CCNA Switching and Network Access Practice Question
An IP phone connected to switch port Gi0/4 is working and receiving calls, but the PC connected to the phone's data port cannot obtain an IP address. The technician confirms that interface Gi0/4 has switchport mode access and shows switchport access vlan 10 and switchport voice vlan 100. What should the technician do next?
⚠ Common exam trap
Cisco often tests the misconception that a working phone implies all features are functional, but the PC port is a separate logical path that can be independently disabled or misconfigured.
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 the IP phone's passthrough mode for the PC port.
The PC connected to the IP phone's data port cannot obtain an IP address because the phone's internal switch (passthrough mode) is likely not forwarding traffic from the PC port to the upstream switch. The switch port is correctly configured with access VLAN 10 for data and voice VLAN 100 for voice, so the issue is not with the switch configuration but with the phone's ability to pass data traffic. Verifying the IP phone's passthrough mode ensures the PC port is enabled and forwarding frames to the switch.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Verify the DHCP scope for VLAN 10 on the DHCP server.
Why it's wrong here
While a depleted DHCP scope could prevent address assignment, the more likely immediate cause given the symptoms is the phone's internal VLAN handling. The technician should first rule out the phone's passthrough configuration before investigating DHCP server issues.
- ✗
Verify that CDP is enabled on the IP phone.
Why it's wrong here
CDP is used for voice VLAN discovery and is likely already functioning because the phone has successfully registered and is operational. CDP does not control the data VLAN for the attached PC; therefore, it is not relevant to this issue.
- ✗
Verify the QoS trust state on the switch port.
Why it's wrong here
QoS trust state on a switch port controls whether the switch preserves or re-marks incoming CoS/DSCP values for prioritization. It does not influence VLAN membership, untagged frame handling, or DHCP address assignment for a downstream PC. A misconfigured trust state could delay or drop packets under congestion, but it will not stop the PC from receiving an IP address, so this check addresses the wrong layer of the problem.
- ✓
Verify the IP phone's passthrough mode for the PC port.
Why this is correct
The IP phone acts as a switch; if the phone's PC port is not configured to pass traffic untagged on the correct VLAN (passthrough mode), the PC's frames will be dropped or placed in the wrong VLAN. Checking this setting directly addresses the path from PC to switch.
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 the IP phone's passthrough mode for the PC port.Correct answer▾
Why this is correct
The IP phone acts as a switch; if the phone's PC port is not configured to pass traffic untagged on the correct VLAN (passthrough mode), the PC's frames will be dropped or placed in the wrong VLAN. Checking this setting directly addresses the path from PC to switch.
✗Verify the DHCP scope for VLAN 10 on the DHCP server.Wrong answer — click to see why▾
Why this is wrong here
Assumes the switch port configuration alone guarantees proper VLAN delivery to the PC, ignoring the phone's role as a transparent bridge.
✗Verify that CDP is enabled on the IP phone.Wrong answer — click to see why▾
Why this is wrong here
Confuses the mechanism for voice VLAN assignment with the requirement for data passthrough; CDP's role is only for the phone's own voice VLAN, not for the PC's data VLAN.
✗Verify the QoS trust state on the switch port.Wrong answer — click to see why▾
Why this is wrong here
Misapplies QoS as a potential cause for a connectivity issue; it is a quality-of-service feature and does not block DHCP or initial network access.
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?”
Visual reference
Go deeper
Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
Voice VLAN
A Voice VLAN is a separate virtual local area network configured on a network switch to carry voice traffic, such as from IP phones, ensuring quality of service and security by isolating it from data traffic.
Key term
Switchport
A switchport is a physical or virtual interface on a network switch that connects devices like computers, printers, or other switches to a local area network.
About these practice questions
Courseiva writes every 200-301 question from scratch — 1,389 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
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.