All domain names on the Internet can be regarded as ending in a full stop character e.g. "www.example.com.". This final dot is generally implied rather than explicit, as modern DNS software does not actually require that the final dot be included when attempting to translate a domain name to an IP address. The empty string after the final dot is called the root domain, and all other domains (.com, .org, .net, and so on) are contained within the root domain.
When a computer on the Internet wants to resolve a domain name, it works from right to left, asking each name server in turn about the element to its left. The root name servers (which have responsibility for the . domain) know which servers are responsible for the top-level domains. Each top-level domain (such as .com) has its own set of servers, which in turn delegate to the name servers responsible for individual domain names (such as example.com), which in turn answer queries for IP addresses of subdomains or hosts (such as www).
In practice, most of this information does not change very often and gets cached, and necessary DNS lookups to the root nameservers are relatively rare. A survey from 2003 found that only 2% of all queries to the root servers were legitimate. Incorrect or non-existent caching was responsible for 75% of the queries, 12.5% were for unknown TLDs, 7% were for lookups using IP addresses as if they were domain names, etc. Some misconfigured desktop computers even tried to update the root server records for the TLDs, which is incorrect. A similar list of observed problems and recommended fixes can be found in RFC 4697.
There are currently 13 root name servers specified, with names in the form letter.root-servers.net, where letter ranges from A to M. (Seven of these are not actual single servers, but represent several physical servers each in multiple geographical locations; cf. below.):
|Letter||IPv4 address||IPv6 address||Old name||Operator||Location||Software|
|A||220.127.116.11||2001:503:ba3e::2:30||ns.internic.net||VeriSign||Dulles, Virginia, U.S.||BIND|
|B||18.104.22.168||2001:478:65::53||ns1.isi.edu||USC-ISI||Marina Del Rey, California, U.S.||BIND|
|C||22.214.171.124||c.psi.net||Cogent Communications||distributed using anycast||BIND|
|D||126.96.36.199||terp.umd.edu||University of Maryland||College Park, Maryland, U.S.||BIND|
|E||188.8.131.52||ns.nasa.gov||NASA||Mountain View, California, U.S.||BIND|
|F||184.108.40.206||2001:500:2f::f||ns.isc.org||ISC||distributed using anycast||BIND|
|G||220.127.116.11||ns.nic.ddn.mil||Defense Information Systems Agency||Columbus, Ohio, U.S.||BIND|
|H||18.104.22.168||2001:500:1::803f:235||aos.arl.army.mil||U.S. Army Research Lab||Aberdeen Proving Ground, Maryland, U.S.||NSD|
|I||22.214.171.124||2001:7fe::53 (testing)||nic.nordu.net||Autonomica||distributed using anycast||BIND|
|J||126.96.36.199||2001:503:C27::2:30||VeriSign||distributed using anycast||BIND|
|K||188.8.131.52||2001:7fd::1||RIPE NCC||distributed using anycast||NSD|
|L||184.108.40.206 (since November 2007; was 220.127.116.11)||2001:500:3::42||ICANN||distributed using anycast||NSD|
|M||18.104.22.168||2001:dc3::35||WIDE Project||distributed using anycast||BIND|
No more names are added because of limitations in the original DNS specification, which specifies a maximum packet size of 512 bytes using the User Datagram Protocol(UDP). This restriction existed because the minimum IP packet size that was required to be transmitted without fragmentation was 576 bytes. The DNS priming exchange is getting close to 512 bytes. However, the C, F, I, J, K, L and M servers now exist in multiple locations on different continents, using anycast address announcements to provide decentralized service. As a result most of the physical, rather than nominal, root servers are now outside the United States.
There are also quite a few alternative namespace systems with their own set of root nameservers that exist in opposition to the mainstream nameservers. The first, AlterNIC, generated a substantial amount of press. See Alternative DNS root for more information.
Root name servers may also be run locally, on provider or other types of networks, synchronized with the US Department of Commerce delegated root zone file as published by ICANN. Such a server is not an alternative root, but a local implementation of A through M.
As the root nameservers function as an important part of the Internet, they have come under attack several times, although none of the attacks have ever been serious enough to severely hamper the performance of the Internet.
Internet Systems Consortium, NIC Mexico, Prodigy Data Center, Avantel and Alestra install the first Root Nameserver in Mexico.(Mexico)(Brief Article)
Apr 01, 2004; Internet Systems Consortium (ISC), NIC Mexico, Prodigy Data Center, Avantel, and Alestra have installed the first Root Nameserver...
Internet Systems Consortium and FCCN install new F-root mirror in Portugal.(Portugal)(Internet Systems Consortium)(Fundacao para a Computacao Cientifica Nacional)(Portuguese Academic & Research Network)(Portugal Internet Exchange)
May 01, 2004; Internet Systems Consortium (ISC) and FCCN have installed a new F-root nameserver in Lisbon, Portugal. The new server was...