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.
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.
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
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
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
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!