When loop protection is enabled on an interface, what happens when the port stops receiving BPDUs?

When loop protection is enabled on an interface and the port stops receiving Bridge Protocol Data Units (BPDUs), the port is indeed placed in a loop-inconsistent role. This mechanism is vital in preventing loops in the network, which can lead to broadcast storms and numerous operational issues.

In a typical Ethernet network using Spanning Tree Protocol (STP), BPDUs are used to determine the network topology and ensure that there are no loops. If a switch port fails to receive BPDUs over a certain threshold or time period, the loop protection feature interprets this as a potential loop condition, usually because the path to the root bridge has become invalid or the switch may be disconnected from the network.

By placing the port into a loop-inconsistent role, the switch takes proactive measures to maintain network stability. This role limits the port's participation in the bridging decisions and prevents it from forwarding frames, thus minimizing the risk of introducing loops into the network.

The other options reflect different operational states that do not align with the intended function of loop protection. For instance, placing the port into listening mode would still allow certain processes to occur but does not specifically apply the logic of loop inconsistencies. Transitioning to a forwarding state contradicts the protective nature of loop