- A
MSTP allows multiple VLANs to be mapped to a single spanning-tree instance.
Correct because MSTP reduces the number of STP instances by grouping VLANs, improving scalability.
- B
MSTP uses an Internal Spanning Tree (IST) to interconnect MST regions.
Correct because the IST is the spanning tree that runs within an MST region and connects to the CST outside.
- C
MSTP is backward compatible with 802.1D and RSTP.
Correct because MSTP can interoperate with legacy STP and RSTP by using the common spanning tree (CST) at region boundaries.
- D
MSTP requires a separate spanning-tree instance for every VLAN.
Why wrong: Incorrect because that describes PVST+, not MSTP; MSTP groups VLANs into instances.
- E
MSTP uses a different BPDU format than RSTP.
Why wrong: Incorrect because MSTP uses the same BPDU format as RSTP but includes additional fields for MSTI information.
Quick Answer
The correct answer is that MSTP is backward compatible with 802.1D and RSTP because it uses the Internal Spanning Tree (IST) to interconnect MST regions while maintaining compatibility through the Common Spanning Tree (CST) at region boundaries. MSTP, defined in 802.1s, allows you to map multiple VLANs to a single spanning-tree instance, significantly reducing the number of STP instances compared to PVST+, and it uses the same BPDU format as RSTP with additional MST-specific fields. On the ENCOR 350-401 exam, this concept tests your understanding of how MSTP scales in large Layer 2 networks—a common trap is confusing MSTP with PVST+, which requires a separate instance per VLAN. Remember that MSTP groups VLANs into instances, and the IST acts as the bridge between regions, making it backward compatible without needing a separate instance for every VLAN. Memory tip: Think "MSTP = Many VLANs, Single Tree" to recall its efficiency.
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 the Multiple Spanning Tree Protocol (MSTP) are true? (Choose three.)
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 mapped to a single spanning-tree instance.
MSTP (802.1s) allows mapping multiple VLANs to a single spanning-tree instance, reducing the number of STP instances needed. It uses an internal spanning tree (IST) to interconnect MST regions. MSTP is backward compatible with 802.1D and RSTP through the use of common spanning tree (CST) at the region boundary. MSTP does not require a separate instance for every VLAN like PVST+; it groups VLANs into instances. MSTP uses the same BPDU format as RSTP with additional MST-specific information.
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 mapped to a single spanning-tree instance.
- ✓
MSTP uses an Internal Spanning Tree (IST) to interconnect MST regions.
Why this is correct
Correct because the IST is the spanning tree that runs within an MST region and connects to the CST outside.
Related concept
Access ports place end devices into a single VLAN.
- ✓
MSTP is backward compatible with 802.1D and RSTP.
- ✗
MSTP requires a separate spanning-tree instance for every VLAN.
Why it's wrong here
Incorrect because that describes PVST+, not MSTP; MSTP groups VLANs into instances.
- ✗
MSTP uses a different BPDU format than RSTP.
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 mapped to a single spanning-tree instance. — MSTP (802.1s) allows mapping multiple VLANs to a single spanning-tree instance, reducing the number of STP instances needed. It uses an internal spanning tree (IST) to interconnect MST regions. MSTP is backward compatible with 802.1D and RSTP through the use of common spanning tree (CST) at the region boundary. MSTP does not require a separate instance for every VLAN like PVST+; it groups VLANs into instances. MSTP uses the same BPDU format as RSTP with additional MST-specific information.
What should I do if I get this 350-401 question wrong?
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.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which three statements about Multiple Spanning Tree Protocol (MSTP) are true? (Choose three.)
hard- ✓ A.MSTP allows multiple VLANs to be grouped into a single spanning-tree instance, reducing CPU and memory usage.
- ✓ B.In MSTP, the Internal Spanning Tree (IST) instance is instance 0 and is always present in every MST region.
- ✓ C.MSTP requires that all switches in the same MST region have the same VLAN-to-instance mapping, revision number, and region name.
- D.MSTP automatically load-balances traffic across all available uplinks without any configuration.
- E.MSTP requires a separate root bridge to be elected for each VLAN in the network.
Why A: 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.
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Last reviewed: Jun 18, 2026
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