Root nameserver
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A root nameserver is a DNS server that answers requests for the root namespace domain, and redirects requests for a particular top-level domain to that TLD's nameservers. Although any local implementation of DNS can implement its own private root nameservers, the term "root nameserver" is generally used to describe the thirteen well-known root nameservers that implement the root namespace domain for the Internet's official global implementation of the Domain Name System.
All domain names on the Internet can be regarded as ending in a full stop character -- Wikipedia, for example, is actually hosted on the domain "www.wikipedia.org." ([try it]). 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 (i.e. .com, .org, .net, etc.) 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 nameserver in turn about the element to its left. The root nameservers (which have responsibility for the . domain) know about which servers are responsible for the top-level domains. Each top-level domain (such as .org) has its own set of servers, which in turn delegate to the nameservers responsible for individual domain names (such as wikipedia.org), which in turn answer queries for IP addresses of subdomains or hosts (such as www).
In practice, most of this information doesn't change very often and gets cached, and necessary DNS lookups to the root nameservers are relatively rare. However, there are a lot of incorrectly configured systems on the Internet that cause most of the traffic to the root servers. For example, queries with the source address 0.0.0.0 (corresponding to anywhere and everywhere) make it to the root servers. Also, misconfigured desktop computers sometimes try to update the root server records for the TLDs, which is incorrect. See the Bogus Queries in the external links for more amusing stories.
There are currently 13 root name servers, with names in the form letter.root-servers.net where letter ranges from A to M :
| Letter | Old name | Operator | Location |
|---|---|---|---|
| A | ns.internic.net | VeriSign | Dulles, Virginia, USA |
| B | ns1.isi.edu | ISI | Marina Del Rey, California, USA |
| C | c.psi.net | Cogent Communications | distributed using anycast |
| D | terp.umd.edu | University of Maryland | College Park, Maryland, USA |
| E | ns.nasa.gov | NASA | Mountain View, California, USA |
| F | ns.isc.org | ISC | distributed using anycast |
| G | ns.nic.ddn.mil | U.S. DoD NIC | Columbus, Ohio, USA |
| H | aos.arl.army.mil | [U.S. Army Research Lab] | Aberdeen Proving Ground, Maryland, USA |
| I | nic.nordu.net | [Autonomica] | distributed using anycast |
| J | VeriSign | distributed using anycast | |
| K | RIPE NCC | distributed using anycast | |
| L | ICANN | Los Angeles, California, USA | |
| M | WIDE Project | distributed using anycast |
Older servers had their own name before the policy of using similar names was established.
No more names can be used because of protocol limitations - UDP packet can only carry 512 bytes reliably and a hint file with more than 13 servers would be larger than 512 bytes - but the C, F, I, J, K and M servers now exist in multiple locations on different continents, using anycast announcements to provide a decentralized service. As a result most of the physical, rather than nominal, root servers are now outside the United States.
There are 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.
See also
- Anycast
- EDNS0 (Extended DNS, version 0)
- 2002 DNS Backbone DDoS
External links
- [Root Server Technical Operations Association]
- [DNS Root Server System Advisory Committee]
- [Location of Root servers in Asia-Pacific]
- [Bogus Queries received at the Root Servers]
- [ORSN, Open Root Server Network with IPv6 support in europe]
- [World map showing the location of all 13 servers.]
- RFC 2826 - IAB Technical Comment on the Unique DNS Root
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