A. If the designated port is connected with P2MP link, it can make a handshake with the connected bridge and enter the forwarding state immediately after it receives a response.

B. Once a port of the switch which is configured as edge port has been enabled, it will become designated port immediately and transit to forwarding state.

C. A new root port is elected on the non-root switch and the previous old root port is no longer in forwarding state. Moreover the designated port of the segment which connects with the new root port already starts to forward the data. In this case, the new root port can enter forwarding state immediately.

D. If the designated port is connected with P2P link, it can make a handshake with the connected bridge and enter the forwarding state immediately after it receives a response.