Operation Manual – MSTP
H3C S5600 Series Ethernet Switches
Chapter 1 MSTP Configuration
1-3
Figure 1-1
shows designated bridges and designated ports. In the figure, AP1 and AP2,
BP1 and BP2, and CP1 and CP2 are ports on Device A, Device B, and Device C
respectively.
z
If Device A forwards BPDUs to Device B through AP1, the designated bridge for
Device B is Device A, and the designated port is the port AP1 on Device A.
z
Two devices are connected to the LAN: Device B and Device C. If Device B
forwards BPDUs to the LAN, the designated bridge for the LAN is Device B, and
the designated port is the port BP2 on Device B.
Figure 1-1
A schematic diagram of designated bridges and designated ports
Note:
All the ports on the root bridge are designated ports.
4) Path
cost
Path cost is a value used for measuring link capacity. By comparing the path costs of
different links, STP selects the most robust links and blocks the other links to prune the
network into a tree.
IV. How STP works
STP identifies the network topology by transmitting configuration BPDUs between
network devices. Configuration BPDUs contain sufficient information for network
devices to complete the spanning tree calculation. Important fields in a configuration
BPDU include:
z
Root bridge ID, consisting of root bridge priority and MAC address.
