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En clair, un nom de domaine est constitué de labels de 1 à 63 octets et séparé de points, et tout cela ne doit pas dépasser 253 caractères. Example : truc.machin.example.netThe hierarchy of domains descends from the right to the left label in the name; each label to the left specifies a subdivision, or subdomain of the domain to the right. For example: the label example specifies a node example.com as a subdomain of the com domain, and www is a label to create www.example.com, a subdomain of example.com. This tree of labels may consist of 127 levels. Each label may contain from 1 to 63 octets. The empty label is reserved for the root node. The full domain name may not exceed a total length of 253 ASCII characters in its textual representation.[5] In practice, some domain registries may have shorter limits.
Il convient donc, en général, s'appliquer ces règles là en plus : un nom constitué de chiffres, lettres et/ou du caractère tiret (-), la première et la dernière lettre ne pouvant être des tirets.Hostnames are composed of series of labels concatenated with dots, as are all domain names. For example, "en.wikipedia.org" is a hostname. Each label must be between 1 and 63 characters long,[2] and the entire hostname (including the delimiting dots but not a trailing dot) has a maximum of 253 ASCII characters.[3]
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.
