R3166-R3206-HP High-End Firewalls Network Management Configuration Guide-6PW101

Root port

On a non-root bridge, the port nearest to the root bridge is called 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

The following table describes designated bridges and designated ports.

Table 10 Description of designated bridges and designated ports:

Classification Desi

nated brid

Desi

nated

ort

For a device

A device directly connected with the local

device and responsible for forwarding

BPDUs to the local device

The port through which the designated

bridge forwards BPDUs to the local

switch

For a LAN

The device responsible for forwarding

BPDUs to this LAN segment

The port through which the designated

bridge forwards BPDUs to this LAN

segment

As shown in Figure 25, 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.

• 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 for the LAN is the port

BP2 on Device B.

Figure 25 A schematic diagram of designated bridges and designated ports

NOTE:

ll the ports on the root brid

e are desi

nated 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.