HP V1910 User Manual page 193

Network diagram for the STP algorithm
a.
As shown in a, the priority values of Device A, Device B, and Device C are 0, 1, and 2, and the path costs
of links among the three devices are 5, 10 and 4 respectively.
Initial state of each device

Initial state of each device
3.
Device
Device A
Device B
Device C
Comparison process and result on each device

Comparison process and result on each device
4.
Device Comparison process

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,
Device A
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.
Port name
AP1
AP2
BP1
BP2
CP1
CP2
181
BPDU of port
{0, 0, 0, AP1}
{0, 0, 0, AP2}
{1, 0, 1, BP1}
{1, 0, 1, BP2}
{2, 0, 2, CP1}
{2, 0, 2, CP2}
Configuration BPDU on
ports after comparison
AP1: {0, 0, 0, AP1}
AP2: {0, 0, 0, AP2}