Google can sometimes think “www and without www” are 2 duplicate websites and it could harm your seach engine result position (SERP)! It is better to force your visitor (including google bot) to view only 1 version of your website.
You can easily redirect all non-www traffic to www version of your domain, along with links to homepage or sub-folder. e.g. redirect yourdomain.com/aboutus.htm to www.yourdomain.com/aboutus.htm
Append code below to your .htaccess file, replace yourdomain.com with your own domain name.
RewriteEngine On
RewriteCond %{HTTP_HOST} ^yourdomain.com$ [NC]
RewriteRule ^(.*)$ http://www.yourdomain.com/$1 [R=301,L]
Code above works with any Apache webserver with RewriteEngine.
Anyone knows what is the solution for IIS ?