Easy way to find the subnetwork address

In this article we learn about the sub-network address and how to find out the sub-network address from the given IP address and mask address.

Sub network address is the address, which is depends upon the IP address and what class is used in IP address. Class of IP address may be the A, B, C. In organization we need to use sub-netting. In sub-netting IP address is split into the many sub-network address. Sub-netting allows us to split network address into several parts of internal use. If we done sub-netting then outside world only see the single network address or act as single network.

Here the term mask address is used; mask address is the address which extracts the address of the physical network address from the given IP address.

Masking is two types. First one is the boundary level masking and second one is the Non boundary level masking.  If the mask address is contain only 0 or 255 then this mask is the boundary level masking. And if the mask numbers are not just 0 or 255 then it is non boundary level masking.

Masking address may be given in two ways.  In first way mask address is written looks like the IP address. Ex-

And in second way the mask is given in numbers, the number is appended to IP address after slash.


If the mask is given in slash number form then we need to calculate the mask address from this. For this write down the number of 1’s as given after slash. And complete the total 32 bits (if the IPv4 ) using fill 0’ in right side. And then divide in 8 bit groups. Write down the equivalent decimal value of each group.

Just like the for-

11111111. 11111111 .11111111 .11000000

Mask address is

Now let’s see how to find sub-network address.  At first check which type of mask address is given either boundary level or non boundary level?

Sub-network address if boundary level mask is given:-

If the mask address is boundary level then it is very easy to find out the sub-network address from IP address and mask.

For this write down mask address below the IP address.

If mask bytes is 255 then IP address bytes is repeated in sub-network address.

And if bytes in the IP address that correspond to 0 in mask then put 0 in sub-network address.

Let’s take an example-


Sub-network address is

Sub-network address if non boundary level mask is given:-

If the mask is non boundary level then we need to binary AND between the IP address and mask address.

Do this in step by step.

Step1- At first write down binary form of IP address and Mask address.

Step2- And then perform binary AND between IP address and Mask address. (If the mask bytes is 255, 0 then same as the boundary mask)

Step3- Write down decimal equivalent of each block.

Let take an example-



Where ‘x’ value is calculated using binary AND between 22 and 192.

123:  01111011
Binary AND   192:  11000000


i.e. 64

Sub-network address is-