Network access control (NAC), also called network admission control, is a method of bolstering the security of a proprietary network by restricting the availability of network resources to endpoint devices that comply with a defined security policy.
A traditional network access server (NAS) is a server that performs authentication and authorisation functions for potential users by verifying logon information. In addition to these functions, NAC restricts the data that each particular user can access, as well as implementing anti-threat applications such as firewalls, antivirus software and spyware-detection programs. NAC also regulates and restricts the things individual subscribers can do once they are connected. NAC is ideal for organisations and agencies where the user environment can be rigidly controlled.