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Basic MSTP Terminologies
Figure 1-4 illustrates basic MSTP terms (assuming that MSTP is enabled on each switch in this figure).
Figure 1-4 Basic MSTP terminologies
CST
BPDU
Region A0:
VLAN 1 mapped to MSTI 1
VLAN 2 mapped to MSTI 2
Other VLANs mapped to CIST
BPDU BPDU
A
D
CB
Region B0:
VLAN 1 mapped to MSTI 1
VLAN 2 mapped to MSTI 2
Other VLANs mapped to CIST
Region C0:
VLAN 1 mapped to MSTI 1
VLAN 2 and 3 mapped to MSTI 2
Other VLANs mapped to CIST
Region D0:
VLAN 1 mapped to MSTI 1, B
as the regional root bridge
VLAN 2 mapped to MSTI 2, C
as the regional root bridge
Other VLANs mapped to CIST
MST region
A multiple spanning tree region (MST region) comprises multiple physically-interconnected
MSTP-enabled switches and the corresponding network segments connected to these switches. These
switches have the same region name, the same VLAN-to-MSTI mapping configuration and the same
MSTP revision level.
A switched network can contain multiple MST regions. You can group multiple switches into one MST
region by using the corresponding MSTP configuration commands.
As shown in
Figure 1-4, all the switches in region A0 are of the same MST region-related configuration,
including:
z Region name
z VLAN-to-MSTI mapping (that is, VLAN 1 is mapped to MSTI 1, VLAN 2 is mapped to MSTI 2, and
the other VLANs are mapped to CIST.)
z MSTP revision level (not shown in Figure 1-4)
MSTI
A multiple spanning tree instance (MSTI) refers to a spanning tree in an MST region.
Multiple spanning trees can be established in one MST region. These spanning trees are independent
of each other. For example, each region in
Figure 1-4 contains multiple spanning trees known as MSTIs.
Each of these spanning trees corresponds to a VLAN.
VLAN-to-MSTI mapping table
A VLAN-to-MSTI mapping table is maintained for each MST region. The table is a collection of
mappings between VLANs and MSTIs. For example, in
Figure 1-4, the VLAN-to-MSTI mapping table of
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