- A
The DHCPv6 Guard policy is applied globally, and the port connected to the DHCP server is not configured as a trusted port for DHCPv6 server messages.
Correct because DHCPv6 Guard by default blocks server messages on untrusted ports; the server port must be explicitly trusted.
- B
RA Guard is blocking the DHCPv6 server's Router Advertisements, causing hosts to not send Solicit messages.
Why wrong: Incorrect because the symptom states Solicit messages reach the server, so RA Guard is not the issue.
- C
IPv6 Source Guard is filtering the server's responses because the server's IPv6 address is not in the binding table.
Why wrong: Incorrect because Source Guard filters based on source address of traffic from hosts, not from servers; also, DHCPv6 server messages are typically not filtered by Source Guard.
- D
The switch has DHCP snooping enabled for IPv4, which is interfering with IPv6 DHCPv6 operation.
Why wrong: Incorrect because IPv4 DHCP snooping does not affect IPv6 DHCPv6; they are separate processes.
Quick Answer
The answer is that the port connected to the legitimate DHCPv6 server is not configured as a trusted port for DHCPv6 server messages. This is because DHCPv6 Guard, when applied globally, drops all DHCPv6 server-originated messages—such as Advertise and Reply—on any port that is not explicitly trusted, even if the server is legitimate. The Solicit messages from hosts reach the server because they are client messages, which are allowed by default on untrusted ports, but the server’s responses are blocked at the switch port. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of DHCPv6 Guard’s asymmetric filtering: it only filters server-to-client traffic on untrusted ports, not client-to-server traffic. A common trap is assuming that because Solicit messages pass, the server is reachable, but the guard policy specifically targets the return path. Remember the memory tip: “Solicit goes through, but Advertise and Reply are denied—trust the server port to let the server speak.”
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 a network where IPv6 hosts cannot obtain IP addresses via DHCPv6. The switch is configured with DHCPv6 Guard to prevent rogue DHCP servers. The legitimate DHCPv6 server is connected to port GigabitEthernet1/0/1. The engineer sees that DHCPv6 Solicit messages from hosts reach the server, but the server's Advertise and Reply messages are not reaching the hosts. What is the most likely root 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.
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 DHCPv6 Guard policy is applied globally, and the port connected to the DHCP server is not configured as a trusted port for DHCPv6 server messages.
DHCPv6 Guard on the switch port connected to the DHCP server will drop DHCPv6 server messages (Advertise, Reply) unless the port is configured as a trusted DHCPv6 server port. If the port is not trusted, the server's responses are dropped.
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 DHCPv6 Guard policy is applied globally, and the port connected to the DHCP server is not configured as a trusted port for DHCPv6 server messages.
Why this is correct
Correct because DHCPv6 Guard by default blocks server messages on untrusted ports; the server port must be explicitly trusted.
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.
- ✗
RA Guard is blocking the DHCPv6 server's Router Advertisements, causing hosts to not send Solicit messages.
Why it's wrong here
Incorrect because the symptom states Solicit messages reach the server, so RA Guard is not the issue.
- ✗
IPv6 Source Guard is filtering the server's responses because the server's IPv6 address is not in the binding table.
Why it's wrong here
Incorrect because Source Guard filters based on source address of traffic from hosts, not from servers; also, DHCPv6 server messages are typically not filtered by Source Guard.
- ✗
The switch has DHCP snooping enabled for IPv4, which is interfering with IPv6 DHCPv6 operation.
Why it's wrong here
Incorrect because IPv4 DHCP snooping does not affect IPv6 DHCPv6; they are separate processes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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 DHCPv6 Guard policy is applied globally, and the port connected to the DHCP server is not configured as a trusted port for DHCPv6 server messages. — DHCPv6 Guard on the switch port connected to the DHCP server will drop DHCPv6 server messages (Advertise, Reply) unless the port is configured as a trusted DHCPv6 server port. If the port is not trusted, the server's responses are dropped.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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.
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 →
Same concept, more angles
3 more ways this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. In IPv6 First Hop Security, what is the purpose of the 'device-role' command in a DHCP guard policy?
medium- ✓ A.It specifies whether the interface is a server, client, or relay for DHCP filtering.
- B.It sets the trust level for ND inspection.
- C.It defines the VLAN membership for the interface.
- D.It enables IPv6 routing on the interface.
Why A: The 'device-role' command defines whether the interface is a DHCP server, client, or relay. This determines which DHCP messages are allowed.
Variation 2. A network engineer runs the following command to troubleshoot DHCPv6 guard: R1# debug ipv6 dhcp guard *Mar 1 00:03:45.678: IPv6-DHCP-Guard: R1, Fa0/0, DHCPv6 SOLICIT from fe80::3, client DUID 00010001abcd1234 *Mar 1 00:03:45.678: IPv6-DHCP-Guard: R1, Fa0/0, DHCPv6 SOLICIT from fe80::3 is allowed by policy DHCP-POLICY *Mar 1 00:03:46.901: IPv6-DHCP-Guard: R1, Fa0/0, DHCPv6 ADVERTISE from fe80::4, server DUID 0001000156789012 *Mar 1 00:03:46.901: IPv6-DHCP-Guard: R1, Fa0/0, DHCPv6 ADVERTISE from fe80::4 is blocked by policy DHCP-POLICY What does this output indicate?
medium- ✓ A.DHCPv6 guard is allowing client messages but blocking server messages from untrusted sources, preventing rogue DHCPv6 servers.
- B.DHCPv6 guard is blocking all DHCPv6 messages, indicating a misconfiguration.
- C.DHCPv6 guard is allowing all messages but logging them for analysis.
- D.DHCPv6 guard is not configured; the debug output is from default DHCPv6 behavior.
Why A: The debug shows DHCPv6 guard filtering DHCPv6 messages. Client SOLICIT is allowed, but server ADVERTISE from fe80::4 is blocked, indicating the source is not a trusted DHCPv6 server.
Variation 3. A network engineer runs the following command to verify DHCPv6 guard policy: R1# show ipv6 dhcp guard policy DHCP-POLICY Policy: DHCP-POLICY Status: Active Device role: dhcp-client Trusted ports: none Untrusted ports: Fa0/0 DHCPv6 guard: enabled DHCPv6 guard action: block DHCPv6 server validation: enabled DHCPv6 server list: 2001:db8::10 What does this output indicate?
medium- ✓ A.The policy blocks DHCPv6 server messages on Fa0/0 except from server 2001:db8::10.
- B.The policy allows all DHCPv6 messages on Fa0/0 without any filtering.
- C.The policy only applies to DHCPv6 client messages and ignores server messages.
- D.The policy is inactive and not applied to any interface.
Why A: The show command displays the DHCPv6 guard policy. The policy blocks DHCPv6 server messages on untrusted port Fa0/0, except from the listed server 2001:db8::10.
Last reviewed: Jun 18, 2026
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