The answer is the Link State Update packet, OSPF type 4. This packet is the correct choice because it is the only OSPF packet type specifically designed to carry link-state advertisements (LSAs) and reliably flood them across the OSPF domain. When a router receives a Link State Update, it must reply with a Link State Acknowledgment packet (type 5) to confirm receipt, ensuring database synchronization without retransmission. On the Cisco CCNP ENARSI 300-410 exam, this question tests your understanding of OSPF’s five packet types and their roles in the neighbor state machine and LSA flooding process. A common trap is confusing the Link State Update with the Database Description packet, which only summarizes LSAs during the exchange state, not carry them. To remember, think of the Update as the “delivery truck” carrying the LSAs, and the Acknowledgment as the “signature upon delivery”—type 4 delivers, type 5 confirms.
300-410 OSPF Troubleshooting (v2/v3) Practice Question
This 300-410 practice question tests your understanding of ospf troubleshooting (v2/v3). 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 OSPF packet type is used to send link-state advertisements (LSAs) and is acknowledged by the receiver?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Link State Update (type 4)
OSPF packet type 4 is the Link State Update packet, used to flood LSAs. It is acknowledged by the receiver via a Link State Acknowledgment packet (type 5).
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.
✗
Hello (type 1)
Why it's wrong here
Incorrect. Hello packets are used for neighbor discovery and keepalive, not for sending LSAs.
✗
Database Description (type 2)
Why it's wrong here
Incorrect. Database Description packets summarize the link-state database during adjacency formation.
✗
Link State Request (type 3)
Why it's wrong here
Incorrect. Link State Request packets request specific LSAs from a neighbor.
✓
Link State Update (type 4)
Why this is correct
Correct. Link State Update packets carry LSAs and are acknowledged by the receiver.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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 300-410 OSPF questions on adjacency and route selection.
OSPF Troubleshooting (v2/v3) — This question tests OSPF Troubleshooting (v2/v3) — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Link State Update (type 4) — OSPF packet type 4 is the Link State Update packet, used to flood LSAs. It is acknowledged by the receiver via a Link State Acknowledgment packet (type 5).
What should I do if I get this 300-410 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 300-410 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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