IP Subnetting Quick Cheat Sheet

If you work in IP Networks then you already know how IP subnetting works and most likely remembers all the subnets… this tutorial is not for you.

Few years back when I was doing my CCNA, I had a good basics of IP subnetting and I knew all the binary calculation which is the first step for understanding through which I was able to calculate subnets, hosts range , etc. However, it used to take me minutes to calculate. So, I had to make something simple for me to remember and I made the following table.

Note: I may not be the only one who created this table , there may be thousands of versions similar to it. But it worked for me. So, it may work for the person who is new to IP just like me when I was trying to polish my skills.

Table-1

subnettable1

Table-2

subnettable2

Example:

Suppose we have an IP address : 10.10.10.163/27

We need to find out the Subnet Mask, Network Address, Broadcast Address and Range of Hosts.

Step 1:

In Table-1 we see /27 has a subnet of ‘224’, we know that /27 is in the last octet so,

Subnet mask=  255.255.255.224

Step 2:

Now from the same Table-1 we see that Number of IPs will be 32 per subnet.

But we know that we have to subtract 2 IP address from 32, one for Network Address and other for Broadcast Address.

No of Host in 27 Network = 32-2= 30

Step 3:

We see Table-2 and go through /27 column, we find that out IP last octet .163 lies in the range between ‘160’ and ‘192’.

So, For network address we always take the lowest one so,

Network Address= 10.10.10.160

For Broadcast address , we will subtract 1 from 192.

Broadcast Address= 10.10.10.191

Step 4:

Range Host of addresses is now easy to find.

We know our Network Address= 10.10.10.160 & Broadcast Address= 10.10.10.191

Range of Hosts= 10.10.10.161 – 10.10.10.190

Ok, That was easy and I know subnetting Class-3 is always easy!