Root Server Definition

A root server is any of the small number domain name system (DNS) servers on the Internet that contain the IP addresses of the top level domain (TLD) registry organizations that maintain the global domains (e.g., .com, .org, net, .gov and .edu) and the country code domains (e.g., .uk, .ca, .cn, .dk, .fr, and .jp).

The domain name system is the network of programs and databases on the Internet that cooperates to translate domain names to IP addresses. A domain name is a name that uniquely identifies a site (e.g., web site or ftp site) on the Internet or other TCP/IP network. Domain names are actually user-friendly substitutes for IP addresses that typically consist of alphabetic characters and consist of words, abbreviations or acronyms.

Also referred to as a root name server, a root server is the first point of entry for resolving (i.e., converting to an IP address) a domain name. It answers requests for the root namespace domain, and redirects requests for a particular top level domain to that TLD's name servers.

The basic role of the DNS root servers is to reliably publish the contents of one small file, called the root zone file, to the Internet. As of December 2004 this file contained 5335 lines of text and had a size of 119KB1.

The root name servers do not store all DNS information. Storing all the information in a single location is not practical, and thus DNS was developed as a distributed database.

There currently are 12 organizations providing root name service at 13 unique IP addresses, designated A through M. The servers are operated at more than 80 locations, which are distributed among 34 countries. Most of them are outside the U.S.

All root server operators have been selected by the IANA (Internet Assigned Numbers Authority). However, IANA does not control the operation of the servers.

Originally, a master zone file was maintained on the A server, and this file was distributed to the other root servers. However, it was soon realized that this was a point of particular vulnerability, and thus the system was changed so that all of the root servers are equally authoritative.

ISPs (Internet service providers) and other organizations routinely download copies of the root server tables so that name resolution (i.e., the conversion of domain names to IP addresses) can be performed locally. There are thousands of these resolver computers throughout the Internet that keep the main root servers from becoming overloaded.

1A sample of the root zone file can be found at

Created October 24, 2005.
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