Final answer:
The authenticator in 802.1x authentication uses RADIUS protocol to communicate with the authentication server. EAP and PEAP are authentication frameworks used within this process, but they are encapsulated within RADIUS for communication with the server.
Step-by-step explanation:
When performing 802.1x authentication, the protocol used by the authenticator to communicate with the authentication server is D. RADIUS (Remote Authentication Dial-In User Service). 802.1x is an IEEE Standard for port-based Network Access Control, providing an authentication mechanism to devices wishing to attach to a LAN or WLAN. RADIUS is a networking protocol that provides centralized Authentication, Authorization, and Accounting (AAA) management for users who connect and use a network service.
EAP (Extensible Authentication Protocol) is used within the 802.1x standard as an authentication framework, which provides some general functions and a method for authenticating users. PEAP (Protected Extensible Authentication Protocol) is a version of EAP, often used in wireless LANs, that provides more secure authentication.
However, EAP and PEAP are not the protocols that directly communicate with the authentication server; they are encapsulated within the RADIUS packets when an authenticator communicates with the authentication server.