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300-410 Practice Question: Which OSPF LSA type is used to describe a default…
Which OSPF LSA type is used to describe a default route injected into a regular area by an Area Border Router (ABR)?
⚠ Common exam trap
Cisco often tests the distinction between Type 3 and Type 5 LSAs for default route injection, and the trap here is that candidates mistakenly think a default route must always be a Type 5 LSA (external) because of the 'default-information originate' command, but when injected by an ABR into a regular area, it is actually a Type 3 LSA.
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)
An ABR uses a Type 3 Summary LSA to advertise a default route (0.0.0.0/0) into a regular area. This LSA type is generated by the ABR to summarize inter-area routes, and when the ABR is configured with the 'area X default-cost' command or the 'default-information originate' command, it injects a default route as a Type 3 LSA into the specified area.
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 a router's own interfaces and links within an area.
- ✗
Type 2 (Network LSA)
Why it's wrong here
Type 2 LSAs are generated by the Designated Router for multi-access networks.
- ✓
Type 3 (Summary LSA)
Why this is correct
Correct: ABRs use Type 3 LSAs to advertise inter-area routes, including default routes.
- ✗
Type 5 (AS-External LSA)
Why it's wrong here
Type 5 LSAs are used for external routes redistributed into OSPF, not for inter-area default routes.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.