Internet Engineering Task Force (IETF)                            E. Kim
Request for Comments: 6606                                          ETRI
Category: Informational                                        D. Kaspar
ISSN: 2070-1721                               Simula Research Laboratory
                                                                C. Gomez
                     Universitat Politecnica de Catalunya/Fundacio i2CAT
                                                              C. Bormann
                                                 Universitaet Bremen TZI
                                                                May 2012

Problem Statement and Requirements for
IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Routing

Abstract

   IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) are
   formed by devices that are compatible with the IEEE 802.15.4
   standard.  However, neither the IEEE 802.15.4 standard nor the
   6LoWPAN format specification defines how mesh topologies could be
   obtained and maintained.  Thus, it should be considered how 6LoWPAN
   formation and multi-hop routing could be supported.

   This document provides the problem statement and design space for
   6LoWPAN routing.  It defines the routing requirements for 6LoWPANs,
   considering the low-power and other particular characteristics of the
   devices and links.  The purpose of this document is not to recommend
   specific solutions but to provide general, layer-agnostic guidelines
   about the design of 6LoWPAN routing that can lead to further analysis
   and protocol design.  This document is intended as input to groups
   working on routing protocols relevant to 6LoWPANs, such as the IETF
   ROLL WG.

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; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6606.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   1. Problem Statement ...............................................2
   2. Terminology .....................................................5
   3. Design Space ....................................................5
      3.1. Reference Network Model ....................................6
   4. Scenario Considerations and Parameters for 6LoWPAN Routing ......8
   5. 6LoWPAN Routing Requirements ...................................13
      5.1. Support of 6LoWPAN Device Properties ......................13
      5.2. Support of 6LoWPAN Link Properties ........................15
      5.3. Support of 6LoWPAN Characteristics ........................18
      5.4. Support of Security .......................................22
      5.5. Support of Mesh-Under Forwarding ..........................25
      5.6. Support of Management .....................................26
   6. Security Considerations ........................................27
   7. Acknowledgments ................................................27
   8. References .....................................................28
      8.1. Normative References ......................................28
      8.2. Informative References ....................................29

1. Problem Statement

   6LoWPANs are formed by devices that are compatible with the
   IEEE 802.15.4 standard [IEEE802.15.4].  Most of the LoWPAN devices
   are distinguished by their low bandwidth, short range, scarce memory
   capacity, limited processing capability, and other attributes of
   inexpensive hardware.  The characteristics of nodes participating in
   LoWPANs are assumed to be those described in the 6LoWPAN problem
   statement [RFC4919], and in the IPv6 over IEEE 802.15.4 document
   [RFC4944], which has specified how to carry IPv6 packets over
   IEEE 802.15.4 and similar networks.  Whereas IEEE 802.15.4
   distinguishes two types of devices called full-function devices
   (FFDs) and reduced-function devices (RFDs), this distinction is based

   on some features of the Medium Access Control (MAC) layer that are
   not always in use.  Hence, the distinction is not made in this
   document.  Nevertheless, some 6LoWPAN nodes may limit themselves to
   the role of hosts only, whereas other 6LoWPAN nodes may take part in
   routing.  This host/ router distinction can correlate with the
   processing and storage capabilities of the device and power available
   in a similar way to the idea of RFDs and FFDs.

   IEEE 802.15.4 networks support star and mesh topologies.  However,
   neither the IEEE 802.15.4 standard nor the 6LoWPAN format
   specification ([RFC4944]) define how mesh topologies could be
   obtained and maintained.  Thus, 6LoWPAN formation and multi-hop
   routing can be supported either below the IP layer (the adaptation
   layer or Logical Link Control (LLC)) or the IP layer.  (Note that in
   the IETF, the term "routing" usually, but not always [RFC5556],
   refers exclusively to the formation of paths and the forwarding at
   the IP layer.  In this document, we distinguish the layer at which
   these services are performed by the terms "route-over" and
   "mesh-under".  See Sections 2 and 3.)  A number of IP routing
   protocols have been developed in various IETF working groups.
   However, these existing routing protocols may not satisfy the
   requirements of multi-hop routing in 6LoWPANs, for the following
   reasons:

   o  6LoWPAN nodes have special types and roles, such as nodes drawing
      their power from primary batteries, power-affluent nodes,
      mains-powered and high-performance gateways, data aggregators,
      etc.  6LoWPAN routing protocols should support multiple device
      types and roles.

   o  More stringent requirements apply to LoWPANs, as opposed to
      higher-performance or non-battery-operated networks.  6LoWPAN
      nodes are characterized by small memory sizes and low processing
      power, and they run on very limited power supplied by primary
      non-rechargeable batteries (a few KB of RAM, a few dozen KB of
      ROM/ flash memory, and a few MHz of CPU is typical).  A node's
      lifetime is usually defined by the lifetime of its battery.

   o  Handling sleeping nodes is very critical in LoWPANs, more so than
      in traditional ad hoc networks.  LoWPAN nodes might stay in sleep
      mode most of the time.  Taking advantage of appropriate times for
      transmissions is important for efficient packet forwarding.

   o  Routing in 6LoWPANs might possibly translate to a simpler problem
      than routing in higher-performance networks.  LoWPANs might be
      either transit networks or stub networks.  Under the assumption
      that LoWPANs are never transit networks (as implied by [RFC4944]),

      routing protocols may be drastically simplified.  This document
      will focus on the requirements for stub networks.  Additional
      requirements may apply to transit networks.

   o  Routing in LoWPANs might possibly translate to a harder problem
      than routing in higher-performance networks.  Routing in LoWPANs
      requires power optimization, stable operation in lossy
      environments, etc.  These requirements are not easily satisfiable
      all at once [ROLL-PROTOCOLS].

   These properties create new challenges for the design of routing
   within LoWPANs.

   The 6LoWPAN problem statement [RFC4919] briefly mentions four
   requirements for routing protocols:

      (a) low overhead on data packets

      (b) low routing overhead

      (c) minimal memory and computation requirements

      (d) support for sleeping nodes (consideration of battery savings)

   These four high-level requirements describe the basic requirements
   for 6LoWPAN routing.  Based on the fundamental features of 6LoWPANs,
   more detailed routing requirements, which can lead to further
   analysis and protocol design, are presented in this document.

   Considering the problems above, detailed 6LoWPAN routing requirements
   must be defined.  Application-specific features affect the design of
   6LoWPAN routing requirements and corresponding solutions.  However,
   various applications can be profiled by similar technical
   characteristics, although the related detailed requirements might
   differ (e.g., a few dozen nodes in a home lighting system need
   appropriate scalability for the system's applications, while millions
   of nodes for a highway infrastructure system also need appropriate
   scalability).

   This routing requirements document states the routing requirements of
   6LoWPAN applications in general, providing examples for different
   cases of routing.  It does not imply that a single routing solution
   will be favorable for all 6LoWPAN applications, and there is no
   requirement for different routing protocols to run simultaneously.

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 are expected to be familiar with all the terms and concepts
   that are discussed in "IPv6 over Low-Power Wireless Personal Area
   Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and
   Goals" [RFC4919] and "Transmission of IPv6 Packets over IEEE 802.15.4
   Networks" [RFC4944].

   This specification makes use of the terminology defined in
   [6LoWPAN-ND].

3. Design Space

   Apart from a wide variety of conceivable routing algorithms for
   6LoWPANs, it is possible to perform routing in the IP layer (using a
   route-over approach) or below IP, as defined by the 6LoWPAN format
   document [RFC4944] (using the mesh-under approach).  See Figure 1.

   The route-over approach relies on IP routing and therefore supports
   routing over possibly various types of interconnected links.
   Note: The ROLL WG is now working on route-over approaches for
   Low-power and Lossy Networks (LLNs), not specifically for 6LoWPANs.
   This document focuses on 6LoWPAN-specific requirements; it may be
   used in conjunction with the more application-oriented requirements
   defined by the ROLL WG.

   The mesh-under approach performs the multi-hop communication below
   the IP link.  The most significant consequence of the mesh-under
   mechanism is that the characteristics of IEEE 802.15.4 directly
   affect the 6LoWPAN routing mechanisms, including the use of 64-bit
   (or 16-bit short) link-layer addresses instead of IP addresses.  A
   6LoWPAN would therefore be seen as a single IP link.

   Most statements in this document consider both the route-over and
   mesh-under cases.

   Figure 1 shows the place of 6LoWPAN routing in the entire network
   stack.

    +---------------------------+  +-----------------------------+
    |      Application Layer    |  |      Application Layer      |
    +---------------------------+  +-----------------------------+
    | Transport Layer (TCP/UDP) |  |  Transport Layer (TCP/UDP)  |
    +---------------------------+  +-----------------------------+
    |     Network Layer (IPv6)  |  |  Network       +---------+  |
    +---------------------------+  |  Layer         | Routing |  |
    |  6LoWPAN                  |  |  (IPv6)        +---------+  |
    |  Adaptation               |  +-----------------------------+
    |  Layer       +----------+ |  |  6LoWPAN Adaptation Layer   |
    +--------------| Routing* |-+  +-----------------------------+
    | 802.15.4 MAC +----------+ |  |        802.15.4 MAC         |
    +---------------------------+  +-----------------------------+
    |         802.15.4 PHY      |  |        802.15.4 PHY         |
    +---------------------------+  +-----------------------------+
     * Here, "Routing" is not equivalent to IP routing,
       but includes the functionalities of path computation and
       forwarding under the IP layer.
       The term "Routing" is used in the figure in order to
       illustrate which layer handles path computation and
       packet forwarding in mesh-under as compared to route-over.

    Figure 1: Mesh-Under Routing (Left) and Route-Over Routing (Right)

   In order to avoid packet fragmentation and the overhead for
   reassembly, routing packets should fit into a single IEEE 802.15.4
   physical frame, and application data should not be expanded to an
   extent that they no longer fit.

3.1. Reference Network Model

   For multi-hop communication in 6LoWPANs, when a route-over mechanism
   is in use, all routers (i.e., 6LoWPAN Border Routers (6LBRs) and
   6LoWPAN Routers (6LRs)) perform IP routing within the stub network
   (see Figure 2).  In this case, the link-local scope covers the set of
   nodes within symmetric radio range of a node.

   When a LoWPAN follows the mesh-under configuration, the 6LBR is the
   only IPv6 router in the LoWPAN (see Figure 3).  This means that the
   IPv6 link-local scope includes all nodes in the LoWPAN.  For this, a
   mesh-under mechanism MUST be provided to support multi-hop
   transmission.

        h   h
       /    |                     6LBR: 6LoWPAN Border Router
   6LBR -- 6LR --- 6LR --- h       6LR: 6LoWPAN Router
           / \                       h: Host
          h  6LR --- h
              |
             / \
          6LR - 6LR -- h

                Figure 2: An Example of a Route-Over LoWPAN

        h   h
       /    |                    6LBR: 6LoWPAN Border Router
   6LBR --- m --- m --- h           m: mesh-under forwarder
           / \                      h: Host
          h   m --- h
              |
             / \
            m - m -- h

                Figure 3: An Example of a Mesh-Under LoWPAN

   Note than in both mesh-under and route-over networks, there is no
   expectation of topologically based address assignment in the 6LoWPAN.
   Instead, addresses are typically assigned based on the EUI-64
   addresses assigned at manufacturing time to nodes, or based on a
   (from a topological point of view) more or less random process
   assigning 16-bit MAC addresses to individual nodes.  Within a
   6LoWPAN, there is therefore no opportunity for aggregation or
   summarization of IPv6 addresses beyond the sharing of (one or more)
   common prefixes.

   Not all devices that are within radio range of each other need to be
   part of the same LoWPAN.  When multiple LoWPANs are formed with
   globally unique IPv6 addresses in the 6LoWPANs, and device (a) of
   LoWPAN [A] wants to communicate with device (b) of LoWPAN [B], the
   normal IPv6 mechanisms will be employed.  For route-over, the IPv6
   address of (b) is set as the destination of the packets, and the
   devices perform IP routing to the 6LBR for these outgoing packets.
   For mesh-under, there is one IP hop from device (a) to the 6LBR of
   [A], no matter how many radio hops they are apart from each other.
   This, of course, assumes the existence of a mesh-under routing
   protocol in order to reach the 6LBR.  Note that a default route to
   the 6LBR could be inserted into the 6LoWPAN routing system for both
   route-over and mesh-under.

4. Scenario Considerations and Parameters for 6LoWPAN Routing

   IP-based LoWPAN technology is still in its early stage of
   development, but the range of conceivable usage scenarios is
   tremendous.  The numerous possible applications of sensor networks
   make it obvious that mesh topologies will be prevalent in LoWPAN
   environments and robust routing will be a necessity for expedient
   communication.  Research efforts in the area of sensor networking
   have put forth a large variety of multi-hop routing algorithms
   [Bulusu].  Most related work focuses on optimizing routing for
   specific application scenarios, which can be realized using several
   modes of communication, including the following [Watteyne]:

   o  Flooding (in very small networks)

   o  Hierarchical routing

   o  Geographic routing

   o  Self-organizing coordinate routing

   Depending on the topology of a LoWPAN and the application(s) running
   over it, different types of routing may be used.  However, this
   document abstracts from application-specific communication and
   describes general routing requirements valid for overall routing in
   LoWPANs.

   The following parameters can be used to describe specific scenarios
   in which the candidate routing protocols could be evaluated.

   a.  Network Properties:

       *  Number of Devices, Density, and Network Diameter:
          These parameters usually affect the routing state directly
          (e.g., the number of entries in a routing table or neighbor
          list).  Especially in large and dense networks, policies must
          be applied for discarding "low-quality" and stale routing
          entries in order to prevent memory overflow.

       *  Connectivity:
          Due to external factors or programmed disconnections, a LoWPAN
          can be in several states of connectivity -- anything in the
          range from "always connected" to "rarely connected".  This
          poses great challenges to the dynamic discovery of routes
          across a LoWPAN.

       *  Dynamicity (including mobility):
          Location changes can be induced by unpredictable external
          factors or by controlled motion, which may in turn cause route
          changes.  Also, nodes may dynamically be introduced into a
          LoWPAN and removed from it later.  The routing state and the
          volume of control messages may heavily depend on the number of
          moving nodes in a LoWPAN and their speed, as well as how
          quickly and frequently environmental characteristics
          influencing radio propagation change.

       *  Deployment:
          In a LoWPAN, it is possible for nodes to be scattered randomly
          or to be deployed in an organized manner.  The deployment can
          occur at once, or as an iterative process, which may also
          affect the routing state.

       *  Spatial Distribution of Nodes and Gateways:
          Network connectivity depends on the spatial distribution of
          the nodes and on other factors, such as device number,
          density, and transmission range.  For instance, nodes can be
          placed on a grid, or randomly located in an area (as can be
          modeled by a two-dimensional Poisson distribution), etc.
          Assuming a random spatial distribution, an average of 7
          neighbors per node are required for approximately 95% network
          connectivity (10 neighbors per node are needed for 99%
          connectivity) [Kuhn].  In addition, if the LoWPAN is connected
          to other networks through infrastructure nodes called
          gateways, the number and spatial distribution of these
          gateways affect network congestion and available data rate,
          among other things.

       *  Traffic Patterns, Topology, and Applications:
          The design of a LoWPAN and the requirements for its
          application have a big impact on the network topology and the
          most efficient routing type to be used.  For different traffic
          patterns (point-to-point, multipoint-to-point, point-to-
          multipoint) and network architectures, various routing
          mechanisms have been developed, such as data-centric, event-
          driven, address-centric, and geographic routing.

       *  Classes of Service:
          For mixing applications of different criticality on one
          LoWPAN, support of multiple classes of service may be required
          in resource-constrained LoWPANs and may require a new routing
          protocol functionality.

       *  Security:
          LoWPANs may carry sensitive information and require a high
          level of security support where the availability, integrity,
          and confidentiality of data are of prime relevance.  Secured
          messages cause overhead and affect the power consumption of
          LoWPAN routing protocols.

   b.  Node Parameters:

       *  Processing Speed and Memory Size:
          These basic parameters define the maximum size of the routing
          state and the maximum complexity of its processing.  LoWPAN
          nodes may have different performance characteristics, queuing
          strategies, and queue buffer sizes.

       *  Power Consumption and Power Source:
          The number of battery- and mains-powered nodes and their
          positions in the topology created by them in a LoWPAN affect
          routing protocols in their selection of paths that optimize
          network lifetime.

       *  Transmission Range:
          This parameter affects routing.  For example, a high
          transmission range may cause a dense network, which in turn
          results in more direct neighbors of a node, higher
          connectivity, and a larger routing state.

       *  Traffic Pattern:
          This parameter affects routing, since highly loaded nodes
          (either because they are the source of packets to be
          transmitted or due to forwarding) may contribute to higher
          delivery delays and may consume more energy than lightly
          loaded nodes.  This applies to both data packets and routing
          control messages.

   c.  Link Parameters:
       This section discusses link parameters that apply to
       IEEE 802.15.4 legacy mode (i.e., not making use of improved
       modulation schemes).

       *  Throughput:
          The maximum user data throughput of a bulk data transmission
          between a single sender and a single receiver through an
          unslotted IEEE 802.15.4 2.4 GHz channel in ideal conditions is
          as follows [Latre]:

          +  16-bit MAC addresses, unreliable mode: 151.6 kbit/s

          +  16-bit MAC addresses, reliable mode: 139.0 kbit/s

          +  64-bit MAC addresses, unreliable mode: 135.6 kbit/s

          +  64-bit MAC addresses, reliable mode: 124.4 kbit/s

          Throughput for the 915 MHz band is as follows:

          +  16-bit MAC addresses, unreliable mode: 31.1 kbit/s

          +  16-bit MAC addresses, reliable mode: 28.6 kbit/s

          +  64-bit MAC addresses, unreliable mode: 27.8 kbit/s

          +  64-bit MAC addresses, reliable mode: 25.6 kbit/s

          Throughput for the 868 MHz band is as follows:

          +  16-bit MAC addresses, unreliable mode: 15.5 kbit/s

          +  16-bit MAC addresses, reliable mode: 14.3 kbit/s

          +  64-bit MAC addresses, unreliable mode: 13.9 kbit/s

          +  64-bit MAC addresses, reliable mode: 12.8 kbit/s

       *  Latency:
          Latency ranges -- depending on payload size -- of a frame
          transmission between a single sender and a single receiver
          through an unslotted IEEE 802.15.4 2.4 GHz channel in ideal
          conditions are as shown below [Latre].  For unreliable mode,
          the actual latency is provided.  For reliable mode, the round-
          trip time, including transmission of a Layer-2 acknowledgment,
          is provided:

          +  16-bit MAC addresses, unreliable mode: [1.92 ms, 6.02 ms]

          +  16-bit MAC addresses, reliable mode: [2.46 ms, 6.56 ms]

          +  64-bit MAC addresses, unreliable mode: [2.75 ms, 6.02 ms]

          +  64-bit MAC addresses, reliable mode: [3.30 ms, 6.56 ms]

          Latency ranges for the 915 MHz band are as follows:

          +  16-bit MAC addresses, unreliable mode: [5.85 ms, 29.35 ms]

          +  16-bit MAC addresses, reliable mode: [8.35 ms, 31.85 ms]

          +  64-bit MAC addresses, unreliable mode: [8.95 ms, 29.35 ms]

          +  64-bit MAC addresses, reliable mode: [11.45 ms, 31.82 ms]

          Latency ranges for the 868 MHz band are as follows:

          +  16-bit MAC addresses, unreliable mode: [11.7 ms, 58.7 ms]

          +  16-bit MAC addresses, reliable mode: [16.7 ms, 63.7 ms]

          +  64-bit MAC addresses, unreliable mode: [17.9 ms, 58.7 ms]

          +  64-bit MAC addresses, reliable mode: [22.9 ms, 63.7 ms]

   Note that some of the parameters presented in this section may be
   used as link or node evaluation metrics.  However, multi-criteria
   routing may be too expensive for 6LoWPAN nodes.  Rather, various
   single-criteria metrics are available and can be selected to suit the
   environment or application.

5. 6LoWPAN Routing Requirements

   This section defines a list of requirements for 6LoWPAN routing.  An
   important design property specific to low-power networks is that
   LoWPANs have to support multiple device types and roles, such as

   o  host nodes drawing their power from primary batteries or using
      energy harvesting (sometimes called "power-constrained nodes")

   o  mains-powered host nodes (an example of what we call "power-
      affluent nodes")

   o  power-affluent (but not necessarily mains-powered) high-
      performance gateway(s)

   o  nodes with various functionality (data aggregators, relays, local
      manager/coordinators, etc.)

   Due to these different device types and roles, LoWPANs need to
   consider the following two primary attributes:

   o  Power conservation: some devices are mains-powered, but many are
      battery-operated and need to last several months to a few years
      with a single AA battery.  Many devices are mains-powered most of
      the time but still need to function on batteries for possibly
      extended periods (e.g., on a construction site before building
      power is switched on for the first time).

   o  Low performance: tiny devices, small memory sizes, low-performance
      processors, low bandwidth, high loss rates, etc.

   These fundamental attributes of LoWPANs affect the design of routing
   solutions.  Whether existing routing specifications are simplified
   and modified, or new solutions are introduced in order to fit the
   low-power requirements of LoWPANs, they need to meet the requirements
   described below.

5.1. Support of 6LoWPAN Device Properties

   The general objectives listed in this section should be met by
   6LoWPAN routing protocols.  The importance of each requirement is
   dependent on what node type the protocol is running on and what the
   role of the node is.  The following requirements consider the
   presence of battery-powered nodes in LoWPANs.

   [R01] 6LoWPAN routing protocols SHOULD allow implementation with
   small code size and require low routing state to fit the typical
   6LoWPAN node capacity.  Generally speaking, the code size is bounded
   by available flash memory size, and the routing table is bounded by
   RAM size, possibly limiting it to less than 32 entries.

      The RAM size of LoWPAN nodes often ranges between 4 KB and 10 KB
      (2 KB minimum), and program flash memory normally consists of 48
      KB to 128 KB.  (For example, in the current market, MICAz has 128
      KB program flash, 4 KB EEPROM, and 512 KB external flash ROM;
      TIP700CM has 48 KB program flash, 10 KB RAM, and 1 MB external
      flash ROM.)

      Due to these hardware restrictions, code SHOULD fit within a small
      memory size -- no more than 48 KB to 128 KB of flash memory,
      including at least a few tens of KB of application code size.  (As
      a general observation, a routing protocol of low complexity may
      help achieve the goal of reducing power consumption, improves
      robustness, requires lower routing state, is easier to analyze,
      and may be less prone to security attacks.)

      In addition, operation with limited amounts of routing state (such
      as routing tables and neighbor lists) SHOULD be maintained, since
      some typical memory sizes preclude storing state of a large number
      of nodes.  For instance, industrial monitoring applications may
      need to support a maximum of 20 hops [RFC5673].  Small networks
      can be designed to support a smaller number of hops.  While the
      need for this is highly dependent on the network architecture,
      there should be at least one mode of operation that can function
      with 32 forwarding entries or less.

   [R02] 6LoWPAN routing protocols SHOULD cause minimal power
   consumption by efficiently using control packets (e.g., minimizing
   expensive IP multicast, which causes link broadcast to the entire
   LoWPAN) and by efficiently routing data packets.

      One way of optimizing battery lifetime is by achieving a minimal
      control message overhead.  Compared to such functions as
      computational operations or taking sensor samples, radio
      communication is by far the dominant factor of power consumption
      [Doherty].  Power consumption of transmission and/or reception
      depends linearly on the length of data units and on the frequency
      of transmission and reception of the data units [Shih].

      The energy consumption of two example radio frequency (RF)
      controllers for low-power nodes is shown in [Hill].  The TR1000
      radio consumes 21 mW when transmitting at 0.75 mW, and 15 mW
      during reception (with a receiver sensitivity of -85 dBm).  The

      CC1000 consumes 31.6 mW when transmitting at 0.75 mW, and 20 mW
      during reception (with a receiver sensitivity of -105 dBm).  Power
      endurance under the concept of an idealized power source is
      explained in [Hill].  Based on the energy of an idealized AA
      battery, the CC1000 can transmit for approximately 4 days straight
      or receive for 9 consecutive days.  Note that availability for
      reception consumes power as well.

      As multicast may cause flooding in the LoWPAN, a 6LoWPAN routing
      protocol SHOULD minimize the control cost by multicasting routing
      packets.

      Control cost of routing protocols in low-power and lossy networks
      is discussed in more detail in [ROLL-PROTOCOLS].

5.2. Support of 6LoWPAN Link Properties

   6LoWPAN links have the characteristics of low data rate and possibly
   high loss rates.  The routing requirements described in this section
   are derived from the link properties.

   [R03] 6LoWPAN routing protocol control messages SHOULD NOT exceed a
   single IEEE 802.15.4 frame size, in order to avoid packet
   fragmentation and the overhead for reassembly.

      In order to save energy, routing overhead should be minimized to
      prevent fragmentation of frames.  Therefore, 6LoWPAN routing
      should not cause packets to exceed the IEEE 802.15.4 frame size.
      This reduces the energy required for transmission, avoids
      unnecessary waste of bandwidth, and prevents the need for packet
      reassembly.  The [IEEE802.15.4] standard specifies an MTU of
      127 bytes, yielding about 80 octets of actual MAC payload with
      security enabled, some of which is taken for the (typically
      compressed) IP header [RFC6282].  Avoiding fragmentation at the
      adaptation layer may imply the use of semantic fragmentation
      and/or algorithms that can work on small increments of routing
      information.

   [R04] The design of routing protocols for LoWPANs must consider the
   fact that packets are to be delivered with sufficient probability
   according to application requirements.

      Requirements for a successful end-to-end packet delivery ratio
      (where delivery may be bounded within certain latency levels)
      vary, depending on the application.  In industrial applications,
      some non-critical monitoring applications may tolerate a
      successful delivery ratio of less than 90% with hours of latency;

      in some other cases, a delivery ratio of 99.9% is required
      [RFC5673].  In building automation applications, application-layer
      errors must be below 0.01% [RFC5867].

      Successful end-to-end delivery of packets in an IEEE 802.15.4 mesh
      depends on the quality of the path selected by the routing
      protocol and on the ability of the routing protocol to cope with
      short-term and long-term quality variation.  The metric of the
      routing protocol strongly influences performance of the routing
      protocol in terms of delivery ratio.

      The quality of a given path depends on the individual qualities of
      the links (including the devices) that compose that path.
      IEEE 802.15.4 settings affect the quality perceived at upper
      layers.  In particular, in IEEE 802.15.4 reliable mode, if an
      acknowledgment frame is not received after a given period, the
      originator retries frame transmission up to a maximum number of
      times.  If an acknowledgment frame is still not received by the
      sender after performing the maximum number of transmission
      attempts, the MAC layer assumes that the transmission has failed
      and notifies the next higher layer of the failure.  Note that
      excessive retransmissions may be detrimental; see RFC 3819
      [RFC3819].

   [R05] The design of routing protocols for LoWPANs must consider the
   latency requirements of applications and IEEE 802.15.4 link latency
   characteristics.

      Latency requirements may differ -- e.g., from a few hundred
      milliseconds to minutes -- depending on the type of application.
      Real-time building automation applications usually need response
      times below 500 ms between egress and ingress, while forced-entry
      security alerts must be routed to one or more fixed or mobile user
      devices within 5 seconds [RFC5867].  Non-critical closed-loop
      applications for industrial automation have latency requirements
      that can be as low as 100 ms, but many control loops are tolerant
      of latencies above 1 s [RFC5673].  In contrast, urban monitoring
      applications allow latencies smaller than the typical intervals
      used for reporting sensed information -- for instance, on the
      order of seconds to minutes [RFC5548].

      The range of latencies of a frame transmission between a single
      sender and a single receiver through an ideal unslotted
      IEEE 802.15.4 2.4 GHz channel is between 2.46 ms and 6.02 ms with
      64-bit MAC addresses in unreliable mode, and between 2.20 ms and
      6.56 ms with 64-bit MAC addresses in reliable mode.  The range of
      latencies of the 868 MHz band is from 11.7 ms to 63.7 ms,
      depending on the address type and mode used (reliable or

      unreliable).  Note that the latencies may be larger than that,
      depending on channel load, the MAC-layer settings, and the choice
      of reliable or unreliable mode.  Note that MAC approaches other
      than legacy 802.15.4 may be used (e.g., TDMA).  Duty cycling may
      further affect latency (see [R08]).  Depending on the routing path
      chosen and the network diameter, multiple hops may contribute to
      the end-to-end latency that an application may experience.

      Note that a tradeoff exists between [R05] and [R04].

   [R06] 6LoWPAN routing protocols SHOULD be robust to dynamic loss
   caused by link failure or device unavailability either in the short
   term (approx. 30 ms) -- due to Received Signal Strength Indication
   (RSSI) variation, interference variation, noise, and asynchrony -- or
   in the long term, due to a depleted power source, hardware breakdown,
   operating system misbehavior, etc.

      An important trait of 6LoWPAN devices is their unreliability,
      which can be due to limited system capabilities and possibly being
      closely coupled to the physical world with all its unpredictable
      variations.  In harsh environments, LoWPANs easily suffer from
      link failure.  Collisions or link failures easily increase send
      and receive queues and can lead to queue overflow and packet
      losses.

      For home applications, where users expect feedback after carrying
      out certain actions (such as handling a remote control while
      moving around), routing protocols must converge within 2 seconds
      if the destination node of the packet has moved and must converge
      within 0.5 seconds if only the sender has moved [RFC5826].  The
      tolerance of the recovery time can vary, depending on the
      application; however, the routing protocol must provide the
      detection of short-term unavailability and long-term
      disappearance.  The routing protocol has to exploit network
      resources (e.g., path redundancy) to offer good network behavior
      despite node failure.

      Different routing protocols may exhibit different scaling
      characteristics with respect to the recovery/convergence time and
      the computational resources to achieve recovery after a
      convergence; see also [R01] and [R10].

   [R07] 6LoWPAN routing protocols SHOULD be designed to correctly
   operate in the presence of link asymmetry.

      Link asymmetry occurs when the probability of successful
      transmission between two nodes is significantly higher in one
      direction than in the other.  This phenomenon has been reported in
      a large number of experimental studies, and it is expected that
      6LoWPANs will exhibit link asymmetry.

5.3. Support of 6LoWPAN Characteristics

   6LoWPANs can be deployed in different sizes and topologies, adhere to
   various models of mobility, be exposed to various levels of
   interference, etc.  In any case, LoWPANs must maintain low energy
   consumption.  The requirements described in this subsection are
   derived from the network attributes of 6LoWPANs.

   [R08] The design of 6LoWPAN routing protocols SHOULD take into
   account that some nodes may be unresponsive during certain time
   intervals, due to periodic hibernation.

      Many nodes in LoWPAN environments might periodically hibernate
      (i.e., disable their transceiver activity) in order to save
      energy.  Therefore, routing protocols must ensure robust packet
      delivery despite nodes frequently shutting off their radio
      transmission interface.  Feedback from the lower IEEE 802.15.4
      layer may be considered to enhance the power awareness of 6LoWPAN
      routing protocols.

      CC1000-based nodes must operate at a duty cycle of approximately
      2% to survive for one year from an idealized AA battery power
      source [Hill].  For home automation purposes, it is suggested that
      the devices have to maximize the sleep phase with a duty cycle
      lower than 1% [RFC5826], while in building automation
      applications, batteries must be operational for at least 5 years
      when the sensing devices are transmitting data (e.g., 64 bytes)
      once per minute [RFC5867].

      Depending on the application in use, packet rates may range from
      one per second to one per day, or beyond.  Routing protocols may
      take advantage of knowledge about the packet transmission rate and
      utilize this information in calculating routing paths.  In many
      IEEE 802.15.4 deployments, and in other wireless low-power
      technologies, forwarders are mains-powered devices (and hence do
      not need to sleep).  However, it cannot be assumed that all
      forwarders are mains-powered.  A routing protocol that addresses
      this case SHOULD provide a mode in which power consumption is a
      metric.  In addition, using nodes in power-saving modes for

      forwarding may increase delay and reduce the probability of packet
      delivery, which in this case also should be available as an input
      into the path computation.

   [R09] The metric used by 6LoWPAN routing protocols SHOULD provide
   some flexibility with respect to the inputs provided by the lower
   layers and other measures to optimize path selection, considering
   energy balance and link qualities.

      In homes, buildings, or infrastructure, some nodes will be
      installed with mains power.  Such power-installed nodes MUST be
      considered as relay points for a prominent role in packet
      delivery.  6LoWPAN routing protocols MUST know the power
      constraints of the nodes.

      Simple hop-count-only mechanisms may be inefficient in 6LoWPANs.
      There is a Link Quality Indication (LQI) and/or RSSI from
      IEEE 802.15.4 that may be taken into account for better metrics.
      The metric to be used (and its goal) may depend on applications
      and requirements.

      The numbers in Figure 4 represent the Link Delivery Ratio (LDR) of
      each pair of nodes.  There are studies that show a piecewise
      linear dependence between the LQI and the LDR [Chen].

                                     0.6
                                  A-------C
                                   \     /
                                0.9 \   / 0.9
                                     \ /
                                      B

                         Figure 4: An Example Network

      In this simple example, there are two options in routing from
      node A to node C, with the following features:

A. Path AC:

          +  (1/0.6) = 1.67 avg. transmissions needed for each packet
             (confirmed link-layer delivery with retransmissions and
             negligible ACK loss have been assumed)

          +  one-hop path

          +  good energy consumption and end-to-end latency of data
             packets, poor delivery ratio (0.6)

          +  poor probability of route reconfigurations

B. Path ABC:

          +  (1/0.9)+(1/0.9) = 2.22 avg. transmissions needed for each
             packet (under the same assumptions as above)

          +  two-hop path

          +  poor energy consumption and end-to-end latency of data
             packets, good delivery ratio (0.81)

      If energy consumption of the network must be minimized, path AC is
      the best (this path would be chosen based on a hop-count metric).
      However, if the delivery ratio in that case is not sufficient, the
      best path is ABC (it would be chosen by an LQI-based metric).
      Combinations of both metrics can be used.

      The metric also affects the probability of route reconfiguration.
      Route reconfiguration, which may be triggered by packet losses,
      may require transmission of routing protocol messages.  It is
      possible to use a metric aimed at selecting the path with a low
      route reconfiguration rate by using the LQI as an input to the
      metric.  Such a path has good properties, including stability and
      low control message overhead.

   Note that a tradeoff exists between [R09] and [R01].

   [R10] 6LoWPAN routing protocols SHOULD be designed to achieve both
   scalability -- from a few nodes to maybe millions of nodes -- and
   minimal use of system resources.

      A LoWPAN may consist of just a couple of nodes (for instance, in a
      body-area network), but may also contain much higher numbers of
      devices (e.g., monitoring of a city infrastructure or a highway).
      For home automation applications, it is envisioned that the
      routing protocol must support 250 devices in the network
      [RFC5826], while routing protocols for metropolitan-scale sensor
      networks must be capable of clustering a large number of sensing
      nodes into regions containing on the order of 10^2 to 10^4 sensing
      nodes each [RFC5548].  It is therefore necessary that routing
      mechanisms are designed to be scalable for operation in networks
      of various sizes.  However, due to a lack of memory size and
      computational power, 6LoWPAN routing might limit forwarding
      entries to a small number, such as a maximum of 32 routing table

      entries.  Particularly in large networks, the routing mechanism
      MUST be designed in such a way that the number of routers is
      smaller than the number of hosts.

   [R11] The procedure of route repair and related control messages
   SHOULD NOT harm overall energy consumption from the routing
   protocols.

      Local repair improves throughput and end-to-end latency,
      especially in large networks.  Since routes are repaired quickly,
      fewer data packets are dropped, and a smaller number of routing
      protocol packet transmissions are needed, since routes can be
      repaired without source-initiated route discovery [Lee].  One
      important consideration here may be to avoid premature energy
      depletion, even if that impairs other requirements.

   [R12] 6LoWPAN routing protocols SHOULD allow for dynamically adaptive
   topologies and mobile nodes.  When supporting dynamic topologies and
   mobile nodes, route maintenance should keep in mind the goal of a
   minimal routing state and routing protocol message overhead.

      Topological node mobility may be the result of physical movement
      and/or a changing radio environment, making it very likely that
      mobility needs to be handled even in a network with physically
      static nodes.  6LoWPANs do not make use of a separate protocol to
      maintain connectivity to moving nodes but expects the routing
      protocol to handle it.

      In addition, some nodes may move from one 6LoWPAN to another and
      are expected to become functional members of the latter 6LoWPAN in
      a limited amount of time.

      Building monitoring applications, for instance, have a number of
      requirements with respect to recovery and settling time for
      mobility that range between 5 and 20 seconds (Section 5.3.1 of
      [RFC5867]).  For more interactive applications such as those used
      in home automation systems, where users provide input and expect
      instant feedback, mobility requirements are also stricter and, for
      moves within a network, a convergence time below 0.5 seconds is
      commonly required (Section 3.2 of [RFC5826]).  In industrial
      environments, where mobile equipment (e.g., cranes) moves around,
      the routing protocol needs to support vehicular speeds of up to
      35 km/h [RFC5673].  Currently, 6LoWPANs are not normally being
      used for such fast mobility, but dynamic association and
      disassociation MUST be supported in 6LoWPANs.

      There are several challenges that should be addressed by a 6LoWPAN
      routing protocol in order to create robust routing in dynamic
      environments:

      *  Mobile Nodes Changing Their Location inside a LoWPAN:
         If the nodes' movement pattern is unknown, mobility cannot
         easily be detected or distinguished by the routing protocols.
         Mobile nodes can be treated as nodes that disappear and
         reappear in another place.  The tracking of movement patterns
         increases complexity and can be avoided by handling moving
         nodes using reactive route updates.

      *  Movement of a LoWPAN with Respect to Other (Inter)Connected
         LoWPANs:
         Within each stub network, (one or more) relatively powerful
         gateway nodes (6LBRs) need to be configured to handle moving
         LoWPANs.

      *  Nodes Permanently Joining or Leaving the LoWPAN:
         In order to ease routing table updates, reduce the size of
         these updates, and minimize error control messages, nodes
         leaving the network may announce their disassociation to the
         closest edge router or to a specific node (if any) that takes
         charge of local association and disassociation.

   [R13] A 6LoWPAN routing protocol SHOULD support various traffic
   patterns -- point-to-point, point-to-multipoint, and multipoint-to-
   point -- while avoiding excessive multicast traffic in a LoWPAN.

      6LoWPANs often have point-to-multipoint or multipoint-to-point
      traffic patterns.  Many emerging applications include point-to-
      point communication as well.  6LoWPAN routing protocols should be
      designed with the consideration of forwarding packets from/to
      multiple sources/destinations.  Current documents of the ROLL WG
      explain that the workload or traffic pattern of use cases for
      LoWPANs tends to be highly structured, unlike the any-to-any data
      transfers that dominate typical client and server workloads.  In
      many cases, exploiting such structure may simplify difficult
      problems arising from resource constraints or variation in
      connectivity.

5.4. Support of Security

   The routing requirement described in this subsection allows secure
   transmission of routing messages.  As in traditional networks,
   routing mechanisms in 6LoWPANs present another window from which an
   attacker might disrupt and significantly degrade the overall
   performance of the 6LoWPAN.  Attacks against non-secure routing aim

   mainly to contaminate WPANs with false routing information, resulting
   in routing inconsistencies.  A malicious node can also snoop packets
   and then launch replay attacks on the 6LoWPAN nodes.  These attacks
   can cause harm, especially when the attacker is a high-power device,
   such as a laptop.  It can also easily drain the batteries of 6LoWPAN
   devices by sending broadcast messages, redirecting routes, etc.

   [R14] 6LoWPAN routing protocols MUST support confidentiality,
   authentication, and integrity services as required for secure
   delivery of control messages.

      A general set of requirements that may apply to these services can
      be found in [KARP-THREATS].

      Security is very important for designing robust routing protocols,
      but it should not cause significant transmission overhead.  The
      security aspect, however, seems to be a bit of a tradeoff in a
      6LoWPAN, since security is always a costly function.  A 6LoWPAN
      poses unique challenges to which traditional security techniques
      cannot be applied directly.  For example, public key cryptography
      primitives are typically avoided (as being too expensive), as are
      relatively heavyweight conventional encryption methods.

      Consequently, it becomes questionable whether the 6LoWPAN devices
      can support IPsec as it is.  While [RFC6434] makes support of the
      IPsec architecture a SHOULD for all IPv6 nodes, considering the
      power constraints and limited processing capabilities of
      IEEE 802.15.4-capable devices, IPsec is computationally expensive.
      Internet Key Exchange (IKEv2) messaging as described in RFC 5996
      [RFC5996] will not work well in 6LoWPANs, as we want to minimize
      the amount of signaling in these networks.  IPsec supports the
      Authentication Header (AH) for authenticating the IP header and
      the Encapsulating Security Payload (ESP) for authenticating and
      encrypting the payload.  The main issues of using IPsec are
      two-fold: (1) processing power and (2) key management.  Since
      these tiny 6LoWPAN devices do not process huge amounts of data or
      communicate with many different nodes, whether complete
      implementation of a Security Association Database (SAD), policy
      database, and dynamic key-management protocol are appropriate for
      these small battery-powered devices or not is not well understood.

      Bandwidth is a very scarce resource in 6LoWPAN environments.  The
      fact that IPsec additionally requires another header (AH or ESP)
      in every packet makes its use problematic in 6LoWPAN environments.
      IPsec requires two communicating peers to share a secret key that
      is typically established dynamically with IKEv2.  Thus, it has an
      additional packet overhead incurred by the exchange of IKEv2
      packets.

      Given existing constraints in 6LoWPAN environments, IPsec may not
      be suitable for use in such environments, especially since a
      6LoWPAN node may not be capable of operating all IPsec algorithms
      on its own.  Thus, a 6LoWPAN may need to define its own keying
      management method(s) that require minimum overhead in packet size
      and in the number of signaling messages that are exchanged.  IPsec
      will provide authentication and confidentiality between end-nodes
      and across multiple LoWPAN links, and may be useful only when two
      nodes want to apply security to all exchanged messages.  However,
      in most cases, the security may be requested at the application
      layer as needed, while other messages can flow in the network
      without security overhead.

      Security threats within LoWPANs may be different from existing
      threat models in ad hoc network environments.  If IEEE 802.15.4
      security is not used, Neighbor Discovery (ND) in IEEE 802.15.4
      links is susceptible to threats.  These include Neighbor
      Solicitation/Neighbor Advertisement (NS/NA) spoofing, a malicious
      router, a default router that is "killed", a good router that goes
      bad, a spoofed redirect, replay attacks, and remote ND DoS
      [RFC3756].  However, if IEEE 802.15.4 security is used, no other
      protection is needed for ND, as long as none of the nodes become
      compromised, because the Corporate Intranet Model of RFC 3756 can
      be assumed [6LoWPAN-ND].

      Bootstrapping may also impose additional threats.  For example, a
      malicious node can obtain initial configuration information in
      order to appear as a legitimate node and then carry out various
      types of attacks.  Such a node can also keep legitimate nodes busy
      by broadcasting authentication/join requests.  One option for
      mitigating such threats is the use of mutual authentication
      schemes based on the use of pre-shared keys [Ikram].

      The IEEE 802.15.4 MAC provides an AES-based security mechanism.
      Routing protocols may define how this mechanism (in conjunction
      with IPsec whenever available) can be used to obtain the intended
      security, either for the routing protocol alone or in conjunction
      with the security used for the data.  Byte overhead of the
      mechanism, which depends on the security services selected, must
      be considered.  In the worst case in terms of overhead, the
      mechanism consumes 21 bytes of MAC payload.

      The IEEE 802.15.4 MAC security is typically supported by crypto
      hardware, even in very simple chips that will be used in a
      6LoWPAN.  Even if the IEEE 802.15.4 MAC security mechanisms are
      not used, this crypto hardware is usually available for use by

      application code running on these chips.  A security protocol
      outside IEEE 802.15.4 MAC security SHOULD therefore provide a mode
      of operation that is covered by this crypto hardware.

      IEEE 802.15.4 does not specify protection for acknowledgment
      frames.  Since the sequence numbers of data frames are sent in the
      clear, an adversary can forge an acknowledgment for each data
      frame.  Exploitation of this weakness can be combined with
      targeted jamming to prevent delivery of selected packets.
      Consequently, IEEE 802.15.4 acknowledgments cannot be relied upon.
      In applications that require high security, the routing protocol
      must not exploit feedback from acknowledgments (e.g., to keep
      track of neighbor connectivity, see [R16]).

5.5. Support of Mesh-Under Forwarding

   One LoWPAN may be built as one IPv6 link.  In this case, mesh-under
   forwarding mechanisms must be supported.  While this document
   provides general, layer-agnostic guidelines about the design of
   6LoWPAN routing, the requirements in this section are specifically
   related to Layer 2.  These requirements are directed to bodies that
   might consider working on mesh-under routing, such as the IEEE.  The
   requirements described in this subsection allow optimization and
   correct operation of routing solutions, taking into account the
   specific features of the mesh-under configuration.

   [R15] Mesh-under requires the development of a routing protocol
   operating below IP.  This protocol MUST support 16-bit short and
   64-bit extended MAC addresses.

   [R16] In order to perform discovery and maintenance of neighbors
   (i.e., neighborhood discovery as opposed to ND-style neighbor
   discovery), LoWPAN nodes SHOULD avoid sending separate "Hello"
   messages.  Instead, link-layer mechanisms (such as acknowledgments)
   MAY be utilized to keep track of active neighbors.

      Reception of an acknowledgment after a frame transmission may
      render unnecessary the transmission of explicit Hello messages,
      for example.  In a more general view, any frame received by a node
      may be used as an input to evaluate the connectivity between the
      sender and receiver of that frame.

   [R17] If the routing protocol functionality includes enabling IP
   multicast, then it MAY employ structure in the network for efficient
   distribution in order to minimize link-layer broadcast.

5.6. Support of Management

   When a new protocol is designed, the operational environment and
   manageability of the protocol should be considered from the start
   [RFC5706].  This subsection provides a requirement for the
   manageability of 6LoWPAN routing protocols.

   [R18] A 6LoWPAN routing protocol SHOULD be designed according to the
   guidelines for operations and management stated in [RFC5706].

      The management operations that a 6LoWPAN routing protocol
      implementation can support depend on the memory and processing
      capabilities of the 6LoWPAN devices used, which are typically
      constrained.  However, 6LoWPANs may benefit significantly from
      supporting such 6LoWPAN routing protocol management operations as
      configuration and performance monitoring.

      The design of 6LoWPAN routing protocols should take into account
      that, according to "Architectural Principles of the Internet"
      [RFC1958], "options and parameters should be configured or
      negotiated dynamically rather than manually".  This is especially
      important for 6LoWPANs, which can be composed of a large number of
      devices (and, in addition, these devices may not have an
      appropriate user interface).  Therefore, parameter
      autoconfiguration is a desirable property for a 6LoWPAN routing
      protocol, although some subset of routing protocol parameters may
      allow other forms of configuration as well.

      In order to verify the correct operation of the 6LoWPAN routing
      protocol and the network itself, a 6LoWPAN routing protocol should
      allow monitoring of the status and/or value of 6LoWPAN routing
      protocol parameters and data structures such as routing table
      entries.  In order to enable fault management, further monitoring
      of the 6LoWPAN routing protocol operation is needed.  For this,
      faults can be reported via error log messages.  These messages may
      contain information such as the number of times a packet could not
      be sent to a valid next hop, the duration of each period without
      connectivity, memory overflow and its causes, etc.

      [RFC5706] -- in particular its Section 3 -- provides a
      comprehensive guide to properly designing the management solution
      for a 6LoWPAN routing protocol.

6. Security Considerations

   Security issues are described in Section 5.4.  The security
   considerations in RFC 4919 [RFC4919], RFC 4944 [RFC4944], and
   RFC 4593 [RFC4593] apply as well.

   The use of wireless links renders a 6LoWPAN susceptible to attacks
   like any other wireless network.  In outdoor 6LoWPANs, the physical
   exposure of the nodes allows an adversary to capture, clone, or
   tamper with these devices.  In ad hoc 6LoWPANs that are dynamic in
   both their topology and node memberships, a static security
   configuration does not suffice.  Spoofed, altered, or replayed
   routing information might occur, while multihopping could delay the
   detection and treatment of attacks.

   This specification expects that the link layer is sufficiently
   protected, either by means of physical or IP security for the
   backbone link, or with MAC-sublayer cryptography.  However, link-
   layer encryption and authentication may not be sufficient to provide
   confidentiality, authentication, integrity, and freshness to both
   data and routing protocol packets.  Time synchronization, self-
   organization, and secure localization for multi-hop routing are also
   critical to support.

   For secure routing protocol operation, it may be necessary to
   consider authenticated broadcast (and multicast) and bidirectional
   link verification.  On the other hand, secure end-to-end data
   delivery can be assisted by the routing protocol.  For example,
   multi-path routing could be considered for increasing security to
   prevent selective forwarding.  However, the challenge is that
   6LoWPANs already have high resource constraints, so that 6LBR and
   LoWPAN nodes may require different security solutions.

7. Acknowledgments

   The authors of this document highly appreciate the authors of "IPv6
   over Low Power WPAN Security Analysis" [6LoWPAN-SEC].  Although their
   security analysis work is not ongoing at the time of this writing,
   the valuable information and text in that document are used in
   Section 5.4 of this document, per advice received during IESG review
   procedures.  Thanks to their work, Section 5.4 is much improved.  The
   authors also thank S. Chakrabarti, who gave valuable comments
   regarding mesh-under requirements, and A. Petrescu for significant
   review.

   Carles Gomez has been supported in part by FEDER and by the Spanish
   Government through projects TIC2006-04504 and TEC2009-11453.

8. References

8.1. Normative References

   [IEEE802.15.4]
              IEEE Computer Society, "IEEE Standard for Local and
              Metropolitan Area Networks -- Part 15.4: Low-Rate
              Wireless Personal Area Networks (LR-WPANs)", IEEE
              Std. 802.15.4-2011, September 2011.

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

   [RFC3756]  Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
              Neighbor Discovery (ND) Trust Models and Threats",
              RFC 3756, May 2004.

   [RFC3819]  Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
              Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
              Wood, "Advice for Internet Subnetwork Designers", BCP 89,
              RFC 3819, July 2004.

   [RFC4593]  Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
              Routing Protocols", RFC 4593, October 2006.

   [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, August 2007.

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

   [RFC5548]  Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and
              D. Barthel, Ed., "Routing Requirements for Urban Low-Power
              and Lossy Networks", RFC 5548, May 2009.

   [RFC5673]  Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
              Phinney, "Industrial Routing Requirements in Low-Power and
              Lossy Networks", RFC 5673, October 2009.

8.2. Informative References

   [6LoWPAN-ND]
              Shelby, Z., Ed., Chakrabarti, S., and E. Nordmark,
              "Neighbor Discovery Optimization for Low Power and Lossy
              Networks (6LoWPAN)", Work in Progress, October 2011.

   [6LoWPAN-SEC]
              Park, S., Kim, K., Haddad, W., Ed., Chakrabarti, S., and
              J. Laganier, "IPv6 over Low Power WPAN Security Analysis",
              Work in Progress, March 2011.

   [Bulusu]   Bulusu, N., Ed., and S. Jha, Ed., "Wireless Sensor
              Networks: A Systems Perspective", Artech House,
              ISBN 9781580538671, July 2005.

   [Chen]     Chen, B., Muniswamy-Reddy, K., and M. Welsh, "Ad-Hoc
              Multicast Routing on Resource-Limited Sensor Nodes", Proc.
              2nd International Workshop on Multi-hop Ad Hoc Networks,
              May 2006.

   [Doherty]  Doherty, L., Warneke, B., Boser, B., and K. Pister,
              "Energy and Performance Considerations for Smart Dust",
              International Journal of Parallel and Distributed Systems
              and Networks, Vol. 4, No. 3, 2001.

   [Hill]     Hill, J., "System Architecture for Wireless Sensor
              Networks", Ph.D. Thesis, UC Berkeley, 2003.

   [Ikram]    Ikram, M., Chowdhury, A., Zafar, B., Cha, H., Kim, K.,
              Yoo, S., and D. Kim, "A Simple Lightweight Authentic
              Bootstrapping Protocol for IPv6-based Low Rate Wireless
              Personal Area Networks (6LoWPANs)", Proc. International
              Conference on Wireless Communications and
              Mobile Computing, June 2009.

   [KARP-THREATS]
              Lebovitz, G. and M. Bhatia, "Keying and Authentication for
              Routing Protocols (KARP) Overview, Threats, and
              Requirements", Work in Progress, May 2012.

   [Kuhn]     Kuhn, F., Wattenhofer, R., and A. Zollinger, "Worst-Case
              Optimal and Average-Case Efficient Ad-Hoc Geometric
              Routing", MobiHoc '03: Proceedings of the 4th ACM
              International Symposium on Mobile Ad Hoc Networking and
              Computing, June 2003.

   [Latre]    Latre, B., De Mil, P., Moerman, I., Dhoedt, B., and P.
              Demeester, "Throughput and Delay Analysis of Unslotted
              IEEE 802.15.4", Journal of Networks, Vol. 1, No. 1,
              May 2006.

   [Lee]      Lee, S., Belding-Royer, E., and C. Perkins, "Scalability
              Study of the Ad Hoc On-Demand Distance-Vector Routing
              Protocol", International Journal of Network Management,
              Vol. 13, pp. 97-114, March 2003.

   [RFC1958]  Carpenter, B., Ed., "Architectural Principles of the
              Internet", RFC 1958, June 1996.

   [RFC5556]  Touch, J. and R. Perlman, "Transparent Interconnection of
              Lots of Links (TRILL): Problem and Applicability
              Statement", RFC 5556, May 2009.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions",
              RFC 5706, November 2009.

   [RFC5826]  Brandt, A., Buron, J., and G. Porcu, "Home Automation
              Routing Requirements in Low-Power and Lossy Networks",
              RFC 5826, April 2010.

   [RFC5867]  Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen,
              "Building Automation Routing Requirements in Low-Power and
              Lossy Networks", RFC 5867, June 2010.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5996, September 2010.

   [RFC6282]  Hui, J., Ed., and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              September 2011.

   [RFC6434]  Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
              Requirements", RFC 6434, December 2011.

   [ROLL-PROTOCOLS]
              Levis, P., Tavakoli, A., and S. Dawson-Haggerty, "Overview
              of Existing Routing Protocols for Low Power and Lossy
              Networks", Work in Progress, April 2009.

   [Shih]     Shih, E., Cho, S., Ickes, N., Min, R., Sinha, A., Wang,
              A., and A. Chandrakasan, "Physical Layer Driven Protocols
              and Algorithm Design for Energy-Efficient Wireless Sensor
              Networks", MobiCom '01: Proceedings of the 7th ACM Annual
              International Conference on Mobile Computing and
              Networking, July 2001.

   [Watteyne] Watteyne, T., Molinaro, A., Richichi, M., and M. Dohler,
              "From MANET To IETF ROLL Standardization: A Paradigm Shift
              in WSN Routing Protocols", IEEE Communications Surveys and
              Tutorials, Vol. 13, Issue 4, pp. 688-707, 2011,
              <http://ieeexplore.ieee.org/xpl/
              articleDetails.jsp?arnumber=5581105>.

Authors' Addresses

   Eunsook Eunah Kim
   ETRI
   161 Gajeong-dong
   Yuseong-gu
   Daejeon  305-700
   Korea

   Phone: +82-42-860-6124
   EMail: eunah.ietf@gmail.com

   Dominik Kaspar
   Simula Research Laboratory
   Martin Linges v 17
   Fornebu  1364
   Norway

   Phone: +47-6782-8223
   EMail: dokaspar.ietf@gmail.com

   Carles Gomez
   Universitat Politecnica de Catalunya/Fundacio i2CAT
   Escola d'Enginyeria de Telecomunicacio i Aeroespacial
      de Castelldefels
   C/Esteve Terradas, 7
   Castelldefels  08860
   Spain

   Phone: +34-93-413-7206
   EMail: carlesgo@entel.upc.edu

   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28359
   Germany

   Phone: +49-421-218-63921
   EMail: cabo@tzi.org