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350-401 Practice Question: Which three statements about the Multiple…
Which three statements about the Multiple Spanning Tree Protocol (MSTP) are true? (Choose three.)
⚠ Common exam trap
350-401 often tests the misconception that MSTP requires one instance per VLAN (that's PVST+) or that it uses a unique BPDU format, when it actually reuses RSTP BPDUs with MSTP extensions.
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.
Option A is correct because MSTP (IEEE 802.1s) lets you group many VLANs into a single Multiple Spanning Tree Instance (MSTI), so one topology serves all VLANs mapped to it, greatly reducing the number of spanning-tree instances compared with PVST+. Option B is correct because MSTP builds an Internal Spanning Tree (IST) as instance 0, which carries the Common and Internal Spanning Tree (CIST) information and connects MST regions to each other and to other STP domains. Option C is correct because MSTP is designed to interoperate with 802.1D (classic STP) and 802.1w (RSTP) devices, treating them as part of the CIST so legacy switches can participate in the topology. Option D is wrong because requiring one instance per VLAN describes PVST+/RPVST+, whereas MSTP's whole purpose is to map multiple VLANs to a single instance. Option E is wrong because MSTP uses the same RSTP-style BPDU format (with MSTP-specific extensions in the MSTI configuration messages), not a fundamentally different BPDU format.
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.
Why this is correct
MSTP maps many VLANs onto a single spanning-tree instance, so a handful of instances can serve hundreds of VLANs. This is the protocol's core efficiency gain over per-VLAN spanning tree, reducing bridge processing and control-plane load.
- ✓
MSTP uses an Internal Spanning Tree (IST) to interconnect MST regions.
Why this is correct
Within each region, MSTP runs one Internal Spanning Tree that carries all instances' topology information and presents the region as a single virtual bridge to outside networks. The IST is what interconnects regions, making this an accurate MSTP statement.
- ✓
MSTP is backward compatible with 802.1D and RSTP.
Why this is correct
MSTP interoperates with legacy 802.1D and RSTP bridges, mapping their single spanning tree into the Common Spanning Tree. This backward compatibility is a genuine MSTP property, letting mixed-vendor and mixed-generation topologies converge without replacing older switches.
- ✗
MSTP requires a separate spanning-tree instance for every VLAN.
Why it's wrong here
MSTP maps multiple VLANs onto a single instance via MSTIs, so it explicitly avoids one instance per VLAN; that per-VLAN model is PVST+, which Cisco switches run when each VLAN needs its own topology. The option inverts MSTP's core scaling benefit, which is reducing instance count.
- ✗
MSTP uses a different BPDU format than RSTP.
Why it's wrong here
MSTP carries the same RSTP-style BPDU structure, extending it with MSTP-specific TLVs for region name, revision and instance mapping; the version field distinguishes them. RSTP's BPDU format is reused, so claiming a wholly different format is false. A distinct format would be needed only for a non-compatible protocol.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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