This 200-901 practice question tests your understanding of network fundamentals. 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.
An IPv6-enabled host is trying to discover the MAC address of another host on the same link. The host knows the destination IPv6 address but does not have a corresponding entry in the neighbor cache. Which protocol and message type does the host use?
Neighbor Advertisement (ICMPv6 type 136)
Why wrong: NA is the reply, not the request.
Router Solicitation (ICMPv6 type 133)
Why wrong: RS is for router discovery.
Neighbor Solicitation (ICMPv6 type 135)
NS is used for address resolution.
Address Resolution Protocol (ARP)
Why wrong: IPv6 does not use ARP.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Neighbor Solicitation (ICMPv6 type 135)
Neighbor Solicitation (NS) is used in IPv6 for address resolution, similar to ARP in IPv4. It is an ICMPv6 message of type 135. Option A is wrong because Neighbor Advertisement (NA) is the reply. Option B is wrong because Router Solicitation (RS) is for discovering routers. Option D is wrong because ARP is not used in IPv6.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Neighbor Advertisement (ICMPv6 type 136)
Why it's wrong here
NA is the reply, not the request.
Router Solicitation (ICMPv6 type 133)
Why it's wrong here
RS is for router discovery.
Neighbor Solicitation (ICMPv6 type 135)
Why this is correct
NS is used for address resolution.
Related concept
OSPF neighbours must agree on key parameters.
Address Resolution Protocol (ARP)
Why it's wrong here
IPv6 does not use ARP.
Common exam traps
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
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.
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
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
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 200-901 OSPF questions on adjacency and route selection.
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FAQ
Network Fundamentals — This question tests Network Fundamentals — OSPF neighbours must agree on key parameters..
The correct answer is: Neighbor Solicitation (ICMPv6 type 135) — Neighbor Solicitation (NS) is used in IPv6 for address resolution, similar to ARP in IPv4. It is an ICMPv6 message of type 135. Option A is wrong because Neighbor Advertisement (NA) is the reply. Option B is wrong because Router Solicitation (RS) is for discovering routers. Option D is wrong because ARP is not used in IPv6.
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 200-901 OSPF questions on adjacency and route selection.
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 24, 2026
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