Final answer:
The method used by routers to prevent routing loops by not advertising a route back to the router from which it was learned is called Split Horizon.
Step-by-step explanation:
The method by which routers prevent routing loops by never advertising a route back to the router from which it was learned is called Split Horizon. Split Horizon is a simple protocol mechanism that prohibits a router from advertising a route through an interface that the router itself uses to reach the destination. It effectively stops information about routes from being sent back in the direction from which they came. This prevents the formation of routing loops, as each router has a more accurate picture of the network topology.