CCNA Switching and Network Access Practice Question
Exhibit
interface Gi1/0/7 switchport mode access switchport voice vlan 20 spanning-tree portfast
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?
⚠ Common exam trap
Ensure both data and voice VLANs are configured when devices share a port. Don't confuse duplex or trunk settings with VLAN issues.
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
✓
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.
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
The 'switchport mode dynamic auto' command sets the port to negotiate trunking via DTP, but it does not assign a specific VLAN for untagged traffic. On a port connected to an IP phone and PC, the switchport typically must be in access mode so that the PC's frames are placed in the configured access VLAN. Dynamic auto could also cause the link to become a trunk if the phone or PC sends DTP frames, which would disrupt the expected VLAN classification.
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 voice VLAN (VLAN 20) is already functioning correctly because the IP phone is operating, indicating the phone has received its VLAN information via CDP or LLDP. The reported problem concerns the PC's data traffic, which is sent untagged from the PC and must be carried in the access VLAN. Changing 'switchport voice vlan 20' would alter only the tagged voice traffic and would not fix the PC's missing data connectivity, so it is not the appropriate corrective action.
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 fails to reach the network because it is untagged on the access port while the switchport is likely in its default VLAN 1 or a mismatched VLAN. Issuing 'switchport access vlan 10' explicitly assigns the data VLAN to the port, ensuring the PC's traffic is placed in the correct Layer 2 domain. The phone can still tag its voice traffic with VLAN 20 via the voice VLAN feature, but the access VLAN governs the untagged PC traffic.
- ✗
spanning-tree guard root
Why it's wrong here
Root Guard is a Spanning Tree Protocol (STP) enhancement that prevents a designated port from becoming a root port if a superior BPDU arrives. It does not influence VLAN assignment or untagged traffic classification on an access port. The PC's lack of connectivity is a data-plane VLAN membership issue, not a control-plane STP topology issue, so enabling Root Guard would leave the symptom unchanged.
When this WOULD be correct
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 fails to reach the network because it is untagged on the access port while the switchport is likely in its default VLAN 1 or a mismatched VLAN. Issuing 'switchport access vlan 10' explicitly assigns the data VLAN to the port, ensuring the PC's traffic is placed in the correct Layer 2 domain. The phone can still tag its voice traffic with VLAN 20 via the voice VLAN feature, but the access VLAN governs the untagged PC traffic.
✗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?”
Visual reference
Go deeper
Related to this question
Learn chapter
Interpreting Packet Capture Output for Layer 2/3 Troubleshooting
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.
Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
About these practice questions
This 200-301 question is part of Courseiva's 1,389-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
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.