hardMultiple SelectObjective-mapped
OSPF LSA Types: A Complete Guide to Type 1-5
Which three statements about OSPF LSA types are true? (Choose three.)
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."
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.
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.
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.
- ✓
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.
- ✓
Type 5 LSAs are generated by ASBRs to advertise routes from other routing domains.
Why this is correct
Correct because AS External LSAs (Type 5) are originated by ASBRs to inject external routes into the OSPF domain.
- ✗
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.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Same concept, more angles
1 more way 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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.