When users want to connect to a network resource such as a web or file server, they typically use a domain name (such as www.example.com) rather than an IP address (such as 192.168.12.12). The Domain Name System (DNS) is a distributed database that maps IP addresses to domain names so users can find the resources by name rather than numerical address.
A DNS server keeps a list of domain names and the IP addresses associated with each name. When a computer needs to find the IP address for a name, it sends a message to the DNS server, also known as a name server.
The name server looks up the IP address and sends it back to the computer. If the name server doesn’t have the IP address locally, it sends messages to other name servers on the Internet until the IP address is found.
Setting up and maintaining a DNS server is a complex process. Therefore, many administrators rely on their ISP to provide DNS service for their external IP addresses. In this case, you only need to configure your network preferences with the IP address of the name server, which is provided by your ISP. Your ISP doesn’t provide DNS service for your internal local network. If you need DNS service on your local network, you must set up your own DNS service. Mail service and Open Directory require DNS to be set up to function properly.
OS X Server uses Berkeley Internet Name Domain (BIND) v9.4.1 for its implementation of DNS protocols. BIND is an open source implementation and is used by most name servers on the Internet.