Fixit – DNS Lookups

This test determines if your page uses more domain names than best practice recommends. Each unique domain name referenced by a webpage requires an additional DNS lookup, a timely network process that will ultimately slow the page loading. Grouping content on a small number of domains ensures the browser can quickly iterate through DNS lookups and proceed with page loading.

Checking for image sprites

This test checks to see if the tested page requires more than four DNS lookups to load. If enough unique domain names are detected then the test reports a FAIL.

If you receive a FAIL for this test, you should consider reducing the number of unique domains used.

Reference

This test is based on a YSlow best practice. See http://yslow.org/faq/ for more details.