Spanning Tree Protocol (Spanning Tree Protocol, STP), a work in the OSI network model in the second layer (data link layer) communication protocols, is applied substantially prevent redundant links generating the switch loop. For ensure logical topology Ethernet loop-free thus avoiding broadcast storm, resource-intensive switch.
STP is relatively perfect, almost no configuration. When STP switch is first powered on, it checks whether the exchange network there is a loop. If it detects a potential loop switch will block certain ports, to keep some other ports to forward frames.
Reproduced in: https: //blog.51cto.com/14216988/2409710