wdiff draft-ietf-roll-trickle-mcast-02.txt draft-ietf-roll-trickle-mcast-03.txt

ROLL J. Hui
Internet-Draft Cisco
Intended status: Standards Track R. Kelsey
Expires: April 22, July 28, 2013 Silicon Labs
October 19, 2012
January 24, 2013

Multicast Protocol for Low power and Lossy Networks (MPL)
draft-ietf-roll-trickle-mcast-02
draft-ietf-roll-trickle-mcast-03

Abstract

This document specifies the Multicast Protocol for Low power and
Lossy Networks (MPL) that provides IPv6 multicast forwarding in
constrained networks. MPL avoids the need to construct or maintain
any multicast forwarding topology, disseminating messages to all MPL
forwarders in an MPL domain. MPL uses the Trickle algorithm to drive
packet
manage message transmissions for both control and data-plane packets.
Specific
messages. Different Trickle parameter configurations allow MPL to
trade between dissemination latency and transmission efficiency.

Status of this Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on April 22, July 28, 2013.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 5
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Information Base Overview . . . . . 5
4. Message Formats . . . . . . . . . . . 6
4.2. Overview . . . . . . . . . . . . . . . . . . . 7
4.1. MPL Option . . . . . . 6
4.3. Signaling Overview . . . . . . . . . . . . . . . . . . . . 7
4.2. ICMPv6
5. MPL Message Constants . . . . . . . . . . . . . . . . . . . . 8
4.2.1. MPL Window . . . . 9
5.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 9
5.
5.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 9
5.3. MPL Forwarder Behavior Parameters . . . . . . . . . . . . . . . . . 9
5.4. Trickle Parameters . . . . . . . . . . . . . . . . . . . . 9
6. Protocol Message Formats . . . . . 11
5.1. Multicast Packet Dissemination . . . . . . . . . . . . . . 11
5.1.1. Trickle Parameters and Variables
6.1. MPL Option . . . . . . . . . . . 12
5.1.2. Proactive Propagation . . . . . . . . . . . . . 11
6.2. MPL Control Message . . . 12
5.1.3. Reactive Propagation . . . . . . . . . . . . . . . . 12
6.3. MPL Seed Info . 13
5.2. Sliding Windows . . . . . . . . . . . . . . . . . . . . . 13
5.3. Transmission of MPL Multicast Packets
7. Information Base . . . . . . . . . . . . . . . . . . . . . . . 15
5.4. Reception of MPL Multicast Packets
7.1. Local Interface Set . . . . . . . . . . . . 16
5.5. Transmission of ICMPv6 MPL Messages . . . . . . . 15
7.2. Domain Set . . . . 16
5.6. Reception of ICMPv6 MPL Messages . . . . . . . . . . . . . 17
6. MPL Parameters . . . . . . . 15
7.3. Seed Set . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . 15
7.4. Buffered Message Set . . . . . . . . . . . . . . . . 20 . . . 15
8. IANA Considerations MPL Domains . . . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . 17
9. MPL Seed Sequence Numbers . . . . . . . . . . . . . . . . . 22 . 18
10. References MPL Data Messages . . . . . . . . . . . . . . . . . . . . . . 19
10.1. MPL Data Message Generation . . . . 23
10.1. Normative References . . . . . . . . . . . 19
10.2. MPL Data Message Transmission . . . . . . . . 23
10.2. Informative References . . . . . . 19
10.3. MPL Data Message Processing . . . . . . . . . . . . 23
Authors' Addresses . . . 20
11. MPL Control Messages . . . . . . . . . . . . . . . . . . . . . 24

1. Introduction

Low power and Lossy Networks typically operate with strict resource
constraints in 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

Low power and Lossy Networks typically operate with strict resource
constraints in communication, computation, memory, and energy. Such
resource constraints may preclude the use of existing IPv6 multicast
topology
routing and forwarding mechanisms. Traditional IP multicast
forwarding delivery
typically relies on topology maintenance mechanisms to
forward multicast messages discover and
maintain routes to all subscribers of a multicast group. However,
maintaining such topologies in LLNs is costly and may not be feasible
given the available resources.

Memory constraints may limit devices to maintaining links/routes to
one or a few neighbors. For this reason, the Routing Protocol for
LLNs (RPL) specifies both storing and non-storing modes [RFC6550].
The latter allows RPL routers to maintain only one or a few default
routes towards a LLN Border Router (LBR) and use source routing to
forward packets messages away from the LBR. For the same reasons, a LLN
device may not be able to maintain a multicast forwarding routing topology when
operating with limited memory.

Furthermore, the dynamic properties of wireless networks can make the
cost of maintaining a multicast forwarding routing topology prohibitively
expensive. In wireless environments, topology maintenance may
involve selecting a connected dominating set used to forward
multicast messages to all nodes in an administrative domain.
However, existing mechanisms often require two-hop topology
information and the cost of maintaining such information grows
polynomially with network density.

This document specifies the Multicast Protocol for Low power and
Lossy Networks (MPL), which provides IPv6 multicast forwarding in
constrained networks. MPL avoids the need to construct or maintain
any multicast forwarding routing topology, disseminating multicast messages to
all MPL forwarders in an MPL domain. By using the Trickle algorithm
[RFC6206], MPL requires only small, constant state for each MPL
device that initiates disseminations. The Trickle algorithm also
allows MPL to be density-aware, allowing the communication rate to
scale logarithmically with density.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC 2119
[RFC2119].

The following terms are used throughout this document:

MPL forwarder An IPv6 Forwarder - A router that subscribes implements this protocol. A MPL
Forwarder is equipped with at least one MPL
Interface.

MPL Interface - An MPL Forwarder's attachment to the a
communications medium, over which it transmits
and receives MPL
multicast group Data Messages and participates in disseminating MPL multicast packets. Control
Messages according to this specification. An MPL multicast scope The multicast scope that
Interface is assigned one or more unicast
addresses and is subscribed to one or more MPL uses when forwarding
Domain Addresses.

MPL multicast packets. In other words, the
multicast scope of the IPv6 Destination Domain Address
of an MPL multicast packet.

MPL domain - A connected set of MPL forwarders multicast address that define the
extent of identifies the MPL dissemination process. As a
form set of flood, all
MPL forwarders in Interfaces within an MPL
domain will receive MPL multicast packets. The Domain. MPL domain MUST be composed of at least one Data
Messages disseminated in an MPL
multicast scope and MAY be composed of multiple Domain have the
associated MPL multicast scopes. Domain Address as their
destination address.

MPL seed Domain - A scope zone, as defined in [RFC4007], in which
MPL forwarder that begins the dissemination
process for an MPL multicast packet. The MPL
seed may be different than the source of Interfaces subscribe to the
original multicast packet. same MPL seed identifier An identifier that uniquely identifies an Domain
Address and participate in disseminating MPL
forwarder within its Data
Messages.

MPL domain.

original multicast packet An IPv6 Data Message - A multicast packet message that is
disseminated using MPL.

MPL multicast packet An IPv6 multicast packet that contains an MPL
Hop-by-Hop Option. When either source or
destinations are beyond the MPL used to communicate
a multicast scope,
the payload between MPL multicast packet is an IPv6-in-IPv6
packet that Forwarders and
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 header. A MPL multicast scope,
Data Message has its destination address set to
the MPL Hop-by-Hop Option may be included
directly within the original multicast packet.

3. Overview Domain Address.

MPL delivers IPv6 Control Message - A link-local multicast packets by disseminating them message that is used to all
communicate information about recently received
MPL
forwarders within an Data Messages to neighboring MPL domain. Forwarders.

MPL dissemination is a form of
flood. Seed - An MPL forwarder may broadcast/multicast Forwarder that generates MPL Data
Messages and serves as an entry point into an MPL
Domain.

3. Applicability Statement

This protocol is an IPv6 multicast
packet out of forwarding protocol for Low-Power
and Lossy Networks. By implementing a controlled dissemination using
the same physical interface on which it was received.
Using link-layer broadcast/multicast allows Trickle algorithm, this protocol is designed for networks that
communicate using low-power and lossy links with widely varying
topologies in both the space and time dimensions.

4. Protocol Overview

The goal of MPL is to forward multicast
packets without explicitly identifying next-hop destinations. An MPL
forwarder may also broadcast/multicast MPL deliver multicast packets out
other messages to all interfaces
that subscribe 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
as an MPL seed for messages' destination address within
an original multicast packet. The MPL seed may or
may not be Domain.

4.1. Information Base Overview

A node records necessary protocol state in the same device as following information
sets:

o The Local Interface Set records the source set of the original multicast
packet. When the original multicast packet's source is outside the
LLN, the local MPL seed may be the ingress router. Even if an original
multicast packet source is within the LLN, the source may first
forward Interfaces
and the multicast packet unicast addresses assigned to the MPL seed using IPv6-in-IPv6
tunneling. Because those MPL state requirements grows with Interfaces.

o The Domain Set records the number set of
active MPL seeds, limiting Domain Addresses and the number of
local MPL seeds reduces the amount
of state Interfaces that subscribe to those addresses.

o The Seed Set records information about received MPL forwarders must maintain.

Because MPL typically broadcasts/multicasts Data Messages
received from an MPL packets out of Seed. The Seed Set maintains the minimum
sequence number that the
same interface on which they were received, MPL forwarders are likely 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 multicast packet more than once. Data
Message, process its payload, and retransmit it.

o The Buffered Message Set records recently received MPL seed tags
each original multicast packet with Data
Messages from an MPL seed identifier and a
sequence number. The Seed. MPL Data Messages resident in the
Buffered Message Set have sequence number provides a total ordering of numbers that are greater than
or equal to the minimum threshold maintained in the Seed Set. MPL multicast packets disseminated
uses the Buffered Message Set to store MPL Data Messages that may
be transmitted by the MPL seed. Forwarder for forwarding.

4.2. Overview

MPL defines achieves its goal by implementing a new IPv6 Hop-by-Hop Option, controlled flood that
attempts to disseminate the MPL Option, multicast data message to include
MPL-specific information along with all interfaces
within an MPL Domain. MPL performs the original following tasks to
disseminate a multicast packet.
Each IPv6 message:

o When having a multicast packet that message to forward into an MPL disseminates Domain, the
MPL Seed generates an MPL Data Message that includes the MPL
Option. Because Seed
Identifier, a newly generated sequence number, and the original multicast packet's source and
message. If the MPL
seed may multicast destination address is not be the same device, the MPL Option may be added to the
original multicast packet en-route. To allow Path MTU discovery
Domain Address, IP-in-IP [RFC2473] is used to
work properly, MPL encapsulates encapsulate the original
multicast packet message in
another IPv6 header that includes the MPL Option. Data Message.

o Upon receiving a new an MPL multicast packet for forwarding, Data Message, the MPL
forwarder may proactively transmit Forwarder extracts the
MPL multicast packet packet a
limited Seed and sequence number of times and then falls back into an optional reactive
mode. In maintenance mode, an determines whether or not the MPL forwarder buffers recently
Data Message was previously received MPL multicast packets using the Seed Set and advertises
Buffered Message Set.

* If the sequence number is less than the lower-bound sequence
number maintained in the Seed Set or a summary of recently 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 multicast packets from time to time, allowing
neighboring Data Message, an MPL forwarders 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 determine if they have any new forward the message.

o Each MPL Forwarder may periodically link-local multicast packets MPL
Control Messages on MPL Interfaces to offer or receive. communicate information
contained in the MPL forwarders schedule their packet (control Forwarder's Seed Set and data) transmissions
using the Trickle algorithm [RFC6206]. Trickle's adaptive
transmission interval allows Buffered Message
Sets.

o Upon receiving an MPL to quickly disseminate messages when Control Message, an MPL Forwarder determines
whether there are any new MPL multicast packets, but reduces transmission
overhead as Data Messages that have yet to be
received by the dissemination process completes. Trickle's
suppression mechanism MPL Control Message's source and transmission time selection allow multicasts those
MPL Data Messages.

MPL's
communication rate 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 scale logarithmically with density.

4. receive the message. After transmitting the MPL Data
Message Formats

4.1. a limited number of times, the MPL Option

The forwarder may terminate
proactive forwarding for the MPL Option is carried in Data Message message.

Reactive Forwarding - With reactive forwarding, an IPv6 Hop-by-Hop Options header,
immediately following the IPv6 header. The MPL Option has Forwarder
link-local multicasts MPL Control Messages using the
following format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Trickle
algorithm [RFC6206]. MPL Forwarders use MPL Control Messages to
discover new MPL Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S |M| rsv | sequence | seed-id (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option Type XX (to be confirmed by IANA).

Opt Messages that have not yet been received.
When discovering that a neighboring MPL Forwarder has not yet
received a new MPL Data Len Length of Message, the Option MPL Forwarder schedules those
MPL Data field in octets. MUST
be set to either 2 or 4.

S 2-bit unsigned integer. Identifies Messages for transmission using the length of
seed-id. 0 indicates that Trickle algorithm.

4.3. Signaling Overview

This protocol generates and processes the seed-id 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 0 and
not included an
address in the Local Interface Set of the MPL Option. 1 indicates Seed that generated
the seed-id message and is a 16-bit unsigned integer. 2
indicates that valid within the seed-id MPL Domain. The MPL Data
Message's destination is a 64-bit unsigned
integer. 3 indicates that the seed-id is a 128-
bit unsigned integer.

M 1-bit flag. 0 indicates that MPL Domain Address corresponding to
the value in
sequence is not MPL Domain. An MPL Data Message contains:

* The Seed Identifier of the greatest sequence number MPL Seed that
was received from generated the MPL seed.

rsv 5-bit reserved field. MUST be set to zero and
incoming MPL multicast packets in which they are
not zero MUST be dropped. Data
Message.

* The sequence 8-bit unsigned integer. Identifies relative
ordering number of MPL multicast packets from the source
identified by seed-id.

seed-id Uniquely identifies the MPL seed Seed that initiated
dissemination of generated the MPL multicast packet. Data
Message.

* The
size of seed-id is indicated original multicast message.

MPL Control Message - Generated by an MPL Forwarder to communicate
information contained in the S field.

The Option Data Seed Set and Buffered Message Set to
neighboring MPL Forwarders. An MPL Control Message contains a
list of tuples for each entry in the Trickle Multicast option MUST NOT change as Seed Set. Each tuple
contains:

* The minimum sequence number maintained in the Seed Set for the
MPL multicast packet is forwarded. Nodes that do not understand Seed.

* A bit-vector indicating the Trickle Multicast option MUST discard sequence numbers of MPL Data
Messages resident in the packet. Thus,
according to [RFC2460] Buffered Message Set for the three high order bits of MPL Seed,
where the Option Type
must be set first bit represents a sequence number equal to '010'. the
minimum threshold maintained in the Seed Set.

* The Option Data length is variable.

The seed-id uniquely identifies an MPL seed within of the bit-vector.

5. MPL domain.
When seed-id is 128 bits (S=3), the Constants

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

5.1. Multicast Addresses

MPL seed MAY makes use an IPv6 address
assigned to one of its interfaces that is unique within the MPL
domain. Managing Domain Addresses to identify MPL seed identifiers is not within scope of this
document.

The sequence field establishes a total ordering Interfaces of
an MPL multicast
packets from the same MPL seed. The Domain. By default, MPL seed MUST increment Forwarders subscribe to the
sequence field's
ALL_MPL_FORWARDERS multicast address with a scope value on of 3 (subnet-
local).

For each new MPL multicast packet Domain Address that it
disseminates. Implementations an MPL Interface subscribes to, the
MPL Interface MUST follow also subscribe to the Serial Number
Arithmetic as defined in [RFC1982] when incrementing MPL Domain Address with a sequence
scope value
or comparing two sequence values.

Future updates to this specification may define additional fields
following of 2 (link-local) when reactive forwarding is in use.
MPL Forwarders use the seed-id field.

4.2. ICMPv6 link-scoped MPL Message

The MPL forwarder uses ICMPv6 Domain Address to communicate
MPL messages Control Messages to advertise information
about recently received neighboring (i.e. on-link) MPL multicast packets. The ICMPv6 Forwarders.

5.2. Message Types

MPL
message has the following format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. defines an IPv6 Option for carrying an MPL Window[1..n] .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP Fields:

Source Address A link-local address assigned to the sending
interface.

Destination Address The link-local all-nodes Seed Identifier and a
sequence number within an MPL forwarders multicast
address (FF02::TBD).

Hop Limit 255

ICMPv6 Fields:

Type XX (to be confirmed by IANA).

Code 0

Checksum Data Message. The ICMP checksum. See [RFC4443].

MPL Window[1..n] List of one or more MPL Windows (defined in
Section 4.2.1).

An IPv6 Option Type has
value MPL_OPT_TYPE.

MPL forwarder transmits defines an ICMPv6 MPL message to advertise Message (MPL Control Message) for communicating
information about buffered MPL multicast packets. More explicitly,
the ICMPv6 MPL message encodes the sliding window state (described contained in
Section 5.2) that the MPL forwarder maintains for each MPL seed. The
advertisement serves to indicate its Seed Set and Buffered Message Set to
neighboring MPL forwarders
regarding newer messages Forwarders. The MPL Control Message has ICMPv6 Type
MPL_ICMP_TYPE.

5.3. MPL Forwarder Parameters

PROACTIVE_FORWARDING A boolean value that it may send or indicates whether the neighboring MPL
forwarders have yet to receive.

4.2.1. MPL Window

An
Forwarder should schedule MPL Window encodes Data Message transmissions after
receiving them for the sliding window state (described first time.

SEED_SET_LIFETIME The minimum lifetime for an entry in
Section 5.2 that the MPL forwarder maintains Seed Set.

5.4. Trickle Parameters

As specified in [RFC6206], a Trickle timer runs for an MPL seed. Each
MPL Window a defined
interval and has three configuration parameters: the following 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 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 | w-min Opt Data Len | w-len
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S |M|V| rsv | sequence | seed-id (0, 2 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (optional) |
. buffered-mpl-packets (0 to 8 octets) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

w-min 8-bit unsigned integer. Indicates the first
sequence number associated with the first bit in
buffered-mpl-packets.

w-len 6-bit unsigned integer. Indicates the size

Option Type MPL_OPT_TYPE

Opt Data Len Length of the sliding window and the number of valid bits Option Data field in buffered-mpl-packets. The sliding window's
upper bound is the sum of w-min and w-len. octets.

S 2-bit unsigned integer. Identifies the length of
seed-id. 0 indicates that the seed-id value is 0 the IPv6
Source Address and not included in the MPL
Option. 1 indicates that the seed-id value is a 16-bit
unsigned integer. 2 indicates that the seed-id value is
a
128-bit 64-bit unsigned integer. 3 is reserved. indicates that the
seed-id Indicates is a 128-bit unsigned integer.

M 1-bit flag. 1 indicates that the value in
sequence is known to be the largest sequence
number that was received from the MPL seed associated with this
sliding window.

buffered-mpl-packets Variable-length bit vector. Identifies Seed.

V 1-bit flag. 0 indicates that the MPL Option
conforms to this specification. MPL Options
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 numbers 8-bit unsigned integer. Identifies relative
ordering of MPL multicast packets Data Messages from the MPL Seed
identified by seed-id.

seed-id Uniquely identifies the MPL Seed that initiated
dissemination of the MPL forwarder has buffered. Data Message. The sequence
number size
of seed-id is determined indicated by w-min + i, where i is the
offset within buffered-mpl-packets. S field.

The Option Data (in particular the M flag) of the MPL Window does not have any octet alignment requirement.

5. Option is
updated by MPL Forwarder Behavior

An Forwarders as the MPL forwarder implementation needs to manage sliding windows for
each active Data Message is forwarded.
Nodes that do not understand the MPL seed. The sliding window allows Option MUST discard the MPL forwarder to
determine what multicast packets Data
Message. Thus, according to accept and what multicast packets [RFC2460] the three high order bits of
the Option Type are buffered. An MPL forwarder must also manage MPL packet
transmissions.

5.1. Multicast Packet Dissemination

MPL uses the Trickle algorithm set to control packet transmissions when
disseminating MPL multicast packets [RFC6206]. MPL provides two
propagation mechanisms for disseminating MPL multicast packets.

1. With proactive propagation, '011'. The Option Data length is
variable.

The seed-id uniquely identifies an MPL forwarder transmits buffered
MPL multicast packets using the Trickle algorithm. This method Seed. When seed-id is called proactive propagation since 128
bits (S=3), the MPL seed MAY use an IPv6 address assigned to one of
its interfaces that is unique within the MPL forwarder actively
transmits domain. Managing MPL multicast packets without discovering that
Seed Identifiers is not within scope of this document.

The sequence field establishes a
neighboring total ordering of MPL forwarder has yet to receive the message.

2. With reactive propagation, Data Messages
generated by an MPL forwarder transmits ICMPv6 MPL
messages using the Trickle algorithm. An Seed for an MPL forwarder only
transmits buffered Domain. The MPL multicast packets upon discovering that
neighboring devices have not yet to receive Seed MUST
increment the corresponding MPL
multicast packets.

When receiving a sequence field's value on each new multicast packet, an MPL forwarder first
utilizes proactive propagation to forward the MPL multicast packet.
Proactive propagation reduces dissemination latency since it does not
require discovering Data Message
that neighboring devices have not yet received
the MPL multicast packet. MPL forwarders utilize proactive
propagation it generates for newly received MPL multicast packets since they can
assume that some neighboring an MPL forwarders have yet to receive Domain. Implementations MUST follow the
MPL multicast packet. After
Serial Number Arithmetic as defined in [RFC1982] when incrementing a limited number of MPL multicast packet
transmissions, the MPL forwarder
sequence value or comparing two sequence values.

Future updates to this specification may terminate proactive propagation
for define additional fields
following the seed-id field.

6.2. MPL multicast packet. Control Message

An MPL forwarder may optionally use reactive propagation Forwarder uses ICMPv6 messages to communicate information
contained in its Seed Set and Buffered Message Set to continue
the dissemination process with lower communication overhead. With
reactive propagation, neighboring MPL forwarders use ICMPv6
Forwarders. The MPL
messages Control Message has the following format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. MPL Seed Info[1..n] .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP Fields:

Source Address A link-local address assigned to discover new the sending
interface.

Destination Address The link-scoped MPL multicast messages Domain Address corresponding
to the MPL Domain.

Hop Limit 255

ICMPv6 Fields:

Type MPL_ICMP_TYPE

Code 0

Checksum The ICMP checksum. See [RFC4443].

MPL Seed Info[1..n] List of one or more MPL Seed Info entries.

The MPL Control Message indicates the sequence numbers of MPL Data
Messages that have not yet
been received. When discovering are within the Buffered Message Set. The MPL Control
Message also indicates the sequence numbers of MPL Data Messages that a
an MPL Forwarder is willing to receive. The MPL Control Message
allows neighboring MPL forwarder has
not yet received a Forwarders to determine whether there are any
new MPL multicast packet, the Data Messages to exchange.

6.3. MPL forwarder
enables proactive propagation again.

5.1.1. Trickle Parameters and Variables

As specified in RFC 6206 [RFC6206], a Trickle timer runs for a
defined interval and has three configuration parameters: Seed Info

An MPL Seed Info encodes the minimum
interval size Imin, sequence number for the maximum interval size Imax, and a redundancy
constant k. MPL defines a fourth configuration parameter, TimerExpirations, which Seed
maintained in the Seed Set. The MPL Seed Info also indicates the number
sequence numbers of Trickle timer expiration events that occur
before terminating MPL Data Messages generated by the Trickle algorithm.

Each MPL forwarder maintains a separate Trickle parameter set for Seed
within the
proactive and reactive propagation methods. TimerExpirations MUST be
greater than Buffered Message Set. The MPL Seed Info has the following
format:

0 for proactive propagation. TimerExpirations MAY be
set to 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| min-seqno | bm-len | S | seed-id (0/2/8/16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. buffered-mpl-messages (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

min-seqno 8-bit unsigned integer. The lower-bound sequence
number for reactive propagation, which effectively disables
reactive propagation.

As specified in RFC 6206 [RFC6206], a Trickle timer has three
variables: the current interval size I, a time within the current
interval t, and a counter c. MPL defines a fourth variable, e, which counts Seed.

bm-len 6-bit unsigned integer. The size of buffered-
mpl-messages in octets.

S 2-bit unsigned integer. Identifies the number length of Trickle
timer expiration events since
seed-id. 0 indicates that the Trickle timer was last reset.

5.1.2. Proactive Propagation

With proactive propagation, seed-id value is
the MPL forwarder transmits buffered MPL
multicast packets using IPv6 Source Address and not included in the Trickle algorithm. Each buffered
MPL
multicast packet Seed Info. 1 indicates that the seed-id value
is proactively being disseminated with
proactive propagation has an associated Trickle timer. Adhering to
Section 5 of RFC 6206 [RFC6206], this document defines a 16-bit unsigned integer. 2 indicates that
the following:

o This document defines seed-id value is a "consistent" transmission for proactive
propagation as receiving an MPL multicast packet 64-bit unsigned integer. 3
indicates that has the same
MPL seed identifier and sequence number as seed-id is a buffered 128-bit unsigned
integer.

seed-id Variable-length unsigned integer. Indicates the
MPL packet.

o This document defines an "inconsistent" transmission for proactive
propagation as receiving an Seed associated with this MPL multicast packet that has Seed Info.

buffered-mpl-messages Variable-length bit vector. Identifies the same
sequence numbers of MPL seed identifier, Data Messages maintained
in the M flag set, and has a Buffered Message Set for the MPL Seed.
The sequence number
less than is determined by min-seqno +
i, where i is the buffered bit offset within buffered-mpl-
messages.

The MPL multicast packet's sequence number.

o This document Seed Info does not define have any external "events".

o This document defines both octet alignment requirement.

7. Information Base

7.1. Local Interface Set

The Local Interface Set records the local MPL multicast packets and ICMPv6 Interfaces of an MPL
multicast packets as Trickle messages. These messages are defined
in
Forwarder. The Local Interface Set consists of Local Interface
Tuples, one per MPL Interface: (AddressSet).

AddressSet - a set of unicast addresses assigned to the sections below.

o MPL
Interface.

7.2. Domain Set

The actions outside Domain Set records the Trickle algorithm MPL Interfaces that the protocol takes
involve managing sliding window state, and is specified in
Section 5.2.

5.1.3. Reactive Propagation

With reactive propagation, the subscribe to each MPL forwarder transmits ICMPv6
Domain Address. The Domain Set consists of MPL
messages using the Trickle algorithm. A Domain Tuples, one
per MPL forwarder maintains Domain: (MPLInterfaceSet).

MPLInterfaceSet - a
single Trickle timer for reactive propagation with each set of MPL domain.
When REACTIVE_TIMER_EXPIRATIONS is 0, Interfaces that subscribe to the MPL forwarder does not
execute
Domain Address that identifies the Trickle algorithm for reactive propagation and reactive
propagation MPL Domain.

7.3. Seed Set

The Seed Set records a sliding window used to determine the sequence
numbers of MPL Data Messages that an MPL Forwarder is disabled. Adhering willing to Section 5
accept generated by the MPL Seed. It consists of RFC 6206
[RFC6206], this document defines MPL Seed Tuples:
(SeedID, MinSequence, Lifetime).

SeedID - the following:

o This document defines a "consistent" transmission identifier for reactive
propagation as receiving an ICMPv6 the MPL message Seed.

MinSequence - a lower-bound sequence number that indicates
neither the receiving nor transmitting node has new MPL multicast
packets to offer.

o This document defines an "inconsistent" transmission for reactive
propagation as receiving an ICMPv6 MPL message that indicates
either the receiving or transmitting node has at least one new MPL
multicast packet to offer.

o This document defines an "event" for reactive propagation as
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
multicast packets as Trickle messages. These messages are defined
in the sections below.

o The actions outside the Trickle algorithm that the protocol takes
involve managing sliding window state, and is specified in
Section 5.2.

5.2. Sliding Windows

Every MPL forwarder MUST maintain a sliding window of sequence
numbers for each MPL seed of recently received MPL packets. The
sliding window performs two functions:

1. Indicate what MPL multicast packets the MPL forwarder should
accept.

2. Indicate what MPL multicast packets are buffered and may be
transmitted to neighboring MPL forwarders.

Each sliding window logically consists of:

1. A lower-bound sequence number, WindowMin, that represents represents the
sequence number of the oldest MPL multicast packet Data Message the MPL
forwarder Forwarder
is willing to receive or has buffered. transmit. An MPL
forwarder Forwarder MUST ignore
any MPL multicast packet Data Message that has sequence value less than than WindowMin.

2. An upper-bound sequence value, WindowMax, that represents the
sequence number of the next MPL multicast packet that the MPL
forwarder expects to receive. An MPL forwarder MUST accept any
MPL multicast packet that has sequence number greater than or
equal to WindowMax.

3. A list of MPL multicast packets, BufferedPackets, buffered by the
MPL forwarder. Each entry in BufferedPackets MUST have a
sequence number in the range [WindowMin, WindowMax).

4. A timer, HoldTimer, that
MinSequence.

Lifetime - indicates the minimum lifetime of the
sliding window. The Seed Set entry. An
MPL forwarder Forwarder MUST NOT free a sliding window Seed Set entry before HoldTimer its expires.

When receiving

7.4. Buffered Message Set

The Buffered Message Set records recently received MPL Data Messages
from an MPL multicast packet, if no existing sliding window
exists for Seed. An MPL Forwarder uses the Buffered Message Set to
buffer MPL seed, Data Messages while the MPL forwarder MUST create a new sliding
window before accepting Forwarder is forwarding the
MPL multicast packet. Data Messages. The MPL forwarder
may reclaim memory resources by freeing a sliding window Buffered Message Set consists of Buffered
Message Tuples: (SeedID, SequenceNumber, DataMessage).

SeedID - the identifier for another the MPL seed if its HoldTimer has expired. If, for any reason, Seed that generated the MPL
forwarder cannot create a new sliding window, it MUST discard Data
Message.

SequenceNumber - the
packet.

If a sliding window exists sequence number for the MPL seed, Data Message.

DataMessage - the MPL forwarder MUST
ignore the Data Message.

All MPL multicast packet if Data Messages within the packet's Buffered Message Set MUST have a
sequence number is
less greater 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 equal to MinSequence for the next higher layer.
corresponding SeedID. When accepting increasing MinSequence for an MPL multicast packet, Seed,
the MPL forwarder Forwarder MUST update
the sliding window based on the packet's sequence number. If delete any MPL Data Messages from the Buffered
Message Set that have sequence number is not numbers less than WindowMax, the MinSequence.

8. MPL forwarder MUST
set WindowMax to 1 greater than the packet's sequence number. If
WindowMax - WindowMin > MPL_MAX_WINDOW_SIZE, the Domains

An MPL forwarder MUST
increment WindowMin such that WindowMax - WindowMin <=
MPL_MAX_WINDOW_SIZE. At Domain is a scope zone, as defined in [RFC4007], in which MPL
Interfaces subscribe to the same time, the MPL forwarder MUST free
any entries Domain Address and participate
in BufferedPackets that have a sequence number less than
WindowMin.

If the disseminating MPL forwarder has available memory resources, it Data Messages.

By default, an MPL Forwarder MUST buffer participate in an MPL Domain
identified by the ALL_MPL_FORWARDERS multicast address with a scope
value of 3 (subnet-local).

An MPL Forwarder MAY participate in additional MPL Domains identified
by other multicast packet for proactive propagation. If not enough
memory resources are available addresses. An MPL Interface MUST subscribe to buffer the packet,
MPL Domain Addresses for the MPL
forwarder MUST increment WindowMin and free entries in
BufferedPackets Domains that have a sequence number less than WindowMin until
enough memory resources are available. Incrementing WindowMin will
ensure it participates in.
The allocation of other multicast addresses is out of scope.

For each MPL Domain Address that the an MPL forwarder does not accept previously received
packets.

An Interface subscribes to, the
MPL forwarder MAY reclaim memory resources from sliding windows
for other Interface MUST also subscribe to the same MPL seeds. If Domain Address with
a sliding window for another MPL seed scope value of 2 (link-local) when reactive forwarding is
actively disseminating messages and has more than one entry in its
BufferedPackets, the use
(i.e. when communicating MPL forwarder may free entries Control Messages).

9. MPL Seed Sequence Numbers

Each MPL Seed maintains a sequence number for each MPL Domain that it
serves. The sequence numbers are included in MPL seed Data Messages
generated by incrementing WindowMin as described above.

If the MPL forwarder cannot free enough memory resources to buffer the MPL multicast packet, the Seed. The MPL forwarder Seed MUST set WindowMin to 1
greater than increment the packet's sequence number.

When memory resources are available, an MPL forwarder SHOULD buffer a
number for each MPL multicast packet until the proactive propagation completes (i.e.
the Trickle algorithm stops execution) and MAY buffer Data Message that it generates for longer.
After proactive propagation completes, the an MPL forwarder may advance
WindowMin to Domain.
Implementations MUST follow the packet's Serial Number Arithmetic as defined
in [RFC1982] when incrementing a sequence value or comparing two
sequence values. This sequence number is used to reclaim memory
resources. When the establish a total
ordering of MPL forwarder no longer buffers any packets, it
MAY set WindowMin equal to WindowMax. When setting WindowMin equal
to WindowMax, the Data Messages generated by an MPL forwarder MUST initialize HoldTimer to
WINDOW_HOLD_TIME and start HoldTimer. After HoldTimer expires, the Seed for an MPL forwarder MAY free the sliding window to reclaim memory
resources.

5.3. Transmission of
Domain.

10. MPL Multicast Packets

The Data Messages

10.1. MPL forwarder manages buffered Data Message Generation

MPL multicast packet transmissions
using the Trickle algorithm. When adding a packet to
BufferedPackets, Data Messages are generated by MPL Seeds when they enter the MPL forwarder
Domain. All MPL Data messages have the following properties:

o The IPv6 Source Address MUST create a Trickle timer for be an address in the packet and start execution AddressSet of the Trickle algorithm.

After PROACTIVE_TIMER_EXPIRATIONS Trickle timer events, a
corresponding MPL Interface and MUST be valid within the MPL
forwarder
Domain.

o The IPv6 Destination Address MUST stop executing be set to the Trickle algorithm. When a buffered MPL multicast packet does not have Domain Address
corresponding to the MPL Domain.

o A MPL Data Message MUST contain an active Trickle timer, MPL Option in its IPv6 Header
to identify the MPL
forwarder MAY free Seed that generated the buffered packet by advancing WindowMin message and the
ordering relative to 1
greater than other MPL Data Messages generated by the packet's sequence number.

Each interface that supports MPL
Seed.

When the source address is configured with exactly one in the AddressList of an MPL
multicast scope. The Interface
corresponding to the MPL multicast scope MUST be site-local or
smaller Domain Address and defaults to link-local. A scope larger than link-local
MAY be used only when that scope corresponds exactly to the destination address
is the MPL
domain.

An Domain Address, the application message and the MPL domain may therefore Data
Message MAY be composed of one or more MPL multicast
scopes. For example, identical. In other words, the MPL domain Data Message may be composed of
contain a single MPL
multicast scope when using a site-local scope. Alternatively, IPv6 header that includes the MPL domain may be composed of multiple MPL multicast scopes when
using a link-local scope. Option.

Otherwise, IPv6-in-IPv6 encapsulation MUST be used when using MPL to forward an
original multicast packet whose source or destination address is
outside the MPL multicast scope. IPv6-in-IPv6 encapsulation is
necessary to support Path MTU discovery when satisfy the MPL forwarder is not
the source of the original multicast packet. IPv6-in-IPv6
encapsulation also allows
Data Message requirements listed above [RFC2473]. The complete IPv6-
in-IPv6 message forms an MPL forwarder Data Message. The outer IPv6 header
conforms to remove the MPL Option
when forwarding the original multicast packet over a link that does
not support MPL. Data Message requirements listed above. The destination address scope for the outer
encapsulated IPv6
header MUST be datagram encodes the MPL multicast scope.

When an MPL domain data message that is composed of multiple MPL multicast scopes (e.g.
when
communicated beyond the MPL multicast scope is link-local), an MPL forwarder MUST
decapsulate and encapsulate the original multicast packet when
crossing between different Domain.

10.2. MPL multicast scopes. In doing so, the Data Message Transmission

An MPL forwarder MUST duplicate the Forwarder manages transmission of MPL Option, unmodified, Data Messages in the new
outer IPv6 header.

The IPv6 destination address of
Buffered Message set using the Trickle algorithm [RFC6206]. An MPL multicast packet
Forwarder MUST use a separate Trickle timer for each MPL Data Message
that it is the all-
MPL-forwarders multicast address (TBD). The scope actively forwarding. In accordance with Section 5 of RFC
6206 [RFC6206], this document defines the IPv6
destination address is set to the MPL multicast scope.

5.4. Reception of MPL Multicast Packets

Upon following:

o This document defines a "consistent" transmission as receiving an
MPL multicast packet, the MPL forwarder first
determines whether or not to accept and buffer Data Message that has the MPL multicast
packet based on its MPL seed same seed-id and sequence value, value as specified in
Section 5.2.

If the MPL forwarder accepts
the MPL multicast packet, Data Message managed by the Trickle timer.

o This document defines an "inconsistent" transmission as receiving
an MPL
forwarder determines whether or not to deliver the original multicast
packet to the next higher layer. For example, if Data Message that has the MPL multicast
packet uses IPv6-in-IPv6 encapsulation, same seed-id value and the M flag
set, but has a sequence value less than MPL forwarder removes Data Message managed
by the
outer IPv6 header, which also removes MPL Option.

5.5. Transmission of ICMPv6 Trickle timer.

o This document does not define any external "events".

o This document defines MPL Data Messages as Trickle messages.

o The MPL forwarder generates actions outside the Trickle algorithm that the protocol takes
involve managing Seed Set and transmits Buffered Message Set

As specified in [RFC6206], a new ICMPv6 MPL message
whenever Trickle requests timer has three variables: the
current interval size I, a transmission. The time within the current interval t, and a
counter c. MPL forwarder includes
an encoding defines a fourth variable, e, which counts the number
of each sliding window in Trickle timer expiration events since the ICMPv6 MPL message.

Each sliding window is encoded using an MPL Window entry, defined in
Section 5.2. The MPL forwarder sets Trickle timer was last
reset.

After DATA_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, the MPL Window fields as
follows:

S If
Forwarder MUST disable the Trickle timer. When a buffered MPL seed identifier is 0, set S to 0. If Data
Message does not have an associated Trickle timer, the MPL seed
identifier is within Forwarder
MAY delete the range [1, 65535], set S to 2. Otherwise,
set S to 3.

w-min Set to message from the lower bound Buffered Message Set by advancing
MinSequence of the sliding window (i.e.
WindowMin).

w-len Set to corresponding MPL Seed in the length of Seed Set. When the window (i.e. WindowMax - WindowMin).

seed-id If S is non-zero, set to
MPL Forwarder no longer buffers any messages for an MPL Seed, the MPL seed identifier.

buffered-mpl-packets Set each bit
Forwarder MUST NOT increment MinSequence for that represents a sequence number
of a packet in BufferedPackets MPL Seed.

When transmitting an MPL Data Message, the MPL Forwarder MUST either
set the M flag to 1. Set all other bits zero or set it to 0.
The i'th bit in buffered-mpl-packets represents a level that indicates whether or
not the message's sequence number
of w-min + i.

5.6. Reception of ICMPv6 is the largest value that has been
received from the MPL Messages

An Seed.

10.3. MPL forwarder processes each ICMPv6 Data Message Processing

Upon receiving an MPL message that it receives
to determine if it has any new MPL multicast packets to receive or
offer.

An Data Message, the MPL forwarder determines if a new Forwarder first processes
the MPL multicast packet has not
been received from a neighboring node if any of Option and updates the Trickle timer associated with the following
conditions hold true:

1. The ICMPv6 MPL message includes
Data Message if one exists.

Upon receiving an MPL Window for Data Message, an MPL seed
that does not have a corresponding sliding window entry on Forwarder MUST perform one
of the following actions:

o Accept the message and enter the MPL forwarder.

2. The neighbor has a packet in its BufferedPackets that has
sequence value greater than or equal to WindowMax (i.e. w-min +
w-len >= WindowMax).

3. The neighbor has a packet Data Message in its BufferedPackets that has
sequence number within range of the sliding window but is not
included in BufferedPackets (i.e. Buffered
Message Set.

o Accept the i'th bit message and update the corresponding MinSequence in buffered-mpl-
packets is set the
Seed Set to 1, where 1 greater than the message's sequence number is w-min + i).

When an number.

o Discard the message without any change to the MPL forwarder determines that it has not yet received Information
Base.

If a new Seed Set entry exists for the MPL multicast packet buffered by a neighboring device, Seed, the MPL
forwarder resets Forwarder MUST
discard the Trickle timer associated with reactive
propagation.

An MPL forwarder determines Data Message if an entry its sequence number is less than
MinSequence or exists in BufferedPackets has not
been received by a neighboring MPL forwarder if any of the following
conditions hold true:

1. The ICMPv6 MPL message Buffered Message Set.

If a Seed Set entry does not include an MPL Window exist for the
packet's MPL seed.

2. The packet's sequence number is greater than or equal to Seed, the
neighbor's WindowMax value (i.e. MPL
Forwarder MUST create a new entry for the packet's sequence number is
greater than or equal to w-min + w-len).

3. The packet's sequence number is within MPL Seed before accepting
the range of MPL Data Message.

If memory is limited, an MPL Forwarder SHOULD reclaim memory
resources by:

o Incrementing MinSequence entries in the
neighbor's sliding window [WindowMin, WindowMax), but not
included Seed Set and deleting MPL
Data Messages in the neighbor's BufferedPacket (i.e. Buffered Message Set that fall below the packet's
sequence number is greater than or equal to w-min, strictly less
than w-min + w-len,
corresponding MinSequence value.

o Deleting other Seed Set entries that have expired and the
corresponding bit in buffered-mpl-
packets is set to 0.

When an MPL forwarder determines that it has at least one buffered MPL multicast packet that has not yet been received by a neighbor, Data Messages in the Buffered Message Set.

If the MPL forwarder resets Forwarder accepts the Trickle timer associated with reactive
propagation. Additionally, for each buffered MPL multicast packet
that should be transferred, Data Message, the MPL forwarder Forwarder
MUST reset perform the following actions:

o If PROACTIVE_PROPAGATION is true, the MPL Forwarder MUST
initialize and start a Trickle timer and reset e to 0 for proactive propagation. the MPL Data Message.

o If the MPL Control Message Trickle timer for proactive propagation has already stopped execution, is not running and
CONTROL_MESSAGE_TIMER_EXPIRATIONS is non-zero, the MPL forwarder Forwarder
MUST initialize a new Trickle timer and start execution
of the Trickle algorithm.

6. MPL Parameters

An MPL forwarder maintains two sets of Control Message Trickle parameters for timer.

o If the
proactive and reactive methods. The Trickle parameters are listed
below:

PROACTIVE_IMIN The minimum Trickle timer interval, as defined in
[RFC6206] for proactive propagation.

PROACTIVE_IMAX The maximum Trickle timer interval, as defined in
[RFC6206] for proactive propagation.

PROACTIVE_K The redundancy constant, as defined in [RFC6206] for
proactive propagation.

PROACTIVE_TIMER_EXPIRATIONS The number of MPL Control Message Trickle timer expirations
that occur before terminating is running, the Trickle algorithm. MPL
Forwarder MUST be set
to a value greater than 0.

REACTIVE_IMIN The minimum reset the MPL Control Message Trickle timer interval, as defined in
[RFC6206] timer.

11. MPL Control Messages

11.1. MPL Control Message Generation

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:

o S set to the size of the seed-id field in the MPL Seed Info entry.

o min-seqno set to MinSequence of the MPL Seed.

o bm-len set to the size of buffered-mpl-messages in octets.

o seed-id set to the MPL seed identifier.

o buffered-mpl-messages with each bit representing whether or not an
MPL Data Message with the corresponding sequence number exists in
the Buffered Message Set. The i'th bit represents a sequence
number of min-seqno + i. '0' indicates that the corresponding MPL
Data Message does not exist in the Buffered Message Set. '1'
indicates that the corresponding MPL Data Message does exist in
the Buffered Message Set.

11.2. MPL Control Message Transmission

An MPL Forwarder transmits MPL Control Messages using the Trickle
algorithm. A MPL forwarder maintains a single Trickle timer for each
MPL Domain. When CONTROL_MESSAGE_TIMER_EXPIRATIONS is 0, the MPL
Forwarder does not execute the Trickle algorithm and does not
transmit MPL Control Messages. In accordance with Section 5 of RFC
6206 [RFC6206], this document defines the following:

o This document defines a "consistent" transmission as receiving an
MPL Control Message that indicates neither the receiving nor
transmitting node has new MPL Data Message.

o This document defines an "inconsistent" transmission as receiving
an MPL Control Message that indicates either the receiving or
transmitting node has at least one new MPL Data Message to offer.

o This document defines an "event" as increasing MinSequence of any
entry in the Seed Set or adding a message to the Buffered Message
Set.

o This document defines an MPL Control Message as a Trickle message.

As specified in [RFC6206], a Trickle timer has three variables: the
current interval size I, a time within the current interval t, and a
counter c. MPL defines a fourth variable, e, which counts the number
of Trickle timer expiration events since the Trickle timer was last
reset. After CONTROL_MESSAGE_TIMER_EXPIRATIONS Trickle timer events,
the MPL Forwarder MUST disable the Trickle timer.

11.3. MPL Control Message Processing

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

An MPL Forwarder determines if a new MPL Data Message has not been
received from a neighboring node if any of the following conditions
hold true:

o The MPL Control Message includes an MPL Seed that does not exist
in the Seed Set.

o The MPL Control Message indicates that the neighbor has an MPL
Data Message in its Buffered Message Set with sequence number
greater than MinSequence (i.e. the i-th bit is set to 1 and min-
seqno + i > MinSequence) and is not included in the MPL
Forwarder's Buffered Message Set.

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

An MPL Forwarder determines if an MPL Data Message in the Buffered
Message Set has not yet been received by a neighboring MPL Forwarder
if any of the following conditions hold true:

o The MPL Control Message does not include an MPL Seed for the MPL
Data Message.

o The MPL Data Message's sequence number is greater than or equal to
min-seqno and not included in the neighbor's Buffered Message Set
(i.e. the MPL Data Message's sequence number does not have a
corresponding bit in buffered-mpl-messages set to 1).

When an MPL Forwarder determines that it has at least one MPL Data
Message in its 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 reactive propagation.

REACTIVE_IMAX The maximum each of those entries in the
Buffered Message Set, the MPL Forwarder MUST reset the Trickle timer interval,
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.

12. Acknowledgements

The authors would like to acknowledge the helpful comments of Robert
Cragie, Esko Dijk, Ralph Droms, Paul Duffy, Ulrich Herberg, Owen
Kirby, Joseph Reddy, Don Sturek, Dario Tedeschi, and Peter van der
Stok, which greatly improved the document.

13. IANA Considerations

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

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

This document registers two well-known multicast addresses from the
IPv6 multicast address space.

13.1. MPL Option Type

IANA is requested to allocate an IPv6 Option Type from the IPv6
"Destination Options and Hop-by-Hop Options" registry of [RFC2780],
as defined specified in
[RFC6206] for reactive propagation.

REACTIVE_K The redundancy constant, Table 1 below:

+--------------+-----+-----+--------------+-------------+-----------+
| Mnemonic | act | chg | rest | Description | Reference |
+--------------+-----+-----+--------------+-------------+-----------+
| MPL_OPT_TYPE | 01 | 1 | TBD | MPL Option | This |
| | | | (suggested | | Document |
| | | | value 01101) | | |
+--------------+-----+-----+--------------+-------------+-----------+

Table 1: IPv6 Option Type Allocation

13.2. MPL ICMPv6 Type

IANA is requested to allocate an ICMPv6 Type from the "ICMPv6 "type"
Numbers" registry of [RFC4443], as defined specified in [RFC6206] for
reactive propagation.

REACTIVE_TIMER_EXPIRATIONS Table 2 below:

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 number use of Trickle timer expirations
that occur before terminating 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 Trickle algorithm. MAY be set
to 0, which disables reactive propagation.

WINDOW_HOLD_TIME The minimum lifetime
Buffered Message List and (ii) increase the MinSequence value for sliding window state.

7. Acknowledgements an
MPL Seed in the Seed Set. The authors would like former side effect allows an attacker
to acknowledge halt the helpful comments forwarding process of Robert
Cragie, Esko Dijk, Ralph Droms, Paul Duffy, Owen Kirby, Joseph Reddy,
Dario Tedeschi, and Peter van der Stok, which greatly improved the
document.

8. IANA Considerations any MPL Data Messages being
disseminated. The Trickle Multicast option requires latter side effect allows an IPv6 Option Number.

HEX act chg rest
--- --- --- -----
C 01 0 TBD

The first two bits indicate attacker to prevent
MPL Forwarders from accepting new MPL Data Messages that an MPL Seed
generates while the IPv6 node MUST discard the
packet if it doesn't recognize sequence number is less than MinSequence.

More generally, the option type, 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 third bit
indicates that the Option Data MPL Forwarder MUST NOT change en-route.

9. Security Considerations

TODO.

10. References

10.1. 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,
August 1996.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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
(IPv6) Specification", RFC 2460, December 1998.

[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
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
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.

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

[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
Lossy Networks", RFC 6550, March 2012.

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

Jonathan W. Hui
Cisco
170 West Tasman Drive
San Jose, California 95134
USA

Phone: +408 424 1547
Email: jonhui@cisco.com

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

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