September 12, 2009
If you've ever used Plesk to create a sub-domain, you may have run into a quirk, depending on how it was configured by your ISP.
In some configurations, if you use Plesk's regular sub-domain functionality, it creates the root of the sub-domain in a directory below the root of the main domain. Which means that "sub.foo.com" can also be accessed via "foo.com/sub". Sometimes this is ok but, usually, it is not what you intended.
Aside from the navigational weirdness this allows, it could also trick Google into thinking you 're posting duplicate content since the same stuff will be available at two URLs.
So how do you work around this? Simple: don't create it as a sub-domain. Create a new top-level domain, but where you would normally enter something like "foo.com", instead enter "sub.foo.com". Be sure that the checkbox next to "WWW" is not checked.
Other than that, configure it as you would any domain. You will now have a true, blue, top-level sub-domain. I'n not sure this is a "correct" way to make a sub-domain, but it seems to work just fine and doesn't allow the weirdness that putting the sub-domain beneath the root of the main domain causes.
Hope this helps someone. BTW, if you know of a better way to do this. Please let me know.