Chapter6.Classless Interdomain Routing (CIDR)

Chapter 6. Classless Interdomain Routing (CIDR)

By June 1992, it had become apparent that the rapid growth of the Internet, caused by its commercialization, was straining its address architecture and space to their breaking points. A portion of the address space was in danger of depletion and the Internet's routing tables were growing so large as to be almost unmanageable. The Internet Engineering Steering Group (IESG) deliberated various approaches as to how best to go about fixing what was ailing the Internet. We looked at many of the subsequent stopgap fixes in Chapter 5, "The Date of Doom."

As a result of these deliberations, consensus within the IESG was that the old class-based IPv4 architecture had to be replaced with a new classless architecture. A classless architecture would enable the formation of network prefixes on any bit boundary within the IP address. This would have the immediate and direct effect of eliminating the ridiculous gaps between Class A-, Class B-, and Class C-sized networks. The new technology was directly based on the concepts and mathematics proven via Variable-Length Subnet Masking (VLSM). It came to be known as Classless Interdomain Routing (CIDR). This chapter explores CIDR's structure, nature, and operational mechanics.