Spanning Tree Protocol (STP)

Spanning Tree Protocol, or STP, is a network protocol designed to prevent loops in redundant Ethernet networks. It operates at Layer 2 of the OSI model and is based on the IEEE 802.1D standard. STP first determines a Root Bridge and then calculates a loop-free logical tree topology. Switches exchange Bridge Protocol Data Units, or BPDUs, for this purpose. Redundant connections that could create a loop are prevented from forwarding regular frames. If an active network path fails, STP can recalculate the topology and make an alternative path available. This enables redundant switch connections without causing broadcast storms and other problems associated with Layer 2 loops. Enhanced versions include Rapid Spanning Tree Protocol and Multiple Spanning Tree Protocol.