3Com Switch 8800 Advanced Software V5 Configuration Guide

MSTP Overview 103
Figure 28 Basic concepts in MSTP
1 MST region
An MST region is composed of multiple devices in a switched network and
network segments among them. These devices have the following characteristics:
■ All are MSTP-enabled,
■ They have the same region name,
■ They have the same VLAN-to-instance mapping configuration,
■ They have the same MSTP revision level configuration, and
■ They are physically linked with one another.
In area A0 in Figure 28, for example, all the device have the same MST region
configuration: the same region name, the same VLAN-to-instance mapping (VLAN
1 is mapped to MST instance 1, VLAN 2 to MST instance 2, and the rest to the
common and internal spanning tree (CIST).), and the same MSTP revision level (not
shown in the figure).
Multiple MST regions can exist in a switched network. You can use an MSTP
command to group multiple devices to the same MST region.
2 VLAN-to-instance mapping table
As an attribute of an MST region, the VLAN-to-instance mapping table describes
the mapping relationships between VLANs and MST instances. In
Figure 28, for
example, the VLAN-to-instance mapping table of region A0 describes that the