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Title: Hostname  
Author: World Heritage Encyclopedia
Language: English
Subject: Uniform resource locator, Domain hack, Nslookup, Domain Name System, Internet Relay Chat
Collection: Computer Networking, Identifiers
Publisher: World Heritage Encyclopedia


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, e-mail or Usenet. Hostnames may be simple names consisting of a single word or phrase, or they may be structured.

On the Internet, hostnames may have appended the name of a Domain Name System (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.


  • Overview 1
  • Example 2
  • Internet hostnames 3
  • Restrictions on valid host names 4
  • See also 5
  • References 6


Hostnames are human-readable nicknames that correspond to the address of a device connected to a network. They are used by various naming systems, e.g., Network Information Service (NIS), Domain Name System (DNS), Server Message Block (SMB), and the meaning of hostname will vary according to the naming system used. A hostname meaningful to a Microsoft NetBIOS workgroup may be an invalid Internet hostname. When presented with a hostname without any context, it is usually safe to assume that the network is the Internet and the hostname's naming system is the DNS.

Hostnames are typically used in an administrative capacity and may appear in computer browser lists, active directory lists, IP address to hostname resolutions, email headers, etc.


Saturn and jupiter may be the hostnames of two devices connected to a network named Example. Within Example the devices are addressed by their hostname. The domain names of the devices would be saturn.example and jupiter.example, respectively. If 'example' is registered as a second-level domain name in the Internet, e.g., the hosts may be addressed by the fully qualified domain names and

Internet hostnames

On the Internet, a hostname is a 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 and are hostnames because they both have

  1. ^ System V/AT Runtime System. Microport. 
  2. ^ RFC 1034, Section 3.1 "Name space specifications and terminology"
  3. ^ What is the real maximum length of a DNS name?
  4. ^ "Underscores in DNS". Retrieved 2011-07-20. 
  5. ^ Internet Explorer Cookie Internals (FAQ)


See also

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

A hostname is considered to be a fully qualified domain name (FQDN) if all the labels up to and including the MIT may be able to send mail to "joe@csail" and have it automatically qualified by the mail system to be sent to

The hostname is composed of the DNS labels en (hostname or leaf domain), WorldHeritage (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.

One common cause of non-compliance with this specification is that the rules are not applied consistently across the board when domain names are chosen and registered.

While a hostname may not contain other characters, such as the underscore character (_), other DNS names may contain the underscore.[4] 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, specifies a service pointer for an SCTP capable webserver host (www) in the domain Note that some applications (e.g. Microsoft Internet Explorer) won't work correctly if any part of the hostname contains an underscore character.[5]

The Internet standards (Requests for Comments) for protocols mandate that component hostname labels may contain only the ASCII letters 'a' through 'z' (in a case-insensitive manner), the digits '0' through '9', and the hyphen ('-'). The original specification of hostnames in RFC 952, mandated that labels could not start with a digit or with a hyphen, and must not end with a hyphen. However, a subsequent specification (RFC 1123) permitted hostname labels to start with digits. No other symbols, punctuation characters, or white space are permitted.

Hostnames are composed of series of [2] and the entire hostname (including the delimiting dots but not a trailing dot) has a maximum of 253 ASCII characters.[3]

Restrictions on valid host names
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