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Your IP Address:

Subnet Mask Calculator

Enter TCP/IP Network Address: 
Force as Class: Default
Class A
Class B
Class C
Enter the required number of sub-networks:
Enter the required number of nodes/host per network:

Subnet Mask Generator Tutorial

Using this tool you can generate and calculate network class, subnet mask, and node per network easily. Just follow this easy steps:

1. Enter network address you want to generate. Example:
2. Choose in what class the network address will be. If you choose default, it will calculate default network class for that IP address.
3. Choose how many number of sub-networks required. Default value is 1 sub network.
4. Or you can choose how many nodes per network required. Leave blank if you want to generate nodes per network value automatically.

Step by Step Guide

To create the subnet mask, first remember that the purpose of the subnet mask is to separate the (32 bit) ip address into the network prefix and the host number. If a bit in the subnet mask is 1, the corresponding bit in the IP address is part of the network address; if the bit in the subnet mask is 0, the corresponding bit in the IP address is part of the host address.

First depict the ip address in binary. For example, we have IP Address: It can be converted to binary:
          ip address: 11000000.10101000.00000000.00000001

First we determine what class of address it is:
	If the first bit is 0 it is a Class A address
	If the first two bits are 10 it is a Class B address
	If the first three bits are 110 it is a Class C address
	If the first four bits are 1110 it is a Class D multicast address
	If the first four bits are 1111 it is a Class E experimental address
Since the first three bits are 110, is a Class C address.

The default subnet mask class are:
	subnet mask Class A: 11111111.00000000.00000000.00000000
	subnet mask Class B: 11111111.11111111.00000000.00000000
        subnet mask Class C: 11111111.11111111.11111111.00000000

The formula for figuring out the number of 'network' bits in a subnet mask is
         2^n=number of subnets          (2^n  means '2' to the power of 'n')
n is the number subnets you want to create. For this example we want to create 2 subnets.

Because we want 2 subnets, we need to add 1 - '1' bits to the default subnet mask since 2 = 2 ^ 1.

This will give us the following subnet mask:
         subnet mask: 11111111.11111111.11111111.10000000
Which is referred to as /25 or in dotted decimal notation as

PDF: IP Address Subnetting Tutorial

[Download this tutorial]