What is the primary purpose of a subnet mask?

The primary purpose of a subnet mask is to identify the network of its connected host. A subnet mask is a 32-bit number that segments an IP address into the network and host portions. It does this by using a series of ones (1s) followed by zeros (0s). The ones indicate which part of the address is the network portion, and the zeros indicate which part is the host portion.

For example, in a typical Class C address like 192.168.1.1 with a subnet mask of 255.255.255.0, the subnet mask reveals that the first three octets (192.168.1) are used to identify the network, while the last octet is used for the host. This mechanism allows routers and other devices on the network to effectively route traffic to the appropriate destination, as they will use the network portion to determine if the destination is local or requires routing to another network.

This understanding of the network identified by the subnet mask is crucial in networking as it enables efficient data transmission and correct routing among multiple networks.