Final answer:
Route Poisoning is a technique where a router advertises a failed route with an infinite metric to prevent routing loops by signaling other routers that the route is unavailable.
Step-by-step explanation:
When a router advertises a failed route as an infinite metric for routing loop prevention, this is known as Route Poisoning. Route poisoning is a technique used to prevent incorrect routing information from being propagated through a network. When a router discovers that a route is no longer reachable, it advertises that route with a metric considered to be infinite (often represented as the maximum value allowed by the routing protocol), effectively telling other routers that the route is unavailable. This helps prevent routing loops, where data could otherwise endlessly circulate between routers due to incorrect routing information.