Useful Facts About the Domain Name System (DNS)

Two papers by Paul Mockapetris published in November ​1983 - called RFC 882 and RFC 883 - marked the beginning of DNS. Before DNS, a public system could be identified only by its host name, and the addresses for all of these hostnames were maintained in one large file (called “hosts.txt”) that became impossibly difficult to manage as computer networks grew during the 1970s and 1980s. The DNS expanded this single-level naming system to a multi-level one by adding support domains – one or more additional names appended to the host name, each separated by a dot (.).

More than 700 top-level domains (TLDs) now exist on the Internet (including some especially odd names like .rocks and .soy). The non-profit governing body Internet Corporation for Assigned Names and Numbers (ICANN) controls their allocation - see the ICANN list of top-level domains.

When first implemented in the 1980s, however, DNS defined only six TLDs - .com, .edu, .gov, .mil, .net and .org. The huge expansion in domain name choices began in 2011 with the goal of better classifying Web sites according to their purpose.

More: Internet Top-Level Domains (TLDs) Explained

Many Internet domain names like “about.com” and “mit.edu” are affiliated with schools or businesses, while individuals register others for personal purposes. Altogether more than 100 million registered domains exist under .com alone. These and other interesting DNS statistics can be found at DomainTools Internet Statistics.

Most requests to the DNS involve converting the host names of Web sites and other Internet servers to IP addresses, so-called forward DNS lookups. DNS also works in the reverse direction, translating addresses to names. While reverse DNS lookups are less commonly used, they help network administrators with troubleshooting.  Utilities like ping and traceroute perform reverse lookups, for example.

More: Forward and Reverse IP Address Lookups

The DNS organizes its name servers into a hierarchy to help optimize communication flow between the servers and also to make system maintenance easier. All hierarchical systems like the DNS create a top level (called the “root” level) from where lower levels can branch out. For technical reasons, today’s DNS supports 13 root name servers rather than just one. Each of these roots, interestingly, is named by a single letter – starting with ‘A’ and extending to the letter ‘M’. (Note that these systems belong to the root-servers.net Internet domain, making their fully-qualified names like "a.root-servers.net," for example.)

More: The 13 DNS Root Name Servers

Stories of DNS hijacking incidents appear in the news much too often. Hijacking entails a hacker gaining access to the DNS server records for a targeted Web site and modifying them to redirect visitors to someone else's site instead, When an Internet user goes to visit a hijacked site, the DNS instructs their browser to request data it's from the bogus location. Note that attackers generally do not need to break into the DNS itself but can instead compromise the domain's hosting service by impersonating as Web administrators.