Do you know the difference between a domain and a sub-domain?
mysite.com is a domain. www.mysite.com is actually a subdomain.
It’s the www. that makes all the difference. Chances are you also have a mail.mysite.com, maybe an ftp.mysite.com, and possibly many others.
Typically the www. subdomain is the default because, well, humans are lazy and we don’t always bother to type www. at the start of a web address.
From an SEO perspective however, being able to see the same site at mysite.com and www.mysite.com is a problem because these two different subdomains can be indexed separately by search engines.
I have my doubts about whether or not Google really see a big issue here – they’re smart enough, surely, to pick up on the fact that www. and non-www. sites are the same but, equally, why take the risk?
If nothing else, making sure that your website redirects one of these two options to the other so that your website either always has www. as the subdomain, or never has it, will give those pesky SEO consultants one fewer thing to
moan about comment on.
This redirect is being configured directly on your web server. If you can load both www. and non-www. versions of your website in your browser, make sure your developer updates your server settings accordingly.