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IPv6 First Hop Security →hardMultiple ChoiceObjective-mapped

300-410 IPv6 First Hop Security Practice Question

This 300-410 practice question tests your understanding of ipv6 first hop security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 administrator configures 'ipv6 dhcp guard' on a switch and sets the policy to 'allow only' for a specific DHCPv6 server. However, clients are still receiving DHCPv6 replies from a rogue server on the same VLAN. The engineer verifies that the rogue server's port is not trusted. What is the most likely reason the rogue server's advertisements are not being blocked?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

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.

A
IPv6 snooping is not enabled globally, so DHCPv6 Guard cannot inspect DHCPv6 messages.
DHCPv6 Guard depends on IPv6 snooping for packet inspection.
B
The rogue server is using a different UDP port for DHCPv6.
Why wrong: DHCPv6 uses well-known ports 546 and 547.
C
The 'allow only' policy only works for DHCPv6 requests, not replies.
Why wrong: It works for both.
D
The rogue server is on a trunk port, and DHCPv6 Guard does not apply to trunk ports.
Why wrong: It applies to all ports.

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

✓

IPv6 snooping is not enabled globally, so DHCPv6 Guard cannot inspect DHCPv6 messages.

DHCPv6 Guard relies on IPv6 snooping (also known as DHCPv6 snooping) to inspect DHCPv6 messages and enforce policies. If IPv6 snooping is not enabled globally on the switch, DHCPv6 Guard has no binding database or inspection mechanism to identify and block rogue DHCPv6 replies, even if the policy is configured and the rogue port is untrusted. The 'ipv6 dhcp guard' command alone is insufficient without the underlying snooping framework.

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.

✓
IPv6 snooping is not enabled globally, so DHCPv6 Guard cannot inspect DHCPv6 messages.
Why this is correct
DHCPv6 Guard depends on IPv6 snooping for packet inspection.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The rogue server is using a different UDP port for DHCPv6.
Why it's wrong here
DHCPv6 uses well-known ports 546 and 547.
✗
The 'allow only' policy only works for DHCPv6 requests, not replies.
Why it's wrong here
It works for both.
✗
The rogue server is on a trunk port, and DHCPv6 Guard does not apply to trunk ports.
Why it's wrong here
It applies to all ports.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the prerequisite dependency between IPv6 snooping and DHCPv6 Guard, trapping candidates who assume that configuring the guard policy alone is sufficient to block rogue servers.

Detailed technical explanation

How to think about this question

DHCPv6 Guard is part of the IPv6 First Hop Security (FHS) suite and requires IPv6 snooping to maintain a binding table of legitimate DHCPv6 servers and clients. Without 'ipv6 snooping' enabled globally, the switch cannot perform the necessary packet validation (e.g., checking source MAC against DHCP Unique Identifier) to enforce the 'allow only' policy. In real-world deployments, administrators often forget to enable IPv6 snooping as a prerequisite, leading to this exact failure scenario.

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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.

Visual reference

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: IPv6 snooping is not enabled globally, so DHCPv6 Guard cannot inspect DHCPv6 messages. — DHCPv6 Guard relies on IPv6 snooping (also known as DHCPv6 snooping) to inspect DHCPv6 messages and enforce policies. If IPv6 snooping is not enabled globally on the switch, DHCPv6 Guard has no binding database or inspection mechanism to identify and block rogue DHCPv6 replies, even if the policy is configured and the rogue port is untrusted. The 'ipv6 dhcp guard' command alone is insufficient without the underlying snooping framework.

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

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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