Hostname

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In computer networking, a hostname (archaically nodename [1] ) 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. 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 associated with it for routing packets for performance and other reasons.

Contents

Internet hostnames may have appended the name of a Domain Name System [2] (DNS) domain, separated from the host-specific label by a period ("dot"). In the latter form, a hostname is also called a domain name. If the domain name is completely specified, including a top-level domain of the Internet, then the hostname is said to be a fully qualified domain name (FQDN). Hostnames that include DNS domains are often stored in the Domain Name System together with the IP addresses 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 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 octets long. [2] The entire hostname, including the delimiting dots, has a maximum of 253 ASCII characters. [3]

The Internet standards (Request for Comments) 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. [4] However, a subsequent specification permitted hostname labels to start with digits. [5] Internationalized domain names are stored in the Domain Name System as ASCII strings using Punycode transcription. [6]

While a hostname may not contain other characters, such as the underscore character (_), other DNS names may contain the underscore. [7] [8] This restriction was lifted by RFC 2181. Systems such as DomainKeys and service records use the underscore as a means to assure that their special character is not confused with hostnames. For example, _http._sctp.www.example.com specifies a service pointer for an SCTP-capable webserver host (www) in the domain example.com. Notwithstanding the standard, Chrome, Firefox, Internet Explorer, Edge and Safari allow underscores in hostnames, although cookies in IE do not work correctly if any part of the hostname contains an underscore character. [9]

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. [10] The Query Name Minimisation feature is enabled by default in BIND 9.14.0. [11]

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 joeAt sign.svgcsail.mit.edu.

General guidelines on choosing a good hostname are outlined in RFC 1178. [12]

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 saturn.PC and jupiter.PC, respectively. If PC is registered as a second-level domain name in the Internet, e.g., as PC.net, the hosts may be addressed by the fully qualified domain names saturn.PC.net and jupiter.PC.net.

See also

Related Research Articles

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 to each of the associated entities. Most prominently, it translates readily memorized domain names to the numerical IP addresses needed for locating and identifying computer services and devices with the underlying network protocols. The Domain Name System has been an essential component of the functionality of the Internet since 1985.

<span class="mw-page-title-main">IPv6</span> Version 6 of the Internet Protocol

Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the long-anticipated problem of IPv4 address exhaustion, and was intended to replace IPv4. In December 1998, IPv6 became a Draft Standard for the IETF, which subsequently ratified it as an Internet Standard on 14 July 2017.

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 lower levels, it is the last part of the domain name, that is, the last non empty label of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is .com. Responsibility for management of most top-level domains is delegated to specific organizations by the ICANN, an Internet multi-stakeholder community, which operates the Internet Assigned Numbers Authority (IANA), and is in charge of maintaining the DNS root zone.

<span class="mw-page-title-main">Domain name</span> Identification string in the Internet

In the Internet, a domain name is a string that identifies a realm of administrative autonomy, authority or control. Domain names are often used to identify services provided through the Internet, such as websites, email services and more. Domain names are used in various networking contexts and for application-specific naming and addressing purposes. In general, a domain name identifies a network domain or an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, or a server computer.

Dynamic DNS (DDNS) is a method of automatically updating a name server in the Domain Name System (DNS), often in real time, with the active DDNS configuration of its configured hostnames, addresses or other information.

An email address identifies an email box to which messages are delivered. While early messaging systems used a variety of formats for addressing, today, email addresses follow a set of specific rules originally standardized by the Internet Engineering Task Force (IETF) in the 1980s, and updated by RFC 5322 and 6854. The term email address in this article refers to just the addr-spec in Section 3.4 of RFC 5322. The RFC defines address more broadly as either a mailbox or group. A mailbox value can be either a name-addr, which contains a display-name and addr-spec, or the more common addr-spec alone.

Zero-configuration networking (zeroconf) is a set of technologies that automatically creates a usable computer network based on the Internet Protocol Suite (TCP/IP) when computers or network peripherals are interconnected. It does not require manual operator intervention or special configuration servers. Without zeroconf, a network administrator must set up network services, such as Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS), or configure each computer's network settings manually.

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, which is called the letter–digit–hyphen (LDH) subset. For example, München is encoded as Mnchen-3ya.

<span class="mw-page-title-main">Internationalized domain name</span> Type of Internet 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 or in the Latin alphabet-based characters with diacritics or ligatures. These writing systems are encoded by computers in multibyte Unicode. Internationalized domain names are stored in the Domain Name System (DNS) as ASCII strings using Punycode transcription.

In computer networking, localhost is a hostname that refers to the current computer used to access it. The name localhost is reserved for loopback purposes. It is used to access the network services that are running on the host via the loopback network interface. Using the loopback interface bypasses any local network interface hardware.

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 the top-level domain and the root zone. A fully qualified domain name is distinguished by its lack of ambiguity in terms of DNS zone location in the hierarchy of DNS labels: it can be interpreted only in one way.

In the Domain Name System (DNS) hierarchy, a subdomain is a domain that is a part of another (main) domain. For example, if a domain offered an online store as part of their website example.com, it might use the subdomain shop.example.com.

The domain name arpa is a top-level domain (TLD) in the Domain Name System (DNS) of the Internet. It is used predominantly for the management of technical network infrastructure. Prominent among such functions are the subdomains in-addr.arpa and ip6.arpa, which provide namespaces for reverse DNS lookup of IPv4 and IPv6 addresses, respectively.

In computer networks, a reverse DNS lookup or reverse DNS resolution (rDNS) is the querying technique of the Domain Name System (DNS) to determine the domain name associated with an IP address – the reverse of the usual "forward" DNS lookup of an IP address from a domain name. The process of reverse resolving of an IP address uses PTR records. rDNS involves searching domain name registry and registrar tables. The reverse DNS database of the Internet is rooted in the .arpa top-level domain.

The name localhost is reserved by the Internet Engineering Task Force (IETF) as a domain name label that may not be installed as a top-level domain in the Domain Name System (DNS) of the Internet.

In computer networking, the multicast DNS (mDNS) protocol resolves hostnames to IP addresses within small networks that do not include a local name server. It is a zero-configuration service, using essentially the same programming interfaces, packet formats and operating semantics as unicast Domain Name System (DNS). It was designed to work as either a stand-alone protocol or compatible with standard DNS servers. It uses IP multicast User Datagram Protocol (UDP) packets and is implemented by the Apple Bonjour and open-source Avahi software packages, included in most Linux distributions. Although the Windows 10 implementation was limited to discovering networked printers, subsequent releases resolved hostnames as well. mDNS can work in conjunction with DNS Service Discovery (DNS-SD), a companion zero-configuration networking technique specified separately in RFC 6763.

The domain name .local is a special-use domain name reserved by the Internet Engineering Task Force (IETF) so that it may not be installed as a top-level domain in the Domain Name System (DNS) of the Internet. As such it is similar to the other special domain names, such as .localhost. However, .local has since been designated for use in link-local networking, in applications of multicast DNS (mDNS) and zero-configuration networking (zeroconf) so that DNS service may be established without local installations of conventional DNS infrastructure on local area networks.

The Dynamic Host Configuration Protocol version 6 (DHCPv6) is a network protocol for configuring Internet Protocol version 6 (IPv6) hosts with IP addresses, IP prefixes, default route, local segment MTU, and other configuration data required to operate in an IPv6 network. It is not just the IPv6 equivalent of the Dynamic Host Configuration Protocol for IPv4.

A search domain is a domain used as part of a domain search list. The search list, as well as the local domain name, is used by a resolver to create a fully qualified domain name (FQDN) from a relative name. For this purpose, the local domain name functions as a single-item search list.

A uniform resource locator (URL), colloquially known as an address on the Web, is a reference to a resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identifier (URI), although many people use the two terms interchangeably. URLs occur most commonly to reference web pages (HTTP/HTTPS) but are also used for file transfer (FTP), email (mailto), database access (JDBC), and many other applications.

References

  1. ↑ System V/AT Runtime System. Microport.
  2. 1 2 RFC 1034, Section 3.1 "Name space specifications and terminology"
  3. ↑ Chen, Raymond (12 April 2012). "What is the real maximum length of a DNS name?". Microsoft devblog. Archived from the original (html) on 18 May 2019. Retrieved 31 July 2019.
  4. ↑ DOD Internet Host Table Specification. October 1985. doi: 10.17487/RFC0952 . RFC 952.
  5. ↑ Requirements for Internet Hosts -- Application and Support. October 1989. doi: 10.17487/RFC1123 . RFC 1123.
  6. ↑ RFC 3492, Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA), A. Costello, The Internet Society (March 2003)
  7. ↑ "Underscores in DNS" . Retrieved 2011-07-20.
  8. ↑ "Common DNS Operational and Configuration Errors" . Retrieved 2018-08-21.
  9. ↑ Internet Explorer Cookie Internals (FAQ)
  10. ↑ DNS Query Name Minimisation to Improve Privacy. doi: 10.17487/RFC7816 . RFC 7816.
  11. ↑ "QNAME Minimization and Your Privacy". 6 March 2019. Retrieved 2019-07-17.
  12. ↑ Libes, D. (August 1990). "Choosing a Name for Your Computer". Ietf Datatracker. IETF (Integrated Systems Group/NIST). Retrieved 21 November 2021.
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