Autonomy of administration
RFC 2317 devised a methodology to address this problem by using canonical name DNS records. However, with the introduction of Classless Inter-Domain Routing, IP addresses were allocated in much smaller blocks, and hence the original design of pointer records was for one of the best kinds of reverse cell phone directory impractical, since autonomy of administration of smaller blocks could not be granted. The structure of the reverse DNS domain was based on this definition. By definition, each block fell upon an octet boundary. Historically, Internet registries and Internet service providers allocated IP addresses in blocks of 256 or larger octet-based blocks for classes B and A.
