Spanning Tree Protocol (STP)

Once upon a time a company called Digital Equipment Corporation (DEC) was purchased and renamed Compaq. But 30 years before that happened, DEC created the original version of Spanning Tree Protocol, or STP. The IEEE later created its own version of STP called 802.1D. Cisco has moved toward another industry standard in its newer switches called 802.1w. I’ll cover that STP version in this section as well, but first, let’s define some important STP basics.

STP’s main task is to stop network loops from occurring on your layer 2 network (bridges or switches). It vigilantly monitors the network to find all links, making sure that no loops occur by shutting down any redundant links. STP uses the spanning-tree algorithm (STA) to first create a topology database and then search out and disable redundant links. With STP running, frames will be forwarded only on the premium, STP-picked links.