Question 781 of 1,020

Common Networking Hardware →mediumMultiple ChoiceObjective-mapped

220-1201 Common Networking Hardware Practice Question

This 220-1201 practice question tests your understanding of common networking hardware. 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.

A user reports that their VoIP phone works but the connected PC cannot access the network. The phone is connected to the wall jack, and the PC is connected to the phone's passthrough port. What is the most likely cause?

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.

A
The PC's network cable is faulty.
Why wrong: While possible, the most likely cause is a configuration issue on the switch, especially since the phone works.
B
The VoIP phone's passthrough port is disabled.
Why wrong: Most phones have the passthrough enabled by default. Disabling it would be an intentional change, not a common issue.
C
The switch port is not configured for the data VLAN, so the PC cannot get an IP address.
Correct. VoIP phones often use separate VLANs. If the switch port only allows the voice VLAN, the PC's traffic is blocked. Configuring the port for both VLANs resolves this.
D
The PC's network adapter is set to a static IP address that conflicts with the phone.
Why wrong: IP conflicts would cause issues for both devices, not just the PC. The phone works fine, so this is unlikely.

Full breakdown with real-world context →

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

✓

The switch port is not configured for the data VLAN, so the PC cannot get an IP address.

The VoIP phone and PC share a single physical switch port via the phone's passthrough port. For the PC to access the network, the switch port must be configured as a trunk (or access port with voice VLAN) carrying both the voice VLAN (for the phone) and the data VLAN (for the PC). If the switch port is not configured for the data VLAN, the PC will not receive an IP address from the DHCP server and cannot communicate on the network, even though the phone works because it uses its own voice VLAN.

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 PC's network cable is faulty.
Why it's wrong here
While possible, the most likely cause is a configuration issue on the switch, especially since the phone works.
✗
The VoIP phone's passthrough port is disabled.
Why it's wrong here
Most phones have the passthrough enabled by default. Disabling it would be an intentional change, not a common issue.
✓
The switch port is not configured for the data VLAN, so the PC cannot get an IP address.
Why this is correct
Correct. VoIP phones often use separate VLANs. If the switch port only allows the voice VLAN, the PC's traffic is blocked. Configuring the port for both VLANs resolves this.
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 PC's network adapter is set to a static IP address that conflicts with the phone.
Why it's wrong here
IP conflicts would cause issues for both devices, not just the PC. The phone works fine, so this is unlikely.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that a working phone implies the entire port is correctly configured, when in fact the phone can operate on its own voice VLAN even if the data VLAN is missing or misconfigured, leaving the PC stranded.

Detailed technical explanation

How to think about this question

In a typical Cisco VoIP deployment, the switch port is configured as an access port with the voice VLAN enabled (using the 'switchport voice vlan' command) or as a trunk allowing both VLANs. The phone uses CDP or LLDP to negotiate the voice VLAN and tags its traffic, while the PC remains untagged on the native VLAN (data VLAN). If the data VLAN is not allowed on the port, the PC's DHCP requests (broadcast frames) are not forwarded to the DHCP server, leaving the PC without an IP address. This is a common misconfiguration when setting up voice VLANs without also ensuring the data VLAN is present.

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.

Visual reference

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 220-1201 question test?

Common Networking Hardware — This question tests Common Networking Hardware — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The switch port is not configured for the data VLAN, so the PC cannot get an IP address. — The VoIP phone and PC share a single physical switch port via the phone's passthrough port. For the PC to access the network, the switch port must be configured as a trunk (or access port with voice VLAN) carrying both the voice VLAN (for the phone) and the data VLAN (for the PC). If the switch port is not configured for the data VLAN, the PC will not receive an IP address from the DHCP server and cannot communicate on the network, even though the phone works because it uses its own voice VLAN.

What should I do if I get this 220-1201 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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