|  | 9.9 | Spanning Tree Protocol
| 9.9.1 | STP function
The main function of the Spanning Tree Protocol (STP) is to allow redundant switched/bridged paths without suffering the effects of loops in the network. Spanning Tree allows for multiple links between switches, but only one link is active (Forwarding mode), while all other redundant links are in standby (Blocking mode) in case the primary link fails. Question: What would happen without Spanning Tree, and if there were multiple links between two switches? Answer: This could cause frames to be forwarded out the wrong switch ports, or even worse, cause layer 2 broadcast storms. Remember that a broadcast storm is when frames keep getting duplicated on a switched network, until it finally overwhelms the network, and bringing the network down. Spanning Tree is important even in networks where there are no redundant links between switches. It is not uncommon for someone to accidentally connect a link between two switches when a connection already exists. Spanning Tree is an excellent safeguard from keeping a mistake like this from bringing down a network. For more information on Spanning Tree Protocol and how it works, review the Power Point presentation on Spanning Tree in Semester 3.