CCNA Switching and Network Access Practice Question
Exhibit
interface gi1/0/10 switchport mode access switchport access vlan 999 switchport voice vlan 20 spanning-tree portfast
A user says the phone connected to a switch port works, but the attached PC does not get network access. What is the most likely switch-side issue?
⚠ Common exam trap
Ensure you understand the difference between voice and access VLANs and how they affect different devices on the same port.
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 access VLAN for the PC is misconfigured
An IP phone can use a voice VLAN while the attached PC uses the access VLAN. If the access VLAN is missing or wrong, the phone may still work while the PC fails.
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 access VLAN for the PC is misconfigured
Why this is correct
In a typical IP phone topology, the phone passes PC traffic toward the switch as untagged frames, relying on the port's access VLAN assignment. If the PC's access VLAN is incorrect or doesn't match the intended data subnet, the PC receives no valid IP connectivity even though the phone registers. The voice VLAN only affects the phone's tagged voice traffic; it does not fix PC data VLAN misconfiguration.
- ✗
The voice VLAN should always match the access VLAN
Why it's wrong here
Voice VLAN and access VLAN serve separate purposes: access VLAN carries PC data and should match the user's subnet, while voice VLAN carries phone traffic and is often a distinct network segment for management and QoS. The two can be the same only if the design intentionally consolidates traffic, but forcing them to match would prevent logical separation and is not a general requirement.
When this WOULD be correct
In a scenario where a switch port is configured with a single VLAN for both voice and data (e.g., a small office without separate voice VLAN), the voice VLAN should match the access VLAN to ensure the phone and PC can communicate on the same network.
- ✗
PortFast blocks the PC from sending traffic
Why it's wrong here
PortFast changes a switch port from spanning-tree listening/learning to forwarding almost immediately, reducing the time to send traffic; it does not filter or block frames. When enabled on an access port with an IP phone, PortFast actually helps the PC connect faster after a link change, so it cannot be the cause of the PC being unable to send traffic.
- ✗
The phone requires the switch to be in trunk mode
Why it's wrong here
An access port configured with a voice VLAN already supports both traffic types: PC frames are untagged in the access VLAN, and phone frames are 802.1Q-tagged with the voice VLAN. This is the standard switchport configuration for IP phones, so placing the port in trunk mode is unnecessary and can introduce VLAN negotiation or security issues.
When this WOULD be correct
If the question stated that the phone is not working at all and the switch port is connected to an IP phone that requires multiple VLANs (e.g., voice and data), then the switch port might need to be in trunk mode to carry both tagged and untagged traffic. For example, a scenario where the phone fails to get an IP address and the PC also has no connectivity could indicate a trunk misconfiguration.
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 access VLAN for the PC is misconfiguredCorrect answer▾
Why this is correct
In a typical IP phone topology, the phone passes PC traffic toward the switch as untagged frames, relying on the port's access VLAN assignment. If the PC's access VLAN is incorrect or doesn't match the intended data subnet, the PC receives no valid IP connectivity even though the phone registers. The voice VLAN only affects the phone's tagged voice traffic; it does not fix PC data VLAN misconfiguration.
✗The voice VLAN should always match the access VLANWrong answer — click to see why▾
Why this is wrong here
The voice VLAN and access VLAN are typically different; matching them would defeat the purpose of separating voice and data traffic, and it would not cause the PC to lose network access.
★ When this WOULD be the correct answer
In a scenario where a switch port is configured with a single VLAN for both voice and data (e.g., a small office without separate voice VLAN), the voice VLAN should match the access VLAN to ensure the phone and PC can communicate on the same network.
Why candidates choose this
Candidates may confuse the concept of VLAN matching with simplicity, thinking that using the same VLAN for voice and data avoids misconfiguration issues.
✗The phone requires the switch to be in trunk modeWrong answer — click to see why▾
Why this is wrong here
In the described scenario, the phone works but the PC does not, indicating a VLAN mismatch for the PC's access VLAN, not a trunk mode issue. Trunk mode is not required for a phone; instead, the switch port typically uses a voice VLAN and an access VLAN, with the phone tagging voice traffic and passing PC traffic untagged.
★ When this WOULD be the correct answer
If the question stated that the phone is not working at all and the switch port is connected to an IP phone that requires multiple VLANs (e.g., voice and data), then the switch port might need to be in trunk mode to carry both tagged and untagged traffic. For example, a scenario where the phone fails to get an IP address and the PC also has no connectivity could indicate a trunk misconfiguration.
Why candidates choose this
Candidates may confuse the need for trunking between switches with the requirement for a switch-to-phone connection, not realizing that most IP phones use a special voice VLAN configuration (access port with voice VLAN) rather than a full trunk.
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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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
VLAN
A VLAN (Virtual Local Area Network) is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location.
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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.