ZyXEL Communications MSC1024G Series User Manual page 484

Chapter 15 Switch Screens
• VLAN-to-MST mapping
15.9.2.3 MST Instance
An MST Instance (MSTI) is a set of VLANs that use the same spanning tree. 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 334 MSTIs in Different Regions
15.9.2.4 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 335 MSTP and Legacy RSTP Network Example
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MSC1000G/1024G/1224G Series User's Guide