Which protocol or feature detects and eliminates Layer 2 loops in a network?

The correct answer is based on the function of the Spanning Tree Protocol (STP), which is specifically designed to detect and eliminate Layer 2 loops within a network. Layer 2 loops can occur in networks where there are redundant paths for Ethernet frames, potentially leading to broadcast storms or multiple frame copies being sent to the same destination. STP actively manages these scenarios by logically blocking certain paths while allowing others, using an election process to determine which switch becomes the root bridge. This way, it ensures that there is a single active path between any two devices in the network, effectively preventing loops from forming.

Other options mentioned do not perform the same function as STP. RTG generally refers to routing protocols but does not address Layer 2 loop prevention. LACP (Link Aggregation Control Protocol) is used for combining multiple Ethernet links to form a single logical link, enhancing bandwidth, but it does not manage loop detection. GVRP (GARP VLAN Registration Protocol) is focused on managing VLAN memberships dynamically but does not address loop prevention at Layer 2. Hence, STP is essential for maintaining a loop-free network topology at the data link layer.