Root server

A root name server is a name server for the root zone of the Domain Name System (DNS) of the Internet. It directly answers requests for records in the root zone and answers other requests by returning a list of the authoritative name servers for the appropriate top-level domain (TLD). The root name servers are a critical part of the Internet infrastructure because they are the first step in translating (resolving) human readable host names into IP addresses that are used in communication between Internet hosts.

A combination of limits in the DNS and certain protocols, namely the practical size of unfragmented (UDP) packets, resulted in a decision to limit the number of root servers to thirteen server addresses. The use of anycast addressing permits the actual number of root server instances to be much larger, and is 632 as of 25 October 2016^[update].

The DNS is a hierarchical naming system for computers, services, or any resource participating in the Internet. The top of that hierarchy is the root domain. The root domain does not have a formal name and its label in the DNS hierarchy is an empty string. All fully qualified domain names (FQDNs) on the Internet can be regarded as ending with this empty string for the root domain, and therefore ending in a full stop character (the label delimiter), e.g., "www.example.com.". This is generally implied rather than explicit, as modern DNS software does not actually require that the terminating dot be included when attempting to translate a domain name to an IP address.

The root domain contains all top-level domains of the Internet. As of July 2015^[update], it contains 1058 TLDs, including 730 generic top-level domains (gTLDs) and 301 country code top-level domains (ccTLDs) in the root domain. In addition, the ARPA domain is used for technical name spaces in the management of Internet addressing and other resources. A TEST domain is used for testing internationalized domain names.

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