H3C Technologies H3C S7500E Series Switches - Manual (Page 159)

13-7
Table 13-5 Comparison process and result on each device
Device Comparison process
BPDU of port after
comparison
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
therefore 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 therefore 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. In this case, it does not make any change to the
configuration BPDU of each port, and starts sending out
configuration BPDUs periodically.
AP1: {0, 0, 0, AP1}
AP2: {0, 0, 0, AP2}
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.
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
therefore discards the received configuration BPDU.
BP1: {0, 0, 0, AP1}
BP2: {1, 0, 1, BP2}
Device B
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. As 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}