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rfc:rfc7731

Internet Engineering Task Force (IETF) J. Hui Request for Comments: 7731 Nest Labs Category: Standards Track R. Kelsey ISSN: 2070-1721 Silicon Labs

                                                         February 2016
     Multicast Protocol for Low-Power and Lossy Networks (MPL)

Abstract

 This document specifies the Multicast Protocol for Low-Power and
 Lossy Networks (MPL), which provides IPv6 multicast forwarding in
 constrained networks.  MPL avoids the need to construct or maintain
 any multicast forwarding topology, disseminating messages to all MPL
 Forwarders in an MPL Domain.
 MPL has two modes of operation.  One mode uses the Trickle algorithm
 to manage control-plane and data-plane message transmissions and is
 applicable for deployments with few multicast sources.  The other
 mode uses classic flooding.  By providing both modes and
 parameterization of the Trickle algorithm, an MPL implementation can
 be used in a variety of multicast deployments and can trade between
 dissemination latency and transmission efficiency.

Status of This Memo

 This is an Internet Standards Track document.
 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).  Further information on
 Internet Standards is available in 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/rfc7731.

Hui & Kelsey Standards Track [Page 1] RFC 7731 MPL February 2016

Copyright Notice

 Copyright (c) 2016 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Hui & Kelsey Standards Track [Page 2] RFC 7731 MPL February 2016

Table of Contents

 1. Introduction ....................................................4
 2. Terminology .....................................................5
 3. Applicability Statement .........................................6
 4. MPL Protocol Overview ...........................................7
    4.1. MPL Domains ................................................7
    4.2. Information Base Overview ..................................8
    4.3. Protocol Overview ..........................................8
    4.4. Signaling Overview ........................................10
 5. MPL Parameters and Constants ...................................11
    5.1. MPL Multicast Addresses ...................................11
    5.2. MPL Message Types .........................................11
    5.3. MPL Seed Identifiers ......................................11
    5.4. MPL Parameters ............................................11
 6. Protocol Message Formats .......................................14
    6.1. MPL Option ................................................14
    6.2. MPL Control Message .......................................15
    6.3. MPL Seed Info .............................................16
 7. Information Base ...............................................17
    7.1. Local Interface Set .......................................17
    7.2. Domain Set ................................................18
    7.3. Seed Set ..................................................18
    7.4. Buffered Message Set ......................................18
 8. MPL Seed Sequence Numbers ......................................19
 9. MPL Data Messages ..............................................19
    9.1. MPL Data Message Generation ...............................19
    9.2. MPL Data Message Transmission .............................20
    9.3. MPL Data Message Processing ...............................21
 10. MPL Control Messages ..........................................22
    10.1. MPL Control Message Generation ...........................22
    10.2. MPL Control Message Transmission .........................22
    10.3. MPL Control Message Processing ...........................23
 11. IANA Considerations ...........................................24
    11.1. MPL Option Type ..........................................24
    11.2. MPL ICMPv6 Type ..........................................25
    11.3. Well-Known Multicast Addresses ...........................25
 12. Security Considerations .......................................25
 13. References ....................................................26
    13.1. Normative References .....................................26
    13.2. Informative References ...................................28
 Acknowledgements ..................................................29
 Authors' Addresses ................................................29

Hui & Kelsey Standards Track [Page 3] RFC 7731 MPL February 2016

1. Introduction

 Low-Power and Lossy Networks (LLNs) typically operate with strict
 resource constraints in communication, computation, memory, and
 energy.  Such resource constraints may preclude the use of existing
 IPv6 multicast routing and forwarding mechanisms.  Traditional IP
 multicast delivery typically relies on topology maintenance
 mechanisms to discover and maintain routes to all subscribers of a
 multicast group (e.g., [RFC3973] [RFC4601]).  However, maintaining
 such topologies in LLNs is costly and may not be feasible given the
 available resources.
 Memory constraints may limit devices to maintaining links/routes to
 one or a few neighbors.  For this reason, the Routing Protocol for
 LLNs (RPL) specifies both storing and non-storing modes [RFC6550].
 The latter allows RPL routers to maintain only one or a few default
 routes towards an LLN Border Router (LBR) and use source routing to
 forward messages away from the LBR.  For the same reasons, an LLN
 device may not be able to maintain a multicast routing topology when
 operating with limited memory.
 Furthermore, the dynamic properties of wireless networks can make the
 cost of maintaining a multicast routing topology prohibitively
 expensive.  In wireless environments, topology maintenance may
 involve selecting a connected dominating set used to forward
 multicast messages to all nodes in an administrative domain.
 However, existing mechanisms often require two-hop topology
 information, and the cost of maintaining such information grows
 polynomially with network density.
 This document specifies the Multicast Protocol for Low-Power and
 Lossy Networks (MPL), which provides IPv6 multicast forwarding in
 constrained networks.  MPL avoids the need to construct or maintain
 any multicast routing topology, disseminating multicast messages to
 all MPL Forwarders in an MPL Domain.  By using the Trickle algorithm
 [RFC6206], MPL requires only small, constant state for each MPL
 device that initiates disseminations.  The Trickle algorithm also
 allows MPL to be density aware, allowing the communication rate to
 scale logarithmically with density.

Hui & Kelsey Standards Track [Page 4] RFC 7731 MPL February 2016

2. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 [RFC2119].
 The following terms are used throughout this document:
 MPL Forwarder  - A router that implements MPL.  An MPL Forwarder is
    equipped with at least one MPL Interface.
 MPL Interface  - An MPL Forwarder's attachment to a communications
    medium, over which it transmits and receives MPL Data Messages and
    MPL Control Messages according to this specification.  An MPL
    Interface is assigned one or more unicast addresses and is
    subscribed to one or more MPL Domain Addresses.
 MPL Domain Address  - A multicast address that identifies the set of
    MPL Interfaces within an MPL Domain.  MPL Data Messages
    disseminated in an MPL Domain have the associated MPL Domain
    Address as their destination address.
 MPL Domain  - A scope zone, as defined in [RFC4007], in which MPL
    Interfaces subscribe to the same MPL Domain Address and
    participate in disseminating MPL Data Messages.
 MPL Data Message  - A multicast message that is used to communicate a
    multicast payload between MPL Forwarders within an MPL Domain.  An
    MPL Data Message contains an MPL Option in the IPv6 header and has
    as its destination address the MPL Domain Address corresponding to
    the MPL Domain.
 MPL Control Message  - A link-local multicast message that is used to
    communicate information about recently received MPL Data Messages
    to neighboring MPL Forwarders.
 MPL Seed  - An MPL Forwarder that generates MPL Data Messages and
    serves as an entry point into an MPL Domain.
 MPL Seed Identifier  - An unsigned integer that uniquely identifies
    an MPL Seed within an MPL Domain.
 Node  - Used within this document to refer to an MPL Forwarder.

Hui & Kelsey Standards Track [Page 5] RFC 7731 MPL February 2016

3. Applicability Statement

 MPL is an IPv6 multicast forwarding protocol designed for the
 communication characteristics and resource constraints of LLNs.  By
 implementing controlled disseminations of multicast messages using
 the Trickle algorithm, MPL is designed for networks that communicate
 using low-power and lossy links with widely varying topologies in
 both the space and time dimensions.
 While designed specifically for LLNs, MPL is not limited to use over
 such networks.  MPL may be applicable to any network where no
 multicast routing state is desired.  MPL may also be used in
 environments where only a subset of links are considered low-power
 and lossy links.
 A host need not be aware that their multicast is supported by MPL as
 long as its attachment router forwards multicast messages between the
 MPL Domain and the host.  However, a host may choose to implement MPL
 so that it can take advantage of the broadcast medium inherent in
 many LLNs and receive multicast messages carried by MPL directly.
 MPL is parameterized to support different dissemination techniques.
 In one parameterization, MPL may utilize the classic flooding method
 that involves having each device receiving a message rebroadcast the
 message.  In another parameterization, MPL may utilize Trickle's
 [RFC6206] "polite gossip" method, which involves transmission
 suppression and adaptive timing techniques.  [Clausen2013] questions
 the efficiency of Trickle's "polite gossip" mechanism in some
 multicast scenarios, so by also including a classic flooding mode of
 operation MPL aims to be able to perform satisfactorily in a variety
 of situations.
 To support efficient message delivery in networks that have many poor
 links, MPL supports a reactive forwarding mode that utilizes MPL
 Control Messages to summarize the current multicast state.  The MPL
 Control Message size grows linearly with the number of simultaneous
 MPL Seeds in the MPL Domain -- 4 octets per MPL Seed.  When reactive
 forwarding is not enabled, MPL Control Messages are not transmitted,
 and the associated overhead is not incurred.
 This document does not specify a cryptographic security mechanism for
 MPL to ensure that MPL messages are not spoofed by anyone with access
 to the LLN.  In general, the basic ability to inject messages into an
 LLN may be used as a denial-of-service attack, regardless of what
 forwarding protocol is used.  For these reasons, LLNs typically
 employ link-layer security mechanisms to mitigate an attacker's
 ability to inject messages.  For example, the IEEE 802.15.4
 [IEEE802.15.4] standard specifies frame security mechanisms using

Hui & Kelsey Standards Track [Page 6] RFC 7731 MPL February 2016

 AES-128 to support access control, message integrity, message
 confidentiality, and replay protection.  However, if the attack
 vector includes attackers that have access to the LLN, then MPL
 SHOULD NOT be used.

4. MPL Protocol Overview

 The goal of MPL is to deliver multicast messages to all interfaces
 that subscribe to the multicast messages' destination address within
 an MPL Domain.

4.1. MPL Domains

 An MPL Domain is a scope zone, as defined in [RFC4007], in which MPL
 Interfaces subscribe to the same MPL Domain Address and participate
 in disseminating MPL Data Messages.
 When participating in only one MPL Domain, the MPL Domain Address is
 the ALL_MPL_FORWARDERS multicast address with Realm-Local scope
 ("scop" value 3) [RFC7346].
 When an MPL Forwarder participates in multiple MPL Domains
 simultaneously, at most one MPL Domain may be assigned an MPL Domain
 Address equal to the ALL_MPL_FORWARDERS multicast address.  All other
 MPL Domains MUST be assigned a unique MPL Domain Address that allows
 the MPL Forwarder to identify each MPL Domain.  The MPL Domains
 SHOULD be configured automatically based on some underlying topology.
 For example, when using RPL [RFC6550], MPL Domains may be configured
 based on RPL Instances.
 When MPL is used in deployments that use administratively defined
 scopes that cover, for example, multiple subnets based on different
 underlying network technologies, Admin-Local scope (scop value 4) or
 Site-Local scope (scop value 5) SHOULD be used.
 An MPL Forwarder MAY participate in additional MPL Domains identified
 by other multicast addresses.  An MPL Interface MUST subscribe to the
 MPL Domain Addresses for the MPL Domains that it participates in.
 The assignment of other multicast addresses is out of scope.
 For each MPL Domain Address that an MPL Interface subscribes to, the
 MPL Interface MUST also subscribe to the same MPL Domain Address with
 Link-Local scope (scop value 2) when reactive forwarding is in use
 (i.e., when communicating MPL Control Messages).

Hui & Kelsey Standards Track [Page 7] RFC 7731 MPL February 2016

4.2. Information Base Overview

 A node records necessary protocol state in the following
 information sets:
 o  The Local Interface Set records the set of local MPL Interfaces
    and the unicast addresses assigned to those MPL Interfaces.
 o  The Domain Set records the set of MPL Domain Addresses and the
    local MPL Interfaces that subscribe to those addresses.
 o  A Seed Set records information about received MPL Data Messages
    received from an MPL Seed within an MPL Domain.  Each MPL Domain
    has an associated Seed Set.  A Seed Set maintains the minimum
    sequence number for MPL Data Messages that the MPL Forwarder is
    willing to receive or has buffered in its Buffered Message Set
    from an MPL Seed.  MPL uses Seed Sets and Buffered Message Sets to
    determine when to accept an MPL Data Message, process its payload,
    and retransmit it.
 o  A Buffered Message Set records recently received MPL Data Messages
    from an MPL Seed within an MPL Domain.  Each MPL Domain has an
    associated Buffered Message Set.  MPL Data Messages resident in a
    Buffered Message Set have sequence numbers that are greater than
    or equal to the minimum threshold maintained in the corresponding
    Seed Set.  MPL uses Buffered Message Sets to store MPL Data
    Messages that may be transmitted by the MPL Forwarder for
    forwarding.

4.3. Protocol Overview

 MPL achieves its goal by implementing a controlled flood that
 attempts to disseminate the multicast data message to all interfaces
 within an MPL Domain.  MPL performs the following tasks to
 disseminate a multicast message:
 o  When having a multicast message to forward into an MPL Domain, the
    MPL Seed generates an MPL Data Message that includes the MPL
    Domain Address as the IPv6 Destination Address, the MPL Seed
    Identifier, a newly generated sequence number, and the multicast
    message.  If the multicast destination address is not the MPL
    Domain Address, IP-in-IP tunneling [RFC2473] is used to
    encapsulate the multicast message in an MPL Data Message,
    preserving the original IPv6 Destination Address.

Hui & Kelsey Standards Track [Page 8] RFC 7731 MPL February 2016

 o  Upon receiving an MPL Data Message, the MPL Forwarder extracts the
    MPL Seed and sequence number and determines whether or not the MPL
    Data Message was previously received using the MPL Domain's Seed
    Set and Buffered Message Set.
  • If the sequence number is less than the lower-bound sequence

number maintained in the Seed Set or a message with the same

       sequence number exists within the Buffered Message Set, the MPL
       Forwarder marks the MPL Data Message as old.
  • Otherwise, the MPL Forwarder marks the MPL Data Message as new.
 o  For each newly received MPL Data Message, an MPL Forwarder updates
    the Seed Set, adds the MPL Data Message into the Buffered Message
    Set, processes its payload, and multicasts the MPL Data Message a
    number of times on all MPL Interfaces participating in the same
    MPL Domain to forward the message.
 o  Each MPL Forwarder may periodically link-local multicast MPL
    Control Messages on MPL Interfaces to communicate information
    contained in an MPL Domain's Seed Set and Buffered Message Set.
 o  Upon receiving an MPL Control Message, an MPL Forwarder determines
    whether or not there are any new MPL Data Messages that have yet
    to be received by the MPL Control Message's source and multicasts
    those MPL Data Messages.
 MPL's configuration parameters allow two forwarding strategies for
 disseminating MPL Data Messages via MPL Interfaces:
 Proactive Forwarding  - With proactive forwarding, an MPL Forwarder
    schedules transmissions of MPL Data Messages using the Trickle
    algorithm, without any prior indication that neighboring nodes
    have yet to receive the message.  After transmitting the MPL Data
    Message a limited number of times, the MPL Forwarder may terminate
    proactive forwarding for the MPL Data Message.
 Reactive Forwarding  - With reactive forwarding, an MPL Forwarder
    link-local multicasts MPL Control Messages using the Trickle
    algorithm [RFC6206].  MPL Forwarders use MPL Control Messages to
    discover new MPL Data Messages that have not yet been received.
    When discovering that a neighboring MPL Forwarder has not yet
    received an MPL Data Message, the MPL Forwarder schedules those
    MPL Data Messages for transmission using the Trickle algorithm.

Hui & Kelsey Standards Track [Page 9] RFC 7731 MPL February 2016

 Note that, when used within the same MPL Domain, proactive and
 reactive forwarding strategies are not mutually exclusive and may be
 used simultaneously.  For example, upon receiving a new MPL Data
 Message when both proactive and reactive forwarding techniques are
 enabled, an MPL Forwarder will proactively retransmit the MPL Data
 Message a limited number of times and schedule further transmissions
 upon receiving MPL Control Messages.

4.4. Signaling Overview

 MPL generates and processes the following messages:
 MPL Data Message  - Generated by an MPL Seed to deliver a multicast
    message across an MPL Domain.  The MPL Data Message's source is an
    address in the Local Interface Set of the MPL Seed that generated
    the message and is valid within the MPL Domain.  The MPL Data
    Message's destination is the MPL Domain Address corresponding to
    the MPL Domain.  An MPL Data Message contains:
  • The Seed Identifier of the MPL Seed that generated the MPL Data

Message.

  • The sequence number of the MPL Seed that generated the MPL Data

Message.

  • The original multicast message.
 MPL Control Message  - Generated by an MPL Forwarder to communicate
    information contained in an MPL Domain's Seed Set and Buffered
    Message Set to neighboring MPL Forwarders.  An MPL Control Message
    contains a list of tuples for each entry in the Seed Set.  Each
    tuple contains:
  • The minimum sequence number maintained in the Seed Set for the

MPL Seed.

  • A bit-vector indicating the sequence numbers of MPL Data

Messages resident in the Buffered Message Set for the MPL Seed,

       where the first bit represents a sequence number equal to the
       minimum threshold maintained in the Seed Set.
  • The length of the bit-vector.

Hui & Kelsey Standards Track [Page 10] RFC 7731 MPL February 2016

5. MPL Parameters and Constants

 This section describes various program and networking parameters and
 constants used by MPL.

5.1. MPL Multicast Addresses

 MPL makes use of MPL Domain Addresses to identify MPL Interfaces of
 an MPL Domain.  By default, MPL Forwarders subscribe to the
 ALL_MPL_FORWARDERS multicast address with Realm-Local scope (scop
 value 3) [RFC7346].
 For each MPL Domain Address that an MPL Interface subscribes to, the
 MPL Interface MUST also subscribe to the MPL Domain Address with
 Link-Local scope (scop value 2) when reactive forwarding is in use.
 MPL Forwarders use the link-scoped MPL Domain Address to communicate
 MPL Control Messages to neighboring (i.e., on-link) MPL Forwarders.

5.2. MPL Message Types

 MPL defines an IPv6 Option for carrying an MPL Seed Identifier and a
 sequence number within an MPL Data Message.  The IPv6 Option Type has
 value 0x6D.
 MPL defines an ICMPv6 Message (MPL Control Message) for communicating
 information contained in an MPL Domain's Seed Set and Buffered
 Message Set to neighboring MPL Forwarders.  The MPL Control Message
 has ICMPv6 Type 159.

5.3. MPL Seed Identifiers

 MPL uses MPL Seed Identifiers to uniquely identify MPL Seeds within
 an MPL Domain.  For each MPL Domain that the MPL Forwarder serves as
 an MPL Seed, the MPL Forwarder MUST have an associated MPL Seed
 Identifier.  An MPL Forwarder MAY use the same MPL Seed Identifier
 across multiple MPL Domains, but the MPL Seed Identifier MUST be
 unique within each MPL Domain.  The mechanism for assigning and
 verifying uniqueness of MPL Seed Identifiers is not specified in this
 document.

5.4. MPL Parameters

 PROACTIVE_FORWARDING  - A boolean value that indicates whether or not
    the MPL Forwarder schedules MPL Data Message transmissions after
    receiving them for the first time.  PROACTIVE_FORWARDING has a
    default value of TRUE.  All MPL Interfaces on the same link SHOULD
    be configured with the same value of PROACTIVE_FORWARDING.  An
    implementation MAY choose to vary the value of

Hui & Kelsey Standards Track [Page 11] RFC 7731 MPL February 2016

    PROACTIVE_FORWARDING across interfaces on the same link if
    reactive forwarding is also in use.  The mechanism for setting
    PROACTIVE_FORWARDING is not specified within this document.
 SEED_SET_ENTRY_LIFETIME  - The minimum lifetime for an entry in the
    Seed Set.  SEED_SET_ENTRY_LIFETIME has a default value of
    30 minutes.  It is RECOMMENDED that all MPL Forwarders use the
    same value for SEED_SET_ENTRY_LIFETIME for a given MPL Domain and
    use a default value of 30 minutes.  Using a value of
    SEED_SET_ENTRY_LIFETIME that is too small can cause the duplicate
    detection mechanism to fail, resulting in an MPL Forwarder
    receiving a given MPL Data Message more than once.  The mechanism
    for setting SEED_SET_ENTRY_LIFETIME is not specified within this
    document.
 As specified in [RFC6206], a Trickle timer runs for a defined
 interval and has three configuration parameters: the minimum interval
 size Imin, the maximum interval size Imax, and a redundancy
 constant k.
 This specification defines a fourth Trickle configuration parameter,
 TimerExpirations, which indicates the number of Trickle timer
 expiration events that occur before terminating the Trickle algorithm
 for a given MPL Data Message or MPL Control Message.
 Each MPL Interface uses the following Trickle parameters for MPL Data
 Message and MPL Control Message transmissions:
 DATA_MESSAGE_IMIN  - The minimum Trickle timer interval, as defined
    in [RFC6206], for MPL Data Message transmissions.
    DATA_MESSAGE_IMIN has a default value of 10 times the expected
    link-layer latency.
 DATA_MESSAGE_IMAX  - The maximum Trickle timer interval, as defined
    in [RFC6206], for MPL Data Message transmissions.
    DATA_MESSAGE_IMAX has a default value equal to DATA_MESSAGE_IMIN.
 DATA_MESSAGE_K  - The redundancy constant, as defined in [RFC6206],
    for MPL Data Message transmissions.  DATA_MESSAGE_K has a default
    value of 1.
 DATA_MESSAGE_TIMER_EXPIRATIONS  - The number of Trickle timer
    expirations that occur before terminating the Trickle algorithm's
    retransmission of a given MPL Data Message.
    DATA_MESSAGE_TIMER_EXPIRATIONS has a default value of 3.

Hui & Kelsey Standards Track [Page 12] RFC 7731 MPL February 2016

 CONTROL_MESSAGE_IMIN  - The minimum Trickle timer interval, as
    defined in [RFC6206], for MPL Control Message transmissions.
    CONTROL_MESSAGE_IMIN has a default value of 10 times the
    worst-case link-layer latency.
 CONTROL_MESSAGE_IMAX  - The maximum Trickle timer interval, as
    defined in [RFC6206], for MPL Control Message transmissions.
    CONTROL_MESSAGE_IMAX has a default value of 5 minutes.
 CONTROL_MESSAGE_K  - The redundancy constant, as defined in
    [RFC6206], for MPL Control Message transmissions.
    CONTROL_MESSAGE_K has a default value of 1.
 CONTROL_MESSAGE_TIMER_EXPIRATIONS  - The number of Trickle timer
    expirations that occur before terminating the Trickle algorithm
    for MPL Control Message transmissions.
    CONTROL_MESSAGE_TIMER_EXPIRATIONS has a default value of 10.
 As described in [RFC6206], if different nodes have different
 configuration parameters, Trickle may have unintended behaviors.
 Therefore, it is RECOMMENDED that all MPL Interfaces attached to the
 same link of a given MPL Domain use the same values for the Trickle
 parameters above for a given MPL Domain.  The mechanism for setting
 the Trickle parameters is not specified within this document.
 The default MPL parameters specify a forwarding strategy that
 utilizes both proactive and reactive techniques.  Using these default
 values, an MPL Forwarder proactively transmits any new MPL Data
 Messages it receives and then uses MPL Control Messages to trigger
 additional MPL Data Message retransmissions where message drops are
 detected.  Setting DATA_MESSAGE_IMAX to the same value as
 DATA_MESSAGE_IMIN in this case is acceptable, since subsequent MPL
 Data Message retransmissions are triggered by MPL Control Messages,
 where CONTROL_MESSAGE_IMAX is greater than CONTROL_MESSAGE_IMIN.

Hui & Kelsey Standards Track [Page 13] RFC 7731 MPL February 2016

6. Protocol Message Formats

 Messages generated and processed by an MPL Forwarder are described in
 this section.

6.1. MPL Option

 The MPL Option is carried in MPL Data Messages in an IPv6 Hop-by-Hop
 Options header, immediately following the IPv6 header.  The MPL
 Option has the following format:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |  Option Type  |  Opt Data Len |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | S |M|V|  rsv  |   sequence    |      seed-id (optional)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Option Type    0x6D.
 Opt Data Len   Length of the Option Data field [RFC2460] in octets.
 S              2-bit unsigned integer.  Identifies the length of the
                seed-id.  '0' indicates that the seed-id is the IPv6
                Source Address and not included in the MPL Option.
                '1' indicates that the seed-id is a 16-bit unsigned
                integer.  '2' indicates that the seed-id is a 64-bit
                unsigned integer.  '3' indicates that the seed-id is a
                128-bit unsigned integer.
 M              1-bit flag.  '1' indicates that the value in the
                sequence field is known to be the largest sequence
                number that was received from the MPL Seed.
 V              1-bit flag.  '0' indicates that the MPL Option
                conforms to this specification.  MPL Data Messages
                with an MPL Option in which this flag is set to 1 MUST
                be dropped.
 rsv            4-bit reserved field.  MUST be set to 0 on
                transmission and ignored on reception.

Hui & Kelsey Standards Track [Page 14] RFC 7731 MPL February 2016

 sequence       8-bit unsigned integer.  Identifies relative ordering
                of MPL Data Messages from the MPL Seed identified by
                the seed-id.
 seed-id        Uniquely identifies the MPL Seed that initiated
                dissemination of the MPL Data Message.  The size of
                the seed-id is indicated by the S field.
 The Option Data (specifically, the M flag) of the MPL Option is
 updated by MPL Forwarders as the MPL Data Message is forwarded.
 Nodes that do not understand the MPL Option MUST discard the MPL Data
 Message.  Thus, according to [RFC2460], the three high-order bits of
 the Option Type are set to '011'.  The Option Data length is
 variable.
 The seed-id uniquely identifies an MPL Seed.  When the seed-id is
 128 bits (S=3), the MPL Seed MAY use an IPv6 address assigned to one
 of its interfaces that is unique within the MPL Domain.  Managing MPL
 Seed Identifiers is not within the scope of this document.
 The sequence field establishes a total ordering of MPL Data Messages
 generated by an MPL Seed for an MPL Domain.  The MPL Seed MUST
 increment the sequence field's value on each new MPL Data Message
 that it generates for an MPL Domain.  Implementations MUST follow the
 Serial Number Arithmetic as defined in [RFC1982] when incrementing a
 sequence value or comparing two sequence values.
 Future updates to this specification may define additional fields
 following the seed-id field.

6.2. MPL Control Message

 An MPL Forwarder uses ICMPv6 Messages to communicate information
 contained in an MPL Domain's Seed Set and Buffered Message Set to
 neighboring MPL Forwarders.  The MPL Control Message has the
 following format:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                      MPL Seed Info[0..n]                      .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Hui & Kelsey Standards Track [Page 15] RFC 7731 MPL February 2016

 IP Fields:
 Source Address        An IPv6 address in the AddressSet of the
                       corresponding MPL Interface.  MUST be valid
                       within the MPL Domain.
 Destination Address   The link-scoped MPL Domain Address
                       corresponding to the MPL Domain.
 Hop Limit             255
 ICMPv6 Fields:
 Type                  159
 Code                  0
 Checksum              The ICMP checksum.  See [RFC4443].
 MPL Seed Info[0..n]   List of zero or more MPL Seed Info entries.
 The MPL Control Message indicates the sequence numbers of MPL Data
 Messages that are within the MPL Domain's Buffered Message Set.  The
 MPL Control Message also indicates the sequence numbers of MPL Data
 Messages that an MPL Forwarder is willing to receive.  The MPL
 Control Message allows neighboring MPL Forwarders to determine
 whether or not there are any new MPL Data Messages to exchange.

6.3. MPL Seed Info

 The MPL Seed Info encodes the minimum sequence number for an MPL Seed
 maintained in the MPL Domain's Seed Set.  The MPL Seed Info also
 indicates the sequence numbers of MPL Data Messages generated by the
 MPL Seed that are stored within the MPL Domain's Buffered Message
 Set.  The MPL Seed Info has the following format:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   min-seqno   |  bm-len   | S |   seed-id (0/2/8/16 octets)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .            buffered-mpl-messages (variable length)            .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Hui & Kelsey Standards Track [Page 16] RFC 7731 MPL February 2016

 min-seqno               8-bit unsigned integer.  The lower-bound
                         sequence number for the MPL Seed.
 bm-len                  6-bit unsigned integer.  The size of
                         buffered-mpl-messages in octets.
 S                       2-bit unsigned integer.  Identifies the
                         length of the seed-id.  '0' indicates that
                         the seed-id value is the IPv6 Source Address
                         and not included in the MPL Seed Info.  '1'
                         indicates that the seed-id value is a 16-bit
                         unsigned integer.  '2' indicates that the
                         seed-id value is a 64-bit unsigned integer.
                         '3' indicates that the seed-id is a 128-bit
                         unsigned integer.
 seed-id                 Variable-length unsigned integer.  Indicates
                         the MPL Seed associated with this MPL
                         Seed Info.
 buffered-mpl-messages   Variable-length bit-vector.  Identifies the
                         sequence numbers of MPL Data Messages
                         maintained in the corresponding Buffered
                         Message Set for the MPL Seed.  The i-th bit
                         represents a sequence number of min-seqno
                         + i.  '0' indicates that the corresponding
                         MPL Data Message does not exist in the
                         Buffered Message Set.  '1' indicates that the
                         corresponding MPL Data Message does exist in
                         the Buffered Message Set.
 The MPL Seed Info does not have any octet alignment requirement.

7. Information Base

7.1. Local Interface Set

 The Local Interface Set records the local MPL Interfaces of an MPL
 Forwarder.  The Local Interface Set consists of Local Interface
 Tuples, one per MPL Interface: (AddressSet).
 AddressSet  - a set of unicast addresses assigned to the MPL
    Interface.

Hui & Kelsey Standards Track [Page 17] RFC 7731 MPL February 2016

7.2. Domain Set

 The Domain Set records the MPL Interfaces that subscribe to each MPL
 Domain Address.  The Domain Set consists of MPL Domain Tuples, one
 per MPL Domain: (MPLInterfaceSet).
 MPLInterfaceSet  - a set of MPL Interfaces that subscribe to the MPL
    Domain Address that identifies the MPL Domain.

7.3. Seed Set

 A Seed Set records a sliding window used to determine the sequence
 numbers of MPL Data Messages (generated by the MPL Seed) that an MPL
 Forwarder is willing to accept.  An MPL Forwarder maintains a Seed
 Set for each MPL Domain that it participates in.  A Seed Set consists
 of MPL Seed Tuples: (SeedID, MinSequence, Lifetime).
 SeedID  - the identifier for the MPL Seed.
 MinSequence  - a lower-bound sequence number that represents the
    sequence number of the oldest MPL Data Message the MPL Forwarder
    is willing to receive or transmit.  An MPL Forwarder MUST ignore
    any MPL Data Message that has a sequence value less than
    MinSequence.
 Lifetime  - indicates the minimum remaining lifetime of the Seed Set
    entry.  An MPL Forwarder MUST NOT free a Seed Set entry before the
    remaining lifetime expires.

7.4. Buffered Message Set

 A Buffered Message Set records recently received MPL Data Messages
 from an MPL Seed within an MPL Domain.  An MPL Forwarder uses a
 Buffered Message Set to buffer MPL Data Messages while the MPL
 Forwarder is forwarding the MPL Data Messages.  An MPL Forwarder
 maintains a Buffered Message Set for each MPL Domain that it
 participates in.  A Buffered Message Set consists of Buffered Message
 Tuples: (SeedID, SequenceNumber, DataMessage).
 SeedID  - the identifier for the MPL Seed that generated the MPL Data
    Message.
 SequenceNumber  - the sequence number for the MPL Data Message.
 DataMessage  - the MPL Data Message.

Hui & Kelsey Standards Track [Page 18] RFC 7731 MPL February 2016

 All MPL Data Messages within a Buffered Message Set MUST have a
 sequence number greater than or equal to MinSequence for the
 corresponding SeedID.  When increasing MinSequence for an MPL Seed,
 the MPL Forwarder MUST delete any MPL Data Messages from the
 corresponding Buffered Message Set that have sequence numbers less
 than MinSequence.

8. MPL Seed Sequence Numbers

 Each MPL Seed maintains a sequence number for each MPL Domain that it
 serves.  The sequence numbers are included in MPL Data Messages
 generated by the MPL Seed.  The MPL Seed MUST increment the sequence
 number for each MPL Data Message that it generates for an MPL Domain.
 Implementations MUST follow the Serial Number Arithmetic as defined
 in [RFC1982] when incrementing a sequence value or comparing two
 sequence values.  This sequence number is used to establish a total
 ordering of MPL Data Messages generated by an MPL Seed for an MPL
 Domain.

9. MPL Data Messages

9.1. MPL Data Message Generation

 MPL Data Messages are generated by MPL Seeds when these messages
 enter the MPL Domain.  All MPL Data Messages have the following
 properties:
 o  The IPv6 Source Address MUST be an address in the AddressSet of a
    corresponding MPL Interface and MUST be valid within the MPL
    Domain.
 o  The IPv6 Destination Address MUST be set to the MPL Domain Address
    corresponding to the MPL Domain.
 o  An MPL Data Message MUST contain an MPL Option in its IPv6 header
    to identify the MPL Seed that generated the message and the
    ordering relative to other MPL Data Messages generated by the
    MPL Seed.
 When the destination address is an MPL Domain Address and the source
 address is in the AddressList of an MPL Interface that belongs to
 that MPL Domain Address, the application message and the MPL Data
 Message MAY be identical.  In other words, the MPL Data Message may
 contain a single IPv6 header that includes the MPL Option.
 Otherwise, IPv6-in-IPv6 encapsulation MUST be used to satisfy the MPL
 Data Message requirements listed above [RFC2473].  The complete
 IPv6-in-IPv6 message forms an MPL Data Message.  The outer IPv6

Hui & Kelsey Standards Track [Page 19] RFC 7731 MPL February 2016

 header conforms to the MPL Data Message requirements listed above.
 The encapsulated IPv6 datagram encodes the multicast data message
 that is communicated beyond the MPL Domain.

9.2. MPL Data Message Transmission

 An MPL Forwarder manages transmission of MPL Data Messages in its
 Buffered Message Sets using the Trickle algorithm [RFC6206].  An MPL
 Forwarder MUST use a separate Trickle timer for each MPL Data Message
 that it is actively forwarding.  In accordance with Section 5 of
 RFC 6206 [RFC6206], the following items apply:
 o  This document defines a "consistent" transmission as receiving an
    MPL Data Message that has the same MPL Domain Address, seed-id,
    and sequence value as the MPL Data Message managed by the
    Trickle timer.
 o  This document defines an "inconsistent" transmission as receiving
    an MPL Data Message that has the same MPL Domain Address, seed-id
    value, and the M flag set, but has a sequence value less than that
    of the MPL Data Message managed by the Trickle timer.
 o  This document does not define any external "events".
 o  This document defines MPL Data Messages as Trickle messages.
 o  The actions outside the Trickle algorithm that MPL takes involve
    managing the MPL Domain's Seed Set and Buffered Message Set.
 As specified in [RFC6206], a Trickle timer has three variables: the
 current interval size I, a time within the current interval t, and a
 counter c.  MPL defines a fourth variable, e, which counts the number
 of Trickle timer expiration events since the Trickle timer was last
 reset.
 After DATA_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, the MPL
 Forwarder MUST disable the Trickle timer.  When a buffered MPL Data
 Message does not have an associated Trickle timer, the MPL Forwarder
 MAY delete the message from the Buffered Message Set by advancing the
 MinSequence value of the corresponding MPL Seed in the Seed Set.
 When the MPL Forwarder no longer buffers any messages for an MPL
 Seed, the MPL Forwarder MUST NOT increment MinSequence for that
 MPL Seed.
 When transmitting an MPL Data Message, the MPL Forwarder MUST either
 set the M flag to zero or set it to a level that indicates whether or
 not the message's sequence number is the largest value that has been
 received from the MPL Seed.

Hui & Kelsey Standards Track [Page 20] RFC 7731 MPL February 2016

9.3. MPL Data Message Processing

 Upon receiving an MPL Data Message, the MPL Forwarder first processes
 the MPL Option and updates the Trickle timer associated with the MPL
 Data Message if one exists.
 Upon receiving an MPL Data Message, an MPL Forwarder MUST perform one
 of the following actions:
 o  Accept the message and enter the MPL Data Message in the MPL
    Domain's Buffered Message Set.
 o  Accept the message and update the corresponding MinSequence in
    the MPL Domain's Seed Set to 1 greater than the message's
    sequence number.
 o  Discard the message without any change to the MPL
    Information Base.
 If a Seed Set entry exists for the MPL Seed, the MPL Forwarder MUST
 discard the MPL Data Message if its sequence number is less than
 MinSequence or exists in the Buffered Message Set.
 If a Seed Set entry does not exist for the MPL Seed, the MPL
 Forwarder MUST create a new entry for the MPL Seed before accepting
 the MPL Data Message.
 If memory is limited, an MPL Forwarder SHOULD reclaim memory
 resources by:
 o  Incrementing MinSequence entries in a Seed Set and deleting MPL
    Data Messages in the corresponding Buffered Message Set that fall
    below the MinSequence value.
 o  Deleting other Seed Set entries that have expired and the
    corresponding MPL Data Messages in the Buffered Message Set.
 If the MPL Forwarder accepts the MPL Data Message, the MPL Forwarder
 MUST perform the following actions:
 o  Reset the Lifetime of the corresponding Seed Set entry to
    SEED_SET_ENTRY_LIFETIME.
 o  If PROACTIVE_FORWARDING is TRUE, the MPL Forwarder MUST initialize
    and start a Trickle timer for the MPL Data Message.

Hui & Kelsey Standards Track [Page 21] RFC 7731 MPL February 2016

 o  If the MPL Control Message Trickle timer is not running and
    CONTROL_MESSAGE_TIMER_EXPIRATIONS is non-zero, the MPL Forwarder
    MUST initialize and start the MPL Control Message Trickle timer.
 o  If the MPL Control Message Trickle timer is running, the MPL
    Forwarder MUST reset the MPL Control Message Trickle timer.

10. MPL Control Messages

10.1. MPL Control Message Generation

 An MPL Forwarder generates MPL Control Messages to communicate an MPL
 Domain's Seed Set and Buffered Message Set to neighboring MPL
 Forwarders.  Each MPL Control Message is generated according to
 Section 6.2, with an MPL Seed Info entry for each entry in the MPL
 Domain's Seed Set.  Each MPL Seed Info entry has the following
 content:
 o  S set to the size of the seed-id field in the MPL Seed Info entry.
 o  min-seqno set to the MinSequence value of the MPL Seed.
 o  bm-len set to the size of buffered-mpl-messages in octets.
 o  seed-id set to the MPL Seed Identifier.
 o  buffered-mpl-messages with each bit representing whether or not an
    MPL Data Message with the corresponding sequence number exists in
    the Buffered Message Set.  The i-th bit represents a sequence
    number of min-seqno + i.  '0' indicates that the corresponding MPL
    Data Message does not exist in the Buffered Message Set.  '1'
    indicates that the corresponding MPL Data Message does exist in
    the Buffered Message Set.

10.2. MPL Control Message Transmission

 An MPL Forwarder transmits MPL Control Messages using the Trickle
 algorithm.  An MPL Forwarder maintains a single Trickle timer for
 each MPL Domain.  When CONTROL_MESSAGE_TIMER_EXPIRATIONS is 0, the
 MPL Forwarder does not execute the Trickle algorithm and does not
 transmit MPL Control Messages.  In accordance with Section 5 of
 RFC 6206 [RFC6206], the following items apply:
 o  This document defines a "consistent" transmission as receiving an
    MPL Control Message that results in a determination that neither
    the receiving nor transmitting node has any new MPL Data Messages
    to offer.

Hui & Kelsey Standards Track [Page 22] RFC 7731 MPL February 2016

 o  This document defines an "inconsistent" transmission as receiving
    an MPL Control Message that results in a determination that either
    the receiving or transmitting node has at least one new MPL Data
    Message to offer.
 o  The Trickle timer is reset in response to external "events".  This
    document defines an "event" as increasing the MinSequence value of
    any entry in the corresponding Seed Set or adding a message to the
    corresponding Buffered Message Set.
 o  This document defines an MPL Control Message as a Trickle message.
 As specified in [RFC6206], a Trickle timer has three variables: the
 current interval size I, a time within the current interval t, and a
 counter c.  MPL defines a fourth variable, e, which counts the number
 of Trickle timer expiration events since the Trickle timer was last
 reset.  After CONTROL_MESSAGE_TIMER_EXPIRATIONS Trickle timer events,
 the MPL Forwarder MUST disable the Trickle timer.

10.3. MPL Control Message Processing

 An MPL Forwarder processes each MPL Control Message that it receives
 to determine if it has any new MPL Data Messages to receive or offer.
 An MPL Forwarder determines if a new MPL Data Message has not been
 received from a neighboring node if any of the following conditions
 hold true:
 o  The MPL Control Message includes an MPL Seed that does not exist
    in the MPL Domain's Seed Set.
 o  The MPL Control Message indicates that the neighbor has an MPL
    Data Message in its Buffered Message Set with sequence number
    greater than MinSequence (i.e., the i-th bit is set to 1 and
    min-seqno + i > MinSequence) and is not included in the MPL
    Domain's Buffered Message Set.
 When an MPL Forwarder determines that it has not yet received an MPL
 Data Message buffered by a neighboring device, the MPL Forwarder MUST
 reset its Trickle timer associated with MPL Control Message
 transmissions.  If an MPL Control Message Trickle timer is not
 running, the MPL Forwarder MUST initialize and start a new
 Trickle timer.

Hui & Kelsey Standards Track [Page 23] RFC 7731 MPL February 2016

 An MPL Forwarder determines if an MPL Data Message in the Buffered
 Message Set has not yet been received by a neighboring MPL Forwarder
 if any of the following conditions hold true:
 o  The MPL Control Message does not include an MPL Seed for the MPL
    Data Message.
 o  The MPL Data Message's sequence number is greater than or equal to
    min-seqno and not included in the neighbor's corresponding
    Buffered Message Set (i.e., the MPL Data Message's sequence number
    does not have a corresponding bit in buffered-mpl-messages
    set to 1).
 When an MPL Forwarder determines that it has at least one MPL Data
 Message in its corresponding Buffered Message Set that has not yet
 been received by a neighbor, the MPL Forwarder MUST reset the MPL
 Control Message Trickle timer.  Additionally, for each of those
 entries in the Buffered Message Set, the MPL Forwarder MUST reset the
 Trickle timer and reset e to 0.  If a Trickle timer is not associated
 with the MPL Data Message, the MPL Forwarder MUST initialize and
 start a new Trickle timer.

11. IANA Considerations

 This document defines one IPv6 Option, a type that has been allocated
 from the IPv6 "Destination Options and Hop-by-Hop Options" registry
 of [RFC2780].
 This document defines one ICMPv6 Message, a type that has been
 allocated from the "ICMPv6 'type' Numbers" registry of [RFC4443].
 This document registers a well-known multicast address from the
 "Variable Scope Multicast Addresses" registry of [RFC3307].

11.1. MPL Option Type

 IANA has allocated an IPv6 Option Type from the IPv6 "Destination
 Options and Hop-by-Hop Options" registry of [RFC2780], as specified
 in Table 1 below:
      +-----------+-----+-----+-------+-------------+-----------+
      | Hex Value | act | chg |  rest | Description | Reference |
      +-----------+-----+-----+-------+-------------+-----------+
      |    0x6D   |  01 |  1  | 01101 |  MPL Option |  RFC 7731 |
      +-----------+-----+-----+-------+-------------+-----------+
                 Table 1: IPv6 Option Type Allocation

Hui & Kelsey Standards Track [Page 24] RFC 7731 MPL February 2016

 Note: IANA has marked the value 0x4D (previously "MPL Option") as
 "Deprecated".

11.2. MPL ICMPv6 Type

 IANA has allocated an ICMPv6 Type from the "ICMPv6 'type' Numbers"
 registry of [RFC4443], as specified in Table 2 below:
              +------+---------------------+-----------+
              | Type |         Name        | Reference |
              +------+---------------------+-----------+
              | 159  | MPL Control Message |  RFC 7731 |
              +------+---------------------+-----------+
                    Table 2: ICMPv6 Type Allocation

11.3. Well-Known Multicast Addresses

 IANA has allocated an IPv6 multicast address, with Group ID in the
 range [0x01,0xFF] for IPv6 over Low-Power Wireless Personal Area
 Network (6LoWPAN) compression [RFC6282], "ALL_MPL_FORWARDERS" from
 the "Variable Scope Multicast Addresses" sub-registry of the "IPv6
 Multicast Address Space Registry" [RFC3307], as specified in Table 3
 below:
 +---------------------+--------------------+-----------+------------+
 |     Address(es)     |    Description     | Reference |    Date    |
 |                     |                    |           | Registered |
 +---------------------+--------------------+-----------+------------+
 | FF0X:0:0:0:0:0:0:FC | ALL_MPL_FORWARDERS |  RFC 7731 | 2013-04-10 |
 +---------------------+--------------------+-----------+------------+
         Table 3: Variable Scope Multicast Address Allocation

12. Security Considerations

 MPL uses sequence numbers to maintain a total ordering of MPL Data
 Messages from an MPL Seed.  The use of sequence numbers allows a
 denial-of-service attack where an attacker can spoof a message with a
 sufficiently large sequence number to (i) flush messages from the
 Buffered Message List and (ii) increase the MinSequence value for an
 MPL Seed in the corresponding Seed Set.  In both cases, the side
 effect allows an attacker to halt the forwarding process of any MPL
 Data Messages being disseminated and prevents MPL Forwarders from
 accepting new MPL Data Messages that an MPL Seed generates while the
 sequence number is less than MinSequence or until the corresponding
 Seed Set Entry expires.  The net effect applies to both proactive and
 reactive forwarding modes.

Hui & Kelsey Standards Track [Page 25] RFC 7731 MPL February 2016

 In general, the basic ability to inject messages into an LLN may be
 used as a denial-of-service attack, regardless of what forwarding
 protocol is used.  Because MPL is a dissemination protocol, the
 ability to spoof MPL messages allows an attacker to affect an entire
 MPL Domain.  For these reasons, LLNs typically employ link-layer
 security mechanisms to mitigate an attacker's ability to inject
 messages.  For example, the IEEE 802.15.4 [IEEE802.15.4] standard
 specifies frame security mechanisms using AES-128 to support access
 control, message integrity, message confidentiality, and replay
 protection.  However, if the attack vector includes attackers that
 have access to the LLN, then MPL SHOULD NOT be used.
 To prevent attackers from injecting packets through an MPL Forwarder,
 the MPL Forwarder MUST NOT accept or forward MPL Data Messages from a
 communication interface that does not subscribe to the MPL Domain
 Address identified in the message's destination address.
 MPL uses the Trickle algorithm to manage message transmissions;
 therefore, the security considerations described in [RFC6206] apply.

13. References

13.1. Normative References

 [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
            DOI 10.17487/RFC1982, August 1996,
            <http://www.rfc-editor.org/info/rfc1982>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
            December 1998, <http://www.rfc-editor.org/info/rfc2460>.
 [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
            IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
            December 1998, <http://www.rfc-editor.org/info/rfc2473>.
 [RFC2780]  Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
            Values In the Internet Protocol and Related Headers",
            BCP 37, RFC 2780, DOI 10.17487/RFC2780, March 2000,
            <http://www.rfc-editor.org/info/rfc2780>.

Hui & Kelsey Standards Track [Page 26] RFC 7731 MPL February 2016

 [RFC3307]  Haberman, B., "Allocation Guidelines for IPv6 Multicast
            Addresses", RFC 3307, DOI 10.17487/RFC3307, August 2002,
            <http://www.rfc-editor.org/info/rfc3307>.
 [RFC4007]  Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
            B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
            DOI 10.17487/RFC4007, March 2005,
            <http://www.rfc-editor.org/info/rfc4007>.
 [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
            Control Message Protocol (ICMPv6) for the Internet
            Protocol Version 6 (IPv6) Specification", RFC 4443,
            DOI 10.17487/RFC4443, March 2006,
            <http://www.rfc-editor.org/info/rfc4443>.
 [RFC6206]  Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
            "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206,
            March 2011, <http://www.rfc-editor.org/info/rfc6206>.
 [RFC6282]  Hui, J., Ed., and P. Thubert, "Compression Format for IPv6
            Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
            DOI 10.17487/RFC6282, September 2011,
            <http://www.rfc-editor.org/info/rfc6282>.
 [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>.
 [RFC7346]  Droms, R., "IPv6 Multicast Address Scopes", RFC 7346,
            DOI 10.17487/RFC7346, August 2014,
            <http://www.rfc-editor.org/info/rfc7346>.

Hui & Kelsey Standards Track [Page 27] RFC 7731 MPL February 2016

13.2. Informative References

 [Clausen2013]
            Clausen, T., de Verdiere, A., and J. Yi, "Performance
            Analysis of Trickle as a Flooding Mechanism", The 15th
            IEEE International Conference on Communication
            Technology (ICCT2013), DOI 10.1109/ICCT.2013.6820439,
            November 2013.
 [IEEE802.15.4]
            IEEE, "IEEE Standard for Local and metropolitan area
            networks--Part 15.4: Low-Rate Wireless Personal Area
            Networks (LR-WPANs)", IEEE 802.15.4,
            DOI 10.1109/ieeestd.2011.6012487,
            <http://ieeexplore.ieee.org/servlet/
            opac?punumber=6012485>.
 [RFC3973]  Adams, A., Nicholas, J., and W. Siadak, "Protocol
            Independent Multicast - Dense Mode (PIM-DM): Protocol
            Specification (Revised)", RFC 3973, DOI 10.17487/RFC3973,
            January 2005, <http://www.rfc-editor.org/info/rfc3973>.
 [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
            "Protocol Independent Multicast - Sparse Mode (PIM-SM):
            Protocol Specification (Revised)", RFC 4601,
            DOI 10.17487/RFC4601, August 2006,
            <http://www.rfc-editor.org/info/rfc4601>.

Hui & Kelsey Standards Track [Page 28] RFC 7731 MPL February 2016

Acknowledgements

 The authors would like to acknowledge the helpful comments of Robert
 Cragie, Esko Dijk, Ralph Droms, Paul Duffy, Adrian Farrel, Ulrich
 Herberg, Owen Kirby, Philip Levis, Kerry Lynn, Joseph Reddy, Michael
 Richardson, Ines Robles, Don Sturek, Dario Tedeschi, and Peter
 van der Stok, which greatly improved the document.

Authors' Addresses

 Jonathan W. Hui
 Nest Labs
 3400 Hillview Ave.
 Palo Alto, California  94304
 United States
 Phone: +650 253 2770
 Email: jonhui@nestlabs.com
 Richard Kelsey
 Silicon Labs
 25 Thomson Place
 Boston, Massachusetts  02210
 United States
 Phone: +617 951 1225
 Email: richard.kelsey@silabs.com

Hui & Kelsey Standards Track [Page 29]

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