Spanning Tree Protocol (STP)

Switches can be used to create redundant connections within a network. However, without proper controls, redundant links can result in switching loops. For example, consider three interconnected switches: Switch A, Switch B, and Switch C. If a PC sends an unknown unicast to Switch A, it forwards the frame to both Switch B and Switch C. If neither Switch B nor C recognizes the destination MAC address, they will send the frame back to Switch A, creating a continuous loop that can overwhelm the network.

The STP prevents such issues by identifying redundant paths and automatically disabling them, thereby eliminating potential switching loops. Switches that support STP typically have the protocol enabled by default. STP-enabled switches use Bridge Protocol Data Units (BPDUs) to communicate with other switches, track changes in the MAC address table, and maintain a loop-free network topology.