Let us know what an IP address is first, if you already know, skip this section. 

IP (Internet Protocol): 
It is one of the fundamental protocols in order to have communications on the Internet. IP describes how the information is addressed, routed by networking devices. An IP address is a number identifying of a computer or another device on the Internet. A simple example could be mailing address.

There are 2 types of IP
1. IPv4 : 32 bit long, Ex: 35.244.11.196
2. IPv6 : 128 bit long, it is so much longer than IPv4

Example for IPv4 :

1. Dotted Decimal Notation

2. Hexadecimal Notation

CLASS ADDRESSING :

• So, In IPv4 addressing, there are 5 classes to range IP Values : Class A, B, C, D and E.
• The order of bits in the first octet determine the classes of IP address.
• IPv4 address is divided into two parts:
  1. Network ID 
  2. Host ID
• The class can determine the bits used for network ID and host ID.
• The number of total networks and hosts possible in that particular class can be calculated.
• Only class A, B and C are commonly used. classes D and E are reserved classes, D for multicast groups and E for future purposes.

CLASS A :

• IP address belonging to class A are assigned to the networks that contain a large number of hosts. Here, class A can support 16 million hosts on 127 networks.
• Here, the network ID is 8 bits long and the host ID is 24 bits long.
• IP addresses belonging to class A ranges from 1.x.x.x – 126.x.x.x
• Default Subnet Mask: 255.x.x.x

Number Of Hosts and Networks:

Number of Hosts: (2^24)-2= 16,777,214 i.e. 16 million hosts
Number of Networks: (2^7)-2=126 
Note: Reducing 2 because, 0.0.0.0 and 127.a.b.c are different addresses

>> The range of class A is 1.0.0.1 to 126.255.255.254

Other classes

Class B: 128.0.0.1 – 191.255.255.254
Class C: 192.0.0.1 – 223.255.255.254
Class D: 224.0.0.1 – 239.255.255.254
Class E: 240.0.0.1 – 255.255.255.254