When configuring a network, what is the purpose of a subnet mask?

The purpose of a subnet mask is to differentiate the network portion from the host portion of an IP address. This allows devices to determine which part of the address refers to the network they belong to and which part refers to the specific device, or host, within that network.

When a device sends data across a network, it uses this information to route the data correctly. The subnet mask consists of a series of bits that indicate how many bits in the IP address represent the network and how many represent the host. For instance, in a common subnet mask of 255.255.255.0, the first three octets indicate the network, while the last octet identifies individual hosts.

Understanding the subnet mask's role is crucial for efficient network design and management, as it aids in creating subnets and managing IP addresses within a given network, enhancing routing and improving security and performance.