class full addressing is replaced with classless addressing.
The problem with this class full addressing method is that millions of class A address are wasted, many of the class B address are wasted,
whereas, number of addresses available in class C is so small that it cannot cater the needs of organizations.
Class D addresses are used for broadcasting routing, and are therefore available as a single block only.
Class E addresses are reserved for research purpose.
Note: Because of these problems, class full networking was replaced by Classless Inter-Domain Routing (CIDR)