3Com 2928 User Guide - Page 217

z MSTP supports mapping VLANs to MST instances (MSTIs) by means of a VLAN-to-MSTI mapping table. MSTP can reduce communication overheads and resource usage by mapping multiple VLANs to one MSTI. z MSTP divides a switched network into multiple regions, each containing multiple spanning trees that are independent of one another. z MSTP prunes a loop network into a loop-free tree, thus avoiding proliferation and endless cycling of packets in a loop network. In addition, it provides multiple redundant paths for data forwarding, thus supporting load balancing of VLAN data. z MSTP is compatible with STP and RSTP. Basic Concepts in MSTP Assume that all the four devices in Figure 1-4 are running MSTP. This section explains some basic concepts of MSTP based on the figure. Figure 1-4 Basic concepts in MSTP Region A0 VLAN 1 mapped to instance 1 VLAN 2 mapped to instance 2 Other VLANs mapped to CIST BPDU A B C D Region D0 VLAN 1 mapped to instance 1, B as regional root bridge. VLAN 2 mapped to instance 2， C as regional root bridge. Other VLANs mapped to CIST CST BPDU BPDU Region B0 VLAN 1 mapped to instance 1 VLAN 2 mapped to instance 2 Other VLANs mapped to CIST Region C0 VLAN 1 mapped to instance 1 VLAN 2,3 mapped to instance 2 Other VLANs mapped to CIST MST region A multiple spanning tree region (MST region) consists of multiple devices in a switched network and the network segments among them. These devices have the following characteristics: z All are MSTP-enabled, z They have the same region name, z They have the same VLAN-to-MSTI mapping configuration, z They have the same MSTP revision level configuration, and z They are physically linked with one another. 1-10