As the title of the task imply and because the few words of the ticket didnt specified it (even undirectly) i didnt considered at all the possibility to set the filter on the interface because for what i've studied from Cisco, the control plane protection means something very specific. So i applied the filter to the control-plane of the router in the outbound direction.
Now if a question like this appear in the lab i havent any doubt i will answer wrong. I honestly hope not because it would make it impossible to pass.