Spanning Tree Protocol
A protocol that prevents switching loops by blocking redundant paths while keeping a backup ready.
Spanning Tree Protocol (STP), defined in IEEE 802.1D, prevents Layer 2 switching loops by electing a single root bridge and placing redundant switch ports into a blocking state. Every non-root switch picks a root port (lowest-cost path to the root), each segment elects a designated port, and all other ports block. Classic STP converges in roughly 30 to 50 seconds, moving through Listening and Learning states before Forwarding. Rapid STP (RSTP, 802.1w) adds Alternate and Backup port roles and converges in seconds by negotiating transitions. Network+ expects you to know both versions plus their port states and roles.
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