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Domain Name System

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The Domain Name System (DNS) is a system used to convert a computer's host name into an IP address on the Internet. For example, if a computer needs to communicate with the web server, your computer needs the IP address of the web server It is the job of the DNS to convert the host name to the IP address of the web server. DNS is defined in RFC 1034 and RFC 1035 and use the UDP Port 53 or TCP Port 53.


Domain names are made up of one or more parts, or labels that are joined and kept separate by dots, such as

  • The order goes down from right to left.
  • The label on the right is the top-level domain or TLD. For example, the top-level domain of is com.
  • The next one along is the subsection (or subdomain as is the proper word) of the TLD. In this is example.
  • The furthest to the left is the www which is a subdomain of example. The www means the site is part of the World Wide Web (NOT the same as the Internet [1][2])
  • Each label can have 63 letters/numbers (characters) and a domain name cannot have more than 253 characters.
  • The only characters allowed in a domain name are:
    • az (lower-case)
    • 19 & 0 and
    • Hyphens ( - )