one of the good practices about speeding up website is to get the components in the webpage to be downloaded faster. One way to do it is to have virtual hosts such that HTML content, CSS and javascript are provided by say http://www.domain.com, while images, flash and the likes are provided by a subdomain like images.domain.com. This practice would make sure that the page loads faster as parallel downloads will happen due to different domain/subdomain names. The RewriteCond that redirects all the sub-domains to http://www.domain.com as provided in this article would be hinder getting the page to be downloaded faster on the browser.

My suggestion would be to slightly modify the condition script as below -

RewriteCond %{HTTP_HOST} .
RewriteCond %{HTTP_HOST} !^images\.yoursite\.com [OR]
RewriteCond %{HTTP_HOST} !^www\.yoursite\.com [NC]
RewriteRule ^(.*)$ http://www.yoursite.com/$1 [R=301,L]

Or better still -

RewriteCond %{HTTP_HOST} .
RewriteCond %{HTTP_HOST} ^yoursite\.com [NC]
RewriteRule ^(.*)$ http://www.yoursite.com/$1 [R=301,L]

That is a very good question and you answered it yourself. Consistency is the key. However, keep in mind that you don’t always have control over how other sites link to yours so implementing the 301 redirect is still a must. www. is just another sub domain, it just happens to be the standard default. When you do http://www.subdomain.domain.com, what you are really doing is sub-subdomain.subdomain.domain.com.

The 301 redirect in this case is all about preventing the indexing of duplicate pages by allowing multiple URLs to display the same content; no matter what the URL or sub sub domain.

how about sub domains? i have a client who insists on using “www” on all their web sites, even if it’s a subdomain. so far, i just recommended using both but after reading your article, i’ll make sure that we are consistent. is there any argument against using http://www.subdomain.domain.com?