some distance-vector routing protocols, such as rip, use a maximum hop count to determine how many routers the traffic must go through to reach the destination. each route has a hop count number assigned to it which is incremented as the routing information is passed from router to router. a route is considered unreachable if the hop count exceeds the maximum allowed. route poisoning is a method of quickly forgetting outdated routing information from other router's routing tables by changing its hop count to be unreachable (higher than the maximum number of hops allowed) and sending a routing update. in the case of rip, the maximum hop count is 15, so to perform route poisoning on a route its hop count is changed to 16, deeming it unreachable, and a routing update is sent.