Planet IGSW-2840 User Manual page 148

User's Manual of IGSW-2840
designed to support independent spanning trees based on VLAN groups. Using multiple spanning trees can provide multiple
forwarding paths and enable load balancing. One or more VLANs can be grouped into a Multiple Spanning Tree Instance
(MSTI). MSTP builds a separate Multiple Spanning Tree (MST) for each instance to 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.
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"). 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.
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