DNS Prefetching

DNS is much like a phone book for the internet. For each domain name (or subdomain like ‘www’), there is an IP address that resembles a phone number. Getting the matching number for each domain can take some time and make your site appear slow, particularly on mobile connections. Fortunately, you can pre-request this information and speed up your site in most cases.

To enable a domains DNS lookup to be performed in advance of the request, you can add a single line to the <head> section of your page.

<link rel="dns-prefetch" href="//giantgeek.com" />

If you want to explicitly turn on (or off) this behavior, you can add one of the following, or their HTTP Header equivalents:

<meta http-equiv="x-dns-prefetch-control" content="on" />
<meta http-equiv="x-dns-prefetch-control" content="off" />

This is supported in all modern browsers:

  • Firefox 3.5+
  • Safari 5.0+
  • MSIE 9.0+

If should be noted that a similar method can be used to prefetch as page, but I will save that for a different article:
<link rel="prefetch" href="http://www.skotfred.com/" />

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