。Listening – the port is waiting to receive BPDU packets that may tell the port to go back to the blocking state
。Learning – the port is adding addresses to its forwarding database, but not yet forwarding packets
。Forwarding – the port is forwarding packets
。Disabled – the port only responds to network management messages and must return to the blocking state first
A port transitions from one state to another as follows:
。From initialization (switch boot) to blocking
。From blocking to listening or to disabled
。From listening to learning or to disabled
。From learning to forwarding or to disabled
。From forwarding to disabled
。From disabled to blocking
Switch
Blocking
Listening 
Disable
Learning
Forwarding
STP Port State Transitions
You can modify each port state by using management software. When you enable STP, every port on every switch in the network goes through the blocking state and then transitions through the states of listening and learning at power up. If properly configured, each port stabilizes to the forwarding or blocking state. No packets (except BPDUs) are forwarded from, or received by, STP enabled ports until the forwarding state is enabled for that port.
2.STP Parameters STP Operation Levels
The Switch allows for two levels of operation: the switch level and the port level. The switch level forms a spanning tree consisting of links between one or more switches. The port level constructs a spanning tree consisting of groups of one or more ports. The STP operates in much the same way for both levels.
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