 A typical use case of pre-admission NAC would be to prevent clients with out-of-date antivirus signatures from talking to sensitive servers.Alternatively, post-admission NAC makes enforcement decisions based on user actions, after those users have been provided with access to the network

The fundamental idea behind NAC is to allow the network to make access control decisions based on intelligence about end-systems, so the manner in which the network is informed about end-systems is a key design decision.A key difference among NAC systems is whether they require agent software to report end-system characteristics, or whether they use scanning and network inventory techniques to discern those characteristics remotely.