Which of the following is the endpoint 802.1X-compliant software service that communicates with NAD authenticators to request network access?

The correct choice is the Supplicant, as it specifically refers to the endpoint device software that initiates the 802.1X authentication process to gain access to network services. A Supplicant acts as the client in this context, sending authentication information to the Network Access Device (NAD), which serves as the Authenticator.

When a device wants to connect to a network, it uses the Supplicant software to communicate with the NAD. This software is responsible for providing identification credentials, such as usernames and passwords or digital certificates, to validate the device's identity. Once the Supplicant sends this information, it waits for a response from the NAD regarding the authentication result.

Understanding the role of the Supplicant is crucial in the context of 802.1X as it is the first step in securing network access and ensuring that only authorized users and devices can connect to the network. This mechanism enhances network security by enabling dynamic port-based access control.