In RSTP, which state combines elements of disabled, blocking, and listening states?

In Rapid Spanning Tree Protocol (RSTP), the state that combines elements of disabled, blocking, and listening states is known as the discarding state. In this state, the port does not forward frames and ignores received bridge protocol data units (BPDUs), effectively ensuring that there are no loops while still maintaining the necessary information about the topology.

The discarding state serves as an optimization by allowing the port to avoid unnecessary processing while it is not actively participating in frame-forwarding. This ensures efficient loop prevention while also being able to transition rapidly to other states as the topology changes.

Learning and forwarding states are involved in processing and forwarding frames, with learning allowing the switch to discover MAC addresses, while forwarding actually transmits frames. The active state is not a recognized term in RSTP; the defined states are discarding, learning, and forwarding. Hence, discarding is the correct answer, as it encapsulates the functions of the previously mentioned disabled, blocking, and listening states within the RSTP framework.