by Odin Kyle

Created on: August 27, 2007   Last Updated: January 21, 2012

Explaining how an internet URL(Uniform Resource Locater) works requires first explaining what the URL is. For most people a URL is just the text address for a website. It's the thing you see in the address bar of your browser.

A more precise and complete explanation of what a URL is becomes slightly more complex. A URL is a standard way of accessing data resources as defined in RFC(Request For Comment) 1738.

From the RFC a URL is defined as "[scheme]:[scheme-specific-part]". This basically means that only two things are required for a valid URL. A scheme which will be described below and a description that is specific to the scheme.

Commonly used schemes:

• ftp
• http
• mailto

The scheme specific part is not defined for all possible schemes but the most common form used by http, and ftp is defined below.

Common scheme syntax:
//[user]:[password]@[host]:[port]/[url-path]

This should be easily recognizable for anyone that's seen a URL in an internet browser.

Here's an example using one of the articles I wrote:
http://www.helium.com/tm/514851/electric-might-happe n-couple

• Scheme - http
• user - empty
• password - empty
• host - www.helium.com
• port - empty (uses default port for protocol 80)
• url-path - tm/514851/electric-might-happen-couple

Not all of the parts of the scheme syntax will be used every time. Here's an example of a URL that uses all of the parts:
ftp://testuser@testpassword:www.somedomain.com:21/my dir/test.file

This is a file request for a file in mydir called test.file that lives on the www.somedomain.com machine accessed via port 21 using the ftp protocol with the user name of testuser and the password of testpassword.

A quick explanation of the typical 3 part domain is quite simple. The .com, .edu. or .net top level domain names were originally defined in such a way that the user could determine the type of website based on the name. This is still true for .gov and .mil but less so for .net and .org. The middle part of the domain is simply the name of the network. The first part is traditionally a computer name but now for large sites is generally the name of the machine that handles handing off the request to an available machine.

That explains what a URL is, how it works depends on the scheme. The ftp scheme and the http scheme work similarly. The domain and path portions of the URL are important to understand how a URL works.

The domain is a textual representation

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