Common And Internal Spanning Tree (Cist) - ZyXEL Communications GS2200-24 User Manual

The following figure shows an example where there are two MST regions. Regions
1 and 2 have 2 spanning tree instances.
Figure 70 MSTIs in Different Regions

13.12.4 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
and single spanning tree devices. A network may contain multiple MST regions
and other network segments running RSTP.
Figure 71 MSTP and Legacy RSTP Network Example
GS2200-24 User's Guide
Chapter 13 Spanning Tree Protocol
137