The first four subsections of the large section covering the Hypertext Transfer Protocol were meant to give you a good understanding of the fundamental concepts and basic operation of the protocol. Modern HTTP, however, goes beyond the simple mechanics by which HTTP requests and responses are exchanged. It includes a number of features and capabilities that extend the basic protocol to improve performance and meet the various needs of organizations using modern TCP/IP internetworks.

In this section, I complete my description of HTTP by discussing several important matters that are essential to the operation of the modern World Wide Web. I begin with an overview of HTTP caching, which is the single most important feature that promotes efficiency in Web transactions. I discuss the different uses of proxies in HTTP and some of the issues associated with them. I briefly examine the issues related to security and privacy in HTTP, and conclude with a discussion of the matter of state management, and how it is implemented despite HTTP being an inherently stateless protocol.