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When we already have classFull Addressing Scheme in which we divided the IP addresses into Class A , Classs B , Class C , Class D and Class E then what was limitation in this that we need to introduce ClassLess IP addressing?

Can anyone tell please what happens in ClassLess IP addressing scheme and what was drawback that classless came from classfull.

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Classful addressing divides an IP address into the Network and Host portions along octet boundaries. Classless addressing treats the IP address as a 32 bit stream of ones and zeroes, where the boundary between network and host portions can fall anywhere between bit 0 and bit 31. The network portion of an IP address is determined by how many 1's are in the subnet mask. Again, this can be a variable number of bits, and although it can fall on an octet boundary, it does not necessarilly need to. A subnet mask is used locally on each host connected to a network, and masks are never carried in IPv4 datagrams. All hosts on the same network are configured with the same mask, and share the same pattern of network bits. The host portion of each host's IP address will be unique. "

Classful addressing assigns an organization a Class A, Class B, or Class C block of addresses. Classless addressing assigns an organization a block of contiguous addresses based on its needs."

All IP addresses have a network and host portion. In classful addressing, the network portion ends on one of the separating dots in the address (on an octet boundary). Classless addressing uses a variable number of bits for the network and host portions of the address. "
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Why we need Classless =>  

If i need to buy a network with minimum host configuration, Let's say, a network with 16 IP.

so with already available network from  Class A,B,C. Class C can provide minimum network capacity that have 28 = 256 IP Possible.

but i need a network with 16 IP only, so what would i do with rest 256-16 = 240 this is nothing but simply 240 IP unused for me.

This is one reason behind Classless.

What is Classless =>    

as we know we have total no of IP available is  232 

so in classless initally they have not devided any prior fix network or block, you have to ask for a valid block range based on your need. (valid block means they have to follow certain rule to check you validness of your demand network or block range) so now exact #no of demand network or block is possible here .

This is a basic general level illustrations.