hardMultiple Select
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."
⚠ Common exam trap
350-401 often tests the ABR vs. ASBR responsibility split for Type 3, 4, and 5 LSAs — the trap is assuming the ASBR generates Type 4 (it does not; the ABR does) or that Type 3 comes from the ASBR (it comes from the ABR).
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 Router LSAs are originated by every OSPF router (in each area it belongs to) to describe its own links, interfaces, and neighbor relationships within that area. Option B is correct because Type 2 Network LSAs are generated only by the Designated Router (DR) on multiaccess segments such as Ethernet, representing the subnet and the routers attached to it. Option C is correct because Type 5 AS External LSAs are originated by ASBRs to advertise routes redistributed from outside the OSPF autonomous system (other routing domains) throughout the OSPF domain. Option D is wrong because Type 3 Summary LSAs are generated by ABRs, not ASBRs, to advertise inter-area routes. Option E is wrong because Type 4 Summary ASBR LSAs are generated by ABRs to advertise the location of an ASBR to other areas, not by 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
Every OSPF router originates a Type 1 Router LSA describing its own interfaces, neighbours and link costs, flooded within its area only. This satisfies the requirement that each router advertises its local topology, forming the basis of the area's shortest-path tree.
- ✓
Type 2 LSAs are generated by the Designated Router on multiaccess networks.
Why this is correct
On multiaccess segments the DR originates the Type 2 Network LSA, listing all routers attached to that segment. This satisfies the requirement to represent the broadcast segment as a single pseudonode, reducing adjacency count and LSA flooding.
- ✓
Type 5 LSAs are generated by ASBRs to advertise routes from other routing domains.
Why this is correct
Type 5 LSAs are originated by ASBRs to flood external routes redistributed from other routing domains throughout the OSPF autonomous system. This satisfies the stem's requirement for a true statement about LSA types, since external route advertisement is precisely the function of Type 5, distinguishing it from intra-area Type 1 and Type 2 LSAs.
- ✗
Type 3 LSAs are generated by ASBRs to summarize routes between areas.
Why it's wrong here
Type 3 LSAs are generated by ABRs, not ASBRs, and they advertise inter-area prefixes rather than summarising routes originated by ASBRs. It is tempting because Type 3 does carry inter-area summary information, and it would be correct if the generating router were the ABR.
- ✗
Type 4 LSAs are generated by the ASBR to advertise its presence to other areas.
Why it's wrong here
Type 4 LSAs are generated by the ABR, not the ASBR, and they describe the ASBR's reachability into other areas. It is tempting because Type 4 summarises ASBR location, and it would be correct if the stem attributed generation to the area border router instead.
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: Option A is correct because Type 1 Router LSAs are originated by every OSPF-enabled router, are scoped to a single area, and describe that router's links (interfaces, IP addresses, metrics) and its neighbors on those links. Option B is correct because Type 2 Network LSAs are generated only by the Designated Router on multi-access segments such as broadcast and NBMA networks, and they list the DR, the BDR, and all attached routers to represent the transit network. Option D is correct because Type 4 ASBR Summary LSAs are produced by Area Border Routers to tell routers in other areas how to reach an Autonomous System Boundary Router located in a different area. Option C is wrong because Type 3 Summary LSAs are generated by ABRs to advertise inter-area routes, not by ASBRs to advertise external routes. Option E is wrong because Type 5 AS External LSAs are flooded throughout the entire OSPF autonomous system (except stub/NSSA areas), not confined to the originating area.
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.