DNS stands for “domain name system.” Domain names are the human-readable website addresses we use every day. For example, Google’s domain name is google.com. If you want to visit Google, you just need to enter google.com into your web browser’s address bar.
However, your computer doesn’t understand where “google.com” is. Behind the scenes, the Internet and other networks use numerical IP addresses (“Internet protocol” addresses). Google.com is located at the IP address 173.194.39.78 on the Internet. If you typed this number into your web browser’s address bar, you’d also end up at Google’s website.
We use google.com instead of 173.194.39.78 because addresses like google.com are more meaningful and easier for us to remember. DNS is often explained as being like a phone book – like a phone book, DNS matches human-readable names to numbers that machines can more easily understand.
Domain name system servers match domain names like google.com to their associated IP addresses — 173.194.39.78 in the case of google.com. When you type google.com into your web browser’s address bar, your computer contacts your current DNS server and asks what IP address is associated with google.com. Your computer then connects to the IP address and displays “google.com” in your web browser – the connection to 173.194.39.78 happens behind the scenes.
The DNS servers you use are likely provided by your Internet service provider (“ISP”). If you’re behind a router, your computer is likely using your router as your DNS server, but the router is likely forwarding requests to your Internet service provider’s DNS servers.
Computers cache DNS responses, so the DNS request doesn’t happen each time you connect to google.com. Once your computer has determined the IP address associated with a domain name, it will remember that for a period of time – this improves connection speed by skipping the DNS request phase. Your computer just needs to connect to Google, not its DNS server and then Google.
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