arison
Device A
• 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 it 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, AP2} is superior to the received configuration BPDU, and
it 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. It does not make any
change to the configuration BPDU of each port, and it starts
sending out configuration BPDUs periodically.
• AP1: {0, 0, 0, AP1}
• AP2: {0, 0, 0, AP2}
Device B
• 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 it updates the configuration BPDU of BP1.
• Port BP2 receives the configuration BPDU of Device C {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 it discards the received
configuration BPDU.
• BP1: {0, 0, 0, AP1}
• BP2: {1, 0, 1, BP2}
• 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.
• Based on the configuration BPDU of BP1 and the path cost
of the root port (5), Device B calculates a designated port
configuration BPDU for BP2 {0, 5, 1, BP2}.
• Device B compares the calculated configuration BPDU {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.
• Root port BP1: {0, 0,
0, AP1}
• Designated port BP2:
{0, 5, 1, BP2}
Device C
• Port CP1 receives the configuration BPDU of Device A {0, 0,
0, AP2}. Device C finds that the received configuration
BPDU is superior to the configuration BPDU of the local port
{2, 0, 2, CP1}, and it updates the configuration BPDU of
CP1.
• Port CP2 receives the configuration BPDU of port BP2 of
Device B {1, 0, 1, BP2} before the configuration BPDU is
updated. Device C finds that the received configuration
BPDU is superior to the configuration BPDU of the local port
{2, 0, 2, CP2}, and it updates the configuration BPDU of
CP2.
• CP1: {0, 0, 0, AP2}
• CP2: {1, 0, 1, BP2}
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