mediumMultiple Choice
350-401 Practice Question: Examine the following configuration: interface…
Examine the following configuration:
interface Port-channel1 switchport mode trunk
!
interface GigabitEthernet0/1 switchport mode trunk channel-group 1 mode active spanning-tree portfast
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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?
⚠ Common exam trap
Cisco often tests the misconception that STP features configured on physical interfaces are inherited by the EtherChannel, when in fact they are ignored and must be applied to the logical port-channel interface.
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.
When interfaces are configured as members of an EtherChannel, any spanning-tree configuration applied directly to the member interfaces (such as 'spanning-tree portfast') is ignored. Spanning-tree operates on the logical port-channel interface, not the individual physical members. Therefore, the PortFast command on GigabitEthernet0/1 and GigabitEthernet0/2 has no effect; instead, PortFast must be configured on the Port-channel interface itself to apply to the bundle.
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
PortFast is a per-interface spanning-tree feature that accelerates the STP state transition from blocking to forwarding. When physical interfaces are bundled into an EtherChannel, the STP protocol operates on the logical port-channel interface (e.g., Port-channel1), not on the individual member links. Configuring PortFast on the member interfaces does not cause it to be applied to the port-channel interface; STP will still run normally on the bundle, and the port-channel will undergo the standard listening/learning process unless PortFast is explicitly set on the port-channel interface itself.
- ✓
The PortFast on the member interfaces will be ignored because they are part of an EtherChannel.
Why this is correct
When interfaces are grouped into an EtherChannel, the software creates a single logical port-channel interface that represents the entire bundle. STP treats this logical port-channel as the spanning-tree port, and per-interface STP parameters on the physical member links are effectively overridden and ignored. The member interfaces are not independent STP ports; they are just physical paths within the aggregated link. Therefore, PortFast configured on the members has no effect on the STP state of the EtherChannel, making this statement correct.
- ✗
The PortFast will cause the EtherChannel to form faster.
Why it's wrong here
PortFast is an STP optimization that skips the listening and learning phases to bring a port into forwarding more quickly; it has absolutely no influence on the process of forming an EtherChannel. EtherChannel formation depends on LACP or PAgP negotiation, which determines whether multiple physical links can be bundled based on speed, duplex, and VLAN configuration. The STP timers or PortFast settings do not speed up or slow down the link aggregation negotiation. Hence, configuring PortFast on members will not make the EtherChannel bundle form any faster.
- ✗
The configuration will cause a spanning-tree loop because PortFast is used on trunk ports.
Why it's wrong here
PortFast on a trunk port can indeed create a loop risk if STP is bypassed on a port connecting two switches, as it may temporarily allow frames to be forwarded before the spanning-tree topology fully converges. However, in this scenario PortFast is placed on the physical member interfaces of an EtherChannel, and because STP only sees the logical port-channel interface, the member-level PortFast settings are ignored. The port-channel will still participate in STP normally unless PortFast is explicitly configured on the port-channel interface itself, so no additional loop is introduced by this configuration.
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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.