3Com 8800 Configuration Manual page 542

3Com Switch 8800 Configuration Guide
Switch B
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.
The specific calculation process of STP algorithm.
The following example illustrates the calculation process of STP.
Figure 38-7 illustrates the practical network.
Switch B
with priority 1
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
Switch A
AP1
BP1
Switch C
BP2
LAN
Switch A
with priority 0
AP1
5
BP1
BP2
4
Switch C
with priority 2
Chapter 38 MSTP Region-configuration
AP2
CP1
CP2
AP2
10
CP1
CP2
38-7