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Root Stability Study Final Report Now Available

LOS ANGELES – 8 March 2017 – The Internet Corporation for Assigned Names and Numbers (ICANN) today published the final report regarding the Continuous Data-Driven Analysis of Root Server System Stability (CDAR). The study examines the New gTLD Program's technical impact of the delegation of new gTLDs on the security and stability of the root Domain Name System (DNS) and is informed by publicly available, historical measurement data.

Read the report [PDF, 3.49 MB].

The CDAR study was conducted by independent research organization TNO and its consortium partners, SIDN and NLnet Labs. The findings will help the ICANN community going forward to determine if any additional steps are necessary if more TLDs are to be added the root zone system.

A draft report was published for comment on 27 October 2016. The revised, final version available today incorporates suggestions received during the public comment period. The revisions include additional discussion regarding the data used and recommendations presented in the original report. Additionally, some of the presented analysis results in the draft report are updated based on data that became available after the publication of the draft report. The report of public comments [PDF, 520 KB], which includes summary and analysis of the comments received regarding the study's findings, was published on 9 February 2017.

ICANN commissioned this study in response to a recommendation from the Governmental Advisory Committee (GAC) to examine the technical impact of the delegation of new gTLDs on the security or stability of the root DNS system. The final report is expected to serve as input for community discussions regarding the future expansion of the root zone. The findings and recommendations will also be presented to the ICANN Board for consideration.

New gTLD Program Reviews

ICANN's New gTLD Program has enabled hundreds of new top-level domains to enter into the Internet's root zone since the first delegations occurred in October 2013. The CDAR study is part of a series of comprehensive reviews of the program that are currently underway in a number of areas, including competition, consumer trust and choice, security and stability, rights protection and other areas.


ICANN's mission is to help ensure a stable, secure and unified global Internet. To reach another person on the Internet, you have to type an address into your computer - a name or a number. That address has to be unique so computers know where to find each other. ICANN helps coordinate and support these unique identifiers across the world. ICANN was formed in 1998 as a not-for-profit public-benefit corporation and a community with participants from all over the world. ICANN and its community help keep the Internet secure, stable and interoperable. It also promotes competition and develops policy for the top-level of the Internet's naming system and facilitates the use of other unique Internet identifiers. For more information please visit:

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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."