- A
Type 1 (Router LSA)
Why wrong: Type 1 LSAs describe a router's own interfaces and links within an area.
- B
Type 2 (Network LSA)
Why wrong: Type 2 LSAs are generated by the Designated Router for multi-access networks.
- C
Type 3 (Summary LSA)
Correct: ABRs use Type 3 LSAs to advertise inter-area routes, including default routes.
- D
Type 5 (AS-External LSA)
Why wrong: Type 5 LSAs are used for external routes redistributed into OSPF, not for inter-area default routes.
Question 1,736 of 2,152
ABR Injects Default Route into Regular Area Using Type 3 LSA
This 300-410 practice question tests your understanding of device management. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 OSPF LSA type is used to describe a default route injected into a regular area by an Area Border Router (ABR)?
Quick Answer
The answer is Type 3 (Summary LSA). This is correct because an Area Border Router (ABR) uses Type 3 LSAs to advertise inter-area routes, including a default route, into regular areas by setting the destination network to 0.0.0.0. In OSPF, Type 3 LSAs are the only mechanism an ABR has to summarize or inject a default route across area boundaries, as they describe networks from one area to another without carrying topology details. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of how ABRs generate and flood summary LSAs, often appearing in questions about default route propagation or area filtering. A common trap is confusing Type 3 with Type 5 (external) or Type 4 (ASBR summary) LSAs—remember that only a Type 3 LSA carries a default route from an ABR into a regular area. For a memory tip, think “3 for the ABR’s summary spree, default route to 0.0.0.0 is key.”
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)
Option C is correct because 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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
When an ABR injects a default route into a regular area using a Type 3 LSA, it sets the metric using the 'area X default-cost' command under the OSPF process. This default route is treated as an inter-area route (O*IA) in the routing table, and it is not flooded into stub or totally stub areas because those areas already have their own default route mechanism via Type 3 LSAs with a special flag. In real-world scenarios, this is commonly used to provide a default gateway for non-backbone areas while still allowing the ABR to summarize other inter-area prefixes.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Type 3 (Summary LSA) — Option C is correct because 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.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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