Specify a DNS server on Mac
A Domain Name System (DNS) server converts internet names to IP addresses so you don’t have to know the IP address of a server you’re trying to reach. For example, using a DNS server allows you to reach the Apple website by typing “www.apple.com” into your browser—you don’t need to know the IP address of the server the Apple website resides on. In most cases, your computer connects to a DNS server automatically when you connect to the internet, but you can also enter DNS server settings manually.
To find out whether you should connect to a specific DNS server, and what address to use, check with your ISP or network administrator.
On your Mac, choose Apple menu > System Preferences, then click Network.
Select the service you use to connect to the internet (such as Ethernet) in the list at the left.
Make sure the IP address for the DNS server you want to use is entered correctly in the DNS Server field. If the address isn’t correct, click Advanced, click DNS, then enter the correct address.
You can enter addresses for several servers by typing a comma between the addresses.
If you get a message such as “server not found” when you try to visit a website, your computer may be unable to contact a DNS server. If you selected a DNS server manually, you may have entered the wrong DNS server address, or your DNS server may be having problems.