IETF RFC 5891 PDF

Introduction

This document supplies the protocol definition for Internationalized Domain Names in Applications (IDNA), with the version specified here known as IDNA2008. Essential definitions and terminology for understanding this document and a road map of the collection of documents that make up IDNA2008 appear in a separate Definitions document [RFC5890]. Appendix A discusses the relationship between this specification and the earlier version of IDNA (referred to here as "IDNA2003"). The rationale for these changes, along with considerable explanatory material and advice to zone administrators who support IDNs, is provided in another document, known informally in this series as the "Rationale document" [RFC5894].

IDNA works by allowing applications to use certain ASCII [ASCII] string labels (beginning with a special prefix) to represent non-ASCII name labels. Lower-layer protocols need not be aware of this; therefore, IDNA does not change any infrastructure. In particular, IDNA does not depend on any changes to DNS servers, resolvers, or DNS protocol elements, because the ASCII name service provided by the existing DNS can be used for IDNA.

IDNA applies only to a specific subset of DNS labels. The base DNS standards [RFC1034] [RFC1035] and their various updates specify how to combine labels into fully-qualified domain names and parse labels out of those names.

This document describes two separate protocols, one for IDN registration (Section 4) and one for IDN lookup (Section 5). These two protocols share some terminology, reference data, and operations.