What is IDN?
Also known as: Internationalized Domain Name
An Internationalized Domain Name (IDN) is a domain name that includes characters outside the ASCII set, encoded as Punycode for compatibility with the DNS.
An Internationalized Domain Name (IDN) is a domain name that contains non-ASCII characters, such as accented letters, Chinese ideographs, Arabic script, or Cyrillic letters. Traditional DNS protocols, defined in RFC 1035, only support ASCII characters (letters, digits, and hyphens). To allow global scripts while preserving backward compatibility, IDNs are encoded into a ASCII-compatible form called Punycode, specified in RFC 3492.
The encoding process, known as IDNA (Internationalized Domain Names in Applications), is defined in RFC 5890 through RFC 5894. When a user types an IDN in a browser, the application layer converts the Unicode labels to Punycode before sending DNS queries. For example, the domain "münchen.example" becomes "xn--mnchen-3ya.example" on the wire. The Punycode prefix "xn--" signals to resolvers that the label is an IDN. The resolver then processes the label as a normal ASCII label, and the response is decoded back to Unicode for display.
IDNs sit at the application layer of the internet stack, above DNS transport. They do not modify the DNS itself; they only transform the representation of domain names. ICANN manages the IDN gTLD program, which allows registries to offer domains in local scripts. Security concerns include homograph attacks, where visually similar characters from different scripts can be used to spoof domain names. Browsers and registries mitigate this through policy and visual indicators.
Key facts
- IDNs allow domain names in scripts like Arabic, Chinese, Cyrillic, and accented Latin.
- Non-ASCII characters are encoded as Punycode (RFC 3492) for DNS transport.
- The Punycode prefix is always 'xn--' for IDN labels.
- IDNA protocol is defined in RFCs 5890-5894, published in 2010.
- Homograph attacks are a known security risk with IDNs.
- ICANN manages the IDN gTLD program for internationalized top-level domains.
How it works in practice
Related terms
References
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