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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-02) exists of draft-bormann-t2trg-rel-impl-00 == Outdated reference: A later version (-09) exists of draft-hartke-t2trg-coral-08 == Outdated reference: A later version (-46) exists of draft-ietf-ace-oauth-authz-24 == Outdated reference: A later version (-05) exists of draft-ietf-core-rd-dns-sd-04 -- Obsolete informational reference (is this intentional?): RFC 7230 (Obsoleted by RFC 9110, RFC 9112) Summary: 0 errors (**), 0 flaws (~~), 13 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CoRE Z. Shelby 3 Internet-Draft ARM 4 Intended status: Standards Track M. Koster 5 Expires: December 15, 2019 SmartThings 6 C. Bormann 7 Universitaet Bremen TZI 8 P. van der Stok 9 consultant 10 C. Amsuess, Ed. 11 June 13, 2019 13 CoRE Resource Directory 14 draft-ietf-core-resource-directory-21 16 Abstract 18 In many IoT applications, direct discovery of resources is not 19 practical due to sleeping nodes, disperse networks, or networks where 20 multicast traffic is inefficient. These problems can be solved by 21 employing an entity called a Resource Directory (RD), which contains 22 information about resources held on other servers, allowing lookups 23 to be performed for those resources. The input to an RD is composed 24 of links and the output is composed of links constructed from the 25 information stored in the RD. This document specifies the web 26 interfaces that a Resource Directory supports for web servers to 27 discover the RD and to register, maintain, lookup and remove 28 information on resources. Furthermore, new target attributes useful 29 in conjunction with an RD are defined. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on December 15, 2019. 48 Copyright Notice 50 Copyright (c) 2019 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (https://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 6 68 3.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 6 69 3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 7 70 3.3. RD Content Model . . . . . . . . . . . . . . . . . . . . 8 71 3.4. Link-local addresses and zone identifiers . . . . . . . . 12 72 3.5. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 12 73 3.6. Use Case: Home and Building Automation . . . . . . . . . 13 74 3.7. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 14 75 4. RD discovery and other interface-independent components . . . 14 76 4.1. Finding a Resource Directory . . . . . . . . . . . . . . 15 77 4.1.1. Resource Directory Address Option (RDAO) . . . . . . 17 78 4.2. Payload Content Formats . . . . . . . . . . . . . . . . . 18 79 4.3. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 19 80 5. Registration . . . . . . . . . . . . . . . . . . . . . . . . 21 81 5.1. Simple Registration . . . . . . . . . . . . . . . . . . . 26 82 5.2. Third-party registration . . . . . . . . . . . . . . . . 28 83 5.3. Operations on the Registration Resource . . . . . . . . . 28 84 5.3.1. Registration Update . . . . . . . . . . . . . . . . . 29 85 5.3.2. Registration Removal . . . . . . . . . . . . . . . . 32 86 5.3.3. Further operations . . . . . . . . . . . . . . . . . 32 87 6. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 33 88 6.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 33 89 6.2. Lookup filtering . . . . . . . . . . . . . . . . . . . . 34 90 6.3. Resource lookup examples . . . . . . . . . . . . . . . . 36 91 6.4. Endpoint lookup . . . . . . . . . . . . . . . . . . . . . 38 92 7. Security policies . . . . . . . . . . . . . . . . . . . . . . 39 93 7.1. Secure RD discovery . . . . . . . . . . . . . . . . . . . 40 94 7.2. Secure RD filtering . . . . . . . . . . . . . . . . . . . 40 95 7.3. Secure endpoint Name assignment . . . . . . . . . . . . . 41 97 8. Security Considerations . . . . . . . . . . . . . . . . . . . 41 98 8.1. Endpoint Identification and Authentication . . . . . . . 41 99 8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 42 100 8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 42 101 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42 102 9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 43 103 9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 43 104 9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 43 105 9.3.1. Full description of the "Endpoint Type" Registration 106 Parameter . . . . . . . . . . . . . . . . . . . . . . 45 107 9.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . . 45 108 9.5. Multicast Address Registration . . . . . . . . . . . . . 46 109 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 46 110 10.1. Lighting Installation . . . . . . . . . . . . . . . . . 46 111 10.1.1. Installation Characteristics . . . . . . . . . . . . 47 112 10.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 48 113 10.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 50 114 10.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 51 115 10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 52 116 10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 54 117 10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 54 118 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 54 119 12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 54 120 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 63 121 13.1. Normative References . . . . . . . . . . . . . . . . . . 63 122 13.2. Informative References . . . . . . . . . . . . . . . . . 64 123 Appendix A. Groups Registration and Lookup . . . . . . . . . . . 66 124 Appendix B. Web links and the Resource Directory . . . . . . . . 67 125 B.1. A simple example . . . . . . . . . . . . . . . . . . . . 68 126 B.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 68 127 B.1.2. Interpreting attributes and relations . . . . . . . . 68 128 B.2. A slightly more complex example . . . . . . . . . . . . . 69 129 B.3. Enter the Resource Directory . . . . . . . . . . . . . . 69 130 B.4. A note on differences between link-format and Link 131 headers . . . . . . . . . . . . . . . . . . . . . . . . . 71 132 Appendix C. Limited Link Format . . . . . . . . . . . . . . . . 72 133 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 73 135 1. Introduction 137 In the work on Constrained RESTful Environments (CoRE), a REST 138 architecture suitable for constrained nodes (e.g. with limited RAM 139 and ROM [RFC7228]) and networks (e.g. 6LoWPAN [RFC4944]) has been 140 established and is used in Internet-of-Things (IoT) or machine-to- 141 machine (M2M) applications such as smart energy and building 142 automation. 144 The discovery of resources offered by a constrained server is very 145 important in machine-to-machine applications where there are no 146 humans in the loop and static interfaces result in fragility. The 147 discovery of resources provided by an HTTP Web Server is typically 148 called Web Linking [RFC8288]. The use of Web Linking for the 149 description and discovery of resources hosted by constrained web 150 servers is specified by the CoRE Link Format [RFC6690]. However, 151 [RFC6690] only describes how to discover resources from the web 152 server that hosts them by querying "/.well-known/core". In many 153 constrained scenarios, direct discovery of resources is not practical 154 due to sleeping nodes, disperse networks, or networks where multicast 155 traffic is inefficient. These problems can be solved by employing an 156 entity called a Resource Directory (RD), which contains information 157 about resources held on other servers, allowing lookups to be 158 performed for those resources. 160 This document specifies the web interfaces that a Resource Directory 161 supports for web servers to discover the RD and to register, 162 maintain, lookup and remove information on resources. Furthermore, 163 new target attributes useful in conjunction with a Resource Directory 164 are defined. Although the examples in this document show the use of 165 these interfaces with CoAP [RFC7252], they can be applied in an 166 equivalent manner to HTTP [RFC7230]. 168 2. Terminology 170 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 171 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 172 "OPTIONAL" in this document are to be interpreted as described in 173 [RFC2119]. The term "byte" is used in its now customary sense as a 174 synonym for "octet". 176 This specification requires readers to be familiar with all the terms 177 and concepts that are discussed in [RFC3986], [RFC8288] and 178 [RFC6690]. Readers should also be familiar with the terms and 179 concepts discussed in [RFC7252]. To describe the REST interfaces 180 defined in this specification, the URI Template format is used 181 [RFC6570]. 183 This specification makes use of the following additional terminology: 185 resolve against 186 The expression "a URI-reference is _resolved against_ a base URI" 187 is used to describe the process of [RFC3986] Section 5.2. 188 Noteworthy corner cases are that if the URI-reference is a (full) 189 URI and resolved against any base URI, that gives the original 190 full URI, and that resolving an empty URI reference gives the base 191 URI without any fragment identifier. 193 Resource Directory 194 A web entity that stores information about web resources and 195 implements the REST interfaces defined in this specification for 196 registration and lookup of those resources. 198 Sector 199 In the context of a Resource Directory, a sector is a logical 200 grouping of endpoints. 202 The abbreviation "d=" is used for the sector in query parameters 203 for compatibility with deployed implementations. 205 Endpoint 206 Endpoint (EP) is a term used to describe a web server or client in 207 [RFC7252]. In the context of this specification an endpoint is 208 used to describe a web server that registers resources to the 209 Resource Directory. An endpoint is identified by its endpoint 210 name, which is included during registration, and has a unique name 211 within the associated sector of the registration. 213 Registration Base URI 214 The Base URI of a Registration is a URI that typically gives 215 scheme and authority information about an Endpoint. The 216 Registration Base URI is provided at registration time, and is 217 used by the Resource Directory to resolve relative references of 218 the registration into URIs. 220 Target 221 The target of a link is the destination address (URI) of the link. 222 It is sometimes identified with "href=", or displayed as 223 "". Relative targets need resolving with respect to the 224 Base URI (section 5.2 of [RFC3986]). 226 This use of the term Target is consistent with [RFC8288]'s use of 227 the term. 229 Context 230 The context of a link is the source address (URI) of the link, and 231 describes which resource is linked to the target. A link's 232 context is made explicit in serialized links as the "anchor=" 233 attribute. 235 This use of the term Context is consistent with [RFC8288]'s use of 236 the term. 238 Directory Resource 239 A resource in the Resource Directory (RD) containing registration 240 resources. 242 Registration Resource 243 A resource in the RD that contains information about an Endpoint 244 and its links. 246 Commissioning Tool 247 Commissioning Tool (CT) is a device that assists during the 248 installation of the network by assigning values to parameters, 249 naming endpoints and groups, or adapting the installation to the 250 needs of the applications. 252 Registrant-ep 253 Registrant-ep is the endpoint that is registered into the RD. The 254 registrant-ep can register itself, or a CT registers the 255 registrant-ep. 257 RDAO 258 Resource Directory Address Option. A new IPv6 Neighbor Discovery 259 option defined for announcing a Resource Directory's address. 261 3. Architecture and Use Cases 263 3.1. Principles 265 The Resource Directory is primarily a tool to make discovery 266 operations more efficient than querying /.well-known/core on all 267 connected devices, or across boundaries that would be limiting those 268 operations. 270 It provides information about resources hosted by other devices that 271 could otherwise only be obtained by directly querying the /.well- 272 known/core resource on these other devices, either by a unicast 273 request or a multicast request. 275 Information SHOULD only be stored in the resource directory if it can 276 be obtained by querying the described device's /.well-known/core 277 resource directly. 279 Data in the resource directory can only be provided by the device 280 which hosts those data or a dedicated Commissioning Tool (CT). These 281 CTs are thought to act on behalf of endpoints too constrained, or 282 generally unable, to present that information themselves. No other 283 client can modify data in the resource directory. Changes to the 284 information in the Resource Directory do not propagate automatically 285 back to the web servers from where the information originated. 287 3.2. Architecture 289 The resource directory architecture is illustrated in Figure 1. A 290 Resource Directory (RD) is used as a repository of registrations 291 describing resources hosted on other web servers, also called 292 endpoints (EP). An endpoint is a web server associated with a 293 scheme, IP address and port. A physical node may host one or more 294 endpoints. The RD implements a set of REST interfaces for endpoints 295 to register and maintain resource directory registrations, and for 296 endpoints to lookup resources from the RD. An RD can be logically 297 segmented by the use of Sectors. 299 A mechanism to discover an RD using CoRE Link Format [RFC6690] is 300 defined. 302 Registrations in the RD are soft state and need to be periodically 303 refreshed. 305 An endpoint uses specific interfaces to register, update and remove a 306 registration. It is also possible for an RD to fetch Web Links from 307 endpoints and add their contents to resource directory registrations. 309 At the first registration of an endpoint, a "registration resource" 310 is created, the location of which is returned to the registering 311 endpoint. The registering endpoint uses this registration resource 312 to manage the contents of registrations. 314 A lookup interface for discovering any of the Web Links stored in the 315 RD is provided using the CoRE Link Format. 317 Registration Lookup 318 Interface Interface 319 +----+ | | 320 | EP |---- | | 321 +----+ ---- | | 322 --|- +------+ | 323 +----+ | ----| | | +--------+ 324 | EP | ---------|-----| RD |----|-----| Client | 325 +----+ | ----| | | +--------+ 326 --|- +------+ | 327 +----+ ---- | | 328 | CT |---- | | 329 +----+ 331 Figure 1: The resource directory architecture. 333 A Registrant-EP MAY keep concurrent registrations to more than one RD 334 at the same time if explicitly configured to do so, but that is not 335 expected to be supported by typical EP implementations. Any such 336 registrations are independent of each other. The usual expectation 337 when multiple discovery mechanisms or addresses are configured is 338 that they constitute a fall-back path for a single registration. 340 3.3. RD Content Model 342 The Entity-Relationship (ER) models shown in Figure 2 and Figure 3 343 model the contents of /.well-known/core and the resource directory 344 respectively, with entity-relationship diagrams [ER]. Entities 345 (rectangles) are used for concepts that exist independently. 346 Attributes (ovals) are used for concepts that exist only in 347 connection with a related entity. Relations (diamonds) give a 348 semantic meaning to the relation between entities. Numbers specify 349 the cardinality of the relations. 351 Some of the attribute values are URIs. Those values are always full 352 URIs and never relative references in the information model. They 353 can, however, be expressed as relative references in serializations, 354 and often are. 356 These models provide an abstract view of the information expressed in 357 link-format documents and a Resource Directory. They cover the 358 concepts, but not necessarily all details of an RD's operation; they 359 are meant to give an overview, and not be a template for 360 implementations. 362 +----------------------+ 363 | /.well-known/core | 364 +----------------------+ 365 | 366 | 1 367 ////////\\\\\\\ 368 < contains > 369 \\\\\\\\/////// 370 | 371 | 0+ 372 +--------------------+ 373 | link | 374 +--------------------+ 375 | 376 | 1 oooooooo 377 +-----o target o 378 | oooooooo 379 oooooooooooo 0+ | 380 o target o--------+ 381 o attribute o | 0+ oooooo 382 oooooooooooo +-----o rel o 383 | oooooo 384 | 385 | 1 ooooooooo 386 +-----o context o 387 ooooooooo 389 Figure 2: E-R Model of the content of /.well-known/core 391 The model shown in Figure 2 models the contents of /.well-known/core 392 which contains: 394 o a set of links belonging to the hosting web server 396 The web server is free to choose links it deems appropriate to be 397 exposed in its ".well-known/core". Typically, the links describe 398 resources that are served by the host, but the set can also contain 399 links to resources on other servers (see examples in [RFC6690] page 400 14). The set does not necessarily contain links to all resources 401 served by the host. 403 A link has the following attributes (see [RFC8288]): 405 o Zero or more link relations: They describe relations between the 406 link context and the link target. 408 In link-format serialization, they are expressed as space- 409 separated values in the "rel" attribute, and default to "hosts". 411 o A link context URI: It defines the source of the relation, e.g. 412 _who_ "hosts" something. 414 In link-format serialization, it is expressed in the "anchor" 415 attribute. It defaults to that document's URI. 417 o A link target URI: It defines the destination of the relation 418 (e.g. _what_ is hosted), and is the topic of all target 419 attributes. 421 In link-format serialization, it is expressed between angular 422 brackets, and sometimes called the "href". 424 o Other target attributes (e.g. resource type (rt), interface (if), 425 or content format (ct)). These provide additional information 426 about the target URI. 428 +----------------------+ 429 | resource-directory | 430 +----------------------+ 431 | 1 432 | 433 | 434 | 435 | 436 //////\\\\ 437 < contains > 438 \\\\\///// 439 | 440 0+ | 441 ooooooo 1 +---------------+ 442 o base o-------| registration | 443 ooooooo +---------------+ 444 | | 1 445 | +--------------+ 446 oooooooo 1 | | 447 o href o----+ /////\\\\ 448 oooooooo | < contains > 449 | \\\\\///// 450 oooooooo 1 | | 451 o ep o----+ | 0+ 452 oooooooo | +------------------+ 453 | | link | 454 oooooooo 0-1 | +------------------+ 455 o d o----+ | 456 oooooooo | | 1 oooooooo 457 | +-----o target o 458 oooooooo 1 | | oooooooo 459 o lt o----+ ooooooooooo 0+ | 460 oooooooo | o target o-----+ 461 | o attribute o | 0+ oooooo 462 ooooooooooo 0+ | ooooooooooo +-----o rel o 463 o endpoint o----+ | oooooo 464 o attribute o | 465 ooooooooooo | 1 ooooooooo 466 +----o context o 467 ooooooooo 469 Figure 3: E-R Model of the content of the Resource Directory 471 The model shown in Figure 3 models the contents of the resource 472 directory which contains in addition to /.well-known/core: 474 o 0 to n Registrations of endpoints, 475 A registration is associated with one endpoint. A registration 476 defines a set of links as defined for /.well-known/core. A 477 Registration has six types of attributes: 479 o an endpoint name ("ep", a Unicode string) unique within a sector 481 o a Registration Base URI ("base", a URI typically describing the 482 scheme://authority part) 484 o a lifetime ("lt"), 486 o a registration resource location inside the RD ("href"), 488 o optionally a sector ("d", a Unicode string) 490 o optional additional endpoint attributes (from Section 9.3) 492 The cardinality of "base" is currently 1; future documents are 493 invited to extend the RD specification to support multiple values 494 (e.g. [I-D.silverajan-core-coap-protocol-negotiation]). Its value 495 is used as a Base URI when resolving URIs in the links contained in 496 the endpoint. 498 Links are modelled as they are in Figure 2. 500 3.4. Link-local addresses and zone identifiers 502 Registration Base URIs can contain link-local IP addresses. To be 503 usable across hosts, those can not be serialized to contain zone 504 identifiers (see [RFC6874] Section 1). 506 Link-local addresses can only be used on a single link (therefore RD 507 servers can not announce them when queried on a different link), and 508 lookup clients using them need to keep track of which interface they 509 got them from. 511 Therefore, it is advisable in many scenarios to use addresses with 512 larger scope if available. 514 3.5. Use Case: Cellular M2M 516 Over the last few years, mobile operators around the world have 517 focused on development of M2M solutions in order to expand the 518 business to the new type of users: machines. The machines are 519 connected directly to a mobile network using an appropriate embedded 520 wireless interface (GSM/GPRS, WCDMA, LTE) or via a gateway providing 521 short and wide range wireless interfaces. From the system design 522 point of view, the ambition is to design horizontal solutions that 523 can enable utilization of machines in different applications 524 depending on their current availability and capabilities as well as 525 application requirements, thus avoiding silo like solutions. One of 526 the crucial enablers of such design is the ability to discover 527 resources (machines -- endpoints) capable of providing required 528 information at a given time or acting on instructions from the end 529 users. 531 Imagine a scenario where endpoints installed on vehicles enable 532 tracking of the position of these vehicles for fleet management 533 purposes and allow monitoring of environment parameters. During the 534 boot-up process endpoints register with a Resource Directory, which 535 is hosted by the mobile operator or somewhere in the cloud. 536 Periodically, these endpoints update their registration and may 537 modify resources they offer. 539 When endpoints are not always connected, for example because they 540 enter a sleep mode, a remote server is usually used to provide proxy 541 access to the endpoints. Mobile apps or web applications for 542 environment monitoring contact the RD, look up the endpoints capable 543 of providing information about the environment using an appropriate 544 set of link parameters, obtain information on how to contact them 545 (URLs of the proxy server), and then initiate interaction to obtain 546 information that is finally processed, displayed on the screen and 547 usually stored in a database. Similarly, fleet management systems 548 provide the appropriate link parameters to the RD to look up for EPs 549 deployed on the vehicles the application is responsible for. 551 3.6. Use Case: Home and Building Automation 553 Home and commercial building automation systems can benefit from the 554 use of M2M web services. The discovery requirements of these 555 applications are demanding. Home automation usually relies on run- 556 time discovery to commission the system, whereas in building 557 automation a combination of professional commissioning and run-time 558 discovery is used. Both home and building automation involve peer- 559 to-peer interactions between endpoints, and involve battery-powered 560 sleeping devices. 562 Two phases can be discerned for a network servicing the system: (1) 563 installation and (2) operation. During the operational phase, the 564 network is connected to the Internet with a Border router (6LBR) and 565 the nodes connected to the network can use the Internet services that 566 are provided by the Internet Provider or the network administrator. 567 During the installation phase, the network is completely stand-alone, 568 no 6LBR is connected, and the network only supports the IP 569 communication between the connected nodes. The installation phase is 570 usually followed by the operational phase. 572 3.7. Use Case: Link Catalogues 574 Resources may be shared through data brokers that have no knowledge 575 beforehand of who is going to consume the data. Resource Directory 576 can be used to hold links about resources and services hosted 577 anywhere to make them discoverable by a general class of 578 applications. 580 For example, environmental and weather sensors that generate data for 581 public consumption may provide data to an intermediary server, or 582 broker. Sensor data are published to the intermediary upon changes 583 or at regular intervals. Descriptions of the sensors that resolve to 584 links to sensor data may be published to a Resource Directory. 585 Applications wishing to consume the data can use RD Lookup to 586 discover and resolve links to the desired resources and endpoints. 587 The Resource Directory service need not be coupled with the data 588 intermediary service. Mapping of Resource Directories to data 589 intermediaries may be many-to-many. 591 Metadata in web link formats like [RFC6690] which may be internally 592 stored as triples, or relation/attribute pairs providing metadata 593 about resource links, need to be supported by Resource Directories . 594 External catalogues that are represented in other formats may be 595 converted to common web linking formats for storage and access by 596 Resource Directories. Since it is common practice for these to be 597 URN encoded, simple and lossless structural transforms should 598 generally be sufficient to store external metadata in Resource 599 Directories. 601 The additional features of Resource Directory allow sectors to be 602 defined to enable access to a particular set of resources from 603 particular applications. This provides isolation and protection of 604 sensitive data when needed. Application groups with multicast 605 addresses may be defined to support efficient data transport. 607 4. RD discovery and other interface-independent components 609 This and the following sections define the required set of REST 610 interfaces between a Resource Directory (RD), endpoints and lookup 611 clients. Although the examples throughout these sections assume the 612 use of CoAP [RFC7252], these REST interfaces can also be realized 613 using HTTP [RFC7230]. Only multicast discovery operations are not 614 possible on HTTP, and Simple Registration can not be executed as base 615 attribute (which is mandatory for HTTP) can not be used there. In 616 all definitions in these sections, both CoAP response codes (with dot 617 notation) and HTTP response codes (without dot notation) are shown. 618 An RD implementing this specification MUST support the discovery, 619 registration, update, lookup, and removal interfaces. 621 All operations on the contents of the Resource Directory MUST be 622 atomic and idempotent. 624 For several operations, interface templates are given in list form; 625 those describe the operation participants, request codes, URIs, 626 content formats and outcomes. Sections of those templates contain 627 normative content about Interaction, Method, URI Template and URI 628 Template Variables as well as the details of the Success condition. 629 The additional sections on options like Content-Format and on Failure 630 codes give typical cases that an implementation of the RD should deal 631 with. Those serve to illustrate the typical responses to readers who 632 are not yet familiar with all the details of CoAP based interfaces; 633 they do not limit what a server may respond under atypical 634 circumstances. 636 REST clients (registrant-EPs / CTs, lookup clients, RD servers during 637 simple registrations) MUST be prepared to receive any unsuccessful 638 code and act upon it according to its definition, options and/or 639 payload to the best of their capabilities, falling back to failing 640 the operation if recovery is not possible. In particular, they 641 should retry the request upon 5.03 (Service Unavailable; 503 in HTTP) 642 according to the Max-Age (Retry-After in HTTP) option, and fall back 643 to link-format when receiving 4.15 (Unsupported Content Format; 415 644 in HTTP). 646 A resource directory MAY make the information submitted to it 647 available to further directories, if it can ensure that a loop does 648 not form. The protocol used between directories to ensure loop-free 649 operation is outside the scope of this document. 651 4.1. Finding a Resource Directory 653 A (re-)starting device may want to find one or more resource 654 directories for discovery purposes. Dependent on the operational 655 conditions, one or more of the techniques below apply. The use of 656 DNS-SD [RFC6763] is described in [I-D.ietf-core-rd-dns-sd]. 658 The device may be pre-configured to exercise specific mechanisms for 659 finding the resource directory: 661 1. It may be configured with a specific IP address for the RD. That 662 IP address may also be an anycast address, allowing the network 663 to forward RD requests to an RD that is topologically close; each 664 target network environment in which some of these preconfigured 665 nodes are to be brought up is then configured with a route for 666 this anycast address that leads to an appropriate RD. (Instead 667 of using an anycast address, a multicast address can also be 668 preconfigured. The RD servers then need to configure one of 669 their interfaces with this multicast address.) 671 2. It may be configured with a DNS name for the RD and use DNS to 672 return the IP address of the RD; it can find a DNS server to 673 perform the lookup using the usual mechanisms for finding DNS 674 servers. 676 For cases where the device is not specifically configured with a way 677 to find a resource directory, the network may want to provide a 678 suitable default. 680 1. If the address configuration of the network is performed via 681 SLAAC, this is provided by the RDAO option Section 4.1.1. 683 2. If the address configuration of the network is performed via 684 DHCP, this could be provided via a DHCP option (no such option is 685 defined at the time of writing). 687 Finally, if neither the device nor the network offers any specific 688 configuration, the device may want to employ heuristics to find a 689 suitable resource directory. 691 The present specification does not fully define these heuristics, but 692 suggests a number of candidates: 694 1. In a 6LoWPAN, just assume the Border Router (6LBR) can act as a 695 resource directory (using the ABRO option to find that 696 [RFC6775]). Confirmation can be obtained by sending a Unicast to 697 "coap://[6LBR]/.well-known/core?rt=core.rd*". 699 2. In a network that supports multicast well, discovering the RD 700 using a multicast query for /.well-known/core as specified in 701 CoRE Link Format [RFC6690]: Sending a Multicast GET to 702 "coap://[MCD1]/.well-known/core?rt=core.rd*". RDs within the 703 multicast scope will answer the query. 705 When answering a multicast request directed at a link-local address, 706 the RD may want to respond from a routable address; this makes it 707 easier for registrants to use one of their own routable addresses for 708 registration. 710 As some of the RD addresses obtained by the methods listed here are 711 just (more or less educated) guesses, endpoints MUST make use of any 712 error messages to very strictly rate-limit requests to candidate IP 713 addresses that don't work out. For example, an ICMP Destination 714 Unreachable message (and, in particular, the port unreachable code 715 for this message) may indicate the lack of a CoAP server on the 716 candidate host, or a CoAP error response code such as 4.05 "Method 717 Not Allowed" may indicate unwillingness of a CoAP server to act as a 718 directory server. 720 The following RD discovery mechanisms are recommended: 722 o In managed networks with border routers that need stand-alone 723 operation, the RDA0 option is recommended (e.g. operational phase 724 described in Section 3.6). 726 o In managed networks without border router (no Internet services 727 available), the use of a preconfigured anycast address is 728 recommended (e.g. installation phase described in Section 3.6). 730 o The use of DNS facilities is described in 731 [I-D.ietf-core-rd-dns-sd]. 733 The use of multicast discovery in mesh networks is NOT recommended. 735 4.1.1. Resource Directory Address Option (RDAO) 737 The Resource Directory Address Option (RDAO) using IPv6 Neighbor 738 Discovery (ND) carries information about the address of the Resource 739 Directory (RD). This information is needed when endpoints cannot 740 discover the Resource Directory with a link-local or realm-local 741 scope multicast address, for instance because the endpoint and the RD 742 are separated by a Border Router (6LBR). In many circumstances the 743 availability of DHCP cannot be guaranteed either during commissioning 744 of the network. The presence and the use of the RD is essential 745 during commissioning. 747 It is possible to send multiple RDAO options in one message, 748 indicating as many resource directory addresses. 750 The RDAO format is: 752 0 1 2 3 753 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 1 754 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 755 | Type | Length = 3 | Valid Lifetime | 756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 757 | Reserved | 758 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 759 | | 760 + + 761 | | 762 + RD Address + 763 | | 764 + + 765 | | 766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 768 Fields: 770 Type: 38 772 Length: 8-bit unsigned integer. The length of 773 the option in units of 8 bytes. 774 Always 3. 776 Valid Lifetime: 16-bit unsigned integer. The length of 777 time in units of 60 seconds (relative to 778 the time the packet is received) that 779 this Resource Directory address is valid. 780 A value of all zero bits (0x0) indicates 781 that this Resource Directory address 782 is not valid anymore. 784 Reserved: This field is unused. It MUST be 785 initialized to zero by the sender and 786 MUST be ignored by the receiver. 788 RD Address: IPv6 address of the RD. 790 Figure 4: Resource Directory Address Option 792 4.2. Payload Content Formats 794 Resource Directory implementations using this specification MUST 795 support the application/link-format content format (ct=40). 797 Resource Directories implementing this specification MAY support 798 additional content formats. 800 Any additional content format supported by a Resource Directory 801 implementing this specification SHOULD be able to express all the 802 information expressible in link-format. It MAY be able to express 803 information that is inexpressible in link-format, but those 804 expressions SHOULD be avoided where possible. 806 4.3. URI Discovery 808 Before an endpoint can make use of an RD, it must first know the RD's 809 address and port, and the URI path information for its REST APIs. 810 This section defines discovery of the RD and its URIs using the well- 811 known interface of the CoRE Link Format [RFC6690]. A complete set of 812 RD discovery methods is described in Section 4.1. 814 Discovery of the RD registration URI path is performed by sending 815 either a multicast or unicast GET request to "/.well-known/core" and 816 including a Resource Type (rt) parameter [RFC6690] with the value 817 "core.rd" in the query string. Likewise, a Resource Type parameter 818 value of "core.rd-lookup*" is used to discover the URIs for RD Lookup 819 operations, core.rd* is used to discover all URI paths for RD 820 operations. Upon success, the response will contain a payload with a 821 link format entry for each RD function discovered, indicating the URI 822 of the RD function returned and the corresponding Resource Type. 823 When performing multicast discovery, the multicast IP address used 824 will depend on the scope required and the multicast capabilities of 825 the network (see Section 9.5). 827 A Resource Directory MAY provide hints about the content-formats it 828 supports in the links it exposes or registers, using the "ct" target 829 attribute, as shown in the example below. Clients MAY use these 830 hints to select alternate content-formats for interaction with the 831 Resource Directory. 833 HTTP does not support multicast and consequently only unicast 834 discovery can be supported using HTTP. The well-known entry points 835 SHOULD be provided to enable unicast discovery. 837 An implementation of this resource directory specification MUST 838 support query filtering for the rt parameter as defined in [RFC6690]. 840 While the link targets in this discovery step are often expressed in 841 path-absolute form, this is not a requirement. Clients of the RD 842 SHOULD therefore accept URIs of all schemes they support, both as 843 URIs and relative references, and not limit the set of discovered 844 URIs to those hosted at the address used for URI discovery. 846 The URI Discovery operation can yield multiple URIs of a given 847 resource type. The client of the RD can use any of the discovered 848 addresses initially. 850 The discovery request interface is specified as follows (this is 851 exactly the Well-Known Interface of [RFC6690] Section 4, with the 852 additional requirement that the server MUST support query filtering): 854 Interaction: EP and Client -> RD 856 Method: GET 858 URI Template: /.well-known/core{?rt} 860 URI Template Variables: 862 rt := Resource Type. SHOULD contain one of the values "core.rd", 863 "core.rd-lookup*", "core.rd-lookup-res", "core.rd-lookup-ep", 864 or "core.rd*" 866 Accept: absent, application/link-format or any other media type 867 representing web links 869 The following response is expected on this interface: 871 Success: 2.05 "Content" or 200 "OK" with an application/link-format 872 or other web link payload containing one or more matching entries 873 for the RD resource. 875 The following example shows an endpoint discovering an RD using this 876 interface, thus learning that the directory resource location, in 877 this example, is /rd, and that the content-format delivered by the 878 server hosting the resource is application/link-format (ct=40). Note 879 that it is up to the RD to choose its RD locations. 881 Req: GET coap://[MCD1]/.well-known/core?rt=core.rd* 883 Res: 2.05 Content 884 ;rt="core.rd";ct=40, 885 ;rt="core.rd-lookup-ep";ct=40, 886 ;rt="core.rd-lookup-res";ct=40, 888 Figure 5: Example discovery exchange 890 The following example shows the way of indicating that a client may 891 request alternate content-formats. The Content-Format code attribute 892 "ct" MAY include a space-separated sequence of Content-Format codes 893 as specified in Section 7.2.1 of [RFC7252], indicating that multiple 894 content-formats are available. The example below shows the required 895 Content-Format 40 (application/link-format) indicated as well as a 896 CBOR and JSON representation from [I-D.ietf-core-links-json] (which 897 have no numeric values assigned yet, so they are shown as TBD64 and 898 TBD504 as in that draft). The RD resource locations /rd, and /rd- 899 lookup are example values. The server in this example also indicates 900 that it is capable of providing observation on resource lookups. 902 [ The RFC editor is asked to replace this and later occurrences of 903 MCD1 with the assigned IPv6 site-local address for "all CoRE Resource 904 Directories". ] 906 Req: GET coap://[MCD1]/.well-known/core?rt=core.rd* 908 Res: 2.05 Content 909 ;rt="core.rd";ct="40 65225", 910 ;rt="core.rd-lookup-res";ct="40 TBD64 TBD504";obs, 911 ;rt="core.rd-lookup-ep";ct="40 TBD64 TBD504", 913 From a management and maintenance perspective, it is necessary to 914 identify the components that constitute the RD server. The 915 identification refers to information about for example client-server 916 incompatibilities, supported features, required updates and other 917 aspects. The URI discovery address, a described in section 4 of 918 [RFC6690] can be used to find the identification. 920 It would typically be stored in an implementation information link 921 (as described in [I-D.bormann-t2trg-rel-impl]): 923 Req: GET /.well-known/core?rel=impl-info 925 Res: 2.05 Content 926 ; 927 rel="impl-info" 929 Note that depending on the particular server's architecture, such a 930 link could be anchored at the RD server's root, at the discovery site 931 (as in this example) or at individual RD components. The latter is 932 to be expected when different applications are run on the same 933 server. 935 5. Registration 937 After discovering the location of an RD, a registrant-ep or CT MAY 938 register the resources of the registrant-ep using the registration 939 interface. This interface accepts a POST from an endpoint containing 940 the list of resources to be added to the directory as the message 941 payload in the CoRE Link Format [RFC6690] or other representations of 942 web links, along with query parameters indicating the name of the 943 endpoint, and optionally the sector, lifetime and base URI of the 944 registration. It is expected that other specifications will define 945 further parameters (see Section 9.3). The RD then creates a new 946 registration resource in the RD and returns its location. The 947 receiving endpoint MUST use that location when refreshing 948 registrations using this interface. Registration resources in the RD 949 are kept active for the period indicated by the lifetime parameter. 950 The creating endpoint is responsible for refreshing the registration 951 resource within this period using either the registration or update 952 interface. The registration interface MUST be implemented to be 953 idempotent, so that registering twice with the same endpoint 954 parameters ep and d (sector) does not create multiple registration 955 resources. 957 The following rules apply for a registration request targeting a 958 given (ep, d) value pair: 960 o When the (ep, d) value pair of the registration-request is 961 different from any existing registration, a new registration is 962 generated. 964 o When the (ep, d) value pair of the registration-request is equal 965 to an existing registration, the content and parameters of the 966 existing registration are replaced with the content of the 967 registration request. 969 The posted link-format document can (and typically does) contain 970 relative references both in its link targets and in its anchors, or 971 contain empty anchors. The RD server needs to resolve these 972 references in order to faithfully represent them in lookups. They 973 are resolved against the base URI of the registration, which is 974 provided either explicitly in the "base" parameter or constructed 975 implicitly from the requester's URI as constructed from its network 976 address and scheme. 978 For media types to which Appendix C applies (i.e. documents in 979 application/link-format), the RD only needs to accept representations 980 in Limited Link Format as described there. Its behavior with 981 representations outside that subset is implementation defined. 983 The registration request interface is specified as follows: 985 Interaction: EP -> RD 987 Method: POST 989 URI Template: {+rd}{?ep,d,lt,base,extra-attrs*} 990 URI Template Variables: 992 rd := RD registration URI (mandatory). This is the location of 993 the RD, as obtained from discovery. 995 ep := Endpoint name (mostly mandatory). The endpoint name is an 996 identifier that MUST be unique within a sector. As the 997 endpoint name is a Unicode string, it is encoded in UTF-8 (and 998 possibly pct-encoding) during variable expansion (see [RFC6570] 999 Section 3.2.1). The endpoint name MUST NOT contain any 1000 character in the inclusive ranges 0-31 or 127-159. The maximum 1001 length of this parameter is 63 UTF-8 encoded bytes. If the RD 1002 is configured to recognize the endpoint (e.g. based on its 1003 security context), the RD assigns an endpoint name based on a 1004 set of configuration parameter values. 1006 d := Sector (optional). The sector to which this endpoint 1007 belongs. When this parameter is not present, the RD MAY 1008 associate the endpoint with a configured default sector or 1009 leave it empty. The sector is encoded like the ep parameter, 1010 and is limited to 63 UTF-8 encoded bytes as well. The endpoint 1011 name and sector name are not set when one or both are set in an 1012 accompanying authorization token. 1014 lt := Lifetime (optional). Lifetime of the registration in 1015 seconds. Range of 60-4294967295. If no lifetime is included 1016 in the initial registration, a default value of 90000 (25 1017 hours) SHOULD be assumed. 1019 base := Base URI (optional). This parameter sets the base URI of 1020 the registration, under which the relative links in the payload 1021 are to be interpreted. The specified URI typically does not 1022 have a path component of its own, and MUST be suitable as a 1023 base URI to resolve any relative references given in the 1024 registration. The parameter is therefore usually of the shape 1025 "scheme://authority" for HTTP and CoAP URIs. The URI SHOULD 1026 NOT have a query or fragment component as any non-empty 1027 relative part in a reference would remove those parts from the 1028 resulting URI. 1030 In the absence of this parameter the scheme of the protocol, 1031 source address and source port of the registration request are 1032 assumed. The Base URI is consecutively constructed by 1033 concatenating the used protocol's scheme with the characters 1034 "://", the requester's source address as an address literal and 1035 ":" followed by its port (if it was not the protocol's default 1036 one) in analogy to [RFC7252] Section 6.5. 1038 This parameter is mandatory when the directory is filled by a 1039 third party such as an commissioning tool. 1041 If the registrant-ep uses an ephemeral port to register with, 1042 it MUST include the base parameter in the registration to 1043 provide a valid network path. 1045 A registrant that can not be reached by potential lookup 1046 clients at the address it registers from (e.g. because it is 1047 behind some form of Network Address Translation (NAT)) MUST 1048 provide a reachable base address with its registration. 1050 If the Base URI contains a link-local IP literal, it MUST NOT 1051 contain a Zone Identifier, and MUST be local to the link on 1052 which the registration request is received. 1054 Endpoints that register with a base that contains a path 1055 component can not meaningfully use [RFC6690] Link Format due to 1056 its prevalence of the Origin concept in relative reference 1057 resolution. Those applications should use different 1058 representations of links to which Appendix C is not applicable 1059 (e.g. [I-D.hartke-t2trg-coral]). 1061 extra-attrs := Additional registration attributes (optional). 1062 The endpoint can pass any parameter registered at Section 9.3 1063 to the directory. If the RD is aware of the parameter's 1064 specified semantics, it processes it accordingly. Otherwise, 1065 it MUST store the unknown key and its value(s) as an endpoint 1066 attribute for further lookup. 1068 Content-Format: application/link-format or any other indicated media 1069 type representing web links 1071 The following response is expected on this interface: 1073 Success: 2.01 "Created" or 201 "Created". The Location-Path option 1074 or Location header MUST be included in the response. This 1075 location MUST be a stable identifier generated by the RD as it is 1076 used for all subsequent operations on this registration resource. 1077 The registration resource location thus returned is for the 1078 purpose of updating the lifetime of the registration and for 1079 maintaining the content of the registered links, including 1080 updating and deleting links. 1082 A registration with an already registered ep and d value pair 1083 responds with the same success code and location as the original 1084 registration; the set of links registered with the endpoint is 1085 replaced with the links from the payload. 1087 The location MUST NOT have a query or fragment component, as that 1088 could conflict with query parameters during the Registration 1089 Update operation. Therefore, the Location-Query option MUST NOT 1090 be present in a successful response. 1092 If the registration fails, including request timeouts, or if delays 1093 from Service Unavailable responses with Max-Age or Retry-After 1094 accumulate to exceed the registrant's configured timeouts, it SHOULD 1095 pick another registration URI from the "URI Discovery" step and if 1096 there is only one or the list is exhausted, pick other choices from 1097 the "Finding a Resource Directory" step. Care has to be taken to 1098 consider the freshness of results obtained earlier, e.g. of the 1099 result of a "/.well-known/core" response, the lifetime of an RDAO 1100 option and of DNS responses. Any rate limits and persistent errors 1101 from the "Finding a Resource Directory" step must be considered for 1102 the whole registration time, not only for a single operation. 1104 The following example shows a registrant-ep with the name "node1" 1105 registering two resources to an RD using this interface. The 1106 location "/rd" is an example RD location discovered in a request 1107 similar to Figure 5. 1109 Req: POST coap://rd.example.com/rd?ep=node1 1110 Content-Format: 40 1111 Payload: 1112 ;ct=41;rt="temperature-c";if="sensor"; 1113 anchor="coap://spurious.example.com:5683", 1114 ;ct=41;rt="light-lux";if="sensor" 1116 Res: 2.01 Created 1117 Location-Path: /rd/4521 1119 Figure 6: Example registration payload 1121 A Resource Directory may optionally support HTTP. Here is an example 1122 of almost the same registration operation above, when done using 1123 HTTP. 1125 Req: POST /rd?ep=node1&base=http://[2001:db8:1::1] HTTP/1.1 1126 Host: example.com 1127 Content-Type: application/link-format 1128 Payload: 1129 ;ct=41;rt="temperature-c";if="sensor"; 1130 anchor="coap://spurious.example.com:5683", 1131 ;ct=41;rt="light-lux";if="sensor" 1133 Res: 201 Created 1134 Location: /rd/4521 1136 5.1. Simple Registration 1138 Not all endpoints hosting resources are expected to know how to 1139 upload links to an RD as described in Section 5. Instead, simple 1140 endpoints can implement the Simple Registration approach described in 1141 this section. An RD implementing this specification MUST implement 1142 Simple Registration. However, there may be security reasons why this 1143 form of directory discovery would be disabled. 1145 This approach requires that the registrant-ep makes available the 1146 hosted resources that it wants to be discovered, as links on its 1147 "/.well-known/core" interface as specified in [RFC6690]. The links 1148 in that document are subject to the same limitations as the payload 1149 of a registration (with respect to Appendix C). 1151 o The registrant-ep finds one or more addresses of the directory 1152 server as described in Section 4.1. 1154 o The registrant-ep sends (and regularly refreshes with) a POST 1155 request to the "/.well-known/core" URI of the directory server of 1156 choice. The body of the POST request is empty, and triggers the 1157 resource directory server to perform GET requests at the 1158 requesting registrant-ep's /.well-known/core to obtain the link- 1159 format payload to register. 1161 The registrant-ep includes the same registration parameters in the 1162 POST request as it would per Section 5. The registration base URI 1163 of the registration is taken from the registrant-ep's network 1164 address (as is default with regular registrations). 1166 Example request from registrant-EP to RD (unanswered until the 1167 next step): 1169 Req: POST /.well-known/core?lt=6000&ep=node1 1170 (No payload) 1172 o The Resource Directory queries the registrant-ep's discovery 1173 resource to determine the success of the operation. It SHOULD 1174 keep a cache of the discovery resource and not query it again as 1175 long as it is fresh. 1177 Example request from the RD to the registrant-EP: 1179 Req: GET /.well-known/core 1180 Accept: 40 1182 Res: 2.05 Content 1183 Content-Format: 40 1184 Payload: 1185 1187 With this response, the RD would answer the previous step's request: 1189 Res: 2.04 Changed 1191 The sequence of fetching the registration content before sending a 1192 successful response was chosen to make responses reliable, and the 1193 caching item was chosen to still allow very constrained registrants. 1194 Registrants MUST be able to serve a GET request to "/.well-known/ 1195 core" after having requested registration. Constrained devices MAY 1196 regard the initial request as temporarily failed when they need RAM 1197 occupied by their own request to serve the RD's GET, and retry later 1198 when the RD already has a cached representation of their discovery 1199 resources. Then, the RD can reply immediately and the registrant can 1200 receive the response. 1202 The simple registration request interface is specified as follows: 1204 Interaction: EP -> RD 1206 Method: POST 1208 URI Template: /.well-known/core{?ep,d,lt,extra-attrs*} 1210 URI Template Variables are as they are for registration in Section 5. 1211 The base attribute is not accepted to keep the registration interface 1212 simple; that rules out registration over CoAP-over-TCP or HTTP that 1213 would need to specify one. 1215 The following response is expected on this interface: 1217 Success: 2.04 "Changed". 1219 For the second interaction triggered by the above, the registrant-ep 1220 takes the role of server and the RD the role of client. (Note that 1221 this is exactly the Well-Known Interface of [RFC6690] Section 4): 1223 Interaction: RD -> EP 1225 Method: GET 1226 URI Template: /.well-known/core 1228 The following response is expected on this interface: 1230 Success: 2.05 "Content". 1232 The RD MUST delete registrations created by simple registration after 1233 the expiration of their lifetime. Additional operations on the 1234 registration resource cannot be executed because no registration 1235 location is returned. 1237 5.2. Third-party registration 1239 For some applications, even Simple Registration may be too taxing for 1240 some very constrained devices, in particular if the security 1241 requirements become too onerous. 1243 In a controlled environment (e.g. building control), the Resource 1244 Directory can be filled by a third party device, called a 1245 Commissioning Tool (CT). The commissioning tool can fill the 1246 Resource Directory from a database or other means. For that purpose 1247 scheme, IP address and port of the URI of the registered device is 1248 the value of the "base" parameter of the registration described in 1249 Section 5. 1251 It should be noted that the value of the "base" parameter applies to 1252 all the links of the registration and has consequences for the anchor 1253 value of the individual links as exemplified in Appendix B. An 1254 eventual (currently non-existing) "base" attribute of the link is not 1255 affected by the value of "base" parameter in the registration. 1257 5.3. Operations on the Registration Resource 1259 This section describes how the registering endpoint can maintain the 1260 registrations that it created. The registering endpoint can be the 1261 registrant-ep or the CT. An endpoint SHOULD NOT use this interface 1262 for registrations that it did not create. The registrations are 1263 resources of the RD. 1265 After the initial registration, the registering endpoint retains the 1266 returned location of the Registration Resource for further 1267 operations, including refreshing the registration in order to extend 1268 the lifetime and "keep-alive" the registration. When the lifetime of 1269 the registration has expired, the RD SHOULD NOT respond to discovery 1270 queries concerning this endpoint. The RD SHOULD continue to provide 1271 access to the Registration Resource after a registration time-out 1272 occurs in order to enable the registering endpoint to eventually 1273 refresh the registration. The RD MAY eventually remove the 1274 registration resource for the purpose of garbage collection. If the 1275 Registration Resource is removed, the corresponding endpoint will 1276 need to be re-registered. 1278 The Registration Resource may also be used cancel the registration 1279 using DELETE, and to perform further operations beyond the scope of 1280 this specification. 1282 These operations are described below. 1284 5.3.1. Registration Update 1286 The update interface is used by the registering endpoint to refresh 1287 or update its registration with an RD. To use the interface, the 1288 registering endpoint sends a POST request to the registration 1289 resource returned by the initial registration operation. 1291 An update MAY update the lifetime or the base URI registration 1292 parameters "lt", "base" as in Section 5. Parameters that are not 1293 being changed SHOULD NOT be included in an update. Adding parameters 1294 that have not changed increases the size of the message but does not 1295 have any other implications. Parameters MUST be included as query 1296 parameters in an update operation as in Section 5. 1298 A registration update resets the timeout of the registration to the 1299 (possibly updated) lifetime of the registration, independent of 1300 whether a "lt" parameter was given. 1302 If the base URI of the registration is changed in an update, relative 1303 references submitted in the original registration or later updates 1304 are resolved anew against the new base. 1306 The registration update operation only describes the use of POST with 1307 an empty payload. Future standards might describe the semantics of 1308 using content formats and payloads with the POST method to update the 1309 links of a registration (see Section 5.3.3). 1311 The update registration request interface is specified as follows: 1313 Interaction: EP -> RD 1315 Method: POST 1317 URI Template: {+location}{?lt,base,extra-attrs*} 1319 URI Template Variables: 1321 location := This is the Location returned by the RD as a result 1322 of a successful earlier registration. 1324 lt := Lifetime (optional). Lifetime of the registration in 1325 seconds. Range of 60-4294967295. If no lifetime is included, 1326 the previous last lifetime set on a previous update or the 1327 original registration (falling back to 90000) SHOULD be used. 1329 base := Base URI (optional). This parameter updates the Base URI 1330 established in the original registration to a new value. If 1331 the parameter is set in an update, it is stored by the RD as 1332 the new Base URI under which to interpret the relative links 1333 present in the payload of the original registration, following 1334 the same restrictions as in the registration. If the parameter 1335 is not set in the request but was set before, the previous Base 1336 URI value is kept unmodified. If the parameter is not set in 1337 the request and was not set before either, the source address 1338 and source port of the update request are stored as the Base 1339 URI. 1341 extra-attrs := Additional registration attributes (optional). As 1342 with the registration, the RD processes them if it knows their 1343 semantics. Otherwise, unknown attributes are stored as 1344 endpoint attributes, overriding any previously stored endpoint 1345 attributes of the same key. 1347 Content-Format: none (no payload) 1349 The following responses are expected on this interface: 1351 Success: 2.04 "Changed" or 204 "No Content" if the update was 1352 successfully processed. 1354 Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not 1355 exist (e.g. may have been removed). 1357 If the registration fails in any way, including "Not Found" and 1358 request timeouts, or if the time indicated in a Service Unabailable 1359 Max-Age/Retry-After exceeds the remaining lifetime, the registering 1360 endpoint SHOULD attempt registration again. 1362 The following example shows how the registering endpoint updates its 1363 registration resource at an RD using this interface with the example 1364 location value: /rd/4521. 1366 Req: POST /rd/4521 1368 Res: 2.04 Changed 1369 The following example shows the registering endpoint updating its 1370 registration resource at an RD using this interface with the example 1371 location value: /rd/4521. The initial registration by the 1372 registering endpoint set the following values: 1374 o endpoint name (ep)=endpoint1 1376 o lifetime (lt)=500 1378 o Base URI (base)=coap://local-proxy-old.example.com:5683 1380 o payload of Figure 6 1382 The initial state of the Resource Directory is reflected in the 1383 following request: 1385 Req: GET /rd-lookup/res?ep=endpoint1 1387 Res: 2.01 Content 1388 Payload: 1389 ;ct=41; 1390 rt="temperature"; anchor="coap://spurious.example.com:5683", 1391 ;ct=41; 1392 rt="light-lux"; if="sensor"; 1393 anchor="coap://local-proxy-old.example.com:5683" 1395 The following example shows the registering endpoint changing the 1396 Base URI to "coaps://new.example.com:5684": 1398 Req: POST /rd/4521?base=coaps://new.example.com:5684 1400 Res: 2.04 Changed 1402 The consecutive query returns: 1404 Req: GET /rd-lookup/res?ep=endpoint1 1406 Res: 2.01 Content 1407 Payload: 1408 ;ct=41;rt="temperature"; 1409 anchor="coap://spurious.example.com:5683", 1410 ;ct=41;rt="light-lux"; 1411 if="sensor"; anchor="coaps://new.example.com:5684", 1413 5.3.2. Registration Removal 1415 Although RD registrations have soft state and will eventually timeout 1416 after their lifetime, the registering endpoint SHOULD explicitly 1417 remove an entry from the RD if it knows it will no longer be 1418 available (for example on shut-down). This is accomplished using a 1419 removal interface on the RD by performing a DELETE on the endpoint 1420 resource. 1422 The removal request interface is specified as follows: 1424 Interaction: EP -> RD 1426 Method: DELETE 1428 URI Template: {+location} 1430 URI Template Variables: 1432 location := This is the Location returned by the RD as a result 1433 of a successful earlier registration. 1435 The following responses are expected on this interface: 1437 Success: 2.02 "Deleted" or 204 "No Content" upon successful deletion 1439 Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not 1440 exist (e.g. may already have been removed). 1442 The following examples shows successful removal of the endpoint from 1443 the RD with example location value /rd/4521. 1445 Req: DELETE /rd/4521 1447 Res: 2.02 Deleted 1449 5.3.3. Further operations 1451 Additional operations on the registration can be specified in future 1452 documents, for example: 1454 o Send iPATCH (or PATCH) updates ([RFC8132]) to add, remove or 1455 change the links of a registration. 1457 o Use GET to read the currently stored set of links in a 1458 registration resource. 1460 Those operations are out of scope of this document, and will require 1461 media types suitable for modifying sets of links. 1463 6. RD Lookup 1465 To discover the resources registered with the RD, a lookup interface 1466 must be provided. This lookup interface is defined as a default, and 1467 it is assumed that RDs may also support lookups to return resource 1468 descriptions in alternative formats (e.g. JSON or CBOR link format 1469 [I-D.ietf-core-links-json]) or using more advanced interfaces (e.g. 1470 supporting context or semantic based lookup) on different resources 1471 that are discovered independently. 1473 RD Lookup allows lookups for endpoints and resources using attributes 1474 defined in this document and for use with the CoRE Link Format. The 1475 result of a lookup request is the list of links (if any) 1476 corresponding to the type of lookup. Thus, an endpoint lookup MUST 1477 return a list of endpoints and a resource lookup MUST return a list 1478 of links to resources. 1480 The lookup type is selected by a URI endpoint, which is indicated by 1481 a Resource Type as per Table 1 below: 1483 +-------------+--------------------+-----------+ 1484 | Lookup Type | Resource Type | Mandatory | 1485 +-------------+--------------------+-----------+ 1486 | Resource | core.rd-lookup-res | Mandatory | 1487 | Endpoint | core.rd-lookup-ep | Mandatory | 1488 +-------------+--------------------+-----------+ 1490 Table 1: Lookup Types 1492 6.1. Resource lookup 1494 Resource lookup results in links that are semantically equivalent to 1495 the links submitted to the RD. The links and link parameters 1496 returned by the lookup are equal to the submitted ones, except that 1497 the target and anchor references are fully resolved. 1499 Links that did not have an anchor attribute are therefore returned 1500 with the base URI of the registration as the anchor. Links of which 1501 href or anchor was submitted as a (full) URI are returned with these 1502 attributes unmodified. 1504 Above rules allow the client to interpret the response as links 1505 without any further knowledge of the storage conventions of the RD. 1506 The Resource Directory MAY replace the registration base URIs with a 1507 configured intermediate proxy, e.g. in the case of an HTTP lookup 1508 interface for CoAP endpoints. 1510 If the base URI of a registration contains a link-local address, the 1511 RD MUST NOT show its links unless the lookup was made from the same 1512 link. The RD MUST NOT include zone identifiers in the resolved URIs. 1514 6.2. Lookup filtering 1516 Using the Accept Option, the requester can control whether the 1517 returned list is returned in CoRE Link Format ("application/link- 1518 format", default) or in alternate content-formats (e.g. from 1519 [I-D.ietf-core-links-json]). 1521 The page and count parameters are used to obtain lookup results in 1522 specified increments using pagination, where count specifies how many 1523 links to return and page specifies which subset of links organized in 1524 sequential pages, each containing 'count' links, starting with link 1525 zero and page zero. Thus, specifying count of 10 and page of 0 will 1526 return the first 10 links in the result set (links 0-9). Count = 10 1527 and page = 1 will return the next 'page' containing links 10-19, and 1528 so on. 1530 Multiple search criteria MAY be included in a lookup. All included 1531 criteria MUST match for a link to be returned. The Resource 1532 Directory MUST support matching with multiple search criteria. 1534 A link matches a search criterion if it has an attribute of the same 1535 name and the same value, allowing for a trailing "*" wildcard 1536 operator as in Section 4.1 of [RFC6690]. Attributes that are defined 1537 as "link-type" match if the search value matches any of their values 1538 (see Section 4.1 of [RFC6690]; e.g. "?if=core.s" matches ";if="abc 1539 core.s";"). A resource link also matches a search criterion if its 1540 endpoint would match the criterion, and vice versa, an endpoint link 1541 matches a search criterion if any of its resource links matches it. 1543 Note that "href" is a valid search criterion and matches target 1544 references. Like all search criteria, on a resource lookup it can 1545 match the target reference of the resource link itself, but also the 1546 registration resource of the endpoint that registered it. Queries 1547 for resource link targets MUST be in URI form (i.e. not relative 1548 references) and are matched against a resolved link target. Queries 1549 for endpoints SHOULD be expressed in path-absolute form if possible 1550 and MUST be expressed in URI form otherwise; the RD SHOULD recognize 1551 either. 1553 Endpoints that are interested in a lookup result repeatedly or 1554 continuously can use mechanisms like ETag caching, resource 1555 observation ([RFC7641]), or any future mechanism that might allow 1556 more efficient observations of collections. These are advertised, 1557 detected and used according to their own specifications and can be 1558 used with the lookup interface as with any other resource. 1560 When resource observation is used, every time the set of matching 1561 links changes, or the content of a matching link changes, the RD 1562 sends a notification with the matching link set. The notification 1563 contains the successful current response to the given request, 1564 especially with respect to representing zero matching links (see 1565 "Success" item below). 1567 The lookup interface is specified as follows: 1569 Interaction: Client -> RD 1571 Method: GET 1573 URI Template: {+type-lookup-location}{?page,count,search*} 1575 URI Template Variables: 1577 type-lookup-location := RD Lookup URI for a given lookup type 1578 (mandatory). The address is discovered as described in 1579 Section 4.3. 1581 search := Search criteria for limiting the number of results 1582 (optional). 1584 page := Page (optional). Parameter cannot be used without the 1585 count parameter. Results are returned from result set in pages 1586 that contain 'count' links starting from index (page * count). 1587 Page numbering starts with zero. 1589 count := Count (optional). Number of results is limited to this 1590 parameter value. If the page parameter is also present, the 1591 response MUST only include 'count' links starting with the 1592 (page * count) link in the result set from the query. If the 1593 count parameter is not present, then the response MUST return 1594 all matching links in the result set. Link numbering starts 1595 with zero. 1597 Accept: absent, application/link-format or any other indicated 1598 media type representing web links 1600 The following responses codes are defined for this interface: 1602 Success: 2.05 "Content" or 200 "OK" with an "application/link- 1603 format" or other web link payload containing matching entries for 1604 the lookup. The payload can contain zero links (which is an empty 1605 payload in [RFC6690] link format, but could also be "[]" in JSON 1606 based formats), indicating that no entities matched the request. 1608 6.3. Resource lookup examples 1610 The examples in this section assume the existence of CoAP hosts with 1611 a default CoAP port 61616. HTTP hosts are possible and do not change 1612 the nature of the examples. 1614 The following example shows a client performing a resource lookup 1615 with the example resource look-up locations discovered in Figure 5: 1617 Req: GET /rd-lookup/res?rt=temperature 1619 Res: 2.05 Content 1620 ;rt="temperature"; 1621 anchor="coap://[2001:db8:3::123]:61616" 1623 A client that wants to be notified of new resources as they show up 1624 can use observation: 1626 Req: GET /rd-lookup/res?rt=light 1627 Observe: 0 1629 Res: 2.05 Content 1630 Observe: 23 1631 Payload: empty 1633 (at a later point in time) 1635 Res: 2.05 Content 1636 Observe: 24 1637 Payload: 1638 ;rt="light"; 1639 anchor="coap://[2001:db8:3::124]", 1640 ;rt="light"; 1641 anchor="coap://[2001:db8:3::124]", 1642 ;rt="light"; 1643 anchor="coap://[2001:db8:3::124]" 1645 The following example shows a client performing a paginated resource 1646 lookup 1647 Req: GET /rd-lookup/res?page=0&count=5 1649 Res: 2.05 Content 1650 ;rt=sensor;ct=60; 1651 anchor="coap://[2001:db8:3::123]:61616", 1652 ;rt=sensor;ct=60; 1653 anchor="coap://[2001:db8:3::123]:61616", 1654 ;rt=sensor;ct=60; 1655 anchor="coap://[2001:db8:3::123]:61616", 1656 ;rt=sensor;ct=60; 1657 anchor="coap://[2001:db8:3::123]:61616", 1658 ;rt=sensor;ct=60; 1659 anchor="coap://[2001:db8:3::123]:61616" 1661 Req: GET /rd-lookup/res?page=1&count=5 1663 Res: 2.05 Content 1664 ;rt=sensor;ct=60; 1665 anchor="coap://[2001:db8:3::123]:61616", 1666 ;rt=sensor;ct=60; 1667 anchor="coap://[2001:db8:3::123]:61616", 1668 ;rt=sensor;ct=60; 1669 anchor="coap://[2001:db8:3::123]:61616", 1670 ;rt=sensor;ct=60; 1671 anchor="coap://[2001:db8:3::123]:61616", 1672 ;rt=sensor;ct=60; 1673 anchor="coap://[2001:db8:3::123]:61616" 1675 The following example shows a client performing a lookup of all 1676 resources from endpoints of all endpoints of a given endpoint type. 1677 It assumes that two endpoints (with endpoint names "sensor1" and 1678 "sensor2") have previously registered with their respective addresses 1679 "coap://sensor1.example.com" and "coap://sensor2.example.com", and 1680 posted the very payload of the 6th request of section 5 of [RFC6690]. 1682 It demonstrates how absolute link targets stay unmodified, while 1683 relative ones are resolved: 1685 Req: GET /rd-lookup/res?et=oic.d.sensor 1687 ;ct=40;title="Sensor Index"; 1688 anchor="coap://sensor1.example.com", 1689 ;rt="temperature-c"; 1690 if="sensor"; anchor="coap://sensor1.example.com", 1691 ;rt="light-lux"; 1692 if="sensor"; anchor="coap://sensor1.example.com", 1693 ;rel="describedby"; 1694 anchor="coap://sensor1.example.com/sensors/temp", 1695 ;rel="alternate"; 1696 anchor="coap://sensor1.example.com/sensors/temp", 1697 ;ct=40;title="Sensor Index"; 1698 anchor="coap://sensor2.example.com", 1699 ;rt="temperature-c"; 1700 if="sensor"; anchor="coap://sensor2.example.com", 1701 ;rt="light-lux"; 1702 if="sensor"; anchor="coap://sensor2.example.com", 1703 ;rel="describedby"; 1704 anchor="coap://sensor2.example.com/sensors/temp", 1705 ;rel="alternate"; 1706 anchor="coap://sensor2.example.com/sensors/temp" 1708 6.4. Endpoint lookup 1710 The endpoint lookup returns registration resources which can only be 1711 manipulated by the registering endpoint. 1713 Endpoint registration resources are annotated with their endpoint 1714 names (ep), sectors (d, if present) and registration base URI (base; 1715 reports the registrant-ep's address if no explicit base was given) as 1716 well as a constant resource type (rt="core.rd-ep"); the lifetime (lt) 1717 is not reported. Additional endpoint attributes are added as target 1718 attributes to their endpoint link unless their specification says 1719 otherwise. 1721 Links to endpoints SHOULD be presented in path-absolute form or, if 1722 required, as absolute references. (This avoids the RFC6690 1723 ambiguities.) 1725 Base addresses that contain link-local addresses MUST NOT include 1726 zone identifiers, and such registrations MUST NOT be shown unless the 1727 lookup was made from the same link from which the registration was 1728 made. 1730 While Endpoint Lookup does expose the registration resources, the RD 1731 does not need to make them accessible to clients. Clients SHOULD NOT 1732 attempt to dereference or manipulate them. 1734 A Resource Directory can report endpoints in lookup that are not 1735 hosted at the same address. Lookup clients MUST be prepared to see 1736 arbitrary URIs as registration resources in the results and treat 1737 them as opaque identifiers; the precise semantics of such links are 1738 left to future specifications. 1740 The following example shows a client performing an endpoint type (et) 1741 lookup with the value oic.d.sensor (which is currently a registered 1742 rt value): 1744 Req: GET /rd-lookup/ep?et=oic.d.sensor 1746 Res: 2.05 Content 1747 ;base="coap://[2001:db8:3::127]:61616";ep="node5"; 1748 et="oic.d.sensor";ct="40";rt="core.rd-ep", 1749 ;base="coap://[2001:db8:3::129]:61616";ep="node7"; 1750 et="oic.d.sensor";ct="40";d="floor-3";rt="core.rd-ep" 1752 7. Security policies 1754 The Resource Directory (RD) provides assistance to applications 1755 situated on a selection of nodes to discover endpoints on connected 1756 nodes. This section discusses different security aspects of 1757 accessing the RD. 1759 The contents of the RD are inserted in two ways: 1761 1. The node hosting the discoverable endpoint fills the RD with the 1762 contents of /.well-known/core by: 1764 * Storing the contents directly into RD (see Section 5) 1766 * Requesting the RD to load the contents from /.well-known/core 1767 (see Section 5.1) 1769 2. A Commissioning Tool (CT) fills the RD with endpoint information 1770 for a set of discoverable nodes. (see Section 5 with 1771 base=authority parameter value) 1773 In both cases, the nodes filling the RD should be authenticated and 1774 authorized to change the contents of the RD. An Authorization Server 1775 (AS) is responsible to assign a token to the registering node to 1776 authorize the node to discover or register endpoints in a given RD 1777 [I-D.ietf-ace-oauth-authz]. 1779 It can be imagined that an installation is divided in a set of 1780 security regions, each one with its own RD(s) to discover the 1781 endpoints that are part of a given security region. An endpoint that 1782 wants to discover an RD, responsible for a given region, needs to be 1783 authorized to learn the contents of a given RD. Within a region, for 1784 a given RD, a more fine-grained security division is possible based 1785 on the values of the endpoint registration parameters. Authorization 1786 to discover endpoints with a given set of filter values is 1787 recommended for those cases. 1789 When a node registers its endpoints, criteria are needed to authorize 1790 the node to enter them. An important aspect is the uniqueness of the 1791 (endpoint name, and optional sector) pair within the RD. Consider 1792 the two cases separately: (1) CT registers endpoints, and (2) the 1793 registering node registers its own endpoint(s). 1795 o A CT needs authorization to register a set of endpoints. This 1796 authorization can be based on the region, i.e. a given CT is 1797 authorized to register any endpoint (endpoint name, sector) into a 1798 given RD, or to register an endpoint with (endpoint name, sector) 1799 value pairs assigned by the AS, or can be more fine-grained, 1800 including a subset of registration parameter values. 1802 o A given endpoint that registers itself, needs to proof its 1803 possession of its unique (endpoint name, sector) value pair. 1804 Alternatively, the AS can authorize the endpoint to register with 1805 an (endpoint name, sector) value pair assigned by the AS. 1807 A separate document needs to specify these aspects to ensure 1808 interoperability between registering nodes and RD. The subsections 1809 below give some hints how to handle a subset of the different 1810 aspects. 1812 7.1. Secure RD discovery 1814 The Resource Server (RS) discussed in [I-D.ietf-ace-oauth-authz] is 1815 equated to the RD. The client (C) needs to discover the RD as 1816 discussed in Section 4.1. C can discover the related AS by sending a 1817 request to the RD. The RD denies the request by sending the address 1818 of the related AS, as discussed in section 5.1 of 1819 [I-D.ietf-ace-oauth-authz]. The client MUST send an authorization 1820 request to the AS. When appropriate, the AS returns a token that 1821 specifies the authorization permission which needs to be specified in 1822 a separate document. 1824 7.2. Secure RD filtering 1826 The authorized parameter values for the queries by a given endpoint 1827 must be registered by the AS. The AS communicates the parameter 1828 values in the token. A separate document needs to specify the 1829 parameter value combinations and their storage in the token. The RD 1830 decodes the token and checks the validity of the queries of the 1831 client. 1833 7.3. Secure endpoint Name assignment 1835 This section only considers the assignment of a name to the endpoint 1836 based on an automatic mechanism without use of AS. More elaborate 1837 protocols are out of scope. The registering endpoint is authorized 1838 by the AS to discover the RD and add registrations. A token is 1839 provided by the AS and communicated from registering endpoint to RD. 1840 It is assumed that DTLS is used to secure the channel between 1841 registering endpoint and RD, where the registering endpoint is the 1842 DTLS client. Assuming that the client is provided by a certificate 1843 at manufacturing time, the certificate is uniquely identified by the 1844 CN field and the serial number. The RD can assign a unique endpoint 1845 name by using the certificate identifier as endpoint name. Proof of 1846 possession of the endpoint name by the registering endpoint is 1847 checked by encrypting the certificate identifier with the private key 1848 of the registering endpoint, which the RD can decrypt with the public 1849 key stored in the certificate. Even simpler, the authorized 1850 registering endpoint can generate a random number (or string) that 1851 identifies the endpoint. The RD can check for the improbable 1852 replication of the random value. The RD MUST check that registering 1853 endpoint uses only one random value for each authorized endpoint. 1855 8. Security Considerations 1857 The security considerations as described in Section 5 of [RFC8288] 1858 and Section 6 of [RFC6690] apply. The "/.well-known/core" resource 1859 may be protected e.g. using DTLS when hosted on a CoAP server as 1860 described in [RFC7252]. DTLS or TLS based security SHOULD be used on 1861 all resource directory interfaces defined in this document. 1863 8.1. Endpoint Identification and Authentication 1865 An Endpoint (name, sector) pair is unique within the et of endpoints 1866 registered by the RD. An Endpoint MUST NOT be identified by its 1867 protocol, port or IP address as these may change over the lifetime of 1868 an Endpoint. 1870 Every operation performed by an Endpoint on a resource directory 1871 SHOULD be mutually authenticated using Pre-Shared Key, Raw Public Key 1872 or Certificate based security. 1874 Consider the following threat: two devices A and B are registered at 1875 a single server. Both devices have unique, per-device credentials 1876 for use with DTLS to make sure that only parties with authorization 1877 to access A or B can do so. 1879 Now, imagine that a malicious device A wants to sabotage the device 1880 B. It uses its credentials during the DTLS exchange. Then, it 1881 specifies the endpoint name of device B as the name of its own 1882 endpoint in device A. If the server does not check whether the 1883 identifier provided in the DTLS handshake matches the identifier used 1884 at the CoAP layer then it may be inclined to use the endpoint name 1885 for looking up what information to provision to the malicious device. 1887 Section 7.3 specifies an example that removes this threat for 1888 endpoints that have a certificate installed. 1890 8.2. Access Control 1892 Access control SHOULD be performed separately for the RD registration 1893 and Lookup API paths, as different endpoints may be authorized to 1894 register with an RD from those authorized to lookup endpoints from 1895 the RD. Such access control SHOULD be performed in as fine-grained a 1896 level as possible. For example access control for lookups could be 1897 performed either at the sector, endpoint or resource level. 1899 8.3. Denial of Service Attacks 1901 Services that run over UDP unprotected are vulnerable to unknowingly 1902 become part of a DDoS attack as UDP does not require return 1903 routability check. Therefore, an attacker can easily spoof the 1904 source IP of the target entity and send requests to such a service 1905 which would then respond to the target entity. This can be used for 1906 large-scale DDoS attacks on the target. Especially, if the service 1907 returns a response that is order of magnitudes larger than the 1908 request, the situation becomes even worse as now the attack can be 1909 amplified. DNS servers have been widely used for DDoS amplification 1910 attacks. There is also a danger that NTP Servers could become 1911 implicated in denial-of-service (DoS) attacks since they run on 1912 unprotected UDP, there is no return routability check, and they can 1913 have a large amplification factor. The responses from the NTP server 1914 were found to be 19 times larger than the request. A Resource 1915 Directory (RD) which responds to wild-card lookups is potentially 1916 vulnerable if run with CoAP over UDP. Since there is no return 1917 routability check and the responses can be significantly larger than 1918 requests, RDs can unknowingly become part of a DDoS amplification 1919 attack. 1921 9. IANA Considerations 1922 9.1. Resource Types 1924 IANA is asked to enter the following values into the Resource Type 1925 (rt=) Link Target Attribute Values sub-registry of the Constrained 1926 Restful Environments (CoRE) Parameters registry defined in [RFC6690]: 1928 +--------------------+--------------------------+-------------------+ 1929 | Value | Description | Reference | 1930 +--------------------+--------------------------+-------------------+ 1931 | core.rd | Directory resource of an | RFCTHIS Section | 1932 | | RD | 4.3 | 1933 | core.rd-lookup-res | Resource lookup of an RD | RFCTHIS Section | 1934 | | | 4.3 | 1935 | core.rd-lookup-ep | Endpoint lookup of an RD | RFCTHIS Section | 1936 | | | 4.3 | 1937 | core.rd-ep | Endpoint resource of an | RFCTHIS Section 6 | 1938 | | RD | | 1939 +--------------------+--------------------------+-------------------+ 1941 9.2. IPv6 ND Resource Directory Address Option 1943 This document registers one new ND option type under the sub-registry 1944 "IPv6 Neighbor Discovery Option Formats": 1946 o Resource Directory Address Option (38) 1948 9.3. RD Parameter Registry 1950 This specification defines a new sub-registry for registration and 1951 lookup parameters called "RD Parameters" under "CoRE Parameters". 1952 Although this specification defines a basic set of parameters, it is 1953 expected that other standards that make use of this interface will 1954 define new ones. 1956 Each entry in the registry must include 1958 o the human readable name of the parameter, 1960 o the short name as used in query parameters or target attributes, 1962 o indication of whether it can be passed as a query parameter at 1963 registration of endpoints, as a query parameter in lookups, or be 1964 expressed as a target attribute, 1966 o validity requirements if any, and 1968 o a description. 1970 The query parameter MUST be both a valid URI query key [RFC3986] and 1971 a token as used in [RFC8288]. 1973 The description must give details on whether the parameter can be 1974 updated, and how it is to be processed in lookups. 1976 The mechanisms around new RD parameters should be designed in such a 1977 way that they tolerate RD implementations that are unaware of the 1978 parameter and expose any parameter passed at registration or updates 1979 on in endpoint lookups. (For example, if a parameter used at 1980 registration were to be confidential, the registering endpoint should 1981 be instructed to only set that parameter if the RD advertises support 1982 for keeping it confidential at the discovery step.) 1984 Initial entries in this sub-registry are as follows: 1986 +--------------+-------+---------------+-----+----------------------+ 1987 | Full name | Short | Validity | Use | Description | 1988 +--------------+-------+---------------+-----+----------------------+ 1989 | Endpoint | ep | | RLA | Name of the | 1990 | Name | | | | endpoint, max 63 | 1991 | | | | | bytes | 1992 | Lifetime | lt | 60-4294967295 | R | Lifetime of the | 1993 | | | | | registration in | 1994 | | | | | seconds | 1995 | Sector | d | | RLA | Sector to which this | 1996 | | | | | endpoint belongs | 1997 | Registration | base | URI | RLA | The scheme, address | 1998 | Base URI | | | | and port and path at | 1999 | | | | | which this server is | 2000 | | | | | available | 2001 | Page | page | Integer | L | Used for pagination | 2002 | Count | count | Integer | L | Used for pagination | 2003 | Endpoint | et | | RLA | Semantic name of the | 2004 | Type | | | | endpoint (see | 2005 | | | | | Section 9.4) | 2006 +--------------+-------+---------------+-----+----------------------+ 2008 Table 2: RD Parameters 2010 (Short: Short name used in query parameters or target attributes. 2011 Use: R = used at registration, L = used at lookup, A = expressed in 2012 target attribute 2014 The descriptions for the options defined in this document are only 2015 summarized here. To which registrations they apply and when they are 2016 to be shown is described in the respective sections of this document. 2018 The IANA policy for future additions to the sub-registry is "Expert 2019 Review" as described in [RFC8126]. The evaluation should consider 2020 formal criteria, duplication of functionality (Is the new entry 2021 redundant with an existing one?), topical suitability (E.g. is the 2022 described property actually a property of the endpoint and not a 2023 property of a particular resource, in which case it should go into 2024 the payload of the registration and need not be registered?), and the 2025 potential for conflict with commonly used target attributes (For 2026 example, "if" could be used as a parameter for conditional 2027 registration if it were not to be used in lookup or attributes, but 2028 would make a bad parameter for lookup, because a resource lookup with 2029 an "if" query parameter could ambiguously filter by the registered 2030 endpoint property or the [RFC6690] target attribute). It is expected 2031 that the registry will receive between 5 and 50 registrations in 2032 total over the next years. 2034 9.3.1. Full description of the "Endpoint Type" Registration Parameter 2036 An endpoint registering at an RD can describe itself with endpoint 2037 types, similar to how resources are described with Resource Types in 2038 [RFC6690]. An endpoint type is expressed as a string, which can be 2039 either a URI or one of the values defined in the Endpoint Type sub- 2040 registry. Endpoint types can be passed in the "et" query parameter 2041 as part of extra-attrs at the Registration step, are shown on 2042 endpoint lookups using the "et" target attribute, and can be filtered 2043 for using "et" as a search criterion in resource and endpoint lookup. 2044 Multiple endpoint types are given as separate query parameters or 2045 link attributes. 2047 Note that Endpoint Type differs from Resource Type in that it uses 2048 multiple attributes rather than space separated values. As a result, 2049 Resource Directory implementations automatically support correct 2050 filtering in the lookup interfaces from the rules for unknown 2051 endpoint attributes. 2053 9.4. "Endpoint Type" (et=) RD Parameter values 2055 This specification establishes a new sub-registry under "CoRE 2056 Parameters" called '"Endpoint Type" (et=) RD Parameter values'. The 2057 registry properties (required policy, requirements, template) are 2058 identical to those of the Resource Type parameters in [RFC6690], in 2059 short: 2061 The review policy is IETF Review for values starting with "core", and 2062 Specification Required for others. 2064 The requirements to be enforced are: 2066 o The values MUST be related to the purpose described in 2067 Section 9.3.1. 2069 o The registered values MUST conform to the ABNF reg-rel-type 2070 definition of [RFC6690] and MUST NOT be a URI. 2072 o It is recommended to use the period "." character for 2073 segmentation. 2075 The registry initially contains one value: 2077 o "core.rd-group": An application group as described in Appendix A. 2079 9.5. Multicast Address Registration 2081 IANA has assigned the following multicast addresses for use by CoAP 2082 nodes: 2084 IPv4 - "all CoRE resource directories" address, from the "IPv4 2085 Multicast Address Space Registry" equal to "All CoAP Nodes", 2086 224.0.1.187. As the address is used for discovery that may span 2087 beyond a single network, it has come from the Internetwork Control 2088 Block (224.0.1.x, RFC 5771). 2090 IPv6 - "all CoRE resource directories" address MCD1 (suggestions 2091 FF0X::FE), from the "IPv6 Multicast Address Space Registry", in the 2092 "Variable Scope Multicast Addresses" space (RFC 3307). Note that 2093 there is a distinct multicast address for each scope that interested 2094 CoAP nodes should listen to; CoAP needs the Link-Local and Site-Local 2095 scopes only. 2097 10. Examples 2099 Two examples are presented: a Lighting Installation example in 2100 Section 10.1 and a LWM2M example in Section 10.2. 2102 10.1. Lighting Installation 2104 This example shows a simplified lighting installation which makes use 2105 of the Resource Directory (RD) with a CoAP interface to facilitate 2106 the installation and start-up of the application code in the lights 2107 and sensors. In particular, the example leads to the definition of a 2108 group and the enabling of the corresponding multicast address as 2109 described in Appendix A. No conclusions must be drawn on the 2110 realization of actual installation or naming procedures, because the 2111 example only "emphasizes" some of the issues that may influence the 2112 use of the RD and does not pretend to be normative. 2114 10.1.1. Installation Characteristics 2116 The example assumes that the installation is managed. That means 2117 that a Commissioning Tool (CT) is used to authorize the addition of 2118 nodes, name them, and name their services. The CT can be connected 2119 to the installation in many ways: the CT can be part of the 2120 installation network, connected by WiFi to the installation network, 2121 or connected via GPRS link, or other method. 2123 It is assumed that there are two naming authorities for the 2124 installation: (1) the network manager that is responsible for the 2125 correct operation of the network and the connected interfaces, and 2126 (2) the lighting manager that is responsible for the correct 2127 functioning of networked lights and sensors. The result is the 2128 existence of two naming schemes coming from the two managing 2129 entities. 2131 The example installation consists of one presence sensor, and two 2132 luminaries, luminary1 and luminary2, each with their own wireless 2133 interface. Each luminary contains three lamps: left, right and 2134 middle. Each luminary is accessible through one endpoint. For each 2135 lamp a resource exists to modify the settings of a lamp in a 2136 luminary. The purpose of the installation is that the presence 2137 sensor notifies the presence of persons to a group of lamps. The 2138 group of lamps consists of: middle and left lamps of luminary1 and 2139 right lamp of luminary2. 2141 Before commissioning by the lighting manager, the network is 2142 installed and access to the interfaces is proven to work by the 2143 network manager. 2145 At the moment of installation, the network under installation is not 2146 necessarily connected to the DNS infra structure. Therefore, SLAAC 2147 IPv6 addresses are assigned to CT, RD, luminaries and sensor shown in 2148 Table 3 below: 2150 +--------------------+----------------+ 2151 | Name | IPv6 address | 2152 +--------------------+----------------+ 2153 | luminary1 | 2001:db8:4::1 | 2154 | luminary2 | 2001:db8:4::2 | 2155 | Presence sensor | 2001:db8:4::3 | 2156 | Resource directory | 2001:db8:4::ff | 2157 +--------------------+----------------+ 2159 Table 3: interface SLAAC addresses 2161 In Section 10.1.2 the use of resource directory during installation 2162 is presented. 2164 10.1.2. RD entries 2166 It is assumed that access to the DNS infrastructure is not always 2167 possible during installation. Therefore, the SLAAC addresses are 2168 used in this section. 2170 For discovery, the resource types (rt) of the devices are important. 2171 The lamps in the luminaries have rt: light, and the presence sensor 2172 has rt: p-sensor. The endpoints have names which are relevant to the 2173 light installation manager. In this case luminary1, luminary2, and 2174 the presence sensor are located in room 2-4-015, where luminary1 is 2175 located at the window and luminary2 and the presence sensor are 2176 located at the door. The endpoint names reflect this physical 2177 location. The middle, left and right lamps are accessed via path 2178 /light/middle, /light/left, and /light/right respectively. The 2179 identifiers relevant to the Resource Directory are shown in Table 4 2180 below: 2182 +----------------+------------------+---------------+---------------+ 2183 | Name | endpoint | resource path | resource type | 2184 +----------------+------------------+---------------+---------------+ 2185 | luminary1 | lm_R2-4-015_wndw | /light/left | light | 2186 | luminary1 | lm_R2-4-015_wndw | /light/middle | light | 2187 | luminary1 | lm_R2-4-015_wndw | /light/right | light | 2188 | luminary2 | lm_R2-4-015_door | /light/left | light | 2189 | luminary2 | lm_R2-4-015_door | /light/middle | light | 2190 | luminary2 | lm_R2-4-015_door | /light/right | light | 2191 | Presence | ps_R2-4-015_door | /ps | p-sensor | 2192 | sensor | | | | 2193 +----------------+------------------+---------------+---------------+ 2195 Table 4: Resource Directory identifiers 2197 It is assumed that the CT knows the RD's address, and has performed 2198 URI discovery on it that returned a response like the one in the 2199 Section 4.3 example. 2201 The CT inserts the endpoints of the luminaries and the sensor in the 2202 RD using the registration base URI parameter (base) to specify the 2203 interface address: 2205 Req: POST coap://[2001:db8:4::ff]/rd 2206 ?ep=lm_R2-4-015_wndw&base=coap://[2001:db8:4::1]&d=R2-4-015 2207 Payload: 2208 ;rt="light", 2209 ;rt="light", 2210 ;rt="light" 2212 Res: 2.01 Created 2213 Location-Path: /rd/4521 2215 Req: POST coap://[2001:db8:4::ff]/rd 2216 ?ep=lm_R2-4-015_door&base=coap://[2001:db8:4::2]&d=R2-4-015 2217 Payload: 2218 ;rt="light", 2219 ;rt="light", 2220 ;rt="light" 2222 Res: 2.01 Created 2223 Location-Path: /rd/4522 2225 Req: POST coap://[2001:db8:4::ff]/rd 2226 ?ep=ps_R2-4-015_door&base=coap://[2001:db8:4::3]d&d=R2-4-015 2227 Payload: 2228 ;rt="p-sensor" 2230 Res: 2.01 Created 2231 Location-Path: /rd/4523 2233 The sector name d=R2-4-015 has been added for an efficient lookup 2234 because filtering on "ep" name is more awkward. The same sector name 2235 is communicated to the two luminaries and the presence sensor by the 2236 CT. 2238 The group is specified in the RD. The base parameter is set to the 2239 site-local multicast address allocated to the group. In the POST in 2240 the example below, the resources supported by all group members are 2241 published. 2243 Req: POST coap://[2001:db8:4::ff]/rd 2244 ?ep=grp_R2-4-015&et=core.rd-group&base=coap://[ff05::1] 2245 Payload: 2246 ;rt="light", 2247 ;rt="light", 2248 ;rt="light" 2250 Res: 2.01 Created 2251 Location-Path: /rd/501 2252 After the filling of the RD by the CT, the application in the 2253 luminaries can learn to which groups they belong, and enable their 2254 interface for the multicast address. 2256 The luminary, knowing its sector and being configured to join any 2257 group containing lights, searches for candidate groups and joins 2258 them: 2260 Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep 2261 ?d=R2-4-015&et=core.rd-group&rt=light 2263 Res: 2.05 Content 2264 ;ep="grp_R2-4-015";et="core.rd-group"; 2265 base="coap://[ff05::1]";rt="core.rd-ep" 2267 From the returned base parameter value, the luminary learns the 2268 multicast address of the multicast group. 2270 Alternatively, the CT can communicate the multicast address directly 2271 to the luminaries by using the "coap-group" resource specified in 2272 [RFC7390]. 2274 Req: POST coap://[2001:db8:4::1]/coap-group 2275 Content-Format: application/coap-group+json 2276 Payload: 2277 { "a": "[ff05::1]", "n": "grp_R2-4-015"} 2279 Res: 2.01 Created 2280 Location-Path: /coap-group/1 2282 Dependent on the situation, only the address, "a", or the name, "n", 2283 is specified in the coap-group resource. 2285 The presence sensor can learn the presence of groups that support 2286 resources with rt=light in its own sector by sending the same 2287 request, as used by the luminary. The presence sensor learns the 2288 multicast address to use for sending messages to the luminaries. 2290 10.2. OMA Lightweight M2M (LWM2M) Example 2292 This example shows how the OMA LWM2M specification makes use of 2293 Resource Directory (RD). 2295 OMA LWM2M is a profile for device services based on CoAP(OMA Name 2296 Authority). LWM2M defines a simple object model and a number of 2297 abstract interfaces and operations for device management and device 2298 service enablement. 2300 An LWM2M server is an instance of an LWM2M middleware service layer, 2301 containing a Resource Directory along with other LWM2M interfaces 2302 defined by the LWM2M specification. 2304 CoRE Resource Directory (RD) is used to provide the LWM2M 2305 Registration interface. 2307 LWM2M does not provide for registration sectors and does not 2308 currently use the rd-lookup interface. 2310 The LWM2M specification describes a set of interfaces and a resource 2311 model used between a LWM2M device and an LWM2M server. Other 2312 interfaces, proxies, and applications are currently out of scope for 2313 LWM2M. 2315 The location of the LWM2M Server and RD URI path is provided by the 2316 LWM2M Bootstrap process, so no dynamic discovery of the RD is used. 2317 LWM2M Servers and endpoints are not required to implement the /.well- 2318 known/core resource. 2320 10.2.1. The LWM2M Object Model 2322 The OMA LWM2M object model is based on a simple 2 level class 2323 hierarchy consisting of Objects and Resources. 2325 An LWM2M Resource is a REST endpoint, allowed to be a single value or 2326 an array of values of the same data type. 2328 An LWM2M Object is a resource template and container type that 2329 encapsulates a set of related resources. An LWM2M Object represents 2330 a specific type of information source; for example, there is a LWM2M 2331 Device Management object that represents a network connection, 2332 containing resources that represent individual properties like radio 2333 signal strength. 2335 Since there may potentially be more than one of a given type object, 2336 for example more than one network connection, LWM2M defines instances 2337 of objects that contain the resources that represent a specific 2338 physical thing. 2340 The URI template for LWM2M consists of a base URI followed by Object, 2341 Instance, and Resource IDs: 2343 {/base-uri}{/object-id}{/object-instance}{/resource-id}{/resource- 2344 instance} 2346 The five variables given here are strings. base-uri can also have 2347 the special value "undefined" (sometimes called "null" in RFC 6570). 2349 Each of the variables object-instance, resource-id, and resource- 2350 instance can be the special value "undefined" only if the values 2351 behind it in this sequence also are "undefined". As a special case, 2352 object-instance can be "empty" (which is different from "undefined") 2353 if resource-id is not "undefined". 2355 base-uri := Base URI for LWM2M resources or "undefined" for default 2356 (empty) base URI 2358 object-id := OMNA (OMA Name Authority) registered object ID (0-65535) 2360 object-instance := Object instance identifier (0-65535) or 2361 "undefined"/"empty" (see above)) to refer to all instances of an 2362 object ID 2364 resource-id := OMNA (OMA Name Authority) registered resource ID 2365 (0-65535) or "undefined" to refer to all resources within an instance 2367 resource-instance := Resource instance identifier or "undefined" to 2368 refer to single instance of a resource 2370 LWM2M IDs are 16 bit unsigned integers represented in decimal (no 2371 leading zeroes except for the value 0) by URI format strings. For 2372 example, a LWM2M URI might be: 2374 /1/0/1 2376 The base uri is empty, the Object ID is 1, the instance ID is 0, the 2377 resource ID is 1, and the resource instance is "undefined". This 2378 example URI points to internal resource 1, which represents the 2379 registration lifetime configured, in instance 0 of a type 1 object 2380 (LWM2M Server Object). 2382 10.2.2. LWM2M Register Endpoint 2384 LWM2M defines a registration interface based on the REST API, 2385 described in Section 5. The RD registration URI path of the LWM2M 2386 Resource Directory is specified to be "/rd". 2388 LWM2M endpoints register object IDs, for example , to indicate 2389 that a particular object type is supported, and register object 2390 instances, for example , to indicate that a particular instance 2391 of that object type exists. 2393 Resources within the LWM2M object instance are not registered with 2394 the RD, but may be discovered by reading the resource links from the 2395 object instance using GET with a CoAP Content-Format of application/ 2396 link-format. Resources may also be read as a structured object by 2397 performing a GET to the object instance with a Content-Format of 2398 senml+json. 2400 When an LWM2M object or instance is registered, this indicates to the 2401 LWM2M server that the object and its resources are available for 2402 management and service enablement (REST API) operations. 2404 LWM2M endpoints may use the following RD registration parameters as 2405 defined in Table 2 : 2407 ep - Endpoint Name 2408 lt - registration lifetime 2410 Endpoint Name, Lifetime, and LWM2M Version are mandatory parameters 2411 for the register operation, all other registration parameters are 2412 optional. 2414 Additional optional LWM2M registration parameters are defined: 2416 +-----------+-------+-------------------------------+---------------+ 2417 | Name | Query | Validity | Description | 2418 +-----------+-------+-------------------------------+---------------+ 2419 | Binding | b | {"U",UQ","S","SQ","US","UQS"} | Available | 2420 | Mode | | | Protocols | 2421 | | | | | 2422 | LWM2M | ver | 1.0 | Spec Version | 2423 | Version | | | | 2424 | | | | | 2425 | SMS | sms | | MSISDN | 2426 | Number | | | | 2427 +-----------+-------+-------------------------------+---------------+ 2429 Table 5: LWM2M Additional Registration Parameters 2431 The following RD registration parameters are not currently specified 2432 for use in LWM2M: 2434 et - Endpoint Type 2435 base - Registration Base URI 2437 The endpoint registration must include a payload containing links to 2438 all supported objects and existing object instances, optionally 2439 including the appropriate link-format relations. 2441 Here is an example LWM2M registration payload: 2443 ,,, 2444 This link format payload indicates that object ID 1 (LWM2M Server 2445 Object) is supported, with a single instance 0 existing, object ID 3 2446 (LWM2M Device object) is supported, with a single instance 0 2447 existing, and object 5 (LWM2M Firmware Object) is supported, with no 2448 existing instances. 2450 10.2.3. LWM2M Update Endpoint Registration 2452 The LwM2M update is really very similar to the registration update as 2453 described in Section 5.3.1, with the only difference that there are 2454 more parameters defined and available. All the parameters listed in 2455 that section are also available with the initial registration but are 2456 all optional: 2458 lt - Registration Lifetime 2459 b - Protocol Binding 2460 sms - MSISDN 2461 link payload - new or modified links 2463 A Registration update is also specified to be used to update the 2464 LWM2M server whenever the endpoint's UDP port or IP address are 2465 changed. 2467 10.2.4. LWM2M De-Register Endpoint 2469 LWM2M allows for de-registration using the delete method on the 2470 returned location from the initial registration operation. LWM2M de- 2471 registration proceeds as described in Section 5.3.2. 2473 11. Acknowledgments 2475 Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders 2476 Brandt, Matthieu Vial, Jim Schaad, Mohit Sethi, Hauke Petersen, 2477 Hannes Tschofenig, Sampo Ukkola, Linyi Tian, Jan Newmarch, Matthias 2478 Kovatsch and Jaime Jimenez have provided helpful comments, 2479 discussions and ideas to improve and shape this document. Zach would 2480 also like to thank his colleagues from the EU FP7 SENSEI project, 2481 where many of the resource directory concepts were originally 2482 developed. 2484 12. Changelog 2486 changes from -19 to -20 2488 (Processing comments from the WG chair review) 2490 o Define the permissible characters in endpoint and sector names 2491 o Express requirements on NAT situations in more abstract terms 2493 o Shifted heading levels to have the interfaces on the same level 2495 o Group instructions for error handling into general section 2497 o Simple Registration: process reflowed into items list 2499 o Updated introduction to reflect state of CoRE in general, 2500 reference RFC7228 (defining "constrained") and use "IoT" term in 2501 addition to "M2M" 2503 o Update acknowledgements 2505 o Assorted editorial changes 2507 * Unify examples style 2509 * Terminology: RDAO defined and not only expanded 2511 * Add CT to Figure 1 2513 * Consistency in the use of the term "Content Format" 2515 changes from -18 to -19 2517 o link-local addresses: allow but prescribe split-horizon fashion 2518 when used, disallow zone identifiers 2520 o Remove informative references to documents not mentioned any more 2522 changes from -17 to -18 2524 o Rather than re-specifying link format (Modernized Link Format), 2525 describe a Limited Link Format that's the uncontested subset of 2526 Link Format 2528 o Acknowledging the -17 version as part of the draft 2530 o Move "Read endpoint links" operation to future specification like 2531 PATCH 2533 o Demote links-json to an informative reference, and removed them 2534 from exchange examples 2536 o Add note on unusability of link-local IP addresses, and describe 2537 mitigation. 2539 o Reshuffling of sections: Move additional operations and endpoint 2540 lookup back from appendix, and groups into one 2542 o Lookup interface tightened to not imply applicability for non 2543 link-format lookups (as those can have vastly different views on 2544 link cardinality) 2546 o Simple registration: Change sequence of GET and POST-response, 2547 ensuring unsuccessful registrations are reported as such, and 2548 suggest how devices that would have required the inverse behavior 2549 can still cope with it. 2551 o Abstract and introduction reworded to avoid the impression that 2552 resources are stored in full in the RD 2554 o Simplify the rules governing when a registration resource can or 2555 must be changed. 2557 o Drop a figure that has become useless due to the changes of and 2558 -13 and -17 2560 o Wording consistency fixes: Use "Registrations" and "target 2561 attributes" 2563 o Fix incorrect use of content negotiation in discovery interface 2564 description (Content-Format -> Accept) 2566 o State that the base attribute value is part of endpoint lookup 2567 even when implicit in the registration 2569 o Update references from RFC5988 to its update RFC8288 2571 o Remove appendix on protocol-negotiation (which had a note to be 2572 removed before publication) 2574 changes from -16 to -17 2576 (Note that -17 is published as a direct follow-up to -16, containing 2577 a single change to be discussed at IETF103) 2579 o Removed groups that are enumerations of registrations and have 2580 dedicated mechanism 2582 o Add groups that are enumerations of shared resources and are a 2583 special case of endpoint registrations 2585 changes from -15 to -16 2586 o Recommend a common set of resources for members of a group 2588 o Clarified use of multicast group in lighting example 2590 o Add note on concurrent registrations from one EP being possible 2591 but not expected 2593 o Refresh web examples appendix to reflect current use of Modernized 2594 Link Format 2596 o Add examples of URIs where Modernized Link Format matters 2598 o Editorial changes 2600 changes from -14 to -15 2602 o Rewrite of section "Security policies" 2604 o Clarify that the "base" parameter text applies both to relative 2605 references both in anchor and href 2607 o Renamed "Registree-EP" to Registrant-EP" 2609 o Talk of "relative references" and "URIs" rather than "relative" 2610 and "absolute" URIs. (The concept of "absolute URIs" of [RFC3986] 2611 is not needed in RD). 2613 o Fixed examples 2615 o Editorial changes 2617 changes from -13 to -14 2619 o Rename "registration context" to "registration base URI" (and 2620 "con" to "base") and "domain" to "sector" (where the abbreviation 2621 "d" stays for compatibility reasons) 2623 o Introduced resource types core.rd-ep and core.rd-gp 2625 o Registration management moved to appendix A, including endpoint 2626 and group lookup 2628 o Minor editorial changes 2630 * PATCH/iPATCH is clearly deferred to another document 2632 * Recommend against query / fragment identifier in con= 2633 * Interface description lists are described as illustrative 2635 * Rewording of Simple Registration 2637 o Simple registration carries no error information and succeeds 2638 immediately (previously, sequence was unspecified) 2640 o Lookup: href are matched against resolved values (previously, this 2641 was unspecified) 2643 o Lookup: lt are not exposed any more 2645 o con/base: Paths are allowed 2647 o Registration resource locations can not have query or fragment 2648 parts 2650 o Default life time extended to 25 hours 2652 o clarified registration update rules 2654 o lt-value semantics for lookup clarified. 2656 o added template for simple registration 2658 changes from -12 to -13 2660 o Added "all resource directory" nodes MC address 2662 o Clarified observation behavior 2664 o version identification 2666 o example rt= and et= values 2668 o domain from figure 2 2670 o more explanatory text 2672 o endpoints of a groups hosted by different RD 2674 o resolve RFC6690-vs-8288 resolution ambiguities: 2676 * require registered links not to be relative when using anchor 2678 * return absolute URIs in resource lookup 2680 changes from -11 to -12 2681 o added Content Model section, including ER diagram 2683 o removed domain lookup interface; domains are now plain attributes 2684 of groups and endpoints 2686 o updated chapter "Finding a Resource Directory"; now distinguishes 2687 configuration-provided, network-provided and heuristic sources 2689 o improved text on: atomicity, idempotency, lookup with multiple 2690 parameters, endpoint removal, simple registration 2692 o updated LWM2M description 2694 o clarified where relative references are resolved, and how context 2695 and anchor interact 2697 o new appendix on the interaction with RFCs 6690, 5988 and 3986 2699 o lookup interface: group and endpoint lookup return group and 2700 registration resources as link targets 2702 o lookup interface: search parameters work the same across all 2703 entities 2705 o removed all methods that modify links in an existing registration 2706 (POST with payload, PATCH and iPATCH) 2708 o removed plurality definition (was only needed for link 2709 modification) 2711 o enhanced IANA registry text 2713 o state that lookup resources can be observable 2715 o More examples and improved text 2717 changes from -09 to -10 2719 o removed "ins" and "exp" link-format extensions. 2721 o removed all text concerning DNS-SD. 2723 o removed inconsistency in RDAO text. 2725 o suggestions taken over from various sources 2727 o replaced "Function Set" with "REST API", "base URI", "base path" 2728 o moved simple registration to registration section 2730 changes from -08 to -09 2732 o clarified the "example use" of the base RD resource values /rd, 2733 /rd-lookup, and /rd-group. 2735 o changed "ins" ABNF notation. 2737 o various editorial improvements, including in examples 2739 o clarifications for RDAO 2741 changes from -07 to -08 2743 o removed link target value returned from domain and group lookup 2744 types 2746 o Maximum length of domain parameter 63 bytes for consistency with 2747 group 2749 o removed option for simple POST of link data, don't require a 2750 .well-known/core resource to accept POST data and handle it in a 2751 special way; we already have /rd for that 2753 o add IPv6 ND Option for discovery of an RD 2755 o clarify group configuration section 6.1 that endpoints must be 2756 registered before including them in a group 2758 o removed all superfluous client-server diagrams 2760 o simplified lighting example 2762 o introduced Commissioning Tool 2764 o RD-Look-up text is extended. 2766 changes from -06 to -07 2768 o added text in the discovery section to allow content format hints 2769 to be exposed in the discovery link attributes 2771 o editorial updates to section 9 2773 o update author information 2775 o minor text corrections 2776 Changes from -05 to -06 2778 o added note that the PATCH section is contingent on the progress of 2779 the PATCH method 2781 changes from -04 to -05 2783 o added Update Endpoint Links using PATCH 2785 o http access made explicit in interface specification 2787 o Added http examples 2789 Changes from -03 to -04: 2791 o Added http response codes 2793 o Clarified endpoint name usage 2795 o Add application/link-format+cbor content-format 2797 Changes from -02 to -03: 2799 o Added an example for lighting and DNS integration 2801 o Added an example for RD use in OMA LWM2M 2803 o Added Read Links operation for link inspection by endpoints 2805 o Expanded DNS-SD section 2807 o Added draft authors Peter van der Stok and Michael Koster 2809 Changes from -01 to -02: 2811 o Added a catalogue use case. 2813 o Changed the registration update to a POST with optional link 2814 format payload. Removed the endpoint type update from the update. 2816 o Additional examples section added for more complex use cases. 2818 o New DNS-SD mapping section. 2820 o Added text on endpoint identification and authentication. 2822 o Error code 4.04 added to Registration Update and Delete requests. 2824 o Made 63 bytes a SHOULD rather than a MUST for endpoint name and 2825 resource type parameters. 2827 Changes from -00 to -01: 2829 o Removed the ETag validation feature. 2831 o Place holder for the DNS-SD mapping section. 2833 o Explicitly disabled GET or POST on returned Location. 2835 o New registry for RD parameters. 2837 o Added support for the JSON Link Format. 2839 o Added reference to the Groupcomm WG draft. 2841 Changes from -05 to WG Document -00: 2843 o Updated the version and date. 2845 Changes from -04 to -05: 2847 o Restricted Update to parameter updates. 2849 o Added pagination support for the Lookup interface. 2851 o Minor editing, bug fixes and reference updates. 2853 o Added group support. 2855 o Changed rt to et for the registration and update interface. 2857 Changes from -03 to -04: 2859 o Added the ins= parameter back for the DNS-SD mapping. 2861 o Integrated the Simple Directory Discovery from Carsten. 2863 o Editorial improvements. 2865 o Fixed the use of ETags. 2867 o Fixed tickets 383 and 372 2869 Changes from -02 to -03: 2871 o Changed the endpoint name back to a single registration parameter 2872 ep= and removed the h= and ins= parameters. 2874 o Updated REST interface descriptions to use RFC6570 URI Template 2875 format. 2877 o Introduced an improved RD Lookup design as its own function set. 2879 o Improved the security considerations section. 2881 o Made the POST registration interface idempotent by requiring the 2882 ep= parameter to be present. 2884 Changes from -01 to -02: 2886 o Added a terminology section. 2888 o Changed the inclusion of an ETag in registration or update to a 2889 MAY. 2891 o Added the concept of an RD Domain and a registration parameter for 2892 it. 2894 o Recommended the Location returned from a registration to be 2895 stable, allowing for endpoint and Domain information to be changed 2896 during updates. 2898 o Changed the lookup interface to accept endpoint and Domain as 2899 query string parameters to control the scope of a lookup. 2901 13. References 2903 13.1. Normative References 2905 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2906 Requirement Levels", BCP 14, RFC 2119, 2907 DOI 10.17487/RFC2119, March 1997, 2908 . 2910 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2911 Resource Identifier (URI): Generic Syntax", STD 66, 2912 RFC 3986, DOI 10.17487/RFC3986, January 2005, 2913 . 2915 [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., 2916 and D. Orchard, "URI Template", RFC 6570, 2917 DOI 10.17487/RFC6570, March 2012, 2918 . 2920 [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link 2921 Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, 2922 . 2924 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 2925 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 2926 . 2928 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2929 Writing an IANA Considerations Section in RFCs", BCP 26, 2930 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2931 . 2933 13.2. Informative References 2935 [ER] Chen, P., "The entity-relationship model---toward a 2936 unified view of data", ACM Transactions on Database 2937 Systems Vol. 1, pp. 9-36, DOI 10.1145/320434.320440, March 2938 1976. 2940 [I-D.bormann-t2trg-rel-impl] 2941 Bormann, C., "impl-info: A link relation type for 2942 disclosing implementation information", draft-bormann- 2943 t2trg-rel-impl-00 (work in progress), January 2018. 2945 [I-D.hartke-t2trg-coral] 2946 Hartke, K., "The Constrained RESTful Application Language 2947 (CoRAL)", draft-hartke-t2trg-coral-08 (work in progress), 2948 March 2019. 2950 [I-D.ietf-ace-oauth-authz] 2951 Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and 2952 H. Tschofenig, "Authentication and Authorization for 2953 Constrained Environments (ACE) using the OAuth 2.0 2954 Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-24 2955 (work in progress), March 2019. 2957 [I-D.ietf-core-links-json] 2958 Li, K., Rahman, A., and C. Bormann, "Representing 2959 Constrained RESTful Environments (CoRE) Link Format in 2960 JSON and CBOR", draft-ietf-core-links-json-10 (work in 2961 progress), February 2018. 2963 [I-D.ietf-core-rd-dns-sd] 2964 Lynn, K., Stok, P., Koster, M., and C. Amsuess, "CoRE 2965 Resource Directory: DNS-SD mapping", draft-ietf-core-rd- 2966 dns-sd-04 (work in progress), March 2019. 2968 [I-D.silverajan-core-coap-protocol-negotiation] 2969 Silverajan, B. and M. Ocak, "CoAP Protocol Negotiation", 2970 draft-silverajan-core-coap-protocol-negotiation-09 (work 2971 in progress), July 2018. 2973 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 2974 "Transmission of IPv6 Packets over IEEE 802.15.4 2975 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 2976 . 2978 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 2979 Bormann, "Neighbor Discovery Optimization for IPv6 over 2980 Low-Power Wireless Personal Area Networks (6LoWPANs)", 2981 RFC 6775, DOI 10.17487/RFC6775, November 2012, 2982 . 2984 [RFC6874] Carpenter, B., Cheshire, S., and R. Hinden, "Representing 2985 IPv6 Zone Identifiers in Address Literals and Uniform 2986 Resource Identifiers", RFC 6874, DOI 10.17487/RFC6874, 2987 February 2013, . 2989 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 2990 Constrained-Node Networks", RFC 7228, 2991 DOI 10.17487/RFC7228, May 2014, 2992 . 2994 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 2995 Protocol (HTTP/1.1): Message Syntax and Routing", 2996 RFC 7230, DOI 10.17487/RFC7230, June 2014, 2997 . 2999 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 3000 Application Protocol (CoAP)", RFC 7252, 3001 DOI 10.17487/RFC7252, June 2014, 3002 . 3004 [RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for 3005 the Constrained Application Protocol (CoAP)", RFC 7390, 3006 DOI 10.17487/RFC7390, October 2014, 3007 . 3009 [RFC7641] Hartke, K., "Observing Resources in the Constrained 3010 Application Protocol (CoAP)", RFC 7641, 3011 DOI 10.17487/RFC7641, September 2015, 3012 . 3014 [RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and 3015 FETCH Methods for the Constrained Application Protocol 3016 (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017, 3017 . 3019 [RFC8288] Nottingham, M., "Web Linking", RFC 8288, 3020 DOI 10.17487/RFC8288, October 2017, 3021 . 3023 Appendix A. Groups Registration and Lookup 3025 The RD-Groups usage pattern allows announcing application groups 3026 inside a Resource Directory. 3028 Groups are represented by endpoint registrations. Their base address 3029 is a multicast address, and they SHOULD be entered with the endpoint 3030 type "core.rd-group". The endpoint name can also be referred to as a 3031 group name in this context. 3033 The registration is inserted into the RD by a Commissioning Tool, 3034 which might also be known as a group manager here. It performs third 3035 party registration and registration updates. 3037 The links it registers SHOULD be available on all members that join 3038 the group. Depending on the application, members that lack some 3039 resource MAY be permissible if requests to them fail gracefully. 3041 The following example shows a CT registering a group with the name 3042 "lights" which provides two resources. The directory resource path 3043 /rd is an example RD location discovered in a request similar to 3044 Figure 5. 3046 Req: POST coap://rd.example.com/rd?ep=lights&et=core.rd-group 3047 &base=coap://[ff35:30:2001:db8::1] 3048 Content-Format: 40 3049 Payload: 3050 ;rt="light";if="core.a", 3051 ;if="core.p";u="K" 3053 Res: 2.01 Created 3054 Location-Path: /rd/12 3056 In this example, the group manager can easily permit devices that 3057 have no writable color-temperature to join, as they would still 3058 respond to brightness changing commands. Had the group instead 3059 contained a single resource that sets brightness and color 3060 temperature atomically, endpoints would need to support both 3061 properties. 3063 The resources of a group can be looked up like any other resource, 3064 and the group registrations (along with any additional registration 3065 parameters) can be looked up using the endpoint lookup interface. 3067 The following example shows a client performing and endpoint lookup 3068 for all groups. 3070 Req: GET /rd-lookup/ep?et=core.rd-group 3072 Res: 2.01 Content 3073 Payload: 3074 ;ep="GRP_R2-4-015";et="core.rd-group"; 3075 base="coap://[ff05::1]", 3076 ;ep=lights&et=core.rd-group; 3077 base="coap://[ff35:30:2001:db8::1]";rt="core.rd-ep" 3079 The following example shows a client performing a lookup of all 3080 resources of all endpoints (groups) with et=core.rd-group. 3082 Req: GET /rd-lookup/res?et=core.rd-group 3084 ;rt="light";if="core.a"; 3085 et="core.rd-group";anchor="coap://[ff35:30:2001:db8::1]", 3086 ;if="core.p";u="K"; 3087 et="core.rd-group"; 3088 anchor="coap://[ff35:30:2001:db8::1]" 3090 Appendix B. Web links and the Resource Directory 3092 Understanding the semantics of a link-format document and its URI 3093 references is a journey through different documents ([RFC3986] 3094 defining URIs, [RFC6690] defining link-format documents based on 3095 [RFC8288] which defines link headers, and [RFC7252] providing the 3096 transport). This appendix summarizes the mechanisms and semantics at 3097 play from an entry in ".well-known/core" to a resource lookup. 3099 This text is primarily aimed at people entering the field of 3100 Constrained Restful Environments from applications that previously 3101 did not use web mechanisms. 3103 The explanation of the steps makes some shortcuts in the more 3104 confusing details of [RFC6690], which are justified as all examples 3105 being in Limited Link Format. 3107 B.1. A simple example 3109 Let's start this example with a very simple host, "2001:db8:f0::1". 3110 A client that follows classical CoAP Discovery ([RFC7252] Section 7), 3111 sends the following multicast request to learn about neighbours 3112 supporting resources with resource-type "temperature". 3114 The client sends a link-local multicast: 3116 GET coap://[ff02::fd]:5683/.well-known/core?rt=temperature 3118 RES 2.05 Content 3119 ;rt=temperature;ct=0 3121 where the response is sent by the server, "[2001:db8:f0::1]:5683". 3123 While the client - on the practical or implementation side - can just 3124 go ahead and create a new request to "[2001:db8:f0::1]:5683" with 3125 Uri-Path: "temp", the full resolution steps for insertion into and 3126 retrieval from the RD without any shortcuts are: 3128 B.1.1. Resolving the URIs 3130 The client parses the single returned record. The link's target 3131 (sometimes called "href") is ""/temp"", which is a relative URI that 3132 needs resolving. The base URI is used to resolve the reference /temp against. 3135 The Base URI of the requested resource can be composed from the 3136 header options of the CoAP GET request by following the steps of 3137 [RFC7252] section 6.5 (with an addition at the end of 8.2) into 3138 ""coap://[2001:db8:f0::1]/.well-known/core"". 3140 Because ""/temp"" starts with a single slash, the record's target is 3141 resolved by replacing the path ""/.well-known/core"" from the Base 3142 URI (section 5.2 [RFC3986]) with the relative target URI ""/temp"" 3143 into ""coap://[2001:db8:f0::1]/temp"". 3145 B.1.2. Interpreting attributes and relations 3147 Some more information but the record's target can be obtained from 3148 the payload: the resource type of the target is "temperature", and 3149 its content format is text/plain (ct=0). 3151 A relation in a web link is a three-part statement that specifies a 3152 named relation between the so-called "context resource" and the 3153 target resource, like "_This page_ has _its table of contents_ at _/ 3154 toc.html_". In link format documents, there is an implicit "host 3155 relation" specified with default parameter: rel="hosts". 3157 In our example, the context resource of the link is the URI specified 3158 in the GET request "coap:://[2001:db8:f0::1]/.well-known/core". A 3159 full English expression of the "host relation" is: 3161 '"coap://[2001:db8:f0::1]/.well-known/core" is hosting the resource 3162 "coap://[2001:db8:f0::1]/temp", which is of the resource type 3163 "temperature" and can be accessed using the text/plain content 3164 format.' 3166 B.2. A slightly more complex example 3168 Omitting the "rt=temperature" filter, the discovery query would have 3169 given some more records in the payload: 3171 GET coap://[ff02::fd]:5683/.well-known/core 3173 RES 2.05 Content 3174 ;rt=temperature;ct=0, 3175 ;rt=light-lux;ct=0, 3176 ;anchor="/sensors/temp";rel=alternate, 3177 ;anchor="/sensors/temp"; 3178 rel="describedby" 3180 Parsing the third record, the client encounters the "anchor" 3181 parameter. It is a URI relative to the Base URI of the request and 3182 is thus resolved to ""coap://[2001:db8:f0::1]/sensors/temp"". That 3183 is the context resource of the link, so the "rel" statement is not 3184 about the target and the Base URI any more, but about the target and 3185 the resolved URI. Thus, the third record could be read as 3186 ""coap://[2001:db8:f0::1]/sensors/temp" has an alternate 3187 representation at "coap://[2001:db8:f0::1]/t"". 3189 Following the same resolution steps, the fourth record can be read as 3190 ""coap://[2001:db8:f0::1]/sensors/temp" is described by 3191 "http://www.example.com/sensors/t123"". 3193 B.3. Enter the Resource Directory 3195 The resource directory tries to carry the semantics obtainable by 3196 classical CoAP discovery over to the resource lookup interface as 3197 faithfully as possible. 3199 For the following queries, we will assume that the simple host has 3200 used Simple Registration to register at the resource directory that 3201 was announced to it, sending this request from its UDP port 3202 "[2001:db8:f0::1]:6553": 3204 POST coap://[2001:db8:f01::ff]/.well-known/core?ep=simple-host1 3206 The resource directory would have accepted the registration, and 3207 queried the simple host's ".well-known/core" by itself. As a result, 3208 the host is registered as an endpoint in the RD with the name 3209 "simple-host1". The registration is active for 90000 seconds, and 3210 the endpoint registration Base URI is ""coap://[2001:db8:f0::1]"" 3211 following the resolution steps described in Appendix B.1.1. It 3212 should be remarked that the Base URI constructed that way always 3213 yields a URI of the form: scheme://authority without path suffix. 3215 If the client now queries the RD as it would previously have issued a 3216 multicast request, it would go through the RD discovery steps by 3217 fetching "coap://[2001:db8:f0::ff]/.well-known/core?rt=core.rd- 3218 lookup-res", obtain "coap://[2001:db8:f0::ff]/rd-lookup/res" as the 3219 resource lookup endpoint, and issue a request to 3220 "coap://[2001:db8:f0::ff]/rd-lookup/res?rt=temperature" to receive 3221 the following data: 3223 ;rt=temperature;ct=0; 3224 anchor="coap://[2001:db8:f0::1]" 3226 This is not _literally_ the same response that it would have received 3227 from a multicast request, but it contains the equivalent statement: 3229 '"coap://[2001:db8:f0::1]" is hosting the resource 3230 "coap://[2001:db8:f0::1]/temp", which is of the resource type 3231 "temperature" and can be accessed using the text/plain content 3232 format.' 3234 (The difference is whether "/" or "/.well-known/core" hosts the 3235 resources, which does not matter in this application; if it did, the 3236 endpoint would have been more explicit. Actually, /.well-known/core 3237 does NOT host the resource but stores a URI reference to the 3238 resource.) 3240 To complete the examples, the client could also query all resources 3241 hosted at the endpoint with the known endpoint name "simple-host1". 3242 A request to "coap://[2001:db8:f0::ff]/rd-lookup/res?ep=simple-host1" 3243 would return 3244 ;rt=temperature;ct=0; 3245 anchor="coap://[2001:db8:f0::1]", 3246 ;rt=light-lux;ct=0; 3247 anchor="coap://[2001:db8:f0::1]", 3248 ; 3249 anchor="coap://[2001:db8:f0::1]/sensors/temp";rel=alternate, 3250 ; 3251 anchor="coap://[2001:db8:f0::1]/sensors/temp";rel="describedby" 3253 All the target and anchor references are already in absolute form 3254 there, which don't need to be resolved any further. 3256 Had the simple host done an equivalent full registration with a base= 3257 parameter (e.g. "?ep=simple-host1&base=coap+tcp://simple- 3258 host1.example.com"), that context would have been used to resolve the 3259 relative anchor values instead, giving 3261 ;rt=temperature;ct=0; 3262 anchor="coap+tcp://simple-host1.example.com" 3264 and analogous records. 3266 B.4. A note on differences between link-format and Link headers 3268 While link-format and Link headers look very similar and are based on 3269 the same model of typed links, there are some differences between 3270 [RFC6690] and [RFC8288], which are dealt with differently: 3272 o "Resolving the target against the anchor": [RFC6690] Section 2.1 3273 states that the anchor of a link is used as the Base URI against 3274 which the term inside the angle brackets (the target) is resolved, 3275 falling back to the resource's URI with paths stripped off (its 3276 "Origin"). In contrast to that, [RFC8288] Section B.2 describes 3277 that the anchor is immaterial to the resolution of the target 3278 reference. 3280 RFC6690, in the same section, also states that absent anchors set 3281 the context of the link to the target's URI with its path stripped 3282 off, while according to [RFC8288] Section 3.2, the context is the 3283 resource's base URI. 3285 The rules introduced in Appendix C ensure that an RD does not need 3286 to deal with those differences when processing input data. Lookup 3287 results are required to be absolute references for the same 3288 reason. 3290 o There is no percent encoding in link-format documents. 3292 A link-format document is a UTF-8 encoded string of Unicode 3293 characters and does not have percent encoding, while Link headers 3294 are practically ASCII strings that use percent encoding for non- 3295 ASCII characters, stating the encoding explicitly when required. 3297 For example, while a Link header in a page about a Swedish city 3298 might read 3300 "Link: ;rel="live-environment-data"" 3302 a link-format document from the same source might describe the 3303 link as 3305 ";rel="live-environment-data"" 3307 Parsers and producers of link-format and header data need to be 3308 aware of this difference. 3310 Appendix C. Limited Link Format 3312 The CoRE Link Format as described in [RFC6690] has been interpreted 3313 differently by implementers, and a strict implementation rules out 3314 some use cases of a Resource Directory (e.g. base values with path 3315 components). 3317 This appendix describes a subset of link format documents called 3318 Limited Link Format. The rules herein are not very limiting in 3319 practice - all examples in RFC6690, and all deployments the authors 3320 are aware of already stick to them - but ease the implementation of 3321 resource directory servers. 3323 It is applicable to representations in the application/link-format 3324 media type, and any other media types that inherit [RFC6690] 3325 Section 2.1. 3327 A link format representation is in Limited Link format if, for each 3328 link in it, the following applies: 3330 o All URI references either follow the URI or the path-absolute ABNF 3331 rule of RFC3986 (i.e. target and anchor each either start with a 3332 scheme or with a single slash), 3334 o if the anchor reference starts with a scheme, the target reference 3335 starts with a scheme as well (i.e. relative references in target 3336 cannot be used when the anchor is a full URI), and 3338 o the application does not care whether links without an explicitly 3339 given anchor have the origin's "/" or "/.well-known/core" resource 3340 as their link context. 3342 Authors' Addresses 3344 Zach Shelby 3345 ARM 3346 150 Rose Orchard 3347 San Jose 95134 3348 USA 3350 Phone: +1-408-203-9434 3351 Email: zach.shelby@arm.com 3353 Michael Koster 3354 SmartThings 3355 665 Clyde Avenue 3356 Mountain View 94043 3357 USA 3359 Phone: +1-707-502-5136 3360 Email: Michael.Koster@smartthings.com 3362 Carsten Bormann 3363 Universitaet Bremen TZI 3364 Postfach 330440 3365 Bremen D-28359 3366 Germany 3368 Phone: +49-421-218-63921 3369 Email: cabo@tzi.org 3371 Peter van der Stok 3372 consultant 3374 Phone: +31-492474673 (Netherlands), +33-966015248 (France) 3375 Email: consultancy@vanderstok.org 3376 URI: www.vanderstok.org 3377 Christian Amsuess (editor) 3378 Hollandstr. 12/4 3379 1020 3380 Austria 3382 Phone: +43-664-9790639 3383 Email: christian@amsuess.com