The knowledge about IP Addressing and Subnetting in a network is essential for a person to pass CCNA 100-101 exam as it is one of the major sections in the course outline.


The understanding of IP addressing and subnetting is essential for every network specialist as it is one of the basic concept in networking. The following terms are necessary to understand before diving into the detail.

  • IP address: It can be referred as a unique ID assigned to different devices in a network for the purpose of identification. The devices can be the computers, printers, routers, switches etc.
  • Subnet: A subnet is a separate or identifiable portion of a network in an organization. It can be located on a floor, building or a specific geographical area.
  • Subnet Mask: It is a 32-bit number used to differentiate the different components in an IP address by dividing the IP address into two parts i.e. network address and host address.
  • NIC: It stands for Network Interface Card. It is a hardware device installed in a computer that enables the computer to connect to a network.

Need of Subnets:

To understand the need of subnets, we start with a simple example. Suppose we have a network that is composed of different devices like computers, laptops, printers, scanners, routers etc. The purpose of network is to enable the devices to communicate with each other. For the purpose of communication we have to assign a unique address to each device in a network so that it can be identifiable by other devices. These addresses are in the form of numbers. This type of address in networking is called as IP address. It is not only used to identify a device but it also defines that how the communication will be carried out.

Suppose we have a network in an organization, for better performance we have to divide this network in smaller units. If this organization has different departments like marketing, sales and development, we’ll split our network into three units each for different departments. This concept is termed as Subnetting. A subnet is a logical organization of devices connected in a network. The devices in a subnet have unique address that is associated with other devices in that subnet.

IP Address:

Here IP stands for Internet Protocol. As clear from the word protocol, it is a set of rules defined for the purpose of communication between different devices in a network. Let’s take the example of wireless communication used by the police officers. When one policeman talk to the other, he ends his statement with a word ‘over’ which is the rule so that the policeman on the other end can start talking. So the understanding of IP Address is essential for a professional to monitor the communication between two devices in a network.

Technically speaking, an IP address is written in the form of numbers i.e XXX.XXX.XXX.XXX, which is called as dotted decimal format. The numbers between these dots can be from 0 to 255. So the IP address can be in the form of or These IP addresses can be written in decimal form by taking their decimal values. can be written as 11001101.01110000.00101101.00111100. Each of these binaries can be referred as Octet as each binary is composed of 8-bits. The IP addresses are divided into different classes i.e. A, B, C, D and E. A specific class is assigned to an IP address on the basis of first octet. The following table will help you to understand the concept of these classes and how IP addresses are arranged in these classes.

IP Adress Classes

Subnetting and Subnet Mask:

For the purpose of subnetting, we have to split our network into a number of units and each unit will be termed as a subnet. The phenomenon of subnetting is applied on the IP address. This is done by borrowing the bits from the host portion of an IP address as IP address is divided into three parts i.e. the network part, subnet part and the last one is host part. Now if we talk about Subnet Mask, it indicates the number of bits that are borrowed from the host part of IP address.

Types of IP Addresses:

There are two types of IP addresses called as Public IP address and Private IP address. The total number of IP addresses that we can generate from all possible combinations 4,228,250,625. This includes public as well as private IP addresses. The private IP addresses are used for specific tasks e.g. is used for the purpose of Loopback which means that the host is referring to itself.

The private IP address is same as the extension used in the offices along with their phone numbers. Suppose we’ve to call some office to talk to a specific person, first we’ll dial the public number of that office then the computer will ask us for a specific extension to talk to that person. Same scenario is followed in case IP addresses, we can have a single public IP addresses and can assign private IP addresses to each device internally in our network.

Concept of VLSM:

VLSM stands for Variable Length Subnet Mask. It is required when a subnet is further divided into multiple subnets. It’s very simple; any subnet subnet can be divided into further subnets by indicating the proper Variable lengths subnet masks.

The knowledge of IP addresses, their assignment to different devices is a network and their classes are essential to understand for the network professional. The concept of subnetting, Subnet Masks and VLSM is one step ahead in this technology.

Learn More:
Visit the link below to get benefit from our Lesson 7 which focuses on Network Address Translation

Preparation of CCNA 100-101 Exam:

After getting all the technical knowledge about 100-101 exam, the candidate have to prepare for passing this exam. The practice tests are a best tool / way to prepare for the real 100-101 exam as it is a simulator of a real exam.