# DNS Domain Name System

The Domain Name System (DNS) is a service of the Internet. It acts as a distributed database that maps domain names and IP addresses to each other, making it easier for people to access the Internet. DNS uses TCP and UDP ports 53. Currently, each level of a domain name contains 63 characters, and the total length of a domain name cannot exceed 253 characters.

Initially, domain names are limited to a subset of ASCII characters. In 2008, ICANN passed a resolution allowing the use of other languages as characters for Internet top-level domains. Using the Punycode-based IDNA system, Unicode strings can be mapped to a valid DNS character set. Therefore, domain names such as "XXX. China" and "XXX. USA" can be entered and accessed directly from the address bar without the need to install a plug-in.