N10-009 Network Implementation Practice Question
A network administrator is configuring OSPF on routers in a multi-area network. The administrator wants to ensure that a router in area 1 does not learn external routes (Type 5 LSAs) injected by an ASBR in area 0, but it must still learn inter-area routes (Type 3 LSAs). The administrator wants to reduce the routing table size. Which OSPF area type should be configured for area 1?
⚠ Common exam trap
The N10-009 exam often tests the distinction between stub and totally stubby areas, where candidates mistakenly choose totally stubby when they only need to block external routes but still require inter-area routes.
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 while still allowing Type 3 LSAs (inter-area routes). This meets the requirement of preventing external routes from the ASBR in area 0 from being learned by routers in area 1, while still permitting inter-area routing and reducing the routing table size.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Stub area
Why this is correct
A stub area is designed to reduce the routing table size within an OSPF area by preventing the flooding of Type 5 External LSAs, which represent routes learned from outside the OSPF domain. Instead of individual external routes, the Area Border Router (ABR) connected to a stub area injects a default route (0.0.0.0/0) as a Type 3 LSA. This allows routers within the stub area to reach external destinations while still learning inter-area routes (Type 3 LSAs) from other OSPF areas, thus optimizing resource usage without isolating them from the rest of the OSPF domain.
- ✗
Totally stubby area
Why it's wrong here
A Totally Stubby Area (TSA) is a more restrictive variant of a stub area, designed for maximum routing table reduction. It blocks both Type 5 External LSAs and Type 3 Summary LSAs (inter-area routes) from entering the area. All external and inter-area destinations are reached via a single default route (0.0.0.0/0) injected by the ABR. While this significantly minimizes routing table entries, it would prevent routers in the area from learning specific inter-area routes, which contradicts the scenario's implied need for inter-area connectivity beyond a default route.
When this WOULD be correct
A totally stubby area would be correct when the requirement is to block both external and inter-area routes, allowing only a default route into the area, such as when an area has only one exit point and you want to minimize the routing table as much as possible.
- ✗
Not-so-stubby-area (NSSA)
Why it's wrong here
Configuring Area 1 as a Not-so-stubby-area is incorrect because, while it blocks Type 5 external LSAs from entering and permits Type 3 inter-area LSAs, the scenario does not indicate a need for an ASBR within Area 1 to inject external routes. NSSA's defining feature is allowing an internal ASBR to originate Type 7 LSAs, which are then translated at the ABR. This option is tempting as it does block external routes, but it is specifically designed for scenarios where an ASBR resides within the stub-like area itself, a condition not present here.
When this WOULD be correct
A question where an ASBR is inside the NSSA (area 1) and needs to inject external routes into OSPF, but the area must still block Type 5 LSAs from other areas. For example: 'An administrator wants to allow redistribution of external routes from a router within area 1 while preventing Type 5 LSAs from other areas. Which area type?'
- ✗
Normal area
Why it's wrong here
A normal area does not block any LSA types; it would receive both Type 3 and Type 5 LSAs, which does not meet the requirement to reduce routing table size by blocking Type 5 LSAs.
When this WOULD be correct
When the requirement is to allow all OSPF route types (including external routes) and there is no need to reduce routing table size, a normal area is appropriate.
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 designed to reduce the routing table size within an OSPF area by preventing the flooding of Type 5 External LSAs, which represent routes learned from outside the OSPF domain. Instead of individual external routes, the Area Border Router (ABR) connected to a stub area injects a default route (0.0.0.0/0) as a Type 3 LSA. This allows routers within the stub area to reach external destinations while still learning inter-area routes (Type 3 LSAs) from other OSPF areas, thus optimizing resource usage without isolating them from the rest of the OSPF domain.
✗Totally stubby areaWrong answer — click to see why▾
Why this is wrong here
A totally stubby area blocks both Type 5 LSAs (external routes) and Type 3 LSAs (inter-area routes), but the question requires that inter-area routes (Type 3 LSAs) still be learned.
★ When this WOULD be the correct answer
A totally stubby area would be correct when the requirement is to block both external and inter-area routes, allowing only a default route into the area, such as when an area has only one exit point and you want to minimize the routing table as much as possible.
Why candidates choose this
Candidates may confuse 'stub' with 'totally stubby' and think that blocking external routes automatically implies blocking inter-area routes, or they may overestimate the need to reduce routing table size without carefully reading the requirement to keep inter-area routes.
✗Not-so-stubby-area (NSSA)Wrong answer — click to see why▾
Why this is wrong here
An NSSA allows Type 7 LSAs (which are converted to Type 5) and does not block external routes from an ASBR in area 0; it only prevents Type 5 LSAs from other areas while allowing redistribution. The question requires blocking all external routes (Type 5 LSAs) from area 0, which a stub area does by default, but an NSSA does not.
★ When this WOULD be the correct answer
A question where an ASBR is inside the NSSA (area 1) and needs to inject external routes into OSPF, but the area must still block Type 5 LSAs from other areas. For example: 'An administrator wants to allow redistribution of external routes from a router within area 1 while preventing Type 5 LSAs from other areas. Which area type?'
Why candidates choose this
Candidates may confuse NSSA with stub area, thinking NSSA also blocks all external routes, but they remember that NSSA allows some external routes (via Type 7), which seems like a compromise. They might also think the 'not-so-stubby' name implies it is a variation of stub that still blocks external routes, but it actually allows them from within the area.
✗Normal areaWrong answer — click to see why▾
Why this is wrong here
A normal area allows all LSA types, including Type 5 external LSAs, so the router in area 1 would still learn external routes, failing the requirement to block them.
★ When this WOULD be the correct answer
When the requirement is to allow all OSPF route types (including external routes) and there is no need to reduce routing table size, a normal area is appropriate.
Why candidates choose this
Candidates may default to a normal area because it is the default OSPF area type, without considering the need to filter external routes.
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
Routing table
A routing table is a data set stored in a router or host that contains information about network paths and is used to determine where to forward data packets.
Key term
Router
A router is a networking device that connects different networks together and directs data traffic between them by choosing the best path for data to travel.
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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.