I have been reading various Cisco docs about STP. The only thing I can't understand so far is how BPDU's are sent to other switches on active interfaces after initialisation when everything I've read so far says that interfaces in the Blocking state (after initialisation) can only receive BPDU's. Is their some weird and intersting interface state between initialisation and blocking?
When the switches initialize the port and recognize the connections, they
will put the port in listening state. It is this phase where you will
actually hear and send BPDUs.
Hope this helps.