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Kolkman 5 Intended status: Standards Track NLnet Labs 6 Expires: July 26, 2013 January 22, 2013 8 The Uniform Resource Identifier (URI) DNS Resource Record 9 draft-faltstrom-uri-07 11 Abstract 13 This document defines a new DNS resource record, called the Uniform 14 Resource Identifier (URI) RR, for publishing mappings from hostnames 15 to URIs. 17 This document updates RFC 3958 and RFC 3404. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on July 26, 2013. 36 Copyright Notice 38 Copyright (c) 2013 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Applicability Statement . . . . . . . . . . . . . . . . . . . 3 55 3. DNS considerations . . . . . . . . . . . . . . . . . . . . . . 4 56 4. The format of the URI RR . . . . . . . . . . . . . . . . . . . 4 57 4.1. Ownername, class and type . . . . . . . . . . . . . . . . 4 58 4.2. Priority . . . . . . . . . . . . . . . . . . . . . . . . . 5 59 4.3. Weight . . . . . . . . . . . . . . . . . . . . . . . . . . 5 60 4.4. Target . . . . . . . . . . . . . . . . . . . . . . . . . . 5 61 4.5. URI RDATA Wire Format . . . . . . . . . . . . . . . . . . 6 62 5. Definition of the flag 'D' for NAPTR records . . . . . . . . . 6 63 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 64 6.1. Homepage at one domain, but two domains in use . . . . . . 7 65 7. Relation to S-NAPTR . . . . . . . . . . . . . . . . . . . . . 7 66 8. Relation to U-NAPTR . . . . . . . . . . . . . . . . . . . . . 7 67 9. Relation to SRV . . . . . . . . . . . . . . . . . . . . . . . 8 68 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 69 10.1. Registration of the URI Resource Record Type . . . . . . . 8 70 10.2. Registration of services . . . . . . . . . . . . . . . . . 8 71 11. Security Considerations . . . . . . . . . . . . . . . . . . . 8 72 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 73 Appendix A. The original RRTYPE Allocation Request . . . . . . . 9 74 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 75 13.1. Normative References . . . . . . . . . . . . . . . . . . . 12 76 13.2. Non-normative references . . . . . . . . . . . . . . . . . 12 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 79 1. Introduction 81 This document explains the use of the Domain Name System (DNS) for 82 the storage of URIs, and how to resolve hostnames to such URIs that 83 can be used by various applications. For resolution the application 84 need to know both the hostname and the protocol that the URI is to be 85 used for. The protocol is registered by IANA. 87 Currently, looking up URIs given a hostname uses the DDDS [RFC3401] 88 application framework with the DNS as a database as specified in RFC 89 3404 [RFC3404]. This has a number of implications such as the 90 inability to select what NAPTR records that match the query are 91 interesting. The RRSet returned will always consist of all URIs 92 "connected" with the domain in question. 94 The URI resource record specified in this document enables the 95 querying party to select which ones of the NAPTR records one is 96 interested in. This because data in the service field of the NAPTR 97 record is included in the owner part of the URI resource record type. 99 Querying for URI resource records is not replacing querying for NAPTR 100 resource records (or use of S-NAPTR [RFC3958]). Instead, the URI 101 resource record type provides a complementary mechanism to use when 102 one already knows what service field is interesting. With it, one 103 can directly query for the specific subset of the otherwise possibly 104 large RRSet given back when querying for NAPTR resource records. 106 This document updates RFC 3958 and RFC 3404 by adding the flag "D" to 107 the list of defined terminal flags in section 2.2.3 of RFC 3958 and 108 4.3 of RFC 3404. 110 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 111 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 112 document are to be interpreted as described in BCP 14, RFC 2119 113 [RFC2119]. 115 2. Applicability Statement 117 In general, it is expected that URI records will be used by clients 118 for applications where the relevant protocol to be used is known, 119 but, for example, an extra abstraction is needed in order to separate 120 a domain name from a point of service (as addressed by the URI). One 121 example of such a situation is when an organisation has many domain 122 names, but only one official web page. 124 Applications MUST know the specific service fields to prepend the 125 hostname with. Using repetitive queries for URI records MUST NOT be 126 a replacement for querying for NAPTR records according to the NAPTR 127 (DDDS) or S-NAPTR algorithms. NAPTR records serve the purpose to 128 discover the various services and URIs for looking up access points 129 for a given service. Those are two very different kinds of needs. 131 3. DNS considerations 133 Using prefix labels, such as underscored service tags, prevents the 134 use of wildcards, as constructs as _s2._s1.*.example.net. are not 135 possible in the DNS, see RFC 4592 [RFC4592]. Besides, underscored 136 service tags used for the URI RR (based on the NAPTR service 137 descriptions) may have slightly different semantics than service tags 138 used for underscored prefix labels that are used in combination with 139 other (yet unspecified) RR types. This may cause subtle management 140 problems when delegation structure that has developed within the 141 context of URI RRs is also to be used for other RR types. Since the 142 service labels might be overloaded, applications should carefully 143 check that the application level protocol is indeed the protocol they 144 expect. 146 Subtle management issues may also arise when the delegations from 147 service to sub service label involves several parties and different 148 stake holders. 150 4. The format of the URI RR 152 This is the presentation format of the URI RR: 154 Ownername TTL Class URI Priority Weight Target 156 The URI RR does not cause any kind of Additional Section processing. 158 4.1. Ownername, class and type 160 The URI ownername is subject to special conventions. 162 Just like the SRV RR [RFC2782] the URI RR has service information 163 encoded in its ownername. In order to encode the service for a 164 specific owner name one uses service parameters. Valid service 165 parameters used are those used for SRV resource records, or 166 registered by IANA for Enumservice Registrations. The Enumservice 167 Registration parameters are reversed (subtype(s) before type), 168 prepended with an underscore (_) and prepended to the owner name in 169 separate labels. The underscore is prepended to the service 170 parameters to avoid collisions with DNS labels that occur in nature, 171 and the order is reversed to make it possible to do delegations, if 172 needed, to different zones (and therefore providers of DNS). 174 It should be noted that the usage of a prefix must be described in 175 detail in for example the Enumservice Registration documentation, or 176 in a specific document that clarifies potential overload of 177 parameters in the same URI. Specifically, registered URI schemes are 178 not automatically acceptable as a service. With the HTTP scheme, one 179 can for example have multiple methods (GET, PUT, etc), and this with 180 the same URI. 182 For example, suppose we are looking for the URI for a service with 183 Service Parameter "A:B:C" for host example.com.. Then we would query 184 for (QNAME,QTYPE)=("_C._B._A.example.com","URI") 186 The type number for the URI record is 256. 188 The URI resource record is class independent. 190 The URI RR has no special TTL requirements. 192 4.2. Priority 194 The priority of the target URI in this RR. Its range is 0-65535. A 195 client MUST attempt to contact the URI with the lowest-numbered 196 priority it can reach; URIs with the same priority SHOULD be tried in 197 the order defined by the weight field. 199 4.3. Weight 201 A server selection mechanism. The weight field specifies a relative 202 weight for entries with the same priority. Larger weights SHOULD be 203 given a proportionately higher probability of being selected. The 204 range of this number is 0-65535. 206 4.4. Target 208 The URI of the target, enclosed in double-quote characters ('"'). 209 Resolution of the URI is according to the definitions for the Scheme 210 of the URI. 212 The URI is encoded as one or more RFC1035 section 213 3.3 [RFC1035]. 215 4.5. URI RDATA Wire Format 217 The RDATA for a URI RR consists of a 2 octet Priority field, a two 218 octet Weight field, and a variable length target field. 220 Priority and Weight are unsigned integers in network byte order. 222 The Target field contains the URI (without the enclosing double- 223 quote characters used in the presentation format), encoded as a 224 sequence of one or more (as specified in section 225 3.3 of RFC 1035 [RFC1035]), where all but the last 226 are filled up to the maximum length of 255 octets. 228 The Target field can also contain an IRI, but with the additional 229 requirements that it is in UTF-8 [RFC3629] and possible to convert to 230 a URI according to section 3.1 of RFC 3987 [RFC3987] and back again 231 to an IRI according to section 3.2. Other character sets than UTF-8 232 are not allowed. The domain name part of the IRI can be either an 233 U-LABEL or A-LABEL as defined in RFC 5890 [RFC5890]. 235 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 236 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 238 | Priority | Weight | 239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 240 / / 241 / Target / 242 / / 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 245 5. Definition of the flag 'D' for NAPTR records 247 This document specifies the flag "D" for use as a flag in NAPTR 248 records. The flag indicate a terminal NAPTR record because it 249 denotes the end of the DDDS/NAPTR processing rules. In the case of a 250 "D" flag, the Replacement field in the NAPTR record, prepended with 251 the service flags, is used as the Owner of a DNS query for URI 252 records, and normal URI processing as defined in this document is 253 applied. 255 The replacement field MUST NOT include any of the service parameters. 256 Those are to be prepended (together with underscore) as described in 257 other places in this document. 259 The Regexp field in the NAPTR record MUST be empty when the 'D' flag 260 is in use. 262 6. Examples 264 6.1. Homepage at one domain, but two domains in use 266 An organisation has the domain names example.com and example.net, but 267 the official URI http://www.example.com/. Given the service type 268 "web" and subtype "http" (from the IANA registry), the following URI 269 Resource Records could be made available in the respective zones 270 (example.com and example.net): 272 $ORIGIN example.com. 273 _http._web IN URI 10 1 "http://www.example.com/" 275 $ORIGIN example.net. 276 _http._web IN URI 10 1 "http://www.example.com/" 278 7. Relation to S-NAPTR 280 The URI resource record type is not a replacement for the S-NAPTR. 281 It is instead an extension and the seond step of the S-NAPTR 282 resolution can resolve a URI resource record instead of using SRV 283 records and yet another algorithm for how to use SRV records for the 284 specific protocol. 286 $ORIGIN example.com. 287 ;; order pref flags 288 IN NAPTR 100 10 "s" "EM:ProtA" ( ; service 289 "" ; regexp 290 _ProtA._tcp.example.com. ; replacement 291 _ProtA._tcp IN URI "schemeA:service.example.com/example" 293 8. Relation to U-NAPTR 295 The URI Resource Record Type, together with S-NAPTR, can be viewed as 296 a replacement for U-NAPTR [RFC4848]. The URI Resource Record Type is 297 though only interesting when one know a base domain name, a protocol 298 and service so that one can compose the record to look up. NAPTR 299 records of any kind are used to look up what services exists for a 300 certain domain, which is one step before the URI resource record is 301 used. 303 9. Relation to SRV 305 The URI Resource Record Type can be viewed as a replacement for the 306 SRV record. This because it like the SRV record can only be looked 307 up if one know the base domain, the protocol and the service. It has 308 a similar functionality, but instead of returning a hostname and port 309 number, the URI record return a full URI. As such, it can be viewed 310 as a more powerful resource record than SRV. 312 10. IANA Considerations 314 10.1. Registration of the URI Resource Record Type 316 After an expert review in February 2011 (see Appendix A) IANA has 317 allocated RRTYPE 256 for the URI Resource Record Type in the registry 318 named Resource Record (RR) TYPEs and QTYPEs as defined in BCP 42 RFC 319 6195 [RFC6195], located at 320 http://www.iana.org/assignments/dns-parameters. 322 IANA is requested to update the reference with that registration to 323 this RFC. 325 10.2. Registration of services 327 No new registry is needed for the registration of services as the 328 Enumservice Registrations registry is used also for the URI resource 329 record type. 331 11. Security Considerations 333 The authors do not believe this resource record cause any new 334 security problems. Deployment must though be done in a proper way as 335 misconfiguration of this resource record might make it impossible to 336 reach the service that was originally intended to be accessed. 338 Using the URI resource record together with security mechanisms that 339 relies on verification of authentication of hostnames, like TLS, 340 makes it important to choose the correct domain name when doing the 341 comparison. 343 The basic mechanism works as follows: 345 1. Announce the fact example.com is hosted at example.org (with 346 some URL) in DNS 347 2. Secure the URI resource record with DNSSEC. 348 3. Verify the TLS (for example) certificate for the connection to 349 example.org matches, i.e. use the hostname in the URI and not 350 the hostname used originally when looking up the URI resource 351 record. 352 4. If needed, do application layer authentication etc over the then 353 encrypted connection. 355 What also can happen is that the URI in the resource record type has 356 errors in it. Applications using the URI resource record type for 357 resolution should behave similarly as if the user typed (or copy and 358 pasted) the URI. At least it must be clear to the user that the 359 error is not due to any error from his side. 361 One SHOULD NOT include userinfo (see User Information, Section 3.2.1, 362 in RFC 3986 [RFC3986]) in a URI that is used in a URI resource record 363 as DNS data must be viewed as publicly available information. 365 12. Acknowledgements 367 Ideas on how to split the two different kind of queries "What 368 services exists for this domain name" and "What is the URI for this 369 service" came from Scott Bradner and Lawrence Conroy. Other people 370 that have contributed to this document include Richard Barnes, Leslie 371 Daigle, Olafur Gudmundsson, Ted Hardie, Peter Koch and Penn Pfautz. 373 Appendix A. The original RRTYPE Allocation Request 375 On February 22, 2011 IANA assigned RRTYPE 256 for the URI resource 376 record based on a request that followed the procedure documented in 377 RFC 6195 [RFC6195]. The DNS RRTYPE PARAMETER ALLOCATION form as 378 submitted to IANA at thet time is replicated below for reference. 380 A. Submission Date: 382 May 23, 2009 384 B. Submission Type: 386 [X] New RRTYPE 387 [ ] Modification to existing RRTYPE 389 C. Contact Information for submitter: 391 Name: Patrik Faltstrom 392 Email Address: paf@cisco.com 393 International telephone number: +46-8-6859131 394 Other contact handles: 395 (Note: This information will be publicly posted.) 397 D. Motivation for the new RRTYPE application? 399 There is no easy way to get from a domain name to a URI (or 400 IRI). Some mechanisms exists via use of the NAPTR [RFC3403] 401 resource record. That implies quite complicated rules that are 402 simplified via the S-NAPTR [RFC3958] specification. But, the 403 ability to directly look up a URI still exists. This 404 specification uses a prefix based naming mechanism originated in 405 the definition of the SRV [RFC2782] resource record, and the 406 RDATA is a URI, encoded as one text field. 408 See also above (Section 1). 410 E. Description of the proposed RR type. 412 The format of the URI resource record is as follows: 414 Ownername TTL Class URI Priority Weight Target 416 The URI RR has service information encoded in its ownername. In 417 order to encode the service for a specific owner name one uses 418 service parameters. Valid service parameters used are either 419 Enumservice Registrations registered by IANA, or prefixes used 420 for the SRV resource record. 422 The wire format of the RDATA is as follows: 424 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 425 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 427 | Priority | Weight | 428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 / / 430 / Target / 431 / / 432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 434 F. What existing RRTYPE or RRTYPEs come closest to filling that 435 need and why are they unsatisfactory? 437 The RRTYPE that come closest is the NAPTR resource record. It 438 is for example used in the DDDS and S-NAPTR algorithms. The 439 main problem with the NAPTR is that selection of what record (or 440 records) one is interested in is based on data stored in the 441 RDATA portion of the NAPTR resource record. This, as explained 442 in RFC 5507 [RFC5507], is not optimal for DNS lookups. Further, 443 most applications using NAPTR resource records uses regular 444 expression based rewrite rules for creation of the URI, and that 445 has shown be complicated to implement. 447 The second closest RRTYPE is the SRV record that given a 448 prefixed based naming just like is suggested for the URI 449 resource record, one get back a port number and domain name. 450 This can also be used for creation of a URI, but, only URIs 451 without path components. 453 G. What mnemonic is requested for the new RRTYPE (optional)? 455 URI 457 H. Does the requested RRTYPE make use of any existing IANA Registry 458 or require the creation of a new IANA sub-registry in DNS 459 Parameters? 461 Yes, partially. 463 One of the mechanisms to select a service is to use the 464 Enumservice Registry managed by IANA. Another is to use 465 services and protocols used for SRV records. 467 I. Does the proposal require/expect any changes in DNS servers/ 468 resolvers that prevent the new type from being processed as an 469 unknown RRTYPE (see [RFC3597])? 471 No 473 J. Comments: 475 None 477 13. References 478 13.1. Normative References 480 [RFC1035] Mockapetris, P., "Domain names - implementation and 481 specification", STD 13, RFC 1035, November 1987. 483 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 484 Requirement Levels", BCP 14, RFC 2119, March 1997. 486 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 487 10646", STD 63, RFC 3629, November 2003. 489 [RFC3958] Daigle, L. and A. Newton, "Domain-Based Application 490 Service Location Using SRV RRs and the Dynamic Delegation 491 Discovery Service (DDDS)", RFC 3958, January 2005. 493 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 494 Identifiers (IRIs)", RFC 3987, January 2005. 496 [RFC5890] Klensin, J., "Internationalized Domain Names for 497 Applications (IDNA): Definitions and Document Framework", 498 RFC 5890, August 2010. 500 [RFC6195] Eastlake, D., "Domain Name System (DNS) IANA 501 Considerations", BCP 42, RFC 6195, March 2011. 503 13.2. Non-normative references 505 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 506 specifying the location of services (DNS SRV)", RFC 2782, 507 February 2000. 509 [RFC3401] Mealling, M., "Dynamic Delegation Discovery System (DDDS) 510 Part One: The Comprehensive DDDS", RFC 3401, October 2002. 512 [RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS) 513 Part Three: The Domain Name System (DNS) Database", 514 RFC 3403, October 2002. 516 [RFC3404] Mealling, M., "Dynamic Delegation Discovery System (DDDS) 517 Part Four: The Uniform Resource Identifiers (URI)", 518 RFC 3404, October 2002. 520 [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record 521 (RR) Types", RFC 3597, September 2003. 523 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 524 Resource Identifier (URI): Generic Syntax", STD 66, 525 RFC 3986, January 2005. 527 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 528 System", RFC 4592, July 2006. 530 [RFC4848] Daigle, L., "Domain-Based Application Service Location 531 Using URIs and the Dynamic Delegation Discovery Service 532 (DDDS)", RFC 4848, April 2007. 534 [RFC5507] IAB, Faltstrom, P., Austein, R., and P. Koch, "Design 535 Choices When Expanding the DNS", RFC 5507, April 2009. 537 Authors' Addresses 539 Patrik Faltstrom 540 Netnod 542 Email: paf@netnod.se 544 Olaf Kolkman 545 NLnet Labs 547 Email: olaf@NLnetLabs.nl