One document matched: draft-ietf-idnabis-protocol-09.txt
Differences from draft-ietf-idnabis-protocol-08.txt
Network Working Group J. Klensin
Internet-Draft February 20, 2009
Obsoletes: 3490, 3491
(if approved)
Updates: 3492 (if approved)
Intended status: Standards Track
Expires: August 24, 2009
Internationalized Domain Names in Applications (IDNA): Protocol
draft-ietf-idnabis-protocol-09.txt
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Abstract
This document supplies the protocol definition for a revised and
updated specification for internationalized domain names (IDNs). The
rationale for these changes, the relationship to the older
specification, and important terminology are provided in other
documents. This document specifies the protocol mechanism, called
Internationalizing 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Discussion Forum . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Requirements and Applicability . . . . . . . . . . . . . . . . 6
3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. DNS Resource Records . . . . . . . . . . . . . . . . . 7
3.2.2. Non-domain-name Data Types Stored in the DNS . . . . . 7
4. Registration Protocol . . . . . . . . . . . . . . . . . . . . 7
4.1. Input to IDNA Registration Process . . . . . . . . . . . . 8
4.2. Permitted Character and Label Validation . . . . . . . . . 8
4.2.1. Input Format . . . . . . . . . . . . . . . . . . . . . 8
4.2.2. Rejection of Characters that are not Permitted . . . . 8
4.2.3. Label Validation . . . . . . . . . . . . . . . . . . . 9
4.2.4. Registration Validation Summary . . . . . . . . . . . 10
4.3. Registry Restrictions . . . . . . . . . . . . . . . . . . 10
4.4. Punycode Conversion . . . . . . . . . . . . . . . . . . . 11
4.5. Insertion in the Zone . . . . . . . . . . . . . . . . . . 11
5. Domain Name Lookup Protocol . . . . . . . . . . . . . . . . . 11
5.1. Label String Input . . . . . . . . . . . . . . . . . . . . 11
5.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 11
5.3. Character Changes in Preprocessing or the User
Interface . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4. A-label Input . . . . . . . . . . . . . . . . . . . . . . 13
5.5. Validation and Character List Testing . . . . . . . . . . 13
5.6. Punycode Conversion . . . . . . . . . . . . . . . . . . . 14
5.7. DNS Name Resolution . . . . . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Summary of Major Changes from IDNA2003 . . . . . . . 18
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 19
B.1. Changes between Version -00 and -01 of
draft-ietf-idnabis-protocol . . . . . . . . . . . . . . . 19
B.2. Version -02 . . . . . . . . . . . . . . . . . . . . . . . 19
B.3. Version -03 . . . . . . . . . . . . . . . . . . . . . . . 19
B.4. Version -04 . . . . . . . . . . . . . . . . . . . . . . . 20
B.5. Version -05 . . . . . . . . . . . . . . . . . . . . . . . 20
B.6. Version -06 . . . . . . . . . . . . . . . . . . . . . . . 20
B.7. Version -07 . . . . . . . . . . . . . . . . . . . . . . . 20
B.8. Version -08 . . . . . . . . . . . . . . . . . . . . . . . 21
B.9. Version -09 . . . . . . . . . . . . . . . . . . . . . . . 21
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
This document supplies the protocol definition for a revised and
updated specification for internationalized domain names. Essential
definitions and terminology for understanding this document and a
road map of the collection of documents that make up IDNA2008 appear
in [IDNA2008-Defs]. Appendix A discusses the relationship between
this specification and the earlier version of IDNA (referred to here
as "IDNA2003") and the rationale for these changes, along with
considerable explanatory material and advice to zone administrators
who support IDNs is provided in another documents, notably
[IDNA2008-Rationale].
IDNA works by allowing applications to use certain 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 depend on changes to any infrastructure. In
particular, IDNA does not depend on any changes to DNS servers,
resolvers, or protocol elements, because the ASCII name service
provided by the existing DNS is entirely sufficient for IDNA.
IDNA is applied only to DNS labels. Standards for combining labels
into fully-qualified domain names and parsing labels out of those
names are covered in the base DNS standards [RFC1034] [RFC1035] and
their various updates. An application may, of course, apply locally-
appropriate conventions to the presentation forms of domain names as
discussed in [IDNA2008-Rationale].
While they share terminology, reference data, and some operations,
this document describes two separate protocols, one for IDN
registration (Section 4) and one for IDN lookup (Section 5).
1.1. Discussion Forum
[[anchor3: RFC Editor: please remove this section.]]
This work is being discussed in the IETF IDNABIS WG and on the
mailing list idna-update@alvestrand.no
2. Terminology
General terminology applicable to IDNA, but with meanings familiar to
those who have worked with Unicode or other character set standards
and the DNS, appears in [IDNA2008-Defs]. Terminology that is an
integral, normative, part of the IDNA definition, including the
definitions of "ACE", appears in that document as well. Familiarity
with the terminology materials in that document is assumed for
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reading this one. The reader of this document is assumed to be
familiar with DNS-specific terminology as defined in RFC 1034
[RFC1034].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].
3. Requirements and Applicability
3.1. Requirements
IDNA conformance means adherence to the following requirements:
1. Whenever a domain name is put into an IDN-unaware domain name
slot (see Section 2 and [IDNA2008-Defs]), it MUST contain only
ASCII characters (i.e., must be either an A-label or an NR-LDH-
label), or must be a label associated with a DNS application that
is not subject to either IDNA or the historical recommendations
for "hostname"-style names [RFC1034].
2. Comparison of labels MUST be done on equivalent forms: either
both A-Label forms or both U-Label forms. Because A-labels and
U-labels can be transformed into each other without loss of
information, these comparisons are equivalent. However, when a
pair of putative A-labels are compared, the comparison MUST use
an ASCII case-insensitive comparison (as with all comparisons of
ASCII DNS labels). Comparisons on putative U-labels must test
that the two strings are identical, without case-folding or other
intermediate steps. Note that it is not necessary to verify that
labels are valid in order to compare them. In many cases,
verification of validity (that the strings actually are A-labels
or U-labels) may be important for other reasons and SHOULD be
performed.
3. Labels being registered MUST conform to the requirements of
Section 4. Labels being looked up and the lookup process MUST
conform to the requirements of Section 5.
3.2. Applicability
IDNA is applicable to all domain names in all domain name slots
except where it is explicitly excluded. It is not applicable to
domain name slots which do not use the LDH syntax rules.
This implies that IDNA is applicable to many protocols that predate
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IDNA. Note that IDNs occupying domain name slots in those older
protocols MUST be in A-label form until and unless those protocols
and implementations of them are upgraded to be IDN-aware. IDNs
actually appearing in DNS queries or responses MUST be A-labels.
3.2.1. DNS Resource Records
IDNA applies only to domain names in the NAME and RDATA fields of DNS
resource records whose CLASS is IN.
There are currently no other exclusions on the applicability of IDNA
to DNS resource records. Applicability depends entirely on the
CLASS, and not on the TYPE except as noted below. This will remain
true, even as new types are defined, unless there is a compelling
reason for a new type that requires type-specific rules. The special
naming conventions applicable to SRV records are examples of type-
specific rules that are incompatible with IDNA coding. Hence the
first two labels (the ones required to start in "_") on a record with
TYPE SRV MUST NOT be A-labels or U-labels (while it would be possible
to write a non-ASCII string with a leading underscore, conversion to
an A-label would be impossible without loss of information because
the underscore is not a letter, digit, or hyphen and is consequently
DISALLOWED in IDNs). Of course, those labels may be part of a domain
that uses IDN labels at higher levels in the tree.
3.2.2. Non-domain-name Data Types Stored in the DNS
Although IDNA enables the representation of non-ASCII characters in
domain names, that does not imply that IDNA enables the
representation of non-ASCII characters in other data types that are
stored in domain names, specifically in the RDATA field for types
that have structured RDATA format. For example, an email address
local part is stored in a domain name in the RNAME field as part of
the RDATA of an SOA record (hostmaster@example.com would be
represented as hostmaster.example.com). IDNA specifically does not
update the existing email standards, which allow only ASCII
characters in local parts. Even though work is in progress to define
internationalization for email addresses [RFC4952], changes to the
email address part of the SOA RDATA would require action in, or
updates to, other standards, specifically those that specify the
format of the SOA RR.
4. Registration Protocol
This section defines the procedure for registering an IDN. The
procedure is implementation independent; any sequence of steps that
produces exactly the same result for all labels is considered a valid
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implementation.
Note that, while the registration and lookup protocols (Section 5)
are very similar in most respects, they are different and
implementers should carefully follow the steps they are implementing.
4.1. Input to IDNA Registration Process
[[anchor8: Note in Draft: This subsection is new in -08, based on
comments on the mailing list in January and February 2009. It
replaces the previous first two subsections of this section and
completely eliminates the discussion of local mapping for
registration.]]
Registration processes are outside the scope of these protocols and
may differ significantly depending on local needs. By the time a
string enters the IDNA registration process as described in this
specification, it is expected to be in Unicode and MUST be in Unicode
Normalization Form C (NFC [Unicode-UAX15]). Entities responsible for
zone files ("registries") are expected to accept only the exact
string for which registration is requested, free of any mappings or
local adjustments. They SHOULD avoid any possible ambiguity by
accepting registrations only for A-labels, possibly paired with the
relevant U-labels so that they can verify the correspondence.
4.2. Permitted Character and Label Validation
4.2.1. Input Format
The registry MAY permit submission of labels in A-label form. If it
does so, it MUST perform a conversion to a U-label, perform the steps
and tests described below, and verify that the A-label produced by
the step in Section 4.4 matches the one provided as input. If, for
some reason, it does not, the registration MUST be rejected. If the
conversion to a U-label is not performed, the registry MUST verify
that the A-label is superficially valid, i.e., that it does not
violate any of the rules of Punycode [RFC3492] encoding such as the
prohibition on trailing hyphen-minus, appearance of non-basic
characters before the delimiter, and so on. Invalid strings that
appear to be A-labels MUST NOT be placed in DNS zones.
4.2.2. Rejection of Characters that are not Permitted
The candidate Unicode string is checked to verify that characters
that IDNA does not permit do not appear in it. Those characters are
identified in the "DISALLOWED" and "UNASSIGNED" lists that are
specified in [IDNA2008-Tables] and described informally in
[IDNA2008-Rationale]. Characters that are either DISALLOWED or
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UNASSIGNED MUST NOT be part of labels to be processed for
registration in the DNS.
4.2.3. Label Validation
The proposed label (in the form of a Unicode string, i.e., a putative
U-label) is then examined, performing tests that require examination
of more than one character.
4.2.3.1. Rejection of Hyphen Sequences in U-labels
The Unicode string MUST NOT contain "--" (two consecutive hyphens) in
the third and fourth character positions when the label is considered
in "on the wire" order.
4.2.3.2. Leading Combining Marks
The first character of the string (when the label is considered in
"on the wire" order) is examined to verify that it is not a combining
mark (or combining character) (see The Unicode Standard, Section 2.11
[Unicode] for an exact definition). If it is a combining mark, the
string MUST NOT be registered.
4.2.3.3. Contextual Rules
Each code point is checked for its identification as a character
requiring contextual processing for registration (the list of
characters appears as the combination of CONTEXTJ and CONTEXTO in
[IDNA2008-Tables] as do the contextual rules themselves). If that
indication appears, the table of contextual rules is checked for a
rule for that character. If no rule is found, the proposed label is
rejected and MUST NOT be installed in a zone file. If one is found,
it is applied (typically as a test on the entire label or on adjacent
characters within the label). If the application of the rule does
not conclude that the character is valid in context, the proposed
label MUST BE rejected. (See the IANA Considerations: IDNA Context
Registry section of [IDNA2008-Tables].)
These contextual rules are required to support the use of characters
that could be used, under other conditions, to produce misleading
labels or to cause unacceptable ambiguity in label matching and
interpretation. For example, labels containing invisible ("zero-
width") characters may be permitted in context with characters whose
presentation forms are significantly changed by the presence or
absence of the zero-width characters, while other labels in which
zero-width characters appear may be rejected.
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4.2.3.4. Labels Containing Characters Written Right to Left
Special tests are required for strings containing characters that are
normally written from right to left. The criteria for classifying
characters in terms of directionality are identified in the "Bidi"
document [IDNA2008-BIDI] in this series. That document also
describes conditions for strings that contain one or more of those
characters to be U-labels. The tests for those conditions, specified
there, are applied. Strings that contain right to left characters
that do not conform to the IDNA Bidi rules MUST NOT be inserted as
labels in zone files.
4.2.4. Registration Validation Summary
Strings that contain at least one non-ASCII character, have been
produced by the steps above, whose contents pass the above tests, and
are 63 or fewer characters long in ACE form (see Section 4.4), are
U-labels.
To summarize, tests are made in Section 4.2 for invalid characters,
invalid combinations of characters, and for labels that are invalid
even if the characters they contain are valid individually.
4.3. Registry Restrictions
Registries at all levels of the DNS, not just the top level, are
expected to establish policies about the labels that may be
registered, and for the processes associated with that action. While
exact policies are not specified as part of IDNA2008 and it is
expected that different registries may specify different policies,
there SHOULD be policies. Even a trivial policy (e.g., "anything can
be registered in this zone that can be represented as an A-label -
U-label pair") has value because it provides notice to users and
applications implementers that the registry cannot be relied upon to
provide even minimal user-protection restrictions. These per-
registry policies and restrictions are an essential element of the
IDNA registration protocol even for registries (and corresponding
zone files) deep in the DNS hierarchy. As discussed in
[IDNA2008-Rationale], such restrictions have always existed in the
DNS. That document also contains a discussion and recommendations
about possible types of rules.
The string produced by the above steps is checked and processed as
appropriate to local registry restrictions. Application of those
registry restrictions may result in the rejection of some labels or
the application of special restrictions to others.
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4.4. Punycode Conversion
The resulting U-label is converted to an A-label. The A-label, more
precisely defined elsewhere, is the encoding of the U-label according
to the Punycode algorithm [RFC3492] with the ACE prefix "xn--" added
at the beginning of the string. The resulting string must, of
course, conform to the length limits imposed by the DNS. This
document updates RFC 3492 only to the extent of replacing the
reference to the discussion of the ACE prefix. The ACE prefix is now
specified in this document rather than as part of RFC 3490 or
Nameprep [RFC3491] but is the same in both sets of documents.
The failure conditions identified in the Punycode encoding procedure
cannot occur if the input is a U-label as determined by the steps
above.
4.5. Insertion in the Zone
The A-label is registered in the DNS by insertion into a zone.
5. Domain Name Lookup Protocol
Lookup is conceptually different from registration and different
tests are applied on the client. Although some validity checks are
necessary to avoid serious problems with the protocol (see
Section 5.5ff.), the lookup-side tests are more permissive and rely
on the assumption that names that are present in the DNS are valid.
That assumption is, however, a weak one because the presence of wild
cards in the DNS might cause a string that is not actually registered
in the DNS to be successfully looked up.
5.1. Label String Input
The user supplies a string in the local character set, typically by
typing it or clicking on, or copying and pasting, a resource
identifier, e.g., a URI [RFC3986] or IRI [RFC3987] from which the
domain name is extracted. Alternately, some process not directly
involving the user may read the string from a file or obtain it in
some other way. Processing in this step and the next two are local
matters, to be accomplished prior to actual invocation of IDNA, but
at least the two steps in Section 5.2 and Section 5.3 must be
accomplished in some way.
5.2. Conversion to Unicode
The string is converted from the local character set into Unicode, if
it is not already Unicode. The exact nature of this conversion is
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beyond the scope of this document, but may involve normalization
identical to that discussed in Section 4.1. The result MUST be a
Unicode string in NFC form.
5.3. Character Changes in Preprocessing or the User Interface
The Unicode string MAY then be processed to prevent confounding of
user expectations. For instance, it might be reasonable, at this
step, to convert all upper case characters to lower case, if this
makes sense in the user's environment, but even this should be
approached with caution due to some edge cases: in the long term, it
is probably better for users to understand IDNs strictly in lower-
case, U-label, form. More generally, preprocessing may be useful to
smooth the transition from IDNA2003, especially for direct user
input, but with similar cautions. In general, IDNs appearing in
files and those transmitted across the network as part of protocols
are expected to be in either ASCII form (including A-labels) or to
contain U-labels, rather than being in forms requiring mapping or
other conversions.
Other examples of processing for localization might be applied,
especially to direct user input, at this point. They include
interpreting various characters as separating domain name components
from each other (label separators) because they either look like
periods or are used to separate sentences, mapping halfwidth or
fullwidth East Asian characters to the common form permitted in
labels, or giving special treatment to characters whose presentation
forms are dependent only on placement in the label. Such
localization changes are also outside the scope of this
specification.
Recommendations for preprocessing for global contexts (i.e., when
local considerations do not apply or cannot be used) and for maximum
interoperability with labels that might have been specified under
liberal readings of IDNA2003 are given in [IDNA2008-Rationale]. It
is important to note that the intent of these specifications is that
labels in application protocols, files, or links are intended to be
in U-label or A-label form. Preprocessing MUST NOT map a character
that is valid in a label as specified elsewhere in this document or
in [IDNA2008-Tables] into another character. Excessively liberal use
of preprocessing, especially to strings stored in files, poses a
threat to consistent and predictable behavior for the user even if
not to actual interoperability.
Because these transformations are local, it is important that domain
names that might be passed between systems (e.g., in IRIs) be
U-labels or A-labels and not forms that might be accepted locally as
a consequence of this step. This step is not standardized as part of
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IDNA, and is not further specified here.
5.4. A-label Input
If the input to this procedure appears to be an A-label (i.e., it
starts in "xn--"), the lookup application MAY attempt to convert it
to a U-label and apply the tests of Section 5.5 and the conversion of
Section 5.6 to that form. If the label is converted to Unicode
(i.e., to U-label form) using the Punycode decoding algorithm, then
the processing specified in those two sections MUST be performed, and
the label MUST be rejected if the resulting label is not identical to
the original. See the Name Server Considerations section of
[IDNA2008-Rationale] for additional discussion on this topic.
That conversion and testing SHOULD be performed if the domain name
will later be presented to the user in native character form (this
requires that the lookup application be IDNA-aware). If those steps
are not performed, the lookup process SHOULD at least make tests to
determine that the string is actually an A-label, examining it for
the invalid formats specified in the Punycode decoding specification.
Applications that are not IDNA-aware will obviously omit that
testing; others MAY treat the string as opaque to avoid the
additional processing at the expense of providing less protection and
information to users.
5.5. Validation and Character List Testing
As with the registration procedure described in Section 4, the
Unicode string is checked to verify that all characters that appear
in it are valid as input to IDNA lookup processing. As discussed
above and in [IDNA2008-Rationale], the lookup check is more liberal
than the registration one. Putative labels with any of the following
characteristics MUST BE rejected prior to DNS lookup:
o Labels containing code points that are unassigned in the version
of Unicode being used by the application, i.e.,in the UNASSIGNED
category of [IDNA2008-Tables].
o Labels that are not in NFC form as defined in [Unicode-UAX15].
o Labels containing prohibited code points, i.e., those that are
assigned to the "DISALLOWED" category in the permitted character
table [IDNA2008-Tables].
o Labels containing code points that are identified in
[IDNA2008-Tables] as "CONTEXTJ", i.e., requiring exceptional
contextual rule processing on lookup, but that do not conform to
that rule. Note that this implies that a rule much be defined,
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not null: a character that requires a contextual rule but for
which the rule is null is treated in this step as having failed to
conform to the rule.
o Labels containing code points that are identified in
[IDNA2008-Tables] as "CONTEXTO", but for which no such rule
appears in the table of rules. Applications resolving DNS names
or carrying out equivalent operations are not required to test
contextual rules for "CONTEXTO" characters, only to verify that a
rule is defined (although they MAY make such tests to give better
information to the user).
o Labels whose first character is a combining mark (see
Section 4.2.3.2.
In addition, the application SHOULD apply the following test. The
test may be omitted in special circumstances, such as when the lookup
application knows that the conditions are enforced elsewhere, because
an attempt to look up and resolve such strings will almost certainly
lead to a DNS lookup failure except when wildcards are present in the
zone. However, applying the test is likely to give much better
information about the reason for a lookup failure -- information that
may be usefully passed to the user when that is feasible -- than DNS
resolution failure information alone. In any event, lookup
applications should avoid attempting to resolve labels that are
invalid under that test.
o Verification that the string is compliant with the requirements
for right to left characters, specified in [IDNA2008-BIDI].
For all other strings, the lookup application MUST rely on the
presence or absence of labels in the DNS to determine the validity of
those labels and the validity of the characters they contain. If
they are registered, they are presumed to be valid; if they are not,
their possible validity is not relevant. A lookup application that
declines to process a string that conforms to the rules above and
does not look it up in the DNS is not in conformance with this
protocol.
5.6. Punycode Conversion
The validated string, a U-label, is converted to an A-label using the
Punycode algorithm with the ACE prefix added.
5.7. DNS Name Resolution
The A-label is looked up in the DNS, using normal DNS resolver
procedures.
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6. Security Considerations
Security Considerations for this version of IDNA except for the
special issues associated with right to left scripts and characters
are described in [IDNA2008-Defs]. Specific issues for labels
containing characters associated with scripts written right to left
appear in [IDNA2008-BIDI].
7. IANA Considerations
IANA actions for this version of IDNA are specified in
[IDNA2008-Tables] and discussed informally in [IDNA2008-Rationale].
The components of IDNA described in this document do not require any
IANA actions.
8. Contributors
While the listed editor held the pen, the original versions of this
document represent the joint work and conclusions of an ad hoc design
team consisting of the editor and, in alphabetic order, Harald
Alvestrand, Tina Dam, Patrik Faltstrom, and Cary Karp. This document
draws significantly on the original version of IDNA [RFC3490] both
conceptually and for specific text. This second-generation version
would not have been possible without the work that went into that
first version and its authors, Patrik Faltstrom, Paul Hoffman, and
Adam Costello. While Faltstrom was actively involved in the creation
of this version, Hoffman and Costello were not and should not be held
responsible for any errors or omissions.
9. Acknowledgments
This revision to IDNA would have been impossible without the
accumulated experience since RFC 3490 was published and resulting
comments and complaints of many people in the IETF, ICANN, and other
communities, too many people to list here. Nor would it have been
possible without RFC 3490 itself and the efforts of the Working Group
that defined it. Those people whose contributions are acknowledged
in RFC 3490, [RFC4690], and [IDNA2008-Rationale] were particularly
important.
Specific textual changes were incorporated into this document after
suggestions from the other contributors, Stephane Bortzmeyer, Vint
Cerf, Mark Davis, Paul Hoffman, Kent Karlsson, Erik van der Poel,
Marcos Sanz, Andrew Sullivan, Ken Whistler, and other WG
participants. Special thanks are due to Paul Hoffman for permission
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to extract material from his Internet-Draft to form the basis for
Appendix A
10. References
10.1. Normative References
[IDNA2008-BIDI]
Alvestrand, H. and C. Karp, "An updated IDNA criterion for
right-to-left scripts", July 2008, <https://
datatracker.ietf.org/drafts/draft-ietf-idnabis-bidi/>.
[IDNA2008-Defs]
Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
February 2009, <https://datatracker.ietf.org/drafts/
draft-ietf-idnabis-defs/>.
[IDNA2008-Tables]
Faltstrom, P., "The Unicode Codepoints and IDNA",
July 2008, <https://datatracker.ietf.org/drafts/
draft-ietf-idnabis-tables/>.
A version of this document is available in HTML format at
http://stupid.domain.name/idnabis/
draft-ietf-idnabis-tables-02.html
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications
(IDNA)", RFC 3492, March 2003.
[Unicode-PropertyValueAliases]
The Unicode Consortium, "Unicode Character Database:
PropertyValueAliases", March 2008, <http://
www.unicode.org/Public/UNIDATA/PropertyValueAliases.txt>.
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[Unicode-RegEx]
The Unicode Consortium, "Unicode Technical Standard #18:
Unicode Regular Expressions", May 2005,
<http://www.unicode.org/reports/tr18/>.
[Unicode-Scripts]
The Unicode Consortium, "Unicode Standard Annex #24:
Unicode Script Property", February 2008,
<http://www.unicode.org/reports/tr24/>.
[Unicode-UAX15]
The Unicode Consortium, "Unicode Standard Annex #15:
Unicode Normalization Forms", 2006,
<http://www.unicode.org/reports/tr15/>.
10.2. Informative References
[ASCII] American National Standards Institute (formerly United
States of America Standards Institute), "USA Code for
Information Interchange", ANSI X3.4-1968, 1968.
ANSI X3.4-1968 has been replaced by newer versions with
slight modifications, but the 1968 version remains
definitive for the Internet.
[IDNA2008-Rationale]
Klensin, J., Ed., "Internationalizing Domain Names for
Applications (IDNA): Issues, Explanation, and Rationale",
February 2009, <https://datatracker.ietf.org/drafts/
draft-ietf-idnabis-rationale>.
[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, April 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2535] Eastlake, D., "Domain Name System Security Extensions",
RFC 2535, March 1999.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, August 1999.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
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[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)",
RFC 3491, March 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and
Recommendations for Internationalized Domain Names
(IDNs)", RFC 4690, September 2006.
[RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", RFC 4952, July 2007.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
5.0", 2007.
Boston, MA, USA: Addison-Wesley. ISBN 0-321-48091-0
Appendix A. Summary of Major Changes from IDNA2003
1. Update base character set from Unicode 3.2 to Unicode version-
agnostic.
2. Separate the definitions for the "registration" and "lookup"
activities.
3. Disallow symbol and punctuation characters except where special
exceptions are necessary.
4. Remove the mapping and normalization steps from the protocol and
have them instead done by the applications themselves, possibly
in a local fashion, before invoking the protocol.
5. Change the way that the protocol specifies which characters are
allowed in labels from "humans decide what the table of
codepoints contains" to "decision about codepoints are based on
Unicode properties plus a small exclusion list created by
humans".
6. Introduce the new concept of characters that can be used only in
specific contexts.
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7. Allow typical words and names in languages such as Dhivehi and
Yiddish to be expressed.
8. Make bidirectional domain names (delimited strings of labels,
not just labels standing on their own) display in a less
surprising fashion whether they appear in obvious domain name
contexts or as part of running text in paragraphs.
9. Remove the dot separator from the mandatory part of the
protocol.
10. Make some currently-valid labels that are not actually IDNA
labels invalid.
Appendix B. Change Log
[[anchor20: RFC Editor: Please remove this appendix.]]
B.1. Changes between Version -00 and -01 of draft-ietf-idnabis-protocol
o Corrected discussion of SRV records.
o Several small corrections for clarity.
o Inserted more "open issue" placeholders.
B.2. Version -02
o Rewrote the "conversion to Unicode" text in Section 5.2 as
requested on-list.
o Added a comment (and reference) about EDNS0 to the "DNS Server
Conventions" section, which was also retitled.
o Made several editorial corrections and improvements in response to
various comments.
o Added several new discussion placeholder anchors and updated some
older ones.
B.3. Version -03
o Trimmed change log, removing information about pre-WG drafts.
o Incorporated a number of changes suggested by Marcos Sanz in his
note of 2008.07.17 and added several more placeholder anchors.
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o Several minor editorial corrections and improvements.
o "Editor" designation temporarily removed because the automatic
posting machinery does not accept it.
B.4. Version -04
o Removed Contextual Rule appendices for transfer to Tables.
o Several changes, including removal of discussion anchors, based on
discussions at IETF 72 (Dublin)
o Rewrote the preprocessing material (Section 5.3) somewhat.
B.5. Version -05
o Updated part of the A-label input explanation (Section 5.4) per
note from Erik van der Poel.
B.6. Version -06
o Corrected a few typographical errors.
o Incorporated the material (formerly in Rationale) on the
relationship between IDNA2003 and IDNA2008 as an appendix and
pointed to the new definitions document.
o Text modified in several places to recognize the dangers of
interaction between DNS wildcards and IDNs.
o Text added to be explicit about the handling of edge and failure
cases in Punycode encoding and decoding.
o Revised for consistency with the new Definitions document and to
make the text read more smoothly.
B.7. Version -07
o Multiple small textual and editorial changes and clarifications.
o Requirement for normalization clarified to apply to all cases and
conditions for preprocessing further clarified.
o Substantive change to Section 4.2.1, turning a SHOULD to a MUST
(see note from Mark Davis, 19 November, 2008 18:14 -0800).
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B.8. Version -08
o Added some references and altered text to improve clarity.
o Changed the description of CONTEXTJ/CONTEXTO to conform to that in
Tables. In other words, these are now treated as distinction
categories (again), rather than as specially-flagged subsets of
PROTOCOL VALID.
o The discussion of label comparisons has been rewritten to make it
more precise and to clarify that one does not need to verify that
a string is a [valid] A-label or U-label in order to test it for
equality with another string. The WG should verify that the
current text is what is desired.
o Other changes to reflect post-IETF discussions or editorial
improvements.
B.9. Version -09
o Removed Security Considerations material to Defs document.
o Removed the Name Server Considerations material to Rationale.
That material is not normative and not needed to implement the
protocol itself.
o Adjusted terminology to match new version of Defs.
o Removed all discussion of local mapping and option for it from
registration protocol.
o Removed some old placeholders and inquiries because no comments
have been received.
o Small editorial corrections.
Author's Address
John C Klensin
1770 Massachusetts Ave, Ste 322
Cambridge, MA 02140
USA
Phone: +1 617 245 1457
Email: john+ietf@jck.com
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