Quick Answer
The answer is DUID-LL (Link-Layer), which is the default DHCPv6 client DUID type on Cisco IOS-XE routers. This is correct because, per RFC 8415, the Link-Layer DUID is generated using the MAC address of the interface, making it a stable and hardware-derived identifier that does not require additional configuration. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of DHCPv6 operation and the default behavior of IOS-XE devices, often appearing in questions that contrast DUID-LL with other types like DUID-LLT (which includes a timestamp) or DUID-EN (enterprise-based). A common trap is assuming that IOS-XE defaults to DUID-LLT, but it does not—only older IOS or specific platforms may differ. For a quick memory tip, think “LL for Link-Layer, MAC stays the same,” reinforcing that the default DUID is tied directly to the interface’s burned-in address.
This 300-410 practice question tests your understanding of dhcp (ipv4 and ipv6). Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
What is the default DHCPv6 client DUID type on a Cisco IOS-XE router?
DUID-LLT (Link-Layer plus Time)
Why wrong: DUID-LLT is used by some implementations but not the default on Cisco IOS-XE.
DUID-EN (Enterprise Number)
Why wrong: DUID-EN is used for vendor-specific DUIDs, not the default.
DUID-LL (Link-Layer)
Cisco IOS-XE defaults to DUID-LL for DHCPv6 clients.
DUID-UUID (Universally Unique Identifier)
Why wrong: DUID-UUID is not a standard DUID type in RFC 8415.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
DUID-LL (Link-Layer)
Cisco IOS-XE defaults to DUID-LL (Link-Layer) for DHCPv6 clients, which uses the MAC address of the interface, per RFC 8415.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
DUID-LLT (Link-Layer plus Time)
Why it's wrong here
DUID-LLT is used by some implementations but not the default on Cisco IOS-XE.
DUID-EN (Enterprise Number)
Why it's wrong here
DUID-EN is used for vendor-specific DUIDs, not the default.
DUID-LL (Link-Layer)
Why this is correct
Cisco IOS-XE defaults to DUID-LL for DHCPv6 clients.
Related concept
Read the scenario before looking for a memorised answer.
DUID-UUID (Universally Unique Identifier)
Why it's wrong here
DUID-UUID is not a standard DUID type in RFC 8415.
Common exam traps
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
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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
DHCP (IPv4 and IPv6) — This question tests DHCP (IPv4 and IPv6) — Read the scenario before looking for a memorised answer..
The correct answer is: DUID-LL (Link-Layer) — Cisco IOS-XE defaults to DUID-LL (Link-Layer) for DHCPv6 clients, which uses the MAC address of the interface, per RFC 8415.
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.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 19, 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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