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Mitigating DNS Namespace Collisions

In line with our ongoing commitment to preserve the security, stability and resiliency of the Internet’s Identifier systems, ICANN today published a report on collisions in the DNS namespace as they relate to the New TLD program.  We would like to thank JAS Global Advisors LLC for its role in performing the studies and in writing the “Mitigating the Risk of DNS Namespace Collisions” report.

It should be noted that the report is technical in nature and requires some understanding of namespace collisions to be fully appreciated. With that in mind, I recommend that readers become familiar with the issue by reading the guide and FAQ at

The full report can be found at: [PDF, 322 KB]

Over the course of the study, JAS found “no evidence to suggest that the security and stability of the global Internet DNS itself is at risk”. The JAS report further confirms the results of the “DNS Stability String Review” performed on each string during Initial Evaluation pursuant to Section of the Applicant Guidebook.

The report includes a series of recommendations for mitigating risks associated with the new gTLD program, specifically those related to Domain Name Collisions. Among the recommendations:

  • The Top Level Domains .corp, .home and .mail should be permanently reserved.
  • ICANN should require new TLD registries to publish a controlled interruption zone immediately upon delegation in the root zone.
    • Details how a controlled interruption mechanism would work are covered in the report.
    • After the 120-day period, there shall be no further collision-related restrictions on the registry.
  • ICANN should have emergency response processes in place on 24x7x365 basis that include the abilities to analyze and act upon reported problems that present “clear and present danger to human life”.
  • ICANN and others in the community should continue to collect and analyze data relating to the root servers and to the controlled interruption.

In studying collision data for the report, JAS uncovered a vulnerability that is “not directly related to ICANN’s New gTLD Program nor to new TLDs in general but has the potential to impact end-systems”. JAS and ICANN are working with affected (vendor) parties pursuant to ICANN’s Coordinated Vulnerability Disclosure Process. [PDF, 470 KB]

Due to the need to keep certain aspects of the discovered vulnerability confidential, as per the vulnerability disclosure process, JAS is reluctant to disclose experimental methods or data at this time, but has in this report provided a summary of recommendations based on its study of the occurrence and severity of namespace collisions in the global Internet DNS.

ICANN is actively seeking community input on the recommendations through ICANN’s public comment processes.

I would encourage anyone with interest to read the report and to make comments.


    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."