Operation Manual – MSTP
H3C S3610&S5510 Series Ethernet Switches
Chapter 1 MSTP Configuration
1-3
LAN
Device A
Device B
Device C
AP 2
BP 1
BP 2
CP 1
CP 2
AP 1
Figure 1-1
A schematic diagram of designated bridges and designated ports
IV. Path cost
Path cost is a reference value used for link selection in STP. By calculating the path
cost, STP selects relatively “robust” links and blocks redundant links, and finally prunes
the network into loop-free tree structure.
Note:
All the ports on the root bridge are designated ports.
V. 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.
z
Root path cost: the cost of the shortest path to the root bridge.
z
Designated bridge ID: designated bridge priority plus MAC address.
z
Designated port ID, designated port priority plus port name.
z
Message age: age of the configuration BPDU while it propagates in the network.
z
Max age: maximum age of the configuration BPDU maintained in the device.
z
Hello time: configuration BPDU interval.
