How trackbacks and pingbacks work

Recently, I received a pingback on one of my posts at this site. This inspired me to find out how trackbacks and pingbacks work. The main question was: how does a site know about posts that are made elsewhere that link back to a local post?

As usual, wikipedia came in handy, complete with a table comparing refbacks, trackbacks, and linkbacks. Here’s my summary:

A trackback occurs when server A notifies server B that A contains a reference to content on B. B can then publish a link back to A’s content (often with a small bit of context); this context-link is often referred to as the “trackback”. Since this activity involves communication between servers, it only works for blogging software that is trackback-enabled. Often the person writing weblog A must also use a special “trackback URL” (specified by B) when referring to the content on B — and not just in the content of their post, but in a separate “trackback” field (e.g., for WordPress).

Note that a trackback doesn’t actually require that A had a legitimate post that pointed to B. Anyone can send the web request to B suggesting a site to link back to. This seems to have quickly become another route for incoming spam on various weblogs, so a new form with additional verification has arisen.

A pingback is a trackback in which server B checks A for an actual link back to B’s content. Again, both A and B must actively support pingbacks for this to work. An advantage is that no special URLs are needed; when A links to B, there is an automatic notification to B (and B can confirm the legitimacy of A’s pingback).

Sounds pretty good, doesn’t it? Well, the pingback I received was a bit perplexing. It wasn’t a pingback in the sense of someone writing a post about something I wrote. But it wasn’t (quite) spam, either. As far as I can tell, it linked to a kind of automated blog that links verbatim to posts on a variety of subjects (probably specified by keyword). I was unable to determine what the purpose of the site was. I’ve deleted the pingback. But it gets a small kudos anyway, for inspiring me to find out something new.