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'IDNA2008-BIDI' == Outdated reference: draft-ietf-idnabis-defs has been published as RFC 5890 == Outdated reference: draft-ietf-idnabis-tables has been published as RFC 5892 -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-PropertyValueAliases' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-RegEx' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-Scripts' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-UAX15' -- No information found for draft-ietf-idnabis-mapping - is the name correct? == Outdated reference: draft-ietf-idnabis-rationale has been published as RFC 5894 -- Obsolete informational reference (is this intentional?): RFC 2535 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) -- Obsolete informational reference (is this intentional?): RFC 2671 (Obsoleted by RFC 6891) -- Obsolete informational reference (is this intentional?): RFC 3490 (Obsoleted by RFC 5890, RFC 5891) -- Obsolete informational reference (is this intentional?): RFC 3491 (Obsoleted by RFC 5891) -- Obsolete informational reference (is this intentional?): RFC 4952 (Obsoleted by RFC 6530) Summary: 1 error (**), 0 flaws (~~), 14 warnings (==), 15 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Klensin 3 Internet-Draft September 13, 2009 4 Obsoletes: 3490, 3491 5 (if approved) 6 Updates: 3492 (if approved) 7 Intended status: Standards Track 8 Expires: March 17, 2010 10 Internationalized Domain Names in Applications (IDNA): Protocol 11 draft-ietf-idnabis-protocol-16.txt 13 Status of this Memo 15 This Internet-Draft is submitted to IETF in full conformance with the 16 provisions of BCP 78 and BCP 79. This document may contain material 17 from IETF Documents or IETF Contributions published or made publicly 18 available before November 10, 2008. The person(s) controlling the 19 copyright in some of this material may not have granted the IETF 20 Trust the right to allow modifications of such material outside the 21 IETF Standards Process. Without obtaining an adequate license from 22 the person(s) controlling the copyright in such materials, this 23 document may not be modified outside the IETF Standards Process, and 24 derivative works of it may not be created outside the IETF Standards 25 Process, except to format it for publication as an RFC or to 26 translate it into languages other than English. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF), its areas, and its working groups. Note that 30 other groups may also distribute working documents as Internet- 31 Drafts. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 The list of current Internet-Drafts can be accessed at 39 http://www.ietf.org/ietf/1id-abstracts.txt. 41 The list of Internet-Draft Shadow Directories can be accessed at 42 http://www.ietf.org/shadow.html. 44 This Internet-Draft will expire on March 17, 2010. 46 Copyright Notice 48 Copyright (c) 2009 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents in effect on the date of 53 publication of this document (http://trustee.ietf.org/license-info). 54 Please review these documents carefully, as they describe your rights 55 and restrictions with respect to this document. 57 Abstract 59 This document is the revised protocol definition for 60 internationalized domain names (IDNs). The rationale for changes, 61 the relationship to the older specification, and important 62 terminology are provided in other documents. This document specifies 63 the protocol mechanism, called Internationalized Domain Names in 64 Applications (IDNA), for registering and looking up IDNs in a way 65 that does not require changes to the DNS itself. IDNA is only meant 66 for processing domain names, not free text. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 71 1.1. Discussion Forum . . . . . . . . . . . . . . . . . . . . . 5 72 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 73 3. Requirements and Applicability . . . . . . . . . . . . . . . . 6 74 3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6 75 3.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 6 76 3.2.1. DNS Resource Records . . . . . . . . . . . . . . . . . 7 77 3.2.2. Non-domain-name Data Types Stored in the DNS . . . . . 7 78 4. Registration Protocol . . . . . . . . . . . . . . . . . . . . 7 79 4.1. Input to IDNA Registration . . . . . . . . . . . . . . . . 8 80 4.2. Permitted Character and Label Validation . . . . . . . . . 8 81 4.2.1. Input Format . . . . . . . . . . . . . . . . . . . . . 8 82 4.2.2. Rejection of Characters that are not Permitted . . . . 9 83 4.2.3. Label Validation . . . . . . . . . . . . . . . . . . . 9 84 4.2.4. Registration Validation Summary . . . . . . . . . . . 9 85 4.3. Registry Restrictions . . . . . . . . . . . . . . . . . . 10 86 4.4. Punycode Conversion . . . . . . . . . . . . . . . . . . . 10 87 4.5. Insertion in the Zone . . . . . . . . . . . . . . . . . . 10 88 5. Domain Name Lookup Protocol . . . . . . . . . . . . . . . . . 11 89 5.1. Label String Input . . . . . . . . . . . . . . . . . . . . 11 90 5.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 11 91 5.3. A-label Input . . . . . . . . . . . . . . . . . . . . . . 11 92 5.4. Validation and Character List Testing . . . . . . . . . . 12 93 5.5. Punycode Conversion . . . . . . . . . . . . . . . . . . . 13 94 5.6. DNS Name Resolution . . . . . . . . . . . . . . . . . . . 13 95 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 96 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 97 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14 98 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 99 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 100 10.1. Normative References . . . . . . . . . . . . . . . . . . . 15 101 10.2. Informative References . . . . . . . . . . . . . . . . . . 16 102 Appendix A. Summary of Major Changes from IDNA2003 . . . . . . . 17 103 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 18 104 B.1. Changes between Version -00 and -01 of 105 draft-ietf-idnabis-protocol . . . . . . . . . . . . . . . 18 106 B.2. Version -02 . . . . . . . . . . . . . . . . . . . . . . . 18 107 B.3. Version -03 . . . . . . . . . . . . . . . . . . . . . . . 19 108 B.4. Version -04 . . . . . . . . . . . . . . . . . . . . . . . 19 109 B.5. Version -05 . . . . . . . . . . . . . . . . . . . . . . . 19 110 B.6. Version -06 . . . . . . . . . . . . . . . . . . . . . . . 19 111 B.7. Version -07 . . . . . . . . . . . . . . . . . . . . . . . 20 112 B.8. Version -08 . . . . . . . . . . . . . . . . . . . . . . . 20 113 B.9. Version -09 . . . . . . . . . . . . . . . . . . . . . . . 20 114 B.10. Version -10 . . . . . . . . . . . . . . . . . . . . . . . 21 115 B.11. Version -11 . . . . . . . . . . . . . . . . . . . . . . . 21 116 B.12. Version -12 . . . . . . . . . . . . . . . . . . . . . . . 21 117 B.13. Version -13 . . . . . . . . . . . . . . . . . . . . . . . 22 118 B.14. Version -14 . . . . . . . . . . . . . . . . . . . . . . . 22 119 B.15. Version -15 . . . . . . . . . . . . . . . . . . . . . . . 22 120 B.16. Version -16 . . . . . . . . . . . . . . . . . . . . . . . 23 121 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23 123 1. Introduction 125 This document supplies the protocol definition for internationalized 126 domain names. Essential definitions and terminology for 127 understanding this document and a road map of the collection of 128 documents that make up IDNA2008 appear in [IDNA2008-Defs]. 129 Appendix A discusses the relationship between this specification and 130 the earlier version of IDNA (referred to here as "IDNA2003"). The 131 rationale for these changes, along with considerable explanatory 132 material and advice to zone administrators who support IDNs is 133 provided in another document, [IDNA2008-Rationale]. 135 IDNA works by allowing applications to use certain ASCII string 136 labels (beginning with a special prefix) to represent non-ASCII name 137 labels. Lower-layer protocols need not be aware of this; therefore 138 IDNA does not change any infrastructure. In particular, IDNA does 139 not depend on any changes to DNS servers, resolvers, or DNS protocol 140 elements, because the ASCII name service provided by the existing DNS 141 can be used for IDNA. 143 IDNA applies only to DNS labels. The base DNS standards [RFC1034] 144 [RFC1035] and their various updates specify how to combine labels 145 into fully-qualified domain names and parse labels out of those 146 names. 148 This document describes two separate protocols, one for IDN 149 registration (Section 4) and one for IDN lookup (Section 5). These 150 two protocols share some terminology, reference data and operations. 152 1.1. Discussion Forum 154 [[ RFC Editor: please remove this section. ]] 156 This work is being discussed in the IETF IDNABIS WG and on the 157 mailing list idna-update@alvestrand.no 159 2. Terminology 161 Terminology used as part of the definition of IDNA appears in 162 [IDNA2008-Defs]. It is worth noting that some of this terminology 163 overlaps with, and is consistent with, that used , but also in 164 Unicode or other character set standards and the DNS. Readers of 165 this document are assumed to be familiar with [IDNA2008-Defs] and 166 with the DNS-specific terminology in RFC 1034 [RFC1034]. 168 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 169 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 170 document are to be interpreted as described in BCP 14, RFC 2119 171 [RFC2119]. 173 3. Requirements and Applicability 175 3.1. Requirements 177 IDNA makes the following requirements: 179 1. Whenever a domain name is put into an IDN-unaware domain name 180 slot (see Section 2 and [IDNA2008-Defs]), it MUST contain only 181 ASCII characters (i.e., must be either an A-label or an NR-LDH- 182 label), unless the DNS application is not subject to historical 183 recommendations for "hostname"-style names (see [RFC1034] and 184 Section 3.2.1). 186 2. Labels MUST be compared using equivalent forms: either both 187 A-Label forms or both U-Label forms. Because A-labels and 188 U-labels can be transformed into each other without loss of 189 information, these comparisons are equivalent. A pair of 190 A-labels MUST be compared as case-insensitive ASCII (as with all 191 comparisons of ASCII DNS labels). U-labels must be compared 192 as-is, without case-folding or other intermediate steps. Note 193 that it is not necessary to validate labels in order to compare 194 them and that successful comparison does not imply validity. In 195 many cases, not limited to comparison, validation may be 196 important for other reasons and SHOULD be performed. 198 3. Labels being registered MUST conform to the requirements of 199 Section 4. Labels being looked up and the lookup process MUST 200 conform to the requirements of Section 5. 202 3.2. Applicability 204 IDNA applies to all domain names in all domain name slots in 205 protocols except where it is explicitly excluded. It does not apply 206 to domain name slots which do not use the Letter/Digit/Hyphen (LDH) 207 syntax rules. 209 Because IDNA uses the DNS, IDNA applies to many protocols that were 210 specified before it was designed. IDNs occupying domain name slots 211 in those older protocols MUST be in A-label form until and unless 212 those protocols and their implementations are explicitly upgraded to 213 be aware of IDNs. IDNs actually appearing in DNS queries or 214 responses MUST be A-labels. 216 IDNA is not defined for extended label types (see RFC 2671, Section 3 218 [RFC2671]). 220 3.2.1. DNS Resource Records 222 IDNA applies only to domain names in the NAME and RDATA fields of DNS 223 resource records whose CLASS is IN. See RFC 1034 [RFC1034] for 224 precise definitions of these terms. 226 The application of IDNA to DNS resource records depends entirely on 227 the CLASS of the record, and not on the TYPE except as noted below. 228 This will remain true, even as new types are defined, unless a new 229 type defines type-specific rules. Special naming conventions for SRV 230 records (and "underscore labels" more generally) are incompatible 231 with IDNA coding as discussed in [IDNA2008-Defs], especially Section 232 2.3.2.3. Of course, underscore labels may be part of a domain that 233 uses IDN labels at higher levels in the tree. 235 3.2.2. Non-domain-name Data Types Stored in the DNS 237 Although IDNA enables the representation of non-ASCII characters in 238 domain names, that does not imply that IDNA enables the 239 representation of non-ASCII characters in other data types that are 240 stored in domain names, specifically in the RDATA field for types 241 that have structured RDATA format. For example, an email address 242 local part is stored in a domain name in the RNAME field as part of 243 the RDATA of an SOA record (hostmaster@example.com would be 244 represented as hostmaster.example.com). IDNA does not update the 245 existing email standards, which allow only ASCII characters in local 246 parts. Even though work is in progress to define 247 internationalization for email addresses [RFC4952], changes to the 248 email address part of the SOA RDATA would require action in, or 249 updates to, other standards, specifically those that specify the 250 format of the SOA RR. 252 4. Registration Protocol 254 This section defines the model for registering an IDN. The model is 255 implementation independent; any sequence of steps that produces 256 exactly the same result for all labels is considered a valid 257 implementation. 259 Note that, while the registration (this section) and lookup protocols 260 (Section 5) are very similar in most respects, they not identical and 261 implementers should carefully follow the steps described in this 262 specification. 264 4.1. Input to IDNA Registration 266 Registration processes, especially processing by entities (often 267 called "registrars") who deal with registrants before the request 268 actually reaches the zone manager ("registry") are outside the scope 269 of this definition and may differ significantly depending on local 270 needs. By the time a string enters the IDNA registration process as 271 described in this specification, it MUST be in Unicode and in 272 Normalization Form C (NFC [Unicode-UAX15]). Entities responsible for 273 zone files ("registries") MUST accept only the exact string for which 274 registration is requested, free of any mappings or local adjustments. 275 They MAY accept that input in any of three forms: 277 1. As a pair of A-label and U-label. 279 2. As an A-label only. 281 3. As a U-label only. 283 The first two of these forms are RECOMMENDED because the use of 284 A-labels avoids any possibility of ambiguity. The first is normally 285 preferred over the second because it permits further verification of 286 user intent (see Section 4.2.1). 288 4.2. Permitted Character and Label Validation 290 4.2.1. Input Format 292 If both the U-label and A-label forms are available, the registry 293 MUST ensure that the A-label form is in lower case, perform a 294 conversion to a U-label, perform the steps and tests described below 295 on that U-label, and then verify that the A-label produced by the 296 step in Section 4.4 matches the one provided as input. In addition, 297 the U-label that was provided as input and the one obtained by 298 conversion of the A-label MUST match exactly. If, for some reason, 299 these tests fail, the registration MUST be rejected. 301 If only an A-label was provided and the conversion to a U-label is 302 not performed, the registry MUST still verify that the A-label is 303 superficially valid, i.e., that it does not violate any of the rules 304 of Punycode [RFC3492] encoding such as the prohibition on trailing 305 hyphen-minus, appearance of non-basic characters before the 306 delimiter, and so on. Fake A-labels, i.e., invalid strings that 307 appear to be A-labels but are not, MUST NOT be placed in DNS zones 308 that support IDNA. 310 4.2.2. Rejection of Characters that are not Permitted 312 The candidate Unicode string MUST NOT contain characters that appear 313 in the "DISALLOWED" and "UNASSIGNED" lists specified in 314 [IDNA2008-Tables]. 316 4.2.3. Label Validation 318 The proposed label (in the form of a Unicode string, i.e., a string 319 that at least superficially appears to be a U-label) is then 320 examined, performing tests that require examination of more than one 321 character. Character order is considered to be the on-the-wire 322 order, not the display order. 324 4.2.3.1. Hyphen Restrictions 326 The Unicode string MUST NOT contain "--" (two consecutive hyphens) in 327 the third and fourth character positions and MUST NOT start or end 328 with a "-" (hyphen). 330 4.2.3.2. Leading Combining Marks 332 The Unicode string MUST NOT begin with a combining mark or combining 333 character (see The Unicode Standard, Section 2.11 [Unicode] for an 334 exact definition). 336 4.2.3.3. Contextual Rules 338 The Unicode string MUST NOT contain any characters whose validity is 339 context-dependent, unless the validity is positively confirmed by a 340 contextual rule. To check this, each code-point marked as CONTEXTJ 341 and CONTEXTO in [IDNA2008-Tables] MUST have a non-null rule. If such 342 a code-point is missing a rule, it is invalid. If the rule exists 343 but the result of applying the rule is negative or inconclusive, the 344 proposed label is invalid. 346 4.2.3.4. Labels Containing Characters Written Right to Left 348 If the proposed label contains any characters that are written from 349 right to left it MUST meet the BIDI criteria [IDNA2008-BIDI]. 351 4.2.4. Registration Validation Summary 353 Strings that contain at least one non-ASCII character, have been 354 produced by the steps above, whose contents pass all of the tests in 355 Section 4.2, and are 63 or fewer characters long in ACE form (see 356 Section 4.4), are U-labels. 358 To summarize, tests are made in Section 4.2 for invalid characters, 359 invalid combinations of characters, for labels that are invalid even 360 if the characters they contain are valid individually, and for labels 361 that do not conform to the restrictions for strings containing right 362 to left characters. 364 4.3. Registry Restrictions 366 In addition to the rules and tests above, there are many reasons why 367 a registry could reject a label. Registries at all levels of the 368 DNS, not just the top level, are expected to establish policies about 369 label registrations. Policies are likely to be informed by the local 370 languages and the scripts that are used to write them and may depend 371 on many factors including what characters are in the label (for 372 example, a label may be rejected based on other labels already 373 registered). See [IDNA2008-Rationale] Section 3.2 for a discussion 374 and recommendations about registry policies. 376 The string produced by the steps in Section 4.2 is checked and 377 processed as appropriate to local registry restrictions. Application 378 of those registry restrictions may result in the rejection of some 379 labels or the application of special restrictions to others. 381 4.4. Punycode Conversion 383 The resulting U-label is converted to an A-label (defined in Section 384 2.3.2.1 of [IDNA2008-Defs]). The A-label is the encoding of the 385 U-label according to the Punycode algorithm [RFC3492] with the ACE 386 prefix "xn--" added at the beginning of the string. The resulting 387 string must, of course, conform to the length limits imposed by the 388 DNS. This document does not update or alter the Punycode algorithm 389 specified in RFC 3492 in any way. That document does make a non- 390 normative reference to the information about the value and 391 construction of the ACE prefix that appears "in RFC 3490 or Nameprep 392 [RFC3491]". For consistency and reader convenience, IDNA2008 393 effectively updates that reference to point to this document. That 394 change does not alter the prefix itself. The prefix, "xn--", is the 395 same in both sets of documents. 397 The failure conditions identified in the Punycode encoding procedure 398 cannot occur if the input is a U-label as determined by the steps 399 above. 401 4.5. Insertion in the Zone 403 The label is registered in the DNS by inserting the A-label into a 404 zone. 406 5. Domain Name Lookup Protocol 408 Lookup is different from registration and different tests are applied 409 on the client. Although some validity checks are necessary to avoid 410 serious problems with the protocol, the lookup-side tests are more 411 permissive and rely on the assumption that names that are present in 412 the DNS are valid. That assumption is, however, a weak one because 413 the presence of wild cards in the DNS might cause a string that is 414 not actually registered in the DNS to be successfully looked up. 416 5.1. Label String Input 418 The user supplies a string in the local character set, for example by 419 typing it or clicking on, or copying and pasting, a resource 420 identifier, e.g., a URI [RFC3986] or IRI [RFC3987] from which the 421 domain name is extracted. Alternately, some process not directly 422 involving the user may read the string from a file or obtain it in 423 some other way. Processing in this step and that specified in 424 Section 5.2 are local matters, to be accomplished prior to actual 425 invocation of IDNA. 427 5.2. Conversion to Unicode 429 The string is converted from the local character set into Unicode, if 430 it is not already in Unicode. Depending on local needs, this 431 conversion may involve mapping some characters into other characters 432 as well as coding conversions. Those issues are discussed in 433 [IDNA2008-Mapping] and the mapping-related sections (Sections 4.4, 6, 434 and 7.3) of [IDNA2008-Rationale]. The result MUST be a Unicode 435 string in NFC form. 437 5.3. A-label Input 439 If the input to this procedure appears to be an A-label (i.e., it 440 starts in "xn--"), the lookup application MAY attempt to convert it 441 to a U-label, first ensuring that the A-label is entirely in lower 442 case, and apply the tests of Section 5.4 and the conversion of 443 Section 5.5 to that form. If the label is converted to Unicode 444 (i.e., to U-label form) using the Punycode decoding algorithm, then 445 the processing specified in those two sections MUST be performed, and 446 the label MUST be rejected if the resulting label is not identical to 447 the original. See Section 8.1 of [IDNA2008-Rationale] for additional 448 discussion on this topic. 450 Conversion from the A-label and testing that the result is a U-label 451 SHOULD be performed if the domain name will later be presented to the 452 user in native character form (this requires that the lookup 453 application be IDNA-aware). If those steps are not performed, the 454 lookup process SHOULD at least test to determine that the string is 455 actually an A-label, examining it for the invalid formats specified 456 in the Punycode decoding specification. Applications that are not 457 IDNA-aware will obviously omit that testing; others MAY treat the 458 string as opaque to avoid the additional processing at the expense of 459 providing less protection and information to users. 461 5.4. Validation and Character List Testing 463 As with the registration procedure described in Section 4, the 464 Unicode string is checked to verify that all characters that appear 465 in it are valid as input to IDNA lookup processing. As discussed 466 above and in [IDNA2008-Rationale], the lookup check is more liberal 467 than the registration one. Labels that have not been fully evaluated 468 for conformance to the applicable rules are referred to as "putative" 469 labels as discussed in Section 2.3.2.1 of [IDNA2008-Defs]. Putative 470 labels with any of the following characteristics MUST be rejected 471 prior to DNS lookup: 473 o Labels that are not in NFC [Unicode-UAX15]. 475 o Labels containing "--" (two consecutive hyphens) in the third and 476 fourth character positions. 478 o Labels whose first character is a combining mark (see The Unicode 479 Standard, Section 2.11 [Unicode]). 481 o Labels containing prohibited code points, i.e., those that are 482 assigned to the "DISALLOWED" category of [IDNA2008-Tables]. 484 o Labels containing code points that are identified in 485 [IDNA2008-Tables] as "CONTEXTJ", i.e., requiring exceptional 486 contextual rule processing on lookup, but that do not conform to 487 those rules. Note that this implies that a rule must be defined, 488 not null: a character that requires a contextual rule but for 489 which the rule is null is treated in this step as having failed to 490 conform to the rule. 492 o Labels containing code points that are identified in 493 [IDNA2008-Tables] as "CONTEXTO", but for which no such rule 494 appears in the table of rules. Applications resolving DNS names 495 or carrying out equivalent operations are not required to test 496 contextual rules for "CONTEXTO" characters, only to verify that a 497 rule is defined (although they MAY make such tests to provide 498 better protection or give better information to the user). 500 o Labels containing code points that are unassigned in the version 501 of Unicode being used by the application, i.e.,in the UNASSIGNED 502 category of [IDNA2008-Tables]. 504 This requirement means that the application must use a list of 505 unassigned characters that is matched to the version of Unicode 506 that is being used for the other requirements in this section. It 507 is not required that the application know which version of Unicode 508 is being used; that information might be part of the operating 509 environment in which the application is running. 511 In addition, the application SHOULD apply the following test. 513 o Verification that the string is compliant with the requirements 514 for right to left characters, specified in [IDNA2008-BIDI]. 516 This test may be omitted in special circumstances, such as when the 517 lookup application knows that the conditions are enforced elsewhere, 518 because an attempt to look up and resolve such strings will almost 519 certainly lead to a DNS lookup failure except when wild cards are 520 present in the zone. However, applying the test is likely to give 521 much better information about the reason for a lookup failure -- 522 information that may be usefully passed to the user when that is 523 feasible -- than DNS resolution failure information alone. 525 For all other strings, the lookup application MUST rely on the 526 presence or absence of labels in the DNS to determine the validity of 527 those labels and the validity of the characters they contain. If 528 they are registered, they are presumed to be valid; if they are not, 529 their possible validity is not relevant. While a lookup application 530 may reasonably issue warnings about strings it believes may be 531 problematic, applications that decline to process a string that 532 conforms to the rules above (i.e., does not look it up in the DNS) 533 are not in conformance with this protocol. 535 5.5. Punycode Conversion 537 The string that has now been validated for lookup is converted to ACE 538 form by applying the Punycode algorithm to the string and then adding 539 the ACE prefix. 541 5.6. DNS Name Resolution 543 The A-label resulting from the conversion in Section 5.5 or supplied 544 directly (see Section 5.3) is looked up in the DNS, using normal DNS 545 resolver procedures. The lookup can obviously either succeed 546 (returning information) or fail. 548 6. Security Considerations 550 Security Considerations for this version of IDNA are described in 551 [IDNA2008-Defs], except for the special issues associated with right 552 to left scripts and characters. The latter are discussed in 553 [IDNA2008-BIDI]. 555 7. IANA Considerations 557 IANA actions for this version of IDNA are specified in 558 [IDNA2008-Tables] and discussed informally in [IDNA2008-Rationale]. 559 The components of IDNA described in this document do not require any 560 IANA actions. 562 8. Contributors 564 While the listed editor held the pen, the original versions of this 565 document represent the joint work and conclusions of an ad hoc design 566 team consisting of the editor and, in alphabetic order, Harald 567 Alvestrand, Tina Dam, Patrik Faltstrom, and Cary Karp. This document 568 draws significantly on the original version of IDNA [RFC3490] both 569 conceptually and for specific text. This second-generation version 570 would not have been possible without the work that went into that 571 first version and especially the contributions of its authors Patrik 572 Faltstrom, Paul Hoffman, and Adam Costello. While Faltstrom was 573 actively involved in the creation of this version, Hoffman and 574 Costello were not and should not be held responsible for any errors 575 or omissions. 577 9. Acknowledgments 579 This revision to IDNA would have been impossible without the 580 accumulated experience since RFC 3490 was published and resulting 581 comments and complaints of many people in the IETF, ICANN, and other 582 communities, too many people to list here. Nor would it have been 583 possible without RFC 3490 itself and the efforts of the Working Group 584 that defined it. Those people whose contributions are acknowledged 585 in RFC 3490, [RFC4690], and [IDNA2008-Rationale] were particularly 586 important. 588 Specific textual changes were incorporated into this document after 589 suggestions from the other contributors, Stephane Bortzmeyer, Vint 590 Cerf, Lisa Dusseault, Paul Hoffman, Kent Karlsson, James Mitchell, 591 Erik van der Poel, Marcos Sanz, Andrew Sullivan, Wil Tan, Ken 592 Whistler, Chris Wright, and other WG participants. Special thanks 593 are due to Paul Hoffman for permission to extract material from his 594 Internet-Draft to form the basis for Appendix A. 596 10. References 598 10.1. Normative References 600 [IDNA2008-BIDI] 601 Alvestrand, H. and C. Karp, "An updated IDNA criterion for 602 right-to-left scripts", August 2009, . 605 [IDNA2008-Defs] 606 Klensin, J., "Internationalized Domain Names for 607 Applications (IDNA): Definitions and Document Framework", 608 August 2009, . 611 [IDNA2008-Tables] 612 Faltstrom, P., "The Unicode Codepoints and IDNA", 613 August 2009, . 616 A version of this document is available in HTML format at 617 http://stupid.domain.name/idnabis/ 618 draft-ietf-idnabis-tables-06.html 620 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 621 STD 13, RFC 1034, November 1987. 623 [RFC1035] Mockapetris, P., "Domain names - implementation and 624 specification", STD 13, RFC 1035, November 1987. 626 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application 627 and Support", STD 3, RFC 1123, October 1989. 629 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 630 Requirement Levels", BCP 14, RFC 2119, March 1997. 632 [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode 633 for Internationalized Domain Names in Applications 634 (IDNA)", RFC 3492, March 2003. 636 [Unicode-PropertyValueAliases] 637 The Unicode Consortium, "Unicode Character Database: 638 PropertyValueAliases", March 2008, . 641 [Unicode-RegEx] 642 The Unicode Consortium, "Unicode Technical Standard #18: 643 Unicode Regular Expressions", May 2005, 644 . 646 [Unicode-Scripts] 647 The Unicode Consortium, "Unicode Standard Annex #24: 648 Unicode Script Property", February 2008, 649 . 651 [Unicode-UAX15] 652 The Unicode Consortium, "Unicode Standard Annex #15: 653 Unicode Normalization Forms", 2006, 654 . 656 10.2. Informative References 658 [ASCII] American National Standards Institute (formerly United 659 States of America Standards Institute), "USA Code for 660 Information Interchange", ANSI X3.4-1968, 1968. 662 ANSI X3.4-1968 has been replaced by newer versions with 663 slight modifications, but the 1968 version remains 664 definitive for the Internet. 666 [IDNA2008-Mapping] 667 Resnick, P. and P. Hoffman, "Mapping Characters in IDNA", 668 September 2009, . 671 [IDNA2008-Rationale] 672 Klensin, J., Ed., "Internationalized Domain Names for 673 Applications (IDNA): Issues, Explanation, and Rationale", 674 February 2009, . 677 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 678 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 679 RFC 2136, April 1997. 681 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 682 Specification", RFC 2181, July 1997. 684 [RFC2535] Eastlake, D., "Domain Name System Security Extensions", 685 RFC 2535, March 1999. 687 [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", 688 RFC 2671, August 1999. 690 [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, 691 "Internationalizing Domain Names in Applications (IDNA)", 692 RFC 3490, March 2003. 694 [RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep 695 Profile for Internationalized Domain Names (IDN)", 696 RFC 3491, March 2003. 698 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 699 Resource Identifier (URI): Generic Syntax", STD 66, 700 RFC 3986, January 2005. 702 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 703 Identifiers (IRIs)", RFC 3987, January 2005. 705 [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and 706 Recommendations for Internationalized Domain Names 707 (IDNs)", RFC 4690, September 2006. 709 [RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for 710 Internationalized Email", RFC 4952, July 2007. 712 [Unicode] The Unicode Consortium, "The Unicode Standard, Version 713 5.0", 2007. 715 Boston, MA, USA: Addison-Wesley. ISBN 0-321-48091-0 717 Appendix A. Summary of Major Changes from IDNA2003 719 1. Update base character set from Unicode 3.2 to Unicode version- 720 agnostic. 722 2. Separate the definitions for the "registration" and "lookup" 723 activities. 725 3. Disallow symbol and punctuation characters except where special 726 exceptions are necessary. 728 4. Remove the mapping and normalization steps from the protocol and 729 have them instead done by the applications themselves, possibly 730 in a local fashion, before invoking the protocol. 732 5. Change the way that the protocol specifies which characters are 733 allowed in labels from "humans decide what the table of 734 codepoints contains" to "decision about codepoints are based on 735 Unicode properties plus a small exclusion list created by 736 humans". 738 6. Introduce the new concept of characters that can be used only in 739 specific contexts. 741 7. Allow typical words and names in languages such as Dhivehi and 742 Yiddish to be expressed. 744 8. Make bidirectional domain names (delimited strings of labels, 745 not just labels standing on their own) display in a less 746 surprising fashion whether they appear in obvious domain name 747 contexts or as part of running text in paragraphs. 749 9. Remove the dot separator from the mandatory part of the 750 protocol. 752 10. Make some currently-valid labels that are not actually IDNA 753 labels invalid. 755 Appendix B. Change Log 757 [[ RFC Editor: Please remove this appendix. ]] 759 B.1. Changes between Version -00 and -01 of draft-ietf-idnabis-protocol 761 o Corrected discussion of SRV records. 763 o Several small corrections for clarity. 765 o Inserted more "open issue" placeholders. 767 B.2. Version -02 769 o Rewrote the "conversion to Unicode" text in Section 5.2 as 770 requested on-list. 772 o Added a comment (and reference) about EDNS0 to the "DNS Server 773 Conventions" section, which was also retitled. 775 o Made several editorial corrections and improvements in response to 776 various comments. 778 o Added several new discussion placeholder anchors and updated some 779 older ones. 781 B.3. Version -03 783 o Trimmed change log, removing information about pre-WG drafts. 785 o Incorporated a number of changes suggested by Marcos Sanz in his 786 note of 2008.07.17 and added several more placeholder anchors. 788 o Several minor editorial corrections and improvements. 790 o "Editor" designation temporarily removed because the automatic 791 posting machinery does not accept it. 793 B.4. Version -04 795 o Removed Contextual Rule appendices for transfer to Tables. 797 o Several changes, including removal of discussion anchors, based on 798 discussions at IETF 72 (Dublin) 800 o Rewrote the preprocessing material (former Section 5.3) somewhat 801 -- see Appendix B.14. 803 B.5. Version -05 805 o Updated part of the A-label input explanation (Section 5.3) per 806 note from Erik van der Poel. 808 B.6. Version -06 810 o Corrected a few typographical errors. 812 o Incorporated the material (formerly in Rationale) on the 813 relationship between IDNA2003 and IDNA2008 as an appendix and 814 pointed to the new definitions document. 816 o Text modified in several places to recognize the dangers of 817 interaction between DNS wild cards and IDNs. 819 o Text added to be explicit about the handling of edge and failure 820 cases in Punycode encoding and decoding. 822 o Revised for consistency with the new Definitions document and to 823 make the text read more smoothly. 825 B.7. Version -07 827 o Multiple small textual and editorial changes and clarifications. 829 o Requirement for normalization clarified to apply to all cases and 830 conditions for preprocessing further clarified. 832 o Substantive change to Section 4.2.1, turning a SHOULD to a MUST 833 (see note from Mark Davis, 19 November, 2008 18:14 -0800). 835 B.8. Version -08 837 o Added some references and altered text to improve clarity. 839 o Changed the description of CONTEXTJ/CONTEXTO to conform to that in 840 Tables. In other words, these are now treated as distinction 841 categories (again), rather than as specially-flagged subsets of 842 PROTOCOL VALID. 844 o The discussion of label comparisons has been rewritten to make it 845 more precise and to clarify that one does not need to verify that 846 a string is a [valid] A-label or U-label in order to test it for 847 equality with another string. The WG should verify that the 848 current text is what is desired. 850 o Other changes to reflect post-IETF discussions or editorial 851 improvements. 853 B.9. Version -09 855 o Removed Security Considerations material to Defs document. 857 o Removed the Name Server Considerations material to Rationale. 858 That material is not normative and not needed to implement the 859 protocol itself. 861 o Adjusted terminology to match new version of Defs. 863 o Removed all discussion of local mapping and option for it from 864 registration protocol. Such mapping is now completely prohibited 865 on Registration. 867 o Removed some old placeholders and inquiries because no comments 868 have been received. 870 o Small editorial corrections. 872 B.10. Version -10 874 o Rewrote the registration input material slightly to further 875 clarify the "no mapping on registration" principle. 877 o Added placeholder notes about several tasks, notably reorganizing 878 Section 4 and Section 5 so that subsection numbers are parallel. 880 o Cleaned up an incorrect use of the terms "A-label" and "U-label" 881 in the lookup phase that was spotted by Mark Davis. Inserted a 882 note there about alternate ways to deal with the resulting 883 terminology problem. 885 o Added a temporarily appendix (above) to document alternate 886 strategies for possible replacements for the former Section 5.3 887 (see Appendix B.14). 889 B.11. Version -11 891 o Removed dangling reference to "C-label" (editing error in prior 892 draft). 894 o Recast the last steps of the Lookup description to eliminate 895 "apparent" (previously "putative") terminology. 897 o Rewrote major portions of the temporary appendix that describes 898 transitional mappings to improve clarity and add context. 900 o Did some fine-tuning of terminology, notably in Section 3.2.1. 902 B.12. Version -12 904 o Extensive editorial improvements, mostly due to suggestions from 905 Lisa Dusseault. 907 o Conformance statements have been made consistent, especially in 908 Section 4.2.1 and subsequent text, which said "SHOULD" in one 909 place and then said "MAY" as the result of incomplete removal of 910 registration-time mapping. Also clarified the definition of 911 "registration processes" in Section 4.1 -- the previous text had 912 confused several people. 914 o A few new "question to the WG notes have been added about 915 appropriateness or placement of text. If there are no comments on 916 the mailing list, the editor will apply his own judgment. 918 o Several of the usual small typos and other editorial errors have 919 been corrected. 921 o Section 5 has still not been reorganized to match Section 4 in 922 structure and subsection numbering -- will be done as soon as the 923 mapping decisions and references are final. 925 B.13. Version -13 927 o Modified the "putative label" text to better explain the term and 928 explicitly point back to Defs. 930 o Slight rewrite of former section 5.3 to clarify the NFC 931 requirement and to start the transition toward having some of the 932 explanation in the Mapping document. That whole section has been 933 removed in -14, see Appendix B.14 for more information. 935 B.14. Version -14 937 o Fixed substantive typographical error caught by Wil Tan. 939 o Added a check for consecutive hyphens in positions 3 and 4 to 940 Lookup. 942 o Reflected several changes suggested by Andrew Sullivan. 944 o Rearranged and rewrote material to reflect the mapping document 945 and its status. 947 o The former Section 5.3 and Appendix A, which discussed mapping 948 alternatives, have been dropped entirely. Such discussion now 949 belongs in the Mapping document, the portion of Rationale that 950 supports it, or not at all. Section 5.2 has been rewritten 951 slightly to point to Mapping for those issues. 953 o Note: With the revised mapping material inserted, I've just about 954 given up on the idea of having the subsections of Sections 4 and 5 955 exactly parallel each other. Anyone who still feels strongly 956 about this should be prepared to make very specific suggestions. 957 --JcK 959 B.15. Version -15 961 o Corrected name of protocol in the abstract ("Internationalization" 962 to "Internationalized") and a few other instances of that error. 964 o Corrected the hyphen test (Section 4.2.3.1). 966 o Added text to deal with the "upper case in A-labels" problem. 968 o Adjusted Acknowledgments to remove Mark Davis's name, per his 969 request and advice from IETF Trust Counsel. 971 o Incorporated other changes from WG Last Call. 973 o Small typographical and editorial corrections. 975 B.16. Version -16 977 o Adjusted references to current versions. 979 o Adjusted discussion of changes to Punycode to make more precise. 981 o Inserted text to clarify version matching between IDNA and 982 Unicode. 984 o Made several small changes based on Martin Duerst's review. 986 o Substituted in Section numbers in references to other IDNA2008 987 documents. 989 Author's Address 991 John C Klensin 992 1770 Massachusetts Ave, Ste 322 993 Cambridge, MA 02140 994 USA 996 Phone: +1 617 245 1457 997 Email: john+ietf@jck.com