Internet Engineering Task Force (IETF) P. Thubert, Ed.
Request for Comments: 9914 Independent
Updates: 6550, 6553, 8138 R.A. Jadhav
Category: Standards Track AccuKnox
ISSN: 2070-1721 M. Richardson
Sandelman
February 2026
Root-Initiated Routing State in the Routing Protocol for Low-Power and
Lossy Networks (RPL)
Abstract
The Routing Protocol for Low-Power and Lossy Networks (RPL) (RFC
6550) enables data packet routing along a Destination-Oriented
Directed Acyclic Graph (DODAG). However, the default route
establishment mechanism relies on hop-by-hop forwarding along the
DODAG, which may not always provide optimal routing efficiency. This
document introduces the concept of Destination Advertisement Object
(DAO) Projection, a mechanism that allows a RPL root Root or an external
controller to install optimized routes within the RPL domain. DAO
Projections enable the creation of optimized unicast or multicast
routes that do not strictly follow the DODAG structure, thereby
improving routing efficiency, reliability, availability, and resource
utilization in the RPL domain. This document specifies two types of
Projected Routes (P-Routes) -- Storing Mode and Non-Storing Mode --
and outlines the signaling procedures necessary to establish,
maintain, and remove these routes. This document updates RFCs 6550,
6553, and 8138.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9914.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction
2. Terminology
2.1. Requirements Language
2.2. References Terms and Concepts
2.3. Glossary
2.4. Domain Terms
2.4.1. Projected Route
2.4.2. Projected DAO
2.4.3. Path
2.4.4. Routing Stretch
2.4.5. Track
3. Context and Goal
3.1. RPL Applicability
3.2. Multi-Topology Routing and Loop Avoidance
3.3. Requirements
3.3.1. Loose Source Routing
3.3.2. Forward Routes
3.4. On Tracks
3.4.1. Building Tracks with RPL
3.4.2. Tracks and RPL Instances
3.5. Path Signaling
3.5.1. Using Storing Mode Segments
3.5.2. Using Non-Storing Mode Joining Tracks
3.6. Complex Tracks
3.7. Scope and Expectations
3.7.1. External Dependencies
3.7.2. Positioning Versus Related Relationship to Other IETF Standards Specifications
4. Extending and Amending Existing RFCs
4.1. Extending RPL RFC 6550
4.1.1. Projected DAO
4.1.2. Projected DAO-ACK
4.1.3. Via Information Option
4.1.4. Sibling Information Option
4.1.5. P-DAO Request
4.1.6. Amending the RPI
4.1.7. Additional Flag in the RPL DODAG Configuration Option
4.2. Extending RPL RFC 6553
4.3. Extending RPL RFC 8138
5. New RPL Control Messages and Options
5.1. New P-DAO Request Control Message
5.2. New PDR-ACK Control Message
5.3. Via Information Options
5.4. Sibling Information Option
6. Root-Initiated Routing State
6.1. RPL Network Setup
6.2. Requesting a Track
6.3. Identifying a Track
6.4. Installing a Track
6.4.1. Signaling a Projected Route
6.4.2. Installing a Track Segment with a Storing Mode P-Route
6.4.3. Installing a Protection Path with a Non-Storing Mode
P-Route
6.5. Tearing Down a P-Route
6.6. Maintaining a Track
6.6.1. Maintaining a Track Segment
6.6.2. Maintaining a Protection Path
6.7. Encapsulating and Forwarding Along a Track
6.8. Compression of RPL Artifacts
7. Less-Constrained Variations
7.1. Storing Mode Main DODAG
7.2. A Track as a Full DODAG
8. Profiles
9. Backwards Compatibility
10. Security Considerations
11. IANA Considerations
11.1. RPL DODAG Configuration Option Flag
11.2. Elective 6LoWPAN Routing Header Type
11.3. Critical 6LoWPAN Routing Header Type
11.4. Registry for RPL Option Flags
11.5. RPL Control Codes
11.6. RPL Control Message Options
11.7. Registry for Projected DAO Request Flags
11.8. Registry for PDR-ACK Flags
11.9. Registry for PDR-ACK Acceptance Status Values
11.10. Registry for PDR-ACK Rejection Status Values
11.11. Registry for Via Information Options Flags
11.12. Registry for Sibling Information Option Flags
11.13. Destination Advertisement Object Flag
11.14. Destination Advertisement Object Acknowledgment Flag
11.15. ICMPv6 Error Code
11.16. RPL Rejection Status Values
12. References
12.1. Normative References
12.2. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
The Routing Protocol for Low-Power and Lossy Networks (RPL) [RPL], is
a Distance Vector protocol that is well-suited for application in a
variety of low-energy Internet of Things (IoT) networks where
constrained nodes cannot maintain the full view of the topology and
stretched P2P paths are acceptable (versus (as opposed to the signaling and state
overhead involved in maintaining the shortest paths across).
Additionally, RPL is anisotropic, meaning that its operation depends
on the orientation of the links, down from or up towards the Root,
with the default route advertised down and more-specific paths
advertised up along a limited set of links.
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 the
graph up towards the Root for the default route and down towards
destinations in the RPL domain for more-specific routes. As a
prerequisite, this specification expects a pre-existing RPL Instance
with an associated DODAG and RPL Root, which are referred to as the
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 a central controller or
collocated with the main Root) interacts with the main Root to
compute additional paths between nodes in the main Instance. In Non-
Storing Mode, the base topological information to be passed to the
PCE, i.e., 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,
which has a global visibility of the system, can optimize the
computed routes for application needs, including the capability to
provide path redundancy. This specification also introduces protocol
extensions that enable the Root to project (i.e., advertise from a
remote location) the computed paths in the RPL domain as Projected
Routes (a.k.a. P-Routes) on behalf of the PCE.
A P-Route may be installed in either Storing or 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 (SRHs), leveraging loose source routing
operations down the main RPL DODAG. A P-Route can also be used as a
protection path, and it can be combined and interleaved with other
P-Routes to form a recovery graph called a Track. A Track is
signaled as a separate RPL Instance that is associated with a main
RPL Instance such that the RPL routers that form the Track are also
members of the main DODAG. The Track provides underlay shortcuts
using its own RIB, which is separate from the RIB of the main
Instance and has a higher precedence.
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
[NEW-TAGS], Section 3.
2.2. References Terms and Concepts
In this document, readers will encounter terms and concepts that are
discussed in the following:
* "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks" [RPL];
[RPL]
* "An Architecture for IPv6 over the Time-Slotted Channel Hopping
Mode of IEEE 802.15.4 (6TiSCH)" [RFC9030]; [RFC9030]
* "Deterministic Networking Architecture" [RFC8655]; [RFC8655]
* "Using RPI Option Type, Routing Header for Source Routes, and
IPv6-in-IPv6 Encapsulation in the RPL Data Plane" [RFC9008]; [RFC9008]
* "Reliable and Available Wireless (RAW) Architecture" [RAW-ARCH]; and [RAW-ARCH]
* "Terms Used in Routing for Low-Power and Lossy Networks" [RFC7102]. [RFC7102]
The 6TiSCH, Deterministic Networking (DetNet), and RAW architectures
utilize the terms "Track" and "recovery graph" to represent the same
concept even though they are in different environments. This
document uses "Track" to represent that concept and only builds
Tracks that are DODAGs, meaning that all links are oriented from Ingress
ingress to Egress. egress. This specification also utilizes the terms
"segment" and "protection path", which 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 Low-Power and Lossy Network (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
interleaved to form new paths that can be activated dynamically upon
failures. This requires additional control in order to take make 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 ingress of the
Track is the Root of the DODAG, whereas the Egress 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.
2.3. Glossary
This document often uses the following abbreviations:
6LR: 6LoWPAN Router (e.g., a RPL router in an LLN)
6LoRH: 6LoWPAN Routing Header
ARQ: Automatic Repeat Request (in other words, retries)
FEC: Forward Error Correction
HARQ: Hybrid Automatic Repeat Request (combines FEC and ARQ)
CMO: Control Message Option
DAO: Destination Advertisement Object
DAG: Directed Acyclic Graph
DIO: DODAG Information Object
DODAG: Destination-Oriented Directed Acyclic Graph. A DAG with
only one vertex (i.e., node) that has no outgoing edge
(i.e., link).
GUA: Global Unicast Address
LLN: Low-Power and Lossy Network
MOP: 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 (i.e., the routing table)
RPI: RPL Packet Information
RPL: Routing Protocol for Low-Power and Lossy Networks
RTO: RPL Target Option
RUL: RPL-Unaware Leaf
SIO: Sibling Information Option
ULA: Unique Local Address
NSM-VIO: Non-Storing Mode Via Information Option. Source-routed
VIO used in Non-Storing Mode P-DAO messages.
SLO: Service Level Objective
SRH: Source Routing Header (i.e., IPv6 RH type 3); see
Section 2.4.5.7.2.
SRH-6LoRH: Source Routing Header 6LoRH. A compressed form of SRH
defined in "IPv6 over Low-Power Wireless Personal Area
Network (6LoWPAN) Routing Header" [RFC8138].
TIO: Transit Information Option
SM-VIO: Storing Mode Via Information Option. Strict VIO used in
Storing Mode P-DAO messages.
VIO: Via Information Option. It can be an SM-VIO or NSM-VIO.
2.4. Domain Terms
This specification uses the terminology defined in the sections that
follow.
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 (i.e., Targets)
are reachable via or along a sequence of nodes.
2.4.2. Projected DAO
A Projected DAO (P-DAO) is a DAO message that is used to install a
P-Route.
2.4.3. Path
Quoting (non-normatively) the definition of path in Section 1.3.3 of
[INT-ARCH]:
| 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.
See Section 2 3.1.1 of [RFC9473] points to [RAW-ARCH] for a longer, more modern definition
of
path:
| 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. path.
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
precisely, polar. RPL does not behave the same way "downwards" (root (Root
towards leaves) with _multicast_ DODAG Information Object (DIO)
messages that form the DODAG and versus "upwards" (leaves towards root) 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 Point-to-Multipoint (P2MP) paths (from the
Root) and Multipoint-to-Point (MP2P) paths (towards the Root), but
the Point-to-Point (P2P) 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
involves more hops and more latency than the minimum possible for a
directional (i.e., forward) 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-ARCH]. 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 that may
enable 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 the Ingress ingress for the
Track, and the mapping of protection paths and segments, i.e., only
forward segments, meaning that they are directional and progressing
towards the destination. Note that East is represented on the left
since the packets are forwarded East-West.
North East North West
A ==> B ==> C -=- F ==> G ==> H T1
/ \ / \ /
I O E -=- T2
\ / \ / \
P ==> Q ==> R -=- T ==> U ==> V T3
South East South West
I: Ingress ingress
E: Egress egress
T1, T2, T3: external targets
Figure 1: A Track and Its Components
Of note:
I ==> A ==> B ==> C: A segment to targets F and O
I --> F --> E: A protection path to targets T1, T2, T3
I, A, B, C, F, G, H, E: A path to T1, T2, T3
This specification builds Tracks that are DODAGs oriented towards a
Track Ingress, ingress, and the forward direction for packets is from the
Track Ingress ingress to one of the possible multiple Track Egress Nodes, 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.
2.4.5.1. TrackID
A RPLInstanceID (typically of a Local Instance) identifies a Track
using the namespace owned by the Track Ingress. ingress. For Local Instances,
the TrackID is associated with the IPv6 address of the Track Ingress ingress
that is used as the 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 complex Complex Track is a Track that can be traversed via more than one
path (e.g., a DODAG).
2.4.5.4. Stand Alone
Stand alone refers to a segment or a protection path 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 the Ingress ingress and
Egress.
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. Protection Path
The concept of protection path is defined in the RAW architecture
[RAW-ARCH] as an end-to-end forward serial path. With this
specification, a protection path 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 protection path to signal the structure of a complex Complex
Track.
Each NSM-VIO for the same TrackID but with a different Segment ID SegmentID
signals a different protection path that the Track Ingress ingress adds to
the topology.
2.4.5.7. Segment
A segment is 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 protection paths that form the structure of a complex Complex Track. The
same segment may be leveraged by more than one protection path where
the protection paths overlap.
Since this specification builds only DODAGs, all segments are
oriented from the Ingress ingress (East) to Egress egress (West), as opposed to the
general Track model in the RAW architecture [RAW-ARCH], which allows
North/South segments that can be bidirectional as well.
2.4.5.7.1. Section of a Segment
The section of a segment refers to 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
In a Non-Storing Mode RPL domain, the IPv6 RH Routing Header used for
source routing is the (RPL) SRH RPL Source Route Header as defined in
[RFC6554]. This specification operates in that context and uses the
acronym SRH to mean IPv6 RH type 3, as opposed to IPv6 RH type 4
defined in [RFC8754] for Segment Routing over IPv6 (SRv6) operation.
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].
This specification uses the term "Segment Routing" generically to
refer to using source routing to hop over segments. As such,
forwarding along segments as specified hereafter can be seen as a
form of Segment Routing [RFC8402] that leverages the (RPL) SRH RPL Source Route
Header for its operation.
Outside of LLNs, the RPL network may be less constrained and operated
in Storing Mode, as discussed in Section 7.1. In that case, this
specification could be extended to accommodate the SRv6 RH.
3. Context and Goal
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
and also situations of high relative mobility between the nodes in
the network (a.k.a. swarming), e.g., within a variable set of
vehicles with a similar global motion or a platoon of drones. In
contrast, this specification only applies when the platoon has a
relatively stable topology where the segments can be attributed
reliability and availability for a certain lifetime; see [RAW-ARCH].
To reach this goal, RPL is primarily designed to minimize the control
plane activity, i.e., activity (i.e., the relative amount of routing protocol
exchanges versus data traffic, traffic) and the amount of state that is
maintained in each node. RPL does not need to converge, and it
provides connectivity to most nodes most of the time.
RPL may form multiple topologies called instances. Instances. Instances can be
created to enforce various optimizations through objective functions Objective Functions
or to reach out through different Root Nodes. nodes. The concept of
objective function
Objective Function allows adapting the activity of the routing
protocol to the use case, e.g., type, speed, and quality of the LLN
links.
RPL instances Instances operate in parallel, unaware of one another. Yet, it
is possible to define a model whereby if a route cannot be found in
the current instance Instance A where a packet is being forwarded, then the
router may look up the routing table (i.e., the RIB) in instance Instance B
and forward along instance Instance B if the route is found there. To avoid
loops, this must happen in such a way that the instances Instances themselves
form a Directed Acyclic Graph (DAG) leading to the last resort
instance,
Instance, which is the "lowest" instance Instance if instance Instance A is considered
"higher" then instance Instance B. This specification uses underlay Tracks as
"lower" instances, Instances, with the main instance Instance being the "highest" of all.
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 (i.e., a RIB) in participating
nodes, and the RIB associated to the instance 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 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).
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 DAG 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 in either RPL Storing Mode or Non-Storing Mode of Operation
(MOP). 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 in this specification.
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, lazy; it is either reactive upon receiving
traffic or as a slow background process. Packets flow via the common
parent and the routing stretch is reduced, compared to the Non-Storing 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 "P-Route" to refer to those routes.
In the simplest mode of this specification, Storing Mode P-Routes can
be deployed to join complete the path between the hops described in the dots of a
loose 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 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 establish the dots complete path between
loose source routing hops using segments expressed as 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 P-Routes are used in a RPL domain: one
between forwarding methods and one between RPL Instances, which are
routing topologies.
The first and strict order is strict and complete and relates to the forwarding
method and, 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; see 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 over another Track.
The second order is strict and partial order is and applies 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 the RPL domain and defines a
DODAG of underlays underlay RPL Instances with the main Instance as the Root.
The relation of RPL instances Instances may be represented as a DODAG of instances
Instances where the main instance Instance is the Root. The rule is that a
RPL Instance may leverage another RPL
instance Instance as an 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 Instance and the main
instance. Instance. It may be done using
network management or future extensions to this specifications. When it
the DODAG of underlay Instances is not communicated, provided, the RPL nodes
consider by default that all Track instances Instances are children of the main instance,
Instance, and they 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 the 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 MOP 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 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 the Root is a single
point of failure for all connectivity to nodes within its domain.
The RPL Root must add a source routing header Source Routing Header to all downward
packets. As a network grows, the size of the source routing header Source Routing Header
increases with the depth of the network. In some use cases, a RPL
network forms long lines along physical structures like streets with
lighting. Limiting the packet size is beneficial to the energy
budget, directly for the current transmission and 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] compared to [RFC8931] for more details.
A limited amount of well-targeted routing state would allow the
source routing operation to be loose as opposed to strict and would
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 sources/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; this would be a global benefit for all
flows by reducing the load at the Root.
To limit the need for source route headers RPL 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, RPL
Source Route Header, which therefore becomes loose, in contrast to
being strict in [RPL].
3.3.2. Forward Routes
[RPL] optimizes P2MP routes from the Root, MP2P routes towards the
Root, and routes from/to the outside of the RPL domain when the Root
also serves as the border router. All routes are installed North-
South (a.k.a. up/down) along the RPL DODAG. Peer-to-Peer (P2P) forward
routes in a RPL network will generally experience elongated
(stretched) paths rather than 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 MOP:
* 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
worst, 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.
It turns out that it is often beneficial to enable direct P2P routes
if either the RPL route presents a stretch from the shortest path or
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
within the IETF was 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 specification 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 Service Level Objective (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. 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). egress(es). If
there is a single Track Egress, egress, then the Track is reversible so that
another DODAG may be formed by reversing the direction of each edge.
A node at the Ingress ingress of more than one segment in a Track may use one
or more of these segments to forward a packet inside the Track.
A RPL Track is a collection of (one or more) parallel loose source-
routed sequences of nodes ordered from Ingress ingress to Egress, egress, each
forming a protection path. The nodes in a Track 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 protection paths are expressed in RPL
Non-Storing Mode and require an encapsulation to add a RPL Source
Route Header, whereas the segments are expressed in RPL Storing Mode.
A path provides only one path between the Ingress ingress and Egress. egress. It
comprises exactly one protection path. A stand-alone segment
implicitly defines a path from its Ingress ingress to Egress. egress.
A complex Complex Track forms a graph that provides a collection of potential
paths to provide redundancy for the packets, either as a collection
of protection paths that may be parallel or interleaved 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
+-+-+-+-+-+-+-+-+
| |
\ \
\ Bit 1 is set to 0 in Track IDs TrackIDs
Bit 0 set to 1 signals a Local RPLInstanceID
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 IP-
in-IP encapsulated with a RPL Option containing RPL Packet
Information (RPI) that signals the RPLInstanceID. The encapsulating
source IP address and RPI Instance are set to the Track Ingress ingress IP
address and Local RPLInstanceID, respectively; see more in
Section 6.3.
A Track typically offers service protection across several protection
paths. As a degraded form of a Track, a path made of a single
protection path (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, Instance, the
packets are encapsulated to signal a more-specific source-routed path
between the loose hops in the encapsulated source routing header. Source Routing Header.
If the encapsulated packet follows a global instance, Global Instance, then the
protection path may be part of that global instance Global Instance as well, e.g.,
the global instance Global Instance of the main DODAG. This can only be done for
global instances
Global Instances because the Ingress ingress node that encapsulates the
packets over the protection path is not the Root of the instance, 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
protection path 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 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 uses the simple case of the path
illustrated in Figure 6. Thus, 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
ingress is used as the source to encapsulate packets along the Track.
The Track is signaled in the DODAGID field of the P-DAO Base Object;
see Figure 8.
This specification introduces the Via Information Option (VIO) to
signal a sequence of hops in a protection path or a segment in the
P-DAO messages, either in Storing Mode (SM-VIO) or in Non-Storing
Mode (NSM-VIO). One P-DAO message contains a single VIO, which is
associated to one or more RPL Target Options that signal the
destination IPv6 addresses that can reached along the Track (see more
in Section 5.3).
Before diving deeper into Track and segment 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
comma-separated Targets, e.g., F is a Target for segment C==>D==>E.
In the example below, A is the Track Ingress ingress and E is the Track
Egress.
egress. C is a stitching point. F and G are "external" Targets for
the Track and become reachable from A via Track A (Ingress) (ingress) to E
(Egress
(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 omitted if P-DAOs 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 an NSM-VIO. With this specification:
* The DODAGID to be used by the Ingress ingress as the 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 ingress node in the loose hop sequence.
* The via list ends with the address of the Egress egress node.
| Note 1: The Egress egress of a Non-Storing Mode P-Route is implicitly
| a target; it is not listed in the RPL Target Options but is
| still accounted for as if it was. The only exception is when
| the Egress egress is the only address listed in the VIO, in which case
| it would indicate via itself, which would be nonsensical.
| Note 2: 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 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:
+======+=============+=========+=============+==========+
| 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 Settings
| Note: The " sign is used throughout the tables in this document
| to indicate the same value as in the row above.
Packets originating at A and 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 Address | IPv6 Destination | TrackID |
| | | Address | 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 in
Table 2:
* 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.
* 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 (see more in Section 6.7).
In this formulation, we set up the protection path 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-DAOs 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 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 RPL Target Option (RTO) for P-DAOs 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:
+======+=============+=========+=============+==========+
| 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 Settings
Packets from A to E do not require an encapsulation. In the tables
below, this is why E may show as an 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 | IPv6 Destination Address | TrackID |
| | Address | | in RPI |
+========+=====================+==========================+=========+
| Outer | A | E | (A, |
| | | | 129) |
+--------+---------------------+--------------------------+---------+
| Inner | X | Either F or G. If X!=A, | N/A |
| | | E is also permitted. | |
+--------+---------------------+--------------------------+---------+
Table 6: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB in
Table 5:
* 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, protection paths are leveraged to combine
segments and form a graph. The packets are source routed from a
segment to the next to adapt the path:
* 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-DAOs 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 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 table 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 protection path. P-DAO 1 generates more signaling since E is
the segment Egress egress when D could be, but a benefit is 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 Settings
Packets originated at A to E do not require an encapsulation, but
they carry an SRH via C. The outer headers of the packets that are
forwarded along the Track have the following settings:
+========+=====================+==========================+=========+
| Header | IPv6 Source | IPv6 Destination Address | TrackID |
| | Address | | in RPI |
+========+=====================+==========================+=========+
| Outer | A | C until C then E | (A, |
| | | | 129) |
+--------+---------------------+--------------------------+---------+
| Inner | X | Either F or G. If X!=A, | N/A |
| | | E is also permitted. | |
+--------+---------------------+--------------------------+---------+
Table 9: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB in
Table 8:
* 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 an SRH signals that the final destination is
E.
* 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 Mode
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 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):
+======+=============+=========+=============+==========+
| 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 Settings
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 Root in a
RPL network in Non-Storing Mode; see Section 8.1.3 of [RFC9008]. The
latter is often preferred since it leads to a single code path, and
when the destination is F or G, it does not need to understand and
process the RPI or the SRH. Either way, the packets to E, F, or G
carry an SRH via B and C, and when they reach C, C needs to
encapsulate them again 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 Address | IPv6 Destination | TrackID |
| | | Address | 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 in
Table 11:
* From P-DAO 2: A encapsulates the packet with a 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
an RPI indicating a TrackID of 131 from A's namespace, which is
distinct from a TrackID of 131 from C's.
* From the SRH: Packets forwarded by B have source A, destination C,
a consumed SRH, and an RPI indicating a TrackID of 131 from A's
namespace. C decapsulates.
* From P-DAO 1: C encapsulates the packet with a 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
an 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-DAOs 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 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
Note in the table above that E is an implicit Target in P-DAO 1 and
so is C in P-DAO 2. As Non-Storing Mode Egress egress node addresses, they
are 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 Settings
The encapsulating headers of packets that are forwarded along the
Track between C and E have the following settings:
+========+=====================+==========================+=========+
| Header | IPv6 Source Address | IPv6 Destination | TrackID |
| | | Address | 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 in
Table 14:
* From P-DAO 3: A encapsulates the packet with a destination of F in
the Track signaled by P-DAO 3. The outer header has source A,
destination E, and an RPI indicating a TrackID of 141 from A's
namespace. This recurses with the following.
* From P-DAO 2: A encapsulates the packet with a 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
an 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 an RPI indicating a TrackID of 129 from A's
namespace. C decapsulates.
* From P-DAO 1: C encapsulates the packet with a 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
an 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-DAOs 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 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 Settings
The encapsulating headers of packets that are forwarded along the
Track between A and B have the following settings:
+========+=====================+==========================+=========+
| Header | IPv6 Source Address | IPv6 Destination | TrackID |
| | | Address | 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 Address | IPv6 Destination | TrackID |
| | | Address | 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 Address | IPv6 Destination | TrackID |
| | | Address | 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 Table 18:
* From P-DAO 3: A encapsulates the packet with a 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
an RPI indicating a TrackID of 141 from A's namespace. This
recurses with the following.
* From P-DAO 2: A encapsulates the packet with a destination of C in
the Track signaled by P-DAO 2. The outer header has source A,
destination B, and an 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 a 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
an 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 protection paths
between the same Ingress ingress and Egress egress Nodes and combining them within
the same TrackID, as shown in Figure 7. Protection paths may be
interleaved at the edges of loose hops or remain parallel.
The segments that join the loose hops of a protection path are
installed with the same TrackID as the protection path. But each
individual protection path and segment has its own P-RouteID that
allows it to be managed separately. Two protection paths of the same
Track may cross at a common node that participates to is a member of a segment of
each protection path or that may be joined by additional segments. The
final path of a packet may then be the result of interleaving those
two (and possibly more) protection paths. 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.
< Controller Plane Functions >
Southbound API
_-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-
_-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-
+----------+
| RPL Root |
+----------+
( main DODAG )
( all around )
<- Protection path 1 via B, E ->
<--- Segment 1 A,B ---> <------- Segment 2 C,D,E ------->
FWD -- Relay -- FWD -- FWD Target 1
/-- Node -- Node -- Node -- Node \ /
--/ (A) (B) \ (C) (D) \ /
Track \ Track
Ingress Segment 5 Egress -- Target
(I) \ -- (E) 2
\ \ / \
\ FWD -- FWD -- Relay -- FWD --/ \
Node -- Node -- Node -- Node Target 3
(F) (G) (H) (J)
<------ Segment 3 F,G,H ------> <---- Segment 4 J,E ---->
<- Protection path 2 via H, E ->
<--- Segment 1 A,B ---> <- S5-> <---- Segment 4 J,E ---->
<- Protection path 3 via B, H, E ->
)
(
( )
Figure 7: Segments and Tracks
Note that while this specification enables building both segments
inside a protection path, for instance instance, segment 2 above which (which is
within protection path 1, 1) and Inter-protection-path segments (i.e.,
North-South), for instance
North-South) such as segment 5 above which (which joins protection
path paths 1
and protection path 2, 2), it does not signal to the Ingress which Inter-protection-path segments are available,
available to the ingress, so the use of North-
South North-South segments and
associated path redundancy functions is currently limited. The only
possibility available at this time is to define overlapping
protection paths as illustrated in Figure 7, with protection path 3
that is congruent with protection path 1 until node B and that is
congruent with protection path 2 from node H on, abstracting segment
5 as a 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 enables 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 Operations,
Administration, and Maintenance (OAM).
3.7.2. Positioning Versus Related Relationship to Other IETF Standards Specifications
3.7.2.1. Extending 6TiSCH
The 6TiSCH architecture [RFC9030] leverages a centralized model that
is similar to that of the DetNet architecture [RFC8655], whereby the
device resources and capabilities are exposed to an external
controller that installs routing states into the network based on its
own objective functions Objective Functions that reside in that external entity.
3.7.2.2. Mapping to DetNet
DetNet Forwarding Nodes forwarding nodes only understand the simple 1-to-1 forwarding
sublayer transport operation along a segment whereas the more
sophisticated Relay relay nodes can also provide service sublayer functions
such as Replication and Elimination.
One possible mapping between DetNet and this specification is to
signal the Relay Nodes relay nodes as the hops of a protection path and the
forwarding nodes as the hops in a segment that join the Relay 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 for computing routes is a PCE. The PCE computes its
routes based on its own objective functions, Objective Functions, as described in
[RFC4655], and typically controls the routes using the PCE
Communication Protocol (PCEP) [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.
Controller. In that the latter case, the protocol between the Root and
the PCE is out of scope and mapped to RPL inside the DODAG; one possibility
possible control protocol between the Root and external PCE is for
the Root to transmit to the PCEs the information it received in the RPL DAOs DAOs,
including all the SIOs that detail the parent/child and sibling information.
information, to the PCEs.
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 are 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-ARCH] extends the definition of Track, Track as
being composed of forward directional segments and North-South
bidirectional segments, segments to enable additional path diversity, diversity using
PAREO
PREOF functions over the available paths, to provide paths. This provides 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 it only
forms DODAGs, which are composed of aggregated end-to-end loose
source-routed protection paths, joined by strict routed segments, all
oriented forward.
The RAW architecture defines a data plane 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 and Amending Existing RFCs
This section explains which changes are extensions and which are
amendments to existing specifications. It is expected that
extensions to existing specifications will 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
function in the new mechanisms and may also cause make the P-DAOs to be
impossible to install. Amendments to existing specifications are
situations where there are semantic changes required to existing code
and where new unit tests may be required to confirm that legacy
operations will continue unaffected.
4.1. Extending RPL 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 P-DAO message (see Section 4.1.1) to the
Track Ingress; ingress; the P-DAO message contains a new VIO that installs a
strict or a loose sequence of hops to form a Track segment or a
protection path, respectively.
The P-DAO Request (PDR) is a new message detailed in Section 5.1. As
per Section 6 of [RPL], if a node receives this message and it does
not understand this new code, it discards the message. When the Root
initiates communication to a node that it has not communicated with
before and that it has not ascertained to implement this
specification (by means such as capabilities), then the Root SHOULD
request a PDR-ACK.
A PDR message enables a Track Ingress ingress to request the Track from the
Root. The resulting Track is also a DODAG for which the Track
Ingress
ingress is the Root, and the owner is the address that serves as the
DODAGID and is 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 ingress forwards the packets toward 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 (CMOs),
including the RPL Target Option (RTO) and Transit Information Option
(TIO), which can be placed in RPL messages such as the DAO. A DAO
message signals routing information to one or more Targets indicated
in the RTOs and provides one and only one via-node in the TIO, with
the via-node being the tunnel endpoint to reach the targets.
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 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 a collection of multiple
P-Routes as expected by the 6TiSCH architecture [RFC9030].
The Root MUST source the P-DAO message with its address that serves
as the 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 of the Flags field in the
DAO Base Object. The Root MUST set it to 1 in a P-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].
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 be sent at a 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 is set to the |
+ IPv6 address of the Track Ingress 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 the Track (see more in Section 6.3).
P: 1-bit flag.
The 'P' flag is set to 1 by the Root to signal a P-DAO; otherwise,
it is set to 0.
The D 'D' flag is set to 1 to signal that the DODAGID field is present.
It may be set to 0 if and only if the destination address of the P-
Projected DAO-ACK (P-DAO-ACK) message is set to the IPv6 address that
serves as the DODAGID, and it MUST be set to one otherwise, meaning
that the DODAGID field MUST then be present.
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 ingress that a Track Track, for which it the sender is the Root Root, can
be used to reach children and siblings of the Track Egress. 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 'P' flag
signals the projected form.
The format of the P-DAO-ACK message is thus 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 is set to the |
+ IPv6 address of the Track Ingress 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 the Track (see more in Section 6.3).
P: 1-bit flag.
The 'P' flag is set to 1 by the Root to signal a P-DAO; otherwise,
it is set to 0.
The D 'D' flag is set to 1 to signal that the DODAGID field is present.
It may be set to 0 if and only if the source address of the P-DAO-ACK
message is set to the IPv6 address that serves as the 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 Via
Information Options (VIOs). The VIOs are the multi-hop alternative
to the TIOs (see 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 protection path at the Track Ingress, ingress, which uses that state
to encapsulate an IP-in-IP packet with a new Routing Header (RH) to
the Track Egress egress (see 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
(see more in Section 6). There are two modes of operation for the
P-Routes: Storing Mode and Non-Storing Mode (see more in Sections
6.4.2 and 6.4.3, respectively).
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 (see
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 specification Amends rules 1 and 2 listed in Section 9.10 of
[RPL] for the multicast DAO operation as follows:
OLD:
| 1. A node MAY multicast a DAO message to the link-local scope
| all-RPL-nodes multicast address.
|
| 2. A multicast DAO message MUST be used only to advertise
| information about the node itself, i.e., prefixes directly
| connected to or owned by the node, such as a multicast group
| that the node is subscribed to or a global address owned by
| the node
NEW:
| 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 SIO).
|
| 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.
4.1.5. P-DAO Request
The set of RPL Control Messages is Extended to include the PDR and
P-DAO Request Acknowledgement (PDR-ACK). These two new RPL Control
Messages enable a RAN to request the establishment of a Track between
itself (as the Track Ingress ingress Node) and a Track Egress. egress. The node
makes its request by sending a new 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 RPI described in Section 11.2 of [RPL] in the outer IPv6
header chain (see [RFC9008]). The RPI carries a Local RPLInstanceID
that, 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
when 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 four 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)
This specification Amends [RPL] to define the new "Projected Routes
Support" (D) flag. The 'D' flag is encoded in bit position 0 of the
reserved Flags in the DODAG Configuration option (this is the most
significant bit). 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 receiving a PDR message.
Section 4.1.2 of [RFC9008] Amends [RPL] to indicate that the
definition of the Flags applies to MOP 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 P-Routes.
The RPL DODAG Configuration option is typically placed in a 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,
Root, and when the 'D' flag is set to 1, it is transparently flooded
to all the nodes in the DODAG.
4.2. Extending RPL RFC 6553
"The Routing Protocol for Low-Power and Lossy Networks (RPL) Option
for Carrying RPL Information in Data-Plane Datagrams" [RFC6553]
describes the RPL Option for use among RPL routers to include the
abstract RPI described in Section 11.2 of [RPL] in data packets.
The RPL Option is commonly referred to as the RPI even 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 Extends the RPL Option to encode the 'P' flag 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 | 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]. These flags MUST be set to
0 by the sender and MUST be 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 MUST be ignored by the receiver if the 'P' flag is set.
4.3. Extending RPL RFC 8138
The 6LoWPAN Routing Header specification [RFC8138] introduces a new
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 6LoRH in
two forms: Elective, which can be ignored and skipped when the router
does not understand it, and 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.
When compression as described in [RFC8138] is used, the Root of the
main DODAG that sets up the Track also constructs the compressed
routing header
Routing Header (SRH-6LoRH) on behalf of the Track Ingress, ingress, which
avoids the complexities of optimizing SRH-6LoRH encoding in
constrained code. The In that case, the SRH-6LoRH is signaled in the
NSM-VIO, and it is expressed in a fashion that it is ready to can be placed as is in
the packet encapsulation by the Track Ingress. ingress.
Section 6.3 of [RFC8138] presents the formats of the 6LoWPAN RH 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, 'O',
'R', and F '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 Tables 22 and 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
6LoRH Type: IANA has defined the value 8 for both the Elective and
Critical forms.
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 Sections 3.4 and 6.3.
Section 6.8 details how a Track Ingress ingress leverages the P-RPI-6LoRH
Header
header as part of the encapsulation of a packet to place it into a
Track.
5. New RPL Control Messages and Options
5.1. New P-DAO Request Control Message
The 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 the node sending
the PDR is the Track Ingress, ingress, and it signals whether or not an
acknowledgment called PDR-ACK is requested. 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 ingress that the Track was
terminated before its time; 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 Track Ingress ingress to be of the requested Track is indicated in the
source IPv6 address of the PDR, 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 egress (see more in
Section 6.2).
The RPL Control Code for the PDR is 0x09. The format of the 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 Sections 3.4 and 6.3. To allocate a new Track, the
Ingress
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.
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 MUST 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. 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.
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, a
Value field that is set to 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 MUST
be ignored by the receiver.
Status Value: 6-bit unsigned integer. Values depend on the
setting of the 'E' flag; see Tables 28 and 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 protection path (using Non-Storing Mode) or a
segment (using Storing Mode) of a Track. A Storing Mode P-DAO
contains one SM-VIO whereas a Non-Storing Mode P-DAO contains one
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 0 is referred as a No-Path P-DAO.
The VIO contains one or more SRH-6LoRH headers, each formed of an
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 an 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.
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 VIO 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seg. 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: 0x0F for SM-VIO and 0x10 for NSM-VIO (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 MUST be ignored by the
receiver.
P-RouteID: 8-bit field that identifies a component of a Track or the
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/protection
path. In an SM-VIO, the P-RouteID indicates a Segment ID. SegmentID. In an
NSM-VIO, it indicates the ID of a protection path that is added
(or updated) 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 initial value
is 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 provides the new information. information about the segment.
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 type 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 ingress to Egress. 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.
In the case of an SM-VIO, the list indicates a sequential (strict)
path through direct neighbors; the complete list starts at the
Ingress
ingress and ends at the Egress, egress, and the nodes listed in the VIO,
including the Egress, egress, MAY be considered as implicit Targets.
In the case of an NSM-VIO, the complete list can be loose and
excludes the Ingress ingress node, starting at the first loose hop and
ending at a Track Egress; egress; the Track Egress 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 SIOs 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 per [RFC8505] for an address (ULA or
GUA) that serves as an 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 '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 directions; this flag indicates to 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 '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:
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 |S|B|Flags|Comp.| Opaque |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Step in Rank | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Sibling DODAGID (if the D flag is not set) .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Sibling Address .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Sibling Information Option Format
Option Type: 0x11 for SIO (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 0 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 needs to report the SIO for the hop. If
'B' is not set, then the SIO only indicates connectivity from the
sibling to this node, and it does not provide information on the
hop from this node to the sibling.
S: 1-bit flag that is set to indicate that the 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.
Comp.: Compression Type; a 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.
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
Industrial Alliances that use RPL for a particular use/
environment, this field MAY be redefined to fit the needs of the
case.
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, which reflects the abstract Rank increment that would
be computed by the Objective Function 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
compressed form [RFC8138] as indicated by the Compression Type
field. This field is present if and only if the D 'D' flag is not
set.
Sibling Address: 2 to 16 bytes. An IPv6 address of the sibling with
a scope that MUST make it reachable from the Root, e.g., it cannot
be a Link Local Address. The IPv6 address is encoded in the
compressed form [RFC8138] 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 by 6LoWPAN endpoints, 6LoWPAN
links are normally defined with an 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 exceed the MTU that is
defined for the RPL domain.
Though fragmentation is possible in a 6LoWPAN LLN, e.g., using
[6LoWPAN], [RFC8930], and/or [RFC8931], it is RECOMMENDED to define
an MTU that is larger than 1280 between the RPL routers that form the
main DODAG to allow for the necessary header additions, while still
exposing 1280 to the 6LoWPAN endpoint stacks.
6.2. Requesting a Track
This specification introduces the PDR message, which is used by an
LLN node to request the formation of a new Track for which the LLN
node is the Ingress. ingress. Note that the namespace for the TrackID is
owned by the Ingress 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 (see 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
the 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 fit and updates/changes the
segments over time to serve the Track as needed. Note that there is
no protocol element to notify the requesting Track Ingress ingress when
changes happen deeper down the Track, so they are transparent to the
Track Ingress. 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. For example, the Root may use shorter lifetimes for the
segments and renew them or change them during the lifetime of the
Track. All the components (protection paths and segments) of a Track
MUST be destroyed (or have their lifetime elapsed) before the TrackID
can be reused.
When the Track Lifetime is relatively close to elapse -- meaning in
the order of 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; otherwise, 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.
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 specification 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 loose source routing and reduces the size of the Routing
Header; see Section 3.3.1. The main Root MAY also install a
protection path 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 it 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 Ingress ingress to Egress 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 ingress that serves as the 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 'D' flag
set to 0 (see also Section 5.1 of [RPL]), indicating that when
used in an RPI, 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.
The Track Ingress ingress is the Root of the DODAGID 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 ingress picking the same value at the same time, it is
RECOMMENDED that the Track Ingress 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-protection-path Track. A single-
protection-path 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. TrackID. The Ingress ingress of a Non-Storing Mode P-Route
is the owner and Root of the DODAGID. The Ingress ingress of a Storing Mode
P-Route must be either the owner of the DODAGID or a hop of a
protection path of the same Track. In the latter case, the Targets
of the P-Route must include the next hop of the protection path 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:
* The longest match MUST be the prime comparison for routing.
* For an equal-length match, the route along the Track MUST be
preferred over the one along the main DODAG.
* There SHOULD NOT be two different Tracks leading to the same
Target from same Ingress ingress node, unless there's a policy for
selecting which packets use which Track; such a policy is out of
scope.
* 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 specification adds a capability whereby the Root of a main DODAG
installs a Track as a collection of P-Routes, using a P-DAO message
for each individual protection path or segment. The P-DAO signals a
collection of Targets in one or more RTOs. 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: Storing and Non-Storing.
A P-DAO message MUST be sent from the address of the Root that serves
as the DODAGID for the main DODAG. It MUST contain either exactly
one sequence of one or more RTOs followed by 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, whereas the
latter corresponds to the variation for less-constrained environments
described in Section 7.2.
A P-DAO that creates or updates a protection path MUST be sent to a
GUA or a ULA of the Ingress ingress of the protection path; it MUST contain
the full list of hops in the protection path unless the protection
path 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 egress and MUST signal the
full list of hops in a 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 MUST signal the full list of hops in the
section starting at the node that immediately precedes the modified
section.
In Non-Storing Mode, as discussed in Section 6.4.3, the Root sends
the P-DAO to the Track Ingress 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 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 protection path, 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 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 rejection status of "Error in VIO" in the DAO-
ACK; see Section 11.16.
Errors, other than those discussed explicitly, that prevent the
installation of the route are acknowledged with a RPL Rejection
Status 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, which may be the one formed
by the main DODAG, or a Track associated with a Local RPL Instance.
------+---------
| 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 egress router of the
routing segment that is being installed. The P-DAO message contains
an SM-VIO with a 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 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 egress recognizes its role.
In a similar fashion, the segment Ingress ingress node recognizes its role
because it matches the first Via Address in the SM-VIO.
The Egress 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 egress node can reach all the Targets, it forwards the P-DAO
with unchanged content to its predecessor in the segment as indicated
in the list of VIOs, and the message is recursively propagated
unchanged along the sequence of routers indicated in the P-DAO, but
in the reverse order, from Egress egress to Ingress. ingress.
The address of the predecessor to be used as the destination of the
propagated DAO message is found in the Via Address list at the
position preceding the one that contains the address of the
propagating node, which is used as the source of the message.
Upon receiving a propagated DAO, all except the Egress 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
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) 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 rejection status of
"Predecessor Unreachable".
The process continues until the P-DAO is propagated to the Ingress 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 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 TrackID or tear down the route.
6.4.3. Installing a Protection Path 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 is needed to add the SRH to an existing
packet. It is sent to the Track Ingress, 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
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 ingress when it
encapsulates a packet to forward it over the Track.
------+---------
| 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 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
protection path(s) of the same Track that uses it, and stitched
segments must be installed in order from the last to the first to
reach the Targets.
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 ingress of a
next segment, which are both already set up; the segments are
associated with the same Track, which avoids needing 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 ingress of a next Track, which
requires de- and re-encapsulation when switching the outer Tracks
that join the loose hops. This is exemplified in Section 3.5.2.3
where Non-Storing Mode P-DAOs 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.
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 DAO. Its
function is to clean up an existing state as opposed to refreshing an
existing one it
or installing a new one. To tear down a Track, the Root must tear
down all the Track segments and protection paths that compose it one
by one.
Since the protection path state of a Track is located only on the
Ingress
ingress Node, the Root cleans up the protection path by sending an
NSM-VIO to the Ingress ingress to indicate the TrackID and the P-RouteID of
the protection path being removed, a Segment Lifetime of 0, and a
newer Segment Sequence. The SRH-6LoRH with Via Addresses in the NSM-
VIO is not needed; it SHOULD NOT be placed in the message and MUST be
ignored by the receiver. Upon that NSM-VIO, the Ingress 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 an updated TrackID and P-RouteID, a
Segment Lifetime of 0, and a newer Segment Sequence. The Via
Addresses in the SM-VIO indicate 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 protection path 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-ARCH] over a highly redundant Track. This
specification allows the use of more than one protection path 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 as well when the in-flight packets are forwarded along the
new section.
6.6.1. Maintaining a Track Segment
To modify a section of a segment between the first node and a second
downstream node (which can be the Ingress ingress and Egress, 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
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 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 amount of time, the Root tears down the remaining
section(s) of the old segments as described in Section 6.5 to enable
the deprecated sections to drain their traffic.
6.6.2. Maintaining a Protection Path
This specification allows the Root to add protection paths to a Track
by sending a Non-Storing Mode P-DAO to the Ingress ingress associated to the
same TrackID and a new Segment ID. SegmentID. If the protection path is loose,
then the segments that join the hops must be created first. It makes
sense to add a new protection path before removing one that is
becoming excessively lossy and switch to the new protection path
before removing the old. Dropping a Track before the new one is
installed would reroute the traffic via the root; Root; this may increase
the latency beyond acceptable thresholds and overload the network
near the root. 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 ingress of the first Track.
It is also possible to update a protection path by sending a Non-
Storing Mode P-DAO to the Ingress ingress with the same Segment ID, SegmentID, an
incremented Segment Sequence, and the new complete list of hops in
the NSM-VIO. Updating a live protection path means changing one or
more of the intermediate loose hops, and it involves laying out new
segments from and to the new loose hops before the NSM-VIO is issued
for the new protection path.
Packets that are in flight over the old version of the protection
path still follow the old source route path over the old segments.
After a reasonable time, the Root tears down those segments as
described in Section 6.5 to enable the deprecated segments to drain
their traffic.
6.7. Encapsulating and Forwarding Along a Track
When injecting a packet in a Track, the Ingress 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. egress.
All properties of a Track's operations are inherited from 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
Configuration option.
When the Track Ingress ingress places a packet in a Track, it encapsulates it
with an additional IPv6 header, a Routing Header, and an IPv6 Hop-by-
Hop Option Header that contains the RPI as follows:
* In the uncompressed form, the source of the packet is the address
that this router uses as the DODAGID for the Track, the
destination is the first Via Address in the NSM-VIO, and the RH is
an SRH [RFC6554] that contains the list of the remaining Via
Addresses, ending with the Track Egress. egress.
* To compress RPL artifacts in data packets as indicated in
[RFC8138], the preferred alternative in In a network where 6LoWPAN header compression [RFC6282] is used in use,
it is preferred to implement "IPv6 over Low-Power Wireless
Personal Area Network (6LoWPAN) Paging Dispatch" [RFC8025]. [RFC8025] and
compress the RPL artifacts as indicated in [RFC8138].
In that case, the source-routed header RPL Source Route Header is the exact copy of the
(chain of) SRH-6LoRH found in the NSM-VIO, also ending with the
Track Egress. egress. The RPI-6LoRH is appended next, followed by an IP-
in-IP 6LoRH Header header that indicates the Ingress ingress router in the
Encapsulator Address field; see a similar case in Figure 20 of
[RFC8138].
To signal the Track in the packet, this specification leverages the
RPL Forwarding 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 MUST be placed in the outer chain
of IPv6 headers.
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 '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
(see more in Section 6.3).
* This specification conforms to the principles of [RFC9008] with
regard to packet forwarding and encapsulation along a Track as
follows:
- With this specification, the Track is a RPL DODAG. From the
perspective of that DODAG, the Track Ingress ingress is the Root, the
Track Egress egress is a RPL-Aware 6LR, and neighbors of the Track
Egress
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 ingress is the originator of the packet and the
Track Egress egress is the destination of the packet, there is no need
for an encapsulation.
- Thus, the Track Ingress 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 detail in 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. 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 TrackID 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 Packet processing
uses a precedence that favors the following precedence: 1) self-delivery or routing
header Routing Header
handling when one is present, then 2) delivery to direct neighbors, then 3)
delivery to indirect neighbors, then 4) routing along a segment along the
Track, and finally as a last resort 5) injecting the packet in another Track. Track, as a last
resort.
To achieve this, the packet handling logic MUST happen in the
following order:
* 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 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 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 the 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 the 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 in any of the reasons steps above MUST send an
ICMPv6 error message [RFC4443] to the Root, with the 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 Tracks. In the case of a broken segment, remove
the Root removes the leftover sections of the segment using SM-
VIOs SM-VIOs
with a lifetime of 0 0, indicating the section to where one or more nodes
are being removed (see Section 6.6).
In case of a permanent forwarding error along a source route path,
the node that fails to forward SHOULD send an ICMP error with the
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 the 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 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
the 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 6LoRH [RFC8138] is used to carry the IPv6 routing
information in the outer header, then the whole 6LoRH information
SHOULD be present in the ICMP message.
6.8. Compression of RPL Artifacts
When using [RFC8138] in the main DODAG in a 6LoWPAN LLN is operated in Non-Storing Mode
in a 6LoWPAN LLN,
and the data packets are compressed using [RFC8138], a typical packet
that circulates in the main DODAG is formatted as shown in Figure 20,
representing the case where an IP-in-IP 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
the page selector is actually removed at encapsulation; therefore,
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.
When encapsulating the inner packet to place in the Track, the first
header that the Ingress ingress appends at the head of the inner packet is an
IP-in-IP 6LoRH Header; 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 ingress node that serves as
the DODAGID for the Track, expressed in a compressed form using the
DODAGID of the main DODAG as a reference for the compression. 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 ingress
then adds a P-RPI-6LoRH header to transport the RPI that carries the TrackID as RPLInstanceID as a P-
RPI-6LoRH Header, in its compressed
form as illustrated in Figure 12, using 12. The RPI carries the TrackID as
RPLInstanceID. Combined with the IP-in-IP 6LoRH Header, header, this allows
identifying 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 SM-VIO that signaled
the selected protection path.
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, which is in
compressed form per [RFC8138], 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
7. Less-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 knows 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 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 fewer resources than alternative IGPs such as OSPF, IS-IS,
the Enhanced Interior Gateway Routing Protocol (EIGRP), BABEL, or RIP
at the expense of a route
when using routing stretch versus rather than the shortest path routes to a
destination that those protocols compute. P-Routes add the
capability to install the shortest and/or constrained routes to
special destinations as discussed in Appendix A.9.4 of the ANIMA ACP "An Autonomic
Control Plane (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 Mode, as it reduces the route routing
stretch and lowers the load on the Root. In that case, the control
path between the Root and the RPL nodes can be maintained more
aggressively and with more redundancy than in LLNs, and the nodes can
be reached to maintain the P-Routes at most times for a finer and
more reactive control.
This section specifies the additions that are needed to support
P-Routes when the main DODAG is operated in Storing Mode. As long as
the RPI can be processed adequately by the data plane, the changes in
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.
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 SIOs, regardless of the relative position in the
DODAG of the advertised node versus 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
the 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 TIO and one or more
SIOs. There is no RPL Target Option so that 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 factorizing
the TIO for multiple SIOs as done in [RPL].
* The TIO is followed by one or more SIOs that provide an address
(ULA or GUA) of the advertised neighbor node.
However, the RPL routing information headers may not be supported on
all types of routed network infrastructures, especially not in high-
speed routers. When the RPI is not supported in the data plane,
there cannot be Local RPL Instances and RPL can only operate as a
single topology (the main DODAG). The RPL Instance is the one that of
runs the main DODAG, and the Ingress ingress node that encapsulates the RPL
Instance 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 egress to avoid
loops that may form if the packet is reinjected in the main DODAG.
7.2. A Track as a Full DODAG
This specification builds Tracks with parallel or interleaved
protection paths 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 a 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 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 protection path and produces
the source route paths.
* The node merely selects one of the proposed paths and applies the
associated pre-computed routing header Routing Header in the encapsulation. This
alleviates both the complexity of computing a path and the
compressed form of the routing header. Routing Header.
The RAW architecture [RAW-ARCH] actually expects the PLR at the Track
Ingress
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 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. ingress. The
expectation is that the PLR's metrics that the PLR uses are of an will be in a different order
other
than that of the PCE, PCE's metrics because of the difference of in the timescale
between routing and forwarding; see more in [RAW-ARCH]. 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, ingress, the Root uses a
P-DAO message that contains sequences of Targets and TIOs 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 the Root can report
information on many Targets, possibly the full Track, with one P-DAO.
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 section describes profiles that can be implemented separately separately,
e.g., using only a portion of this specification to meet a particular
use case, 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 ingress, using its the
namespace of the Track ingress for the 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
RPL Source Route Header in the most common LLN deployments. Profile
2 is RECOMMENDED in a high-speed or wired (e.g., 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. introduces.
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 source-routed 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
an additional SRH between the loose source routing hops. With
Profile 2, the Tracks MUST be installed as subTracks of the main
DODAG, and the main Instance MUST be used as the TrackID. Note
that the Ingress 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 an SIO 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 ingress (in the SM-VIO) is the same as the IPv6 address of
the Track Ingress ingress (in the Projected DAO Base Object), the P-DAO
creates an implicit Track between the segment Ingress ingress and the
segment Egress. egress.
Profile 4:
Profile 4 extends Profile 2 with strict source routing source-routed 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 ingress and the Track Egress egress that is the last node.
Profile 5:
Profile 5 combines Profile 4 with Profile 1 and enables loose
source routing between the Ingress ingress and the Egress 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 enables loose
source routing between the Ingress ingress and the Egress 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 Profiles 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, 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 the TrackID.
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 Root knows the node
capabilities and whether they support this specification are 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 or 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 for success are in place, in particular when all the
nodes that could be on the path of the Tracks are upgraded.
10. Security Considerations
It is worth noting that per [RPL], every node in the LLN is RPL-aware
and can inject any RPL-based attack in the network. This
specification uses messages that are already present in RPL [RPL]
with optional secured versions. The same secured versions may be
used with this specification, and whatever security is deployed for a
given network also applies to the flows in this specification.
The LLN nodes depend on the RPL Root and RANs for their operation. A
trust model is necessary to ensure that the right devices are acting
in these roles, avoiding sinkhole attacks (as is done in Section 7 of
[RFC7416]). This trust model could be, at a minimum, based on a
Layer 2 secure joining and link-layer security. This is a generic
6LoWPAN requirement; see Req-5.1 in Appendix B.5 of [RFC8505].
In a general manner, the Security Considerations in [RPL] and
[RFC7416] apply to this specification as well. In particular, link-
layer security is needed 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.
When applied to radio LLNs such as IEEE Std 802.15.4, the lower-layer
frame protection can be leveraged with an appropriate join protocol.
The 6TiSCH defined Constrained Join Protocol (CoJP) [RFC9031] with uses the RPL
Root acting as 6LBR. The join protocol could be extended to provide
additional key material for pledges to 6LBR communication when
additional end-to-end security is desired beyond the hop-by-hop
security from the lower layer.
With this specification, the Root MAY generate P-DAO messages but
other nodes MUST NOT do so. PDR messages MUST be sent to the Root.
This specification expects that the communication with the Root is
authenticated but does not enforce which method is used.
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 egress to Ingress ingress in the case of a Storing Mode P-DAO.
This specification suggests some validation of the VIO to prevent
basic loops loops, i.e., by avoiding that a node that appears twice. But that
is only a minimal protection. Arguably, an attacker that can inject
P-DAOs can reroute any traffic and rapidly deplete critical resources
such as the spectrum and battery in the LLN.
11. IANA Considerations
11.1. RPL DODAG Configuration Option Flag
IANA has assigned a flag in the "DODAG Configuration Option Flags for
MOP 0..6" registry [RFC9008] under the "Routing Protocol for Low
Power and Lossy Networks (RPL)" registry group [IANA-RPL] as follows:
+============+==============================+===========+
| Bit Number | Capability Description | Reference |
+============+==============================+===========+
| 0 | Projected Routes Support (D) | RFC 9914 |
+------------+------------------------------+-----------+
Table 21: New DODAG Configuration Option Flag
IANA has added this RFC as an additional reference for MOP 7 in the
"Mode of Operation" registry under the "Routing Protocol for Low
Power and Lossy Networks (RPL)" registry group [IANA-RPL].
11.2. Elective 6LoWPAN Routing Header Type
IANA has updated the "Elective 6LoWPAN Routing Header Type" registry
[RFC8138] under the "IPv6 Low Power Personal Area Network Parameters"
registry group [IANA-6LO] as follows:
+=======+=============+===========+
| Value | Description | Reference |
+=======+=============+===========+
| 8 | P-RPI-6LoRH | RFC 9914 |
+-------+-------------+-----------+
Table 22: New Elective 6LoWPAN
Routing Header Type
11.3. Critical 6LoWPAN Routing Header Type
IANA has updated the "Critical 6LoWPAN Routing Header Type" registry
[RFC8138] under the "IPv6 Low Power Personal Area Network Parameters"
registry group [IANA-6LO] as follows:
+=======+=============+===========+
| Value | Description | Reference |
+=======+=============+===========+
| 8 | P-RPI-6LoRH | RFC 9914 |
+-------+-------------+-----------+
Table 23: New Critical 6LoWPAN
Routing Header Type
11.4. Registry for RPL Option Flags
IANA has created the "RPL Option Flags" registry, for the 8-bit RPL
Option flags field as detailed in Figure 11, under the "Routing
Protocol for Low Power and Lossy Networks (RPL)" registry group
[IANA-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
The 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 | Projected-Route (P) | RFC 9914 |
+------------+----------------------+-----------+
| 4..255 | Unassigned | |
+------------+----------------------+-----------+
Table 24: Initial PDR Flags
11.5. RPL Control Codes
IANA has updated the "RPL Control Codes" registry under the "Routing
Protocol for Low Power and Lossy Networks (RPL)" registry group
[IANA-RPL] as indicated in Table 25:
+======+=============================+===========+
| Code | Description | Reference |
+======+=============================+===========+
| 0x09 | Projected DAO Request (PDR) | RFC 9914 |
+------+-----------------------------+-----------+
| 0x0A | PDR-ACK | RFC 9914 |
+------+-----------------------------+-----------+
Table 25: New RPL Control Codes
11.6. RPL Control Message Options
IANA has updated the "RPL Control Message Options" registry under the
"Routing Protocol for Low Power and Lossy Networks (RPL)" registry
group [IANA-RPL] as indicated in Table 26:
+=======+==================================+===========+
+=======+==============================================+===========+
| Value | Meaning | Reference |
+=======+==================================+===========+
+=======+==============================================+===========+
| 0x0F | Stateful Storing Mode VIO (SM-VIO) | RFC 9914 |
+-------+----------------------------------+-----------+
+-------+----------------------------------------------+-----------+
| 0x10 | Source-Routed Non-Storing Mode VIO (NSM-VIO) | RFC 9914 |
+-------+----------------------------------+-----------+
+-------+----------------------------------------------+-----------+
| 0x11 | Sibling Information Option (SIO) | RFC 9914 |
+-------+----------------------------------+-----------+
+-------+----------------------------------------------+-----------+
Table 26: RPL Control Message Options
11.7. Registry for Projected DAO Request Flags
IANA has created the "Projected DAO Request (PDR) Flags" registry
under the "Routing Protocol for Low Power and Lossy Networks (RPL)"
registry group [IANA-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
The 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) | RFC 9914 |
+------------+----------------------------------------+-----------+
| 1 | Requested path should be redundant (R) | RFC 9914 |
+------------+----------------------------------------+-----------+
| 2..255 | Unassigned | |
+------------+----------------------------------------+-----------+
Table 27: Initial PDR Flags
11.8. Registry for PDR-ACK Flags
IANA has created the "PDR-ACK Flags" registry under the "Routing
Protocol for Low Power and Lossy Networks (RPL)" registry group
[IANA-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
The registration procedure is Standards Action [RFC8126]. At the
time of publication of this document, no bit has been assigned in
this registry.
11.9. Registry for PDR-ACK Acceptance Status Values
IANA has created the "PDR-ACK Acceptance Status Values" registry
under the "Routing Protocol for Low Power and Lossy Networks (RPL)"
registry group [IANA-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 initial allocation is as indicated in Table 28:
+=======+========================+===========+
| Value | Meaning | Reference |
+=======+========================+===========+
| 0 | Unqualified Acceptance | RFC 9914 |
+-------+------------------------+-----------+
| 1..63 | Unassigned | |
+-------+------------------------+-----------+
Table 28: Acceptance Values of the PDR-ACK
Status
11.10. Registry for PDR-ACK Rejection Status Values
IANA has created the "PDR-ACK Rejection Status Values" registry under
the "Routing Protocol for Low Power and Lossy Networks (RPL)"
registry group [IANA-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 initial allocation is as indicated in Table 29:
+=======+=======================+===========+
| Value | Meaning | Reference |
+=======+=======================+===========+
| 0 | Unqualified Rejection | RFC 9914 |
+-------+-----------------------+-----------+
| 1 | Transient Failure | RFC 9914 |
+-------+-----------------------+-----------+
| 2..63 | Unassigned | |
+-------+-----------------------+-----------+
Table 29: PDR-ACK Rejection Status Values
11.11. Registry for Via Information Options Flags
IANA has created the "Via Information Options (VIO) Flags" registry
under the "Routing Protocol for Low Power and Lossy Networks (RPL)"
registry group [IANA-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
The registration procedure is Standards Action [RFC8126]. At the
time of publication of this document, no bit has been assigned in
this registry (see more in Section 5.3).
11.12. Registry for Sibling Information Option Flags
IANA has created the "Sibling Information Option (SIO) Flags"
registry under the "Routing Protocol for Low Power and Lossy Networks
(RPL)" registry group [IANA-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
The registration procedure is Standards Action [RFC8126]. The
initial allocation is as indicated in Table 30 (see more in
Figure 17):
+============+=========================================+===========+
| Bit Number | Capability Description | Reference |
+============+=========================================+===========+
| 0 | 'S' flag: Sibling in same DODAG as self | RFC 9914 |
+------------+-----------------------------------------+-----------+
| 1..4 | Unassigned | |
+------------+-----------------------------------------+-----------+
Table 30: Initial SIO Flags
11.13. Destination Advertisement Object Flag
IANA has updated the "Destination Advertisement Object (DAO) Flags"
registry, created in Section 20.11 of [RPL], under the "Routing
Protocol for Low Power and Lossy Networks (RPL)" registry group
[IANA-RPL] as indicated in Table 31 (see more in Section 4.1.1):
+============+========================+===========+
| Bit Number | Capability Description | Reference |
+============+========================+===========+
| 2 | Projected DAO (P) | RFC 9914 |
+------------+------------------------+-----------+
Table 31: New Destination Advertisement Object
(DAO) Flag
11.14. Destination Advertisement Object Acknowledgment Flag
IANA has updated the "Destination Advertisement Object (DAO)
Acknowledgment Flags" registry, created in Section 20.12 of [RPL],
under the "Routing Protocol for Low Power and Lossy Networks (RPL)"
registry group [IANA-RPL] as indicated in Table 32 (see more in
Section 4.1.2):
+============+========================+===========+
| Bit Number | Capability Description | Reference |
+============+========================+===========+
| 1 | Projected DAO-ACK (P) | RFC 9914 |
+------------+------------------------+-----------+
Table 32: New Destination Advertisement Object
Acknowledgment Flag
11.15. ICMPv6 Error Code
In some cases, RPL will return an ICMPv6 error message when a message
cannot be forwarded along a P-Route.
Per this specification, IANA has updated the "Type 1 - Destination
Unreachable" registry, in the "ICMPv6 'Code' Fields" registry, under
the "Internet Control Message Protocol version 6 (ICMPv6) Parameters"
registry group [IANA-ICMP] as indicated in Table 33.
+======+==================+===========+
| Code | Name | Reference |
+======+==================+===========+
| 9 | Error in P-Route | RFC 9914 |
+------+------------------+-----------+
Table 33: New ICMPv6 Error Code
11.16. RPL Rejection Status Values
IANA has updated the "RPL Rejection Status" registry under the
"Routing Protocol for Low Power and Lossy Networks (RPL)" registry
group [IANA-RPL] as indicated in Table 34:
+=======+=========================+===========+
| Value | Meaning | Reference |
+=======+=========================+===========+
| 2 | Out of Resources | RFC 9914 |
+-------+-------------------------+-----------+
| 3 | Error in VIO | RFC 9914 |
+-------+-------------------------+-----------+
| 4 | Predecessor Unreachable | RFC 9914 |
+-------+-------------------------+-----------+
| 5 | Unreachable Target | RFC 9914 |
+-------+-------------------------+-----------+
| 6..63 | Unassigned | |
+-------+-------------------------+-----------+
Table 34: RPL Rejection Status Values
12. References
12.1. Normative References
[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>.
[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>.
[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-ARCH] Thubert, P., Ed., "Reliable and Available Wireless (RAW)
Architecture", RFC 9912, DOI 10.17487/RFC9912, February
2026, <https://www.rfc-editor.org/info/rfc9912>.
12.2. Informative References
[INT-ARCH] 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>.
[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>.
[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>.
[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>.
[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>.
[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>.
[RFC9031] Vučinić, M., Ed., Simon, J., Pister, K., and M.
Richardson, "Constrained Join Protocol (CoJP) for 6TiSCH",
RFC 9031, DOI 10.17487/RFC9031, May 2021,
<https://www.rfc-editor.org/info/rfc9031>.
[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>.
[RFC9473] Enghardt, R. and C. Krähenbühl, "A Vocabulary of Path
Properties", RFC 9473, DOI 10.17487/RFC9473, September
2023, <https://www.rfc-editor.org/info/rfc9473>.
[NEW-TAGS] Kühlewind, M. and S. Krishnan, "Definition of new tags for
relations between RFCs", Work in Progress, Internet-Draft,
draft-kuehlewind-rswg-updates-tag-02, 8 July 2024,
<https://datatracker.ietf.org/doc/html/draft-kuehlewind-
rswg-updates-tag-02>.
[IANA-6LO] IANA, "IPv6 Low Power Personal Area Network Parameters",
<https://www.iana.org/assignments/_6lowpan-parameters>.
[IANA-RPL] IANA, "Routing Protocol for Low Power and Lossy Networks
(RPL)", <https://www.iana.org/assignments/rpl/>.
[IANA-ICMP]
IANA, "Internet Control Message Protocol version 6
(ICMPv6) Parameters",
<https://www.iana.org/assignments/icmpv6-parameters/>.
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
S.V.R. 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 the content
of the specification. Many thanks to Remous-Aris Koutsiamanis for
his review during WG Last Call and to Maria Ines Robles for her
thorough shepherd review. Many thanks to Warren Kumari, Ran Chen,
Murray Kucherawy, Roman Danyliw, Klaas Wierenga, Deb Cooley, Éric
Vyncke, Gunter Van de Velde, Sue Hares, and John Scudder for their
comments and suggestions during the IETF Last Call and IESG review
cycle.
Authors' Addresses
Pascal Thubert (editor)
Independent
06330 Roquefort-les-Pins
France
Email: pascal.thubert@gmail.com
Rahul Arvind Jadhav
AccuKnox
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/