CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: a VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs.. 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.
Exhibit
SW1# show interfaces trunk
Port Mode Encapsulation Status Native vlan
Gi1/0/24 on 802.1q trunking 1
Port Vlans allowed on trunk
Gi1/0/24 10,20,40
Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/24 10,20,40
After a switch replacement, users in VLAN 30 cannot reach devices in other VLANs. The replacement switch has a trunk link to the distribution switch that shows as up/up. What is the most likely cause?
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.
SW1# show interfaces trunk
Port Mode Encapsulation Status Native vlan
Gi1/0/24 on 802.1q trunking 1
Port Vlans allowed on trunk
Gi1/0/24 10,20,40
Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/24 10,20,40
A
The native VLAN must be changed to 30
Why wrong: A native VLAN mismatch is a different issue and does not specifically explain why only VLAN 30 is failing here.
B
VLAN 30 is not permitted on the trunk link
The trunk allowed list does not include VLAN 30.
C
The uplink should be configured as an access port
Why wrong: Switch uplinks carrying multiple VLANs should remain trunks.
D
STP must be disabled on VLAN 30
Why wrong: Disabling STP would be dangerous and would not fix a missing trunk allowance.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VLAN 30 is not permitted on the trunk link
The trunk is up, but VLAN 30 is not allowed on it. Traffic from that VLAN never crosses the uplink, so inter-VLAN reachability fails for users in VLAN 30 even though the local access ports may still look fine.
Key principle: A VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs.
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 native VLAN must be changed to 30
Why it's wrong here
A native VLAN mismatch is a different issue and does not specifically explain why only VLAN 30 is failing here.
When this WOULD be correct
In a different scenario where a network administrator is troubleshooting a switch that has been configured with a native VLAN of 30, and the requirement is to ensure that untagged traffic is handled correctly, changing the native VLAN to 30 would be appropriate if the design specifies that all untagged traffic should belong to VLAN 30.
The clue word "most likely" in the question point toward this answer.
Related concept
A VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs.
✗
The uplink should be configured as an access port
Why it's wrong here
Switch uplinks carrying multiple VLANs should remain trunks.
When this WOULD be correct
In a different question context where the prompt indicates that a switch port must connect to a single VLAN and no inter-VLAN routing is required, stating that the uplink should be configured as an access port would be correct. For example, if the question specifies that all devices on the same VLAN need to communicate without routing, this option would be valid.
✗
STP must be disabled on VLAN 30
Why it's wrong here
Disabling STP would be dangerous and would not fix a missing trunk allowance.
When this WOULD be correct
In a scenario where a question states that VLAN 30 is experiencing broadcast storms or loops, and the exam asks for a method to stabilize the network, disabling STP on VLAN 30 could be considered correct to allow for immediate traffic flow, assuming there are no other VLANs affected.
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.
✓VLAN 30 is not permitted on the trunk linkCorrect answer▾
Why this is correct
The trunk allowed list does not include VLAN 30.
✗The native VLAN must be changed to 30Wrong answer — click to see why▾
Why this is wrong here
Changing the native VLAN to 30 would not resolve the issue because the native VLAN is used for untagged traffic on a trunk, and the problem is that VLAN 30 traffic is not being allowed at all. Additionally, native VLAN mismatch can cause connectivity issues, but it does not specifically prevent only VLAN 30 from reaching other VLANs.
★ When this WOULD be the correct answer
In a different scenario where a network administrator is troubleshooting a switch that has been configured with a native VLAN of 30, and the requirement is to ensure that untagged traffic is handled correctly, changing the native VLAN to 30 would be appropriate if the design specifies that all untagged traffic should belong to VLAN 30.
Why candidates choose this
Students might confuse native VLAN with the VLAN that is allowed on the trunk, or think that setting the native VLAN to 30 would automatically permit VLAN 30 traffic.
✗The uplink should be configured as an access portWrong answer — click to see why▾
Why this is wrong here
Configuring the uplink as an access port would place it in a single VLAN, preventing traffic from multiple VLANs (including VLAN 30) from traversing the link. Since the switch needs to carry traffic for multiple VLANs, the uplink must remain a trunk port.
★ When this WOULD be the correct answer
In a different question context where the prompt indicates that a switch port must connect to a single VLAN and no inter-VLAN routing is required, stating that the uplink should be configured as an access port would be correct. For example, if the question specifies that all devices on the same VLAN need to communicate without routing, this option would be valid.
Why candidates choose this
Students might think that using an access port simplifies configuration, but they overlook the need to carry multiple VLANs between switches.
✗STP must be disabled on VLAN 30Wrong answer — click to see why▾
Why this is wrong here
Disabling STP on VLAN 30 would be dangerous as it could cause bridging loops and network instability. Moreover, STP does not control whether a VLAN is allowed on a trunk; it only prevents loops. The issue is a missing VLAN in the trunk allowed list, not a spanning-tree problem.
★ When this WOULD be the correct answer
In a scenario where a question states that VLAN 30 is experiencing broadcast storms or loops, and the exam asks for a method to stabilize the network, disabling STP on VLAN 30 could be considered correct to allow for immediate traffic flow, assuming there are no other VLANs affected.
Why candidates choose this
Students might associate STP with VLAN issues because STP operates per VLAN, but they incorrectly assume that disabling STP can fix connectivity problems caused by trunk misconfiguration.
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
Ensure you distinguish between management settings and VLAN configuration. Focus on trunk settings when inter-VLAN issues arise.
Detailed technical explanation
How to think about this question
VLANs (Virtual Local Area Networks) logically segment a physical network into multiple broadcast domains, allowing devices in different VLANs to communicate only through a Layer 3 device or inter-VLAN routing. Switch ports assigned to a VLAN forward traffic only for that VLAN, and trunk links carry traffic for multiple VLANs between switches by tagging frames with VLAN identifiers using protocols like IEEE 802.1Q.
When a trunk link is configured between switches, it must be allowed to carry traffic for all VLANs that need to communicate across the link. Cisco switches use a trunk allowed VLAN list to control which VLANs are permitted on the trunk. If a VLAN is not included in this allowed list, frames tagged with that VLAN ID are dropped on the trunk, preventing devices in that VLAN from reaching other VLANs or networks beyond the switch.
The exam trap here is confusing VLAN trunking issues with native VLAN mismatches or port mode misconfigurations. While native VLAN mismatches cause untagged traffic problems, they do not selectively block a single VLAN’s traffic. Similarly, configuring an uplink as an access port disables VLAN tagging and restricts traffic to a single VLAN, which is incorrect for inter-VLAN communication. The practical impact is that users in VLAN 30 cannot reach other VLANs because their traffic never crosses the trunk link due to VLAN 30 being excluded from the allowed VLAN list.
KKey Concepts to Remember
A VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs.
Trunk links carry traffic for multiple VLANs by tagging frames with VLAN IDs using 802.1Q encapsulation.
The trunk allowed VLAN list controls which VLANs are permitted to send traffic across a trunk link between switches.
If a VLAN is not permitted on a trunk, traffic from that VLAN is dropped and cannot reach other VLANs or networks beyond the trunk.
Native VLAN mismatches cause untagged traffic issues but do not selectively block traffic from a specific VLAN like VLAN 30.
Configuring an uplink as an access port restricts traffic to a single VLAN and prevents inter-VLAN communication over that link.
Switches forward VLAN-tagged frames only if the VLAN is allowed on the trunk, ensuring proper segmentation and traffic flow.
Inter-VLAN communication depends on both correct VLAN membership on access ports and proper VLAN allowance on trunk links.
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 VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs.
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 VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs., 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 VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs..
What is the correct answer to this question?
The correct answer is: VLAN 30 is not permitted on the trunk link — The trunk is up, but VLAN 30 is not allowed on it. Traffic from that VLAN never crosses the uplink, so inter-VLAN reachability fails for users in VLAN 30 even though the local access ports may still look fine.
What should I do if I get this 200-301 question wrong?
Review a VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs., 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 VLAN segments a network into separate broadcast domains, requiring inter-VLAN routing for communication between VLANs.
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