TL-SL3428_V3_User_Guide - TP-Link

• Port: Port 3 is the root port of switch B and port 5 is the root port of switch C; port 1 is thedesignated port of switch A and port 4 is the designated port of switch B; port 6 is the blockedport of switch C.‣ STP TimersHello Time:Figure 7-1 Basic STP diagramHello Time ranges from 1 to 10 seconds. It specifies the interval to send BPDU packets. It is usedto test the links.Max. Age:Max. Age ranges from 6 to 40 seconds. It specifies the maximum time the switch can wait withoutreceiving a BPDU before attempting to reconfigure.Forward Delay:Forward Delay ranges from 4 to 30 seconds. It specifies the time for the port to transit its stateafter the network topology is changed.When the STP regeneration caused by network malfunction occurs, the STP structure will getsome corresponding change. However, as the new configuration BPDUs cannot be spread in thewhole network at once, the temporal loop will occur if the port transits its state immediately.Therefore, STP adopts a state transit mechanism, that is, the new root port and the designatedport begins to forward data after twice forward delay, which ensures the new configuration BPDUsare spread in the whole network.‣ BPDU Comparing Principle in STP modeAssuming two BPDUs: BPDU X and BPDU YIf the root bridge ID of X is smaller than that of Y, X is superior to Y.If the root bridge ID of X equals that of Y, but the root path cost of X is smaller than that of Y, X issuperior to Y.If the root bridge ID and the root path cost of X equal those of Y, but the bridge ID of X is smallerthan that of Y, X is superior to Y.If the root bridge ID, the root path cost and bridge ID of X equal those of Y, but the port ID of X issmaller than that of Y, X is superior to Y.70