- A
Inter-area route summarization is configured on ABRs using the "area range" command.
Correct because ABRs use the "area range" command to summarize routes between areas, reducing Type 3 LSAs.
- B
External route summarization is configured on ASBRs using the "summary-address" command.
Correct because ASBRs use the "summary-address" command to summarize redistributed external routes, reducing Type 5 LSAs.
- C
Route summarization reduces the size of the LSDB and improves network convergence.
Correct because summarization reduces the number of LSAs, which in turn reduces LSDB size and speeds up convergence.
- D
Route summarization can be configured on any OSPF router to reduce Type 1 LSAs.
Why wrong: Incorrect because summarization is only performed on ABRs or ASBRs; internal routers cannot summarize routes.
- E
Summarization in OSPF can be applied to Type 1 and Type 2 LSAs to reduce flooding.
Why wrong: Incorrect because summarization only applies to Type 3 (inter-area) and Type 5 (external) LSAs, not to Type 1 or Type 2.
Quick Answer
The correct answer identifies that OSPF route summarization reduces the size of the link-state database (LSDB) and improves network convergence, with inter-area summarization configured on ABRs to reduce Type 3 LSAs and external route summarization on ASBRs to reduce Type 5 LSAs. This works because ABRs and ASBRs are the only routers that can summarize routes—ABRs summarize between areas, while ASBRs summarize redistributed external routes—thereby limiting the propagation of specific prefixes and lowering the routing table overhead. On the ENCOR 350-401 exam, this topic tests your understanding of where summarization occurs in OSPF, often appearing in multiple-choice questions that ask which statements are true; a common trap is assuming internal routers can summarize, but they cannot, as summarization only affects Type 3 and Type 5 LSAs, not Type 1 or Type 2. A helpful memory tip is “ABR for inter-area, ASBR for external—summarization lives at the border.”
350-401 OSPF Practice Question
This 350-401 practice question tests your understanding of ospf. 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.
Which three statements about OSPF route summarization are true? (Choose three.)
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
Inter-area route summarization is configured on ABRs using the "area range" command.
Option A is correct because inter-area summarization is configured on ABRs to reduce the number of Type 3 LSAs. Option B is correct because external route summarization is configured on ASBRs to reduce Type 5 LSAs. Option C is correct because summarization helps reduce the routing table size and LSA flooding, improving network stability. Option D is incorrect because summarization is not supported on internal routers; it is only performed on ABRs and ASBRs. Option E is incorrect because summarization does not affect Type 1 or Type 2 LSAs; it only affects Type 3 and Type 5 LSAs.
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.
- ✓
Inter-area route summarization is configured on ABRs using the "area range" command.
Why this is correct
Correct because ABRs use the "area range" command to summarize routes between areas, reducing Type 3 LSAs.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
External route summarization is configured on ASBRs using the "summary-address" command.
Why this is correct
Correct because ASBRs use the "summary-address" command to summarize redistributed external routes, reducing Type 5 LSAs.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
Route summarization reduces the size of the LSDB and improves network convergence.
Why this is correct
Correct because summarization reduces the number of LSAs, which in turn reduces LSDB size and speeds up convergence.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
Route summarization can be configured on any OSPF router to reduce Type 1 LSAs.
Why it's wrong here
Incorrect because summarization is only performed on ABRs or ASBRs; internal routers cannot summarize routes.
- ✗
Summarization in OSPF can be applied to Type 1 and Type 2 LSAs to reduce flooding.
Why it's wrong here
Incorrect because summarization only applies to Type 3 (inter-area) and Type 5 (external) LSAs, not to Type 1 or Type 2.
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 350-401 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 350-401 question test?
OSPF — This question tests OSPF — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Inter-area route summarization is configured on ABRs using the "area range" command. — Option A is correct because inter-area summarization is configured on ABRs to reduce the number of Type 3 LSAs. Option B is correct because external route summarization is configured on ASBRs to reduce Type 5 LSAs. Option C is correct because summarization helps reduce the routing table size and LSA flooding, improving network stability. Option D is incorrect because summarization is not supported on internal routers; it is only performed on ABRs and ASBRs. Option E is incorrect because summarization does not affect Type 1 or Type 2 LSAs; it only affects Type 3 and Type 5 LSAs.
What should I do if I get this 350-401 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 350-401 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
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