Question 27 of 2,015

Spanning Tree Protocol →mediumMultiple SelectObjective-mapped

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 Rapid PVST+ are true? (Choose two.)

Question 1mediummulti select

Full question →

A
Rapid PVST+ converges faster than classic STP because it uses synchronized handshakes between switches.
Correct. RSTP uses a proposal-agreement handshake mechanism to achieve rapid transition to forwarding state, unlike classic STP which relies on timers.
B
Rapid PVST+ uses a separate BPDU version for each VLAN to maintain per-VLAN spanning-tree instances.
Why wrong: Incorrect. Rapid PVST+ uses the same RSTP BPDU format (version 2) for all VLANs; per-VLAN instances are identified by the VLAN ID in the BPDU, not a separate version.
C
In Rapid PVST+, an alternate port provides a backup path to the root bridge and is in a discarding state when the root port is operational.
Correct. An alternate port is a backup to the root port and remains in discarding state until the root port fails.
D
Rapid PVST+ requires the use of UplinkFast and BackboneFast features to achieve sub-second convergence.
Why wrong: Incorrect. UplinkFast and BackboneFast are proprietary Cisco enhancements for classic STP; RSTP integrates these mechanisms natively.
E
Rapid PVST+ supports only one spanning-tree instance per VLAN, but it can load-balance traffic across multiple VLANs.
Why wrong: Incorrect. Rapid PVST+ does run one instance per VLAN, but the statement is true only in part; however, the question asks for two true statements, and this is not the best choice because the other two are more directly correct.

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

✓

Rapid PVST+ converges faster than classic STP because it uses synchronized handshakes between switches.

Rapid PVST+ is the Cisco implementation of RSTP per VLAN. It provides faster convergence than classic STP and uses port roles (root, designated, alternate, backup) and port states (discarding, learning, forwarding). The alternate port provides a backup to the root port, and the backup port provides a backup to the designated port. Rapid PVST+ does not use a separate BPDU version for each VLAN; it uses the same RSTP BPDU format. It does not require UplinkFast or BackboneFast since those features are integrated into RSTP.

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.

✓
Rapid PVST+ converges faster than classic STP because it uses synchronized handshakes between switches.
Why this is correct
Correct. RSTP uses a proposal-agreement handshake mechanism to achieve rapid transition to forwarding state, unlike classic STP which relies on timers.
Related concept
Access ports place end devices into a single VLAN.
✗
Rapid PVST+ uses a separate BPDU version for each VLAN to maintain per-VLAN spanning-tree instances.
Why it's wrong here
Incorrect. Rapid PVST+ uses the same RSTP BPDU format (version 2) for all VLANs; per-VLAN instances are identified by the VLAN ID in the BPDU, not a separate version.
✓
In Rapid PVST+, an alternate port provides a backup path to the root bridge and is in a discarding state when the root port is operational.
Why this is correct
Correct. An alternate port is a backup to the root port and remains in discarding state until the root port fails.
Related concept
Access ports place end devices into a single VLAN.
✗
Rapid PVST+ requires the use of UplinkFast and BackboneFast features to achieve sub-second convergence.
Why it's wrong here
Incorrect. UplinkFast and BackboneFast are proprietary Cisco enhancements for classic STP; RSTP integrates these mechanisms natively.
✗
Rapid PVST+ supports only one spanning-tree instance per VLAN, but it can load-balance traffic across multiple VLANs.
Why it's wrong here
Incorrect. Rapid PVST+ does run one instance per VLAN, but the statement is true only in part; however, the question asks for two true statements, and this is not the best choice because the other two are more directly correct.

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: Rapid PVST+ converges faster than classic STP because it uses synchronized handshakes between switches. — Rapid PVST+ is the Cisco implementation of RSTP per VLAN. It provides faster convergence than classic STP and uses port roles (root, designated, alternate, backup) and port states (discarding, learning, forwarding). The alternate port provides a backup to the root port, and the backup port provides a backup to the designated port. Rapid PVST+ does not use a separate BPDU version for each VLAN; it uses the same RSTP BPDU format. It does not require UplinkFast or BackboneFast since those features are integrated into RSTP.

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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