Which protocol helps prevent switching loops in Ethernet networks?

• A. RARP
• B. STP
• C. BGP
• D. ARP

Answer: (B)

Switching loops in Ethernet networks happen when there are multiple active paths between switches, creating a cycle that can cause frames to circulate endlessly and flood the network. Spanning Tree Protocol prevents this by building a loop-free topology. It uses bridge protocol data to elect a root switch and determine the best path to that root for every switch. Then it designates certain ports to forward frames toward the root and blocks the other redundant ports on each network segment. By keeping one active path and blocking the rest, STP eliminates loops while preserving redundancy—so if a link fails, a blocked port can be brought into forwarding to maintain connectivity. The other options don’t address this Layer 2 loop problem: ARP resolves IP-to-MAC addresses, RARP is an older form of address resolution, and BGP is a Layer 3 routing protocol between autonomous systems.