Subnet Mask

Subnet Mask means sub-network. The purpose is to create partition in the IP address after network part.

• A Subnet mask is a 32-bit number that  masks an IP address.
• It separates the IP address into Network and Host address. The 1's represent the Network bits and 0's represent the Host bits.
• Subnetting further divides the host part of an IP into another IP and host address, if additional subnet is required.

Subnetting of an IP address is to separate a big network into smaller multiple networks for security purpose and easy access.

•  Subnet mask is something that draws a line somewhere in the IP address to help logical partition of an IP address.

 

The Default subnet mask for each of the classes that we use in the IP address.

• Class A - 255.0.0.0
• Class B - 255.255.0.0
• Class c - 255.255.255.0

Network with different Subnet Mask's

• A bitwise AND between the two given IP address and the Subnet mask gives the Network address.
• A bitwise OR between the Network address and inverted Subnet mask gives the Broadcast address.

How the Network address is determined :

• Subnet mask           255.255.240.000      11111111.11111111.11110000.00000000
• IP Address              150.215.017.009      10010110.11010111.00010001.00001001
• Network Address    150.215.016.000      10010110.11010111.00010000.00000000

Subnet Calculator :

It automatically calculates the Subnets. It allows to input an IP address and choose the subnet mask.

Some of free online IP subnet calculators are :

• Online IP Subnet Calculator.
• IPcalc.
• Monitis Subnet calculator.