IP SUBNETTING

IP SUBNETTING
As commonly assumed by most students pursuing their career in IP Networking, subnetting - an integral part of efficient network design and management is a herculean task.
Based on this assumption and my fight-to-finish to help people understand and make IP subnetting to be at their beck and call, I have structured out this simple way of getting it over with.
Now, let’s delve into the topic.
To properly understand this topic we have to quickly be reminded of some basics;
A Network – simply, group of interconnected devices communicating and sharing resources on the same segment.
SUBNET – Owing to the definition above, we can simply refer to SUBNET as separate groups of interconnected devices carved out of the already existing one large group.
IP ADDRESS – An IP Address is used to identify individual devices on a network. You can picture it as NAME of a person in a Family. Hence, in a Family everyone must have a name, and the name must be unique. Likewise, in a Network every device (PC etc.) must have a unique IP address.
In order to help you understand the concept, I am going to approach the topic using my hypothetical Family story theory.
Let’s get started;
An IP Address is made of 4 octets or bytes containing 8 bits of information each. This makes the 32bits size of an average IP Address. Also, every IP address is made of TWO portions; Network & Host portions – this is determined by the Subnet mask of that IP Address.
It takes this format:

For the rest of this note, please endeavor to take note of the correlation below:
Computer Network Human Network
Network Family
Network portion of the IP address Surname
Host portion of the IP address First name

 
Going by my hypothetical family story, there is a Mr Onifade who has 3 sons – Onifade John, Onifade James, and Onifade Mark. After many years, these 3 sons grew up and gave birth to their own sons too.
Onifade John gave birth to Onifade John Ade and Onifade John Wale
Onifade James gave birth to Onifade James Bade and Onifade James sola
So also, Onifade Mark gave birth to Onifade Mark Mary and Onifade Mark Rose

From the diagram above, we see that everyone on the network has Onifade in a portion of their names, which means they all belong to that network at the 1st level. This level contains the 192.168.X.X network
At the 2nd level we have 3 different sub-networks (SUBNETS) – showing us that the network has been subnetted or in other words sub-divided into 3 groups. This level has the 192.168.10.X, 192.168.11.X, and 192.168.12.X networks.
Simply put, the rule of the thumb is that for computers to know and be able to speak with other computers on the network, they must have some portions of their IP addresses the similar, and this similarity is justified by the Subnet Mask.
The Subnet Mask tells the computer or any network device which portions of their IP Address is the Network and which portion is the Host.
The Subnet Mask also state the range or pool of address (network) that device belongs.
 
Having understood my story, I know the question still remains – how really do we subnet?
Ok! Let’s find out…
HOW TO SUBNET
The whole concept of Subnetting is actually the act and art of creating more networks from a single network. But before we start digging deep let’s have a look at a few mathematical concept that we need to be able to effortlessly subnet.
MATHEMATICAL RECALL
I like to bring to your remembrance about our little mathematical friend – Binary. Binary is the expression of values in the base 2. As human we have 10 fingers so we easily relate with figures using the base 10.
Now let’s try to bring some devotedness between these two – Binary and Decimal.
Taking 56 for example;
Decimal = 56 - Binary = 0 0 1 1 1 0 0 0
How is that true?
Recall that 1 byte = 8 bits
That is; 1 byte = X  X  X  X  X  X  X  X
Also recall that to convert a figure from Binary to Decimal and vice versa you have to know this;

So, for 56 the translation looks like this;

For 104, it looks like this;

THE INCREAMENT a.k.a BLOCK SIZE
To aid your ability to subnet you have to know this by heart.
The Block size otherwise called Increament is resulting exponential of 2 at every position within the 8 bits of Binary.

And all of the 8 bits when converted to the base 10 sums up to 255. Hence each of the octets of IP address can only be any number between 0 and 255.
                                 
Recall that each octet contains 8 bit of data:
                                     
Hence the address 192.168.10.1 takes this form;


SUBNET MASK IN BINARY FORM
Since you now understand the IP address from the binary point of view, now let’s see Subnet Mask from a Binary point of view as well.