Product guide

Spanning-Tree Operation
802.1s Multiple Spanning Tree Protocol (MSTP)
IST
Instance
MSTI
(Optional)
MSTI
(Optional)
IST
Instance
MSTI
(Optional)
MSTI
(Optional)
MSTI
(Optional)
Switch
Running STP
Switch
Running STP
Switch
Running STP
Switch
Running RSTP
Switch
Running RSTP
Switch
Running RSTP
Common Spanning Tree (CST)
MST Region
MST Region
Common and Internal Spanning Tree (CIST)
Figure 6-25. Example of MSTP Network with Legacy STP and RSTP Devices
Connected
Common and Internal Spanning Tree (CIST): The CIST identifies the
regions in a network and administers the CIST root bridge for the network,
the root bridge for each region, and the root bridge for each spanning-tree
instance in each region.
Common Spanning Tree (CST): The CST administers the connectivity
among the MST regions, STP LANs, and RSTP LANs in a bridged network.
MST Region: An MST region comprises the VLANs configured on physically
connected MSTP switches. All switches in a given region must be configured
with the same VLANs and Multiple Spanning Tree Instances (MSTIs).
Internal Spanning Tree (IST): The IST administers the topology within a
given MST region. When you configure a switch for MSTP operation, the
switch automatically includes all of the static VLANs configured on the switch
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