How does Internationalized Domain Names (IDN) work?

By the introduction of Internationalized Domain Names (IDN) it is now possible to register domain names on the Internet, containing regional characters, like for example www.räksmörgå is possible for a number of the Top Level Domains (TLD), like .se and .nu.


The Domain Name System (DNS) only supports the characters a-z, 0-9 and the hyphen character (‘-‘). To be able to use other international characters in the domain name, it has to be coded using ASCII Compatible Encoding (ACE). When an Internationalized Domain Name is encoded using ACE, it is prepended with the prefix ‘xn--‘. It is the converted domain name that will be registered in the Domain Name System (DNS). By making browsers IDN-aware, they will let the user type an IDN URL (like ‘www.räksmörgå’), then encode it using ACE and the computer and network will handle it as it would be a regular a-z, 0-9 and ‘-‘ domain name.

ASCII Compatible Encoding (ACE)

The domain name ‘www.räksmörgå’ will be ‘’ when converted using ACE. When registering an IDN, it is recommended that you also register the same domain name but using the standard characters supported by DNS as well (i.e. a-z, 0-9 and ‘-‘). That way users that do not have the regional characters on their keyboard, or users using older browsers that do not support IDN, still will be able to visit your website. For the example above, you would additionally register ‘’.

By using one of these ACE converters, you can convert your IDN to ACE.

Browsers that support IDN

Microsoft Internet Explorer (version 7.0 or later)
Mozilla Firefox (some earlier versions came with IDN disabled due to security)
Google Chrome

For Microsoft Internet Explorer earlier than 7.0 there are a couple of plugins that can be installed to support IDN. One is available from VeriSign and another is from Internet Systems Consortium (ISC).

Other softwares using Domain Name System (DNS) will not be able to use IDN unless they are specifically modified to support it.  Most e-mail programs do not support IDN. The ACE converted domain name (like ‘’) can of course be used in any existing application as it only will contain the valid characters for the DNS, but that kind of takes away the entire idea with IDN.

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