- A
One of the physical ports in the EtherChannel has VLAN 100 removed from its allowed list.
Correct because the allowed VLAN list on physical ports must match; if one port does not allow VLAN 100, the trunk may not pass that VLAN.
- B
The native VLAN is configured as VLAN 100 on one side.
Why wrong: Incorrect because native VLAN mismatch would cause issues for all VLANs, not just one.
- C
The port-channel is configured with 'switchport trunk allowed vlan add 100' but the physical ports have 'switchport trunk allowed vlan except 100'.
Why wrong: Incorrect because if the physical ports exclude VLAN 100, the port-channel would also exclude it.
- D
The VLAN 100 does not exist on the switch.
Why wrong: Incorrect because if the VLAN did not exist, the trunk would not show it in the allowed list.
350-401 EtherChannel Practice Question
This 350-401 practice question tests your understanding of etherchannel. 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.
A network engineer is troubleshooting an EtherChannel between two Cisco switches. The show etherchannel summary command shows the port-channel is up, but the show interfaces trunk command shows that the trunk is not passing traffic for VLAN 100. The allowed VLAN list on the port-channel interface includes VLAN 100. 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.
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
One of the physical ports in the EtherChannel has VLAN 100 removed from its allowed list.
The correct answer is that the VLAN is not allowed on one of the physical ports. The wrong answers involve issues that would affect all VLANs or are unrelated.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
One of the physical ports in the EtherChannel has VLAN 100 removed from its allowed list.
Why this is correct
Correct because the allowed VLAN list on physical ports must match; if one port does not allow VLAN 100, the trunk may not pass that VLAN.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
- ✗
The native VLAN is configured as VLAN 100 on one side.
Why it's wrong here
Incorrect because native VLAN mismatch would cause issues for all VLANs, not just one.
- ✗
The port-channel is configured with 'switchport trunk allowed vlan add 100' but the physical ports have 'switchport trunk allowed vlan except 100'.
Why it's wrong here
Incorrect because if the physical ports exclude VLAN 100, the port-channel would also exclude it.
- ✗
The VLAN 100 does not exist on the switch.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Trap categories for this question
Command / output trap
Incorrect because if the VLAN did not exist, the trunk would not show it in the allowed list.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 350-401 question test?
EtherChannel — This question tests EtherChannel — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: One of the physical ports in the EtherChannel has VLAN 100 removed from its allowed list. — The correct answer is that the VLAN is not allowed on one of the physical ports. The wrong answers involve issues that would affect all VLANs or are unrelated.
What should I do if I get this 350-401 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.
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?
Access ports place end devices into a single VLAN.
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Last reviewed: Jun 18, 2026
This 350-401 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 350-401 exam.
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