Why does Google index only one of my domains even though the same site is available on several?

Question

How can Google only index one specific domain when I have multiple domains? These domains all have same code and content. Google seems to treat the rest like they are redirected to the one domain that is indexed.

For example my site is example.com and it is the same as example.net and example.org. I have same the same content and same code on all the domain names.

I haven’t implemented any robots.txt code or meta refresh that would prevent Google from crawling any of the sites. But when I check Google, only the example.com site is indexed. When I check example.net Google seems to think it is redirected to example.com because it shows that for the cached version of page in Google.

What is the reason behind it? All the domains are in working condition.

Answer 1

Google has algorithms to detect duplicate content. When Google detects that two pages have the same, it picks one index and ignores the others. See: What is duplicate content and how can I avoid being penalized for it on my site?

If you want to choose which one Google indexes, you should pick one and make it the canonical domain. Redirect the others to it, or use meta link rel canonical tags. It used to be very important for SEO to do so. These days Google is better at ranking your site appropriately even when it is available under different names.

It doesn't help from a search engine optimization standpoint to own many domains for the same site. Those domain names end up only being useful for visitors that may type your domain name in multiple ways.