Good question, rfcat_vk. The original post is asking for details on a particular solution for a problem that's not spelled out. The best solution for the actual problem could range from hotspot/sign-in requirements to assigning the target client a static IP address that can be handled separately, or as you answer closing the network to clients not on a pre-specified list. (And of course there are multiple levels of keeping someone off of the network -- depending on what kind of access they actually have.)
So I'd give you an answer credit if I could, since you got to the root of the problem.
