Final answer:
The number of usable IPv4 addresses in a subnet is calculated by subtracting network and subnet bits from the total bits available in IPv4 and then subtracting 2 for the network and broadcast addresses. A /24 subnet mask provides 254 usable addresses.
Step-by-step explanation:
The size of a subnet, or the number of usable IPv4 addresses, can be determined by the subnet mask associated with it. To calculate the number of usable addresses, you subtract the number of bits used for the network and subnet portion from the total number of bits available in an IPv4 address, which is 32 bits. The subnet mask is expressed in slash notation as /x, where x represents the number of bits used for the network and subnet portion.
For example, if you have a subnet mask of /24, this means that 24 bits are used for the network and subnet, leaving 8 bits for the host portion. The formula to calculate the number of usable addresses is 2^(32-x) - 2, where 'x' is the number of bits used for network and subnet. Subtracting 2 accounts for the network address and the broadcast address, which cannot be assigned to hosts. Therefore, a /24 subnet mask allows for 2^(32-24) - 2 = 254 usable IP addresses.