An SEO client of mine has an unusual setup and runs the risk of getting penalized for duplicate content - 2 domain names for 1 website. Search engines will consider them as different websites having the same (i.e. duplicate) content and you end up having parts of each show up in the search results.

Let me explain the situation as I understand it.

You register 2 domain names, name.com and name.net, for whatever reasons (e.g. to prevent brand theft or to have a country-level domain) and point them to the same website. You do this by entering the same DNS for both domains and then “parking” name.net on the name.com hosting account. Domain Parking is a silent redirect that uses the DNS system and as far as browsers or search engines are concerned, there is NO redirect happening.

Hence, the search engines consider them as different websites and index both. And to prevent from showing duplicate content, parts of your website show up under each domain name. For example, when your type:

site:www.name.com into Google, you see…
- www.name.com/page1.html
- www.name.com/page3.html
- www.name.com/page4.html

site:www.name.net into Google, you see…
- www.name.net/page2.html
- www.name.net/page5.html

in the search results. Different webmasters have had different results, but here are the possibilities:
a) nothing bad happens and all your pages are indexed.
b) all your pages are removed from the search results.
c) your inbound links are split between name.com and name.net.
d) lower average PageRanks because of the split and your results go Supplemental.
e) lower PageRanks give you lower scores and you drop in search rankings.

There are many more possibilities because as far as I know, the search engines are still not good enough at managing duplicate content. There have been discussions on this subject from as far back as 2003 to as recent as 2007.

Here’s how it should’ve been done to avoid the problems - do a permanent 301 redirect from name.net to name.com. This way, all the “linkjuice” (PageRank, etc.) from name.net is passed on to name.com. You can implement a permanent 301 redirect by:

a) Domain Name Forwarding
Most domain registrars let you do this. Below is a screenshot of the function at GoDaddy.

b) Modifying The .htaccess File
Create a hosting account for name.net and add an entry in the .htaccess file in the root directory. Herman Drost has written quite extensively on how to implement a 301 redirect using .htaccess.

Method (b) can also be used for addressing canonical problems, where the search engines don’t know which URL to pick, e.g. the following URLs:
- www.name.com
- name.com/
- www.name.com/index.html

The URLs above are technically different, as can be seen from the different content served on http://phpicalendar.net/ and http://www.phpicalendar.net/

Again, do a search on Google for site:www.name.com, etc. to see if you have the different URLs in the search results. If you do and it was unintended, then it’s advisable to implement a 301 redirect.