Split Horizon or Route poisoning

[Logic]

Which takes precedence? Split horizon states that routes will not be advertised back out the interface they came in on, however, route poisoning states that it will send that advertised route back out the same interface with a hop count of 16 (unreachable).

Just so I'm 100% clear on this, I take it route poisoning will take precedence only when a network becomes unreachable.

[tketchin]

Which takes precedence? Split horizon states that routes will not be advertised back out the interface they came in on, however, route poisoning states that it will send that advertised route back out the same interface with a hop count of 16 (unreachable).

Just so I'm 100% clear on this, I take it route poisoning will take precedence only when a network becomes unreachable.


This doesnt make sense to me either. What is the logic of sending a poison reverse back to the router that initiated the poisoning.
Furthermore, if the metric is used to choose the best route, then surely an unpoisoned incorrect route with a lower metric would always be chosen over a poisoned route?