Operation Manual – MSTP
H3C S5100-SI/EI Series Ethernet Switches
Chapter 1 MSTP Configuration
1-13
I. 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
)
II. 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.
III. 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 region A0 contains these mappings: VLAN 1 to MSTI 1;
VLAN 2 to MSTI 2, and other VLANs to CIST. In an MST region, load balancing is
implemented according to the VLAN-to-MSTI mapping table.
IV. IST
An internal spanning tree (IST) is a spanning tree in an MST region.
ISTs together with the common spanning tree (CST) form the common and internal
spanning tree (CIST) of the entire switched network. An IST is a special MSTI; it is a
branch of CIST in the MST region.
In
Figure 1-4
, each MST region has an IST, which is a branch of the CIST.
V. CST
A CST is a single spanning tree in a switched network that connects all MST regions in
the network. If you regard each MST region in the network as a “switch”, then the CST
is the spanning tree generated by STP or RSTP running on the "switches".
