All applications that provide communication between computers on the Internet use IP addresses to identify communicating hosts. However, IP addresses are difficult for human users to remember. That is why we use the name of a network interface instead of an IP address. For each IP address, there is the name of a network interface (computer)—or to be exact, a domain name. This domain name can be used in all commands where it is possible to use an IP address. (One exception where only an IP address can be used is the specification of an actual name server.) A single IP address can have several domain names affiliated with it.
The relationship between the name of a computer and an IP address is defined in the Domain Name System (DNS) database. The DNS database is distributed worldwide. It contains individual records that are called Resource Records (RR) . Individual parts of the DNS database called zones are placed on particular name servers...