My movie forum (example) gets some subdomains: movie.com which displays all forums horror.movie.com which displays the general forums and the horror forums Every thread and every forum only belong to one "subdomain" to avoid redundant links. When a user visits a horror movie thread he will be redirected to horror.movie.com/threads/324 if he came from movie.com. If the user accesses the same thread from horror.movie.com the thread will be displayed and he will not be redirected. From a programmers perspective every forum is targeted with a subdomain or with being a general forum (no subdomain) ControllerPublic/Index will check the subdomain (horror.movie.com or movie.com) and manipulates the forum list to either only display horror movies (along with the general forums) or display everything when accessed from movie.com ControllerPublic/Forum will 1. check the database and manipulate the thread target url (adds "horror." to some threads) and when accessed from movie.com/forums 2. checks against being accessed within the right subforum and if not it will send out a redirect to display the forum on horror.movie.com/forums ControllerPublic/LinkForum same as Forum ControllerPublic/Thread will check the database and do the same as for the ControllerPublic/Forum. And of course do something within the models like: getThreadRedirectById ControllerPublic/Post same as Thread Are there cookie problems and other things to care about?