In the classified addressing system all available IP addresses are divided into five classes A, B, C, D and E, where classes A, B and C are often 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 so that are class addresses. Previously this addressing system had no name, but when the classless addressing system came into existence then it is called the classic addressing system. The main disadvantage of classified addressing is that it limits the flexibility and the number of addresses that can be assigned to any device. One of the major disadvantages of classified addressing is that it does not send subnet information but will send the complete network address. The router will provide 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 classy network address.