Internationalized Domain Names for Applications (IDNA): Background, Explanation, and Rationale
RFC 5894
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RFC - Informational
(August 2010; No errata)
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Author |
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John Klensin
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Last updated |
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2015-10-14
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IETF
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plain text
html
pdf
htmlized
bibtex
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WG state
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WG Document
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Document shepherd |
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No shepherd assigned
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IESG |
IESG state |
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RFC 5894 (Informational)
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Consensus Boilerplate |
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Unknown
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Telechat date |
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Responsible AD |
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Lisa Dusseault
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Send notices to |
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(None)
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Internet Engineering Task Force (IETF) J. Klensin
Request for Comments: 5894 August 2010
Category: Informational
ISSN: 2070-1721
Internationalized Domain Names for Applications (IDNA):
Background, Explanation, and Rationale
Abstract
Several years have passed since the original protocol for
Internationalized Domain Names (IDNs) was completed and deployed.
During that time, a number of issues have arisen, including the need
to update the system to deal with newer versions of Unicode. Some of
these issues require tuning of the existing protocols and the tables
on which they depend. This document provides an overview of a
revised system and provides explanatory material for its components.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see 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/rfc5894.
Klensin Informational [Page 1]
RFC 5894 IDNA Rationale 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Context and Overview . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1. DNS "Name" Terminology . . . . . . . . . . . . . . . . 5
1.2.2. New Terminology and Restrictions . . . . . . . . . . . 6
1.3. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. Applicability and Function of IDNA . . . . . . . . . . . . 7
1.5. Comprehensibility of IDNA Mechanisms and Processing . . . 8
2. Processing in IDNA2008 . . . . . . . . . . . . . . . . . . . . 9
3. Permitted Characters: An Inclusion List . . . . . . . . . . . 9
3.1. A Tiered Model of Permitted Characters and Labels . . . . 10
3.1.1. PROTOCOL-VALID . . . . . . . . . . . . . . . . . . . . 10
3.1.2. CONTEXTUAL RULE REQUIRED . . . . . . . . . . . . . . . 11
3.1.2.1. Contextual Restrictions . . . . . . . . . . . . . 11
3.1.2.2. Rules and Their Application . . . . . . . . . . . 12
3.1.3. DISALLOWED . . . . . . . . . . . . . . . . . . . . . . 12
3.1.4. UNASSIGNED . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Registration Policy . . . . . . . . . . . . . . . . . . . 14
Klensin Informational [Page 2]
RFC 5894 IDNA Rationale August 2010
3.3. Layered Restrictions: Tables, Context, Registration, and
Applications . . . . . . . . . . . . . . . . . . . . . . . 15
4. Application-Related Issues . . . . . . . . . . . . . . . . . . 15
4.1. Display and Network Order . . . . . . . . . . . . . . . . 15
4.2. Entry and Display in Applications . . . . . . . . . . . . 16
4.3. Linguistic Expectations: Ligatures, Digraphs, and
Alternate Character Forms . . . . . . . . . . . . . . . . 19
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