N10-009 Network Implementation Practice Question
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?
⚠ Common exam trap
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.
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
✓
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.
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 OSPF backbone area, designated as Area 0, serves as the central hub through which all non-backbone areas must connect and exchange inter-area routing information. Its primary function is to provide full connectivity and a complete topological view for all OSPF areas, meaning it must carry all LSA types, including Type 5 LSAs for external routes. Blocking any LSA types in Area 0 would disrupt inter-area routing and prevent proper reachability across the OSPF domain, thus it cannot be used to reduce external routes.
When this WOULD be correct
When the question asks for the area that must be present for all other OSPF areas to communicate, and which is responsible for inter-area routing and distributing external routes, the backbone area 0 is the correct answer.
- ✗
Standard area
Why it's wrong here
A standard OSPF area is the default area type and does not impose any restrictions on the types of Link-State Advertisements (LSAs) that can be propagated within it. All LSA types, including Type 1 (router), Type 2 (network), Type 3 (summary), Type 4 (ASBR summary), and Type 5 (AS external), are allowed to flow freely. Consequently, a standard area maintains a complete and detailed routing table, which is contrary to the goal of reducing external routes and routing table size, making it unsuitable for this specific design requirement.
When this WOULD be correct
A standard area would be correct if the question required full OSPF functionality with no restrictions on LSA types, such as when inter-area and external routes must be propagated without summarization or filtering.
- ✓
Stub area
Why this is correct
A stub area is specifically designed to reduce the size of routing tables within an OSPF area by preventing the propagation of Type 5 Link-State Advertisements (LSAs), which carry information about external AS routes. Instead of learning every external route, a stub area's Area Border Router (ABR) injects a default route (0.0.0.0/0) into the area. This significantly simplifies routing decisions for internal routers, as all traffic destined for external networks is simply forwarded to the ABR, while still allowing inter-area routes (Type 3 LSAs) to be learned.
- ✗
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.
When this WOULD be correct
A network engineer wants to minimize routing table size by blocking all external and inter-area routes, relying solely on a default route for any traffic leaving the area. In this scenario, a totally stubby area would be correct because it blocks Type 3, 4, and 5 LSAs and injects a default route.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓Stub areaCorrect answer▾
Why this is correct
A stub area is specifically designed to reduce the size of routing tables within an OSPF area by preventing the propagation of Type 5 Link-State Advertisements (LSAs), which carry information about external AS routes. Instead of learning every external route, a stub area's Area Border Router (ABR) injects a default route (0.0.0.0/0) into the area. This significantly simplifies routing decisions for internal routers, as all traffic destined for external networks is simply forwarded to the ABR, while still allowing inter-area routes (Type 3 LSAs) to be learned.
✗Backbone area 0Wrong answer — click to see why▾
Why this is wrong here
The backbone area (area 0) does not block Type 5 LSAs; it is the transit area for all OSPF areas and propagates external routes. The question requires an area that blocks Type 5 LSAs and provides a default route, which is a stub area, not the backbone.
★ When this WOULD be the correct answer
When the question asks for the area that must be present for all other OSPF areas to communicate, and which is responsible for inter-area routing and distributing external routes, the backbone area 0 is the correct answer.
Why candidates choose this
Candidates may mistakenly think that the backbone area is a special area that can be configured to block certain LSAs, or they confuse the backbone's role in inter-area routing with the stub area's filtering behavior.
✗Standard areaWrong answer — click to see why▾
Why this is wrong here
A standard area does not block Type 5 LSAs; it allows external routes from other areas, which contradicts the requirement to limit propagation of external routes.
★ When this WOULD be the correct answer
A standard area would be correct if the question required full OSPF functionality with no restrictions on LSA types, such as when inter-area and external routes must be propagated without summarization or filtering.
Why candidates choose this
Candidates may think 'standard' is a safe default choice, not realizing that stub areas are specifically designed to reduce routing tables and block external LSAs while still providing inter-area connectivity via a default route.
✗Totally stubby areaWrong answer — click to see why▾
Why this is wrong here
A totally stubby area blocks Type 3, 4, and 5 LSAs, but the question requires that inter-area routes (Type 3) be allowed via a default route. A totally stubby area only injects a default route for external routes, not for inter-area routes, so it does not meet the requirement.
★ When this WOULD be the correct answer
A network engineer wants to minimize routing table size by blocking all external and inter-area routes, relying solely on a default route for any traffic leaving the area. In this scenario, a totally stubby area would be correct because it blocks Type 3, 4, and 5 LSAs and injects a default route.
Why candidates choose this
Candidates may confuse 'stub' with 'totally stubby' and think that blocking more LSAs is always better, or they may misremember that a totally stubby area still allows inter-area routes via a default route, which it does not.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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.
Go deeper
Related to this question
Learn chapter
Physical Network Infrastructure
Key term
OSPF
OSPF is a link-state routing protocol used to find the best path for data packets to travel across IP networks, like a smart GPS that recalculates routes when traffic changes.
Key term
Default route
A default route is a catch-all routing entry that tells a network device where to send packets when no specific route matches the destination address.
About these practice questions
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA 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 N10-009 exam.