The answer is that VLAN 50 is not in the allowed VLAN list on the trunk. This is the most likely cause because the `show interfaces GigabitEthernet0/1 trunk` command reveals which VLANs are permitted to traverse the trunk link; if VLAN 50 is omitted from that list, all frames tagged with VLAN 50 are dropped at the trunk port, even though the physical link is up and other VLANs may pass. This scenario directly tests your understanding of DTP and trunk pruning—a classic CCNA 200-301 v2 exam trap where you might assume a working trunk means all VLANs are forwarded, but the allowed VLAN list acts as a filter. When troubleshooting trunk allowed VLANs issues, always verify the list with the `show interfaces trunk` command before checking STP or native VLAN mismatches. Memory tip: think of the allowed VLAN list as a bouncer at a club—if VLAN 50 isn’t on the guest list, it doesn’t get through the door.
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. 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.
Exhibit
SW1# show interfaces GigabitEthernet0/1 trunk
Port Mode Encapsulation Status Native vlan
Gi0/1 on 802.1q trunking 1
Port Vlans allowed on trunk
Gi0/1 1-49,60-4094
Port Vlans allowed and active in management domain
Gi0/1 1-49,60-4094
Port Vlans in spanning tree forwarding state and not pruned
Gi0/1 1-49,60-4094
Refer to the exhibit. A network administrator is troubleshooting connectivity issues for hosts on VLAN 50 on SW1. The hosts on VLAN 50 cannot reach any devices outside SW1, even though the trunk link between SW1 and SW2 is up. The administrator issues the 'show interfaces GigabitEthernet0/1 trunk' command on SW1. Based on the output, what is the most likely cause of the issue?
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 GigabitEthernet0/1 trunk
Port Mode Encapsulation Status Native vlan
Gi0/1 on 802.1q trunking 1
Port Vlans allowed on trunk
Gi0/1 1-49,60-4094
Port Vlans allowed and active in management domain
Gi0/1 1-49,60-4094
Port Vlans in spanning tree forwarding state and not pruned
Gi0/1 1-49,60-4094
A
The native VLAN on the trunk is misconfigured, causing VLAN 50 traffic to be dropped.
Why wrong: A native VLAN mismatch affects only untagged frames; VLAN 50 is tagged traffic, so a native VLAN issue would not cause its isolation. The output shows native VLAN 1, which is default and not misconfigured.
B
The trunk is operating in access mode instead of trunk mode, preventing VLAN 50 traffic.
Why wrong: The 'Mode' column shows 'on' and the 'Status' column shows 'trunking', confirming the interface is correctly functioning as a trunk, not as an access port.
C
VLAN 50 is not in the allowed VLAN list on the trunk.
The exhibit explicitly shows the allowed VLANs as '1-49,60-4094', which omits VLAN 50. This prevents traffic for VLAN 50 from traversing the trunk.
D
Spanning tree protocol has blocked the trunk port for VLAN 50, isolating the hosts.
Why wrong: The 'Vlans in spanning tree forwarding state' column shows the exact same list '1-49,60-4094', meaning VLAN 50 is not even participating in spanning tree on this trunk because it is not allowed, not that it is blocked.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VLAN 50 is not in the allowed VLAN list on the trunk.
The 'show interfaces GigabitEthernet0/1 trunk' output would list the allowed VLANs on the trunk. If VLAN 50 is not included in the allowed VLAN list, traffic from VLAN 50 will be dropped at the trunk, preventing hosts on SW1 from reaching devices outside SW1. This is the most likely cause because the trunk is up but VLAN 50 traffic is not forwarded.
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.
✗
The native VLAN on the trunk is misconfigured, causing VLAN 50 traffic to be dropped.
Why it's wrong here
A native VLAN mismatch affects only untagged frames; VLAN 50 is tagged traffic, so a native VLAN issue would not cause its isolation. The output shows native VLAN 1, which is default and not misconfigured.
✗
The trunk is operating in access mode instead of trunk mode, preventing VLAN 50 traffic.
Why it's wrong here
The 'Mode' column shows 'on' and the 'Status' column shows 'trunking', confirming the interface is correctly functioning as a trunk, not as an access port.
✓
VLAN 50 is not in the allowed VLAN list on the trunk.
Why this is correct
The exhibit explicitly shows the allowed VLANs as '1-49,60-4094', which omits VLAN 50. This prevents traffic for VLAN 50 from traversing the trunk.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Spanning tree protocol has blocked the trunk port for VLAN 50, isolating the hosts.
Why it's wrong here
The 'Vlans in spanning tree forwarding state' column shows the exact same list '1-49,60-4094', meaning VLAN 50 is not even participating in spanning tree on this trunk because it is not allowed, not that it is blocked.
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 50 is not in the allowed VLAN list on the trunk.Correct answer▾
Why this is correct
The exhibit explicitly shows the allowed VLANs as '1-49,60-4094', which omits VLAN 50. This prevents traffic for VLAN 50 from traversing the trunk.
✗The native VLAN on the trunk is misconfigured, causing VLAN 50 traffic to be dropped.Wrong answer — click to see why▾
Why this is wrong here
The assumption that a native VLAN mismatch can drop tagged VLAN traffic is a common misunderstanding.
✗The trunk is operating in access mode instead of trunk mode, preventing VLAN 50 traffic.Wrong answer — click to see why▾
Why this is wrong here
Misreading the output may lead to believing the trunk is not in trunking mode.
✗Spanning tree protocol has blocked the trunk port for VLAN 50, isolating the hosts.Wrong answer — click to see why▾
Why this is wrong here
Confusing spanning tree blocking with allowed VLAN filtering; the output shows no block state, only absence of the VLAN.
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 distinction between native VLAN misconfiguration and allowed VLAN list misconfiguration, where candidates mistakenly attribute all trunk issues to native VLAN mismatches rather than checking the allowed VLAN list.
Trap categories for this question
Command / output trap
A native VLAN mismatch affects only untagged frames; VLAN 50 is tagged traffic, so a native VLAN issue would not cause its isolation. The output shows native VLAN 1, which is default and not misconfigured.
Detailed technical explanation
How to think about this question
The 'switchport trunk allowed vlan' command controls which VLANs are permitted to traverse a trunk link. If a VLAN is not in the allowed list, its frames are dropped at the trunk egress. This is a common misconfiguration when adding new VLANs to a network; the trunk must be explicitly updated to include the new VLAN. In contrast, the native VLAN is used for untagged traffic and is configured separately with 'switchport trunk native vlan'.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
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: VLAN 50 is not in the allowed VLAN list on the trunk. — The 'show interfaces GigabitEthernet0/1 trunk' output would list the allowed VLANs on the trunk. If VLAN 50 is not included in the allowed VLAN list, traffic from VLAN 50 will be dropped at the trunk, preventing hosts on SW1 from reaching devices outside SW1. This is the most likely cause because the trunk is up but VLAN 50 traffic is not forwarded.
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.
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?
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 →
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. 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?
medium
A.The native VLAN must be changed to 30
✓ B.VLAN 30 is not permitted on the trunk link
C.The uplink should be configured as an access port
D.STP must be disabled on VLAN 30
Why B: 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.
Last reviewed: Jun 25, 2026
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