STP / Spanning Tree Basics

Spanning Tree Protocol draws a loop-free logical topology over a physically redundant switch fabric, by blocking backup ports until a link fails. Classic STP converges in 30 to 50 seconds, RSTP in 1 to 6. It takes only one accidental patch between two switch ports, with no STP, to close a loop that drowns the network in broadcast traffic until it saturates — sound, video and control cut off in one go.