Content

| 2.2 |  | IP Addressing Crisis and Solutions |
| 2.2.1 |  | IP addressing crisis |

Class A and B addresses make up 75 percent of the IPv4 address space. However, a relative handful of organizations, fewer than 17,000, can be assigned a Class A or B network number. Class C network addresses are far more numerous than Class A and Class B addresses, although they account for only 12.5 percent of the possible 4 billion, or 232 IP hosts.

Unfortunately, Class C addresses are limited to 254 hosts, which will not meet the needs of larger organizations that cannot acquire a Class A or B address. Even if there were more Class A, B, and C addresses, too many network addresses would cause Internet routers to grind to a halt under the weight of enormous routing tables.

Ultimately, the classful system of IP addressing, even with subnetting, could not scale to effectively handle global demand for Internet connectivity. As early as 1992, the Internet Engineering Task Force (IETF) identified two specific concerns:

- Exhaustion of the remaining, unassigned IPv4 network addresses. At the time, the Class B space was on the verge of depletion.
- The rapid and substantial increase in the size of the Internet routing tables is because of its growth. As more Class C addresses came online, the resulting flood of new network information threatened the capability of Internet routers to cope effectively.

In the short term, the IETF decided that a retooled IPv4 would have to hold out long enough for engineers to design and deploy a completely new Internet Protocol. That new protocol, IPv6, solves the address crisis by using a 128-bit address space. After years of planning and development, IPv6 promises to be ready for wide scale implementation. However, IPv6 continues, for the most part, to wait for that implementation.

One reason that IPv6 has not been rushed into service is that the short-term extensions to IPv4 have been so effective. By eliminating the rules of class, IPv4 now enjoys renewed viability.