at vBSDCon 2013 they explained the immense redundancy and diversity of their NS hosting of .com, .net, and .org. At their POPs they have:<p><pre><code>  * Diverse switches
  * Diverse load balancers
  * Diverse servers (from different mfgrs AND hardware generations)
  * Diverse OSes (Linux &amp; FreeBSD)
  * Diverse DNS software: BIND, NSD, and ATLAS
</code></pre>
I don&#x27;t know how they decide the exact configurations here, but the idea is that a single vulnerability or bug is unlikely to cause a full outage at the POP.<p>The complexity here is immense and they must have a really great system for managing the configurations and replicating DNS changes. It certainly would not be cheap to build.