- A
The LAN interfaces are missing the 'ipv6 enable' command.
Why wrong: Incorrect because 'ipv6 address ... eui-64' enables IPv6 on the interface; 'ipv6 enable' is not required.
- B
The ISP's DHCPv6 server is not configured to delegate a prefix.
Correct because if the server does not delegate a prefix, the client's 'ipv6 dhcp client pd' request will fail, and the LAN interfaces will not receive any addresses from the delegated prefix.
- C
The 'ipv6 dhcp client pd' command should be 'ipv6 dhcp client pd ISP-PREFIX hint ::/48'.
Why wrong: Incorrect because the 'hint' option is optional and does not prevent delegation; the server may still delegate a different prefix.
- D
The WAN interface needs the 'ipv6 nd other-config-flag' command.
Why wrong: Incorrect because the 'other-config-flag' is for LAN interfaces to indicate additional information; it is not related to prefix delegation on the WAN.
300-410 DHCP (IPv4 and IPv6) Practice Question
This 300-410 practice question tests your understanding of dhcp (ipv4 and ipv6). 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 DHCPv6 prefix delegation scenario. The router (R1) is a DHCPv6 client on its WAN interface and is supposed to receive a /48 prefix from the ISP's DHCPv6 server to delegate to LAN interfaces. The WAN interface is configured with 'ipv6 address dhcp' and 'ipv6 dhcp client pd ISP-PREFIX'. The LAN interfaces have 'ipv6 address ISP-PREFIX 0:0:0:1::/64 eui-64'. The engineer sees that the WAN interface gets a global IPv6 address, but the LAN interfaces do not get any IPv6 address. What is the most likely 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 ISP's DHCPv6 server is not configured to delegate a prefix.
The WAN interface successfully obtains a global IPv6 address via DHCPv6, but the LAN interfaces lack IPv6 addresses because the DHCPv6 client process on R1 has not received a delegated prefix. The 'ipv6 dhcp client pd ISP-PREFIX' command requests a prefix delegation from the ISP's DHCPv6 server; if the server is not configured to delegate prefixes (e.g., missing the 'prefix-delegation' pool or 'ipv6 dhcp server' with prefix assignment), the client never receives a prefix to assign to LAN interfaces. This is the most likely cause given the symptom.
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 LAN interfaces are missing the 'ipv6 enable' command.
Why it's wrong here
Incorrect because 'ipv6 address ... eui-64' enables IPv6 on the interface; 'ipv6 enable' is not required.
- ✓
The ISP's DHCPv6 server is not configured to delegate a prefix.
Why this is correct
Correct because if the server does not delegate a prefix, the client's 'ipv6 dhcp client pd' request will fail, and the LAN interfaces will not receive any addresses from the delegated prefix.
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.
- ✗
The 'ipv6 dhcp client pd' command should be 'ipv6 dhcp client pd ISP-PREFIX hint ::/48'.
Why it's wrong here
Incorrect because the 'hint' option is optional and does not prevent delegation; the server may still delegate a different prefix.
- ✗
The WAN interface needs the 'ipv6 nd other-config-flag' command.
Why it's wrong here
Incorrect because the 'other-config-flag' is for LAN interfaces to indicate additional information; it is not related to prefix delegation on the WAN.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between DHCPv6 address assignment (IA_NA) and prefix delegation (IA_PD), trapping candidates who assume that obtaining a WAN address automatically implies a delegated prefix is also received.
Detailed technical explanation
How to think about this question
DHCPv6 prefix delegation (RFC 3633) uses a separate Identity Association for Prefix Delegation (IA_PD) distinct from the IA_NA used for address assignment. The 'ipv6 dhcp client pd' command creates an IA_PD request; the server must have a 'prefix-delegation pool' configured with an available prefix (e.g., 'ipv6 local pool ISP-POOL 2001:db8::/48 48') and bind it to the client's DUID. Without this server-side configuration, the client's IA_PD request is ignored, and no prefix is assigned to the LAN interfaces.
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 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.
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FAQ
Questions learners often ask
What does this 300-410 question test?
DHCP (IPv4 and IPv6) — This question tests DHCP (IPv4 and IPv6) — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ISP's DHCPv6 server is not configured to delegate a prefix. — The WAN interface successfully obtains a global IPv6 address via DHCPv6, but the LAN interfaces lack IPv6 addresses because the DHCPv6 client process on R1 has not received a delegated prefix. The 'ipv6 dhcp client pd ISP-PREFIX' command requests a prefix delegation from the ISP's DHCPv6 server; if the server is not configured to delegate prefixes (e.g., missing the 'prefix-delegation' pool or 'ipv6 dhcp server' with prefix assignment), the client never receives a prefix to assign to LAN interfaces. This is the most likely cause given the symptom.
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: "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.
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Last reviewed: Jun 24, 2026
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.
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