Which of the following describes a subnet mask?

A subnet mask is a crucial part of IP networking because it defines how an IP address is split into two main components: the network portion and the host portion. This differentiation is vital for routing data accurately within and between networks.

When a subnet mask is applied to an IP address, it allows devices on the same local area network (LAN) to communicate effectively without the need for a router, as they can recognize which part of the address identifies the network and which part identifies the specific device (host) within that network. The subnet mask uses a series of binary numbers to indicate which bits of the IP address are used for the network identifier and which are assigned to host devices.

For instance, a common subnet mask of 255.255.255.0 indicates that the first three octets of the IP address are designated for the network, while the last octet is reserved for host addresses. This structure enables efficient routing and helps maintain organized network architecture by allowing proper IP address allocation and management.

The other choices describe elements of networking but do not accurately describe what a subnet mask does. An address identifying a device refers to the IP address itself rather than the subnet mask. A protocol used for routing data is distinct from a subnet mask, which merely assists