- A
The DHCPv6 relay agent is not functioning because messages are not being forwarded.
Why wrong: The output clearly shows messages being forwarded in both directions.
- B
The DHCPv6 relay agent is successfully forwarding messages between the client and server.
The relay receives client messages, forwards them to the server, and forwards server responses back to the client.
- C
The DHCPv6 server is unreachable because no REPLY is received.
Why wrong: A REPLY is received and forwarded to the client.
- D
The DHCPv6 client is using a global unicast address as its link-local address.
Why wrong: The client uses FE80::1, which is a link-local address.
Question 1,258 of 2,152
DHCPv6 Relay Operation: debug ipv6 dhcp relay Output
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 runs the following command to troubleshoot DHCPv6 relay on router R1:
R1# debug ipv6 dhcp relay
Output: IPv6 DHCP relay: Received SOLICIT message from FE80::1 on GigabitEthernet0/0 IPv6 DHCP relay: Forwarding SOLICIT to server 2001:DB8:2::1 via GigabitEthernet0/1 IPv6 DHCP relay: Received ADVERTISE message from server 2001:DB8:2::1 via GigabitEthernet0/1 IPv6 DHCP relay: Forwarding ADVERTISE to client FE80::1 via GigabitEthernet0/0 IPv6 DHCP relay: Received REQUEST message from FE80::1 on GigabitEthernet0/0 IPv6 DHCP relay: Forwarding REQUEST to server 2001:DB8:2::1 via GigabitEthernet0/1 IPv6 DHCP relay: Received REPLY message from server 2001:DB8:2::1 via GigabitEthernet0/1 IPv6 DHCP relay: Forwarding REPLY to client FE80::1 via GigabitEthernet0/0
What does this output indicate?
Quick Answer
The correct answer is that the DHCPv6 relay agent is successfully forwarding messages between the client and server. This output from the debug ipv6 dhcp relay command shows the complete four-message exchange—SOLICIT, ADVERTISE, REQUEST, and REPLY—being relayed between the client at FE80::1 on GigabitEthernet0/0 and the server at 2001:DB8:2::1 via GigabitEthernet0/1, confirming that the relay is operating correctly as an intermediary. On the Cisco CCNP ENARSI 300-410 exam, interpreting this debug output tests your understanding of DHCPv6 relay operation, specifically how the relay agent modifies the source and destination addresses while preserving the client’s link-local address in the relay-forward and relay-reply messages. A common trap is confusing this with a DHCPv6 server debug, but remember that a relay never generates its own messages—it only forwards. A helpful memory tip is “Relay Reflects, Server Selects”: the relay simply reflects client messages to the server and server responses back to the client, as seen in this output.
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 relay agent is successfully forwarding messages between the client and server.
The debug output shows a complete DHCPv6 four-message exchange (SOLICIT-ADVERTISE-REQUEST-REPLY) being relayed between the client (FE80::1) and the server (2001:DB8:2::1). Each message is received on one interface and forwarded out the other, confirming the relay agent is functioning correctly. Therefore, option B is correct.
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 relay agent is not functioning because messages are not being forwarded.
Why it's wrong here
The output clearly shows messages being forwarded in both directions.
- ✓
The DHCPv6 relay agent is successfully forwarding messages between the client and server.
Why this is correct
The relay receives client messages, forwards them to the server, and forwards server responses back to the client.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The DHCPv6 server is unreachable because no REPLY is received.
Why it's wrong here
A REPLY is received and forwarded to the client.
- ✗
The DHCPv6 client is using a global unicast address as its link-local address.
Why it's wrong here
The client uses FE80::1, which is a link-local address.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the ability to interpret debug output by showing a successful message flow, leading candidates to incorrectly assume a failure because they expect an error message or because they misread the link-local address as a global address.
Trap categories for this question
Command / output trap
The output clearly shows messages being forwarded in both directions.
Detailed technical explanation
How to think about this question
DHCPv6 relay agents use the 'ipv6 dhcp relay destination' command to forward client messages to a server, encapsulating them in a Relay-forward message (RFC 3315). The relay agent does not modify the client's link-local address (FE80::1) but adds a Relay Message option containing the original client message. In production, misconfigured relay destinations or ACLs blocking UDP port 547 can cause silent failures, but this debug output confirms successful relaying.
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 relay agent is successfully forwarding messages between the client and server. — The debug output shows a complete DHCPv6 four-message exchange (SOLICIT-ADVERTISE-REQUEST-REPLY) being relayed between the client (FE80::1) and the server (2001:DB8:2::1). Each message is received on one interface and forwarded out the other, confirming the relay agent is functioning correctly. Therefore, option B is correct.
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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