IDN whois Lookup
Internationalized domain name
An internationalized domain name (IDN) is an Internet domain name that contains one or more non-ASCII characters. Such domain names could contain letters with diacritics, as required by many non-English languages, or characters from non-Latin scripts such as Arabic, Hebrew, Chinese or Hindi. However, the standard for domain names does not allow such characters, and much work has gone into finding a way to internationalize domain names into a standard ASCII format, thereby preserving the stability of the domain name system. IDN has, by the standards of the Internet, a long history; it was originally proposed in 1996 (by M. Drst) and implemented in 1998 (by James Seng under the guidance of T.W.Tan). After much debate and many competing proposals, a system called Internationalizing Domain Names in Applications (IDNA was adopted as the chosen standard, and has been rolled out in several top level domains. In IDNA, the term internationalized domain name means specifically any domain name consisting only of labels to which the IDNA ToASCII algorithm can be successfully applied. (For the meaning of 'label' and 'ToASCII', see the section ToASCII and ToUnicode below.) In March 2008, the IETF formed a new IDN Working Group to update the current IDNA protocol.
Internationalizing domain names in applications
Internationalizing Domain Names in Applications (IDNA) is a mechanism defined in 2003 for handling internationalized domain names containing non-ASCII characters. While much of the Domain Name System can technically support non-ASCII characters, applications such as e-mail and web browsers restrict domain names to what can be used as a hostname. Rather than redesigning the existing DNS infrastructure, it was decided that non-ASCII domain names should be converted to a suitable ASCII-based form by web browsers and other user applications; IDNA specifies how this conversion is to be done. IDNA was designed for maximum backward compatibility with the existing DNS system, which was designed for use with names using only a subset of the ASCII character set. An IDNA-enabled application is able to convert between the restricted-ASCII and non-ASCII representations of a domain, using the ASCII form in cases where it is needed (such as for DNS lookup), but being able to present the more readable non-ASCII form to users. Applications that do not support IDNA will not be able to handle domain names with non-ASCII characters, but will still be able to access such domains if given the (usually rather cryptic) ASCII equivalent. ICANN issued guidelines for the use of IDNA in June 2003, and it was already possible to register .jp domains using this system in July 2003 and .info domains in March 2004. Several other top-level domain registries started accepting registrations in 2004 and 2005. IDN Guidelines were first created in June 2003, and have been updated to respond to phishing concerns in November 2005. An ICANN working group focused on country code domain names at the top level was formed in November 2007 and promoted jointly by the country code supporting organization and the Governmental Advisory Committee. Mozilla 1.4, Netscape 7.1, Opera 7.11 and Safari are among the first applications to support IDNA. A browser plugin is available for Internet Explorer 6 to provide IDN support. Internet Explorer 7.0 and Windows Vista's URL APIs provide native support for IDN.
ToASCII and ToUnicode
The conversions between ASCII and non-ASCII forms of a domain name are accomplished by algorithms called ToASCII and ToUnicode. These algorithms are not applied to the domain name as a whole, but rather to individual labels. For example, if the domain name is www.example.com, then the labels are www, example, and com, and ToASCII or ToUnicode would be applied to each of these three separately. The details of these two algorithms are complex, and are specified in the RFCs linked at the end of this article. The following gives an overview of their behaviour. ToASCII leaves unchanged any ASCII label, but will fail if the label is unsuitable for DNS. If given a label containing at least one non-ASCII character, ToASCII will apply the Nameprep algorithm (which converts the label to lowercase and performs other normalization) and will then translate the result to ASCII using Punycode before prepending the 4-character string "xn--". This 4-character string is called the ACE prefix, where ACE means ASCII Compatible Encoding, and is used to distinguish Punycode-encoded labels from ordinary ASCII labels. Note that the ToASCII algorithm can fail in a number of ways; for example, the final string could exceed the 63-character limit for the DNS. A label on which ToASCII fails cannot be used in an internationalized domain name. ToUnicode reverses the action of ToASCII, stripping off the ACE prefix and applying the Punycode decode algorithm. It does not reverse the Nameprep processing, since that is merely a normalization and is by nature irreversible. Unlike ToASCII, ToUnicode always succeeds, because it simply returns the original string if decoding would fail. In particular, this means that ToUnicode has no effect on a string that does not begin with the ACE prefix.