Network Working Group J. Klensin
Internet-Draft September 26, 2008
Obsoletes: 3490 (if approved)
Intended status: Standards Track
Expires: March 30, 2009
Internationalized Domain Names in Applications (IDNA): Protocol
draft-ietf-idnabis-protocol-05.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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Discussion Forum . . . . . . . . . . . . . . . . . . . . . 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. Proposed label . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Conversion to Unicode and Normalization . . . . . . . . . 7
4.3. Permitted Character and Label Validation . . . . . . . . . 7
4.3.1. Rejection of Characters that are not Permitted . . . . 7
4.3.2. Label Validation . . . . . . . . . . . . . . . . . . . 8
4.3.3. Registration Validation Summary . . . . . . . . . . . 8
4.4. Registry Restrictions . . . . . . . . . . . . . . . . . . 9
4.5. Punycode Conversion . . . . . . . . . . . . . . . . . . . 9
4.6. Insertion in the Zone . . . . . . . . . . . . . . . . . . 9
5. Domain Name Lookup Protocol . . . . . . . . . . . . . . . . . 9
5.1. Label String Input . . . . . . . . . . . . . . . . . . . . 10
5.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 10
5.3. Character Changes in Preprocessing or the User
Interface . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4. A-label Input . . . . . . . . . . . . . . . . . . . . . . 11
5.5. Validation and Character List Testing . . . . . . . . . . 11
5.6. Punycode Conversion . . . . . . . . . . . . . . . . . . . 13
5.7. DNS Name Resolution . . . . . . . . . . . . . . . . . . . 13
6. Name Server Considerations . . . . . . . . . . . . . . . . . . 13
6.1. Processing Non-ASCII Strings . . . . . . . . . . . . . . . 13
6.2. DNSSEC Authentication of IDN Domain Names . . . . . . . . 13
6.3. Root and other DNS Server Considerations . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Changes between Version -00 and -01 of
draft-ietf-idnabis-protocol . . . . . . . . . . . . . . . 15
9.2. Version -02 . . . . . . . . . . . . . . . . . . . . . . . 15
9.3. Version -03 . . . . . . . . . . . . . . . . . . . . . . . 16
9.4. Version -04 . . . . . . . . . . . . . . . . . . . . . . . 16
9.5. Version -05 . . . . . . . . . . . . . . . . . . . . . . . 16
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . . 17
12.2. Informative References . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19
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Intellectual Property and Copyright Statements . . . . . . . . . . 20
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1. Introduction
This document supplies the protocol definition for a revised and
updated specification for internationalized domain names. The
rationale for these changes and relationship to the older
specification and some new terminology is provided in other
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 [RFC1035]. 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).
A good deal of the background material that appeared in RFC 3490 has
been removed from this update. That material is either of historical
interest only or has been covered from a more recent perspective in
RFC 4690 [RFC4690] and [IDNA2008-Rationale].
[[anchor2: Note in Draft: This document still needs more specifics
about how to perform some of the tests in the Registration and Lookup
protocols described below. Those details will be supplied in a later
revision, but the intent should be clear from the existing text.]]
1.1. Discussion Forum
[[anchor4: 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
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those who have worked with Unicode or other character set standards
and the DNS, appears in [IDNA2008-Rationale]. 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
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-Rationale]), it MUST contain
only ASCII characters (i.e., must be either an A-label or an 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 the A-label form, using an
ASCII case-insensitive comparison as with all comparisons of DNS
labels.
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
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.
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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). 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 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
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.
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4.1. Proposed label
The registrant submits a request for an IDN. The user typically
produces the request string by the keyboard entry of a character
sequence in the local native character set (which might, of course,
be Unicode). The registry MAY permit submission of labels in A-label
form. If it does so, it SHOULD 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 4.5 matches the one provided
as input. If, for some reason, it does not, the registration MUST be
rejected.
[[anchor9: Editorial: Should the sentences starting with "The
registry" be moved to 4.3? I.e., would they be more in sequence
there?]]
4.2. Conversion to Unicode and Normalization
Some system routine, or a localized front-end to the IDNA process,
ensures that the proposed label is a Unicode string or converts it to
one as appropriate. That string MUST be in Unicode Normalization
Form C (NFC [Unicode-UAX15]).
As a local implementation choice, the implementation MAY choose to
map some forbidden characters to permitted characters (for instance
mapping uppercase characters to lowercase ones), displaying the
result to the user, and allowing processing to continue. However, it
is strongly recommended that, to avoid any possible ambiguity,
entities responsible for zone files ("registries") accept
registrations only for A-labels (to be converted to U-labels by the
registry) or U-labels actually produced from A-labels, not forms
expected to be converted by some other process.
4.3. Permitted Character and Label Validation
4.3.1. Rejection of Characters that are not Permitted
The Unicode string is checked to verify that no characters that IDNA
does not permit in input appear in it. Those characters are
identified in the "DISALLOWED" and "UNASSIGNED" lists that are
discussed in [IDNA2008-Rationale]. The normative rules for producing
that list and the initial version of it are specified in
[IDNA2008-Tables]. Characters that are either DISALLOWED or
UNASSIGNED MUST NOT be part of labels being processed for
registration in the DNS.
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4.3.2. 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.
4.3.2.1. Rejection of Confusing or Hostile Sequences in U-labels
The Unicode string MUST NOT contain "--" (two consecutive hyphens) in
the third and fourth character positions.
4.3.2.2. Leading Combining Marks
The first character of the string is examined to verify that it is
not a combining mark. If it is a combining mark, the string MUST NOT
be registered.
4.3.2.3. Contextual Rules
Each code point is checked for its identification as characters
requiring contextual processing for registration (the list of
characters appears as the combination of CONTEXTJ and CONTEXTO in
[IDNA2008-Tables]). 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). 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-Rationale].)
4.3.2.4. Labels Containing Characters Written Right to Left
Additional special tests for right-to-left strings are applied (See
[IDNA2008-BIDI]. Strings that contain right to left characters that
do not conform to the rule(s) identified there MUST NOT be inserted
as labels in zone files.
4.3.3. Registration Validation Summary
Strings that have been produced by the steps above, and whose
contents pass the above tests, are U-labels.
To summarize, tests are made here for invalid characters, invalid
combinations of characters, and for labels that are invalid even if
the characters they contain are valid individually. For example,
labels containing invisible ("zero-width") characters may be
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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.
[[anchor16: Should the example text be removed or moved? Note that
I've been strongly encouraged to supply specific examples to reduce
abstraction and questions about the appropriateness of the text.
-JcK]]
4.4. 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.
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.
4.5. Punycode Conversion
The resulting U-label is converted to an A-label (i.e., the encoding
of that label according to the Punycode algorithm [RFC3492] with the
ACE prefix added, i.e., the "xn--..." form).
[[anchor17: Explain why 3492 failures cannot occur or explain what to
do if they do.]]
4.6. 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
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tests are applied on the client. Although some validity checks are
necessary to avoid serious problems with the protocol (see
Section 5.5 ff.), the lookup-side tests are more permissive and rely
heavily on the assumption that names that are present in the DNS are
valid.
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. Or 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 these
two steps 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
beyond the scope of this document, but may involve normalization, as
described in Section 4.2.
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 would be reasonable, at this
step, to convert all upper case characters to lower case, if this
makes sense in the user's environment. The procedures described in
this section are ordinarily useful only for processing direct user
input and when needed for backward compatibility with IDNA2003. 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, not 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.
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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 (i.e., one that is PROTOCOL-VALID or
permitted in any context) 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
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, of course, 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 also Section 6.1.
In general, 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).
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, the Unicode string is checked to
verify that all characters that appear in it are valid for IDNA
lookup processing input. 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:
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o Labels containing code points that are unassigned in the version
of Unicode being used by the application, i.e., in the
"Unassigned" Unicode category or the UNASSIGNED category of
[IDNA2008-Tables].
o Labels that are not in NFC form.
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 shown in the permitted
character table as requiring a contextual rule and that are
flagged as requiring exceptional special processing on lookup
("CONTEXTJ" in the Tables) but do not conform to that rule.
o Labels containing other code points that are shown in the
permitted character table as requiring a contextual rule
("CONTEXTO" in the tables), but for which no such rule appears in
the table of rules. With the exception in the rule immediately
above, applications resolving DNS names or carrying out equivalent
operations are not required to test contextual rules, only to
verify that a rule exists.
o Labels whose first character is a combining mark.>
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. 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 -- then 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 and resolve up a string that conforms to the
above rules is not in conformance with this protocol.
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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.
6. Name Server Considerations
6.1. Processing Non-ASCII Strings
Existing DNS servers do not know the IDNA rules for handling non-
ASCII forms of IDNs, and therefore need to be shielded from them.
All existing channels through which names can enter a DNS server
database (for example, master files (as described in RFC 1034) and
DNS update messages [RFC2136]) are IDN-unaware because they predate
IDNA. Other sections of this document provide the needed shielding
by ensuring that internationalized domain names entering DNS server
databases through such channels have already been converted to their
equivalent ASCII A-label forms.
Because of the design of the algorithms in Section 4 and Section 5 (a
domain name containing only ASCII codepoints can not be converted to
an A-label), there can not be more than one A-label form for any
given U-label.
The current update to the definition of the DNS protocol [RFC2181]
explicitly allows domain labels to contain octets beyond the ASCII
range (0000..007F), and this document does not change that. Note,
however, that there is no defined interpretation of octets 0080..00FF
as characters. If labels containing these octets are returned to
applications, unpredictable behavior could result. The A-label form,
which cannot contain those characters, is the only standard
representation for internationalized labels in the current DNS
protocol.
6.2. DNSSEC Authentication of IDN Domain Names
DNS Security [RFC2535] is a method for supplying cryptographic
verification information along with DNS messages. Public Key
Cryptography is used in conjunction with digital signatures to
provide a means for a requester of domain information to authenticate
the source of the data. This ensures that it can be traced back to a
trusted source, either directly or via a chain of trust linking the
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source of the information to the top of the DNS hierarchy.
IDNA specifies that all internationalized domain names served by DNS
servers that cannot be represented directly in ASCII must use the
A-label form. Conversion to A-labels must be performed prior to a
zone being signed by the private key for that zone. Because of this
ordering, it is important to recognize that DNSSEC authenticates a
domain name containing A-labels or conventional LDH-labels, not
U-labels. In the presence of DNSSEC, no form of a zone file or query
response that contains a U-label may be signed or the signature
validated.
One consequence of this for sites deploying IDNA in the presence of
DNSSEC is that any special purpose proxies or forwarders used to
transform user input into IDNs must be earlier in the lookup flow
than DNSSEC authenticating nameservers for DNSSEC to work.
6.3. Root and other DNS Server Considerations
IDNs in A-label form will generally be somewhat longer than current
domain names, so the bandwidth needed by the root servers is likely
to go up by a small amount. Also, queries and responses for IDNs
will probably be somewhat longer than typical queries historically,
so EDNS0 [RFC2671] support may be more important (otherwise, queries
and responses may be forced to go to TCP instead of UDP).
7. Security Considerations
The general security principles and issues for IDNA appear in
[IDNA2008-Rationale]. The comments below are specific to this pair
of protocols, but should be read in the context of that material and
the definitions and specifications, identified there, on which this
one depends.
This memo describes procedures for registering and looking up labels
that are not compatible with the preferred syntax described in the
base DNS specifications (STD13 [RFC1034] [RFC1035] and Host
Requirements [RFC1123]) because they contain non-ASCII characters.
These procedures depend on the use of a special ASCII-compatible
encoding form that contains only characters permitted in host names
by those earlier specifications. The encoding is specified in
[RFC3492]. No security issues such as string length increases or new
allowed values are introduced by the encoding process or the use of
these encoded values, apart from those introduced by the ACE encoding
itself.
Domain names (or portions of them) are sometimes compared against a
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set domains to be given special treatment if a match occurs, e.g.,
treated as more privileged than others or blocked in some way. In
such situations it is especially important that the comparisons be
done properly, as specified in requirement 2 of Section 3.1. For
labels already in ASCII form (i.e., are LDH-labels or A-labels), the
proper comparison reduces to the same case-insensitive ASCII
comparison that has always been used for ASCII labels.
The introduction of IDNA means that any existing labels that start
with the ACE prefix would be construed as A-labels, at least until
they failed one of the relevant tests, whether or not that was the
intent of the zone administrator or registrant. There is no evidence
that this has caused any practical problems since RFC 3490 was
adopted, but the risk still exists in principle.
8. IANA Considerations
IANA actions for this version of IDNA are specified in
[IDNA2008-Rationale]. The component of IDNA described in this
document does not require any IANA actions.
9. Change Log
[[anchor23: RFC Editor: Please remove this section.]]
9.1. 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.
9.2. 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.
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9.3. 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.
o Several minor editorial corrections and improvements.
o "Editor" designation temporarily removed because the automatic
posting machinery does not accept it.
9.4. 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.
9.5. Version -05
o Updated part of the A-label input explanation (Section 5.4) per
note from Erik van der Poel.
10. 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.
11. Acknowledgements
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
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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 Stephane Bortzmeyer, Mark Davis, Paul Hoffman, Erik
van der Poel, Marcos Sanz and others.
12. References
12.1. Normative References
[IDNA2008-BIDI]
Alvestrand, H. and C. Karp, "An updated IDNA criterion for
right-to-left scripts", July 2008, .
[IDNA2008-Rationale]
Klensin, J., Ed., "Internationalizing Domain Names for
Applications (IDNA): Issues, Explanation, and Rationale",
July 2008, .
[IDNA2008-Tables]
Faltstrom, P., "The Unicode Codepoints and IDNA",
July 2008, .
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
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Internet-Draft IDNA2008 Protocol September 2008
(IDNA)", RFC 3492, March 2003.
[Unicode-PropertyValueAliases]
The Unicode Consortium, "Unicode Character Database:
PropertyValueAliases", March 2008, .
[Unicode-RegEx]
The Unicode Consortium, "Unicode Technical Standard #18:
Unicode Regular Expressions", May 2005,
.
[Unicode-Scripts]
The Unicode Consortium, "Unicode Standard Annex #24:
Unicode Script Property", February 2008,
.
[Unicode-UAX15]
The Unicode Consortium, "Unicode Standard Annex #15:
Unicode Normalization Forms", 2006,
.
12.2. 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.
[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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[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
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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