Question 633 of 2,015

EtherChannel →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that spanning-tree portfast configured on individual member interfaces of an EtherChannel is ignored because the port-channel interface itself controls the Spanning Tree Protocol state. This occurs because STP operates on the logical port-channel, not on the physical member links; once interfaces are bundled into an EtherChannel, the channel group supersedes per-interface STP settings, and PortFast must be applied directly to the port-channel interface to take effect. On the ENCOR 350-401 exam, this concept tests your understanding of how STP interacts with EtherChannel aggregation, often appearing as a trap where candidates assume per-interface commands remain active after bundling. A common memory tip is to remember that the port-channel is the single STP bridge port, so all STP tuning—including PortFast—must be done at the channel level, not on the members. Think of it as “one channel, one STP decision.”

CCNP 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.

Examine the following configuration:

interface Port-channel1
 switchport mode trunk

interface GigabitEthernet0/1
 switchport mode trunk
 channel-group 1 mode active
 spanning-tree portfast

interface GigabitEthernet0/2
 switchport mode trunk
 channel-group 1 mode active
 spanning-tree portfast

What is the effect of the 'spanning-tree portfast' command on the member interfaces of this EtherChannel?

Question 1mediummultiple choice

Open the full VLAN trunking answer →

A
The PortFast will be applied to the EtherChannel, causing it to immediately transition to forwarding.
Why wrong: Incorrect. PortFast on member interfaces is not inherited by the port-channel; it must be applied to the port-channel interface.
B
The PortFast on the member interfaces will be ignored because they are part of an EtherChannel.
Correct. When interfaces are bundled into an EtherChannel, STP is handled at the port-channel level, and per-interface PortFast is overridden.
C
The PortFast will cause the EtherChannel to form faster.
Why wrong: Incorrect. PortFast does not affect EtherChannel formation; it affects STP state.
D
The configuration will cause a spanning-tree loop because PortFast is used on trunk ports.
Why wrong: Incorrect. While PortFast on trunks can be risky, in this case it is ignored, so no loop is created.

Full breakdown with real-world context →

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 PortFast on the member interfaces will be ignored because they are part of an EtherChannel.

PortFast is used on access ports to immediately transition to forwarding state, bypassing STP listening/learning. However, on trunk ports, PortFast can cause loops if used incorrectly. In this case, the member interfaces are part of an EtherChannel, and PortFast is applied at the interface level. But the port-channel interface itself does not have PortFast. The PortFast on member interfaces is ignored because the channel is a trunk; the port-channel interface controls STP. The correct practice is to apply PortFast on the port-channel interface, not on individual members.

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 PortFast will be applied to the EtherChannel, causing it to immediately transition to forwarding.
Why it's wrong here
Incorrect. PortFast on member interfaces is not inherited by the port-channel; it must be applied to the port-channel interface.
✓
The PortFast on the member interfaces will be ignored because they are part of an EtherChannel.
Why this is correct
Correct. When interfaces are bundled into an EtherChannel, STP is handled at the port-channel level, and per-interface PortFast is overridden.
Related concept
Access ports place end devices into a single VLAN.
✗
The PortFast will cause the EtherChannel to form faster.
Why it's wrong here
Incorrect. PortFast does not affect EtherChannel formation; it affects STP state.
✗
The configuration will cause a spanning-tree loop because PortFast is used on trunk ports.
Why it's wrong here
Incorrect. While PortFast on trunks can be risky, in this case it is ignored, so no loop is created.

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 PortFast on the member interfaces will be ignored because they are part of an EtherChannel. — PortFast is used on access ports to immediately transition to forwarding state, bypassing STP listening/learning. However, on trunk ports, PortFast can cause loops if used incorrectly. In this case, the member interfaces are part of an EtherChannel, and PortFast is applied at the interface level. But the port-channel interface itself does not have PortFast. The PortFast on member interfaces is ignored because the channel is a trunk; the port-channel interface controls STP. The correct practice is to apply PortFast on the port-channel interface, not on individual members.

What should I do if I get this 350-401 question wrong?

What is the key concept behind this question?

Access ports place end devices into a single VLAN.

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