(a) 227.56.83.0

(b)114.22.43.21

(c)129.14.12.1

Classful Addressing

IPv4 addressing, at its inception, used the concept of classes. This architecture is called classful addressing. Although this scheme is becoming obsolete, we briefly discuss it here to show the rationale behind classless addressing.

In classful addressing, the address space is divided into five classes: A, B, C, D, and E. Each class occupies some part of the address space.

We can find the class of an address when given the address in binary notation or dotted-decimal notation. If the address is given in binary notation, the first few bits can immediately tell us the class of the address. If the address is given in decimal-dotted notation, the first byte defines the class.

Classes and Blocks:

One problem with classful addressing is that each class is divided into a fixed number of blocks with each block having a fixed size.

• Class A addresses were designed for large organizations with a large number of attached hosts or routers.
• Class B addresses was designed for midsize organizations with tens of thousands of attached hosts or routers.
• Class C addresses were designed for small organizations with a small number of attached hosts or routers.

We can see the flaw in this design. A block in class A address is too large for almost any organization. This means most of the addresses in class A were wasted and were not used. A block in class B is also very large, probably too large for many of the organizations that received a class B block. A block in class C is probably too small for many organizations. Class D addresses were designed for multicasting

In classful addressing, a large part of the available addresses were wasted.