The IETF (Internet Engineering Task Force) led the effort to create standards for using non-ASCII characters in the Domain Name System (DNS).

The DNS only recognises ASCII characters A-Z, 0-9 and '-'. This limits the number of characters that can be utilised to build domain names to 37 of the more than 96,000 characters identified within Unicode. To create domain names from the range of Unicode characters, a character-encoding scheme that uniquely maps Unicode code points to an ASCII representation must be used and standardised.

The IETF published these standards relating to Internationalised Domain Names (IDN): Encoding Schemes, Framework, Protocol, Unicode and Right-to-Left Scripts.


The encoding scheme for IDNs uses punycode, an ASCII Compatible Encoding (ACE) that encodes local language characters into ASCII characters such that the DNS can accurately answer a request for an address record. To select punycode as the ACE standard, IETF considered the balance between compression and implementation. Punycode allows the greatest number of characters (code points) to be represented and is not difficult to deploy.


This RFC is one of a collection that, together, describe the protocol and usage context for a revision of Internationalised Domain Names for Applications (IDNA) that was largely completed in 2008, known within the series and elsewhere as "IDNA2008". The series replaces an earlier version of IDNA [RFC 3490] [RFC 3491]. For convenience, that version of IDNA is referred to as "IDNA2003". The newer version continues to use the Punycode algorithm [RFC3492] and the ACE (ASCII-compatible encoding) prefix from the earlier version.


This RFC describes the core IDNA2008 protocol and its operations. In combination with the "Bidi" (bi-directional) document described below, it explicitly updates and replaces [RFC 3490].


This RFC specifies rules for deciding whether a code point, considered in isolation or in context, is a candidate for inclusion in an Internationalised Domain Name (IDN). It is part of the specification of Internationalising Domain Names in Applications 2008 (IDNA2008).


The use of right-to-left scripts in Internationalised Domain Names (IDNs) has presented several challenges. This RFC provides new Bidi rules for Internationalised Domain Names for Applications (IDNA) labels, based on the problems encountered with some scripts and some shortcomings in the 2003 IDNA Bidi criterion.


This RFC provides the background, explanation and rationale for the need for new RFCs to tackle issues that have arisen from the previous version(s) of IDNA. The need to update the version of Unicode supported in IDNs is also discussed in this RFC.


These standards have been published and are now available:

Verisign is committed to following the IETF standards and supporting rapid deployment of this new technology.