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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)
                     9  TCP/IP Hypertext Transfer Protocol (HTTP)

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HTTP Status Code Format, Status Codes and Reason Phrases
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HTTP General Headers
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HTTP Message Headers

HTTP communication takes place through the relatively simple exchange of request and response messages. There are only a small number of methods (commands) supported by the protocol, which might give one the impression that the protocol is quite limited. Looks can be deceiving, however. Much of the functionality in HTTP is actually implemented in the form of message headers, which convey important details between clients and servers.

Some headers can appear in only HTTP requests, some in only HTTP responses, and some in either type of message. Since they are so important, there are literally dozens of them, and many apply to both requests and responses, I decided to describe them in detail in a separate section rather than try to summarize them too much in the course of describing the message formats

In this section I provide a description of each of the many headers used in HTTP request and response messages. The section contains four topics, each of which covers one of the four basic types of HTTP headers: general headers, request headers, response headers and entity headers.

Background Information: I assume here that you have already read the preceding section describing HTTP message formats.

Note: For the purpose of determining how Web caches treat HTTP messages, HTTP headers are categorized as either end-to-end or hop-by-hop headers. The former are meaningful only to the ultimate recipient of a message, while the latter are relevant to each device in the chain of devices (such as proxies) connecting a client and server. To avoid unnecessary complication I have not categorized the headers in this section using these categories; see the topic on caching for more information. In the descriptions of the individual headers, I indicate which headers are hop-by-hop; all others are end-to-end.

Quick navigation to subsections and regular topics in this section

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Version 3.0 - Version Date: September 20, 2005

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