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IDN Implementation Guidelines

Guidelines for Implementation of IDNs

The Guidelines are a list of general standards for IDN registration policies and practices that are designed to minimize the risk of cybersquatting and consumer confusion, and respect the interests of local languages and character sets. Registries seeking to deploy IDNs under their agreements with ICANN have been authorized to do so on the basis of the Guidelines.

Version 4.1 (22 September 2022) [PDF, 240 KB]. From the set of guidelines proposed in version 4.0, version 4.1 defers guidelines 6a, 11, 12, 13 and 18, as resolved by the ICANN Board.

Final Proposed Draft Version 4.0 [PDF, 486 KB] finalized by the expert working group formed after the Call for Community Experts to Review the IDN Implementation Guidelines. For details on the progress, visit the wiki page.

Version 3.0 (2 September 2011) | [PDF, 79 KB]

Version 2.2 [PDF, 49 KB] (26 April 2007)

Version 2.1, by ICANN and leading IDN Registries (22 February 2006)

Version 2.0, by ICANN and leading IDN Registries (7 November 2005)

Version 1.0, by ICANN and leading IDN Registries (20 June 2003)

Domain Name System
Internationalized Domain Name ,IDN,"IDNs are domain names that include characters used in the local representation of languages that are not written with the twenty-six letters of the basic Latin alphabet ""a-z"". An IDN can contain Latin letters with diacritical marks, as required by many European languages, or may consist of characters from non-Latin scripts such as Arabic or Chinese. Many languages also use other types of digits than the European ""0-9"". The basic Latin alphabet together with the European-Arabic digits are, for the purpose of domain names, termed ""ASCII characters"" (ASCII = American Standard Code for Information Interchange). These are also included in the broader range of ""Unicode characters"" that provides the basis for IDNs. The ""hostname rule"" requires that all domain names of the type under consideration here are stored in the DNS using only the ASCII characters listed above, with the one further addition of the hyphen ""-"". The Unicode form of an IDN therefore requires special encoding before it is entered into the DNS. The following terminology is used when distinguishing between these forms: A domain name consists of a series of ""labels"" (separated by ""dots""). The ASCII form of an IDN label is termed an ""A-label"". All operations defined in the DNS protocol use A-labels exclusively. The Unicode form, which a user expects to be displayed, is termed a ""U-label"". The difference may be illustrated with the Hindi word for ""test"" — परीका — appearing here as a U-label would (in the Devanagari script). A special form of ""ASCII compatible encoding"" (abbreviated ACE) is applied to this to produce the corresponding A-label: xn--11b5bs1di. A domain name that only includes ASCII letters, digits, and hyphens is termed an ""LDH label"". Although the definitions of A-labels and LDH-labels overlap, a name consisting exclusively of LDH labels, such as""icann.org"" is not an IDN."