I was reviewing the waterfall results from a WebPageTest.org test recently and I came across a third party resource that look 5 seconds to do a DNS lookup:

To be exact it took 5.031 seconds. The parameters of the test itself were nothing exciting, Chrome from Virginia with the “Cable” network profile ( 5/1 Mbps, 28 ms RTT ). The DNS lookup for the initial page request only took 0.059 seconds, so this wasn’t a function of the test parameters.

When you see an entry like that it is a good reminder not to take DNS performance for granted.