Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

Protocol Overview

MSTP allows multiple spanning tree instances and allows you to map many VLANs to one spanning tree instance to reduce the total number of required instances.

In contrast, PVST+ allows a spanning tree instance for each VLAN. This 1:1 approach is not suitable if you have many VLANs, because each spanning tree instance costs bandwidth and processing resources.

In the following illustration, three VLANs are mapped to two multiple spanning tree instances (MSTI). VLAN 100 traffic takes a different path than VLAN 200 and 300 traffic. The behavior demonstrates how you can use MSTP to achieve load balancing.

Figure 1. MSTP with Three VLANs Mapped to TWO Spanning Tree Instances