Which state in STP allows a switch to send and receive BPDUs but not forward network traffic?

In Spanning Tree Protocol (STP), the listening state is crucial for maintaining the topology of the network while ensuring that loops do not occur. During the listening state, a switch is actively participating in the STP process by sending and receiving Bridge Protocol Data Units (BPDUs), which are used for electing the root bridge and determining the best path to it.

While a switch is in the listening state, it does not forward user data frames. Instead, it focuses on gathering information about the network topology. This behavior is vital for determining which ports should be transitioned into states that may forward traffic later on. By not forwarding traffic yet still being involved in the STP process, the switch helps preserve the integrity of the data flow and maintain a loop-free environment.

The other choices are distinct SPAN states with different roles in traffic handling. In contrast to the listening state, the blocking state prevents any forwarding of traffic entirely, and the learning state allows the switch to begin recording the MAC addresses of devices it hears but still does not forward traffic. The forwarding state, as the name suggests, is where the switch actively sends and receives both BPDUs and user data frames, making it fundamentally different from the listening state.