Introduction to Subnet Masks

This tutorial is an introduction to subnet masks. It helps to understand the need of subnet masks and why it is used. The answers to the Quiz are provided at the End.

Do I know this Quiz

1. What is derived when the IP address and Subnet mask of a device is ‘AND’ ed.
2. Where is the subnet mask configured on a system.
3. What is the value of subnet mask of Class B networks.
4. What is the value of subnet mask of device which is configured with IP address when classless addressing is used.

What is a subnet mask

A subnet mask is a unique number which is assigned along with the IP address of a system. In TCP/IP v4, it is a 32 bit number and is configured on the TCP/IP adapter of the respective system.

Why is a subnet mask used.

A subnet mask is used along with the IP address to derive it’s network address. Every device on a network is associated with a network address. The IP address along with the subnet mask yields the network address of the device.

How is a network address derived

The network address is derived by performing ‘AND’ operation with the IP address and subnet mask of the device. This operation is performed by the operating system of the device on which TCP/IP is installed. For ex, when the IP address is ‘AND’ ed with the subnet mask, the resulting value would be, which is the network address.

What happens after the network address is derived

After the network address is derived, the routing table of the device is populated with the network address. The device in this case can be a router , PC etc.

Is the subnet mask value constant

The value of subnet masks are unique based on the type of addressing used. There are 3 classes which are commonly used in classfull addressing, which are class a, b,c. The value of subnet masks for each of the classes would be,, In classless addressing, the value changes based on the number of bits which are used for subnetting.

Answers to the Quiz

1. The network address is derived.
2. The subnet mask is configured on the TCP/IP adapter of the system
4. For classless addressing, the number of bits used in subnetting would decide the value of subnet masks.

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