Device
Comparison process
Configuration BPDU on
ports after comparison
•
Device B compares the configuration BPDUs of all its
ports, decides that the configuration BPDU of Port B1 is
the optimum, and selects Port B1 as the root port with the
configuration BPDU unchanged.
•
Based on the configuration BPDU and path cost of the
root port, Device B calculates a designated port
configuration BPDU for Port B2 {0, 5, 1, Port B2}, and
compares it with the existing configuration BPDU of Port
B2 {1, 0, 1, Port B2}. Device B finds that the calculated
one is superior, decides that Port B2 is the designated
port, replaces the configuration BPDU on Port B2 with the
calculated one, and periodically sends the calculated
configuration BPDU.
•
Root port (Port B1): {0,
0, 0, Port A1}
•
Designated port (Port
B2): {0, 5, 1, Port B2}
•
Port C1 receives the configuration BPDU of Port A2 {0, 0,
0, Port A2}, finds that the received configuration BPDU is
superior to its existing configuration BPDU {2, 0, 2, Port
C1}, and updates its configuration BPDU.
•
Port C2 receives the original configuration BPDU of Port
B2 {1, 0, 1, Port B2}, finds that the received configuration
BPDU is superior to the existing configuration BPDU {2,
0, 2, Port C2}, and updates its configuration BPDU.
•
Port C1: {0, 0, 0, Port
A2}
•
Port C2: {1, 0, 1, Port
B2}
•
Device C compares the configuration BPDUs of all its
ports, decides that the configuration BPDU of Port C1 is
the optimum, and selects Port C1 as the root port with the
configuration BPDU unchanged.
•
Based on the configuration BPDU and path cost of the
root port, Device C calculates the configuration BPDU of
Port C2 {0, 10, 2, Port C2}, and compares it with the
existing configuration BPDU of Port C2 {1, 0, 1, Port B2}.
Device C finds that the calculated configuration BPDU is
superior to the existing one, selects Port C2 as the
designated port, and replaces the configuration BPDU of
Port C2 with the calculated one.
•
Root port (Port C1): {0,
0, 0, Port A2}
•
Designated port (Port
C2): {0, 10, 2, Port
C2}
Device C
•
Port C2 receives the updated configuration BPDU of Port
B2 {0, 5, 1, Port B2}, finds that the received
configuration BPDU is superior to its existing
configuration BPDU {0, 10, 2, Port C2}, and updates its
configuration BPDU.
•
Port C1 receives a periodic configuration BPDU {0, 0, 0,
Port A2} from Port A2, finds that it is the same as the
existing configuration BPDU, and discards the received
one.
•
Port C1: {0, 0, 0, Port
A2}
•
Port C2: {0, 5, 1, Port
B2}
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