- A
Type 1 LSAs (Router LSAs) are generated by every OSPF router and describe the router's interfaces and neighbors within an area.
Correct because Router LSAs are the fundamental LSA type, created by each router to advertise its directly connected links and state.
- B
Type 2 LSAs (Network LSAs) are generated by the DR on broadcast and NBMA networks to list all routers attached to the segment.
Correct because the DR generates Network LSAs to describe the set of routers connected to the multiaccess network.
- C
Type 3 LSAs (Summary LSAs) are generated by ASBRs to advertise external routes into the OSPF domain.
Why wrong: Incorrect because Type 3 LSAs are generated by ABRs to advertise routes between areas, not by ASBRs. ASBRs generate Type 5 LSAs for external routes.
- D
Type 4 LSAs (ASBR Summary LSAs) are generated by ABRs to advertise the location of an ASBR to routers in other areas.
Correct because Type 4 LSAs are used to propagate reachability information about an ASBR across area boundaries.
- E
Type 5 LSAs (AS External LSAs) are flooded only within the area where they originate.
Why wrong: Incorrect because Type 5 LSAs are flooded throughout the entire OSPF domain (except stub areas) and are not limited to a single area.
350-401 OSPF Practice Question
This 350-401 practice question tests your understanding of ospf. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 LSA types are correct? (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
Type 1 LSAs (Router LSAs) are generated by every OSPF router and describe the router's interfaces and neighbors within an area.
OSPF uses various LSA types to describe different routing information. Type 1 (Router LSA) is generated by every router. Type 2 (Network LSA) is generated by the DR. Type 3 (Summary LSA) is generated by ABRs. Type 4 (ASBR Summary LSA) is also generated by ABRs. Type 5 (AS External LSA) originates from ASBRs and is flooded throughout the entire OSPF domain.
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.
- ✓
Type 1 LSAs (Router LSAs) are generated by every OSPF router and describe the router's interfaces and neighbors within an area.
- ✓
Type 2 LSAs (Network LSAs) are generated by the DR on broadcast and NBMA networks to list all routers attached to the segment.
Why this is correct
Correct because the DR generates Network LSAs to describe the set of routers connected to the multiaccess network.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
Type 3 LSAs (Summary LSAs) are generated by ASBRs to advertise external routes into the OSPF domain.
Why it's wrong here
Incorrect because Type 3 LSAs are generated by ABRs to advertise routes between areas, not by ASBRs. ASBRs generate Type 5 LSAs for external routes.
- ✓
Type 4 LSAs (ASBR Summary LSAs) are generated by ABRs to advertise the location of an ASBR to routers in other areas.
Why this is correct
Correct because Type 4 LSAs are used to propagate reachability information about an ASBR across area boundaries.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
Type 5 LSAs (AS External LSAs) are flooded only within the area where they originate.
Why it's wrong here
Incorrect because Type 5 LSAs are flooded throughout the entire OSPF domain (except stub areas) and are not limited to a single area.
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: Type 1 LSAs (Router LSAs) are generated by every OSPF router and describe the router's interfaces and neighbors within an area. — OSPF uses various LSA types to describe different routing information. Type 1 (Router LSA) is generated by every router. Type 2 (Network LSA) is generated by the DR. Type 3 (Summary LSA) is generated by ABRs. Type 4 (ASBR Summary LSA) is also generated by ABRs. Type 5 (AS External LSA) originates from ASBRs and is flooded throughout the entire OSPF domain.
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
This 350-401 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 350-401 exam.
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