- A
A stub area blocks Type 5 AS External LSAs but allows Type 3 Summary LSAs and a default route.
Correct because stub areas are designed to reduce the LSDB by preventing Type 5 LSAs, while still receiving inter-area routes via Type 3 and a default route.
- B
A totally stubby area blocks both Type 5 and Type 3 LSAs, injecting only a default route into the area.
Correct because totally stubby areas further restrict Type 3 LSAs (except the default route), minimizing the LSDB size.
- C
A not-so-stubby-area (NSSA) allows Type 5 LSAs to be imported from external networks.
Why wrong: Incorrect because NSSA blocks Type 5 LSAs but allows Type 7 LSAs to carry external routes, which are then translated to Type 5 by the ABR.
- D
A standard area can contain Type 1, 2, 3, 4, and 5 LSAs.
Correct because a standard (non-stub) area has no restrictions and can carry all OSPF LSA types.
- E
A totally NSSA blocks Type 3 LSAs but allows Type 5 LSAs from external sources.
Why wrong: Incorrect because a totally NSSA blocks both Type 3 and Type 5 LSAs, using Type 7 for external routes and injecting a default route.
Quick Answer
The correct answer is that a standard area can contain Type 1, 2, 3, 4, and 5 LSAs, as this is the baseline for all OSPF area types. This is correct because OSPF area types like stub, NSSA, and totally stubby are designed to restrict LSA propagation to reduce routing table size and CPU load; a standard area has no such restrictions, allowing full visibility of all routes. On the ENCOR 350-401 exam, this concept tests your ability to differentiate how each area type filters LSAs—a common trap is confusing which LSAs a stub area blocks (Type 5 only) versus a totally stubby area (Type 5 and Type 3, except a default). For memory, remember that "stub" stops Type 5s, "totally stubby" stops both Type 5 and Type 3, and NSSA swaps Type 5 for Type 7. A quick mnemonic: "Standard sees all, Stub stops 5, Totally Stubby stops 3 and 5, NSSA swaps 5 for 7."
350-401 OSPF Practice Question
This 350-401 practice question tests your understanding of ospf. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 three statements about OSPF area types are correct? (Choose three.)
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
A stub area blocks Type 5 AS External LSAs but allows Type 3 Summary LSAs and a default route.
OSPF area types control the propagation of LSAs. A standard area can carry all LSA types. A stub area blocks Type 5 LSAs but allows Type 3. A totally stubby area blocks both Type 5 and Type 3 (except a default route). A not-so-stubby-area (NSSA) blocks Type 5 but allows Type 7 for external routes. A totally NSSA further blocks Type 3.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A stub area blocks Type 5 AS External LSAs but allows Type 3 Summary LSAs and a default route.
Why this is correct
Correct because stub areas are designed to reduce the LSDB by preventing Type 5 LSAs, while still receiving inter-area routes via Type 3 and a default route.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
A totally stubby area blocks both Type 5 and Type 3 LSAs, injecting only a default route into the area.
Why this is correct
Correct because totally stubby areas further restrict Type 3 LSAs (except the default route), minimizing the LSDB size.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
A not-so-stubby-area (NSSA) allows Type 5 LSAs to be imported from external networks.
Why it's wrong here
Incorrect because NSSA blocks Type 5 LSAs but allows Type 7 LSAs to carry external routes, which are then translated to Type 5 by the ABR.
- ✓
A standard area can contain Type 1, 2, 3, 4, and 5 LSAs.
- ✗
A totally NSSA blocks Type 3 LSAs but allows Type 5 LSAs from external sources.
Why it's wrong here
Incorrect because a totally NSSA blocks both Type 3 and Type 5 LSAs, using Type 7 for external routes and injecting a default route.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-401 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 350-401 question test?
OSPF — This question tests OSPF — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: A stub area blocks Type 5 AS External LSAs but allows Type 3 Summary LSAs and a default route. — OSPF area types control the propagation of LSAs. A standard area can carry all LSA types. A stub area blocks Type 5 LSAs but allows Type 3. A totally stubby area blocks both Type 5 and Type 3 (except a default route). A not-so-stubby-area (NSSA) blocks Type 5 but allows Type 7 for external routes. A totally NSSA further blocks Type 3.
What should I do if I get this 350-401 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-401 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
This 350-401 practice question is part of Courseiva's free Cisco 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 350-401 exam.
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