Misplaced Pages

Revision as of 05:48, 4 July 2007

For the rare occasions where de-referring links is needed in Misplaced Pages, see Template:Derefer.

The referer, or HTTP referer, identifies, from the point of view of an internet webpage or resource, the address of the webpage (commonly the URL, the more generic URI or the i18n updated IRI) of the resource which links to it. By checking the referer, the new page can see where the request came from. Referer logging is used to allow websites and web servers to identify where people are visiting them from, for promotional or security purposes. Since the referer can easily be spoofed (faked), however, it is of limited use in this regard except on a casual basis.

A dereferer is a means to strip the details of the referring website from a link request so that the target website cannot identify the page which was clicked on to originate a request.

Referer is a common misspelling of the word referrer. It is so common, in fact, that it made it into the official specification of HTTP – the communication protocol of the World Wide Web – and has therefore become the standard industry spelling when discussing HTTP referers.

More

When visiting a webpage, the referer or referring page is the URL of the previous webpage from which a link was followed.

More generally, a referer is the URL of a previous item which led to this request. The referer for an image, for example, is generally the HTML page on which it is to be displayed. The referer is part of the HTTP request sent by the browser program to the web server.

Many web sites log referers as part of their attempt to track their users. Most web log analysis software can process this information. As referer information can violate privacy, some browsers allow the user to disable the sending of referer information. Some proxy and firewall software will also filter out referer information, to avoid leaking the location of non-public websites. This can in turn cause problems: some servers block parts of their site to browsers that don't send the right referer information, in an attempt to prevent deep linking or unauthorised use of images (bandwidth theft). Some proxy software has the ability to give the top-level address of the target site as the referer, which usually prevents these problems while still not divulging the user's last visited site.

Recently many blogs have started publishing referer information in order to link back to people who are linking to them, and hence broaden the conversation. This has led, in turn, to the rise of referer spam: the sending of fake referer information in order to popularize the spammer's site.

Many pornographic paysites utilize referer information to secure their materials: only browsers arriving from a small set of approved (login-) pages are given access; this facilitates the sharing of materials among a group of cooperating paysites. Referer spoofing is often used to gain free access to these sites.

Dereferer

Since a web server and site can log where visitors have apparently arrived from (ie the page which was clicked to reach the page they are loading), there are a number of dereferer services, which allow web pages to link to others without giving referer information. An example of a derefered link using a common dereferer service is:

• http://www.dereferer.org/?http://en.wikipedia.org/

In the above example, your browser first goes to the dereferer.org site and then is redirected to en.wikipedia.org. To the webmaster of the wikipedia server they can only track back to the dereferer's URL instead of the original URL.

Tools of this nature take advantage of behavioral quirks of web browsers. For instance, most browsers will not send a Referer when redirected via a META REFRESH tag.

Dereferer services

There are many free dereferer services (with no ads) offered on different websites, namely:

• http://www.dereferer.org/?<url>
• http://www.dereferer.ws/?<url>
• http://www.anonym.to/?<url>
• http://ultimod.org/?url=<url>

Legends: <url> = the target URL

See also

• Referer spoofing, changing referer information to gain unauthorized access to a web site.
• Referer spam, providing fake referer information in order to popularize a spammer's website.

References and external links

• RFC 2616: Hypertext Transfer Protocol – HTTP/1.1
• IRI – Internationalized Resource Identifiers

• URI scheme
• HTTP