3Com 4007, Implementation Manual, Page: 171 / 684

STP Terms and Concepts 171
The bridges that are chosen as the best path, called designated bridges ,
form the second level of the hierarchy.
■
A designated bridge relays network transmissions to the root bridge
through its
root port . Any port that transmits to the root bridge is a
root port.
■
The designated bridges also have designated ports — the ports that
are attached to the LANs from which the bridge is receiving
information.
Figure 3 shows the hierarchy of the STP bridges and their ports.
Figure 3 Hierarchy of the Root Bridge and the Designated Bridge
Actions That Result from CBPDU Information
From the information that the CBPDUs provide:
■
Bridges elect a single bridge to be the root bridge . The root bridge has
the lowest bridge ID among all the bridges on the extended network.
■
Bridges calculate the best path between themselves and the root
bridge.
Root bridge
Designated bridge
To designated port
Bridge
L2/3
L2/3
L2/3
To root port
To root port
To designated port