HP FlexNetwork NJ5000 User Manual page 163

Table 61 Initial state of each device
Device
Device A
Device B
Device C
Configuration BPDUs comparison on each device.
2.
In Table 62, each configuration BPDU contains the following fields: root bridge ID, root path
cost, designated bridge ID, and designated port ID.
Table 62 Comparison process and result on each device
Device Comparison process
•
•
Device A
•
•
•
•
Device B
•
•
Port name
AP1
AP2
BP1
BP2
CP1
CP2
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 it 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 it 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. It does not
make any change to the configuration BPDU of each
port, and it starts sending out configuration BPDUs
periodically.
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 it 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 it discards the
received configuration BPDU.
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. If the
calculated BPDU is superior, BP2 will act as the
designated port, and the configuration BPDU on this port
151
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}
•
BP1: {0, 0, 0, AP1}
•
BP2: {1, 0, 1, BP2}
•
Root port BP1: {0,
0, 0, AP1}
•
Designated port
BP2: {0, 5, 1, BP2}