Skip to main content

About Reserved Names and Name Collision Occurrence Management

All registry operators are required by their Registry Agreement (RA) to exclude certain domain names from registration in a Top Level Domain (TLD). These reserved names include strings that are for Country Code Top Level Domains (ccTLDs), ICANN-related names (such as ICANN), IANA-related names (such as example), country and territory names, international and intergovernmental organizations and names that the registry operator can use in connection with the operation of the TLD.

A list of reserved names required for each TLD is in its RA, and may vary depending on the TLD. For some TLDs, their registry operators may withhold from registration at all levels domain names that are not activated in the DNS and release them for registration to another person or entity at the registry operator's discretion. To determine which RA applies to a TLD, please see ICANN's webpage with all current registry agreements.

Registry operators may obtain authorization to release certain reserved names as described in the relevant RA. However, they are not required by the RA to release those names, even if authorized to do so. Authorizations granted by ICANN are published on the RA webpage for the TLD.

For information about Name Collision Occurrence Management, please visit

If you have a complaint about reserved names or Name Collision, please submit a Reserved Names and Name Collision Occurrence Management Complaint Form.

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."