R3721-F3210-F3171-HP High-End Firewalls Network Management Configuration Guide-6PW101

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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 42, 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.
In Figure 42, f
or example, the CIST has a section in each MST region, and this section is the IST in the
res
pective 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 42.
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 42, f
or example, the ISTs in all MST regions plus the inter-region CST constitute the CIST of the
entir
e 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 42, f
or example, multiple MSTIs can exist in each MST region, each MSTI corresponding to the
specif
ied VLANs.
Regional root bridge
The root bridge of the IST or an MSTI within an MST region is the regional root bridge of the IST or the
MSTI. Based on the topology, different spanning trees in an MST region may have different regional
roots.
For example, in region D0 in Figure 42, the r
egi
onal root of MSTI 1 is device B, and that of MSTI 2 is
device C.
Common root bridge
The common root bridge is the root bridge of the CIST.
In Figure 42, for example, the common root bridge is a device in region A0.
Boundary port
A boundary port is a port that connects an MST region to another MST region, or to a single
spanning-tree region running STP, or to a single spanning-tree region running RSTP. It is at the boundary
of an MST region.