H3C Technologies H3C WX5500E Series Access Controllers - Manual (Page 174)

164
Root port
On a non-root bridge, the port nearest to the root bridge is the root port. The root port is responsible for
communication with the root bridge. Each non-root bridge has one and only one root port. The root
bridge has no root port.
Designated bridge and designated port
Table 55 Description of designated bridges and designated ports:
Classification Designated bridge Designated port
For a device
Device directly connected to the local
device and responsible for forwarding
BPDUs to the local device. Port through which the designated
bridge forwards BPDUs to the local
device.
For a LAN
Device responsible for forwarding BPDUs
to this LAN segment.
Port through which the designated
bridge forwards BPDUs to this LAN
segment.
As shown in Figure 163 , AP1 and AP2, BP1 and BP2, and CP1 and CP2 are ports on Device A, Device
B, and Device C, respectively.
• If Device A forwards BPDUs to Device B through AP1, the designated bridge for Device B is Device
A, and the designated port of Device B is port AP1 on Device A.
• Device B and Device C are connected to the LAN. If Device B forwards BPDUs to the LAN, the
designated bridge for the LAN is Device B, and the designated port for the LAN is the port BP2 on
Device B.
Figure 163 Designated bridges and designated ports
Path cost
Path cost is a reference value used for link selection in STP. By calculating path costs, STP selects relatively
robust links and blocks redundant links, and finally prunes the network into a loop-free tree.
All the ports on the root bridge are designated ports.