mediumMultiple Choice
300-410 Practice Question: Which OSPF LSA type is used to advertise prefixes…
Which OSPF LSA type is used to advertise prefixes from other areas into the backbone area?
⚠ Common exam trap
A common mix-up: candidates confuse the LSA types that operate within an area (Type 1 and 2) with those that cross area boundaries (Type 3) and those that cross the OSPF domain boundary (Type 5) — candidates often pick Type 5 because 'external' sounds like 'other areas', but external means outside OSPF entirely.
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 3 (Summary LSA)
Type 3 Summary LSAs are generated by Area Border Routers (ABRs) to advertise inter-area prefixes — networks learned in one area — into other areas, including the backbone (Area 0). When an ABR connects Area 0 to a non-backbone area, it converts Type 1/2 topology information from one area into Type 3 LSAs flooded into the other, enabling prefix reachability across area boundaries. This is the fundamental mechanism of OSPF's two-tier hierarchical design.
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 (Router LSA)
Why it's wrong here
Type 1 LSAs describe routers and their links within a single area, so they cannot carry inter-area prefixes into the backbone. They are tempting because every OSPF router originates them, but Type 3 Summary LSAs perform the area-to-backbone prefix advertisement.
- ✗
Type 2 (Network LSA)
Why it's wrong here
Type 2 LSAs describe multi-access network segments and their attached routers within one area, not prefixes from other areas. They are tempting because they flood across the area, yet only Type 3 Summary LSAs advertise inter-area prefixes into the backbone.
- ✓
Type 3 (Summary LSA)
Why this is correct
Type 3 Summary LSAs are generated by ABRs to advertise inter-area prefixes, including networks from non-backbone areas, into the backbone. This flooding of prefixes between areas satisfies the requirement to advertise other-area prefixes into area 0.
- ✗
Type 5 (External LSA)
Why it's wrong here
Type 5 LSAs flood external routes redistributed into OSPF from outside the domain; inter-area prefixes are carried by Type 3 summary LSAs generated by ABRs. It is tempting because external routes do traverse the backbone, and would be correct when advertising routes redistributed from another protocol or autonomous system.
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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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 300-410 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 300-410 exam.