Google News, Inside.

How Does REL=Canonical Actually Work?

Posted at 8:51am EST on 09/17/2009

Googler Greg Grothaus gave spoke at SES San Jose last month and did a follow-up post to the Google Webmaster Central blog with similar content.

Here are some great tips for understanding how rel="canonical" actually works.

rel=canonical
Questions and Answers
Q: Does this work across hosts (aka: subdomains)?
A: Yes. So zeta.zappos.com could suggest www.zappos.com as a canonical url

Q: Does this work across domains?
A: No, only on the same domain.

Q: Can I use this to suggest http://example.com/ be the canonical url instead of https://example.com/?
A: Yes, absolutely.

Q: Should I use rel=canonical or a 301/perm redirect?
A: It depends, you have more tools in your arsenal.

Q: Do the pages have to be bit-for-bit identical?
A: No, but they should be similar. Slight differences are okay.

Here is the actual slide show,

The content I posted can be found on page #14 of the slideshow.

Additionally, here is his video follow-up.