Reference:
In the Administering Windows Server Hybrid Core Infrastructure materials for DHCP, reservations are defined as mappings that "bind a specific hardware (MAC) address to a single, permanent IPv4 address from a scope." The guide emphasizes that DHCP reservations ensure devices-such as servers using DHCP rather than static addressing-"always receive the same address whenever they request a lease," and that the required inputs when creating a reservation are the IP address, MAC address (also called hardware address), and a descriptive name. The exam prep further notes that while DHCPv4 supports an optional "Client Identifier," Windows Server hosts typically use the MAC address by default unless explicitly configured otherwise. Because your 10 Windows Server machines currently use static IPs and you want DHCP to always assign them the same IP, the correct identifier for each reservation is the MAC address. FQDNs and NetBIOS names are not valid unique identifiers for DHCP reservations, and UUIDs are unrelated to DHCP addressing.
Therefore, selecting MAC address meets the reservation requirement and aligns with the documented DHCP best practices in the hybrid core infrastructure objectives.