This N10-009 practice question tests your understanding of network implementation. 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.
A network engineer is designing an OSPF network for a large enterprise. To reduce the size of routing tables and limit the propagation of external routes, the engineer wants to use a special area that blocks Type 5 LSAs but still allows inter-area routes via a default route. Which type of OSPF area should be configured?
Why wrong: The backbone area carries all inter-area traffic and does not block Type 5 LSAs; it must have full routing information.
B
Standard area
Why wrong: A standard area allows all LSA types (1-5) and does not reduce routing tables.
C
Stub area
A stub area blocks Type 5 LSAs (AS external routes) and injects a default route instead, reducing routing table size and external route propagation.
D
Totally stubby area
Why wrong: A totally stubby area blocks both Type 3 (inter-area) and Type 5 LSAs, further reducing routes but also blocking inter-area routes beyond the default. The question specifies only blocking external routes and keeping inter-area routes, so stub area is appropriate.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Stub area
A stub area blocks Type 5 LSAs (external routes) from entering the area, forcing the area border router (ABR) to inject a default route (0.0.0.0/0) for reaching external destinations. This reduces the routing table size while still allowing inter-area routes (Type 3 LSAs) to propagate, exactly matching the requirement.
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.
✗
Backbone area 0
Why it's wrong here
The backbone area carries all inter-area traffic and does not block Type 5 LSAs; it must have full routing information.
✗
Standard area
Why it's wrong here
A standard area allows all LSA types (1-5) and does not reduce routing tables.
✓
Stub area
Why this is correct
A stub area blocks Type 5 LSAs (AS external routes) and injects a default route instead, reducing routing table size and external route propagation.
Related concept
Read the scenario before looking for a memorised answer.
✗
Totally stubby area
Why it's wrong here
A totally stubby area blocks both Type 3 (inter-area) and Type 5 LSAs, further reducing routes but also blocking inter-area routes beyond the default. The question specifies only blocking external routes and keeping inter-area routes, so stub area is appropriate.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between stub and totally stubby areas, where candidates mistakenly choose 'totally stubby' because they think it blocks more routes, but the question explicitly requires inter-area routes to still be allowed, which only a stub area provides.
Detailed technical explanation
How to think about this question
In OSPF, stub areas use the 'area X stub' command on all routers in the area, and the ABR automatically generates a default Type 3 LSA (0.0.0.0/0) into the area. Type 4 LSAs (ASBR summary) are also blocked in stub areas because there is no ASBR reachable within the area. A real-world scenario is a remote branch office that only needs to reach the corporate network and the internet via a default route, keeping its routing table small.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Stub area — A stub area blocks Type 5 LSAs (external routes) from entering the area, forcing the area border router (ABR) to inject a default route (0.0.0.0/0) for reaching external destinations. This reduces the routing table size while still allowing inter-area routes (Type 3 LSAs) to propagate, exactly matching the requirement.
What should I do if I get this N10-009 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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Question Discussion
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