hardMultiple Choice
300-410 Practice Question: Is troubleshooting a DHCPv6 prefix delegation…
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?
⚠ Common exam trap
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.
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.
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.
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 debug clearly shows the server replying with Status Code NoPrefixAvail, meaning the requested prefix was refused, not assigned. It tempts because ADVERTISE and REPLY messages appear, which superficially resemble successful negotiation. The pool lacks 2001:DB8:1::/48, so delegation failed despite the client's REQUEST being received.
- ✓
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 debug line "Prefix 2001:DB8:1::/48 not available in pool DHCP_POOL" and the NoPrefixAvail status confirm the server's pool exists but lacks that prefix, either because it was never configured within DHCP_POOL or is already leased to another requesting router.
- ✗
The DHCPv6 client is using a relay agent because the SOLICIT was received on a different interface.
Why it's wrong here
The SOLICIT arrived directly on GigabitEthernet0/0 from a link-local address, and no relay-forward messages appear, so no relay agent is involved. This option tempts because DHCPv6-PD across subnets normally requires a relay. The actual fault is the pool lacking the requested 2001:DB8:1::/48 prefix, producing NoPrefixAvail.
- ✗
The DHCPv6 server is configured with a stateless configuration because it sent an ADVERTISE without a prefix.
Why it's wrong here
Stateless DHCPv6 supplies only DNS and other options, never addresses or prefixes, so an ADVERTISE would carry no IA_PD container at all. Here the server did process a prefix request and replied NoPrefixAvail, proving stateful operation with an exhausted or misconfigured pool. Stateless mode suits hosts using SLAAC for addressing.
Visual reference
Go deeper
Related to this question
About these practice questions
This 300-410 question is part of Courseiva's 1,401-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.