hardMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting an issue where IPv6 hosts are…
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?
⚠ Common exam trap
Cisco often tests the distinction between ND Inspection and IPv6 Source Guard, where candidates mistakenly think Source Guard drops DAD messages, but it is actually ND Inspection that drops Neighbor Solicitations with an unspecified source address due to missing bindings.
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 Inspection drops Neighbor Solicitations with an unspecified source address (::) because it requires a valid binding for the source address in its binding table. During Duplicate Address Detection (DAD), the source address is :: (RFC 4862), which has no corresponding binding, causing ND Inspection to drop the message and preventing DAD from completing.
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.