What is a common mechanism for preventing routing loops?

Split-Horizon is a technique used in routing protocols to prevent routing loops. It works by prohibiting a router from sending routing information about a particular route back out the same interface from which it was received. This prevents the router from mistakenly believing there is a valid route to a destination if it already learned about that route from a neighboring router through the same link. By enforcing this rule, split-horizon effectively reduces the risk of routing loops that can occur in distance-vector routing protocols, where routers share information about the routes they know.

The other options, while important in networking, do not directly address the issue of routing loops. Full-duplex refers to the ability of a communication channel to send and receive data simultaneously, which does not prevent routing loops. Route aggregation simplifies routing tables by combining multiple routes into a single route, but it does not inherently stop routing loops. VLAN tagging is used in Ethernet networks to segregate traffic into different VLANs, assisting in traffic management but not specifically in preventing routing loops.