3Com Switch 8800 Configuration Guide
Chapter 38 MSTP Region-configuration
38-7
Switch A
Switch C
Switch B
CP2
BP2
CP1
BP1
AP2
AP1
LAN
Figure 38-6
Designated bridge and designated port
For a switch, the designated bridge is a switch in charge of forwarding BPDU to the
local switch via a port called the designated port accordingly. For a LAN, the designated
bridge is a switch that is in charge of forwarding BPDU to the network segment via a
port called the designated port accordingly. As illustrated in the Figure 38-6, Switch A
forwards data to Switch B via the port AP1. To Switch B, the designated bridge is Switch
A and the designated port is AP1. In the figure, Switch B and Switch C are connected to
the LAN and Switch B forwards BPDU to LAN. So the designated bridge of LAN is
Switch B and the designated port is BP2.
z
The specific calculation process of STP algorithm.
The following example illustrates the calculation process of STP.
Figure 38-7 illustrates the practical network.
Switch A
with priority 0
Switch C
with priority 2
Switch B
with priority 1
CP2
BP2
CP1
BP1
AP2
AP1
4
10
5
Figure 38-7
Ethernet switch networking
To facilitate the descriptions, only the first four parts of the configuration BPDU are
described in the example. They are root ID (expressed as Ethernet switch priority), path
cost to the root, designated bridge ID (expressed as Ethernet switch priority) and the
designated port ID (expressed as the port number). As illustrated Figure 38-7, the
