wdiff draft-ietf-roll-trickle-mcast-01.txt draft-ietf-roll-trickle-mcast-02.txt

ROLL J. Hui
Internet-Draft Cisco
Intended status: Standards Track R. Kelsey
Expires: January 14, April 22, 2013 Silicon Labs
July 13,
October 19, 2012

Multicast Forwarding Using Trickle
draft-ietf-roll-trickle-mcast-01 Protocol for Low power and Lossy Networks (MPL)
draft-ietf-roll-trickle-mcast-02

Abstract

This document specifies the Multicast Protocol for Low power and
Lossy Networks (LLNs) are typically composed of
resource constrained nodes communicating over links (MPL) that have dynamic
characteristics. Memory constraints coupled with temporal variations
in link connectivity makes the use of topology maintenance to support provides IPv6 multicast challenging. This document describes forwarding in
constrained networks. MPL avoids the use of
Trickle need to efficiently forward construct or maintain
any multicast forwarding topology, disseminating messages without to all MPL
forwarders in an MPL domain. MPL uses the need Trickle algorithm to drive
packet transmissions for topology maintenance. both control and data-plane packets.
Specific Trickle parameter configurations allow MPL to trade between
dissemination latency and transmission efficiency.

Status of this Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

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

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

This Internet-Draft will expire on January 14, April 22, 2013.

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

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language
2. Terminology . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . 5
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . 5
4. Trickle Multicast Parameters . 7
4.1. MPL Option . . . . . . . . . . . . . . . . . . . . . . . . 7
5.
4.2. ICMPv6 MPL Message Formats . . . . . . . . . . . . . . . . . . . . 8
4.2.1. MPL Window . . . . . 9
5.1. Trickle Multicast Option . . . . . . . . . . . . . . . . . 9
5.2. Trickle ICMPv6 Message
5. MPL Forwarder Behavior . . . . . . . . . . . . . . . . . . 10
5.2.1. Sequence List . . 11
5.1. Multicast Packet Dissemination . . . . . . . . . . . . . . 11
5.1.1. Trickle Parameters and Variables . . . . . . . . 11
6. Trickle Multicast Forwarder Behavior . . . 12
5.1.2. Proactive Propagation . . . . . . . . . . . . . . . . 12
6.1. Managing
5.1.3. Reactive Propagation . . . . . . . . . . . . . . . . . 13
5.2. Sliding Windows . . . . . . . . . . . . . . . . . 12
6.2. Trickle Timers . . . . 13
5.3. Transmission of MPL Multicast Packets . . . . . . . . . . 15
5.4. Reception of MPL Multicast Packets . . . . . . . . . 12
6.3. Trickle Multicast Option Processing . . . 16
5.5. Transmission of ICMPv6 MPL Messages . . . . . . . . . 13
6.4. Trickle ICMP Processing . . 16
5.6. Reception of ICMPv6 MPL Messages . . . . . . . . . . . . . 17
6. MPL Parameters . . 13 . . . . . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 23
10.1. Normative References . . . . . . . . . . . . . . . . . . . 18 23
10.2. Informative References . . . . . . . . . . . . . . . . . . 18 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 24

1. Introduction

The resource constraints of

Low power and Lossy Networks (LLNs) typically operate with strict resource
constraints in communication, computation, memory, and energy. Such
resource constraints may preclude the use of existing IPv6 multicast
topology and forwarding mechanisms.
Such networks are typically constrained in resources (limited channel
capacity, processing power, energy capacity, memory). In particular
memory constraints may limit nodes to maintaining state for only a
small subset of neighbors. Limited channel and energy capacity
require protocols to remain efficient and robust even in dense
topologies. Traditional IP multicast
forwarding typically relies on topology maintenance mechanisms to efficiently
forward multicast messages to
the intended destinations. In some cases, topology maintenance
involves maintaining multicast trees to reach all subscribers of a multicast group. Maintaining
However, maintaining such topologies in LLNs is difficult especially
when memory costly and may not be
feasible given the available resources.

Memory constraints are such that nodes can only 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 route. Dynamic
routes towards a LLN Border Router (LBR) and use source routing to
forward packets away from the LBR. For the same reasons, a LLN
device may not be able to maintain a multicast forwarding topology
when operating with limited memory.

Furthermore, the dynamic properties of wireless networks can make
control traffic the
cost of maintaining a multicast forwarding 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, which is more state than a LLN node may be able to
handle.
information and the cost of maintaining such information grows
polynomially with network density.

This document describes specifies the use of Trickle Multicast Protocol for Low power and
Lossy Networks (MPL), which provides IPv6 multicast forwarding in LLNs. Trickle provides a mechanism for controlled,
density-aware flooding without
constrained networks. MPL avoids the need to construct or maintain a
any multicast forwarding
topology [RFC6206].

1.1. Requirements Language 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", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

2. Terminology

Trickle Multicast Message A IPv6 multicast datagram that includes a
Trickle Multicast option in the IPv6 Hop-by-Hop
Options header.

Trickle Multicast Forwarder A

The following terms are used throughout this document:

MPL forwarder An IPv6 router that can process a Trickle
Multicast option and follows subscribes to the forwarding rules
specified MPL
multicast group and participates in this document.

Trickle Multicast Domain An administrative domain disseminating
MPL multicast packets.

MPL multicast scope The multicast scope that defines MPL uses when forwarding
MPL multicast packets. In other words, the
multicast scope of Trickle dissemination. All routers
within a Trickle Multicast Domain participate in the same dissemination process.

Seed IPv6 Destination Address
of an MPL multicast packet.

MPL domain A connected set of MPL forwarders that define the
extent of the MPL dissemination process. As a
form of flood, all MPL forwarders in an MPL
domain will receive MPL multicast packets. The router
MPL domain MUST be composed of at least one MPL
multicast scope and MAY be composed of multiple
MPL multicast scopes.

MPL seed A MPL forwarder that starts begins the dissemination
process for a Trickle an MPL multicast message. packet. The Seed MPL
seed may be different than the node identified by the IPv6
Source address source of the
original multicast message.

3. Overview

Trickle packet.

MPL seed identifier An identifier that uniquely identifies an MPL
forwarder within its MPL domain.

original multicast forwarding implements a controlled, density-aware
flood to disseminate a packet An IPv6 multicast message to all nodes within a
Trickle Multicast Domain. The basic process packet that is similar to
traditional flooding - nodes forward newly received multicast
messages
disseminated using link-layer broadcasts. Nodes maintain state of
recently received MPL.

MPL multicast messages to detect duplicates and ensure packet An IPv6 multicast packet that each node receives at most one copy of each contains an MPL
Hop-by-Hop Option. When either source or
destinations are beyond the MPL multicast message.

Each Trickle scope,
the MPL multicast message carries a Trickle Multicast option packet is an IPv6-in-IPv6
packet that includes a SeedID contains an MPL Hop-by-Hop Option in
the outer IPv6 header and Sequence value. The SeedID uniquely
identifies encapsulates an
original multicast packet. When both source and
destinations are within the Seed that initiated MPL multicast scope,
the message's dissemination
process MPL Hop-by-Hop Option may be included
directly within the Trickle Multicast Domain. Note that the Seed does
not have original multicast packet.

3. Overview

MPL delivers IPv6 multicast packets by disseminating them to be all MPL
forwarders within an MPL domain. MPL dissemination is a form of
flood. An MPL forwarder may broadcast/multicast an MPL multicast
packet out of the same node as the message's source. It is possible physical interface on which it was received.
Using link-layer broadcast/multicast allows MPL to tunnel a forward multicast message
packets without explicitly identifying next-hop destinations. An MPL
forwarder may also broadcast/multicast MPL multicast packets out
other interfaces to a Seed node and start disseminate the
dissemination process from a message across different node within the Trickle
Multicast Domain.

The Sequence value establishes links.
MPL does not build or maintain a total ordering of multicast messages
disseminated by SeedID. Nodes maintain a sliding window of recently
received forwarding topology to
forward multicast messages packets.

Any MPL forwarder may initiate the dissemination process by serving
as an MPL seed for each SeedID. an original multicast packet. The sliding window
establishes what messages can MPL seed may or
may not be received and ensure at most one copy the same device as the source of each the original multicast message
packet. When the original multicast packet's source is received. Messages 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 sequence values
lower than the lower bound number of
active MPL seeds, limiting the window MUST be ignored. Messages number of MPL seeds reduces the amount
of state that MPL forwarders must maintain.

Because MPL typically broadcasts/multicasts MPL packets out of the
same interface on which they were received, MPL forwarders are likely
to receive an MPL multicast packet more than once. The MPL seed tags
each original multicast packet with an MPL seed identifier and a
sequence values stored within number. The sequence number provides a total ordering of
MPL multicast packets disseminated by the sliding window MUST be
ignored. All other messages MUST MPL seed.

MPL defines a new IPv6 Hop-by-Hop Option, the MPL Option, to include
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 received, advancing the sliding
window if necessary. Larger sequence values always take precedence.
The sliding window can same device, the MPL Option may be of variable size, trading memory
requirements 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 reliability forwarding, the MPL
forwarder may proactively transmit the MPL multicast packet packet a
limited number of disseminating multiple messages
simultaneously.

Trickle's density-aware properties come from its suppression
mechanism. When suppression is enabled, nodes periodically advertise 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 messages. These
advertisements allow nodes packets from time to time, allowing
neighboring MPL forwarders to determine if they have any additional
multicasts new
multicast packets to offer to neighboring nodes. A multicast message is
only retransmitted upon receiving positive indication that a neighbor
has not yet received that multicast message.

Nodes suppress advertisement transmissions or receive.

MPL forwarders schedule their packet (control and multicast
retransmissions after recently receiving "consistent" advertisements.
A node determines that a neighbor's advertisement is "consistent" data) transmissions
using the Trickle algorithm [RFC6206]. Trickle's adaptive
transmission interval allows MPL to quickly disseminate messages when neither node has
there are new MPL multicast messages to offer to the other.
The suppression packets, but reduces transmission
overhead as the number of redundant transmissions dissemination process completes. Trickle's
suppression mechanism and is
what allows Trickle transmission time selection allow MPL's
communication rate to maintain low channel utilization scale logarithmically with density.

4. Message Formats

4.1. MPL Option

The MPL Option is carried in dense
environments. However, suppression trades low control overhead for
longer propagation times. When using suppression, Trickle's
propagation times often have a long-tail distribution.

Trickle provides an adaptive timer, called IPv6 Hop-by-Hop Options header,
immediately following the Trickle timer. When
receiving an "inconsistent" advertisement, nodes reset IPv6 header. The MPL Option has the Trickle
timer period
following format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S |M| rsv | sequence | seed-id (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option Type XX (to be confirmed by IANA).

Opt Data Len Length of the Option Data field in octets. MUST
be set to a small period so that dissemination happens quickly.
The Trickle timer period doubles when either 2 or 4.

S 2-bit unsigned integer. Identifies the period expires and no
"inconsistent" advertisements have been received, reducing control
overhead when length of
seed-id. 0 indicates that the network seed-id is 0 and
not included in a consistent state.

This document does allow configurations the MPL Option. 1 indicates that disable
the suppression
mechanism, reducing Trickle Multicast Forwarding to simple flooding.
This can be done by setting seed-id is a 16-bit unsigned integer. 2
indicates that the suppression threshold for seed-id 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 the value in
sequence is not the greatest sequence number that
was received
"consistent" advertisements from the MPL seed.

rsv 5-bit reserved field. MUST be set to infinity. In this mode, Trickle
advertisements are not sent since consistency checks are not
performed. Instead, nodes simply retransmit zero and
incoming MPL multicast messages packets in which they are trying to forward.

4. Trickle Multicast Parameters

All Trickle multicast forwarders within a Trickle multicast domain
not zero MUST be configured with two sets dropped.

sequence 8-bit unsigned integer. Identifies relative
ordering of configurations (one for each
value MPL multicast packets from the source
identified by seed-id.

seed-id Uniquely identifies the MPL seed that initiated
dissemination of the M flag). Each configuration has five parameters:

Imin MPL multicast packet. The minimum Trickle timer interval as defined in
[RFC6206].

Imax
size of seed-id is indicated by the S field.

The maximum Option Data of the Trickle timer interval as defined in
[RFC6206].

k The redundancy constant Multicast option MUST NOT change as defined in [RFC6206].

Tactive The duration that a multicast forwarder can
attempt to forward a
the MPL multicast message.
Specified in units of Imax.

Tdwell The duration packet is forwarded. Nodes that a multicast forwarder must
maintain sliding window state for SeedID after
receiving do not understand
the last multicast message from SeedID.
Specified in units of Imax.

Tactive specifies Trickle Multicast option MUST discard the time duration that a node may retransmit a
multicast message in attempt to forward it packet. Thus,
according to neighboring nodes.
Larger values of Tactive increases [RFC2460] the number three high order bits of retransmissions and
overall dissemination reliability.

Tdwell specifies the time duration for maintaining sliding window
state Option Type
must be set to ensure that a multicast message from SeedID '010'. The Option Data length is received at
most once. Larger values of Tdwell decreases variable.

The seed-id uniquely identifies an MPL seed within the MPL domain.
When seed-id is 128 bits (S=3), the likelihood MPL seed MAY use an IPv6 address
assigned to one of its interfaces that a
node will receive a multicast message more than once.

The specific values are left out of is unique within the MPL
domain. Managing MPL seed identifiers is not within scope of this document as they
are dependent on link-specific properties. How those parameters are
configured are also left out of scope.
document.

The Trickle multicast parameters allow both aggressive and
conservative multicast forwarding strategies. For example, an
aggressive strategy may specify each multicast forwarder to
retransmit any newly received message 3 times on a short fixed period
and maintain state for 12 retransmission periods to avoid receiving
duplicate messages. This aggressive policy can be specified using sequence field establishes a
Trickle parameter set total ordering of Imin = Imax = 100ms, k = infinity, Tactive =
3, and Tdwell = 12. Setting k to infinity disables MPL multicast
packets from the Trickle
suppression mechanism.

A conservative same MPL seed. The MPL seed MUST increment the
sequence field's value on each new MPL multicast forwarding strategy utilizes Trickle
suppression and packet that it
disseminates. Implementations MUST follow the Serial Number
Arithmetic as defined in [RFC1982] when incrementing a larger Imax sequence value
or comparing two sequence values.

Future updates to minimize redundant
transmissions. One such conservative policy is a Trickle parameter
set of Imin = 100ms, Imax = 30min, k = 1, Tactive = 3, and Tdwell =
12.

5. Message Formats

5.1. Trickle Multicast Option

The Trickle Multicast option is carried in an IPv6 Hop-by-Hop Options
header, immediately this specification may define additional fields
following the IPv6 header. seed-id field.

4.2. ICMPv6 MPL Message

The Trickle Multicast
option MPL forwarder uses ICMPv6 MPL messages to advertise information
about recently received MPL multicast packets. The ICMPv6 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SeedID (optional) |M| Sequence |
. MPL Window[1..n] .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option

IP Fields:

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

Destination Address The link-local all-nodes MPL forwarders multicast
address (FF02::TBD).

Hop Limit 255

ICMPv6 Fields:

Type XX (to be confirmed by IANA).

Opt Data Len Length

Code 0

Checksum The ICMP checksum. See [RFC4443].

MPL Window[1..n] List of the Option Data field one or more MPL Windows (defined in octets. MUST
be set
Section 4.2.1).

An MPL forwarder transmits an ICMPv6 MPL message to either 2 or 4.

SeedID Uniquely identifies a Trickle advertise
information about buffered MPL multicast seed packets. More explicitly,
the ICMPv6 MPL message encodes the sliding window state (described in
Section 5.2) that
initiated the dissemination process. MPL forwarder maintains for each MPL seed. The SeedID
field is optional and only appears when Opt Data
Len is set
advertisement serves to 4. When Opt Data Len is set indicate to 2, neighboring MPL forwarders
regarding newer messages that it may send or the SeedID is equivalent neighboring MPL
forwarders have yet to receive.

4.2.1. MPL Window

An MPL Window encodes the IPv6 Source
address.

M Mode flag. Identifies one of two Trickle
parameters sliding window state (described in
Section 5.2 that the MPL forwarder maintains for an MPL seed. Each
MPL Window 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| w-min | w-len | S | seed-id (0, 2 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. buffered-mpl-packets (0 to use when forwarding this multicast
message.

Sequence Identifies relative ordering 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 of multicast
messages from
the source identified by SeedID. sliding window and the number of valid bits
in buffered-mpl-packets. The Option Data sliding window's
upper bound is the sum of w-min and w-len.

S 2-bit unsigned integer. Identifies the Trickle Multicast option MUST NOT change en-
route. Nodes length of
seed-id. 0 indicates that do not understand the Trickle Multicast option
MUST skip over this option seed-id value is 0
and continue processing the header. Thus,
according to [RFC2460] not included in the three high order bits of MPL Option. 1 indicates
that the Option Type
must be equal set to zero. The Option Data length seed-id value is variable.

The SeedID uniquely identifies a Trickle multicast seed within 16-bit unsigned
integer. 2 indicates that the
Trickle multicast domain. The SeedID field may either be an IPv6
address assigned to the seed node or seed-id value is a managed 16-bit value. In
either case,
128-bit unsigned integer. 3 is reserved.

seed-id Indicates the SeedID MUST be unique within MPL seed associated with this
sliding window.

buffered-mpl-packets Variable-length bit vector. Identifies the Trickle
sequence numbers of MPL multicast
domain. Managing packets that
the SeedID namespace MPL forwarder has buffered. The sequence
number is left out of scope. determined by w-min + i, where i is the
offset within buffered-mpl-packets.

The M flag identifies one of two Trickle parameters MPL Window does not have any octet alignment requirement.

5. MPL Forwarder Behavior

An MPL forwarder implementation needs to use when
forwarding the message. This capability manage sliding windows for
each active MPL seed. The sliding window allows a Trickle 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
Domain Packet Dissemination

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

1. With proactive propagation, an MPL forwarder transmits buffered
MPL multicast packets using the Trickle parameter sets that make
different algorithm. This method
is called proactive propagation time vs. control overhead trade-offs.

Sequence establishes a relative ordering of 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
messages from using the same SeedID. The source MUST increment Trickle algorithm. An MPL forwarder only
transmits buffered MPL multicast packets upon discovering that
neighboring devices have not yet to receive the Sequence value when
sourcing corresponding MPL
multicast packets.

When receiving a new Trickle multicast message. Implementations MUST
follow the Serial Number Arithmetic as defined in [RFC1982].

5.2. Trickle ICMPv6 Message

The Trickle ICMP message is used packet, an MPL forwarder first
utilizes proactive propagation to advertise metadata forward the MPL multicast packet.
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 recently newly received Trickle MPL multicast messages. The Trickle ICMP 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Sequence List[1..n] .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP Fields:

Source Address A link-local address assigned packets since they can
assume that some neighboring MPL forwarders have yet to receive the sending
interface.

Destination Address The link-local all-nodes (FF02::1) or link-local
all-routers (FF02::2)
MPL multicast address.

Hop Limit 255

ICMP Fields:

Type XX (to 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
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

As specified in RFC 6206 [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.

MPL defines a fourth 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 the
proactive and reactive propagation methods. TimerExpirations MUST be confirmed by IANA).

Code
greater than 0

Checksum The ICMP checksum. See [RFC4443].

Sequence List[1..n] List of zero, one, or more Sequence Lists
(defined for proactive propagation. TimerExpirations MAY be
set to 0 for reactive propagation, which effectively disables
reactive propagation.

As specified in Section 5.2.1).

The RFC 6206 [RFC6206], a Trickle ICMP message advertises sliding windows maintained by 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.

5.1.2. Proactive Propagation

With proactive propagation, the MPL forwarder transmits buffered MPL
multicast packets using the Trickle algorithm. Each buffered MPL
multicast forwarder. The advertisement serves packet that is proactively being disseminated with
proactive propagation has an associated Trickle timer. Adhering to notify neighbors
Section 5 of
newer messages RFC 6206 [RFC6206], this document defines the following:

o This document defines a "consistent" transmission for proactive
propagation as receiving an MPL multicast packet that it can propagate or has yet to receive. Only
entries the same
MPL seed identifier and sequence number as a buffered MPL packet.

o This document defines an "inconsistent" transmission for messages where Tactive proactive
propagation as receiving an MPL multicast packet that has the same
MPL seed identifier, the M flag set, and has a sequence number
less than the buffered MPL multicast packet's sequence number.

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

o This document defines both MPL multicast packets and ICMPv6 MPL
multicast packets as Trickle messages. These messages are included defined
in the ICMP message. sections below.

o The actions outside the Trickle algorithm that the protocol takes
involve managing sliding windows are encoded using a Sequence
List, defined window state, and is specified in
Section 5.2.1.

5.2.1. Sequence List 5.2.

5.1.3. Reactive Propagation

With reactive propagation, the MPL forwarder transmits ICMPv6 MPL
messages using the Trickle algorithm. A Sequence List contains MPL forwarder maintains a list of Sequence values
single Trickle timer for a SeedID.
Each Sequence List 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|M| rsv | SeqLen | SeedID (2 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Sequence[1..SeqLen] .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

S Indicates length of SeedID. When set to 0,
SeedID is 16 octets. reactive propagation with each MPL domain.
When set to 1, SeedID REACTIVE_TIMER_EXPIRATIONS is 2
octets.

M Indicates one of two 0, the MPL forwarder does not
execute the Trickle parameter sets used algorithm for disseminating multicast messages.

SeqLen Number reactive propagation and reactive
propagation is disabled. Adhering to Section 5 of 2-octet Sequence entries.

SeedID Copied from RFC 6206
[RFC6206], this document defines the following:

o This document defines a recently received Trickle Multicast
option.

Sequence[1..SeqLen] List of recently received Sequence values from
SeedID. Note "consistent" transmission for reactive
propagation as receiving an ICMPv6 MPL message that indicates
neither the Sequence value is only 15
bits and the highest order bit MUST be set receiving nor transmitting node has new MPL multicast
packets to 0.

6. Trickle Multicast Forwarder Behavior

A Trickle Multicast Forwarder implementation needs 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 manage offer.

o This document defines an "event" for reactive propagation as
updating any sliding
windows 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 timers. messages. These mechanisms are used to determine
when received messages should be accepted, when ICMP messages are
transmitted, defined
in the sections below.

o The actions outside the Trickle algorithm that the protocol takes
involve managing sliding window state, and when multicast messages are retransmitted.

6.1. Managing is specified in
Section 5.2.

5.2. Sliding Windows

Every Trickle multicast MPL forwarder MUST maintain a sliding window of
Sequence values sequence
numbers for each SeedID that generated MPL seed of recently received MPL packets. The
sliding window performs two functions:

1. Indicate what MPL multicast messages. 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 the
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
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 indicates the minimum lifetime of the
sliding window. The MPL forwarder MUST NOT free a sliding window
before HoldTimer expires.

When receiving a Trickle an MPL multicast message, packet, if no existing sliding window
exists for the SeedID, MPL seed, the MPL forwarder MUST create a new sliding
window MUST be created before accepting the message. If MPL multicast packet. The MPL forwarder
may reclaim memory constraints are such that resources by freeing a
new sliding window for another
MPL seed if its HoldTimer has expired. If, for any reason, the MPL
forwarder cannot be created, then create a new sliding window, it MUST discard the message must be
ignored.
packet.

If a sliding window exists for the SeedID, MPL seed, the message must be
ignored MPL forwarder MUST
ignore the MPL multicast packet if the message's Sequence value falls below 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 lower bound
of packet and/or pass the window or appears in packet to the list of stored Sequence values within next higher layer.

When accepting an MPL multicast packet, the window. All other messages MPL forwarder MUST be received.

When receiving a message, update
the sliding window MUST be updated with based on the
message's Sequence value. packet's sequence number. If the Sequence value
sequence number is larger not less than WindowMax, the
upper bound of MPL forwarder MUST
set WindowMax to 1 greater than the window, packet's sequence number. If
WindowMax - WindowMin > MPL_MAX_WINDOW_SIZE, the new message establishes MPL forwarder MUST
increment WindowMin such that WindowMax - WindowMin <=
MPL_MAX_WINDOW_SIZE. At the new upper
bound.

Memory constraints may limit same time, the total number of Sequence values MPL forwarder MUST free
any entries in BufferedPackets that
can be stored. An entry may be reclaimed before have a sequence number less than
WindowMin.

If the dwell time
expires if MPL forwarder has available memory resources, it serves as MUST buffer
the lower bound of MPL multicast packet for proactive propagation. If not enough
memory resources are available to buffer the window and packet, the window
has more MPL
forwarder MUST increment WindowMin and free entries in
BufferedPackets that have a sequence number less than one entry. Note WindowMin until
enough memory resources are available. Incrementing WindowMin will
ensure that entries can be reclaimed the MPL forwarder does not accept previously received
packets.

An MPL forwarder MAY reclaim memory resources from sliding windows
for other SeedIDs.

When only MPL seeds. If a sliding window for another MPL seed is
actively disseminating messages and has more than one entry in its
BufferedPackets, the MPL forwarder may free entries for that MPL seed
by incrementing WindowMin as described above.

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

When memory resources are available, an MPL forwarder SHOULD buffer a
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 remains, that entry to reclaim memory
resources.

5.3. Transmission of MPL Multicast Packets

The MPL forwarder manages buffered MPL multicast packet transmissions
using the Trickle algorithm. When adding a packet to
BufferedPackets, the MPL forwarder MUST NOT
be reclaimed until its dwell create a Trickle timer expires. Maintaining for
the packet and start execution of the largest
sequence value received from a SeedID ensures that earlier messages
are received at most once.

6.2. Trickle Timers

A algorithm.

After PROACTIVE_TIMER_EXPIRATIONS Trickle multicast timer events, the MPL
forwarder maintains two Trickle timers
parameterized on MUST stop executing the S flag. The Trickle timer is maintained as
described in [RFC6206]. algorithm. When suppression is enabled (i.e. k is finite), a Trickle
transmission event consists of transmitting a Trickle ICMP message.

If buffered
MPL multicast packet does not have an "inconsistent" advertisement was received during 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 period, supports MPL is configured with exactly one MPL
multicast messages scope. The MPL multicast scope MUST be site-local or
smaller and defaults to link-local. A scope larger than link-local
MAY be used only when that caused scope corresponds exactly to the inconsistency are also
retransmitted.

When suppression is disabled (i.e. k is infinite), a Trickle
transmission event consists MPL
domain.

An MPL domain may therefore be composed of transmitting one or more MPL multicast messages that
have been received within
scopes. For example, the Tactive time window.

This document defines receiving MPL domain may be composed of a "consistent" transmission as
receiving single MPL
multicast scope when using a Trickle ICMP message that indicates neither site-local scope. Alternatively, the receiving
nor transmitting node has new
MPL domain may be composed of multiple MPL multicast messages scopes when
using a link-local scope.

IPv6-in-IPv6 encapsulation MUST be used when using MPL to offer.

This document defines receiving forward an "inconsistent" transmission as
receiving a Trickle ICMP message that indicates either receiving
original multicast packet whose source or
transmitting node has destination address is
outside the MPL multicast scope. IPv6-in-IPv6 encapsulation is
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 new 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 message to offer. An
"inconsistent" transmission also includes receiving a new scopes (e.g.
when the MPL multicast
message.

6.3. Trickle Multicast Option Processing

All IPv6 datagrams containing a Trickle Multicast option scope is link-local), an MPL forwarder MUST have a
decapsulate and encapsulate the original multicast packet when
crossing between different MPL multicast scopes. In doing so, the
MPL forwarder MUST duplicate the MPL Option, unmodified, in the new
outer IPv6 Destination address. If header.

The IPv6 destination address of the MPL multicast packet is the all-
MPL-forwarders multicast address (TBD). The scope of the IPv6 Destination
destination address is not a set to the MPL multicast scope.

5.4. Reception of MPL Multicast Packets

Upon receiving an MPL multicast address, packet, the MPL forwarder first
determines whether or not to accept and buffer the MPL multicast
packet based on its MPL seed and sequence value, as specified in
Section 5.2.

If the MPL forwarder MUST drop accepts the datagram.

A MPL multicast packet, the MPL
forwarder MUST drop determines whether or not to deliver the original multicast message
packet to the next higher layer. For example, if it cannot
ensure that 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

The MPL forwarder generates and transmits a new ICMPv6 MPL message has never been received before. This occurs
when
whenever Trickle requests a transmission. The MPL forwarder includes
an encoding of each sliding window in the Sequence value ICMPv6 MPL message.

Each sliding window is encoded using an MPL Window entry, defined in
Section 5.2. The MPL forwarder sets the MPL Window fields as
follows:

S If the MPL seed identifier is 0, set S to 0. If the MPL seed
identifier is below 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 for SeedID or when an entry already exists for (i.e.
WindowMin).

w-len Set to the length of the Sequence
value.

If no sliding window state for SeedID exists, (i.e. WindowMax - WindowMin).

seed-id If S is non-zero, set to the MPL seed identifier.

buffered-mpl-packets Set each bit that represents a sequence number
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

An MPL forwarder processes each ICMPv6 MPL message that it receives
to determine if it has any new MPL multicast packets to receive or
offer.

An MPL forwarder
MUST allocate determines if a new sliding window for the SeedID before accepting MPL multicast packet has not
been received from a neighboring node if any of the message. If following
conditions hold true:

1. The ICMPv6 MPL message includes an MPL Window for an MPL seed
that does not have a corresponding sliding window cannot be allocated, the forwarder
MUST drop the message.

Upon accepting the message, the forwarder MUST enter entry on 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 in its BufferedPackets that has
sequence number within range of the sliding window and decrement the IPv6 Hop Limit. If but is not
included in BufferedPackets (i.e. the
IPv6 Hop Limit i'th bit in buffered-mpl-
packets is non-zero, set to 1, where the sequence number is w-min + i).

When an MPL forwarder MUST buffer the message for
retransmission for the duration specified determines that it has not yet received a new
MPL multicast packet buffered by Tactive.

6.4. Trickle ICMP Processing

Processing a neighboring device, the MPL
forwarder resets the Trickle ICMP message involves determining timer associated with reactive
propagation.

An MPL forwarder determines if either the
receiver or transmitter has new multicast messages to offer.

The transmitter an entry in BufferedPackets has new multicast messages to offer not
been received by a neighboring MPL forwarder if any (SeedID,
Sequence) pair falls within an existing sliding window for SeedID but of the following
conditions hold true:

1. The ICMPv6 MPL message does not have include an associated entry. MPL Window for the
packet's MPL seed.

2. The transmitter has new multicast messages packet's sequence number is greater than or equal to offer if the (SeedID,
Sequence) pair
neighbor's WindowMax value (i.e. the packet's sequence number is great
greater than or equal to w-min + w-len).

3. The packet's sequence number is within the upper bound range of an existing the
neighbor's sliding window for SeedID.

The receiver has new multicast messages [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 offer if any 0.

When an MPL forwarder determines that it has at least one buffered
messages are
MPL multicast packet that has not listed in yet been received by a neighbor,
the Trickle ICMP message and MPL forwarder resets the Trickle
ICMP message contains a (SeedID, Sequence) pair timer associated with reactive
propagation. Additionally, for a prior multicast
message.

The receiver has a new multicast message to offer if any each buffered
messages does not have an associated SeedID entry in MPL multicast packet
that should be transferred, the MPL forwarder MUST reset the Trickle ICMP
message.
timer and reset e to 0 for proactive propagation. If neither receiver nor transmitter the Trickle
timer for proactive propagation has new multicast messages to
offer, already stopped execution, the multicast
MPL forwarder logs MUST initialize a consistent event by
incrementing c, as described in [RFC6206].

If either receiver or transmitter has new multicast messages to
offer, Trickle timer and start execution
of the multicast Trickle algorithm.

6. MPL Parameters

An MPL forwarder logs an inconsistent event by
resetting maintains two sets of Trickle parameters for the
proactive and reactive methods. The Trickle parameters are listed
below:

PROACTIVE_IMIN The minimum Trickle timer T[M], interval, as described defined in [RFC6206]. All new
messages
[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 Trickle timer expirations
that occur before terminating the receiver can offer Trickle algorithm. MUST be scheduled set
to a value greater than 0.

REACTIVE_IMIN The minimum Trickle timer interval, as defined in
[RFC6206] for
transmission at the next transmission event. Note reactive propagation.

REACTIVE_IMAX The maximum Trickle timer interval, as defined in
[RFC6206] for reactive propagation.

REACTIVE_K The redundancy constant, as defined in [RFC6206] for
reactive propagation.

REACTIVE_TIMER_EXPIRATIONS The number of Trickle timer expirations
that these
transmissions may be suppressed if occur before terminating the transmission event is
suppressed. Trickle algorithm. MAY be set
to 0, which disables reactive propagation.

WINDOW_HOLD_TIME The minimum lifetime for sliding window state.

7. Acknowledgements

TODO.

The authors would like to acknowledge the helpful comments 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

The Trickle Multicast option requires an IPv6 Option Number.

HEX act chg rest
--- --- --- -----
C 00 01 0 01100 TBD

The first two bits indicate that the IPv6 node may skip over this
option and continue processing MUST discard the header
packet if it doesn't recognize the option type, and the third bit
indicates that the Option Data MUST NOT change en-route.

9. Security Considerations

TODO.

10. References

10.1. Normative References

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

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

[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.

[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