Question 1,224 of 2,152

IPv6 First Hop Security →mediumMultiple SelectObjective-mapped

IPv6 First Hop Security Misconfiguration: Common Symptoms

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.

Which THREE symptoms indicate that IPv6 First Hop Security features are misconfigured or not functioning correctly? (Choose THREE.)

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 hosts on a segment are unable to obtain a global unicast address via SLAAC, even though a legitimate router is present.
This could be due to RA Guard blocking the router's Router Advertisements, preventing SLAAC.
B
A newly connected switch causes existing hosts to lose IPv6 connectivity to the default gateway.
This may indicate ND Inspection or IPv6 Source Guard dropping valid ND packets from the new switch, or a binding table issue.
C
Hosts on a VLAN receive Router Advertisements but do not update their default gateway.
RA Guard can be configured to drop RAs from unauthorized sources, or the policy may incorrectly mark the legitimate router as a host, causing hosts to ignore the RAs.
D
IPv6 pings between two hosts on the same VLAN succeed, but pings to the router fail.
Why wrong: This could be a routing or gateway issue, but not necessarily an FHS problem; FHS typically blocks at Layer 2, not Layer 3 forwarding.
E
The switch logs show frequent 'IPv6 address collision' messages.
Why wrong: Address collisions are typically detected by DAD (Duplicate Address Detection) and are not directly caused by FHS misconfiguration; they indicate a different issue.

Full breakdown with real-world context →

Quick Answer

The answer is that the three symptoms indicating IPv6 First Hop Security misconfiguration are hosts failing to obtain IPv6 addresses via DHCPv6, sudden connectivity loss after a new switch is introduced, and hosts receiving Router Advertisements but not updating their default gateway. These symptoms point directly to specific FHS features being blocked or misapplied: DHCPv6 Guard prevents legitimate DHCP servers from assigning addresses, ND Inspection or Source Guard can drop traffic from an unknown switch port, and RA Guard misconfiguration can cause hosts to ignore valid RAs, leaving their gateway unchanged. On the Cisco CCNP ENARSI 300-410 exam, this question tests your ability to map real-world behavior to FHS mechanisms like RA Guard, ND Inspection, and DHCPv6 Guard, often with distractors that describe normal IPv6 operations or unrelated issues like duplicate address detection. A common trap is confusing a host’s failure to update its gateway with a simple routing problem, when the root cause is RA Guard filtering. Remember the mnemonic “DNR” for the three symptoms: DHCP failure, New switch disruption, and Router Advertisement ignored.

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 hosts on a segment are unable to obtain a global unicast address via SLAAC, even though a legitimate router is present.

Option A is correct because SLAAC relies on Router Advertisements (RAs) to provide the prefix and other configuration information. If IPv6 First Hop Security features such as RA Guard or RA snooping are misconfigured, they may block or drop legitimate RAs, preventing hosts from generating a global unicast address via SLAAC even though a valid router is present.

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 hosts on a segment are unable to obtain a global unicast address via SLAAC, even though a legitimate router is present.
Why this is correct
This could be due to RA Guard blocking the router's Router Advertisements, preventing SLAAC.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
A newly connected switch causes existing hosts to lose IPv6 connectivity to the default gateway.
Why this is correct
This may indicate ND Inspection or IPv6 Source Guard dropping valid ND packets from the new switch, or a binding table issue.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Hosts on a VLAN receive Router Advertisements but do not update their default gateway.
Why this is correct
RA Guard can be configured to drop RAs from unauthorized sources, or the policy may incorrectly mark the legitimate router as a host, causing hosts to ignore the RAs.
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 pings between two hosts on the same VLAN succeed, but pings to the router fail.
Why it's wrong here
This could be a routing or gateway issue, but not necessarily an FHS problem; FHS typically blocks at Layer 2, not Layer 3 forwarding.
✗
The switch logs show frequent 'IPv6 address collision' messages.
Why it's wrong here
Address collisions are typically detected by DAD (Duplicate Address Detection) and are not directly caused by FHS misconfiguration; they indicate a different issue.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between First Hop Security failures (which block control-plane messages like RAs and DHCPv6) and other IPv6 issues like routing problems or DAD collisions, so candidates must recognize that symptoms like inter-host ping success but router ping failure point to routing, not First Hop Security.

Detailed technical explanation

How to think about this question

IPv6 First Hop Security encompasses features like RA Guard (RFC 6105), DHCPv6 Guard, and Source Guard, which operate at Layer 2 to filter rogue RAs and DHCPv6 messages. RA Guard, for example, uses ACLs or snooping to permit only authorized routers to send RAs; if a legitimate router's RA is blocked, hosts cannot obtain prefixes or default gateway information via SLAAC. In real-world deployments, misconfigured RA Guard policies are a common cause of IPv6 connectivity loss after switch replacements or firmware upgrades.

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.

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 hosts on a segment are unable to obtain a global unicast address via SLAAC, even though a legitimate router is present. — Option A is correct because SLAAC relies on Router Advertisements (RAs) to provide the prefix and other configuration information. If IPv6 First Hop Security features such as RA Guard or RA snooping are misconfigured, they may block or drop legitimate RAs, preventing hosts from generating a global unicast address via SLAAC even though a valid router is present.

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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