CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: a trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN.. 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 trunk link has a native VLAN mismatch between two switches. What is the most likely result?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Untagged frames can be interpreted as belonging to different VLANs on each switch.
Untagged traffic may be placed into different VLANs on each side of the trunk, causing traffic leakage or connectivity problems.
Key principle: A trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
All VLANs except the native VLAN stop forwarding immediately.
Why it's wrong here
A native VLAN mismatch does not automatically shut down all other VLANs.
When this WOULD be correct
In a different scenario, if the question stated that a switch was configured to drop all VLAN traffic except the native VLAN due to a specific security policy, then this option could be correct. This would imply a configuration that restricts forwarding based on VLAN settings.
✓
Untagged frames can be interpreted as belonging to different VLANs on each switch.
Why this is correct
Correct. That is the classic native VLAN mismatch issue.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
A trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN.
✗
The trunk automatically converts to an access port.
Why it's wrong here
Trunks do not auto-convert because of a native VLAN mismatch.
When this WOULD be correct
In a different scenario where the question states that a trunk port is configured incorrectly and the switch is set to automatically convert misconfigured ports, option C could be correct. For example, if the exam asks what happens when a trunk port is misconfigured and the switch has a feature enabled that forces a trunk to revert to access mode, then this option would apply.
✗
STP is disabled on the trunk until the mismatch is corrected.
In a different scenario where the question specifies that a trunk link has been configured to disable STP for performance reasons, a native VLAN mismatch could lead to STP being disabled, making this option correct. The question would need to clarify that STP behavior is altered due to specific configurations.
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.
✓Untagged frames can be interpreted as belonging to different VLANs on each switch.Correct answer▾
Why this is correct
Correct. That is the classic native VLAN mismatch issue.
✗All VLANs except the native VLAN stop forwarding immediately.Wrong answer — click to see why▾
Why this is wrong here
A native VLAN mismatch does not cause all other VLANs to stop forwarding. The trunk continues to forward frames for all VLANs, but untagged frames (native VLAN) are miscommunicated.
★ When this WOULD be the correct answer
In a different scenario, if the question stated that a switch was configured to drop all VLAN traffic except the native VLAN due to a specific security policy, then this option could be correct. This would imply a configuration that restricts forwarding based on VLAN settings.
Why candidates choose this
Students might think that a misconfiguration on the native VLAN would disrupt all VLAN traffic, but in reality, only the native VLAN traffic is affected.
✗The trunk automatically converts to an access port.Wrong answer — click to see why▾
Why this is wrong here
A trunk port does not automatically convert to an access port due to a native VLAN mismatch. The trunk remains operational, but the native VLAN mismatch causes problems for untagged traffic.
★ When this WOULD be the correct answer
In a different scenario where the question states that a trunk port is configured incorrectly and the switch is set to automatically convert misconfigured ports, option C could be correct. For example, if the exam asks what happens when a trunk port is misconfigured and the switch has a feature enabled that forces a trunk to revert to access mode, then this option would apply.
Why candidates choose this
Some might confuse a native VLAN mismatch with other trunk misconfigurations that cause the port to revert to access mode, such as a VLAN mismatch on a DTP negotiation.
✗STP is disabled on the trunk until the mismatch is corrected.Wrong answer — click to see why▾
Why this is wrong here
STP continues to run normally on the trunk link despite a native VLAN mismatch. The mismatch does not disable STP; it only affects the handling of untagged frames.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that a trunk link has been configured to disable STP for performance reasons, a native VLAN mismatch could lead to STP being disabled, making this option correct. The question would need to clarify that STP behavior is altered due to specific configurations.
Why candidates choose this
Students may think that any misconfiguration on a trunk would cause STP to shut down the port for safety, but STP only blocks ports to prevent loops, not due to native VLAN mismatches.
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
Be careful not to confuse native VLAN mismatches with issues that affect tagged traffic or automatic switch behavior.
Detailed technical explanation
How to think about this question
A trunk link in Cisco networking carries traffic for multiple VLANs between switches by tagging frames with VLAN identifiers. The native VLAN is a special VLAN on a trunk port where untagged frames are placed. By default, the native VLAN is VLAN 1, but it can be changed. When two switches have a trunk link, they must agree on the native VLAN to correctly interpret untagged traffic. If there is a native VLAN mismatch, untagged frames sent from one switch are assigned to a different VLAN on the receiving switch, causing VLAN leakage and connectivity issues.
The native VLAN mismatch problem arises because untagged frames are assumed to belong to the native VLAN on each side of the trunk. If Switch A uses VLAN 10 as native and Switch B uses VLAN 20, untagged frames sent by Switch A are placed into VLAN 10, but Switch B treats those same frames as VLAN 20 traffic. This mismatch leads to frames being misclassified, which can cause traffic to be forwarded incorrectly or dropped, and can also introduce security risks by leaking traffic between VLANs.
In practical Cisco environments, a native VLAN mismatch does not disable the trunk or shut down VLANs; instead, it causes subtle and hard-to-diagnose connectivity problems. The Spanning Tree Protocol (STP) continues to operate normally despite the mismatch. Network engineers must verify and align native VLAN settings on both ends of a trunk to prevent these issues. The exam trap is assuming that a native VLAN mismatch causes trunks to fail or convert to access ports, which does not happen in Cisco switches.
KKey Concepts to Remember
A trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN.
The native VLAN on a trunk port determines how untagged frames are classified and forwarded between switches.
A native VLAN mismatch occurs when two switches on a trunk link have different native VLAN configurations, causing untagged frames to be misclassified.
Untagged frames sent on a trunk are assigned to the native VLAN configured on the receiving switch, which can differ if there is a mismatch.
A native VLAN mismatch does not cause the trunk to shut down or convert to an access port automatically on Cisco switches.
Spanning Tree Protocol (STP) continues to operate normally on trunks even if there is a native VLAN mismatch.
Traffic leakage or connectivity problems occur because untagged frames are interpreted as belonging to different VLANs on each side of the trunk.
Network engineers must ensure native VLAN consistency on both ends of a trunk to maintain proper VLAN segregation and traffic forwarding.
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 trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN.
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 trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN., 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 trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN..
What is the correct answer to this question?
The correct answer is: Untagged frames can be interpreted as belonging to different VLANs on each switch. — Untagged traffic may be placed into different VLANs on each side of the trunk, causing traffic leakage or connectivity problems.
What should I do if I get this 200-301 question wrong?
Review a trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN., 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". 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 trunk link carries traffic for multiple VLANs by tagging frames with VLAN identifiers except for untagged frames assigned to the native VLAN.
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