Internationalized Domain Names in Applications (IDNA): Protocol
RFC 5891

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Internet Engineering Task Force (IETF)                        J. Klensin
Request for Comments: 5891                                   August 2010
Obsoletes: 3490, 3491
Updates: 3492
Category: Standards Track
ISSN: 2070-1721

    Internationalized Domain Names in Applications (IDNA): Protocol

Abstract

   This document is the revised protocol definition for
   Internationalized Domain Names (IDNs).  The rationale for changes,
   the relationship to the older specification, and important
   terminology are provided in other documents.  This document specifies
   the protocol mechanism, called Internationalized Domain Names in
   Applications (IDNA), for registering and looking up IDNs in a way
   that does not require changes to the DNS itself.  IDNA is only meant
   for processing domain names, not free text.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5891.

Klensin                      Standards Track                    [Page 1]
RFC 5891                    IDNA2008 Protocol                August 2010

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Klensin                      Standards Track                    [Page 2]
RFC 5891                    IDNA2008 Protocol                August 2010

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Requirements and Applicability . . . . . . . . . . . . . . . .  5
     3.1.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  5
       3.2.1.  DNS Resource Records . . . . . . . . . . . . . . . . .  6
       3.2.2.  Non-Domain-Name Data Types Stored in the DNS . . . . .  6
   4.  Registration Protocol  . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Input to IDNA Registration . . . . . . . . . . . . . . . .  7
     4.2.  Permitted Character and Label Validation . . . . . . . . .  7
       4.2.1.  Input Format . . . . . . . . . . . . . . . . . . . . .  7
       4.2.2.  Rejection of Characters That Are Not Permitted . . . .  8
       4.2.3.  Label Validation . . . . . . . . . . . . . . . . . . .  8
       4.2.4.  Registration Validation Requirements . . . . . . . . .  9
     4.3.  Registry Restrictions  . . . . . . . . . . . . . . . . . .  9
     4.4.  Punycode Conversion  . . . . . . . . . . . . . . . . . . .  9
     4.5.  Insertion in the Zone  . . . . . . . . . . . . . . . . . . 10
   5.  Domain Name Lookup Protocol  . . . . . . . . . . . . . . . . . 10
     5.1.  Label String Input . . . . . . . . . . . . . . . . . . . . 10
     5.2.  Conversion to Unicode  . . . . . . . . . . . . . . . . . . 10
     5.3.  A-label Input  . . . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Validation and Character List Testing  . . . . . . . . . . 11
     5.5.  Punycode Conversion  . . . . . . . . . . . . . . . . . . . 13
     5.6.  DNS Name Resolution  . . . . . . . . . . . . . . . . . . . 13
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13