Question 1,800 of 2,015

Spanning Tree Protocol →hardMultiple 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 three statements about Multiple Spanning Tree Protocol (MSTP) are true? (Choose three.)

Question 1hardmulti select

Open the full STP breakdown →

A
MSTP allows multiple VLANs to be grouped into a single spanning-tree instance, reducing CPU and memory usage.
Correct. This is the primary benefit of MSTP: mapping many VLANs to fewer STP instances.
B
In MSTP, the Internal Spanning Tree (IST) instance is instance 0 and is always present in every MST region.
Correct. IST (instance 0) is mandatory and provides connectivity within the region and to other regions.
C
MSTP requires that all switches in the same MST region have the same VLAN-to-instance mapping, revision number, and region name.
Correct. These three parameters define an MST region; mismatches cause switches to treat each other as separate regions.
D
MSTP automatically load-balances traffic across all available uplinks without any configuration.
Why wrong: Incorrect. MSTP does not automatically load-balance; you must manually map VLANs to different instances to achieve load balancing.
E
MSTP requires a separate root bridge to be elected for each VLAN in the network.
Why wrong: Incorrect. In MSTP, a root bridge is elected per MST instance, not per VLAN. Multiple VLANs share the same root within an instance.

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

✓

MSTP allows multiple VLANs to be grouped into a single spanning-tree instance, reducing CPU and memory usage.

MSTP (IEEE 802.1s) allows multiple VLANs to be mapped to a single spanning-tree instance (MST instance), reducing the number of STP instances needed. It uses an Internal Spanning Tree (IST) instance (instance 0) that always runs and carries BPDUs for the region. Switches in the same MST region must have identical VLAN-to-instance mappings, revision number, and region name. MSTP interoperates with Rapid PVST+ at region boundaries by using PVST simulation mode. MSTP does not require a separate root bridge for each VLAN; instead, each MST instance has its own root bridge.

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.

✓
MSTP allows multiple VLANs to be grouped into a single spanning-tree instance, reducing CPU and memory usage.
Why this is correct
Correct. This is the primary benefit of MSTP: mapping many VLANs to fewer STP instances.
Related concept
Access ports place end devices into a single VLAN.
✓
In MSTP, the Internal Spanning Tree (IST) instance is instance 0 and is always present in every MST region.
Why this is correct
Correct. IST (instance 0) is mandatory and provides connectivity within the region and to other regions.
Related concept
Access ports place end devices into a single VLAN.
✓
MSTP requires that all switches in the same MST region have the same VLAN-to-instance mapping, revision number, and region name.
Why this is correct
Correct. These three parameters define an MST region; mismatches cause switches to treat each other as separate regions.
Related concept
Access ports place end devices into a single VLAN.
✗
MSTP automatically load-balances traffic across all available uplinks without any configuration.
Why it's wrong here
Incorrect. MSTP does not automatically load-balance; you must manually map VLANs to different instances to achieve load balancing.
✗
MSTP requires a separate root bridge to be elected for each VLAN in the network.
Why it's wrong here
Incorrect. In MSTP, a root bridge is elected per MST instance, not per VLAN. Multiple VLANs share the same root within an instance.

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: MSTP allows multiple VLANs to be grouped into a single spanning-tree instance, reducing CPU and memory usage. — MSTP (IEEE 802.1s) allows multiple VLANs to be mapped to a single spanning-tree instance (MST instance), reducing the number of STP instances needed. It uses an Internal Spanning Tree (IST) instance (instance 0) that always runs and carries BPDUs for the region. Switches in the same MST region must have identical VLAN-to-instance mappings, revision number, and region name. MSTP interoperates with Rapid PVST+ at region boundaries by using PVST simulation mode. MSTP does not require a separate root bridge for each VLAN; instead, each MST instance has its own root bridge.

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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