< draft-ietf-roll-dao-projection-12.txt   draft-ietf-roll-dao-projection-13.txt >
ROLL P. Thubert, Ed. ROLL P. Thubert, Ed.
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Updates: 6550 (if approved) R.A. Jadhav Updates: 6550 (if approved) R.A. Jadhav
Intended status: Standards Track Huawei Tech Intended status: Standards Track Huawei Tech
Expires: 25 March 2021 M. Gillmore Expires: 2 April 2021 M. Gillmore
Itron Itron
21 September 2020 29 September 2020
Root initiated routing state in RPL Root initiated routing state in RPL
draft-ietf-roll-dao-projection-12 draft-ietf-roll-dao-projection-13
Abstract Abstract
This document enables a RPL Root to install and maintain Projected This document updates RFC 6550 to enable a RPL Root to install and
Routes within its DODAG, along a selected set of nodes that may or maintain Projected Routes within its DODAG, along a selected set of
may not include self, for a chosen duration. This potentially nodes that may or may not include self, for a chosen duration. This
enables routes that are more optimized or resilient than those potentially enables routes that are more optimized or resilient than
obtained with the classical distributed operation of RPL, either in those obtained with the classical distributed operation of RPL,
terms of the size of a source-route header or in terms of path either in terms of the size of a source-route header or in terms of
length, which impacts both the latency and the packet delivery ratio. path length, which impacts both the latency and the packet delivery
ratio.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on 25 March 2021. This Internet-Draft will expire on 2 April 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Other Terms . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Other Terms . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. References . . . . . . . . . . . . . . . . . . . . . . . 6 2.4. References . . . . . . . . . . . . . . . . . . . . . . . 6
3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 6 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 6
4. Identifying a Path . . . . . . . . . . . . . . . . . . . . . 7 4. Identifying a Track . . . . . . . . . . . . . . . . . . . . . 8
5. New RPL Control Messages and Options . . . . . . . . . . . . 8 5. New RPL Control Messages and Options . . . . . . . . . . . . 9
5.1. New P-DAO Request Control Message . . . . . . . . . . . . 8 5.1. New P-DAO Request Control Message . . . . . . . . . . . . 9
5.2. New PDR-ACK Control Message . . . . . . . . . . . . . . . 9 5.2. New PDR-ACK Control Message . . . . . . . . . . . . . . . 10
5.3. Route Projection Options . . . . . . . . . . . . . . . . 10 5.3. Route Projection Options . . . . . . . . . . . . . . . . 12
5.4. Sibling Information Option . . . . . . . . . . . . . . . 13 5.4. Sibling Information Option . . . . . . . . . . . . . . . 14
6. Projected DAO . . . . . . . . . . . . . . . . . . . . . . . . 14 6. Projected DAO . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Requesting a Track . . . . . . . . . . . . . . . . . . . 16 6.1. Requesting a Track . . . . . . . . . . . . . . . . . . . 17
6.2. Routing over a Track . . . . . . . . . . . . . . . . . . 16 6.2. Routing over a Track . . . . . . . . . . . . . . . . . . 18
6.3. Non-Storing Mode Projected Route . . . . . . . . . . . . 17 6.3. Non-Storing Mode Projected Route . . . . . . . . . . . . 18
6.4. Storing-Mode Projected Route . . . . . . . . . . . . . . 18 6.4. Storing Mode Projected Route . . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7. Security Considerations . . . . . . . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
8.1. New RPL Control Codes . . . . . . . . . . . . . . . . . . 21 8.1. New RPL Control Codes . . . . . . . . . . . . . . . . . . 22
8.2. New RPL Control Message Options . . . . . . . . . . . . . 21 8.2. New RPL Control Message Options . . . . . . . . . . . . . 22
8.3. SubRegistry for the Projected DAO Request Flags . . . . . 22 8.3. SubRegistry for the Projected DAO Request Flags . . . . . 23
8.4. SubRegistry for the PDR-ACK Flags . . . . . . . . . . . . 22 8.4. SubRegistry for the PDR-ACK Flags . . . . . . . . . . . . 23
8.5. Subregistry for the PDR-ACK Acceptance Status Values . . 22 8.5. Subregistry for the PDR-ACK Acceptance Status Values . . 24
8.6. Subregistry for the PDR-ACK Rejection Status Values . . . 23 8.6. Subregistry for the PDR-ACK Rejection Status Values . . . 24
8.7. SubRegistry for the Route Projection Options Flags . . . 23 8.7. SubRegistry for the Route Projection Options Flags . . . 24
8.8. SubRegistry for the Sibling Information Option Flags . . 24 8.8. SubRegistry for the Sibling Information Option Flags . . 25
8.9. Error in Projected Route ICMPv6 Code . . . . . . . . . . 24 8.9. Error in Projected Route ICMPv6 Code . . . . . . . . . . 25
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
10. Normative References . . . . . . . . . . . . . . . . . . . . 24 10. Normative References . . . . . . . . . . . . . . . . . . . . 26
11. Informative References . . . . . . . . . . . . . . . . . . . 25 11. Informative References . . . . . . . . . . . . . . . . . . . 26
Appendix A. Applications . . . . . . . . . . . . . . . . . . . . 26 Appendix A. Applications . . . . . . . . . . . . . . . . . . . . 28
A.1. Loose Source Routing . . . . . . . . . . . . . . . . . . 27 A.1. Loose Source Routing . . . . . . . . . . . . . . . . . . 28
A.2. Transversal Routes . . . . . . . . . . . . . . . . . . . 28 A.2. Transversal Routes . . . . . . . . . . . . . . . . . . . 29
Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 30 Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 31
B.1. Using Storing Mode P-DAO in Non-Storing Mode MOP . . . . 30 B.1. Using Storing Mode P-DAO in Non-Storing Mode MOP . . . . 31
B.2. Projecting a storing-mode transversal route . . . . . . . 31 B.2. Projecting a Storing Mode transversal route . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction 1. Introduction
RPL, the "Routing Protocol for Low Power and Lossy Networks" [RPL] RPL, the "Routing Protocol for Low Power and Lossy Networks" [RPL]
(LLNs), is a generic Distance Vector protocol that is well suited for (LLNs), is a generic Distance Vector protocol that is well suited for
application in a variety of low energy Internet of Things (IoT) application in a variety of low energy Internet of Things (IoT)
networks. RPL forms Destination Oriented Directed Acyclic Graphs networks. RPL forms Destination Oriented Directed Acyclic Graphs
(DODAGs) in which the Root often acts as the Border Router to connect (DODAGs) in which the Root often acts as the Border Router to connect
the RPL domain to the Internet. The Root is responsible to select the RPL domain to the Internet. The Root is responsible to select
the RPL Instance that is used to forward a packet coming from the the RPL Instance that is used to forward a packet coming from the
Internet into the RPL domain and set the related RPL information in Internet into the RPL domain and set the related RPL information in
the packets. The "6TiSCH Architecture" [6TiSCH-ARCHI] uses RPL for the packets. 6TiSCH uses RPL for its routing operations.
its routing operations.
The 6TiSCH Architecture also leverages the "Deterministic Networking The "6TiSCH Architecture" [6TiSCH-ARCHI] also leverages the
Architecture" [RFC8655] centralized model whereby the device "Deterministic Networking Architecture" [RFC8655] centralized model
resources and capabilities are exposed to an external controller whereby the device resources and capabilities are exposed to an
which installs routing states into the network based on some external controller which installs routing states into the network
objective functions that reside in that external entity. With DetNet based on some objective functions that reside in that external
and 6TiSCH, the component of the controller that is responsible of entity. With DetNet and 6TiSCH, the component of the controller that
computing routes is called a Path Computation Element ([PCE]). is responsible of computing routes is called a Path Computation
Element ([PCE]).
Based on heuristics of usage, path length, and knowledge of device Based on heuristics of usage, path length, and knowledge of device
capacity and available resources such as battery levels and capacity and available resources such as battery levels and
reservable buffers, a PCE with a global visibility on the system can reservable buffers, the PCE with a global visibility on the system
compute P2P routes that are more optimized for the current needs as can compute direct Peer to Peer (P2P) routes that are optimized for
expressed by the objective function. the needs expressed by an objective function. This document
specifies protocol extensions to RPL [RPL] that enable the Root of a
This draft proposes protocol extensions to RPL that enable the Root main DODAG to install centrally-computed routes inside the DODAG on
to install a limited amount of centrally-computed routes in a RPL behalf of a PCE.
graph, on behalf of a PCE that may be collocated or separated from
the Root. Those extensions enable loose source routing down and
transversal routes inside the main DODAG running a base RPL Instance.
This specification expects that the base RPL Instance is operated in This specification expects that the main RPL Instance is operated in
RPL Non-Storing Mode of Operation (MOP) to sustain the exchanges with RPL Non-Storing Mode of Operation (MOP) to sustain the exchanges with
the Root. In that Mode, the Root has enough information to build a the Root. In that Mode, the Root has enough information to build a
basic DODAG topology based on parents and children, but lacks the basic DODAG topology based on parents and children, but lacks the
knowledge of siblings. This document adds the capability for nodes knowledge of siblings. This document adds the capability for nodes
to advertise sibling information in order to improve the topological to advertise sibling information in order to improve the topological
awareness of the Root. awareness of the Root.
As opposed to the classical RPL operations where routes are injected As opposed to the classical RPL operations where routes are injected
by the Target nodes, the protocol extensions enable the Root of a by the Target nodes, the protocol extensions enable the Root of a
DODAG to project the routes that are needed onto the nodes where they DODAG to project the routes that are needed onto the nodes where they
should be installed. This specification uses the term Projected should be installed. This specification uses the term Projected
Route to refer to those routes. Route to refer to those routes. Projected Routes can be used to
reduce the size of the source routing headers with loose source
routing operations down the main RPL DODAG. Projected Routes can
also be used to build transversal routes for route optimization and
Traffic Engineering purposes, between nodes of the DODAG.
A Projected Route may be installed in either Storing and Non-Storing A Projected Route may be installed in either Storing and Non-Storing
Mode, potentially resulting in hybrid situations where the Mode of Mode, potentially resulting in hybrid situations where the Mode of
the Projected Route is different from that of the main RPL Instance. the Projected Route is different from that of the main RPL Instance.
A Projected Route may be a stand-alone end-to-end path to a Target or A Projected Route may be a stand-alone end-to-end path or a Segment
a Segment in a more complex forwarding graph called a Track. in a more complex forwarding graph called a Track.
The concept of a Track was introduced in the 6TiSCH architecture, as The concept of a Track was introduced in the 6TiSCH architecture, as
a complex path to a Target destination with redundant forwarding a potentially complex path with redundant forwarding solutions along
solutions along the way. A node at the ingress of more than one the way. A node at the ingress of more than one Segment in a Track
Segment in a Track may use any combination of those Segments to may use any combination of those Segments to forward a packet towards
forward a packet towards the Target. the Track Egress.
The "Reliable and Available Wireless (RAW) Architecture/Framework" The "Reliable and Available Wireless (RAW) Architecture/Framework"
[RAW-ARCHI] enables a dynamic path selection within the Track to [RAW-ARCHI] defines the Path Selection Engine (PSE) that adapts the
increase the transmission diversity and combat diverse causes of use of the path redundancy within a Track to defeat the diverse
packet loss. causes of packet loss.
To that effect, RAW defines the Path Selection Engine (PSE) as a The PSE is a dataplane extension of the PCE; it controls the
complement of the PCE operating in the dataplane. The PSE controls forwarding operation of the packets within a Track, using Packet ARQ,
the use of the Packet ARQ, Replication, Elimination, and Overhearing Replication, Elimination, and Overhearing (PAREO) functions over the
(PAREO) functions over the Track segments. Track segments, to provide a dynamic balance between the reliability
and availability requirements of the flows and the need to conserve
energy and spectrum.
While the time scale at which the PCE (re)computes the Track can be The time scale at which the PCE (re)computes the Track can be long,
long, for an operation based on long-term statistical metrics to using long-term statistical metrics to perform global optimizations
perform global optimizations at the scale of the whole network, the at the scale of the whole network. Conversely, the PSE makes
PSE makes forwarding decision at the time scale of one or a small forwarding decisions at the time scale of one or a small collection
collection of packets, using a knowledge that is changing rapidly but of packets, based on a knowledge that is limited in scope to the
limited in scope of the Track itself. This way, the PSE can provide Track itself, so it can be refreshed at a fast pace.
a dynamic balance between the reliability and availability
requirements of the flows and the need to conserve energy and
spectrum.
Projected Routes must be used with the parsimony to limit the amount Projected Routes must be used with the parsimony to limit the amount
of state that is installed in each device to fit within the device of state that is installed in each device to fit within the device
resources, and to maintain the amount of rerouted traffic within the resources, and to maintain the amount of rerouted traffic within the
capabilities of the transmission links. The methods used to learn capabilities of the transmission links. The methods used to learn
the node capabilities and the resources that are available in the the node capabilities and the resources that are available in the
devices and in the network are out of scope for this document. devices and in the network are out of scope for this document.
This specification uses the RPL Root as a proxy to the PCE. The PCE 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 may be collocated with the Root, or may reside in an external
Controller. In that case, the PCE exchanges control messages with Controller.
the Root over a Southbound API, that is out of scope for this
specification. The algorithm to compute the paths and the protocol In that case, the PCE exchanges control messages with the Root over a
used by an external PCE to obtain the topology of the network from Southbound API that is out of scope for this specification. The
the Root are also out of scope. algorithm to compute the paths and the protocol used by an external
PCE to obtain the topology of the network from the Root are also out
of scope.
2. Terminology 2. Terminology
2.1. Requirements Language 2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all 14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2.2. Glossary 2.2. Glossary
This document often uses the following acronyms: This document often uses the following acronyms:
CMO: Control Message Option CMO: Control Message Option
DAO: Destination Advertisement Object DAO: Destination Advertisement Object
DAG: Directed Acyclic Graph DAG: Directed Acyclic Graph
DODAG: Destination-Oriented Directed Acyclic Graph; A DAG with only DODAG: Destination-Oriented Directed Acyclic Graph; A DAG with only
one vertice (i.e., node) that has no outgoing edge (i.e., link) one vertex (i.e., node) that has no outgoing edge (i.e., link)
LLN: Low-Power and Lossy Network LLN: Low-Power and Lossy Network
MOP: RPL Mode of Operation MOP: RPL Mode of Operation
P-DAO: Projected DAO P-DAO: Projected DAO
PDR: P-DAO Request PDR: P-DAO Request
RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf) RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf)
RAL: RPL-Aware Leaf RAL: RPL-Aware Leaf
RPI: RPL Packet Information RPI: RPL Packet Information
RPL: IPv6 Routing Protocol for LLNs [RPL] RPL: IPv6 Routing Protocol for LLNs [RPL]
RPO: A Route Projection Option; it can be a VIO or an SRVIO. RPO: A Route Projection Option; it can be a VIO or an SRVIO.
RTO: RPL Target Option RTO: RPL Target Option
skipping to change at page 5, line 45 skipping to change at page 5, line 45
SIO: RPL Sibling Information Option SIO: RPL Sibling Information Option
SRVIO: A Source-Routed Via Information Option, used in Non-Storing SRVIO: A Source-Routed Via Information Option, used in Non-Storing
Mode P-DAO messages. Mode P-DAO messages.
SubDAG: A DODAG rooted at a node which is a child of that node and a SubDAG: A DODAG rooted at a node which is a child of that node and a
subset of a larger DAG subset of a larger DAG
TIO: RPL Transit Information Option TIO: RPL Transit Information Option
VIO: A Via Information Option, used in Storing Mode P-DAO messages. VIO: A Via Information Option, used in Storing Mode P-DAO messages.
2.3. Other Terms 2.3. Other Terms
Projected Route: A Projected Route is a serial path that is Projected Route: A Projected Route is a path segment that is
computed, installed and maintained remotely by a RPL Root. computed remotely, and installed and maintained by a RPL Root.
Projected DAO: A DAO message used to install a Projected Route. Projected DAO: A DAO message used to install a Projected Route.
Track: A complex path with redundant Segments to a destination. Track: A complex path with redundant Segments to a destination.
TrackID: A RPL Local InstanceID with the 'D' bit set. The TrackId TrackID: A RPL Local InstanceID with the 'D' bit set. The TrackID
is associated with a Target address that is the Track destination. is associated with a IPv6 Address to the Track Egress Node.
2.4. References 2.4. References
In this document, readers will encounter terms and concepts that are In this document, readers will encounter terms and concepts that are
discussed in the "Routing Protocol for Low Power and Lossy Networks" discussed in the "Routing Protocol for Low Power and Lossy Networks"
[RPL] and "Terminology in Low power And Lossy Networks" [RFC7102]. [RPL] and "Terminology in Low power And Lossy Networks" [RFC7102].
3. Updating RFC 6550 3. Updating RFC 6550
This specification introduces two new RPL Control Messages to enable Section 6 of [RPL] introduces the RPL Control Message Options (CMO),
a RPL Aware Node (RAN) to request the establisment of a Track from including the RPL Target Option (RTO) and Transit Information Option
self to a Target. The RAN makes its request by sending a new P-DAO (TIO), which can be placed in RPL messages such as the Destination
Request (PDR) Message to the Root. The Root confirms with a new PDR- Advertisement Object (DAO). This specification extends the DAO
ACK message back to the requester RAN, see Section 5.1 for more. message with the Projected DAO (P-DAO); a P-DAO message signals a
Projected Route using new CMOs presented therein.
Section 6.7 of [RPL] specifies the RPL Control Message Options (CMO) A Projected Route can be an additional route of higher precedence
to be placed in RPL messages such as the Destination Advertisement within the main DODAG, in which case it is installed with the
Object (DAO) message. The RPL Target Option (RTO) and the Transit RPLInstanceID and DODAGID of the main DODAG.
Information Option (TIO) are such options.
In Non-Storing Mode, the TIO option is used in the DAO message to A Projected Route can also be a Segment within a Track. A stand-
inform the root of the parent-child relationships within the DODAG, alone Segment can be used as a Serial (end-to-end) Track. Segments
and the Root has a full knowledge of the DODAG structure. The TIO can also be combined to form a Complex Track. The Root uses a local
applies to the RTOs that preceed it immediately in the message. RPL Instance rooted at the Track Egress to establish and maintain the
Options may be factorized; multiple TIOs may be present to indicate Track. The local RPLInstanceID of the Track is called the TrackID,
multiple routes to the one or more contiguous addresses indicated in more in Section 4.
the RTOs that immediately precede the TIOs in the RPL message.
This specification introduces two new CMOs referred to as Route 0 1 2 3
Projection Options (RPO) to install Projected Routes. One RPO is the 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
Via Information Option (VIO) and the other is the Source-Routed VIO +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(SRVIO). The VIO installs a route on each hop along a Projected | TrackID |K|D| Flags | Reserved | DAOSequence |
Route (in a fashion analogous to RPL Storing Mode) whereas the SRVIO +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
installs a source-routing state at the ingress node, which uses that | |
state to encapsulate a packet with an IPv6 Routing Header in a + +
fashion similar to RPL Non-Storing Mode. | |
+ IPv6 Address of the Track Egress +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
Like the TIO, the RPOs MUST be preceded by exactly one RTO to which Figure 1: Projected DAO Format for a Track
they apply, and SRVIOs MAY be factorized, though VIOs MUST NOT be.
Factorized contiguous SRVIOs indicate alternate paths to the Target,
more in Section 5.3.
This specification also introduces a new CMO to enable a RAN to A P-DAO message signals the IPv6 Address of the Track Egress in the
advertise a selection of its candidate neighbors as siblings to the DODAGID field of the DAO Base Object, and the TrackID in the
Root, using a new Sibling Information Option (SIO) as specified in RPLInstanceID field, as shown in Figure 1.
Section 5.4.
4. Identifying a Path 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. Options may
be factorized; multiple RTOs may be present to signal a collection of
children that can be reached via the parent(s) indicated in the
TIO(s) that follows the RTOs.
It must be noted that RPL has a concept of Instance to represent This specification generalizes the case of a parent that can be used
different routing topologies but does not have a concept of an to reach a child with that of a whole Track through which both
administrative distance, which exists in certain proprietary children and siblings may be reached.
implementations to sort out conflicts between multiple sources of
routing information within one routing topology.
This draft conforms the Instance model as follows: New CMOs called the Route Projection Options (RPO) are introduced for
use in P-DAO messages as a multihop alternative to the TIO. One RPO
is the Via Information Option (VIO); the VIO installs a state at each
hop along a Storing Mode Projected Route. The other is the Source-
Routed VIO (SRVIO); the SRVIO installs a source-routing state at the
Segment ingress, which uses that state to encapsulate a packet with a
Source-Routing Header along a Non-Storing Mode Projected Route.
* If the PCE needs to influence a particular Instance to add better Like in a DAO message, the RTOs can be factorized in a P-DAO, but the
routes in conformance with the routing objectives in that CMOs cannot. A P-DAO contains one or more RTOs that indicate the
Instance, it may do so as long as it does not create a loop. A destinations that can be reached via the Track, and either one SRVIO
Projected Route is always preferred over a route that is learned or one VIO signal the sequence of hops between the Track Ingress and
via RPL. the (penultimate) node before the Track Egress. In Non-Storing Mode,
the Root sends the P-DAO to the Track Ingress where the source-
routing state is stored. In Storing Mode, the P-DAO is sent to the
Track Egress and forwarded along the Segment in the reverse
direction, installing a Storing Mode state at each hop.
* The PCE may use P-DAOs to install a specific (say, Traffic This specification adds another CMO called the Sibling Information
Engineered) and possibly complex path, that we refer to as a Option (SIO) that is used by a RPL Aware Node (RAN) to advertise a
Track, towards a particular Target. In that case it MUST use a selection of its candidate neighbors as siblings to the Root, more in
Local RPL Instance (see section 5 of [RPL]) associated to that Section 5.4. The sibling selection process is out of scope.
Target to identify the Track.
We refer to the local RPLInstanceID as TrackID. The TrackID MUST Two new RPL Control Messages are also introduced, to enable a RAN to
be unique for a particular Target IPv6 address. The Track is request the establishment of a Track between self as the Track
uniquely identified within the RPL domain by the tuple (Target Ingress Node and a Track Egress. The RAN makes its request by
address, TrackID) where the TrackID is always represented with the sending a new P-DAO Request (PDR) Message to the Root. The Root
'D' flag set. confirms with a new PDR-ACK message back to the requester RAN, see
Section 5.1 for more. A positive PDR-ACK indicates that the Track
was built and that the Roots commits to maintain the Track for a
negotiated lifetime.
The Track where a packet is placed is signaled by a RPL Packet In the case of a complex Track, each Segment is maintained
Information (RPI) (see [USEofRPLinfo]) in the outer chain of IPv6 independently and asynchronously by the Root, with its own lifetime
Headers. The RPI contains the TrackID as RPLInstanceID and the that may be shorter, the same, or longer than that of the Track. The
'D' flag is set to indicate that the destination address in the Root may use an asynchronous PDR-ACK with an negative status to
IPv6 header is the Target that is used to identify the Track, more indicate that the Track was terminated before its time.
in Section 6.2.
* The PCE may also install a projected Route as a complement to the 4. Identifying a Track
main DODAG, e.g., using the Storing-Mode Mode along a Source-
Routed path in order to enable loose source routing and reduce the
Routing Header. In that case, the global RPLInstanceID of the
main DODAG is signaled in place of the TrackId on the P-DAO, and
the RPI in the packet indicates the global RPLInstanceID, more in
Appendix A.1.
* A packet that is routed over the RPL Instance associated to a RPL defines the concept of an Instance to signal an individual
Track MUST NOT be placed over a different RPL Instance again. routing topology but does not have a concept of an administrative
Conversely, a packet that is placed on a Global Instance MAY be distance, which exists in certain proprietary implementations to sort
injected in a Local Instance based on a network policy and the out conflicts between multiple sources of routing information within
Local Instance configuration. one routing topology.
A Projected Route is a serial path that may represent the end-to-end This draft conforms the RPL Instance model as follows:
route or only a Segment in a complex Track, in which case multiple
Projected Routes are installed with the same tuple (Target address,
TrackID) and a different Segment ID each.
All properties of a Track operations are inherited form the main * The PCE MAY use P-DAO messages to add better routes in the main
instance that is used to install the Track. For instance, the use of (Global) Instance in conformance with the routing objectives in
that Instance. To achieve this, the PCE MAY install a Storing
Mode Projected Route along a path down the main (Non-Storing Mode)
DODAG. This enables a loose source routing and reduces the size
of the Source Routing Header, see Appendix A.1.
When adding a Storing Mode Projected Route to the main RPL
Instance, the Root MUST set the RPLInstanceID field of the DAO
message (see section 6.4.1. of [RPL]) to the RPLInstanceID of the
main DODAG, and set the DODAGID field to the Segment Egress. The
Projected Route provides a longer match to the Egress than the
default route via the Root, so it is preferred. Once the
Projected Route is installed, the intermediate nodes listed in the
VIO between the first (excluded) and the last (included) can be
elided in a Source-Route Header that signals that Segment.
* The Root MAY also use P-DAO messages to install a specific (say,
Traffic Engineered) path as a Serial of a Complex Track, to a
particular endpoint that is the Track Egress. In that case, the
Root MUST use a Local RPL Instance (see section 5 of [RPL]) as
TrackID.
The TrackID MUST be unique for the Global Unique IPv6 Address
(GUA) or Unique-Local Address (ULA) of the Track Egress that
serves as DODAGID for the Track. This way, a Track is uniquely
identified by the tuple (Track Egress Address, TrackID) where the
TrackID is always represented with the 'D' flag set. The Track
Egress Address and the TrackID are signaled in the P-DAO message
as shown in Figure 1.
* In the data packets, the Track Egress Address and the TrackID are
respectively signaled in IPv6 Address of the final destination and
the RPLInstanceID field of the RPL Packet Information (RPI) (see
[USEofRPLinfo]) in the outer chain of IPv6 Headers.
If the outer chain of IPv6 Headers contains a Source-Routing
Header that is not fully consumed, then the final destination is
the last entry in the Source-Routing Header; else it is the
Destination Address in the IPv6 Header. When using the [RFC8138]
compression, it is the last hop of the last SRH-6LoRH of the outer
header in either case.
The 'D' flag in the RPLInstanceID MUST be set to indicate that the
final destination address in the IPv6 header owns the local
RPLInstanceID, more in Section 6.2.
* A packet that is being routed over the RPL Instance associated to
a first Non-Storing Mode Track MAY be placed (encapsulated) in a
second Track to cover one loose hop of the first Track. On the
other hand, a Storing Mode Track must be strict and a packet that
it placed in a Storing Mode Track MUST follow that Track till the
Track Egress.
When a Track Egress extracts a packet from a Track (decapsulates
the packet), the Destination of the inner packet MUST be either
this node or a direct neighbor, otherwise the packet MUST be
dropped. That Destination may be the next Hop in a Non-Storing
Mode Track.
All properties of a Track operations are inherited form the main RPL
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 compression per [RFC8138] is determined by whether it is used in the
main instance, e.g., by setting the "T" flag [TURN-ON_RFC8138] in the main instance, e.g., by setting the "T" flag [TURN-ON_RFC8138] in the
RPL configuration option. RPL configuration option.
5. New RPL Control Messages and Options 5. New RPL Control Messages and Options
5.1. New P-DAO Request Control Message 5.1. New P-DAO Request Control Message
The P-DAO Request (PDR) message is sent to the Root to request a new The P-DAO Request (PDR) message is sent to the Root to request a new
that the PCE establishes a new a projected route from self ot the that the PCE establishes a new a projected route from self to the
Target indicated in the Target Option as a full path of a collection Track Egress indicated in the TIO as a full path of a collection of
of Segments in a Track. Exactly one Target Option MUST be present, Segments in a Track. Exactly one TIO MUST be present, more in
more in Section 6.1. Section 6.1.
The RPL Control Code for the PDR is 0x09, to be confirmed by IANA. The RPL Control Code for the PDR is 0x09, to be confirmed by IANA.
The format of PDR Base Object is as follows: The format of PDR Base Object is as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TrackID |K|R| Flags | ReqLifetime | PDRSequence | | TrackID |K|R| Flags | ReqLifetime | PDRSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)... | Option(s)...
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 1: New P-DAO Request Format Figure 2: New P-DAO Request Format
TrackID: 8-bit field indicating the RPLInstanceID associated with TrackID: 8-bit field indicating the RPLInstanceID associated with
the Track. It is set to zero upon the first request for a new the Track. It is set to zero upon the first request for a new
Track and then to the TrackID once the Track was created, to Track and then to the TrackID once the Track was created, to
either renew it of destroy it. either renew it of destroy it.
K: The 'K' flag is set to indicate that the recipient is expected to K: The 'K' flag is set to indicate that the recipient is expected to
send a PDR-ACK back. send a PDR-ACK back.
R: The 'R' flag is set to indicate that the Requested path should be R: The 'R' flag is set to indicate that the Requested path should be
skipping to change at page 9, line 17 skipping to change at page 10, line 41
The requested lifetime for the Track expressed in Lifetime Units The requested lifetime for the Track expressed in Lifetime Units
(obtained from the DODAG Configuration option). (obtained from the DODAG Configuration option).
A PDR with a fresher PDRSequence refreshes the lifetime, and a A PDR with a fresher PDRSequence refreshes the lifetime, and a
PDRLifetime of 0 indicates that the track should be destroyed. PDRLifetime of 0 indicates that the track should be destroyed.
PDRSequence: 8-bit wrapping sequence number, obeying the operation PDRSequence: 8-bit wrapping sequence number, obeying the operation
in section 7.2 of [RPL]. in section 7.2 of [RPL].
The PDRSequence is used to correlate a PDR-ACK message with the The PDRSequence is used to correlate a PDR-ACK message with the
PDR message that triggeted it. It is incremented at each PDR PDR message that triggered it. It is incremented at each PDR
message and echoed in the PDR-ACK by the Root. message and echoed in the PDR-ACK by the Root.
5.2. New PDR-ACK Control Message 5.2. New PDR-ACK Control Message
The new PDR-ACK is sent as a response to a PDR message with the 'K' The new PDR-ACK is sent as a response to a PDR message with the 'K'
flag set. The RPL Control Code for the PDR-ACK is 0x0A, to be flag set. The RPL Control Code for the PDR-ACK is 0x0A, to be
confirmed by IANA. Its format is as follows: confirmed by IANA. Its format is as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TrackID | Flags | Track Lifetime| PDRSequence | | TrackID | Flags | Track Lifetime| PDRSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDR-ACK Status| Reserved | | PDR-ACK Status| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)... | Option(s)...
+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+
Figure 2: New PDR-ACK Control Message Format Figure 3: New PDR-ACK Control Message Format
TrackID: The RPLInstanceID of the Track that was created. The value TrackID: The RPLInstanceID of the Track that was created. The value
of 0x00 is used to when no Track was created. of 0x00 is used to when no Track was created.
Flags: Reserved. The Flags field MUST initialized to zero by the Flags: Reserved. The Flags field MUST initialized to zero by the
sender and MUST be ignored by the receiver sender and MUST be ignored by the receiver
Track Lifetime: Indicates that remaining Lifetime for the Track, Track Lifetime: Indicates that remaining Lifetime for the Track,
expressed in Lifetime Units; a value of zero (0x00) indicates that expressed in Lifetime Units; a value of zero (0x00) indicates that
the Track was destroyed or not created. the Track was destroyed or not created.
PDRSequence: 8-bit wrapping sequence number. It is incremented at PDRSequence: 8-bit wrapping sequence number. It is incremented at
each PDR message and echoed in the PDR-ACK. each PDR message and echoed in the PDR-ACK.
PDR-ACK Status: 8-bit field indicating the completion. PDR-ACK Status: 8-bit field indicating the completion.
The PDR-ACK Status is substructured as indicated in Figure 3: The PDR-ACK Status is substructured as indicated in Figure 4:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|E|R| Value | |E|R| Value |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 3: PDR-ACK status Format Figure 4: PDR-ACK status Format
E: 1-bit flag. Set to indicate a rejection. When not set, a E: 1-bit flag. Set to indicate a rejection. When not set, a
value of 0 indicates Success/Unqualified acceptance and other value of 0 indicates Success/Unqualified acceptance and other
values indicate "not an outright rejection". values indicate "not an outright rejection".
R: 1-bit flag. Reserved, MUST be set to 0 by the sender and R: 1-bit flag. Reserved, MUST be set to 0 by the sender and
ignored by the receiver. ignored by the receiver.
Status Value: 6-bit unsigned integer. Values depending on the Status Value: 6-bit unsigned integer. Values depending on the
setting of the 'E' flag as indicated respectively in Table 4 setting of the 'E' flag as indicated respectively in Table 4
skipping to change at page 10, line 35 skipping to change at page 12, line 13
Reserved: The Reserved field MUST initialized to zero by the sender Reserved: The Reserved field MUST initialized to zero by the sender
and MUST be ignored by the receiver and MUST be ignored by the receiver
5.3. Route Projection Options 5.3. Route Projection Options
The RPOs indicate a series of IPv6 addresses that can be compressed The RPOs indicate a series of IPv6 addresses that can be compressed
using the method defined in the "6LoWPAN Routing Header" [RFC8138] using the method defined in the "6LoWPAN Routing Header" [RFC8138]
specification using the address of the Root found in the DODAGID specification using the address of the Root found in the DODAGID
field of DIO messages as Compression Reference. field of DIO messages as Compression Reference.
An RPO indicates a Projected Route that can be a serial Track in full An RPO indicates a Projected Route that can be a Serial Track in full
or a Segment of a more complex Track. In Non-Storing Mode, multiple or a Segment of a more Complex Track. In Non-Storing Mode, multiple
RPO may be placed after a same Target Option to reflect different RPO may be placed after a TIO to reflect different Segments
Segments originated at this node. The Track is identified by a originated at this node. The Track is identified by a TrackID that
TrackID that is a Local RPLInstanceID to the Target of the Track. is a Local RPLInstanceID to the Track Egress of the Track.
The format of RPOs is as follows: The format of RPOs is as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Option Length |C| Flags | Reserved | | Type | Option Length | Flags | SegmentID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TrackID | SegmentID |Segm. Sequence | Seg. Lifetime | |Segm. Sequence | Seg. Lifetime | SRH-6LoRH header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
. . . .
. Via Address 1 . . Via Address 1 .
. . . .
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
skipping to change at page 11, line 33 skipping to change at page 12, line 49
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
. . . .
. Via Address n . . Via Address n .
. . . .
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Route Projection Option format (uncompressed form) Figure 5: Route Projection Option format (uncompressed form)
Option Type: 0x0B for VIO, 0x0C for SRVIO (to be confirmed by IANA) Option Type: 0x0B for VIO, 0x0C for SRVIO (to be confirmed by IANA)
Option Length: In bytes; variable, depending on the number of Via Option Length: In bytes; variable, depending on the number of Via
Addresses. Addresses and the compression.
C: 1-bit flag. Set to indicate that the following Via Addresses are
expressed as one or more SRH-6LoRH as defined in section 5.1 of
[RFC8138]. Figure 4 illustrates the case where the "C" flag is
not set, meaning that the Via Addresses are expressed in 128 bits.
Flags: Reserved. The Flags field MUST initialized to zero by the Flags: Reserved. The Flags field MUST initialized to zero by the
sender and MUST be ignored by the receiver sender and MUST be ignored by the receiver
Reserved: The Reserved field MUST initialized to zero by the sender
and MUST be ignored by the receiver
TrackID: 8-bit field indicating the topology Instance associated
with the Track. This field carries either a TrackID, such that
the tuple (Target Address, TrackID) forms a unique ID of the Track
in the RPL domain, or the glocal InstanceID of the main DODAG, in
which case the RPO adds a route to the main DODAG as an individual
Segment.
SegmentID: 8-bit field that identifies a Segment within a Track or SegmentID: 8-bit field that identifies a Segment within a Track or
the main DODAG as indicated by the TrackId field. A Value of 0 is the main DODAG as indicated by the TrackID field. A Value of 0 is
used to signal a serial path, i.e., made of a single segment. used to signal a Serial Track, i.e., made of a single segment.
Segment Sequence: 8-bit unsigned integer. The Segment Sequence Segment Sequence: 8-bit unsigned integer. The Segment Sequence
obeys the operation in section 7.2 of [RPL] and the lollipop obeys the operation in section 7.2 of [RPL] and the lollipop
starts at 255. When the Root of the DODAG needs to refresh or starts at 255. When the Root of the DODAG needs to refresh or
update a Segment in a Track, it increments the Segment Sequence update a Segment in a Track, it increments the Segment Sequence
individually for that Segment. The Segment information indicated individually for that Segment. The Segment information indicated
in the RTO deprecates any state for the Segment indicated by the in the RTO deprecates any state for the Segment indicated by the
SegmentID within the indicated Track and sets up the new SegmentID within the indicated Track and sets up the new
information. A RTO with a Segment Sequence that is not as fresh information. A RTO with a Segment Sequence that is not as fresh
as the current one is ignored. a RTO for a given target with the as the current one is ignored. a RTO for a given Track Egress
same (TrackID, SegmentID, Segment Sequence) indicates a retry; it with the same (TrackID, SegmentID, Segment Sequence) indicates a
MUST NOT change the Segment and MUST be propagated or answered as retry; it MUST NOT change the Segment and MUST be propagated or
the first copy. answered as the first copy.
Segment Lifetime: 8-bit unsigned integer. The length of time in Segment Lifetime: 8-bit unsigned integer. The length of time in
Lifetime Units (obtained from the Configuration option) that the Lifetime Units (obtained from the Configuration option) that the
Segment is usable. The period starts when a new Segment Sequence Segment is usable. The period starts when a new Segment Sequence
is seen. A value of 255 (0xFF) represents infinity. A value of is seen. A value of 255 (0xFF) represents infinity. A value of
zero (0x00) indicates a loss of reachability. A DAO message that zero (0x00) indicates a loss of reachability. A DAO message that
contains a Via Information option with a Segment Lifetime of zero contains a Via Information option with a Segment Lifetime of zero
for a Target is referred as a No-Path (for that Target) in this for a Track Egress is referred as a No-Path (for that Track
document. Egress) in this document.
Via Address: The collection of Via Addresses along one Segment, SRH-6LoRH header: The first 2 bytes of the SRH-6LoRH as shown in
indicated in the order of the path from the ingress to the egress Figure 6 of [RFC8138]. A 6LoRH Type of 4 means that the VIA
nodes. If the "C" flag is set, the fields Via Address 1 .. Via Addresses are provided in full with no compression.
Address n in Figure 4 are replaced by one or more of the headers
illustrated in Fig. 6 of [RFC8138]. In the case of a VIO, or if Via Address: A Luistof Via Addresses along one Segment, indicated in
[RFC8138] is turned off, then the Root MUST use only one SRH- the order of the path from the ingress to the egress nodes.
6LoRH, and the compression is the same for all addresses. If
[RFC8138] is turned on, then the Root SHOULD optimize the size of In a VIO, the list is a strict path between direct neighbors,
the SRVIO; in that case, more than one SRH-6LoRH are needed if the whereas for an SRVIO, the list may be loose, provided that each
compression of the addresses change inside the Segment and listed node has a path to the next listed node, e.g., via another
Track.
In the case of a VIO, or if [RFC8138] is turned off, then the Root
MUST use only one SRH-6LoRH per RPO, and the compression is the
same for all the addresses, as shown in Figure 5.
If [RFC8138] is turned on, then the Root SHOULD optimize the size
of the SRVIO; in that case, more than one SRH-6LoRH may be needed
if the compression of the addresses changes inside the Segment and
different SRH-6LoRH Types are used. different SRH-6LoRH Types are used.
An RPO MUST contain at least one Via Address, and a Via Address MUST An RPO MUST contain at least one Via Address, and a Via Address MUST
NOT be present more than once, otherwise the RPO MUST be ignored. NOT be present more than once, otherwise the RPO MUST be ignored.
5.4. Sibling Information Option 5.4. Sibling Information Option
The Sibling Information Option (SIO) provides indication on siblings The Sibling Information Option (SIO) provides indication on siblings
that could be used by the Root to form Projected Routes. The format that could be used by the Root to form Projected Routes. The format
of SIOs is as follows: of SIOs is as follows:
skipping to change at page 13, line 35 skipping to change at page 14, line 47
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
. . . .
. Sibling Address . . Sibling Address .
. . . .
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Sibling Information Option Format Figure 6: Sibling Information Option Format
Option Type: 0x0D (to be confirmed by IANA) Option Type: 0x0D (to be confirmed by IANA)
Option Length: In bytes; variable, depending on the number of Via Option Length: In bytes; variable, depending on the number of Via
Addresses. Addresses.
Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH
Type as defined in figure 7 in section 5.1 of [RFC8138] that Type as defined in figure 7 in section 5.1 of [RFC8138] that
corresponds to the compression used for the Sibling Address. corresponds to the compression used for the Sibling Address.
skipping to change at page 14, line 45 skipping to change at page 16, line 8
[RFC8138] compressed form as indicated by the Compression Type [RFC8138] compressed form as indicated by the Compression Type
field. field.
An SIO MAY be immediately followed by a DAG Metric Container. In An SIO MAY be immediately followed by a DAG Metric Container. In
that case the DAG Metric Container provides additional metrics for that case the DAG Metric Container provides additional metrics for
the hop from the Sibling to this node. the hop from the Sibling to this node.
6. Projected DAO 6. Projected DAO
This draft adds a capability to RPL whereby the Root of a DODAG This draft adds a capability to RPL whereby the Root of a DODAG
projects a route by sending one or more extended DAO message called projects a Track by sending one or more extended DAO message called
Projected-DAO (P-DAO) messages to an arbitrary router in the DODAG, Projected-DAO (P-DAO) messages to chosen routers in the DODAG,
indicating one or more sequence(s) of routers inside the DODAG via indicating one or more sequence(s) of routers inside the DODAG via
which the Target(s) indicated in the RPL Target Option(s) (RTO) can which the Target(s) indicated in the RPL Target Option(s) (RTO) can
be reached. be reached.
A P-DAO is sent from a global address of the Root to a global address A P-DAO is sent from a global address of the Root to a global address
of the recipient, and MUST be confirmed by a DAO-ACK, which is sent of the recipient, and MUST be confirmed by a DAO-ACK, which is sent
back to a global address of the Root. back to a global address of the Root.
A P-DAO message MUST contain exactly one RTO and either one VIO or A P-DAO message MUST contain exactly one RTO and either one VIO or
one or more SRVIOs following it. There can be at most one such one or more SRVIOs following it. There can be at most one such
skipping to change at page 15, line 25 skipping to change at page 16, line 34
the RPL specification [RPL]; this is determined using the Segment the RPL specification [RPL]; this is determined using the Segment
Sequence information from the RPO as opposed to the Path Sequence Sequence information from the RPO as opposed to the Path Sequence
from a TIO. Also, a Segment Lifetime of 0 in an RPO indicates that from a TIO. Also, a Segment Lifetime of 0 in an RPO indicates that
the projected route associated to the Segment is to be removed. the projected route associated to the Segment is to be removed.
There are two kinds of operation for the Projected Routes, the There are two kinds of operation for the Projected Routes, the
Storing Mode and the Non-Storing Mode. Storing Mode and the Non-Storing Mode.
* The Non-Storing Mode is discussed in Section 6.3. It uses an * The Non-Storing Mode is discussed in Section 6.3. It uses an
SRVIO that carries a list of Via Addresses to be used as a source- SRVIO that carries a list of Via Addresses to be used as a source-
routed path to the Target. The recipient of the P-DAO is the routed Segment to the Track Egress. The recipient of the P-DAO is
ingress router of the source-routed path. Upon a Non-Storing Mode the ingress router of the source-routed Segment. Upon a Non-
P-DAO, the ingress router installs a source-routed state to the Storing Mode P-DAO, the ingress router installs a source-routed
Target and replies to the Root directly with a DAO-ACK message. state to the Track Egress and replies to the Root directly with a
DAO-ACK message.
* The Storing Mode is discussed in Section 6.4. It uses a VIO with * The Storing Mode is discussed in Section 6.4. It uses a single
one Via Address per consecutive hop, from the ingress to the VIO, within which are signaled one Via Address per consecutive
egress of the path, including the list of all intermediate routers hop, from the ingress to the egress of the path, including the
in the data path order. The Via Addresses indicate the routers in list of all intermediate routers in the data path order. The Via
which the routing state to the Target have to be installed via the Addresses indicate the routers in which the routing state to the
next Via Address in the VIO. In normal operations, the P-DAO is Track Egress have to be installed via the next Via Address in the
propagated along the chain of Via Routers from the egress router VIO. In normal operations, the P-DAO is propagated along the
of the path till the ingress one, which confirms the installation chain of Via Routers from the egress router of the path till the
to the Root with a DAO-ACK message. Note that the Root may be the ingress one, which confirms the installation to the Root with a
ingress and it may be the egress of the path, that it can also be DAO-ACK message. Note that the Root may be the ingress and it may
neither but it cannot be both. be the egress of the path, that it can also be neither but it
cannot be both.
In case of a forwarding error along a Projected Route, an ICMP error In case of a forwarding error along a Projected Route, an ICMP error
is sent to the Root with a new Code "Error in Projected Route" (See is sent to the Root with a new Code "Error in Projected Route" (See
Section 8.9). The Root can then modify or remove the Projected Section 8.9). The Root can then modify or remove the Projected
Route. The "Error in Projected Route" message has the same format as Route. The "Error in Projected Route" message has the same format as
the "Destination Unreachable Message", as specified in RFC 4443 the "Destination Unreachable Message", as specified in RFC 4443
[RFC4443]. The portion of the invoking packet that is sent back in [RFC4443]. The portion of the invoking packet that is sent back in
the ICMP message SHOULD record at least up to the routing header if the ICMP message SHOULD record at least up to the routing header if
one is present, and the routing header SHOULD be consumed by this one is present, and the routing header SHOULD be consumed by this
node so that the destination in the IPv6 header is the next hop that node so that the destination in the IPv6 header is the next hop that
skipping to change at page 16, line 36 skipping to change at page 17, line 46
Track is not renewed. Track is not renewed.
The Root is free to install which ever Segments it wants, and change The Root is free to install which ever Segments it wants, and change
them overtime, to serve the Track as needed, without notifying the them overtime, to serve the Track as needed, without notifying the
resquesting Node. If the Track fails and cannot be reestablished, resquesting Node. If the Track fails and cannot be reestablished,
the Root notifies the resquesting Node asynchronously with a PDR-ACK the Root notifies the resquesting Node asynchronously with a PDR-ACK
with a Track Lifetime of 0, indicating that the Track has failed, and with a Track Lifetime of 0, indicating that the Track has failed, and
a PDR-ACK Status indicating the reason of the fault. a PDR-ACK Status indicating the reason of the fault.
All the Segments MUST be of a same mode, either Storing or Non- All the Segments MUST be of a same mode, either Storing or Non-
Storing. All the Segments MUST be created with the same TrackId and Storing. All the Segments MUST be created with the same TrackID and
Target in the P-DAO. Track Egress in the P-DAO.
6.2. Routing over a Track 6.2. Routing over a Track
Sending a packet over a Track implies the addition of a RPI to Sending a packet over a Track implies the addition of a RPI to
indicate the Track, in association with the IPv6 destination. In indicate the Track, in association with the IPv6 destination. In
case of a Non-Storing Mode Projected Route, a Source Routing Header case of a Non-Storing Mode Projected Route, a Source Routing Header
is needed as well. is needed as well.
The Destination IPv6 Address of a packet that is place in a Track The Destination IPv6 Address of a packet that is placed in a Track
MUST be that of the Target of Track. The outer header of the packet MUST be that of the Track Egress of Track. The outer header of the
MUST contain an RPI that indicates the TrackId as RPL Instance ID. packet MUST contain an RPI that indicates the TrackID as RPL Instance
ID.
If the Track Ingress is the originator of the packet and the Track If the Track Ingress is the originator of the packet and the Track
Egress (i.e., the Target) is the destination of the packet, there is Egress is the destination of the packet, there is no need for an
no need of an encapsulation. Else, i.e., if the Track Ingress is encapsulation. Else, i.e., if the Track Ingress is forwarding a
forwarding a packet into the Track, or if the the final destination packet into the Track, or if the the final destination is reached via
is reached via is not the Target, but reached over the Track via the is not the Track Egress, but reached over the Track via the Track
Track Egress, then an IP-in-IP encapsulation is needed. Egress, then an IP-in-IP encapsulation is needed.
6.3. Non-Storing Mode Projected Route 6.3. Non-Storing Mode Projected Route
As illustrated in Figure 6, a P-DAO that carries an SRVIO enables the As illustrated in Figure 7, a P-DAO that carries an SRVIO enables the
Root to install a source-routed path towards a Target in any Root to install a source-routed path towards a Track Egress in any
particular router; with this path information the router can add a particular router; with this path information the router can add a
source routed header reflecting the Projected Route to any packet for source routed header reflecting the Projected Route to any packet for
which the current destination either is the said Target or can be which the current destination either is the said Track Egress or can
reached via the Target. be reached via the Track Egress.
------+--------- ------+---------
| Internet | Internet
| |
+-----+ +-----+
| | Border Router | | Border Router
| | (RPL Root) | | (RPL Root)
+-----+ | P ^ | +-----+ | P ^ |
| | DAO | ACK | Loose | | DAO | ACK | Loose
o o o o router V | | Source o o o o router V | | Source
o o o o o o o o o | P-DAO . Route o o o o o o o o o | P-DAO . Route
o o o o o o o o o o | Source . Path o o o o o o o o o o | Source . Path
o o o o o o o o o | Route . From o o o o o o o o o | Route . From
o o o o o o o o | Path . Root o o o o o o o o | Path . Root
o o o o o Target V . To o o o o o Track Egress V . To
o o o o | Desti- o o o o | Desti-
o o o o | nation o o o o | nation
destination V destination V
LLN LLN
Figure 6: Projecting a Non-Storing Route Figure 7: Projecting a Non-Storing Route
A route indicated by an SRVIO may be loose, meaning that the node A route indicated by an SRVIO may be loose, meaning that the node
that owns the next listed Via Address is not necessarily a neighbor. that owns the next listed Via Address is not necessarily a neighbor.
Without proper loop avoidance mechanisms, the interaction of loose Without proper loop avoidance mechanisms, the interaction of loose
source routing and other mechanisms may effectively cause loops. In source routing and other mechanisms may effectively cause loops. In
order to avoid those loops, if the router that installs a Projected order to avoid those loops, if the router that installs a Projected
Route does not have a connected route (a direct adjacency) to the Route does not have a connected route (a direct adjacency) to the
next soure routed hop and fails to locate it as a neighbor or a next soure routed hop and fails to locate it as a neighbor or a
neighbor of a neighbor, then it MUST ensure that it has another neighbor of a neighbor, then it MUST ensure that it has another
Projected Route to the next loose hop under the control of the same Projected Route to the next loose hop under the control of the same
route computation system, otherwise the P-DAO is rejected. route computation system, otherwise the P-DAO is rejected.
When forwarding a packet to a destination for which the router When forwarding a packet to a destination for which the router
determines that routing happens via the Target, the router inserts determines that routing happens via the Track Egress, the router
the source routing header in the packet to reach the Target. In inserts the source routing header in the packet with the destination
order to add a source-routing header, the router encapsulates the set to the Track Egress. In order to add a source-routing header,
packet with an IP-in-IP header and a Non-Storing Mode source routing the router encapsulates the packet with an IP-in-IP header and a Non-
header (SRH) [RFC6554]. In the uncompressed form the source of the Storing Mode source routing header (SRH) [RFC6554]. In the
packet would be self, the destination would be the first Via Address uncompressed form the source of the packet would be self, the
in the SRVIO, and the SRH would contain the list of the remaining Via destination would be the first Via Address in the SRVIO, and the SRH
Addresses and then the Target. would contain the list of the remaining Via Addresses and then the
Track Egress.
In the case of a loose source-routed path, there MUST be either a In the case of a loose source-routed path, there MUST be either a
neighbor that is adjacent to the loose next hop, on which case the neighbor that is adjacent to the loose next hop, on which case the
packet is forwarded to that neighbor, or a source-routed path to the packet is forwarded to that neighbor, or a source-routed path to the
loose next hop; in the latter case, another encapsulation takes place loose next hop; in the latter case, another encapsulation takes place
and the process possibly recurses; otherwise the packet is dropped. and the process possibly recurses; otherwise the packet is dropped.
In practice, the router will normally use the "IPv6 over Low-Power In practice, the router will normally use the "IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch" [RFC8025] Wireless Personal Area Network (6LoWPAN) Paging Dispatch" [RFC8025]
to compress the RPL artifacts as indicated in [RFC8138]. In that to compress the RPL artifacts as indicated in [RFC8138]. In that
case, the router indicates self as encapsulator in an IP-in-IP 6LoRH case, the router indicates self as encapsulator in an IP-in-IP 6LoRH
Header, and places the list of Via Addresses in the order of the VIO Header, and places the list of Via Addresses in the order of the
and then the Target in the SRH 6LoRH Header. SRVIO and then the Track Egress in the SRH 6LoRH Header.
In case of a forwarding error along a Source Route path, the node In case of a forwarding error along a Source Route path, the node
that fails to forward SHOULD send an ICMP error with a code "Error in that fails to forward SHOULD send an ICMP error with a code "Error in
Source Routing Header" back to the source of the packet, as described Source Routing Header" back to the source of the packet, as described
in section 11.2.2.3. of [RPL]. Upon this message, the encapsulating in section 11.2.2.3. of [RPL]. Upon this message, the encapsulating
node SHOULD stop using the source route path for a period of time and node SHOULD stop using the source route path for a period of time and
it SHOULD send an ICMP message with a Code "Error in Projected Route" it SHOULD send an ICMP message with a Code "Error in Projected Route"
to the Root. Failure to follow these steps may result in packet loss to the Root. Failure to follow these steps may result in packet loss
and wasted resources along the source route path that is broken. and wasted resources along the source route path that is broken.
6.4. Storing-Mode Projected Route 6.4. Storing Mode Projected Route
As illustrated in Figure 7, the Storing Mode route projection is used As illustrated in Figure 8, the Storing Mode route projection is used
by the Root to install a routing state towards a Target in the by the Root to install a routing state in the routers along a Segment
routers along a Segment between an ingress and an egress router; this between an Ingress and an Egress router this enables the routers to
enables the routers to forward along that Segment any packet for forward along that Segment any packet for which the next loose hop is
which the next loose hop is the said Target, for Instance a loose the Egress node, for instance a loose source routed packet for which
source routed packet for which the next loose hop is the Target, or a the next loose hop is the Egress node, or a packet for which the
packet for which the router has a routing state to the final router has a routing state to the final destination via the Egress
destination via the Target. node.
------+--------- ------+---------
| Internet | Internet
| |
+-----+ +-----+
| | Border Router | | Border Router
| | (RPL Root) | | (RPL Root)
+-----+ | ^ | +-----+ | ^ |
| | DAO | ACK | | | DAO | ACK |
o o o o | | | o o o o | | |
o o o o o o o o o | ^ | Projected . o o o o o o o o o | ^ | Projected .
o o o o o o o o o o | | DAO | Route . o o o o o o o o o o | | DAO | Route .
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 v | DAO v . o o o o o o o o v | DAO v .
o o LLN o o o | o o LLN o o o |
o o o o o Loose Source Route Path | o o o o o Loose Source Route Path |
o o o o From Root To Destination v o o o o From Root To Destination v
Figure 7: Projecting a route Figure 8: Projecting a route
In order to install the relevant routing state along the Segment In order to install the relevant routing state along the Segment
between an ingress and an egress routers, the Root sends a unicast between an ingress and an egress routers, the Root sends a unicast
P-DAO message to the egress router of the routing Segment that must P-DAO message to the egress router of the routing Segment that must
be installed. The P-DAO message contains the ordered list of hops be installed. The P-DAO message contains the ordered list of hops
along the Segment as a direct sequence of Via Information options along the Segment as a direct sequence of Via Information options
that are preceded by one or more RPL Target options to which they that are preceded by one or more RPL Target options to which they
relate. Each Via Information option contains a Segment Lifetime for relate. Each Via Information option contains a Segment Lifetime for
which the state is to be maintained. which the state is to be maintained.
The Root sends the P-DAO directly to the egress node of the Segment. The Root sends the P-DAO directly to the egress node of the Segment.
In that P-DAO, the destination IP address matches the Via Address in In that P-DAO, the destination IP address matches the last Via
the last VIO. This is how the egress recognizes its role. In a Address in the VIO. This is how the egress recognizes its role. In
similar fashion, the ingress node recognizes its role as it matches a similar fashion, the ingress node recognizes its role as it matches
Via Address in the first VIO. first Via Address in the VIO.
The egress node of the Segment is the only node in the path that does The Egress node of the Segment is the only node in the path that does
not install a route in response to the P-DAO; it is expected to be not install a route in response to the P-DAO; it is expected to be
already able to route to the Target(s) on its own. It may either be already able to route to the Target(s) on its own. It may either be
the Target, or may have some existing information to reach the the Target, or may have some existing information to reach the
Target(s), such as a connected route or an already installed Target(s), such as a connected route or an already installed
Projected Route. If one of the Targets cannot be located, the node Projected Route. If one of the Targets cannot be located, the node
MUST answer to the Root with a negative DAO-ACK listing the Target(s) MUST answer to the Root with a negative DAO-ACK listing the Target(s)
that could not be located (suggested status 10 to be confirmed by that could not be located (suggested status 10 to be confirmed by
IANA). IANA).
If the egress node can reach all the Targets, then it forwards the If the egress node can reach all the Targets, then it forwards the
skipping to change at page 20, line 19 skipping to change at page 21, line 25
indicated in the P-DAO, but in the reverse order, from egress to indicated in the P-DAO, but in the reverse order, from egress to
ingress. ingress.
The address of the predecessor to be used as destination of the The address of the predecessor to be used as destination of the
propagated DAO message is found in the Via Information option the propagated DAO message is found in the Via Information option the
precedes the one that contain the address of the propagating node, precedes the one that contain the address of the propagating node,
which is used as source of the packet. which is used as source of the packet.
Upon receiving a propagated DAO, an intermediate router as well as Upon receiving a propagated DAO, an intermediate router as well as
the ingress router install a route towards the DAO Target(s) via its the ingress router install a route towards the DAO Target(s) via its
successor in the P-DAO; the router locates the VIO that contains its successor in the P-DAO; the router locates its address in the VIO,
address, and uses as next hop the address found in the Via Address and uses as next hop the address found in the previous Via Address
field in the following VIO. The router MAY install additional routes field in the VIO. The router MAY install additional routes towards
towards the addresses that are located in VIOs that are after the the VIA Addresses that are the VIO after the next one, if any, but in
next one, if any, but in case of a conflict or a lack of resource, a case of a conflict or a lack of resource, the route(s) to the
route to a Target installed by the Root has precedence. Target(s) have precedence.
The process recurses till the P-DAO is propagated to ingress router The process recurses till the P-DAO is propagated to ingress router
of the Segment, which answers with a DAO-ACK to the Root. of the Segment, which answers with a DAO-ACK to the Root.
Also, the path indicated in a P-DAO may be loose, in which case the Also, the path indicated in a P-DAO may be loose, in which case the
reachability to the next hop has to be asserted. Each router along reachability to the next hop has to be asserted. Each router along
the path indicated in a P-DAO is expected to be able to reach its the path indicated in a P-DAO is expected to be able to reach its
successor, either with a connected route (direct neighbor), or by successor, either with a connected route (direct neighbor), or by
routing, for Instance following a route installed previously by a DAO routing, for Instance following a route installed previously by a DAO
or a P-DAO message. If that route is not connected then a recursive or a P-DAO message. If that route is not connected then a recursive
skipping to change at page 27, line 4 skipping to change at page 28, line 6
Option Type, Routing Header for Source Routes and IPv6-in- Option Type, Routing Header for Source Routes and IPv6-in-
IPv6 encapsulation in the RPL Data Plane", Work in IPv6 encapsulation in the RPL Data Plane", Work in
Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-40, Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-40,
25 June 2020, <https://tools.ietf.org/html/draft-ietf- 25 June 2020, <https://tools.ietf.org/html/draft-ietf-
roll-useofrplinfo-40>. roll-useofrplinfo-40>.
[PCE] IETF, "Path Computation Element", [PCE] IETF, "Path Computation Element",
<https://datatracker.ietf.org/doc/charter-ietf-pce/>. <https://datatracker.ietf.org/doc/charter-ietf-pce/>.
Appendix A. Applications Appendix A. Applications
A.1. Loose Source Routing A.1. Loose Source Routing
A RPL implementation operating in a very constrained LLN typically A RPL implementation operating in a very constrained LLN typically
uses the Non-Storing Mode of Operation as represented in Figure 8. uses the Non-Storing Mode of Operation as represented in Figure 9.
In that mode, a RPL node indicates a parent-child relationship to the In that mode, a RPL node indicates a parent-child relationship to the
Root, using a Destination Advertisement Object (DAO) that is unicast Root, using a Destination Advertisement Object (DAO) that is unicast
from the node directly to the Root, and the Root typically builds a from the node directly to the Root, and the Root typically builds a
source routed path to a destination down the DODAG by recursively source routed path to a destination down the DODAG by recursively
concatenating this information. concatenating this information.
------+--------- ------+---------
| Internet | Internet
| |
+-----+ +-----+
skipping to change at page 27, line 30 skipping to change at page 28, line 33
+-----+ ^ | | +-----+ ^ | |
| | DAO | ACK | | | DAO | ACK |
o o o o | | | Strict o o o o | | | Strict
o o o o o o o o o | | | Source 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 | | | Route
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 | v v o o o o o o o o | v v
o o o o o o o o
LLN LLN
Figure 8: RPL Non-Storing Mode of operation Figure 9: RPL Non-Storing Mode of operation
Based on the parent-children relationships expressed in the non- Based on the parent-children relationships expressed in the non-
storing DAO messages,the Root possesses topological information about storing DAO messages,the Root possesses topological information about
the whole network, though this information is limited to the the whole network, though this information is limited to the
structure of the DODAG for which it is the destination. A packet structure of the DODAG for which it is the destination. A packet
that is generated within the domain will always reach the Root, which that is generated within the domain will always reach the Root, which
can then apply a source routing information to reach the destination can then apply a source routing information to reach the destination
if the destination is also in the DODAG. Similarly, a packet coming 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 from the outside of the domain for a destination that is expected to
be in a RPL domain reaches the Root. be in a RPL domain reaches the Root.
skipping to change at page 28, line 36 skipping to change at page 29, line 36
effectively become loose. effectively become loose.
A.2. Transversal Routes A.2. Transversal Routes
RPL is optimized for Point-to-Multipoint (P2MP) and Multipoint-to- RPL is optimized for Point-to-Multipoint (P2MP) and Multipoint-to-
Point (MP2P), whereby routes are always installed along the RPL DODAG Point (MP2P), whereby routes are always installed along the RPL DODAG
respectively from and towards the DODAG Root. Transversal Peer to respectively from and towards the DODAG Root. Transversal Peer to
Peer (P2P) routes in a RPL network will generally suffer from some Peer (P2P) routes in a RPL network will generally suffer from some
elongated (stretched) path versus the best possible path, since elongated (stretched) path versus the best possible path, since
routing between 2 nodes always happens via a common parent, as routing between 2 nodes always happens via a common parent, as
illustrated in Figure 9: illustrated in Figure 10:
* In Storing Mode, unless the destination is a child of the source, * In Storing Mode, unless the destination is a child of the source,
the packets will follow the default route up the DODAG as well. the packets will follow the default route up the DODAG as well.
If the destination is in the same DODAG, they will eventually If the destination is in the same DODAG, they will eventually
reach a common parent that has a route to the destination; at reach a common parent that has a route to the destination; at
worse, the common parent may also be the Root. From that common worse, the common parent may also be the Root. From that common
parent, the packet will follow a path down the DODAG that is parent, the packet will follow a path down the DODAG that is
optimized for the Objective Function that was used to build the optimized for the Objective Function that was used to build the
DODAG. DODAG.
skipping to change at page 29, line 29 skipping to change at page 30, line 29
+-----+ +-----+
X X
^ v o o ^ v o o
^ o o v o o o o o ^ o o v o o o o 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 ^ o o v o o o o o
S o o o D o o o S o o o D o o o
o o o o o o o o
LLN LLN
Figure 9: Routing Stretch between S and D via common parent X Figure 10: Routing Stretch between S and D via common parent X
It results that it is often beneficial to enable transversal P2P It results that it is often beneficial to enable transversal P2P
routes, either if the RPL route presents a stretch from shortest routes, either if the RPL route presents a stretch from shortest
path, or if the new route is engineered with a different objective, path, or if the new route is engineered with a different objective,
and that it is even more critical in Non-Storing Mode than it is in and that it is even more critical in Non-Storing Mode than it is in
Storing Mode, because the routing stretch is wider. For that reason, Storing Mode, because the routing stretch is wider. For that reason,
earlier work at the IETF introduced the "Reactive Discovery of earlier work at the IETF introduced the "Reactive Discovery of
Point-to-Point Routes in Low Power and Lossy Networks" [RFC6997], Point-to-Point Routes in Low Power and Lossy Networks" [RFC6997],
which specifies a distributed method for establishing optimized P2P which specifies a distributed method for establishing optimized P2P
routes. This draft proposes an alternate based on a centralized routes. This draft proposes an alternate based on a centralized
skipping to change at page 30, line 21 skipping to change at page 31, line 21
+-----+ +-----+
| |
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 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 S>>A>>>B>>C>>>D o o o
o o o o o o o o
LLN LLN
Figure 10: Projected Transversal Route Figure 11: Projected Transversal Route
This specification enables to store source-routed or Storing Mode This specification enables to store source-routed or Storing Mode
state in intermediate routers, which enables to limit the stretch of state in intermediate routers, which enables to limit the stretch of
a P2P route and maintain the characteristics within a given SLA. An a P2P route and maintain the characteristics within a given SLA. An
example of service using this mechanism oculd be a control loop that example of service using this mechanism oculd be a control loop that
would be installed in a network that uses classical RPL for would be installed in a network that uses classical RPL for
asynchronous data collection. In that case, the P2P path may be asynchronous data collection. In that case, the P2P path may be
installed in a different RPL Instance, with a different objective installed in a different RPL Instance, with a different objective
function. function.
Appendix B. Examples Appendix B. Examples
B.1. Using Storing Mode P-DAO in Non-Storing Mode MOP B.1. Using Storing Mode P-DAO in Non-Storing Mode MOP
In Non-Storing Mode, the DAG Root maintains the knowledge of the In Non-Storing Mode, the DAG Root maintains the knowledge of the
whole DODAG topology, so when both the source and the destination of whole DODAG topology, so when both the source and the destination of
a packet are in the DODAG, the Root can determine the common parent a packet are in the DODAG, the Root can determine the common parent
that would have been used in Storing Mode, and thus the list of nodes that would have been used in Storing Mode, and thus the list of nodes
in the path between the common parent and the destination. For in the path between the common parent and the destination. For
Instance in the diagram shown in Figure 11, if the source is node 41 Instance in the diagram shown in Figure 12, if the source is node 41
and the destination is node 52, then the common parent is node 22. and the destination is node 52, then the common parent is node 22.
------+--------- ------+---------
| Internet | Internet
| |
+-----+ +-----+
| | Border Router | | Border Router
| | (RPL Root) | | (RPL Root)
+-----+ +-----+
| \ \____ | \ \____
skipping to change at page 31, line 26 skipping to change at page 32, line 26
o 22 o 23 o 24 o 25 o 22 o 23 o 24 o 25
/ \ | \ \ / \ | \ \
o 31 o 32 o o o 35 o 31 o 32 o o o 35
/ / | \ | \ / / | \ | \
o 41 o 42 o o o 45 o 46 o 41 o 42 o o o 45 o 46
| | | | \ | | | | | \ |
o 51 o 52 o 53 o o 55 o 56 o 51 o 52 o 53 o o 55 o 56
LLN LLN
Figure 11: Example DODAG forming a logical tree topology Figure 12: Example DODAG forming a logical tree topology
With this draft, the Root can install a Storing Mode routing states With this draft, the Root can install a Storing Mode routing states
along a Segment that is either from itself to the destination, or along a Segment that is either from itself to the destination, or
from one or more common parents for a particular source/destination from one or more common parents for a particular source/destination
pair towards that destination (in this particular example, this would pair towards that destination (in this particular example, this would
be the Segment made of nodes 22, 32, 42). be the Segment made of nodes 22, 32, 42).
In the example below, say that there is a lot of traffic to nodes 55 In the example below, say that there is a lot of traffic to nodes 55
and 56 and the Root decides to reduce the size of routing headers to and 56 and the Root decides to reduce the size of routing headers to
those destinations. The Root can first send a DAO to node 45 those destinations. The Root can first send a DAO to node 45
skipping to change at page 31, line 48 skipping to change at page 32, line 48
DAO to node 46 indicating Target 56 and a Via Segment (35, 46). This DAO to node 46 indicating Target 56 and a Via Segment (35, 46). This
will save one entry in the routing header on both sides. The Root will save one entry in the routing header on both sides. The Root
may then send a DAO to node 35 indicating Targets 55 and 56 a Via may then send a DAO to node 35 indicating Targets 55 and 56 a Via
Segment (13, 24, 35) to fully optimize that path. Segment (13, 24, 35) to fully optimize that path.
Alternatively, the Root may send a DAO to node 45 indicating Target Alternatively, the Root may send a DAO to node 45 indicating Target
55 and a Via Segment (13, 24, 35, 45) and then a DAO to node 46 55 and a Via Segment (13, 24, 35, 45) and then a DAO to node 46
indicating Target 56 and a Via Segment (13, 24, 35, 46), indicating indicating Target 56 and a Via Segment (13, 24, 35, 46), indicating
the same DAO Sequence. the same DAO Sequence.
B.2. Projecting a storing-mode transversal route B.2. Projecting a Storing Mode transversal route
In this example, say that a PCE determines that a path must be In this example, say that a PCE determines that a path must be
installed between node S and node D via routers A, B and C, in order installed between node I and node D via routers A, B and E, in order
to serve the needs of a particular application. to serve the needs of a particular application.
The Root sends a P-DAO with a Target option indicating the The Root sends a P-DAO to node E, with an RTO indicating the
destination D and a sequence Via Information option, one for S, which destination D, a TIO optionally indicating the Track Egress in the
is the ingress router of the Segment, one for A and then for B, which Parent Address field, and a sequence of Via Information options
are an intermediate routers, and one for C, which is the egress indicating the hops, one for S, which is the ingress router of the
router. Segment, one for A, and then one for B, which are respectively the
intermediate and penultimate routers.
------+--------- ------+---------
| Internet | Internet
| |
+-----+ +-----+
| | Border Router | | Border Router
| | (RPL Root) | | (RPL Root)
+-----+ +-----+
| P-DAO message to C | P-DAO message to C
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 o o | o o o o o o
o o V o o o o o o o o V o o o o o o
S A B C D o o o S A B E D o o o
o o o o o o o o
LLN LLN
Figure 12: P-DAO from Root Figure 13: P-DAO from Root
Upon reception of the P-DAO, C validates that it can reach D, e.g. Upon reception of the P-DAO, C validates that it can reach D, e.g.
using IPv6 Neighbor Discovery, and if so, propagates the P-DAO using IPv6 Neighbor Discovery, and if so, propagates the P-DAO
unchanged to B. unchanged to B.
B checks that it can reach C and of so, installs a route towards D B checks that it can reach C and of so, installs a route towards D
via C. Then it propagates the P-DAO to A. via C. Then it propagates the P-DAO to A.
The process recurses till the P-DAO reaches S, the ingress of the The process recurses till the P-DAO reaches S, the ingress of the
Segment, which installs a route to D via A and sends a DAO-ACK to the Segment, which installs a route to D via A and sends a DAO-ACK to the
skipping to change at page 33, line 21 skipping to change at page 34, line 21
+-----+ +-----+
^ P-DAO-ACK from S ^ P-DAO-ACK from S
/ 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 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 S A B C D o o o
o o o o o o o o
LLN LLN
Figure 13: P-DAO-ACK to Root Figure 14: P-DAO-ACK to Root
As a result, a transversal route is installed that does not need to As a result, a transversal route is installed that does not need to
follow the DODAG structure. follow the DODAG structure.
------+--------- ------+---------
| Internet | Internet
| |
+-----+ +-----+
| | Border Router | | Border Router
| | (RPL Root) | | (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 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 S>>A>>>B>>C>>>D o o o
o o o o o o o o
LLN LLN
Figure 14: Projected Transversal Route Figure 15: Projected Transversal Route
Authors' Addresses Authors' Addresses
Pascal Thubert (editor) Pascal Thubert (editor)
Cisco Systems, Inc Cisco Systems, Inc
Building D Building D
45 Allee des Ormes - BP1200 45 Allee des Ormes - BP1200
06254 Mougins - Sophia Antipolis 06254 Mougins - Sophia Antipolis
France France
Phone: +33 497 23 26 34 Phone: +33 497 23 26 34
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