Same content, different domains? There’s a tag for that. Using rel=canonical to tell Google that similar or identical content exists on multiple domains has a number of clever applications.
Cross domain rel=canonical is a unique and uniquely powerful tool that is designed to basically say, “You know what, Google? There is the same content on multiple different domains.”
So in this simplistic example, MyFriendSite.com/green-turtles contains this content that I said, “Sure, it’s totally fine for you, my friend, to republish, but I know I don’t want SEO issues. I know I don’t want duplicate content. I know I don’t want a problem where my friend’s site ends up outranking me, because maybe they have better links or other ranking signals, and I know that I would like any ranking credit, any link or authority signals that they accrue to actually come to my website.
There’s a way that you can do this. Google introduced it back in 2009. It is the cross-domain rel=canonical. So essentially, in the header tag of the page, I can add this link, rel=canonical href — it’s a link tag, so there’s an href — to the place where I want the link or the canonical, in this case, to point to and then close the tag. Google will transfer over, this is an estimate, but roughly in the SEO world, we think it’s pretty similar to what you get in a 301 redirect. So something above 90% of the link authority and ranking signals will transfer from FriendSite.com to MySite.com.
So my green turtles page is going to be the one that Google will be more likely to rank. As this one accrues any links or other ranking signals, that authority, those links should transfer over to my page. That’s an ideal situation for a bunch of different things. I’ll talk about those in a sec.
Multiple domains and pages can point to any URL
Multiple domains and pages are totally cool to point to any URL. I can do this for FriendSite.com. I can also do this for TurtleDudes.com and LeatherbackFriends.net and SeaTees.com and NatureIsLit.com. All of them can contain this cross-domain rel=canonical pointing back to the site or the page that I want it to go to. This is a great way to potentially license content out there, give people republishing permissions without losing any of the SEO value.