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Guide to Name Collision Identification and Mitigation for IT Professionals

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Guide to Name Collision Identification and Mitigation for IT Professionals (version 1.1) [PDF, 476 KB]


Name collisions have the potential to create unanticipated results for organizations that use private namespaces. This document lists some of those potential results and specifies best practices for changing the way that private namespaces are used within organizations.

For namespaces that used a private TLD that is becoming (or is already) a TLD in the global DNS, mitigation best comes in the form of migrating the namespace to a namespace that is rooted in the global DNS. For namespaces that use name shortening with search lists, mitigation can come only by eliminating the use of search lists. Steps to achieve these mitigations also include long-term monitoring in the private network to be sure that all instances of names that might cause collisions are no longer being used.

The comprehensive mitigation for the problems of name collisions is to use FQDNs in all places where a domain name is used. In a network that is already using the global DNS, this means not using search lists. In a network that uses a private namespace, this means that the private namespace should be rooted in the global DNS, and should not be using search lists.

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."