- A
The preferred lifetime is 3600 seconds and the valid lifetime is 600 seconds, which is invalid because the valid lifetime must be greater than or equal to the preferred lifetime.
Per RFC 4862, the valid lifetime must be greater than or equal to the preferred lifetime. A shorter valid lifetime is not allowed and will cause a configuration error.
- B
The preferred lifetime is 600 seconds and the valid lifetime is 3600 seconds, which is a typical configuration.
Why wrong: The order is preferred lifetime first, then valid lifetime. Here, preferred is 3600 and valid is 600, which is reversed from typical and invalid.
- C
The lifetimes are applied to the DNS server address, not the address prefix.
Why wrong: Lifetimes apply to the address prefix, not to DNS server options.
- D
The configuration is valid and will work as expected.
Why wrong: The configuration is invalid because the valid lifetime is shorter than the preferred lifetime, which violates RFC standards.
Quick Answer
The correct answer is that the preferred lifetime is 3600 seconds and the valid lifetime is 600 seconds, making the configuration invalid because the valid lifetime must be greater than or equal to the preferred lifetime. This order is defined by RFC 4862, where the first value in the `lifetime` command always sets the preferred lifetime, and the second sets the valid lifetime; a valid lifetime shorter than the preferred lifetime violates the standard and causes the router to reject the prefix assignment. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of DHCPv6 prefix delegation and the critical lifetime relationship, often appearing as a trap where candidates mistakenly reverse the order or assume any values are acceptable. A common memory tip is to think of the preferred lifetime as the “good” period and the valid lifetime as the “total” period—the total must always be longer or equal, so remember “preferred first, valid last, valid must be greater or equal.”
300-410 DHCP (IPv4 and IPv6) Practice Question
This 300-410 practice question tests your understanding of dhcp (ipv4 and ipv6). 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.
Router R6 has the following DHCPv6 configuration:
ipv6 dhcp pool DHCP6_POOL3 address prefix 2001:db8:3::/64 lifetime 3600 600 dns-server 2001:db8::1 !
interface GigabitEthernet0/2
ipv6 address 2001:db8:3::1/64 ipv6 dhcp server DHCP6_POOL3 ipv6 nd managed-config-flag
no shutdown
What is the effect of the lifetime parameters 3600 and 600?
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 preferred lifetime is 3600 seconds and the valid lifetime is 600 seconds, which is invalid because the valid lifetime must be greater than or equal to the preferred lifetime.
Option A is correct because in the `ipv6 dhcp pool` configuration, the `lifetime` command specifies the preferred lifetime first (3600 seconds) and the valid lifetime second (600 seconds). According to RFC 4862, the valid lifetime must be greater than or equal to the preferred lifetime; otherwise, the configuration is invalid and will be rejected by the router. This mismatch causes the DHCPv6 pool to fail to apply the prefix.
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 preferred lifetime is 3600 seconds and the valid lifetime is 600 seconds, which is invalid because the valid lifetime must be greater than or equal to the preferred lifetime.
Why this is correct
Per RFC 4862, the valid lifetime must be greater than or equal to the preferred lifetime. A shorter valid lifetime is not allowed and will cause a configuration error.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The preferred lifetime is 600 seconds and the valid lifetime is 3600 seconds, which is a typical configuration.
Why it's wrong here
The order is preferred lifetime first, then valid lifetime. Here, preferred is 3600 and valid is 600, which is reversed from typical and invalid.
- ✗
The lifetimes are applied to the DNS server address, not the address prefix.
Why it's wrong here
Lifetimes apply to the address prefix, not to DNS server options.
- ✗
The configuration is valid and will work as expected.
Why it's wrong here
The configuration is invalid because the valid lifetime is shorter than the preferred lifetime, which violates RFC standards.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that Cisco tests whether candidates know the correct order of the preferred and valid lifetime parameters in the `lifetime` command, as many mistakenly assume the valid lifetime comes first or that the router will accept an invalid lifetime relationship.
Detailed technical explanation
How to think about this question
Under the hood, the `lifetime` command in an IPv6 DHCP pool sets the preferred and valid lifetimes for addresses assigned from the prefix, as defined in RFC 4861 and RFC 4862. The preferred lifetime is the time until an address becomes deprecated, while the valid lifetime is the total time the address is usable; if the valid lifetime is less than the preferred lifetime, the address would be deprecated before it expires, which violates the protocol and causes the router to reject the configuration. In real-world scenarios, misconfiguring these lifetimes can lead to clients receiving invalid address leases, causing connectivity issues that are difficult to troubleshoot.
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
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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 preferred lifetime is 3600 seconds and the valid lifetime is 600 seconds, which is invalid because the valid lifetime must be greater than or equal to the preferred lifetime. — Option A is correct because in the `ipv6 dhcp pool` configuration, the `lifetime` command specifies the preferred lifetime first (3600 seconds) and the valid lifetime second (600 seconds). According to RFC 4862, the valid lifetime must be greater than or equal to the preferred lifetime; otherwise, the configuration is invalid and will be rejected by the router. This mismatch causes the DHCPv6 pool to fail to apply the prefix.
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: 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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