Allied-telesis AT-GS950/16 User Manual download pdf (Page 378)

Appendix A: MSTP Overview

378

Each MSTI functions as an independent spanning tree within a region.

Consequently, each MSTI must have a root bridge to locate physical loops

within the spanning tree instance. An MSTI’s root bridge is called a regional

root. The MSTIs within a region may share the same regional root or they can

have different regional roots.

A regional root for an MSTI must be within the region where the MSTI is

located. An MSTI cannot have a regional root that is outside its region.

A regional root is selected by a combination of the MSTI Bridge Priority value

and the bridge’s MAC address. The MSTI priority is analogous to the RSTP

bridge priority value. Where they differ is that while the RSTP bridge priority is

used to determine the root bridge for an entire bridged network, the MSTI

priority is used only to determine the regional root for a particular MSTI.

The range for this parameter is the same as the RSTP bridge priority; from 0

to 61,440 in sixteen increments of 4,096. To set the parameter, you select the

increment that represents the desired MSTI priority value according to

Table 8.

MST Region

Guidelines

Following are several points to remember about regions.

 A network can contain any number of regions, and a region can contain

any number of switches.

 The AT-GS950/16 switch can belong to only one region at a time.

 A region can contain any number of VLANs.

 All of the bridges in a region must have the same configuration name,

revision level, VLANs, and VLAN to MSTI associations.

 An MSTI cannot span multiple regions.

Table 8. Regional Bridge Priority Value Increments

Bridge Priority

Selections

0 32768

4096 36864

8192 40960

12288 45056

16384 49152

20480 53248

24576 57344

28672 61440

1 2 ... 373 374 375 376 377 378 379 380 381 382 383 ... 403 404

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Allied-telesis AT-GS950/16 User Manual Page 378