Subnet Mask – Definition & Detailed Explanation – Computer Networks Glossary Terms

I. What is a Subnet Mask?

A subnet mask is a 32-bit number that is used to divide an IP address into network and host portions. It is used in conjunction with an IP address to determine which part of the address is the network portion and which part is the host portion. The subnet mask is represented in decimal format, such as, or in binary format, such as 11111111.11111111.11111111.00000000.

II. How does a Subnet Mask work?

When a device on a network wants to communicate with another device, it uses the subnet mask to determine if the destination device is on the same network or a different network. The subnet mask is applied to the IP address of the destination device using a bitwise AND operation. If the result of the operation matches the network portion of the IP address, the devices are on the same network. If the result does not match, the devices are on different networks and communication will need to go through a router.

III. What is the purpose of a Subnet Mask?

The main purpose of a subnet mask is to help devices on a network determine which part of an IP address is the network portion and which part is the host portion. By dividing the IP address in this way, devices can efficiently route traffic to the correct destination without sending unnecessary data to devices on different networks.

IV. How is a Subnet Mask different from an IP address?

An IP address is a unique identifier assigned to each device on a network, while a subnet mask is used to determine the network portion of the IP address. The subnet mask is not assigned to individual devices but is used by devices to calculate whether another device is on the same network or a different network.

V. How to determine the Subnet Mask for a network?

To determine the subnet mask for a network, you first need to know the IP address range that will be used on the network. The subnet mask is typically chosen based on the number of devices that will be on the network and the desired network structure. Common subnet mask values include for a Class C network, for a Class B network, and for a Class A network.

VI. What are common Subnet Mask formats?

Common subnet mask formats include decimal notation, such as, and binary notation, such as 11111111.11111111.11111111.00000000. Subnet masks can also be represented in CIDR notation, which specifies the number of network bits in the mask, such as /24 for a subnet mask of Different subnet mask formats are used depending on the network configuration and requirements.