H3C Technologies H3C S12500-X Series Switches User Manual
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Device
Port name
Configuration BPDU on the
port
Port B2
{1, 0, 1, Port B2}
Device C
Port C1
{2, 0, 2, Port C1}
Port C2
{2, 0, 2, Port C2}
2.
Configuration BPDUs comparison on each device.
In
, each configuration BPDU contains the following fields: root bridge ID, root path cost,
designated bridge ID, and designated port ID.
Table 7 Comparison process and result on each device
Device
Comparison process
Configuration BPDU on
ports after comparison
Device A
•
Port A1 receives the configuration BPDU of Port B1 {1, 0,
1, Port B1}, finds that its existing configuration BPDU {0, 0,
0, Port A1} is superior to the received configuration BPDU,
and discards the received one.
•
Port A2 receives the configuration BPDU of Port C1 {2, 0,
2, Port C1}, finds that its existing configuration BPDU {0,
0, 0, Port A2} is superior to the received configuration
BPDU, and discards the received one.
•
Device A finds that it is both the root bridge and
designated bridge in the configuration BPDUs of all its
ports, and considers itself as the root bridge. It does not
change the configuration BPDU of any port and starts to
periodically send configuration BPDUs.
•
Port A1: {0, 0, 0, Port
A1}
•
Port A2: {0, 0, 0, Port
A2}
Device B
•
Port B1 receives the configuration BPDU of Port A1 {0, 0,
0, Port A1}, finds that the received configuration BPDU is
superior to its existing configuration BPDU {1, 0, 1, Port
B1}, and updates its configuration BPDU.
•
Port B2 receives the configuration BPDU of Port C2 {2, 0,
2, Port C2}, finds that its existing configuration BPDU {1,
0, 1, Port B2} is superior to the received configuration
BPDU, and discards the received one.
•
Port B1: {0, 0, 0, Port
A1}
•
Port B2: {1, 0, 1, Port
B2}
•
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}