CCNA Network Infrastructure and Connectivity Practice Question
A user reports that their computer cannot access the network. The technician checks the computer's IP configuration and finds an APIPA address (169.254.x.x). The computer is connected to a switch port on VLAN 20. The DHCP server is located on VLAN 1. The technician then examines the router's interfaces using 'show ip interface brief' and sees that all interfaces shown are up/up. What should the technician do next?
⚠ Common exam trap
Cisco often tests the concept that a DHCP relay (ip helper-address) is required when the DHCP server is on a different subnet, and candidates mistakenly focus on server-side issues or ping tests instead of the router configuration.
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
✓
Verify that the ip helper-address command is configured on the router's VLAN 20 interface.
The APIPA address (169.254.x.x) indicates the host failed to obtain a DHCP lease. Since the DHCP server is on VLAN 1 and the host is on VLAN 20, a DHCP relay (ip helper-address) must be configured on the router's VLAN 20 interface to forward DHCP broadcast messages to the server. The 'show ip interface brief' shows all interfaces are up/up, so the next logical step is to verify the relay configuration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Check the DHCP server logs to see if it is receiving Discover messages.
Why it's wrong here
Checking the DHCP server logs for Discover messages is premature in this scenario. Because the DHCP server resides on a different subnet than the clients, server-side logs will only show Discover packets if the router's VLAN 20 interface has an IP helper-address configured to forward broadcast DHCP requests. If the helper-address is missing, the router drops the broadcast at the VLAN boundary, and the server never sees any Discover traffic—so the absence of such messages in the logs would merely confirm the relay misconfiguration, not diagnose it. This step is valid only after confirming that the relay configuration is correct, and it wastes troubleshooting time by skipping the most fundamental cause.
- ✓
Verify that the ip helper-address command is configured on the router's VLAN 20 interface.
Why this is correct
The router is the intervlan router, and the DHCP server is on a different subnet. For a DHCP Discover broadcast to cross VLANs, the router must have an IP helper-address pointing to the DHCP server's IP address on the VLAN 20 interface. Since all ports are up/up, the problem is almost certainly the missing relay. Checking this config directly addresses the most probable cause.
- ✗
Attempt to ping the DHCP server's IP address from the host's APIPA address.
Why it's wrong here
The host's APIPA address (169.254.x.x) is a link-local address. Without a default gateway or a routable IP, pinging an address on a different subnet will not work, even if the DHCP server is reachable. This test does not confirm DHCP functionality and is not a standard troubleshooting step for DHCP failures.
- ✗
Restart the DHCP service on the server and recheck the host.
Why it's wrong here
Restarting the DHCP service is a disruptive action and should not be the first step, especially when the root cause likely lies in the network configuration (missing relay). It does not address the underlying issue and may cause unnecessary downtime.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Verify that the ip helper-address command is configured on the router's VLAN 20 interface.Correct answer▾
Why this is correct
The router is the intervlan router, and the DHCP server is on a different subnet. For a DHCP Discover broadcast to cross VLANs, the router must have an IP helper-address pointing to the DHCP server's IP address on the VLAN 20 interface. Since all ports are up/up, the problem is almost certainly the missing relay. Checking this config directly addresses the most probable cause.
✗Check the DHCP server logs to see if it is receiving Discover messages.Wrong answer — click to see why▾
Why this is wrong here
This action assumes the DHCP request has already reached the server; it bypasses verifying the network path that would deliver the broadcast to the server, which is the most likely missing piece.
✗Attempt to ping the DHCP server's IP address from the host's APIPA address.Wrong answer — click to see why▾
Why this is wrong here
Candidates might think that if the ping fails, the problem is network connectivity, but APIPA addresses are non-routable and the test itself is invalid in this context.
✗Restart the DHCP service on the server and recheck the host.Wrong answer — click to see why▾
Why this is wrong here
Many techs jump to rebooting a service when a simple configuration check would reveal the real problem. This violates the principle of least intrusive troubleshooting.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Related to this question
Learn chapter
IPv4 Addressing and Address Classes
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.