Question 1mediumdrag order
Review the full OSPF breakdown →Question 904 of 2,015
Quick Answer
The answer is that the final step of OSPFv3 neighbor formation is sending Link State Acknowledgment packets. This is correct because OSPFv3, like its IPv4 counterpart, uses a reliable flooding mechanism where every Link State Update must be explicitly acknowledged to ensure the link-state database is synchronized. The full OSPFv3 neighbor formation steps follow a strict sequence: Hello exchange to discover neighbors, Database Description packets to summarize the LSDB, Link State Requests for missing LSAs, Link State Updates to deliver them, and finally Link State Acknowledgments to confirm receipt. On the ENCOR 350-401 exam, this drag-and-drop question tests your ability to sequence the IPv6 adjacency steps without confusing them with the OSPFv2 process or the DR/BDR election, which occurs after adjacency. A common trap is placing the acknowledgment before the update, but remember that updates must be received before they can be confirmed. For a quick memory tip, think of the mnemonic “Hello, Describe, Request, Update, Acknowledge” — or simply “H-D-R-U-A” to lock in the correct order.
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.
Drag and drop the steps of OSPFv3 IPv6 neighbor adjacency formation into the correct order, from first to last.
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"first"Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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
✓
Send Hello packets on IPv6 link
OSPFv3 neighbor formation begins with the router sending Hello packets on the link. The neighbor receives the Hello and replies with its own Hello, including the router ID. Both routers then exchange Database Description packets to summarize their LSDB. Link State Request packets are sent for missing LSAs, and Link State Update packets provide the requested LSAs. Finally, Link State Acknowledgment packets confirm receipt, completing the adjacency.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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: Send Hello packets on IPv6 link — OSPFv3 neighbor formation begins with the router sending Hello packets on the link. The neighbor receives the Hello and replies with its own Hello, including the router ID. Both routers then exchange Database Description packets to summarize their LSDB. Link State Request packets are sent for missing LSAs, and Link State Update packets provide the requested LSAs. Finally, Link State Acknowledgment packets confirm receipt, completing the adjacency.
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.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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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. Drag and drop the steps of OSPFv3 IPv6 neighbor adjacency formation into the correct order, from first to last.
medium- ✓ A.Router sends Hello with its router ID
- ✓ B.Neighbor seen in Hello, state becomes 2-Way
- ✓ C.Master/slave negotiation in ExStart
- ✓ D.Exchange DBD packets describing LSDB
- ✓ E.Send LSR, receive LSU, become Full
Why A: OSPFv3 neighbor formation follows the same state machine as OSPFv2: Down, Init, 2-Way, ExStart, Exchange, Loading, Full. The steps reflect the key actions at each state.
Last reviewed: Jun 18, 2026
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