draft-ietf-roll-trickle-mcast-02.txt   draft-ietf-roll-trickle-mcast-03.txt 
ROLL J. Hui ROLL J. Hui
Internet-Draft Cisco Internet-Draft Cisco
Intended status: Standards Track R. Kelsey Intended status: Standards Track R. Kelsey
Expires: April 22, 2013 Silicon Labs Expires: July 28, 2013 Silicon Labs
October 19, 2012 January 24, 2013
Multicast Protocol for Low power and Lossy Networks (MPL) Multicast Protocol for Low power and Lossy Networks (MPL)
draft-ietf-roll-trickle-mcast-02 draft-ietf-roll-trickle-mcast-03
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) that 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 an MPL domain. MPL uses the Trickle algorithm to drive forwarders in an MPL domain. MPL uses the Trickle algorithm to
packet transmissions for both control and data-plane packets. manage message transmissions for both control and data-plane
Specific Trickle parameter configurations allow MPL to trade between messages. Different Trickle parameter configurations allow MPL to
dissemination latency and transmission efficiency. trade between dissemination latency and transmission efficiency.
Status of this Memo Status of this Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 22, 2013. This Internet-Draft will expire on July 28, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Applicability Statement . . . . . . . . . . . . . . . . . . . 5
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 7 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
4.1. MPL Option . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Information Base Overview . . . . . . . . . . . . . . . . 6
4.2. ICMPv6 MPL Message . . . . . . . . . . . . . . . . . . . . 8 4.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2.1. MPL Window . . . . . . . . . . . . . . . . . . . . . . 9 4.3. Signaling Overview . . . . . . . . . . . . . . . . . . . . 7
5. MPL Forwarder Behavior . . . . . . . . . . . . . . . . . . . . 11 5. MPL Constants . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Multicast Packet Dissemination . . . . . . . . . . . . . . 11 5.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 9
5.1.1. Trickle Parameters and Variables . . . . . . . . . . . 12 5.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 9
5.1.2. Proactive Propagation . . . . . . . . . . . . . . . . 12 5.3. MPL Forwarder Parameters . . . . . . . . . . . . . . . . . 9
5.1.3. Reactive Propagation . . . . . . . . . . . . . . . . . 13 5.4. Trickle Parameters . . . . . . . . . . . . . . . . . . . . 9
5.2. Sliding Windows . . . . . . . . . . . . . . . . . . . . . 13 6. Protocol Message Formats . . . . . . . . . . . . . . . . . . . 11
5.3. Transmission of MPL Multicast Packets . . . . . . . . . . 15 6.1. MPL Option . . . . . . . . . . . . . . . . . . . . . . . . 11
5.4. Reception of MPL Multicast Packets . . . . . . . . . . . . 16 6.2. MPL Control Message . . . . . . . . . . . . . . . . . . . 12
5.5. Transmission of ICMPv6 MPL Messages . . . . . . . . . . . 16 6.3. MPL Seed Info . . . . . . . . . . . . . . . . . . . . . . 13
5.6. Reception of ICMPv6 MPL Messages . . . . . . . . . . . . . 17 7. Information Base . . . . . . . . . . . . . . . . . . . . . . . 15
6. MPL Parameters . . . . . . . . . . . . . . . . . . . . . . . . 19 7.1. Local Interface Set . . . . . . . . . . . . . . . . . . . 15
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20 7.2. Domain Set . . . . . . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 7.3. Seed Set . . . . . . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22 7.4. Buffered Message Set . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 8. MPL Domains . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . . 23 9. MPL Seed Sequence Numbers . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . . 23 10. MPL Data Messages . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 10.1. MPL Data Message Generation . . . . . . . . . . . . . . . 19
10.2. MPL Data Message Transmission . . . . . . . . . . . . . . 19
10.3. MPL Data Message Processing . . . . . . . . . . . . . . . 20
11. MPL Control Messages . . . . . . . . . . . . . . . . . . . . . 22
11.1. MPL Control Message Generation . . . . . . . . . . . . . . 22
11.2. MPL Control Message Transmission . . . . . . . . . . . . . 22
11.3. MPL Control Message Processing . . . . . . . . . . . . . . 23
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
13.1. MPL Option Type . . . . . . . . . . . . . . . . . . . . . 26
13.2. MPL ICMPv6 Type . . . . . . . . . . . . . . . . . . . . . 26
13.3. Well-known Multicast Addresses . . . . . . . . . . . . . . 26
14. Security Considerations . . . . . . . . . . . . . . . . . . . 27
15. Normative References . . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction 1. Introduction
Low power and Lossy Networks typically operate with strict resource Low power and Lossy Networks typically operate with strict resource
constraints in communication, computation, memory, and energy. Such constraints in communication, computation, memory, and energy. Such
resource constraints may preclude the use of existing IPv6 multicast resource constraints may preclude the use of existing IPv6 multicast
topology and forwarding mechanisms. Traditional IP multicast routing and forwarding mechanisms. Traditional IP multicast delivery
forwarding typically relies on topology maintenance mechanisms to typically relies on topology maintenance mechanisms to discover and
forward multicast messages to all subscribers of a multicast group. maintain routes to all subscribers of a multicast group. However,
However, maintaining such topologies in LLNs is costly and may not be maintaining such topologies in LLNs is costly and may not be feasible
feasible given the available resources. given the 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 a LLN Border Router (LBR) and use source routing to
forward packets away from the LBR. For the same reasons, a LLN forward messages away from the LBR. For the same reasons, a LLN
device may not be able to maintain a multicast forwarding topology device may not be able to maintain a multicast routing topology when
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 forwarding 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 forwarding topology, disseminating multicast messages any multicast routing topology, disseminating multicast messages to
to all MPL forwarders in an MPL domain. By using the Trickle all MPL forwarders in an MPL domain. By using the Trickle algorithm
algorithm [RFC6206], MPL requires only small, constant state for each [RFC6206], MPL requires only small, constant state for each MPL
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", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The following terms are used throughout this document: The following terms are used throughout this document:
MPL forwarder An IPv6 router that subscribes to the MPL MPL Forwarder - A router that implements this protocol. A MPL
multicast group and participates in disseminating Forwarder is equipped with at least one MPL
MPL multicast packets. Interface.
MPL multicast scope The multicast scope that MPL uses when forwarding MPL Interface - An MPL Forwarder's attachment to a
MPL multicast packets. In other words, the communications medium, over which it transmits
multicast scope of the IPv6 Destination Address and receives MPL Data Messages and MPL Control
of an MPL multicast packet. Messages according to this specification. An MPL
Interface is assigned one or more unicast
addresses and is subscribed to one or more MPL
Domain Addresses.
MPL domain A connected set of MPL forwarders that define the MPL Domain Address - A multicast address that identifies the set of
extent of the MPL dissemination process. As a MPL Interfaces within an MPL Domain. MPL Data
form of flood, all MPL forwarders in an MPL Messages disseminated in an MPL Domain have the
domain will receive MPL multicast packets. The associated MPL Domain Address as their
MPL domain MUST be composed of at least one MPL destination address.
multicast scope and MAY be composed of multiple
MPL multicast scopes.
MPL seed A MPL forwarder that begins the dissemination MPL Domain - A scope zone, as defined in [RFC4007], in which
process for an MPL multicast packet. The MPL MPL Interfaces subscribe to the same MPL Domain
seed may be different than the source of the Address and participate in disseminating MPL Data
original multicast packet. Messages.
MPL seed identifier An identifier that uniquely identifies an MPL MPL Data Message - A multicast message that is used to communicate
forwarder within its MPL domain. a multicast payload between MPL Forwarders and
contains an MPL Option in the IPv6 header. A MPL
Data Message has its destination address set to
the MPL Domain Address.
original multicast packet An IPv6 multicast packet that is MPL Control Message - A link-local multicast message that is used to
disseminated using MPL. communicate information about recently received
MPL Data Messages to neighboring MPL Forwarders.
MPL multicast packet An IPv6 multicast packet that contains an MPL MPL Seed - An MPL Forwarder that generates MPL Data
Hop-by-Hop Option. When either source or Messages and serves as an entry point into an MPL
destinations are beyond the MPL multicast scope, Domain.
the MPL multicast packet is an IPv6-in-IPv6
packet that contains an MPL Hop-by-Hop Option in
the outer IPv6 header and encapsulates an
original multicast packet. When both source and
destinations are within the MPL multicast scope,
the MPL Hop-by-Hop Option may be included
directly within the original multicast packet.
3. Overview 3. Applicability Statement
MPL delivers IPv6 multicast packets by disseminating them to all MPL This protocol is an IPv6 multicast forwarding protocol for Low-Power
forwarders within an MPL domain. MPL dissemination is a form of and Lossy Networks. By implementing a controlled dissemination using
flood. An MPL forwarder may broadcast/multicast an MPL multicast the Trickle algorithm, this protocol is designed for networks that
packet out of the same physical interface on which it was received. communicate using low-power and lossy links with widely varying
Using link-layer broadcast/multicast allows MPL to forward multicast topologies in both the space and time dimensions.
packets without explicitly identifying next-hop destinations. An MPL
forwarder may also broadcast/multicast MPL multicast packets out
other interfaces to disseminate the message across different links.
MPL does not build or maintain a multicast forwarding topology to
forward multicast packets.
Any MPL forwarder may initiate the dissemination process by serving 4. Protocol Overview
as an MPL seed for an original multicast packet. The MPL seed may or
may not be the same device as the source of the original multicast
packet. When the original multicast packet's source is outside the
LLN, the MPL seed may be the ingress router. Even if an original
multicast packet source is within the LLN, the source may first
forward the multicast packet to the MPL seed using IPv6-in-IPv6
tunneling. Because MPL state requirements grows with the number of
active MPL seeds, limiting the number of MPL seeds reduces the amount
of state that MPL forwarders must maintain.
Because MPL typically broadcasts/multicasts MPL packets out of the The goal of MPL is to deliver multicast messages to all interfaces
same interface on which they were received, MPL forwarders are likely that subscribe to the multicast messages' destination address within
to receive an MPL multicast packet more than once. The MPL seed tags an MPL Domain.
each original multicast packet with an MPL seed identifier and a
sequence number. The sequence number provides a total ordering of
MPL multicast packets disseminated by the MPL seed.
MPL defines a new IPv6 Hop-by-Hop Option, the MPL Option, to include 4.1. Information Base Overview
MPL-specific information along with the original multicast packet.
Each IPv6 multicast packet that MPL disseminates includes the MPL
Option. Because the original multicast packet's source and the MPL
seed may not be the same device, the MPL Option may be added to the
original multicast packet en-route. To allow Path MTU discovery to
work properly, MPL encapsulates the original multicast packet in
another IPv6 header that includes the MPL Option.
Upon receiving a new MPL multicast packet for forwarding, the MPL A node records necessary protocol state in the following information
forwarder may proactively transmit the MPL multicast packet packet a sets:
limited number of times and then falls back into an optional reactive
mode. In maintenance mode, an MPL forwarder buffers recently
received MPL multicast packets and advertises a summary of recently
received MPL multicast packets from time to time, allowing
neighboring MPL forwarders to determine if they have any new
multicast packets to offer or receive.
MPL forwarders schedule their packet (control and data) transmissions o The Local Interface Set records the set of local MPL Interfaces
using the Trickle algorithm [RFC6206]. Trickle's adaptive and the unicast addresses assigned to those MPL Interfaces.
transmission interval allows MPL to quickly disseminate messages when
there are new MPL multicast packets, but reduces transmission
overhead as the dissemination process completes. Trickle's
suppression mechanism and transmission time selection allow MPL's
communication rate to scale logarithmically with density.
4. Message Formats o The Domain Set records the set of MPL Domain Addresses and the
local MPL Interfaces that subscribe to those addresses.
4.1. MPL Option o The Seed Set records information about received MPL Data Messages
received from an MPL Seed. The Seed Set maintains the minimum
sequence number that the MPL Forwarder is willing to receive or
has buffered in its Buffered Message Set. MPL uses the Seed Set
and Buffered Message Set to determine when to accept an MPL Data
Message, process its payload, and retransmit it.
The MPL Option is carried in an IPv6 Hop-by-Hop Options header, o The Buffered Message Set records recently received MPL Data
immediately following the IPv6 header. The MPL Option has the Messages from an MPL Seed. MPL Data Messages resident in the
following format: Buffered Message Set have sequence numbers that are greater than
or equal to the minimum threshold maintained in the Seed Set. MPL
uses the Buffered Message Set to store MPL Data Messages that may
be transmitted by the MPL Forwarder for forwarding.
4.2. Overview
MPL achieves its goal by implementing a controlled flood that
attempts to disseminate the multicast data message to all interfaces
within an MPL Domain. MPL performs the following tasks to
disseminate a multicast message:
o When having a multicast message to forward into an MPL Domain, the
MPL Seed generates an MPL Data Message that includes the MPL Seed
Identifier, a newly generated sequence number, and the multicast
message. If the multicast destination address is not the MPL
Domain Address, IP-in-IP [RFC2473] is used to encapsulate the
multicast message in the MPL Data Message.
o Upon receiving an MPL Data Message, the MPL Forwarder extracts the
MPL Seed and sequence number and determines whether or not the MPL
Data Message was previously received using the Seed Set and
Buffered Message Set.
* If the sequence number is less than the lower-bound sequence
number maintained in the Seed Set or a message with the same
sequence number exists within the Buffered Message Set, the MPL
Forwarder marks the MPL Data Message as old.
* Otherwise, the MPL Forwarder marks the MPL Data Message as new.
o For each newly received MPL Data Message, an MPL Forwarder updates
the Seed Set, adds the MPL Data Message into the Buffered Message
Set, processes its payload, and multicasts the MPL Data Message a
number of times on all MPL Interfaces participating in the same
MPL Domain to forward the message.
o Each MPL Forwarder may periodically link-local multicast MPL
Control Messages on MPL Interfaces to communicate information
contained in the MPL Forwarder's Seed Set and Buffered Message
Sets.
o Upon receiving an MPL Control Message, an MPL Forwarder determines
whether there are any new MPL Data Messages that have yet to be
received by the MPL Control Message's source and multicasts those
MPL Data Messages.
MPL's configuration parameters allow two forwarding strategies for
disseminating MPL Data Messages.
Proactive Forwarding - With proactive forwarding, an MPL Forwarder
schedules transmissions of MPL Data Messages using the Trickle
algorithm, without any prior indication that neighboring nodes
have yet to receive the message. After transmitting the MPL Data
Message a limited number of times, the MPL forwarder may terminate
proactive forwarding for the MPL Data Message message.
Reactive Forwarding - With reactive forwarding, an MPL Forwarder
link-local multicasts MPL Control Messages using the Trickle
algorithm [RFC6206]. MPL Forwarders use MPL Control Messages to
discover new MPL Data Messages that have not yet been received.
When discovering that a neighboring MPL Forwarder has not yet
received a new MPL Data Message, the MPL Forwarder schedules those
MPL Data Messages for transmission using the Trickle algorithm.
4.3. Signaling Overview
This protocol generates and processes the following messages:
MPL Data Message - Generated by an MPL Seed to deliver a multicast
message across an MPL Domain. The MPL Data Message's source is an
address in the Local Interface Set of the MPL Seed that generated
the message and is valid within the MPL Domain. The MPL Data
Message's destination is the MPL Domain Address corresponding to
the MPL Domain. An MPL Data Message contains:
* The Seed Identifier of the MPL Seed that generated the MPL Data
Message.
* The sequence number of the MPL Seed that generated the MPL Data
Message.
* The original multicast message.
MPL Control Message - Generated by an MPL Forwarder to communicate
information contained in the Seed Set and Buffered Message Set to
neighboring MPL Forwarders. An MPL Control Message contains a
list of tuples for each entry in the Seed Set. Each tuple
contains:
* The minimum sequence number maintained in the Seed Set for the
MPL Seed.
* A bit-vector indicating the sequence numbers of MPL Data
Messages resident in the Buffered Message Set for the MPL Seed,
where the first bit represents a sequence number equal to the
minimum threshold maintained in the Seed Set.
* The length of the bit-vector.
5. MPL Constants
This section describes various program and networking constants used
by MPL.
5.1. Multicast Addresses
MPL makes use of MPL Domain Addresses to identify MPL Interfaces of
an MPL Domain. By default, MPL Forwarders subscribe to the
ALL_MPL_FORWARDERS multicast address with a scope value of 3 (subnet-
local).
For each MPL Domain Address that an MPL Interface subscribes to, the
MPL Interface MUST also subscribe to the MPL Domain Address with a
scope value of 2 (link-local) when reactive forwarding is in use.
MPL Forwarders use the link-scoped MPL Domain Address to communicate
MPL Control Messages to neighboring (i.e. on-link) MPL Forwarders.
5.2. Message Types
MPL defines an IPv6 Option for carrying an MPL Seed Identifier and a
sequence number within an MPL Data Message. The IPv6 Option Type has
value MPL_OPT_TYPE.
MPL defines an ICMPv6 Message (MPL Control Message) for communicating
information contained in its Seed Set and Buffered Message Set to
neighboring MPL Forwarders. The MPL Control Message has ICMPv6 Type
MPL_ICMP_TYPE.
5.3. MPL Forwarder Parameters
PROACTIVE_FORWARDING A boolean value that indicates whether the MPL
Forwarder should schedule MPL Data Message transmissions after
receiving them for the first time.
SEED_SET_LIFETIME The minimum lifetime for an entry in the Seed Set.
5.4. Trickle Parameters
As specified in [RFC6206], a Trickle timer runs for a defined
interval and has three configuration parameters: the minimum interval
size Imin, the maximum interval size Imax, and a redundancy constant
k.
This specification defines a fourth Trickle configuration parameter,
TimerExpirations, which indicates the number of Trickle timer
expiration events that occur before terminating the Trickle
algorithm.
Each MPL forwarder maintains a separate Trickle parameter set for MPL
Data Message and MPL Control Message transmissions. The Trickle
parameters are listed below:
DATA_MESSAGE_IMIN The minimum Trickle timer interval, as defined in
[RFC6206], for MPL Data Message transmissions.
DATA MESSAGE_IMAX The maximum Trickle timer interval, as defined in
[RFC6206], for MPL Data Message transmissions.
DATA_MESSAGE_K The redundancy constant, as defined in [RFC6206], for
MPL Data Message transmissions.
DATA_MESSAGE_TIMER_EXPIRATIONS The number of Trickle timer
expirations that occur before terminating the Trickle algorithm
for MPL Data Message transmissions.
CONTROL_MESSAGE_IMIN The minimum Trickle timer interval, as defined
in [RFC6206], for MPL Control Message transmissions.
CONTROL_MESSAGE_IMAX The maximum Trickle timer interval, as defined
in [RFC6206], for MPL Control Message transmissions.
CONTROL_MESSAGE_K The redundancy constant, as defined in [RFC6206],
for MPL Control Message transmissions.
CONTROL_MESSAGE_TIMER_EXPIRATIONS The number of Trickle timer
expirations that occur before terminating the Trickle algorithm
for MPL Control Message transmissions.
It is RECOMMENDED that all MPL Forwarder within an MPL Domain use the
same values for the Trickle Parameters above, as specified in
[RFC6206].
6. Protocol Message Formats
The protocol messages generated and processed by an MPL Forwarder are
described in this section.
6.1. MPL Option
The MPL Option is carried in MPL Data Messages in an IPv6 Hop-by-Hop
Options header, immediately following the IPv6 header. The MPL
Option has the following format:
0 1 2 3 0 1 2 3
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| rsv | sequence | seed-id (optional) | | S |M|V| rsv | sequence | seed-id (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type XX (to be confirmed by IANA). Option Type MPL_OPT_TYPE
Opt Data Len Length of the Option Data field in octets. MUST Opt Data Len Length of the Option Data field in octets.
be set to either 2 or 4.
S 2-bit unsigned integer. Identifies the length of S 2-bit unsigned integer. Identifies the length of
seed-id. 0 indicates that the seed-id is 0 and seed-id. 0 indicates that the seed-id is the IPv6
not included in the MPL Option. 1 indicates that Source Address and not included in the MPL
the seed-id is a 16-bit unsigned integer. 2 Option. 1 indicates that the seed-id is a 16-bit
indicates that the seed-id is a 64-bit unsigned unsigned integer. 2 indicates that the seed-id is
integer. 3 indicates that the seed-id is a 128- a 64-bit unsigned integer. 3 indicates that the
bit unsigned integer. seed-id is a 128-bit unsigned integer.
M 1-bit flag. 0 indicates that the value in M 1-bit flag. 1 indicates that the value in
sequence is not the greatest sequence number that sequence is known to be the largest sequence
was received from the MPL seed. number that was received from the MPL Seed.
rsv 5-bit reserved field. MUST be set to zero and V 1-bit flag. 0 indicates that the MPL Option
incoming MPL multicast packets in which they are conforms to this specification. MPL Options
not zero MUST be dropped. received in which this flag is 1 MUST be dropped.
rsv 4-bit reserved field. MUST be set to 0 on
transmission and ignored on reception.
sequence 8-bit unsigned integer. Identifies relative sequence 8-bit unsigned integer. Identifies relative
ordering of MPL multicast packets from the source ordering of MPL Data Messages from the MPL Seed
identified by seed-id. identified by seed-id.
seed-id Uniquely identifies the MPL seed that initiated seed-id Uniquely identifies the MPL Seed that initiated
dissemination of the MPL multicast packet. The dissemination of the MPL Data Message. The size
size of seed-id is indicated by the S field. of seed-id is indicated by the S field.
The Option Data of the Trickle Multicast option MUST NOT change as The Option Data (in particular the M flag) of the MPL Option is
the MPL multicast packet is forwarded. Nodes that do not understand updated by MPL Forwarders as the MPL Data Message is forwarded.
the Trickle Multicast option MUST discard the packet. Thus, Nodes that do not understand the MPL Option MUST discard the MPL Data
according to [RFC2460] the three high order bits of the Option Type Message. Thus, according to [RFC2460] the three high order bits of
must be set to '010'. The Option Data length is variable. the Option Type are set to '011'. The Option Data length is
variable.
The seed-id uniquely identifies an MPL seed within the MPL domain. The seed-id uniquely identifies an MPL Seed. When seed-id is 128
When seed-id is 128 bits (S=3), the MPL seed MAY use an IPv6 address bits (S=3), the MPL seed MAY use an IPv6 address assigned to one of
assigned to one of its interfaces that is unique within the MPL its interfaces that is unique within the MPL domain. Managing MPL
domain. Managing MPL seed identifiers is not within scope of this Seed Identifiers is not within scope of this document.
document.
The sequence field establishes a total ordering of MPL multicast The sequence field establishes a total ordering of MPL Data Messages
packets from the same MPL seed. The MPL seed MUST increment the generated by an MPL Seed for an MPL Domain. The MPL Seed MUST
sequence field's value on each new MPL multicast packet that it increment the sequence field's value on each new MPL Data Message
disseminates. Implementations MUST follow the Serial Number that it generates for an MPL Domain. Implementations MUST follow the
Arithmetic as defined in [RFC1982] when incrementing a sequence value Serial Number Arithmetic as defined in [RFC1982] when incrementing a
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.
4.2. ICMPv6 MPL Message 6.2. MPL Control Message
The MPL forwarder uses ICMPv6 MPL messages to advertise information An MPL Forwarder uses ICMPv6 messages to communicate information
about recently received MPL multicast packets. The ICMPv6 MPL contained in its Seed Set and Buffered Message Set to neighboring MPL
message has the following format: Forwarders. The MPL Control Message 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum | | Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. MPL Window[1..n] . . MPL Seed Info[1..n] .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP Fields: IP Fields:
Source Address A link-local address assigned to the sending Source Address A link-local address assigned to the sending
interface. interface.
Destination Address The link-local all-nodes MPL forwarders multicast Destination Address The link-scoped MPL Domain Address corresponding
address (FF02::TBD). to the MPL Domain.
Hop Limit 255 Hop Limit 255
ICMPv6 Fields: ICMPv6 Fields:
Type XX (to be confirmed by IANA). Type MPL_ICMP_TYPE
Code 0 Code 0
Checksum The ICMP checksum. See [RFC4443]. Checksum The ICMP checksum. See [RFC4443].
MPL Window[1..n] List of one or more MPL Windows (defined in MPL Seed Info[1..n] List of one or more MPL Seed Info entries.
Section 4.2.1).
An MPL forwarder transmits an ICMPv6 MPL message to advertise The MPL Control Message indicates the sequence numbers of MPL Data
information about buffered MPL multicast packets. More explicitly, Messages that are within the Buffered Message Set. The MPL Control
the ICMPv6 MPL message encodes the sliding window state (described in Message also indicates the sequence numbers of MPL Data Messages that
Section 5.2) that the MPL forwarder maintains for each MPL seed. The an MPL Forwarder is willing to receive. The MPL Control Message
advertisement serves to indicate to neighboring MPL forwarders allows neighboring MPL Forwarders to determine whether there are any
regarding newer messages that it may send or the neighboring MPL new MPL Data Messages to exchange.
forwarders have yet to receive.
4.2.1. MPL Window 6.3. MPL Seed Info
An MPL Window encodes the sliding window state (described in An MPL Seed Info encodes the minimum sequence number for the MPL Seed
Section 5.2 that the MPL forwarder maintains for an MPL seed. Each maintained in the Seed Set. The MPL Seed Info also indicates the
MPL Window has the following format: sequence numbers of MPL Data Messages generated by the MPL Seed
within the Buffered Message 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| w-min | w-len | S | seed-id (0, 2 or 16 octets) | | min-seqno | bm-len | S | seed-id (0/2/8/16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. buffered-mpl-packets (0 to 8 octets) . . buffered-mpl-messages (variable length) .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
w-min 8-bit unsigned integer. Indicates the first min-seqno 8-bit unsigned integer. The lower-bound sequence
sequence number associated with the first bit in number for the MPL Seed.
buffered-mpl-packets.
w-len 6-bit unsigned integer. Indicates the size of bm-len 6-bit unsigned integer. The size of buffered-
the sliding window and the number of valid bits mpl-messages in octets.
in buffered-mpl-packets. The sliding window's
upper bound is the sum of w-min and w-len.
S 2-bit unsigned integer. Identifies the length of S 2-bit unsigned integer. Identifies the length of
seed-id. 0 indicates that the seed-id value is 0 seed-id. 0 indicates that the seed-id value is
and not included in the MPL Option. 1 indicates the IPv6 Source Address and not included in the
that the seed-id value is a 16-bit unsigned MPL Seed Info. 1 indicates that the seed-id value
integer. 2 indicates that the seed-id value is a is a 16-bit unsigned integer. 2 indicates that
128-bit unsigned integer. 3 is reserved. the seed-id value is a 64-bit unsigned integer. 3
indicates that the seed-id is a 128-bit unsigned
integer.
seed-id Indicates the MPL seed associated with this seed-id Variable-length unsigned integer. Indicates the
sliding window. MPL Seed associated with this MPL Seed Info.
buffered-mpl-packets Variable-length bit vector. Identifies the buffered-mpl-messages Variable-length bit vector. Identifies the
sequence numbers of MPL multicast packets that sequence numbers of MPL Data Messages maintained
the MPL forwarder has buffered. The sequence in the Buffered Message Set for the MPL Seed.
number is determined by w-min + i, where i is the The sequence number is determined by min-seqno +
offset within buffered-mpl-packets. i, where i is the bit offset within buffered-mpl-
messages.
The MPL Window does not have any octet alignment requirement. The MPL Seed Info does not have any octet alignment requirement.
5. MPL Forwarder Behavior 7. Information Base
An MPL forwarder implementation needs to manage sliding windows for 7.1. Local Interface Set
each active MPL seed. The sliding window allows the MPL forwarder to
determine what multicast packets to accept and what multicast packets
are buffered. An MPL forwarder must also manage MPL packet
transmissions.
5.1. Multicast Packet Dissemination The Local Interface Set records the local MPL Interfaces of an MPL
Forwarder. The Local Interface Set consists of Local Interface
Tuples, one per MPL Interface: (AddressSet).
MPL uses the Trickle algorithm to control packet transmissions when AddressSet - a set of unicast addresses assigned to the MPL
disseminating MPL multicast packets [RFC6206]. MPL provides two Interface.
propagation mechanisms for disseminating MPL multicast packets.
1. With proactive propagation, an MPL forwarder transmits buffered 7.2. Domain Set
MPL multicast packets using the Trickle algorithm. This method
is called proactive propagation since an MPL forwarder actively
transmits MPL multicast packets without discovering that a
neighboring MPL forwarder has yet to receive the message.
2. With reactive propagation, an MPL forwarder transmits ICMPv6 MPL The Domain Set records the MPL Interfaces that subscribe to each MPL
messages using the Trickle algorithm. An MPL forwarder only Domain Address. The Domain Set consists of MPL Domain Tuples, one
transmits buffered MPL multicast packets upon discovering that per MPL Domain: (MPLInterfaceSet).
neighboring devices have not yet to receive the corresponding MPL
multicast packets.
When receiving a new multicast packet, an MPL forwarder first MPLInterfaceSet - a set of MPL Interfaces that subscribe to the MPL
utilizes proactive propagation to forward the MPL multicast packet. Domain Address that identifies the MPL Domain.
Proactive propagation reduces dissemination latency since it does not
require discovering that neighboring devices have not yet received
the MPL multicast packet. MPL forwarders utilize proactive
propagation for newly received MPL multicast packets since they can
assume that some neighboring MPL forwarders have yet to receive the
MPL multicast packet. After a limited number of MPL multicast packet
transmissions, the MPL forwarder may terminate proactive propagation
for the MPL multicast packet.
An MPL forwarder may optionally use reactive propagation to continue 7.3. Seed Set
the dissemination process with lower communication overhead. With
reactive propagation, neighboring MPL forwarders use ICMPv6 MPL
messages to discover new MPL multicast messages that have not yet
been received. When discovering that a neighboring MPL forwarder has
not yet received a new MPL multicast packet, the MPL forwarder
enables proactive propagation again.
5.1.1. Trickle Parameters and Variables The Seed Set records a sliding window used to determine the sequence
numbers of MPL Data Messages that an MPL Forwarder is willing to
accept generated by the MPL Seed. It consists of MPL Seed Tuples:
(SeedID, MinSequence, Lifetime).
As specified in RFC 6206 [RFC6206], a Trickle timer runs for a SeedID - the identifier for the MPL Seed.
defined interval and has three configuration parameters: the minimum
interval size Imin, the maximum interval size Imax, and a redundancy
constant k.
MPL defines a fourth configuration parameter, TimerExpirations, which MinSequence - a lower-bound sequence number that represents the
indicates the number of Trickle timer expiration events that occur sequence number of the oldest MPL Data Message the MPL Forwarder
before terminating the Trickle algorithm. is willing to receive or transmit. An MPL Forwarder MUST ignore
any MPL Data Message that has sequence value less than than
MinSequence.
Each MPL forwarder maintains a separate Trickle parameter set for the Lifetime - indicates the minimum lifetime of the Seed Set entry. An
proactive and reactive propagation methods. TimerExpirations MUST be MPL Forwarder MUST NOT free a Seed Set entry before its expires.
greater than 0 for proactive propagation. TimerExpirations MAY be
set to 0 for reactive propagation, which effectively disables
reactive propagation.
As specified in RFC 6206 [RFC6206], a Trickle timer has three 7.4. Buffered Message Set
variables: the current interval size I, a time within the current
interval t, and a counter c.
MPL defines a fourth variable, e, which counts the number of Trickle The Buffered Message Set records recently received MPL Data Messages
timer expiration events since the Trickle timer was last reset. from an MPL Seed. An MPL Forwarder uses the Buffered Message Set to
buffer MPL Data Messages while the MPL Forwarder is forwarding the
MPL Data Messages. The Buffered Message Set consists of Buffered
Message Tuples: (SeedID, SequenceNumber, DataMessage).
5.1.2. Proactive Propagation SeedID - the identifier for the MPL Seed that generated the MPL Data
Message.
With proactive propagation, the MPL forwarder transmits buffered MPL SequenceNumber - the sequence number for the MPL Data Message.
multicast packets using the Trickle algorithm. Each buffered MPL
multicast packet that is proactively being disseminated with
proactive propagation has an associated Trickle timer. Adhering to
Section 5 of RFC 6206 [RFC6206], this document defines the following:
o This document defines a "consistent" transmission for proactive DataMessage - the MPL Data Message.
propagation as receiving an MPL multicast packet that has the same
MPL seed identifier and sequence number as a buffered MPL packet.
o This document defines an "inconsistent" transmission for proactive All MPL Data Messages within the Buffered Message Set MUST have a
propagation as receiving an MPL multicast packet that has the same sequence number greater than or equal to MinSequence for the
MPL seed identifier, the M flag set, and has a sequence number corresponding SeedID. When increasing MinSequence for an MPL Seed,
less than the buffered MPL multicast packet's sequence number. the MPL Forwarder MUST delete any MPL Data Messages from the Buffered
Message Set that have sequence numbers less than MinSequence.
o This document does not define any external "events". 8. MPL Domains
o This document defines both MPL multicast packets and ICMPv6 MPL An MPL Domain is a scope zone, as defined in [RFC4007], in which MPL
multicast packets as Trickle messages. These messages are defined Interfaces subscribe to the same MPL Domain Address and participate
in the sections below. in disseminating MPL Data Messages.
o The actions outside the Trickle algorithm that the protocol takes By default, an MPL Forwarder MUST participate in an MPL Domain
involve managing sliding window state, and is specified in identified by the ALL_MPL_FORWARDERS multicast address with a scope
Section 5.2. value of 3 (subnet-local).
5.1.3. Reactive Propagation An MPL Forwarder MAY participate in additional MPL Domains identified
by other multicast addresses. An MPL Interface MUST subscribe to the
MPL Domain Addresses for the MPL Domains that it participates in.
The allocation of other multicast addresses is out of scope.
With reactive propagation, the MPL forwarder transmits ICMPv6 MPL For each MPL Domain Address that an MPL Interface subscribes to, the
messages using the Trickle algorithm. A MPL forwarder maintains a MPL Interface MUST also subscribe to the same MPL Domain Address with
single Trickle timer for reactive propagation with each MPL domain. a scope value of 2 (link-local) when reactive forwarding is in use
When REACTIVE_TIMER_EXPIRATIONS is 0, the MPL forwarder does not (i.e. when communicating MPL Control Messages).
execute the Trickle algorithm for reactive propagation and reactive
propagation is disabled. Adhering to Section 5 of RFC 6206
[RFC6206], this document defines the following:
o This document defines a "consistent" transmission for reactive 9. MPL Seed Sequence Numbers
propagation as receiving an ICMPv6 MPL message that indicates
neither the receiving nor transmitting node has new MPL multicast
packets to offer.
o This document defines an "inconsistent" transmission for reactive Each MPL Seed maintains a sequence number for each MPL Domain that it
propagation as receiving an ICMPv6 MPL message that indicates serves. The sequence numbers are included in MPL Data Messages
either the receiving or transmitting node has at least one new MPL generated by the MPL Seed. The MPL Seed MUST increment the sequence
multicast packet to offer. number for each MPL Data Message that it generates for an MPL Domain.
Implementations MUST follow the Serial Number Arithmetic as defined
in [RFC1982] when incrementing a sequence value or comparing two
sequence values. This sequence number is used to establish a total
ordering of MPL Data Messages generated by an MPL Seed for an MPL
Domain.
o This document defines an "event" for reactive propagation as 10. MPL Data Messages
updating any sliding window (i.e. changing the value of WindowMin,
WindowMax, or the set of buffered MPL multicast packets) in
response to receiving an MPL multicast packet.
o This document defines both MPL multicast packets and ICMPv6 MPL 10.1. MPL Data Message Generation
multicast packets as Trickle messages. These messages are defined
in the sections below.
o The actions outside the Trickle algorithm that the protocol takes MPL Data Messages are generated by MPL Seeds when they enter the MPL
involve managing sliding window state, and is specified in Domain. All MPL Data messages have the following properties:
Section 5.2.
5.2. Sliding Windows o The IPv6 Source Address MUST be an address in the AddressSet of a
corresponding MPL Interface and MUST be valid within the MPL
Domain.
Every MPL forwarder MUST maintain a sliding window of sequence o The IPv6 Destination Address MUST be set to the MPL Domain Address
numbers for each MPL seed of recently received MPL packets. The corresponding to the MPL Domain.
sliding window performs two functions:
1. Indicate what MPL multicast packets the MPL forwarder should o A MPL Data Message MUST contain an MPL Option in its IPv6 Header
accept. to identify the MPL Seed that generated the message and the
ordering relative to other MPL Data Messages generated by the MPL
Seed.
2. Indicate what MPL multicast packets are buffered and may be When the source address is in the AddressList of an MPL Interface
transmitted to neighboring MPL forwarders. corresponding to the MPL Domain Address and the destination address
is the MPL Domain Address, the application message and the MPL Data
Message MAY be identical. In other words, the MPL Data Message may
contain a single IPv6 header that includes the MPL Option.
Each sliding window logically consists of: Otherwise, IPv6-in-IPv6 encapsulation MUST be used to satisfy the MPL
Data Message requirements listed above [RFC2473]. The complete IPv6-
in-IPv6 message forms an MPL Data Message. The outer IPv6 header
conforms to the MPL Data Message requirements listed above. The
encapsulated IPv6 datagram encodes the multicast data message that is
communicated beyond the MPL Domain.
1. A lower-bound sequence number, WindowMin, that represents the 10.2. MPL Data Message Transmission
sequence number of the oldest MPL multicast packet the MPL
forwarder is willing to receive or has buffered. An MPL
forwarder MUST ignore any MPL multicast packet that has sequence
value less than than WindowMin.
2. An upper-bound sequence value, WindowMax, that represents the An MPL Forwarder manages transmission of MPL Data Messages in the
sequence number of the next MPL multicast packet that the MPL Buffered Message set using the Trickle algorithm [RFC6206]. An MPL
forwarder expects to receive. An MPL forwarder MUST accept any Forwarder MUST use a separate Trickle timer for each MPL Data Message
MPL multicast packet that has sequence number greater than or that it is actively forwarding. In accordance with Section 5 of RFC
equal to WindowMax. 6206 [RFC6206], this document defines the following:
3. A list of MPL multicast packets, BufferedPackets, buffered by the o This document defines a "consistent" transmission as receiving an
MPL forwarder. Each entry in BufferedPackets MUST have a MPL Data Message that has the same seed-id and sequence value as
sequence number in the range [WindowMin, WindowMax). the MPL Data Message managed by the Trickle timer.
4. A timer, HoldTimer, that indicates the minimum lifetime of the o This document defines an "inconsistent" transmission as receiving
sliding window. The MPL forwarder MUST NOT free a sliding window an MPL Data Message that has the same seed-id value and the M flag
before HoldTimer expires. set, but has a sequence value less than MPL Data Message managed
by the Trickle timer.
When receiving an MPL multicast packet, if no existing sliding window o This document does not define any external "events".
exists for the MPL seed, the MPL forwarder MUST create a new sliding
window before accepting the MPL multicast packet. The MPL forwarder
may reclaim memory resources by freeing a sliding window for another
MPL seed if its HoldTimer has expired. If, for any reason, the MPL
forwarder cannot create a new sliding window, it MUST discard the
packet.
If a sliding window exists for the MPL seed, the MPL forwarder MUST o This document defines MPL Data Messages as Trickle messages.
ignore the MPL multicast packet if the packet's sequence number is
less than WindowMin or appears in BufferedPackets. Otherwise, the
MPL forwarder MUST accept the packet and determine whether or not to
forward the packet and/or pass the packet to the next higher layer.
When accepting an MPL multicast packet, the MPL forwarder MUST update o The actions outside the Trickle algorithm that the protocol takes
the sliding window based on the packet's sequence number. If the involve managing Seed Set and Buffered Message Set
sequence number is not less than WindowMax, the MPL forwarder MUST
set WindowMax to 1 greater than the packet's sequence number. If
WindowMax - WindowMin > MPL_MAX_WINDOW_SIZE, the MPL forwarder MUST
increment WindowMin such that WindowMax - WindowMin <=
MPL_MAX_WINDOW_SIZE. At the same time, the MPL forwarder MUST free
any entries in BufferedPackets that have a sequence number less than
WindowMin.
If the MPL forwarder has available memory resources, it MUST buffer As specified in [RFC6206], a Trickle timer has three variables: the
the MPL multicast packet for proactive propagation. If not enough current interval size I, a time within the current interval t, and a
memory resources are available to buffer the packet, the MPL counter c. MPL defines a fourth variable, e, which counts the number
forwarder MUST increment WindowMin and free entries in of Trickle timer expiration events since the Trickle timer was last
BufferedPackets that have a sequence number less than WindowMin until reset.
enough memory resources are available. Incrementing WindowMin will
ensure that the MPL forwarder does not accept previously received
packets.
An MPL forwarder MAY reclaim memory resources from sliding windows After DATA_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, the MPL
for other MPL seeds. If a sliding window for another MPL seed is Forwarder MUST disable the Trickle timer. When a buffered MPL Data
actively disseminating messages and has more than one entry in its Message does not have an associated Trickle timer, the MPL Forwarder
BufferedPackets, the MPL forwarder may free entries for that MPL seed MAY delete the message from the Buffered Message Set by advancing
by incrementing WindowMin as described above. MinSequence of the corresponding MPL Seed in the Seed Set. When the
MPL Forwarder no longer buffers any messages for an MPL Seed, the MPL
Forwarder MUST NOT increment MinSequence for that MPL Seed.
If the MPL forwarder cannot free enough memory resources to buffer When transmitting an MPL Data Message, the MPL Forwarder MUST either
the MPL multicast packet, the MPL forwarder MUST set WindowMin to 1 set the M flag to zero or set it to a level that indicates whether or
greater than the packet's sequence number. not the message's sequence number is the largest value that has been
received from the MPL Seed.
When memory resources are available, an MPL forwarder SHOULD buffer a 10.3. MPL Data Message Processing
MPL multicast packet until the proactive propagation completes (i.e.
the Trickle algorithm stops execution) and MAY buffer for longer.
After proactive propagation completes, the MPL forwarder may advance
WindowMin to the packet's sequence number to reclaim memory
resources. When the MPL forwarder no longer buffers any packets, it
MAY set WindowMin equal to WindowMax. When setting WindowMin equal
to WindowMax, the MPL forwarder MUST initialize HoldTimer to
WINDOW_HOLD_TIME and start HoldTimer. After HoldTimer expires, the
MPL forwarder MAY free the sliding window to reclaim memory
resources.
5.3. Transmission of MPL Multicast Packets Upon receiving an MPL Data Message, the MPL Forwarder first processes
the MPL Option and updates the Trickle timer associated with the MPL
Data Message if one exists.
The MPL forwarder manages buffered MPL multicast packet transmissions Upon receiving an MPL Data Message, an MPL Forwarder MUST perform one
using the Trickle algorithm. When adding a packet to of the following actions:
BufferedPackets, the MPL forwarder MUST create a Trickle timer for
the packet and start execution of the Trickle algorithm.
After PROACTIVE_TIMER_EXPIRATIONS Trickle timer events, the MPL o Accept the message and enter the MPL Data Message in the Buffered
forwarder MUST stop executing the Trickle algorithm. When a buffered Message Set.
MPL multicast packet does not have an active Trickle timer, the MPL
forwarder MAY free the buffered packet by advancing WindowMin to 1
greater than the packet's sequence number.
Each interface that supports MPL is configured with exactly one MPL o Accept the message and update the corresponding MinSequence in the
multicast scope. The MPL multicast scope MUST be site-local or Seed Set to 1 greater than the message's sequence number.
smaller and defaults to link-local. A scope larger than link-local
MAY be used only when that scope corresponds exactly to the MPL
domain.
An MPL domain may therefore be composed of one or more MPL multicast o Discard the message without any change to the MPL Information
scopes. For example, the MPL domain may be composed of a single MPL Base.
multicast scope when using a site-local scope. Alternatively, the
MPL domain may be composed of multiple MPL multicast scopes when
using a link-local scope.
IPv6-in-IPv6 encapsulation MUST be used when using MPL to forward an If a Seed Set entry exists for the MPL Seed, the MPL Forwarder MUST
original multicast packet whose source or destination address is discard the MPL Data Message if its sequence number is less than
outside the MPL multicast scope. IPv6-in-IPv6 encapsulation is MinSequence or exists in the Buffered Message Set.
necessary to support Path MTU discovery when the MPL forwarder is not
the source of the original multicast packet. IPv6-in-IPv6
encapsulation also allows an MPL forwarder to remove the MPL Option
when forwarding the original multicast packet over a link that does
not support MPL. The destination address scope for the outer IPv6
header MUST be the MPL multicast scope.
When an MPL domain is composed of multiple MPL multicast scopes (e.g. If a Seed Set entry does not exist for the MPL Seed, the MPL
when the MPL multicast scope is link-local), an MPL forwarder MUST Forwarder MUST create a new entry for the MPL Seed before accepting
decapsulate and encapsulate the original multicast packet when the MPL Data Message.
crossing between different MPL multicast scopes. In doing so, the
MPL forwarder MUST duplicate the MPL Option, unmodified, in the new
outer IPv6 header.
The IPv6 destination address of the MPL multicast packet is the all- If memory is limited, an MPL Forwarder SHOULD reclaim memory
MPL-forwarders multicast address (TBD). The scope of the IPv6 resources by:
destination address is set to the MPL multicast scope.
5.4. Reception of MPL Multicast Packets o Incrementing MinSequence entries in the Seed Set and deleting MPL
Data Messages in the Buffered Message Set that fall below the
corresponding MinSequence value.
Upon receiving an MPL multicast packet, the MPL forwarder first o Deleting other Seed Set entries that have expired and the
determines whether or not to accept and buffer the MPL multicast corresponding MPL Data Messages in the Buffered Message Set.
packet based on its MPL seed and sequence value, as specified in
Section 5.2.
If the MPL forwarder accepts the MPL multicast packet, the MPL If the MPL Forwarder accepts the MPL Data Message, the MPL Forwarder
forwarder determines whether or not to deliver the original multicast MUST perform the following actions:
packet to the next higher layer. For example, if the MPL multicast
packet uses IPv6-in-IPv6 encapsulation, the MPL forwarder removes the
outer IPv6 header, which also removes MPL Option.
5.5. Transmission of ICMPv6 MPL Messages o If PROACTIVE_PROPAGATION is true, the MPL Forwarder MUST
initialize and start a Trickle timer for the MPL Data Message.
The MPL forwarder generates and transmits a new ICMPv6 MPL message o If the MPL Control Message Trickle timer is not running and
whenever Trickle requests a transmission. The MPL forwarder includes CONTROL_MESSAGE_TIMER_EXPIRATIONS is non-zero, the MPL Forwarder
an encoding of each sliding window in the ICMPv6 MPL message. MUST initialize and start the MPL Control Message Trickle timer.
Each sliding window is encoded using an MPL Window entry, defined in o If the MPL Control Message Trickle timer is running, the MPL
Section 5.2. The MPL forwarder sets the MPL Window fields as Forwarder MUST reset the MPL Control Message Trickle timer.
follows:
S If the MPL seed identifier is 0, set S to 0. If the MPL seed 11. MPL Control Messages
identifier is within the range [1, 65535], set S to 2. Otherwise,
set S to 3.
w-min Set to the lower bound of the sliding window (i.e. 11.1. MPL Control Message Generation
WindowMin).
w-len Set to the length of the window (i.e. WindowMax - WindowMin). An MPL Forwarder generates MPL Control Messages to communicate its
Seed Set and Buffered Message Set to neighboring MPL Forwarders.
Each MPL Control Message is generated according to Section 6.2, with
an MPL Seed Info for each entry in Seed Set. Each MPL Seed Info entry
has the following content:
seed-id If S is non-zero, set to the MPL seed identifier. o S set to the size of the seed-id field in the MPL Seed Info entry.
buffered-mpl-packets Set each bit that represents a sequence number o min-seqno set to MinSequence of the MPL Seed.
of a packet in BufferedPackets to 1. Set all other bits to 0.
The i'th bit in buffered-mpl-packets represents a sequence number
of w-min + i.
5.6. Reception of ICMPv6 MPL Messages o bm-len set to the size of buffered-mpl-messages in octets.
An MPL forwarder processes each ICMPv6 MPL message that it receives o seed-id set to the MPL seed identifier.
to determine if it has any new MPL multicast packets to receive or
offer.
An MPL forwarder determines if a new MPL multicast packet has not o buffered-mpl-messages with each bit representing whether or not an
been received from a neighboring node if any of the following MPL Data Message with the corresponding sequence number exists in
conditions hold true: the Buffered Message Set. The i'th bit represents a sequence
number of min-seqno + i. '0' indicates that the corresponding MPL
Data Message does not exist in the Buffered Message Set. '1'
indicates that the corresponding MPL Data Message does exist in
the Buffered Message Set.
1. The ICMPv6 MPL message includes an MPL Window for an MPL seed 11.2. MPL Control Message Transmission
that does not have a corresponding sliding window entry on the
MPL forwarder.
2. The neighbor has a packet in its BufferedPackets that has An MPL Forwarder transmits MPL Control Messages using the Trickle
sequence value greater than or equal to WindowMax (i.e. w-min + algorithm. A MPL forwarder maintains a single Trickle timer for each
w-len >= WindowMax). MPL Domain. When CONTROL_MESSAGE_TIMER_EXPIRATIONS is 0, the MPL
Forwarder does not execute the Trickle algorithm and does not
transmit MPL Control Messages. In accordance with Section 5 of RFC
6206 [RFC6206], this document defines the following:
3. The neighbor has a packet in its BufferedPackets that has o This document defines a "consistent" transmission as receiving an
sequence number within range of the sliding window but is not MPL Control Message that indicates neither the receiving nor
included in BufferedPackets (i.e. the i'th bit in buffered-mpl- transmitting node has new MPL Data Message.
packets is set to 1, where the sequence number is w-min + i).
When an MPL forwarder determines that it has not yet received a new o This document defines an "inconsistent" transmission as receiving
MPL multicast packet buffered by a neighboring device, the MPL an MPL Control Message that indicates either the receiving or
forwarder resets the Trickle timer associated with reactive transmitting node has at least one new MPL Data Message to offer.
propagation.
An MPL forwarder determines if an entry in BufferedPackets has not o This document defines an "event" as increasing MinSequence of any
been received by a neighboring MPL forwarder if any of the following entry in the Seed Set or adding a message to the Buffered Message
conditions hold true: Set.
1. The ICMPv6 MPL message does not include an MPL Window for the o This document defines an MPL Control Message as a Trickle message.
packet's MPL seed.
2. The packet's sequence number is greater than or equal to the As specified in [RFC6206], a Trickle timer has three variables: the
neighbor's WindowMax value (i.e. the packet's sequence number is current interval size I, a time within the current interval t, and a
greater than or equal to w-min + w-len). counter c. MPL defines a fourth variable, e, which counts the number
of Trickle timer expiration events since the Trickle timer was last
reset. After CONTROL_MESSAGE_TIMER_EXPIRATIONS Trickle timer events,
the MPL Forwarder MUST disable the Trickle timer.
3. The packet's sequence number is within the range of the 11.3. MPL Control Message Processing
neighbor's sliding window [WindowMin, WindowMax), but not
included in the neighbor's BufferedPacket (i.e. the packet's
sequence number is greater than or equal to w-min, strictly less
than w-min + w-len, and the corresponding bit in buffered-mpl-
packets is set to 0.
When an MPL forwarder determines that it has at least one buffered An MPL Forwarder processes each MPL Control Message that it receives
MPL multicast packet that has not yet been received by a neighbor, to determine if it has any new MPL Data Messages to receive or offer.
the MPL forwarder resets the Trickle timer associated with reactive
propagation. Additionally, for each buffered MPL multicast packet
that should be transferred, the MPL forwarder MUST reset the Trickle
timer and reset e to 0 for proactive propagation. If the Trickle
timer for proactive propagation has already stopped execution, the
MPL forwarder MUST initialize a new Trickle timer and start execution
of the Trickle algorithm.
6. MPL Parameters An MPL Forwarder determines if a new MPL Data Message has not been
received from a neighboring node if any of the following conditions
hold true:
An MPL forwarder maintains two sets of Trickle parameters for the o The MPL Control Message includes an MPL Seed that does not exist
proactive and reactive methods. The Trickle parameters are listed in the Seed Set.
below:
PROACTIVE_IMIN The minimum Trickle timer interval, as defined in o The MPL Control Message indicates that the neighbor has an MPL
[RFC6206] for proactive propagation. Data Message in its Buffered Message Set with sequence number
greater than MinSequence (i.e. the i-th bit is set to 1 and min-
seqno + i > MinSequence) and is not included in the MPL
Forwarder's Buffered Message Set.
PROACTIVE_IMAX The maximum Trickle timer interval, as defined in When an MPL Forwarder determines that it has not yet received an MPL
[RFC6206] for proactive propagation. Data Message buffered by a neighboring device, the MPL Forwarder MUST
reset its Trickle timer associated with MPL Control Message
transmissions. If an MPL Control Message Trickle timer is not
running, the MPL Forwarder MUST initialize and start a new Trickle
timer.
PROACTIVE_K The redundancy constant, as defined in [RFC6206] for An MPL Forwarder determines if an MPL Data Message in the Buffered
proactive propagation. Message Set has not yet been received by a neighboring MPL Forwarder
if any of the following conditions hold true:
PROACTIVE_TIMER_EXPIRATIONS The number of Trickle timer expirations o The MPL Control Message does not include an MPL Seed for the MPL
that occur before terminating the Trickle algorithm. MUST be set Data Message.
to a value greater than 0.
REACTIVE_IMIN The minimum Trickle timer interval, as defined in o The MPL Data Message's sequence number is greater than or equal to
[RFC6206] for reactive propagation. min-seqno and not included in the neighbor's Buffered Message Set
(i.e. the MPL Data Message's sequence number does not have a
corresponding bit in buffered-mpl-messages set to 1).
REACTIVE_IMAX The maximum Trickle timer interval, as defined in When an MPL Forwarder determines that it has at least one MPL Data
[RFC6206] for reactive propagation. Message in its Buffered Message Set that has not yet been received by
a neighbor, the MPL Forwarder MUST reset the MPL Control Message
Trickle timer. Additionally, for each of those entries in the
Buffered Message Set, the MPL Forwarder MUST reset the Trickle timer
and reset e to 0. If a Trickle timer is not associated with the MPL
Data Message, the MPL Forwarder MUST initialize and start a new
Trickle timer.
REACTIVE_K The redundancy constant, as defined in [RFC6206] for 12. Acknowledgements
reactive propagation.
REACTIVE_TIMER_EXPIRATIONS The number of Trickle timer expirations The authors would like to acknowledge the helpful comments of Robert
that occur before terminating the Trickle algorithm. MAY be set Cragie, Esko Dijk, Ralph Droms, Paul Duffy, Ulrich Herberg, Owen
to 0, which disables reactive propagation. Kirby, Joseph Reddy, Don Sturek, Dario Tedeschi, and Peter van der
Stok, which greatly improved the document.
WINDOW_HOLD_TIME The minimum lifetime for sliding window state. 13. IANA Considerations
7. Acknowledgements This document defines one IPv6 Option, a type that must be allocated
from the IPv6 "Destination Options and Hop-by-Hop Options" registry
of [RFC2780].
The authors would like to acknowledge the helpful comments of Robert This document defines one ICMPv6 Message, a type that must be
Cragie, Esko Dijk, Ralph Droms, Paul Duffy, Owen Kirby, Joseph Reddy, allocated from the "ICMPv6 "type" Numbers" registry of [RFC4443].
Dario Tedeschi, and Peter van der Stok, which greatly improved the
document.
8. IANA Considerations This document registers two well-known multicast addresses from the
IPv6 multicast address space.
The Trickle Multicast option requires an IPv6 Option Number. 13.1. MPL Option Type
HEX act chg rest IANA is requested to allocate an IPv6 Option Type from the IPv6
--- --- --- ----- "Destination Options and Hop-by-Hop Options" registry of [RFC2780],
C 01 0 TBD as specified in Table 1 below:
The first two bits indicate that the IPv6 node MUST discard the +--------------+-----+-----+--------------+-------------+-----------+
packet if it doesn't recognize the option type, and the third bit | Mnemonic | act | chg | rest | Description | Reference |
indicates that the Option Data MUST NOT change en-route. +--------------+-----+-----+--------------+-------------+-----------+
| MPL_OPT_TYPE | 01 | 1 | TBD | MPL Option | This |
| | | | (suggested | | Document |
| | | | value 01101) | | |
+--------------+-----+-----+--------------+-------------+-----------+
9. Security Considerations Table 1: IPv6 Option Type Allocation
TODO. 13.2. MPL ICMPv6 Type
10. References IANA is requested to allocate an ICMPv6 Type from the "ICMPv6 "type"
Numbers" registry of [RFC4443], as specified in Table 2 below:
10.1. Normative References +---------------+------+---------------------+---------------+
| Mnemonic | Type | Name | Reference |
+---------------+------+---------------------+---------------+
| MPL_ICMP_TYPE | TBD | MPL Control Message | This Document |
+---------------+------+---------------------+---------------+
Table 2: IPv6 Option Type Allocation
13.3. Well-known Multicast Addresses
IANA is requested to allocate an IPv6 multicast address
"ALL_MPL_FORWARDERS" from the "Variable Scope Multicast Addresses"
sub-registry of the "INTERNET PROTOCOL VERSION 6 MULTICAST ADDRESSES"
registry.
14. Security Considerations
MPL uses sequence numbers to maintain a total ordering of MPL Data
Messages from an MPL Seed. The use of sequence numbers allows a
denial-of-service attack where an attacker can spoof a message with a
sufficiently large sequence number to: (i) flush messages from the
Buffered Message List and (ii) increase the MinSequence value for an
MPL Seed in the Seed Set. The former side effect allows an attacker
to halt the forwarding process of any MPL Data Messages being
disseminated. The latter side effect allows an attacker to prevent
MPL Forwarders from accepting new MPL Data Messages that an MPL Seed
generates while the sequence number is less than MinSequence.
More generally, the basic ability to inject messages into a Low-power
and Lossy Network can be used as a denial-of-service attack
regardless of what forwarding protocol is used. For these reasons,
Low-power and Lossy Networks typically employ link-layer security
mechanisms to disable an attacker's ability to inject messages.
To prevent attackers from injecting packets through an MPL Forwarder,
the MPL Forwarder MUST NOT accept or forward MPL Data Messages from a
communication interface that does not subscribe to the MPL Domain
Address identified in message's destination address.
MPL uses the Trickle algorithm to manage message transmissions and
the security considerations described in [RFC6206] apply.
15. 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. August 1996.
[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, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[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, December 1998.
[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, December 1998.
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers",
BCP 37, RFC 2780, March 2000.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
March 2005.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006. Version 6 (IPv6) Specification", RFC 4443, March 2006.
[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, March 2011.
[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., [RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
Lossy Networks", RFC 6550, March 2012. Lossy Networks", RFC 6550, March 2012.
10.2. Informative References
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-06 (work in
progress), September 2011.
Authors' Addresses Authors' Addresses
Jonathan W. Hui Jonathan W. Hui
Cisco Cisco
170 West Tasman Drive 170 West Tasman Drive
San Jose, California 95134 San Jose, California 95134
USA USA
Phone: +408 424 1547 Phone: +408 424 1547
Email: jonhui@cisco.com Email: jonhui@cisco.com
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