Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide

NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Read offline with no ads or diagram watermarks!
The TCP/IP Guide

Custom Search

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 World Wide Web and Hypertext Overview and Concepts

Previous Topic/Section
World Wide Web Media and the Hypertext Markup Language (HTML)
Previous Page
Pages in Current Topic/Section
Next Page
TCP/IP Hypertext Transfer Protocol (HTTP)
Next Topic/Section

World Wide Web Addressing: HTTP Uniform Resource Locators (URLs)
(Page 2 of 3)


HTTP URLs may be absolute or relative. Absolute URLs are usually used for hyperlinks from one Web site to another, or by users requesting a new document without any prior context. Absolute HTTP URLs are based on the following common Internet URL syntax:


For the Web, the scheme is “http:” and the semantics of the different URL elements is defined to have meanings that are relevant to the Web. The general structure of an HTTP URL is thus:


The following shows how these syntactic elements are specifically defined for HTTP absolute URLs:

  • <user> and <password>: Optional authentication information, for resources located on password-protected servers. This construct is rarely used in practice and so most people don't realize it is an option; it has thus become a target of abuse by con artists who use it to obscure undesirable URLs.

  • <host>: The host name of the Web server upon which the resource is located. This is usually a fully-qualified DNS domain name, but may also be an IP address.

  • <port>: The TCP port number to use for connecting to the Web server. This defaults to 80 for HTTP and is usually omitted. Rarely, you may see some other port number used, sometimes to allow two copies of Web server software devoted to different uses on the same IP address; port 8080 is especially common as an alternative.

  • <url-path>: The path pointing to the specific resource to be retrieved using HTTP. This is usually a full directory path expressing the sequence of directories to be traversed from the root directory to the place where the resource is located, and then the resource's name. It’s important to remember that the path is case-sensitive, even though DNS domain names are not.

  • <query>: An optional query or other information to be passed to the Web server. This feature is commonly used to implement interactive functions, because the query value can be specified by the user and then be passed from the Web browser to the Web server. The alternative method is by using the HTTP POST method.

  • <bookmark>: Identifies a particular location within an HTML document. This is commonly used in very large HTML documents to allow a user to click a hyperlink and scroll to a particular place in the document. See the example in the previous topic (near the end of Table 273).

Although the URL syntax for the Web is quite “rich” and potentially complex, most Web URLs are actually quite short. The vast majority of these components are omitted, especially the user, password, port and bookmark elements; queries are also used only for special purposes. This leaves the more simplified form you will usually encounter for URLs:


Previous Topic/Section
World Wide Web Media and the Hypertext Markup Language (HTML)
Previous Page
Pages in Current Topic/Section
Next Page
TCP/IP Hypertext Transfer Protocol (HTTP)
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $

Home - Table Of Contents - Contact Us

The TCP/IP Guide (
Version 3.0 - Version Date: September 20, 2005

Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.