802.1X provides an authentication framework that allows network devices, such as switches and wireless access points, to become part of an authentication process before allowing further access to the network. This protocol works by encapsulating and transporting the authentication data between the client and the authentication server, typically using the Extensible Authentication Protocol (EAP). Port-based Network Access Control is a feature of 802.1X that denies all access to the network via the port to which the client is connected until the client's identity is verified and authorized. This involves blocking all traffic, except authentication messages, until the client is authenticated, serving to prevent unauthorized access. The other options, while related to network security, do not directly describe the function of 802.1X as thoroughly or accurately.