HP FlexFabric 12900 Series Configuration Manual page 78

Example of STP calculation
Figure 18 provides an example showing how the STP algorithm works.
Figure 18 The STP algorithm
Port B1
Port B2
Device B
Priority = 1
As shown in
respectively. The path costs of links among the three devices are 5, 10, and 4.
1. Device state initialization.
In Table
designated bridge ID, and designated port ID.
Table 6 Initial state of each device
Device
Device A
Device B
Device C
2. Configuration BPDUs comparison on each device.
In Table
designated bridge ID, and designated port ID.
Device A
Priority = 0
Port A1 Port A2
Port C2
Path cost = 4
Device C
Priority = 2
Figure 18, the priority values of Device A, Device B, and Device C are 0, 1, and 2,
6, each configuration BPDU contains the following fields: root bridge ID, root path cost,
Port name
Port A1
Port A2
Port B1
Port B2
Port C1
Port C2
7, each configuration BPDU contains the following fields: root bridge ID, root path cost,
Port C1
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Configuration BPDU on the
port
{0, 0, 0, Port A1}
{0, 0, 0, Port A2}
{1, 0, 1, Port B1}
{1, 0, 1, Port B2}
{2, 0, 2, Port C1}
{2, 0, 2, Port C2}