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. A key principle to apply: a Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly.. 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 phone and a PC are attached to the same switchport. The intended data VLAN is VLAN 10, and the phone uses voice VLAN 20. The switchport currently has `switchport voice vlan 20` configured. The phone works, but the PC cannot reach the data network. Which command is most likely missing?
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.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
switchport access vlan 10
When a Cisco IP phone and a PC share one port, the switchport often needs both a data VLAN and a voice VLAN. If the voice VLAN exists but the data access VLAN is wrong or missing, the phone can work while the PC fails.
Key principle: A Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
switchport mode dynamic auto
Why it's wrong here
Dynamic auto is not the standard requirement for an endpoint-facing phone port.
When this WOULD be correct
This command would be correct when the question asks for a switchport configuration that allows dynamic trunk negotiation with a neighboring switch, such as in a scenario where you want the port to become a trunk if the neighbor is set to 'dynamic desirable' or 'trunk'.
✗
switchport voice vlan 20
Why it's wrong here
The phone is already working, so the voice VLAN likely exists.
When this WOULD be correct
In a scenario where a phone and PC are connected to the same switchport, and the phone works but the PC cannot reach the data network, the missing setting is the access VLAN for the PC. Option C (switchport access vlan 10) would be correct if VLAN 10 is the data VLAN.
✓
switchport access vlan 10
Why this is correct
The PC needs the correct data VLAN assignment on the access side.
Clue confirmation
The clue words "most likely", "which command" in the question point toward this answer.
Related concept
A Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly.
A question where a switchport is connected to a switch that should not become the root bridge, and the network experiences instability due to rogue root bridge elections. The correct answer would be to enable root guard on that port.
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.
✓switchport access vlan 10Correct answer▾
Why this is correct
The PC needs the correct data VLAN assignment on the access side.
✗switchport mode dynamic autoWrong answer — click to see why▾
Why this is wrong here
The phone works but the PC cannot reach the data network, indicating the PC is not in the correct VLAN. 'switchport mode dynamic auto' sets the port to negotiate trunking via DTP, which does not assign a data VLAN to the PC.
★ When this WOULD be the correct answer
This command would be correct when the question asks for a switchport configuration that allows dynamic trunk negotiation with a neighboring switch, such as in a scenario where you want the port to become a trunk if the neighbor is set to 'dynamic desirable' or 'trunk'.
Why candidates choose this
Candidates may confuse dynamic trunking protocols with VLAN assignment, thinking that 'dynamic auto' will automatically assign the PC to the correct VLAN, but it only affects trunking mode, not access VLAN.
✗switchport voice vlan 20Wrong answer — click to see why▾
Why this is wrong here
The PC cannot reach the data network because the switchport is likely configured as a voice VLAN only, but the data VLAN (access VLAN) is missing. Option B configures the voice VLAN, which is correct for the phone, but does not set the access VLAN for the PC.
★ When this WOULD be the correct answer
In a scenario where a phone and PC are connected to the same switchport, and the phone works but the PC cannot reach the data network, the missing setting is the access VLAN for the PC. Option C (switchport access vlan 10) would be correct if VLAN 10 is the data VLAN.
Why candidates choose this
Candidates may think that since the phone works, the voice VLAN is correctly configured, and they might overlook that the PC needs a separate data VLAN. They might assume the voice VLAN setting is the missing piece, but it is already present.
✗spanning-tree guard rootWrong answer — click to see why▾
Why this is wrong here
The issue is that the PC cannot reach the data network, which is typically configured via the access VLAN. Spanning-tree guard root is unrelated to VLAN assignment; it prevents a switch from becoming the root bridge, not connectivity issues on a specific VLAN.
★ When this WOULD be the correct answer
A question where a switchport is connected to a switch that should not become the root bridge, and the network experiences instability due to rogue root bridge elections. The correct answer would be to enable root guard on that port.
Why candidates choose this
Candidates may confuse root guard with other security features or think that spanning-tree issues could cause connectivity loss for the PC, but the symptom here is VLAN-specific, not spanning-tree related.
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
Ensure both data and voice VLANs are configured when devices share a port. Don't confuse duplex or trunk settings with VLAN issues.
Detailed technical explanation
How to think about this question
When a Cisco IP phone and a PC share a single switchport, the switch must handle two types of traffic: voice and data. The phone typically tags its voice traffic with a specific VLAN ID known as the voice VLAN, while the PC sends untagged frames that belong to the data VLAN. This separation allows the switch to apply different policies such as Quality of Service (QoS) for voice traffic and standard forwarding for data traffic. The switchport voice VLAN command configures the VLAN for tagged voice frames, and the switchport access VLAN command assigns the VLAN for untagged data frames from the PC.
The decision process for configuring such a port involves ensuring that the voice VLAN is set for the IP phone and that the access VLAN is correctly assigned for the PC. If the voice VLAN is configured but the access VLAN is missing or incorrect, the phone will still register and function because its traffic is tagged and recognized. However, the PC's untagged frames will not be assigned to the correct VLAN, causing it to fail to reach the data network. Dynamic auto mode is irrelevant here because endpoint ports typically operate as access ports, not trunks. Similarly, spanning-tree root guard does not influence VLAN assignment or endpoint connectivity.
A common exam trap is assuming that configuring the voice VLAN alone is sufficient for both devices to work. Candidates often overlook the need for the access VLAN, which leads to the PC failing to communicate despite the phone working. In practical networks, this misconfiguration causes user complaints about data connectivity while voice remains operational. Understanding that the access VLAN handles untagged PC traffic and the voice VLAN handles tagged phone traffic is crucial to avoid this mistake and ensure both devices function correctly on the same port.
KKey Concepts to Remember
A Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly.
The switchport access VLAN setting assigns the VLAN for untagged data traffic from devices like PCs connected behind an IP phone.
The switchport voice VLAN command assigns a special VLAN for tagged voice traffic from Cisco IP phones, enabling QoS and traffic separation.
If the voice VLAN is configured but the access VLAN is missing or incorrect, the phone can function while the PC cannot access the data network.
Dynamic auto mode on a switchport allows the port to negotiate trunking but is not required or recommended for endpoint ports with IP phones.
Spanning-tree root guard protects the root bridge placement in STP and does not affect VLAN assignment or endpoint connectivity on access ports.
Cisco IP phones tag voice traffic with the voice VLAN ID, while PCs send untagged frames that must be assigned to the correct access VLAN.
Proper VLAN configuration on switchports ensures that voice and data traffic are separated and forwarded correctly, preventing connectivity issues.
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
A Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly.
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.
Review a Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly., then practise related 200-301 questions on the same topic to reinforce the concept.
Switching and Network Access — This question tests Switching and Network Access — A Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly..
What is the correct answer to this question?
The correct answer is: switchport access vlan 10 — When a Cisco IP phone and a PC share one port, the switchport often needs both a data VLAN and a voice VLAN. If the voice VLAN exists but the data access VLAN is wrong or missing, the phone can work while the PC fails.
What should I do if I get this 200-301 question wrong?
Review a Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly., then practise related 200-301 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "which command". 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?
A Cisco switchport configured for an IP phone and PC must have both a voice VLAN and a data VLAN to separate voice and data traffic properly.
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