Domain Name System (DNS) and its ability to translate names to IP addresses and back. The DNS that you may already be aware of, even if you don’t actively think about it, is the one used to translate names to IPs on the Internet. DNS is incredibly powerful and easy to use, but at the end of the day it is simply a database that contains name-to-IP mappings that can be queried by any DNS-aware applications.
The Internet root servers, or top-level servers, include the addresses of the DNS servers for all of the top-level domains, such as .com and .org. Each top-level server contains a DNS database of all the names and addresses in that domain.
Local networks that are isolated from the Internet may use their own domain name systems. These translate only the names and addresses that are on the local network. They often use DNS management software and protocols, which are similar or identical to those used by the Internet implementation.