draft-ietf-roll-trickle-mcast-12.txt   rfc7731.txt 
ROLL J. Hui Internet Engineering Task Force (IETF) J. Hui
Internet-Draft Nest Labs Request for Comments: 7731 Nest Labs
Intended status: Standards Track R. Kelsey Category: Standards Track R. Kelsey
Expires: December 4, 2015 Silicon Labs ISSN: 2070-1721 Silicon Labs
June 2, 2015 February 2016
Multicast Protocol for Low power and Lossy Networks (MPL) Multicast Protocol for Low-Power and Lossy Networks (MPL)
draft-ietf-roll-trickle-mcast-12
Abstract Abstract
This document specifies the Multicast Protocol for Low power and This document specifies the Multicast Protocol for Low-Power and
Lossy Networks (MPL) that provides IPv6 multicast forwarding in Lossy Networks (MPL), which provides IPv6 multicast forwarding in
constrained networks. MPL avoids the need to construct or maintain constrained networks. MPL avoids the need to construct or maintain
any multicast forwarding topology, disseminating messages to all MPL any multicast forwarding topology, disseminating messages to all MPL
Forwarders in a MPL Domain. Forwarders in an MPL Domain.
MPL has two modes of operation. One mode uses the Trickle algorithm MPL has two modes of operation. One mode uses the Trickle algorithm
to manage control- and data-plane message transmissions, and is to manage control-plane and data-plane message transmissions and is
applicable for deployments with few multicast sources. The other applicable for deployments with few multicast sources. The other
mode uses classic flooding. By providing both modes and mode uses classic flooding. By providing both modes and
parameterization of the Trickle algorithm, a MPL implementation can parameterization of the Trickle algorithm, an MPL implementation can
be used in a variety of multicast deployments and can trade between be used in a variety of multicast deployments and can trade between
dissemination latency and transmission efficiency. dissemination latency and transmission efficiency.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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 This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on December 4, 2015. 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.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology .....................................................5
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 5 3. Applicability Statement .........................................6
4. MPL Protocol Overview . . . . . . . . . . . . . . . . . . . . 6 4. MPL Protocol Overview ...........................................7
4.1. MPL Domains . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. MPL Domains ................................................7
4.2. Information Base Overview . . . . . . . . . . . . . . . . 7 4.2. Information Base Overview ..................................8
4.3. Protocol Overview . . . . . . . . . . . . . . . . . . . . 7 4.3. Protocol Overview ..........................................8
4.4. Signaling Overview . . . . . . . . . . . . . . . . . . . 9 4.4. Signaling Overview ........................................10
5. MPL Parameters and Constants . . . . . . . . . . . . . . . . 9 5. MPL Parameters and Constants ...................................11
5.1. MPL Multicast Addresses . . . . . . . . . . . . . . . . . 9 5.1. MPL Multicast Addresses ...................................11
5.2. MPL Message Types . . . . . . . . . . . . . . . . . . . . 10 5.2. MPL Message Types .........................................11
5.3. MPL Seed Identifiers . . . . . . . . . . . . . . . . . . 10 5.3. MPL Seed Identifiers ......................................11
5.4. MPL Parameters . . . . . . . . . . . . . . . . . . . . . 10 5.4. MPL Parameters ............................................11
6. Protocol Message Formats . . . . . . . . . . . . . . . . . . 12 6. Protocol Message Formats .......................................14
6.1. MPL Option . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. MPL Option ................................................14
6.2. MPL Control Message . . . . . . . . . . . . . . . . . . . 14 6.2. MPL Control Message .......................................15
6.3. MPL Seed Info . . . . . . . . . . . . . . . . . . . . . . 15 6.3. MPL Seed Info .............................................16
7. Information Base . . . . . . . . . . . . . . . . . . . . . . 16 7. Information Base ...............................................17
7.1. Local Interface Set . . . . . . . . . . . . . . . . . . . 16 7.1. Local Interface Set .......................................17
7.2. Domain Set . . . . . . . . . . . . . . . . . . . . . . . 16 7.2. Domain Set ................................................18
7.3. Seed Set . . . . . . . . . . . . . . . . . . . . . . . . 16 7.3. Seed Set ..................................................18
7.4. Buffered Message Set . . . . . . . . . . . . . . . . . . 16 7.4. Buffered Message Set ......................................18
8. MPL Seed Sequence Numbers . . . . . . . . . . . . . . . . . . 17 8. MPL Seed Sequence Numbers ......................................19
9. MPL Data Messages . . . . . . . . . . . . . . . . . . . . . . 17 9. MPL Data Messages ..............................................19
9.1. MPL Data Message Generation . . . . . . . . . . . . . . . 17 9.1. MPL Data Message Generation ...............................19
9.2. MPL Data Message Transmission . . . . . . . . . . . . . . 18 9.2. MPL Data Message Transmission .............................20
9.3. MPL Data Message Processing . . . . . . . . . . . . . . . 19 9.3. MPL Data Message Processing ...............................21
10. MPL Control Messages . . . . . . . . . . . . . . . . . . . . 20 10. MPL Control Messages ..........................................22
10.1. MPL Control Message Generation . . . . . . . . . . . . . 20 10.1. MPL Control Message Generation ...........................22
10.2. MPL Control Message Transmission . . . . . . . . . . . . 20 10.2. MPL Control Message Transmission .........................22
10.3. MPL Control Message Processing . . . . . . . . . . . . . 21 10.3. MPL Control Message Processing ...........................23
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 11. IANA Considerations ...........................................24
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 11.1. MPL Option Type ..........................................24
12.1. MPL Option Type . . . . . . . . . . . . . . . . . . . . 22 11.2. MPL ICMPv6 Type ..........................................25
12.2. MPL ICMPv6 Type . . . . . . . . . . . . . . . . . . . . 23 11.3. Well-Known Multicast Addresses ...........................25
12.3. Well-known Multicast Addresses . . . . . . . . . . . . . 23 12. Security Considerations .......................................25
13. References ....................................................26
13. Security Considerations . . . . . . . . . . . . . . . . . . . 23 13.1. Normative References .....................................26
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 13.2. Informative References ...................................28
14.1. Normative References . . . . . . . . . . . . . . . . . . 24 Acknowledgements ..................................................29
14.2. Informative References . . . . . . . . . . . . . . . . . 25 Authors' Addresses ................................................29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction 1. Introduction
Low power and Lossy Networks (LLNs) typically operate with strict Low-Power and Lossy Networks (LLNs) typically operate with strict
resource constraints in communication, computation, memory, and resource constraints in communication, computation, memory, and
energy. Such resource constraints may preclude the use of existing energy. Such resource constraints may preclude the use of existing
IPv6 multicast routing and forwarding mechanisms. Traditional IP IPv6 multicast routing and forwarding mechanisms. Traditional IP
multicast delivery typically relies on topology maintenance multicast delivery typically relies on topology maintenance
mechanisms to discover and maintain routes to all subscribers of a mechanisms to discover and maintain routes to all subscribers of a
multicast group (e.g. [RFC3973] [RFC4601]). However, maintaining multicast group (e.g., [RFC3973] [RFC4601]). However, maintaining
such topologies in Low power and Lossy Networks is costly and may not such topologies in LLNs is costly and may not be feasible given the
be feasible given the available resources. available resources.
Memory constraints may limit devices to maintaining links/routes to Memory constraints may limit devices to maintaining links/routes to
one or a few neighbors. For this reason, the Routing Protocol for one or a few neighbors. For this reason, the Routing Protocol for
LLNs (RPL) specifies both storing and non-storing modes [RFC6550]. LLNs (RPL) specifies both storing and non-storing modes [RFC6550].
The latter allows RPL routers to maintain only one or a few default 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 routes towards an LLN Border Router (LBR) and use source routing to
forward messages away from the LBR. For the same reasons, a LLN forward messages away from the LBR. For the same reasons, an LLN
device may not be able to maintain a multicast routing topology when device may not be able to maintain a multicast routing topology when
operating with limited memory. operating with limited memory.
Furthermore, the dynamic properties of wireless networks can make the Furthermore, the dynamic properties of wireless networks can make the
cost of maintaining a multicast routing topology prohibitively cost of maintaining a multicast routing topology prohibitively
expensive. In wireless environments, topology maintenance may expensive. In wireless environments, topology maintenance may
involve selecting a connected dominating set used to forward involve selecting a connected dominating set used to forward
multicast messages to all nodes in an administrative domain. multicast messages to all nodes in an administrative domain.
However, existing mechanisms often require two-hop topology However, existing mechanisms often require two-hop topology
information and the cost of maintaining such information grows information, and the cost of maintaining such information grows
polynomially with network density. polynomially with network density.
This document specifies the Multicast Protocol for Low power and This document specifies the Multicast Protocol for Low-Power and
Lossy Networks (MPL), which provides IPv6 multicast forwarding in Lossy Networks (MPL), which provides IPv6 multicast forwarding in
constrained networks. MPL avoids the need to construct or maintain constrained networks. MPL avoids the need to construct or maintain
any multicast routing topology, disseminating multicast messages to any multicast routing topology, disseminating multicast messages to
all MPL Forwarders in a MPL Domain. By using the Trickle algorithm all MPL Forwarders in an MPL Domain. By using the Trickle algorithm
[RFC6206], MPL requires only small, constant state for each MPL [RFC6206], MPL requires only small, constant state for each MPL
device that initiates disseminations. The Trickle algorithm also device that initiates disseminations. The Trickle algorithm also
allows MPL to be density-aware, allowing the communication rate to allows MPL to be density aware, allowing the communication rate to
scale logarithmically with density. scale logarithmically with density.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
The following terms are used throughout this document: The following terms are used throughout this document:
MPL Forwarder - A router that implements MPL. A MPL Forwarder MPL Forwarder - A router that implements MPL. An MPL Forwarder is
is equipped with at least one MPL Interface. equipped with at least one MPL Interface.
MPL Interface - A MPL Forwarder's attachment to a MPL Interface - An MPL Forwarder's attachment to a communications
communications medium, over which it transmits medium, over which it transmits and receives MPL Data Messages and
and receives MPL Data Messages and MPL Control MPL Control Messages according to this specification. An MPL
Messages according to this specification. A MPL Interface is assigned one or more unicast addresses and is
Interface is assigned one or more unicast subscribed to one or more MPL Domain Addresses.
addresses and is subscribed to one or more MPL
Domain Addresses.
MPL Domain Address - A multicast address that identifies the set of MPL Domain Address - A multicast address that identifies the set of
MPL Interfaces within a MPL Domain. MPL Data MPL Interfaces within an MPL Domain. MPL Data Messages
Messages disseminated in a MPL Domain have the disseminated in an MPL Domain have the associated MPL Domain
associated MPL Domain Address as their Address as their destination address.
destination address.
MPL Domain - A scope zone, as defined in [RFC4007], in which MPL Domain - A scope zone, as defined in [RFC4007], in which MPL
MPL Interfaces subscribe to the same MPL Domain Interfaces subscribe to the same MPL Domain Address and
Address and participate in disseminating MPL Data participate in disseminating MPL Data Messages.
Messages.
MPL Data Message - A multicast message that is used to communicate MPL Data Message - A multicast message that is used to communicate a
a multicast payload between MPL Forwarders within multicast payload between MPL Forwarders within an MPL Domain. An
a MPL domain. A MPL Data Message contains a MPL MPL Data Message contains an MPL Option in the IPv6 header and has
Option in the IPv6 header and has as its as its destination address the MPL Domain Address corresponding to
destination address the MPL Domain Address the MPL Domain.
corresponding to the MPL Domain.
MPL Control Message - A link-local multicast message that is used to MPL Control Message - A link-local multicast message that is used to
communicate information about recently received communicate information about recently received MPL Data Messages
MPL Data Messages to neighboring MPL Forwarders. to neighboring MPL Forwarders.
MPL Seed - A MPL Forwarder that generates MPL Data MPL Seed - An MPL Forwarder that generates MPL Data Messages and
Messages and serves as an entry point into a MPL serves as an entry point into an MPL Domain.
Domain.
MPL Seed Identifier - An unsigned integer that uniquely identifies a MPL Seed Identifier - An unsigned integer that uniquely identifies
MPL Seed within a MPL Domain. an MPL Seed within an MPL Domain.
Node - The term "node" is used within this document to Node - Used within this document to refer to an MPL Forwarder.
refer to a MPL Forwarder.
3. Applicability Statement 3. Applicability Statement
MPL is an IPv6 multicast forwarding protocol designed for the MPL is an IPv6 multicast forwarding protocol designed for the
communication characteristics and resource constraints of Low-Power communication characteristics and resource constraints of LLNs. By
and Lossy Networks. By implementing controlled disseminations of implementing controlled disseminations of multicast messages using
multicast messages using the Trickle algorithm, MPL is designed for the Trickle algorithm, MPL is designed for networks that communicate
networks that communicate using low-power and lossy links with widely using low-power and lossy links with widely varying topologies in
varying topologies in both the space and time dimensions. both the space and time dimensions.
While designed specifically for Low-Power and Lossy Networks, MPL is While designed specifically for LLNs, MPL is not limited to use over
not limited to use over such networks. MPL may be applicable to any such networks. MPL may be applicable to any network where no
network where no multicast routing state is desired. MPL may also be multicast routing state is desired. MPL may also be used in
used in environments where only a subset of links are considered Low- environments where only a subset of links are considered low-power
Power and Lossy links. and lossy links.
A host need not be aware that their multicast is supported by MPL as A host need not be aware that their multicast is supported by MPL as
long as its attachment router forwards multicast messages between the long as its attachment router forwards multicast messages between the
MPL Domain and the host. However, a host may choose to implement MPL 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 so that it can take advantage of the broadcast medium inherent in
many Low-Power and Lossy Networks and receive multicast messages many LLNs and receive multicast messages carried by MPL directly.
carried by MPL directly.
MPL is parameterized to support different dissemination techniques. MPL is parameterized to support different dissemination techniques.
In one parameterization, MPL may utilize the classic flooding method In one parameterization, MPL may utilize the classic flooding method
that involves having each device receiving a message rebroadcast the that involves having each device receiving a message rebroadcast the
message. In another parameterization, MPL may utilize Trickle's message. In another parameterization, MPL may utilize Trickle's
[RFC6206] "polite gossip" method that involves transmission [RFC6206] "polite gossip" method, which involves transmission
suppression and adaptive timing techniques. [Clausen2013] questions suppression and adaptive timing techniques. [Clausen2013] questions
the efficiency of Trickle's "polite gossip" mechanism in some the efficiency of Trickle's "polite gossip" mechanism in some
multicast scenarios, so by also including a classic flooding mode of multicast scenarios, so by also including a classic flooding mode of
operation MPL aims to be able to perform satisfactorily in a variety operation MPL aims to be able to perform satisfactorily in a variety
of situations. of situations.
To support efficient message delivery in networks that have many poor To support efficient message delivery in networks that have many poor
links, MPL supports a reactive forwarding mode that utilizes MPL links, MPL supports a reactive forwarding mode that utilizes MPL
Control Messages to summarize the current multicast state. The MPL Control Messages to summarize the current multicast state. The MPL
Control Message size grows linearly with the number of simultaneous Control Message size grows linearly with the number of simultaneous
MPL Seeds in the MPL Domain - 4 octets per MPL Seed. When reactive MPL Seeds in the MPL Domain -- 4 octets per MPL Seed. When reactive
forwarding is not enabled, MPL Control Messages are not transmitted forwarding is not enabled, MPL Control Messages are not transmitted,
and the associated overhead is not incurred. and the associated overhead is not incurred.
This document does not specify a cryptographic security mechanism for This document does not specify a cryptographic security mechanism for
MPL to ensure that MPL messages are not spoofed by anyone with access 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 to the LLN. In general, the basic ability to inject messages into an
Low-power and Lossy Network may be used as a denial-of-service attack LLN may be used as a denial-of-service attack, regardless of what
regardless of what forwarding protocol is used. For these reasons, forwarding protocol is used. For these reasons, LLNs typically
Low-power and Lossy Networks typically employ link-layer security employ link-layer security mechanisms to mitigate an attacker's
mechanisms to mitigate an attacker's ability to inject messages. For ability to inject messages. For example, the IEEE 802.15.4
example, the IEEE 802.15.4 [IEEE802154] standard specifies frame [IEEE802.15.4] standard specifies frame security mechanisms using
security mechanisms using AES-128 to support access control, message AES-128 to support access control, message integrity, message
integrity, message confidentiality, and replay protection. However, confidentiality, and replay protection. However, if the attack
if the attack vector includes attackers that have access to the LLN, vector includes attackers that have access to the LLN, then MPL
then MPL SHOULD NOT be used. SHOULD NOT be used.
4. MPL Protocol Overview 4. MPL Protocol Overview
The goal of MPL is to deliver multicast messages to all interfaces The goal of MPL is to deliver multicast messages to all interfaces
that subscribe to the multicast messages' destination address within that subscribe to the multicast messages' destination address within
a MPL Domain. an MPL Domain.
4.1. MPL Domains 4.1. MPL Domains
A MPL Domain is a scope zone, as defined in [RFC4007], in which MPL An MPL Domain is a scope zone, as defined in [RFC4007], in which MPL
Interfaces subscribe to the same MPL Domain Address and participate Interfaces subscribe to the same MPL Domain Address and participate
in disseminating MPL Data Messages. in disseminating MPL Data Messages.
When participating in only one MPL Domain, the MPL Domain Address is When participating in only one MPL Domain, the MPL Domain Address is
the ALL_MPL_FORWARDERS multicast address with Realm-Local scope (scop the ALL_MPL_FORWARDERS multicast address with Realm-Local scope
value 3) [RFC7346]. ("scop" value 3) [RFC7346].
When a MPL Forwarder participates in multiple MPL Domains When an MPL Forwarder participates in multiple MPL Domains
simultaneously, at most one MPL Domain may be assigned a MPL Domain simultaneously, at most one MPL Domain may be assigned an MPL Domain
Address equal to the ALL_MPL_FORWARDERS multicast address. All other Address equal to the ALL_MPL_FORWARDERS multicast address. All other
MPL Domains MUST be assigned a unique MPL Domain Address that allows MPL Domains MUST be assigned a unique MPL Domain Address that allows
the MPL Forwarder to identify each MPL Domain. The MPL Domains the MPL Forwarder to identify each MPL Domain. The MPL Domains
SHOULD be configured automatically based on some underlying topology. SHOULD be configured automatically based on some underlying topology.
For example, when using RPL [RFC6550], MPL Domains may be configured For example, when using RPL [RFC6550], MPL Domains may be configured
based on RPL Instances. based on RPL Instances.
When MPL is used in deployments that use administratively defined When MPL is used in deployments that use administratively defined
scopes that cover, for example, multiple subnets based on different scopes that cover, for example, multiple subnets based on different
underlying network technologies, Admin-Local scope (scop value 4) or underlying network technologies, Admin-Local scope (scop value 4) or
Site-Local scope (scop value 5) SHOULD be used. Site-Local scope (scop value 5) SHOULD be used.
A MPL Forwarder MAY participate in additional MPL Domains identified An MPL Forwarder MAY participate in additional MPL Domains identified
by other multicast addresses. A MPL Interface MUST subscribe to the by other multicast addresses. An MPL Interface MUST subscribe to the
MPL Domain Addresses for the MPL Domains that it participates in. MPL Domain Addresses for the MPL Domains that it participates in.
The assignment of other multicast addresses is out of scope. The assignment of other multicast addresses is out of scope.
For each MPL Domain Address that a MPL Interface subscribes to, the For each MPL Domain Address that an MPL Interface subscribes to, the
MPL Interface MUST also subscribe to the same MPL Domain Address with MPL Interface MUST also subscribe to the same MPL Domain Address with
Link-Local scope (scop value 2) when reactive forwarding is in use Link-Local scope (scop value 2) when reactive forwarding is in use
(i.e. when communicating MPL Control Messages). (i.e., when communicating MPL Control Messages).
4.2. Information Base Overview 4.2. Information Base Overview
A node records necessary protocol state in the following information A node records necessary protocol state in the following
sets: information sets:
o The Local Interface Set records the set of local MPL Interfaces o The Local Interface Set records the set of local MPL Interfaces
and the unicast addresses assigned to those MPL Interfaces. and the unicast addresses assigned to those MPL Interfaces.
o The Domain Set records the set of MPL Domain Addresses and the o The Domain Set records the set of MPL Domain Addresses and the
local MPL Interfaces that subscribe to those addresses. local MPL Interfaces that subscribe to those addresses.
o A Seed Set records information about received MPL Data Messages o A Seed Set records information about received MPL Data Messages
received from a MPL Seed within a MPL Domain. Each MPL Domain has received from an MPL Seed within an MPL Domain. Each MPL Domain
an associated Seed Set. A Seed Set maintains the minimum sequence has an associated Seed Set. A Seed Set maintains the minimum
number for MPL Data Messages that the MPL Forwarder is willing to sequence number for MPL Data Messages that the MPL Forwarder is
receive or has buffered in its Buffered Message Set from a MPL willing to receive or has buffered in its Buffered Message Set
Seed. MPL uses Seed Sets and Buffered Message Sets to determine from an MPL Seed. MPL uses Seed Sets and Buffered Message Sets to
when to accept a MPL Data Message, process its payload, and determine when to accept an MPL Data Message, process its payload,
retransmit it. and retransmit it.
o A Buffered Message Set records recently received MPL Data Messages o A Buffered Message Set records recently received MPL Data Messages
from a MPL Seed within a MPL Domain. Each MPL Domain has an from an MPL Seed within an MPL Domain. Each MPL Domain has an
associated Buffered Message Set. MPL Data Messages resident in a associated Buffered Message Set. MPL Data Messages resident in a
Buffered Message Set have sequence numbers that are greater than Buffered Message Set have sequence numbers that are greater than
or equal to the minimum threshold maintained in the corresponding or equal to the minimum threshold maintained in the corresponding
Seed Set. MPL uses Buffered Message Sets to store MPL Data Seed Set. MPL uses Buffered Message Sets to store MPL Data
Messages that may be transmitted by the MPL Forwarder for Messages that may be transmitted by the MPL Forwarder for
forwarding. forwarding.
4.3. Protocol Overview 4.3. Protocol Overview
MPL achieves its goal by implementing a controlled flood that MPL achieves its goal by implementing a controlled flood that
attempts to disseminate the multicast data message to all interfaces attempts to disseminate the multicast data message to all interfaces
within a MPL Domain. MPL performs the following tasks to disseminate within an MPL Domain. MPL performs the following tasks to
a multicast message: disseminate a multicast message:
o When having a multicast message to forward into a MPL Domain, the o When having a multicast message to forward into an MPL Domain, the
MPL Seed generates a MPL Data Message that includes the MPL Domain MPL Seed generates an MPL Data Message that includes the MPL
Address as the IPv6 Destination Address, the MPL Seed Identifier, Domain Address as the IPv6 Destination Address, the MPL Seed
a newly generated sequence number, and the multicast message. If Identifier, a newly generated sequence number, and the multicast
the multicast destination address is not the MPL Domain Address, message. If the multicast destination address is not the MPL
IP-in-IP [RFC2473] is used to encapsulate the multicast message in Domain Address, IP-in-IP tunneling [RFC2473] is used to
a MPL Data Message, preserving the original IPv6 Destination encapsulate the multicast message in an MPL Data Message,
Address. preserving the original IPv6 Destination Address.
o Upon receiving a MPL Data Message, the MPL Forwarder extracts the o Upon receiving an MPL Data Message, the MPL Forwarder extracts the
MPL Seed and sequence number and determines whether or not the MPL MPL Seed and sequence number and determines whether or not the MPL
Data Message was previously received using the MPL Domain's Seed Data Message was previously received using the MPL Domain's Seed
Set and Buffered Message Set. Set and Buffered Message Set.
* If the sequence number is less than the lower-bound sequence * If the sequence number is less than the lower-bound sequence
number maintained in the Seed Set or a message with the same number maintained in the Seed Set or a message with the same
sequence number exists within the Buffered Message Set, the MPL sequence number exists within the Buffered Message Set, the MPL
Forwarder marks the MPL Data Message as old. Forwarder marks the MPL Data Message as old.
* Otherwise, the MPL Forwarder marks the MPL Data Message as new. * Otherwise, the MPL Forwarder marks the MPL Data Message as new.
o For each newly received MPL Data Message, a MPL Forwarder updates o For each newly received MPL Data Message, an MPL Forwarder updates
the Seed Set, adds the MPL Data Message into the Buffered Message the Seed Set, adds the MPL Data Message into the Buffered Message
Set, processes its payload, and multicasts the MPL Data Message a Set, processes its payload, and multicasts the MPL Data Message a
number of times on all MPL Interfaces participating in the same number of times on all MPL Interfaces participating in the same
MPL Domain to forward the message. MPL Domain to forward the message.
o Each MPL Forwarder may periodically link-local multicast MPL o Each MPL Forwarder may periodically link-local multicast MPL
Control Messages on MPL Interfaces to communicate information Control Messages on MPL Interfaces to communicate information
contained in a MPL Domain's Seed Set and Buffered Message Set. contained in an MPL Domain's Seed Set and Buffered Message Set.
o Upon receiving a MPL Control Message, a MPL Forwarder determines o Upon receiving an MPL Control Message, an MPL Forwarder determines
whether there are any new MPL Data Messages that have yet to be whether or not there are any new MPL Data Messages that have yet
received by the MPL Control Message's source and multicasts those to be received by the MPL Control Message's source and multicasts
MPL Data Messages. those MPL Data Messages.
MPL's configuration parameters allow two forwarding strategies for MPL's configuration parameters allow two forwarding strategies for
disseminating MPL Data Messages via MPL Interfaces. disseminating MPL Data Messages via MPL Interfaces:
Proactive Forwarding - With proactive forwarding, a MPL Forwarder Proactive Forwarding - With proactive forwarding, an MPL Forwarder
schedules transmissions of MPL Data Messages using the Trickle schedules transmissions of MPL Data Messages using the Trickle
algorithm, without any prior indication that neighboring nodes algorithm, without any prior indication that neighboring nodes
have yet to receive the message. After transmitting the MPL Data have yet to receive the message. After transmitting the MPL Data
Message a limited number of times, the MPL Forwarder may terminate Message a limited number of times, the MPL Forwarder may terminate
proactive forwarding for the MPL Data Message. proactive forwarding for the MPL Data Message.
Reactive Forwarding - With reactive forwarding, a MPL Forwarder Reactive Forwarding - With reactive forwarding, an MPL Forwarder
link-local multicasts MPL Control Messages using the Trickle link-local multicasts MPL Control Messages using the Trickle
algorithm [RFC6206]. MPL Forwarders use MPL Control Messages to algorithm [RFC6206]. MPL Forwarders use MPL Control Messages to
discover new MPL Data Messages that have not yet been received. discover new MPL Data Messages that have not yet been received.
When discovering that a neighboring MPL Forwarder has not yet When discovering that a neighboring MPL Forwarder has not yet
received a MPL Data Message, the MPL Forwarder schedules those MPL received an MPL Data Message, the MPL Forwarder schedules those
Data Messages for transmission using the Trickle algorithm. MPL Data Messages for transmission using the Trickle algorithm.
Note that the use of proactive and reactive forwarding strategies Note that, when used within the same MPL Domain, proactive and
within the same MPL Domain are not mutually exclusive and may be used reactive forwarding strategies are not mutually exclusive and may be
simultaneously. For example, upon receiving a new MPL Data Message used simultaneously. For example, upon receiving a new MPL Data
when both proactive and reactive forwarding techniques are enabled, a Message when both proactive and reactive forwarding techniques are
MPL Forwarder will proactively retransmit the MPL Data Message a enabled, an MPL Forwarder will proactively retransmit the MPL Data
limited number of times and schedule further transmissions upon Message a limited number of times and schedule further transmissions
receiving MPL Control Messages. upon receiving MPL Control Messages.
4.4. Signaling Overview 4.4. Signaling Overview
MPL generates and processes the following messages: MPL generates and processes the following messages:
MPL Data Message - Generated by a MPL Seed to deliver a multicast MPL Data Message - Generated by an MPL Seed to deliver a multicast
message across a MPL Domain. The MPL Data Message's source is an 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 address in the Local Interface Set of the MPL Seed that generated
the message and is valid within the MPL Domain. The MPL Data the message and is valid within the MPL Domain. The MPL Data
Message's destination is the MPL Domain Address corresponding to Message's destination is the MPL Domain Address corresponding to
the MPL Domain. A MPL Data Message contains: the MPL Domain. An MPL Data Message contains:
* The Seed Identifier of the MPL Seed that generated the MPL Data * The Seed Identifier of the MPL Seed that generated the MPL Data
Message. Message.
* The sequence number of the MPL Seed that generated the MPL Data * The sequence number of the MPL Seed that generated the MPL Data
Message. Message.
* The original multicast message. * The original multicast message.
MPL Control Message - Generated by a MPL Forwarder to communicate MPL Control Message - Generated by an MPL Forwarder to communicate
information contained in a MPL Domain's Seed Set and Buffered information contained in an MPL Domain's Seed Set and Buffered
Message Set to neighboring MPL Forwarders. A MPL Control Message Message Set to neighboring MPL Forwarders. An MPL Control Message
contains a list of tuples for each entry in the Seed Set. Each contains a list of tuples for each entry in the Seed Set. Each
tuple contains: tuple contains:
* The minimum sequence number maintained in the Seed Set for the * The minimum sequence number maintained in the Seed Set for the
MPL Seed. MPL Seed.
* A bit-vector indicating the sequence numbers of MPL Data * A bit-vector indicating the sequence numbers of MPL Data
Messages resident in the Buffered Message Set for the MPL Seed, Messages resident in the Buffered Message Set for the MPL Seed,
where the first bit represents a sequence number equal to the where the first bit represents a sequence number equal to the
minimum threshold maintained in the Seed Set. minimum threshold maintained in the Seed Set.
* The length of the bit-vector. * The length of the bit-vector.
5. MPL Parameters and Constants 5. MPL Parameters and Constants
This section describes various program and networking parameters and This section describes various program and networking parameters and
constants used by MPL. constants used by MPL.
5.1. MPL Multicast Addresses 5.1. MPL Multicast Addresses
MPL makes use of MPL Domain Addresses to identify MPL Interfaces of a MPL makes use of MPL Domain Addresses to identify MPL Interfaces of
MPL Domain. By default, MPL Forwarders subscribe to the an MPL Domain. By default, MPL Forwarders subscribe to the
ALL_MPL_FORWARDERS multicast address with Realm-Local scope (scop ALL_MPL_FORWARDERS multicast address with Realm-Local scope (scop
value 3) [RFC7346]. value 3) [RFC7346].
For each MPL Domain Address that a MPL Interface subscribes to, the For each MPL Domain Address that an MPL Interface subscribes to, the
MPL Interface MUST also subscribe to the MPL Domain Address with MPL Interface MUST also subscribe to the MPL Domain Address with
Link-Local scope (scop value 2) when reactive forwarding is in use. Link-Local scope (scop value 2) when reactive forwarding is in use.
MPL Forwarders use the link-scoped MPL Domain Address to communicate MPL Forwarders use the link-scoped MPL Domain Address to communicate
MPL Control Messages to neighboring (i.e. on-link) MPL Forwarders. MPL Control Messages to neighboring (i.e., on-link) MPL Forwarders.
5.2. MPL Message Types 5.2. MPL Message Types
MPL defines an IPv6 Option for carrying a MPL Seed Identifier and a MPL defines an IPv6 Option for carrying an MPL Seed Identifier and a
sequence number within a MPL Data Message. The IPv6 Option Type has sequence number within an MPL Data Message. The IPv6 Option Type has
value 0x6D. value 0x6D.
MPL defines an ICMPv6 Message (MPL Control Message) for communicating MPL defines an ICMPv6 Message (MPL Control Message) for communicating
information contained in a MPL Domain's Seed Set and Buffered Message information contained in an MPL Domain's Seed Set and Buffered
Set to neighboring MPL Forwarders. The MPL Control Message has Message Set to neighboring MPL Forwarders. The MPL Control Message
ICMPv6 Type MPL_ICMP_TYPE. has ICMPv6 Type 159.
5.3. MPL Seed Identifiers 5.3. MPL Seed Identifiers
MPL uses MPL Seed Identifiers to uniquely identify MPL Seeds within a MPL uses MPL Seed Identifiers to uniquely identify MPL Seeds within
MPL Domain. For each MPL Domain that the MPL Forwarder serves as a an MPL Domain. For each MPL Domain that the MPL Forwarder serves as
MPL Seed, the MPL Forwarder MUST have an associated MPL Seed an MPL Seed, the MPL Forwarder MUST have an associated MPL Seed
Identifier. A MPL Forwarder MAY use the same MPL Seed Identifier Identifier. An MPL Forwarder MAY use the same MPL Seed Identifier
across multiple MPL Domains, but the MPL Seed Identifier MUST be across multiple MPL Domains, but the MPL Seed Identifier MUST be
unique within each MPL Domain. The mechanism for assigning and unique within each MPL Domain. The mechanism for assigning and
verifying uniqueness of MPL Seed Identifiers is not specified in this verifying uniqueness of MPL Seed Identifiers is not specified in this
document. document.
5.4. MPL Parameters 5.4. MPL Parameters
PROACTIVE_FORWARDING A boolean value that indicates whether the MPL PROACTIVE_FORWARDING - A boolean value that indicates whether or not
Forwarder schedules MPL Data Message transmissions after receiving the MPL Forwarder schedules MPL Data Message transmissions after
them for the first time. PROACTIVE_FORWARDING has a default value receiving them for the first time. PROACTIVE_FORWARDING has a
of TRUE. All MPL interfaces on the same link SHOULD be configured default value of TRUE. All MPL Interfaces on the same link SHOULD
with the same value of PROACTIVE_FORWARDING. An implementation be configured with the same value of PROACTIVE_FORWARDING. An
MAY choose to vary the value of PROACTIVE_FORWARDING across implementation MAY choose to vary the value of
interfaces on the same link if reactive forwarding is also in use. PROACTIVE_FORWARDING across interfaces on the same link if
The mechanism for setting PROACTIVE_FORWARDING is not specified reactive forwarding is also in use. The mechanism for setting
within this document. PROACTIVE_FORWARDING is not specified within this document.
SEED_SET_ENTRY_LIFETIME The minimum lifetime for an entry in the SEED_SET_ENTRY_LIFETIME - The minimum lifetime for an entry in the
Seed Set. SEED_SET_ENTRY_LIFETIME has a default value of 30 Seed Set. SEED_SET_ENTRY_LIFETIME has a default value of
minutes. It is RECOMMENDED that all MPL Forwarders use the same 30 minutes. It is RECOMMENDED that all MPL Forwarders use the
value for SEED_SET_ENTRY_LIFETIME for a given MPL Domain and use a same value for SEED_SET_ENTRY_LIFETIME for a given MPL Domain and
default value of 30 minutes. Using a value of use a default value of 30 minutes. Using a value of
SEED_SET_ENTRY_LIFETIME that is too small can cause the duplicate SEED_SET_ENTRY_LIFETIME that is too small can cause the duplicate
detection mechanism to fail, resulting in a MPL Forwarder to detection mechanism to fail, resulting in an MPL Forwarder
receive a given MPL Data Message more than once. The mechanism receiving a given MPL Data Message more than once. The mechanism
for setting SEED_SET_ENTRY_LIFETIME is not specified within this for setting SEED_SET_ENTRY_LIFETIME is not specified within this
document. document.
As specified in [RFC6206], a Trickle timer runs for a defined As specified in [RFC6206], a Trickle timer runs for a defined
interval and has three configuration parameters: the minimum interval interval and has three configuration parameters: the minimum interval
size Imin, the maximum interval size Imax, and a redundancy constant size Imin, the maximum interval size Imax, and a redundancy
k. constant k.
This specification defines a fourth Trickle configuration parameter, This specification defines a fourth Trickle configuration parameter,
TimerExpirations, which indicates the number of Trickle timer TimerExpirations, which indicates the number of Trickle timer
expiration events that occur before terminating the Trickle algorithm expiration events that occur before terminating the Trickle algorithm
for a given MPL Data Message or MPL Control Message. for a given MPL Data Message or MPL Control Message.
Each MPL Interface uses the following Trickle parameters for MPL Data Each MPL Interface uses the following Trickle parameters for MPL Data
Message and MPL Control Message transmissions. Message and MPL Control Message transmissions:
DATA_MESSAGE_IMIN The minimum Trickle timer interval, as defined in DATA_MESSAGE_IMIN - The minimum Trickle timer interval, as defined
[RFC6206], for MPL Data Message transmissions. DATA_MESSAGE_IMIN in [RFC6206], for MPL Data Message transmissions.
has a default value of 10 times the expected link-layer latency. 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 DATA_MESSAGE_IMAX - The maximum Trickle timer interval, as defined
[RFC6206], for MPL Data Message transmissions. DATA_MESSAGE_IMAX in [RFC6206], for MPL Data Message transmissions.
has a default value equal to DATA_MESSAGE_IMIN. DATA_MESSAGE_IMAX has a default value equal to DATA_MESSAGE_IMIN.
DATA_MESSAGE_K The redundancy constant, as defined in [RFC6206], for DATA_MESSAGE_K - The redundancy constant, as defined in [RFC6206],
MPL Data Message transmissions. DATA_MESSAGE_K has a default for MPL Data Message transmissions. DATA_MESSAGE_K has a default
value of 1. value of 1.
DATA_MESSAGE_TIMER_EXPIRATIONS The number of Trickle timer DATA_MESSAGE_TIMER_EXPIRATIONS - The number of Trickle timer
expirations that occur before terminating the Trickle algorithm's expirations that occur before terminating the Trickle algorithm's
retransmission of a given MPL Data Message. retransmission of a given MPL Data Message.
DATA_MESSAGE_TIMER_EXPIRATIONS has a default value of 3. DATA_MESSAGE_TIMER_EXPIRATIONS has a default value of 3.
CONTROL_MESSAGE_IMIN The minimum Trickle timer interval, as defined CONTROL_MESSAGE_IMIN - The minimum Trickle timer interval, as
in [RFC6206], for MPL Control Message transmissions. defined in [RFC6206], for MPL Control Message transmissions.
CONTROL_MESSAGE_IMIN has a default value of 10 times the worst- CONTROL_MESSAGE_IMIN has a default value of 10 times the
case link-layer latency. worst-case link-layer latency.
CONTROL_MESSAGE_IMAX The maximum Trickle timer interval, as defined CONTROL_MESSAGE_IMAX - The maximum Trickle timer interval, as
in [RFC6206], for MPL Control Message transmissions. defined in [RFC6206], for MPL Control Message transmissions.
CONTROL_MESSAGE_IMAX has a default value of 5 minutes. CONTROL_MESSAGE_IMAX has a default value of 5 minutes.
CONTROL_MESSAGE_K The redundancy constant, as defined in [RFC6206], CONTROL_MESSAGE_K - The redundancy constant, as defined in
for MPL Control Message transmissions. CONTROL_MESSAGE_K has a [RFC6206], for MPL Control Message transmissions.
default value of 1. CONTROL_MESSAGE_K has a default value of 1.
CONTROL_MESSAGE_TIMER_EXPIRATIONS The number of Trickle timer CONTROL_MESSAGE_TIMER_EXPIRATIONS - The number of Trickle timer
expirations that occur before terminating the Trickle algorithm expirations that occur before terminating the Trickle algorithm
for MPL Control Message transmissions. for MPL Control Message transmissions.
CONTROL_MESSAGE_TIMER_EXPIRATIONS has a default value of 10. CONTROL_MESSAGE_TIMER_EXPIRATIONS has a default value of 10.
As described in [RFC6206], if different nodes have different As described in [RFC6206], if different nodes have different
configuration parameters, Trickle may have unintended behaviors. configuration parameters, Trickle may have unintended behaviors.
Therefore, it is RECOMMENDED that all MPL Interfaces attached to the 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 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 parameters above for a given MPL Domain. The mechanism for setting
the Trickle Parameters is not specified within this document. the Trickle parameters is not specified within this document.
The default MPL parameters specify a forwarding strategy that The default MPL parameters specify a forwarding strategy that
utilizes both proactive and reactive techniques. Using these default utilizes both proactive and reactive techniques. Using these default
values, a MPL Forwarder proactively transmits any new MPL Data values, an MPL Forwarder proactively transmits any new MPL Data
Messages it receives then uses MPL Control Messages to trigger Messages it receives and then uses MPL Control Messages to trigger
additional MPL Data Message retransmissions where message drops are additional MPL Data Message retransmissions where message drops are
detected. Setting DATA_MESSAGE_IMAX to the same as DATA_MESSAGE_IMIN detected. Setting DATA_MESSAGE_IMAX to the same value as
in this case is acceptable since subsequent MPL Data Message DATA_MESSAGE_IMIN in this case is acceptable, since subsequent MPL
retransmissions are triggered by MPL Control Messages, where Data Message retransmissions are triggered by MPL Control Messages,
CONTROL_MESSAGE_IMAX is greater than CONTROL_MESSAGE_IMIN. where CONTROL_MESSAGE_IMAX is greater than CONTROL_MESSAGE_IMIN.
6. Protocol Message Formats 6. Protocol Message Formats
Messages generated and processed by a MPL Forwarder are described in Messages generated and processed by an MPL Forwarder are described in
this section. this section.
6.1. MPL Option 6.1. MPL Option
The MPL Option is carried in MPL Data Messages in an IPv6 Hop-by-Hop The MPL Option is carried in MPL Data Messages in an IPv6 Hop-by-Hop
Options header, immediately following the IPv6 header. The MPL Options header, immediately following the IPv6 header. The MPL
Option has the following format: Option has the following format:
0 1 2 3 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 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 | | Option Type | Opt Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S |M|V| rsv | sequence | seed-id (optional) | | S |M|V| rsv | sequence | seed-id (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type 0x6D. Option Type 0x6D.
Opt Data Len Length of the Option Data field in octets. Opt Data Len Length of the Option Data field [RFC2460] in octets.
S 2-bit unsigned integer. Identifies the length of S 2-bit unsigned integer. Identifies the length of the
seed-id. 0 indicates that the seed-id is the seed-id. '0' indicates that the seed-id is the IPv6
IPv6 Source Address and not included in the MPL Source Address and not included in the MPL Option.
Option. 1 indicates that the seed-id is a 16-bit '1' indicates that the seed-id is a 16-bit unsigned
unsigned integer. 2 indicates that the seed-id integer. '2' indicates that the seed-id is a 64-bit
is a 64-bit unsigned integer. 3 indicates that unsigned integer. '3' indicates that the seed-id is a
the seed-id is a 128-bit unsigned integer. 128-bit unsigned integer.
M 1-bit flag. 1 indicates that the value in M 1-bit flag. '1' indicates that the value in the
sequence is known to be the largest sequence sequence field is known to be the largest sequence
number that was received from the MPL Seed. number that was received from the MPL Seed.
V 1-bit flag. 0 indicates that the MPL Option V 1-bit flag. '0' indicates that the MPL Option
conforms to this specification. MPL Data conforms to this specification. MPL Data Messages
Messages with a MPL Option in which this flag is with an MPL Option in which this flag is set to 1 MUST
1 MUST be dropped. be dropped.
rsv 4-bit reserved field. MUST be set to 0 on rsv 4-bit reserved field. MUST be set to 0 on
transmission and ignored on reception. transmission and ignored on reception.
sequence 8-bit unsigned integer. Identifies relative sequence 8-bit unsigned integer. Identifies relative ordering
ordering of MPL Data Messages from the MPL Seed of MPL Data Messages from the MPL Seed identified by
identified by seed-id. the seed-id.
seed-id Uniquely identifies the MPL Seed that initiated seed-id Uniquely identifies the MPL Seed that initiated
dissemination of the MPL Data Message. The size dissemination of the MPL Data Message. The size of
of seed-id is indicated by the S field. the seed-id is indicated by the S field.
The Option Data (specifically the M flag) of the MPL Option is The Option Data (specifically, the M flag) of the MPL Option is
updated by MPL Forwarders as the MPL Data Message is forwarded. updated by MPL Forwarders as the MPL Data Message is forwarded.
Nodes that do not understand the MPL Option MUST discard the MPL Data Nodes that do not understand the MPL Option MUST discard the MPL Data
Message. Thus, according to [RFC2460] the three high order bits of Message. Thus, according to [RFC2460], the three high-order bits of
the Option Type are set to '011'. The Option Data length is the Option Type are set to '011'. The Option Data length is
variable. variable.
The seed-id uniquely identifies a MPL Seed. When seed-id is 128 bits The seed-id uniquely identifies an MPL Seed. When the seed-id is
(S=3), the MPL Seed MAY use an IPv6 address assigned to one of its 128 bits (S=3), the MPL Seed MAY use an IPv6 address assigned to one
interfaces that is unique within the MPL Domain. Managing MPL Seed of its interfaces that is unique within the MPL Domain. Managing MPL
Identifiers is not within scope of this document. Seed Identifiers is not within the scope of this document.
The sequence field establishes a total ordering of MPL Data Messages The sequence field establishes a total ordering of MPL Data Messages
generated by a MPL Seed for a MPL Domain. The MPL Seed MUST 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 increment the sequence field's value on each new MPL Data Message
that it generates for a MPL Domain. Implementations MUST follow the that it generates for an MPL Domain. Implementations MUST follow the
Serial Number Arithmetic as defined in [RFC1982] when incrementing a Serial Number Arithmetic as defined in [RFC1982] when incrementing a
sequence value or comparing two sequence values. sequence value or comparing two sequence values.
Future updates to this specification may define additional fields Future updates to this specification may define additional fields
following the seed-id field. following the seed-id field.
6.2. MPL Control Message 6.2. MPL Control Message
A MPL Forwarder uses ICMPv6 messages to communicate information An MPL Forwarder uses ICMPv6 Messages to communicate information
contained in a MPL Domain's Seed Set and Buffered Message Set to contained in an MPL Domain's Seed Set and Buffered Message Set to
neighboring MPL Forwarders. The MPL Control Message has the neighboring MPL Forwarders. The MPL Control Message has the
following format: following format:
0 1 2 3 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 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 | | Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. MPL Seed Info[0..n] . . MPL Seed Info[0..n] .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP Fields: IP Fields:
Source Address An IPv6 address in the AddressSet of the Source Address An IPv6 address in the AddressSet of the
corresponding MPL Interface and MUST be valid corresponding MPL Interface. MUST be valid
within the MPL Domain. within the MPL Domain.
Destination Address The link-scoped MPL Domain Address corresponding Destination Address The link-scoped MPL Domain Address
to the MPL Domain. corresponding to the MPL Domain.
Hop Limit 255 Hop Limit 255
ICMPv6 Fields: ICMPv6 Fields:
Type MPL_ICMP_TYPE Type 159
Code 0 Code 0
Checksum The ICMP checksum. See [RFC4443]. Checksum The ICMP checksum. See [RFC4443].
MPL Seed Info[0..n] List of zero or more MPL Seed Info entries. 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 The MPL Control Message indicates the sequence numbers of MPL Data
Messages that are within the MPL Domain's Buffered Message Set. The Messages that are within the MPL Domain's Buffered Message Set. The
MPL Control Message also indicates the sequence numbers of MPL Data MPL Control Message also indicates the sequence numbers of MPL Data
Messages that a MPL Forwarder is willing to receive. The MPL Control Messages that an MPL Forwarder is willing to receive. The MPL
Message allows neighboring MPL Forwarders to determine whether there Control Message allows neighboring MPL Forwarders to determine
are any new MPL Data Messages to exchange. whether or not there are any new MPL Data Messages to exchange.
6.3. MPL Seed Info 6.3. MPL Seed Info
A MPL Seed Info encodes the minimum sequence number for an MPL Seed 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 maintained in the MPL Domain's Seed Set. The MPL Seed Info also
indicates the sequence numbers of MPL Data Messages generated by the indicates the sequence numbers of MPL Data Messages generated by the
MPL Seed that are stored within the MPL Domain's Buffered Message MPL Seed that are stored within the MPL Domain's Buffered Message
Set. The MPL Seed Info has the following format: Set. The MPL Seed Info has the following format:
0 1 2 3 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 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) | | min-seqno | bm-len | S | seed-id (0/2/8/16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. buffered-mpl-messages (variable length) . . buffered-mpl-messages (variable length) .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
min-seqno 8-bit unsigned integer. The lower-bound sequence min-seqno 8-bit unsigned integer. The lower-bound
number for the MPL Seed. sequence number for the MPL Seed.
bm-len 6-bit unsigned integer. The size of buffered- bm-len 6-bit unsigned integer. The size of
mpl-messages in octets. buffered-mpl-messages in octets.
S 2-bit unsigned integer. Identifies the length of S 2-bit unsigned integer. Identifies the
seed-id. 0 indicates that the seed-id value is length of the seed-id. '0' indicates that
the IPv6 Source Address and not included in the the seed-id value is the IPv6 Source Address
MPL Seed Info. 1 indicates that the seed-id and not included in the MPL Seed Info. '1'
value is a 16-bit unsigned integer. 2 indicates indicates that the seed-id value is a 16-bit
that the seed-id value is a 64-bit unsigned unsigned integer. '2' indicates that the
integer. 3 indicates that the seed-id is a seed-id value is a 64-bit unsigned integer.
128-bit unsigned integer. '3' indicates that the seed-id is a 128-bit
unsigned integer.
seed-id Variable-length unsigned integer. Indicates the seed-id Variable-length unsigned integer. Indicates
MPL Seed associated with this MPL Seed Info. the MPL Seed associated with this MPL
Seed Info.
buffered-mpl-messages Variable-length bit vector. Identifies the buffered-mpl-messages Variable-length bit-vector. Identifies the
sequence numbers of MPL Data Messages maintained sequence numbers of MPL Data Messages
in the corresponding Buffered Message Set for the maintained in the corresponding Buffered
MPL Seed. The i'th bit represents a sequence Message Set for the MPL Seed. The i-th bit
number of min-seqno + i. '0' indicates that the represents a sequence number of min-seqno
corresponding MPL Data Message does not exist in + i. '0' indicates that the corresponding
the Buffered Message Set. '1' indicates that the MPL Data Message does not exist in the
corresponding MPL Data Message does exist in the Buffered Message Set. '1' indicates that the
Buffered Message Set. corresponding MPL Data Message does exist in
the Buffered Message Set.
The MPL Seed Info does not have any octet alignment requirement. The MPL Seed Info does not have any octet alignment requirement.
7. Information Base 7. Information Base
7.1. Local Interface Set 7.1. Local Interface Set
The Local Interface Set records the local MPL Interfaces of a MPL The Local Interface Set records the local MPL Interfaces of an MPL
Forwarder. The Local Interface Set consists of Local Interface Forwarder. The Local Interface Set consists of Local Interface
Tuples, one per MPL Interface: (AddressSet). Tuples, one per MPL Interface: (AddressSet).
AddressSet - a set of unicast addresses assigned to the MPL AddressSet - a set of unicast addresses assigned to the MPL
Interface. Interface.
7.2. Domain Set 7.2. Domain Set
The Domain Set records the MPL Interfaces that subscribe to each MPL The Domain Set records the MPL Interfaces that subscribe to each MPL
Domain Address. The Domain Set consists of MPL Domain Tuples, one Domain Address. The Domain Set consists of MPL Domain Tuples, one
per MPL Domain: (MPLInterfaceSet). per MPL Domain: (MPLInterfaceSet).
MPLInterfaceSet - a set of MPL Interfaces that subscribe to the MPL MPLInterfaceSet - a set of MPL Interfaces that subscribe to the MPL
Domain Address that identifies the MPL Domain. Domain Address that identifies the MPL Domain.
7.3. Seed Set 7.3. Seed Set
A Seed Set records a sliding window used to determine the sequence A Seed Set records a sliding window used to determine the sequence
numbers of MPL Data Messages that a MPL Forwarder is willing to numbers of MPL Data Messages (generated by the MPL Seed) that an MPL
accept generated by the MPL Seed. A MPL Forwarder maintains a Seed Forwarder is willing to accept. An MPL Forwarder maintains a Seed
Set for each MPL Domain that it participates in. A Seed Set consists Set for each MPL Domain that it participates in. A Seed Set consists
of MPL Seed Tuples: (SeedID, MinSequence, Lifetime). of MPL Seed Tuples: (SeedID, MinSequence, Lifetime).
SeedID - the identifier for the MPL Seed. SeedID - the identifier for the MPL Seed.
MinSequence - a lower-bound sequence number that represents the MinSequence - a lower-bound sequence number that represents the
sequence number of the oldest MPL Data Message the MPL Forwarder sequence number of the oldest MPL Data Message the MPL Forwarder
is willing to receive or transmit. A MPL Forwarder MUST ignore is willing to receive or transmit. An MPL Forwarder MUST ignore
any MPL Data Message that has sequence value less than than any MPL Data Message that has a sequence value less than
MinSequence. MinSequence.
Lifetime - indicates the minimum remaining lifetime of the Seed Set Lifetime - indicates the minimum remaining lifetime of the Seed Set
entry. A MPL Forwarder MUST NOT free a Seed Set entry before the entry. An MPL Forwarder MUST NOT free a Seed Set entry before the
remaining lifetime expires. remaining lifetime expires.
7.4. Buffered Message Set 7.4. Buffered Message Set
A Buffered Message Set records recently received MPL Data Messages A Buffered Message Set records recently received MPL Data Messages
from a MPL Seed within a MPL Domain. A MPL Forwarder uses a Buffered from an MPL Seed within an MPL Domain. An MPL Forwarder uses a
Message Set to buffer MPL Data Messages while the MPL Forwarder is Buffered Message Set to buffer MPL Data Messages while the MPL
forwarding the MPL Data Messages. A MPL Forwarder maintains a Forwarder is forwarding the MPL Data Messages. An MPL Forwarder
Buffered Message Set for each MPL Domain that it participates in. A maintains a Buffered Message Set for each MPL Domain that it
Buffered Message Set consists of Buffered Message Tuples: (SeedID, participates in. A Buffered Message Set consists of Buffered Message
SequenceNumber, DataMessage). Tuples: (SeedID, SequenceNumber, DataMessage).
SeedID - the identifier for the MPL Seed that generated the MPL Data SeedID - the identifier for the MPL Seed that generated the MPL Data
Message. Message.
SequenceNumber - the sequence number for the MPL Data Message. SequenceNumber - the sequence number for the MPL Data Message.
DataMessage - the MPL Data Message. DataMessage - the MPL Data Message.
All MPL Data Messages within a Buffered Message Set MUST have a All MPL Data Messages within a Buffered Message Set MUST have a
sequence number greater than or equal to MinSequence for the sequence number greater than or equal to MinSequence for the
corresponding SeedID. When increasing MinSequence for a MPL Seed, corresponding SeedID. When increasing MinSequence for an MPL Seed,
the MPL Forwarder MUST delete any MPL Data Messages from the the MPL Forwarder MUST delete any MPL Data Messages from the
corresponding Buffered Message Set that have sequence numbers less corresponding Buffered Message Set that have sequence numbers less
than MinSequence. than MinSequence.
8. MPL Seed Sequence Numbers 8. MPL Seed Sequence Numbers
Each MPL Seed maintains a sequence number for each MPL Domain that it Each MPL Seed maintains a sequence number for each MPL Domain that it
serves. The sequence numbers are included in MPL Data Messages serves. The sequence numbers are included in MPL Data Messages
generated by the MPL Seed. The MPL Seed MUST increment the sequence 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. number for each MPL Data Message that it generates for an MPL Domain.
Implementations MUST follow the Serial Number Arithmetic as defined Implementations MUST follow the Serial Number Arithmetic as defined
in [RFC1982] when incrementing a sequence value or comparing two in [RFC1982] when incrementing a sequence value or comparing two
sequence values. This sequence number is used to establish a total sequence values. This sequence number is used to establish a total
ordering of MPL Data Messages generated by a MPL Seed for a MPL ordering of MPL Data Messages generated by an MPL Seed for an MPL
Domain. Domain.
9. MPL Data Messages 9. MPL Data Messages
9.1. MPL Data Message Generation 9.1. MPL Data Message Generation
MPL Data Messages are generated by MPL Seeds when these messages MPL Data Messages are generated by MPL Seeds when these messages
enter the MPL Domain. All MPL Data messages have the following enter the MPL Domain. All MPL Data Messages have the following
properties: properties:
o The IPv6 Source Address MUST be an address in the AddressSet of a o The IPv6 Source Address MUST be an address in the AddressSet of a
corresponding MPL Interface and MUST be valid within the MPL corresponding MPL Interface and MUST be valid within the MPL
Domain. Domain.
o The IPv6 Destination Address MUST be set to the MPL Domain Address o The IPv6 Destination Address MUST be set to the MPL Domain Address
corresponding to the MPL Domain. corresponding to the MPL Domain.
o A MPL Data Message MUST contain a MPL Option in its IPv6 Header to o An MPL Data Message MUST contain an MPL Option in its IPv6 header
identify the MPL Seed that generated the message and the ordering to identify the MPL Seed that generated the message and the
relative to other MPL Data Messages generated by the MPL Seed. ordering relative to other MPL Data Messages generated by the
MPL Seed.
When the destination address is a MPL Domain Address and the source When the destination address is an MPL Domain Address and the source
address is in the AddressLIst of a MPL Interface that belongs to that address is in the AddressList of an MPL Interface that belongs to
MPL Domain Address, the application message and the MPL Data Message that MPL Domain Address, the application message and the MPL Data
MAY be identical. In other words, the MPL Data Message may contain a Message MAY be identical. In other words, the MPL Data Message may
single IPv6 header that includes the MPL Option. contain a single IPv6 header that includes the MPL Option.
Otherwise, IPv6-in-IPv6 encapsulation MUST be used to satisfy the MPL Otherwise, IPv6-in-IPv6 encapsulation MUST be used to satisfy the MPL
Data Message requirements listed above [RFC2473]. The complete IPv6- Data Message requirements listed above [RFC2473]. The complete
in-IPv6 message forms a MPL Data Message. The outer IPv6 header IPv6-in-IPv6 message forms an MPL Data Message. The outer IPv6
conforms to the MPL Data Message requirements listed above. The header conforms to the MPL Data Message requirements listed above.
encapsulated IPv6 datagram encodes the multicast data message that is The encapsulated IPv6 datagram encodes the multicast data message
communicated beyond the MPL Domain. that is communicated beyond the MPL Domain.
9.2. MPL Data Message Transmission 9.2. MPL Data Message Transmission
A MPL Forwarder manages transmission of MPL Data Messages in its An MPL Forwarder manages transmission of MPL Data Messages in its
Buffered Message Sets using the Trickle algorithm [RFC6206]. A MPL Buffered Message Sets using the Trickle algorithm [RFC6206]. An MPL
Forwarder MUST use a separate Trickle timer for each MPL Data Message Forwarder MUST use a separate Trickle timer for each MPL Data Message
that it is actively forwarding. In accordance with Section 5 of RFC that it is actively forwarding. In accordance with Section 5 of
6206 [RFC6206], this document defines the following: RFC 6206 [RFC6206], the following items apply:
o This document defines a "consistent" transmission as receiving a o This document defines a "consistent" transmission as receiving an
MPL Data Message that has the same MPL Domain Address, seed-id, MPL Data Message that has the same MPL Domain Address, seed-id,
and sequence value as the MPL Data Message managed by the Trickle and sequence value as the MPL Data Message managed by the
timer. Trickle timer.
o This document defines an "inconsistent" transmission as receiving o This document defines an "inconsistent" transmission as receiving
a MPL Data Message that has the same MPL Domain Address, seed-id 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 MPL value, and the M flag set, but has a sequence value less than that
Data Message managed by the Trickle timer. of the MPL Data Message managed by the Trickle timer.
o This document does not define any external "events". o This document does not define any external "events".
o This document defines MPL Data Messages as Trickle messages. o This document defines MPL Data Messages as Trickle messages.
o The actions outside the Trickle algorithm that MPL takes involve o The actions outside the Trickle algorithm that MPL takes involve
managing the MPL Domain's Seed Set and Buffered Message Set. managing the MPL Domain's Seed Set and Buffered Message Set.
As specified in [RFC6206], a Trickle timer has three variables: the As specified in [RFC6206], a Trickle timer has three variables: the
current interval size I, a time within the current interval t, and a 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 counter c. MPL defines a fourth variable, e, which counts the number
of Trickle timer expiration events since the Trickle timer was last of Trickle timer expiration events since the Trickle timer was last
reset. reset.
After DATA_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, the MPL After DATA_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, the MPL
Forwarder MUST disable the Trickle timer. When a buffered MPL Data Forwarder MUST disable the Trickle timer. When a buffered MPL Data
Message does not have an associated Trickle timer, the MPL Forwarder Message does not have an associated Trickle timer, the MPL Forwarder
MAY delete the message from the Buffered Message Set by advancing MAY delete the message from the Buffered Message Set by advancing the
MinSequence of the corresponding MPL Seed in the Seed Set. When the MinSequence value of the corresponding MPL Seed in the Seed Set.
MPL Forwarder no longer buffers any messages for a MPL Seed, the MPL When the MPL Forwarder no longer buffers any messages for an MPL
Forwarder MUST NOT increment MinSequence for that MPL Seed. Seed, the MPL Forwarder MUST NOT increment MinSequence for that
MPL Seed.
When transmitting a MPL Data Message, the MPL Forwarder MUST either 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 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 not the message's sequence number is the largest value that has been
received from the MPL Seed. received from the MPL Seed.
9.3. MPL Data Message Processing 9.3. MPL Data Message Processing
Upon receiving a MPL Data Message, the MPL Forwarder first processes Upon receiving an MPL Data Message, the MPL Forwarder first processes
the MPL Option and updates the Trickle timer associated with the MPL the MPL Option and updates the Trickle timer associated with the MPL
Data Message if one exists. Data Message if one exists.
Upon receiving a MPL Data Message, a MPL Forwarder MUST perform one Upon receiving an MPL Data Message, an MPL Forwarder MUST perform one
of the following actions: of the following actions:
o Accept the message and enter the MPL Data Message in the MPL o Accept the message and enter the MPL Data Message in the MPL
Domain's Buffered Message Set. Domain's Buffered Message Set.
o Accept the message and update the corresponding MinSequence in the o Accept the message and update the corresponding MinSequence in
MPL Domain's Seed Set to 1 greater than the message's sequence the MPL Domain's Seed Set to 1 greater than the message's
number. sequence number.
o Discard the message without any change to the MPL Information o Discard the message without any change to the MPL
Base. Information Base.
If a Seed Set entry exists for the MPL Seed, the MPL Forwarder MUST 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 discard the MPL Data Message if its sequence number is less than
MinSequence or exists in the Buffered Message Set. MinSequence or exists in the Buffered Message Set.
If a Seed Set entry does not exist for the MPL Seed, the MPL 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 Forwarder MUST create a new entry for the MPL Seed before accepting
the MPL Data Message. the MPL Data Message.
If memory is limited, a MPL Forwarder SHOULD reclaim memory resources If memory is limited, an MPL Forwarder SHOULD reclaim memory
by: resources by:
o Incrementing MinSequence entries in a Seed Set and deleting MPL o Incrementing MinSequence entries in a Seed Set and deleting MPL
Data Messages in the corresponding Buffered Message Set that fall Data Messages in the corresponding Buffered Message Set that fall
below the MinSequence value. below the MinSequence value.
o Deleting other Seed Set entries that have expired and the o Deleting other Seed Set entries that have expired and the
corresponding MPL Data Messages in the Buffered Message Set. corresponding MPL Data Messages in the Buffered Message Set.
If the MPL Forwarder accepts the MPL Data Message, the MPL Forwarder If the MPL Forwarder accepts the MPL Data Message, the MPL Forwarder
MUST perform the following actions: MUST perform the following actions:
o Reset the Lifetime of the corresponding Seed Set entry to o Reset the Lifetime of the corresponding Seed Set entry to
SEED_SET_ENTRY_LIFETIME. SEED_SET_ENTRY_LIFETIME.
o If PROACTIVE_FORWARDING is true, the MPL Forwarder MUST initialize o If PROACTIVE_FORWARDING is TRUE, the MPL Forwarder MUST initialize
and start a Trickle timer for the MPL Data Message. and start a Trickle timer for the MPL Data Message.
o If the MPL Control Message Trickle timer is not running and o If the MPL Control Message Trickle timer is not running and
CONTROL_MESSAGE_TIMER_EXPIRATIONS is non-zero, the MPL Forwarder CONTROL_MESSAGE_TIMER_EXPIRATIONS is non-zero, the MPL Forwarder
MUST initialize and start the MPL Control Message Trickle timer. MUST initialize and start the MPL Control Message Trickle timer.
o If the MPL Control Message Trickle timer is running, the MPL o If the MPL Control Message Trickle timer is running, the MPL
Forwarder MUST reset the MPL Control Message Trickle timer. Forwarder MUST reset the MPL Control Message Trickle timer.
10. MPL Control Messages 10. MPL Control Messages
10.1. MPL Control Message Generation 10.1. MPL Control Message Generation
A MPL Forwarder generates MPL Control Messages to communicate a MPL An MPL Forwarder generates MPL Control Messages to communicate an MPL
Domain's Seed Set and Buffered Message Set to neighboring MPL Domain's Seed Set and Buffered Message Set to neighboring MPL
Forwarders. Each MPL Control Message is generated according to 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 Section 6.2, with an MPL Seed Info entry for each entry in the MPL
Seed Set. Each MPL Seed Info entry has the following content: 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 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 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 bm-len set to the size of buffered-mpl-messages in octets.
o seed-id set to the MPL seed identifier. o seed-id set to the MPL Seed Identifier.
o buffered-mpl-messages with each bit representing whether or not a o buffered-mpl-messages with each bit representing whether or not an
MPL Data Message with the corresponding sequence number exists in MPL Data Message with the corresponding sequence number exists in
the Buffered Message Set. The i'th bit represents a sequence the Buffered Message Set. The i-th bit represents a sequence
number of min-seqno + i. '0' indicates that the corresponding MPL number of min-seqno + i. '0' indicates that the corresponding MPL
Data Message does not exist in the Buffered Message Set. '1' Data Message does not exist in the Buffered Message Set. '1'
indicates that the corresponding MPL Data Message does exist in indicates that the corresponding MPL Data Message does exist in
the Buffered Message Set. the Buffered Message Set.
10.2. MPL Control Message Transmission 10.2. MPL Control Message Transmission
A MPL Forwarder transmits MPL Control Messages using the Trickle An MPL Forwarder transmits MPL Control Messages using the Trickle
algorithm. A MPL Forwarder maintains a single Trickle timer for each algorithm. An MPL Forwarder maintains a single Trickle timer for
MPL Domain. When CONTROL_MESSAGE_TIMER_EXPIRATIONS is 0, the MPL each MPL Domain. When CONTROL_MESSAGE_TIMER_EXPIRATIONS is 0, the
Forwarder does not execute the Trickle algorithm and does not MPL Forwarder does not execute the Trickle algorithm and does not
transmit MPL Control Messages. In accordance with Section 5 of RFC transmit MPL Control Messages. In accordance with Section 5 of
6206 [RFC6206], this document defines the following: RFC 6206 [RFC6206], the following items apply:
o This document defines a "consistent" transmission as receiving a o This document defines a "consistent" transmission as receiving an
MPL Control Message that results in a determination that neither MPL Control Message that results in a determination that neither
the receiving nor transmitting node has any new MPL Data Messages the receiving nor transmitting node has any new MPL Data Messages
to offer. to offer.
o This document defines an "inconsistent" transmission as receiving o This document defines an "inconsistent" transmission as receiving
a MPL Control Message that results in a determination that either an MPL Control Message that results in a determination that either
the receiving or transmitting node has at least one new MPL Data the receiving or transmitting node has at least one new MPL Data
Message to offer. Message to offer.
o The Trickle timer is reset in response to external "events." This o The Trickle timer is reset in response to external "events". This
document defines an "event" as increasing MinSequence of any entry document defines an "event" as increasing the MinSequence value of
in the corresponding Seed Set or adding a message to the any entry in the corresponding Seed Set or adding a message to the
corresponding Buffered Message Set. corresponding Buffered Message Set.
o This document defines a MPL Control Message as a Trickle message. o This document defines an MPL Control Message as a Trickle message.
As specified in [RFC6206], a Trickle timer has three variables: the As specified in [RFC6206], a Trickle timer has three variables: the
current interval size I, a time within the current interval t, and a 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 counter c. MPL defines a fourth variable, e, which counts the number
of Trickle timer expiration events since the Trickle timer was last of Trickle timer expiration events since the Trickle timer was last
reset. After CONTROL_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, reset. After CONTROL_MESSAGE_TIMER_EXPIRATIONS Trickle timer events,
the MPL Forwarder MUST disable the Trickle timer. the MPL Forwarder MUST disable the Trickle timer.
10.3. MPL Control Message Processing 10.3. MPL Control Message Processing
A MPL Forwarder processes each MPL Control Message that it receives 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. 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 An MPL Forwarder determines if a new MPL Data Message has not been
received from a neighboring node if any of the following conditions received from a neighboring node if any of the following conditions
hold true: hold true:
o The MPL Control Message includes a MPL Seed that does not exist in o The MPL Control Message includes an MPL Seed that does not exist
the MPL Domain's Seed Set. in the MPL Domain's Seed Set.
o The MPL Control Message indicates that the neighbor has a MPL Data o The MPL Control Message indicates that the neighbor has an MPL
Message in its Buffered Message Set with sequence number greater Data Message in its Buffered Message Set with sequence number
than MinSequence (i.e. the i-th bit is set to 1 and min-seqno + i greater than MinSequence (i.e., the i-th bit is set to 1 and
> MinSequence) and is not included in the MPL Domain's Buffered min-seqno + i > MinSequence) and is not included in the MPL
Message Set. Domain's Buffered Message Set.
When a MPL Forwarder determines that it has not yet received a MPL When an MPL Forwarder determines that it has not yet received an MPL
Data Message buffered by a neighboring device, the MPL Forwarder MUST Data Message buffered by a neighboring device, the MPL Forwarder MUST
reset its Trickle timer associated with MPL Control Message reset its Trickle timer associated with MPL Control Message
transmissions. If a MPL Control Message Trickle timer is not transmissions. If an MPL Control Message Trickle timer is not
running, the MPL Forwarder MUST initialize and start a new Trickle running, the MPL Forwarder MUST initialize and start a new
timer. Trickle timer.
A MPL Forwarder determines if a MPL Data Message in the Buffered An MPL Forwarder determines if an MPL Data Message in the Buffered
Message Set has not yet been received by a neighboring MPL Forwarder Message Set has not yet been received by a neighboring MPL Forwarder
if any of the following conditions hold true: if any of the following conditions hold true:
o The MPL Control Message does not include a MPL Seed for the MPL o The MPL Control Message does not include an MPL Seed for the MPL
Data Message. Data Message.
o The MPL Data Message's sequence number is greater than or equal to o The MPL Data Message's sequence number is greater than or equal to
min-seqno and not included in the neighbor's corresponding min-seqno and not included in the neighbor's corresponding
Buffered Message Set (i.e. the MPL Data Message's sequence number Buffered Message Set (i.e., the MPL Data Message's sequence number
does not have a corresponding bit in buffered-mpl-messages set to does not have a corresponding bit in buffered-mpl-messages
1). set to 1).
When a MPL Forwarder determines that it has at least one MPL Data When an MPL Forwarder determines that it has at least one MPL Data
Message in its corresponding Buffered Message Set that has not yet Message in its corresponding Buffered Message Set that has not yet
been received by a neighbor, the MPL Forwarder MUST reset the MPL been received by a neighbor, the MPL Forwarder MUST reset the MPL
Control Message Trickle timer. Additionally, for each of those Control Message Trickle timer. Additionally, for each of those
entries in the Buffered Message Set, the MPL Forwarder MUST reset the 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 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 with the MPL Data Message, the MPL Forwarder MUST initialize and
start a new Trickle timer. start a new Trickle timer.
11. Acknowledgements 11. IANA Considerations
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 This document defines one IPv6 Option, a type that has been allocated
from the IPv6 "Destination Options and Hop-by-Hop Options" registry from the IPv6 "Destination Options and Hop-by-Hop Options" registry
of [RFC2780]. of [RFC2780].
This document defines one ICMPv6 Message, a type that must be This document defines one ICMPv6 Message, a type that has been
allocated from the "ICMPv6 "type" Numbers" registry of [RFC4443]. allocated from the "ICMPv6 'type' Numbers" registry of [RFC4443].
This document registers a well-known multicast address from the This document registers a well-known multicast address from the
Variable Scope Multicast Address registry. "Variable Scope Multicast Addresses" registry of [RFC3307].
12.1. MPL Option Type 11.1. MPL Option Type
IANA is requested to allocate an IPv6 Option Type from the IPv6 IANA has allocated an IPv6 Option Type from the IPv6 "Destination
"Destination Options and Hop-by-Hop Options" registry of [RFC2780], Options and Hop-by-Hop Options" registry of [RFC2780], as specified
as specified in Table 1 below: in Table 1 below:
+-----------+-----+-----+-------+-------------+---------------+ +-----------+-----+-----+-------+-------------+-----------+
| Hex Value | act | chg | rest | Description | Reference | | Hex Value | act | chg | rest | Description | Reference |
+-----------+-----+-----+-------+-------------+---------------+ +-----------+-----+-----+-------+-------------+-----------+
| 0x6D | 01 | 1 | 01101 | MPL Option | This Document | | 0x6D | 01 | 1 | 01101 | MPL Option | RFC 7731 |
+-----------+-----+-----+-------+-------------+---------------+ +-----------+-----+-----+-------+-------------+-----------+
Table 1: IPv6 Option Type Allocation Table 1: IPv6 Option Type Allocation
12.2. MPL ICMPv6 Type Note: IANA has marked the value 0x4D (previously "MPL Option") as
"Deprecated".
IANA is requested to allocate an ICMPv6 Type from the "ICMPv6 "type" 11.2. MPL ICMPv6 Type
Numbers" registry of [RFC4443], as specified in Table 2 below:
+------+---------------------+---------------+ IANA has allocated an ICMPv6 Type from the "ICMPv6 'type' Numbers"
| Type | Name | Reference | registry of [RFC4443], as specified in Table 2 below:
+------+---------------------+---------------+
| TBD | MPL Control Message | This Document |
+------+---------------------+---------------+
Table 2: IPv6 Option Type Allocation +------+---------------------+-----------+
| Type | Name | Reference |
+------+---------------------+-----------+
| 159 | MPL Control Message | RFC 7731 |
+------+---------------------+-----------+
In this document, the mnemonic MPL_ICMP_TYPE was used to refer to the Table 2: ICMPv6 Type Allocation
ICMPv6 Type above, which is TBD by IANA.
12.3. Well-known Multicast Addresses 11.3. Well-Known Multicast Addresses
IANA is requested to allocate an IPv6 multicast address, with Group IANA has allocated an IPv6 multicast address, with Group ID in the
ID in the range [0x01,0xFF] for 6LoWPAN compression [RFC6282], range [0x01,0xFF] for IPv6 over Low-Power Wireless Personal Area
"ALL_MPL_FORWARDERS" from the "Variable Scope Multicast Addresses" Network (6LoWPAN) compression [RFC6282], "ALL_MPL_FORWARDERS" from
sub-registry of the "IPv6 Multicast Address Space" registry [RFC3307] the "Variable Scope Multicast Addresses" sub-registry of the "IPv6
as specified in Table 3 below: Multicast Address Space Registry" [RFC3307], as specified in Table 3
below:
+---------------------+--------------------+-----------+------------+ +---------------------+--------------------+-----------+------------+
| Address(s) | Description | Reference | Date | | Address(es) | Description | Reference | Date |
| | | | Registered | | | | | Registered |
+---------------------+--------------------+-----------+------------+ +---------------------+--------------------+-----------+------------+
| FF0X:0:0:0:0:0:0:FC | ALL_MPL_FORWARDERS | This | 2013-04-10 | | FF0X:0:0:0:0:0:0:FC | ALL_MPL_FORWARDERS | RFC 7731 | 2013-04-10 |
| | | Document | |
+---------------------+--------------------+-----------+------------+ +---------------------+--------------------+-----------+------------+
Table 3: Variable Scope Multicast Address Allocation Table 3: Variable Scope Multicast Address Allocation
13. Security Considerations 12. Security Considerations
MPL uses sequence numbers to maintain a total ordering of MPL Data MPL uses sequence numbers to maintain a total ordering of MPL Data
Messages from a MPL Seed. The use of sequence numbers allows a 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 denial-of-service attack where an attacker can spoof a message with a
sufficiently large sequence number to: (i) flush messages from the sufficiently large sequence number to (i) flush messages from the
Buffered Message List and (ii) increase the MinSequence value for a Buffered Message List and (ii) increase the MinSequence value for an
MPL Seed in the corresponding Seed Set. In both cases, the side MPL Seed in the corresponding Seed Set. In both cases, the side
effect allows an attacker to halt the forwarding process of any MPL effect allows an attacker to halt the forwarding process of any MPL
Data Messages being disseminated and prevents MPL Forwarders from Data Messages being disseminated and prevents MPL Forwarders from
accepting new MPL Data Messages that a MPL Seed generates while the accepting new MPL Data Messages that an MPL Seed generates while the
sequence number is less than MinSequence or until the corresponding sequence number is less than MinSequence or until the corresponding
Seed Set Entry expires. The net effect applies to both proactive and Seed Set Entry expires. The net effect applies to both proactive and
reactive forwarding modes. reactive forwarding modes.
In general, the basic ability to inject messages into a Low-power and In general, the basic ability to inject messages into an LLN may be
Lossy Network may be used as a denial-of-service attack regardless of used as a denial-of-service attack, regardless of what forwarding
what forwarding protocol is used. Because MPL is a dissemination protocol is used. Because MPL is a dissemination protocol, the
protocol, the ability to spoof MPL messages allows an attacker to ability to spoof MPL messages allows an attacker to affect an entire
affect an entire MPL Domain. For these reasons, Low-power and Lossy MPL Domain. For these reasons, LLNs typically employ link-layer
Networks typically employ link-layer security mechanisms to mitigate security mechanisms to mitigate an attacker's ability to inject
an attacker's ability to inject messages. For example, the IEEE messages. For example, the IEEE 802.15.4 [IEEE802.15.4] standard
802.15.4 [IEEE802154] standard specifies frame security mechanisms specifies frame security mechanisms using AES-128 to support access
using AES-128 to support access control, message integrity, message control, message integrity, message confidentiality, and replay
confidentiality, and replay protection. However, if the attack protection. However, if the attack vector includes attackers that
vector includes attackers that have access to the LLN, then MPL have access to the LLN, then MPL SHOULD NOT be used.
SHOULD NOT be used.
To prevent attackers from injecting packets through a MPL Forwarder, To prevent attackers from injecting packets through an MPL Forwarder,
the MPL Forwarder MUST NOT accept or forward MPL Data Messages from a the MPL Forwarder MUST NOT accept or forward MPL Data Messages from a
communication interface that does not subscribe to the MPL Domain communication interface that does not subscribe to the MPL Domain
Address identified in message's destination address. Address identified in the message's destination address.
MPL uses the Trickle algorithm to manage message transmissions and MPL uses the Trickle algorithm to manage message transmissions;
the security considerations described in [RFC6206] apply. therefore, the security considerations described in [RFC6206] apply.
14. References 13. References
14.1. Normative References 13.1. Normative References
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
August 1996. DOI 10.17487/RFC1982, August 1996,
<http://www.rfc-editor.org/info/rfc1982>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. 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 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998. (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 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998. 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 [RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", BCP Values In the Internet Protocol and Related Headers",
37, RFC 2780, March 2000. BCP 37, RFC 2780, DOI 10.17487/RFC2780, March 2000,
<http://www.rfc-editor.org/info/rfc2780>.
[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast [RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
Addresses", RFC 3307, August 2002. 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 [RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007, B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
March 2005. DOI 10.17487/RFC4007, March 2005,
<http://www.rfc-editor.org/info/rfc4007>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Message Protocol (ICMPv6) for the Internet Protocol Control Message Protocol (ICMPv6) for the Internet
Version 6 (IPv6) Specification", RFC 4443, March 2006. 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, [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
"The Trickle Algorithm", RFC 6206, March 2011. "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206,
March 2011, <http://www.rfc-editor.org/info/rfc6206>.
[RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 [RFC6282] Hui, J., Ed., and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
September 2011. DOI 10.17487/RFC6282, September 2011,
<http://www.rfc-editor.org/info/rfc6282>.
[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Lossy Networks", RFC 6550, March 2012. 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, [RFC7346] Droms, R., "IPv6 Multicast Address Scopes", RFC 7346,
August 2014. DOI 10.17487/RFC7346, August 2014,
<http://www.rfc-editor.org/info/rfc7346>.
14.2. Informative References 13.2. Informative References
[Clausen2013] [Clausen2013]
Clausen, T., Colin de Verdiere, A., and J. Yi, Clausen, T., de Verdiere, A., and J. Yi, "Performance
"Performance Analysis of Trickle as a Flooding Mechanism", Analysis of Trickle as a Flooding Mechanism", The 15th
The 5th IEEE International Conference on Communication IEEE International Conference on Communication
Technology (ICCT2013), November 2013. Technology (ICCT2013), DOI 10.1109/ICCT.2013.6820439,
November 2013.
[IEEE802154] [IEEE802.15.4]
"IEEE Std. 802.15.4-2006", October 2006. 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 [RFC3973] Adams, A., Nicholas, J., and W. Siadak, "Protocol
Independent Multicast - Dense Mode (PIM-DM): Protocol Independent Multicast - Dense Mode (PIM-DM): Protocol
Specification (Revised)", RFC 3973, January 2005. 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, [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM): "Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006. Protocol Specification (Revised)", RFC 4601,
DOI 10.17487/RFC4601, August 2006,
<http://www.rfc-editor.org/info/rfc4601>.
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 Authors' Addresses
Jonathan W. Hui Jonathan W. Hui
Nest Labs Nest Labs
3400 Hillview Ave 3400 Hillview Ave.
Palo Alto, California 94304 Palo Alto, California 94304
USA United States
Phone: +650 253 2770 Phone: +650 253 2770
Email: jonhui@nestlabs.com Email: jonhui@nestlabs.com
Richard Kelsey Richard Kelsey
Silicon Labs Silicon Labs
25 Thomson Place 25 Thomson Place
Boston, Massachusetts 02210 Boston, Massachusetts 02210
USA United States
Phone: +617 951 1225 Phone: +617 951 1225
Email: richard.kelsey@silabs.com Email: richard.kelsey@silabs.com
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