a.Network diagram for the STP algorithm
As shown in a, the priority values of Device A, Device B, and Device C are 0, 1, and 2, and the path costs of links among the three devices are 5, 10 and 4 respectively.
∙Initial state of each device
3.Initial state of each device
Device | Port name | BPDU of port | |
Device A | AP1 | {0, 0, 0, AP1} | |
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AP2 | {0, 0, 0, AP2} | ||
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Device B | BP1 | {1, 0, 1, BP1} | |
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BP2 | {1, 0, 1, BP2} | ||
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Device C | CP1 | {2, 0, 2, CP1} | |
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CP2 | {2, 0, 2, CP2} | ||
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∙Comparison process and result on each device
4.Comparison process and result on each device
Device | Comparison process | Configuration BPDU on | |
ports after comparison | |||
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∙Port AP1 receives the configuration BPDU of Device B {1, 0, 1, BP1}. Device A finds that the configuration BPDU of the local port {0, 0, 0, AP1} is superior to the received configuration BPDU, and therefore discards the received configuration BPDU.
∙Port AP2 receives the configuration BPDU of Device C {2, 0, 2,
CP1}. Device A finds that the BPDU of the local port {0, 0, 0,
Device A AP2} is superior to the received configuration BPDU, and therefore discards the received configuration BPDU.
∙Device A finds that both the root bridge and designated bridge in the configuration BPDUs of all its ports are itself, so it assumes itself to be the root bridge. In this case, it does not make any change to the configuration BPDU of each port, and starts sending out configuration BPDUs periodically.
AP1: {0, 0, 0, AP1}
AP2: {0, 0, 0, AP2}
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