3com 3.01.01 Benutzerhandbuch

Figure 5   Port Roles

MSTP divides the entire Layer 2 network into several MST regions, and calculates 
and generates CST for them. Multiple spanning trees are generated in a region 
and each of them is called an MSTI. The instance 0 is called IST, and others are 
called MSTI. 

The CIST root is the highest-priority switch, elected from the switches on the entire 
network by comparing their configuration BPDUs. MSTP calculates and generates 
an IST in an MST region and also the CST connecting the regions. CIST is the 
unique single spanning tree of the entire switching network. 

Inside an MST region, MSTP generates different MSTIs for different VLANs 
according to the association between the VLAN and the spanning tree. 

In this way, the packets of a VLAN travel along the corresponding MSTI; inside the 
MST region and the CST between different regions. 

Configuring MSTP includes tasks that are described in the following sections:

■

■

■

■

■

■

■

■

■