What is the primary purpose of Spanning Tree Protocol in switched networks?

• A. It elects a root bridge, computes shortest paths, and blocks redundant links to prevent loops.
• B. It dynamically assigns IP addresses to devices in a VLAN.
• C. It encrypts traffic between switches for security.
• D. It manages QoS priority for frames.

Answer: (B)

Spanning Tree Protocol's job is to prevent loops in switched Ethernet by building a single active path while preserving redundancy. Switches exchange BPDUs to elect a root bridge—the switch with the lowest bridge ID (priority plus MAC). From there every switch chooses the port with the best path toward the root; that port becomes the root port on that switch. For each network segment, one switch port is chosen as the designated port. All other ports that would create a loop are put into a blocking state so frames cannot circulate endlessly. If a link fails, STP can reconfigure and activate a previously blocked link to restore a path, maintaining connectivity. This is why STP is about preventing loops, not IP address assignment, encryption, or QoS.