How do I prevent search engines from indexing a website duplicated on a second domain?

Question

Let's say I run a website example.com with a dedicated IP A.B.C.D. Then I find out doing a search on Google, that my website is also being indexed through a domain A-B-C-D.example.com (where the A-B-C-D is equivalent to the dedicated IP). Obviously this is seen as a duplicated content.

I don't have access to that second domain so I can't get rid of it (according to support team at the hosting company, that domain was set up as "rDNS" to the dedicated IP by a third party that manages the domain). How can I stop it from being indexed in Google while my main domain still is?

Answer 1

The explanation of your site showing up on a second domain due to Reverse DNS doesn't sound right. rDNS is used to determine the IP address associated with a domain, and is served via DNS servers, not HTTP servers (or accessible through a browser like a website). I would certainly talk with your support team again about your hosting configuration.

Until you get that sorted out, you could add a canonical URL to your pages to indicate the prefered source that you'd like to be indexed. See this for more: Google Webmaster Tools - About rel="canonical"

Then resubmit your sitemap for Google to re-crawl, and request them to remove the unwanted pages: Google Webmaster Tools - Remove your own content from Google search results