Hostnames

A hostname is a label assigned to a device on a network to identify it in communications. It is typically used by people and software to address the device, for example in file transfers, remote login, and service discovery. In many networks the hostname is part of a larger domain name stored in the Domain Name System (DNS); the fully qualified domain name (FQDN) combines the hostname with its domain components, for example printer.example.com. A host may also be reachable via a local name in hosts files or local discovery protocols without DNS.

Hostname structure and rules: In DNS-based naming, a hostname is composed of one or more labels separated by dots. Each label can contain letters, digits, and hyphens, must be between 1 and 63 characters, and must not start or end with a hyphen. The complete FQDN is typically at most 253 ASCII characters; in practice many systems limit to 255 bytes including dots and a trailing dot. DNS names are case-insensitive. For internationalized names, Unicode is used in user interfaces but is encoded in the DNS via punycode.

Management and resolution: Hostnames are assigned by system administrators or dynamically by DHCP (option 12) and can be set in the operating system or in configuration files. DNS resolves hostnames to IP addresses through A/AAAA records, while reverse resolution uses PTR records. Local networks may use multicast DNS (mDNS) or hosts files for name resolution when DNS is unavailable.