mediumMultiple ChoiceObjective-mapped
EtherChannel VLAN Mismatch Configuration Requirements
A network engineer is configuring EtherChannel between two Cisco Catalyst switches. The ports are configured as access ports in VLAN 10. After configuring the port-channel interface and adding the physical ports, the engineer notices that the EtherChannel does not come up. The show etherchannel summary command shows the port-channel in a down state. What is the most likely cause?
Quick Answer
The answer is that the port-channel interface itself was not configured as an access port in VLAN 10, causing the EtherChannel not to form due to a VLAN mismatch. For an EtherChannel to successfully bundle, all physical member ports and the logical port-channel interface must share identical Layer 2 configurations, including the VLAN assignment on access ports. If the physical ports are set to access VLAN 10 but the port-channel interface remains in its default state (often VLAN 1 or a trunk), the switch sees a mismatch and prevents the channel from coming up. On the ENCOR 350-401 exam, this scenario tests your understanding that the port-channel interface inherits no configuration from the physical ports—you must explicitly configure it. A common trap is assuming the physical port settings automatically propagate to the logical interface. Remember the memory tip: “Match the port-channel to the ports—same VLAN, same type, or the bundle won’t ignite.”
⚠ Common exam trap
Cisco often tests the requirement that the port-channel interface must be explicitly configured with the same VLAN as the member ports, even when the physical ports are already set, because candidates assume the port-channel inherits the VLAN from the physical ports.
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 physical ports are configured as access ports in VLAN 10, but the port-channel interface is not configured with the same VLAN.
When configuring an EtherChannel, the port-channel interface must have the same VLAN configuration as the physical member ports. In this scenario, the physical ports are access ports in VLAN 10, but the port-channel interface was not explicitly configured with the same VLAN. Cisco switches require the port-channel interface to be configured with the same switchport mode and VLAN assignment as the member ports; otherwise, the EtherChannel will remain down because the logical interface does not match the operational state of the physical ports.
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 physical ports are configured as access ports in VLAN 10, but the port-channel interface is not configured with the same VLAN.
Why this is correct
Correct because the port-channel interface must have the same access VLAN as the physical ports, or the channel will not form.
- ✗
The physical ports have different duplex settings.
Why it's wrong here
Incorrect because duplex mismatch would cause issues, but the scenario states the ports are configured identically as access ports, so duplex should match.
- ✗
The switch is using PAgP and the neighbor is using LACP.
Why it's wrong here
Incorrect because if both sides use different protocols, the channel will not form, but the scenario does not specify protocol mismatch.
- ✗
The physical ports are in different VLANs.
Why it's wrong here
Incorrect because the scenario says both are in VLAN 10, so VLANs match.
Visual reference
About these practice questions
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Same concept, more angles
1 more way this is tested on 350-401
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 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?
hard- ✓ A.One of the physical ports in the EtherChannel has VLAN 100 removed from its allowed list.
- B.The native VLAN is configured as VLAN 100 on one side.
- C.The port-channel is configured with 'switchport trunk allowed vlan add 100' but the physical ports have 'switchport trunk allowed vlan except 100'.
- D.The VLAN 100 does not exist on the switch.
Why A: In an EtherChannel, the allowed VLAN list on the port-channel interface is a logical representation, but the physical member ports enforce their own VLAN lists independently. If one physical port has VLAN 100 removed from its allowed list, traffic for that VLAN will be dropped on that link, causing the trunk to appear up but not passing VLAN 100 traffic, even though the port-channel interface shows VLAN 100 as allowed.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.