Name server
Encyclopedia
In computing
, a name server (also spelled nameserver) is a program or computer server
that implements a name-service protocol. It maps
a human-recognizable identifier to a system-internal, often numeric, identification or addressing component.
The most prominent types of name servers in operation today are the name servers of the Domain Name System
(DNS), one of the two principal name spaces of the Internet
. The most important function of these DNS servers is the translation (resolution) of humanly memorable domain name
s and hostname
s into the corresponding numeric Internet Protocol
(IP) addresses, the second principal Internet name space which is used to identify and locate computer systems and resources on the Internet.
s, the domain name hierarchy and the Internet Protocol
(IP) address system. The Domain Name System
maintains the domain namespace and provides translation services between these two namespaces. Internet name servers implement the Domain Name System. A DNS name server is a server that stores the DNS records, such as address (A, AAAA) records, name server (NS) records, and mail exchanger (MX) records for a domain name (see also List of DNS record types) and responds with answers to queries against its database.
The top hierarchy of the Internet Domain Name System is served by the root name servers
maintained by delegation by the Internet Corporation for Assigned Names and Numbers (ICANN).
. An authoritative-only name server only returns answers to queries about domain names that have been specifically configured by the administrator. Name servers can also be configured to give authoritative answers to queries in some zones, while acting as a caching name server for all other zones.
An authoritative name server can either be a master server or a slave server. A master server for a zone is the server that stores the definitive versions of all records in that zone. A slave server for a zone uses an automatic updating mechanism to maintain an identical copy of the master records. Examples of such mechanisms include DNS zone transfers and file transfer protocols. DNS provides a mechanism whereby the master for a zone can notify all the known slaves for that zone when the contents of the zone have changed. The contents of a zone are either manually configured by an administrator, or managed using Dynamic DNS
.
Every domain name
appears in a zone served by one or more authoritative name servers. The fully qualified domain names of the authoritative name servers of a zone are listed in the NS records of that zone. If the server for a zone is not also authoritative for its parent zone, the server for the parent zone must be configured with a delegation for the zone.
When a domain is registered with a domain name registrar
, the zone administrator provides a list of name servers (typically at least two, for redundancy) that are authoritative for the zone that contains the domain. The registrar provides the names of these servers to the domain registry for the top level domain containing the zone. The domain registry in turn configures the authoritative name servers for that top level domain with delegations for each server for the zone. If the fully qualified domain name of any name server for a zone appears within that zone, the zone administrator provides IP addresses for that name server, which are installed in the parent zone as glue records; otherwise, the delegation consists of the list of NS records for that zone.
of the Domain Name System and each user system must implement resolver software capable of recursive operation.
Caching name servers, also called DNS caches, store DNS query results for a period of time determined in the configuration (time-to-live) of each domain name record. DNS caches improve the efficiency of the DNS by reducing DNS traffic across the Internet, and by reducing load on authoritative name servers, particularly root name servers. Because they can answer questions more quickly, they also increase the performance of end-user applications that use the DNS.
Recursive name servers resolve any query they receive, even if they are not authoritative for the question being asked, by consulting the server or servers that are authoritative for the question.
Caching name servers are often also recursive name servers—they perform every step necessary to answer any DNS query they receive. To do this the name server queries each authoritative name server in turn, starting from the DNS root zone. It continues until it reaches the authoritative server for the zone that contains the queried domain name. That server provides the answer to the question, or definitively says it can't be answered, and the caching resolver then returns this response to the client that asked the question.
The authority, resolving and caching functions can all be present in a DNS server implementation, but this is not required: a DNS server can implement any one of these functions alone, without implementing the others.
Internet service providers typically provide caching resolvers for their customers. In addition, many home networking routers implement caching resolvers to improve efficiency in the local network.
networks where one host can take the role of NetBIOS
browse master and act as a NBNS server. Small local networks
of Windows systems require no central name server, and generally perform name-resolution using a broadcast
algorithm.
There is also Windows Internet Name Service (WINS), which is effectively the same to NetBIOS names what DNS is to domain names.
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, a name server (also spelled nameserver) is a program or computer server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
that implements a name-service protocol. It maps
Associative array
In computer science, an associative array is an abstract data type composed of a collection of pairs, such that each possible key appears at most once in the collection....
a human-recognizable identifier to a system-internal, often numeric, identification or addressing component.
The most prominent types of name servers in operation today are the name servers of the Domain Name System
Domain name system
The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
(DNS), one of the two principal name spaces of the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
. The most important function of these DNS servers is the translation (resolution) of humanly memorable domain name
Domain name
A domain name is an identification string that defines a realm of administrative autonomy, authority, or control in the Internet. Domain names are formed by the rules and procedures of the Domain Name System ....
s and hostname
Hostname
A hostname is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet...
s into the corresponding numeric Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) addresses, the second principal Internet name space which is used to identify and locate computer systems and resources on the Internet.
Domain Name System
The Internet maintains two principal namespaceNamespace
In general, a namespace is a container that provides context for the identifiers it holds, and allows the disambiguation of homonym identifiers residing in different namespaces....
s, the domain name hierarchy and the Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) address system. The Domain Name System
Domain name system
The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
maintains the domain namespace and provides translation services between these two namespaces. Internet name servers implement the Domain Name System. A DNS name server is a server that stores the DNS records, such as address (A, AAAA) records, name server (NS) records, and mail exchanger (MX) records for a domain name (see also List of DNS record types) and responds with answers to queries against its database.
The top hierarchy of the Internet Domain Name System is served by the root name servers
Root nameserver
A root name server is a name server for the Domain Name System's root zone. It directly answers requests for records in the root zone and answers other requests returning a list of the designated authoritative name servers for the appropriate top-level domain...
maintained by delegation by the Internet Corporation for Assigned Names and Numbers (ICANN).
Authoritative name server
An authoritative name server is a name server that gives answers in response to questions asked about names in a zonesDNS zone
A DNS zone is a portion of the global Domain Name System namespace for which administrative responsibility has been delegated.-Definition:...
. An authoritative-only name server only returns answers to queries about domain names that have been specifically configured by the administrator. Name servers can also be configured to give authoritative answers to queries in some zones, while acting as a caching name server for all other zones.
An authoritative name server can either be a master server or a slave server. A master server for a zone is the server that stores the definitive versions of all records in that zone. A slave server for a zone uses an automatic updating mechanism to maintain an identical copy of the master records. Examples of such mechanisms include DNS zone transfers and file transfer protocols. DNS provides a mechanism whereby the master for a zone can notify all the known slaves for that zone when the contents of the zone have changed. The contents of a zone are either manually configured by an administrator, or managed using Dynamic DNS
Dynamic DNS
Dynamic DNS or DDNS is a term used for the updating in real time of Internet Domain Name System name servers to keep up to date the active DNS configuration of their configured hostnames, addresses and other information....
.
Every domain name
Domain name
A domain name is an identification string that defines a realm of administrative autonomy, authority, or control in the Internet. Domain names are formed by the rules and procedures of the Domain Name System ....
appears in a zone served by one or more authoritative name servers. The fully qualified domain names of the authoritative name servers of a zone are listed in the NS records of that zone. If the server for a zone is not also authoritative for its parent zone, the server for the parent zone must be configured with a delegation for the zone.
When a domain is registered with a domain name registrar
Domain name registrar
A domain name registrar is an organization or commercial entity, accredited by both ICANN and generic top-level domain registry to sell gTLDs and/or by a country code top-level domain registry to sell ccTLDs; to manage the reservation of Internet domain names in accordance with the guidelines of...
, the zone administrator provides a list of name servers (typically at least two, for redundancy) that are authoritative for the zone that contains the domain. The registrar provides the names of these servers to the domain registry for the top level domain containing the zone. The domain registry in turn configures the authoritative name servers for that top level domain with delegations for each server for the zone. If the fully qualified domain name of any name server for a zone appears within that zone, the zone administrator provides IP addresses for that name server, which are installed in the parent zone as glue records; otherwise, the delegation consists of the list of NS records for that zone.
Authoritative answer
A name server indicates that its response is authoritative by setting the Authoritative Answer (AA) bit in the response to a query on a name for which it is authoritative. Name servers providing answers for which they are not authoritative (for example, name servers for parent zones), do not set the AA bit.Recursive and caching name server
In principle, authoritative name servers are sufficient for the operation of the Internet. However, with only authoritative name servers operating, every DNS query must start with recursive queries at the root zoneDNS root zone
A DNS root zone is the top-level DNS zone in a Domain Name System hierarchy. Most commonly it refers to the root zone of the largest global DNS, deployed for the Internet. Ultimate authority over the DNS root zone rests with the US Department of Commerce NTIA...
of the Domain Name System and each user system must implement resolver software capable of recursive operation.
Caching name servers, also called DNS caches, store DNS query results for a period of time determined in the configuration (time-to-live) of each domain name record. DNS caches improve the efficiency of the DNS by reducing DNS traffic across the Internet, and by reducing load on authoritative name servers, particularly root name servers. Because they can answer questions more quickly, they also increase the performance of end-user applications that use the DNS.
Recursive name servers resolve any query they receive, even if they are not authoritative for the question being asked, by consulting the server or servers that are authoritative for the question.
Caching name servers are often also recursive name servers—they perform every step necessary to answer any DNS query they receive. To do this the name server queries each authoritative name server in turn, starting from the DNS root zone. It continues until it reaches the authoritative server for the zone that contains the queried domain name. That server provides the answer to the question, or definitively says it can't be answered, and the caching resolver then returns this response to the client that asked the question.
The authority, resolving and caching functions can all be present in a DNS server implementation, but this is not required: a DNS server can implement any one of these functions alone, without implementing the others.
Internet service providers typically provide caching resolvers for their customers. In addition, many home networking routers implement caching resolvers to improve efficiency in the local network.
Microsoft networking
Name servers also exist on some Microsoft WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
networks where one host can take the role of NetBIOS
NetBIOS
NetBIOS is an acronym for Network Basic Input/Output System. It provides services related to the session layer of the OSI model allowing applications on separate computers to communicate over a local area network. As strictly an API, NetBIOS is not a networking protocol...
browse master and act as a NBNS server. Small local networks
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
of Windows systems require no central name server, and generally perform name-resolution using a broadcast
Broadcasting (networks)
right|250pxIn telecommunication and information theory, broadcasting refers to a method of transferring a message to all recipients simultaneously...
algorithm.
There is also Windows Internet Name Service (WINS), which is effectively the same to NetBIOS names what DNS is to domain names.
See also
- BINDBINDBIND , or named , is the most widely used DNS software on the Internet.On Unix-like operating systems it is the de facto standard.Originally written by four graduate students at the Computer Systems Research Group at the University of California, Berkeley , the name originates as an acronym from...
- Comparison of DNS server softwareComparison of DNS server softwareThis article presents a comparison of the features, platform support, and packaging of independent implementations of Domain Name System name server software.- Servers compared :...
- Directory serviceDirectory serviceA directory service is the software system that stores, organizes and provides access to information in a directory. In software engineering, a directory is a map between names and values. It allows the lookup of values given a name, similar to a dictionary...
- DNS Security Extensions (DNSSEC)
- Lightweight Directory Access ProtocolLightweight Directory Access ProtocolThe Lightweight Directory Access Protocol is an application protocol for accessing and maintaining distributed directory information services over an Internet Protocol network...
(LDAP) - Network Information ServiceNetwork Information ServiceThe Network Information Service, or NIS is a client–server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network...
(NIS) - Name Service SwitchName Service SwitchThe Name Service Switch is a facility in Unix-like operating systems that provides a variety of sources for common configuration databases and name resolution mechanisms...
(NSS) - resolver, resolv.confResolv.confresolv.conf is the name of a computer file used in various operating systems to configure the Domain Name System resolver library. The file is a plain-text file usually created by the network administrator or by applications that manage the configuration tasks of the system...
, resolvconfResolvconfIn some Linux distributions and related computer operating systems, the resolvconf program maintains the system information about the currently available nameservers and manages the contents of the configuration file resolv.conf, which determines Domain Name System resolver parameters.Before a...
for UnixUnixUnix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
/LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
- OpenNICOpenNICOpenNIC is an alternate network information center/alternative DNS root which lists itself as an alternative to ICANN and its registries. users of the OpenNIC DNS servers are able to resolve all existing ICANN top-level domains as well as their own....
- DNS AdvantageDNS AdvantageDNS Advantage is a proprietary opt-in DNS service. It does not follow internet standards—for example, the component of its service that implements typographical checking constitutes DNS hijacking.-Services:...
- OpenDNSOpenDNSOpenDNS is a DNS resolution service. OpenDNS extends DNS adding features such as misspelling correction, phishing protection, and optional content filtering...
- Google Public DNSGoogle Public DNSGoogle Public DNS is a freely provided closed-source DNS service announced on 3 December 2009, as part of Google's self-proclaimed effort to make the web faster....
- Open Root Server NetworkOpen Root Server NetworkOpen Root Server Network was a network of root nameservers for the Internet, operating from February 2002 until the end of 2008. Its root zone information was normally kept in synchronization with that of the network coordinated by ICANN. The networks were thus compatible, although ORSN was...
- RealNamesRealNamesRealNames was a company founded in 1997 by Keith Teare. Its goal was to create a multilingual keyword-based naming system for the Internet that would translate keywords typed into the address bar of Microsoft's Internet Explorer web browser to Uniform Resource Identifiers, based on the existing...