incorrect. The symptom is specific to one subnet; neighbor relationships are likely up.
✗
The engineer forgot to configure the 'network' command for the summary route under OSPF.
Why it's wrong here
Incorrect. The summary-address command does not require a network statement; it is applied to redistributed routes.

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.

Trap categories for this question

Keyword trap
Incorrect. The tag keyword does not cause the summary to be ignored; it is used for route tagging.
Command / output trap
Incorrect. The summary-address command does not require a network statement; it is applied to redistributed routes.

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 summary route 10.0.0.0/8 is not being generated because the component routes are not all present in the OSPF database. — The issue is that the summary-address command in OSPF can suppress the advertisement of more specific routes, but if the summary route is not installed due to a missing component or metric issue, it can cause a routing black hole.

What should I do if I get this 300-410 question wrong?

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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