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<h2 id="overview">Overview</h2> <p>"Linkback" is the generalized term used to reference four methods of communication between websites. While sometimes confused with one another, linkbacks and <a href="/facts/Backlink/IAn4CgAu">backlinks</a> are not the same type of entity. A backlink is what the person referring to a page creates while a linkback is what the publisher of the page being referred to receives. </p><p>Any of the four terms—linkback, trackback, pingback, or (rarely) refback—might also refer colloquially to items within a section upon the linked page that display the received notifications, usually along with a <a href="/facts/Reciprocal_link/KKVBqy8b">reciprocal link</a>; trackback is used most often for this purpose. Also, the word trackback is often used colloquially to mean any kind of linkback. </p> <table><tbody><tr><th></th><th><a href="/facts/Refback/1QDy6YCJ">Refback</a></th><th><a href="/facts/Trackback/WbD4ztVE">Trackback</a></th><th><a href="/facts/Pingback/mjX5tHfv">Pingback</a></th><th><a href="/facts/Webmention/3CVLQDlI">Webmention</a></th></tr><tr><td>Trigger mechanism</td><td>Visitor to linking site clicks on the link, and their browser takes them to the linked site</td><td>Code on linking server examines added or updated documents, extracts links, and sends notification to linked server for each link found</td><td>Code on linking server examines added or updated documents, extracts links, and sends notification to linked server for each link found</td><td>Code on linking server examines added or updated documents, extracts links, and sends notification to linked server for each link found</td></tr><tr><td>Notification medium</td><td><a href="/facts/HTTP_referrer/WMQI4h4K">HTTP referrer</a> value</td><td>HTTP POST<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a></td><td><a href="/facts/XML-RPC/UleaeVRo">XML-RPC</a> call</td><td>HTTP POST with source and target parameters<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a></td></tr><tr><td>Capture mechanism</td><td>Examination of incoming HTTP referrer values</td><td>Trackback capture script</td><td>XML-RPC function</td><td>Webmention capture script</td></tr><tr><td>Information sent by linking server</td><td>None</td><td><ul><li>Linking site name <i>(Optional)</i></li><li>Linking post title <i>(Optional)</i></li><li>Linking post excerpt <i>(Optional)</i></li><li>Linking post URL</li></ul></td><td><ul><li>Linked post URL</li><li>Linking post URL</li></ul></td><td><ul><li>Linked post URL (target)</li><li>Linking post URL (source)</li></ul></td></tr><tr><td>Additional information presented to linked server</td><td>HTTP referrer sent by a visitor's browser upon clicking the link</td><td>IP address of linking server</td><td>IP address of linking server</td><td>IP address of linking server</td></tr><tr><td>Autodiscovery mechanism (how the linking server finds out how and where to send the notification)</td><td>None</td><td>LINK tag in the header of the linked page or trackback RDF documents</td><td>Special HTTP header or LINK tag on the linked page</td><td>HTTP Link header or link element on the linked page</td></tr><tr><td>Action required when notification is received</td><td><ul><li>Extract <a href="/facts/HTTP_referrer/WMQI4h4K">referrer</a> value from incoming HTTP headers</li><li>Retrieve referring page</li><li>Parse retrieved page for desired information</li></ul></td><td><ul><li>Gather desired information from<ul><li>Given parameters</li><li>or retrieving and parsing the given URL</li></ul></li></ul></td><td><ul><li>Retrieve page at "linking post URL"</li><li>Parse retrieved page for desired information</li></ul></td><td>Verifying that linking page does indeed link to linked page is recommended, not explicitly required</td></tr><tr><td>Advantages</td><td>Requires no special code on linking server (the link itself becomes the notification when someone clicks on it)</td><td>All the information desired by the linked server (Linking site name, post title, excerpt) is present in the notification itself</td><td><ul><li>Notification mechanism has a complete technical specification</li><li>Less susceptible to spamming</li></ul></td><td><ul><li>Uses well-known parts of HTTP wherever possible (autodiscovery, encoding of data, response status)</li><li>Reuses pingback's existing semantics</li><li>Minimum amount of data transferred on-the-wire</li></ul></td></tr><tr><td>Disadvantages</td><td><ul><li>No notification unless someone actually clicks on the link</li><li>Relies upon visitors' browsers sending proper HTTP referrer information</li><li>Linked site must retrieve and parse linking site's page to extract the information it wants</li></ul></td><td><ul><li>Notification requires positive action by linking server</li><li>Notification mechanism has only a partial technical specification</li><li>Autodiscovery information may prevent XHTML validation</li></ul></td><td><ul><li>Notification requires positive action by linking server</li><li>Linked site must retrieve and parse linking site's page to extract the information it wants</li><li>Can be abused for DDOS attacks<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></li></ul></td><td><ul><li>Notification requires positive action by linking server</li><li>Linked site must retrieve and parse linking site's page to extract the information it wants</li><li>Relatively new, so less widely implemented</li></ul></td></tr></tbody></table> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Backlink/IAn4CgAu">Backlink</a></li> <li><a href="/facts/Page_Rank/KtJRJFUX">Page rank</a></li> <li><a href="/facts/Search_engine_optimization/RNzIbb62">Search engine optimization</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Trackback specification draft". Archived from the original on 2012-11-30. Retrieved 2012-09-24. <a href="https://web.archive.org/web/20121130025719/http://www.lifewiki.net/attachments/view/101/2.1" target="_blank">https://web.archive.org/web/20121130025719/http://www.lifewiki.net/attachments/view/101/2.1</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Webmention Specification". <a href="http://webmention.org" target="_blank">http://webmention.org</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Constantin, Lucian (2014-03-11). "Over 160,000 WordPress sites used as DDoS zombies". PC World. Retrieved 2020-03-11. <a href="https://www.pcworld.com/article/2106940/large-ddos-attack-brings-wordpress-pingback-abuse-back-into-spotlight.html" target="_blank">https://www.pcworld.com/article/2106940/large-ddos-attack-brings-wordpress-pingback-abuse-back-into-spotlight.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> </ol>