Unforeseen Limitations to Classful Addressing

Unforeseen Limitations to Classful Addressing


The original designers never envisioned that the Internet would grow into what it has

become today. Many of the problems that the Internet is facing today can be traced back

to the early decisions that were made during its formative years.

- During the early days of the Internet, the seemingly unlimited address space allowed

IP addresses to be allocated to an organization based on its request rather than its

actual need. As a result, addresses were freely assigned to those who asked for

them without concerns about the eventual depletion of the IP address space.

- The decision to standardize on a 32-bit address space meant that there were only 232

(4,294,967,296) IPv4 addresses available. A decision to support a slightly larger

address space would have exponentially increased the number of addresses thus

eliminating the current address shortage problem.

- The classful A, B, and C octet boundaries were easy to understand and implement,

but they did not foster the efficient allocation of a finite address space. Problems

resulted from the lack of a network class that was designed to support mediumsized

organizations. A /24, which supports 254 hosts, is too small while a /16,

which supports 65,534 hosts, is too large. In the past, the Internet has assigned sites

with several hundred hosts a single /16 address instead of a couple of /24s

addresses. Unfortunately, this has resulted in a premature depletion of the /16

network address space. The only readily available addresses for medium-size

organizations are /24s which have the potentially negative impact of increasing the

size of the global Internet's routing table.

The subsequent history of Internet addressing is focused on a series of steps that

overcome these addressing issues and have supported the growth of the global Internet.