Speed Up Your Webpage By Using DNS Prefetching

DNS resolution time can lead to a significant amount of user perceived latency. The time that DNS resolution takes is highly variable. Latency delays range from around 1ms (locally cached results) to commonly reported times of several seconds."
Source: http://www.chromium.org/developers/design-documents/dns-prefetching)

If you have serveral external resources included in your Website DNS prefetching will speed up your website for customers especially for mobile users.

As an example if a script or css file on your page loads images from an external host or cdn and you are using some google services you can use the following tags in your html header to prefetch the dedicated hostname:

<link rel="dns-prefetch" href="//images.some-other-host.com" />
<link rel="dns-prefetch" href="//subdomain.my-cdn.com" />
<link rel="dns-prefetch" href="//ssl.google-analytics.com">
<link rel="dns-prefetch" href="//www.googleadservices.com">
<link rel="dns-prefetch" href="//googleads.g.doubleclick.net">
<link rel="dns-prefetch" href="//www.google.com">