Question 138 of 2,152

IPv6 First Hop Security →hardMultiple SelectObjective-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.

Which TWO statements about IPv6 First Hop Security (FHS) Source Guard are true? (Choose TWO.)

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
IPv6 Source Guard dynamically creates binding entries for all IPv6 addresses learned via ND.
Why wrong: Incorrect. Source Guard does not create bindings; it relies on DHCPv6 snooping or ND snooping to populate the binding table.
B
IPv6 Source Guard uses the IPv6 binding table to permit or deny traffic based on source address.
Correct. Source Guard checks the source IPv6 address and MAC against the binding table and drops unauthorized traffic.
C
IPv6 Source Guard filters traffic based on the destination IPv6 address in the packet.
Why wrong: Incorrect. Source Guard filters based on source address, not destination.
D
IPv6 Source Guard can be enabled on a per-interface or per-VLAN basis.
Correct. The 'ipv6 source-guard' command can be applied to an interface or a VLAN.
E
IPv6 Source Guard only works with addresses learned via DHCPv6.
Why wrong: Incorrect. It can also work with addresses learned via ND snooping, not just DHCPv6.

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 Source Guard uses the IPv6 binding table to permit or deny traffic based on source address.

IPv6 Source Guard uses the IPv6 binding table (populated by ND snooping and/or DHCPv6 snooping) to permit or deny traffic based on the source IPv6 address in the packet. This prevents spoofing attacks by ensuring that only traffic from legitimate, learned source addresses is forwarded, similar to IPv4 Source Guard.

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 Source Guard dynamically creates binding entries for all IPv6 addresses learned via ND.
Why it's wrong here
Incorrect. Source Guard does not create bindings; it relies on DHCPv6 snooping or ND snooping to populate the binding table.
✓
IPv6 Source Guard uses the IPv6 binding table to permit or deny traffic based on source address.
Why this is correct
Correct. Source Guard checks the source IPv6 address and MAC against the binding table and drops unauthorized traffic.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
IPv6 Source Guard filters traffic based on the destination IPv6 address in the packet.
Why it's wrong here
Incorrect. Source Guard filters based on source address, not destination.
✓
IPv6 Source Guard can be enabled on a per-interface or per-VLAN basis.
Why this is correct
Correct. The 'ipv6 source-guard' command can be applied to an interface or a VLAN.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
IPv6 Source Guard only works with addresses learned via DHCPv6.
Why it's wrong here
Incorrect. It can also work with addresses learned via ND snooping, not just DHCPv6.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that IPv6 Source Guard creates its own bindings or only works with DHCPv6, when in fact it relies on the binding table built by ND snooping and DHCPv6 snooping, and it filters based on source address, not destination.

Detailed technical explanation

How to think about this question

IPv6 Source Guard operates by consulting the IPv6 neighbor binding table, which is populated by ND snooping (for stateless addresses) and DHCPv6 snooping (for stateful addresses). When enabled on an interface, it drops any IPv6 packet whose source address does not have a corresponding binding entry, effectively preventing address spoofing from rogue devices. In real-world deployments, this is critical on access-layer switches to mitigate attacks like ND spoofing or duplicate address detection (DAD) exploitation.

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 Source Guard uses the IPv6 binding table to permit or deny traffic based on source address. — IPv6 Source Guard uses the IPv6 binding table (populated by ND snooping and/or DHCPv6 snooping) to permit or deny traffic based on the source IPv6 address in the packet. This prevents spoofing attacks by ensuring that only traffic from legitimate, learned source addresses is forwarded, similar to IPv4 Source Guard.

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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