Route poisoning immediately advertises a failed route with an infinite metric. Instead of waiting for the route to time out, you actively tell neighbors it's unreachable.
In RIP, the infinite metric is . When a link fails, the router sends an update:
Network 10.0.0.0/8, metric 16 (unreachable)
Neighbors receive this and immediately remove the route. This is faster than waiting for the regular update timer to expire.
Poison reverse complements route poisoning. When a router receives a poisoned route, it sends an acknowledgment back with the same infinite metric. This confirms that both routers agree the route is dead.