Spanning tree is a protocol that prevents network loops by dynamically disabling or enabling switch ports based on the network topology. Network loops can cause intermittent connectivity issues, such as broadcast storms, MAC address table instability, and multiple frame transmission. By enabling spanning tree, the network administrator can ensure that there is only one active path between any two network devices at any given time. Reference: CompTIA Network+ N10-008 Certification Exam Objectives, page 91 CompTIA Network+ Cert Guide: Switching and Virtual LANs, page 172