Classfull Vs classless address

Classfull addressing:

            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). Classful addressing divides an IP address into the Network and Host portions along octet boundaries.In the classful addressing system all the IP addresses that are available are divided into the five classes A,B,C,D and E, in which class A,B and C address are frequently used because class D is for Multicast and is rarely used and class E is reserved and is not currently used.

Each of the IP address belongs to a particular class that's why they are classful addresses.Earlier this addressing system did not have any name,but when classless addressing system came into existence then it is named as Classful addressing system.The main disadvantage of classful addressing is that it limited the flexibility and number of addresses that can be assigned to any device.One of the major disadvantage of classful addressing is that it does not send subnet information but it will send the complete network address. The router will supply its own subnet mask based on its locally configured subnets. As long as you have the same subnet mask and the network is contiguous, you can use subnets of a classful network address.

Classless Addressing:
Classless addressing uses a variable number of bits for the network and host portions of the address.

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.Classless addressing system is also known as CIDR(Classless Inter-Domain Routing).Classless addressing is a way to allocate and specify the Internet addresses used in inter-domain routing more flexibly than with the original system of Internet Protocol (IP) address classes.CIDR (Classless Internet Domain Routing), defines arbitrarily-sized subnets solely by base address and number of significant bits in the address. A CIDR address of 192.168.0.0/24 defines a block of addresses in the range 192.168.0.0 through 192.168.0.255, while 192.168.0.0/20 would define a network 16 times as large - from 192.168.0.0 through 192.168.15.255.

Decimal	192	160	20	48
Binary	11000000	10100000	00010100	0011	0000
	<-------- 28 bits Network ------->				4 bits host