The answer is that the switchport access vlan should be changed to the data VLAN to match the subnet expected by the desktop. This is because on a voice-access port, the switch treats the access VLAN as the native VLAN for the PC traffic, while the voice VLAN is tagged for the phone; if the access VLAN is incorrectly set to the voice VLAN, the desktop PC will be placed in the voice subnet and cannot obtain a DHCP address from the data network. On the CCNA 200-301 v2 exam, this scenario tests your understanding of the "voice VLAN" feature and the critical distinction between the access VLAN (for data devices) and the voice VLAN (for IP phones)—a common trap is assuming the PC gets its IP from the phone itself, when in reality the phone simply passes the PC traffic untagged to the switch. Remember the memory tip: "Access for data, voice for the phone"—the access VLAN always serves the PC, so if the PC fails DHCP, check that the access VLAN is set to the correct data subnet.
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
interface GigabitEthernet1/0/24
description VoIP and Desktop
switchport mode access
switchport access vlan 10
switchport voice vlan 20
spanning-tree portfast
!
A network administrator has configured a switch port to support a VoIP phone and a desktop PC. Users report that the desktop PC cannot obtain an IP address via DHCP, while the VoIP phone registers successfully. The switch port is up/up, and the desktop is connected to the phone's PC port. What is the most likely cause of the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
interface GigabitEthernet1/0/24
description VoIP and Desktop
switchport mode access
switchport access vlan 10
switchport voice vlan 20
spanning-tree portfast
!
A
The switchport mode access should be changed to switchport mode trunk to allow both vlans.
Why wrong: Changing to trunk mode would require the phone to tag traffic, which might not be supported and could cause further issues.
B
The switchport access vlan should be changed to the data VLAN to match the subnet expected by the desktop.
With the phone's PC port forwarding the switch's access VLAN, correcting the access VLAN to the data VLAN ensures the desktop receives a DHCP offer from the data subnet.
C
The switchport voice vlan should be removed because the desktop cannot use it.
Why wrong: Removing the voice vlan would prevent the VoIP phone from registering, as it needs a dedicated voice vlan.
D
The spanning-tree portfast should be disabled to prevent DHCP delays.
Why wrong: Portfast actually helps speed up DHCP by immediately transitioning the port to forwarding state. Disabling it would cause delays, not resolve the IP assignment failure.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The switchport access vlan should be changed to the data VLAN to match the subnet expected by the desktop.
The desktop PC obtains its IP address from the data VLAN, but the switch port's access VLAN is likely misconfigured to the voice VLAN. Changing the access VLAN to the correct data VLAN places the PC in the proper subnet and allows DHCP to function. Option A is unnecessary because a voice-access port does not need to be a trunk. Option C would break the VoIP phone without fixing the PC's VLAN assignment. Option D is irrelevant; PortFast speeds up STP convergence and does not block DHCP.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The switchport mode access should be changed to switchport mode trunk to allow both vlans.
Why it's wrong here
Changing to trunk mode would require the phone to tag traffic, which might not be supported and could cause further issues.
✓
The switchport access vlan should be changed to the data VLAN to match the subnet expected by the desktop.
Why this is correct
With the phone's PC port forwarding the switch's access VLAN, correcting the access VLAN to the data VLAN ensures the desktop receives a DHCP offer from the data subnet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The switchport voice vlan should be removed because the desktop cannot use it.
Why it's wrong here
Removing the voice vlan would prevent the VoIP phone from registering, as it needs a dedicated voice vlan.
✗
The spanning-tree portfast should be disabled to prevent DHCP delays.
Why it's wrong here
Portfast actually helps speed up DHCP by immediately transitioning the port to forwarding state. Disabling it would cause delays, not resolve the IP assignment failure.
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.
✓The switchport access vlan should be changed to the data VLAN to match the subnet expected by the desktop.Correct answer▾
Why this is correct
With the phone's PC port forwarding the switch's access VLAN, correcting the access VLAN to the data VLAN ensures the desktop receives a DHCP offer from the data subnet.
✗The switchport mode access should be changed to switchport mode trunk to allow both vlans.Wrong answer — click to see why▾
Why this is wrong here
The current configuration uses access mode with voice vlan, which is correct for a phone+PC setup. Trunk mode is unnecessary and could break the phone's untagged traffic expectations.
✗The switchport voice vlan should be removed because the desktop cannot use it.Wrong answer — click to see why▾
Why this is wrong here
The voice vlan is correctly configured for the phone; the problem is with the data vlan assignment for the desktop.
✗The spanning-tree portfast should be disabled to prevent DHCP delays.Wrong answer — click to see why▾
Why this is wrong here
Portfast is beneficial for host ports; disabling it would worsen the issue by introducing STP convergence delays.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that the PC uses the voice VLAN or that the port must be a trunk, when in reality the phone handles the VLAN separation internally and the switch port remains an access port with a separate voice VLAN.
Detailed technical explanation
How to think about this question
Cisco IP phones use a built-in switch that tags voice traffic with the voice VLAN (via 802.1Q) and passes data traffic untagged on the access VLAN. The switch port must be configured with both an access VLAN (for the PC) and a voice VLAN (for the phone) using the 'switchport voice vlan' command. If the access VLAN is misconfigured to the voice VLAN ID, the PC will be in the wrong subnet and DHCP will fail, while the phone still works because it tags its traffic with the voice VLAN regardless of the access VLAN setting.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The switchport access vlan should be changed to the data VLAN to match the subnet expected by the desktop. — The desktop PC obtains its IP address from the data VLAN, but the switch port's access VLAN is likely misconfigured to the voice VLAN. Changing the access VLAN to the correct data VLAN places the PC in the proper subnet and allows DHCP to function. Option A is unnecessary because a voice-access port does not need to be a trunk. Option C would break the VoIP phone without fixing the PC's VLAN assignment. Option D is irrelevant; PortFast speeds up STP convergence and does not block DHCP.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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