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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. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 engineer enables 'ipv6 destination guard' on a switch to prevent IPv6 address spoofing. After configuration, a legitimate host on a port is unable to receive traffic from the network, although it can send traffic. The host has a global unicast address. The switch logs show that destination guard is dropping packets destined to that host. 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: "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
The host uses IPv6 privacy extensions and changes its address frequently, but the binding table only has the original address.
Destination Guard relies on static bindings; privacy addresses are not learned.
B
Destination Guard blocks all global unicast addresses by default.
Why wrong: It only blocks addresses not in the binding table.
C
The switch port is not configured as 'trusted' for destination guard.
Why wrong: Destination Guard does not have a trust concept.
D
The host is using a link-local address, which destination guard does not support.
Why wrong: Destination Guard works with all unicast addresses.

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

✓

The host uses IPv6 privacy extensions and changes its address frequently, but the binding table only has the original address.

Option A is correct because IPv6 destination guard relies on the IPv6 neighbor discovery (ND) binding table to validate destination addresses. If the host uses IPv6 privacy extensions (RFC 4941), it generates temporary addresses that change frequently. The binding table only contains the original address learned from the initial ND exchange, so packets destined to the new temporary address are dropped as spoofed, even though the traffic is legitimate.

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.

✓
The host uses IPv6 privacy extensions and changes its address frequently, but the binding table only has the original address.
Why this is correct
Destination Guard relies on static bindings; privacy addresses are not learned.
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.
✗
Destination Guard blocks all global unicast addresses by default.
Why it's wrong here
It only blocks addresses not in the binding table.
✗
The switch port is not configured as 'trusted' for destination guard.
Why it's wrong here
Destination Guard does not have a trust concept.
✗
The host is using a link-local address, which destination guard does not support.
Why it's wrong here
Destination Guard works with all unicast addresses.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the interaction between IPv6 first-hop security features and privacy extensions, where candidates mistakenly think the issue is a trust configuration or address type rather than the dynamic nature of temporary addresses in the binding table.

Detailed technical explanation

How to think about this question

IPv6 destination guard inspects the destination IPv6 address of incoming packets and compares it against the ND binding table, which is populated by snooping Neighbor Solicitation and Advertisement messages. When privacy extensions generate a new temporary address, the host sends Neighbor Advertisements for that address, but the switch may not update the binding table if it only learns from the initial Duplicate Address Detection (DAD) process. In real-world deployments, this can cause intermittent connectivity for hosts with privacy extensions unless the switch is configured to learn from all ND messages or the binding table is refreshed dynamically.

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.

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: The host uses IPv6 privacy extensions and changes its address frequently, but the binding table only has the original address. — Option A is correct because IPv6 destination guard relies on the IPv6 neighbor discovery (ND) binding table to validate destination addresses. If the host uses IPv6 privacy extensions (RFC 4941), it generates temporary addresses that change frequently. The binding table only contains the original address learned from the initial ND exchange, so packets destined to the new temporary address are dropped as spoofed, even though the traffic is legitimate.

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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