- A
DUID-LLT (Link-Layer plus Time)
Why wrong: DUID-LLT is used by some implementations but not the default on Cisco IOS-XE.
- B
DUID-EN (Enterprise Number)
Why wrong: DUID-EN is used for vendor-specific DUIDs, not the default.
- C
DUID-LL (Link-Layer)
Cisco IOS-XE defaults to DUID-LL for DHCPv6 clients.
- D
DUID-UUID (Universally Unique Identifier)
Why wrong: DUID-UUID is not a standard DUID type in RFC 8415.
Question 465 of 2,152
Default DHCPv6 Client DUID: DUID-LL (Link-Layer)
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?
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.
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
✓
DUID-LL (Link-Layer)
Cisco IOS-XE routers default to DUID-LL (Link-Layer) as the DHCPv6 client DUID type, as defined in RFC 8415. This DUID is generated using the router's link-layer address (MAC address) without a timestamp, making it stable across reboots. The DUID-LL is the default because it provides a consistent identifier without requiring clock synchronization or enterprise registration.
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.
- ✗
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
Common exam trap: answer the scenario, not the keyword
Cisco often tests the default DUID type by contrasting it with DUID-LLT, leading candidates to mistakenly choose DUID-LLT because they recall that DHCPv6 clients can use a time-based identifier, but they forget that Cisco defaults to the simpler, non-timestamped DUID-LL.
Detailed technical explanation
How to think about this question
The DUID-LL is constructed by concatenating the DUID type (0x0003 for DUID-LL), the hardware type (e.g., 0x0001 for Ethernet), and the MAC address. On Cisco IOS-XE, the default DUID can be verified with 'show ipv6 dhcp' or 'show ipv6 dhcp interface', and it remains constant even after a reload, unlike DUID-LLT which would change if the system time resets. In real-world scenarios, using DUID-LL ensures that DHCPv6 prefix delegation or address assignments persist across reboots, which is critical for stable network operations.
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.
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
What to study next
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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: DUID-LL (Link-Layer) — Cisco IOS-XE routers default to DUID-LL (Link-Layer) as the DHCPv6 client DUID type, as defined in RFC 8415. This DUID is generated using the router's link-layer address (MAC address) without a timestamp, making it stable across reboots. The DUID-LL is the default because it provides a consistent identifier without requiring clock synchronization or enterprise registration.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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