Configuration Guide 304
Configuring Spanning Tree Spanning Tree
downstream switch. The value of the accumulated root path cost increases as the BPDU
spreads further.
BPDU
BPDU is a kind of packet that is used to generate and maintain the spanning tree. The
BPDUs (Bridge Protocol Data Unit) contain a lot of information, like bridge ID, root path cost,
port priority and so on. Switches share these information to help determine the spanning
tree topology.
1.2.2 MSTP Concepts
MSTP, compatible with STP and RSTP, has the same basic elements used in STP and RSTP.
Based on the networking topology, this section will introduce some concepts only used in
MSTP.
Figure 1-3 MSTP Topology
region 1
region 3
region 4
CST
IST
Blocked Port
region 2
MST Region
An MST region consists of multiple interconnected switches. The switches with the same
following characteristics are considered as in the same region:
Same region name
Same revision level
Same VLAN-Instance mapping
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