The HTTP DNS Prefetch header

This can be used in server config, .htaccess or even a webpage.

It tells the browser to lookup a new domain name that will be used soon, e.g.say in an AJAX call, or on rest of the website, it can be your domain name, or someone elses.

<link rel="dns-prefetch" href="http://images.example.com/">
<link rel="dns-prefetch" href="http://maps.google.com/">
<link rel="dns-prefetch" href="http://www.cdnjs.com/">