Introduction to "International Domain Name"

You may or may not have heard about IDN and are wondering about what it is. In this blog post I’ll introduce the concept of IDN.

Most modern operating systems and applications natively support Unicode. However, both the DNS and SMTP protocols predate the development of Unicode. They were designed at a time when ASCII was the only character set that was safe to use across systems. As a result, only ASCII characters have been used in domain name registries and email addresses. Now, thanks to the adoption of RFC 5891/IDNA2008 Protocol, this long-standing restriction has recently been lifted for domain names.

Internationalizing Domain Names in Applications, or IDNA, allows the seamless use of IDN within application UI. For IDN to work, an ASCII-based transform of the Unicode characters, called Punycode, is registered with a Domain Name Server. Punycode-aware applications (such as Internet Explorer 8) then use ASCII-to-Unicode conversion algorithms to perform the appropriate transforms.

Applications that support the input, display, and indexing of IDNs, will provide users with a richer local experience and allow more users to enjoy the web in the language that they’re most comfortable with.

Here are some examples:




An IDN (Internationalized Domain Name) is an Internet domain name that contains one or more non-ASCII characters.


http://www. schö


ccTLD – country-code Top Level Domain


gTLD – generic Top Level Domain







Sub domain may contain non-ASCII as well, without having to have second and/or top level domains in IDN.



http://non-ASCII. ASCII. ASCII

Demand for IDN registrations is strong around the world especially in Asia. Countries could soon mandate support for IDN. So it’s important for you to know what IDNs are and support them in your applications.

To see more IDN examples and testing tips visit:



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