350-401 Infrastructure Practice Question
A network engineer is configuring a Cisco IOS router to act as a DHCP relay agent for a subnet that has no local DHCP server. The DHCP server is at 10.10.10.5, and the router interface facing the clients is GigabitEthernet0/1 with IP address 10.20.20.1. Which command must be applied to the interface so that client DHCP broadcasts are forwarded to the server?
⚠ Common exam trap
Watch out — candidates often confuse DHCP server pool configuration with DHCP relay configuration, which are separate features applied in different configuration modes.
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 10.10.10.5
DHCP relay is enabled by placing ip helper-address on the interface receiving client broadcasts. The router then converts those broadcasts into unicast packets toward the specified server and populates the giaddr field so the server can identify the correct subnet. The other commands either do not exist, do not specify a server, or configure the router as a server rather than a relay, so they do not meet the requirement.
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 10.10.10.5
Why this is correct
The ip helper-address command is configured on the client-facing interface and instructs the router to forward UDP broadcasts, including DHCP DISCOVER and REQUEST, to the specified server as unicast packets. It also inserts the giaddr field with the interface IP so the server can select the correct pool. This directly satisfies the scenario.
- ✗
ip dhcp relay 10.10.10.5
Why it's wrong here
There is no Cisco IOS command named ip dhcp relay with an address argument. DHCP relay on IOS is implemented through ip helper-address, which also controls which UDP broadcast types are forwarded. This option is a fabricated command that would be rejected by the CLI and would not configure relay behavior.
- ✗
ip forward-protocol udp 67
Why it's wrong here
The ip forward-protocol udp command controls which UDP ports are forwarded when a helper address exists, but it does not itself designate a destination server. Without ip helper-address, DHCP broadcasts are not relayed to 10.10.10.5. This command is a modifier, not a relay configuration.
- ✗
ip dhcp pool CLIENT relay 10.10.10.5
Why it's wrong here
The ip dhcp pool command configures the router as a DHCP server, not a relay agent. The syntax shown is invalid and would not forward client broadcasts to an external server. Relay requires ip helper-address on the client-facing interface, so this configuration is wrong for the scenario.
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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 350-401 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 350-401 exam.