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 tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$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!

Enjoy The TCP/IP Guide? Get the complete PDF!
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 Application Layer Addressing: Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs)
                9  Uniform Resource Locators (URLs)

Previous Topic/Section
Uniform Resource Locators (URLs)
Previous Page
Pages in Current Topic/Section
12
3
4
Next Page
URL Schemes (Applications / Access Methods) and Scheme-Specific Syntaxes
Next Topic/Section

URL General Syntax
(Page 3 of 4)

Omission of URL Syntax Elements

The full URL syntax may seem very complicated, but bear in mind that this is a formal definition and shows all of the possible elements in a URL at once. Most schemes do not use every one of these elements, and furthermore, many of them are optional even when they are valid in a particular scheme. For example, the <login> and <password> are officially supported for HTTP URLs, but are very rarely used. Similarly, port numbers are most often omitted, telling the client software to just use the default port number for the scheme. The next topic describes some of the most common URL schemes and the specific syntaxes used for them, including discussing how and when these elements are employed.

Even though the richness of the URL syntax isn't often needed, it can be useful for supplying a wide variety of information in special cases. URLs are also very flexible in terms of how they may be expressed. For example, while a “<host>” is usually a DNS name, it can also be an IP address expressed in many forms including dotted-decimal, regular decimal, hexadecimal, octal and even a combination of these. Unfortunately, the lack of familiarity that most people have with some of these “esoterics” has led to URLs being abused through deliberate obscuration, to get people to visit “resources” they would normally want to avoid.

URL Fragments

Technically, a “<fragment>” is not considered a formal part of the URL by the standards that describe resource naming. The reason is that it only identifies a portion of a resource, and is not part of the information required to identify the resource itself. It is not sent to the server but retained by the client software, to guide it in how to display or use the resource. Some would make a valid argument, however, that this distinction is somewhat arbitrary; consider, for example, that the scheme itself is also used only by the client, as is the host itself.

The most common example of a URL fragment is specifying a particular bookmark to “scroll” to in displaying a Web page. In practice, a fragment identifier is often treated as if it were part of a URL since it is part of the string that specifies a URL.


Previous Topic/Section
Uniform Resource Locators (URLs)
Previous Page
Pages in Current Topic/Section
12
3
4
Next Page
URL Schemes (Applications / Access Methods) and Scheme-Specific Syntaxes
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 (http://www.TCPIPGuide.com)
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.