CCNA Switching and Network Access Practice Question
Which TWO switch port configurations are required when connecting a Cisco IP phone and a desktop PC to a single access port?
⚠ Common exam trap
Cisco often tests the misconception that a trunk port is needed to carry both voice and data VLANs, but the correct approach uses a single access port with the 'switchport voice vlan' command to handle both VLANs without trunking.
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
✓
Use the 'switchport voice vlan' command to assign a dedicated voice VLAN.
The 'switchport voice vlan' command assigns a dedicated VLAN for voice traffic, allowing the IP phone to tag its packets with the voice VLAN ID while the PC remains in the native (data) VLAN. Option D is correct because 'mls qos trust cos' preserves the Layer 2 Class of Service (CoS) markings from the IP phone, ensuring voice packets receive appropriate QoS treatment across the network. Option A is incorrect because a trunk port is not required—the access port with the voice VLAN command handles both VLANs without trunking. Option C is incorrect because disabling Spanning Tree Protocol (STP) is not a recommended practice and does not prevent voice delays; STP is essential for loop prevention and can be tuned with PortFast instead. Option E is incorrect because the port must remain a Layer 2 access port, not a routed port, to support both the PC and IP phone.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure the port as a trunk and allow both VLANs.
Why it's wrong here
Configuring a trunk port is incorrect here because an IP phone and a PC are end hosts, not uplinks between switches or routers. A trunk would indiscriminately carry multiple tagged VLANs, whereas this wired infrastructure relies on an access port with a designated voice VLAN. The phone tags its own voice frames, and the PC's traffic remains untagged in the access VLAN. This avoids trunk negotiation and keeps the switch-to-device link secure and deterministic.
- ✓
Use the 'switchport voice vlan' command to assign a dedicated voice VLAN.
Why this is correct
The 'switchport voice vlan' command is the correct method because it configures an access port to carry both data and voice while keeping them logically separate. The Cisco IP phone uses CDP or LLDP to learn the configured voice VLAN, tags all voice frames with that VLAN's 802.1Q header, and passes the PC's untagged traffic in the access VLAN. This preserves the normal access port behavior for the connected PC while ensuring voice traffic is segmented for QoS and security.
- ✗
Disable spanning tree on the port to prevent voice delays.
Why it's wrong here
Disabling spanning tree is a dangerous overcorrection because STP is categorically required to prevent Layer 2 forwarding loops that would disable the entire network. Voice delays on switchports are not caused by STP itself but by the classic listening and learning states on an access port; the proper fix is enabling 'spanning-tree portfast' on the port. PortFast brings the port to forwarding immediately while STP remains enabled globally to protect against loops.
- ✓
Apply 'mls qos trust cos' on the interface to preserve voice packet markings.
Why this is correct
'mls qos trust cos' is correct because Cisco IP phones mark their voice traffic with a Class of Service of 5 and signaling with 3, and by default the access port does not trust ingress CoS, reclassifying it as 0. This command instructs the switchport to honor the phone's CoS markings, extending the QoS trust boundary down to the phone itself. Without this trust, voice packets would lose their priority and could be queued alongside best-effort data, causing jitter and latency.
- ✗
Configure the port as a routed port with an IP address for management.
Why it's wrong here
A routed port disables Layer 2 switching and VLAN segmentation entirely, which is the opposite of what this scenario requires. The phone and PC need to reside in separate VLANs on the same physical connection, but a routed port offers only a single IP subnet without 802.1Q tagging for multiple VLANs. This configuration is meant for connecting routers or interconnecting switches at Layer 3, not for attaching end devices that rely on a switchport's LAN switching functions.
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.
✓Use the 'switchport voice vlan' command to assign a dedicated voice VLAN.Correct answer▾
Why this is correct
The 'switchport voice vlan' command is the correct method because it configures an access port to carry both data and voice while keeping them logically separate. The Cisco IP phone uses CDP or LLDP to learn the configured voice VLAN, tags all voice frames with that VLAN's 802.1Q header, and passes the PC's untagged traffic in the access VLAN. This preserves the normal access port behavior for the connected PC while ensuring voice traffic is segmented for QoS and security.
✗Configure the port as a trunk and allow both VLANs.Wrong answer — click to see why▾
Why this is wrong here
Using a trunk port for a single device connection is unnecessary and violates standard access port design; it would also require the phone to support trunking, which is not the typical Cisco IP phone configuration.
✗Disable spanning tree on the port to prevent voice delays.Wrong answer — click to see why▾
Why this is wrong here
STP does not introduce significant delays in normal operation, and disabling it risks broadcast storms and network loops.
✗Configure the port as a routed port with an IP address for management.Wrong answer — click to see why▾
Why this is wrong here
Access ports operate at Layer 2; converting to a routed port would prevent the phone and PC from communicating within their respective VLANs.
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
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
Key term
QoS
QoS (Quality of Service) is a network technique that manages data traffic to ensure critical applications get the bandwidth and low latency they need.
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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.