3Com 7757 Configuration Manual page 242

242 C 30: MSTP C
HAPTER ONFIGURATION
Figure 60 Basic MSTP terminologies
B
Region D0
VLAN 1 mapped to instance 1,
B as regional root bridge
VLAN 2 mapped to instance 2,
C as regional root bridge
Other VLANs mapped to CIST
MST region
An MST region (multiple spanning tree 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-spanning-tree 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. For example, all switches in region A0 shown in Figure 60 have the
same MST region configuration: the same region name, the same
VLAN-to-spanning-tree mappings (that is, VLAN 1 is mapped to spanning tree
instance 1, VLAN 2 is mapped to spanning tree instance 2, and other VLANs are
mapped to CIST), the same MSTP revision level (not shown in Figure 60).
MSTI
A multiple spanning tree instance (MSTI) refers to a spanning tree in a 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 60
contains multiple spanning trees known as MSTIs (multiple spanning tree
instances). Each of these spanning trees corresponds to a VLAN.
VLAN mapping table
A VLAN mapping table is a property of an MST region. It contains information
about how VLANs are mapped to MSTIs. For example, in Figure 60, the
information contained in the VLAN mapping table of region A0 is: VLAN 1 is
mapped to MSTI 1; VLAN 2 is mapped to MSTI 2; and other VLANs are mapped to
CIST. In an MST region, load balancing is achieved by the VLAN mapping table.
A
BPDU
CST
C
BPDU
D
Region A0
VLAN 1 mapped to instance 1
VLAN 2 mapped to instance 2
Other VLANs mapped to CIST
BPDU
Region B0
VLAN 1 mapped to instance 1
VLAN 2 mapped to instance 2
Other VLANs mapped to CIST
Region C0
VLAN 1 mapped to instance 1
VLAN 2 mapped to instance 2
Other VLANs mapped to CIST