- A
Type 1 LSAs are generated by every OSPF router to describe its own interfaces and neighbors.
Correct because Router LSAs (Type 1) are created by each router to advertise its directly connected links.
- B
Type 2 LSAs are generated by the Designated Router on multiaccess networks.
Correct because Network LSAs (Type 2) are generated by the DR to list all routers attached to the segment.
- C
Type 5 LSAs are generated by ASBRs to advertise routes from other routing domains.
Correct because AS External LSAs (Type 5) are originated by ASBRs to inject external routes into the OSPF domain.
- D
Type 3 LSAs are generated by ASBRs to summarize routes between areas.
Why wrong: Incorrect because Type 3 Summary LSAs are generated by ABRs, not ASBRs.
- E
Type 4 LSAs are generated by the ASBR to advertise its presence to other areas.
Why wrong: Incorrect because Type 4 LSAs are generated by ABRs to advertise the location of an ASBR to other areas.
Quick Answer
The correct answer is that Type 5 LSAs are generated by ASBRs to advertise routes from other routing domains, which is a foundational concept for OSPF LSA types. This is true because Autonomous System Boundary Routers (ASBRs) inject external routes into the OSPF domain, and these routes are advertised as Type 5 LSAs, which flood throughout the entire OSPF network. On the ENCOR 350-401 exam, you must distinguish between the roles of ABRs and ASBRs: Type 3 and Type 4 LSAs are generated by ABRs, while Type 5 LSAs are exclusive to ASBRs. A common trap is confusing Type 4 LSAs (which are generated by ABRs to advertise the location of an ASBR) with Type 5 LSAs. To remember the hierarchy, think of the mnemonic "1-2-3-4-5: Every router does 1, DR does 2, ABR does 3 and 4, ASBR does 5."
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 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
Type 1 LSAs are generated by every OSPF router to describe its own interfaces and neighbors.
Option A is correct because Type 1 LSAs (Router LSAs) are generated by every router and describe the router's directly attached links. Option B is correct because Type 2 LSAs (Network LSAs) are generated by the DR on broadcast and NBMA networks to describe the segment and attached routers. Option C is correct because Type 5 LSAs (AS External LSAs) are generated by ASBRs to advertise external routes. Option D is incorrect because Type 3 LSAs (Summary LSAs) are generated by ABRs, not ASBRs. Option E is incorrect because Type 4 LSAs (ASBR Summary LSAs) are generated by ABRs, not the ASBR itself.
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 are generated by every OSPF router to describe its own interfaces and neighbors.
Why this is correct
Correct because Router LSAs (Type 1) are created by each router to advertise its directly connected links.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
Type 2 LSAs are generated by the Designated Router on multiaccess networks.
Why this is correct
Correct because Network LSAs (Type 2) are generated by the DR to list all routers attached to the segment.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
Type 5 LSAs are generated by ASBRs to advertise routes from other routing domains.
- ✗
Type 3 LSAs are generated by ASBRs to summarize routes between areas.
Why it's wrong here
Incorrect because Type 3 Summary LSAs are generated by ABRs, not ASBRs.
- ✗
Type 4 LSAs are generated by the ASBR to advertise its presence to other areas.
Why it's wrong here
Incorrect because Type 4 LSAs are generated by ABRs to advertise the location of an ASBR to other areas.
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 are generated by every OSPF router to describe its own interfaces and neighbors. — Option A is correct because Type 1 LSAs (Router LSAs) are generated by every router and describe the router's directly attached links. Option B is correct because Type 2 LSAs (Network LSAs) are generated by the DR on broadcast and NBMA networks to describe the segment and attached routers. Option C is correct because Type 5 LSAs (AS External LSAs) are generated by ASBRs to advertise external routes. Option D is incorrect because Type 3 LSAs (Summary LSAs) are generated by ABRs, not ASBRs. Option E is incorrect because Type 4 LSAs (ASBR Summary LSAs) are generated by ABRs, not the ASBR itself.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on 350-401
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. Which three statements about OSPF LSA types are correct? (Choose three.)
hard- ✓ A.Type 1 LSAs (Router LSAs) are generated by every OSPF router and describe the router's interfaces and neighbors within an area.
- ✓ B.Type 2 LSAs (Network LSAs) are generated by the DR on broadcast and NBMA networks to list all routers attached to the segment.
- C.Type 3 LSAs (Summary LSAs) are generated by ASBRs to advertise external routes into the OSPF domain.
- ✓ D.Type 4 LSAs (ASBR Summary LSAs) are generated by ABRs to advertise the location of an ASBR to routers in other areas.
- E.Type 5 LSAs (AS External LSAs) are flooded only within the area where they originate.
Why A: 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.
Last reviewed: Jun 18, 2026
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