SMC Networks SMC8126L2 Management Manual page 148

3
Configuring the Switch
An MST Region consists of a group of interconnected bridges that have the same
MST Configuration Identifiers (including the Region Name, Revision Level and
Configuration Digest-V see 3-116). An MST Region may contain multiple MSTP
Instances. An Internal Spanning Tree (IST) is used to connect all the MSTP switches
within an MST region. A Common Spanning Tree (CST) interconnects all adjacent
MST Regions, and acts as a virtual bridge node for communications with STP or
RSTP nodes in the global network.
MSTP connects all bridges and LAN segments with a single Common and Internal
Spanning Tree (CIST). The CIST is formed as a result of the running spanning tree
algorithm between switches that support the STP, RSTP, MSTP protocols.
Once you specify the VLANs to include in a Multiple Spanning Tree Instance (MSTI),
the protocol will automatically build an MSTI tree to maintain connectivity among
each of the VLANs. MSTP maintains contact with the global network because each
instance is treated as an RSTP node in the Common Spanning Tree (CST).
3-104