computer networking
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
, a hostname (archaically nodename) is a label that is assigned to a device connected to a
computer network
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
and that is used to identify the device in various forms of electronic communication, such as the
World Wide Web
The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet.
Documents and downloadable media are made available to the network through web ...
. Hostnames may be simple names consisting of a single word or phrase, or they may be structured. Each hostname usually has at least one numeric
network address
A network address is an identifier for a node or host on a telecommunications network. Network addresses are designed to be unique identifiers across the network, although some networks allow for local, private addresses, or locally admini ...
associated with it for routing packets for performance and other reasons.
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...
hostnames may have appended the name of a
Domain Name System
The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned t ...
(DNS) domain, separated from the host-specific label by a period ("dot"). In the latter form, a hostname is also called a
domain name
A domain name is a string that identifies a realm of administrative autonomy, authority or control within the Internet. Domain names are often used to identify services provided through the Internet, such as websites, email services and more. As ...
. If the domain name is completely specified, including a
top-level domain
A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. The top-level domain names are installed in the root zone of the name space. For all domains in ...
of the Internet, then the hostname is said to be a
fully qualified domain name
A fully qualified domain name (FQDN), sometimes also referred to as an ''absolute domain name'', is a domain name that specifies its exact location in the tree hierarchy of the Domain Name System (DNS). It specifies all domain levels, including th ...
(FQDN). Hostnames that include DNS domains are often stored in the Domain Name System together with the
IP address
An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
es of the host they represent for the purpose of mapping the hostname to an address, or the reverse process.
Internet hostnames
In the Internet, a hostname is a domain name assigned to a host computer. This is usually a combination of the host's local name with its parent domain's name. For example, ''en.wikipedia.org'' consists of a local hostname (''en'') and the domain name ''wikipedia.org''. This kind of hostname is translated into an IP address via the local hosts file, or the Domain Name System (DNS) resolver. It is possible for a single host computer to have several hostnames; but generally the
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
of the host prefers to have one hostname that the host uses for itself.
Any domain name can also be a hostname, as long as the restrictions mentioned below are followed. So, for example, both ''en.wikipedia.org'' and ''wikipedia.org'' are hostnames because they both have IP addresses assigned to them. A hostname may be a domain name, if it is properly organized into the domain name system. A domain name may be a hostname if it has been assigned to an Internet host and associated with the host's IP address.
Syntax
Hostnames are composed of a sequence of labels concatenated with dots. For example, "en.wikipedia.org" is a hostname. Each label must be from 1 to 63 characters long.RFC 1034, Section 3.1 "Name space specifications and terminology" /ref> The entire hostname, including the delimiting dots, has a maximum of 253
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...
characters.
The Internet standards (
Request for Comments
A Request for Comments (RFC) is a publication in a series from the principal technical development and standards-setting bodies for the Internet, most prominently the Internet Engineering Task Force (IETF). An RFC is authored by individuals or g ...
) for protocols specify that labels may contain only the ASCII letters ''a'' through ''z'' (in a case-insensitive manner), the digits ''0'' through ''9'', and the hyphen-minus character ('-'). The original specification of hostnames required that labels start with an alpha character, and not end with a hyphen. However, a subsequent specification permitted hostname labels to start with digits.
Internationalized domain name
An internationalized domain name (IDN) is an Internet domain name that contains at least one label displayed in software applications, in whole or in part, in non-latin script or alphabet, such as Arabic, Bengali, Chinese ( Mandarin, simplif ...
s are stored in the Domain Name System as ASCII strings using
Punycode
Punycode is a representation of Unicode with the limited ASCII character subset used for Internet hostnames. Using Punycode, host names containing Unicode characters are transcoded to a subset of ASCII consisting of letters, digits, and hyphens, wh ...
transcription.RFC 3492, ''Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)'', A. Costello, The Internet Society (March 2003)
While a hostname may not contain other characters, such as the underscore character (''_''), other DNS names may contain the underscore. This restriction was lifted by RFC 2181. Systems such as
DomainKeys DomainKeys (informally ''DK'') is a deprecated e-mail authentication system designed by Yahoo to verify the domain name of an e-mail sender and the message integrity.
Aspects of DomainKeys, along with parts of Identified Internet Mail, were combine ...
and
service records
Service was an independent record label formed in Gothenburg, Sweden in December 2001 by Ola Borgström together with Dan Lissvik. In 2012 Borgström announced that the label would stop issuing new material.SCTP-capable webserver host (www) in the domain ''example.com''. Notwithstanding the standard, Chrome,
Firefox
Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current ...
,
Internet Explorer
Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, commonly abbreviated IE or MSIE) is a series of graphical web browsers developed by Microsoft which was used in the Windows line of operating systems (in ...
,
Edge
Edge or EDGE may refer to:
Technology Computing
* Edge computing, a network load-balancing system
* Edge device, an entry point to a computer network
* Adobe Edge, a graphical development application
* Microsoft Edge, a web browser developed ...
and
Safari
A safari (; ) is an overland journey to observe wild animals, especially in eastern or southern Africa. The so-called "Big Five" game animals of Africa – lion, leopard, rhinoceros, elephant, and Cape buffalo – particularly form an impor ...
allow underscores in hostnames, although cookies in IE do not work correctly if any part of the hostname contains an underscore character.
However, it is valid to attempt to resolve a hostname that consists of an underscore. E.g. ''_.example.com''. This is used by RFC 7816 to reduce the amount of information that is made available to intermediate DNS servers during an iterative query. The Query Name Minimisation feature is enabled by default in
BIND
BIND () is a suite of software for interacting with the Domain Name System (DNS). Its most prominent component, named (pronounced ''name-dee'': , short for ''name daemon''), performs both of the main DNS server roles, acting as an authoritative ...
9.14.0.
The hostname ''en.wikipedia.org'' is composed of the DNS labels ''en'' (hostname or leaf domain), ''wikipedia'' (second-level domain) and ''org'' (top-level domain). Labels such as ''2600'' and ''3abc'' may be used in hostnames, but ''-hi-'', ''_hi_'' and ''*hi*'' are invalid.
A hostname is considered to be a fully qualified domain name (FQDN) when all labels up to and including the top-level domain name (TLD) are specified. The hostname ''en.wikipedia.org'' terminates with the top-level domain ''org'' and is thus fully qualified. Depending on the operating system DNS software implementation, an unqualified hostname may be automatically combined with a default domain name configured into the system, in order to complete the fully qualified domain name. As an example, a student at MIT may be able to send mail to "joe@csail" and have it automatically qualified by the mail system to be sent to ''joecsail.mit.edu''.
General guidelines on choosing a good hostname are outlined in RFC 1178.
Example
''saturn'' and ''jupiter'' may be the hostnames of two devices connected to a network named ''PC''. Within ''PC'', the devices are addressed by their hostnames. The domain names of the devices are ' and ', respectively. If ''PC'' is registered as a second-level domain name in the Internet, e.g., as ', the hosts may be addressed by the fully qualified domain names ' and '.
See also
*
Domain hijacking
Domain hijacking or domain theft is the act of changing the registration of a domain name without the permission of its original registrant, or by abuse of privileges on domain hosting and registrar software systems.
This can be devastating to ...