H3C Technologies H3C WX5500E Series Access Controllers - Manual (Page 182)

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MST region
A multiple spanning tree region (MST region) consists of multiple devices in a switched network and the
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-MSTI mapping configuration.
• They have the same MSTP revision level configuration.
• They are physically linked with one another.
For example, all the devices in region A0 in Figure 166 have the same MST region configuration:
• The same region name.
• The same VLAN-to-MSTI mapping configuration (VLAN 1 is mapped to MSTI 1, VLAN 2 to MSTI 2,
and the rest to the common and internal spanning tree (CIST, or MSTI 0).
• The same MSTP revision level (not shown in the figure).
Multiple MST regions can exist in a switched network. You can assign multiple devices to the same MST
region.
VLAN-to-MSTI mapping table
As an attribute of an MST region, the VLAN-to-MSTI mapping table describes the mapping relationships
between VLANs and MSTIs. In Figure 166 , for example, the VLAN-to-MSTI mapping table of region A0
is: VLAN 1 is mapped to MSTI 1, VLAN 2 to MSTI 2, and the rest to CIST. MSTP achieves load balancing
by means of the VLAN-to-MSTI mapping table.
IST
An internal spanning tree (IST) is a spanning tree that runs in an MST region.
ISTs in all MST regions and the common spanning tree (CST) jointly constitute the common and internal
spanning tree (CIST) of the entire network. An IST is a section of the CIST. An IST is a special MSTI.
In
Figure 166 , for example, the CIST has a section in each MST region, and this section is the IST in the
respective MST region.
CST
The CST is a single spanning tree that connects all MST regions in a switched network. If you regard each
MST region as a "device," the CST is a spanning tree calculated by these devices through STP or RSTP.
CSTs are indicated by red lines in Figure 166 .
CIST
Jointly constituted by ISTs and the CST, the CIST is a single spanning tree that connects all devices in a
switched network.
In
Figure 166 , for example, the ISTs in all MST regions plus the inter-region CST constitute the CIST of the
entire network.
MSTI
Multiple spanning trees can be generated in an MST region through MSTP, one spanning tree being
independent of another. Each spanning tree is referred to as a multiple spanning tree instance (MSTI).
In
Figure 166 , for example, multiple MSTIs can exist in each MST region, each MSTI corresponding to the
specified VLANs.