A. If a port does not receive configuration BPDUs from the upstream device within four Hello intervals, the switch considers that the negotiation with the neighbor fails.

B. The non-root switch running RSTP sends configuration BPDUs at the interval specified by the Hello timer, which is performed independently by each device.

C. RSTP reduces five port states to three port states based on user traffic forwarding and MAC address learning.

D. RSTP deletes three port states and adds two port roles.