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