H3C S7500E-X Configuration Manual page 77

Device
After the comparison processes described in
bridge is established, as shown in
Figure 20 The final calculated spanning tree
The configuration BPDU forwarding mechanism of STP
The configuration BPDUs of STP are forwarded according to these guidelines:
•
Upon network initiation, every device regards itself as the root bridge and generates
configuration BPDUs with itself as the root. Then it sends the configuration BPDUs at a regular
hello interval.
•
If the root port receives a configuration BPDU superior to the configuration BPDU of the port,
the device performs the following operations:
Increases the message age carried in the configuration BPDU.
Starts a timer to time the configuration BPDU.
Sends this configuration BPDU through the designated port.
•
If a designated port receives a configuration BPDU with a lower priority than its configuration
BPDU, the port immediately responds with its configuration BPDU.
•
If a path fails, the root port on this path no longer receives new configuration BPDUs and the old
configuration BPDUs will be discarded due to timeout. The device generates a configuration
BPDU with itself as the root and sends the BPDUs and TCN BPDUs. This triggers a new
spanning tree calculation process to establish a new path to restore the network connectivity.
Comparison process
plus path cost of Port C2 (4). Device C determines that the
configuration BPDU of Port C2 is the optimum, and selects
Port C2 as the root port with the configuration BPDU
unchanged.
Based on the configuration BPDU and path cost of the root
port, Device C performs the following operations:
37. Calculates a designated port configuration BPDU for
Port C1 {0, 9, 2, Port C1}.
38. Compares it with the existing configuration BPDU of
Port C1 {0, 0, 0, Port A2}.
39. Determines that the existing configuration BPDU is
superior to the calculated one and blocks Port C1 with
the configuration BPDU unchanged.
Port C1 does not forward data until a new event triggers a
spanning tree calculation process: for example, the link
between Device B and Device C is down.
Figure
Table 6, a spanning tree with Device A as the root
20.
64
Configuration BPDU
on ports after
comparison