3Com MSR 50 Series Configuration Manual page 449

Table 14 Comparison process and result on each device
Device Comparison process
Device B 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 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 computed configuration BPDU {0,
■
5, 1, BP2} with the configuration BPDU of BP2. If the
computed BPDU is superior, BP2 will act as the designated
port, and the configuration BPDU on this port will be
replaced with the computed configuration BPDU, which
will be sent out periodically.
MSTP Overview 449
BPDU of port
after
comparison
BP1: {0, 0, 0,
AP1}
BP2: {1, 0, 1,
BP2}
Root port BP1:
{0, 0, 0, AP1}
Designated port
BP2:
{0, 5, 1, BP2}