The answer is a stub area. This OSPF area type is the correct choice because it blocks Type 5 LSAs, which carry external routes from other autonomous systems, while still allowing Type 3 summary LSAs from area 0. This configuration ensures routers in area 2 can reach networks in area 0 via inter-area routes but never learn external routes, perfectly matching the design requirement. On the ENCOR 350-401 exam, this concept tests your understanding of OSPF LSA types and area filtering, often appearing in scenario-based questions where you must distinguish between stub, totally stubby, and NSSA areas. A common trap is confusing a stub area with a totally stubby area—remember that a stub area still accepts Type 3 inter-area summaries, while a totally stubby area blocks both Type 5 and Type 3 LSAs except for a default route. For a quick memory tip: think "Stub stops Type 5s, but keeps the summaries."
350-401 OSPF Practice Question
This 350-401 practice question tests your understanding of ospf. 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 with multiple areas. The engineer wants to ensure that routers in area 2 can reach networks in area 0, but they should not learn any external routes from other ASs. Which OSPF area type should be configured for area 2?
Correct because a stub area blocks type 5 LSAs, preventing external routes from being learned, and uses a default route for external destinations.
B
Not-so-stubby area (NSSA)
Why wrong: Incorrect because NSSA allows import of external routes as type 7 LSAs, which does not meet the requirement of not learning external routes.
C
Totally stubby area
Why wrong: Incorrect because a totally stubby area blocks both type 3 and type 5 LSAs, which would prevent learning networks in area 0 as well.
D
Standard area
Why wrong: Incorrect because a standard area allows all LSA types, including type 5 external routes.
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 other ASs) while allowing Type 3 summary LSAs from area 0. This ensures routers in area 2 can reach networks in area 0 via inter-area routes but do not learn external routes, meeting the requirement exactly.
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.
✓
Stub area
Why this is correct
Correct because a stub area blocks type 5 LSAs, preventing external routes from being learned, and uses a default route for external destinations.
Related concept
Read the scenario before looking for a memorised answer.
✗
Not-so-stubby area (NSSA)
Why it's wrong here
Incorrect because NSSA allows import of external routes as type 7 LSAs, which does not meet the requirement of not learning external routes.
✗
Totally stubby area
Why it's wrong here
Incorrect because a totally stubby area blocks both type 3 and type 5 LSAs, which would prevent learning networks in area 0 as well.
✗
Standard area
Why it's wrong here
Incorrect because a standard area allows all LSA types, including type 5 external routes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between stub and totally stubby areas: candidates confuse 'blocking external routes' with 'blocking all routes except the default,' forgetting that a stub area still allows inter-area summary LSAs (Type 3) from area 0.
Detailed technical explanation
How to think about this question
Under the hood, a stub area sets the E-bit in the OSPF Hello and DBD packets to 0, signaling that no Type 5 LSAs should be flooded. The ABR for a stub area generates a default route (Type 3 LSA with 0.0.0.0/0) to provide connectivity to external destinations, but the area itself never sees external LSAs. In real-world designs, stub areas are commonly used in hub-and-spoke topologies to reduce the routing table size and memory usage on lower-end routers.
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 350-401 question in full detail.
OSPF — This question tests OSPF — 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 other ASs) while allowing Type 3 summary LSAs from area 0. This ensures routers in area 2 can reach networks in area 0 via inter-area routes but do not learn external routes, meeting the requirement exactly.
What should I do if I get this 350-401 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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