3Com Switch 8800 Family Configuration Guide

Introduction to MSTP 127
Figure 28 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 28, 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.
■ The specific calculation process of STP algorithm.
The following example illustrates the calculation process of STP.
Figure 29 illustrates the practical network.
Switch A
Switch C
Switch B
CP2
BP2
CP1
BP1
AP2AP1
LAN