How to make an invite only forum

hi everybody I'm wondering if there is a forum software (or forum plugin) that makes it possible to have an invite only forum. What I mean is that if you aren't registered or logged in, you can not view the forums. Instead, the user would be redirected to the registration page and informed that they can not access the forums without registering, and in order to register, they need an invitation from another member. It would be like Turntable - US only Vanilla Forums (Vanilla - Free, Open-Source Forum Software) has a feature that let's you set registration to invitation only, but I'm having trouble getting the homepage to redirect to a registration/login page for new users who haven't registered/loged in yet. Does anyone have any advice on how to do this? UPDATE: I figured it out: you need to use this plugin: Private Community 1.0 by Tim - Vanilla Forums

 

Make your forum invisible by having it viewable ONLY to registered members.

Then create a forum just for guests.Where you can then make it possible for people to register and join.