As a webpage becomes more feature-rich it often uses more DNS lookups which makes it render much slower.
DNS stands for "Domain name system". For any resource to be downloaded for your page, the browser must "look it up". The browser must do this at least once for each domain your webpage is receiving resources from.
This process can slow down your webpage considerably and one of the most important decisions you can make about your pagespeed is how many DNS lookups are too much.
A very small webpage that should load in one second, can become a monster webpage that takes 3 or 6 seconds to download, simply because of additional DNS lookups. If you are experiencing slow page loads, see how many DNS lookups your webpage requires and see why you are using whatever you are.
One example of this might be a social button (facebook / twitter/ google +) these social buttons may request one or more other resources that you don't really think about which can add even more DNS lookups. Many features of a modern webpage are resource heavy and call different domains to do their job. Another example of this is Google webfonts. They actually require two DNS lookups.
To get a good idea of what your webpage is asking for overall is one of the first steps in creating a faster more enjoyable page for your users. A great starting point is the request checker tool which tells you how many requests your webpage is making.
Is a webfont worth an extra half a second? Sometimes yes, sometimes no. Are social buttons more important than pagespeed? Depends.
Creating a good balance between pagespeed and DNS lookups is mostly a matter of deciding what is important for you webpage.
See how many requests your page is loading with our resource check tool.
Go to Webpagetest.org and test your page there. It will display how many requests your webpage is making. Look carefully at the results and count the DNS lookups.
by Patrick Sexton