What protocol is related to NAC?

802.1Q is the IEEE standard for VLAN tagging on trunk links, not for network access control or authentication.

802.1X is the IEEE standard specifically designed for port-based Network Access Control, requiring devices to authenticate via an authenticator (such as a switch or wireless AP) to a backend RADIUS server before being granted network access. It is the foundational protocol underlying NAC solutions from vendors like Cisco and Microsoft, making it directly and exclusively associated with NAC.

802.1E is not a widely recognized or relevant IEEE standard associated with NAC or port-based authentication.

802.1F is not a recognized IEEE standard associated with NAC, authentication, or access control protocols.