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core                                                     P. van der Stok
Internet-Draft                                                consultant
Intended status: Informational                           B. Greevenbosch
Expires: November 9, 2014                            Huawei Technologies
                                                             May 8, 2014


                       CoAp Management Interfaces
                     draft-vanderstok-core-comi-04

Abstract

   The draft describes an interface based on CoAP to manage constrained
   devices via MIBs.  The proposed integration of CoAP with SNMP reduces
   the code- and application development complexity by accessing MIBs
   via a standard CoAP server.  The payload of the MIB request is CBOR
   based on JSON.  The mapping from SMI to CBOR is specified.  The
   introduction motivates the choices of CoMI with respect to
   utilization of YANG, NETCONF, SMI, CBOR, CoAP, and URI structure.

Note

   Discussion and suggestions for improvement are requested, and should
   be sent to core@ietf.org.

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 November 9, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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
     1.1.  Design considerations . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  CoAP Interface  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  MIB Function Set  . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  SNMP/MIB architecture . . . . . . . . . . . . . . . . . .   6
       3.1.1.  SNMP functions  . . . . . . . . . . . . . . . . . . .   7
       3.1.2.  MIB structure . . . . . . . . . . . . . . . . . . . .   7
     3.2.  CoMI Function Set . . . . . . . . . . . . . . . . . . . .   9
       3.2.1.  Single MIB values . . . . . . . . . . . . . . . . . .  10
       3.2.2.  multi MIB values  . . . . . . . . . . . . . . . . . .  12
       3.2.3.  Table row . . . . . . . . . . . . . . . . . . . . . .  14
       3.2.4.  MIB discovery . . . . . . . . . . . . . . . . . . . .  15
       3.2.5.  Error returns . . . . . . . . . . . . . . . . . . . .  16
   4.  Mapping SMI to CoMI payload . . . . . . . . . . . . . . . . .  16
     4.1.  CBOR format for MIB data  . . . . . . . . . . . . . . . .  16
     4.2.  Table generation  . . . . . . . . . . . . . . . . . . . .  17
     4.3.  Mapping SMI to CBOR . . . . . . . . . . . . . . . . . . .  18
       4.3.1.  General overview  . . . . . . . . . . . . . . . . . .  18
       4.3.2.  Conversion from YANG datatypes to CBOR datatypes  . .  18
       4.3.3.  Examples  . . . . . . . . . . . . . . . . . . . . . .  20
       4.3.4.  6LoWPAN MIB . . . . . . . . . . . . . . . . . . . . .  22
   5.  Trap functions  . . . . . . . . . . . . . . . . . . . . . . .  23
   6.  MIB access management . . . . . . . . . . . . . . . . . . . .  23
     6.1.  Notify destinations . . . . . . . . . . . . . . . . . . .  23
     6.2.  Conversion table management . . . . . . . . . . . . . . .  23
   7.  Error handling  . . . . . . . . . . . . . . . . . . . . . . .  24
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  26
   11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .  26
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  27
     12.2.  Informative References . . . . . . . . . . . . . . . . .  28
   Appendix A.  Notational Convention for CBOR data  . . . . . . . .  30
   Appendix B.  Example conversion table and instance for the LOWPAN



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                MIB  . . . . . . . . . . . . . . . . . . . . . . . .  31
     B.1.  Generating the convTableId  . . . . . . . . . . . . . . .  31
     B.2.  Generating the string numbers . . . . . . . . . . . . . .  31
     B.3.  Example instance  . . . . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  37

1.  Introduction

   The Constrained RESTful Environments (CoRE) working group aims at
   Machine to Machine (M2M) applications such as smart energy and
   building control.

   Small M2M devices need to be managed in an automatic fashion to
   handle the large quantities of devices that are expected to be
   installed in future installations.  The management protocol of choice
   for Internet is SNMP [RFC3410] as is testified by the large number of
   Management Information Base (MIB) [RFC3418]  specifications currently
   published [STD0001].  More recently, the NETCONF protocol [RFC6241]
   was developed with an extended set of messages using XML [XML] as
   data format.  The data syntax is specified with YANG [RFC6020] and a
   mapping from Yang to XML is specified.  In [RFC6643]  SMIv2 syntax is
   expressed in Yang.  Contrary to SNMP and also CoAP, NETCONF assumes
   persistent connections for example provided by SSH.  The NETCONF
   protocol provides operations to retrieve, configure, copy, and delete
   configuration data-stores.  Configuring data-stores distinguishes
   NETCONF from SNMP which operates on standardized MIBs.

   The CoRE Management Interface (CoMI) is intended to work on
   standardized data-sets in a stateless client-server fashion and is
   thus closer to SNMP than to NETCONF.  Standardized data sets promote
   interoperability between small devices and applications from
   different manufacturers.  Stateless communication is encouraged to
   keep communications simple and the amount of state information small
   in line with the design objectives of 6lowpan [RFC4944] [RFC6775],
   RPL [RFC6650], and CoAP [I-D.ietf-core-coap].

   The draft [I-D.bierman-netconf-restconf] describes a restful
   interface to NETCONF data stores and approaches the CoMI approach.
   CoMI uses SMI encoded in CBOR, and CoAP/UDP to access MIBs, whereas
   RESTCONF uses YANG encoded in JSON and HTTP/TCP to access NETCONF
   data stores.  CoMI is more low resource oriented than RESTCONF is,
   and only supports the methods GET, PUT, POST and DELETE.  RESTCONF
   also uses uses the HTTP methods HEAD, OPTIONS and PATCH, which are
   not available in CoAP.

   Given the automatic conversion from SMI to YANG, from YANG to JSON,
   from YANG to XML and from JSON to CBOR, the transported data format
   is not strongly related to the chosen management protocol.



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   Currently, managed devices need to support two protocols: CoAP and
   SNMP.  When the MIB can be accessed with the CoAP protocol, the SNMP
   protocol can be replaced with the CoAP protocol.  This arrangement
   reduces the code complexity of the stack in the constrained device,
   and harmonizes applications development.

   The objective of CoMI is to provide a CoAP based Function Set that
   reads and sets values of MIB variables in devices to (1) initialize
   parameter values at start-up, (2) acquire statistics during
   operation, and (3) maintain nodes by adjusting parameter values
   during operation.

   The payload of CoMI is encoded in CBOR [RFC7049] which is similar to
   JSON [JSON], but has a binary format and hence has more coding
   efficiency.  CoMI is intended for small devices.  The JSON overhead
   can be prohibitive.  It is therefore chosen to transport CBOR in the
   payload.  CBOR, like BER used for SNMP, transports the data type in
   the payload.

   The end goal of CoMI is to provide information exchange over the CoAP
   transport protocol in a uniform manner as a first step to the full
   management functionality as specified in
   [I-D.ersue-constrained-mgmt].

1.1.  Design considerations

   COMI supports discovery of resources, accompanied by reading, writing
   and notification of resource values.  As such it is close to the
   device management of the Open Mobile Alliance described in [OMA].
   However, the structure of the MIB does not reflect the structure of
   the OMA management objects.  It is assumed that the structure and
   semantics of the management data are the most important aspect of a
   standard like the MIB.  The right path forward to integrate OMA
   management with COMI is the adapatation of the MIB structure by OMA.

   COMI supports the conversion of SMIv2 via YANG to CBOR.  Assuming
   that CBOR is used for the tanport of NETCONF data, the utilization of
   the CBOR conversion table to reduce payload size can be envisaged for
   NETCONF data as well.

   COMI uses a simple URI to access the MIB resources.  Complexity
   introduced by module name, context specification, or row selection,
   is expressed with uri-query attributes.  The choice for uri-query
   attributes makes the uri structure less context dependent.







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1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Readers of this specification are required to be familiar with all
   the terms and concepts discussed in [RFC3410], [RFC3416], and
   [RFC2578].

   Core Management Interface (CoMI) specifies the profile of Function
   Sets which access MIBs with the purpose of managing the operation of
   constrained devices in a network.

   The following list defines the terms used in this document:

   Managing Entity:  An entity that manages one or more managed devices.
      Within the CoMI framework, the managing entity acts as a CoAP
      client for CoMI.

   Managed Device:  An entity that is being managed.  The managed device
      acts as a CoAP server for CoMI.

   NOTE: It is assumed that the managed device is the most constrained
   entity.  The managing entity might be more capable, however this is
   not necessarily the case.

   The following list contains the abbreviations used in this document.

   OID:  ASN.1 OBJECT-IDENTIFIER, which is used to uniquely identify MIB
      objects in the managed device.

2.  CoAP Interface

   In CoRE a group of links can constitute a Function Set. The format of
   the links is specified in [I-D.ietf-core-interfaces].  This note
   specifies a Management Function Set. CoMI end-points that implement
   the CoMI management protocol support at least one discoverable
   management resource of resource type (rt): core.mg, with path: /mg,
   where mg is short-hand for management.  The mg resource has two sub-
   resources accessible with the paths:

   o  MIB with path /mg/mib and a CBOR content format.

   o  conv with path /mg/conv and CBOR content format.

   The mib resource provides access to the MIBs as described in
   Section 3.2.  The conv resource provides access to a table that maps



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   a string to CBOR identifier, as described in Section 4.1.  The mib
   and conv resources are introduced as sub resources to mg to permit
   later additions to CoMI mg resource.

   The profile of the management function set, with IF=core.mg.mib, is
   shown in the table below, following the guidelines of
   [I-D.ietf-core-interfaces]:

    +-----------------+-----------+---------------+-------------------+
    | name            | path      | RT            | Data Type         |
    +-----------------+-----------+---------------+-------------------+
    | Management      | /mg       | core.mg       | n/a               |
    |                 |           |               |                   |
    | MIB             | /mg/mib   | core.mg.mib   | application/cbor  |
    |                 |           |               |                   |
    | conv            | /mg/conv  | core.mg.conv  | application/cbor  |
    +-----------------+-----------+---------------+-------------------+

3.  MIB Function Set

   The MIB Function Set provides a CoAP interface to perform equivalent
   functions to the ones provided by SNMP.  Section 3.1 explains the
   structure of SNMP Protocol Data Units (PDU), their transport, and the
   structure of the MIB modules.  An excellent overview of the documents
   describing the SNMP/MIB architecture is provided in section 7 of
   [RFC3410].

3.1.  SNMP/MIB architecture

   The architecture of the Internet Standard management framework
   consists of:

   o  A data definition language that is referred to as Structure of
      Management Information (SMI)[RFC2578].

   o  The Management Information Base (MIB) which contains the
      information to be managed and is defined for each specific
      function to be managed [RFC3418].

   o  A protocol definition referred to as Simple Network Management
      Protocol (SNMP) [RFC3416].

   o  Security and administration that provides SNMP message based
      security on the basis of the user-based security model [RFC3414].

   o  A management domain definition where a SNMP entity has access to a
      collection of management information called a "context" [RFC3411].




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   In addition [RFC4088] describes a URI scheme to refer to a specific
   MIB instance.

   Separation in modules was motivated by the wish to respond to the
   evolution of Internet.  The protocol part (SNMP) and data definition
   part (MIB) are independent of each other.  The separation has enabled
   the progressive passage from SNMPv1 via SNMPv2 to SNMPv3.  This draft
   leverages this separation to replace the SNMP protocol with a CoAP
   based protocol.

3.1.1.  SNMP functions

   The SNMP protocol supports seven types of access supported by as many
   Protocol Data Unit (PDU) types:

   o  Get Request, transmits a list of OBJECT-IDENTIFIERs to be paired
      with values.

   o  GetNext Request, transmits a list of OBJECT-IDENTIFIERs to which
      lexicographic successors are returned for table traversal.

   o  GetBulk Request, transmits a list of OBJECT-IDENTIFIERs and the
      maximum number of expected paired values.

   o  Response, returns an error or the (OBJECT-IDENTIFIER, value) pairs
      for the OBJECT-IDENTIFIERs specified in Get, GetNext, GetBulk,
      Set, or Inform Requests.

   o  Set Request, transmits a list of (OBJECT-IDENTIFIERs, value) pairs
      to be set in the specified MIB object.

   o  Trap, sends an unconfirmed message with a list of (OBJECT-
      IDENTIFIERs, value) pairs to a notification requesting end-point.

   o  Inform Request, sends a confirmed message with a list of (OBJECT-
      IDENTIFIERs, value) pairs to a notification requesting end-point.

3.1.2.  MIB structure

   A MIB module is composed of MIB objects.  MIB objects are
   standardized by the IETF or by other relevant Standards Developing
   Organizations (SDO).

   MIB objects have a descriptor and an identifier: OBJECT-IDENTIFIER
   (OID).  The identifier, following the OSI hierarchy, is an ordered
   list of non-negative numbers [RFC2578].  OID values are unique.  Each
   number in the list is referred as a sub-identifier.  The descriptor
   is unique within a module.  Different modules may contain the same



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   descriptor.  Consequently, a descriptor can be related to several
   OIDs.

   Many instances of an object type exist within a management domain.
   Each instance can be identified within some scope or "context", where
   there are multiple such contexts within the management domain.
   Often, a context is a physical or logical device.  A context is
   always defined as a subset of a single SNMP entity.  To identify an
   individual item of management information within the management
   domain, its contextName and contextEngineID must be identified in
   addition to its object type and its instance.  A default context is
   assumed when no context is specified.

   A MIB object is usually a scalar object.  A MIB object may have a
   tabular form with rows and columns.  Such an object is composed of a
   sequence of rows, with each row composed of a sequence of typed
   values.  The index is a subset (1-2 items) of the typed values in the
   row.  An index value identifies the row in the table.

   In SMI, a table is constructed as a SEQUENCE OF its entries.  For
   example, the IpAddrTable from [RFC4293] has the following definition:






























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   ipv6InterfaceTable OBJECT-TYPE
     SYNTAX                      SEQUENCE OF Ipv6InterfaceEntry
     MAX-ACCESS                  not-accessible
     STATUS                      current
     DESCRIPTION
       "The table containing per-interface IPv6-specific
       information."
   ::= { ip 30 }

   ipv6InterfaceEntry OBJECT-TYPE
     SYNTAX                      Ipv6InterfaceEntry
     MAX-ACCESS                  not-accessible
     STATUS current
     DESCRIPTION
       "An entry containing IPv6-specific information for a given
       interface."
     INDEX { ipv6InterfaceIfIndex }
   ::= { ipv6InterfaceTable 1 }

   Ipv6InterfaceEntry ::= SEQUENCE {
     ipv6InterfaceIfIndex        InterfaceIndex,
     ipv6InterfaceReasmMaxSize   Unsigned32,
     ipv6InterfaceIdentifier     Ipv6AddressIfIdentifierTC,
     ipv6InterfaceEnableStatus   INTEGER,
     ipv6InterfaceReachableTime  Unsigned32,
     ipv6InterfaceRetransmitTime Unsigned32,
     ipv6InterfaceForwarding     INTEGER
   }


   The descriptor (name) of the MIB table is used for the name of the
   CoMI variable.  However, there is no explicit mention of the names
   "ipv6InterfaceEntry" and "Ipv6InterfaceEntry".  Instead, the value of
   the main CoMI variable, ipv6InterfaceTable, consists of an array,
   each element of which contains 7 CoMI variables: one element for
   "ipv6InterfaceIfIndex", one for "ipv6InterfaceReasmMaxSize" and so on
   until "ipv6InterfaceForwarding".

3.2.  CoMI Function Set

   Three types of interfaces are supported by CoMI:

   Single value:  Reading/Writing one MIB variable, specified in the URI
      with path /mg/mib/descriptor or with path /mg/mib/OID.

   Multiple values:  Reading writing arrays or multiple MIB variables,
      specified in the payload.




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   Discovery:  Discovery of MIB descriptors as specified in [RFC6690].

   The examples in this section use a JSON payload with one or more
   entries describing the pair (descriptor, value), or (OID, value).
   CoMI transports the CBOR format to transport the equivalent contents.
   The CBOR syntax of the payloads is specified in Section 4.

3.2.1.  Single MIB values

   A request to read the value of a MIB variable is sent with a
   confirmable CoAP GET message.  The single MIB variable is specified
   in the URI path with the OID or descriptor suffixing the /mg/mib/
   path name.  When the descriptor is used to specify the MIB value, the
   same descriptor may be present in multiple module.  To disambiguate
   the descriptor the "mod" uri-query attribute specifies the enveloping
   modules.  A request to set the value of a MIB variable is sent with a
   confirmable CoAP PUT message.  The Response is piggybacked to the
   CoAP ACK message corresponding with the Request.

   TODO: for multicast send unconfirmed PUT

   Using for example the same MIB from [RFC1213] as used in [RFC3416], a
   request is sent to retrieve the value of sysUpTime specified in
   module SNMPv2-MIB.  The answer to the request returns a (descriptor,
   value) pair.

   As announced, in all examples the payload is expressed in JSON,
   although the operational payload is specified to be in CBOR.


   REQ: GET example.com/mg/mib/sysUpTime?mod=SNMPv2-MIB

   RES: 2.05 Content (Content-Format: application/json)
   {
       "sysUpTime" : 123456
   }

   Another way to express the descriptor of the required value is by
   specifying the pair (descriptor or oid, null value) in the payload of
   the request message.











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   REQ: GET example.com/mg/mib/(Content-Format: application/json)
   {
       "SNMPv2-MIB.sysUpTime" : "null"
   }

   RES: 2.05 Content (Content-Format: application/json)
   {
       "SNMPv2-MIB.sysUpTime" : 123456
   }

   The module name SNMPv2-MIB can be omitted when there is no
   possibility of ambiguity.  The module.descriptor can of course be
   replaced with the corresponding oid.

   In some cases it is necessary to determine the "context" by
   specifying a context name and a contextEngine identifier.  The
   context can be specified in the URI with the uri-query attribute
   "con".  Based on the example of figure 3 in section 3.3 of [RFC3411],
   the context name, bridge1, and the context Engine Identifier,
   800002b804616263, separated by an underscore, are specified in the
   following example:


   REQ: GET example.com/mg/mib/sysUPTime?con=bridge1_800002b804616263

   RES: 2.05 Content (Content-Format: application/json)
   {
       "sysUpTime" : 123456
   }

   The specified object can be a table.  The returned payload is
   composed of all the rows associated with the table.  Each row is
   returned as a set of (column name, value) pairs.  For example the GET
   of the ipNetToMediaTable, sent by the managing entity, results in the
   following returned payload sent by the managed entity:
















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   REQ: GET example.com/mg/mib/ipNetToMediaTable

   RES: 2.05 Content (Content-Format: application/json)
   {
      "ipNetTOMediaTable" : [
        {
       "ipNetToMediaIfIndex" : 1,
       "ipNetToMediaPhysAddress" : "00:00::10:01:23:45",
       "ipNetToMediaNetAddress" : "10.0.0.51",
       "ipNetToMediaType" : "static"
       },
        {
       "ipNetToMediaIfIndex" : 1,
       "ipNetToMediaPhysAddress" : "00:00::10:54:32:10",
       "ipNetToMediaNetAddress" : "9.2.3.4",
       "ipNetToMediaType" : "dynamic"
         },
         {
       "ipNetToMediaIfIndex" : 2,
       "ipNetToMediaPhysAddress" : "00:00::10:98:76:54",
       "ipNetToMediaNetAddress" : "10.0.0.15",
       "ipNetToMediaType" : "dynamic"
         }
       ]
   }

   It is possible that the size of the returned payload is too large to
   fit in a single message.

   CoMI gives the possibility to send the contents of the objects in
   several fragments with a maximum size.  The "sz" link-format
   attribute [RFC6690] can be used to specify the expected maximum size
   of the mib resource in (identifier, value) pairs.  The returned data
   MUST terminate with a complete (identifier, value) pair.

   In the case that management data is bigger than the maximum supported
   payload size, the Block mechanism from [I-D.ietf-core-block] is used.
   Notice that the Block mechanism splits the data at fixed positions,
   such that individual data fields may become fragmented.  Therefore,
   assembly of multiple blocks may be required to process the complete
   data field.

3.2.2.  multi MIB values

   A request to read multiple MIB variables is done by expressing the
   pairs (MIB descriptor, null) in the payload of the GET request
   message.  A request to set multiple MIB variables is done by
   expressing the pairs (MIB descriptor, value) in the payload of the



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   PUT request message.  The key word _multiMIB is used as array name to
   signal that the payload contains multiple MIB values as separate
   _multiMIB array entries.

   The following example shows a request that specifies to return the
   values of sysUpTime and ipNetToMediaTable:


   REQ: GET example.com/mg/mib (Content-Format: application/json)
   {
      "_multiMIB" : [
        { "sysUpTime" : "null"},
        { "ipNetToMediaTable" : "null" }
       ]
   }

   RES: 2.05 Content (Content-Format: application/json)
   {
      "_multiMIB" : [
      { "sysUpTime" : 123456},
      { "ipNetTOMediaTable" : [
        {
       "ipNetToMediaIfIndex" : 1,
       "ipNetToMediaPhysAddress" : "00:00::10:01:23:45",
       "ipNetToMediaNetAddress" : "10.0.0.51",
       "ipNetToMediaType" : "static"
       },
        {
       "ipNetToMediaIfIndex" : 1,
       "ipNetToMediaPhysAddress" : "00:00::10:54:32:10",
       "ipNetToMediaNetAddress" : "9.2.3.4",
       "ipNetToMediaType" : "dynamic"
         },
         {
       "ipNetToMediaIfIndex" : 2,
       "ipNetToMediaPhysAddress" : "00:00::10:98:76:54",
       "ipNetToMediaNetAddress" : "10.0.0.15",
       "ipNetToMediaType" : "dynamic"
         }
       ]
       }
      ]
   }








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3.2.3.  Table row

   The managing entity MAY be interested only in certain table entries.
   One way to specify a row is to specify its row number in the URI with
   the "row" uri-query attribute.  The specification of row=1 returns
   row 1 values of the ipNetToMediaTable in the example:


   REQ: GET example.com/mg/mib/ipNetToMediaTable?row=1

   RES: 2.05 Content (Content-Format: application/json)
   { "ipNetTOMediaTable" : [
        {
       "ipNetToMediaIfIndex" : 1,
       "ipNetToMediaPhysAddress" : "00:00::10:01:23:45",
       "ipNetToMediaNetAddress" : "10.0.0.51",
       "ipNetToMediaType" : "static"
       }
       ]
   }

   An alternative mode of selection is by specifying the value of the
   INDEX attributes.  Towards this end, the managing entity can include
   the required entries in the payload of its "GET" request by
   specifying the values of the index attributes.  The key word
   _indexMIB is used to specify the index value.

   For example, to obtain a table entry from ipNetToMediaTable, the rows
   are specified by specifying the index attributes: ipNetToMediaIfIndex
   and ipNetToMediaNetAddress.  The managing entity could have sent a
   GET with the following payload:




















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REQ: GET example.com/mg/mib/ipNetToMediaTable(Content-Format: application/json)

{ "_indexMIB" :
     {
      "ipNetToMediaIfIndex" : 1,
      "ipNetToMediaNetAddress" : "9.2.3.4"
     }
}

RES: 2.05 Content (Content-Format: application/json)
{ "ipNetTOMediaTable" : [
     {
    "ipNetToMediaIfIndex" : 1,
    "ipNetToMediaPhysAddress" : "00:00::10:01:23:45",
    "ipNetToMediaNetAddress" : "9.2.3.4",
    "ipNetToMediaType" : "static"
    }
    ]
}

   Constrained devices MAY support this kind of filtering.  However, if
   they don't support it, they MUST ignore the payload in the GET
   request and handle the message as if the payload was empty.

   It is advised to keep MIBs for constrained entities as simple as
   possible, and therefore it would be best to avoid extensive tables.

   TODO: Describe how the contents of the next lexicographical row can
   be returned.

3.2.4.  MIB discovery

   MIB objects are discovered like resources with the standard CoAP
   resource discovery.  Performing a GET on "/.well-known/core" with
   rt=core.mg.mib returns all MIB descriptors and all OIDs which are
   available on this device.  For table objects there is no further
   possibility to discover the row descriptors.  For example, consider
   there are two MIB objects with descriptors "sysUpTime" and
   "ipNetToMediaTable" associated with OID 1.3.6.1.2.1.1.3 and
   1.3.6.1.2.1.4.22

   REQ: GET example.com/.well-known/core?rt=core.mg.mib

   RES: 2.05 Content (Content-Format: application/text)
   </mg/mib/sysUpTime>;rt="core.mg.mib";oid="1.3.6.1.2.1.1.3";
     mod="SNMPv2-MIB"
   </mg/mib/ipNetToMediaTable>;rt="core.mg.mib";oid="1.3.6.1.2.1.4.22";
     mod="ipMIB"



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   The link format attribute 'oid' is used to associate the name of the
   MIB resource with its OID.  The OID is written as a string in its
   conventional form.

   Notice that a MIB variable normally is associated with a descriptor
   and an OID.  The OID is unique, whereas the descriptor is unique in
   combination with the module name.

   The "mod", "con", and "rt" attributes can be used to filter resource
   queries as specified in [RFC6690].

3.2.5.  Error returns

   When a variable with the specified name cannot be processed, CoAP
   Error code 5.01 is returned.  In addition, a MIB specific error can
   be returned in the payload as specified in Section 7.

4.  Mapping SMI to CoMI payload

   The SMI syntax is mapped to CBOR necessary for the transport of MIB
   data in the CoAP payload.  This section first describes an additional
   data reduction technique by creating a table that maps string values
   to numbers used in CBOR encoded data.

   The section continues by describing the mapping from SMI to CBOR.
   The mapping is inspired by the mapping from SMI to JSON via YANG
   [RFC6020], as described in [RFC6643] defining a mapping from SMI to
   YANG, and [I-D.lhotka-netmod-yang-json] defining a mapping from YANG
   to JSON.

   Notice that such conversion chain MAY be virtual only, as SMI could
   be converted directly to JSON by combining the rules from the above
   documents.

4.1.  CBOR format for MIB data

   Because descriptors may be rather long and may occur repeatedly, CoMI
   allows for association of a given string value with an integer,
   henceforth called "string number".  The association between string
   value and string number is done through a conversion table,
   leveraging CBOR encoding.  Section 4.2 defines how the conversion
   table is generated.

   Using the notational convention from Appendix A, the CBOR data has
   the following syntax:






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   cBorMIB       : CBorMIB;

   *CBorMIB {
     convTableId : tstr;
     mibData     : map( uint, . );
   }

   The main structure consist of an array of two elements: "convTableId"
   and "mibData".

   The conversion table identifier "convTableId" is constructed from the
   LAST_UPDATED attribute and module name as defined in Section 4.2.

   The values of the MIB variables are stored in the "mibData" field.
   This field consist of integer-value pairs.  The integers correspond
   to the string numbers, whereas the values contain the actual value of
   the associated MIB variable.  Section 4.3 elaborates on the mapping
   from SMI to CBOR.

4.2.  Table generation

   The conversion table contents MUST be automatically generated from
   the MIB module as specified in this section.  Automatic generation in
   the managed device removes the need to transport the tables and
   subsequently store them in the nodes, and avoids a cumbersome
   management of the conversion tables.

   The conversion table identifier "convTableId" is generated from the
   LAST-UPDATED field in the MODULE IDENTITY macro, and the module name
   as follows:

          convTableId = moduleName UNDERSCORE lastUpdateTimestamp
          UNDERSCORE  = %x5F

   where moduleName is the module name, and lastUpdateTimestamp is the
   value of the related LAST-UPDATED field in the MODULE-IDENTITY macro,
   using the format with four year digits as defined in [RFC2578].

   The conversion table is generated using the following algorithm:

   1.  Collect all used OIDs/descriptors defined in the MIB object, and
       as well as those imported using IMPORTS.

   2.  Sort the collection of OIDs according to the following rules:

       1.  x.y.z < x.y.z.k

       2.  x.y.z... < x.y.k... if z<k



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   3.  Assign the string numbers to the sorted list of OIDs, in
       numerical order starting with 1.

   Note that variables imported with IMPORTS could be tables, such that
   the OIDs of the table entries need to be included in the collection
   of OIDs as well.

4.3.  Mapping SMI to CBOR

4.3.1.  General overview

   Starting from the intermediate conversion from SMI to YANG as defined
   in [RFC6643], This section defines how to convert the resulting YANG
   structure to CBOR [RFC7049].  The actual conversion code from SMI to
   CBOR MAY be direct conversion code from SMI to CBOR or a sequence of
   existing SMI to YANG conversion code followed by YANG to CBOR
   conversion code.

4.3.2.  Conversion from YANG datatypes to CBOR datatypes

   Table 1 defines the mapping between YANG datatypes and CBOR
   datatypes.

   Elements of types not in this table, and of which the type cannot be
   inferred from a type in this table, are ignored in the CBOR encoding
   by default.  Examples include the "description" and "key" elements.
   However, conversion rules for some elements to CBOR MAY be defined
   elsewhere.

   +-------------+------------------+----------------------------------+
   | YANG type   | CBOR type        | Specification                    |
   +-------------+------------------+----------------------------------+
   | int8,       | unsigned int     | The CBOR integer type depends on |
   | int16,      | (major type 0)   | the sign of the actual value.    |
   | int32,      | or negative int  |                                  |
   | int64,      | (mayor type 1)   |                                  |
   | uint16,     |                  |                                  |
   | uint32,     |                  |                                  |
   | uint64,     |                  |                                  |
   | decimal64   |                  |                                  |
   |             |                  |                                  |
   | boolean     | either "true"    |                                  |
   |             | (major type 7,   |                                  |
   |             | simple value 21) |                                  |
   |             | or "false"       |                                  |
   |             | (major type 7,   |                                  |
   |             | simple value 20) |                                  |
   |             |                  |                                  |



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   | string      | text string      |                                  |
   |             | (major type 3)   |                                  |
   |             |                  |                                  |
   | enumeration | unsigned int     |                                  |
   |             | (major type 0)   |                                  |
   |             |                  |                                  |
   | bits        | array of text    | Each text string contains the    |
   |             | strings          | name of a bit value that is set. |
   |             |                  |                                  |
   | binary      | byte string      |                                  |
   |             | (major type 2)   |                                  |
   |             |                  |                                  |
   | empty       | null (major type | TBD: This MAY not be applicable  |
   |             | 7, simple value  | to true MIBs, as SNMP may not    |
   |             | 22)              | support empty variables...       |
   |             |                  |                                  |
   | union       |                  | Similar ot the JSON              |
   |             |                  | transcription from               |
   |             |                  | [I-D.lhotka-netmod-yang-json],   |
   |             |                  | the elements in a union MUST be  |
   |             |                  | determined using the procedure   |
   |             |                  | specified in section 9.12 of     |
   |             |                  | [RFC6020].                       |
   |             |                  |                                  |
   | leaf-list   | array (major     | The array is encapsulated in the |
   |             | type 4)          | map associated with the          |
   |             |                  | descriptor.                      |
   |             |                  |                                  |
   | list        | map (major type  | Like the higher level map, the   |
   |             | 4)               | lower level map contains         |
   |             |                  | descriptor number - value pairs  |
   |             |                  | of the elements in the list.     |
   |             |                  |                                  |
   | container   | map (major type  | The map contains decriptor       |
   |             | 5)               | number - value pairs             |
   |             |                  | corresponding to the elements in |
   |             |                  | the container.                   |
   |             |                  |                                  |
   | smiv2:oid   | array of         | Each integer contains an element |
   |             | integers         | of the OID, the first integer in |
   |             |                  | the array corresponds to the     |
   |             |                  | most left element in the OID.    |
   +-------------+------------------+----------------------------------+

               Table 1: Conversion of YANG datatypes to CBOR






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4.3.3.  Examples

4.3.3.1.  ipNetToMediaTable to JSON/CBOR

   The YANG translation of the SMI specifying the
   ipNetToMediaTable yields:


   container ipNetToMediaTable {
       list ipNetToMediaEntry {
          leaf ipNetToMediaIfIndex {
             type: int32;
          }
          leaf ipNetToPhysAddress {
             type: phys-address;
          }
          leaf ipNetToMediaNetAddress {
             type: ipv4-address;
          }
          leaf ipNetToMediaType {
             type: int32;
          }
       }
    }

   The coresponding JSON looks like:


   {
   "ipNetToMediaTable" : {
       "ipNetToMediaEntry" : [
           {
           "ipNetToMediaIfIndex" : 1.
           "ipNetToMediaPhysAddress" : "00:00::10:01:23:45",
           "ipNetToMediaNetAddress" : "10.0.0.51",
           "ipNetToMediaType" : "static"
           },
           {
           "ipNetToMediaIfIndex " : 1,
           "ipNetToMediaPhysAddress " : "00:00::10:54:32:10",
           "ipNetToMediaNetAddress" : "9.2.3.4",
           "ipNetToMediaType " : "dynamic"
           }
       ]
       }
   }





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   An example CBOR instance of the MIB can be found in Figure 1.  The
   names "ipNetToMediaTable", "ipNetToMediaEntry", and
   "ipNetToMediaIfIndex" are represented with the string numbers 00, 01,
   and 02 as described in Section 4.1.


   82                         # two element array
      74 49 50 2d 4d 49 42 5f
      32 30 30 36 30 32 30 32
      30 30 30 30 5a          # "IP-MIB_200602020000Z"
      BF                      # indefinite length map
        00                    # descriptor number related to
                              # ipNetToMediaTable
        BF                    # indefinite length map related to
                              # ipNetToMediaTable
           01                 # descriptor number related to
                              # ipNetToMediaEntry
           BF                 # map related to ipNetToMediaEntry
              02              # descriptor number associated with
                              # ipNetToMediaIfIndex
              1A 00 00 00 01  # associated value as 32-bit integer
              # ...
           FF
        FF
      FF

                Figure 1: Example CBOR encoding for ifTable

   The associated "descriptor string" to "string number" conversion
   table is given in Figure 2.





















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   82                         # two element array
      74 49 50 2d 4d 49 42 5f
      32 30 30 36 30 32 30 32
      30 30 30 30 5a          # "IP-MIB_200602020000Z"
      BF                      # indefinite length map
         00                   # descriptor number related to
                              # ipNetToMediaTable
         72 69 70 50 65 74 57
         6F 51 65 64 61 57 61
         62 6C 65             # "ipNetToMediaTable"
         01                   # descriptor number related to
                              # ipNetToMediaEntry
         72 69 70 50 65 74 57
         6F 51 65 64 61 45 6E
         74 72 78                 # "ipNetToMediaEntry"
         02                   # descriptor number related to
                              # ipNetToMediaIfIndex
         75 69 70 50 65 74 57
         6F 51 65 64 61 61 49
         66 49 6E 64 65 77    # "ipNetToMediaIfIndex"
         # ...
      FF

                  Figure 2: Conversion table for ifTable

4.3.4.  6LoWPAN MIB

   A MIB for 6LoWPAN is defined in [I-D.ietf-6lo-lowpan-mib] with an
   example JSON representation in its Appendix A.  Appendix B.3 shows
   the associated CBOR representation with string number, and the
   corresponding string to string number conversion table.

   In this example, a GET to /mg/mib/lowpanOutFragFails would give:


   82                         # two element array
      78 18 4c 4f 57 50 41 4e
      2d 4d 49 42 5f 32 30 31
      34 30 34 30 38 30 30 30
      30 5a                   # conversion table id:
                              # "LOWPAN-MIB_201404080000Z"
      BF                      # indefinite length map
        18 1B                 # "lowpanOutFragFails"
        00                    # 0
      FF






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5.  Trap functions

   A trap can be set through the CoAP Observe [I-D.ietf-core-observe]
   function.  As regular with Observe, the managing entity subscribes to
   the variable by sending a GET request with an "Observe" option.

   TODO: Observe example

   In the registration request, the managing entity MAY include a
   "Response-To-Uri-Host" and optionally "Response-To-Uri-Port" option
   as defined in [I-D.becker-core-coap-sms-gprs].  In this case, the
   observations SHOULD be sent to the address and port indicated in
   these options.  This can be useful when the managing entity wants the
   managed device to send the trap information to a multicast address.

6.  MIB access management

   Two topics are relevant: (1) the definition of the destination of
   Notify messages, and (2) the creation and maintenance of "string to
   number" tables.

6.1.  Notify destinations

   The destination of notifications need to be communicated to the
   applications sending them.  Draft [I-D.ietf-core-interfaces]
   describes the binding of end-points to end-points on remote devices.
   The object with type "binding table" contains a sequence of bindings.
   The contents of bindings contains the methods, location, the interval
   specifications, and the step value as suggested in
   [I-D.ietf-core-interfaces].  The method "notify" has been added to
   the binding methods "poll", "obs" and "push", to cater for the
   binding of notification source to the receiver.

   TODO: describe interface for NOTIFY destination definition.

6.2.  Conversion table management

   Since the conversion table is unique for a MIB, it can be generated
   off-line by a managing entity, and independently generated in the
   managed device with the same result.  Because different versions of a
   given MIB may be available the managing entity must be able to check
   the version on the managed device.  The convTableId can be acquired
   with a confirmable GET request:








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   REQ: GET example.com/mg/conv/ident

   RES: 2.05 Content (Content-Format: application/json)
   {
       "convTableId" : convTableId
   }

   The conversion table MAY be available on a managed device, and can
   then be acquired as follows:

   GET /mg/conv/[convTableId]

   where "[convTableId]" is replaced by the the value of convTableId
   from the CBorMIB structure.

   In case the managed device provides the table, it must be transmitted
   in the payload of the GET response using the following format:


   convTable     : ConvTable;

   *ConvTable {
     convTableId : tstr;
     convData    : map( uint, tstr );
   }

   where "convTableId" is the conversion table identifier, as defined in
   Section 4.2, and "convData" is a CBOR map between the string number
   and associated variable descriptor.

7.  Error handling

   In case a request is received which cannot be processed properly, the
   managed entity MUST return an error message.  This error message MUST
   contain a CoAP 4.xx or 5.xx response code, and SHOULD include
   additional information in the payload.

   Such an error message payload is encoded in CBOR, using the following
   structure:


   errorMsg     : ErrorMsg;

   *ErrorMsg {
     errorCode  : uint;
     ?errorText : tstr;
   }




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   The variable "errorCode" has one of the values from the table below,
   and the OPTIONAL "errorText" field contains a human readible
   explanation of the error.

   +----------------+----------------+---------------------------------+
   | CoMI Error     | CoAP Error     | Description                     |
   | Code           | Code           |                                 |
   +----------------+----------------+---------------------------------+
   | 0              | 4.00           | General error                   |
   |                |                |                                 |
   | 1              | 4.00           | Malformed CBOR data             |
   |                |                |                                 |
   | 2              | 4.00           | Incorrect CBOR datatype         |
   |                |                |                                 |
   | 3              | 4.00           | Unknown MIB variable            |
   |                |                |                                 |
   | 4              | 4.00           | Unknown conversion table        |
   |                |                |                                 |
   | 5              | 4.05           | Attempt to write read-only      |
   |                |                | variable                        |
   |                |                |                                 |
   | 0..2           | 5.01           | Access exceptions               |
   |                |                |                                 |
   | 0..18          | 5.00           | SMI error status                |
   +----------------+----------------+---------------------------------+

   The CoAP error code 5.01 is associted with the exceptions defined in
   [RFC3416] and CoAP error code 5.00 is associated with the error-
   status defined in [RFC3416].

8.  Security Considerations

   For secure network management, it is important to restrict access to
   MIB variables only to authorised parties.  This requires integrity
   protection of both requests and responses, and depending on the
   application encryption.

   CoMI re-uses the security mechanisms already available to CoAP as
   much as possible.  This includes DTLS for protected access to
   resources, as well suitable authentication and authorisation
   mechanisms.

   Among the security decisions that need to be made are selecting
   security modes and encryption mechanisms (see [I-D.ietf-core-coap]).
   This requires a trade-off, as the NoKey mode gives no protection at
   all, but is easy to implement, whereas the X.509 mode is quite
   secure, but may be too complex for constrained devices.




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   In addition, mechanisms for authentication and authorisation may need
   to be selected.

   CoMI avoids defining new security mechanisms as much as possible.
   However some adaptations may still be required, to cater for CoMI's
   specific requirements.

9.  IANA Considerations

   'rt="core.mg.mib"' needs registration with IANA.

   Content types to be registered:

   o  application/comi+json

   o  application/comi+cbor

10.  Acknowledgements

   Mehmet Ersue and Bert Wijnen explained the encoding aspects of PDUs
   transported under SNMP.  Carsten Bormann has given feedback on the
   use of CBOR.  Juergen Schoenwalder has commented on inconsistencies
   and missing aspects of SNMP in earlier versions of the draft.  The
   draft has benefited from comments (alphabetical order) by Dee
   Denteneer, Esko Dijk, Michael van Hartskamp, Zach Shelby, Michael
   Verschoor, and Thomas Watteyne.  The CBOR encoding borrows
   extensively from Ladislav Lhotka's description on conversion from
   YANG to JSON.

11.  Changelog

   Changes from version 00 to version 01

   o  Focus on MIB only

   o  Introduced CBOR, JSON, removed BER

   o  defined mappings from SMI to xx

   o  Introduced the concept of addressable table rows

   Changes from version 01 to version 02

   o  Focus on CBOR, used JSON for examples, removed XML and EXI

   o  added uri-query attributes mod and con to specify modules and
      contexts




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   o  Definition of CBOR string conversion tables for data reduction

   o  use of Block for multiple fragments

   o  Error returns generalized

   o  SMI - YANG - CBOR conversion

   Changes from version 02 to version 03

   o  Added security considerations

   Changes from version 03 to version 04

   o  Added design considerations section

   o  Extended comparison of management protocols in introduction

   o  Added automatic generation of CBOR tables

   o  Moved lowpan table to Appendix

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, October 2013.

   [I-D.becker-core-coap-sms-gprs]
              Becker, M., Li, K., Poetsch, T., and K. Kuladinithi,
              "Transport of CoAP over SMS", draft-becker-core-coap-sms-
              gprs-04 (work in progress), August 2013.

   [I-D.ietf-core-block]
              Bormann, C. and Z. Shelby, "Blockwise transfers in CoAP",
              draft-ietf-core-block-14 (work in progress), October 2013.







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   [I-D.ietf-core-coap]
              Shelby, Z., Hartke, K., and C. Bormann, "Constrained
              Application Protocol (CoAP)", draft-ietf-core-coap-18
              (work in progress), June 2013.

   [I-D.ietf-core-observe]
              Hartke, K., "Observing Resources in CoAP", draft-ietf-
              core-observe-13 (work in progress), April 2014.

   [I-D.ietf-json-rfc4627bis]
              Bray, T., "The JSON Data Interchange Format", draft-ietf-
              json-rfc4627bis-10 (work in progress), December 2013.

   [I-D.lhotka-netmod-yang-json]
              Lhotka, L., "Modeling JSON Text with YANG", draft-lhotka-
              netmod-yang-json-02 (work in progress), September 2013.

12.2.  Informative References

   [RFC1213]  McCloghrie, K. and M. Rose, "Management Information Base
              for Network Management of TCP/IP-based internets:MIB-II",
              STD 17, RFC 1213, March 1991.

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, June 2000.

   [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              December 2002.

   [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
              (USM) for version 3 of the Simple Network Management
              Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.

   [RFC3416]  Presuhn, R., "Version 2 of the Protocol Operations for the
              Simple Network Management Protocol (SNMP)", STD 62, RFC
              3416, December 2002.





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   [RFC3418]  Presuhn, R., "Management Information Base (MIB) for the
              Simple Network Management Protocol (SNMP)", STD 62, RFC
              3418, December 2002.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC4088]  Black, D., McCloghrie, K., and J. Schoenwaelder, "Uniform
              Resource Identifier (URI) Scheme for the Simple Network
              Management Protocol (SNMP)", RFC 4088, June 2005.

   [RFC4113]  Fenner, B. and J. Flick, "Management Information Base for
              the User Datagram Protocol (UDP)", RFC 4113, June 2005.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4293]  Routhier, S., "Management Information Base for the
              Internet Protocol (IP)", RFC 4293, April 2006.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, September 2007.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC6643]  Schoenwaelder, J., "Translation of Structure of Management
              Information Version 2 (SMIv2) MIB Modules to YANG
              Modules", RFC 6643, July 2012.

   [RFC6650]  Falk, J. and M. Kucherawy, "Creation and Use of Email
              Feedback Reports: An Applicability Statement for the Abuse
              Reporting Format (ARF)", RFC 6650, June 2012.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, August 2012.

   [RFC6775]  Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
              "Neighbor Discovery Optimization for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
              November 2012.




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   [I-D.ietf-core-groupcomm]
              Rahman, A. and E. Dijk, "Group Communication for CoAP",
              draft-ietf-core-groupcomm-18 (work in progress), December
              2013.

   [I-D.ietf-core-interfaces]
              Shelby, Z. and M. Vial, "CoRE Interfaces", draft-ietf-
              core-interfaces-01 (work in progress), December 2013.

   [I-D.ersue-constrained-mgmt]
              Ersue, M., Romascanu, D., and J. Schoenwaelder,
              "Management of Networks with Constrained Devices: Problem
              Statement, Use Cases and Requirements", draft-ersue-
              constrained-mgmt-03 (work in progress), February 2013.

   [I-D.ietf-6lo-lowpan-mib]
              Schoenwaelder, J., Sehgal, A., Tsou, T., and C. Zhou,
              "Definition of Managed Objects for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", draft-ietf-
              6lo-lowpan-mib-01 (work in progress), April 2014.

   [I-D.bierman-netconf-restconf]
              Bierman, A., Bjorklund, M., Watsen, K., and R. Fernando,
              "RESTCONF Protocol", draft-bierman-netconf-restconf-04
              (work in progress), February 2014.

   [STD0001]  "Official Internet Protocols Standard", Web
              http://www.rfc-editor.org/rfcxx00.html, .

   [XML]      "Extensible Markup Language (XML)", Web
              http://www.w3.org/xml, .

   [JSON]     "JavaScript Object Notation (JSON)", Web
              http://www.json.org, .

   [OMA]      "OMA-TS-LightweightM2M-V1_0-20131210-C", Web
              http://technical.openmobilealliance.org/Technical/
              current_releases.aspx, .

Appendix A.  Notational Convention for CBOR data

   To express CBOR structures [RFC7049], this document uses the
   following conventions:

   A declaration of a CBOR variable has the form:

      name : datatype;




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   where "name" is the name of the variable, and "datatype" its CBOR
   datatype.

   The name of the variable has no encoding in the CBOR data.

   "datatype" can be a CBOR primitive such as:

   tstr:  A text string (major type 3)

   uint:  An unsigned integer (major type 0)

   map(x,y):  A map (major type 5), where each first element of a pair
      is of datatype x, and each second element of datatype y.  A '.'
      character for either x or y means that all datatypes for that
      element are valid.

   A datatype can also be a CBOR structure, in which case the variable's
   "datatype" field contains the name of the CBOR structure.  Such CBOR
   structure is defined by a character sequence consisting of first its
   name, then a '{' character, then its subfields and finally a '}'
   character.

   A CBOR structure can be encapsulated in an array, in which case its
   name in its definition is preceeded by a '*' character.  Otherwise
   the structure is just a grouping of fields, but without actual
   encoding of such grouping.

   The name of an optional field is preceded by a '?' character.  This
   means, that the field may be omitted if not required.

Appendix B.  Example conversion table and instance for the LOWPAN MIB

   The conversion table of the 6LoWPAN MIB [I-D.ietf-6lo-lowpan-mib] is
   generated as described in this section.

B.1.  Generating the convTableId

   The module name is "LOWPAN-MIB", and the LAST-UPDATED field in the
   MODULE-IDENTITY has the value "201404080000Z".  Hence the convId has
   the value "LOWPAN-MIB_201404080000Z".

B.2.  Generating the string numbers

   The following table shows how the string numbers are associated with
   the related strings and object IDs.

   +--------------------------+-------------------------------+--------+
   | Object ID                | Descriptor                    | String |



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   |                          |                               | number |
   +--------------------------+-------------------------------+--------+
   | 1.3.6.1.2.1              | mib-2                         |      1 |
   |                          |                               |        |
   | 1.3.6.1.2.1.2.2.1.1      | ifIndex                       |      2 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX         | lowpanMib                     |      3 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.0       | lowpanNotifications           |      4 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1       | lowpanObjects                 |      5 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.2       | lowpanConformance             |      6 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1     | lowpanStats                   |      7 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.1   | lowpanReasmTimeout            |      8 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.2   | lowpanInReceives              |      9 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.3   | lowpanInHdrErrors             |     10 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.4   | lowpanInMeshReceives          |     11 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.5   | lowpanInMeshForwds            |     12 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.6   | lowpanInMeshDelivers          |     13 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.7   | lowpanInReasmReqds            |     14 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.8   | lowpanInReasmFails            |     15 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.9   | lowpanInReasmOKs              |     16 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.10  | lowpanInCompReqds             |     17 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.11  | lowpanInCompFails             |     18 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.12  | lowpanInCompOKs               |     19 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.13  | lowpanInDiscards              |     20 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.14  | lowpanInDelivers              |     21 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.15  | lowpanOutRequests             |     22 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.16  | lowpanOutCompReqds            |     23 |
   |                          |                               |        |



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   | 1.3.6.1.2.1.XXXX.1.1.17  | lowpanOutCompFails            |     24 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.18  | lowpanOutCompOKs              |     25 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.19  | lowpanOutFragReqds            |     26 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.20  | lowpanOutFragFails            |     27 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.21  | lowpanOutFragOKs              |     28 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.22  | lowpanOutFragCreates          |     29 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.23  | lowpanOutMeshHopLimitExceeds  |     30 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.24  | lowpanOutMeshNoRoutes         |     31 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.25  | lowpanOutMeshRequests         |     32 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.26  | lowpanOutMeshForwds           |     33 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.27  | lowpanOutMeshTransmits        |     34 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.28  | lowpanOutDiscards             |     35 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.1.29  | lowpanOutTransmits            |     36 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2     | lowpanIfStatsTable            |     37 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1   | lowpanIfStatsEntry            |     38 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfReasmTimeout          |     39 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfInReceives            |     40 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.3 | lowpanIfInHdrErrors           |     41 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.4 | lowpanIfInMeshReceives        |     42 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.5 | lowpanIfInMeshForwds          |     43 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.6 | lowpanIfInMeshDelivers        |     44 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.7 | lowpanIfInReasmReqds          |     45 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.8 | lowpanIfInReasmFails          |     46 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.9 | lowpanIfInReasmOKs            |     47 |
   |                          |                               |        |



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   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfInCompReqds           |     48 |
   | 0                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfInCompFails           |     49 |
   | 1                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfInCompOKs             |     50 |
   | 2                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfInDiscards            |     51 |
   | 3                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfInDelivers            |     52 |
   | 4                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfOutRequests           |     53 |
   | 5                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfOutCompReqds          |     54 |
   | 6                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfOutCompFails          |     55 |
   | 7                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfOutCompOKs            |     56 |
   | 8                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.1 | lowpanIfOutFraqRegds          |     57 |
   | 9                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutFragFails          |     58 |
   | 0                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutFragOKs            |     59 |
   | 1                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutFragCreates        |     60 |
   | 2                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutMeshHopLimitExceed |     61 |
   | 3                        | s                             |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutMeshNoRoutes       |     62 |
   | 4                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutMeshRequests       |     63 |
   | 5                        |                               |        |
   |                          |                               |        |



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   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutMeshForwds         |     64 |
   | 6                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutMeshTransmits      |     65 |
   | 7                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutDiscards           |     66 |
   | 8                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.1.2.1.2 | lowpanIfOutTransmits          |     67 |
   | 9                        |                               |        |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.2.1     | lowpanGroups                  |     68 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.2.1.1   | lowpanStatsGroup              |     69 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.2.1.2   | lowpanStatsMeshGroup          |     70 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.2.1.3   | lowpanIfStatsGroup            |     71 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.2.1.4   | lowpanIfStatsMeshGroup        |     72 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.2.2     | lowpanCompliances             |     73 |
   |                          |                               |        |
   | 1.3.6.1.2.1.XXXX.2.2.1   | lowpanCompliance              |     74 |
   +--------------------------+-------------------------------+--------+

   Notes:

   o  The IMPORTS "MODULE-IDENTITY", "OBJECT-TYPE", "Unsigned32",
      "Counter32", "OBJECT-GROUP" and "MODULE-COMPLIANCE" do not have
      associated Object IDs, and hence do not show up in the table.

   o  The OBJECT-GROUPs lowpanStatsGroup, lowpanIfStatsGroup,
      lowpanIfStatsMeshGroup cannot appear in the CBOR instance, as they
      are lost in the intermediate MIB to YANG conversion step.
      However, as they have been defined in the original MIB, they still
      appear in the conversion table.

   o  (FOR THE EDITOR:) the value XXXX is defined to be the RFC number
      once [I-D.ietf-6lo-lowpan-mib] becomes an RFC.  It is logically
      greater than 7000.

B.3.  Example instance

   A MIB for 6LoWPAN is defined in [I-D.ietf-6lo-lowpan-mib].  The
   document also provides an example JSON representation in its




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   Appendix A.  Figure 3 shows the associated CBOR representation with
   string number, using the string numbers derived in Appendix B.2.

   The request would have been as follows:

   GET /mg/mib/lowpanIfStatsTable

   The resulting table would be as follows:

   82                         # two element array
      78 18 4c 4f 57 50 41 4e
      2d 4d 49 42 5f 32 30 31
      34 30 34 30 38 30 30 30
      30 5a                   # conversion table id:
                              # "LOWPAN-MIB_201404080000Z"
      BF                      # indefinite length map
        18 25                 # "lowpanIfStatsTable"
        BF                    # indefinite length map related
                              # to lowpanIfStatsTable
           18 27              # "lowpanIfReasmTimeout"
           14                 # 20
           18 28              # "lowpanIfInReceives"
           18 2A              # 42
           18 29              # "lowpanIfInHdrErrors"
           00                 # 0
           18 2A              # "lowpanIfInMeshReceives"
           08                 # 8
           18 2B              # "lowpanIfInMeshForwds"
           00                 # 0
           18 2C              # "lowpanIfInMeshDelivers"
           00                 # 0
           18 2D              # "lowpanIfInReasmReqds"
           16                 # 22
           18 2E              # "lowpanIfInReasmFails"
           02                 # 02
           18 2F              # "lowpanIfInReasmOKs"
           14                 # 20
           18 30              # "lowpanIfInCompReqds"
           10                 # 16
           18 31              # "lowpanIfInCompFails"
           02                 # 2
           18 32              # "lowpanIfInCompOKs"
           0E                 # 14
           18 33              # "lowpanIfInDiscards"
           01                 # 01
           18 34              # "lowpanIfInDelivers"
           0C                 # 12
           18 35              # "lowpanIfOutRequests"



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           0C                 # 12
           18 36              # "lowpanIfOutCompReqds"
           00                 # 0
           18 37              # "lowpanIfOutCompFails"
           00                 # 0
           18 38              # "lowpanIfOutCompOKs"
           00                 # 0
           18 39              # "lowpanIfOutFragReqds"
           05                 # 5
           18 3A              # "lowpanIfOutFragFails"
           00                 # 0
           18 3B              # "lowpanIfOutFragOKs"
           05                 # 5
           18 3C              # "lowpanIfOutFragCreates"
           08                 # 8
           18 3D              # "lowpanIfOutMeshHopLimitExceeds"
           00                 # 0
           18 3E              # "lowpanIfOutMeshNoRoutes"
           00                 # 0
           18 3F              # "lowpanIfOutMeshRequests"
           00                 # 0
           18 40              # "lowpanIfOutMeshForwds"
           00                 # 0
           18 41              # "lowpanIfOutMeshTransmits"
           00                 # 0
           18 42              # "lowpanIfOutDiscards"
           00                 # 0
           18 43              # "lowpanIfOutTransmits"
           0F                 # 15
        FF
      FF

            Figure 3: Example CBOR encoding for the 6LoWPAN MIB

Authors' Addresses

   Peter van der Stok
   consultant

   Phone: +31-492474673 (Netherlands), +33-966015248 (France)
   Email: consultancy@vanderstok.org
   URI:   www.vanderstok.org









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   Bert Greevenbosch
   Huawei Technologies Co., Ltd.
   Huawei Industrial Base
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Email: bert.greevenbosch@huawei.com











































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