3com 2928 User Guide

 

1-10 

z

 

MSTP supports mapping VLANs to MST instances (MSTIs) by means of a VLAN-to-MSTI mapping 
table. MSTP can reduce communication overheads and resource usage by mapping multiple 
VLANs to one MSTI.  

z

 

MSTP divides a switched network into multiple regions, each containing multiple spanning trees 
that are independent of one another.  

z

 

MSTP prunes a loop network into a loop-free tree, thus avoiding proliferation and endless cycling of 
packets in a loop network. In addition, it provides multiple redundant paths for data forwarding, thus 
supporting load balancing of VLAN data.  

z

 

MSTP is compatible with STP and RSTP.  

Assume that all the four devices in 

 are running MSTP. This section explains some basic 

concepts of MSTP based on the figure.  

Basic concepts in MSTP 

CST

Region A0
VLAN 1 mapped to instance 1
VLAN 2 mapped to instance 2
Other VLANs mapped to CIST

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 2,3 mapped to instance 2
Other VLANs mapped to CIST

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

BPDU

BPDU

C

D

B

A

BPDU

 

 

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:  

z

 

All are MSTP-enabled, 

z

 

They have the same region name,  

z

 

They have the same VLAN-to-MSTI mapping configuration,  

z

 

They have the same MSTP revision level configuration, and  

z

 

They are physically linked with one another.