What does a /24 CIDR subnet mask signify in terms of host addresses?

A /24 CIDR (Classless Inter-Domain Routing) subnet mask signifies that the first 24 bits of the IP address are used for the network portion, while the remaining 8 bits are available for host addresses. This allows for a total of 2^8, or 256 possible IP addresses within that subnet.

However, two of these addresses cannot be used for hosts: the network address, which identifies the subnet itself, and the broadcast address, which is used to send data to all devices on that subnet. Therefore, the number of usable IP addresses for hosts is 256 - 2, resulting in 254 usable addresses. This makes option D the correct choice.

Understanding CIDR notation and subnetting is crucial for network design and management, as it directly impacts how many devices can be connected within a single network segment.