3Com 5500-EI PWR Install Manual page 213

Two devices are connected to the LAN: Device B and Device C. If Device B forwards BPDUs to the
LAN, the designated bridge for the LAN is Device B, and the designated port is the port BP2 on
Device B.
Figure 1-1 A schematic diagram of designated bridges and designated ports
All the ports on the root bridge are designated ports.
4) Bridge ID
A bridge ID consists of eight bytes, where the first two bytes represent the bridge priority of the device,
and the latter six bytes represent the MAC address of the device.
The default bridge priority of a 3Com switch 5500-EI is 32768. You can use a command to configure the
bridge priority of a device. For details, see
5) Path cost
STP uses path costs to indicate the quality of links. A small path cost indicates a higher link quality. The
path cost of a port is related to the rate of the link connecting the port. The higher the link rate, the
smaller the path cost.
By comparing the path costs of different links, STP selects the most robust links and blocks the other
links to prune the network into a tree.
Configuring the Bridge Priority of the Current
1-3
Switch.