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Certified Basic Network Support Professional Universal Resource Locators

Universal Resource Locators

A URL (Uniform Resource Locator, previously Universal Resource Locator) - usually pronounced by sounding out each letter but, in some quarters, pronounced "Earl" - is the unique address for a file that is accessible on the Internet. A common way to get to a Web site is to enter the URL of its home page file in your Web browser's address line. However, any file within that Web site can also be specified with a URL. Such a file might be any Web (HTML) page other than the home page, an image file, or a program such as a common gateway interface application or Java applet. The URL contains the name of the protocol to be used to access the file resource, a domain name that identifies a specific computer on the Internet, and a pathname, a hierarchical description that specifies the location of a file in that computer.

On the Web (which uses the Hypertext Transfer Protocol, or HTTP), an example of a URL is:

which specifies the use of a HTTP (Web browser) application, a unique computer named, and the location of a text file or page to be accessed on that computer whose pathname is /rfc/rfc2396.txt.


Every URL consists of some of the following: the scheme name (commonly called protocol), followed by a colon, two slashes, then, depending on scheme, a server name (exp. ftp., www., smtp., etc.) followed by a dot (.) then a domain name |group="note"}} (alternatively, IP address), a port number, the path of the resource to be fetched or the program to be run, then, for programs such as Common Gateway Interface (CGI) scripts, a query string, and an optional fragment identifier.

The syntax is:

  • The scheme name defines the namespace, purpose, and the syntax of the remaining part of the URL. Software will try to process a URL according to its scheme and context. For example, a web browser will usually dereference the URL by performing an HTTP request to the host at, using port number 80. The URL may start an e-mail composer with the address in the To field.

Other examples of scheme names include https:, gopher:, wais:, ftp:. URLs with https as a scheme (such as require that requests and responses will be made over a secure connection to the website. Some schemes that require authentication allow a username, and perhaps a password too, to be embedded in the URL, for example Passwords embedded in this way are not conducive to secure working, but the full possible syntax is

  • The domain name or IP address gives the destination location for the URL. The domain, or its IP address, is the address of Google's website.
  • The domain name portion of a URL is not case sensitive since DNS ignores case: and HTTP://EN.EXAMPLE.ORG/ both open the same page.
  • The port number is optional; if omitted, the default for the scheme is used. For example, connects to port 5800 of, which may be appropriate for a VNC remote control session. If the port number is omitted for an https: URL, the browser will connect on port 80, the default HTTP port. The default port for an https: request is 443.
  • The path is used to specify and perhaps find the resource requested. It is case-sensitive, though it may be treated as case-insensitive by some servers, especially those based on Microsoft Windows. If the server is case sensitive and is correct, or will display an HTTP 404 error page, unless these URLs point to valid resources themselves.
  • The query string contains data to be passed to software running on the server. It may contain name/value pairs separated by ampersands, for example ?first_name=John&last_name=Doe.
  • The fragment identifier, if present, specifies a part or a position within the overall resource or document. When used with HTTP, it usually specifies a section or location within the page, and the browser may scroll to display that part of the page.