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Versions: (draft-hui-6man-trickle-mcast) 00 01 02 03 04 05 06 07 08 09 10 11 12

ROLL                                                              J. Hui
Internet-Draft                                                 Nest Labs
Intended status: Standards Track                               R. Kelsey
Expires: December 4, 2015                                   Silicon Labs
                                                            June 2, 2015


       Multicast Protocol for Low power and Lossy Networks (MPL)
                    draft-ietf-roll-trickle-mcast-12

Abstract

   This document specifies the Multicast Protocol for Low power and
   Lossy Networks (MPL) that 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 a MPL Domain.

   MPL has two modes of operation.  One mode uses the Trickle algorithm
   to manage control- 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, a 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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 4, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Applicability Statement . . . . . . . . . . . . . . . . . . .   5
   4.  MPL Protocol Overview . . . . . . . . . . . . . . . . . . . .   6
     4.1.  MPL Domains . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Information Base Overview . . . . . . . . . . . . . . . .   7
     4.3.  Protocol Overview . . . . . . . . . . . . . . . . . . . .   7
     4.4.  Signaling Overview  . . . . . . . . . . . . . . . . . . .   9
   5.  MPL Parameters and Constants  . . . . . . . . . . . . . . . .   9
     5.1.  MPL Multicast Addresses . . . . . . . . . . . . . . . . .   9
     5.2.  MPL Message Types . . . . . . . . . . . . . . . . . . . .  10
     5.3.  MPL Seed Identifiers  . . . . . . . . . . . . . . . . . .  10
     5.4.  MPL Parameters  . . . . . . . . . . . . . . . . . . . . .  10
   6.  Protocol Message Formats  . . . . . . . . . . . . . . . . . .  12
     6.1.  MPL Option  . . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  MPL Control Message . . . . . . . . . . . . . . . . . . .  14
     6.3.  MPL Seed Info . . . . . . . . . . . . . . . . . . . . . .  15
   7.  Information Base  . . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  Local Interface Set . . . . . . . . . . . . . . . . . . .  16
     7.2.  Domain Set  . . . . . . . . . . . . . . . . . . . . . . .  16
     7.3.  Seed Set  . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.4.  Buffered Message Set  . . . . . . . . . . . . . . . . . .  16
   8.  MPL Seed Sequence Numbers . . . . . . . . . . . . . . . . . .  17
   9.  MPL Data Messages . . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  MPL Data Message Generation . . . . . . . . . . . . . . .  17
     9.2.  MPL Data Message Transmission . . . . . . . . . . . . . .  18
     9.3.  MPL Data Message Processing . . . . . . . . . . . . . . .  19
   10. MPL Control Messages  . . . . . . . . . . . . . . . . . . . .  20
     10.1.  MPL Control Message Generation . . . . . . . . . . . . .  20
     10.2.  MPL Control Message Transmission . . . . . . . . . . . .  20
     10.3.  MPL Control Message Processing . . . . . . . . . . . . .  21
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     12.1.  MPL Option Type  . . . . . . . . . . . . . . . . . . . .  22
     12.2.  MPL ICMPv6 Type  . . . . . . . . . . . . . . . . . . . .  23
     12.3.  Well-known Multicast Addresses . . . . . . . . . . . . .  23



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   13. Security Considerations . . . . . . . . . . . . . . . . . . .  23
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     14.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

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 Low power and Lossy Networks 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 a LLN Border Router (LBR) and use source routing to
   forward messages away from the LBR.  For the same reasons, a 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 a 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.






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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.  A MPL Forwarder
                       is equipped with at least one MPL Interface.

   MPL Interface       - A 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.  A 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 a MPL Domain.  MPL Data
                       Messages disseminated in a 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
                       a MPL domain.  A MPL Data Message contains a 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            - A MPL Forwarder that generates MPL Data
                       Messages and serves as an entry point into a MPL
                       Domain.

   MPL Seed Identifier - An unsigned integer that uniquely identifies a
                       MPL Seed within a MPL Domain.



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   Node                - The term "node" is used within this document to
                       refer to a MPL Forwarder.

3.  Applicability Statement

   MPL is an IPv6 multicast forwarding protocol designed for the
   communication characteristics and resource constraints of Low-Power
   and Lossy Networks.  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 Low-Power and Lossy Networks, 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 Low-Power and Lossy Networks 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 that 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 a
   Low-power and Lossy Network may be used as a denial-of-service attack



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   regardless of what forwarding protocol is used.  For these reasons,
   Low-power and Lossy Networks typically employ link-layer security
   mechanisms to mitigate an attacker's ability to inject messages.  For
   example, the IEEE 802.15.4 [IEEE802154] 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.

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
   a MPL Domain.

4.1.  MPL Domains

   A 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 a MPL Forwarder participates in multiple MPL Domains
   simultaneously, at most one MPL Domain may be assigned a 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.

   A MPL Forwarder MAY participate in additional MPL Domains identified
   by other multicast addresses.  A 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 a 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).



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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 a MPL Seed within a 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 a MPL
      Seed.  MPL uses Seed Sets and Buffered Message Sets to determine
      when to accept a MPL Data Message, process its payload, and
      retransmit it.

   o  A Buffered Message Set records recently received MPL Data Messages
      from a MPL Seed within a 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 a MPL Domain.  MPL performs the following tasks to disseminate
   a multicast message:

   o  When having a multicast message to forward into a MPL Domain, the
      MPL Seed generates a 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 [RFC2473] is used to encapsulate the multicast message in
      a MPL Data Message, preserving the original IPv6 Destination
      Address.

   o  Upon receiving a MPL Data Message, the MPL Forwarder extracts the
      MPL Seed and sequence number and determines whether or not the MPL




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      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, a 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 a MPL Domain's Seed Set and Buffered Message Set.

   o  Upon receiving a MPL Control Message, a MPL Forwarder determines
      whether 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, a 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, a 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 a MPL Data Message, the MPL Forwarder schedules those MPL
      Data Messages for transmission using the Trickle algorithm.

   Note that the use of proactive and reactive forwarding strategies
   within the same MPL Domain 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, a
   MPL Forwarder will proactively retransmit the MPL Data Message a



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   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 a MPL Seed to deliver a multicast
      message across a 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.  A 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 a MPL Forwarder to communicate
      information contained in a MPL Domain's Seed Set and Buffered
      Message Set to neighboring MPL Forwarders.  A 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.

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 a
   MPL Domain.  By default, MPL Forwarders subscribe to the




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   ALL_MPL_FORWARDERS multicast address with Realm-Local scope (scop
   value 3) [RFC7346].

   For each MPL Domain Address that a 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 a MPL Seed Identifier and a
   sequence number within a MPL Data Message.  The IPv6 Option Type has
   value 0x6D.

   MPL defines an ICMPv6 Message (MPL Control Message) for communicating
   information contained in a MPL Domain's Seed Set and Buffered Message
   Set to neighboring MPL Forwarders.  The MPL Control Message has
   ICMPv6 Type MPL_ICMP_TYPE.

5.3.  MPL Seed Identifiers

   MPL uses MPL Seed Identifiers to uniquely identify MPL Seeds within a
   MPL Domain.  For each MPL Domain that the MPL Forwarder serves as a
   MPL Seed, the MPL Forwarder MUST have an associated MPL Seed
   Identifier.  A 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 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 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



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      SEED_SET_ENTRY_LIFETIME that is too small can cause the duplicate
      detection mechanism to fail, resulting in a MPL Forwarder to
      receive 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.

   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.



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   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, a MPL Forwarder proactively transmits any new MPL Data
   Messages it receives then uses MPL Control Messages to trigger
   additional MPL Data Message retransmissions where message drops are
   detected.  Setting DATA_MESSAGE_IMAX to the same 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.

6.  Protocol Message Formats

   Messages generated and processed by a 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 in octets.

   S                   2-bit unsigned integer.  Identifies the length of
                       seed-id.  0 indicates that the seed-id is the



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                       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
                       sequence 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 a MPL Option in which this flag is
                       1 MUST be dropped.

   rsv                 4-bit reserved field.  MUST be set to 0 on
                       transmission and ignored on reception.

   sequence            8-bit unsigned integer.  Identifies relative
                       ordering of MPL Data Messages from the MPL Seed
                       identified by seed-id.

   seed-id             Uniquely identifies the MPL Seed that initiated
                       dissemination of the MPL Data Message.  The size
                       of 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 a MPL Seed.  When 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 scope of this document.

   The sequence field establishes a total ordering of MPL Data Messages
   generated by a MPL Seed for a MPL Domain.  The MPL Seed MUST
   increment the sequence field's value on each new MPL Data Message
   that it generates for a 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.




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6.2.  MPL Control Message

   A MPL Forwarder uses ICMPv6 messages to communicate information
   contained in a 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]                      .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   IP Fields:

   Source Address      An IPv6 address in the AddressSet of the
                       corresponding MPL Interface and 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                MPL_ICMP_TYPE

   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 a MPL Forwarder is willing to receive.  The MPL Control
   Message allows neighboring MPL Forwarders to determine whether there
   are any new MPL Data Messages to exchange.






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6.3.  MPL Seed Info

   A 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)            .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   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
                       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.



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7.  Information Base

7.1.  Local Interface Set

   The Local Interface Set records the local MPL Interfaces of a 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.

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 that a MPL Forwarder is willing to
   accept generated by the MPL Seed.  A 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.  A MPL Forwarder MUST ignore
      any MPL Data Message that has sequence value less than than
      MinSequence.

   Lifetime  - indicates the minimum remaining lifetime of the Seed Set
      entry.  A 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 a MPL Seed within a MPL Domain.  A MPL Forwarder uses a Buffered
   Message Set to buffer MPL Data Messages while the MPL Forwarder is
   forwarding the MPL Data Messages.  A MPL Forwarder maintains a
   Buffered Message Set for each MPL Domain that it participates in.  A




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   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.

   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 a 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 a 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 a MPL Seed for a 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  A MPL Data Message MUST contain a 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.




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   When the destination address is a MPL Domain Address and the source
   address is in the AddressLIst of a 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 a MPL Data Message.  The outer IPv6 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

   A MPL Forwarder manages transmission of MPL Data Messages in its
   Buffered Message Sets using the Trickle algorithm [RFC6206].  A 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], this document defines the following:

   o  This document defines a "consistent" transmission as receiving a
      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
      a 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 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



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   MinSequence of the corresponding MPL Seed in the Seed Set.  When the
   MPL Forwarder no longer buffers any messages for a MPL Seed, the MPL
   Forwarder MUST NOT increment MinSequence for that MPL Seed.

   When transmitting a 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.

9.3.  MPL Data Message Processing

   Upon receiving a 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 a MPL Data Message, a 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, a 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:



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   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.

   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

   A MPL Forwarder generates MPL Control Messages to communicate a 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 a MPL Seed Info 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 MinSequence 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 a
      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

   A MPL Forwarder transmits MPL Control Messages using the Trickle
   algorithm.  A 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], this document defines the following:




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   o  This document defines a "consistent" transmission as receiving a
      MPL Control Message that results in a determination that neither
      the receiving nor transmitting node has any new MPL Data Messages
      to offer.

   o  This document defines an "inconsistent" transmission as receiving
      a 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 MinSequence of any entry
      in the corresponding Seed Set or adding a message to the
      corresponding Buffered Message Set.

   o  This document defines a 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

   A MPL Forwarder processes each MPL Control Message that it receives
   to determine if it has any new MPL Data Messages to receive or offer.

   A 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 a MPL Seed that does not exist in
      the MPL Domain's Seed Set.

   o  The MPL Control Message indicates that the neighbor has a 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 a MPL Forwarder determines that it has not yet received a MPL
   Data Message buffered by a neighboring device, the MPL Forwarder MUST
   reset its Trickle timer associated with MPL Control Message
   transmissions.  If a MPL Control Message Trickle timer is not
   running, the MPL Forwarder MUST initialize and start a new Trickle
   timer.



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   A MPL Forwarder determines if a 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 a 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 a 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.  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.

12.  IANA Considerations

   This document defines one IPv6 Option, a type that must be allocated
   from the IPv6 "Destination Options and Hop-by-Hop Options" registry
   of [RFC2780].

   This document defines one ICMPv6 Message, a type that must be
   allocated from the "ICMPv6 "type" Numbers" registry of [RFC4443].

   This document registers a well-known multicast address from the
   Variable Scope Multicast Address registry.

12.1.  MPL Option Type

   IANA is requested to allocate an IPv6 Option Type from the IPv6
   "Destination Options and Hop-by-Hop Options" registry of [RFC2780],
   as specified in Table 1 below:




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      +-----------+-----+-----+-------+-------------+---------------+
      | Hex Value | act | chg |  rest | Description |   Reference   |
      +-----------+-----+-----+-------+-------------+---------------+
      |    0x6D   |  01 |  1  | 01101 |  MPL Option | This Document |
      +-----------+-----+-----+-------+-------------+---------------+

                   Table 1: IPv6 Option Type Allocation

12.2.  MPL ICMPv6 Type

   IANA is requested to allocate an ICMPv6 Type from the "ICMPv6 "type"
   Numbers" registry of [RFC4443], as specified in Table 2 below:

              +------+---------------------+---------------+
              | Type |         Name        |   Reference   |
              +------+---------------------+---------------+
              | TBD  | MPL Control Message | This Document |
              +------+---------------------+---------------+

                   Table 2: IPv6 Option Type Allocation

   In this document, the mnemonic MPL_ICMP_TYPE was used to refer to the
   ICMPv6 Type above, which is TBD by IANA.

12.3.  Well-known Multicast Addresses

   IANA is requested to allocate an IPv6 multicast address, with Group
   ID in the range [0x01,0xFF] for 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(s)     |    Description     | Reference |    Date    |
   |                     |                    |           | Registered |
   +---------------------+--------------------+-----------+------------+
   | FF0X:0:0:0:0:0:0:FC | ALL_MPL_FORWARDERS |    This   | 2013-04-10 |
   |                     |                    |  Document |            |
   +---------------------+--------------------+-----------+------------+

           Table 3: Variable Scope Multicast Address Allocation

13.  Security Considerations

   MPL uses sequence numbers to maintain a total ordering of MPL Data
   Messages from a 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



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   Buffered Message List and (ii) increase the MinSequence value for a
   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 a 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.

   In general, the basic ability to inject messages into a Low-power and
   Lossy Network 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, Low-power and Lossy
   Networks typically employ link-layer security mechanisms to mitigate
   an attacker's ability to inject messages.  For example, the IEEE
   802.15.4 [IEEE802154] 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 a 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 message's destination address.

   MPL uses the Trickle algorithm to manage message transmissions and
   the security considerations described in [RFC6206] apply.

14.  References

14.1.  Normative References

   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              August 1996.

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.






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   [RFC2780]  Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
              Values In the Internet Protocol and Related Headers", BCP
              37, RFC 2780, March 2000.

   [RFC3307]  Haberman, B., "Allocation Guidelines for IPv6 Multicast
              Addresses", RFC 3307, August 2002.

   [RFC4007]  Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
              B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
              March 2005.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC6206]  Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
              "The Trickle Algorithm", RFC 6206, March 2011.

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

   [RFC6550]  Winter, T., Thubert, P., 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, March 2012.

   [RFC7346]  Droms, R., "IPv6 Multicast Address Scopes", RFC 7346,
              August 2014.

14.2.  Informative References

   [Clausen2013]
              Clausen, T., Colin de Verdiere, A., and J. Yi,
              "Performance Analysis of Trickle as a Flooding Mechanism",
              The 5th IEEE International Conference on Communication
              Technology (ICCT2013), November 2013.

   [IEEE802154]
              "IEEE Std. 802.15.4-2006", October 2006.

   [RFC3973]  Adams, A., Nicholas, J., and W. Siadak, "Protocol
              Independent Multicast - Dense Mode (PIM-DM): Protocol
              Specification (Revised)", RFC 3973, January 2005.

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601, August 2006.



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Internet-Draft                     MPL                         June 2015


Authors' Addresses

   Jonathan W. Hui
   Nest Labs
   3400 Hillview Ave
   Palo Alto, California  94304
   USA

   Phone: +650 253 2770
   Email: jonhui@nestlabs.com


   Richard Kelsey
   Silicon Labs
   25 Thomson Place
   Boston, Massachusetts  02210
   USA

   Phone: +617 951 1225
   Email: richard.kelsey@silabs.com































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