Internet DRAFT - draft-ietf-roll-dao-projection
draft-ietf-roll-dao-projection
ROLL P. Thubert, Ed.
Internet-Draft
Updates: 6550, 6553, 8138 (if approved) R.A. Jadhav
Intended status: Standards Track Huawei Tech
Expires: 2 June 2024 M. Richardson
Sandelman
30 November 2023
Root initiated routing state in RPL
draft-ietf-roll-dao-projection-34
Abstract
This document extends RFC 6550, RFC 6553, and RFC 8138 to enable a
RPL Root to install and maintain Projected Routes within its DODAG,
along a selected set of nodes that may or may not include itself, for
a chosen duration. This potentially enables routes that are more
optimized or resilient than those obtained with the classical
distributed operation of RPL, either in terms of the size of a
Routing Header or in terms of path length, which impacts both the
latency and the packet delivery ratio.
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 https://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 2 June 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Thubert, et al. Expires 2 June 2024 [Page 1]
Internet-Draft DAO Projection November 2023
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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2.2. References . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Domain Terms . . . . . . . . . . . . . . . . . . . . . . 6
2.4.1. Projected Route . . . . . . . . . . . . . . . . . . . 6
2.4.2. Projected DAO . . . . . . . . . . . . . . . . . . . . 7
2.4.3. Path . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4.4. Routing Stretch . . . . . . . . . . . . . . . . . . . 7
2.4.5. Track . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Context and Goal . . . . . . . . . . . . . . . . . . . . . . 10
3.1. RPL Applicability . . . . . . . . . . . . . . . . . . . . 11
3.2. Multi-Topology Routing and Loop Avoidance . . . . . . . . 12
3.3. Requirements . . . . . . . . . . . . . . . . . . . . . . 14
3.3.1. Loose Source Routing . . . . . . . . . . . . . . . . 14
3.3.2. forward Routes . . . . . . . . . . . . . . . . . . . 16
3.4. On Tracks . . . . . . . . . . . . . . . . . . . . . . . . 17
3.4.1. Building Tracks With RPL . . . . . . . . . . . . . . 17
3.4.2. Tracks and RPL Instances . . . . . . . . . . . . . . 18
3.5. path Signaling . . . . . . . . . . . . . . . . . . . . . 19
3.5.1. Using Storing Mode Segments . . . . . . . . . . . . . 21
3.5.2. Using Non-Storing Mode joining Tracks . . . . . . . . 27
3.6. Complex Tracks . . . . . . . . . . . . . . . . . . . . . 34
3.7. Scope and Expectations . . . . . . . . . . . . . . . . . 36
3.7.1. External Dependencies . . . . . . . . . . . . . . . . 36
3.7.2. Positioning vs. Related IETF Standards . . . . . . . 36
4. Extending existing RFCs . . . . . . . . . . . . . . . . . . . 38
4.1. Extending RFC 6550 . . . . . . . . . . . . . . . . . . . 38
4.1.1. Projected DAO . . . . . . . . . . . . . . . . . . . . 39
4.1.2. Projected DAO-ACK . . . . . . . . . . . . . . . . . . 41
4.1.3. Via Information Option . . . . . . . . . . . . . . . 42
4.1.4. Sibling Information Option . . . . . . . . . . . . . 42
4.1.5. P-DAO Request . . . . . . . . . . . . . . . . . . . . 43
4.1.6. Amending the RPI . . . . . . . . . . . . . . . . . . 43
4.1.7. Additional Flag in the RPL DODAG Configuration
Option . . . . . . . . . . . . . . . . . . . . . . . 43
4.2. Extending RFC 6553 . . . . . . . . . . . . . . . . . . . 44
4.3. Extending RFC 8138 . . . . . . . . . . . . . . . . . . . 45
5. New RPL Control Messages and Options . . . . . . . . . . . . 46
Thubert, et al. Expires 2 June 2024 [Page 2]
Internet-Draft DAO Projection November 2023
5.1. New P-DAO Request Control Message . . . . . . . . . . . . 47
5.2. New PDR-ACK Control Message . . . . . . . . . . . . . . . 48
5.3. Via Information Options . . . . . . . . . . . . . . . . . 49
5.4. Sibling Information Option . . . . . . . . . . . . . . . 52
6. Root Initiated Routing State . . . . . . . . . . . . . . . . 54
6.1. RPL Network Setup . . . . . . . . . . . . . . . . . . . . 54
6.2. Requesting a Track . . . . . . . . . . . . . . . . . . . 55
6.3. Identifying a Track . . . . . . . . . . . . . . . . . . . 56
6.4. Installing a Track . . . . . . . . . . . . . . . . . . . 57
6.4.1. Signaling a Projected Route . . . . . . . . . . . . . 58
6.4.2. Installing a Track Segment with a Storing Mode
P-Route . . . . . . . . . . . . . . . . . . . . . . . 59
6.4.3. Installing a lane with a Non-Storing Mode P-Route . . 61
6.5. Tearing Down a P-Route . . . . . . . . . . . . . . . . . 63
6.6. Maintaining a Track . . . . . . . . . . . . . . . . . . . 63
6.6.1. Maintaining a Track Segment . . . . . . . . . . . . . 64
6.6.2. Maintaining a lane . . . . . . . . . . . . . . . . . 64
6.7. Encapsulating and Forwarding Along a Track . . . . . . . 65
6.8. Compression of the RPL Artifacts . . . . . . . . . . . . 68
7. Lesser Constrained Variations . . . . . . . . . . . . . . . . 70
7.1. Storing Mode main DODAG . . . . . . . . . . . . . . . . . 70
7.2. A Track as a Full DODAG . . . . . . . . . . . . . . . . . 72
8. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 73
9. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 75
10. Security Considerations . . . . . . . . . . . . . . . . . . . 75
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 76
11.1. RPL DODAG Configuration Option Flag . . . . . . . . . . 76
11.2. Elective 6LoWPAN Routing Header Type . . . . . . . . . . 76
11.3. Critical 6LoWPAN Routing Header Type . . . . . . . . . . 77
11.4. Registry For The RPL Option Flags . . . . . . . . . . . 77
11.5. RPL Control Codes . . . . . . . . . . . . . . . . . . . 78
11.6. RPL Control Message Options . . . . . . . . . . . . . . 78
11.7. SubRegistry for the Projected DAO Request Flags . . . . 78
11.8. SubRegistry for the PDR-ACK Flags . . . . . . . . . . . 79
11.9. Registry for the PDR-ACK Acceptance Status Values . . . 79
11.10. Registry for the PDR-ACK Rejection Status Values . . . . 80
11.11. SubRegistry for the Via Information Options Flags . . . 80
11.12. SubRegistry for the Sibling Information Option Flags . . 81
11.13. Destination Advertisement Object Flag . . . . . . . . . 81
11.14. Destination Advertisement Object Acknowledgment Flag . . 82
11.15. New ICMPv6 Error Code . . . . . . . . . . . . . . . . . 82
11.16. RPL Rejection Status values . . . . . . . . . . . . . . 82
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 83
13. Normative References . . . . . . . . . . . . . . . . . . . . 83
14. Informative References . . . . . . . . . . . . . . . . . . . 85
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 87
Thubert, et al. Expires 2 June 2024 [Page 3]
Internet-Draft DAO Projection November 2023
1. Introduction
RPL, the "Routing Protocol for Low Power and Lossy Networks" [RPL]
(LLNs), is an anisotropic Distance Vector protocol that is well-
suited for application in a variety of low energy Internet of Things
(IoT) networks where stretched P2P paths are acceptable vs. the
signaling and state overhead involved in maintaining the shortest
paths across.
RPL forms Destination Oriented Directed Acyclic Graphs (DODAGs) in
which the Root often acts as the Border router to connect the RPL
domain to the IP backbone. Routers inside the DODAG route along that
graph up towards the Root for the default route and down towards
destinations in the RPL domain for more specific routes. This
specification expects as a pre-requisite a pre-existing RPL Instance
with an associated DODAG and RPL Root, which are referred to as main
Instance, main DODAG and main Root respectively. The main Instance
is operated in RPL Non-Storing Mode of Operation (MOP).
With this specification, an abstract routing function called a Path
Computation Element [PCE] (e.g., located in an central controller or
collocated with the main Root) interacts with the main Root to
compute Peer-to-Peer (P2P) paths within the main Instance. In Non-
Storing Mode, the base topological information to be passed to the
PCE, that is the knowledge of the main DODAG, is already available at
the Root. This specification introduces protocol extensions that
enrich the topological information available to the Root with sibling
relationships that are usable but not leveraged to form the main
DODAG.
Based on usage, path length, and knowledge of available resources
such as battery levels and reservable buffers in the nodes, the PCE
with a global visibility of the system can optimize the computed
routes for the application needs, including the capability to provide
path redundancy. This specification also introduces protocol
extensions that enable the Root to translate the computed paths into
RPL and install them as Projected Routes (aka P-Routes) inside the
DODAG on behalf of a PCE.
A P-Route may be installed in either Storing and Non-Storing Mode,
potentially resulting in hybrid situations where the Mode in which
the P-Route operates is different from that of the RPL main Instance.
P-Routes can be used as stand-alone Segments meant to reduce the size
of the source routing headers, leveraging loose source routing
operations down the main RPL DODAG. P-Routes can also be combined
with other P-Routes to form a protection Path called a Track and
signaled as a RPL Instance. A Track provides underlay shortcuts in
an existing main Instance, each with its own RIB.
Thubert, et al. Expires 2 June 2024 [Page 4]
Internet-Draft DAO Projection November 2023
2. Terminology
2.1. Requirements Language
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 BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
In addition, the terms "Extends" and "Amends" are used as per
[I-D.kuehlewind-update-tag] section 3.
2.2. References
In this document, readers will encounter terms and concepts that are
discussed in the "Routing Protocol for Low Power and Lossy Networks"
[RPL], the "6TiSCH Architecture" [RFC9030], the "Deterministic
Networking Architecture" [RFC8655], the "Using RPI Option Type,
Routing Header for Source Routes, and IPv6-in-IPv6 Encapsulation in
the RPL Data Plane" [RFC9008], the "Reliable and Available Wireless
(RAW) Architecture" [RAW-ARCHI], and "Terminology in Low power And
Lossy Networks" [RFC7102]. Both architecture documents define the
concept of Track in a compatible fashion. This documents only builds
Tracks that are DODAGs, meaning that all links are oriented From
Ingress to Egress. This specification also utilizes the terms
Segment and Lane that are also defined in the RAW Architecture.
As opposed to routing trees, RPL DODAGs are typically constructed to
provide redundancy and dynamically adapt the forwarding operation to
the state of the LLN links. Note that the plain forwarding operation
over DODAGs does not provide redundancy for all nodes, since at least
the node nearest to the Root does not have an alternate feasible
successor.
RAW solves that problem by defining Protection Paths that can be
fully non-congruent and can be activated dynamically upon failures.
This requires additional control to take the routing decision early
enough along the Track to route around the failure.
RAW only uses single-ended DODAGs, meaning that they can be reversed
in another DODAG by reversing all the links. The Ingress of the
Track is the Root of the DODAG, whereas the Egress is the Root of the
reversed DODAG. From the RAW perspective, single-ended DODAGs are
special Tracks that only have forward links, and that can be
leveraged to provide Protection services by defining destination-
oriented Protection Paths within the DODAG.
Thubert, et al. Expires 2 June 2024 [Page 5]
Internet-Draft DAO Projection November 2023
2.3. Glossary
This document often uses the following acronyms:
ARQ: Automatic Repeat Request, in other words retries
FEC: Forward Error Correction
HARQ: Hybrid Automatic Repeat Request, combining FEC and ARQ
CMO: Control Message Option
DAO: Destination Advertisement Object
DAG: Directed Acyclic Graph
DODAG: Destination-Oriented Directed Acyclic Graph; A DAG with only
one vertex (i.e., node) that has no outgoing edge (i.e., link)
GUA: IPv6 Global Unicast Address
LLN: Low-Power and Lossy Network
MOP: RPL Mode of Operation
P-DAO: Projected DAO
P-Route: Projected Route
PDR: P-DAO Request
PCE: Path Computation Element
PLR: Point of Local Repair
RAN: RPL-Aware Node (either a RPL router or a RPL-Aware Leaf)
RAL: RPL-Aware Leaf
RH: Routing Header
RIB: Routing Information Base, aka the routing table.
RPI: RPL Packet Information
RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks
RTO: RPL Target Option
RUL: RPL-Unaware Leaf
SIO: RPL Sibling Information Option
ULA: IPv6 Unique Local Address
NSM-VIO: A Source-Routed Via Information Option, used in Non-Storing
Mode P-DAO messages
SLO: Service Level Objective
TIO: RPL Transit Information Option
SM-VIO: A strict Via Information Option, used in Storing Mode P-DAO
messages
VIO: A Via Information Option; it can be an SM-VIO or a NSM-VIO
2.4. Domain Terms
This specification uses the following terminology:
2.4.1. Projected Route
A RPL P-Route is a RPL route that is computed remotely by a PCE, and
installed and maintained by a RPL Root on behalf of the PCE. It is
installed as a state that signals that destinations (aka Targets) are
reachable along a sequence of nodes.
Thubert, et al. Expires 2 June 2024 [Page 6]
Internet-Draft DAO Projection November 2023
2.4.2. Projected DAO
A DAO message used to install a P-Route.
2.4.3. Path
Quoting section 1.1.3 of [INT-ARCHI]:
| At a given moment, all the IP datagrams from a particular source
| host to a particular destination host will typically traverse the
| same sequence of gateways. We use the term "path" for this
| sequence. Note that a path is uni-directional; it is not unusual
| to have different paths in the two directions between a given host
| pair.
Section 2 of [I-D.irtf-panrg-path-properties] points to a longer,
more modern definition of path, which begins as follows:
| A sequence of adjacent path elements over which a packet can be
| transmitted, starting and ending with a node. A path is
| unidirectional. Paths are time-dependent, i.e., the sequence of
| path elements over which packets are sent from one node to another
| may change. A path is defined between two nodes.
It follows that the general acceptance of a path is a linear sequence
of nodes, as opposed to a multi-dimensional graph. In the context of
this document, a path is observed by following one copy of a packet
that is injected in a Track and possibly replicated within.
2.4.4. Routing Stretch
RPL is anisotropic, meaning that it is directional, or more exactly
polar. RPL does not behave the same way "downwards" (root towards
leaves) with _multicast_ DIO messages that form the DODAG and
"upwards" (leaves towards root) with _unicast_ DAO messages that
follow the DODAG. This is in contrast with traditional IGPs that
operate the same way in all directions and are thus called isotropic.
The term Routing Stretch denotes the length of a path, in comparison
to the length of the shortest path, which can be an abstract concept
in RPL when the metrics are statistical and dynamic, and the concept
of distance varies with the Objective Function.
The RPL DODAG optimizes the P2MP (Point-to-MultiPoint) (from the
Root) and MP2P (MultiPoint-to-Point) (towards the Root) paths, but
the P2P (Point-to-Point) traffic has to follow the same DODAG.
Following the DODAG, the RPL datapath passes via a common parent in
Storing Mode and via the Root in Non-Storing Mode. This typically
Thubert, et al. Expires 2 June 2024 [Page 7]
Internet-Draft DAO Projection November 2023
involves more hops and more latency than the minimum possible for a
direct P2P path that an isotropic protocol would compute. We refer
to this elongated path as stretched.
2.4.5. Track
The concept of Track is inherited from the "6TiSCH Architecture"
[RFC9030] and matches that of a Protection Path in the RAW
Architecture" [RAW-ARCHI]. A Track is a networking graph that can be
followed to transport packets with equivalent treatment; as opposed
to the definition of a path above, a Track is not necessarily linear.
It may contain multiple paths that may fork and rejoin, and may
enable the RAW Packet ARQ, Replication, Elimination, and Overhearing
(PAREO) operations.
Figure 1 illustrates the mapping of the DODAG with the generic
concept of a Track, with the DODAG Root acting as Ingress for the
Track, and the mapping of Lanes and Segments, and only forward
Segments, meaning that they are directional and progressing towards
the destination.
North East North West
A ==> B ==> C -=- F ==> G ==> H T1 I: Ingress
/ \ / \ / E: Egress
I O E -=- T2 T1, T2, T3:
\ / \ / \ External
P ==> Q ==> R -=- T ==> U ==> V T3 Targets
South East South West
I ==> A ==> B ==> C : a Segment to targets F and O
I --> F --> E : a Lane to targets T1, T2, T3
I, A, B, C, F, G, H, E : a path to T1, T2, T3
Figure 1: A Track and its Components
This specification builds Tracks that are DODAGs oriented towards a
Track Ingress, and the forward direction for packets (aka forward) is
from the Track Ingress to one of the possibly multiple Track Egress
Nodes, which is also down the DODAG.
The Track may be strictly connected, meaning that the vertices are
adjacent, or loosely connected, meaning that the vertices are
connected using Segments that are associated to the same Track.
Thubert, et al. Expires 2 June 2024 [Page 8]
Internet-Draft DAO Projection November 2023
2.4.5.1. TrackID
A RPL InstanceID (typically of a Local Instance) that identifies a
Track using the namespace owned by the Track Ingress. For Local
Instances, the TrackID is associated with the IPv6 Address of the
Track Ingress that is used as DODAGID, and together they form a
unique identification of the Track (see the definition of DODAGID in
section 2 of [RPL].
2.4.5.2. Namespace
The term namespace is used to refer to the scope of the TrackID. The
TrackID is locally significant within its namespace. For Local
Instances, the namespace is identified by the DODAGID for the Track
and the tuple (DODAGID, TrackID) is globally unique. For Global
Instances, the namespace is the whole RPL domain.
2.4.5.3. Complex Track
A Track that can be traversed via more than one path (e.g., a DODAG).
2.4.5.4. Stand-Alone
Refers to a Segment or a Lane that is installed with a single P-DAO
that fully defines the path, e.g., a stand-alone segment is installed
with a single Storing Mode Via Information option (SM-VIO) all the
way between Ingress and Egress.
2.4.5.5. Stitching
This specification uses the term stitching to indicate that a track
is piped to another one, meaning that traffic out of the first track
is injected into the other track.
2.4.5.6. Lane
The concept of Lane is defined in the RAW Architecture" [RAW-ARCHI]
as an end-to-end forward serial path. With this specification, a
Lane is installed by the Root of the main DODAG using a Non-Storing
Mode P-DAO message, e.g., I --> F --> E in Figure 1.
As the Non-Storing Mode Via Information option (NSM-VIO) can only
signal sequences of nodes, it takes one Non-Storing Mode P-DAO
message per Lane to signal the structure of a complex Track.
Each NSM-VIO for the same TrackId but with a different Segment ID
signals a different Lane that the Track Ingress adds to the topology.
Thubert, et al. Expires 2 June 2024 [Page 9]
Internet-Draft DAO Projection November 2023
2.4.5.7. Segment
A serial path formed by a strict sequence of nodes, along which a
P-Route is installed, e.g., I ==> A ==> B ==> C in Figure 1. With
this specification, a Segment is typically installed by the Root of
the main DODAG using Storing Mode P-DAO messages. A Segment is used
as the topological edge of a Track joining the loose steps along the
Lanes that form the structure of a complex Track. The same Segment
may be leveraged by more than one Lane where the Lanes overlap.
Since this specification builds only DODAGs, all Segments are
oriented from Ingress (East) to Egress (West), as opposed to the
general Track model in the RAW Architecture [RAW-ARCHI], which allows
North/South Segments that can be bidirectional as well.
2.4.5.7.1. Section of a Segment
A continuous subset of a Segment that may be replaced while the
Segment remains. For instance, in Segment A=>B=>C=>D=>E=>F, say that
the link C to D might be misbehaving. The section B=>C=>D=>E in the
Segment may be replaced by B=>C’=>D’=>E to route around the problem.
The Segment becomes A=>B=>C’=>D’=>E=>F.
2.4.5.7.2. Segment Routing and SRH
The terms Segment Routing and SRH refer to using source-routing to
hop over Segments. In a Non-Storing mode RPL domain, the SRH is
typically a RPL Source Route Header (the IPv6 RH of type 3) as
defined in [RFC6554].
If the network is a 6LoWPAN Network, the expectation is that the SRH
is compressed and encoded as a 6LoWPAN Routing Header (6LoRH), as
specified in section 5 of [RFC8138].
On the other hand, if the RPL Network is less constrained and
operated in Storing Mode, as discussed in Section 7.1, the Segment
Routing operation and the SRH could be as specified in [RFC8754].
This specification applies equally to both forms of source routing
and SRH.
3. Context and Goal
Thubert, et al. Expires 2 June 2024 [Page 10]
Internet-Draft DAO Projection November 2023
3.1. RPL Applicability
RPL is optimized for situations where the power is scarce, the
bandwidth is constrained and the transmissions are unreliable. This
matches the use case of an IoT LLN where RPL is typically used today,
but also situations of high relative mobility between the nodes in
the network (aka swarming), e.g., within a variable set of vehicles
with a similar global motion, or a platoon of drones.
To reach this goal, RPL is primarily designed to minimize the control
plane activity, that is the relative amount of routing protocol
exchanges vs. data traffic, and the amount of state that is
maintained in each node. RPL does not need to converge, and provides
connectivity to most nodes most of the time.
RPL may form multiple topologies called instances. Instances can be
created to enforce various optimizations through objective functions,
or to reach out through different Root Nodes. The concept of
objective function allows to adapt the activity of the routing
protocol to the use case, e.g., type, speed, and quality of the LLN
links.
RPL instances operate as ships passing in the night, unbeknownst of
one another. The RPL Root is responsible for selecting the RPL
Instance that is used to forward a packet coming from the Backbone
into the RPL domain and for setting the related RPL information in
the packets. Each Instance creates its own routing table (RIB) in
participating nodes, and the RIB associated to the instance must be
used end to end in the RPL domain. To that effect, RPL tags the
packets with the Instance ID in a Hop-by-Hop extension Header.
6TiSCH leverages RPL for its distributed routing operations.
To reduce the routing exchanges, RPL leverages an anisotropic
Distance Vector approach, which does not need a global knowledge of
the topology, and only optimizes the routes to and from the RPL Root,
allowing P2P paths to be stretched. Although RPL installs its routes
proactively, it only maintains them lazily, in reaction to actual
traffic, or as a slow background activity.
This is simple and efficient in situations where the traffic is
mostly directed from or to a central node, such as the control
traffic between routers and a controller of a Software Defined
Networking (SDN) infrastructure or an Autonomic Control Plane (ACP).
Thubert, et al. Expires 2 June 2024 [Page 11]
Internet-Draft DAO Projection November 2023
But stretch in P2P routing is counter-productive to both reliability
and latency as it introduces additional delay and chances of loss.
As a result, [RPL] is not a good fit for the use cases listed in the
RAW use cases document [RFC9450], which demand high availability and
reliability, and as a consequence require both short and diverse
paths.
3.2. Multi-Topology Routing and Loop Avoidance
RPL first forms a default route in each node towards the Root, and
those routes together coalesce as a Directed Acyclic Graph oriented
upwards. RPL then constructs routes to destinations signaled as
Targets in the reverse direction, down the same DODAG. To do so, a
RPL Instance can be operated either in RPL Storing or Non-Storing
Mode of Operation (MOP). The default route towards the Root is
maintained aggressively and may change while a packet progresses
without causing loops, so the packet will still reach the Root.
In Non-Storing Mode, each node advertises itself as a Target directly
to the Root, indicating the parents that may be used to reach itself.
Recursively, the Root builds and maintains an image of the whole
DODAG in memory, and leverages that abstraction to compute source
route paths for the packets to their destinations down the DODAG.
When a node changes its point(s) of attachment to the DODAG, it takes
a single unicast packet to the Root along the default route to update
it, and the connectivity to the node is restored immediately; this
mode is preferable for use cases where internet connectivity is
dominant, or when the Root controls the network activity in the
nodes, which is the case of this draft.
In Storing Mode, the routing information percolates upwards, and each
node maintains the routes to the subDAG of its descendants down the
DODAG. The maintenance is lazy, either reactive upon traffic or as a
slow background process. Packets flow via the common parent and the
routing stretch is reduced compared to Non-Storing MOP, for better
P2P connectivity. However, a new route takes a longer time to
propagate to the Root, since it takes time for the Distance-Vector
protocol to operate hop-by-hop, and the connectivity from the
internet to the node is restored more slowly upon node movement.
Either way, the RPL routes are injected by the Target nodes, in a
distributed fashion. To complement RPL and eliminate routing
stretch, this specification introduces a hybrid mode that combines
Storing and Non-Storing operations to build and project routes onto
the nodes where they should be installed. This specification uses
the term Projected Route (P-Route) to refer to those routes.
Thubert, et al. Expires 2 June 2024 [Page 12]
Internet-Draft DAO Projection November 2023
In the simplest mode of this specification, Storing-Mode P-Routes can
be deployed to join the dots of a loose source routing header (SRH)
in the main DODAG. In that case, all the routes (source routed and
P-Routes) belong to the Routing Information base (RIB) associated
with the main Instance. Storing-Mode P-Routes are referred to as
Segments in this specification.
A set of P-Routes can also be projected to form a dotted-line
underlay of the main Instance and provide Traffic Engineered paths
for an application. In that case, the P-Routes are installed in Non-
Storing Mode and the set of P-Routes is called a Track. A Track is
associated with its own RPL Instance, and, as any RPL Instance, with
its own Routing Information base (RIB). As a result, each Track
defines a routing topology in the RPL domain. As for the main DODAG,
Segments associated to the Track Instance may be deployed to join the
dots using Storing-Mode P-Routes.
Routing in a multi-topology domain may cause loops unless strict
rules are applied. This specification defines two strict orders to
ensure loop avoidance when projected routes are used in a RPL domain,
one between forwarding methods and one between RPL Instances, seen as
routing topologies.
The first and strict order relates to the forwarding method and the
more specifically the origin of the information used in the next-hop
computation. The possible forwarding methods are: 1) to a direct
next hop, 2) to an indirect neighbor via a common neighbor, 3) along
a Segment, and 4) along a nested Track. The methods are strictly
ordered as listed above, more in Section 6.7. A forwarding method
may leverage any of the lower order ones, but never one with a higher
order; for instance, when forwarding a packet along a Segment, the
router may use direct or indirect neighbors but cannot use a Track.
The lower order methods have a strict precedence, so the router will
always prefer a direct neighbor over an indirect one, or a Segment
within the current RPL Instance vs. another Track.
The second strict and partial order is between RPL Instances. It
allows the RPL node to detect an error in the state installed by the
PCE, e.g., after a desynchronization. That order must be defined by
the administrator for his RPL domain and defines a DODAG of underlays
with the main Instance as Root. The relation of RPL instances may be
represented as a DODAG of instances where the main instance is Root.
The rule is that a RPL Instance may leverage another RPL instance as
underlay if and only if that other Instance is one of its descendants
in the graph. Supporting this method is OPTIONAL for nested Tracks
and REQUIRED between a Track instance and the main instance. It may
be done using network management, or future extensions to this
specifications. When it is not communicated, then the RPL nodes
Thubert, et al. Expires 2 June 2024 [Page 13]
Internet-Draft DAO Projection November 2023
consider by default that all Track instances are children of the main
instance, and do not attempt to validate the order for nested Tracks,
trusting the PCE implicitly. As a result, a packet that is being
forwarded along the main Instance may be encapsulated in any Track,
but a packet that was forwarded along a Track MUST NOT be forwarded
along the default route of main Instance.
3.3. Requirements
3.3.1. Loose Source Routing
A RPL implementation operating in a very constrained LLN typically
uses the Non-Storing Mode of Operation as represented in Figure 2.
In that mode, a RPL node indicates a parent-child relationship to the
Root, using a destination Advertisement Object (DAO) that is unicast
from the node directly to the Root, and the Root typically builds a
source routed path to a destination down the DODAG by recursively
concatenating this information.
+-----+
| | Border router
| | (RPL Root)
+-----+ ^ | |
| | DAO | ACK |
o o o o | | | Strict
o o o o o o o o o | | | Source
o o o o o o o o o o | | | Route
o o o o o o o o o | | |
o o o o o o o o | v v
o o o o
LLN
Figure 2: RPL Non-Storing Mode of operation
Based on the parent-children relationships expressed in the Non-
Storing DAO messages, the Root possesses topological information
about the whole network, though this information is limited to the
structure of the DODAG for which it is the destination. A packet
that is generated within the domain will always reach the Root, which
can then apply a source routing information to reach the destination
if the destination is also in the DODAG. Similarly, a packet coming
from the outside of the domain for a destination that is expected to
be in a RPL domain reaches the Root. This results in the wireless
bandwidth near the Root being the limiting factor for all
transmissions towards or within the domain, and that the Root is a
single point of failure for all connectivity to nodes within its
domain.
Thubert, et al. Expires 2 June 2024 [Page 14]
Internet-Draft DAO Projection November 2023
The RPL Root must add a source routing header to all downward
packets. As a network grows, the size of the source routing header
increases with the depth of the network. In some use cases, a RPL
network forms long lines along physical structures such as streets
for lighting. Limiting the packet size is beneficial to the energy
budget, directly for the current transmission, but also indirectly
since it reduces the chances of frame loss and energy spent in
retries, e.g., by ARQ over one hop at Layer-2, or end-to-end at upper
layers. Using smaller packets also reduces the chances of packet
fragmentation, which is highly detrimental to the LLN operation, in
particular when fragments are forwarded but not recovered, see
[RFC8930] vs. [RFC8931] for more.
A limited amount of well-targeted routing state would allow the
source routing operation to be loose as opposed to strict, and reduce
the overhead of routing information in packets. Because the
capability to store routing state in every node is limited, the
decision of which route is installed where can only be optimized with
global knowledge of the system, knowledge that the Root or an
associated PCE may possess by means that are outside the scope of
this specification.
Being on-path for all packets in Non-Storing mode, the Root may
determine the number of P2P packets in its RPL domain per source and
destination, the latency incurred, and the amount of energy and
bandwidth that is consumed to reach itself and then back down,
including possible fragmentation when encapsulating larger packets.
Enabling a shorter path that would not traverse the Root for select
P2P source/destinations may improve the latency, lower the
consumption of constrained resources, free bandwidth at the
bottleneck near the Root, improve the delivery ratio and reduce the
latency for those P2P flows with a global benefit for all flows by
reducing the load at the Root.
To limit the need for source route headers in deep networks, one
possibility is to store a routing state associated with the main
DODAG in select RPL routers down the path. The Root may elide the
sequence of routers that is installed in the network from its source
route header, which therefore becomes loose, in contrast to being
strict in [RPL].
Thubert, et al. Expires 2 June 2024 [Page 15]
Internet-Draft DAO Projection November 2023
3.3.2. forward Routes
[RPL] optimizes Point-to-Multipoint (P2MP) routes from the Root,
Multipoint-to-Point (MP2P) routes to the DODAG Root, and Internet
access when the Root also serves as Border Router. All routes are
installed North-South (aka up/down) along the RPL DODAG. Peer to
Peer (P2P) forward routes in a RPL network will generally experience
elongated (stretched) paths versus direct (optimized) paths, since
routing between two nodes always happens via a common parent, as
illustrated in Figure 3:
------+---------
| Internet
+-----+
| | Border router
| | (RPL Root)
+-----+
X
^ v o o
^ o o v o o o o o
^ o o o v o o o o o
^ o o v o o o o o
S o o o D o o o
o o o o
LLN
Figure 3: Routing Stretch between S and D via common parent X
along North-South Paths
As described in [RFC9008], the amount of stretch depends on the Mode
of Operation:
* in Non-Storing Mode, all packets routed within the DODAG flow all
the way up to the Root of the DODAG. If the destination is in the
same DODAG, the Root must encapsulate the packet to place an RH
that has the strict source route information down the DODAG to the
destination. This will be the case even if the destination is
relatively close to the source and the Root is relatively far off.
* In Storing Mode, unless the destination is a child of the source,
the packets will follow the default route up the DODAG as well.
If the destination is in the same DODAG, they will eventually
reach a common parent that has a route to the destination; at
worse, the common parent may also be the Root. From that common
parent, the packet will follow a path down the DODAG that is
optimized for the Objective Function that was used to build the
DODAG.
Thubert, et al. Expires 2 June 2024 [Page 16]
Internet-Draft DAO Projection November 2023
It turns out that it is often beneficial to enable forward P2P
routes, either if the RPL route presents a stretch from the shortest
path, or if the new route is engineered with a different objective,
and this is even more critical in Non-Storing Mode than it is in
Storing Mode, because the routing stretch is wider. For that reason,
earlier work at the IETF introduced the "Reactive Discovery of
Point-to-Point Routes in Low Power and Lossy Networks" [RFC6997],
which specifies a distributed method for establishing optimized P2P
routes. This draft proposes an alternative based on centralized
route computation.
+-----+
| | Border router
| | (RPL Root)
+-----+
|
o o o o
o o o o o o o o o
o o o o o o o o o o
o o o o o o o o o
S>>A>>>B>>C>>>D o o o
o o o o
LLN
Figure 4: More direct forward Route between S and D
The requirement is to install additional routes in the RPL routers,
to reduce the stretch of some P2P routes and maintain the
characteristics within a given SLO, e.g., in terms of latency and/or
reliability.
3.4. On Tracks
3.4.1. Building Tracks With RPL
The concept of a Track was introduced in the "6TiSCH Architecture"
[RFC9030], as a collection of potential paths that leverage redundant
forwarding solutions along the way. This can be a DODAG or a more
complex structure that is only partially acyclic (e.g., per packet).
With this specification, a Track is shaped as a DODAG, and following
the directed edges leads to a Track Ingress. Storing Mode P-DAO
messages follow the direction of the edges to set up routes for
traffic that flows the other way, towards the Track Egress(es). If
there is a single Track Egress, then the Track is reversible to form
another DODAG by reversing the direction of each edge. A node at the
Ingress of more than one Segment in a Track may use one or more of
these Segments to forward a packet inside the Track.
Thubert, et al. Expires 2 June 2024 [Page 17]
Internet-Draft DAO Projection November 2023
A RPL Track is a collection of (one or more) parallel loose source
routed sequences of nodes ordered from Ingress to Egress, each
forming a lane. The nodes that are directly connected, reachable via
existing Tracks as illustrated in Section 3.5.2.3 or joined with
strict Segments of other nodes as shown in Section 3.5.1.3. The
Lanes are expressed in RPL Non-Storing Mode and require an
encapsulation to add a Source Route Header, whereas the Segments are
expressed in RPL Storing Mode.
A path provides only one path between Ingress and Egress. It
comprises at most one Lane. A Stand-Alone Segment implicitly defines
a path from its Ingress to Egress.
A complex Track forms a graph that provides a collection of potential
paths to provide redundancy for the packets, either as a collection
of Lanes that may be parallel or cross at certain points, or as a
more generic DODAG.
3.4.2. Tracks and RPL Instances
Section 5.1. of [RPL] describes the RPL Instance and its encoding.
There can be up to 128 Global RPL Instances, for which there can be
one or more DODAGs, and there can be 64 local RPL Instances, with a
namespace that is indexed by a DODAGID, where the DODAGID is a Unique
Local Address (ULA) or a Global Unicast Address (GUA) of the Root of
the DODAG. Bit 0 (most significant) is set to 1 to signal a Local
RPLInstanceID, as shown in Figure 5. By extension, this
specification expresses the value of the RPLInstanceID as a single
integer between 128 and 191, representing both the Local
RPLInstanceID in 0..63 in the rightmost bits and Bit 0 set.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1|D| ID | Local RPLInstanceID in 0..63
+-+-+-+-+-+-+-+-+
Figure 5: Local RPLInstanceID Encoding
A Track typically forms an underlay to the main Instance, and is
associated with a Local RPL Instance from which the RPLInstanceID is
used as the TrackID. When a packet is placed on a Track, it is
encapsulated IP-in-IP with a RPL Option containing a RPI which
signals the RPLInstanceID. The encapsulating source IP address and
RPI Instance are set to the Track Ingress IP address and local
RPLInstanceID, respectively, more in Section 6.3.
Thubert, et al. Expires 2 June 2024 [Page 18]
Internet-Draft DAO Projection November 2023
A Track typically offers service protection across several lanes. As
a degraded form of a Track, a path made of a single lane (i.e.,
offering no protection) can be used as an alternative to a Segment
for forwarding along a RPL Instance. In that case, instead of
following native routes along the instance, the packets are
encapsulated to signal a more specific source-routed path between the
loose hops in the encapsulated source routing header.
If the encapsulated packet follows a global instance, then the lane
may be part that global instance as well, for instance the global
instance of the main DODAG. This can only be done for global
instances because the Ingress node that encapsulates the packets over
the lane is not the Root of the instance, so the source address of
the encapsulated packet cannot be used to determine the Track along
the way.
3.5. path Signaling
This specification enables setting up a P-Route along either a lane
or a Segment. A P-Route is installed and maintained by the Root of
the main DODAG using an extended RPL DAO message called a Projected
DAO (P-DAO), and a Track is composed of the combination of one or
more P-Routes. In order to clarify the techniques that may be used
to install a P-Route, this section takes the simple case of the path
illustrated in Figure 6. So the goal is to build a path from node A
to E for packets towards E's neighbors F and G along A, B, C, D and E
as opposed to via the Root:
/===> F
A ===> B ===> C ===> D===> E <
\===> G
Figure 6: Reference Track
A P-DAO message for a Track signals the TrackID in the RPLInstanceID
field. In the case of a local RPL Instance, the address of the Track
Ingress is used as source to encapsulate packets along the Track.
The Track is signaled in the DODAGID field of the Projected DAO Base
Object, see Figure 8.
This specification introduces the Via Information Option (VIO) to
signal a sequence of hops in a Lane or a Segment in the P-DAO
messages, either in Storing Mode (SM-VIO) or Non-Storing Mode (NSM-
VIO). One P-DAO message contains a single VIO, associated to one or
more RPL Target Options that signal the destination IPv6 addresses
that can reached along the Track (more in Section 5.3).
Thubert, et al. Expires 2 June 2024 [Page 19]
Internet-Draft DAO Projection November 2023
Before diving deeper into Track Lanes and Segments signaling and
operation, this section provides examples of how route projection
works through variations of a simple example. This simple example
illustrates the case of host routes, though RPL Targets can also be
prefixes.
Conventionally we use ==> to represent a strict hop and --> for a
loose hop. We use "-to-", such as in C==>D==>E-to-F to represent
coma-separated Targets, e.g., F is a Target for Segment C==>D==>E.
In this example, A is the Track Ingress and E is the Track Egress. C
is a stitching point. F and G are "external” Targets for the Track,
and become reachable from A via the Track A (Ingress) to E (Egress
and implicit Target in Non-Storing Mode) leading to F and G (explicit
Targets).
In a general manner the desired outcome is as follows:
* Targets are E, F, and G
* P-DAO 1 signals C==>D==>E
* P-DAO 2 signals A==>B==>C
* P-DAO 3 signals F and G via the A-->E Track
P-DAO 3 may be ommitted if P-DAO 1 and 2 signal F and G as Targets.
Loose sequences of hops are expressed in Non-Storing Mode; this is
why P-DAO 3 contains a NSM-VIO. With this specification:
* the DODAGID to be used by the Ingress as source address is
signaled in the DAO base object (see Figure 8) .
* the via list in the VIO is encoded as an SRH-6LoRH (see
Figure 16), and it starts with the address of the first hop node
after the Ingress node in the loose hop sequence.
* the via list ends with the address of the Egress node.
Note well:
| The Egress of a Non-Storing Mode P-Route is implicitly a target;
| it is not listed in the RPL Target Options but still accounted for
| as if it was. The only exception is when the Egress is the only
| address listed in the VIO, in which case it would indicate via
| itself which would be non-sensical.
Also:
Thubert, et al. Expires 2 June 2024 [Page 20]
Internet-Draft DAO Projection November 2023
| By design, the list of nodes in a VIO in Non-Storing Mode is
| exactly the list that shows in the encapsulation SRH. So in the
| cases detailed below, if the Mode of the P-DAO is Non-Storing,
| then the VIO row can be read as indicating the SRH as well.
3.5.1. Using Storing Mode Segments
A==>B==>C and C==>D==>E are Segments of the same Track. Note that
the Storing Mode signaling imposes strict continuity in a Segment,
since the P-DAO is passed hop by hop, as a classical DAO is, along
the reverse datapath that it signals. One benefit of strict routing
is that loops are avoided along the Track.
3.5.1.1. Stitched Segments
In this formulation:
* P-DAO 1 signals C==>D==>E-to-F,G
* P-DAO 2 signals A==>B==>C-to-F,G
Storing Mode P-DAO 1 is sent to E and when it is successfully
acknowledged, Storing Mode P-DAO 2 is sent to C, as follows:
+====================+==============+==============+
| Field | P-DAO 1 to E | P-DAO 2 to C |
+====================+==============+==============+
| Mode | Storing | Storing |
+--------------------+--------------+--------------+
| Track Ingress | A | A |
+--------------------+--------------+--------------+
| (DODAGID, TrackID) | (A, 129) | (A, 129) |
+--------------------+--------------+--------------+
| SegmentID | 1 | 2 |
+--------------------+--------------+--------------+
| VIO | C, D, E | A, B, C |
+--------------------+--------------+--------------+
| Targets | F, G | F, G |
+--------------------+--------------+--------------+
Table 1: P-DAO Messages
As a result the RIBs are set as follows:
Thubert, et al. Expires 2 June 2024 [Page 21]
Internet-Draft DAO Projection November 2023
+======+=============+=========+=============+==========+
| Node | Destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| D | E | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 1 | E | (A, 129) |
+------+-------------+---------+-------------+----------+
| C | D | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 1 | D | (A, 129) |
+------+-------------+---------+-------------+----------+
| B | C | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 2 | C | (A, 129) |
+------+-------------+---------+-------------+----------+
| A | B | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 2 | B | (A, 129) |
+------+-------------+---------+-------------+----------+
Table 2: RIB setting
Note:
| the " sign is used throughout those tables to indicate the same
| value as in the row above.
Packets originating at A going to F or G do not require encapsulation
as the RPI can be placed in the native header chain. For packets
that it routes, A must encapsulate to add the RPI that signals the
trackID; the outer headers of the packets that are forwarded along
the Track have the following settings:
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | A | F or G | (A, 129) |
+--------+-------------------+-------------------+----------------+
| Inner | Any but A | F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 3: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 2: A forwards to B and B forwards to C.
Thubert, et al. Expires 2 June 2024 [Page 22]
Internet-Draft DAO Projection November 2023
* From P-DAO 1: C forwards to D and D forwards to E.
* From Neighbor Cache Entry: E delivers the packet to F.
3.5.1.2. External Routes
In this example, we consider F and G as destinations that are
external to the Track as a DODAG, as discussed in section 4.1.1. of
[RFC9008]. We then apply the directives for encapsulating in that
case (more in Section 6.7).
In this formulation, we set up the lane explicitly, which creates
less routing state in intermediate hops at the expense of larger
packets to accommodate source routing:
* P-DAO 1 signals C==>D==>E-to-E
* P-DAO 2 signals A==>B==>C-to-E
* P-DAO 3 signals F and G via the A-->E-to-F,G Track
Storing Mode P-DAO 1 and 2, and Non-Storing Mode P-DAO 3, are sent to
E, C and A, respectively, as follows:
+====================+==============+==============+==============+
| | P-DAO 1 to E | P-DAO 2 to C | P-DAO 3 to A |
+====================+==============+==============+==============+
| Mode | Storing | Storing | Non-Storing |
+--------------------+--------------+--------------+--------------+
| Track Ingress | A | A | A |
+--------------------+--------------+--------------+--------------+
| (DODAGID, TrackID) | (A, 129) | (A, 129) | (A, 129) |
+--------------------+--------------+--------------+--------------+
| SegmentID | 1 | 2 | 3 |
+--------------------+--------------+--------------+--------------+
| VIO | C, D, E | A, B, C | E |
+--------------------+--------------+--------------+--------------+
| Targets | E | E | F, G |
+--------------------+--------------+--------------+--------------+
Table 4: P-DAO Messages
Note in the above that E is not an implicit Target in Storing mode,
so it must be added in the RTO for P-DAO 1 and 2. E is not an
implicit Target for P-DAO 3 either, since E is the only entry in the
VIO.
As a result the RIBs are set as follows:
Thubert, et al. Expires 2 June 2024 [Page 23]
Internet-Draft DAO Projection November 2023
+======+=============+=========+=============+==========+
| Node | Destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| D | E | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| C | D | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E | P-DAO 1 | D | (A, 129) |
+------+-------------+---------+-------------+----------+
| B | C | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E | P-DAO 2 | C | (A, 129) |
+------+-------------+---------+-------------+----------+
| A | B | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E | P-DAO 2 | B | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 3 | E | (A, 129) |
+------+-------------+---------+-------------+----------+
Table 5: RIB setting
Packets from A to E do not require an encapsulation. This is why in
the tables below, E may show as IPv6 Destination Address only if the
IPv6 Source Address X is different from A. Conversely, the
encapsulation is always done when the IPv6 Destination Address is F
or G. Other destination addresses do not match this P-Route and are
not subject to encapsulation.
The outer headers of the packets that are forwarded along the Track
have the following settings:
+========+===================+====================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+====================+================+
| Outer | A | E | (A, 129) |
+--------+-------------------+--------------------+----------------+
| Inner | X | either E if(X!=A), | N/A |
| | | or F, or G | |
+--------+-------------------+--------------------+----------------+
Table 6: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
Thubert, et al. Expires 2 June 2024 [Page 24]
Internet-Draft DAO Projection November 2023
* From P-DAO 3: A encapsulates the packet and sends it down the
Track signaled by P-DAO 3, with the outer header above. Now the
packet destination is E.
* From P-DAO 2: A forwards to B and B forwards to C.
* From P-DAO 1: C forwards to D and D forwards to E; E decapsulates
the packet.
* From Neighbor Cache Entry: E delivers packets to F or G.
3.5.1.3. Segment Routing
In this formulation Track Lanes are leveraged to combine Segments and
form a Graph. The packets are source routed from a Segment to the
next to adapt the path. As such, this can be seen as a form of
Segment Routing [RFC8402]:
* P-DAO 1 signals C==>D==>E-to-E
* P-DAO 2 signals A==>B-to-B,C
* P-DAO 3 signals F and G via the A-->C-->E-to-(E),F,G Track
Storing Mode P-DAO 1 and 2, and Non-Storing Mode P-DAO 3, are sent to
E, B and A, respectively, as follows:
+====================+==============+==============+==============+
| | P-DAO 1 to E | P-DAO 2 to B | P-DAO 3 to A |
+====================+==============+==============+==============+
| Mode | Storing | Storing | Non-Storing |
+--------------------+--------------+--------------+--------------+
| Track Ingress | A | A | A |
+--------------------+--------------+--------------+--------------+
| (DODAGID, TrackID) | (A, 129) | (A, 129) | (A, 129) |
+--------------------+--------------+--------------+--------------+
| SegmentID | 1 | 2 | 3 |
+--------------------+--------------+--------------+--------------+
| VIO | C, D, E | A, B | C, E |
+--------------------+--------------+--------------+--------------+
| Targets | E | B, C | F, G |
+--------------------+--------------+--------------+--------------+
Table 7: P-DAO Messages
Note in the above that the Segment can terminate at the loose hop as
used in the example of P-DAO 1 or at the previous hop as done with
P-DAO 2. Both methods are possible on any Segment joined by a loose
Thubert, et al. Expires 2 June 2024 [Page 25]
Internet-Draft DAO Projection November 2023
lane. P-DAO 1 generates more signaling since E is the Segment Egress
when D could be, but has the benefit that it validates that the
connectivity between D and E still exists.
As a result the RIBs are set as follows:
+======+=============+=========+=============+==========+
| Node | Destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| D | E | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| C | D | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E | P-DAO 1 | D | (A, 129) |
+------+-------------+---------+-------------+----------+
| B | C | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| A | B | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | C | P-DAO 2 | B | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E, F, G | P-DAO 3 | C, E | (A, 129) |
+------+-------------+---------+-------------+----------+
Table 8: RIB setting
Packets originated at A to E do not require an encapsulation, but
carry a SRH via C. The outer headers of the packets that are
forwarded along the Track have the following settings:
+========+===================+====================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+====================+================+
| Outer | A | C until C then E | (A, 129) |
+--------+-------------------+--------------------+----------------+
| Inner | X | either E if(X!=A), | N/A |
| | | or F, or G | |
+--------+-------------------+--------------------+----------------+
Table 9: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 3: A encapsulates the packet the Track signaled by
P-DAO 3, with the outer header above. Now the destination in the
IPv6 Header is C, and a SRH signals the final destination is E.
Thubert, et al. Expires 2 June 2024 [Page 26]
Internet-Draft DAO Projection November 2023
* From P-DAO 2: A forwards to B and B forwards to C.
* From P-DAO 3: C processes the SRH and sets the destination in the
IPv6 Header to E.
* From P-DAO 1: C forwards to D and D forwards to E; E decapsulates
the packet.
* From the Neighbor Cache Entry: E delivers packets to F or G.
3.5.2. Using Non-Storing Mode joining Tracks
In this formulation:
* P-DAO 1 signals C==>D==>E-to-(E),F,G
* P-DAO 2 signals A==>B==>C-to-(C),E,F,G
A==>B==>C and C==>D==>E are Tracks expressed as Non-Storing P-DAOs.
3.5.2.1. Stitched Tracks
Non-Storing Mode P-DAO 1 and 2 are sent to C and A respectively, as
follows:
+====================+==============+==============+
| | P-DAO 1 to C | P-DAO 2 to A |
+====================+==============+==============+
| Mode | Non-Storing | Non-Storing |
+--------------------+--------------+--------------+
| Track Ingress | C | A |
+--------------------+--------------+--------------+
| (DODAGID, TrackID) | (C, 131) | (A, 131) |
+--------------------+--------------+--------------+
| SegmentID | 1 | 1 |
+--------------------+--------------+--------------+
| VIO | D, E | B, C |
+--------------------+--------------+--------------+
| Targets | F, G | E, F, G |
+--------------------+--------------+--------------+
Table 10: P-DAO Messages
As a result the RIBs are set as follows (using ND to indicate that
the address is discovered by IPv6 Neighbor Discovery
[RFC4861][RFC8505] or an equivalent method:
Thubert, et al. Expires 2 June 2024 [Page 27]
Internet-Draft DAO Projection November 2023
+======+=============+=========+=============+==========+
| Node | Destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| D | E | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| C | D | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | E, F, G | P-DAO 1 | D, E | (C, 131) |
+------+-------------+---------+-------------+----------+
| B | C | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| A | B | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | C, E, F, G | P-DAO 2 | B, C | (A, 131) |
+------+-------------+---------+-------------+----------+
Table 11: RIB setting
Packets originated at A to E, F and G could be generated with the RPI
and the SRH, and no encapsulation. Alternatively, A may generate a
native packet to the target, and then encapsulate it with an RPI and
an SRH indicating the source-routed path leading to E, as it would
for a packet that it routes coming from another node. This is
effectively the same case as for packets generated by the root in a
RPL network in Non-Storing mode, see section 8.1.3 of [RFC9008]. The
latter is often is preferred since it leads to a single code path,
and the destination when it is F or G, does no understand and process
the RPI or the SRH. Either way, they carry a SRH via B and C, and C
needs to encapsulate to E, F, or G to add an SRH via D and E. The
encapsulating headers of packets that are forwarded along the Track
between C and E have the following settings:
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | C | D until D then E | (C, 131) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F, or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 12: Packet Header Settings between C and E
As an example, say that A has a packet for F. Using the RIB above:
Thubert, et al. Expires 2 June 2024 [Page 28]
Internet-Draft DAO Projection November 2023
* From P-DAO 2: A encapsulates the packet with destination of F in
the Track signaled by P-DAO 2. The outer header has source A,
destination B, an SRH that indicates C as the next loose hop, and
a RPI indicating a TrackId of 131 from A's namespace, which is
distinct from TrackId of 131 from C's.
* From the SRH: Packets forwarded by B have source A, destination C,
a consumed SRH, and a RPI indicating a TrackId of 131 from A's
namespace. C decapsulates.
* From P-DAO 1: C encapsulates the packet with destination of F in
the Track signaled by P-DAO 1. The outer header has source C,
destination D, an SRH that indicates E as the next loose hop, and
a RPI indicating a TrackId of 131 from C's namespace. E
decapsulates.
3.5.2.2. External Routes
In this formulation:
* P-DAO 1 signals C==>D==>E-to-(E)
* P-DAO 2 signals A==>B==>C-to-(C),E
* P-DAO 3 signals F and G via the A-->E-to-F,G Track
Non-Storing Mode P-DAO 1 is sent to C and Non-Storing Mode P-DAO 2
and 3 are sent to A, as follows:
+====================+==============+==============+==============+
| | P-DAO 1 to C | P-DAO 2 to A | P-DAO 3 to A |
+====================+==============+==============+==============+
| Mode | Non-Storing | Non-Storing | Non-Storing |
+--------------------+--------------+--------------+--------------+
| Track Ingress | C | A | A |
+--------------------+--------------+--------------+--------------+
| (DODAGID, TrackID) | (C, 131) | (A, 129) | (A, 141) |
+--------------------+--------------+--------------+--------------+
| SegmentID | 1 | 1 | 1 |
+--------------------+--------------+--------------+--------------+
| VIO | D, E | B, C | E |
+--------------------+--------------+--------------+--------------+
| Targets | | E | F, G |
+--------------------+--------------+--------------+--------------+
Table 13: P-DAO Messages
Thubert, et al. Expires 2 June 2024 [Page 29]
Internet-Draft DAO Projection November 2023
Note in the above that E is an implicit Target in P-DAO 1 and so is C
in P-DAO 2. As Non-Storing Mode Egress nodes addresses, they not
listed in the respective RTOs.
As a result the RIBs are set as follows:
+======+=============+=========+=============+==========+
| Node | Destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| D | E | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| C | D | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | E | P-DAO 1 | D, E | (C, 131) |
+------+-------------+---------+-------------+----------+
| B | C | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| A | B | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | C, E | P-DAO 2 | B, C | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 3 | E | (A, 141) |
+------+-------------+---------+-------------+----------+
Table 14: RIB setting
The encapsulating headers of packets that are forwarded along the
Track between C and E have the following settings:
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | C | D until D then E | (C, 131) |
+--------+-------------------+-------------------+----------------+
| Middle | A | E | (A, 141) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 15: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
Thubert, et al. Expires 2 June 2024 [Page 30]
Internet-Draft DAO Projection November 2023
* From P-DAO 3: A encapsulates the packet with destination of F in
the Track signaled by P-DAO 3. The outer header has source A,
destination E, and a RPI indicating a TrackId of 141 from A's
namespace. This recurses with:
* From P-DAO 2: A encapsulates the packet with destination of E in
the Track signaled by P-DAO 2. The outer header has source A,
destination B, an SRH that indicates C as the next loose hop, and
a RPI indicating a TrackId of 129 from A's namespace.
* From the SRH: Packets forwarded by B have source A, destination C
, a consumed SRH, and a RPI indicating a TrackId of 129 from A's
namespace. C decapsulates.
* From P-DAO 1: C encapsulates the packet with destination of E in
the Track signaled by P-DAO 1. The outer header has source C,
destination D, an SRH that indicates E as the next loose hop, and
a RPI indicating a TrackId of 131 from C's namespace. E
decapsulates.
3.5.2.3. Segment Routing
In this formulation:
* P-DAO 1 signals C==>D==>E-to-(E)
* P-DAO 2 signals A==>B-to-C
* P-DAO 3 signals F and G via the A-->C-->E-to-(E),F,G Track
Non-Storing Mode P-DAO 1 is sent to C and Non-Storing Mode P-DAO 2
and 3 are sent to A, as follows:
Thubert, et al. Expires 2 June 2024 [Page 31]
Internet-Draft DAO Projection November 2023
+====================+==============+==============+==============+
| | P-DAO 1 to C | P-DAO 2 to A | P-DAO 3 to A |
+====================+==============+==============+==============+
| Mode | Non-Storing | Non-Storing | Non-Storing |
+--------------------+--------------+--------------+--------------+
| Track Ingress | C | A | A |
+--------------------+--------------+--------------+--------------+
| (DODAGID, TrackID) | (C, 131) | (A, 129) | (A, 141) |
+--------------------+--------------+--------------+--------------+
| SegmentID | 1 | 1 | 1 |
+--------------------+--------------+--------------+--------------+
| VIO | D, E | B | C, E |
+--------------------+--------------+--------------+--------------+
| Targets | | C | F, G |
+--------------------+--------------+--------------+--------------+
Table 16: P-DAO Messages
As a result the RIBs are set as follows:
+======+=============+=========+=============+==========+
| Node | Destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| D | E | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| C | D | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | E | P-DAO 1 | D, E | (C, 131) |
+------+-------------+---------+-------------+----------+
| B | C | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| A | B | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | B, C | P-DAO 2 | C | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E, F, G | P-DAO 3 | C, E | (A, 141) |
+------+-------------+---------+-------------+----------+
Table 17: RIB setting
The encapsulating headers of packets that are forwarded along the
Track between A and B have the following settings:
Thubert, et al. Expires 2 June 2024 [Page 32]
Internet-Draft DAO Projection November 2023
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | A | B until D then E | (A, 129) |
+--------+-------------------+-------------------+----------------+
| Middle | A | C | (A, 141) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 18: Packet Header Settings
The encapsulating headers of packets that are forwarded along the
Track between B and C have the following settings:
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | A | C | (A, 141) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 19: Packet Header Settings
The encapsulating headers of packets that are forwarded along the
Track between C and E have the following settings:
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | C | D until D then E | (C, 131) |
+--------+-------------------+-------------------+----------------+
| Middle | A | E | (A, 141) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 20: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 3: A encapsulates the packet with destination of F in
the Track signaled by P-DAO 3. The outer header has source A,
destination C, an SRH that indicates E as the next loose hop, and
a RPI indicating a TrackId of 141 from A's namespace. This
recurses with:
Thubert, et al. Expires 2 June 2024 [Page 33]
Internet-Draft DAO Projection November 2023
* From P-DAO 2: A encapsulates the packet with destination of C in
the Track signaled by P-DAO 2. The outer header has source A,
destination B, and a RPI indicating a TrackId of 129 from A's
namespace. B decapsulates forwards to C based on a sibling
connected route.
* From the SRH: C consumes the SRH and makes the destination E.
* From P-DAO 1: C encapsulates the packet with destination of E in
the Track signaled by P-DAO 1. The outer header has source C,
destination D, an SRH that indicates E as the next loose hop, and
a RPI indicating a TrackId of 131 from C's namespace. E
decapsulates.
3.6. Complex Tracks
To increase the reliability of the P2P transmission, this
specification enables building a collection of Lanes between the same
Ingress and Egress Nodes and combining them within the same TrackID,
as shown in Figure 7. Lanes may cross at the edges of loose hops or
remain parallel.
The Segments that join the loose hops of a Lane are installed with
the same TrackID as the Lane. But each individual Lane and Segment
has its own P-RouteID which allows it to be managed separately. 2
Lanes of the same Track may cross at a common node that participates
to a Segment of Each Lane. In that case the common node has more
than one next hop in its RIB associated to the Track, but no specific
signal in the packet to indicate which Segment is being followed. A
next hop that can reach the loose hop is selected.
Thubert, et al. Expires 2 June 2024 [Page 34]
Internet-Draft DAO Projection November 2023
CPF CPF CPF CPF
Southbound API
_-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-
_-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-
+----------+
| RPL Root |
+----------+
( )
( )
( DODAG )
( )
( )
)
<- Lane 1 B, E ->
<--- Segment 1 A,B ---> <------- Segment 2 C,D,E ------->
FWD --z Relay --z FWD --z FWD Target 1
z-- Node z-- Node z-- Node z-- Node --z /
--z (A) (B) \ (C) (D) z-- /
Track \ Track
Ingress Segment 5 Egress - Tgt 2
(I) \ (E)
--z \ z-- \
z-- FWD --z FWD --z Relay --z FWD --z \
Node z-- Node z-- Node z-- Node Target 3
(F) (G) (H) (J)
<------ Segment 3 F,G,H ------> <---- Segment 4 J,E ---->
<- Lane 2 H, E ->
<--- Segment 1 A,B ---> <- S5-> <---- Segment 4 J,E ---->
<- Lane 3 B, H, E ->
)
(
( )
Figure 7: Segments and Tracks
Note that while this specification enables building both Segments
inside a Lane (aka forward), such as Segment 2 above which is within
Lane 1, and Inter-Lane Segments (aka North-South), such as Segment 5
above which joins Lane 1 and Lane 2, it does not signal to the
Ingress which Inter-Lane Segments are available, so the use of North-
South Segments and associated PAREO functions is curently limited.
The only possibility available at this time is to define overlapping
Thubert, et al. Expires 2 June 2024 [Page 35]
Internet-Draft DAO Projection November 2023
Lanes as illustrated in Figure 7, with Lane 3 that is congruent with
Lane 1 until node B and congruent with Lane 2 from node H on,
abstracting Segment 5 as an forward Segment.
3.7. Scope and Expectations
3.7.1. External Dependencies
This specification expects that the main DODAG is operated in RPL
Non-Storing Mode to sustain the exchanges with the Root. Based on
its comprehensive knowledge of the parent-child relationship, the
Root can form an abstracted view of the whole DODAG topology. This
document adds the capability for nodes to advertise additional
sibling information to complement the topological awareness of the
Root to be passed on to the PCE, and enable the PCE to build more /
better paths that traverse those siblings.
P-Routes require resources such as routing table space in the routers
and bandwidth on the links; the amount of state that is installed in
each node must be computed to fit within the node's memory, and the
amount of rerouted traffic must fit within the capabilities of the
transmission links. The methods used to learn the node capabilities
and the resources that are available in the devices and in the
network are out of scope for this document. The method to capture
and report the LLN link capacity and reliability statistics are also
out of scope. They may be fetched from the nodes through network
management functions or other forms of telemetry such as OAM.
3.7.2. Positioning vs. Related IETF Standards
3.7.2.1. Extending 6TiSCH
The "6TiSCH Architecture" [RFC9030] leverages a centralized model
that is similar to that of "Deterministic Networking Architecture"
[RFC8655], whereby the device resources and capabilities are exposed
to an external controller which installs routing states into the
network based on its own objective functions that reside in that
external entity.
3.7.2.2. Mapping to DetNet
DetNet Forwarding Nodes only understand the simple 1-to-1 forwarding
sublayer transport operation along a Segment whereas the more
sophisticated Relay nodes can also provide service sublayer functions
such as Replication and Elimination.
Thubert, et al. Expires 2 June 2024 [Page 36]
Internet-Draft DAO Projection November 2023
One possible mapping between DetNet and this specification is to
signal the Relay Nodes as the hops of a Lane and the forwarding Nodes
as the hops in a Segment that join the Relay nodes as illustrated in
Figure 7.
3.7.2.3. Leveraging PCE
With DetNet and 6TiSCH, the component of the controller that is
responsible of computing routes is a PCE. The PCE computes its
routes based on its own objective functions such as described in
[RFC4655], and typically controls the routes using the PCE Protocol
(PCEP) by [RFC5440]. While this specification expects a PCE and
while PCEP might effectively be used between the Root and the PCE,
the control protocol between the PCE and the Root is out of scope.
This specification also expects a single PCE with a full view of the
network. Distributing the PCE function for a large network is out of
scope. This specification uses the RPL Root as a proxy to the PCE.
The PCE may be collocated with the Root, or may reside in an external
Controller. In that case, the protocol between the Root and the PCE
is out of scope and abstracted by / mapped to RPL inside the DODAG;
one possibility is for the Root to transmit the RPL DAOs with the
SIOs that detail the parent/child and sibling information.
The algorithm to compute the paths, the protocol used by the PCE and
the metrics and link statistics involved in the computation are also
out of scope. The effectiveness of the route computation by the PCE
depends on the quality of the metrics that are reported from the RPL
network. Which metrics are used and how they are reported is out of
scope, but the expectation is that they are mostly of a long-term,
statistical nature, and provide visibility on link throughput,
latency, stability and availability over relatively long periods.
3.7.2.4. Providing for RAW
The RAW Architecture [RAW-ARCHI] extends the definition of Track, as
being composed of forward directional Segments and North-South
bidirectional Segments, to enable additional path diversity, using
Packet ARQ, Replication, Elimination, and Overhearing (PAREO)
functions over the available paths, to provide a dynamic balance
between the reliability and availability requirements of the flows
and the need to conserve energy and spectrum. This specification
prepares for RAW by setting up the Tracks, but only forms DODAGs,
which are composed of aggregated end-to-end loose source routed
Lanes, joined by strict routed Segments, all oriented forward.
Thubert, et al. Expires 2 June 2024 [Page 37]
Internet-Draft DAO Projection November 2023
The RAW Architecture defines a dataplane extension of the PCE called
the Point of Local Repair (PLR), that adapts the use of the path
redundancy within a Track to defeat the diverse causes of packet
loss. The PLR controls the forwarding operation of the packets
within a Track. This specification can use but does not impose a PLR
and does not provide the policies that would select which packets are
routed through which path within a Track, in other words, how the PLR
may use the path redundancy within the Track. By default, the use of
the available redundancy is limited to simple load balancing, and all
the Segments are forward unidirectional only.
A Track may be set up to reduce the load around the Root, or to
enable urgent traffic to flow more directly. This specification does
not provide the policies that would decide which flows are routed
through which Track. In a Non-Storing Mode RPL Instance, the main
DODAG provides a default route via the Root, and the Tracks provide
more specific routes to the Track Targets.
4. Extending existing RFCs
This section explains which changes are extensions to existing
specifications, and which changes are amendments to existing
specifications. It is expected that extensions to existing
specifications do not cause existing code on legacy 6LRs to
malfunction, as the extensions will simply be ignored. New code is
required for an extension. Those 6LRs will be unable to participate
in the new mechanisms, but may also cause projected DAOs to be
impossible to install. Amendments to existing specifications are
situations where there are semantic changes required to existing
code, and which may require new unit tests to confirm that legacy
operations will continue unaffected.
4.1. Extending RFC 6550
This specification Extends RPL [RPL] to enable the Root to install
forward routes inside a main DODAG that is operated as Non-Storing
Mode. The Root issues a Projected DAO (P-DAO) message (see
Section 4.1.1) to the Track Ingress; the P-DAO message contains a new
Via Information Option (VIO) that installs a strict or a loose
sequence of hops to form a Track Segment or a lane, respectively.
The P-DAO Request (PDR) is a new message detailed in Section 5.1. As
per [RPL] section 6, if a node receives this message and it does not
understand this new Code, it then discards the message. When the
Root initiates communication to a node that it has not communicated
with before and which it has not ascertained to implement this
specification (by means such as capabilities), then the Root SHOULD
request a PDR-ACK.
Thubert, et al. Expires 2 June 2024 [Page 38]
Internet-Draft DAO Projection November 2023
A P-DAO Request (PDR) message enables a Track Ingress to request the
Track from the Root. The resulting Track is also a DODAG for which
the Track Ingress is the Root, the owner the address that serves as
DODAGID and authoritative for the associated namespace from which the
TrackID is selected. In the context of this specification, the
installed route appears as a more specific route to the Track
Targets, and the Track Ingress forwards the packets towards the
Targets via the Track using normal longest match IP forwarding.
To ensure that the PDR and P-DAO messages can flow at most times, it
is RECOMMENDED that the nodes involved in a Track maintain multiple
parents in the main DODAG, advertise them all to the Root, and use
them in turn to retry similar packets. It is also RECOMMENDED that
the Root uses diverse source route paths to retry similar messages to
the nodes in the Track.
4.1.1. Projected DAO
Section 6 of [RPL] introduces the RPL Control Message Options (CMO),
including the RPL Target Option (RTO) and Transit Information Option
(TIO), which can be placed in RPL messages such as the destination
Advertisement Object (DAO). A DAO message signals routing
information to one or more Targets indicated in RTOs, providing one
hop information at a time in the TIO.
This document Amends the specification of the DAO to create the P-DAO
message. This Amended DAO is signaled with a new "Projected DAO" (P)
flag, see Figure 8.
A Projected DAO (P-DAO) is a special DAO message generated by the
Root to install a P-Route formed of multiple hops in its DODAG. This
provides a RPL-based method to install the Tracks as expected by the
6TiSCH Architecture [RFC9030] as a collection of multiple P-Routes.
The Root MUST source the P-DAO message with its address that serves
as DODAGID for the main DODAG. The receiver MUST NOT accept a P-DAO
message that is not sent by the Root of its DODAG and MUST ignore
such messages silently.
The 'P' flag is encoded in bit position 2 (to be confirmed by IANA)
of the Flags field in the DAO Base Object. The Root MUST set it to 1
in a Projected DAO message. Otherwise it MUST be set to 0. It is
set to 0 in Legacy implementations as specified respectively in
Sections 20.11 and 6.4 of [RPL].
Thubert, et al. Expires 2 June 2024 [Page 39]
Internet-Draft DAO Projection November 2023
The P-DAO is a part of control plane signaling and should not be
stuck behind high traffic levels. The expectation is that the P-DAO
message is sent at high QoS level, above that of data traffic,
typically with the Network Control precedence.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TrackID |K|D|P| Flags | Reserved | DAOSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| DODAGID field set to the |
+ IPv6 Address of the Track Ingress +
| used to source encapsulated packets |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
Figure 8: Projected DAO Base Object
New fields:
TrackID: The local or global RPLInstanceID of the DODAG that serves
as Track (more in Section 6.3).
P: 1-bit flag (position to be confirmed by IANA).
The 'P' flag is set to 1 by the Root to signal a Projected DAO,
and it is set to 0 otherwise.
The D flag is set to one to signal that the DODAGID field is present.
It may be set to zero if and only if the destination address of the
P-DAO-ACK message is set to the IPv6 address that serves as DODAGID
and it MUST be set to one otherwise, meaning that the DODAGID field
MUST then be present.
Thubert, et al. Expires 2 June 2024 [Page 40]
Internet-Draft DAO Projection November 2023
In RPL Non-Storing Mode, the TIO and RTO are combined in a DAO
message to inform the DODAG Root of all the edges in the DODAG, which
are formed by the directed parent-child relationships. The DAO
message signals to the Root that a given parent can be used to reach
a given child. The P-DAO message generalizes the DAO to signal to
the Track Ingress that a Track for which it is Root can be used to
reach children and siblings of the Track Egress. In both cases,
options may be factorized and multiple RTOs may be present to signal
a collection of children that can be reached through the parent or
the Track, respectively.
4.1.2. Projected DAO-ACK
This document also Amends the DAO-ACK message. The new P flag
signals the projected form.
The format of the P-DAO-ACK message is thus as illustrated in
Figure 9:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TrackID |D|P| Reserved | DAOSequence | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| DODAGID field set to the |
+ IPv6 Address of the Track Ingress +
| used to source encapsulated packets |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
Figure 9: Projected DAO-ACK Base Object
New fields:
TrackID: The local or global RPLInstanceID of the DODAG that serves
as Track (more in Section 6.3).
P: 1-bit flag (position to be confirmed by IANA).
The 'P' flag is set to 1 by the Root to signal a Projected DAO,
and it is set to 0 otherwise.
Thubert, et al. Expires 2 June 2024 [Page 41]
Internet-Draft DAO Projection November 2023
The D flag is set to one to signal that the DODAGID field is present.
It may be set to zero if and only if the source address of the P-DAO-
ACK message is set to the IPv6 address that serves as DODAGID and it
MUST be set to one otherwise, meaning that the DODAGID field MUST
then be present.
4.1.3. Via Information Option
This document Extends the CMO to create new objects called the Via
Information Options (VIO). The VIOs are the multihop alternative to
the TIO (more in Section 5.3). One VIO is the stateful Storing Mode
VIO (SM-VIO); an SM-VIO installs a strict hop-by-hop P-Route called a
Track Segment. The other is the Non-Storing Mode VIO (NSM-VIO); the
NSM-VIO installs a loose source-routed P-Route called a lane at the
Track Ingress, which uses that state to encapsulate a packet
IPv6_in_IPv6 with a new Routing Header (RH) to the Track Egress (more
in Section 6.7).
A P-DAO contains one or more RTOs to indicate the Target
(destinations) that can be reached via the P-Route, followed by
exactly one VIO that signals the sequence of nodes to be followed
(more in Section 6). There are two modes of operation for the
P-Routes, the Storing Mode and the Non-Storing Mode, see
Section 6.4.2 and Section 6.4.3 respectively for more.
4.1.4. Sibling Information Option
This specification Extends the CMO to create the Sibling Information
Option (SIO). The SIO is used by a RPL Aware Node (RAN) to advertise
a selection of its candidate neighbors as siblings to the Root (more
in Section 5.4). The SIO is placed in DAO messages that are sent
directly to the main Root, including multicast DAO (see section 9.10
of [RPL]).
This draft AMENDS the multicast DAO operation as follows:
1. A multicast DAO message MUST be used only to advertise
information about the node (using the Target Option), and direct
Link Neighbors such as learned by Neighbor Discovery (using the
Sibling Information Option).
2. The multicast DAO may be used to enable direct and indirect (via
a common neighbor) P2P communication without needing the DODAG to
relay the packets. The multicast DAO exposes the sender's
addresses as Targets in RTOs and the sender's neighbors addresses
as siblings in SIOs; this tells the sender's neighbors that the
sender is willing to act as a relay between those of its
neighbors that are too far apart.
Thubert, et al. Expires 2 June 2024 [Page 42]
Internet-Draft DAO Projection November 2023
4.1.5. P-DAO Request
The set of RPL Control Messages is Extended to include the P-DAO
Request (PDR) and P-DAO Request Acknowledgement (PDR-ACK). These two
new RPL Control Messages enable an RPL-Aware Node to request the
establishment of a Track between itself as the Track Ingress Node and
a Track Egress. The node makes its request by sending a new P-DAO
Request (PDR) Message to the Root. The Root confirms with a new PDR-
ACK message back to the requester RAN, see Section 5.1 for more.
4.1.6. Amending the RPI
Sending a Packet within a RPL Local Instance requires the presence of
the abstract RPL Packet Information (RPI) described in section 11.2.
of [RPL] in the outer IPv6 Header chain (see [RFC9008]). The RPI
carries a local RPLInstanceID which, in association with either the
source or the destination address in the IPv6 Header, indicates the
RPL Instance that the packet follows.
This specification Amends [RPL] to create a new flag that signals
that a packet is forwarded along a P-Route.
Projected-Route 'P': 1-bit flag. It is set to 1 in the RPI that is
added in the encapsulation when a packet is sent over a Track. It
is set to 0 when a packet is forwarded along the main DODAG (as a
Track), including when the packet follows a Segment that joins
loose hops of the main DODAG. The flag is not mutable en-route.
The encoding of the 'P' flag in native format is shown in Section 4.2
while the compressed format is indicated in Section 4.3.
4.1.7. Additional Flag in the RPL DODAG Configuration Option
The DODAG Configuration Option is defined in Section 6.7.6 of [RPL].
Its purpose is extended to distribute configuration information
affecting the construction and maintenance of the DODAG, as well as
operational parameters for RPL on the DODAG, through the DODAG. This
Option was originally designed with 4 bit positions reserved for
future use as Flags.
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 = 0x04 |Opt Length = 14|D| | | |A| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
|4 bits |
Figure 10: DODAG Configuration Option (Partial View)
Thubert, et al. Expires 2 June 2024 [Page 43]
Internet-Draft DAO Projection November 2023
This specification Amends the specification to define a new flag
"Projected Routes Support" (D). The 'D' flag is encoded in bit
position 0 of the reserved Flags in the DODAG Configuration Option
(this is the most significant bit)(to be confirmed by IANA but
there's little choice). It is set to 0 in legacy implementations as
specified respectively in Sections 20.14 and 6.7.6 of [RPL].
The 'D' flag is set to 1 to indicate that this specification is
enabled in the network and that the Root will install the requested
Tracks when feasible upon a PDR message.
Section 4.1.2. of [RFC9008] Amends [RPL] to indicate that the
definition of the Flags applies to Mode of Operation values from zero
(0) to six (6) only. For a MOP value of 7, the implementation MUST
consider that the Root accepts PDR messages and will install
Projected Routes.
The RPL DODAG Configuration option is typically placed in a DODAG
Information Object (DIO) message. The DIO message propagates down
the DODAG to form and then maintain its structure. The DODAG
Configuration option is copied unmodified from parents to children.
[RPL] states that:
| Nodes other than the DODAG root MUST NOT modify this information
| when propagating the DODAG Configuration option.
Therefore, a legacy parent propagates the 'D' flag as set by the
root, and when the 'D' flag is set to 1, it is transparently flooded
to all the nodes in the DODAG.
4.2. Extending RFC 6553
"The RPL Option for Carrying RPL Information in Data-Plane Datagrams"
[RFC6553] describes the RPL Option for use among RPL routers to
include the abstract RPL Packet Information (RPI) described in
section 11.2. of [RPL] in data packets.
The RPL Option is commonly referred to as the RPI though the RPI is
really the abstract information that is transported in the RPL
Option. [RFC9008] updated the Option Type from 0x63 to 0x23.
This specification Amends the RPL Option to encode the 'P' flag as
follows:
Thubert, et al. Expires 2 June 2024 [Page 44]
Internet-Draft DAO Projection November 2023
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|R|F|P|0|0|0|0| RPLInstanceID | SenderRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (sub-TLVs) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Amended RPL Option Format
Option Type: 0x23 or 0x63, see [RFC9008]
Opt Data Len: See [RFC6553]
'O', 'R' and 'F' flags: See [RFC6553]. Those flags MUST be set to 0
by the sender and ignored by the receiver if the 'P' flag is set.
Projected-Route 'P': 1-bit flag as defined in Section 4.1.6.
RPLInstanceID: See [RFC6553]. Indicates the TrackId if the 'P' flag
is set, as discussed in Section 4.1.1.
SenderRank: See [RFC6553]. This field MUST be set to 0 by the
sender and ignored by the receiver if the 'P' flag is set.
4.3. Extending RFC 8138
The 6LoWPAN Routing Header [RFC8138] specification introduces a new
IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN)
[RFC6282] dispatch type for use in 6LoWPAN route-over topologies,
which initially covers the needs of RPL data packet compression.
Section 4 of [RFC8138] presents the generic formats of the 6LoWPAN
Routing Header (6LoRH) with two forms, one Elective that can be
ignored and skipped when the router does not understand it, and one
Critical which causes the packet to be dropped when the router cannot
process it. The 'E' Flag in the 6LoRH indicates its form. In order
to skip the Elective 6LoRHs, their format imposes a fixed expression
of the size, whereas the size of a Critical 6LoRH may be signaled in
variable forms to enable additional optimizations.
Thubert, et al. Expires 2 June 2024 [Page 45]
Internet-Draft DAO Projection November 2023
When the [RFC8138] compression is used, the Root of the main DODAG
that sets up the Track also constructs the compressed routing header
(SRH-6LoRH) on behalf of the Track Ingress, which saves the
complexities of optimizing the SRH-6LoRH encoding in constrained
code. The SRH-6LoRH is signaled in the NSM-VIO, in a fashion that it
is ready to be placed as is in the packet encapsulation by the Track
Ingress.
Section 6.3 of [RFC8138] presents the formats of the 6LoWPAN Routing
Header of type 5 (RPI-6LoRH) that compresses the RPI for normal RPL
operation. The format of the RPI-6LoRH is not suited for P-Routes
since the O,R,F flags are not used and the Rank is unknown and
ignored.
This specification extends [RFC8138] to introduce a new 6LoRH, the P-
RPI-6LoRH that can be used in either Elective or Critical 6LoRH form,
see Table 22 and Table 23 respectively. The new 6LoRH MUST be used
as a Critical 6LoRH, unless an SRH-6LoRH is present and controls the
routing decision, in which case it MAY be used in Elective form.
The P-RPI-6LoRH is designed to compress the RPI along RPL P-Routes.
Its format is as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|E| Length | 6LoRH Type | RPLInstanceID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: P-RPI-6LoRH Format
Type: IANA is requested to define the same value of the type for
both Elective and Critical forms. A type of 8 is suggested.
Elective 'E': See [RFC8138]. The 'E' flag is set to 1 to indicate
an Elective 6LoRH, meaning that it can be ignored when forwarding.
RPLInstanceID : In the context of this specification, the
RPLInstanceID field signals the TrackID, see Section 3.4 and
Section 6.3 .
Section 6.8 details how a Track Ingress leverages the P-RPI-6LoRH
Header as part of the encapsulation of a packet to place it into a
Track.
5. New RPL Control Messages and Options
Thubert, et al. Expires 2 June 2024 [Page 46]
Internet-Draft DAO Projection November 2023
5.1. New P-DAO Request Control Message
The P-DAO Request (PDR) message is sent by a Node in the main DODAG
to the Root. It is a request to establish or refresh a Track where
this node is Track Ingress, and signals whether an acknowledgment
called PDR-ACK is requested or not. A positive PDR-ACK indicates
that the Track was built and that the Root commits to maintaining the
Track for the negotiated lifetime.
The main Root MAY indicate to the Track Ingress that the Track was
terminated before its time and to do so, it MUST use an asynchronous
PDR-ACK with a negative status. A status of "Transient Failure" (see
Section 11.10) is an indication that the PDR may be retried after a
reasonable time that depends on the deployment. Other negative
status values indicate a permanent error; the attempt must be
abandoned until a corrective action is taken at the application layer
or through network management.
The source IPv6 address of the PDR signals the Track Ingress to-be of
the requested Track, and the TrackID is indicated in the message
itself. At least one RPL Target Option MUST be present in the
message. If more than one RPL Target Option is present, the Root
will provide a Track that reaches the first listed Target and a
subset of the other Targets; the details of the subset selection are
out of scope. The RTO signals the Track Egress (more in
Section 6.2).
The RPL Control Code for the PDR is 0x09, to be confirmed by IANA.
The format of PDR Base Object is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TrackID |K|R| Flags | ReqLifetime | PDRSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
Figure 13: New P-DAO Request Format
TrackID: 8-bit field. In the context of this specification, the
TrackID field signals the RPLInstanceID of the DODAG formed by the
Track, see Section 3.4 and Section 6.3. To allocate a new Track,
the Ingress Node must provide a value that is not in use at this
time.
K: The 'K' flag is set to indicate that the recipient is expected to
send a PDR-ACK back.
Thubert, et al. Expires 2 June 2024 [Page 47]
Internet-Draft DAO Projection November 2023
R: The 'R' flag is set to request a Complex Track for redundancy.
Flags: Reserved. The Flags field MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
ReqLifetime: 8-bit unsigned integer. The requested lifetime for the
Track expressed in Lifetime Units (obtained from the DODAG
Configuration option). The value of 255 (0xFF) represents
infinity (never time out).
A PDR with a fresher PDRSequence refreshes the lifetime, and a
PDRLifetime of 0 indicates that the Track should be destroyed,
e.g., when the application that requested the Track terminates.
PDRSequence: 8-bit wrapping sequence number, obeying the operation
in section 7.2 of [RPL]. The PDRSequence is used to correlate a
PDR-ACK message with the PDR message that triggered it. It is
incremented at each PDR message and echoed in the PDR-ACK by the
Root.
5.2. New PDR-ACK Control Message
The new PDR-ACK is sent as a response to a PDR message with the 'K'
flag set. The RPL Control Code for the PDR-ACK is 0x0A, to be
confirmed by IANA. Its format is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TrackID | Flags | Track Lifetime| PDRSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDR-ACK Status| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+
Figure 14: New PDR-ACK Control Message Format
TrackID: Set to the TrackID indicated in the TrackID field of the
PDR messages that this replies to.
Flags: Reserved. The Flags field MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Track Lifetime: Indicates the remaining Lifetime for the Track,
expressed in Lifetime Units; The value of 255 (0xFF) represents
infinity. The value of zero (0x00) indicates that the Track was
destroyed or not created.
Thubert, et al. Expires 2 June 2024 [Page 48]
Internet-Draft DAO Projection November 2023
PDRSequence: 8-bit wrapping sequence number. It is incremented at
each PDR message and echoed in the PDR-ACK.
PDR-ACK Status: 8-bit field indicating the completion. The PDR-ACK
Status is substructured as indicated in Figure 15:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|E|R| Value |
+-+-+-+-+-+-+-+-+
Figure 15: PDR-ACK status Format
E: 1-bit flag. Set to indicate a rejection. When not set, the
value of 0 indicates Success/Unqualified Acceptance and other
values indicate "not an outright rejection".
R: 1-bit flag. Reserved, MUST be set to 0 by the sender and
ignored by the receiver.
Status Value: 6-bit unsigned integer. Values depending on the
setting of the 'E' flag, see Table 28 and Table 29.
Reserved: The Reserved field MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
5.3. Via Information Options
A VIO signals the ordered list of IPv6 Via Addresses that constitutes
the hops of either a Lane (using Non-Storing Mode) or a Segment
(using Storing mode) of a Track. A Storing Mode P-DAO contains one
Storing Mode VIO (SM-VIO) whereas a Non-Storing Mode P-DAO contains
one Non-Storing Mode VIO (NSM-VIO).
The duration of the validity of a VIO is indicated in a Segment
Lifetime field. A P-DAO message that contains a VIO with a Segment
Lifetime of zero is referred as a No-Path P-DAO.
The VIO contains one or more SRH-6LoRH header(s), each formed of a
SRH-6LoRH head and a collection of compressed Via Addresses, except
in the case of a Non-Storing Mode No-Path P-DAO where the SRH-6LoRH
header is not present.
In the case of a SM-VIO, or if [RFC8138] is not used in the data
packets, then the Root MUST use only one SRH-6LoRH per Via
Information Option, and the compression is the same for all the
addresses, as shown in Figure 16, for simplicity.
Thubert, et al. Expires 2 June 2024 [Page 49]
Internet-Draft DAO Projection November 2023
In case of an NSM-VIO and if [RFC8138] is in use in the main DODAG,
the Root SHOULD optimize the size of the NSM-VIO if using different
SRH-6LoRH Types would make the VIO globally shorter; this means that
more than one SRH-6LoRH may be present.
The format of the Via Information Option is as follows:
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 | Option Length | Flags | P-RouteID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Segm. Sequence | Seg. Lifetime | SRH-6LoRH head |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Via Address 1 (compressed by RFC 8138) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .... .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Via Address n (compressed by RFC 8138) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Additional SRH-6LoRH Header(s) .
| |
. .... .
Figure 16: VIO format
Option Type: 0x0E for SM-VIO, 0x0F for NSM-VIO (to be confirmed by
IANA) (see Table 26).
Option Length: 8-bit unsigned integer, representing the length in
octets of the option, not including the Option Type and Length
fields (see section 6.7.1. of [RPL]); the Option Length is
variable, depending on the number of Via Addresses and the
compression applied.
Flags: 8-bit field. No flag is defined in this specification. The
field MUST be set to 0 by the sender and ignored by the receiver.
P-RouteID: 8-bit field that identifies a component of a Track or the
Thubert, et al. Expires 2 June 2024 [Page 50]
Internet-Draft DAO Projection November 2023
main DODAG as indicated by the TrackID field. The value of 0 is
used to signal a path, i.e., made of a single Segment/Lane. In an
SM-VIO, the P-RouteID indicates an actual Segment. In an NSM-VIO,
it indicates a Lane, that is a path that is added to the overall
topology of the Track.
Segment Sequence: 8-bit unsigned integer. The Segment Sequence
obeys the operation in section 7.2 of [RPL] and the lollipop
starts at 255.
When the Root of the DODAG needs to refresh or update a Segment in
a Track, it increments the Segment Sequence individually for that
Segment.
The Segment information indicated in the VIO deprecates any state
for the Segment indicated by the P-RouteID within the indicated
Track and sets up the new information.
A VIO with a Segment Sequence that is not as fresh as the current
one is ignored.
A VIO for a given DODAGID with the same (TrackID, P-RouteID,
Segment Sequence) indicates a retry; it MUST NOT change the
Segment and MUST be propagated or answered as the first copy.
Segment Lifetime: 8-bit unsigned integer. The length of time in
Lifetime Units (obtained from the Configuration option) that the
Segment is usable.
The period starts when a new Segment Sequence is seen. The value
of 255 (0xFF) represents infinity. The value of zero (0x00)
indicates a loss of reachability.
SRH-6LoRH head: The first 2 bytes of the (first) SRH-6LoRH as shown
in Figure 6 of [RFC8138]. As an example, a 6LoRH Type of 4 means
that the VIA Addresses are provided in full with no compression.
Via Address: An IPv6 ULA or GUA of a node along the Segment. The
VIO contains one or more IPv6 Via Addresses listed in the datapath
order from Ingress to Egress. The list is expressed in a
compressed form as signaled by the preceding SRH-6LoRH header.
In a Storing Mode P-DAO that updates or removes a section of an
already existing Segment, the list in the SM-VIO may represent
only the section of the Segment that is being updated; at the
extreme, the SM-VIO updates only one node, in which case it
contains only one IPv6 address. In all other cases, the list in
the VIO MUST be complete.
Thubert, et al. Expires 2 June 2024 [Page 51]
Internet-Draft DAO Projection November 2023
In the case of an SM-VIO, the list indicates a sequential (strict)
path through direct neighbors, the complete list starts at Ingress
and ends at Egress, and the nodes listed in the VIO, including the
Egress, MAY be considered as implicit Targets.
In the case of an NSM-VIO, the complete list can be loose and
excludes the Ingress node, starting at the first loose hop and
ending at a Track Egress; the Track Egress MUST be considered as
an implicit Target, so it MUST NOT be signaled in a RPL Target
Option.
5.4. Sibling Information Option
The Sibling Information Option (SIO) provides information about
siblings that could be used by the Root to form P-Routes. One or
more SIO(s) may be placed in the DAO messages that are sent to the
Root in Non-Storing Mode.
To advertise a neighbor node, the router MUST have an active Address
Registration from that sibling using [RFC8505], for an address (ULA
or GUA) that serves as identifier for the node. If this router also
registers an address to that sibling, and the link has similar
properties in both directions, only the router with the lowest
Interface ID in its registered address needs to report the SIO, with
the B flag set, and the Root will assume symmetry.
The SIO carries a flag (B) that is set when similar performance can
be expected in both directions, so the routing can consider that the
information provided for one direction is valid for both. If the SIO
is effectively received from both sides then the B flag MUST be
ignored. The policy that describes the performance criteria, and how
they are asserted is out of scope. In the absence of an external
protocol to assert the link quality, the flag SHOULD NOT be set.
The format of the SIO is as follows:
Thubert, et al. Expires 2 June 2024 [Page 52]
Internet-Draft DAO Projection November 2023
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 | Option Length |S|B|Flags|Comp.| Opaque |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Step in Rank | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Sibling DODAGID (if the D flag not set) .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Sibling Address .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Sibling Information Option Format
Option Type: 0x10 for SIO (to be confirmed by IANA) (see Table 26).
Option Length: 8-bit unsigned integer, representing the length in
octets of the option, not including the Option Type and Length
fields (see section 6.7.1. of [RPL]).
Reserved for Flags: MUST be set to zero by the sender and MUST be
ignored by the receiver.
B: 1-bit flag that is set to indicate that the connectivity to the
sibling is bidirectional and roughly symmetrical. In that case,
only one of the siblings may report the SIO for the hop. If 'B'
is not set then the SIO only indicates connectivity from the
sibling to this node, and does not provide information on the hop
from this node to the sibling.
S: 1-bit flag that is set to indicate that sibling belongs to the
same DODAG. When not set, the Sibling DODAGID is indicated.
Flags: Reserved. The Flags field MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Thubert, et al. Expires 2 June 2024 [Page 53]
Internet-Draft DAO Projection November 2023
Opaque: MAY be used to carry information that the node and the Root
understand, e.g., a particular representation of the Link
properties such as a proprietary Link Quality Information for
packets received from the sibling. In some scenarios such as the
case of an Industrial Alliances that uses RPL for a particular use
/ environment, this field MAY be redefined to fit the needs of
that case.
Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH
Type as defined in figure 7 in section 5.1 of [RFC8138] that
corresponds to the compression used for the Sibling Address and
its DODAGID if present. The Compression reference is the Root of
the main DODAG.
Step in Rank: 16-bit unsigned integer. This is the Step in Rank
[RPL] as computed by the Objective Function between this node and
the sibling, that reflects the abstract Rank increment that would
be computed by the OF if the sibling was the preferred parent.
Reserved: The Reserved field MUST be initialized to zero by the
sender and MUST be ignored by the receiver
Sibling DODAGID: 2 to 16 bytes, the DODAGID of the sibling in a
[RFC8138] compressed form as indicated by the Compression Type
field. This field is present if and only if the D flag is not
set.
Sibling Address: 2 to 16 bytes, an IPv6 Address of the sibling, with
a scope that MUST be make it reachable from the Root, e.g., it
cannot be a Link Local Address. The IPv6 address is encoded in
the [RFC8138] compressed form indicated by the Compression Type
field.
An SIO MAY be immediately followed by a DAG Metric Container. In
that case the DAG Metric Container provides additional metrics for
the hop from the Sibling to this node.
6. Root Initiated Routing State
6.1. RPL Network Setup
To avoid the need of Path MTU Discovery, 6LoWPAN links are normally
defined with a MTU of 1280 (see section 4 of [6LoWPAN]). Injecting
packets in a Track typically involves an IP-in-IP encapsulation and
additional IPv6 Extension Headers. This may cause fragmentation if
the resulting packets exceeds the MTU that is defined for the RPL
domain.
Thubert, et al. Expires 2 June 2024 [Page 54]
Internet-Draft DAO Projection November 2023
Though fragmentation is possible in a 6LoWPAN LLN, e.g., using
[6LoWPAN], [RFC8930], and/or [RFC8931], it is RECOMMENDED to allow an
MTU that is larger than 1280 in the main DODAG and which allows for
the additional headers while exposing only 1280 to the 6LoWPAN Nodes.
6.2. Requesting a Track
This specification introduces the PDR message, used by an LLN node to
request the formation of a new Track for which this node is the
Ingress. Note that the namespace for the TrackID is owned by the
Ingress node, and in the absence of a PDR, there must be some
procedure for the Root to assign TrackIDs in that namespace while
avoiding collisions (more in Section 6.3).
The PDR signals the desired TrackID and the duration for which the
Track should be established. Upon a PDR, the Root MAY install the
Track as requested, in which case it answers with a PDR-ACK
indicating the granted Track Lifetime. All the Segments MUST be of a
same mode, either Storing or Non-Storing. All the Segments MUST be
created with the same TrackID and the same DODAGID signaled in the
P-DAO.
The Root designs the Track as it sees best, and updates / changes the
Segments over time to serve the Track as needed. Note that there is
no protocol element to notify to the requesting Track Ingress when
changes happen deeper down the Track, so they are transparent to the
Track Ingress. If the main Root cannot maintain an expected service
level, then it needs to tear down the Track completely. The Segment
Lifetime in the P-DAO messages does not need to be aligned to the
Requested Lifetime in the PDR, or between P-DAO messages for
different Segments. The Root may use shorter lifetimes for the
Segments and renew them faster than the Track is, or longer lifetimes
in which case it will need to tear down the Segments if the Track is
not renewed.
When the Track Lifetime that was returned in the PDR-ACK is close to
elaPLR - vs. the trip time from the node to the Root, the requesting
node SHOULD resend a PDR using the TrackID in the PDR-ACK to extend
the lifetime of the Track, else the Track will time out and the Root
will tear down the whole structure.
If the Track fails and cannot be restored, the Root notifies the
requesting node asynchronously with a PDR-ACK with a Track Lifetime
of 0, indicating that the Track has failed, and a PDR-ACK Status
indicating the reason of the fault.
Thubert, et al. Expires 2 June 2024 [Page 55]
Internet-Draft DAO Projection November 2023
6.3. Identifying a Track
RPL defines the concept of an Instance to signal an individual
routing topology, and multiple topologies can coexist in the same
network. The RPLInstanceID is tagged in the RPI of every packet to
signal which topology the packet actually follows.
This draft leverages the RPL Instance model as follows:
* The main Root MAY use P-DAO messages to add better routes in the
main Instance in conformance with the routing objectives in that
Instance.
To achieve this, the main Root MAY install a Segment along a path
down the main DODAG, which is operated in Non-Storing Mode. This
enables a loose source routing and reduces the size of the Routing
Header, see Section 3.3.1. The main Root MAY also install a lane
across the main DODAG to complement the routing topology.
When adding a P-Route to the RPL main DODAG, the main Root MUST
set the RPLInstanceID field of the P-DAO Base Object (see section
6.4.1. of [RPL]) to the RPLInstanceID of the main DODAG, and MUST
NOT use the DODAGID field. A P-Route provides a longer match to
the Target Address than the default route via the main Root, so it
is preferred.
* The main Root MAY also use P-DAO messages to install a Track as an
independent routing topology (say, Traffic Engineered) to achieve
particular routing characteristics from an Ingress to Egress
Endpoints. To achieve this, the main Root MUST set up a Local RPL
Instance (see section 5 of [RPL]), and the Local RPLInstanceID
serves as the TrackID. The TrackID MUST be unique for the IPv6
ULA or GUA of the Track Ingress that serves as DODAGID for the
Track.
This way, a Track is uniquely identified by the tuple (DODAGID,
TrackID) where the TrackID is always represented with the D flag
set to 0 (see also section 5.1. of [RPL]), indicating when used in
an RPI that the source address of the IPv6 packet signals the
DODAGID.
The P-DAO Base Object MUST indicate the tuple (DODAGID, TrackID)
that identifies the Track as shown in Figure 8, and the P-RouteID
that identifies the P-Route MUST be signaled in the VIO as shown
in Figure 16.
Thubert, et al. Expires 2 June 2024 [Page 56]
Internet-Draft DAO Projection November 2023
The Track Ingress is the Root of the DODAG ID formed by the local
RPL Instance. It owns the namespace of its TrackIDs, so it can
pick any unused value to request a new Track with a PDR. In a
particular deployment where PDRs are not used, a portion of the
namespace can be administratively delegated to the main Root,
meaning that the main Root is authoritative for assigning the
TrackIDs for the Tracks it creates.
With this specification, the main Root is aware of all the active
Tracks, so it can also pick any unused value to form Tracks
without a PDR. To avoid a collision of the main Root and the
Track Ingress picking the same value at the same time, it is
RECOMMENDED that the Track Ingress starts allocating the ID value
of the Local RPLInstanceID (see section 5.1. of [RPL]) used as
TrackIDs with the value 0 incrementing, while the Root starts with
63 decrementing.
6.4. Installing a Track
A path can be installed by a single P-Route that signals the sequence
of consecutive nodes, either in Storing Mode as a single-Segment
Track, or in Non-Storing Mode as a single-Lane Track. A single-Lane
Track can be installed as a loose Non-Storing Mode P-Route, in which
case the next loose entry must recursively be reached over a path.
A Complex Track can be installed as a collection of P-Routes with the
same DODAGID and Track ID. The Ingress of a Non-Storing Mode P-Route
is the owner and Root of the DODAGID. The Ingress of a Storing Mode
P-Route must be either the owner of the DODAGID, or a hop of a Lane
of the same Track. In the latter case, the Targets of the P-Route
must include the next hop of the Lane if there is one, to ensure
forwarding continuity. In the case of a Complex Track, each Segment
is maintained independently and asynchronously by the Root, with its
own lifetime that may be shorter, the same, or longer than that of
the Track.
A route along a Track for which the TrackID is not the RPLInstanceID
of the main DODAG MUST be installed with a higher precedence than the
routes along the main DODAG, meaning that:
* Longest match MUST be the prime comparison for routing.
* In case of equal length match, the route along the Track MUST be
preferred vs. the one along the main DODAG.
* There SHOULD NOT be 2 different Tracks leading to the same Target
from same Ingress node, unless there's a policy for selecting
which packets use which Track; such a policy is out of scope.
Thubert, et al. Expires 2 June 2024 [Page 57]
Internet-Draft DAO Projection November 2023
* A packet that was routed along a Track MUST NOT be routed along
the main DODAG again; if the destination is not reachable as a
neighbor by the node where the packet exits the Track then the
packet MUST be dropped.
6.4.1. Signaling a Projected Route
This draft adds a capability whereby the Root of a main DODAG
installs a Track as a collection of P-Routes, using a Projected-DAO
(P-DAO) message for each individual lane or Segment. The P-DAO
signals a collection of Targets in the RPL Target Option(s) (RTO).
Those Targets can be reached via a sequence of routers indicated in a
VIO.
Like a classical DAO message, a P-DAO causes a change of state only
if it is "new" per section 9.2.2. "Generation of DAO Messages" of
the RPL specification [RPL]; this is determined using the Segment
Sequence information from the VIO as opposed to the Path Sequence
from a TIO. Also, a Segment Lifetime of 0 in a VIO indicates that
the P-Route associated to the Segment is to be removed. There are
two Modes of operation for the P-Routes, the Storing and the Non-
Storing Modes.
A P-DAO message MUST be sent from the address of the Root that serves
as DODAGID for the main DODAG. It MUST contain either exactly one
sequence of one or more RTOs followed one VIO, or any number of
sequences of one or more RTOs followed by one or more TIOs. The
former is the normal expression for this specification, where as the
latter corresponds to the variation for lesser constrained
environments described in Section 7.2.
A P-DAO that creates or updates a lane MUST be sent to a GUA or a ULA
of the Ingress of the Lane; it must contain the full list of hops in
the Lane unless the Lane is being removed. A P-DAO that creates a
new Track Segment MUST be sent to a GUA or a ULA of the Segment
Egress and MUST signal the full list of hops in Segment; a P-DAO that
updates (including deletes) a section of a Segment MUST be sent to
the first node after the modified Segment and signal the full list of
hops in the section starting at the node that immediately precedes
the modified section.
Thubert, et al. Expires 2 June 2024 [Page 58]
Internet-Draft DAO Projection November 2023
In Non-Storing Mode, as discussed in Section 6.4.3, the Root sends
the P-DAO to the Track Ingress where the source-routing state is
applied, whereas in Storing Mode, the P-DAO is sent to the last node
on the installed path and forwarded in the reverse direction,
installing a Storing Mode state at each hop, as discussed in
Section 6.4.2. In both cases the Track Ingress is the owner of the
Track, and it generates the P-DAO-ACK when the installation is
successful.
If the 'K' Flag is present in the P-DAO, the P-DAO must be
acknowledged using a DAO-ACK that is sent back to the address of the
Root from which the P-DAO was received. In most cases, the first
node of the Lane, Segment, or updated section of the Segment is the
node that sends the acknowledgment. The exception to the rule is
when an intermediate node in a Segment fails to forward a Storing
Mode P-DAO to the previous node in the SM-VIO.
In a No-Path Non-Storing Mode P-DAO, the SRH-6LoRH MUST NOT be
present in the NSM-VIO; the state in the Ingress is erased
regardless. In all other cases, a VIO MUST contain at least one Via
Address, and a Via Address MUST NOT be present more than once, which
would create a loop.
A node that processes a VIO MAY verify whether any of these
conditions happen, and when one does, it MUST ignore the P-DAO and
reject it with a RPL Rejection Status of "Error in VIO" in the DAO-
ACK, see Section 11.16.
Other errors than those discussed explicitly that prevent the
installation of the route are acknowledged with a RPL Rejection
Status of "Unqualified Rejection" in the DAO-ACK.
6.4.2. Installing a Track Segment with a Storing Mode P-Route
As illustrated in Figure 18, a Storing Mode P-DAO installs a route
along the Segment signaled by the SM-VIO towards the Targets
indicated in the Target Options. The Segment is to be included in a
DODAG indicated by the P-DAO Base Object, that may be the one formed
by the main DODAG, or a Track associated with a local RPL Instance.
Thubert, et al. Expires 2 June 2024 [Page 59]
Internet-Draft DAO Projection November 2023
------+---------
| Internet
|
+-----+
| | Border router
| | (RPL Root)
+-----+ | ^ |
| | DAO | ACK |
o o o o | | |
o o o o Ingress o o o | ^ | Projected .
o o o o o \\ o o o | | DAO | Route .
o o o o \\ o o o o | ^ | .
o o o o o Egress o o v | DAO v .
o o LLN o o o |
o o o o o Loose Source Route Path |
o o o o v
Figure 18: Projecting a route
In order to install the relevant routing state along the Segment ,
the Root sends a unicast P-DAO message to the Track Egress router of
the routing Segment that is being installed. The P-DAO message
contains a SM-VIO with the strict sequence of Via Addresses. The SM-
VIO follows one or more RTOs indicating the Targets to which the
Track leads. The SM-VIO contains a Segment Lifetime for which the
state is to be maintained.
The Root sends the P-DAO directly to the Egress node of the Segment.
In that P-DAO, the destination IP address matches the last Via
Address in the SM-VIO. This is how the Egress recognizes its role.
In a similar fashion, the Segment Ingress node recognizes its role
because it matches the first Via Address in the SM-VIO.
The Egress node of the Segment is the only node in the path that does
not install a route in response to the P-DAO; it is expected to be
already able to route to the Target(s) based on its existing tables.
If one of the Targets is not known, the node MUST answer to the Root
with a DAO-ACK listing the unreachable Target(s) in an RTO and a
rejection status of "Unreachable Target".
If the Egress node can reach all the Targets, then it forwards the
P-DAO with unchanged content to its predecessor in the Segment as
indicated in the list of Via Information options, and recursively the
message is propagated unchanged along the sequence of routers
indicated in the P-DAO, but in the reverse order, from Egress to
Ingress.
Thubert, et al. Expires 2 June 2024 [Page 60]
Internet-Draft DAO Projection November 2023
The address of the predecessor to be used as destination of the
propagated DAO message is found in the Via Address list, at the
position preceeding the one that contains the address of the
propagating node, which is used as source of the message.
Upon receiving a propagated DAO, all except the Egress router MUST
install a route towards the DAO Target(s) via their successor in the
SM-VIO. A router that cannot store the routes to all the Targets in
a P-DAO MUST reject the P-DAO by sending a DAO-ACK to the Root with a
Rejection Status of "Out of Resources" as opposed to forwarding the
DAO to its predecessor in the list. The router MAY install
additional routes towards the Via Addresses that appear in the SM-VIO
after its own address, if any, but in case of a conflict or a lack of
resource, the route(s) to the Target(s) are the ones that must be
installed in priority.
If a router cannot reach its predecessor in the SM-VIO, the router
MUST send the DAO-ACK to the Root with a Rejection Status of
"Predecessor Unreachable".
The process continues until the P-DAO is propagated to the Ingress
router of the Segment, which answers with a DAO-ACK to the Root. The
Root always expects a DAO-ACK, either from the Track Ingress with a
positive status or from any node along the Segment with a negative
status. If the DAO-ACK is not received, the Root may retry the DAO
with the same TID, or tear down the route.
6.4.3. Installing a lane with a Non-Storing Mode P-Route
As illustrated in Figure 19, a Non-Storing Mode P-DAO installs a
source-routed path within the Track indicated by the P-DAO Base
Object, towards the Targets indicated in the Target Options. The
source-routed path requires a Source-Routing header which implies an
IP-in-IP encapsulation to add the SRH to an existing packet. It is
sent to the Track Ingress which creates a tunnel associated with the
Track, and connected routes over the tunnel to the Targets in the
RTO. The tunnel encapsulation MUST incorporate a routing header via
the list addresses listed in the VIO in the same order. The content
of the NSM-VIO starting at the first SRH-6LoRH header MUST be used
verbatim by the Track Ingress when it encapsulates a packet to
forward it over the Track.
Thubert, et al. Expires 2 June 2024 [Page 61]
Internet-Draft DAO Projection November 2023
------+---------
| Internet
|
+-----+
| | Border router
| | (RPL Root)
+-----+ | P ^ ACK
| Track | DAO |
o o o o Ingress X V | X
o o o o o o o X o X Source
o o o o o o o o X o o X Routed
o o ° o o o o X o X Segment
o o o o o o o o X Egress X
o o o o o |
Target
o o LLN o o
o o o o
Figure 19: Projecting a Non-Storing Route
The next entry in the source-routed path must be either a neighbor of
the previous entry, or reachable as a Target via another P-Route,
either Storing or Non-Storing, which implies that the nested P-Route
has to be installed before the loose sequence is, and that P-Routes
must be installed from the last to the first along the datapath. For
instance, a Segment of a Track must be installed before the Lane(s)
of the same Track that use it, and stitched Segments must be
installed in order from the last that reaches to the Targets to the
first.
If the next entry in the loose sequence is reachable over a Storing
Mode P-Route, it MUST be the Target of a Segment and the Ingress of a
next Segment, both already setup; the Segments are associated with
the same Track, which avoids the need of an additional encapsulation.
For instance, in Section 3.5.1.3, Segments A==>B-to-C and
C==>D==>E-to-F must be installed with Storing Mode P-DAO messages 1
and 2 before the Track A-->C-->E-to-F that joins them can be
installed with Non-Storing Mode P-DAO 3.
Conversely, if it is reachable over a Non-Storing Mode P-Route, the
next loose source-routed hop of the inner Track is a Target of a
previously installed Track and the Ingress of a next Track, which
requires a de- and a re-encapsulation when switching the outer Tracks
that join the loose hops. This is examplified in Section 3.5.2.3
where Non-Storing Mode P-DAO 1 and 2 install strict Tracks that Non-
Storing Mode P-DAO 3 joins as a super Track. In such a case, packets
are subject to double IP-in-IP encapsulation.
Thubert, et al. Expires 2 June 2024 [Page 62]
Internet-Draft DAO Projection November 2023
6.5. Tearing Down a P-Route
A P-DAO with a lifetime of 0 is interpreted as a No-Path DAO and
results in cleaning up existing state as opposed to refreshing an
existing one or installing a new one. To tear down a Track, the Root
must tear down all the Track Segments and Lanes that compose it one
by one.
Since the state about a Lane of a Track is located only on the
Ingress Node, the Root cleans up the Lane by sending an NSM-VIO to
the Ingress indicating the TrackID and the P-RouteID of the Lane
being removed, a Segment Lifetime of 0 and a newer Segment Sequence.
The SRH-6LoRH with the Via Addresses in the NSM-VIO are not needed;
it SHOULD NOT be placed in the message and MUST be ignored by the
receiver. Upon that NSM-VIO, the Ingress node removes all state for
that Track if any, and replies positively anyway.
The Root cleans up a section of a Segment by sending an SM-VIO to the
last node of the Segment, with the TrackID and the P-RouteID of the
Segment being updated, a Segment Lifetime of zero (0) and a newer
Segment Sequence. The Via Addresses in the SM-VIO indicates the
section of the Segment being modified, from the first to the last
node that is impacted. This can be the whole Segment if it is
totally removed, or a sequence of one or more nodes that have been
bypassed by a Segment update.
The No-Path P-DAO is forwarded normally along the reverse list, even
if the intermediate node does not find a Segment state to clean up.
This results in cleaning up the existing Segment state if any, as
opposed to refreshing an existing one or installing a new one.
6.6. Maintaining a Track
Repathing a Track Segment or Lane may cause jitter and packet
misordering. For critical flows that require timely and/or in-order
delivery, it might be necessary to deploy the PAREO functions
[RAW-ARCHI] over a highly redundant Track. This specification allows
to use more than one Lane for a Track, and 1+N packet redundancy.
This section provides the steps to ensure that no packet is lost due
to the operation itself. This is ensured by installing the new
section from its last node to the first, so when an intermediate node
installs a route along the new section, all the downstream nodes in
the section have already installed their own. The disabled section
is removed when the packets in-flight are forwarded along the new
section as well.
Thubert, et al. Expires 2 June 2024 [Page 63]
Internet-Draft DAO Projection November 2023
6.6.1. Maintaining a Track Segment
To modify a section of a Segment between a first node and a second,
downstream node (which can be the Ingress and Egress, respectively),
while retaining those nodes in the Segment, the Root sends an SM-VIO
to the second node indicating the sequence of nodes in the new
section of the Segment. The SM-VIO indicates the TrackID and the
P-RouteID of the Segment being updated, and a newer Segment Sequence.
The P-DAO is propagated from the second to the first node and on the
way, it updates the state on the nodes that are common to the old and
the new section of the Segment and creates a state in the new nodes.
When the state is updated in an intermediate node, that node might
still receive packets that were in flight from the Ingress to self
over the old section of the Segment. Since the remainder of the
Segment is already updated, the packets are forwarded along the new
version of the Segment from that node on.
After a reasonable time to enable the deprecated sections to drain
their traffic, the Root tears down the remaining section(s) of the
old Segments as described in Section 6.5.
6.6.2. Maintaining a lane
This specification allows the Root to add Lanes to a Track by sending
a Non-Storing Mode P-DAO to the Ingress associated to the same
TrackID, and a new Segment ID. If the Lane is loose, then the
Segments that join the hops must be created first. It makes sense to
add a new Lane before removing one that is becoming excessively
lossy, and switch to the new Lane before removing the old. Dropping
a Track before the new one is installed would reroute the traffic via
the root; this may increase the latency beyond acceptable thresholds,
and overload the network near the root. This may also cause loops in
the case of stitched Tracks: the packets that cannot be injected in
the second Track might be routed back and reinjected at the Ingress
of the first.
It is also possible to update a lane by sending a Non-Storing Mode
P-DAO to the Ingress with the same Segment ID, an incremented Segment
Sequence, and the new complete list of hops in the NSM-VIO. Updating
a live Lane means changing one or more of the intermediate loose
hops, and involves laying out new Segments from and to the new loose
hops before the NSM-VIO for the new Lane is issued.
Thubert, et al. Expires 2 June 2024 [Page 64]
Internet-Draft DAO Projection November 2023
Packets that are in flight over the old version of the lane still
follow the old source route path over the old Segments. After a
reasonable time to enable the deprecated Segments to drain their
traffic, the Root tears down those Segments as described in
Section 6.5.
6.7. Encapsulating and Forwarding Along a Track
When injecting a packet in a Track, the Ingress router must
encapsulate the packet using IP-in-IP to add the Source Routing
Header with the final destination set to the Track Egress.
All properties of a Track operations are inherited form the main
Instance that is used to install the Track. For instance, the use of
compression per [RFC8138] is determined by whether it is used in the
RPL main DODAG, e.g., by setting the "T" flag [RFC9035] in the RPL
configuration option.
The Track Ingress that places a packet in a Track encapsulates it
with an IP-in-IP header, a Routing Header, and an IPv6 Hop-by-Hop
Option Header that contains the RPL Packet Information (RPI) as
follows:
* In the uncompressed form, the source of the packet is the address
that this router uses as DODAGID for the Track, the destination is
the first Via Address in the NSM-VIO, and the RH is a Source
Routing Header (SRH) [RFC6554] that contains the list of the
remaining Via Addresses, ending with the Track Egress.
* The preferred alternative in a network where 6LoWPAN Header
Compression [RFC6282] is used is to leverage "IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch"
[RFC8025] to compress the RPL artifacts as indicated in [RFC8138].
In that case, the source routed header is the exact copy of the
(chain of) SRH-6LoRH found in the NSM-VIO, also ending with the
Track Egress. The RPI-6LoRH is appended next, followed by an IP-
in-IP 6LoRH Header that indicates the Ingress router in the
Encapsulator Address field, see as a similar case Figure 20 of
[RFC9035].
To signal the Track in the packet, this specification leverages the
RPL Forwarding model as follows:
* In the data packets, the Track DODAGID and the TrackID MUST be
respectively signaled as the IPv6 Source Address and the
RPLInstanceID field of the RPI that MUST be placed in the outer
chain of IPv6 Headers.
Thubert, et al. Expires 2 June 2024 [Page 65]
Internet-Draft DAO Projection November 2023
The RPI carries a local RPLInstanceID called the TrackID, which,
in association with the DODAGID, indicates the Track along which
the packet is forwarded.
The D flag in the RPLInstanceID MUST be set to 0 to indicate that
the source address in the IPv6 header is set to the DODAGID (more
in Section 6.3).
* This draft conforms to the principles of [RFC9008] with regards to
packet forwarding and encapsulation along a Track, as follows:
- With this draft, the Track is a RPL DODAG. From the
perspective of that DODAG, the Track Ingress is the Root, the
Track Egress is a RPL-Aware 6LR, and neighbors of the Track
Egress that can be reached via the Track, but are external to
it, are external destinations and treated as RPL-Unaware Leaves
(RULs). The encapsulation rules in [RFC9008] apply.
- If the Track Ingress is the originator of the packet and the
Track Egress is the destination of the packet, there is no need
for an encapsulation.
- So the Track Ingress must encapsulate the traffic that it did
not originate, and it must include an RPI in the encapsulation
to signal the TrackID.
A packet that is being routed over the RPL Instance associated to
a first Non-Storing Mode Track MAY be placed recursively in a
second Track to cover one loose hop of the first Track as
discussed in more details Section 3.5.2.3. On the other hand, a
Storing Mode Segment must be strict and a packet that it placed in
a Storing Mode Segment MUST follow that Segment till the Segment
Egress.
It is known that a packet is forwarded along a Track by the source
address and the RPI in the encapsulation. The Track ID is used to
identify the RIB entries associated to that Track, which, in
intermediate nodes, correspond to the P-routes for the segments of
the Track that the forwarding router is aware of. The packet
processing uses a precedence that favors self delivery or routing
header handling when one is present, then delivery to direct
neighbors, then to indirect neighbors, then routing along a segment
along the Track, and finally as a last resort injecting the packet in
another Track.
To achieve this, the packet handling logic MUST happen in the
following order:
Thubert, et al. Expires 2 June 2024 [Page 66]
Internet-Draft DAO Projection November 2023
* If the destination of the packet is self:
1. if the header chain contains a RPL Source Route Header that is
not fully consumed, then the packet is forwarded along the
Track as prescribed by [RFC6554], meaning that the next entry
in the routing header becomes the destination;
2. otherwise: if the packet was encapsulated, then the packet is
decapsulated and the forwarding process recurses; else the
packet is delivered to the stack.
* Otherwise, the packet is forwarded as follows:
1. If the destination of the packet is a direct neighbor, e.g.,
installed by IPv6 Neighbor Discovery, then the packet the
packet MUST be forwarded to that neighbor;
2. Else If the destination of the packet is an indirect neighbor,
e.g., installed by a multicast DAO message from a common
neighbor, see Section 4.1.4, then the packet MUST be forwarded
to the common neighbor;
3. Else, if there is a RIB entry for the same Track (e.g.,
installed by an SM-VIO in a DAO message with the destination
as target), and the next hop in the RIB entry is a direct
neighbor, then the packet is passed to that neighbor;
4. Else, if there is a RIB entry for the different Track (e.g.,
installed by an NSM-VIO in a DAO message with the destination
as target), then the packet is encapsulated to be forwarded
along that Track and the forwarding process recurses;
otherwise the packet is dropped.
5. To avoid loops, and as opposed to packets that were not
encapsulated, a packet that was decapsulated from a Track MUST
NOT be routed along the default route of the main DODAG; this
would mean that the end-to-end path is uncontrolled. The node
that discovers the fault MUST discard the packet.
The node that drops a packet for either of the reasons above MUST
send an ICMPv6 Error message [RFC4443] to the Root, with a new Code
"Error in P-Route" (See Section 11.15). The Root can then repair by
updating the broken Segment and/or Tracks, and in the case of a
broken Segment, remove the leftover sections of the Segment using SM-
VIOs with a lifetime of 0 indicating the section to one or more nodes
being removed (See Section 6.6).
Thubert, et al. Expires 2 June 2024 [Page 67]
Internet-Draft DAO Projection November 2023
In case of a permanent forwarding error along a Source Route path,
the node that fails to forward SHOULD send an ICMP error with a code
"Error in Source Routing Header" back to the source of the packet, as
described in section 11.2.2.3. of [RPL]. Upon receiving this
message, the encapsulating node SHOULD stop using the source route
path for a reasonable period of time which depends on the deployment,
and it SHOULD send an ICMP message with a Code "Error in P-Route" to
the Root. Failure to follow these steps may result in packet loss
and wasted resources along the source route path that is broken.
Either way, the ICMP message MUST be throttled in case of consecutive
occurrences. It MUST be sourced at the ULA or a GUA that is used in
this Track for the source node, so the Root can establish where the
error happened.
The portion of the invoking packet that is sent back in the ICMP
message SHOULD record at least up to the RH if one is present, and
this hop of the RH SHOULD be consumed by this node so that the
destination in the IPv6 header is the next hop that this node could
not reach. If a 6LoWPAN Routing Header (6LoRH) [RFC8138] is used to
carry the IPv6 routing information in the outer header then that
whole 6LoRH information SHOULD be present in the ICMP message.
6.8. Compression of the RPL Artifacts
When using [RFC8138] in the main DODAG operated in Non-Storing Mode
in a 6LoWPAN LLN, a typical packet that circulates in the main DODAG
is formatted as shown in Figure 20, representing the case where an
IPv6-in-IPv6 encapsulation is needed (see Table 19 of [RFC9008]):
+-+ ... -+- ... -+- ... -+-+- ... +-+-+-+ ... +-+-+ ... -+ ... +-...
|11110001| SRH- | RPI- | IP-in-IP | NH=1 |11110CPP| UDP | UDP
| Page 1 | 6LoRH | 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld
+-+ ... -+- ... -+- ... -+-+- ... +-+-+-+ ... +-+-+ ... -+ ... +-...
<= RFC 6282 =>
<================ Inner packet ==================== = =
Figure 20: A Packet as Forwarded along the main DODAG
Since there is no page switch between the encapsulated packet and the
encapsulation, the first octet of the compressed packet that acts as
page selector is actually removed at encapsulation, so the inner
packet used in the descriptions below starts with the SRH-6LoRH, and
is exactly the packet represented in Figure 20, from the second octet
onward.
Thubert, et al. Expires 2 June 2024 [Page 68]
Internet-Draft DAO Projection November 2023
When encapsulating that inner packet to place it in the Track, the
first header that the Ingress appends at the head of the inner packet
is an IP-in-IP 6LoRH Header; in that header, the encapsulator
address, which maps to the IPv6 source address in the uncompressed
form, contains a GUA or ULA IPv6 address of the Ingress node that
serves as DODAG ID for the Track, expressed in the compressed form
and using the DODAGID of the main DODAG as compression reference. If
the address is compressed to 2 bytes, the resulting value for the
Length field shown in Figure 21 is 3, meaning that the SRH-6LoRH as a
whole is 5-octets long.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
|1|0|1| Length | 6LoRH Type 6 | Hop Limit | Track DODAGID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
Figure 21: The IP-in-IP 6LoRH Header
At the head of the resulting sequence of bytes, the track Ingress
then adds the RPI that carries the TrackID as RPLinstanceID as a P-
RPI-6LoRH Header, as illustrated in Figure 12, using the TrackID as
RPLInstanceID. Combined with the IP-in-IP 6LoRH Header, this allows
to identify the Track without ambiguity.
The SRH-6LoRH is then added at the head of the resulting sequence of
bytes as a verbatim copy of the content of the SR-VIO that signaled
the selected lane.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 .. .. ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+
|1|0|0| Size |6LoRH Type 0..4| Hop1 | Hop2 | | HopN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+
Where N = Size + 1
Figure 22: The SRH 6LoRH Header
The format of the resulting encapsulated packet in [RFC8138]
compressed form is illustrated in Figure 23:
+-+ ... -+-+-+- ... -+-+-+- ... -+-+-+-+-+- ... +-+-+-+-+-+-+- ...
| Page 1 | SRH-6LoRH | P-RPI-6LoRH | IP-in-IP 6LoRH | Inner Packet
+-+ ... -+-+-+- ... -+-+-+- ... -+-+-+-+-+- ... +-+-+-+-+-+-+- ...
Signals : Loose Hops : TrackID : Track DODAGID :
Figure 23: A Packet as Forwarded along a Track
Thubert, et al. Expires 2 June 2024 [Page 69]
Internet-Draft DAO Projection November 2023
7. Lesser Constrained Variations
7.1. Storing Mode main DODAG
This specification expects that the main DODAG is operated in Non-
Storing Mode. The reasons for that limitation are mostly related to
LLN operations, power and spectrum conservation:
* In Non-Storing Mode, the Root already knowns the DODAG topology,
so the additional topological information is reduced to the
siblings.
* The downward routes are updated with unicast messages to the Root,
which ensures that the Root can reach back to the LLN nodes after
a repair faster than in the case of Storing Mode. Also the Root
can control the use of the path diversity in the DODAG to reach
the LLN nodes. For both reasons, Non-Storing Mode provides better
capabilities for the Root to maintain the P-Routes.
* When the main DODAG is operated in Non-Storing Mode, P-Routes
enable loose Source Routing, which is only an advantage in that
mode. Storing Mode does not use Source Routing Headers, and does
not derive the same benefits from this capability.
On the other hand, since RPL is a Layer-3 routing protocol, its
applicability extends beyond LLNs to a generic IP network. RPL
requires less resources than alternative IGPs like OSPF, ISIS, EIGRP,
BABEL or RIP at the expense of a route stretch vs. the shortest path
routes to a destination that those protocols compute. P-Routes add
the capability to install shortest and/or constrained routes to
special destinations such as discussed in section A.9.4. of the ANIMA
ACP [RFC8994].
In a powered and wired network, when enough memory to store the
needed routes is available, the RPL Storing Mode proposes a better
trade-off than the Non-Storing, as it reduces the route stretch and
lowers the load on the Root. In that case, the control path between
the Root and the LLN nodes is highly available compared to LLNs, and
the nodes can be reached to maintain the P-Routes at most times.
This section specifies the additions that are needed to support
Projected Routes when the main DODAG is operated in Storing Mode. As
long as the RPI can be processed adequately by the dataplane, the
changes to this specification are limited to the DAO message. The
Track structure, routes and forwarding operations remain the same.
Since there is no capability negotiation, the expectation is that all
the nodes in the network support this specification in the same
fashion, or are configured the same way through management.
Thubert, et al. Expires 2 June 2024 [Page 70]
Internet-Draft DAO Projection November 2023
In Storing Mode, the Root misses the Child to Parent relationship
that forms the main DODAG, as well as the sibling information. To
provide that knowledge the nodes in the network MUST send additional
DAO messages that are unicast to the Root just like Non-Storing DAO
messages are.
In the DAO message, the originating router advertises a set of
neighbor nodes using Sibling Information Options (SIO)s, regardless
of the relative position in the DODAG of the advertised node vs. this
router.
The DAO message MUST be formed as follows:
* The originating router is identified by the source address of the
DAO. That address MUST be the one that this router registers to
neighbor routers so the Root can correlate the DAOs from those
routers when they advertise this router as their neighbor. The
DAO contains one or more sequences of one Transit Information
Option and one or more Sibling Information Options. There is no
RPL Target Option so the Root is not confused into adding a
Storing Mode route to the Target.
* The TIO is formed as in Storing Mode, and the Parent Address is
not present. The Path Sequence and Path Lifetime fields are
aligned with the values used in the Address Registration of the
node(s) advertised in the SIO, as explained in Section 9.1. of
[RFC9010]. Having similar values in all nodes allows factorising
the TIO for multiple SIOs as done with [RPL].
* The TIO is followed by one or more SIOs that provide an address
(ULA or GUA) of the advertised neighbor node.
But the RPL routing information headers may not be supported on all
type of routed network infrastructures, especially not in high-speed
routers. When the RPI is not supported in the dataplane, there
cannot be local RPL Instances and RPL can only operate as a single
topology (the main DODAG). The RPL Instance is that of the main
DODAG and the Ingress node that encapsulates is not the Root. The
routes along the Tracks are alternate routes to those available along
the main DODAG. They MAY conflict with routes to children and MUST
take precedence in the routing table. The Targets MUST be adjacent
to the Track Egress to avoid loops that may form if the packet is
reinjected in the main DODAG.
Thubert, et al. Expires 2 June 2024 [Page 71]
Internet-Draft DAO Projection November 2023
7.2. A Track as a Full DODAG
This specification builds parallel or crossing Track Lanes as opposed
to a more complex DODAG with interconnections at any place desirable.
The reason for that limitation is related to constrained node
operations, and the capability to store large amount of topological
information and compute complex paths:
* With this specification, the node in the LLN has no topological
awareness, and does not need to maintain dynamic information about
the link quality and availability.
* The Root has a complete topological information and statistical
metrics that allow it or its PCE to perform a global optimization
of all Tracks in its DODAG. Based on that information, the Root
computes the lane and produces the source route paths.
* The node merely selects one of the proposed paths and applies the
associated pre-computed routing header in the encapsulation. This
alleviates both the complexity of computing a path and the
compressed form of the routing header.
The RAW Architecture [RAW-ARCHI] actually expects the PLR at the
Track Ingress to react to changes in the forwarding conditions along
the Track, and reroute packets to maintain the required degree of
reliability. To achieve this, the PLR needs the full richness of a
DODAG to form any path that could meet the Service Level Objective
(SLO).
This section specifies the additions that are needed to turn the
Track into a full DODAG and enable the main Root to provide the
necessary topological information to the Track Ingress. The
expectation is that the metrics that the PLR uses are of an order
other than that of the PCE, because of the difference of time scale
between routing and forwarding, more in [RAW-ARCHI]. It follows that
the PLR will learn the metrics it needs from an alternate source,
e.g., OAM frames.
To pass the topological information to the Ingress, the Root uses a
P-DAO messages that contains sequences of Target and Transit
Information options that collectively represent the Track, expressed
in the same fashion as in classical Non-Storing Mode. The difference
is that the Root is the source as opposed to the destination, and can
report information on many Targets, possibly the full Track, with one
P-DAO.
Thubert, et al. Expires 2 June 2024 [Page 72]
Internet-Draft DAO Projection November 2023
Note that the Path Sequence and Lifetime in the TIO are selected by
the Root, and that the Target/Transit information tuples in the P-DAO
are not those received by the Root in the DAO messages about the said
Targets. The Track may follow sibling routes and does not need to be
congruent with the main DODAG.
8. Profiles
This document provides a set of tools that may or may not be needed
by an implementation depending on the type of application it serves.
This sections described profiles that can be implemented separately
and can be used to discriminate what an implementation can and cannot
do. This section describes profiles that enable implementing only a
portion of this specification to meet a particular use case.
Profiles 0 to 2 operate in the main Instance and do not require the
support of local RPL Instances or the indication of the RPL Instance
in the data plane. Profile 3 and above leverage Local RPL Instances
to build arbitrary Tracks Rooted at the Track Ingress and using its
namespace for TrackID.
Profiles 0 and 1 are REQUIRED by all implementations that may be used
in LLNs; Profile 1 leverages Storing Mode to reduce the size of the
Source Route Header in the most common LLN deployments. Profile 2 is
RECOMMENDED in high speed / wired environment to enable traffic
Engineering and network automation. All the other profile /
environment combinations are OPTIONAL.
Profile 0 Profile 0 is the Legacy support of [RPL] Non-Storing Mode,
with default routing Northwards (up) and strict source routing
Southwards (down the main DODAG). It provides the minimal common
functionality that must be implemented as a prerequisite to all
the Track-supporting profiles. The other Profiles extend Profile
0 with selected capabilities that this specification introduces on
top.
Profile 1 (Storing Mode P-Route Segments along the main DODAG)
Profile 1 does not create new paths; compared to Profile 0, it
combines Storing and Non-Storing Modes to balance the size of the
Routing Header in the packet and the amount of state in the
intermediate routers in a Non-Storing Mode RPL DODAG.
Profile 2 (Non-Storing Mode P-Route Segments along the main DODAG)
Profile 2 extends Profile 0 with Strict Source-Routing Non-Storing
Mode P-Routes along the main DODAG, which is the same as Profile 1
but using NSM VIOs as opposed to SM VIOs. Profile 2 provides the
same capability to compress the SRH in packets down the main DODAG
as Profile 1, but it requires an encapsulation, in order to insert
Thubert, et al. Expires 2 June 2024 [Page 73]
Internet-Draft DAO Projection November 2023
an additional SRH between the loose source routing hops. In that
case, the Tracks MUST be installed as subTracks of the main DODAG,
the main Instance MUST be used as TrackID. Note that the Ingress
node encapsulates but is not the Root, as it does not own the
DODAGID.
Profile 3 In order to form the best path possible, this Profile
requires the support of Sibling Information Option to inform the
Root of additional possible hops. Profile 3 extends Profile 1
with additional Storing Mode P-Routes that install Segments that
do not follow the main DODAG. If the Segment Ingress (in the SM-
VIO) is the same as the IPv6 Address of the Track Ingress (in the
projected DAO base Object), the P-DAO creates an implicit Track
between the Segment Ingress and the Segment Egress.
Profile 4 Profile 4 extends Profile 2 with Strict Source-Routing
Non-Storing Mode P-Routes to form forward Tracks that are inside
the main DODAG but do not necessarily follow it. A Track is
formed as one or more strict source routed paths between the Root
that is the Track Ingress, and the Track Egress that is the last
node.
Profile 5 Profile 5 Combines Profile 4 with Profile 1 and enables
loose source routing between the Ingress and the Egress of the
Track. As in Profile 1, Storing Mode P-Routes form the
connections in the loose source route.
Profile 6 Profile 6 Combines Profile 4 with Profile 2 and also
enables loose source routing between the Ingress and the Egress of
the Track.
Profile 7 Profile 7 implements Profile 5 in a main DODAG that is
operated in Storing Mode as presented in Section 7.1. As in
Profile 1 and 2, the TrackID is the RPLInstanceID of the main
DODAG. Longest match rules decide whether a packet is sent along
the main DODAG or rerouted in a track.
Profile 8 Profile 8 is offered in preparation of the RAW work, and
for use cases where an arbitrary node in the network can afford
the same code complexity as the RPL Root in a traditional
deployment. It offers a full DODAG visibility to the Track
Ingress as specified in Section 7.2 in a Non-Storing Mode main
DODAG.
Profile 9 Profile 9 combines profiles 7 and 8, operating the Track
as a full DODAG within a Storing Mode main DODAG, using only the
main DODAG RPLInstanceID as TrackID.
Thubert, et al. Expires 2 June 2024 [Page 74]
Internet-Draft DAO Projection November 2023
9. Backwards Compatibility
This specification can operate in a mixed network where some nodes
support it and some do not. There are restrictions, though. All
nodes that need to process a P-DAO MUST support this specification.
As discussed in Section 3.7.1, how the root knows the node
capabilities and whether they support this specification is out of
scope.
This specification defines the 'D' flag in the RPL DODAG
Configuration Option (see Section 4.1.7) to signal that the RPL nodes
can request the creation of Tracks. The requester may not know
whether the Track can effectively be constructed, and whether enough
nodes along the preferred paths support this specification.
Therefore, it makes sense to only set the 'D' flags in the DIO when
the conditions of success are in place, in particular when all the
nodes that could be on the path of tracks are upgraded.
10. Security Considerations
It is worth noting that with [RPL], every node in the LLN is RPL-
aware and can inject any RPL-based attack in the network. This draft
uses messages that are already present in RPL [RPL] with optional
secured versions. The same secured versions may be used with this
draft, and whatever security is deployed for a given network also
applies to the flows in this draft.
The LLN nodes depend on the 6LBR and the RPL participants for their
operation. A trust model is necessary to ensure that the right
devices are acting in these roles, so as to avoid threats such as
black-holing, (see [RFC7416] section 7). This trust model could be
at a minimum based on a Layer-2 Secure joining and the Link-Layer
security. This is a generic 6LoWPAN requirement, see Req5.1 in
Appendix B.5 of [RFC8505].
In a general manner, the Security Considerations in [RPL], and
[RFC7416] apply to this specification as well. The Link-Layer
security is needed in particular to prevent Denial-Of-Service attacks
whereby a rogue router creates a high churn in the RPL network by
constantly injecting forged P-DAO messages and using up all the
available storage in the attacked routers.
With this specification, only the Root may generate P-DAO messages.
PDR messages may only be sent to the Root. This specification
expects that the communication with the Root is authenticated but
does not enforce which method is used.
Thubert, et al. Expires 2 June 2024 [Page 75]
Internet-Draft DAO Projection November 2023
Additionally, the trust model could include a role validation (e.g.,
using a role-based authorization) to ensure that the node that claims
to be a RPL Root is entitled to do so. That trust should propagate
from Egress to Ingress in the case of a Storing Mode P-DAO.
This specification suggests some validation of the VIO to prevent
basic loops by avoiding that a node appears twice. But that is only
a minimal protection. Arguably, an attacker that can inject P-DAOs
can reroute any traffic and deplete critical resources such as
spectrum and battery in the LLN rapidly.
11. IANA Considerations
11.1. RPL DODAG Configuration Option Flag
IANA is requested to assign a flag from the "DODAG Configuration
Option Flags for MOP 0..6" [RFC9010] registry under the heading
"Routing Protocol for Low Power and Lossy Networks (RPL)" as follows:
+---------------+------------------------------+-----------+
| Bit Number | Capability Description | Reference |
+---------------+------------------------------+-----------+
| 0 (suggested) | Projected Routes Support (D) | THIS RFC |
+---------------+------------------------------+-----------+
Table 21: New DODAG Configuration Option Flag
IANA is requested to add [THIS RFC] as a reference for MOP 7 in the
RPL Mode of Operation registry.
11.2. Elective 6LoWPAN Routing Header Type
IANA is requested to update the "Elective 6LoWPAN Routing Header
Type" registry that was created for [RFC8138] under the heading
"Elective 6LoWPAN Routing Header Type" in [IANA-6LO] and assign the
following value:
+===============+=============+===========+
| Value | Description | Reference |
+===============+=============+===========+
| 8 (Suggested) | P-RPI-6LoRH | THIS RFC |
+---------------+-------------+-----------+
Table 22: New Elective 6LoWPAN Routing
Header Type
Thubert, et al. Expires 2 June 2024 [Page 76]
Internet-Draft DAO Projection November 2023
11.3. Critical 6LoWPAN Routing Header Type
IANA is requested to update the "Critical 6LoWPAN Routing Header
Type" registry that was created for [RFC8138] under the heading
"Critical 6LoWPAN Routing Header Type" in [IANA-6LO] and assign the
following value:
+===============+=============+===========+
| Value | Description | Reference |
+===============+=============+===========+
| 8 (Suggested) | P-RPI-6LoRH | THIS RFC |
+---------------+-------------+-----------+
Table 23: New Critical 6LoWPAN Routing
Header Type
11.4. Registry For The RPL Option Flags
IANA is requested to create a registry for the 8-bit "RPL Option
Flags" field, as detailed in Figure 11, under the heading "Routing
Protocol for Low Power and Lossy Networks (RPL)". The bits are
indexed from 0 (leftmost) to 7. Each bit is tracked with the
following qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Indication When Set
* Reference
Registration procedure is "Standards Action" [RFC8126]. The initial
allocation is as indicated in Table 24:
+===============+======================+===========+
| Bit number | Indication When Set | Reference |
+===============+======================+===========+
| 0 | Down 'O' | [RFC6553] |
+---------------+----------------------+-----------+
| 1 | Rank-Error (R) | [RFC6553] |
+---------------+----------------------+-----------+
| 2 | Forwarding-Error (F) | [RFC6553] |
+---------------+----------------------+-----------+
| 3 (Suggested) | Projected-Route (P) | THIS RFC |
+---------------+----------------------+-----------+
| 4..255 | Unassigned | |
+---------------+----------------------+-----------+
Table 24: Initial PDR Flags
Thubert, et al. Expires 2 June 2024 [Page 77]
Internet-Draft DAO Projection November 2023
11.5. RPL Control Codes
IANA is requested to update the "RPL Control Codes" registry under
the heading "Routing Protocol for Low Power and Lossy Networks (RPL)"
as indicated in Table 25:
+==================+=============================+===========+
| Code | Description | Reference |
+==================+=============================+===========+
| 0x09 (Suggested) | Projected DAO Request (PDR) | THIS RFC |
+------------------+-----------------------------+-----------+
| 0x0A (Suggested) | PDR-ACK | THIS RFC |
+------------------+-----------------------------+-----------+
Table 25: New RPL Control Codes
11.6. RPL Control Message Options
IANA is requested to update the "RPL Control Message Options"
registry under the heading "Routing Protocol for Low Power and Lossy
Networks (RPL)" as indicated in Table 26:
+==================+=============================+===========+
| Value | Meaning | Reference |
+==================+=============================+===========+
| 0x0E (Suggested) | Stateful VIO (SM-VIO) | THIS RFC |
+------------------+-----------------------------+-----------+
| 0x0F (Suggested) | Source-Routed VIO (NSM-VIO) | THIS RFC |
+------------------+-----------------------------+-----------+
| 0x10 (Suggested) | Sibling Information option | THIS RFC |
+------------------+-----------------------------+-----------+
Table 26: RPL Control Message Options
11.7. SubRegistry for the Projected DAO Request Flags
IANA is requested to create a registry for the 8-bit "Projected DAO
Request (PDR)" field under the heading "Routing Protocol for Low
Power and Lossy Networks (RPL)". The bits are indexed from 0
(leftmost) to 7. Each bit is tracked with the following qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Reference
Thubert, et al. Expires 2 June 2024 [Page 78]
Internet-Draft DAO Projection November 2023
Registration procedure is "Standards Action" [RFC8126]. The initial
allocation is as indicated in Table 27:
+============+========================================+===========+
| Bit number | Capability description | Reference |
+============+========================================+===========+
| 0 | PDR-ACK request (K) | THIS RFC |
+------------+----------------------------------------+-----------+
| 1 | Requested path should be redundant (R) | THIS RFC |
+------------+----------------------------------------+-----------+
| 2..255 | Unassigned | |
+------------+----------------------------------------+-----------+
Table 27: Initial PDR Flags
11.8. SubRegistry for the PDR-ACK Flags
IANA is requested to create a registry for the 8-bit "PDR-ACK Flags"
field under the heading "Routing Protocol for Low Power and Lossy
Networks (RPL)". The bits are indexed from 0 (leftmost) to 7. Each
bit is tracked with the following qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Reference
Registration procedure is "Standards Action" [RFC8126]. No bit is
currently assigned for the PDR-ACK Flags.
11.9. Registry for the PDR-ACK Acceptance Status Values
IANA is requested to create a registry for the 8-bit "PDR-ACK
Acceptance Status Values" under the heading "Routing Protocol for Low
Power and Lossy Networks (RPL)". Each value is tracked with the
following qualities:
* Value
* Meaning
* Reference
the possible values are expressed as a 6-bit unsigned integer
(0..63). the registration procedure is "Standards Action" [RFC8126].
The (suggected) initial allocation is as indicated in Table 28:
Thubert, et al. Expires 2 June 2024 [Page 79]
Internet-Draft DAO Projection November 2023
+-------+------------------------+-----------+
| Value | Meaning | Reference |
+-------+------------------------+-----------+
| 0 | Unqualified Acceptance | THIS RFC |
+-------+------------------------+-----------+
| 1..63 | Unassigned | |
+-------+------------------------+-----------+
Table 28: Acceptance values of the PDR-ACK
Status
11.10. Registry for the PDR-ACK Rejection Status Values
IANA is requested to create a registry for the 6-bit "PDR-ACK
Rejection Status Values" under the heading "Routing Protocol for Low
Power and Lossy Networks (RPL)". Each value is tracked with the
following qualities:
* Value
* Meaning
* Reference
the possible values are expressed as a 6-bit unsigned integer
(0..63). the registration procedure is "Standards Action" [RFC8126].
The (suggected) initial allocation is as indicated in Table 29:
+-------+-----------------------+-----------+
| Value | Meaning | Reference |
+-------+-----------------------+-----------+
| 0 | Unqualified Rejection | THIS RFC |
+-------+-----------------------+-----------+
| 1 | Transient Failure | THIS RFC |
+-------+-----------------------+-----------+
| 2..63 | Unassigned | |
+-------+-----------------------+-----------+
Table 29: Rejection values of the PDR-ACK
Status
11.11. SubRegistry for the Via Information Options Flags
IANA is requested to create a registry for the 8-bit "Via Information
Options (VIO) Flags" field under the heading "Routing Protocol for
Low Power and Lossy Networks (RPL)". The bits are indexed from 0
(leftmost) to 7. Each bit is tracked with the following qualities:
Thubert, et al. Expires 2 June 2024 [Page 80]
Internet-Draft DAO Projection November 2023
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Reference
Registration procedure is "Standards Action" [RFC8126]. No bit is
currently assigned for the VIO Flags, more in Section 5.3.
11.12. SubRegistry for the Sibling Information Option Flags
IANA is requested to create a registry for the 5-bit "Sibling
Information Option (SIO) Flags" field under the heading "Routing
Protocol for Low Power and Lossy Networks (RPL)". The bits are
indexed from 0 (leftmost) to 4. Each bit is tracked with the
following qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Reference
Registration procedure is "Standards Action" [RFC8126]. The initial
allocation is as indicated in Table 30, more in Figure 17:
+===============+========================+===========+
| Bit number | Capability description | Reference |
+===============+========================+===========+
| 0 (Suggested) | "S" flag: Sibling in | THIS RFC |
| | same DODAG as Self | |
+---------------+------------------------+-----------+
| 1..4 | Unassigned | |
+---------------+------------------------+-----------+
Table 30: Initial SIO Flags
11.13. Destination Advertisement Object Flag
IANA is requested to update the "Destination Advertisement Object
(DAO) Flags" registry created in Section 20.11 of [RPL] under the
heading "Routing Protocol for Low Power and Lossy Networks (RPL)" as
indicated in Table 31, more in Section 4.1.1:
Thubert, et al. Expires 2 June 2024 [Page 81]
Internet-Draft DAO Projection November 2023
+---------------+------------------------+-----------+
| Bit Number | Capability Description | Reference |
+---------------+------------------------+-----------+
| 2 (Suggested) | Projected DAO (P) | THIS RFC |
+---------------+------------------------+-----------+
Table 31: New Destination Advertisement Object
(DAO) Flag
11.14. Destination Advertisement Object Acknowledgment Flag
IANA is requested to update the "Destination Advertisement Object
(DAO) Acknowledgment Flags" registry created in Section 20.12 of
[RPL] under the heading "Routing Protocol for Low Power and Lossy
Networks (RPL)" as indicated in Table 32, more in Section 4.1.2:
+---------------+------------------------+-----------+
| Bit Number | Capability Description | Reference |
+---------------+------------------------+-----------+
| 1 (Suggested) | Projected DAO-ACK (P) | THIS RFC |
+---------------+------------------------+-----------+
Table 32: New Destination Advertisement Object
Acknowledgment Flag
11.15. New ICMPv6 Error Code
In some cases RPL will return an ICMPv6 error message when a message
cannot be forwarded along a P-Route.
This specification requires that a new code is allocated from the
'ICMPv6 "Code" Fields' heading of the "Internet Control Message
Protocol version 6 (ICMPv6) Parameters" Registry for "Type 1 -
Destination Unreachable", with a suggested code value of 9, to be
confirmed by IANA to indicate an "Error in P-Route".
11.16. RPL Rejection Status values
IANA is requested to update the "RPL Rejection Status" registry under
the heading "Routing Protocol for Low Power and Lossy Networks (RPL)"
as indicated in Table 33:
Thubert, et al. Expires 2 June 2024 [Page 82]
Internet-Draft DAO Projection November 2023
+---------------+-------------------------+-----------+
| Value | Meaning | Reference |
+---------------+-------------------------+-----------+
| 2 (Suggested) | Out of Resources | THIS RFC |
+---------------+-------------------------+-----------+
| 3 (Suggested) | Error in VIO | THIS RFC |
+---------------+-------------------------+-----------+
| 4 (Suggested) | Predecessor Unreachable | THIS RFC |
+---------------+-------------------------+-----------+
| 5 (Suggested) | Unreachable Target | THIS RFC |
+---------------+-------------------------+-----------+
| 6..63 | Unassigned | |
+---------------+-------------------------+-----------+
Table 33: Rejection values of the RPL Status
12. Acknowledgments
The authors wish to acknowledge JP Vasseur, Remy Liubing, James
Pylakutty, and Patrick Wetterwald for their contributions to the
ideas developed here. Many thanks to Dominique Barthel and SVR Anand
for their global contribution to 6TiSCH, RAW and this RFC, as well as
text suggestions that were incorporated. Also special thanks to
Remous-Aris Koutsiamanis, Li Zhao, Dominique Barthel, and Toerless
Eckert for their in-depth reviews, with many excellent suggestions
that improved the readability and well as the content of the
specification. Many thanks to Remous-Aris Koutsiamanis for his
review during WGLC and to Ines Robles for her shepherding and
thorough review. Many thanks to Sue Hares for their comments and
suggestions during the IETF last call and IESG review cycle.
13. Normative References
[INT-ARCHI]
Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
Thubert, et al. Expires 2 June 2024 [Page 83]
Internet-Draft DAO Projection November 2023
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RPL] Winter, T., Ed., Thubert, P., Ed., 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,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<https://www.rfc-editor.org/info/rfc6553>.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<https://www.rfc-editor.org/info/rfc6554>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
"IPv6 over Low-Power Wireless Personal Area Network
(6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
April 2017, <https://www.rfc-editor.org/info/rfc8138>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
Thubert, et al. Expires 2 June 2024 [Page 84]
Internet-Draft DAO Projection November 2023
[RFC9008] Robles, M.I., Richardson, M., and P. Thubert, "Using RPI
Option Type, Routing Header for Source Routes, and IPv6-
in-IPv6 Encapsulation in the RPL Data Plane", RFC 9008,
DOI 10.17487/RFC9008, April 2021,
<https://www.rfc-editor.org/info/rfc9008>.
[RFC9030] Thubert, P., Ed., "An Architecture for IPv6 over the Time-
Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)",
RFC 9030, DOI 10.17487/RFC9030, May 2021,
<https://www.rfc-editor.org/info/rfc9030>.
[RAW-ARCHI]
Thubert, P., "Reliable and Available Wireless
Architecture", Work in Progress, Internet-Draft, draft-
ietf-raw-architecture-16, 20 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-raw-
architecture-16>.
14. Informative References
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[6LoWPAN] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and
J. Martocci, "Reactive Discovery of Point-to-Point Routes
in Low-Power and Lossy Networks", RFC 6997,
DOI 10.17487/RFC6997, August 2013,
<https://www.rfc-editor.org/info/rfc6997>.
Thubert, et al. Expires 2 June 2024 [Page 85]
Internet-Draft DAO Projection November 2023
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
[RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A.,
and M. Richardson, Ed., "A Security Threat Analysis for
the Routing Protocol for Low-Power and Lossy Networks
(RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015,
<https://www.rfc-editor.org/info/rfc7416>.
[RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
RFC 8025, DOI 10.17487/RFC8025, November 2016,
<https://www.rfc-editor.org/info/rfc8025>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC8930] Watteyne, T., Ed., Thubert, P., Ed., and C. Bormann, "On
Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6
Network", RFC 8930, DOI 10.17487/RFC8930, November 2020,
<https://www.rfc-editor.org/info/rfc8930>.
[RFC8931] Thubert, P., Ed., "IPv6 over Low-Power Wireless Personal
Area Network (6LoWPAN) Selective Fragment Recovery",
RFC 8931, DOI 10.17487/RFC8931, November 2020,
<https://www.rfc-editor.org/info/rfc8931>.
[RFC8994] Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
Autonomic Control Plane (ACP)", RFC 8994,
DOI 10.17487/RFC8994, May 2021,
<https://www.rfc-editor.org/info/rfc8994>.
Thubert, et al. Expires 2 June 2024 [Page 86]
Internet-Draft DAO Projection November 2023
[RFC9010] Thubert, P., Ed. and M. Richardson, "Routing for RPL
(Routing Protocol for Low-Power and Lossy Networks)
Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021,
<https://www.rfc-editor.org/info/rfc9010>.
[RFC9035] Thubert, P., Ed. and L. Zhao, "A Routing Protocol for Low-
Power and Lossy Networks (RPL) Destination-Oriented
Directed Acyclic Graph (DODAG) Configuration Option for
the 6LoWPAN Routing Header", RFC 9035,
DOI 10.17487/RFC9035, April 2021,
<https://www.rfc-editor.org/info/rfc9035>.
[RFC9450] Bernardos, CJ., Ed., Papadopoulos, G., Thubert, P., and F.
Theoleyre, "Reliable and Available Wireless (RAW) Use
Cases", RFC 9450, DOI 10.17487/RFC9450, August 2023,
<https://www.rfc-editor.org/info/rfc9450>.
[I-D.kuehlewind-update-tag]
Kühlewind, M. and S. Krishnan, "Definition of new tags for
relations between RFCs", Work in Progress, Internet-Draft,
draft-kuehlewind-update-tag-04, 12 July 2021,
<https://datatracker.ietf.org/doc/html/draft-kuehlewind-
update-tag-04>.
[I-D.irtf-panrg-path-properties]
Enghardt, R. and C. Krähenbühl, "A Vocabulary of Path
Properties", Work in Progress, Internet-Draft, draft-irtf-
panrg-path-properties-08, 6 March 2023,
<https://datatracker.ietf.org/doc/html/draft-irtf-panrg-
path-properties-08>.
[PCE] IETF, "Path Computation Element",
<https://dataTracker.ietf.org/doc/charter-ietf-pce/>.
[IANA-6LO] IETF, "IPv6 Low Power Personal Area Network Parameters",
<https://www.iana.org/assignments/_6lowpan-
parameters/_6lowpan-parameters.xhtml>.
Authors' Addresses
Pascal Thubert (editor)
06330 Roquefort-les-Pins
France
Email: pascal.thubert@gmail.com
Thubert, et al. Expires 2 June 2024 [Page 87]
Internet-Draft DAO Projection November 2023
Rahul Arvind Jadhav
Huawei Tech
Kundalahalli Village, Whitefield,
Bangalore 560037
Karnataka
India
Phone: +91-080-49160700
Email: rahul.ietf@gmail.com
Michael C. Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
Thubert, et al. Expires 2 June 2024 [Page 88]
