300-410 Infrastructure Services Practice Question
A network engineer is configuring a Cisco IOS router to support a new branch office that requires dynamic IPv4 addressing for clients. The router is already configured with a DHCP pool named BRANCH_POOL. The engineer notices that clients are not receiving IP addresses. Which command, when applied globally, is required to enable the DHCP service on the router?
⚠ Common exam trap
The trap here is assuming that configuring a DHCP pool automatically enables the DHCP service, but the service must be globally enabled with 'service dhcp'.
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
✓
service dhcp
The DHCP service on a Cisco IOS router must be enabled globally with the 'service dhcp' command. Although it is enabled by default, it can be disabled, preventing the router from responding to DHCP requests. Configuring a pool alone is insufficient. The correct command activates the service, allowing the router to lease addresses from the configured pool.
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 10.1.1.1
Why it's wrong here
The 'ip helper-address' command is used on an interface to forward UDP broadcasts, including DHCP requests, to a remote DHCP server. It does not enable the local DHCP server service. In this scenario, the router itself is the DHCP server, so this command is not applicable for enabling the service.
- ✗
ip dhcp pool BRANCH_POOL
Why it's wrong here
The 'ip dhcp pool BRANCH_POOL' command enters DHCP pool configuration mode but does not globally enable the DHCP service. It is used to define pool parameters. If the service is disabled, configuring a pool alone will not make the router respond to DHCP requests. This command is necessary but not sufficient.
- ✗
ip dhcp relay information option
Why it's wrong here
The 'ip dhcp relay information option' command globally enables the DHCP relay agent to insert relay agent information option (option 82) into DHCP requests. It is used when the router acts as a relay agent, not when it is the DHCP server. It does not enable the DHCP server service.
- ✓
service dhcp
Why this is correct
The 'service dhcp' command in global configuration mode enables the DHCP server and relay agent functionality on the router. By default, this service is enabled, but it may have been disabled. Without it, the router will not process DHCP requests even if a pool is configured. This command is essential to activate the DHCP service.
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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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