phranque - 8:58 am on Aug 31, 2011 (gmt 0)
welcome to WebmasterWorld, anticipation!
you can only have a single robots.txt file per hostname and it must be in that site's root document directory.
But whenever i visit forum.mysite.com the url is same. On clicking internal links, it turns out to be mysite.com/forum/somelink
this is the problem you must resolve.
all your internal links must refer to the forum subdomain and any external requests for the forum subdirectory must be 301-redirected to the forum subdomain.
except then i found this gem in the vbulletin documentation...
We do not currently support subdomains due to the way vBulletin handles AJAX calls and cookies.