It is commonly known that you can link to your site with www or non-www ( http://www.yoursite.com or http://yoursite.com ), as on most servers, your site will open with both. So there is no difference from the user’s point of view as they will see the same site with both link structures. But the search engines will treat your website differently if web pages link to http://www.yoursite.com/ or http://yoursite.com/ as they can also be pointed to different destinations. The search engine will treat one URL as real and inbound links on the other URL may not be counted. The subject is also the Canonical URL Issue in the search engine industry. This issue is part of on-page SEO or Technical SEO.
What is the effect of linking with a Non-Similar URL?
The Major impact is a decrease in link popularity as search engines consider them as two URLs and count link popularity separately for both.
How to verify that both my site versions exist in search engines?
You can see the Google PR of your pages with the www version and non-www version. You will find different PR for both versions.
What to do to prevent this?
Select the same form of your URL for inbound and internal linking. Ensure all incoming links are pointed to the same form as your URL. When setting up your links, stay consistent with your URL structure. Follow the same structure within your website. Make sure that your internal links on your website link to the same URL as your inbound links.
Which Format is to be adopted?
There’s no difference between search engines for the www or non-www versions. Different people have different views. Some say with www Version, and you have to type four more characters. Whereas many believe that all users first type www while opening the browser. Many directories require the WWW in the site location, so it is preferable to use the WWW version if you can www is very common, and people can get confused if you have a domain without it. Don’t forget, in your browser, when you type “SEO” in the address bar and hit ctrl+enter; it automatically adds the www along with the rest of the URL. For that reason alone, some suggest the www version. You may adopt any version of the URL, but consistency should be there in internal linking.
What to do If both URL structures exist on the old site
If you have both yoursite.com and www.yoursite.com, you must consolidate two “sites” into one. Showing your content under two different URLs is never a good idea.
First, find out the PageRank of each version. and can choose a version with higher PR, as other websites mostly link it. You must adopt 301 redirects, so there aren’t two versions of your site (www.yoursite.com and yoursite.com). It will most likely change your rankings positively as you no longer “split” your site across two sets of URLs. Hence each URL will get more link power. You may not see the effect in the short term as search engines take time to update the web. You can make 301 redirections in many, but the most popular is to use either the .htaccess file or a set on the server. You can also set up your server with the right default hostname when you do this stuff (or have your host do it for you). If the web server is not configured to have the proper default (www or non-www), there will be so many redirects that it will take ages to load the site. You can use the 301 redirect tools to help you on this subject.
By now providing a redirect, people will naturally link to you using the one you want. Ensure all of your internal links go to the correct one too.
Linking your site with a consistent URL will force the search engine to index real URLs and people to link the URL structure you want. It will result in the saving of leakage of PageRank, Domain authority, and an increase in link popularity to improve your search engine ranking. Each website owner’s goal is to increase traffic.