SPECIFICATION) • RFC 1034 (DOMAIN NAMES - CONCEPTS AND FACILITIES) • RFC 1035 (DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION) • RFC 1123 (Requirements for Internet Hosts -- Application and Support) • RFC 2181 (Clarifications to the DNS Specification)
◦ A "name" (Net, Host, Gateway, or Domain name) is a text string up to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus sign (-), and period (.). Note that periods are only allowed when they serve to delimit components of "domain style names". (See RFC-921, "Domain Name System Implementation Schedule", for background). ◦ No blank or space characters are permitted as part of a name. ◦ No distinction is made between upper and lower case. ◦ The first character must be an alpha character. ◦ The last character must not be a minus sign or period.
most common interpretation uses the root "." as either the single origin or as one of the members of the search list, so a multi-label relative name is often one where the trailing dot has been omitted to save typing. RFC 1034 (DOMAIN NAMES - CONCEPTS AND FACILITIES)
follow the rules for ARPANET host names. They must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphen. There are also some restrictions on the length. Labels must be 63 characters or less. • 2.3.4. Size limits ◦ Various objects and parameters in the DNS have size limits. They are listed below. Some could be easily changed, others are more fundamental. ▪ labels 63 octets or less ▪ names 255 octets or less • 3.1. Name space definitions ◦ Since every domain name ends with the null label of the root, a domain name is terminated by a length byte of zero. ◦ To simplify implementations, the total length of a domain name (i.e., label octets and label length octets) is restricted to 255 octets or less. RFC 1035 (DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION)
of a legal Internet host name was specified in RFC-952 [DNS:4]. One aspect of host name syntax is hereby changed: the restriction on the first character is relaxed to allow either a letter or a digit. Host software MUST support this more liberal syntax. ◦ Host software MUST handle host names of up to 63 characters and SHOULD handle host names of up to 255 characters. RFC 1123 (Requirements for Internet Hosts -- Application and Support)
one label is limited to between 1 and 63 octets. ◦ A full domain name is limited to 255 octets (including the separators). ◦ The zero length full name is defined as representing the root of the DNS tree, and is typically written and displayed as ".". RFC 2181 (Clarifications to the DNS Specification)
www.www.www.www.www.www.www.www.www.www.www.www.www.www.www.www.www.w ww.www.www.www.www.www.www.www.www.www.www.www.www.www.www.www.www.ww w.www.www.www.www.www.www.www.www.www.tsunagi.me' is not a legal IDNA2008 name (domain name longer than 255 characters), use +noidnin
'.') { 537 /* The first and the last character of a label must be alphanumeric */ 538 if (*(s + 1) == '.' || (hostname && (!isalnum((int)*(unsigned char *)(s - 1)) || !isalnum((int)*(unsigned char *)(s + 1))))) { 539 return 0; 540 } ・ ・ 50 ラベルの最初及び最後の文字 は英数字 最初及び最後の文字が「.」（ドット）または 英数字以外の場合はfalse
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