Refer to the exhibit. This layer 2 network is expected to add 150 VLANS over the next year, In addition to the existing 50 VLANs within the network which STP types will support this design…

Question

Exhibit

Options

• APVST+
• BCST
• CMST
• DRSTP

• A
  19% (7)
• B
  8% (3)
• C
  67% (24)
• D
  6% (2)

Explanation

MST (Multiple Spanning Tree, IEEE 802.1s) is correct because it maps multiple VLANs to a small number of STP instances - so even with 200 VLANs, you might only run 2–4 instances. This drastically reduces CPU overhead compared to running one instance per VLAN, while still enabling load balancing by assigning different VLAN groups to different instances.

Why the distractors are wrong:

• PVST+ runs one STP instance per VLAN, so 200 VLANs = 200 instances - the highest CPU cost of all options.
• CST runs a single instance for all VLANs (lowest CPU), but provides no load balancing since every VLAN follows the same tree.
• RSTP improves convergence speed but is still a single-instance protocol like CST - no per-VLAN or per-group load balancing.

Memory tip: Think of MST as "Groups save CPU" - it groups many VLANs into few instances, giving you the load balancing of PVST+ at a fraction of the CPU cost. If a question mentions both scale and load balancing, MST is almost always the answer.

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