1. Constant Change

   In searching for Internet architectural principles, we must remember
   that technical change is continuous in the information technology
   industry. The Internet reflects this.  Over the 25 years since the
   ARPANET started, various measures of the size of the Internet have
   increased by factors between 1000 (backbone speed) and 1000000
   (number of hosts). In this environment, some architectural principles
   inevitably change.  Principles that seemed inviolable a few years ago
   are deprecated today. Principles that seem sacred today will be
   deprecated tomorrow. The principle of constant change is perhaps the
   only principle of the Internet that should survive indefinitely.

   The purpose of this document is not, therefore, to lay down dogma
   about how Internet protocols should be designed, or even about how
   they should fit together. Rather, it is to convey various guidelines
   that have been found useful in the past, and that may be useful to
   those designing new protocols or evaluating such designs.

   A good analogy for the development of the Internet is that of
   constantly renewing the individual streets and buildings of a city,
   rather than razing the city and rebuilding it. The architectural
   principles therefore aim to provide a framework for creating
   cooperation and standards, as a small "spanning set" of rules that
   generates a large, varied and evolving space of technology.

   Some current technical triggers for change include the limits to the
   scaling of IPv4, the fact that gigabit/second networks and multimedia
   present fundamentally new challenges, and the need for quality of
   service and security guarantees in the commercial Internet.

   As Lord Kelvin stated in 1895, "Heavier-than-air flying machines are
   impossible." We would be foolish to imagine that the principles
   listed below are more than a snapshot of our current understanding.