apache - domain.com/sub redirecting to sub.domain.com/sub -

my main page wordpress, have forum installed on sub-directory. i've set sub-domain @ forum.domain.com.

going sub-domain works fine, going domain.com/forum redirects me forum.subdomain.com/forum tad annoying not website breaking.

i've been fiddling around .htaccess , mod_rewrite stuff i'm new i'll end making lasagna instead of working urls. both homepage wordpress installation , forum have .htaccess files own mod_rewrite stuff.

any help, insight, , enlightenment appreciated.

you should able achieve using rule in root .htaccess:

rewriteengine on rewritebase /   rewritecond %{http_host} !^sub\.domain\.com/sub$ [nc]  rewriterule ^sub/$ http://sub.website.com/sub [l,nc,r=301] 

this rule first checks if you're on subdomain, if are, nothing happens. if not on sub.domain.com/sub redirect it.

make sure clear cache before test this.

edit

i've re-read question number of times , feel above not answer you're looking for. feel you're trying redirect sub.domain.com/sub sub.domain.com ? if case, need use this:

rewriteengine on rewritebase /   rewritecond %{http_host} ^sub\.domain\.com/sub$ [nc]  rewriterule ^sub/$ http://sub.website.com [l,nc,r=301]