- A
The DHCPv6 client successfully received the prefix 2001:DB8:1::/48.
Why wrong: The server sent a REPLY with NoPrefixAvail, meaning the prefix was not assigned.
- B
The DHCPv6 server has a pool configured but the requested prefix is not in that pool or is already allocated.
The server used pool DHCP_POOL but the prefix 2001:DB8:1::/48 is not available, likely because it is not included in the pool or is already assigned to another client.
- C
The DHCPv6 client is using a relay agent because the SOLICIT was received on a different interface.
Why wrong: The SOLICIT was received directly on GigabitEthernet0/0; no relay is indicated.
- D
The DHCPv6 server is configured with a stateless configuration because it sent an ADVERTISE without a prefix.
Why wrong: The ADVERTISE was sent, but the server later indicated the prefix was not available; this is stateful DHCPv6 for prefix delegation.
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.
A network engineer is troubleshooting a DHCPv6 prefix delegation issue on router R1 and runs the following command:
R1# debug ipv6 dhcp detail
Output: IPv6 DHCP: Received SOLICIT message from FE80::21A:2BFF:FE3C:4D01 on GigabitEthernet0/0 IPv6 DHCP: Using interface pool DHCP_POOL IPv6 DHCP: Sending ADVERTISE message to FE80::21A:2BFF:FE3C:4D01 IPv6 DHCP: Received REQUEST message from FE80::21A:2BFF:FE3C:4D01 IPv6 DHCP: Client requests prefix 2001:DB8:1::/48 IPv6 DHCP: Prefix 2001:DB8:1::/48 not available in pool DHCP_POOL IPv6 DHCP: Sending REPLY message with Status Code NoPrefixAvail
What does this output indicate?
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 server has a pool configured but the requested prefix is not in that pool or is already allocated.
Option B is correct because the debug output shows the client sent a REQUEST for prefix 2001:DB8:1::/48, but the server responded with a REPLY containing the status code NoPrefixAvail. This indicates the requested prefix is either not defined in the DHCP_POOL or has already been allocated to another client, so the server cannot assign it.
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 client successfully received the prefix 2001:DB8:1::/48.
Why it's wrong here
The server sent a REPLY with NoPrefixAvail, meaning the prefix was not assigned.
- ✓
The DHCPv6 server has a pool configured but the requested prefix is not in that pool or is already allocated.
Why this is correct
The server used pool DHCP_POOL but the prefix 2001:DB8:1::/48 is not available, likely because it is not included in the pool or is already assigned to another client.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The DHCPv6 client is using a relay agent because the SOLICIT was received on a different interface.
Why it's wrong here
The SOLICIT was received directly on GigabitEthernet0/0; no relay is indicated.
- ✗
The DHCPv6 server is configured with a stateless configuration because it sent an ADVERTISE without a prefix.
Why it's wrong here
The ADVERTISE was sent, but the server later indicated the prefix was not available; this is stateful DHCPv6 for prefix delegation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misinterpretation of the NoPrefixAvail status code, where candidates assume the prefix was successfully assigned because they see a REPLY message, without reading the status code field.
Detailed technical explanation
How to think about this question
In DHCPv6 prefix delegation (RFC 3633), the client sends a SOLICIT, the server replies with an ADVERTISE containing available prefixes, and the client then sends a REQUEST for a specific prefix. The NoPrefixAvail status code (value 2) is defined in RFC 3315 and indicates the server has no prefixes to assign, often due to pool exhaustion or misconfiguration. A real-world scenario is when a CPE router requests a /48 from an ISP, but the ISP's pool is depleted or the requested prefix is outside the configured range.
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.
Visual reference
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 DHCPv6 server has a pool configured but the requested prefix is not in that pool or is already allocated. — Option B is correct because the debug output shows the client sent a REQUEST for prefix 2001:DB8:1::/48, but the server responded with a REPLY containing the status code NoPrefixAvail. This indicates the requested prefix is either not defined in the DHCP_POOL or has already been allocated to another client, so the server cannot assign it.
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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