STP topology of a Switched Network

Active STP topology of a switched network is determined by these elements:

1. The unique bridge ID (switch priority and MAC address) associated with each  VLAN on each switch
   
2. The STP path cost to the root switch
   
3. The port identifier (port priority and MAC address) associated with each interface
   
4. The BPDUs are transmitted in one direction from the root switch,
   
5. and each switch sends configuration BPDUs to communicate and to compute the STP topology.
   

Each configuration BPDU contains this information:

1. The unique bridge ID of the switch that the transmitting switch identifies as theroot switch
   
2. The STP path cost to the root
   
3. The bridge ID of the transmitting switch
   
4. Message age
   
5. The identifier of the transmitting interface
   
6. Values for the hello, forward delay, and max-age protocol timers