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

The purpose of a subnet mask in IP addressing is to define network boundaries. A subnet mask is used in conjunction with an IP address to determine which portion of the address represents the network and which part represents the host. This separation allows devices on the same network (identified by the network portion) to communicate directly with each other while also enabling routing of traffic between different networks.

When a device sends data, the subnet mask helps it identify the destination's network, allowing it to send the data directly to devices within the same subnet without needing to route it through an external router. This is crucial for efficient network management and helps organize IP addresses into manageable segments, making it easier to implement IP address schemes and enhance network security and performance.