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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)
                          9  HTTP Message Headers

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HTTP General Headers
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HTTP Response Headers
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HTTP Request Headers
(Page 4 of 4)

Range

Allows the client to request that the server send it only a portion of an entity, by specifying a range of bytes in the entity to be retrieved. If the requested range is valid, the server sends only the indicated part of the file, using a 206 (“Partial Content”) status code; if the range requested cannot be filled, the reply is 416 (“Requested Range Not Satisfiable”).

Referer [sic]

Tells the server the URL of the resource from which the URL of the current request was obtained. Typically, when a user clicks a link on one Web page to load another, the address of the original Web page is put into the Referer line when the request for the clicked link is sent. This allows tracking and logging of how the server is accessed. If a human user manually enters a URI into a Web browser, this header is not included in the request. Since this header provides information related to how Web pages are used, it has certain privacy implications.

The proper spelling of this word is “referrer”. It was misspelled years ago in an earlier version of the HTTP standard, and before this was noticed and corrected, became incorporated into so much software that the IETF chose not to correct the spelling in HTTP/1.1.

TE

Provides information to the server about how the client wishes to deal with transfer encodings for entities sent by the server. If extensions to the standard HTTP transfer encodings are defined, the client can indicate its willingness to accept them in this header. The header “TE: trailers” can also be used by the client to indicate its ability to handle having headers sent as trailers following data when “chunking” of data is done. This is a hop-by-hop header and applies only to the immediate connection.

User-Agent

Provides information about the client software. This is normally the name and version number of the Web browser or other program sending the request. It is used for server access statistic logging and also may be used to tailor how the server responds to the needs of different clients. Note that proxies do not modify this field when forwarding a request; rather, they use the Via header.

Key Concept: HTTP request headers are used only in HTTP Request messages. They allow a client to provide information about itself to a server, and provide more details about a request and control over how it is carried out.



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Version 3.0 - Version Date: September 20, 2005

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