Qtech QSW-3900-24-Т-DC [251/313] Note all the ports on the root bridge are designated ports

Qtech QSW-3900-24-SFP-DC [251/313] Note all the ports on the root bridge are designated ports
QTECH Software Configuration Manual
17-250
Classification Designated bridge Designated port
For a device
The device directly connected with
this device and responsible for
forwarding BPDUs
The port through which the
designated bridge forwards
BPDUs to this device
For a LAN
The device responsible for
forwarding BPDUs to this LAN
segment
The port through which the
designated forwards BPDUs to
this LAN segment
Figure 1 shows designated bridges and designated ports. In the figure, 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 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 A schematic diagram of designated bridges and designated ports
Note :
All the ports on the root bridge are designated ports.
17.1.1.4 How STP works
STP identifies the network topology by transmitting configuration BPDUs between network devices.
Configuration BPDUs contain sufficient information for network devices to complete the spanning tree computing.
Important fields in a configuration BPDU include :
Root bridge ID : consisting of root bridge priority and MAC address.
Root path cost : the cost of the shortest path to the root bridge.
Designated bridge ID : designated bridge priority plus MAC address.
Designated port ID, designated port priority plus port name.
Message age : age of the configuration BPDU
Max age : maximum age of the configuration BPDU.
Hello time : configuration BPDU interval.
Forward delay : forward delay of the port.

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