- A
Add VLAN 99 to the allowed VLAN list on the trunk interface of SW1.
Why wrong: Even if VLAN 99 were added to the allowed list, the native VLANs would still be mismatched. The CDP warning is about the inconsistency of the untagged VLAN, not about VLAN 99 being absent from the allowed list. Untagged traffic would continue to be placed into different VLANs on each switch, preserving the loop risk.
- B
Remove the trunk configuration and set both interfaces as access ports in VLAN 1.
Why wrong: This action is unnecessarily disruptive. The trunk is working (data traffic flows), so removing it would break connectivity across switches. The issue is only a configuration mismatch, which can be fixed without changing the port type. This skips the straightforward corrective step and introduces a network outage.
- C
Enable spanning‑tree PortFast on the trunk ports.
Why wrong: PortFast is designed for access ports (edge ports) to bypass listening and learning states. Applying PortFast to a trunk port is inappropriate and would not resolve the native VLAN mismatch. It also risks creating immediate forwarding loops, worsening the problem.
- D
Configure the native VLAN to match on both ends of the trunk.
The root cause is a configured native VLAN mismatch (1 vs 99). Changing one switch’s native VLAN to match the other (or setting both to a common VLAN) immediately resolves the CDP warning and eliminates the potential for broadcast loops caused by the mismatch. This is the most direct and least disruptive next step.
Quick Answer
The correct next step is to configure the native VLAN to match on both ends of the trunk. This resolves the CDP native VLAN mismatch because 802.1Q trunks leave the native VLAN untagged, so when SW1 expects VLAN 1 and SW2 expects VLAN 99, broadcast traffic from one side can leak into the wrong VLAN on the other, creating loops and security holes—even though data frames may still pass. On the CCNA 200-301 v2 exam, this scenario tests your understanding of trunking behavior and the hidden dangers of mismatched native VLANs; a common trap is assuming that because traffic flows, the configuration is fine. Remember the memory tip: “Untagged means unguarded—match your native VLANs to keep broadcasts from crossing boundaries.”
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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 network technician notices CDP native VLAN mismatch warnings between switches SW1 and SW2 on their trunk link. The technician runs 'show interfaces trunk' on SW1 and sees native VLAN 1, then on SW2 and sees native VLAN 99. Data traffic is currently passing, but the mismatch can cause broadcast loops. What should the technician do next?
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
Configure the native VLAN to match on both ends of the trunk.
The correct action is to configure the native VLAN to match on both ends of the trunk. CDP reports a native VLAN mismatch when the native VLANs differ on the two sides of a trunk link. Although data traffic may still pass because 802.1Q does not tag frames on the native VLAN, the mismatch can cause broadcast loops and security risks, as frames from one native VLAN may be misinterpreted on the other side. Setting both sides to the same native VLAN (e.g., VLAN 1 or VLAN 99) resolves the mismatch and ensures proper Layer 2 behavior.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add VLAN 99 to the allowed VLAN list on the trunk interface of SW1.
Why it's wrong here
Even if VLAN 99 were added to the allowed list, the native VLANs would still be mismatched. The CDP warning is about the inconsistency of the untagged VLAN, not about VLAN 99 being absent from the allowed list. Untagged traffic would continue to be placed into different VLANs on each switch, preserving the loop risk.
- ✗
Remove the trunk configuration and set both interfaces as access ports in VLAN 1.
Why it's wrong here
This action is unnecessarily disruptive. The trunk is working (data traffic flows), so removing it would break connectivity across switches. The issue is only a configuration mismatch, which can be fixed without changing the port type. This skips the straightforward corrective step and introduces a network outage.
- ✗
Enable spanning‑tree PortFast on the trunk ports.
Why it's wrong here
PortFast is designed for access ports (edge ports) to bypass listening and learning states. Applying PortFast to a trunk port is inappropriate and would not resolve the native VLAN mismatch. It also risks creating immediate forwarding loops, worsening the problem.
- ✓
Configure the native VLAN to match on both ends of the trunk.
Why this is correct
The root cause is a configured native VLAN mismatch (1 vs 99). Changing one switch’s native VLAN to match the other (or setting both to a common VLAN) immediately resolves the CDP warning and eliminates the potential for broadcast loops caused by the mismatch. This is the most direct and least disruptive next step.
Related concept
Read the scenario before looking for a memorised answer.
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.
✓Configure the native VLAN to match on both ends of the trunk.Correct answer▾
Why this is correct
The root cause is a configured native VLAN mismatch (1 vs 99). Changing one switch’s native VLAN to match the other (or setting both to a common VLAN) immediately resolves the CDP warning and eliminates the potential for broadcast loops caused by the mismatch. This is the most direct and least disruptive next step.
✗Add VLAN 99 to the allowed VLAN list on the trunk interface of SW1.Wrong answer — click to see why▾
Why this is wrong here
Common misconception: the warning message implies a VLAN is not allowed, but native VLAN mismatch means the trunk ports disagree on the native VLAN, not that a VLAN is missing from the allowed list.
✗Remove the trunk configuration and set both interfaces as access ports in VLAN 1.Wrong answer — click to see why▾
Why this is wrong here
Over‑reaction: candidates might think a trunk problem requires eliminating the trunk, but the correct approach is to correct the native VLAN parameter on the existing trunk.
✗Enable spanning‑tree PortFast on the trunk ports.Wrong answer — click to see why▾
Why this is wrong here
Wrong feature: PortFast addresses access port convergence, not VLAN mismatches. Candidates may reach for any familiar command, but it targets the wrong layer and port type.
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
Cisco often tests the misconception that data traffic passing means the configuration is fine, but the trap here is that the native VLAN mismatch can still cause serious issues like broadcast loops and security vulnerabilities, even if user data appears to work.
Detailed technical explanation
How to think about this question
In 802.1Q trunking, the native VLAN is the only VLAN whose frames are sent untagged across the trunk. When the native VLANs differ, a switch receiving an untagged frame will place it into its own configured native VLAN, potentially causing VLAN hopping or broadcast domain leakage. CDP detects this mismatch and logs warnings, but the mismatch can also cause spanning-tree topology changes if BPDUs are received on the wrong VLAN. In production, best practice is to use a dedicated, unused VLAN (e.g., VLAN 999) as the native VLAN to avoid security risks and simplify troubleshooting.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure the native VLAN to match on both ends of the trunk. — The correct action is to configure the native VLAN to match on both ends of the trunk. CDP reports a native VLAN mismatch when the native VLANs differ on the two sides of a trunk link. Although data traffic may still pass because 802.1Q does not tag frames on the native VLAN, the mismatch can cause broadcast loops and security risks, as frames from one native VLAN may be misinterpreted on the other side. Setting both sides to the same native VLAN (e.g., VLAN 1 or VLAN 99) resolves the mismatch and ensures proper Layer 2 behavior.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on 200-301
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A trunk link between two switches is operational, but one side shows a native VLAN mismatch warning. What is the main concern with that condition?
hard- ✓ A.Untagged traffic may be associated with different VLANs on each end of the trunk
- B.All tagged VLAN traffic is automatically converted to routed traffic
- C.The mismatch forces OSPF adjacency reset on all routers
- D.The trunk can carry only one VLAN until the mismatch is cleared
Why A: A native VLAN mismatch can cause untagged traffic to be interpreted as belonging to different VLANs on each end of the trunk. In plain language, the two switches disagree about where untagged frames belong. That can lead to confusing traffic behavior, reachability problems for certain flows, and operational warnings. It is not always a total outage, but it is a design inconsistency that should be corrected. This matters because trunks carry multiple VLANs, and the native VLAN defines how untagged traffic is handled. If both ends do not agree, the logical treatment of those frames becomes inconsistent. The correct answer is the one that focuses on misclassification of untagged traffic, not on unrelated routing behavior.
Last reviewed: Jun 25, 2026
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.
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