Question 935 of 2,152

IPv6 First Hop Security →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that ND Inspection is configured to drop Neighbor Solicitations with an unspecified source address (::) because it has no binding for that address. This occurs because Duplicate Address Detection (DAD) inherently uses the unspecified source address (::) when a host probes for a duplicate address, and ND Inspection, which validates traffic against the binding table, sees no entry for that source and drops the packet. In the context of the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of IPv6 First Hop Security interactions, specifically how ND Inspection and ND Suppress work together—a common trap is confusing ND Suppress (which only suppresses advertisements) with ND Inspection (which enforces bindings). The key distinction is that DAD solicitations are dropped not by ND Suppress, but by ND Inspection’s default behavior toward unbound unspecified addresses. Memory tip: DAD uses ::, and ND Inspection says “no binding, no passing.”

300-410 IPv6 First Hop Security Practice Question

This 300-410 practice question tests your understanding of ipv6 first hop security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

A network engineer is troubleshooting an issue where IPv6 hosts are unable to perform Duplicate Address Detection (DAD) successfully. The switch is configured with IPv6 First Hop Security features including ND Inspection and ND Suppress. The engineer notices that Neighbor Solicitation messages for DAD are being dropped by the switch. What is the most likely cause?

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.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1hardmultiple choice

Study the full IPv6 explanation →

A
ND Inspection is configured to drop Neighbor Solicitations with an unspecified source address (::) because it has no binding for that address.
Correct because ND Inspection typically requires a valid binding for the source address; DAD uses :: as source, which is not in the binding table, causing drops.
B
RA Guard is configured to drop all multicast traffic, including Neighbor Solicitations.
Why wrong: Incorrect because RA Guard only filters Router Advertisements and Redirect messages, not Neighbor Solicitations.
C
DHCPv6 Guard is blocking the DAD messages because they are considered DHCPv6 traffic.
Why wrong: Incorrect because DHCPv6 Guard only filters DHCPv6 messages, not Neighbor Discovery messages.
D
IPv6 Source Guard is dropping the DAD messages because the source address :: is not in the binding table.
Why wrong: Incorrect because IPv6 Source Guard filters data traffic based on source address, but DAD messages are control plane and typically not filtered by Source Guard; ND Inspection is the correct feature.

Full breakdown with real-world context →

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

✓

ND Inspection is configured to drop Neighbor Solicitations with an unspecified source address (::) because it has no binding for that address.

ND Suppress is a feature that suppresses Neighbor Advertisements for addresses that are in the binding table. However, if ND Inspection is misconfigured, it may drop Neighbor Solicitations that are part of DAD because the source address is the unspecified address (::) and the switch may not have a binding for it.

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.

✓
ND Inspection is configured to drop Neighbor Solicitations with an unspecified source address (::) because it has no binding for that address.
Why this is correct
Correct because ND Inspection typically requires a valid binding for the source address; DAD uses :: as source, which is not in the binding table, causing drops.
Clue confirmation
The clue words "first", "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
RA Guard is configured to drop all multicast traffic, including Neighbor Solicitations.
Why it's wrong here
Incorrect because RA Guard only filters Router Advertisements and Redirect messages, not Neighbor Solicitations.
✗
DHCPv6 Guard is blocking the DAD messages because they are considered DHCPv6 traffic.
Why it's wrong here
Incorrect because DHCPv6 Guard only filters DHCPv6 messages, not Neighbor Discovery messages.
✗
IPv6 Source Guard is dropping the DAD messages because the source address :: is not in the binding table.
Why it's wrong here
Incorrect because IPv6 Source Guard filters data traffic based on source address, but DAD messages are control plane and typically not filtered by Source Guard; ND Inspection is the correct feature.

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 300-410 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 300-410 question test?

IPv6 First Hop Security — This question tests IPv6 First Hop Security — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: ND Inspection is configured to drop Neighbor Solicitations with an unspecified source address (::) because it has no binding for that address. — ND Suppress is a feature that suppresses Neighbor Advertisements for addresses that are in the binding table. However, if ND Inspection is misconfigured, it may drop Neighbor Solicitations that are part of DAD because the source address is the unspecified address (::) and the switch may not have a binding for it.

What should I do if I get this 300-410 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "first", "most likely". 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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