Question 2,152 of 2,152

IPv6 First Hop Security →mediumMultiple ChoiceObjective-mapped

300-410 IPv6 First Hop Security Practice Question

This 300-410 practice question tests your understanding of ipv6 first hop security. 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.

In IPv6 First Hop Security, which feature is used to prevent duplicate address detection (DAD) attacks by snooping Neighbor Discovery (ND) messages?

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.

A
RA Guard
Why wrong: RA Guard filters Router Advertisements to prevent rogue RA attacks, but it does not specifically prevent DAD attacks via snooping.
B
DHCPv6 Guard
Why wrong: DHCPv6 Guard filters DHCPv6 messages to prevent rogue DHCP servers, not DAD attacks.
C
ND Snooping
Correct. ND Snooping monitors ND messages to prevent DAD attacks and other ND-based threats.
D
Source Guard
Why wrong: Source Guard filters traffic based on the source address and binding table, but it is not specifically for DAD attack prevention.

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 Snooping

C is correct because ND Snooping (Neighbor Discovery Snooping) is the IPv6 First Hop Security feature that prevents duplicate address detection (DAD) attacks by inspecting Neighbor Solicitation (NS) and Neighbor Advertisement (NA) messages. It builds a binding table of valid IPv6-to-MAC address mappings and drops any NS messages that attempt to claim an address already in use by another device, thereby blocking DAD-based spoofing attacks.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
RA Guard
Why it's wrong here
RA Guard filters Router Advertisements to prevent rogue RA attacks, but it does not specifically prevent DAD attacks via snooping.
✗
DHCPv6 Guard
Why it's wrong here
DHCPv6 Guard filters DHCPv6 messages to prevent rogue DHCP servers, not DAD attacks.
✓
ND Snooping
Why this is correct
Correct. ND Snooping monitors ND messages to prevent DAD attacks and other ND-based threats.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Source Guard
Why it's wrong here
Source Guard filters traffic based on the source address and binding table, but it is not specifically for DAD attack prevention.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse ND Snooping with RA Guard or DHCPv6 Guard, thinking any 'Guard' feature handles DAD attacks, but only ND Snooping directly inspects Neighbor Discovery messages used in the DAD process.

Detailed technical explanation

How to think about this question

ND Snooping works by intercepting Neighbor Solicitation messages sent during DAD (with an unspecified source address ::) and verifying that the target address is not already present in the snooping binding table. If a duplicate is detected, the NS is dropped, preventing the attacker from claiming an address already in use. This feature is configured globally and per interface using the 'ipv6 nd snooping' command, and it relies on the switch maintaining a binding table that is also used by IPv6 Source Guard and IPv6 Device Tracking.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.

Quick reference

Access Control Model Comparison

Model	Acronym	Who Controls Access?	Best For
Discretionary Access Control	DAC	Resource owner	Small teams, file shares
Mandatory Access Control	MAC	System / security labels	Classified govt / military
Role-Based Access Control	RBAC	Administrator (via roles)	Enterprise environments
Attribute-Based Access Control	ABAC	Policy engine (user + resource attributes)	Fine-grained, dynamic policies
Rule-Based Access Control	RuBAC	System rules / ACLs	Firewall rules, network ACLs

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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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 — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: ND Snooping — C is correct because ND Snooping (Neighbor Discovery Snooping) is the IPv6 First Hop Security feature that prevents duplicate address detection (DAD) attacks by inspecting Neighbor Solicitation (NS) and Neighbor Advertisement (NA) messages. It builds a binding table of valid IPv6-to-MAC address mappings and drops any NS messages that attempt to claim an address already in use by another device, thereby blocking DAD-based spoofing attacks.

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

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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?

Read the scenario before looking for a memorised answer.

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