What does a Subnet Mask (e.g., 255.255.255.0) tell a computer?

1. A It serves as the pre-shared cryptographic key (password) required for a physical device to authenticate and join a protected enterprise-level network.
2. B It identifies which portion of an IP address represents the shared 'Network ID' and which portion represents the 'Host ID' that is unique to a specific device.
3. C It provides a real-time measurement of the current network utilization and speed, allowing the machine to throttle large downloads during periods of high congestion.
4. D It specifies the machine-readable address of the recursive DNS server that the computer should use to resolve domain names of various public web services.