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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 2 of 4)

Authorization

Used by the client to present authentication information (called “credentials”) to the server to allow the client to be authenticated. This is required only when the server requests authentication, often by sending a 401 (“Unauthorized”) response to the client's initial request. This response will contain a WWW-Authenticate header providing the client with details on how to authenticate with the server. See the topic on security and privacy.

Expect

Indicates certain types of actions that the client is expecting the server to perform. Usually the server will accept the indicated parameters; if not, it will send back a 417 (“Expectation Failed”) response. The most common use of this field is to control when the server sends a 100 (“Continue”) response. The client indicates that it wants the server to send this preliminary reply by including the “Expect: 100-continue” header in its request. (See the end of the topic on status codes for details.)

From

Contains the e-mail address of the human user making the request. This is optional, and since it is easily spoofed, should be used only for informational purposes, and not for any type of access rights determination or authentication.

Host

Specifies the Internet host as a DNS domain name, and may also contain a port number specification as well (typically, only if a port other than the HTTP default of 80 is to be used). This header is used to allow multiple domains to be served by the same Web server on a particular IP host. It has the distinction of being the only mandatory header—it must be present in all HTTP/1.1 requests.


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HTTP General Headers
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HTTP Response Headers
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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