apache 2.2 - Rewriting main domain to subdomain (mod_rewrite)

So I'm trying to write a mod_rewrite rule that will send everything on my main domain to a subdomain.

For example, redirect

http://example.com/1/2/3/4/5?n=6&i=7

to

http://sub.example.com/1/2/3/4/5?n=6&i=7

Here's what I have so far:

RewriteEngine On
RewriteCond ^http://www\.example.com\/ [NC]
RewriteRule ^(.*)$ http://sub.example.com/$1 [R=301,L]

But it doesn't seem to working. Any tips?