In STP, which port state prevents network loops?

In Spanning Tree Protocol (STP), the blocking port state plays a crucial role in preventing network loops by stopping traffic on a port, effectively ensuring that no frames are sent or received through that port. When a port is in the blocking state, it does not participate in the frame forwarding process and does not learn MAC addresses. This means that the port will not pass any data frames or contribute to any potential loops in the network topology.

The blocking state is a fundamental aspect of the Spanning Tree Protocol's function to maintain a loop-free topology. By keeping certain ports in a blocking state, STP allows for alternate paths to be kept available but inactive, which can be activated if the active path fails. This dynamic adjustment is essential for resilience but also guarantees that only one active path will forward traffic at any given time.

Other port states, such as listening, learning, and forwarding, have specific roles that are part of the overall process of establishing a loop-free network. Listening and learning states allow for the collection of information and preparation for data forwarding, while the forwarding state is where data can flow. However, it is the blocking state that directly prevents the potential for loops by ensuring that unnecessary paths are shut down.