3Com 4500 PWR 26-Port Configuration Manual page 233

Figure 20-1 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 4500 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.
The 3Com switches 4500 support using multiple standards to calculate the path costs of ports, as well
as using commands to configure the path costs of ports. For details, see
a Port.
Configuring the Bridge Priority of the Current
20-3
Switch.
Configuring the Path Cost for