Hostname

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A hostname (occasionally also, a sitename) is the unique name by which a network attached device (which could consist of a computer, file server, network storage device, fax machine, copier, cable modem, etc. ) is known on a network. The hostname is used to identify a particular host in various forms of electronic communication such as E-mail or Usenet. Hostnames are used by various naming systems: NIS, DNS, SMB, etc.

Host names 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. They are human readable nick-names which ultimately correlate to unique network hardware MAC addresses. In some cases the host name may contain embedded domain names and/or locations, non-dotted IP addresses, etc.

On a simple local area network, a hostname is usually a single word: for instance, an organization's CVS server might be named "cvs" or "server-1".

On the Internet, a hostname is a domain name assigned to the host. 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 host label ("en") and the domain name label "wikipedia.org". This kind of hostname (also known as an FQDN) is translated into an Internet address via the local hosts file, or the Domain Name System (DNS) resolver. It is possible for a single host to have several hostnames; but generally the OS of the host prefers to have one hostname that the host uses for itself.

It is often possible to guess a hostname for a particular institution. This is useful if you want to know if they operate network services like anonymous FTP, World-Wide Web or finger. First try the institution's name or obvious abbreviations thereof, with the appropriate domain appended, e.g. "mit.edu". If this fails, prepend "ftp." or "www." as appropriate, e.g. "www.data-io.com". You can use the ping command as a quick way to test whether a hostname is valid.

The folklore interest of hostnames stems from the creativity and humour they often display. Interpreting a sitename is not unlike interpreting a vanity licence plate; one has to mentally unpack it, allowing for mono-case and length restrictions and the lack of whitespace. Hacker tradition deprecates dull, institutional-sounding names in favour of punchy, humorous, and clever coinages (except that it is considered appropriate for the official public gateway machine of an organisation to bear the organisation's name or acronym). Mythological references, cartoon characters, animal names, and allusions to SF or fantasy literature are probably the most popular sources for sitenames (in roughly descending order). The obligatory comment is Harris' Lament: "All the good ones are taken!"

Only letters and digits are legal in hostnames. Special characters other than the dash (and the dot between components) are not allowed in the hostname designation although cohesion may cause them to appear. Underscore characters are commonly used by Windows systems but according to RFC-952 they are not allowed. The use of the underscore has caused many subtle problems in systems that connect to the wider world...

Another restriction imposed by RFC-952 was that names had to start with a letter - RFC-1123 relaxed this restriction so names could start with a digit instead.

Also specified in RFC-952 (as in the earlier RFC-810) was the assumption that host names could not be longer than 24 characters. RFC-1123 specifies that, "Host software MUST handle host names of up to 63 characters and SHOULD handle host names of up to 255 characters."

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