The DNS, or Domain Name System, is the protocol that converts domain names to the IP (Internet Protocol) addresses so the browsers can load the necessary resources. DNS servers removes the responsibility for us humans to memorize long IP addresses and numbers, and instead, just remember the domain name. Think of the DNS as a directory or a map that matches names to numbers.
Reduce DNS Lookups
What is DNS?
How DNS Lookups Work
When you land on a website, a DNS lookup must be made for each unique domain requested. For example, there may be 10 HTTP requests, but out of those 10, six have the same domain, so there would be a total of four DNS lookups. If you run a website speed test for a specific web page, you can see this for yourself in the waterfall chart. Each of these DNS lookups need to occur before any content can begin to load. So, while they are completely unavoidable and add load time, it is necessary to reduce DNS lookups, if feasible. As we showed in our previous example, you can see that if your site has a lot of DNS lookups, it can add up quickly.
Avoid Additional DNS Lookups
Now, for repeat visits, this is typically not an issue, as hopefully the DNS has been cached, so it does not have to load every time. This can be set from anywhere from five minutes to 24 hours. Setting an appropriate TTL (time-to-live) value for the DNS cache can help avoid additional DNS lookups. However, these are simply different methods to speed up DNS lookups. To reduce DNS lookups, one of the easiest ways is to simply remove the number of domains. Easier said than done, but if there is an opportunity to remove the number of unique domains or specific resources, especially ones that take a long time to load, it can go a long way to reduce overall page load times.
Lighthouse is an open-source tool that is used to run an audit against your web pages and provides scores and suggestions for improving page performance, accessibility, SEO, and more.
PageSpeed Insights is a tool created by Google that reports on the performance of a page on both mobile and desktop devices, and provides suggestions on how that page may be improved.