How it works:

1. Each switch generates an ID for itself (PBDU ID)
   1. BPDU ID has two parts - priority:System-Mac
2. Each switch sends BPDUs out of all its ports (as multicast)
3. After BPDUs are exchanged, Root switch is elected
   1. Root is having the smallest priority, and if equal - smallest System-Mac
   2. Only Root switch keeps sending BPDUs
   3. On the Root switch all ports are Designated
4. All non-Root switches will elect a Root port - port closest to the Root switch
   1. Root port is having the smallest Cost to the Root switch