- A
The EtherChannel will drop all untagged frames because the native VLAN is not in the allowed list.
Why wrong: Incorrect. The native VLAN does not need to be in the allowed list; it is used for untagged traffic.
- B
The EtherChannel will use VLAN 999 as the native VLAN, and any untagged frames will be associated with VLAN 999.
Correct. The native VLAN is set to 999, so untagged frames are placed in that VLAN.
- C
The EtherChannel will not form because the native VLAN must be the same across all interfaces, which it is.
Why wrong: Incorrect. The native VLAN is consistent, so it will not prevent channel formation.
- D
The EtherChannel will form but the native VLAN will be ignored on the port-channel.
Why wrong: Incorrect. The port-channel inherits the native VLAN configuration.
Quick Answer
The answer is that the EtherChannel will use VLAN 999 as the native VLAN, causing any untagged frames on the trunk to be associated with VLAN 999. This is correct because the native VLAN on an EtherChannel trunk must be configured identically on the physical member interfaces and the port-channel interface itself; here, the consistent setting of VLAN 999 across all interfaces ensures the channel forms and operates properly. On the ENCOR 350-401 exam, this tests your understanding that mismatched native VLANs between the port-channel and its members will prevent the EtherChannel from coming up, and a common trap is assuming the port-channel interface inherits the native VLAN from the member interfaces automatically. A key memory tip is "consistent native VLAN or no channel"—always verify that the native VLAN ID matches on every interface in the bundle, and using an unused VLAN like 999 is a security best practice to drop untagged traffic.
350-401 EtherChannel Practice Question
This 350-401 practice question tests your understanding of etherchannel. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Consider this configuration:
interface Port-channel1 switchport mode trunk switchport trunk native vlan 999
!
interface GigabitEthernet0/1 switchport mode trunk switchport trunk native vlan 999 channel-group 1 mode active
!
interface GigabitEthernet0/2 switchport mode trunk switchport trunk native vlan 999 channel-group 1 mode active
What is the effect of the 'switchport trunk native vlan 999' command on the EtherChannel?
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
The EtherChannel will use VLAN 999 as the native VLAN, and any untagged frames will be associated with VLAN 999.
The native VLAN is used for untagged traffic on a trunk. Setting it to 999 (an unused VLAN) helps prevent VLAN hopping attacks and ensures that any untagged frames are dropped. The configuration is consistent across all member interfaces and the port-channel, so the channel will form.
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.
- ✗
The EtherChannel will drop all untagged frames because the native VLAN is not in the allowed list.
Why it's wrong here
Incorrect. The native VLAN does not need to be in the allowed list; it is used for untagged traffic.
- ✓
The EtherChannel will use VLAN 999 as the native VLAN, and any untagged frames will be associated with VLAN 999.
Why this is correct
Correct. The native VLAN is set to 999, so untagged frames are placed in that VLAN.
Related concept
Access ports place end devices into a single VLAN.
- ✗
The EtherChannel will not form because the native VLAN must be the same across all interfaces, which it is.
Why it's wrong here
Incorrect. The native VLAN is consistent, so it will not prevent channel formation.
- ✗
The EtherChannel will form but the native VLAN will be ignored on the port-channel.
Why it's wrong here
Incorrect. The port-channel inherits the native VLAN configuration.
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.
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: The EtherChannel will use VLAN 999 as the native VLAN, and any untagged frames will be associated with VLAN 999. — The native VLAN is used for untagged traffic on a trunk. Setting it to 999 (an unused VLAN) helps prevent VLAN hopping attacks and ensures that any untagged frames are dropped. The configuration is consistent across all member interfaces and the port-channel, so the channel will form.
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.
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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