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Chapter 13 Spanning Tree Protocol

GS2200-8/24 User’s Guide

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Devices that belong to the same MST region are configured to have the same MSTP configuration

identification settings. These include the following parameters:

• Name of the MST region

• Revision level as the unique number for the MST region

• VLAN-to-MST Instance mapping

13.10.3 MST Instance

An MST Instance (MSTI) is a spanning tree instance. VLANs can be configured to run on a specific

MSTI. Each created MSTI is identified by a unique number (known as an MST ID) known internally

to a region. Thus an MSTI does not span across MST regions.

The following figure shows an example where there are two MST regions. Regions 1 and 2 have 2

spanning tree instances.

Figure 80 MSTIs in Different Regions

13.10.4 Common and Internal Spanning Tree (CIST)

A CIST represents the connectivity of the entire network and it is equivalent to a spanning tree in

an STP/RSTP. The CIST is the default MST instance (MSTID 0). Any VLANs that are not members of

an MST instance are members of the CIST. In an MSTP-enabled network, there is only one CIST