Name server

In computing, a name server (also spelled nameserver) consists of 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.

For example, on the Internet, a special case of name servers, so called Domain Name System (DNS) servers, are used to translate a hostname or a domain name (for example, 'en.wikipedia.org') to its corresponding binary identifier (the IP address 145.97.39.155), or vice versa.

Domain Name System

The Internet maintains two principal namespaces, the domain name hierarchy^[1] and the Internet Protocol (IP) address system.^[2] The Domain Name System maintains the domain namespace and provides translation services between these two namespaces. Internet name servers implement the Domain Name System.^[3] A DNS name server is a server that stores the DNS records, such as address (A) 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).

Authoritative name server

An authoritative name server is a name server that gives answers that have been configured by an original source, for example, the domain administrator or by dynamic DNS methods, in contrast to answers that were obtained via a regular DNS query to another name server. An authoritative-only name server only returns answers to queries about domain names that have been specifically configured by the administrator.

An authoritative name server can either be a master server or a slave server. A master server is a server that stores the original (master) copies of all zone records. A slave server uses an automatic updating mechanism of the DNS protocol in communication with its master to maintain an identical copy of the master records.

Every domain name must be assigned a set of authoritative name servers that are installed in NS records in the parent domain.

When domain names are registered with a domain name registrar their installation at the domain registry of a top level domain requires the assignment of a primary name server and at least one secondary name server. The requirement of multiple name servers aims to make the domain still functional even if one name server becomes inaccessible or inoperable.^[4] The designation of a primary name server is solely determined by the priority given to the domain name registrar. For this purpose generally only the fully qualified domain name of the name server is required, unless the servers are contained in the registered domain, in which case the corresponding IP address is needed as well.

Primary name servers are often master name servers, while secondary name server may be implemented as slave servers.

Authoritative answer

An authoritative server indicates its status of supplying definitive answers, deemed authoritative, by setting a software flag (a protocol structure bit), called the Authoritative Answer (AA) bit in its responses.^[3] This flag is usually reproduced prominently in the output of DNS administration query tools (such as dig) to indicate that the responding name server is an authority for the domain name in question.^[3]

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 zone of the Domain Name System and each user system must implement resolver software capable of recursive operation.

To improve efficiency, reduce DNS traffic across the Internet, and increase performance in end-user applications, the Domain Name System supports DNS cache servers which store DNS query results for a period of time determined in the configuration (time-to-live) of the domain name record in question. Typically, such caching DNS servers, also called DNS caches, also implement the recursive algorithm necessary to resolve a given name starting with the DNS root through to the authoritative name servers of the queried domain. With this function implemented in the name server, user applications gain efficiency in design and operation.

The combination of DNS caching and recursive functions in a name server is not mandatory, the functions can be implemented independently in servers for special purposes.

Internet service providers typically provide recursive and caching name servers for their customers. In addition, many home networking routers implement DNS caches and recursors to improve efficiency in the local network.

Microsoft networking

Name servers also exist on some Microsoft Windows networks where one host can take the role of NetBIOS master browser 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.

See also

• Comparison of DNS server software
• Directory service
• DNS Security Extensions (DNSSEC)
• Lightweight Directory Access Protocol (LDAP)
• Network Information Service (NIS)
• Name Service Switch (NSS)
• resolver, resolv.conf, resolvconf for Unix/Linux
• BIND
• OpenDNS

References

External links

• DNS Resource Directory
• DNS & BIND Resources