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Chapter 13 Spanning Tree Protocol
MGS3700-12C User’s Guide
152
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
13.1.5.3 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 68 MSTIs in Different Regions
13.1.5.4 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 that runs between MST regions