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Internet Engineering Task Force (IETF)                     M. Ersue, Ed.Request for Comments: 7547                                Nokia NetworksCategory: Informational                                     D. RomascanuISSN: 2070-1721                                                    Avaya                                                        J. Schoenwaelder                                                Jacobs University Bremen                                                              U. Herberg                                                                May 2015Management of Networks with Constrained Devices:Problem Statement and RequirementsAbstract   This document provides a problem statement, deployment and management   topology options, as well as requirements addressing the different   use cases of the management of networks where constrained devices are   involved.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7547.Ersue, et al.                 Informational                     [Page 1]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1. Introduction ....................................................31.1. Overview ...................................................31.2. Terminology ................................................41.3. Network Types and Characteristics in Focus .................51.4. Constrained Device Deployment Options ......................91.5. Management Topology Options ...............................101.6. Managing the Constrainedness of a Device or Network .......101.7. Configuration and Monitoring Functionality Levels .........132. Problem Statement ..............................................14   3. Requirements on the Management of Networks with      Constrained Devices ............................................163.1. Management Architecture/System ............................183.2. Management Protocols and Data Models ......................223.3. Configuration Management ..................................253.4. Monitoring Functionality ..................................273.5. Self-Management ...........................................323.6. Security and Access Control ...............................333.7. Energy Management .........................................353.8. Software Distribution .....................................373.9. Traffic Management ........................................373.10. Transport Layer ..........................................393.11. Implementation Requirements ..............................404. Security Considerations ........................................415. Informative References .........................................42   Acknowledgments ...................................................44   Authors' Addresses ................................................44Ersue, et al.                 Informational                     [Page 2]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 20151.  Introduction1.1.  Overview   Constrained devices (also known as sensors, smart objects, or smart   devices) with limited CPU, memory, and power resources can be   connected to a network.  It might be based on unreliable or lossy   channels, it may use wireless technologies with limited bandwidth and   a dynamic topology, or it may need the service of a gateway or proxy   to connect to the Internet.  In other scenarios, the constrained   devices can be connected to a unconstrained network using off-the-   shelf protocol stacks.   Constrained devices might be in charge of gathering information in   diverse settings including natural ecosystems, buildings, and   factories and sending the information to one or more server stations.   Constrained devices may also work under severe resource constraints   such as limited battery and computing power, little memory and   insufficient wireless bandwidth, and communication capabilities.  A   central entity, e.g., a base station or controlling server, might   have more computational and communication resources and can act as a   gateway between the constrained devices and the application logic in   the core network.   Today, constrained devices of diverse size and with different   resources and capabilities are being connected.  Mobile personal   gadgets, building-automation devices, cellular phones, machine-to-   machine (M2M) devices, etc., benefit from interacting with other   "things" in the near or somewhere in the Internet.  With this the   Internet of Things (IoT) becomes a reality, built up of uniquely   identifiable objects (things).  And over the next decade, this could   grow to trillions of constrained devices and will greatly increase   the Internet's size and scope.   Network management is characterized by monitoring network status,   detecting faults (and inferring their causes), setting network   parameters, and carrying out actions to remove faults, maintain   normal operation, and improve network efficiency and application   performance.  The traditional network monitoring application   periodically collects information from a set of managed network   elements, it processes the data, and it presents the results to the   network management users.  Constrained devices, however, often have   limited power, have low transmission range, and might be unreliable.   They might also need to work in hostile environments with advanced   security requirements or need to be used in harsh environments for a   long time without supervision.  Due to such constraints, theErsue, et al.                 Informational                     [Page 3]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   management of a network with constrained devices faces a different   type of challenges compared to the management of a traditional IP   network.   The IETF has already done substantial standardization work to enable   communication in IP networks and to manage such networks as well as   the manifold types of nodes in these networks [RFC6632].  However,   the IETF so far has not developed any specific technologies for the   management of constrained devices and the networks comprised by   constrained devices.  IP-based sensors or constrained devices in such   an environment (i.e., devices with very limited memory, CPU, and   energy resources) nowadays use application-layer protocols in an ad   hoc manner to do simple resource management and monitoring.   This document provides a problem statement and lists requirements for   the different use cases of management of a network with constrained   devices.  Sections1.3 and1.5 describe different topology options   for the networking and management of constrained devices.Section 2   provides a problem statement on the issue of the management of   networked constrained devices.Section 3 lists requirements on the   management of applications and networks with constrained devices.   Note that the requirements listed inSection 3 have been separated   from the context in which they may appear.  Depending on the concrete   circumstances, an implementer may decide to address a certain   relevant subset of the requirements.   The use cases in the context of networks with constrained devices can   be found in [RFC7548].  This document provides a list of objectives   for discussions and does not aim to be a strict requirements document   for all use cases.  In fact, there likely is not a single solution   that works equally well for all the use cases.1.2.  Terminology   Concerning constrained devices and networks, this document generally   builds on the terminology defined in [RFC7228], where the terms   "constrained device", "constrained network", and others are defined.   Additionally, the following terms are used throughout:   AMI:   (Advanced Metering Infrastructure) A system including          hardware, software, and networking technologies that measures,          collects, and analyzes energy use and that communicates with a          hierarchically deployed network of metering devices, either on          request or on a schedule.   C0:    Class 0 constrained device as defined inSection 3 of          [RFC7228].Ersue, et al.                 Informational                     [Page 4]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   C1:    Class 1 constrained device as defined inSection 3 of          [RFC7228].   C2:    Class 2 constrained device as defined inSection 3 of          [RFC7228].   Network of Constrained Devices:  A network to which constrained          devices are connected that may or may not be a constrained          network (see [RFC7228] for the definition of the term          constrained network).   M2M:   (Machine to Machine) The automatic data transfer between          devices of different kinds.  In M2M scenarios, a device (such          as a sensor or meter) captures an event, which is relayed          through a network (wireless, wired, or hybrid) to an          application.   MANET: (Mobile Ad Hoc Network [RFC2501]) A self-configuring and          infrastructureless network of mobile devices connected by          wireless technologies.   Smart Grid:  An electrical grid that uses communication technologies          to gather and act on information in an automated fashion to          improve the efficiency, reliability, and sustainability of the          production and distribution of electricity.   Smart Meter:  An electrical meter in the context of a smart grid.   For a detailed discussion on the constrained networks as well as   classes of constrained devices and their capabilities, please see   [RFC7228].1.3.  Network Types and Characteristics in Focus   In this document, we differentiate the following types of networks   concerning their transport and communication technologies:   (Note that a network in general can involve constrained and   unconstrained devices.)   1.  Wireline unconstrained networks, e.g., an Ethernet LAN with       constrained and unconstrained devices involved.   2.  A combination of wireline and wireless networks, possibly with a       multi-hop connectivity between constrained devices, utilizing       dynamic routing in both the wireless and wireline portions of the       network.  Such networks usually support highly distributed       applications with many nodes (e.g., environmental monitoring) andErsue, et al.                 Informational                     [Page 5]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015       tend to deal with large-scale multipoint-to-point (MP2P) systems.       Wireless Mesh Networks (WMNs), as a specific variant, use off-       the-shelf radio technology such as Wi-Fi, WiMAX, and cellular       3G/4G.  WMNs are reliable based on the redundancy they offer and       have often a more planned deployment to provide dynamic and cost       effective connectivity over a certain geographic area.   3.  A combination of wireline and wireless networks with point-to-       point (P2P) or point-to-multipoint (P2MP) communication generally       with single-hop connectivity to constrained devices, utilizing       static routing over the wireless network.  Such networks support       short-range, P2P, low-data-rate, source-to-sink types of       applications, such as RFID systems, light switches, fire/smoke       detectors, and home appliances.  This type of network also       supports confined short-range spaces such as a home, a factory, a       building, or the human body.  [IEEE802.15.1] (Bluetooth) and       [IEEE802.15.4] are well-known examples of applicable standards       for such networks.  By using 6LoWPANs (IPv6 over Low-Power       Wireless Personal Area Networks) [RFC4919] and RPL (Routing       Protocol for Low-Power and Lossy Networks) [RFC6550] on top of       IEEE 802.15.4, multi-hop connectivity and dynamic routing can be       achieved.  With RPL, the IETF has specified a proactive "route-       over" architecture where routing and forwarding is implemented at       the network layer.  The protocol provides a mechanism whereby       MP2P, P2MP, and P2P traffic are supported.   4.  Self-configuring infrastructureless networks of mobile devices       (e.g., MANET) are a particular type of network connected by       wireless technologies.  Infrastructureless networks are mostly       based on P2P communications of devices moving independently in       any direction and changing the links to other devices frequently.       Such devices do act as a router to forward traffic unrelated to       their own use.   Wireline unconstrained networks with constrained and unconstrained   devices are mainly used for specific applications like Building   Automation or Infrastructure Monitoring.  Wireline and wireless   networks with multi-hop or P2MP connectivity are used, e.g., for   environmental monitoring as well as transport and mobile   applications.   Furthermore, different network characteristics are determined by   multiple dimensions: dynamicity of the topology, bandwidth, and loss   rate.  In the following, each dimension is explained, and networks in   scope for this document are outlined:Ersue, et al.                 Informational                     [Page 6]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Network Topology:   The topology of a network can be represented as a graph, with edges   (i.e., links) and vertices (routers and hosts).  Examples of   different topologies include "star" topologies (with one central node   and multiple nodes in one-hop distance), tree structures (with each   node having exactly one parent), directed acyclic graphs (with each   node having one or more parents), clustered topologies (where one or   more "cluster heads" are responsible for a certain area of the   network), mesh topologies (fully distributed), etc.   Management protocols may take advantage of specific network   topologies, for example, by distributing large-scale management tasks   amongst multiple distributed network management stations (e.g., in   case of a mesh topology), or by using a hierarchical management   approach (e.g., in case of a tree or clustered topology).  These   different management topology options are described inSection 1.6.   Note that in certain network deployments, such as community ad hoc   networks (see the use case "Community Network Applications" in   [RFC7548]), the topology is not preplanned; thus, it may be unknown   for management purposes.  In other use cases, such as industrial   applications (see the use case "Industrial Applications" in   [RFC7548]), the topology may be designed in advance and therefore   taken advantage of when managing the network.   Dynamicity of the network topology:   The dynamicity of the network topology determines the rate of change   of the graph as a function of time.  Such changes can occur due to   different factors, such as mobility of nodes (e.g., in MANETs or   cellular networks), duty cycles (for low-power devices enabling their   network interface only periodically to transmit or receive packets),   or unstable links (in particular wireless links with strongly   fluctuating link quality).   Examples of different levels of dynamicity of the topology are   Ethernets (with typically a very static topology) on the one side,   and Low-power and Lossy Networks (LLNs) on the other side.  LLNs   nodes are often duty-cycled and operate on unreliable wireless links   and are potentially mobile (e.g., for sensor networks).   The more dynamic the topology is, the more have routing, transport   and application-layer protocols to cope with interrupted connectivity   and/or longer delays.  For example, management protocols (with a   given underlying transport protocol) that expect continuous session   flows without changes of routes during a communication flow, may fail   to operate.Ersue, et al.                 Informational                     [Page 7]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Networks with a very low dynamicity (e.g., Ethernet) with no or   infrequent topology changes (e.g., less than once every 30 minutes),   are in the scope of this document if they are used with constrained   devices (see, e.g., the use case "Building Automation" in [RFC7548]).   Traffic flows:   The traffic flow in a network determines from which sources data   traffic is sent to which destinations in the network.  Several   different traffic flows are defined in [RFC7102], including P2P,   MP2P, and P2MP flows as:   o  P2P: Point-to-point refers to traffic exchanged between two nodes      (regardless of the number of hops between the two nodes).   o  P2MP: Point-to-multipoint traffic refers to traffic between one      node and a set of nodes.  This is similar to the P2MP concept in      Multicast or MPLS Traffic Engineering.   o  MP2P: Multipoint-to-point is used to describe a particular traffic      pattern (e.g., MP2P flows collecting information from many nodes      flowing inwards towards a collecting sink).   If one of these traffic patterns is predominant in a network,   protocols (routing, transport, application) may be optimized for the   specific traffic flow.  For example, in a network with a tree   topology and MP2P traffic, collection tree protocols are efficient to   send data from the leaves of the tree to the root of the tree, via   each node's parent.   Bandwidth:   The bandwidth of the network is the amount of data that can be sent   per unit of time between two communication endpoints.  It is usually   determined by the link with the minimum bandwidth on the path from   the source to the destination of data packets.  The bandwidth in   networks can range from a few kilobytes per second (such as on some   IEEE 802.15.4 link layers) to many gigabytes per second (e.g., on   fiber optics).   For management purposes, the management protocol typically requires   the sending of information between the network management station and   the clients, for monitoring or control purposes.  If the available   bandwidth is insufficient for the management protocol, packets will   be buffered and eventually dropped; thus, management is not possible   with such a protocol.Ersue, et al.                 Informational                     [Page 8]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Networks without bandwidth limitation (e.g., Ethernet) are in the   scope of this document if they are used with constrained devices (see   the use case "Building Automation" in [RFC7548]).   Loss rate:   The loss rate (or bit error rate) is the number of bit errors divided   by the total number of bits transmitted.  For wired networks, loss   rates are typically extremely low, e.g., around 10^-12 or 10^-13 for   the latest 10 Gbit Ethernet.  For wireless networks, such as IEEE   802.15.4, the bit error rate can be as high as 10^-1 to 1 in case of   interferences.  Even when using a reliable transport protocol,   management operations can fail if the loss rate is too high, unless   they are specifically designed to cope with these situations.1.4.  Constrained Device Deployment Options   We differentiate the following deployment options for the constrained   devices:   o  A network of constrained devices that communicate with each other,   o  Constrained devices that are connected directly to an IP network,   o  A network of constrained devices that communicate with a gateway      or proxy with more communication capabilities possibly acting as a      representative of the device to entities in the unconstrained      network,   o  Constrained devices that are connected to the Internet or an IP      network via a gateway/proxy,   o  A hierarchy of constrained devices, e.g., a network of C0 devices      connected to one or more C1 devices -- connected to one or more C2      devices -- connected to one or more gateways -- connected to some      application servers or NMS, and   o  The possibility of device grouping (possibly in a dynamic manner)      such as that the grouped devices can act as one logical device at      the edge of the network and one device in this group can act as      the managing entity.Ersue, et al.                 Informational                     [Page 9]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 20151.5.  Management Topology Options   We differentiate the following options for the management of networks   of constrained devices:   o  A network of constrained devices managed by one central manager.      A logically centralized management might be implemented in a      hierarchical fashion for scalability and robustness reasons.  The      manager and the management application logic might have a gateway/      proxy in between or might be on different nodes in different      networks, e.g., management application running on a cloud server.   o  Distributed management, where a network of constrained devices is      managed by more than one manager.  Each manager controls a      subnetwork and may communicate directly with other manager      stations in a cooperative fashion.  The distributed management may      be weakly distributed, where functions are broken down and      assigned to many managers dynamically, or strongly distributed,      where almost all managed things have embedded management      functionality and explicit management disappears, which usually      comes with the price that the strongly distributed management      logic now needs to be managed.   o  Hierarchical management, where a hierarchy of networks with      constrained devices are managed by the managers at their      corresponding hierarchy level.  That is, each manager is      responsible for managing the nodes in its subnetwork.  It passes      information from its subnetwork to its higher-level manager and      disseminates management functions received from the higher-level      manager to its subnetwork.  Hierarchical management is essentially      a scalability mechanism, logically the decision-making may be      still centralized.1.6.  Managing the Constrainedness of a Device or Network   The capabilities of a constrained device or network and the   constrainedness thereof influence and have an impact on the   requirements for the management of such a network or devices.   Note that the list below gives examples and does not claim   completeness.   A constrained device:   o  might only support an unreliable (e.g., lossy) radio link, i.e.,      the client and server of a management protocol need to gracefully      handle incomplete command exchanges or missing commands.Ersue, et al.                 Informational                    [Page 10]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   o  might only be able to go online from time to time, where it is      reachable, i.e., a command might be necessary to repeat after a      longer timeout or the timeout value with which one endpoint waits      on a response needs to be sufficiently high.   o  might only be able to support a limited operating time (e.g.,      based on the available battery) or may behave as 'sleepy      endpoints', setting their network links to a disconnected state      during long periods of time, i.e., the devices need to economize      their energy usage with suitable mechanisms and the managing      entity needs to monitor and control the energy status of the      constrained devices it manages.   o  might only be able to support one simple communication protocol,      i.e., the management protocol needs to be possible to downscale      from constrained (C2) to very constrained (C0) devices with      modular implementation and a very basic version with just a few      simple commands.   o  might only be able to support a communication protocol, which is      not IP based.   o  might only be able to support limited or no user and/or transport      security, i.e., the management system needs to support a less-      costly and simple but sufficiently secure authentication      mechanism.   o  might not be able to support compression and decompression of      exchanged data based on limited CPU power, i.e., an intermediary      entity which is capable of data compression should be able to      communicate with both, devices that support data compression      (e.g., C2) and devices that do not support data compression (e.g.,      C1 and C0).   o  might only be able to support a simple encryption, i.e., it would      be beneficial if the devices use cryptographic algorithms that are      supported in hardware and the encryption used is efficient in      terms of memory and CPU usage.   o  might only be able to communicate with one single managing entity      and cannot support the parallel access of many managing entities.Ersue, et al.                 Informational                    [Page 11]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   o  might depend on a self-configuration feature, i.e., the managing      entity might not know all devices in a network and the device      needs to be able to initiate connection setup for the device      configuration.   o  might depend on self- or neighbor-monitoring features, i.e., the      managing entity might not be able to monitor all devices in a      network continuously.   o  might only be able to communicate with its neighbors, i.e., the      device should be able to get its configuration from a neighbor.   o  might only be able to support parsing of data models with limited      size, i.e., the device data models need to be compact containing      the most necessary data and if possible parsable as a stream.   o  might only be able to support a limited or no-failure detection,      i.e., the managing entity needs to handle the situation, where a      failure does not get detected or gets detected late gracefully,      e.g., with asking repeatedly.   o  might only be able to support the reporting of just one or a      limited set failure types.   o  might only be able to support a limited set of notifications,      possible only an "I am alive." message.   o  might only be able to support a soft-reset from failure recovery.   o  might possibly generate a large amount of redundant reporting      data, i.e., the intermediary management entity (see [RFC7252])      should be able to filter and aggregate redundant data.   A network of constrained devices:   o  might only support an unreliable (e.g., lossy) radio link, i.e.,      the client and server of a management protocol need to repeat      commands as necessary or gracefully ignore incomplete commands.   o  might be necessary to manage based on multicast communication,      i.e., the managing entity needs to be prepared to configure many      devices at once based on the same data model.   o  might have a very large topology supporting 10,000 or more nodes      for some applications and as such node naming is a specific issue      for constrained networks.Ersue, et al.                 Informational                    [Page 12]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   o  needs to support self-organization, i.e., given the large number      of nodes and their potential placement in hostile locations and      frequently changing topology, manual configuration of nodes is      typically not feasible.  As such, the network would benefit from      the ability to reconfigure itself so that it can continue to      operate properly and support reliable connectivity.   o  might need a management solution that is energy efficient, using      as little wireless bandwidth as possible since communication is      highly energy demanding.   o  needs to support localization schemes to determine the location of      devices since the devices might be moving and location information      is important for some applications.   o  needs a management solution that is scalable as the network may      consist of thousands of nodes and may need to be extended      continuously.   o  needs to provide fault tolerance.  Faults in network operation      including hardware and software errors or failures detected by the      transport protocol should be handled smoothly.  In such a case, it      should be possible to run the protocol at a reduced level but      avoid failing completely.  For example, self-monitoring mechanisms      or graceful degradation of features can be used to provide fault      tolerance.   o  might require new management capabilities, for example, network      coverage information and a constrained device power distribution      map.   o  might require a new management function for data management, since      the type and amount of data collected in constrained networks is      different from those of the traditional networks.   o  might also need energy-efficient key management.1.7.  Configuration and Monitoring Functionality Levels   Devices often differ significantly on the level of configuration   management support they provide.  This document classifies the   configuration management functionality as follows:   CL0:  Devices are preconfigured and allow no runtime configuration         changes.  Configuration parameters are often hard coded and         compiled directly into the firmware image.Ersue, et al.                 Informational                    [Page 13]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   CL1:  Devices have explicit configuration objects.  However, changes         require a restart of the device to take effect.   CL2:  Devices allow management systems to replace the entire         configuration (or predetermined subsets) in bulk.         Configuration changes take effect by soft-restarts of the         system (or subsystems).   CL3:  Devices allow management systems to modify configuration         objects without bulk replacements and changes take effect         immediately.   CL4:  Devices support multiple configuration datastores and they         might distinguish between the currently running and the next         startup configuration.   CL5:  Devices support configuration datastore locking and device-         local configuration change transactions, i.e., either all         configuration changes are applied or none of them are.   CL6:  Devices support configuration change transactions across         devices.   This document defines a classification of devices with regard to   different levels of monitoring support.  In general, a device may be   in several of the levels listed below:   ML0:  Devices push predefined monitoring data.   ML1:  Devices allow management systems to pull predefined monitoring         data.   ML2:  Devices allow management systems to pull user-defined filtered         subsets of monitoring data.   ML3:  Devices are able to locally process monitoring data in order to         detect threshold crossings or to aggregate data.   At the time of this writing, constrained devices often implement a   combination of one of CL0-CL2 with one of ML0-ML1.2.  Problem Statement   The terminology for the "Internet of Things" is still nascent, and   depending on the network type or layer in focus, diverse technologies   and terms are in use.  Common to all these considerations is the   "Things" or "Objects" are supposed to have physical or virtual   identities using interfaces to communicate.  In this context, we needErsue, et al.                 Informational                    [Page 14]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   to differentiate between the constrained and smart devices identified   by an IP address compared to virtual entities such as Smart Objects,   which can be identified as a resource or a virtual object by using a   unique identifier.  Furthermore, the smart devices usually have   limited memory and CPU power as well as aim to be self-configuring   and easy to deploy.   However, the constraints of the network nodes require a rethinking of   the protocol characteristics concerning power consumption,   performance, bandwidth consumption, memory, and CPU usage.  As such,   there is a demand for protocol simplification, energy-efficient   communication, less CPU usage, and a smaller memory footprint.   On the application layer, the IETF is already developing protocols   like the Constrained Application Protocol (CoAP) [RFC7252] enabling   the communication of constrained devices and networks, e.g., for   smart energy applications or home automation environments.  In fact,   the deployment of such an environment involves many, in some   scenarios up to million, constrained devices (e.g., smart meters),   which produce a large amount of data.  This data needs to be   collected, filtered, and preprocessed for further use in diverse   services.   Considering the high number of nodes to deploy, one has to think   about the manageability aspects of the smart devices and plan for   easy deployment, configuration, and management of the networks of   constrained devices as well as the devices themselves.  Consequently,   seamless monitoring and self-configuration of such network nodes   becomes more and more imperative.  Self-configuration and self-   management are already a reality in the standards of some   organizations such as 3GPP.  To introduce self-configuration of smart   devices successfully, a device-initiated connection establishment is   often required.   A simple and efficient application-layer protocol, such as CoAP, is   essential to address the issue of efficient object-to-object   communication and information exchange.  Such an information exchange   should be done based on interoperable data models to enable the   exchange and interpretation of diverse application- and management-   related data.   In an ideal world, we would have only one network management protocol   for monitoring, configuration, and exchanging management data,   independently of the type of the network (e.g., smart grid, wireless   access, or core network).  Furthermore, it would be desirable to   derive the basic data models for constrained devices from the core   models used today to enable reuse of functionality and end-to-end   information exchange.  However, the current management protocols seemErsue, et al.                 Informational                    [Page 15]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   to be too heavyweight compared to the capabilities the constrained   devices have and are not applicable directly for use in a network of   constrained devices.  Furthermore, the data models addressing the   requirements of such smart devices need yet to be designed.   So far, the IETF has not developed any specific technologies for the   management of constrained devices and the networks comprised by   constrained devices.  IP-based sensors or constrained devices in such   an environment, i.e., today, devices with very limited memory and CPU   resources use, e.g., application-layer protocols to do simple   resource management and monitoring.  This might be sufficient for   some basic cases; however, there is a need to reconsider the network   management mechanisms based on the new, changed, and reduced   requirements coming from smart devices and the network of such   constrained devices.  Although it is questionable whether we can take   the same comprehensive approach we use in an IP network and use it   for the management of constrained devices.  Hence, the management of   a network with constrained devices is necessarily designed in a   simplified and less complex manner.   AsSection 1.6 highlights, there are diverse characteristics of   constrained devices or networks, which stem from their   constrainedness and therefore have an impact on the requirements for   the management of such a network with constrained devices.  The use   cases discussed in [RFC7548] show that the requirements on   constrained networks are manifold and need to be analyzed from   different angles, e.g., concerning the design of the management   architecture, the selection of the appropriate protocol features, as   well as the specific issues that are new in the context of   constrained devices.  Examples of such issues are careful management   of scarce energy resources, the necessity for self-organization and   self-management of such devices but also the implementation   considerations to enable the use of common communication technologies   on a constrained hardware in an efficient manner.  For an exhaustive   list of issues and requirements that need to be addressed for the   management of a network with constrained devices, please see Sections   1.6 and 3.3.  Requirements on the Management of Networks with Constrained Devices   This section describes the requirements categorized by management   areas listed in subsections.   Note that the requirements listed in this section have been separated   from the context in which they may appear.  In general, this document   does not recommend the realization of any subset of the described   requirements.  As such, this document avoids selecting any of the   requirements as mandatory to implement.  A device might be able toErsue, et al.                 Informational                    [Page 16]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   provide only a particular selected set of requirements and might not   be capable to provide all requirements in this document.  On the   other hand, a device vendor might select a specific relevant subset   of the requirements to implement.   The following template is used for the definition of the   requirements.   Req-ID:  An ID composed of two numbers: a section number indicating      the topic area and a unique three-digit number per section.   Title:  The title of the requirement.   Description:  The rationale and description of the requirement.   Source:  The origin of the requirement and the matching use case or      application.  For the discussion of referred use cases for      constrained management, please see [RFC7548].   Requirement Type:  Functional Requirement, Non-functional      Requirement.  A functional requirement is related to a function or      component.  As such, functional requirements may be technical      details or specific functionality that define what a system is      supposed to accomplish.  Non-functional requirements (also known      as design constraints or quality requirements) impose      implementation-related considerations such as performance      requirements, security, or reliability.   Device type:  The device types by which this requirement can be      supported: C0, C1, and/or C2.   Priority:  The priority of the requirement showing its importance for      a particular type of device: High, Medium, and Low.  The priority      of a requirement can be High, e.g., for a C2 device, but Low for a      C1 or C0 device, as the realization of complex features in a C1      device is in many cases not possible.Ersue, et al.                 Informational                    [Page 17]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 20153.1.  Management Architecture/System   Req-ID:  1.001   Title:  Support multiple device classes within a single network   Description:  Larger networks usually consist of devices belonging to      different device classes (e.g., constrained mesh endpoints and      less constrained routers) communicating with each other.  Hence,      the management architecture must be applicable to networks that      have a mix of different device classes.  SeeSection 3 of      [RFC7228] for the definition of Constrained Device Classes.   Source:  All use cases   Requirement Type:  Non-functional Requirement   Device type:  C1 and/or C2   Priority:  High   ---   Req-ID:  1.002   Title:  Management scalability   Description:  The management architecture must be able to scale with      the number of devices involved and operate efficiently in any      network size and topology.  This implies that, e.g., the managing      entity is able to handle large amounts of device monitoring data      and the management protocol is not sensitive to the decrease of      the time between two client requests.  To achieve good      scalability, caching techniques, in-network data aggregation      techniques, and hierarchical management models may be used.   Source:  General requirement for all use cases to enable large-scale      networks   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---   Req-ID:  1.003Ersue, et al.                 Informational                    [Page 18]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Title:  Hierarchical management   Description:  Provide a means of hierarchical management, i.e.,      provide intermediary management entities on different levels,      which can take over the responsibility for the management of a      subhierarchy of the network of constraint devices.  The      intermediary management entity can, e.g., support management data      aggregation to handle, e.g., high-frequent monitoring data or      provide a caching mechanism for the uplink and downlink      communication.  Hierarchical management contributes to management      scalability.   Source:  Use cases where a large amount of devices are deployed with      a hierarchical topology   Requirement Type:  Non-functional Requirement   Device type:  Managing and intermediary entities   Priority:  Medium   ---   Req-ID:  1.004   Title:  Minimize state maintained on constrained devices   Description:  The amount of state that needs to be maintained on      constrained devices should be minimized.  This is important in      order to save memory (especially relevant for C0 and C1 devices)      and in order to allow devices to restart, for example, to apply      configuration changes or to recover from extended periods of      inactivity.   Note:  One way to achieve this is to adopt a RESTful architecture      that minimizes the amount of state maintained by managed      constrained devices and that makes resources of a device      addressable via URIs.   Source:  Basic requirement that concerns all use cases   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---Ersue, et al.                 Informational                    [Page 19]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  1.005   Title:  Automatic resynchronization with eventual consistency   Description:  To support large scale networks, where some constrained      devices may be offline at any point in time, it is necessary to      distribute configuration parameters in a way that allows temporary      inconsistencies but eventually converges, after a sufficiently      long period of time without further changes, towards global      consistency.   Source:  Use cases with large-scale networks with many devices   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---   Req-ID:  1.006   Title:  Support for lossy links and unreachable devices   Description:  Some constrained devices will only be able to support      lossy and unreliable links characterized by a limited data rate, a      high latency, and a high transmission error rate.  Furthermore,      constrained devices often duty cycle their radio or the whole      device in order to save energy.  Some classes of devices labeled      as 'sleepy endpoints' set their network links to a disconnected      state during long periods of time.  In all cases, the management      system must not assume that constrained devices are always      reachable.   Source:  Basic requirement for networks of constrained devices with      unreliable links and constrained devices that sleep to save energy   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---Ersue, et al.                 Informational                    [Page 20]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  1.007   Title:  Network-wide configuration   Description:  Provide means by which the behavior of the network can      be specified at a level of abstraction (network-wide      configuration) higher than a set of configuration information      specific to individual devices.  It is useful to derive the      device-specific configuration from the network-wide configuration.      Such a repository can be used to configure predefined device or      protocol parameters for the whole network.  Furthermore, such a      network-wide view can be used to monitor and manage a group of      routers or a whole network.  For example, monitoring the      performance of a network requires information additional to what      can be acquired from a single router using a management protocol.   Note:  The identification of the relevant subset of the policies to      be provisioned is according to the capabilities of each device and      can be obtained from a preconfigured data-repository.   Source:  In general, all use cases of network and device      configuration based on a network view in a top-down manner   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium   ---   Req-ID:  1.008   Title:  Distributed management   Description:  Provide a means of simple distributed management, where      a network of constrained devices can be managed or monitored by      more than one manager.  Since the connectivity to a server cannot      be guaranteed at all times, a distributed approach may provide      higher reliability, at the cost of increased complexity.  This      requirement implies the handling of data consistency in case of      concurrent read and write access to the device datastore.  It      might also happen that no management (configuration) server is      accessible and the only reachable node is a peer device.  In this      case, the device should be able to obtain its configuration from      peer devices.Ersue, et al.                 Informational                    [Page 21]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Source:  Use cases where the count of devices to manage is high   Requirement Type:  Non-functional Requirement   Device type:  C1 and C2   Priority:  Medium3.2.  Management Protocols and Data Models   Req-ID:  2.001   Title:  Modular implementation of management protocols   Description:  Management protocols should be specified to allow for      modular implementations, i.e., it should be possible to implement      only a basic set of protocol primitives on highly constrained      devices, while devices with additional resources may provide more      support for additional protocol primitives.  SeeSection 1.7 for a      discussion on the level of configuration management and monitoring      support constrained devices may provide.   Source:  Basic requirement interesting for all use cases   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---   Req-ID:  2.002   Title:  Compact encoding of management data   Description:  The encoding of management data should be compact and      space efficient, enabling small message sizes.   Source:  General requirement to save memory for the receiver buffer      and on-air bandwidth   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  HighErsue, et al.                 Informational                    [Page 22]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   ---   Req-ID:  2.003   Title:  Compression of management data or complete messages   Description:  Management data exchanges can be further optimized by      applying data compression techniques or delta encoding techniques.      Compression typically requires additional code size and some      additional buffers and/or the maintenance of some additional state      information.  For C0 devices, compression may not be feasible.   Source:  Use cases where it is beneficial to reduce transmission time      and bandwidth, e.g., mobile applications that require saving on-      air bandwidth   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  Medium   ---   Req-ID:  2.004   Title:  Mapping of management protocol interactions   Description:  It is desirable to have a lossless automated mapping      between the management protocol used to manage constrained devices      and the management protocols used to manage regular devices.  In      the ideal case, the same core management protocol can be used with      certain restrictions taking into account the resource limitations      of constrained devices.  However, for very resource-constrained      devices, this goal might not be achievable.   Source:  Use cases where high-frequency interaction with the      management system of a unconstrained network is required   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  Medium   ---Ersue, et al.                 Informational                    [Page 23]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  2.005   Title:  Consistency of data models with the underlying information      model   Description:  The data models used by the management protocol must be      consistent with the information model used to define data models      for unconstrained networks.  This is essential to facilitate the      integration of the management of constrained networks with the      management of unconstrained networks.  Using an underlying      information model for future data model design enables further      top-down model design and model reuse as well as data      interoperability (i.e., exchange of management information between      the constrained and unconstrained networks).  This is a strong      requirement, despite the fact that the underlying information      models are often not explicitly documented in the IETF.   Source:  General requirement to support data interoperability,      consistency, and model reuse   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---   Req-ID:  2.006   Title:  Lossless mapping of management data models   Description:  It is desirable to have a lossless automated mapping      between the management data models used to manage regular devices      and the management data models used for managing constrained      devices.  In the ideal case, the same core data models can be used      with certain restrictions taking into account the resource      limitations of constrained devices.  However, for very resource-      constrained devices, this goal might not be achievable.   Source:  Use cases where consistent data exchange with the management      system of a unconstrained network is required   Requirement Type:  Functional Requirement   Device type:  C2   Priority:  MediumErsue, et al.                 Informational                    [Page 24]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   ---   Req-ID:  2.007   Title:  Protocol extensibility   Description:  Provide means of extensibility for the management      protocol, i.e., by adding new protocol messages or mechanisms that      can deal with changing requirements on a supported message and      data types effectively, without causing interoperability problems      or having to replace/update large amount of deployed devices.   Source:  Basic requirement useful for all use cases   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High3.3.  Configuration Management   Req-ID:  3.001   Title:  Self-configuration capability   Description:  Automatic configuration and reconfiguration of devices      without manual intervention.  Compared to the traditional      management of devices where the management application is the      central entity configuring the devices, in the autoconfiguration      scenario the device is the active part and initiates the      configuration process.  Self-configuration can be initiated during      the initial configuration or for subsequent configurations, where      the configuration data needs to be refreshed.  Self-configuration      should be also supported during the initialization phase or in the      event of failures, where prior knowledge of the network topology      is not available or the topology of the network is uncertain.   Source:  In general, all use cases requiring easy deployment and      plug&play behavior as well as easy maintenance of many constrained      devices   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High for device categories C0 and C1; Medium for C2Ersue, et al.                 Informational                    [Page 25]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   ---   Req-ID:  3.002   Title:  Capability discovery   Description:  Enable the discovery of supported optional management      capabilities of a device and their exposure via at least one      protocol and/or data model.   Source:  Use cases where the device interaction with other devices or      applications is a function of the level of support for its      capabilities   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  Medium   ---   Req-ID:  3.003   Title:  Asynchronous transaction support   Description:  Provide configuration management with asynchronous      (event-driven) transaction support.  Configuration operations must      support a transactional model, with asynchronous indications that      the transaction was completed.   Source:  Use cases that require transaction-oriented processing      because of reliability or distributed architecture functional      requirements   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  Medium   ---Ersue, et al.                 Informational                    [Page 26]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  3.004   Title:  Network reconfiguration   Description:  Provide a means of iterative network reconfiguration in      order to recover the network from node and communication failures.      The network reconfiguration can be failure-driven and self-      initiated (automatic reconfiguration).  The network      reconfiguration can be also performed on the whole hierarchical      structure of a network (network topology).   Source:  Practically all use cases, as network connectivity is a      basic requirement   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium3.4.  Monitoring Functionality   Req-ID:  4.001   Title:  Device status monitoring   Description:  Provide a monitoring function to collect and expose      information about device status and expose it via at least one      management interface.  The device monitoring might make use of the      hierarchical management through the intermediary entities and the      caching mechanism.  The device monitoring might also make use of      neighbor-monitoring (fault detection in the local network) to      support fast fault detection and recovery, e.g., in a scenario      where a managing entity is unreachable and a neighbor can take      over the monitoring responsibility.   Source:  All use cases   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High; Medium for neighbor-monitoring   ---Ersue, et al.                 Informational                    [Page 27]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  4.002   Title:  Energy status monitoring   Description:  Provide a monitoring function to collect and expose      information about device energy parameters and usage (e.g.,      battery level and average power consumption).   Source:  Use case "Energy Management"   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High for energy reporting devices; Low for others   ---   Req-ID:  4.003   Title:  Monitoring of current and estimated device availability   Description:  Provide a monitoring function to collect and expose      information about current device availability (energy, memory,      computing power, forwarding-plane utilization, queue buffers,      etc.) and estimation of remaining available resources.   Source:  All use cases.  Note that monitoring energy resources (like      battery status) may be required on all kinds of devices.   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium   ---Ersue, et al.                 Informational                    [Page 28]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  4.004   Title:  Network status monitoring   Description:  Provide a monitoring function to collect, analyze, and      expose information related to the status of a network or network      segments connected to the interface of the device.   Source:  All use cases   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  Low, based on the realization complexity   ---   Req-ID:  4.005   Title:  Self-monitoring   Description:  Provide self-monitoring (local fault detection) feature      for fast fault detection and recovery.   Source:  Use cases where the devices cannot be monitored centrally in      an appropriate manner, e.g., self-healing is required   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  High for C2; Medium for C1   ---   Req-ID:  4.006   Title:  Performance monitoring   Description:  The device will provide a monitoring function to      collect and expose information about the basic performance      parameter of the device.  The performance management functionality      might make use of the hierarchical management through the      intermediary devices.Ersue, et al.                 Informational                    [Page 29]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Source:  Use cases "Building Automation" and "Transport Applications"   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  Low   ---   Req-ID:  4.007   Title:  Fault detection monitoring   Description:  The device will provide fault detection monitoring.      The system collects information about network states in order to      identify whether faults have occurred.  In some cases, the      detection of the faults might be based on the processing and      analysis of the parameters retrieved from the network or other      devices.  In case of C0 devices, the monitoring might be limited      to the check whether or not the device is alive.   Source:  Use cases "Environmental Monitoring", "Building Automation",      "Energy Management", "Infrastructure Monitoring"   Requirement Type:  Functional Requirement   Device type:  C0, C1 and C2   Priority:  Medium   ---   Req-ID:  4.008   Title:  Passive and reactive monitoring   Description:  The device will provide passive and reactive monitoring      capabilities.  The system or manager collects information about      device components and network states (passive monitoring) and may      perform postmortem analysis of collected data.  In case events of      interest have occurred, the system or the manager can adaptively      react (reactive monitoring), e.g., reconfigure the network.      Typically, actions (reactions) will be executed or sent as      commands by the management applications.   Source:  Diverse use cases relevant for device status and network      state monitoringErsue, et al.                 Informational                    [Page 30]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Requirement Type:  Functional Requirement   Device type:  C2   Priority:  Medium   ---   Req-ID:  4.009   Title:  Recovery   Description:  Provide local, central and hierarchical recovery      mechanisms (recovery is in some cases achieved by recovering the      whole network of constrained devices).   Source:  Use cases "Industrial Applications", "Home Automation", and      "Building Automation", as well as mobile applications that involve      different forms of clustering or area managers   Requirement Type:  Functional Requirement   Device type:  C2   Priority:  Medium   ---   Req-ID:  4.010   Title:  Network topology discovery   Description:  Provide a network topology discovery capability (e.g.,      use of topology extraction algorithms to retrieve the network      state) and a monitoring function to collect and expose information      about the network topology.   Source:  Use cases "Community Network Applications" and mobile      applications   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  Low, based on the realization complexity   ---Ersue, et al.                 Informational                    [Page 31]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  4.011   Title:  Notifications   Description:  The device will provide the capability of sending      notifications on critical events and faults.   Source:  All use cases   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium for C2; Low for C0 and C1   ---   Req-ID:  4.012   Title:  Logging   Description:  The device will provide the capability of building,      keeping, and allowing retrieval of logs of events (including but      not limited to critical faults and alarms).   Source:  Use cases "Industrial Applications", "Building Automation",      and "Infrastructure Monitoring"   Requirement Type:  Functional Requirement   Device type:  C2   Priority:  High for some medical or industrial applications; Medium      otherwise3.5.  Self-Management   Req-ID:  5.001   Title:  Self-management -- Self-healing   Description:  Enable event-driven and/or periodic self-management      functionality in a device.  The device should be able to react in      case of a failure, e.g., by initiating a fully or partly reset and      initiate a self-configuration or management data update as      necessary.  A device might be further able to check for failuresErsue, et al.                 Informational                    [Page 32]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015      cyclically or on a schedule in order to trigger self-management as      necessary.  It is a matter of device design and subject for      discussion how much self-management a C1 device can support.      Failure detection and self-management logic are assumed to be      generally useful for the self-healing of a device.   Source:  The requirement generally relates to all use cases in this      document.   Requirement Type:  Functional Requirement   Device type:  C1 and C2   Priority:  High for C2; Medium for C13.6.  Security and Access Control   Req-ID:  6.001   Title:  Authentication of management system and devices   Description:  Systems having a management role must be properly      authenticated to the device such that the device can exercise      proper access control and in particular distinguish rightful      management systems from rogue systems.  On the other hand, managed      devices must authenticate themselves to systems having a      management role such that management systems can protect      themselves from rogue devices.  In certain application scenarios,      it is possible that a large number of devices need to be      (re-)started at about the same time.  Protocols and authentication      systems should be designed such that a large number of devices      (re-)starting simultaneously does not negatively impact the device      authentication process.   Source:  Basic security requirement for all use cases   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High; Medium for the (re-)start of a large number of      devices   ---Ersue, et al.                 Informational                    [Page 33]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  6.002   Title:  Support suitable security bootstrapping mechanisms   Description:  Mechanisms should be supported that simplify the      bootstrapping of device that is the discovery of newly deployed      devices in order to provide them with appropriate access control      permissions.   Source:  Basic security requirement for all use cases   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---   Req-ID:  6.003   Title:  Access control on management system and devices   Description:  Systems acting in a management role must provide an      access control mechanism that allows the security administrator to      restrict which devices can access the managing system (e.g., using      an access control white list of known devices).  On the other      hand, managed constrained devices must provide an access control      mechanism that allows the security administrator to restrict how      systems in a management role can access the device (e.g., no-      access, read-only access, and read-write access).   Source:  Basic security requirement for use cases where access      control is essential   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---   Req-ID:  6.004   Title:  Select cryptographic algorithms that are efficient in both      code space and execution timeErsue, et al.                 Informational                    [Page 34]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Description:  Cryptographic algorithms have a major impact in terms      of both code size and overall execution time.  Therefore, it is      necessary to select mandatory to implement cryptographic      algorithms that are reasonable to implement with the available      code space and that have a small impact at runtime.  Furthermore,      some wireless technologies (e.g., IEEE 802.15.4) require the      support of certain cryptographic algorithms.  It might be useful      to choose algorithms that are likely to be supported in wireless      chipsets for certain wireless technologies.   Source:  Generic requirement to reduce the footprint and CPU usage of      a constrained device   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  High; Medium for hardware-supported algorithms3.7.  Energy Management   Req-ID:  7.001   Title:  Management of energy resources   Description:  Enable managing power resources in the network, e.g.,      reduce the sampling rate of nodes with critical battery and reduce      node transmission power, put nodes to sleep, put single interfaces      to sleep, reject a management job based on available energy or      criteria predefined by the management application (such as      importance levels forcing execution even if the energy level is      low), etc.  The device may further implement standard data models      for energy management and expose it through a management protocol      interface, e.g., EMAN MIB modules [RFC7460] and [RFC7461] as well      as other EMAN extensions.  It might be necessary to use a subset      of EMAN MIBs for C1 and C2 devices.   Source:  Use case "Energy Management"   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium for the use case "Energy Management"; Low otherwise   ---Ersue, et al.                 Informational                    [Page 35]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Req-ID:  7.002   Title:  Support of energy-optimized communication protocols   Description:  Use an optimized communication protocol to minimize      energy usage for the device (radio) receiver/transmitter, on-air      bandwidth usage (i.e., maximize protocol efficiency), and the      amount of data communication between nodes.  Minimizing data      communication implies data aggregation and filtering but also a      compact format for the transferred data.   Source:  Use cases "Energy Management" and mobile applications   Requirement Type:  Non-functional Requirement   Device type:  C2   Priority:  Medium   ---   Req-ID:  7.003   Title:  Support for Layer 2 (L2) energy-aware protocols   Description:  The device will support L2 energy-management protocols      (e.g., energy-efficient Ethernet [IEEE802.3az]) and be able to      report on these.   Source:  Use case "Energy Management"   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium   ---   Req-ID:  7.004   Title:  Dying gasp   Description:  When energy resources draw below the red-line level,      the device will send a "dying gasp" notification and perform, if      still possible, a graceful shutdown including conservation of      critical device configuration and status information.Ersue, et al.                 Informational                    [Page 36]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Source:  Use case "Energy Management"   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium3.8.  Software Distribution   Req-ID:  8.001   Title:  Group-based provisioning   Description:  Support group-based provisioning, i.e., firmware update      and configuration management of a large set of constrained devices      with eventual consistency and coordinated reload times.  The      device should accept group-based configuration management based on      bulk commands, which aim similar configurations of a large set of      constrained devices of the same type in a given group and which      may share a common data model.  Activation of configuration may be      based on preloaded sets of default values.   Source:  All use cases   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium3.9.  Traffic Management   Req-ID:  9.001   Title:  Congestion avoidance   Description:  Support congestion control principles as defined in      [RFC2914], e.g., the ability to avoid congestion by modifying the      device's reporting rate for periodical data (which is usually      redundant) based on the importance and reliability level of the      management data.  This functionality is usually controlled by the      managing entity, where the managing entity marks the data as      important or relevant for reliability.  However, reducing a      device's reporting rate can also be initiated by a device if it is      able to detect congestion or has insufficient buffer memory.Ersue, et al.                 Informational                    [Page 37]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Source:  Use cases with high reporting rate and traffic, e.g., AMI or      M2M   Requirement Type:  Non-functional Requirement   Device type:  C1 and C2   Priority:  Medium   ---   Req-ID:  9.002   Title:  Reroute traffic   Description:  Provide the ability for network nodes to redirect      traffic from overloaded intermediary nodes in a network to another      path in order to prevent congestion on a central server and in the      primary network.   Source:  Use cases with high reporting rate and traffic, e.g., AMI or      M2M   Requirement Type:  Non-functional Requirement   Device type:  Intermediary entity in the network   Priority:  Medium   ---   Req-ID:  9.003   Title:  Traffic Shaping   Description:  Provide the ability to apply traffic-shaping policies      to incoming and outgoing links on an overloaded intermediary node      (as necessary) in order to reduce the amount of traffic in the      network.   Source:  Use cases with high reporting rate and traffic, e.g., AMI or      M2M   Requirement Type:  Non-functional Requirement   Device type:  Intermediary entity in the network   Priority:  MediumErsue, et al.                 Informational                    [Page 38]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 20153.10.  Transport Layer   Req-ID:  10.001   Title:  Scalable transport layer   Description:  Enable the use of a scalable transport layer, i.e., not      sensitive to a high rate of incoming client requests, which is      useful for applications requiring frequent access to device data.   Source:  Applications with frequent access to the device data   Requirement Type:  Non-functional Requirement   Device type:  C0, C1 and C2   Priority:  Medium   ---   Req-ID:  10.002   Title:  Reliable unicast transport of messages   Description:  Diverse applications need a reliable transport of      messages.  The reliability might be achieved based on a transport      protocol such as TCP or can be supported based on message      repetition if an acknowledgment is missing.   Source:  Generally, applications benefit from the reliability of the      message transport   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---   Req-ID:  10.003   Title:  Best-effort multicast   Description:  Provide best-effort multicast of messages, which is      generally useful when devices need to discover a service provided      by a server or many devices need to be configured by a managing      entity at once based on the same data model.Ersue, et al.                 Informational                    [Page 39]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Source:  Use cases where a device needs to discover services as well      as use cases with high amount of devices to manage, which are      hierarchically deployed, e.g., AMI or M2M   Requirement Type:  Functional Requirement   Device type:  C0, C1, and C2   Priority:  Medium   ---   Req-ID:  10.004   Title:  Secure message transport   Description:  Enable secure message transport providing      authentication, data integrity, and confidentiality by using      existing transport-layer technologies with a small footprint such      as TLS/DTLS.   Source:  All use cases   Requirement Type:  Non-functional Requirements   Device type:  C1 and C2   Priority:  High3.11.  Implementation Requirements   Req-ID:  11.001   Title:  Avoid complex application-layer transactions requiring large      application-layer messages   Description:  Complex application-layer transactions tend to require      large memory buffers that are typically not available on C0 or C1      devices and only by limiting functionality on C2 devices.      Furthermore, the failure of a single large transaction requires      repeating the whole transaction.  On constrained devices, it is      often more desirable to split a large transaction into a sequence      of smaller transactions that require less resources and allow      making progress using a sequence of smaller steps.   Source:  Basic requirement that concerns all use cases with memory      constrained devicesErsue, et al.                 Informational                    [Page 40]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  High   ---   Req-ID:  11.002   Title:  Avoid reassembly of messages at multiple layers in the      protocol stack   Description:  Reassembly of messages at multiple layers in the      protocol stack requires buffers at multiple layers, which leads to      inefficient use of memory resources.  This can be avoided by      making sure the application layer, the security layer, the      transport layer, the IPv6 layer, and any adaptation layers are      aware of the limitations of each other such that unnecessary      fragmentation and reassembly can be avoided.  In addition, message      size constraints must be announced to protocol peers such that      they can adapt and avoid sending messages that can't be processed      due to resource constraints on the receiving device.   Source:  Basic requirement that concerns all use cases with memory      constrained devices   Requirement Type:  Non-functional Requirement   Device type:  C0, C1, and C2   Priority:  High4.  Security Considerations   This document discusses the problem statement and requirements on   networks of constrained devices.Section 1.6 mentions a number of   limitations that could prevent the implementation of strong   cryptographic algorithms.  Requirements for security and access   control are listed inSection 3.6.   Often, constrained devices might be deployed in unsafe environments   where attackers can gain physical access to the devices.  As a   consequence, it is crucial that devices are robust and tamper   resistant, have no backdoors, do not provide services that are not   essential for the primary function, and properly protect any security   credentials that may be stored on the device (e.g., by using hardware   protection mechanisms).  Furthermore, it is important that anyErsue, et al.                 Informational                    [Page 41]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   credentials leaking from a single device do not simplify the attack   on other (similar) devices.  In particular, security credentials   should never be shared.   Since constrained devices often have limited computational resources,   care should be taken in choosing efficient but cryptographically   strong cryptographic algorithms.  Designers of constrained devices   that have a long expected lifetime need to ensure that cryptographic   algorithms can be updated once devices have been deployed.  The   ability to perform secure firmware and software updates is an   important management requirement.   Constrained devices might also generate sensitive data or require the   processing of sensitive data.  Therefore, it is an important   requirement to properly protect access to the data in order to   protect the privacy of humans using Internet-enabled devices.  For   certain types of data, protection during the transmission over the   network may not be sufficient, and methods should be investigated   that provide protection of data while it is cached or stored (e.g.,   when using a store-and-forward transport mechanism).5.  Informative References   [RFC2914]  Floyd, S., "Congestion Control Principles",BCP 41,RFC 2914, DOI 10.17487/RFC2914, September 2000,              <http://www.rfc-editor.org/info/rfc2914>.   [RFC2501]  Corson, S. and J. Macker, "Mobile Ad hoc Networking              (MANET): Routing Protocol Performance Issues and              Evaluation Considerations",RFC 2501,              DOI 10.17487/RFC2501, January 1999,              <http://www.rfc-editor.org/info/rfc2501>.   [RFC6632]  Ersue, M., Ed. and B. Claise, "An Overview of the IETF              Network Management Standards",RFC 6632,              DOI 10.17487/RFC6632, June 2012,              <http://www.rfc-editor.org/info/rfc6632>.   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and              Lossy Networks",RFC 7102, DOI 10.17487/RFC7102, January              2014, <http://www.rfc-editor.org/info/rfc7102>.   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for              Constrained-Node Networks",RFC 7228,              DOI 10.17487/RFC7228, May 2014,              <http://www.rfc-editor.org/info/rfc7228>.Ersue, et al.                 Informational                    [Page 42]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015   [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>.   [RFC4919]  Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6              over Low-Power Wireless Personal Area Networks (6LoWPANs):              Overview, Assumptions, Problem Statement, and Goals",RFC 4919, DOI 10.17487/RFC4919, August 2007,              <http://www.rfc-editor.org/info/rfc4919>.   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for              Low-Power and Lossy Networks",RFC 6550,              DOI 10.17487/RFC6550, March 2012,              <http://www.rfc-editor.org/info/rfc6550>.   [RFC7460]  Chandramouli, M., Claise, B., Schoening, B., Quittek, J.,              and T. Dietz, "Monitoring and Control MIB for Power and              Energy",RFC 7460, DOI 10.17487/RFC7460, March 2015,              <http://www.rfc-editor.org/info/rfc7460>.   [RFC7461]  Parello, J., Claise, B., and M. Chandramouli, "Energy              Object Context MIB",RFC 7461, DOI 10.17487/RFC7461, March              2015, <http://www.rfc-editor.org/info/rfc7461>.   [RFC7548]  Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A.              Sehgal, "Management of Networks with Constrained Devices:              Use Cases",RFC 7548, DOI 10.17487/RFC7548, May 2015,              <http://www.rfc-editor.org/info/rfc7548>.   [IEEE802.15.4]              IEEE, "Part 15.4: Low-Rate Wireless Personal Area Networks              (LR-WPANs)", IEEE Standard 802.15.4, September 2011,              <https://standards.ieee.org/about/get/802/802.15.html>.   [IEEE802.15.1]              IEEE, "Part 15.1: Wireless medium access control (MAC) and              physical layer (PHY) specifications for wireless personal              area networks (WPANs)", IEEE Standard 802.15.1, June 2005,              <https://standards.ieee.org/about/get/802/802.15.html>.   [IEEE802.3az]              IEEE, "ETHERNET", IEEE Standard 802.3az, 2012-2014,              <https://standards.ieee.org/about/get/802/802.3.html>.Ersue, et al.                 Informational                    [Page 43]

RFC 7547       Constrained Mgmt. Problem Statement & Reqs.      May 2015Acknowledgments   The following reviewed and provided valuable comments during the   creation of this document:   Dominique Barthel, Andy Bierman, Carsten Bormann, Zhen Cao, Benoit   Claise, Hui Deng, Bert Greevenbosch, Joel M. Halpern, Ulrich Herberg,   James Nguyen, Anuj Sehgal, Zach Shelby, Peter van der Stok, Thomas   Watteyne, and Bert Wijnen.   The authors would like to thank the reviewers and the participants on   the Coman and OPSAWG mailing lists for their valuable contributions   and comments.   Juergen Schoenwaelder was partly funded by Flamingo, a Network of   Excellence project (ICT-318488) supported by the European Commission   under its Seventh Framework Programme.Authors' Addresses   Mehmet Ersue (editor)   Nokia Networks   EMail: mehmet.ersue@nokia.com   Dan Romascanu   Avaya   EMail: dromasca@avaya.com   Juergen Schoenwaelder   Jacobs University Bremen   EMail: j.schoenwaelder@jacobs-university.de   Ulrich Herberg   EMail: ulrich@herberg.nameErsue, et al.                 Informational                    [Page 44]