Assigning Port States

All ports are blocking when the operational status switches from disabled to enabled. By default, automatic edge detection is enabled and ports are configured as non-edge ports. In this scenario a user port will become forwarding in several seconds. A port configured as an edge port will forward immediately.

Ports which are selected as alternate or backup ports are immediately put into the discarding state and remain discarding until a new port role is selected. The root port may go to the forwarding state as long as any recent former root ports are synchronized with the new root information. Designated ports may forward as soon as the attached port signals agreement as specified by RSTP. In the absence of the above conditions, root and designated ports get to the forwarding state through the use of timers. The value of the timers is dependent on the value of ForceVersion. The default value is MSTP. If the value is StpCompatible, the timer values are derived from forward delay. Otherwise the values are derived from hello time.

Spanning Tree Port States provides a summary of STP port states.

Spanning Tree Port States

Port State	Behavior
Blocking	Actively preventing traffic from using this path. Still receiving BPDUs, so continuing to monitor for management and STA information.
Listening	Continuing to block traffic while waiting for protocol information to determine whether to go back to the blocking state or continue to the learning state. Listens to BPDUs to ensure no loops occur on the network.
Learning	Learning station location information but continuing to block traffic.
Forwarding	Forwarding traffic and continuing to learn station location information.
Disabled	Disabled administratively or by failure.
Discarding	Used as shorthand for blocking, listening, or learning state.