What is the purpose of Spanning Tree Protocol (STP) in a switched network?

• A. A protocol that prevents Layer 2 loops by placing ports into blocking or forwarding states.
• B. A routing protocol that selects paths between subnets.
• C. A mechanism for resolving domain names to IP addresses.
• D. A method for tagging VLANs on trunk links.

Answer: (B)

STP creates a loop-free topology at Layer 2 by designating a root bridge and calculating the best paths to it. To prevent the possibility of switching loops in a network with redundant connections, it places some switch ports into blocking states while others remain in forwarding states. This ensures that only one active path exists between any two devices, which stops broadcast storms and frames from endlessly circulating. If the network topology changes, STP can reconcile by moving a previously blocked port into forwarding to maintain connectivity, while still preventing loops. This is distinct from routing protocols, which choose paths between subnets, DNS, which resolves names to IPs, or VLAN tagging on trunks, which handles how traffic for different VLANs is carried.