What is the purpose of a subnet mask in IP addressing?

A subnet mask plays a crucial role in IP addressing by defining the network and host portions of an IP address. It serves as a guide that tells the networking devices how to interpret the bits of an IP address, specifically which part of the address belongs to the network and which part is designated for individual hosts within that network.

In a typical IP address, the subnet mask is applied by performing a bitwise AND operation with the IP address. This enables devices to understand whether an IP address belongs to the same local network or requires routing to reach a different network. For example, if you have an IP address like 192.168.1.10 with a subnet mask of 255.255.255.0, the first three octets (192.168.1) indicate the network portion, while the last octet (.10) indicates the specific host on that network.

This identification of the network and host portions is essential for various networking functions, including routing decisions, efficient address allocation, and network segmentation, allowing for improved organization and management of IP addresses within a network.