MSTP is compatible with both STP and RSTP.
MSTP Elements
MST Region
(Multiple Spanning Tree Region): An MST region consists of multiple
interconnected switches. These switches have the same region name, the same revision level
and the same VLAN-Instance mapping table.
MSTI
(Multiple Spanning Tree Instance): The MST instance is a spanning tree running in the
MST region. Multiple MST instances can be established in one MST region and they are
independent of each other. Each spanning tree is referred to as a multiple spanning tree
instance.
VLAN-Instance Mapping:
VLAN-Instance Mapping describes the mapping relationship
between VLANs and instances. Multiple VLANs can be mapped to a same instance, but one
VLAN can be mapped to only one instance.
IST
(Internal Spanning Tree)
:
A special MST instance with an instance ID of 0. By default, all the
VLANs are mapped to IST.
CST
(Common Spanning Tree): A CST is the spanning tree in a switched network that connects
all MST regions in the network.
CIST
(Common and Internal Spanning Tree): A CIST, comprising IST and CST, is the spanning
tree in a switched network that connects all switches in the network.
The following figure shows the network diagram in MSTP.
Figure 8-2 Basic MSTP diagram
MSTP
MSTP divides a network into several MST regions. The CST is generated between these MST
regions, and multiple spanning trees can be generated in each MST region. Each spanning
trees is called an instance. As well as STP, MSTP uses BPDUs to generate spanning tree. The
only difference is that the BPDU for MSTP carries the MSTP configuration information on the
switches.
Port States
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