300-410 Infrastructure Services Practice Question
A network engineer is configuring a Cisco IOS XE router to act as a DHCPv6 relay agent. The router is connected to a LAN segment with DHCPv6 clients and must forward DHCPv6 messages to a DHCPv6 server at 2001:DB8::100. The engineer has configured the interface with ipv6 address 2001:DB8:1::1/64 and ipv6 enable. Which command is required to enable DHCPv6 relay on the interface?
⚠ Common exam trap
The trap here is assuming the IPv6 relay command follows the IPv4 ip helper-address pattern, but Cisco IOS XE uses ipv6 dhcp relay destination instead.
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
✓
ipv6 dhcp relay destination 2001:DB8::100
To configure a Cisco IOS XE router as a DHCPv6 relay agent, you must use the ipv6 dhcp relay destination command on the interface facing the clients. This command specifies the DHCPv6 server address to which client messages are forwarded. It is the direct analog to the IPv4 ip helper-address command, but with IPv6-specific syntax. Without it, the router will not relay DHCPv6 messages, and clients will not receive addresses from the remote server. The other options either configure the router as a server or set RA flags, neither of which enables relay.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ipv6 dhcp server 2001:DB8::100
Why it's wrong here
The ipv6 dhcp server command is used to configure the router as a DHCPv6 server, not a relay agent. It binds a DHCPv6 pool to the interface. In this scenario, the router must relay messages to an external server, not serve addresses itself. Using this command would require a local pool and would not forward requests to the specified server. Therefore, it is incorrect for a relay configuration.
- ✗
ipv6 helper-address 2001:DB8::100
Why it's wrong here
The ipv6 helper-address command does not exist in Cisco IOS XE for DHCPv6 relay. The correct command is ipv6 dhcp relay destination. This option is a common misconception because IPv4 uses ip helper-address for DHCP relay. For IPv6, the syntax is different. Therefore, this command will not enable DHCPv6 relay and will likely be rejected by the router.
- ✗
ipv6 nd managed-config-flag
Why it's wrong here
The ipv6 nd managed-config-flag command sets the M flag in Router Advertisements, indicating that clients should use DHCPv6 to obtain addresses. While this is often used alongside DHCPv6 relay to signal clients, it does not enable the relay function itself. The router will still not forward DHCPv6 messages to the server without the ipv6 dhcp relay destination command. Therefore, this command alone does not achieve the goal.
- ✓
ipv6 dhcp relay destination 2001:DB8::100
Why this is correct
The ipv6 dhcp relay destination command configures the interface as a DHCPv6 relay agent and specifies the destination DHCPv6 server address. This command is applied to the interface facing the clients. The router will then forward DHCPv6 messages from clients to the specified server and relay responses back. Without this command, the router will not relay DHCPv6 messages, and clients will not receive addresses from the remote server.
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Related to this question
Learn chapter
Infrastructure Services: DHCP, NAT, and IPv6
Key term
DHCP Relay Configuration
A DHCP relay configuration allows a router to forward DHCP broadcast requests from clients on one subnet to a DHCP server on a different subnet, enabling centralized IP address management across multiple networks.
Key term
DHCP Client and Server
A DHCP client is any device that requests network configuration settings from a DHCP server, which automatically assigns IP addresses and other parameters to devices on a network.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.