Motorola WS5100 Series Reference Manual page 197

The following definitions describe the STP instances that define an MST configuration:
• Common Spanning (CST) – MST runs a single spanning tree instance (called the Common Spanning Tree)
that interconnects all the bridges in a network. This instance treats each region as a single bridge. In all
other ways, it operates exactly like Rapid Spanning Tree (RSTP).
• Common and Internal Spanning Trees (CIST) – CIST contains all of the ISTs and bridges not formally
configured into a region. This instance interoperates with bridges running legacy STP and RSTP
implementations.
• Multiple Spanning Tree Instance (MSTI) – The MSTI is identified by an MST identifier (MSTid) value from
1 and 15. This defines an individual instance of a spanning tree. One or more VLANs can be assigned to
an MSTI. A VLAN cannot be assigned to multiple MSTIs. The multiple spanning tree instance 0 is always
present. VLANs not explicitly assigned to an instance are assigned to instance 0.
• MSTP Region – These are clusters of bridges that run multiple instances of the MST protocol. Multiple
bridges detect they are in the same region by exchanging their configuration (instance to VLAN mapping),
name, and revision-level. If you need to have two bridges in the same region, the two bridges must have
identical configurations, names, and revision-levels.
To configure the switch for MST support, configure the name and the revision on each switch being
configured. This name is unique to each region. Then create an Instance and assign an ID. VLANs are then
assigned to instances. These instances must be configured on switches that interoperate with the same
VLAN assignments. Port cost, priority and global parameters can then be configured for individual ports and
instances.
The Multiple Spanning Tree option contains separate tabs for the following activities:
• Configuring a Bridge
• Viewing and Configuring Bridge Instance Details
• Configuring a Port
• Viewing and Configuring Port Instance Details
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Network Setup