STP enables efficient communication on a network that includes multiple bridges.
Devices on these networks can learn multiple (that is, redundant) paths to the
same endpoint. While path redundancy is desirable for maintaining traffic flow
when particular links are down, it can lead to a traffic loops that affect network
performance and confuse forwarding algorithms.

Each STP-enabled bridge exchanges Bridge Protocol Data Units (BPDUs) with
other bridges. BPDUs identify the bridge port MAC addresses and the priority and
cost associated with each port. STP uses this information to build a topology that
provides one active path between any two stations on the network. Duplicate
paths between those stations are placed in a stand-by state for use only when the
active path becomes unavailable.