Mobile Device Management (MDM) solutions are used to manage and secure Apple devices remotely. To link a device to an MDM solution, an enrollment profile is required. This profile is a configuration file that, once installed on the device, establishes a connection between the device and the MDM server, allowing the server to send commands and policies to the device. The enrollment profile contains information such as the MDM server's URL and authentication details, enabling secure communication via Apple Push Notification service (APNs). While APNs (option A) facilitates communication between the MDM server and the device after enrollment, it is not the mechanism that links the device to the MDM solution. A firewall (option B) is a network security tool and unrelated to linking a device to MDM, and a restriction (option C) is a policy applied via MDM, not the linking mechanism itself. According to Apple's official documentation, such as the Apple Platform Deployment Guide, the enrollment profile is the foundational step for MDM enrollment.