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Configuring MSTP 249
Figure 5 Port Roles
MSTP Principles 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.
CIST calculation
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.
MSTI calculation
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 Configuring MSTP includes tasks that are described in the following sections:
■ Configuring the MST Region for a Switch
■ Specifying the Switch as Primary or Secondary Root Switch
■ Configuring the MSTP Operating Mode
■ Configuring the Bridge Priority for a Switch
■ Configuring the Max Hops in an MST Region
■ Configuring the Switching Network Diameter
■ Configuring the Time Parameters of a Switch
■ Configuring the Max Transmission Speed on a Port
■ Configuring a Port as an Edge Port