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19.9 Description of Multiple Spanning Tree
19.9.1 Overview
The following explains the features of Multiple Spanning Tree. MST instances can be used
to perform load balancing. MST regions can be used to divide large network configurations
into smaller configurations, to simplify network design. The following gives a functional
overview of how Multiple Spanning Tree can be used to achieve these goals.
(1) MST instance
Multiple Spanning Tree allows Spanning Tree Protocols to be built for each group that
aggregates multiple VLANs, called MST instances or MSTI, enabling load balancing for
each MST instance. For load balancing using PVST+, a tree is needed for each VLAN, but
with Multiple Spanning Tree, MST instances can be used to use only the trees needed
through planned load balancing. Therefore, unlike PVST+, increases in CPU load and
network load can be kept to a minimum for each increase in VLAN count. The Switch allows
as many as 16 MST instances to be set for a Switch.
The following figure shows an example MST instance setup.
Figure 19-12 Example MST instance setup
(2) MST regions
Multiple Spanning Tree allows multiple switches to be grouped and handled as an MST
region. To belong in the same MST region, the region name, revision number, MST
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