The requirements of the classful came from the increasing number of users of the internet. Before the internet did not become popular and there were only a few hundreds of users of the internet which were mainly companies that were trying experimentation of the internet or some research facility to transfer their data within an organization. Therefore at that point time, only a few users were assigned the address on the network, and the addresses that they were assigned to also have to take care of some internet protocol and in that address also there were many times that these protocols were occupying some part of their address, therefore, the number of address that can be assigned were also reduced.
The need for the classful address came when the earlier way of addressing was not efficient at all, then a new method was introduced to accommodate more users as the number of users of the internet grew. The concept of ipv4 helped to accommodate 2^32 addresses but as the internet boom came and there were more users than the internet was designed for this therefore has to introduce the concept of subnetting. The IP address started to be divided into various networks and the divide of these IP addresses led to the classful addressing.
There are many classful addresses such as class A, B, C, D, E addressing and all these types of addresses have different types of subnetting to define the network. Some of the bits of the ipv4 address were kept constant that is either one or zero and this defined the number of the network address it can have and the number of the hostname that it can support. Class A has the largest number of the hostnames that a network can support and therefore it also accounts for more than twelve percent of the ipv4 address whereas in class b and class c the number of hostnames supports goes down and the number of the network address name support is more.
The classful addressing also created a major problem and that was the wastage of the IP address. If say an MNC required only five thousand of the ip address to create a network within an organization then if it ordered uses the method of classful ip addressing and then selected the class a ip addressing which will have the number of ip address in millions so in order to fulfil the demand of only five thousand ip address then you will be wasting a lot of ip address as the class a ip addressing is used and also if you think that the problem is solved by the other classes such as class b or class c then you are wrong because the other class addressing will then increase the number of network address and the hence the wastage of the network address will be occurring rather than the hostnames therefore the concept of the classful address brought some wastage of the ip address and this created the demand for the classless ip addressing and also the demand for the maintenance also increases in the classful ip address because there are many number of ip address that are not used and therefore this can create loopholes within a network and this can also lead to further troubles. The errors in such a great number of classful IP addresses are also great because when the errors occur it becomes very difficult to find the real place from where the error is arising and thus the tracking of error inside a network is also a tedious job.
To handle all these difficulties the concept of the classless IP addressing and submitting was introduced where the network was divided into a various number of the smaller network by keeping some of the IP bits constant and these both concepts of IP addressing and subnetting provides the exact number of the hostnames and the network address that was required by the organization and therefore there was no wastage of the IP address from then.