Several of my clients created an "A" record to point a sub domain of their site to my server. E.g., http://subdomain.clientsite.com points to my IP address.
This works fine. However, if I manually insert a prefix such as "www" to make the URL look like "http://www.subdomain.clientsite.com" it resolves to my website instead of the client's site. I can add anything besides "www" as a prefix.
What is the best way to disable a "sub-subdomain"? It seems like it would be possible to do via the vHost file for each client or perhaps through an .htacess command. However, I don't know the best way to proceed.
Thanks for your thoughts.