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Root Zone Label Generation Rules

Root Zone Label Generation Rules (RZ-LGR) provide a conservative mechanism to determine valid IDN TLDs and their variant labels, for stable and secure operation of the DNS Root Zone.

Using the RZ-LGR

Root Zone Label Generation Rules (LGR)

With the availability of the Root Zone Label Generation Rules (RZ-LGR) and its fundamental role envisaged for defining the variant labels of top-level domains (TLDs), the ICANN Board asked the ICANN community to form the RZ-LGR Study Group (SG) to study and recommend how to technically apply the RZ-LGR in a harmonized way to generic and country code top top-level domains (gTLDs/ccTLDs).

The Recommendations for the Technical Utilization of the Root Zone Label Generation Rules were published by the WG and have been approved by the board. Further details of the SG's work are available at the wiki page.

Current Versions of Root Zone Label Generation Rules

Root Zone Label Generation Rules Version 3 (RZ-LGR-3) is now available, covering the following sixteen scripts: Arabic, Devanagari, Ethiopic, Georgian, Gujarati, Gurmukhi, Hebrew, Kannada, Khmer, Lao, Malayalam, Oriya, Sinhala, Tamil, Telugu, and Thai scripts. The RZ-LGR-3 package includes the following documents:

These files can be collectively downloaded with this package.

Successful development of Label Generation Rules depends on having community based Generation Panels for each script or writing system that will be used in the Root Zone. The Generation Panels start with a broad set of code points for the relevant script(s), known as the Maximal Starting Repertoire, and propose relevant Label Generation Rules. These proposals are reviewed by the community through public comment and then by the Integration Panel for approval and integration into the LGR for the Root Zone. The details are defined in Procedure to Develop and Maintain the Label Generation Rules for the Root Zone in Respect of IDNA Labels [PDF, 1.39 MB].

For related information, visit the following links:

Speak up for your language. Please email at to contribute to the relevant Generation Panel.

Earlier Versions of Root Zone Label Generation Rules

Root Zone Label Generation Rules Version 2 (RZ-LGR-2) covered Arabic, Ethiopic, Georgian, Khmer, Lao and Thai scripts. The RZ-LGR-2 package included the following documents:

These files can be collectively downloaded with this package.

Root Zone Label Generation Rules Version 1 (RZ-LGR-1) covered the Arabic script. The RZ-LGR-1 package included the following documents:

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"""" is not an IDN."