Hostname

Characteristics and format

A hostname is typically composed of one or more labels separated by dots. Each label commonly uses letters (A–Z), digits (0–9) and hyphens, and labels are case-insensitive. Standards used on the Internet generally limit each label to 63 characters and the full name to 255 characters in total. A fully qualified hostname may end with a trailing dot to indicate the absolute root of the naming hierarchy.

• Allowed characters: letters, digits, hyphens (no leading or trailing hyphen in a label).
• Length limits: per-label and overall limits set by naming standards.
• International names: non-ASCII names use an encoding (IDNA/Punycode) to represent Unicode characters.

History and standards

Hostnames grew out of early network experiments and were standardized with the Domain Name System (DNS) developed in the 1980s. DNS introduced a hierarchical namespace that maps hostnames and domain names to Internet Protocol addresses. Key technical specifications are published as RFCs and have evolved to handle internationalization, security extensions and higher scale.

Uses and examples

Hostnames appear in many contexts: web addresses such as www.example.com for the World Wide Web (WWW), mail servers used by e-mail systems, discussion service names on networks such as Usenet, and internal names on corporate LANs. A hostname is resolved by name services like DNS to one or more IP addresses so clients can connect to the correct device.

Hostname versus domain name

The words "hostname" and "domain name" are sometimes used interchangeably but have distinct senses. A domain name identifies a point in the DNS hierarchy (for example example.com); a hostname usually denotes a specific machine or service within that domain (for example mail.example.com). In many contexts a hostname is simply a domain name assigned to a host (domain name).

Practical notes

Common administrative practices include using meaningful, stable hostnames, avoiding special characters, and documenting mappings between names and addresses. Special names such as localhost have reserved meanings, and local naming systems (NetBIOS, mDNS, hosts files) coexist with DNS. When designing naming schemes keep security, clarity and manageability in mind.