Within my CMS I can add multiple domains. IE: domain-1.com and domain-2.com.

The way my CMS is setup I can access the same content across both domains. For instance: domain-1.com/contact and domain-2.com/contact would be the same pages. Because of this I am concerned about duplicate content.

What I plan to do is use canonical URLs for each domain and use absolute URLs in the navigation of the site, however, I have read that canonical do not work, or is less effective, cross domain.

If I use:

<link rel="canonical" href="http://www.domain-1.org/page-1" />


<link rel="canonical" href="http://www.domain-2.org/page-2" />

on each respective page for each domain will I be able to avoid duplicate content?

Also should I use sitemap.xml and robots.txt in the efforts to prevent duplicate content?

  • Why not set up a redirect from one to the other?
    – MrWhite
    Commented Dec 20, 2013 at 9:23

2 Answers 2


The first question might be why do you have two duplicate sites? Is there a particular reason? If there is no reason then I would suggest not to have duplicate domains, but if you must, then yes you can use cross domain canonical tag to avoid duplicate content issues in Google.

However, its seems that you may be a bit confused about cross domain canonical tags. To use cross domain canonical tags you have to chose one website that is the 'canonical' site that you want to be the main site that will rank in Google. The other site is the duplicate site and if using cross domain canonical tags will eventually be de-indexed in Google.

To use cross domain canonical tags, one of the canonical tags must reference the other website.


Main site http://www.domain-1.org/page-1

Could have a self referencing canonical tag:

<link rel="canonical" href="http://www.domain-1.org/page-1" />

Then the duplciate site http://www.domain-2.org/page-2

Would have a canonical tag referencing the main site:

<link rel="canonical" href="http://www.domain-1.org/page-1" />

More info from Google on Canonical tags here About rel="canonical"

  • The duplication of the sites isn't intentional, it is the way my CMS handles two domains under one hosting account. I could separate them (solving this issue) but it would add cost and would add complications that are solved if I keep them under one account. Hard to explain but it is the easiest and less costly route doing it this way. Thank you for your help. I read that somewhere about cross domain canonical tags but I cannot find that now. Thank you for clarifying.
    – L84
    Commented Dec 20, 2013 at 23:20

How ever your CMS works on this case is not a big deal, but each domain is different site (except sub domain) So the duplicate content is an issue within your one domain.

In your case the domain-1 's page repeated in domain-2 so its not a duplicate content in domain-1 or domain-2 . Only the bad impact on this case is, exact same content available on two sites(different domain) that have some bad impression in Search Engines.

Google Says

There are situations where it's not easily possible to set up redirects. This could be the case when you need to migrate to a new domain name using a web server that cannot create server-side redirects. In this case, you can use the rel="canonical" link element to specify the exact URL of the domain preferred for indexing. While the rel="canonical" link element is seen as a hint and not an absolute directive, we do try to follow it where possible.

I think there is no role for robot.txt or sitemap.xml in this case.

For more reading.

In your case the same content on both site is not ignorable, try to consider domain as Primary and another one as Secondary (boost any of the one website as main in ranking) and other one can point a canonical URL to the main domain.

  • The "duplicate content issue" is that Google will only return 1 domain for every duplicate page and without specifying a canonical URL or redirect the OP will have no control over which domain is returned - they could end up with a mix of both domains in the SERPs. If this is not a concern then it's not an issue, however, it can be confusing for users.
    – MrWhite
    Commented Dec 20, 2013 at 9:21
  • @w3d I think now its avoid confuse.
    – Jobin
    Commented Dec 20, 2013 at 10:07

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