H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – MSTP

H3C S7500E Series Ethernet Switches Chapter 1 MSTP Configuration

1-4

z Forward delay: forward delay of the port.

 Note:

For the convenience of description, the description and examples below involve only

four parts of a configuration BPDU:

z Root bridge ID (in the form of device priority)

z Root path cost

z Designated bridge ID (in the form of device priority)

z Designated port ID (in the form of port name)

1) Specific calculation process of the STP algorithm

z Initial state

Upon initialization of a device, each port generates a BPDU with itself as the root bridge,

in which the root path cost is 0, designated bridge ID is the device ID, and the

designated port is the local port.

z Selection of the optimum configuration BPDU

Each device sends out its configuration BPDUs and receives configuration BPDUs

from other devices.

The process of selecting the optimum configuration BPDU is as follows:

Table 1-2 Selection of the optimum configuration BPDU

Step Description

Upon receiving a configuration BPDU on a port, the device performs the

following processing:

z If the received configuration BPDU has a lower priority than that of the

configuration BPDU generated by the port, the device will discard the

received configuration BPDU without doing any processing on the

configuration BPDU of this port.

z If the received configuration BPDU has a higher priority than that of

the configuration BPDU generated by the port, the device will replace

the content of the configuration BPDU generated by the port with the

content of the received configuration BPDU.

The device compares the configuration BPDUs of all the ports and

chooses the optimum configuration BPDU.