81
Device Comparison
process
Configuration BPDU
on ports after
comparison
Port C1}.
2.
Determines that its existing configuration BPDU {0, 0,
0, Port A2} is superior to the received configuration
BPDU.
3.
Discards the received one.
Device A determines that it is both the root bridge and
designated bridge in the configuration BPDUs of all its
ports. It considers itself as the root bridge. It does not
change the configuration BPDU of any port and starts to
periodically send configuration BPDUs.
Device B
Port B1 performs the following operations:
1.
Receives the configuration BPDU of Port A1 {0, 0, 0,
Port A1}.
2.
Determines that the received configuration BPDU is
superior to its existing configuration BPDU {1, 0, 1,
Port B1}.
3.
Updates its configuration BPDU.
Port B2 performs the following operations:
1.
Receives the configuration BPDU of Port C2 {2, 0, 2,
Port C2}.
2.
Determines that its existing configuration BPDU {1, 0,
1, Port B2} is superior to the received configuration
BPDU.
3.
Discards the received BPDU.
•
Port B1: {0, 0, 0, Port
A1}
•
Port B2: {1, 0, 1, Port
B2}
Device B performs the following operations:
1.
Compares the configuration BPDUs of all its ports.
2.
Decides that the configuration BPDU of Port B1 is the
optimum.
3.
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}. Device B compares it
with the existing configuration BPDU of Port B2 {1, 0, 1, Port
B2}. Device B determines that the calculated one is
superior, and determines that Port B2 is the designated
port. It 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}
Device C
Port C1 performs the following operations:
1.
Receives the configuration BPDU of Port A2 {0, 0, 0,
Port A2}.
2.
Determines that the received configuration BPDU is
superior to its existing configuration BPDU {2, 0, 2,
Port C1}.
3.
Updates its configuration BPDU.
Port C2 performs the following operations:
1.
Receives the original configuration BPDU of Port B2
{1, 0, 1, Port B2}.
2.
Determines that the received configuration BPDU is
superior to the existing configuration BPDU {2, 0, 2,
Port C2}.
3.
Updates its configuration BPDU.
•
Port C1: {0, 0, 0, Port
A2}
•
Port C2: {1, 0, 1, Port
B2}