A subnet mask is a numerical value assigned to a computer network that helps identify which portion of an IP address corresponds to the network and which portion corresponds to the host.

In simpler terms, a subnet mask is used to divide an IP address into two parts: the network address and the host address. When a device on a network wants to communicate with another device, it uses the subnet mask to determine if the destination IP address is on the same network or a different network.

If the destination IP address is on the same network, the device can communicate directly with it.

If the destination IP address is on a different network, the device will send the data to a router, which will then forward it to the correct network. Subnet masks are typically expressed in dotted decimal notation, such as 255.255.255.0.

This notation represents a 32-bit binary number, where each "1" bit in the subnet mask corresponds to a network bit, and each "0" bit corresponds to a host bit. By using subnet masks, network administrators can create smaller, more manageable subnetworks within a larger network.

This allows for more efficient use of IP addresses and better control over network traffic.

Subnetting also helps improve network security by segmenting traffic and isolating potential security threats. In conclusion, a subnet mask is a crucial component of network communication that helps devices identify and communicate with each other on a network.

It plays a vital role in IP addressing and subnetting, making it an essential tool for network administrators and IT professionals.