Chapter 13 Spanning Tree Protocol
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
•
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 69 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
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