Magento: Stop domain redirect with multistores

I'm currently trying to set up multistores for a magento site on our dev site.

I have two stores, the main store and the french store, with the following domain setup:

main store: main.devsite.com

french store: mainfr.devsite.com

I have a vhost set up for main.devsite.com. In this vhost, I have set up a serverAlias for m开发者_JAVA技巧ainfr.devsite.com.

Then, within the index.php I have the following code snippet.

$serverName = explode('.',$_SERVER['SERVER_NAME']);
if($serverName[0] == "mainfr") {
    mage::run("fr", "website");
} else {
    Mage::run($mageRunCode, $mageRunType);
}

The problem I have here is that magento seems to automatically redirect mainfr.devsite.net to main.devsite.net when Mage::run() is called.

Is there a way to stop this happening?

you need to add store and website in magento backend ... System > Manage Stores and set your stores' base urls both got secure and insecure? should just work at the moment all request is being taken to the default site I think