Which mechanism helps ensure a loop-free topology by preventing forwarding loops in a LAN?

• A. Spanning Tree Protocol.
• B. Routing Information Protocol.
• C. Dynamic Host Configuration Protocol.
• D. Address Resolution Protocol.

Answer: (A)

Spanning Tree Protocol creates a loop-free LAN by preventing forwarding loops that can occur when switches are connected with multiple active paths. It does this by electing a root switch and then choosing for each switch the best path to that root (the root port) and, for each network segment, a designated port that will forward toward that segment. All other ports on that segment are put into a blocking state, so there’s only one active path between any two devices. Switches exchange topology information using BPDUs, and if the network changes, STP recalculates and may re-activate ports as needed to maintain a loop-free, yet resilient, topology.

RIP, DHCP, and ARP don’t provide this kind of loop-prevention mechanism: RIP is a Layer 3 routing protocol, DHCP handles IP address assignment, and ARP translates IP addresses to MAC addresses. They do not enforce a loop-free path in the LAN switch fabric.