CoRE                                                           Z. ShelbyInternet-Draft                                                       ARMIntended status: Standards Track                               M. KosterExpires: January 8, 2017                                     SmartThings                                                              C. Bormann                                                 Universitaet Bremen TZI                                                         P. van der Stok                                                              consultant                                                           July 07, 2016                        CoRE Resource Directory                 draft-ietf-core-resource-directory-08Abstract   In many M2M applications, direct discovery of resources is not   practical due to sleeping nodes, disperse networks, or networks where   multicast traffic is inefficient.  These problems can be solved by   employing an entity called a Resource Directory (RD), which hosts   descriptions of resources held on other servers, allowing lookups to   be performed for those resources.  This document specifies the web   interfaces that a Resource Directory supports in order for web   servers to discover the RD and to register, maintain, lookup and   remove resources descriptions.  Furthermore, new link attributes   useful in conjunction with an RD are defined.Status of This Memo   This Internet-Draft is submitted in full conformance with the   provisions of BCP 78 and BCP 79.   Internet-Drafts are working documents of the Internet Engineering   Task Force (IETF).  Note that other groups may also distribute   working documents as Internet-Drafts.  The list of current Internet-   Drafts is at http://datatracker.ietf.org/drafts/current/.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   time.  It is inappropriate to use Internet-Drafts as reference   material or to cite them other than as "work in progress."   This Internet-Draft will expire on January 8, 2017.Shelby, et al.           Expires January 8, 2017                [Page 1]Internet-Draft           CoRE Resource Directory               July 2016Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject to BCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4   3.  Architecture and Use Cases  . . . . . . . . . . . . . . . . .   5     3.1.  Use Case: Cellular M2M  . . . . . . . . . . . . . . . . .   6     3.2.  Use Case: Home and Building Automation  . . . . . . . . .   7     3.3.  Use Case: Link Catalogues . . . . . . . . . . . . . . . .   7   4.  Finding a Directory Server  . . . . . . . . . . . . . . . . .   8     4.1.  Resource Directory Address Option (RDAO)  . . . . . . . .   9   5.  Simple Registration . . . . . . . . . . . . . . . . . . . . .  10     5.1.  Simple publishing to Resource Directory Server  . . . . .  11     5.2.  Third-party registration  . . . . . . . . . . . . . . . .  12   6.  Resource Directory Function Set . . . . . . . . . . . . . . .  12     6.1.  Content Formats . . . . . . . . . . . . . . . . . . . . .  13     6.2.  Discovery . . . . . . . . . . . . . . . . . . . . . . . .  13     6.3.  Registration  . . . . . . . . . . . . . . . . . . . . . .  15     6.4.  Registration Update . . . . . . . . . . . . . . . . . . .  18     6.5.  Registration Removal  . . . . . . . . . . . . . . . . . .  20     6.6.  Read Endpoint Links . . . . . . . . . . . . . . . . . . .  21     6.7.  Update Endpoint Links . . . . . . . . . . . . . . . . . .  22   7.  Group Function Set  . . . . . . . . . . . . . . . . . . . . .  24     7.1.  Register a Group  . . . . . . . . . . . . . . . . . . . .  24     7.2.  Group Removal . . . . . . . . . . . . . . . . . . . . . .  26   8.  RD Lookup Function Set  . . . . . . . . . . . . . . . . . . .  27   9.  New Link-Format Attributes  . . . . . . . . . . . . . . . . .  32     9.1.  Resource Instance attribute 'ins' . . . . . . . . . . . .  32     9.2.  Export attribute 'exp'  . . . . . . . . . . . . . . . . .  33   10. DNS-SD Mapping  . . . . . . . . . . . . . . . . . . . . . . .  33     10.1.  DNS-based Service discovery  . . . . . . . . . . . . . .  33     10.2.  mapping ins to <Instance>  . . . . . . . . . . . . . . .  34     10.3.  Mapping rt to <ServiceType>  . . . . . . . . . . . . . .  35     10.4.  Domain mapping . . . . . . . . . . . . . . . . . . . . .  35Shelby, et al.           Expires January 8, 2017                [Page 2]Internet-Draft           CoRE Resource Directory               July 2016     10.5.  TXT Record key=value strings . . . . . . . . . . . . . .  35     10.6.  Importing resource links into DNS-SD . . . . . . . . . .  36   11. Security Considerations . . . . . . . . . . . . . . . . . . .  36     11.1.  Endpoint Identification and Authentication . . . . . . .  37     11.2.  Access Control . . . . . . . . . . . . . . . . . . . . .  37     11.3.  Denial of Service Attacks  . . . . . . . . . . . . . . .  37   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  38     12.1.  Resource Types . . . . . . . . . . . . . . . . . . . . .  38     12.2.  Link Extension . . . . . . . . . . . . . . . . . . . . .  38     12.3.  IPv6 ND Resource Directory Address Option  . . . . . . .  38     12.4.  RD Parameter Registry  . . . . . . . . . . . . . . . . .  38   13. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  39     13.1.  Lighting Installation  . . . . . . . . . . . . . . . . .  39       13.1.1.  Installation Characteristics . . . . . . . . . . . .  40       13.1.2.  RD entries . . . . . . . . . . . . . . . . . . . . .  41       13.1.3.  DNS entries  . . . . . . . . . . . . . . . . . . . .  44     13.2.  OMA Lightweight M2M (LWM2M) Example  . . . . . . . . . .  44       13.2.1.  The LWM2M Object Model . . . . . . . . . . . . . . .  45       13.2.2.  LWM2M Register Endpoint  . . . . . . . . . . . . . .  46       13.2.3.  Alternate Base URI . . . . . . . . . . . . . . . . .  48       13.2.4.  LWM2M Update Endpoint Registration . . . . . . . . .  48       13.2.5.  LWM2M De-Register Endpoint . . . . . . . . . . . . .  48   14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  48   15. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .  49   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  52     16.1.  Normative References . . . . . . . . . . . . . . . . . .  52     16.2.  Informative References . . . . . . . . . . . . . . . . .  53   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  541.  Introduction   The work on Constrained RESTful Environments (CoRE) aims at realizing   the REST architecture in a suitable form for the most constrained   nodes (e.g., 8-bit microcontrollers with limited RAM and ROM) and   networks (e.g. 6LoWPAN).  CoRE is aimed at machine-to-machine (M2M)   applications such as smart energy and building automation.   The discovery of resources offered by a constrained server is very   important in machine-to-machine applications where there are no   humans in the loop and static interfaces result in fragility.  The   discovery of resources provided by an HTTP Web Server is typically   called Web Linking [RFC5988].  The use of Web Linking for the   description and discovery of resources hosted by constrained web   servers is specified by the CoRE Link Format [RFC6690].  However,   [RFC6690] only describes how to discover resources from the web   server that hosts them by requesting "/.well-known/core".  In many   M2M scenarios, direct discovery of resources is not practical due to   sleeping nodes, disperse networks, or networks where multicastShelby, et al.           Expires January 8, 2017                [Page 3]Internet-Draft           CoRE Resource Directory               July 2016   traffic is inefficient.  These problems can be solved by employing an   entity called a Resource Directory (RD), which hosts descriptions of   resources held on other servers, allowing lookups to be performed for   those resources.   This document specifies the web interfaces that a Resource Directory   supports in order for web servers to discover the RD and to register,   maintain, lookup and remove resource descriptions.  Furthermore, new   link attributes useful in conjunction with a Resource Directory are   defined.  Although the examples in this document show the use of   these interfaces with CoAP [RFC7252], they can be applied in an   equivalent manner to HTTP [RFC7230].2.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described in   [RFC2119].  The term "byte" is used in its now customary sense as a   synonym for "octet".   This specification requires readers to be familiar with all the terms   and concepts that are discussed in [RFC5988] and [RFC6690].  Readers   should also be familiar with the terms and concepts discussed in   [RFC7252].  To describe the REST interfaces defined in this   specification, the URI Template format is used [RFC6570].   This specification makes use of the following additional terminology:   Resource Directory      A web entity that stores information about web resources and      implements the REST interfaces defined in this specification for      registration and lookup of those resources.   Domain      In the context of a Resource Directory, a domain is a logical      grouping of endpoints.  This specification assumes that the list      of Domains supported by an RD is pre-configured by that RD.  When      a domain is exported to DNS, the domain value equates to the DNS      domain name.   Group      In the context of a Resource Directory, a group is a logical      grouping of endpoints for the purpose of group communications.      All groups within a domain are unique.   EndpointShelby, et al.           Expires January 8, 2017                [Page 4]Internet-Draft           CoRE Resource Directory               July 2016      Endpoint (EP) is a term used to describe a web server or client in      [RFC7252].  In the context of this specification an endpoint is      used to describe a web server that registers resources to the      Resource Directory.  An endpoint is identified by its endpoint      name, which is included during registration, and is unique within      the associated domain of the registration.   Commissioning Tool  Commissioning Tool (CT) is a device that assists      during the installation of the network by assigning values to      parameters, naming endpoints and groups, or adapting the      installation to the needs of the applications.3.  Architecture and Use Cases   The resource directory architecture is illustrated in Figure 1.  A   Resource Directory (RD) is used as a repository for Web Links   [RFC5988] about resources hosted on other web servers, which are   called endpoints (EP).  An endpoint is a web server associated with a   scheme, IP address and port (called Context), thus a physical node   may host one or more endpoints.  The RD implements a set of REST   interfaces for endpoints to register and maintain sets of Web Links   (called resource directory entries), and for clients to lookup   resources from the RD or maintain groups.  Endpoints themselves can   also act as clients.  An RD can be logically segmented by the use of   Domains.  The domain an endpoint is associated with can be defined by   the RD or configured by an outside entity.  This information   hierarchy is shown in Figure 2.   Endpoints are assumed to proactively register and maintain resource   directory entries on the RD, which are soft state and need to be   periodically refreshed.  An endpoint is provided with interfaces to   register, update and remove a resource directory entry.  Furthermore,   a mechanism to discover an RD using the CoRE Link Format [RFC6690] is   defined.  It is also possible for an RD to proactively discover Web   Links from endpoints and add them as resource directory entries.  A   lookup interface for discovering any of the Web Links held in the RD   is provided using the CoRE Link Format.Shelby, et al.           Expires January 8, 2017                [Page 5]Internet-Draft           CoRE Resource Directory               July 2016                Registration     Lookup, Group                 Interface        Interfaces     +----+          |                 |     | EP |----      |                 |     +----+    ----  |                 |                   --|-    +------+    |     +----+          | ----|      |    |     +--------+     | EP | ---------|-----|  RD  |----|-----| Client |     +----+          | ----|      |    |     +--------+                   --|-    +------+    |     +----+    ----  |                 |     | EP |----      |                 |     +----+              Figure 1: The resource directory architecture.                  +------------+                  |   Domain   | <-- Name                  +------------+                       |     |                       |   +------------+                       |   |   Group    | <-- Name, Scheme, IP, Port                       |   +------------+                       |     |                  +------------+                  |  Endpoint  |  <-- Name, Scheme, IP, Port                  +------------+                        |                        |                  +------------+                  |  Resource  |  <-- Target, Parameters                  +------------+          Figure 2: The resource directory information hierarchy.3.1.  Use Case: Cellular M2M   Over the last few years, mobile operators around the world have   focused on development of M2M solutions in order to expand the   business to the new type of users: machines.  The machines are   connected directly to a mobile network using an appropriate embedded   air interface (GSM/GPRS, WCDMA, LTE) or via a gateway providing short   and wide range wireless interfaces.  From the system design point of   view, the ambition is to design horizontal solutions that can enable   utilization of machines in different applications depending on their   current availability and capabilities as well as applicationShelby, et al.           Expires January 8, 2017                [Page 6]Internet-Draft           CoRE Resource Directory               July 2016   requirements, thus avoiding silo like solutions.  One of the crucial   enablers of such design is the ability to discover resources   (machines -- endpoints) capable of providing required information at   a given time or acting on instructions from the end users.   In a typical scenario, during a boot-up procedure (and periodically   afterwards), the machines (endpoints) register with a Resource   Directory (for example EPs installed on vehicles enabling tracking of   their position for fleet management purposes and monitoring   environment parameters) hosted by the mobile operator or somewhere   else in the network, periodically a description of its own   capabilities.  Due to the usual network configuration of mobile   networks, the EPs attached to the mobile network may not always be   efficiently reachable.  Therefore, a remote server is usually used to   provide proxy access to the EPs.  The address of each (proxy)   endpoint on this server is included in the resource description   stored in the RD.  The users, for example mobile applications for   environment monitoring, contact the RD, look up the endpoints capable   of providing information about the environment using appropriate set   of link parameters, obtain information on how to contact them (URLs   of the proxy server) and then initiate interaction to obtain   information that is finally processed, displayed on the screen and   usually stored in a database.  Similarly, fleet management systems   provide the appropriate link parameters to the RD to look up for EPs   deployed on the vehicles the application is responsible for.3.2.  Use Case: Home and Building Automation   Home and commercial building automation systems can benefit from the   use of M2M web services.  The discovery requirements of these   applications are demanding.  Home automation usually relies on run-   time discovery to commission the system, whereas in building   automation a combination of professional commissioning and run-time   discovery is used.  Both home and building automation involve peer-   to-peer interactions between endpoints, and involve battery-powered   sleeping devices.   The exporting of resource information to other discovery systems is   also important in these automation applications.  In home automation   there is a need to interact with other consumer electronics, which   may already support DNS-SD, and in building automation DNS-SD in   combination with resource directories can cover multiple buildings.3.3.  Use Case: Link Catalogues   Resources may be shared through data brokers that have no knowledge   beforehand of who is going to consume the data.  Resource Directory   can be used to hold links about resources and services hostedShelby, et al.           Expires January 8, 2017                [Page 7]Internet-Draft           CoRE Resource Directory               July 2016   anywhere to make them discoverable by a general class of   applications.   For example, environmental and weather sensors that generate data for   public consumption may provide the data to an intermediary server, or   broker.  Sensor data are published to the intermediary upon changes   or at regular intervals.  Descriptions of the sensors that resolve to   links to sensor data may be published to a Resource Directory.   Applications wishing to consume the data can use the Resource   Directory lookup function set to discover and resolve links to the   desired resources and endpoints.  The Resource Directory service need   not be coupled with the data intermediary service.  Mapping of   Resource Directories to data intermediaries may be many-to-many.   Metadata in web link compatible representations are supplied by   Resource Directories, which may be internally stored as triples, or   relation/attribute pairs providing metadata about resource links.   External catalogs that are represented in other formats may be   converted to common web linking formats for storage and access by   Resource Directories.  Since it is common practice for these to be   URN encoded, simple and lossless structural transforms should   generally be sufficient to store external metadata in Resource   Directories.   The additional features of Resource Directory allow domains to be   defined to enable access to a particular set of resources from   particular applications.  This provides isolation and protection of   sensitive data when needed.  Resource groups may defined to allow   batched reads from multiple resources.4.  Finding a Directory Server   Endpoints that want to contact a directory server can obtain   candidate IP addresses for such servers in a number of ways.   In a 6LoWPAN, good candidates can be taken from:   o  specific static configuration (e.g., anycast addresses), if any,   o  the ABRO option of 6LoWPAN-ND [RFC6775],   o  other ND options that happen to point to servers (such as RDNSS),   o  DHCPv6 options that might be defined later.   o  The IPv6 Neighbor Discovery Resource Directory Address Option      described in Section 4.1Shelby, et al.           Expires January 8, 2017                [Page 8]Internet-Draft           CoRE Resource Directory               July 2016   In networks with more inexpensive use of multicast, the candidate IP   address may be a well-known multicast address, i.e. directory servers   are found by simply sending GET requests to that well-known multicast   address (see Section 6.2).   As some of these sources are just (more or less educated) guesses,   endpoints MUST make use of any error messages to very strictly rate-   limit requests to candidate IP addresses that don't work out.  For   example, an ICMP Destination Unreachable message (and, in particular,   the port unreachable code for this message) may indicate the lack of   a CoAP server on the candidate host, or a CoAP error response code   such as 4.05 "Method Not Allowed" may indicate unwillingness of a   CoAP server to act as a directory server.4.1.  Resource Directory Address Option (RDAO)   The Resource Directory Option (RDAO) using IPv6 neighbor Discovery   (ND) carries information about the address of the Resource Directory   (RD).  This information is needed when endpoints cannot discover the   Resource Directory with link-local multicast address because the   endpoint and the RD are separated by a border Router (6LBR).  In many   circumstances the availability of DHCP cannot be guaranteed either   during commissioning of the network.  The presence and the use of the   RD is essential during commissioning.   The RDAO format is:Shelby, et al.           Expires January 8, 2017                [Page 9]Internet-Draft           CoRE Resource Directory               July 2016   0                   1                   2                   3   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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |  Length = 3   |       Valid Lifetime          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Reserved                            |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                                                               |   +                                                               +   |                                                               |   +                          RD Address                           +   |                                                               |   +                                                               +   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Fields:   Type:                   38   Length:                 8-bit unsigned integer.  The length of                           the option in units of 8 bytes.                           Always 3.   Valid Lifetime:         16-bit unsigned integer.  The length of                           time in units of 60 seconds (relative to                           the time the packet is received) that                           this set of border router information is                           valid.  A value of all zero bits (0x0)                           assumes a default value of 10,000                           (~one week).   Reserved:               This field is unused.  It MUST be                           initialized to zero by the sender and                           MUST be ignored by the receiver.   RD Address:             IPv6 address of the RD.                Figure 3: Resource Directory Address Option5.  Simple Registration   Not all endpoints hosting resources are expected to know how to   implement the Resource Directory Function Set (see Section 6) hence   cannot register with a Resource Directory.  Instead, simple endpoints   can implement the generic Simple Directory Discovery approach   described in this section.  An RD implementing this specification   MUST implement Simple Directory Discovery.  However, there may beShelby, et al.           Expires January 8, 2017               [Page 10]Internet-Draft           CoRE Resource Directory               July 2016   security reasons why this form of directory discovery would be   disabled.   This approach requires that the endpoint makes available the hosted   resources that it wants to be discovered, as links on its "/.well-   known/core" interface as specified in [RFC6690].   The endpoint then finds one or more addresses of the directory server   as described in Section 4.   An endpoint can send (a selection of) hosted resources to a directory   server for publication as described in Section 5.1.   The directory server integrates the information it received this way   into its resource directory.  It MAY make the information available   to further directories, if it can ensure that a loop does not form.   The protocol used between directories to ensure loop-free operation   is outside the scope of this document.5.1.  Simple publishing to Resource Directory Server   An endpoint that wants to make itself discoverable occasionally sends   a POST request to the "/.well-known/core" URI of any candidate   directory server that it finds.  The body of the POST request is   empty, which triggers the resource directory server to perform GET   requests at the requesting server's default discovery URI to obtain   the link-format payload to register.   The endpoint MAY include registration parameters in the POST request   as per Section 6.3   The following example shows an endpoint using simple publishing, by   simply sending an empty POST to a resource directory.Shelby, et al.           Expires January 8, 2017               [Page 11]Internet-Draft           CoRE Resource Directory               July 2016   Req:(to RD server from [ff02::1])   POST coap://rd.example.com/.well-known/core?lt=6000   Content-Format: 40   payload:   (empty payload)   Res: 2.04 Changed   (later)   Req: (from RD server to [ff02::1])   GET coap://[ff02::1]/.well-known/core   Accept: 40   Res: 2.05 Content   payload:   </sen/temp>5.2.  Third-party registration   For some applications, even Simple Directory Discovery may be too   taxing for certain very constrained devices, in particular if the   security requirements become too onerous.   In a controlled environment (e.g. building control), the Resource   Directory can be filled by a third device, called a commissioning   tool.  The commissioning tool can fill the Resource Directory from a   database or other means.  For that purpose the scheme, IP address and   port of the registered device is indicated in the Context parameter   of the registration described in Section 6.3.6.  Resource Directory Function Set   This section defines the REST interfaces between an RD and endpoints,   which is called the Resource Directory Function Set. Although the   examples throughout this section assume the use of CoAP [RFC7252],   these REST interfaces can also be realized using HTTP [RFC7230].  In   all definitions in this section, both CoAP response codes (with dot   notation) and HTTP response codes (without dot notation) are shown.   An RD implementing this specification MUST support the discovery,   registration, update, lookup, and removal interfaces defined in this   section.Shelby, et al.           Expires January 8, 2017               [Page 12]Internet-Draft           CoRE Resource Directory               July 2016   Resource directory entries are designed to be easily exported to   other discovery mechanisms such as DNS-SD.  For that reason,   parameters that would meaningfully be mapped to DNS SHOULD be limited   to a maximum length of 63 bytes.6.1.  Content Formats   Resource Directory implementations using this specification MUST   support the application/link-format content format (ct=40).   Resource Directories implementing this specification MAY support   additional content formats.   Any additional content format supported by a Resource Directory   implementing this specification MUST have an equivalent serialization   in the application/link-format content format.6.2.  Discovery   Before an endpoint can make use of an RD, it must first know the RD's   address and port, and the path of its RD Function Set. There can be   several mechanisms for discovering the RD including assuming a   default location (e.g. on an Edge Router in a LoWPAN), by assigning   an anycast address to the RD, using DHCP, or by discovering the RD   using the CoRE Link Format (see also Section 4).  This section   defines discovery of the RD using the well-known interface of the   CoRE Link Format [RFC6690] as the required mechanism.  It is however   expected that RDs will also be discoverable via other methods   depending on the deployment.   Discovery of the RD function set is performed by sending either a   multicast or unicast GET request to "/.well-known/core" and including   a Resource Type (rt) parameter [RFC6690] with the value "core.rd" in   the query string.  Likewise, a Resource Type parameter value of   "core.rd-lookup" is used to discover the RD Lookup Function Set.   Upon success, the response will contain a payload with a link format   entry for each RD discovered, with the URL indicating the root   resource of the RD.  When performing multicast discovery, the   multicast IP address used will depend on the scope required and the   multicast capabilities of the network.   A Resource Directory MAY provide hints about the content-formats it   supports in the links it exposes or registers, using the "ct" link   attribute, as shown in the example below.  Clients MAY use these   hints to select alternate content-formats for interaction with the   Resource Directory.Shelby, et al.           Expires January 8, 2017               [Page 13]Internet-Draft           CoRE Resource Directory               July 2016   HTTP does not support multicast and consequently only unicast   discovery can be supported using HTTP.  Links to Resource Directories   MAY be registered in other Resource Directories, and well-known entry   points SHOULD be provided to enable the bootstrapping of unicast   discovery.   An RD implementation of this specification MUST support query   filtering for the rt parameter as defined in [RFC6690].   The discovery request interface is specified as follows:   Interaction:  EP -> RD   Method:  GET   URI Template:  /.well-known/core{?rt}   URI Template Variables:      rt :=  Resource Type (optional).  MAY contain one or more of the         values "core.rd", "core.rd-lookup", "core.rd-group" or         "core.rd*"   Content-Format:  application/link-format (if any)   Content-Format:  application/link-format+json (if any)   Content-Format:  application/link-format+cbor (if any)   The following response codes are defined for this interface:   Success:  2.05 "Content" with an application/link-format,      application/link-format+json, or application/link-format+cbor      payload containing one or more matching entries for the RD      resource.   Failure:  4.04 "Not Found" is returned in case no matching entry is      found for a unicast request.   Failure:  4.00 "Bad Request" is returned in case of a malformed      request for a unicast request.   Failure:  No error response to a multicast request.   HTTP support :  YES (Unicast only)   The following example shows an endpoint discovering an RD using this   interface, thus learning that the base RD resource is, in thisShelby, et al.           Expires January 8, 2017               [Page 14]Internet-Draft           CoRE Resource Directory               July 2016   example, at /rd and that the content_format delivered by the server   hosting the resource is application.xml (ct=40).  Note that it is up   to the RD to choose its base RD resource, although diagnostics and   debugging is facilitated by using the base paths specified here where   possible.   Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*   Res: 2.05 Content   </rd>;rt="core.rd";ct=40,   </rd-lookup>;rt="core.rd-lookup";ct=40,   </rd-group>;rt="core.rd-group";ct=40   The following example shows the way of indicating that a client may   request alternate content-formats.  The Content-Format code attribute   "ct" MAY include a space-separated sequence of Content-Format codes   as specified in [RFC7252], indicating that multiple content-formats   are available.  The example below shows the required ct=40   (application/link-format) indicated as well as a vendor-specific   content format (21225).   Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*   Res: 2.05 Content   </rd>;rt="core.rd";ct="40 21225",   </rd-lookup>;rt="core.rd-lookup";ct="40 21225",   </rd-group>;rt="core.rd-group";ct="40 21225"6.3.  Registration   After discovering the location of an RD Function Set, an endpoint MAY   register its resources using the registration interface.  This   interface accepts a POST from an endpoint containing the list of   resources to be added to the directory as the message payload in the   CoRE Link Format [RFC6690], JSON CoRE Link Format (application/link-   format+json), or CBOR CoRE Link Format (application/link-format+cbor)   [I-D.ietf-core-links-json], along with query string parameters   indicating the name of the endpoint, its domain and the lifetime of   the registration.  All parameters except the endpoint name are   optional.  It is expected that other specifications will define   further parameters (see Section 12.4).  The RD then creates a new   resource or updates an existing resource in the RD and returns its   location.  An endpoint MUST use that location when refreshing   registrations using this interface.  Endpoint resources in the RD are   kept active for the period indicated by the lifetime parameter.  The   endpoint is responsible for refreshing the entry within this period   using either the registration or update interface.  The registration   interface MUST be implemented to be idempotent, so that registeringShelby, et al.           Expires January 8, 2017               [Page 15]Internet-Draft           CoRE Resource Directory               July 2016   twice with the same endpoint parameter does not create multiple RD   entries.  A new registration may be created at any time to supercede   an existing registration, replacing the registration parameters and   links.   The registration request interface is specified as follows:   Interaction:  EP -> RD   Method:  POST   URI Template:  /{+rd}{?ep,d,et,lt,con}   URI Template Variables:      rd :=  RD Function Set path (mandatory).  This is the path of the         RD Function Set, as obtained from discovery.  An RD SHOULD use         the value "rd" for this variable whenever possible.      ep :=  Endpoint name (mandatory).  The endpoint name is an         identifier that MUST be unique within a domain.  The maximum         length of this parameter is 63 bytes.      d :=  Domain (optional).  The domain to which this endpoint         belongs.  The maximum length of this parameter is 63 bytes.         When this parameter is elided, the RD MAY associate the         endpoint with a configured default domain.  The domain value is         needed to export the endpoint to DNS-SD (see Section 10).      et :=  Endpoint Type (optional).  The semantic type of the         endpoint.  This parameter SHOULD be less than 63 bytes.      lt :=  Lifetime (optional).  Lifetime of the registration in         seconds.  Range of 60-4294967295.  If no lifetime is included,         a default value of 86400 (24 hours) SHOULD be assumed.      con :=  Context (optional).  This parameter sets the scheme,         address and port at which this server is available in the form         scheme://host:port.  In the absence of this parameter the         scheme of the protocol, source IP address and source port of         the register request are assumed.  This parameter is mandatory         when the directory is filled by a third party such as an         commissioning tool.   Content-Format:  application/link-format   Content-Format:  application/link-format+jsonShelby, et al.           Expires January 8, 2017               [Page 16]Internet-Draft           CoRE Resource Directory               July 2016   Content-Format:  application/link-format+cbor   The following response codes are defined for this interface:   Success:  2.01 "Created" or 201 "Created".  The Location header MUST      be included with the new resource entry for the endpoint.  This      Location MUST be a stable identifier generated by the RD as it is      used for all subsequent operations on this registration.  The      resource returned in the Location is for the purpose of updating      the lifetime of the registration and for maintaining the content      of the registered links, including updating and deleting links.   Failure:  4.00 "Bad Request" or 400 "Bad Request".  Malformed      request.   Failure:  5.03 "Service Unavailable" or 503 "Service Unavailable".      Service could not perform the operation.   HTTP support:  YES   The following example shows an endpoint with the name "node1"   registering two resources to an RD using this interface.  The   resulting location /rd/4521 is just an example of an RD generated   location.   Req: POST coap://rd.example.com/rd?ep=node1   Content-Format: 40   Payload:   </sensors/temp>;ct=41;rt="temperature-c";if="sensor",   </sensors/light>;ct=41;rt="light-lux";if="sensor"   Res: 2.01 Created   Location: /rd/4521   Req: POST /rd?ep=node1 HTTP/1.1   Host : example.com   Content-Type: application/link-format   Payload:   </sensors/temp>;ct=41;rt="temperature-c";if="sensor",   </sensors/light>;ct=41;rt="light-lux";if="sensor"   Res: 201 Created   Location: /rd/4521Shelby, et al.           Expires January 8, 2017               [Page 17]Internet-Draft           CoRE Resource Directory               July 20166.4.  Registration Update   The update interface is used by an endpoint to refresh or update its   registration with an RD.  To use the interface, the endpoint sends a   POST request to the resource returned in the Location option in the   response to the first registration.   An update MAY update the lifetime or context registration parameters   "lt", "con" as in Section 6.3 ) if they have changed since the last   registration or update.  Parameters that have not changed SHOULD NOT   be included in an update.  Adding parameters that have not changed   increases the size of the message but does not have any other   implications.  Parameters MUST be included as query parameters in an   update operation as in {registration}.   Upon receiving an update request, an RD MUST reset the timeout for   that endpoint and update the scheme, IP address and port of the   endpoint, using the source address of the update, or the context   ("con") parameter if present.  If the lifetime parameter "lt" is   included in the received update request, the RD MUST update the   lifetime of the registration and set the timeout equal to the new   lifetime.   An update MAY optionally add or replace links for the endpoint by   including those links in the payload of the update as a CoRE Link   Format document.  A link is replaced only if both the target URI and   relation type match.   In addition to the use of POST, as described in this section, there   is an alternate way to add, replace, and delete links using PATCH as   described in Section 6.7.   The update registration request interface is specified as follows:   Interaction:  EP -> RD   Method:  POST   URI Template:  /{+location}{?lt,con}   URI Template Variables:      location :=  This is the Location path returned by the RD as a         result of a successful earlier registration.      lt :=  Lifetime (optional).  Lifetime of the registration in         seconds.  Range of 60-4294967295.  If no lifetime is included,         a default value of 86400 (24 hours) SHOULD be assumed.Shelby, et al.           Expires January 8, 2017               [Page 18]Internet-Draft           CoRE Resource Directory               July 2016      con :=  Context (optional).  This parameter sets the scheme,         address and port at which this server is available in the form         scheme://host:port.  Optional.  In the absence of this         parameter the scheme of the protocol, source IP address and         source port used to register are assumed.  This parameter is         compulsory when the directory is filled by a third party such         as a commissioning tool.   Content-Format:  application/link-format (mandatory)   Content-Format:  application/link-format+json (optional)   Content-Format:  application/link-format+cbor (optional)   The following response codes are defined for this interface:   Success:  2.04 "Changed" or 204 "No Content" if the update was      successfully processed.   Failure:  4.00 "Bad Request" or 400 "Bad Request".  Malformed      request.   Failure:  4.04 "Not Found" or 404 "Not Found".  Registration does not      exist (e.g. may have expired).   Failure:  5.03 "Service Unavailable" or 503 "Service Unavailable".      Service could not perform the operation.   HTTP support:  YES   The following example shows an endpoint updating its registration at   an RD using this interface.   Req: POST /rd/4521   Res: 2.04 Changed   The following example shows an endpoint updating its registration   with a new lifetime and context, changing an existing link, and   adding a new link using this interface.  With the initial   registration the client set the following values:   o  lifetime (lt)=500   o  context (con)=coap://local-proxy-old.example.com:5683   o  resource= </sensors/temp>;ct=41;rt="foobar";if="sensor"Shelby, et al.           Expires January 8, 2017               [Page 19]Internet-Draft           CoRE Resource Directory               July 2016   Req: POST /rd/4521?lt=600&con="coap://local-proxy.example.com:5683"   Content-Format: 40   Payload:   </sensors/temp>;ct=41;rt="temperature-f";if="sensor",   </sensors/door>;ct=41;rt="door";if="sensor"   Res: 2.04 Changed6.5.  Registration Removal   Although RD entries have soft state and will eventually timeout after   their lifetime, an endpoint SHOULD explicitly remove its entry from   the RD if it knows it will no longer be available (for example on   shut-down).  This is accomplished using a removal interface on the RD   by performing a DELETE on the endpoint resource.   The removal request interface is specified as follows:   Interaction:  EP -> RD   Method:  DELETE   URI Template:  /{+location}   URI Template Variables:      location :=  This is the Location path returned by the RD as a         result of a successful earlier registration.   The following responses codes are defined for this interface:   Success:  2.02 "Deleted" or 204 "No Content" upon successful deletion   Failure:  4.00 "Bad Request" or 400 "Bad request".  Malformed      request.   Failure:  4.04 "Not Found" or 404 "Not Found".  Registration does not      exist (e.g. may have expired).   Failure:  5.03 "Service Unavailable" or 503 "Service Unavailable".      Service could not perform the operation.   HTTP support: YES   The following examples shows successful removal of the endpoint from   the RD.Shelby, et al.           Expires January 8, 2017               [Page 20]Internet-Draft           CoRE Resource Directory               July 2016   Req: DELETE /rd/4521   Res: 2.02 Deleted6.6.  Read Endpoint Links   Some endpoints may wish to manage their links as a collection, and   may need to read the current set of links in order to determine link   maintenance operations.   One or more links MAY be selected by using query filtering as   specified in [RFC6690] Section 4.1   The read request interface is specified as follows:   Interaction:  EP -> RD   Method:  GET   URI Template:  /{+location}{?href,rel,rt,if,ct}   URI Template Variables:      location :=  This is the Location path returned by the RD as a         result of a successful earlier registration.      href,rel,rt,if,ct := link relations and attributes specified in      the query in order to select particular links based on their      relations and attributes. "href" denotes the URI target of the      link.  See [RFC6690] Sec. 4.1   The following responses codes are defined for this interface:   Success:  2.05 "Content" or 200 "OK" upon success with an      "application/link-format", "application/link-format+cbor", or      "application/link-format+json" payload.   Failure:  4.00 "Bad Request" or 400 "Bad Request".  Malformed      request.   Failure:  4.04 "Not Found" or 404 "Not Found".  Registration does not      exist (e.g. may have expired).   Failure:  5.03 "Service Unavailable" or 503 "Service Unavailable".      Service could not perform the operation.   HTTP support: YESShelby, et al.           Expires January 8, 2017               [Page 21]Internet-Draft           CoRE Resource Directory               July 2016   The following examples show successful read of the endpoint links   from the RD.   Req: GET /rd/4521   Res: 2.01 Content   Payload:   </sensors/temp>;ct=41;rt="temperature-c";if="sensor",   </sensors/light>;ct=41;rt="light-lux";if="sensor"6.7.  Update Endpoint Links   [This section will be removed before or as a result of a working-   group last-call if the PATCH methods do not achieve the same level of   consensus as the present document.]   A PATCH update adds, removes or changes links for the endpoint by   including link update information in the payload of the update as a   merge-patch+json format [RFC7396] document.   One or more links are selected for update by using query filtering as   specified in [RFC6690] Section 4.1   The query filter selects the links to be modified or deleted, by   matching the query parameter values to the values of the link   attributes.   When the query parameters are not present in the request, the payload   specifies links to be added to the target document.  When the query   parameters are present, the attribute names and values in the query   parameters select one or more links on which to apply the PATCH   operation.   If an attribute name specified in the PATCH document exists in any   the set of selected links, all occurrences of the attribute value in   the target document MUST be updated using the value from the PATCH   payload.  If the attribute name is not present in any selected links,   the attribute MUST be added to the links.   The update request interface is specified as follows:   Interaction:  EP -> RD   Method:  PATCH   URI Template:  /{+location}{?href,rel,rt,if,ct}   URI Template Variables:Shelby, et al.           Expires January 8, 2017               [Page 22]Internet-Draft           CoRE Resource Directory               July 2016      location :=  This is the Location path returned by the RD as a         result of a successful earlier registration.      href,rel,rt,if,ct := link relations and attributes specified in      the query in order to select particular links based on their      relations and attributes. "href" denotes the URI target of the      link.  See [RFC6690] Sec. 4.1   Content-Format:  application/merge-patch+json (mandatory)   The following response codes are defined for this interface:   Success:  2.04 "Changed" 0r 204 "No Content" in the update was      successfully processed.   Failure:  4.00 "Bad Request" or 400 "Bad Request".  Malformed      request.   Failure:  4.04 "Not Found" or 404 "Not Found".  Registration resource      does not exist (e.g. may have expired).   Failure:  5.03 "Service Unavailable" or 503 "Service Unavailable".      Service could not perform the operation.   HTTP support: YES   The following examples show an endpoint adding </sensors/humid>,   modifying </sensors/temp>, and removing </sensors/light> links in RD   using the Update Endpoint Links function.   The following example shows an EP adding the link </sensors/   humid>;ct=41;rt="humid-s";if="sensor" to the collection of links at   the location /rd/4521.   Req: PATCH /rd/4521   Payload:   [{"href":"/sensors/humid","ct": 41, "rt": "humid-s", "if": "sensor"}]   Content-Format:   application/merge-patch+json   Res: 2.04 Changed   The following example shows an EP modifying all links at the location   /rd/4521 which are identified by href="/sensors/temp", from the   initial link-value of </sensors/temp>;rt="temperature" to the new   link-value </sensors/temp>;rt="temperature-c";if="sensor" by changingShelby, et al.           Expires January 8, 2017               [Page 23]Internet-Draft           CoRE Resource Directory               July 2016   the value of the link attribute "rt" and adding the link attribute   if="sensor" using the PATCH operation with the supplied merge-   patch+json document payload.   Req: PATCH /rd/4521?href="/sensors/temp"   Payload:   {"rt": "temperature-c", "if": "sensor"},   Content-Format:   application/merge-patch+json   Res: 2.04 Changed   This example shows an EP removing all links at the location /rd/4521   which are identified by href="/sensors/light".   Req: PATCH /rd/4521?href="/sensors/light"   Payload:   {null}   Content-Format:   application/merge-patch+json   Res: 2.04 Changed7.  Group Function Set   This section defines a function set for the creation of groups of   endpoints for the purpose of managing and looking up endpoints for   group operations.  The group function set is similar to the resource   directory function set, in that a group may be created or removed.   However unlike an endpoint entry, a group entry consists of a list of   endpoints and does not have a lifetime associated with it.  In order   to make use of multicast requests with CoAP, a group MAY have a   multicast address associated with it.7.1.  Register a Group   In order to create a group, a commissioning tool (CT) used to   configure groups, makes a request to the RD indicating the name of   the group to create (or update), optionally the domain the group   belongs to, and optionally the multicast address of the group.  The   registration message includes the list of endpoints that belong to   that group.Shelby, et al.           Expires January 8, 2017               [Page 24]Internet-Draft           CoRE Resource Directory               July 2016   All the endpoints in the group MUST be registered with the RD before   registering a group.  If an endpoint is not yet registered to the RD   before registering the group, the registration message returns an   error.  The RD sends a blank target URI for every endpoint link when   registering the group.   Configuration of the endpoints themselves is out of scope of this   specification.  Such an interface for managing the group membership   of an endpoint has been defined in [RFC7390].   The registration request interface is specified as follows:   Interaction:  CT -> RD   Method:  POST   URI Template:  /{+rd-group}{?gp,d,con}   URI Template Variables:      rd-group :=  RD Group Function Set path (mandatory).  This is the         path of the RD Group Function Set. An RD SHOULD use the value         "rd-group" for this variable whenever possible.      gp :=  Group Name (mandatory).  The name of the group to be         created or replaced, unique within that domain.  The maximum         length of this parameter is 63 bytes.      d :=  Domain (optional).  The domain to which this group belongs.         The maximum length of this parameter is 63 bytes.  Optional.         When this parameter is elided, the RD MAY associate the         endpoint with a configured default domain.  The domain value is         needed to export the endpoint to DNS-SD (see Section 10)      con :=  Context (optional).  This parameter is used to set the IP         multicast address at which this server is available in the form         scheme://multicast-address:port.  Optional.  In the absence of         this parameter no multicast address is configured.  This         parameter is compulsory when the directory is filled by a         commissioning tool.   Content-Format:  application/link-format   Content-Format:  application/link-format+json   Content-Format:  application/link-format+cbor   The following response codes are defined for this interface:Shelby, et al.           Expires January 8, 2017               [Page 25]Internet-Draft           CoRE Resource Directory               July 2016   Success:  2.01 "Created" or 201 "Created".  The Location header MUST      be included with the new group entry.  This Location MUST be a      stable identifier generated by the RD as it is used for delete      operations on this registration.   Failure:  4.00 "Bad Request" or 400 "Bad Request".  Malformed      request.   Failure:  4.04 "Not Found" or 404 "Not Found".  An Endpoint is not      registered in the RD (e.g. may have expired).   Failure:  5.03 "Service Unavailable" or 503 "Service Unavailable".      Service could not perform the operation.   HTTP support:  YES   The following example shows an EP registering a group with the name   "lights" which has two endpoints to an RD using this interface.  The   resulting location /rd-group/12 is just an example of an RD generated   group location.   Req: POST coap://rd.example.com/rd-group?gp=lights   Content-Format: 40   Payload:   <>;ep="node1",   <>;ep="node2"   Res: 2.01 Created   Location: /rd-group/12   Req: POST /rd-group?gp=lights HTTP/1.1   Host: example.com   Content-Type: application/link-format   Payload:   <>;ep="node1",   <>;ep="node2"   Res: 201 Created   Location: /rd-group/127.2.  Group Removal   A group can be removed simply by sending a removal message to the   location returned when registering the group.  Removing a group MUST   NOT remove the endpoints of the group from the RD.   The removal request interface is specified as follows:Shelby, et al.           Expires January 8, 2017               [Page 26]Internet-Draft           CoRE Resource Directory               July 2016   Interaction:  CT -> RD   Method:  DELETE   URI Template:  /{+location}   URI Template Variables:      location :=  This is the Location path returned by the RD as a         result of a successful group registration.   The following responses codes are defined for this interface:   Success:  2.02 "Deleted" or 204 "No Content" upon successful deletion   Failure:  4.00 "Bad Request" or 400 "Bad Request".  Malformed      request.   Failure:  4.04 "Not Found" or 404 "Not Found".  Group does not exist.   Failure:  5.03 "Service Unavailable" or 503 "Service Unavailable".      Service could not perform the operation.   HTTP support:  YES   The following examples shows successful removal of the group from the   RD.   Req: DELETE /rd-group/12   Res: 2.02 Deleted8.  RD Lookup Function Set   In order for an RD to be used for discovering resources registered   with it, a lookup interface can be provided using this function set.   This lookup interface is defined as a default, and it is assumed that   RDs may also support lookups to return resource descriptions in   alternative formats (e.g.  Atom or HTML Link) or using more advanced   interfaces (e.g. supporting context or semantic based lookup).   This function set allows lookups for domains, groups, endpoints and   resources using attributes defined in the RD Function Set and for use   with the CoRE Link Format.  The result of a lookup request is the   list of links (if any) corresponding to the type of lookup.  Thus, a   domain lookup MUST return a list of domains, a group lookup MUST   return a list of groups, an endpoint lookup MUST return a list ofShelby, et al.           Expires January 8, 2017               [Page 27]Internet-Draft           CoRE Resource Directory               July 2016   endpoints and a resource lookup MUST return a list of links to   resources.   Each endpoint and resource lookup result returns respectively the   scheme (IP address and port) followed by the path part of the URI of   every endpoint and resource inside angle brackets ("<>") and followed   by the other parameters.   The target of these links SHOULD be the actual location of the   domain, endpoint or resource, but MAY be an intermediate proxy e.g.   in the case of an HTTP lookup interface for CoAP endpoints.   The domain lookup returns every lookup domain with a "/rd" value   encapsulated within angle brackets.   In case that a group does not implement any multicast address, the   group lookup returns every group lookup with a "/rd-group" value   encapsulated within angle brackets.  Otherwise, the group lookup   returns the multicast address of the group inside angle brackets.   Using the Accept Option, the requester can control whether this list   is returned in CoRE Link Format ("application/link-format", default)   or its alternate content-formats ("application/link-format+json" or   "application/link-format+cbor").   The page and count parameters are used to obtain lookup results in   specified increments using pagination, where count specifies how many   links to return and page specifies which subset of links organized in   sequential pages , each containing 'count' links, starting with link   zero and page zero.  Thus, specifying count of 10 and page of 0 will   return the first 10 links in the result set (links 0-9).  Count = 10   and page = 1 will return the next 'page' containing links 10-19, and   so on.   Multiple query parameters MAY be included in a lookup, all included   parameters MUST match for a resource to be returned.  The   character'*' MAY be included at the end of a parameter value as a   wildcard operator.   The rd-lookup interface MAY use any set of query parameters to match   the registered attributes and relations.  In addition, this interface   MAY be used with queries that specify domains, endpoints, and groups.   For example, a domain lookup filtering on groups would return a list   of domains that contain the specified groups.  An endpoint lookup   filtering on groups would return a list of endpoints that are in the   specified groups.   The lookup interface is specified as follows:Shelby, et al.           Expires January 8, 2017               [Page 28]Internet-Draft           CoRE Resource Directory               July 2016   Interaction:  Client -> RD   Method:  GET   URI Template:  /{+rd-lookup-base}/{lookup-      type}{?d,ep,gp,et,rt,page,count,resource-param}   URI Template Variables:      rd-lookup-base :=  RD Lookup Function Set path (mandatory).  This         is the path of the RD Lookup Function Set. An RD SHOULD use the         value "rd-lookup" for this variable whenever possible.      lookup-type :=  ("d", "ep", "res", "gp") (mandatory) This variable         is used to select the kind of lookup to perform (domain,         endpoint, resource, or group).      ep :=  Endpoint name (optional).  Used for endpoint, group and         resource lookups.      d :=  Domain (optional).  Used for domain, group, endpoint and         resource lookups.      res :=  resource (optional).  Used for domain, group, endpoint and         resource lookups.      gp := Group name (optional).  Used for endpoint, group and      resource lookups.      page :=  Page (optional).  Parameter can not be used without the         count parameter.  Results are returned from result set in pages         that contain 'count' links starting from index (page * count).         Page numbering starts with zero.      count :=  Count (optional).  Number of results is limited to this         parameter value.  If the page parameter is also present, the         response MUST only include 'count' links starting with the         (page * count) link in the result set from the query.  If the         count parameter is not present, then the response MUST return         all matching links in the result set.  Link numbering starts         with zero.      rt :=  Resource type (optional).  Used for group, endpoint and         resource lookups.      et :=  Endpoint type (optional).  Used for group, endpoint and         resource lookups.Shelby, et al.           Expires January 8, 2017               [Page 29]Internet-Draft           CoRE Resource Directory               July 2016      resource-param :=  Link attribute parameters (optional).  Any link         attribute as defined in Section 4.1 of [RFC6690], used for         resource lookups.      Content-Format:  application/link-format (optional)      Content-Format:  application/link-format+json (optional)      Content-Format:  application/link-format+cbor (optional)   The following responses codes are defined for this interface:   Success:  2.05 "Content" or 200 "OK" with an "application/link-      format", "application/link-format+cbor", or "application/link-      format+json" payload containing matching entries for the lookup.   Failure:  4.04 "Not Found" or 404 "Not Found" in case no matching      entry is found for a unicast request.   Failure:  No error response to a multicast request.   Failure:  4.00 "Bad Request" or 400 "Bad Request".  Malformed      request.   Failure:  5.03 "Service Unavailable" or 503 "Service Unavailable".      Service could not perform the operation.   HTTP support:  YES   The examples in this section assume a CoAP host with IP address   FDFD::123 and a default CoAP port 61616.  HTTP hosts are possible and   do not change the nature of the examples.\   The following example shows a client performing a resource lookup:   Req: GET /rd-lookup/res?rt=temperature   Res: 2.05 Content   <coap://[FDFD::123]:61616/temp>;rt="temperature"   The following example shows a client performing an endpoint type   lookup:   Req: GET /rd-lookup/ep?et=power-node   Res: 2.05 Content   <coap://[FDFD::123]:61616>;ep="node5",   <coap://[FDFD::123]:61616>;ep="node7"Shelby, et al.           Expires January 8, 2017               [Page 30]Internet-Draft           CoRE Resource Directory               July 2016   The following example shows a client performing a domain lookup:   Req: GET /rd-lookup/d   Res: 2.05 Content   <>;d="domain1",   <>;d="domain2"   The following example shows a client performing a group lookup for   all groups:   Req: GET /rd-lookup/gp   Res: 2.05 Content   <>;gp="lights1";d="example.com"   <>;gp="lights2";d="ecample.com"   The following example shows a client performing a lookup for all   endpoints in a particular group:   Req: GET /rd-lookup/ep?gp=lights1   Res: 2.05 Content   <coap://[FDFD::123]:61616>;ep="node1",   <coap://[FDFD::123]:61616>;ep="node2"   The following example shows a client performing a lookup for all   groups an endpoint belongs to:   Req: GET /rd-lookup/gp?ep=node1   Res: 2.05 Content   <>;gp="lights1"   The following example shows a client performing a paginated lookupShelby, et al.           Expires January 8, 2017               [Page 31]Internet-Draft           CoRE Resource Directory               July 2016   Req: GET /rd-lookup/res?page=0&count=5   Res: 2.05 Content   <coap://[FDFD::123]:61616/res/0>;rt=sensor;ct=60   <coap://[FDFD::123]:61616/res/1>;rt=sensor;ct=60   <coap://[FDFD::123]:61616/res/2>;rt=sensor;ct=60   <coap://[FDFD::123]:61616/res/3>;rt=sensor;ct=60   <coap://[FDFD::123]:61616/res/4>;rt=sensor;ct=60   Req: GET /rd-lookup/res?page=1&count=5   Res: 2.05 Content   <coap://[FDFD::123]:61616/res/5>;rt=sensor;ct=60   <coap://[FDFD::123]:61616/res/6>;rt=sensor;ct=60   <coap://[FDFD::123]:61616/res/7>;rt=sensor;ct=60   <coap://[FDFD::123]:61616/res/8>;rt=sensor;ct=60   <coap://[FDFD::123]:61616/res/9>;rt=sensor;ct=609.  New Link-Format Attributes   When using the CoRE Link Format to describe resources being   discovered by or posted to a resource directory service, additional   information about those resources is useful.  This specification   defines the following new attributes for use in the CoRE Link Format   [RFC6690]:      link-extension    = ( "ins" "=" quoted-string ) ; Max 63 bytes      link-extension    = ( "exp" )9.1.  Resource Instance attribute 'ins'   The Resource Instance "ins" attribute is an identifier for this   resource, which makes it possible to distinguish it from other   similar resources.  This attribute is similar in use to the   <Instance> portion of a DNS-SD record (see Section 10.1, and SHOULD   be unique across resources with the same Resource Type attribute in   the domain it is used.  A Resource Instance might be a descriptive   string like "Ceiling Light, Room 3", a short ID like "AF39" or a   unique UUID or iNumber.  This attribute is used by a Resource   Directory to distinguish between multiple instances of the same   resource type within the directory.   This attribute MUST be no more than 63 bytes in length.  The resource   identifier attribute MUST NOT appear more than once in a link   description.  This attribute MAY be used as a query parameter in the   RD Lookup Function Set defined in Section 7.Shelby, et al.           Expires January 8, 2017               [Page 32]Internet-Draft           CoRE Resource Directory               July 20169.2.  Export attribute 'exp'   The Export "exp" attribute is used as a flag to indicate that a link   description MAY be exported by a resource directory to external   directories.   The CoRE Link Format is used for many purposes between CoAP   endpoints.  Some are useful mainly locally, for example checking the   observability of a resource before accessing it, determining the size   of a resource, or traversing dynamic resource structures.  However,   other links are very useful to be exported to other directories, for   example the entry point resource to a functional service.  This   attribute MAY be used as a query parameter in the RD Lookup Function   Set defined in Section 7.10.  DNS-SD Mapping   CoRE Resource Discovery is intended to support fine-grained discovery   of hosted resources, their attributes, and possibly other resource   relations [RFC6690].  In contrast, service discovery generally refers   to a coarse-grained resolution of an endpoint's IP address, port   number, and protocol.   Resource and service discovery are complementary in the case of large   networks, where the latter can facilitate scaling.  This document   defines a mapping between CoRE Link Format attributes and DNS-Based   Service Discovery [RFC6763] fields that permits discovery of CoAP   services by either method.10.1.  DNS-based Service discovery   DNS-Based Service Discovery (DNS-SD) defines a conventional method of   configuring DNS PTR, SRV, and TXT resource records to facilitate   discovery of services (such as CoAP servers in a subdomain) using the   existing DNS infrastructure.  This section gives a brief overview of   DNS-SD; see [RFC6763] for a detailed specification.   DNS-SD service names are limited to 255 octets and are of the form:   Service Name = <Instance>.<ServiceType>.<Domain>.   The service name is the label of SRV/TXT resource records.  The SRV   RR specifies the host and the port of the endpoint.  The TXT RR   provides additional information in the form of key/value pairs.   The <Domain> part of the service name is identical to the global (DNS   subdomain) part of the authority in URIs that identify servers or   groups of servers.Shelby, et al.           Expires January 8, 2017               [Page 33]Internet-Draft           CoRE Resource Directory               July 2016   The <ServiceType> part is composed of at least two labels.  The first   label of the pair is the application protocol name [RFC6335] preceded   by an underscore character.  The second label indicates the transport   and is always "_udp" for UDP-based CoAP services.  In cases where   narrowing the scope of the search may be useful, these labels may be   optionally preceded by a subtype name followed by the "_sub" label.   An example of this more specific <ServiceType> is   "light._sub._dali._udp".   A default <Instance> part of the service name may be set at the   factory or during the commissioning process.  It SHOULD uniquely   identify an instance of <ServiceType> within a <Domain>.  Taken   together, these three elements comprise a unique name for an SRV/ TXT   record pair within the DNS subdomain.   The granularity of a service name MAY be that of a host or group, or   it could represent a particular resource within a CoAP server.  The   SRV record contains the host name (AAAA record name) and port of the   service while protocol is part of the service name.  In the case   where a service name identifies a particular resource, the path part   of the URI must be carried in a corresponding TXT record.   A DNS TXT record is in practice limited to a few hundred octets in   length, which is indicated in the resource record header in the DNS   response message.  The data consists of one or more strings   comprising a key=value pair.  By convention, the first pair is   txtver=<number> (to support different versions of a service   description).10.2.  mapping ins to <Instance>   The Resource Instance "ins" attribute maps to the <Instance> part of   a DNS-SD service name.  It is stored directly in the DNS as a single   DNS label of canonical precomposed UTF-8 [RFC3629] "Net-Unicode"   (Unicode Normalization Form C) [RFC5198] text.  However, to the   extent that the "ins" attribute may be chosen to match the DNS host   name of a service, it SHOULD use the syntax defined in Section 3.5 of   [RFC1034] and Section 2.1 of [RFC1123].   The <Instance> part of the name of a service being offered on the   network SHOULD be configurable by the user setting up the service, so   that he or she may give it an informative name.  However, the device   or service SHOULD NOT require the user to configure a name before it   can be used.  A sensible choice of default name can allow the device   or service to be accessed in many cases without any manual   configuration at all.  The default name should be short and   descriptive, and MAY include a collision-resistant substring such as   the lower bits of the device's MAC address, serial number,Shelby, et al.           Expires January 8, 2017               [Page 34]Internet-Draft           CoRE Resource Directory               July 2016   fingerprint, or other identifier in an attempt to make the name   relatively unique.   DNS labels are currently limited to 63 octets in length and the   entire service name may not exceed 255 octets.10.3.  Mapping rt to <ServiceType>   The resource type "rt" attribute is mapped into the <ServiceType>   part of a DNS-SD service name and SHOULD conform to the reg-rel-type   production of the Link Format defined in Section 2 of [RFC6690].  The   "rt" attribute MUST be composed of at least a single Net-Unicode text   string, without underscore '_' or period '.' and limited to 15 octets   in length, which represents the application protocol name.  This   string is mapped to the DNS-SD <ServiceType> by prepending an   underscore and appending a period followed by the "_udp" label.  For   example, rt="dali" is mapped into "_dali._udp".   The application protocol name may be optionally followed by a period   and a service subtype name consisting of a Net-Unicode text string,   without underscore or period and limited to 63 octets.  This string   is mapped to the DNS-SD <ServiceType> by appending a period followed   by the "_sub" label and then appending a period followed by the   service type label pair derived as in the previous paragraph.  For   example, rt="dali.light" is mapped into "light._sub._dali._udp".   The resulting string is used to form labels for DNS-SD records which   are stored directly in the DNS.10.4.  Domain mapping   DNS domains may be derived from the "d" attribute.  The domain   attribute may be suffixed with the zone name of the authoritative DNS   server to generate the domain name.  The "ep" attribute is prefixed   to the domain name to generate the FQDN to be stored into DNS with an   AAAA RR.10.5.  TXT Record key=value strings   A number of [RFC6763] key/value pairs are derived from link-format   information, to be exported in the DNS-SD as key=value strings in a   TXT record ([RFC6763], Section 6.3).   The resource <URI> is exported as key/value pair "path=<URI>".   The Interface Description "if" attribute is exported as key/value   pair "if=<Interface Description>".Shelby, et al.           Expires January 8, 2017               [Page 35]Internet-Draft           CoRE Resource Directory               July 2016   The DNS TXT record can be further populated by importing any other   resource description attributes as they share the same key=value   format specified in Section 6 of [RFC6763].10.6.  Importing resource links into DNS-SD   Assuming the ability to query a Resource Directory or multicast a GET   (?exp) over the local link, CoAP resource discovery may be used to   populate the DNS-SD database in an automated fashion.  CoAP resource   descriptions (links) can be exported to DNS-SD for exposure to   service discovery by using the Resource Instance attribute as the   basis for a unique service name, composed with the Resource Type as   the <ServiceType>, and registered in the correct <Domain>.  The agent   responsible for exporting records to the DNS zone file SHOULD be   authenticated to the DNS server.  The following example shows an   agent discovering a resource to be exported:      Req: GET /rd-lookup/res?exp      Res: 2.05 Content      <coap://[FDFD::1234]:5683/light/1>;        exp;rt="dali.light";ins="Spot";                  d="office";ep="node1"   The agent subsequently registers the following DNS-SD RRs, assuming a   zone name "example.com" prefixed with "office":   node1.office.example.com.          IN AAAA        FDFD::1234   _dali._udp.office.example.com      IN PTR                             Spot._dali._udp.office.example.com   light._sub._dali._udp.example.com  IN PTR                             Spot._dali._udp.office.example.com   Spot._dali._udp.office.example.com IN SRV  0 0 5683                             node1.office.example.com.   Spot._dali._udp.office.example.com IN TXT                             txtver=1;path=/light/1   In the above figure the Service Name is chosen as   Spot._dali._udp.office.example.com without the light._sub service   prefix.  An alternative Service Name would be:   Spot.light._sub._dali._udp.office.example.com.11.  Security Considerations   The security considerations as described in Section 7 of [RFC5988]   and Section 6 of [RFC6690] apply.  The "/.well-known/core" resource   may be protected e.g. using DTLS when hosted on a CoAP server asShelby, et al.           Expires January 8, 2017               [Page 36]Internet-Draft           CoRE Resource Directory               July 2016   described in [RFC7252].  DTLS or TLS based security SHOULD be used on   all resource directory interfaces defined in this document.11.1.  Endpoint Identification and Authentication   An Endpoint is determined to be unique by an RD by the Endpoint   identifier parameter included during Registration, and any associated   TLS or DTLS security bindings.  An Endpoint MUST NOT be identified by   its protocol, port or IP address as these may change over the   lifetime of an Endpoint.   Every operation performed by an Endpoint or Client on a resource   directory SHOULD be mutually authenticated using Pre-Shared Key, Raw   Public Key or Certificate based security.  Endpoints using a   Certificate MUST include the Endpoint identifier as the Subject of   the Certificate, and this identifier MUST be checked by a resource   directory to match the Endpoint identifier included in the   Registration message.11.2.  Access Control   Access control SHOULD be performed separately for the RD Function Set   and the RD Lookup Function Set, as different endpoints may be   authorized to register with an RD from those authorized to lookup   endpoints from the RD.  Such access control SHOULD be performed in as   fine-grained a level as possible.  For example access control for   lookups could be performed either at the domain, endpoint or resource   level.11.3.  Denial of Service Attacks   Services that run over UDP unprotected are vulnerable to unknowingly   become part of a DDoS attack as UDP does not require return   routability check.  Therefore, an attacker can easily spoof the   source IP of the target entity and send requests to such a service   which would then respond to the target entity.  This can be used for   large-scale DDoS attacks on the target.  Especially, if the service   returns a response that is order of magnitudes larger than the   request, the situation becomes even worse as now the attack can be   amplified.  DNS servers have been widely used for DDoS amplification   attacks.  There is also a danger that NTP Servers could become   implicated in denial-of-service (DoS) attacks since they run on   unprotected UDP, there is no return routability check, and they can   have a large amplification factor.  The responses from the NTP server   were found to be 19 times larger than the request.  A Resource   Directory (RD) which responds to wild-card lookups is potentially   vulnerable if run with CoAP over UDP.  Since there is no return   routability check and the responses can be significantly larger thanShelby, et al.           Expires January 8, 2017               [Page 37]Internet-Draft           CoRE Resource Directory               July 2016   requests, RDs can unknowingly become part of a DDoS amplification   attack.  Therefore, it is RECOMMENDED that implementations ensure   return routability.  This can be done, for example by responding to   wild card lookups only over DTLS or TLS or TCP.12.  IANA Considerations12.1.  Resource Types   "core.rd", "core.rd-group" and "core.rd-lookup" resource types need   to be registered with the resource type registry defined by   [RFC6690].12.2.  Link Extension   The "exp" and "ins" attributes need to be registered when a future   Web Linking link-extension registry is created (e.g. in RFC5988bis).12.3.  IPv6 ND Resource Directory Address Option   This document registers one new ND option type under the subregistry   "IPv6 Neighbor Discovery Option Formats":   o  Resource Directory address Option (38)12.4.  RD Parameter Registry   This specification defines a new sub-registry for registration and   lookup parameters called "RD Parameters" under "CoRE Parameters".   Although this specification defines a basic set of parameters, it is   expected that other standards that make use of this interface will   define new ones.   Each entry in the registry must include the human readable name of   the parameter, the query parameter, validity requirements if any and   a description.  The query parameter MUST be a valid URI query key   [RFC3986].   Initial entries in this sub-registry are as follows:Shelby, et al.           Expires January 8, 2017               [Page 38]Internet-Draft           CoRE Resource Directory               July 2016   +-----------+-------+---------------+-------------------------------+   | Name      | Query | Validity      | Description                   |   +-----------+-------+---------------+-------------------------------+   | Endpoint  | ep    |               | Name of the endpoint, max 63  |   | Name      |       |               | bytes                         |   | Lifetime  | lt    | 60-4294967295 | Lifetime of the registration  |   |           |       |               | in seconds                    |   | Domain    | d     |               | Domain to which this endpoint |   |           |       |               | belongs                       |   | Endpoint  | et    |               | Semantic name of the endpoint |   | Type      |       |               |                               |   | Context   | con   | URI           | The scheme, address and port  |   |           |       |               | at which this server is       |   |           |       |               | available                     |   | Resource  | res   |               | Name of the resource          |   | Name      |       |               |                               |   | Group     | gp    |               | Name of a group in the RD     |   | Name      |       |               |                               |   | Page      | page  | Integer       | Used for pagination           |   | Count     | count | Integer       | Used for pagination           |   | Resource  | ins   |               | Instance Identifier           |   | Instance  |       |               |                               |   | Export    | exp   |               | A link MAY be exported to     |   |           |       |               | another Resource Directory    |   +-----------+-------+---------------+-------------------------------+                          Table 1: RD Parameters   The IANA policy for future additions to the sub-registry is "Expert   Review" as described in [RFC5226].13.  Examples   Examples are added here.13.1.  Lighting Installation   This example shows a simplified lighting installation which makes use   of the Resource Directory (RD) with a CoAP interface to facilitate   the installation and start up of the application code in the lights   and sensors.  In particular, the example leads to the definition of a   group and the enabling of the corresponding multicast address.  No   conclusions must be drawn on the realization of actual installation   or naming procedures, because the example only "emphasizes" some of   the issues that may influence the use of the RD and does not pretend   to be normative.Shelby, et al.           Expires January 8, 2017               [Page 39]Internet-Draft           CoRE Resource Directory               July 201613.1.1.  Installation Characteristics   The example assumes that the installation is managed.  That means   that a Commissioning Tool (CT) is used to authorize the addition of   nodes, name them, and name their services.  The CT can be connected   to the installation in many ways: the CT can be part of the   installation network, connected by WiFi to the installation network,   or connected via GPRS link, or other method.   It is assumed that there are two naming authorities for the   installation: (1) the network manager that is responsible for the   correct operation of the network and the connected interfaces, and   (2) the lighting manager that is responsible for the correct   functioning of networked lights and sensors.  The result is the   existence of two naming schemes coming from the two managing   entities.   The example installation consists of one presence sensor, and two   luminaries, luminary1 and luminary2, each with their own wireless   interface.  Each luminary contains three lamps: left, right and   middle.  Each luminary is accessible through one endpoint.  For each   lamp a resource exists to modify the settings of a lamp in a   luminary.  The purpose of the installation is that the presence   sensor notifies the presence of persons to a group of lamps.  The   group of lamps consists of: middle and left lamps of luminary1 and   right lamp of luminary2.   Before commissioning by the lighting manager, the network is   installed and access to the interfaces is proven to work by the   network manager.   At the moment of installation, the network under installation is not   necessarily connected to the DNS infra structure.  Therefore, SLAAC   IPv6 addresses are assigned to CT, RD, luminaries and sensor shown in   Table 2 below:                   +--------------------+--------------+                   | Name               | IPv6 address |                   +--------------------+--------------+                   | luminary1          | FDFD::ABCD:1 |                   | luminary2          | FDFD::ABCD:2 |                   | Presence sensor    | FDFD::ABCD:3 |                   | Resource directory | FDFD::ABCD:0 |                   +--------------------+--------------+                    Table 2: interface SLAAC addressesShelby, et al.           Expires January 8, 2017               [Page 40]Internet-Draft           CoRE Resource Directory               July 2016   In Section 13.1.2 the use of resource directory during installation   is presented.  In Section 13.1.3 the connection to DNS is discussed.13.1.2.  RD entries   It is assumed that access to the DNS infrastructure is not always   possible during installation.  Therefore, the SLAAC addresses are   used in this section.   For discovery, the resource types (rt) of the devices are important.   The lamps in the luminaries have rt: light, and the presence sensor   has rt: p-sensor.  The endpoints have names which are relevant to the   light installation manager.  In this case luminary1, luminary2, and   the presence sensor are located in room 2-4-015, where luminary1 is   located at the window and luminary2 and the presence sensor are   located at the door.  The endpoint names reflect this physical   location.  The middle, left and right lamps are accessed via path   /light/middle, /light/left, and /light/right respectively.  The   identifiers relevant to the Resource Directory are shown in Table 3   below:   +----------------+------------------+---------------+---------------+   | Name           | endpoint         | resource path | resource type |   +----------------+------------------+---------------+---------------+   | luminary1      | lm_R2-4-015_wndw | /light/left   | light         |   | luminary1      | lm_R2-4-015_wndw | /light/middle | light         |   | luminary1      | lm_R2-4-015_wndw | /light/right  | light         |   | luminary2      | lm_R2-4-015_door | /light/left   | light         |   | luminary2      | lm_R2-4-015_door | /light/middle | light         |   | luminary2      | lm_R2-4-015_door | /light/right  | light         |   | Presence       | ps_R2-4-015_door | /ps           | p-sensor      |   | sensor         |                  |               |               |   +----------------+------------------+---------------+---------------+                  Table 3: Resource Directory identifiers   The CT inserts the endpoints of the luminaries and the sensor in the   RD using the Context parameter (con) to specify the interface   address:Shelby, et al.           Expires January 8, 2017               [Page 41]Internet-Draft           CoRE Resource Directory               July 2016   Req: POST coap://[FDFD::ABCD:0]/rd     ?ep=lm_R2-4-015_wndw&con=coap://[FDFD::ABCD:1]   Payload:   </light/left>;rt="light"; d="R2-4-015",   </light/middle>;rt="light"; d="R2-4-015",   </light/right>;rt="light";d="R2-4-015"   Res: 2.01 Created   Location: /rd/4521   Req: POST coap://[FDFD::ABCD:0]/rd     ?ep=lm_R2-4-015_door&con=coap://[FDFD::ABCD:2]   Payload:   </light/left>;rt="light"; d="R2-4-015",   </light/middle>;rt="light"; d="R2-4-015",   </light/right>;rt="light"; d="R2-4-015"   Res: 2.01 Created   Location: /rd/4522   Req: POST coap://[FDFD::ABCD:0]/rd     ?ep=ps_R2-4-015_door&con=coap://[FDFD::ABCD:3]   Payload:   </ps>;rt="p-sensor"; d="R2-4-015"   Res: 2.01 Created   Location: /rd/4523   The domain name d="R2-4-015" has been added for an efficient lookup   because filtering on "ep" name is more awkward.  The same domain name   is communicated to the two luminaries and the presence sensor by the   CT.   The group is specified in the RD.  The Context parameter is set to   the site-local multicast address allocated to the group.  In the POST   in the example below, these two endpoints and the endpoint of the   presence sensor are registered as members of the group.   Req: POST coap://[FDFD::ABCD:0]/rd-group   ?gp=grp_R2-4-015;con="coap//[FF05::1]";exp;ins="grp1234"   Payload:   <>ep=lm_R2-4-015_wndw,   <>ep=lm_R2-4-015_door,   <>ep=ps_R2-4-015_door   Res: 2.01 Created   Location: /rd-group/501Shelby, et al.           Expires January 8, 2017               [Page 42]Internet-Draft           CoRE Resource Directory               July 2016   After the filling of the RD by the CT, the application in the   luminaries can learn to which groups they belong, and enable their   interface for the multicast address.   The luminary, knowing its domain, queries the RD for the endpoint   with rt=light and d=R2-4-015.  The RD returns all endpoints in the   domain.   Req: GET coap://[FDFD::ABCD:0]/rd-lookup/ep     ?d=R2-4-015;rt=light   Res: 2.05 Content   <coap://[FDFD::ABCD:1]>;     ep="lm_R2-4-015_wndw",   <coap://[FDFD::ABCD:2]>;      ep="lm_R2-4-015_door"   Knowing its own IPv6 address, the luminary discovers its endpoint   name.  With the endpoint name the luminary queries the RD for all   groups to which the endpoint belongs.   Req: GET coap://[FDFD::ABCD:0]/rd-lookup/gp     ?ep=lm_R2-4-015_wndw   Res: 2.05 Content   <coap://[FF05::1]>;gp="grp_R2-4-015"   From the context parameter value, the luminary learns the multicast   address of the multicast group.   Alternatively, the CT can communicate the multicast address directly   to the luminaries by using the "coap-group" resource specified in   [RFC7390].   Req: POST //[FDFD::ABCD:1]/coap-group             Content-Format: application/coap-group+json          { "a": "[FF05::1]",             "n": "grp_R2-4-015"}   Res: 2.01 Created   Location-Path: /coap-group/1   Dependent on the situation only the address ,"a", or the name, "n",   is specified in the coap-group resource.Shelby, et al.           Expires January 8, 2017               [Page 43]Internet-Draft           CoRE Resource Directory               July 201613.1.3.  DNS entries   It may be profitable to discover the light groups for applications,   which are unaware ot the existence of the RD.  An agent needs to   query the RD to return all groups which are exported to be inserted   into DNS.      Req: GET /rd-lookup/gp?exp      Res: 2.05 Content      <coap://[FF05::1]/>;exp;gp="grp_R2-4-015;ins="grp1234";   ep="lm_R2-4-015_wndw";   ep="lm_R2-4-015_door   The group with FQDN grp_R2-4-015.bc.example.com can be entered into   the DNS by the agent.  The accompanying instance name is grp1234.   The <ServiceType> is chosen to be _group._udp.  The agent enters the   following RRs into the DNS.   grp_R2-4-015.bc.example.com.        IN AAAA            FF05::1   _group._udp.bc.example.com          IN PTR                               grp1234._group._udp.bc.example.com   grp1234._group._udp.bc.example.com  IN SRV  0 0 5683                                grp_R2-4-015_door.bc.example.com.   grp1234._group._udp.bc.example.com  IN TXT                                        txtver=1;path=/light/grp1   From then on applications, not familiar with the existence of the RD,   can use DNS to access the lighting group.13.2.  OMA Lightweight M2M (LWM2M) Example   This example shows how the OMA LWM2M specification makes use of   Resource Directory (RD).   OMA LWM2M is a profile for device services based on CoAP(OMA Name   Authority).  LWM2M defines a simple object model and a number of   abstract interfaces and operations for device management and device   service enablement.   An LWM2M server is an instance of an LWM2M middleware service layer,   containing a Resource Directory along with other LWM2M interfaces   defined by the LWM2M specification.   CoRE Resource Directory (RD) is used to provide the LWM2M   Registration interface.Shelby, et al.           Expires January 8, 2017               [Page 44]Internet-Draft           CoRE Resource Directory               July 2016   LWM2M does not provide for registration domains and does not   currently use the rd-group or rd-lookup interfaces.   The LWM2M specification describes a set of interfaces and a resource   model used between a LWM2M device and an LWM2M server.  Other   interfaces, proxies, applications, and function sets are currently   out of scope for LWM2M.   The location of the LWM2M Server and RD Function Set is provided by   the LWM2M Bootstrap process, so no dynamic discovery of the RD   function set is used.  LWM2M Servers and endpoints are not required   to implement the ./well-known/core resource.13.2.1.  The LWM2M Object Model   The OMA LWM2M object model is based on a simple 2 level class   hierarchy consisting of Objects and Resources.   An LWM2M Resource is a REST endpoint, allowed to be a single value or   an array of values of the same data type.   An LWM2M Object is a resource template and container type that   encapsulates a set of related resources.  An LWM2M Object represents   a specific type of information source; for example, there is a LWM2M   Device Management object that represents a network connection,   containing resources that represent individual properties like radio   signal strength.   Since there may potentially be more than one of a given type object,   for example more than one network connection, LWM2M defines instances   of objects that contain the resources that represent a specific   physical thing.   The URI template for LWM2M consists of a base URI followed by Object,   Instance, and Resource IDs:   {/base-uri}{/object-id}{/object-instance}{/resource-id}{/resource-   instance}   The five variables given here are strings.  base-uri can also have   the special value "undefined" (sometimes called "null" in RFC 6570).   Each of the variables object-instance, resource-id, and resource-   instance can be the special value "undefined" only if the values   behind it in this sequence also are "undefined".  As a special case,   object-instance can be "empty" (which is different from "undefined")   if resource-id is not "undefined".  [_TEMPLATE_TODO]Shelby, et al.           Expires January 8, 2017               [Page 45]Internet-Draft           CoRE Resource Directory               July 2016   base-uri := Base URI for LWM2M resources or "undefined" for default   (empty) base URI   object-id := OMNA (OMA Name Authority) registered object ID (0-65535)   object-instance := Object instance identifier (0-65535) or   "undefined"/"empty" (see above)) to refer to all instances of an   object ID   resource-id := OMNA (OMA Name Authority) registered resource ID   (0-65535) or "undefined" to refer to all resources within an instance   resource-instance := Resource instance identifier or "undefined" to   refer to single instance of a resource   LWM2M IDs are 16 bit unsigned integers represented in decimal (no   leading zeroes except for the value 0) by URI format strings.  For   example, a LWM2M URI might be:   /1/0/1   The base uri is empty, the Object ID is 1, the instance ID is 0, the   resource ID is 1, and the resource instance is "undefined".  This   example URI points to internal resource 1, which represents the   registration lifetime configured, in instance 0 of a type 1 object   (LWM2M Server Object).13.2.2.  LWM2M Register Endpoint   LWM2M defines a registration interface based on the Resource   Directory Function Set, described in Section 6.  The URI of the LWM2M   Resource Directory function set is specified to be "/rd" as   recommended in Section 6.3.   LWM2M endpoints register object IDs, for example </1>, to indicate   that a particular object type is supported, and register object   instances, for example </1/0>, to indicate that a particular instance   of that object type exists.   Resources within the LWM2M object instance are not registered with   the RD, but may be discovered by reading the resource links from the   object instance using GET with a CoAP Content-Format of application/   link-format.  Resources may also be read as a structured object by   performing a GET to the object instance with a Content-Format of   senml+json.Shelby, et al.           Expires January 8, 2017               [Page 46]Internet-Draft           CoRE Resource Directory               July 2016   When an LWM2M object or instance is registered, this indicates to the   LWM2M server that the object and its resources are available for   management and service enablement (REST API) operations.   LWM2M endpoints may use the following RD registration parameters as   defined in Table 1 :   ep - Endpoint Name   lt - registration lifetime   Endpoint Name is mandatory, all other registration parameters are   optional.   Additional optional LWM2M registration parameters are defined:   +------------+-------+-------------------------------+--------------+   | Name       | Query | Validity                      | Description  |   +------------+-------+-------------------------------+--------------+   | Protocol   | b     | {"U",UQ","S","SQ","US","UQS"} | Available    |   | Binding    |       |                               | Protocols    |   |            |       |                               |              |   | LWM2M      | ver   | 1.0                           | Spec Version |   | Version    |       |                               |              |   |            |       |                               |              |   | SMS Number | sms   |                               | MSISDN       |   +------------+-------+-------------------------------+--------------+             Table 4: LWM2M Additional Registration Parameters   The following RD registration parameters are not currently specified   for use in LWM2M:   et - Endpoint Type   con - Context   The endpoint registration must include a payload containing links to   all supported objects and existing object instances, optionally   including the appropriate link-format relations.   Here is an example LWM2M registration payload:   </1>,</1/0>,</3/0>,</5>   This link format payload indicates that object ID 1 (LWM2M Server   Object) is supported, with a single instance 0 existing, object ID 3   (LWM2M Device object) is supported, with a single instance 0   existing, and object 5 (LWM2M Firmware Object) is supported, with no   existing instances.Shelby, et al.           Expires January 8, 2017               [Page 47]Internet-Draft           CoRE Resource Directory               July 201613.2.3.  Alternate Base URI   If the LWM2M endpoint exposes objects at a base URI other than the   default empty base path, the endpoint must register the base URI   using rt="oma.lwm2m".  An example link payload using alternate base   URI would be:   </my_lwm2m>;rt="oma.lwm2m",</my_lwm2m/1>,<my_lwm2m/1/0>,<my_lwm2m/5>   This link payload indicates that the lwm2m objects will be placed   under the base URI "/my_lwm2m" and that object ID 1 (server) is   supported, with a single instance 0 existing, and object 5 (firmware   update) is supported.13.2.4.  LWM2M Update Endpoint Registration   An LWM2M Registration update proceeds as described in Section 6.4,   and adds some optional parameter updates:   lt - Registration Lifetime   b - Protocol Binding   sms - MSISDN   link payload - new or modified links   A Registration update is also specified to be used to update the   LWM2M server whenever the endpoint's UDP port or IP address are   changed.13.2.5.  LWM2M De-Register Endpoint   LWM2M allows for de-registration using the delete method on the   returned location from the initial registration operation.  LWM2M de-   registration proceeds as described in Section 6.5.14.  Acknowledgments   Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders   Brandt, Matthieu Vial, Mohit Sethi, Sampo Ukkola and Linyi Tian have   provided helpful comments, discussions and ideas to improve and shape   this document.  Section 9 is based on an earlier draft by Kerry Lynn.   Zach would also like to thank his colleagues from the EU FP7 SENSEI   project, where many of the resource directory concepts were   originally developed.Shelby, et al.           Expires January 8, 2017               [Page 48]Internet-Draft           CoRE Resource Directory               July 201615.  Changelog   changes from -07 to -08   o  removed link target value returned from domain and group lookup      types   o  Maximum length of domain parameter 63 bytes for consistency with      group   o  removed option for simple POST of link data, don't require a      .well-known/core resource to accept POST data and handle it in a      special way; we already have /rd for that   o  add IPv6 ND Option for discovery of an RD   o  clarify group configuration section 6.1 that endpoints must be      registered before including them in a group   o  removed all superfluous client-server diagrams   o  simplified lighting example   o  introduced Commissioning Tool   o  RD-Look-up text is extended.   changes from -06 to -07   o  added text in the discovery section to allow content format hints      to be exposed in the discovery link attributes   o  editorial updates to section 9   o  update author information   o  minor text corrections   Changes from -05 to -06   o  added note that the PATCH section is contingent on the progress of      the PATCH method   changes from -04 to -05   o  added Update Endpoint Links using PATCH   o  http access made explicit in interface specificationShelby, et al.           Expires January 8, 2017               [Page 49]Internet-Draft           CoRE Resource Directory               July 2016   o  Added http examples   Changes from -03 to -04:   o  Added http response codes   o  Clarified endpoint name usage   o  Add application/link-format+cbor content-format   Changes from -02 to -03:   o  Added an example for lighting and DNS integration   o  Added an example for RD use in OMA LWM2M   o  Added Read Links operation for link inspection by endpoints   o  Expanded DNS-SD section   o  Added draft authors Peter van der Stok and Michael Koster   Changes from -01 to -02:   o  Added a catalogue use case.   o  Changed the registration update to a POST with optional link      format payload.  Removed the endpoint type update from the update.   o  Additional examples section added for more complex use cases.   o  New DNS-SD mapping section.   o  Added text on endpoint identification and authentication.   o  Error code 4.04 added to Registration Update and Delete requests.   o  Made 63 bytes a SHOULD rather than a MUST for endpoint name and      resource type parameters.   Changes from -00 to -01:   o  Removed the ETag validation feature.   o  Place holder for the DNS-SD mapping section.   o  Explicitly disabled GET or POST on returned Location.Shelby, et al.           Expires January 8, 2017               [Page 50]Internet-Draft           CoRE Resource Directory               July 2016   o  New registry for RD parameters.   o  Added support for the JSON Link Format.   o  Added reference to the Groupcomm WG draft.   Changes from -05 to WG Document -00:   o  Updated the version and date.   Changes from -04 to -05:   o  Restricted Update to parameter updates.   o  Added pagination support for the Lookup interface.   o  Minor editing, bug fixes and reference updates.   o  Added group support.   o  Changed rt to et for the registration and update interface.   Changes from -03 to -04:   o  Added the ins= parameter back for the DNS-SD mapping.   o  Integrated the Simple Directory Discovery from Carsten.   o  Editorial improvements.   o  Fixed the use of ETags.   o  Fixed tickets 383 and 372   Changes from -02 to -03:   o  Changed the endpoint name back to a single registration parameter      ep= and removed the h= and ins= parameters.   o  Updated REST interface descriptions to use RFC6570 URI Template      format.   o  Introduced an improved RD Lookup design as its own function set.   o  Improved the security considerations section.   o  Made the POST registration interface idempotent by requiring the      ep= parameter to be present.Shelby, et al.           Expires January 8, 2017               [Page 51]Internet-Draft           CoRE Resource Directory               July 2016   Changes from -01 to -02:   o  Added a terminology section.   o  Changed the inclusion of an ETag in registration or update to a      MAY.   o  Added the concept of an RD Domain and a registration parameter for      it.   o  Recommended the Location returned from a registration to be      stable, allowing for endpoint and Domain information to be changed      during updates.   o  Changed the lookup interface to accept endpoint and Domain as      query string parameters to control the scope of a lookup.16.  References16.1.  Normative References   [I-D.ietf-core-links-json]              Li, K., Rahman, A., and D. Bormann, "Representing CoRE              Formats in JSON and CBOR", draft-ietf-core-links-json-05              (work in progress), April 2016.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels", BCP 14, RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform              Resource Identifier (URI): Generic Syntax", STD 66,              RFC 3986, DOI 10.17487/RFC3986, January 2005,              <http://www.rfc-editor.org/info/rfc3986>.   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an              IANA Considerations Section in RFCs", BCP 26, RFC 5226,              DOI 10.17487/RFC5226, May 2008,              <http://www.rfc-editor.org/info/rfc5226>.   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988,              DOI 10.17487/RFC5988, October 2010,              <http://www.rfc-editor.org/info/rfc5988>.Shelby, et al.           Expires January 8, 2017               [Page 52]Internet-Draft           CoRE Resource Directory               July 2016   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.              Cheshire, "Internet Assigned Numbers Authority (IANA)              Procedures for the Management of the Service Name and              Transport Protocol Port Number Registry", BCP 165,              RFC 6335, DOI 10.17487/RFC6335, August 2011,              <http://www.rfc-editor.org/info/rfc6335>.   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,              and D. Orchard, "URI Template", RFC 6570,              DOI 10.17487/RFC6570, March 2012,              <http://www.rfc-editor.org/info/rfc6570>.   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,              <http://www.rfc-editor.org/info/rfc6690>.   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,              <http://www.rfc-editor.org/info/rfc6763>.   [RFC7396]  Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,              DOI 10.17487/RFC7396, October 2014,              <http://www.rfc-editor.org/info/rfc7396>.16.2.  Informative References   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,              <http://www.rfc-editor.org/info/rfc1034>.   [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts -              Application and Support", STD 3, RFC 1123,              DOI 10.17487/RFC1123, October 1989,              <http://www.rfc-editor.org/info/rfc1123>.   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November              2003, <http://www.rfc-editor.org/info/rfc3629>.   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,              <http://www.rfc-editor.org/info/rfc5198>.   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.              Bormann, "Neighbor Discovery Optimization for IPv6 over              Low-Power Wireless Personal Area Networks (6LoWPANs)",              RFC 6775, DOI 10.17487/RFC6775, November 2012,              <http://www.rfc-editor.org/info/rfc6775>.Shelby, et al.           Expires January 8, 2017               [Page 53]Internet-Draft           CoRE Resource Directory               July 2016   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer              Protocol (HTTP/1.1): Message Syntax and Routing",              RFC 7230, DOI 10.17487/RFC7230, June 2014,              <http://www.rfc-editor.org/info/rfc7230>.   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained              Application Protocol (CoAP)", RFC 7252,              DOI 10.17487/RFC7252, June 2014,              <http://www.rfc-editor.org/info/rfc7252>.   [RFC7390]  Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for              the Constrained Application Protocol (CoAP)", RFC 7390,              DOI 10.17487/RFC7390, October 2014,              <http://www.rfc-editor.org/info/rfc7390>.Editorial Comments[_TEMPLATE_TODO] This text needs some help from an RFC 6570 expert.Authors' Addresses   Zach Shelby   ARM   150 Rose Orchard   San Jose  95134   USA   Phone: +1-408-203-9434   Email: zach.shelby@arm.com   Michael Koster   SmartThings   665 Clyde Avenue   Mountain View  94043   USA   Phone: +1-707-502-5136   Email: Michael.Koster@smartthings.comShelby, et al.           Expires January 8, 2017               [Page 54]Internet-Draft           CoRE Resource Directory               July 2016   Carsten Bormann   Universitaet Bremen TZI   Postfach 330440   Bremen  D-28359   Germany   Phone: +49-421-218-63921   Email: cabo@tzi.org   Peter van der Stok   consultant   Phone: +31-492474673 (Netherlands), +33-966015248 (France)   Email: consultancy@vanderstok.org   URI:   www.vanderstok.orgShelby, et al.           Expires January 8, 2017               [Page 55]