Computers use IP addresses to connect to one another. When you type a web address in your browser, your Mac routes the domain address through a Domain Name System (DNS), the DNS translates the human-friendly web address into a computer-friendly IP address.
Every ISP usually has their own DNS server, but it’s not always the fastest. Also third-party DNS servers can also have other advantages, like content filtering. Google Public DNS and OpenDNS are probably the best free DNS server you may consider as great alternatives to the DNS server offered by your ISP.
In most cases, the IP addresses used by your ISP’s domain name servers are automatically set by your ISP via the Dynamic Host Configuration Protocol (DHCP).
Configuring your network DNS settings on Mac
Before you change your DNS settings on Mac computer, be sure to write down the current server addresses or settings on a piece of paper. It is very important that you keep these numbers for backup purposes, in case you need to revert to them at any time.
Changing DNS server settings on Mac OS X
1. From the Apple menu, click System Preferences, then click Network.
2. If the lock icon in the lower left-hand corner of the window is locked, click the icon to make changes, and when prompted to authenticate, enter your password.
3. Select the connection for which you want to configure its DNS. For instance
To change the settings for an Ethernet connection, select Built-In Ethernet, and click Advanced.
To change the settings for a wireless connection, select Airport, and click Advanced.
4. Select the DNS tab.
5. Click + to replace any listed addresses with, or add, the new IP addresses at the top of the list.
6. Click Apply and OK.
7. Test that your DNS setup is working properly.