300-410 Infrastructure Services Practice Question
A network engineer is configuring a Cisco router to act as a DHCP relay agent. The DHCP server is located on a different subnet. Which command is required on the router's interface to forward DHCP requests to the server?
⚠ Common exam trap
Many exam-takers confuse the DHCP relay command with DHCP server configuration commands; ip helper-address is for relay, while ip dhcp pool is for local server.
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
✓
ip helper-address <server-ip>
The ip helper-address command on an interface enables the router to forward DHCP broadcast requests to a specified DHCP server on another subnet. This is essential when clients and the DHCP server are on different broadcast domains. The command also forwards other UDP broadcasts by default, but DHCP relay is the primary use case here.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
ip helper-address <server-ip>
Why this is correct
The ip helper-address command configured on the router interface enables DHCP relay by forwarding UDP broadcasts (including DHCP DISCOVER) to the specified server IP address. This allows clients on a subnet without a local DHCP server to obtain addresses from a centralized server. It is the standard method for DHCP relay in Cisco IOS.
- ✗
ip forward-protocol udp 67
Why it's wrong here
The ip forward-protocol udp command is used to control which UDP ports are forwarded by the ip helper-address feature. It does not by itself enable DHCP relay; it only specifies that UDP port 67 (DHCP server) should be forwarded. Without ip helper-address, no relay occurs. This command is typically used to disable forwarding of certain UDP ports.
- ✗
ip dhcp pool <name>
Why it's wrong here
The ip dhcp pool command is used to configure the router as a DHCP server, not as a relay agent. It defines an address pool for local DHCP clients. In this scenario, the router must relay requests to an external DHCP server, so ip helper-address is the correct command, not ip dhcp pool.
- ✗
ip dhcp relay <server-ip>
Why it's wrong here
The command ip dhcp relay is not valid Cisco IOS syntax for DHCP relay. The correct command is ip helper-address. While some platforms may support similar commands, in standard CCNP ENARSI context, ip helper-address is the required configuration to forward DHCP requests to a 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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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
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