Canonical redirect on IIS using PHP

According to the seo experts of the world, it is good practice to force your website to always use the same domain. So, instead of having your site work at both and, choose one. Once you’ve chosen which form of your site to use, it’s time to setup 301 redirects to enforce that.

If you’re using Apache, it’s very easy, just add a quick mod_rewrite rule. You can remove the www or force the use of www. But since IIS doesn’t use .htaccess files, it takes a little more effort.

Create a php.ini with the following content and upload it to your site root

cgi.force_redirect = 0
auto_prepend_file = C:\php_includes\canonical.php

Keep in mind that you’ll need to change the file path to reflect the setup of your server.

Upload canonical.php with the following contents

// Any directory index filenames should go in here with a leading /
// This is removed when doing the redirect in order to maintain consistency,
// without this, when visiting you would be redirected to
$index_files = array('/index.htm','/index.html','/index.php');

// The rewrite only kicks in if the host does not begin with www. and the code is not running
// on localhost. When developing a site I setup on my dev machine and use
// the same code as is on the live server, so I don't want to be redirected if I'm
// accessing the code locally.
if(substr($_SERVER['HTTP_HOST'],0,4) !== 'www.' && $_SERVER['LOCAL_ADDR'] !== ''){
    $url = 'http://www.'.$_SERVER['HTTP_HOST'].str_replace($index_files, '', $_SERVER['PATH_INFO']);
    header ('HTTP/1.1 301 Moved Permanently');
    header("Location: $url");


  • This method assumes that you don’t have access to modify the server settings, ie: shared windows hosting. If you are able to modify how IIS is setup I’m sure there’s a better way to do this.
  • When PHP is run as a cgi, you can overwrite the php.ini settings by putting a php.ini in the site root. So if your windows host is not running php as a cgi, this won’t work. I think that php is always run as a cgi on IIS, but I could be wrong.
  • This will only work if the site is using PHP – if you have a completely static site this won’t help you. In order to use this with a static site, you’d have to change the server settings to treat your html files as php files.