How does STP prevent loops in a network?

Spanning Tree Protocol (STP) is crucial for preventing loops in Layer 2 networks, which can cause significant disruptions and broadcast storms that degrade network performance. The correct approach STP uses is to selectively block some ports while keeping others active, thereby creating a loop-free topology.

STP operates by first identifying all the switches in the network and determining the best paths between them. It designates one switch as the root bridge and then calculates the cost of paths to this bridge. In this process, STP places certain ports in a blocking state. These blocked ports act as a safeguard against potential loops; if the active topology fails or changes, STP can quickly enable one of the previously blocked ports to maintain connectivity. This mechanism allows the network to adapt dynamically without the risk of looping traffic, which would otherwise overwhelm the switches.

Blocking ports is a fundamental aspect of how STP effectively ensures a loop-free environment, allowing for redundancy in the network without the detrimental effects of loops.