Question 5 of 2,152

IPv6 First Hop Security →hardMultiple SelectObjective-mapped

Quick Answer

The answer is to add the router’s MAC address to the ND inspection allowed-list and adjust the RA Guard policy to permit the router’s port. SLAAC depends on legitimate Router Advertisements (RAs) from a trusted router; RA Guard blocks RAs from unauthorized ports, while ND inspection drops RAs from unknown MAC addresses, so both features can inadvertently prevent clients from obtaining a valid IPv6 address. On the Cisco CCNP ENARSI 300-410 exam, this question tests your understanding of IPv6 First Hop Security features and how they interact with SLAAC—a common trap is confusing DHCPv6 snooping or Source Guard with RA filtering. Remember that SLAAC uses only RAs, not DHCPv6, so disabling DHCPv6 snooping or configuring a DHCPv6 pool is irrelevant. Memory tip: “RA Guard guards the port, ND inspects the MAC—both must trust the router for SLAAC to work.”

300-410 IPv6 First Hop Security Practice Question

This 300-410 practice question tests your understanding of ipv6 first hop security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is troubleshooting IPv6 connectivity issues on a switch that has IPv6 First Hop Security features enabled. Clients are unable to obtain a valid IPv6 address via SLAAC. Which TWO configuration changes could resolve this issue? (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.

Question 1hardmulti select

Study the full IPv6 explanation →

A
Modify the RA Guard policy to permit Router Advertisements from the trusted router port.
Correct. If RA Guard is blocking legitimate RAs, permitting the trusted port resolves the issue.
B
Disable DHCPv6 snooping on the VLAN to allow RAs to be forwarded.
Why wrong: Incorrect. DHCPv6 snooping does not affect RA forwarding; it only monitors DHCPv6 messages.
C
Enable IPv6 Source Guard on the client-facing interfaces.
Why wrong: Incorrect. Source Guard filters source addresses, not RAs, and would not help with RA delivery.
D
Add the router's MAC address to the ND inspection allowed-list.
Correct. ND inspection can drop RAs from unknown sources; adding the router's MAC allows them.
E
Configure a DHCPv6 pool on the switch to provide addresses to clients.
Why wrong: Incorrect. SLAAC does not use DHCPv6; a DHCPv6 pool is for stateful DHCPv6, not SLAAC.

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

✓

Modify the RA Guard policy to permit Router Advertisements from the trusted router port.

SLAAC relies on Router Advertisements (RAs) from a router. If RA Guard is blocking legitimate RAs, or if ND inspection is dropping them, clients cannot obtain addresses. Option A is correct: if RA Guard is blocking RAs from the legitimate router, adjusting the policy to permit that router's port will fix the issue. Option D is correct: if ND inspection is enabled and the router's MAC is not in the allowed list, adding it will allow RAs to pass. Option B is incorrect: disabling DHCPv6 snooping would not help SLAAC, as SLAAC does not use DHCPv6. Option C is incorrect: enabling IPv6 Source Guard would not help; it filters source addresses, not RAs. Option E is incorrect: configuring a DHCPv6 pool is for stateful DHCPv6, not SLAAC.

Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.

Answer analysis

Option-by-option breakdown

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

✓
Modify the RA Guard policy to permit Router Advertisements from the trusted router port.
Why this is correct
Correct. If RA Guard is blocking legitimate RAs, permitting the trusted port resolves the issue.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
✗
Disable DHCPv6 snooping on the VLAN to allow RAs to be forwarded.
Why it's wrong here
Incorrect. DHCPv6 snooping does not affect RA forwarding; it only monitors DHCPv6 messages.
✗
Enable IPv6 Source Guard on the client-facing interfaces.
Why it's wrong here
Incorrect. Source Guard filters source addresses, not RAs, and would not help with RA delivery.
✓
Add the router's MAC address to the ND inspection allowed-list.
Why this is correct
Correct. ND inspection can drop RAs from unknown sources; adding the router's MAC allows them.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
✗
Configure a DHCPv6 pool on the switch to provide addresses to clients.
Why it's wrong here
Incorrect. SLAAC does not use DHCPv6; a DHCPv6 pool is for stateful DHCPv6, not SLAAC.

Common exam traps

Common exam trap: an active trunk can still block the VLAN you need

A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.

Detailed technical explanation

How to think about this question

VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.

KKey Concepts to Remember

Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.

TExam Day Tips

Use show vlan brief to verify access VLANs.
Use show interfaces trunk to verify trunk state and allowed VLANs.
Do not treat every same-VLAN issue as a routing problem.

Key takeaway

A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.

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.

What to study next

Got this wrong? Here's your next step.

Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 300-410 questions on switching, trunking, and access-port configuration.

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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 — Access ports place end devices into a single VLAN..

What is the correct answer to this question?

The correct answer is: Modify the RA Guard policy to permit Router Advertisements from the trusted router port. — SLAAC relies on Router Advertisements (RAs) from a router. If RA Guard is blocking legitimate RAs, or if ND inspection is dropping them, clients cannot obtain addresses. Option A is correct: if RA Guard is blocking RAs from the legitimate router, adjusting the policy to permit that router's port will fix the issue. Option D is correct: if ND inspection is enabled and the router's MAC is not in the allowed list, adding it will allow RAs to pass. Option B is incorrect: disabling DHCPv6 snooping would not help SLAAC, as SLAAC does not use DHCPv6. Option C is incorrect: enabling IPv6 Source Guard would not help; it filters source addresses, not RAs. Option E is incorrect: configuring a DHCPv6 pool is for stateful DHCPv6, not SLAAC.

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

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?

Access ports place end devices into a single VLAN.

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