SMC Networks TigerStack II SMC8848M Management Manual page 255

maintain connectivity among each of the assigned VLAN groups. MSTP
then builds a Internal Spanning Tree (IST) for the Region containing all
commonly configured MSTP bridges.
IST
(for this Region)
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 – see "Configuring Multiple
Spanning Trees" on page 21). 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.
Region 1
CIST
IST
Region 2
Region R
Region 4
Region 3
MST 1
MST 2
Region 1
CST
Region 2
Region 4
Region 3
10-3