3Com S7906E Configuration Manual page 93

Figure 1-2 Network diagram for the STP algorithm
Device A
With priority 0
AP1 AP2
5
10
BP1
BP2
4
Device B
With priority 1
Initial state of each device
Table 1-4 shows the initial state of each device.
Table 1-4 Initial state of each device
Device
Device A
Device B
Device C
Comparison process and result on each device
Table 1-5 shows the comparison process and result on each device.
Table 1-5 Comparison process and result on each device
Device
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.
CP1
CP2
Device C
With priority 2
Port name
AP1
AP2
BP1
BP2
CP1
CP2
Comparison process
1-6
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}
BPDU of port
after comparison
AP1: {0, 0, 0, AP1}
AP2: {0, 0, 0, AP2}