86
Figure 25 The STP algorithm
As shown in Figure 25, the priority values of Device A, Device B, and Device C are 0, 1, and 2,
respectively. The path costs of links among the three devices are 5, 10, and 4.
1. Device state initialization.
In Table 8, ea
ch configuration BPDU contains the following fields: root bridge ID, root path cost,
designated bridge ID, and designated port ID.
Table 8 Initial state of each device
Device Port name
Configuration BPDU on
the port
Device A
Port A1 {0, 0, 0, Port A1}
Port A2 {0, 0, 0, Port A2}
Device B
Port B1 {1, 0, 1, Port B1}
Port B2 {1, 0, 1, Port B2}
Device C
Port C1 {2, 0, 2, Port C1}
Port C2 {2, 0, 2, Port C2}
2. Configuration BPDUs comparison on each device.
In Table 9, ea
ch configuration BPDU contains the following fields: root bridge ID, root path cost,
designated bridge ID, and designated port ID.
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