3Com 2928 User Guide - Page 213
Port AP2 receives the configuration BPDU of Device C
UPC - 662705557113
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Device Device C Port name CP1 CP2 BPDU of port {2, 0, 2, CP1} {2, 0, 2, CP2} z Comparison process and result on each device The following table shows the comparison process and result on each device. Table 1-5 Comparison process and result on each device Device Device A Device B Comparison process BPDU of port after comparison z 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. z 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, AP2} is superior to the received AP1: {0, 0, 0, AP1} configuration BPDU, and therefore discards the received AP2: {0, 0, 0, AP2} configuration BPDU. z 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. z Port BP1 receives the configuration BPDU of Device A {0, 0, 0, AP1}. Device B finds that the received configuration BPDU is superior to the configuration BPDU of the local port {1, 0, 1, BP1}, and updates the configuration BPDU of BP1. BP1: {0, 0, 0, AP1} z Port BP2 receives the configuration BPDU of Device C BP2: {1, 0, 1, BP2} {2, 0, 2, CP2}. Device B finds that the configuration BPDU of the local port {1, 0, 1, BP2} is superior to the received configuration BPDU, and therefore discards the received configuration BPDU. z Device B compares the configuration BPDUs of all its ports, and determines that the configuration BPDU of BP1 is the optimum configuration BPDU. Then, it uses BP1 as the root port, the configuration BPDUs of which will not be changed. z Based on the configuration BPDU of BP1 and the path Root port BP1: cost of the root port (5), Device B calculates a designated {0, 0, 0, AP1} port configuration BPDU for BP2 {0, 5, 1, BP2}. Designated port BP2: z Device B compares the calculated configuration BPDU {0, 5, 1, BP2} {0, 5, 1, BP2} with the configuration BPDU of BP2. If the calculated BPDU is superior, BP2 will act as the designated port, and the configuration BPDU on this port will be replaced with the calculated configuration BPDU, which will be sent out periodically. 1-6