H3C S3100 8C SI Operation Manual page 243

Operation Manual – MSTP
H3C S3100 Series Ethernet Switches
2) Root port
On a non-root bridge device, the root port is the port with the lowest path cost to the root
bridge. The root port is used for communicating with the root bridge. A non-root-bridge
device has one and only one root port. The root bridge has no root port.
3) Designated bridge and designated port
Refer to the following table for the description of designated bridge and designated
port.
Table 1-1 Designated bridge and designated port
Classification
For a device
For a LAN
Figure 1-1
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 is the 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 is the port BP2 on Device B.
Figure 1-1 A schematic diagram of designated bridges and designated ports
Designated bridge
A designated bridge is a device
that is directly connected to a
switch and is responsible for
forwarding BPDUs to this switch.
A designated bridge is a device
responsible for forwarding BPDUs
to this LAN segment.
shows designated bridges and designated ports. In the figure, AP1 and AP2,
The port through which the
designated bridge forwards
BPDUs to this device
The port through which the
designated bridge forwards
BPDUs to this LAN segment
1-2
Chapter 1 MSTP Configuration
Designated port