- A
The 2-Way state indicates that both routers have seen their own router ID in the neighbor's hello packet.
Correct because 2-Way confirms bidirectional communication, which is required before proceeding to database synchronization.
- B
The Full state indicates that the routers have synchronized their LSDBs and are fully adjacent.
Correct because Full is the final adjacency state where both routers have identical link-state databases.
- C
In the ExStart state, routers exchange Database Description packets containing LSA headers.
Why wrong: Incorrect because ExStart establishes the master/slave relationship and initial sequence numbers; DBD exchange occurs in the Exchange state.
- D
In the Exchange state, routers send Link State Requests and receive Link State Updates.
Why wrong: Incorrect because LSRs and LSUs are exchanged in the Loading state, not the Exchange state.
- E
The Down state is the final state when a neighbor is unreachable.
Why wrong: Incorrect because Down is the initial state; when a neighbor becomes unreachable, the state transitions to Down but it is not the final state in the normal progression.
Quick Answer
The correct answer is that the Full state indicates synchronized LSDBs and full adjacency, while the 2-Way state confirms bidirectional hello packet reception. In OSPF, the 2-Way state is reached when both routers see their own Router ID in the neighbor’s hello packet, proving two-way communication is established. The Full state, by contrast, means the routers have completed LSA exchange and their link-state databases are identical, forming a fully adjacent relationship. On the ENCOR 350-401 exam, this distinction tests your understanding of OSPF neighbor state progression, often appearing in multiple-choice questions that pair these two states as correct. A common trap is confusing the 2-Way state with adjacency—remember that 2-Way is only for broadcast networks and does not imply database synchronization. A helpful memory tip: “2-Way for hello, Full for sync.”
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 two statements about OSPF neighbor states are true? (Choose two.)
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
The 2-Way state indicates that both routers have seen their own router ID in the neighbor's hello packet.
Option A is correct because the 2-Way state indicates that both routers have received each other's hello packets, confirming bidirectional communication. Option B is correct because the Full state means that the routers have exchanged all LSAs and their databases are synchronized. Option C is incorrect because the ExStart state is where the master/slave relationship is established, not where LSAs are exchanged. Option D is incorrect because the Loading state is where LSRs and LSUs are exchanged, not the Exchange state. Option E is incorrect because the Down state is the initial state before any hello packets are received.
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.
- ✓
The 2-Way state indicates that both routers have seen their own router ID in the neighbor's hello packet.
Why this is correct
Correct because 2-Way confirms bidirectional communication, which is required before proceeding to database synchronization.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
The Full state indicates that the routers have synchronized their LSDBs and are fully adjacent.
Why this is correct
Correct because Full is the final adjacency state where both routers have identical link-state databases.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
In the ExStart state, routers exchange Database Description packets containing LSA headers.
Why it's wrong here
Incorrect because ExStart establishes the master/slave relationship and initial sequence numbers; DBD exchange occurs in the Exchange state.
- ✗
In the Exchange state, routers send Link State Requests and receive Link State Updates.
Why it's wrong here
Incorrect because LSRs and LSUs are exchanged in the Loading state, not the Exchange state.
- ✗
The Down state is the final state when a neighbor is unreachable.
Why it's wrong here
Incorrect because Down is the initial state; when a neighbor becomes unreachable, the state transitions to Down but it is not the final state in the normal progression.
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: The 2-Way state indicates that both routers have seen their own router ID in the neighbor's hello packet. — Option A is correct because the 2-Way state indicates that both routers have received each other's hello packets, confirming bidirectional communication. Option B is correct because the Full state means that the routers have exchanged all LSAs and their databases are synchronized. Option C is incorrect because the ExStart state is where the master/slave relationship is established, not where LSAs are exchanged. Option D is incorrect because the Loading state is where LSRs and LSUs are exchanged, not the Exchange state. Option E is incorrect because the Down state is the initial state before any hello packets are received.
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.
About these practice questions
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Same concept, more angles
1 more ways this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which two statements about OSPF neighbor states are true? (Choose two.)
medium- ✓ A.The 2-Way state indicates that the router has received a Hello packet from the neighbor with its own Router ID in the neighbor list.
- B.In the ExStart state, routers exchange Database Description (DBD) packets to describe their LSDB contents.
- ✓ C.The Full state means the routers have synchronized their link-state databases and are fully adjacent.
- D.The Loading state occurs before the Exchange state in the neighbor state machine.
- E.The Down state means the router has received a Hello packet from the neighbor but has not yet established two-way communication.
Why A: OSPF neighbor state machine progresses through several states. The 2-Way state indicates bidirectional communication has been established. The Full state means the routers have exchanged complete LSDB information. The ExStart state is where the master/slave relationship is determined. The Loading state occurs after the Database Description (DBD) exchange.
Last reviewed: Jun 18, 2026
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