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.
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 works by intercepting DHCPv6 server messages (Advertise and Reply) and checking them against the policy. However, if the switch does not have 'ipv6 snooping' enabled globally, DHCPv6 Guard may not be able to inspect the packets because it relies on the snooping database. The edge case is that DHCPv6 Guard requires IPv6 snooping to be enabled to function properly; without it, the guard may not be applied or may not filter correctly. Many engineers forget to enable 'ipv6 snooping' globally.
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.
✓
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
Access ports place end devices into a single VLAN.
✗
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: 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
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: IPv6 snooping is not enabled globally, so DHCPv6 Guard cannot inspect DHCPv6 messages. — DHCPv6 Guard works by intercepting DHCPv6 server messages (Advertise and Reply) and checking them against the policy. However, if the switch does not have 'ipv6 snooping' enabled globally, DHCPv6 Guard may not be able to inspect the packets because it relies on the snooping database. The edge case is that DHCPv6 Guard requires IPv6 snooping to be enabled to function properly; without it, the guard may not be applied or may not filter correctly. Many engineers forget to enable 'ipv6 snooping' globally.
What should I do if I get this 300-410 question wrong?
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.
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?
Access ports place end devices into a single VLAN.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.