Network Access Control (NAC) is a computer networking solution that uses a set of
protocols to define and implement a policy that describes how to secure access to
network nodes by devices when they initially attempt to access the network.
NAC might integrate the automatic remediation process (fixing non-compliant nodes before allowing access) into the network systems, allowing the network infrastructure such as routers, switches and firewalls to work together with back office servers and end user computing equipment to ensure the information system is operating securely before interoperability is allowed.
A basic form of NAC is the 802.1X standard.
NAC aims to do exactly what the name implies—control access to a network with policies, including pre-admission endpoint security policy checks and post-admission controls over where users and devices can go on a network and what they can do.