What does the subnet mask 255.255.255.0 specify for an IPv4 address?

The subnet mask 255.255.255.0, often referred to as a /24 subnet mask, indicates that the first three octets (the 255s) of the address are used for the network portion, while the last octet (the 0) is used for the host portion. This configuration allows for a total of 256 IP addresses within that subnet.

However, two addresses are reserved: one for the network identifier (usually the first address in the range) and one for the broadcast address (usually the last address in the range). As a result, while there are 256 possible addresses, only 254 addresses are available for assignment to hosts. Therefore, the correct interpretation of what the subnet mask 255.255.255.0 allows in terms of usable addresses is that it supports 254 hosts on the network.

This addresses the scenario accurately because it reflects the standard practice in subnetting where network and broadcast addresses are not assignable to hosts.