IPv4 addresses are divided into classes A, B and C. Class A provides addresses for a small number of very large networks. Class C provides addresses for a large number of small networks and class B provides a balance between the two.
IPv6 has 22 classes of address. Classes range in size from of the address space to of the address space. Of the 22 address classes 17 are reserved for future expansion. The remaining 5 classes represent approximately 15% of the address space (see the pie chart).
Figure 2: The IPv6 Address Space