Question 324 of 2,015

Spanning Tree Protocol →easyMultiple SelectObjective-mapped

Quick Answer

The correct answer is that PortFast should be enabled on ports that connect to end-user devices because it forces a port to bypass the listening and learning STP states, transitioning immediately from blocking to forwarding. This is critical for end-host ports, where the brief delay caused by normal STP convergence would disrupt user connectivity; PortFast assumes no switch is connected downstream, so there is no risk of a bridging loop. On the ENCOR 350-401 exam, this concept tests your understanding of STP optimization for access ports, and a common trap is assuming PortFast disables BPDU processing—it does not, which is why BPDU guard is often paired with it for protection. Remember the memory tip: “PortFast for hosts, not for switches—skip the wait, but guard the BPDU gate.”

350-401 Spanning Tree Protocol Practice Question

This 350-401 practice question tests your understanding of spanning tree protocol. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.

Which two statements about PortFast are true? (Choose two.)

Question 1easymulti select

Full question →

A
PortFast allows a port to transition directly from blocking to forwarding state.
Correct because PortFast bypasses the listening and learning states, enabling immediate forwarding.
B
PortFast should be enabled on ports that connect to end-user devices.
Correct because these ports are not expected to participate in STP loops, so fast access is beneficial.
C
PortFast disables BPDU processing on the port.
Why wrong: Incorrect because PortFast does not disable BPDU processing; BPDU guard is a separate feature that can be used to disable the port upon receiving a BPDU.
D
PortFast is automatically enabled on all trunk ports.
Why wrong: Incorrect because trunk ports typically connect to other switches and should not use PortFast; it must be manually configured.
E
PortFast changes the root bridge election process.
Why wrong: Incorrect because PortFast only affects the port state transition, not the STP topology or root election.

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

✓

PortFast allows a port to transition directly from blocking to forwarding state.

PortFast is a Cisco enhancement that allows a port to transition immediately from blocking to forwarding, bypassing the listening and learning states. It is intended for ports connected to end hosts, not to other switches. When PortFast is enabled, the port still participates in STP BPDU processing, but the BPDU guard feature can be used to protect against accidental loops. PortFast does not affect the root bridge election or the designated port selection process.

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.

✓
PortFast allows a port to transition directly from blocking to forwarding state.
Why this is correct
Correct because PortFast bypasses the listening and learning states, enabling immediate forwarding.
Related concept
Access ports place end devices into a single VLAN.
✓
PortFast should be enabled on ports that connect to end-user devices.
Why this is correct
Correct because these ports are not expected to participate in STP loops, so fast access is beneficial.
Related concept
Access ports place end devices into a single VLAN.
✗
PortFast disables BPDU processing on the port.
Why it's wrong here
Incorrect because PortFast does not disable BPDU processing; BPDU guard is a separate feature that can be used to disable the port upon receiving a BPDU.
✗
PortFast is automatically enabled on all trunk ports.
Why it's wrong here
Incorrect because trunk ports typically connect to other switches and should not use PortFast; it must be manually configured.
✗
PortFast changes the root bridge election process.
Why it's wrong here
Incorrect because PortFast only affects the port state transition, not the STP topology or root election.

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?

Spanning Tree Protocol — This question tests Spanning Tree Protocol — Access ports place end devices into a single VLAN..

What is the correct answer to this question?

The correct answer is: PortFast allows a port to transition directly from blocking to forwarding state. — PortFast is a Cisco enhancement that allows a port to transition immediately from blocking to forwarding, bypassing the listening and learning states. It is intended for ports connected to end hosts, not to other switches. When PortFast is enabled, the port still participates in STP BPDU processing, but the BPDU guard feature can be used to protect against accidental loops. PortFast does not affect the root bridge election or the designated port selection process.

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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