Spanning Tree States

Blocking

• port is in non-designate role
• does not forward or send traffic
• can receive BPDU's to determine what roles its ports need to be and also to where the root bridge is located.
• 20 sec in this stage by default.

Listening 

• stp determines that the port can forward traffic according to the BPDU's that have been recieved.
• switchport is receiving BPDU's and also sending its own BPDU's
• 15 sec in this state

Learning

•   switchport prepares to forward traffic by populating the CAM table (MAC) from source MAC's that it learns from traffic received. 
• 15 sec in this state 

Forwarding

• Layer 2 port is considered part of the active topology and forwards frames.
• sends and receives BPDU's

  Disabled

• Switchport does not participate in spanning tree
• does not forward frames.