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Editorial Team
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Asked: 2026-06-12T20:41:06+00:00

Today I saw this snippet in the HTML source of a webpage: <!– prefetch

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Today I saw this snippet in the HTML source of a webpage:

<!-- prefetch dns -->
<link rel="dns-prefetch" href="//s3.amazonaws.com">
<link rel="dns-prefetch" href="//cdn.api.twitter.com">
<link rel="dns-prefetch" href="//graph.facebook.com">
<link rel="dns-prefetch" href="//connect.facebook.net">
<link rel="dns-prefetch" href="//api.pinterest.com">
<link rel="dns-prefetch" href="//google-analytics.com">

How much can you gain by doing this? I haven’t seen this before, nor in the Yahoo! Developer Networks guidelines for optimization. The only thing that seems related is “Reduce DNS Lookups”.

In a similar fashion, why doesn’t these services expose an IP address to their services and avoid the DNS look-up altogether?

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1 Answer

  1. Editorial Team

    I guess that this gives parallel DNS lookup of those links later used for a bunch of JavaScript’s.

    Direct IP-numbers does not work well with CDN’s. They resolve to a host close to the caller. If you are in the US they give you the IP of a server in US. If you are in Europe they give you the IP of a server in Europe, etc. You can’t cheat like that with direct IP numbers.

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