CCNA Switching and Network Access Practice Question
A phone and PC share one switchport. The phone works, but the PC cannot reach its normal data resources. The switchport voice VLAN is configured, and the access VLAN is incorrect. Which explanation is strongest?
⚠ Common exam trap
Cisco often tests the misconception that a working phone implies the PC is also correctly configured, but the trap here is that voice and data VLANs are independent, so a misconfigured access VLAN only affects the PC.
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 PC is likely in the wrong data VLAN even though the phone still uses the correct voice VLAN.
The switchport is configured with a voice VLAN for the phone and an access VLAN for the PC. If the access VLAN is incorrect, the PC will be placed in the wrong data VLAN, preventing it from reaching its normal data resources, while the phone continues to operate correctly on its designated voice VLAN. This is a common misconfiguration where the data VLAN ID does not match the network segment the PC expects.
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 is likely in the wrong data VLAN even though the phone still uses the correct voice VLAN.
Why this is correct
The PC is likely in the wrong data VLAN even though the phone still uses the correct voice VLAN because a single switchport can serve two logical VLANs simultaneously: an access VLAN for untagged data traffic and a voice VLAN for tagged voice traffic. In a typical Cisco IP phone deployment, the phone tags its voice frames with the voice VLAN and passes the PC's untagged frames onto the access VLAN, so the phone's operation only proves the voice VLAN path is healthy. The PC's connectivity depends entirely on the access VLAN configuration—if the access VLAN ID, subnet, or DHCP scope is misconfigured, the PC will fail while the phone continues to work. Thus, the symptom directly points to a data VLAN issue, not a voice VLAN problem.
- ✗
If the phone works, the PC must also work because both use the same VLAN always.
Why it's wrong here
The assumption that the phone and PC must use the same VLAN is incorrect because an IP phone's internal three-port switch effectively creates two separate Layer 2 paths on the same physical port: one for voice (tagged, using the voice VLAN) and one for data (untagged, using the access VLAN). The phone's Ethernet uplink to the switch operates as an 802.1Q trunk, carrying both VLANs simultaneously, so the voice and data traffic are isolated at Layer 2. A functional phone confirms only that the voice VLAN is correctly configured and reachable; the PC's success depends on the access VLAN, which can easily be misconfigured, blocked by an ACL, or assigned to the wrong subnet. Thus, a working phone and non-working PC are entirely consistent and point to different VLAN configurations, not a shared-fate condition.
When this WOULD be correct
In a different scenario where both devices are explicitly stated to be on the same VLAN and the question focuses on a situation where a misconfiguration affects both devices equally, this option could be correct. For example, if the question specified that both the phone and PC are configured on the same VLAN and the VLAN is down, then this option would apply.
- ✗
The issue must be BGP because phones cannot use VLANs.
Why it's wrong here
The issue cannot be BGP because BGP (Border Gateway Protocol) is a Layer 3 routing protocol used between autonomous systems, whereas this scenario describes a Layer 2 switching problem on a single access port. Furthermore, phones absolutely can use VLANs: Cisco IP phones use CDP or LLDP to discover the voice VLAN and tag their voice traffic with an 802.1Q VLAN ID, so the claim that 'phones cannot use VLANs' is factually incorrect. The question's context is clearly about voice/data VLAN separation on a switchport, not inter-domain routing, making BGP a completely irrelevant diagnosis.
When this WOULD be correct
In a different question setup where the context involves a network configuration issue specifically related to BGP routing and VLANs, this option could be correct if the question states that BGP is misconfigured, causing devices on the same VLAN to fail to communicate. For example, if the question describes a scenario where both devices are on the same VLAN but cannot reach external resources due to BGP issues.
- ✗
The access VLAN becomes irrelevant whenever a voice VLAN is configured.
Why it's wrong here
The access VLAN does not become irrelevant when a voice VLAN is configured; rather, the switchport becomes a multi-VLAN port where both VLANs remain active and serve different functions. The access VLAN carries the PC's untagged data frames, while the voice VLAN carries the phone's tagged voice frames, and the PC's IP addressing, DHCP, and security policies are all tied to the access VLAN. If the access VLAN is misconfigured—for example, assigned to a nonexistent VLAN or not matching the PC's subnet—the PC will lose connectivity even though the phone, operating on a separate voice VLAN, continues to function normally. Therefore, the access VLAN is essential for the PC's data traffic and cannot be ignored.
When this WOULD be correct
In a scenario where a switchport is configured to only support voice traffic and is set to trunk mode without any access VLAN specified, this option could be correct. For example, if the question states that the switchport is exclusively for voice traffic and does not allow data traffic, then the access VLAN would indeed be irrelevant.
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 PC is likely in the wrong data VLAN even though the phone still uses the correct voice VLAN.Correct answer▾
Why this is correct
The PC is likely in the wrong data VLAN even though the phone still uses the correct voice VLAN because a single switchport can serve two logical VLANs simultaneously: an access VLAN for untagged data traffic and a voice VLAN for tagged voice traffic. In a typical Cisco IP phone deployment, the phone tags its voice frames with the voice VLAN and passes the PC's untagged frames onto the access VLAN, so the phone's operation only proves the voice VLAN path is healthy. The PC's connectivity depends entirely on the access VLAN configuration—if the access VLAN ID, subnet, or DHCP scope is misconfigured, the PC will fail while the phone continues to work. Thus, the symptom directly points to a data VLAN issue, not a voice VLAN problem.
✗If the phone works, the PC must also work because both use the same VLAN always.Wrong answer — click to see why▾
Why this is wrong here
This statement is incorrect because the phone and PC can operate on different VLANs on the same port. The phone uses the voice VLAN, while the PC uses the access (data) VLAN. They are not required to use the same VLAN, and misconfiguration of the access VLAN can cause the PC to fail while the phone works.
★ When this WOULD be the correct answer
In a different scenario where both devices are explicitly stated to be on the same VLAN and the question focuses on a situation where a misconfiguration affects both devices equally, this option could be correct. For example, if the question specified that both the phone and PC are configured on the same VLAN and the VLAN is down, then this option would apply.
Why candidates choose this
Students might assume that since both devices share the same physical port, they must be on the same VLAN. This confusion arises from a lack of understanding of how voice VLANs work, where the switchport is configured to carry multiple VLANs and the phone is placed on a separate VLAN from the PC.
✗The issue must be BGP because phones cannot use VLANs.Wrong answer — click to see why▾
Why this is wrong here
BGP (Border Gateway Protocol) is a routing protocol used between autonomous systems, not related to VLAN configuration on a switchport. The issue described is about Layer 2 VLAN assignment, not Layer 3 routing. BGP has no role in this scenario.
★ When this WOULD be the correct answer
In a different question setup where the context involves a network configuration issue specifically related to BGP routing and VLANs, this option could be correct if the question states that BGP is misconfigured, causing devices on the same VLAN to fail to communicate. For example, if the question describes a scenario where both devices are on the same VLAN but cannot reach external resources due to BGP issues.
Why candidates choose this
Students might confuse BGP with other protocols or think that any network issue involving phones must involve a routing protocol. The mention of 'phones' might trigger an association with VoIP and routing, but the problem is clearly about VLANs, not BGP.
✗The access VLAN becomes irrelevant whenever a voice VLAN is configured.Wrong answer — click to see why▾
Why this is wrong here
The access VLAN remains relevant even when a voice VLAN is configured. The access VLAN is used for the PC's data traffic, while the voice VLAN is used for the phone's traffic. If the access VLAN is incorrect, the PC will not be able to communicate on the correct data network.
★ When this WOULD be the correct answer
In a scenario where a switchport is configured to only support voice traffic and is set to trunk mode without any access VLAN specified, this option could be correct. For example, if the question states that the switchport is exclusively for voice traffic and does not allow data traffic, then the access VLAN would indeed be irrelevant.
Why candidates choose this
Students might think that configuring a voice VLAN overrides or makes the access VLAN unnecessary. However, both VLANs are active on the port, and the access VLAN still determines the VLAN for untagged data traffic from the PC.
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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Interpreting Packet Capture Output for Layer 2/3 Troubleshooting
Key term
Segment
A segment is a division of a larger network, such as a collision domain, broadcast domain, or a portion of a TCP data stream, used to organize traffic and improve performance.
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.
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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.