350-401 Infrastructure Practice Question
A network engineer at a branch office needs to configure a Cisco IOS router to obtain its WAN interface IPv4 address dynamically from the ISP using DHCP while also ensuring the ISP can reach a web server hosted on the internal LAN at 10.10.10.50. Which single command on the router's WAN interface accomplishes the address acquisition requirement?
⚠ Common exam trap
A common mix-up: candidates confuse DHCP client and DHCP server roles, or assuming that ip address negotiated works for Ethernet 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
✓
ip address dhcp
The requirement is for the router to dynamically obtain an IPv4 address from the ISP. The ip address dhcp interface command enables DHCP client functionality, which is the correct method for Ethernet WAN interfaces. Other options either configure the router as a DHCP server, forward DHCP requests, or use PPP-based negotiation, none of which meet the scenario's need for standard DHCP client behavior on an Ethernet WAN link.
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 dhcp pool WAN_POOL
Why it's wrong here
This command creates a DHCP address pool on the router, enabling it to act as a DHCP server for other devices. It does not configure the router to request an address from an upstream DHCP server. In this scenario, the router needs to be a client, not a server, so this command is incorrect.
- ✗
ip helper-address 203.0.113.1
Why it's wrong here
The ip helper-address command is used to forward UDP broadcast packets, such as DHCP requests from clients on a LAN, to a remote DHCP server. It does not make the router itself a DHCP client on its WAN interface. Applying it here would not cause the router to obtain an address from the ISP and would be irrelevant to the stated requirement.
- ✓
ip address dhcp
Why this is correct
This command configures the interface as a DHCP client, allowing it to dynamically request an IPv4 address, subnet mask, default gateway, and DNS servers from the ISP's DHCP server. It satisfies the requirement to obtain the WAN address dynamically without manual configuration, and is the standard Cisco IOS method for client-side DHCP on an interface.
- ✗
ip address negotiated
Why it's wrong here
This command is used with PPP or IPCP to negotiate an IP address, typically for dialer or serial interfaces. It is not intended for Ethernet WAN interfaces using DHCP. While it can obtain an address dynamically, it relies on PPP negotiation and would not work for a standard Ethernet handoff from an ISP using DHCP.
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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.