Root initiated routing state in RPL
draft-ietf-roll-dao-projection-21
ROLL P. Thubert, Ed.
Internet-Draft Cisco Systems
Intended status: Standards Track R.A. Jadhav
Expires: 31 March 2022 Huawei Tech
M. Gillmore
Itron
27 September 2021
Root initiated routing state in RPL
draft-ietf-roll-dao-projection-21
Abstract
This document extends RFC 6550, RFC 6553,and RFC 8138 to enable a RPL
Root to install and maintain Projected Routes within its DODAG, along
a selected set of nodes that may or may not include self, for a
chosen duration. This potentially enables routes that are more
optimized or resilient than those obtained with the classical
distributed operation of RPL, either in terms of the size of a
Routing Header or in terms of path length, which impacts both the
latency and the packet delivery ratio.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 31 March 2022.
Copyright Notice
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. References . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Domain Terms . . . . . . . . . . . . . . . . . . . . . . 5
3. Context and Goal . . . . . . . . . . . . . . . . . . . . . . 6
3.1. RPL Applicability . . . . . . . . . . . . . . . . . . . . 7
3.2. RPL Routing Modes . . . . . . . . . . . . . . . . . . . . 8
3.3. Requirements . . . . . . . . . . . . . . . . . . . . . . 9
3.3.1. Loose Source Routing . . . . . . . . . . . . . . . . 9
3.3.2. East-West Routes . . . . . . . . . . . . . . . . . . 10
3.4. On Tracks . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Serial Track Signaling . . . . . . . . . . . . . . . . . 13
3.5.1. Using Storing Mode Segments . . . . . . . . . . . . . 14
3.5.2. Using Non-Storing Mode joining Tracks . . . . . . . . 20
3.6. Complex Tracks . . . . . . . . . . . . . . . . . . . . . 27
3.7. Scope and Expectations . . . . . . . . . . . . . . . . . 29
4. Extending existing RFCs . . . . . . . . . . . . . . . . . . . 31
4.1. Extending RFC 6550 . . . . . . . . . . . . . . . . . . . 31
4.1.1. Projected DAO . . . . . . . . . . . . . . . . . . . . 31
4.1.2. Via Information Option . . . . . . . . . . . . . . . 33
4.1.3. Sibling Information Option . . . . . . . . . . . . . 33
4.1.4. P-DAO Request . . . . . . . . . . . . . . . . . . . . 33
4.1.5. Extending the RPI . . . . . . . . . . . . . . . . . . 33
4.2. Extending RFC 6553 . . . . . . . . . . . . . . . . . . . 34
4.3. Extending RFC 8138 . . . . . . . . . . . . . . . . . . . 35
5. New RPL Control Messages and Options . . . . . . . . . . . . 36
5.1. New P-DAO Request Control Message . . . . . . . . . . . . 36
5.2. New PDR-ACK Control Message . . . . . . . . . . . . . . . 37
5.3. Via Information Options . . . . . . . . . . . . . . . . . 39
5.4. Sibling Information Option . . . . . . . . . . . . . . . 42
6. Root Initiated Routing State . . . . . . . . . . . . . . . . 44
6.1. Requesting a Track . . . . . . . . . . . . . . . . . . . 44
6.2. Identifying a Track . . . . . . . . . . . . . . . . . . . 45
6.3. Installing a Track . . . . . . . . . . . . . . . . . . . 46
6.3.1. Signaling a Projected Route . . . . . . . . . . . . . 47
6.3.2. Installing a Track Segment with a Storing Mode
P-Route . . . . . . . . . . . . . . . . . . . . . . . 48
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6.3.3. Installing a Track Leg with a Non-Storing Mode
P-Route . . . . . . . . . . . . . . . . . . . . . . . 50
6.4. Tearing Down a P-Route . . . . . . . . . . . . . . . . . 52
6.5. Maintaining a Track . . . . . . . . . . . . . . . . . . . 52
6.5.1. Maintaining a Track Segment . . . . . . . . . . . . . 53
6.5.2. Maintaining a Track Leg . . . . . . . . . . . . . . . 53
6.6. Encapsulating and Forwarding Along a Track . . . . . . . 54
6.7. Compression of the RPL Artifacts . . . . . . . . . . . . 56
7. Lesser Constrained Variations . . . . . . . . . . . . . . . . 58
7.1. Storing Mode Main DODAG . . . . . . . . . . . . . . . . . 58
7.2. A Track as a Full DODAG . . . . . . . . . . . . . . . . . 60
8. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 61
9. Security Considerations . . . . . . . . . . . . . . . . . . . 63
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 63
10.1. New Elective 6LoWPAN Routing Header Type . . . . . . . . 64
10.2. New Critical 6LoWPAN Routing Header Type . . . . . . . . 64
10.3. New Subregistry For The RPL Option Flags . . . . . . . . 64
10.4. New RPL Control Codes . . . . . . . . . . . . . . . . . 65
10.5. New RPL Control Message Options . . . . . . . . . . . . 65
10.6. SubRegistry for the Projected DAO Request Flags . . . . 66
10.7. SubRegistry for the PDR-ACK Flags . . . . . . . . . . . 66
10.8. Subregistry for the PDR-ACK Acceptance Status Values . . 66
10.9. Subregistry for the PDR-ACK Rejection Status Values . . 67
10.10. SubRegistry for the Via Information Options Flags . . . 67
10.11. SubRegistry for the Sibling Information Option Flags . . 68
10.12. New destination Advertisement Object Flag . . . . . . . 68
10.13. New ICMPv6 Error Code . . . . . . . . . . . . . . . . . 68
10.14. New RPL Rejection Status values . . . . . . . . . . . . 69
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 69
12. Normative References . . . . . . . . . . . . . . . . . . . . 69
13. Informative References . . . . . . . . . . . . . . . . . . . 71
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 73
1. Introduction
RPL, the "Routing Protocol for Low Power and Lossy Networks" [RPL]
(LLNs), is an anisotropic Distance Vector protocol that is well-
suited for application in a variety of low energy Internet of Things
(IoT) networks where stretched P2P paths are acceptable vs. the
signaling and state overhead involved in maintaining shortest paths
across.
RPL forms destination Oriented Directed Acyclic Graphs (DODAGs) in
which the Root often acts as the Border router to connect the RPL
domain to the IP backbone and routes along that graph up, towards the
Root, and down towards the nodes.
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With this specification, a Path Computation Element [PCE] in an
external controller interacts with the RPL Root to compute centrally
shorter Peer to Peer (P2P) paths within a pre-existing RPL Main
DODAG. The topological information that is passed to the PCE is
derived from the DODAG that is already available at the Root in RPL
Non-Storing Mode. This specification introduces protocol extensions
that enrich the topological information that is available at the Root
and passed to the PCE.
Based on usage, path length, and knowledge of available resources
such as battery levels and reservable buffers in the nodes, the PCE
with a global visibility on the system can optimize the computed
routes for the application needs, including the capability to provide
path redundancy. This specification also introduces protocol
extensions that enable the Root to translates the computed paths into
RPL and install them as Projected Routes (aka P-Routes) inside the
DODAG on behalf of a PCE.
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.
2.2. References
In this document, readers will encounter terms and concepts that are
discussed in the "Routing Protocol for Low Power and Lossy Networks"
[RPL], the "6TiSCH Architecture" [6TiSCH-ARCHI], the "Deterministic
Networking Architecture" [RFC8655], the "Reliable and Available
Wireless (RAW) Architecture/Framework" [RAW-ARCHI], and "Terminology
in Low power And Lossy Networks" [RFC7102].
2.3. Glossary
This document often uses the following acronyms:
CMO: Control Message Option
DAO: destination Advertisement Object
DAG: Directed Acyclic Graph
DODAG: destination-Oriented Directed Acyclic Graph; A DAG with only
one vertex (i.e., node) that has no outgoing edge (i.e., link)
GUA: IPv6 Global Unicast Address
LLN: Low-Power and Lossy Network
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MOP: RPL Mode of Operation
P-DAO: Projected DAO
P-Route: Projected Route
PDR: P-DAO Request
RAN: RPL-Aware Node (either a RPL router or a RPL-Aware Leaf)
RAL: RPL-Aware Leaf
RH: Routing Header
RPI: RPL Packet Information
RTO: RPL Target Option
RUL: RPL-Unaware Leaf
SIO: RPL Sibling Information Option
ULA: IPv6 Unique Local Address
NSM-VIO: A Source-Routed Via Information Option, used in Non-Storing
Mode P-DAO messages.
SLO: Service Level Objective
TIO: RPL Transit Information Option
SM-VIO: A strict Via Information Option, used in Storing Mode P-DAO
messages.
VIO: A Via Information Option; it can be a SM-VIO or an NSM-VIO.
2.4. Domain Terms
Projected Route: A RPL P-Route is a RPL route that is computed
remotely by a PCE, and installed and maintained by a RPL Root on
behalf of the PCE. It is installed as a state that signals that
destinations (aka Targets) are reachable along a sequence of
nodes.
Projected DAO: A DAO message used to install a P-Route.
Path: Quoting section 1.1.3 of [INT-ARCHI]: "At a given moment, all
the IP datagrams from a particular source host to a particular
destination host will typically traverse the same sequence of
gateways. We use the term "path" for this sequence. Note that a
path is uni-directional; it is not unusual to have different paths
in the two directions between a given host pair.".
Section 2 of [I-D.irtf-panrg-path-properties] points to a longer,
more modern definition of path, which begins as follows: " A
sequence of adjacent path elements over which a packet can be
transmitted, starting and ending with a node. A path is
unidirectional. Paths are time-dependent, i.e., the sequence of
path elements over which packets are sent from one node to another
may change. A path is defined between two nodes. "
It follows that the general acceptance of a path is a linear
sequence of nodes, as opposed to a multi-dimensional graph. In
the context of this document, a path is observed by following one
copy of a packet that is injected in a Track and possibly
replicated within.
Track: A networking graph that can be followed to transport packets
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with equivalent treatment; as opposed to the definition of a path
above, a Track Track is not necessarily linear. It may contain
multiple paths that may fork and rejoin, and may enable the RAW
Packet ARQ, Replication, Elimination, and Overhearing (PAREO)
operations.
This specification builds Tracks that are DODAGs oriented towards
a Track Ingress, and the forward direction for packets is East-
West from the Track Ingress to one of the possibly multiple Track
Egress Nodes, which is also down the DODAG.
The Track may be strictly connected, meaning that the vertices are
adjacent, or loosely connected, meaning that the vertices are
connected using Segments that are associated to the same Track.
TrackID: A RPL Local InstanceID that identifies a Track using the
namespace owned ny the Track Ingress. The TrackID is associated
with the IPv6 Address of the Track Ingress that is used as
DODAGID, and together they form a unique identification of the
Track (see the definition of DODAGID in section 2 of [RPL].
Serial Track: A Track that has only one path.
Stand-Alone: A single P-DAO that fully defines a Track, e.g., a
Serial Track installed with a single Storing Mode Via Information
option (SM-VIO).
subTrack: A Track within a Track. As the Non-Storing Mode Via
Information option (NSM-VIO) can only signal a loose sequence of
nodes, it takes a number of them to signal a complex Track. Each
NSM-VIO for the same TrackId but a different Segment ID signals a
different subTracks that the Track Ingress adds to the topology.
Track Leg: An end-to-end East-West serial path that can be a Track
by itself or a subTrack of a complex Track. With this
specification, a Leg is is installed by the Root of the main DODAG
using Non-Storing Mode P-DAO messages, and it is expressed as a
loose sequence of nodes that are joined by Track Segments.
Track Segment: A serial path formed by a strict sequence of nodes,
along which a P-Route is installed. With this specification, a
Segment is typically installed by the Root of the main DODAG using
Storing Mode P-DAO messages. A Segment used as the topological
edge of a Track. Since this specification builds only DODAGs, all
Segments are oriented from Ingress (East) to Egress (West), as
opposed to the general RAW model, which allows North/South
Segments that can be bidirectional.
3. Context and Goal
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3.1. RPL Applicability
RPL is optimized for situations where the power is scarce, the
bandwidth constrained and the transmissions unreliable. This matches
the use case of an IoT LLN where RPL is typically used today, but
also situations of high relative mobility between the nodes in the
network (aka swarming), e.g., within a variable set of vehicles with
a similar global motion, or a toon of drones.
To reach this goal, RPL is primarily designed to minimize the control
plane activity, that is the relative amount of routing protocol
exchanges vs. data traffic, and the amount of state that is
maintained in each node. RPL does not need converge, and provides
connectivity to most nodes most of the time.
RPL may form multiple topologies called instances. Instances can be
created to enforce various optimizations through objective functions,
or to reach out through different Root Nodes. The concept of
objective function allows to adapt the activity of the routing
protocol to the use case, e.g., type, speed, and quality of the LLN
links.
RPL instances operate as ships in the night, unbeknownst of one
another. The RPL Root is responsible to select the RPL Instance that
is used to forward a packet coming from the Backbone into the RPL
domain and set the related RPL information in the packets. 6TiSCH
leverages RPL for its distributed routing operations.
To reduce the routing exchanges, RPL leverages an anisotropic
Distance Vector approach, which does not need a global knowledge of
the topology, and only optimizes the routes to and from the RPL Root,
allowing P2P paths to be stretched. Although RPL installs its routes
proactively, it only maintains them lazily, in reaction to actual
traffic, or as a slow background activity.
This is simple and efficient in situations where the traffic is
mostly directed from or to a central node, such as the control
traffic between routers and a controller of a Software Defined
Networking (SDN) infrastructure or an Autonomic Control Plane (ACP).
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 [USE-CASES], which demand high availability
and reliability, and as a consequence require both short and diverse
paths.
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3.2. RPL Routing Modes
RPL first forms a default route in each node towards the a Root, and
those routes together coalesce as a Directed Acyclic Graph upwards.
RPL then constructs routes to so-called Targets in the reverse
direction, down the same DODAG. So do so, a RPL Instance can be
operated either in RPL Storing or Non-Storing Mode of Operation (MOP)
The default route towards the Root is maintained aggressively and may
change while a packet progresses without causing loops, so the packet
will still reach the Root.
In Non-Storing Mode, each node advertises itself as a Target directly
to the Root, indicating the parents that may be used to reach self.
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
single unicast packet to the Root along the default route to update
it, and the connectivity is restored immediately; this mode is
preferable for use cases where internet connectivity is dominant, or
when, like here, the Root controls the network activity in the nodes.
In Storing Mode, the routing information percolates upwards, and each
node maintains the routes to the subDAG of its descendants down the
DODAG. The maintenance is lazy, either reactive upon traffic or as a
slow background process. Packets flow via the common parent and the
routing stretch is reduced vs. Non-Storing, for a better P2P
connectivity, while the internet connectivity is restored more
slowly, time for the DV operation to operate hop-by-hop.
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 an 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.
A P-Route may be installed in either Storing and Non-Storing Mode,
potentially resulting in hybrid situations where the Mode of the P-
Route is different from that of the RPL Main DODAG. P-Routes can be
used as stand-alone segments to reduce the size of the source routing
headers with loose source routing operations down the main RPL DODAG.
P-Routes can also be combined with other P-Routes to form a more
complex forwarding graph called a Track.
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3.3. Requirements
3.3.1. Loose Source Routing
A RPL implementation operating in a very constrained LLN typically
uses the Non-Storing Mode of Operation as represented in Figure 1.
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 1: RPL Non-Storing Mode of operation
Based on the parent-children relationships expressed in the Non-
Storing DAO messages,the Root possesses topological information about
the whole network, though this information is limited to the
structure of the DODAG for which it is the destination. A packet
that is generated within the domain will always reach the Root, which
can then apply a source routing information to reach the destination
if the destination is also in the DODAG. Similarly, a packet coming
from the outside of the domain for a destination that is expected to
be in a RPL domain reaches the Root.
It results that the Root, or then some associated centralized
computation engine such as a PCE, can determine the amount of packets
that reach a destination in the RPL domain, and thus the amount of
energy and bandwidth that is wasted for transmission, between itself
and the destination, as well as the risk of fragmentation, any
potential delays because of a paths longer than necessary (shorter
paths exist that would not traverse the Root).
As a network gets deep, the size of the source routing header that
the Root must add to all the downward packets becomes an issue for
nodes that are many hops away. In some use cases, a RPL network
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forms long lines and a limited amount of well-targeted routing state
would allow to make the source routing operation loose as opposed to
strict, and save packet size. Limiting the packet size is directly
beneficial to the energy budget, but, mostly, it reduces the chances
of frame loss and/or packet fragmentation, which is highly
detrimental to the LLN operation. Because the capability to store a
routing state in every node is limited, the decision of which route
is installed where can only be optimized with a global knowledge of
the system, a knowledge that the Root or an associated PCE may
possess by means that are outside of the scope of this specification.
This requirement is to store a routing state associated with the Main
DODAG in selected RPL routers, to limit the excursion of the source
route headers in deep networks. The Root may elide the sequence of
routers that is installed in the network from its source route
header, which becomes loose while it is strict in [RPL].
3.3.2. East-West Routes
RPL is optimized for INternet access, with Point-to-Multipoint (P2MP)
and Multipoint-to-Point (MP2P), whereby routes are always installed
North-South (aka up/down) along the RPL DODAG respectively from and
towards the Border Router that also serves as DODAG Root. Peer to
Peer (P2P) East-West routes in a RPL network will generally suffer
from some elongated (stretched) path versus a direct (optimized)
path, since routing between two nodes always happens via a common
parent, as illustrated in Figure 2:
------+---------
| 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 2: Routing Stretch between S and D via common parent X
along North-South Paths
The amount of stretch depends on the Mode of Operation:
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* in Non-Storing Mode, all packets routed within the DODAG flow all
the way up to the Root of the DODAG. If the destination is in the
same DODAG, the Root must encapsulate the packet to place an RH
that has the strict source route information down the DODAG to the
destination. This will be the case even if the destination is
relatively close to the source and the Root is relatively far off.
* In Storing Mode, unless the destination is a child of the source,
the packets will follow the default route up the DODAG as well.
If the destination is in the same DODAG, they will eventually
reach a common parent that has a route to the destination; at
worse, the common parent may also be the Root. From that common
parent, the packet will follow a path down the DODAG that is
optimized for the Objective Function that was used to build the
DODAG.
It results that it is often beneficial to enable East-West P2P
routes, either if the RPL route presents a stretch from shortest
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
Storing Mode, because the routing stretch is wider. For that reason,
earlier work at the IETF introduced the "Reactive Discovery of
Point-to-Point Routes in Low Power and Lossy Networks" [RFC6997],
which specifies a distributed method for establishing optimized P2P
routes. This draft proposes an alternate based on a 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 3: More direct East-West Route between S and D
The requirement is to install additional routes in the RPL routers,
to reduce the stretch of some P2P routes and maintain the
characteristics within a given SLO, e.g., in terms of latency and/or
reliability.
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3.4. On Tracks
A Track is typically a collection of parallel loose source routed
sequences of nodes from Ingress to Egress, forming so-called Track
Legs, that are joined with strict Segments of other nodes. The Legs
are expressed in RPL Non-Storing Modes and require an encapsulation
to add a Source Route Header, whereas the Segments are expressed in
Storing Mode.
A Serial Track comprises provides only one path between Ingress and
Egress. It comprises at most one Leg. A Stand-Alone Segment defines
implicitly a Serial Track from its Ingress to Egress.
A complex Track forms a graph that provides a collection of potential
paths to provide redundancy for the packets, either as a collection
of Legs that may be parallel or cross at certain points, or as a more
generic DODAG.
The concept of a Track was introduced in the "6TiSCH Architecture"
[6TiSCH-ARCHI], as a collection of potential paths that leverage
redundant forwarding solutions along the way. With this
specification, a Track forms DODAG that is directed towards a Track
Ingress. If there is a single Track Egress, then the Track is
reversible to form another DODAG by reversing the direction of each
edge. A node at the Ingress of more than one Segment in a Track may
use one or more of these Segments to forward a packet inside the
Track.
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.
A Track is normally associated with a Local RPL Instance which
RPLInstanceID is used as the TrackID, more in Section 6.2. A Track
Leg may also be used as a subTrack that extends the RPL main DODAG.
In that case, the TrackID is set to the global RPLInstanceID of the
main DODAG, which suffices to identify the routing topology. As
opposed to local RPL instances, the Track Ingress that encapsulates
the packets over a subtrack is not Root, and that the source address
of the encapsulated packet is not used to determine the Track.
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3.5. Serial Track Signaling
This specification enables to set up a P-Route along either a Track
Leg or a Segment. A P-Route is installed and maintained using an
extended RPL DAO message called a Projected DAO (P-DAO), and a Track
is composed of the combination of one or more P-Routes.
A P-DAO message for a Track signals the TrackID in the RPLInstanceID
field. In the case of a local RPL Instance, the address of the Track
Ingress is used as source to encapsulated packets along the Track is
signaled in the DODAGID field of the Projected DAO Base Object, see
Figure 6.
This specification introduces the Via Information Option (VIO) to
signal a sequence of hops in a Leg or a Segment in the P-DAO
messages, either in Storing Mode (SM-VIO) or NON-Storing Mode (NSM-
VIO). One P-DAO messages contains a single VIO, associated to one or
more RPL Target Options that signal the destination IPv6 addresses
that can reached along the Track, more in Section 5.3.
Before diving deeper into Track Legs and Segments signaling and
operation, this section provides examples of what how route
projection works through variations of a simple example. This simple
example illustrates the case of host routes, though RPL Targets can
be prefixes.
Say we want to build a Serial Track from node A to E in Figure 4, so
A can route packets to 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 4: Reference Track
Conventionally we use ==> to represent a strict hop and --> for a
loose hop. We use -to- like in C==>D==>E-to-F to represent coma-
separated Targets, e.g., F is a Target for Segment C==>D==>E. In
this example, A is Track Ingress, E is Track Egress. C is a
stitching point. F and G are "external" Targets for the Track, and
become reachable from A via the Track A(ingress) to E (Egress and
implicit Target in Non-Storing Mode) leading to F and G (explicit
Targets).
In a general manner the desired outcome is as follows:
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* Targets are E, F, and G
* P-DAO 1 signals C==>D==>E
* P-DAO 2 signals A==>B==>C
* P-DAO 3 signals F and G via the A-->E Track
P-DAO 3 may be ommitted if P-DAO 1 and 2 signal F and G as Targets.
Loose sequences of hops must be expressed in Non-Storing Mode, so
P-DAO 3 contains a NSM-VIO. With this specification, the DODAGID to
be used by the Ingress as source address is signaled if needed in the
DAO base object, the via list starts at the first loose hop and
matches the source route header, and the Egress of a Non-Storing Mode
P-DAO is an implicit Target that is not listed in the RTO.
3.5.1. Using Storing Mode Segments
A==>B==>C and C==>D==>E are segments of a 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 succesfully
acknowledged, Storing Mode P-DAO 2 is sent to C, as follows:
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+====================+==============+==============+
| Field | P-DAO 1 to E | P-DAO 2 to C |
+====================+==============+==============+
| Mode | Storing | Storing |
+--------------------+--------------+--------------+
| Track Ingress | A | A |
+--------------------+--------------+--------------+
| (DODAGID, TrackID) | (A, 129) | (A, 129) |
+--------------------+--------------+--------------+
| SegmentID | 1 | 2 |
+--------------------+--------------+--------------+
| VIO | C, D, E | A, B, C |
+--------------------+--------------+--------------+
| Targets | F, G | F, G |
+--------------------+--------------+--------------+
Table 1: P-DAO Messages
As a result the RIBs are set as follows:
+======+=============+=========+=============+==========+
| Node | destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| D | E | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 1 | E | (A, 129) |
+------+-------------+---------+-------------+----------+
| C | D | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 1 | D | (A, 129) |
+------+-------------+---------+-------------+----------+
| B | C | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 2 | C | (A, 129) |
+------+-------------+---------+-------------+----------+
| A | B | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 2 | B | (A, 129) |
+------+-------------+---------+-------------+----------+
Table 2: RIB setting
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Packets originated by A to F or G do not require an encapsulation as
the RPI can be placed in the native header chain. For packets that
it routes, A must encapsulate to add the RPI that signals the
trackID; the outer headers of the packets that are forwarded along
the Track have the following settings:
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | A | F or G | (A, 129) |
+--------+-------------------+-------------------+----------------+
| Inner | X != A | F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 3: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 2: A forwards to B and B forwards to C.
* From P-DAO 1: C forwards to D and D forwards to E.
* From Neighbor Cache Entry: C delivers the packet to F.
3.5.1.2. External routes
In this example, we consider F and G as destinations that are
external to the Track as a DODAG, as discussed in section 4.1.1. of
[RFC9008]. We then apply the directives for encapsulating in that
case, more in Section 6.6.
In this formulation, we set up the Track Leg explicitly, which
creates less routing state in intermediate hops at the expense of
larger packets to accommodate source routing:
* P-DAO 1 signals C==>D==>E-to-E
* P-DAO 2 signals A==>B==>C-to-E
* P-DAO 3 signals F and G via the A-->E-to-F,G Track
Storing Mode P-DAO 1 and 2, and Non-Storing Mode P-DAO 3, are sent to
E, C and A, respectively, as follows:
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+====================+==============+==============+==============+
| | P-DAO 1 to E | P-DAO 2 to C | P-DAO 3 to A |
+====================+==============+==============+==============+
| Mode | Storing | Storing | Non-Storing |
+--------------------+--------------+--------------+--------------+
| Track Ingress | A | A | A |
+--------------------+--------------+--------------+--------------+
| (DODAGID, TrackID) | (A, 129) | (A, 129) | (A, 129) |
+--------------------+--------------+--------------+--------------+
| SegmentID | 1 | 2 | 3 |
+--------------------+--------------+--------------+--------------+
| VIO | C, D, E | A, B, C | E |
+--------------------+--------------+--------------+--------------+
| Targets | E | E | F, G |
+--------------------+--------------+--------------+--------------+
Table 4: P-DAO Messages
Note in the above that E is not an implicit Target in Storing mode,
so it must be added in the RTO.
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 setting
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Packets from A to E do not require an encapsulation. The outer
headers of the packets that are forwarded along the Track have the
following settings:
+========+===================+====================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+====================+================+
| Outer | A | E | (A, 129) |
+--------+-------------------+--------------------+----------------+
| Inner | X | E (X != A), F or G | N/A |
+--------+-------------------+--------------------+----------------+
Table 6: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 3: A encapsulates the packet the Track signaled by
P-DAO 3, with the outer header above. Now the 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: C delivers packets to F or G.
3.5.1.3. Segment Routing
In this formulation leverages Track Legs to combine Segments and form
a Graph. The packets are source routed from a Segment to the next to
adapt the path. As such, this can be seen as a form of Segment
Routing [RFC8402]:
* P-DAO 1 signals C==>D==>E-to-E
* P-DAO 2 signals A==>B-to-B,C
* P-DAO 3 signals F and G via the A-->C-->E-to-F,G Track
Storing Mode P-DAO 1 and 2, and Non-Storing Mode P-DAO 3, are sent to
E, B and A, respectively, as follows:
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+====================+==============+==============+==============+
| | P-DAO 1 to E | P-DAO 2 to B | P-DAO 3 to A |
+====================+==============+==============+==============+
| Mode | Storing | Storing | Non-Storing |
+--------------------+--------------+--------------+--------------+
| Track Ingress | A | A | A |
+--------------------+--------------+--------------+--------------+
| (DODAGID, TrackID) | (A, 129) | (A, 129) | (A, 129) |
+--------------------+--------------+--------------+--------------+
| SegmentID | 1 | 2 | 3 |
+--------------------+--------------+--------------+--------------+
| VIO | C, D, E | A, B | C, E |
+--------------------+--------------+--------------+--------------+
| Targets | E | C | F, G |
+--------------------+--------------+--------------+--------------+
Table 7: P-DAO Messages
Note in the above that the Segment can terminate at the loose hop as
used in the example of P-DAO 1 or at the previous hop as done with
P-DAO 2. Both methods are possible on any Segment joined by a loose
Track Leg. P-DAO 1 generates more signaling since E is the Segment
Egress when D could be, but has the benefit that it validates that
the connectivity between D and E still exists.
As a result the RIBs are set as follows:
+======+=============+=========+=============+==========+
| Node | destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| D | E | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| C | D | P-DAO 1 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E | P-DAO 1 | D | (A, 129) |
+------+-------------+---------+-------------+----------+
| B | C | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| A | B | P-DAO 2 | Neighbor | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | C | P-DAO 2 | B | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E, F, G | P-DAO 3 | C, E | (A, 129) |
+------+-------------+---------+-------------+----------+
Table 8: RIB setting
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Packets originated at A to E do not require an encapsulation, but
carry a SRH via C. The outer headers of the packets that are
forwarded along the Track have the following settings:
+========+===================+====================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+====================+================+
| Outer | A | C till C then E | (A, 129) |
+--------+-------------------+--------------------+----------------+
| Inner | X | E (X != A), F or G | N/A |
+--------+-------------------+--------------------+----------------+
Table 9: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 3: A encapsulates the packet the Track signaled by
P-DAO 3, with the outer header above. Now the destination in the
IPv6 Header is C, and a SRH signals the final destination is E.
* 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: C 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-F,G
* P-DAO 2 signals A==>B==>C-to-C,F,G
A==>B==>C and C==>D==>E are Tracks expressed as Non-Storing P-DAOs.
3.5.2.1. Stitched Tracks
Non-Storing Mode P-DAO 1 and 2 are sent to C and A respectively, as
follows:
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+====================+==============+==============+
| | P-DAO 1 to C | P-DAO 2 to A |
+====================+==============+==============+
| Mode | Non-Storing | Non-Storing |
+--------------------+--------------+--------------+
| Track Ingress | C | A |
+--------------------+--------------+--------------+
| (DODAGID, TrackID) | (C, 131) | (A, 131) |
+--------------------+--------------+--------------+
| SegmentID | 1 | 1 |
+--------------------+--------------+--------------+
| VIO | D, E | B, C |
+--------------------+--------------+--------------+
| Targets | F, G | E, F, G |
+--------------------+--------------+--------------+
Table 10: P-DAO Messages
As a result the RIBs are set as follows:
+======+=============+=========+=============+==========+
| Node | destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| D | E | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| C | D | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | E, F, G | P-DAO 1 | D, E | (C, 131) |
+------+-------------+---------+-------------+----------+
| B | C | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| A | B | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | C, E, F, G | P-DAO 2 | B, C | (A, 131) |
+------+-------------+---------+-------------+----------+
Table 11: RIB setting
Packets originated at A to E, F and G do not require an
encapsulation, though it is preferred that A encapsulates and C
decapsulates. Either way, they carry a SRH via B and C, and C needs
to encapsulate to E, F, or G to add an SRH via D and E. The
encapsulating headers of packets that are forwarded along the Track
between C and E have the following settings:
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+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | C | D till D then E | (C, 131) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F, or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 12: Packet Header Settings between C and E
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 2: A encapsulates the packet with destination of F in
the Track signaled by P-DAO 2. The outer header has source A,
destination B, an SRH that indicates C as the next loose hop, and
a RPI indicating a TrackId of 131 from A's namespace, which is
distinct from TrackId of 131 from C's.
* From the SRH: Packets forwarded by B have source A, destination C,
a consumed SRH, and a RPI indicating a TrackId of 131 from A's
namespace. C decapsulates.
* From P-DAO 1: C encapsulates the packet with destination of F in
the Track signaled by P-DAO 1. The outer header has source C,
destination D, an SRH that indicates E as the next loose hop, and
a RPI indicating a TrackId of 131 from C's namespace. E
decapsulates.
3.5.2.2. External routes
In this formulation:
* P-DAO 1 signals C==>D==>E-to-E
* P-DAO 2 signals A==>B==>C-to-C,E
* P-DAO 3 signals F and G via the A-->E-to-F,G Track
Non-Storing Mode P-DAO 1 is sent to C and Non-Storing Mode P-DAO 2
and 3 are sent A, as follows:
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+====================+==============+==============+==============+
| | P-DAO 1 to C | P-DAO 2 to A | P-DAO 3 to A |
+====================+==============+==============+==============+
| Mode | Non-Storing | Non-Storing | Non-Storing |
+--------------------+--------------+--------------+--------------+
| Track Ingress | C | A | A |
+--------------------+--------------+--------------+--------------+
| (DODAGID, TrackID) | (C, 131) | (A, 129) | (A, 141) |
+--------------------+--------------+--------------+--------------+
| SegmentID | 1 | 1 | 1 |
+--------------------+--------------+--------------+--------------+
| VIO | D, E | B, C | E |
+--------------------+--------------+--------------+--------------+
| Targets | E | E | F, G |
+--------------------+--------------+--------------+--------------+
Table 13: 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 |
+------+-------------+---------+-------------+----------+
| " | C, E | P-DAO 2 | B, C | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | F, G | P-DAO 3 | E | (A, 141) |
+------+-------------+---------+-------------+----------+
Table 14: RIB setting
The encapsulating headers of packets that are forwarded along the
Track between C and E have the following settings:
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+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | C | D till D then E | (C, 131) |
+--------+-------------------+-------------------+----------------+
| Middle | A | E | (A, 141) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 15: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 3: A encapsulates the packet with destination of F in
the Track signaled by P-DAO 3. The outer header has source A,
destination E, and a RPI indicating a TrackId of 141 from A's
namespace. This recurses with:
* From P-DAO 2: A encapsulates the packet with destination of E in
the Track signaled by P-DAO 2. The outer header has source A,
destination B, an SRH that indicates C as the next loose hop, and
a RPI indicating a TrackId of 129 from A's namespace.
* From the SRH: Packets forwarded by B have source A, destination C
, a consumed SRH, and a RPI indicating a TrackId of 129 from A's
namespace. C decapsulates.
* From P-DAO 1: C encapsulates the packet with destination of E in
the Track signaled by P-DAO 1. The outer header has source C,
destination D, an SRH that indicates E as the next loose hop, and
a RPI indicating a TrackId of 131 from C's namespace. E
decapsulates.
3.5.2.3. Segment Routing
In this formulation:
* P-DAO 1 signals C==>D==>E-to-E
* P-DAO 2 signals A==>B-to-C
* P-DAO 3 signals F and G via the A-->C-->E-to-F,G Track
Non-Storing Mode P-DAO 1 is sent to C and Non-Storing Mode P-DAO 2
and 3 are sent A, as follows:
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+====================+==============+==============+==============+
| | P-DAO 1 to C | P-DAO 2 to A | P-DAO 3 to A |
+====================+==============+==============+==============+
| Mode | Non-Storing | Non-Storing | Non-Storing |
+--------------------+--------------+--------------+--------------+
| Track Ingress | C | A | A |
+--------------------+--------------+--------------+--------------+
| (DODAGID, TrackID) | (C, 131) | (A, 129) | (A, 141) |
+--------------------+--------------+--------------+--------------+
| SegmentID | 1 | 1 | 1 |
+--------------------+--------------+--------------+--------------+
| VIO | D, E | B | C, E |
+--------------------+--------------+--------------+--------------+
| Targets | | C | F, G |
+--------------------+--------------+--------------+--------------+
Table 16: P-DAO Messages
As a result the RIBs are set as follows:
+======+=============+=========+=============+==========+
| Node | destination | Origin | Next Hop(s) | TrackID |
+======+=============+=========+=============+==========+
| E | F, G | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| D | E | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| C | D | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | E | P-DAO 1 | D, E | (C, 131) |
+------+-------------+---------+-------------+----------+
| B | C | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| A | B | ND | Neighbor | Any |
+------+-------------+---------+-------------+----------+
| " | C | P-DAO 2 | B, C | (A, 129) |
+------+-------------+---------+-------------+----------+
| " | E, F, G | P-DAO 3 | C, E | (A, 141) |
+------+-------------+---------+-------------+----------+
Table 17: RIB setting
The encapsulating headers of packets that are forwarded along the
Track between A and B have the following settings:
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+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | A | B till D then E | (A, 129) |
+--------+-------------------+-------------------+----------------+
| Middle | A | C | (A, 141) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 18: Packet Header Settings
The encapsulating headers of packets that are forwarded along the
Track between B and C have the following settings:
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | A | C | (A, 141) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 19: Packet Header Settings
The encapsulating headers of packets that are forwarded along the
Track between C and E have the following settings:
+========+===================+===================+================+
| Header | IPv6 Source Addr. | IPv6 Dest. Addr. | TrackID in RPI |
+========+===================+===================+================+
| Outer | C | D till D then E | (C, 131) |
+--------+-------------------+-------------------+----------------+
| Middle | A | E | (A, 141) |
+--------+-------------------+-------------------+----------------+
| Inner | X | E, F or G | N/A |
+--------+-------------------+-------------------+----------------+
Table 20: Packet Header Settings
As an example, say that A has a packet for F. Using the RIB above:
* From P-DAO 3: A encapsulates the packet with destination of F in
the Track signaled by P-DAO 3. The outer header has source A,
destination C, an SRH that indicates E as the next loose hop, and
a RPI indicating a TrackId of 141 from A's namespace. This
recurses with:
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* From P-DAO 2: A encapsulates the packet with destination of C in
the Track signaled by P-DAO 2. The outer header has source A,
destination B, and a RPI indicating a TrackId of 129 from A's
namespace. B decapsulates forwards to C based on a sibling
connected route.
* From the SRH: C consumes the SRH and makes the destination E.
* From P-DAO 1: C encapsulates the packet with destination of E in
the Track signaled by P-DAO 1. The outer header has source C,
destination D, an SRH that indicates E as the next loose hop, and
a RPI indicating a TrackId of 131 from C's namespace. E
decapsulates.
3.6. Complex Tracks
To increase the reliability of the P2P transmission, this
specification enables to build a collection of Legs between the same
Ingress and Egress Nodes and combine them with the same TrackID, as
shown in Figure 5. Legs may cross at loose hops edges or remain
parallel.
The Segments that join the loose hops of a Leg are installed with the
same TrackID as the Leg. But each individual Leg and Segment has its
own P-RouteID which allows to manage it separately. When Legs cross
within respsective Segment, the next loose hop (the current
destination of the packet) indicates which Leg is being followed and
a Segment that can reach that next loose hop is selected.
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CPF CPF CPF CPF
Southbound API
_-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-
_-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-
+----------+
| RPL Root |
+----------+
( )
( )
( DODAG )
( )
( )
)
<- Leg 1 B, E ->
<--- Segment 1 A,B ---> <------- Segment 2 C,D,E ------->
FWD --z Relay --z FWD --z FWD Target 1
z-- Node z-- Node z-- Node z-- Node --z /
--z (A) (B) \ (C) (D) z-- /
Track \ Track
Ingress Segment 5 Egress - Tgt 2
(I) \ (E)
--z \ z-- \
z-- FWD --z FWD --z Relay --z FWD --z \
Node z-- Node z-- Node z-- Node Target 3
(F) (G) (H) (J)
<------ Segment 3 F,G,H ------> <---- Segment 4 J,E ---->
<- Leg 2 H, E ->
<--- Segment 1 A,B ---> <- S5-> <---- Segment 4 J,E ---->
<- Leg 3 B, H, E ->
)
(
( )
Figure 5: Segments and Tracks
Note that while this specification enables to build both Segments
inside a Leg (aka East-West), such as Segment 2 above which is within
Leg 1, and Inter-Leg Segments (aka North-South), such as Segment 2
above which joins Leg 1 and Leg 2, it does not signal to the Ingress
which Inter-Leg Segments are available, so the use of North-South
Segments and associated PAREO functions is curently limited. The
only possibility available at this time is to define overlapping Legs
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as illustrated in Figure 5, with Leg 3 that is congruent with Leg 1
till node B and congruent with Leg 2 from node H on, abstracting
Segment 5 as an East-West Segment.
DetNet Forwarding Nodes only understand the simple 1-to-1 forwarding
sublayer transport operation along a segment whereas the more
sophisticated Relay nodes can also provide service sublayer functions
such as Replication and Elimination. One possible mapping between
DetNet and this specification is to signal the Relay Nodes as the
hops of a Leg and the forwarding Nodes as the hops in a Segment that
join the Relay nodes as illustrated in Figure 5.
3.7. Scope and Expectations
This specification expects that the RPL Main DODAG is operated in RPL
Non-Storing Mode to sustain the exchanges with the Root. Based on
its comprehensive knowledge of the parent-child relationship, the
Root can form an abstracted view of the whole DODAG topology. This
document adds the capability for nodes to advertise additional
sibling information to complement the topological awareness of the
Root to be passed on to the PCE, and enable the PCE to build more /
better paths that traverse those siblings.
P-Routes require resources such as routing table space in the routers
and bandwidth on the links; the amount of state that is installed in
each node must be computed to fit within the node's memory, and the
amount of rerouted traffic must fit within the capabilities of the
transmission links. The methods used to learn the node capabilities
and the resources that are available in the devices and in the
network are out of scope for this document. The method to capture
and report the LLN link capacity and reliability statistics are also
out of scope. They may be fetched from the nodes through network
management functions or other forms of telemetry such as OAM.
The "6TiSCH Architecture" [6TiSCH-ARCHI] leverages a centralized
model that is similar to that of "Deterministic Networking
Architecture" [RFC8655], whereby the device resources and
capabilities are exposed to an external controller which installs
routing states into the network based on its own objective functions
that reside in that external entity. With DetNet and 6TiSCH, the
component of the controller that is responsible of computing routes
is a PCE. The PCE computes its routes based on its own objective
functions such as described in [RFC4655], and typically controls the
routes using the PCE Protocol (PCEP) by [RFC5440]. While this
specification expects a PCE and while PCEP might effectively be used
between the Root and the PCE, the control protocol between the PCE
and the Root is out of scope.
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This specification expects a single PCE with a full view of the
network. Distributing the PCE function for a large network is out of
scope. This specification uses the RPL Root as a proxy to the PCE.
The PCE may be collocated with the Root, or may reside in an external
Controller. In that case, the protocol between the Root and the PCE
is out of scope and abstracted by / mapped to RPL inside the DODAG;
one possibility is for the Root to transmit the RPL DAOs with the
SIOs that detail the parent/child and sibling information.
The algorithm to compute the paths and the protocol used by the PCE
and the metrics and link statistics involved in the computation are
also out of scope. The effectiveness of the route computation by the
PCE depends on the quality of the metrics that are reported from the
RPL network. Which metrics are used and how they are reported is out
of scope, but the expectation is that they are mostly of long-term,
statistical nature, and provide visibility on link throughput,
latency, stability and availability over relatively long periods.
The "Reliable and Available Wireless (RAW) Architecture/Framework"
[RAW-ARCHI] extends the definition of Track, as being composed of
East-West directional segments and North-South bidirectional
segments, to enable additional path diversity, using Packet ARQ,
Replication, Elimination, and Overhearing (PAREO) functions over the
available paths, to provide a dynamic balance between the reliability
and availability requirements of the flows and the need to conserve
energy and spectrum. This specification prepares for RAW by setting
up the Tracks, but only forms DODAGs, which are composed of
aggregated end-to-end loose source routed Legs, joined by strict
routed Segments, all oriented East-West.
The RAW Architecture defines a dataplane extension of the PCE called
the Path Selection Engine (PSE), that adapts the use of the path
redundancy within a Track to defeat the diverse causes of packet
loss. The PSE controls the forwarding operation of the packets
within a Track This specification can use but does not impose a PSE
and does not provide the policies that wouldselect which packets are
routed through which path within a Track, IOW, how the PSE 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 East-West 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.
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4. Extending existing RFCs
4.1. Extending RFC 6550
This specification extends RPL [RPL] to enable the Root to install
East-West routes inside a Main DODAG that is operated as non-Storing
Mode. A Projected DAO (P-DAO) message (see Section 4.1.1) contains a
new Via Information Option that installs a strict or a loose sequence
of hops to form respectively a Track Segment or a Track Leg. A new
P-DAO Request (PDR) message (see Section 5.1) enables a Track Ingress
to request the Track from the Root for which it is the Root and it
owns the address that serves as TrackID, as well as the associated
namespace from which it selects the TrackID. In the context of this
specification, the installed route appears as a more specific route
to the Track Targets, and the Track Ingress routes the packets
towards the Targets via the Track using the longest match as usual.
To ensure that the PDR and P-DAO messages can flow at most times, it
is RECOMMENDED that the nodes involved in a Track mantain 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 ot
the nodes in the Track.
4.1.1. Projected DAO
Section 6 of [RPL] introduces the RPL Control Message Options (CMO),
including the RPL Target Option (RTO) and Transit Information Option
(TIO), which can be placed in RPL messages such as the destination
Advertisement Object (DAO). A DAO message signals routing
information to one or more Targets indicated in RTOs, providing one
hop information at a time in the TIO. A Projected DAO (P-DAO) is a
special DAO message generated by the Root to install a P-Route formed
of multiple hops in its DODAG. This provides a RPL-based method to
install the Tracks as expected by the 6TiSCH Architecture
[6TiSCH-ARCHI] as a collection of multiple P-Routes.
The P-DAO is signaled with a new "Projected DAO" (P) flag, see
Figure 6. The 'P' flag is encoded in bit position 2 (to be confirmed
by IANA) of the Flags field in the DAO Base Object. The Root MUST
set it to 1 in a Projected DAO message. Otherwise it MUST be set to
0. It is set to 0 in Legacy implementations as specified
respectively in Sections 20.11 and 6.4 of [RPL]
The P-DAO is control plane signaling and should not be stuck behind
high traffic levels. The expectation is that the P-DAO message is
sent as high QoS level, above that of data traffic, typically with
the Network Control precedence.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TrackID |K|D|P| Flags | Reserved | DAOSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| DODAGID field set to the |
+ IPv6 Address of the Track Ingress +
| used to source encapsulated packets |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
Figure 6: Projected DAO Base Object
New fields:
TrackID: The local or global RPLInstanceID of the DODAG that serves
as Track, more in Section 6.2
P: 1-bit flag (position to be confirmed by IANA).
The 'P' flag is set to 1 by the Root to signal a Projected DAO,
and it is set to 0 otherwise.
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. This specification generalizes the
case of a parent that can be used to reach a child with that of a
whole Track through which children and siblings of the Track Egress
are reachable.
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4.1.2. Via Information Option
New CMOs called the Via Information Options (VIO) are introduced for
use in P-DAO messages as a multihop alternative to the TIO, more in
Section 5.3. One VIO is the stateful Storing Mode VIO (SM-VIO); an
SM-VIO installs a strict hop-by-hop P-Route called a Track Segment.
The other is the Non-Storing Mode VIO (NSM-VIO); the NSM-VIO installs
a loose source-routed P-Route called a Track Leg at the Track
Ingress, which uses that state to encapsulate a packet IPv6_in_IPv6
with a new Routing Header (RH) to the Track Egress, more in
Section 6.6.
A P-DAO contains one or more RTOs to indicate the Target
(destinations) that can be reached via the P-Route, followed by
exactly one VIO that signals the sequence of nodes to be followed,
more in Section 6. There are two modes of operation for the
P-Routes, the Storing Mode and the Non-Storing Mode, see
Section 6.3.2 and Section 6.3.3 respectively for more.
4.1.3. Sibling Information Option
This specification adds another CMO called the Sibling Information
Option (SIO) that is used by a RPL Aware Node (RAN) to advertise a
selection of its candidate neighbors as siblings to the Root, more in
Section 5.4. The SIO is placed in DAO messages that are sent
directly to the Root of the main DODAG.
4.1.4. P-DAO Request
Two new RPL Control Messages are also introduced, to enable a RPL-
Aware Node to request the establishment of a Track between self as
the Track Ingress Node and a Track Egress. The node makes its
request by sending a new P-DAO Request (PDR) Message to the Root.
The Root confirms with a new PDR-ACK message back to the requester
RAN, see Section 5.1 for more.
4.1.5. Extending the RPI
Sending a Packet within a RPL Local Instance requires the presence of
the abstract RPL Packet Information (RPI) described in section 11.2.
of [RPL] in the outer IPv6 Header chain (see [RFC9008]). The RPI
carries a local RPLInstanceID which, in association with either the
source or the destination address in the IPv6 Header, indicates the
RPL Instance that the packet follows.
This specification extends [RPL] to create a new flag that signals
that a packet is forwarded along a P-Route.
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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 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.
4.2. Extending RFC 6553
"The RPL Option for Carrying RPL Information in Data-Plane Datagrams"
[RFC6553]describes the RPL Option for use among RPL routers to
include the abstract RPL Packet Information (RPI) described in
section 11.2. of [RPL] in data packets.
The RPL Option is commonly referred to as the RPI though the RPI is
really the abstract information that is transported in the RPL
Option. [RFC9008] updated the Option Type from 0x63 to 0x23.
This specification modifies 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 7: Extended RPL Option Format
Option Type: 0x23 or 0x63, see [RFC9008]
Opt Data Len: See [RFC6553]
'O', 'R' and 'F' flags: See [RFC6553]. Those flags MUST be set to 0
by the sender and ignored by the receiver if the 'P' flag is set.
Projected-Route 'P': 1-bit flag as defined in Section 4.1.5.
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
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sender and ignored by the receiver if the 'P'flag is set.
4.3. Extending RFC 8138
The 6LoWPAN Routing Header [RFC8138] specification introduces a new
IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN)
[RFC6282] dispatch type for use in 6LoWPAN route-over topologies,
which initially covers the needs of RPL data packet compression.
Section 4 of [RFC8138] presents the generic formats of the 6LoWPAN
Routing Header (6LoRH) with two forms, one Elective that can be
ignored and skipped when the router does not understand it, and one
Critical which causes the packet to be dropped when the router cannot
process it. The 'E' Flag in the 6LoRH indicates its form. In order
to skip the Elective 6LoRHs, their format imposes a fixed expression
of the size, whereas the size of a Critical 6LoRH may be signaled in
variable forms to enable additional optimizations.
When the [RFC8138] compression is used, the Root of the Main DODAG
that sets up the Track also constructs the compressed routing header
(SRH-6LoRH) on behalf of the Track Ingress, which saves the
complexities of optimizing the SRH-6LoRH encoding in constrained
code. The SRH-6LoRH is signaled in the NSM-VIO, in a fashion that it
is ready to be placed as is in the packet encapsulation by the Track
Ingress.
Section 6.3 of [RFC8138] presents the formats of the 6LoWPAN Routing
Header of type 5 (RPI-6LoRH) that compresses the RPI for normal RPL
operation. The format of the RPI-6LoRH is not suited for P-Routes
since the O,R,F flags are not used and the Rank is unknown and
ignored.
This specification introduces a new 6LoRH, the P-RPI-6LoRH that can
be used in either Elective or Critical 6LoRH form, see Table 21 and
Table 22 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 8: P-RPI-6LoRH Format
Type: IANA is requested to define the same value of the type for
both Elective and Critical forms. A type of 8 is suggested.
Elective 'E': See [RFC8138]. The 'E' flag is set to 1 to indicate
an Elective 6LoRH, meaning that it can be ignored when forwarding.
RPLInstanceID : In the context of this specification, the
RPLInstanceID field signals the TrackID, see Section 3.4 and
Section 6.2 .
Section 6.7 details how a a Track Ingress leverages the P-RPI-6LoRH
Header as part of the encapsulation of a packet to place it into a
Track.
5. New RPL Control Messages and Options
5.1. New P-DAO Request Control Message
The P-DAO Request (PDR) message is sent by a Node in the Main DODAG
to the Root. It is a request to establish or refresh a Track where
this node is Track Ingress, and signals whether an acknowledgment
called PDR-ACK is requested or not. A positive PDR-ACK indicates
that the Track was built and that the Roots commits to maintain the
Track for the negotiated lifetime.
The Root may use an asynchronous PDR-ACK with an negative status to
indicate that the Track was terminated before its time. A status of
"Transient Failure" (see Section 10.9) 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 tentative must be abandoned until a corrective action is taken at
the application layer or through network management.
The source IPv6 address of the PDR signals the Track Ingress to-be of
the requested Track, and the TrackID is indicated in the message
itself. One and only one RPL Target Option MUST be present in the
message. The RTO signals the Track Egress, more in Section 6.1.
The RPL Control Code for the PDR is 0x09, to be confirmed by IANA.
The format of PDR Base Object is as follows:
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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 9: New P-DAO Request Format
TrackID: 8-bit field. In the context of this specification, the
TrackID field signals the RPLInstanceID of the DODAG formed by the
Track, see Section 3.4 and Section 6.2. To allocate a new Track,
the Ingress Node must provide a value that is not in use at this
time.
K: The 'K' flag is set to indicate that the recipient is expected to
send a PDR-ACK back.
R: The 'R' flag is set to request a Complex Track for redundancy.
Flags: Reserved. The Flags field MUST 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).
A PDR with a fresher PDRSequence refreshes the lifetime, and a
PDRLifetime of 0 indicates that the Track should be destroyed,
e.g., when the application that requested the Track terminates.
PDRSequence: 8-bit wrapping sequence number, obeying the operation
in section 7.2 of [RPL]. The PDRSequence is used to correlate a
PDR-ACK message with the PDR message that triggered it. It is
incremented at each PDR message and echoed in the PDR-ACK by the
Root.
5.2. New PDR-ACK Control Message
The new PDR-ACK is sent as a response to a PDR message with the 'K'
flag set. The RPL Control Code for the PDR-ACK is 0x0A, to be
confirmed by IANA. Its format is as follows:
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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 10: 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 initialized to zero by the
sender and MUST be ignored by the receiver
Track Lifetime: Indicates that remaining Lifetime for the Track,
expressed in Lifetime Units; 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 11:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|E|R| Value |
+-+-+-+-+-+-+-+-+
Figure 11: PDR-ACK status Format
E: 1-bit flag. Set to indicate a rejection. When not set, the
value of 0 indicates Success/Unqualified Acceptance and other
values indicate "not an outright rejection".
R: 1-bit flag. Reserved, MUST be set to 0 by the sender and
ignored by the receiver.
Status Value: 6-bit unsigned integer. Values depending on the
setting of the 'E' flag, see Table 27 and Table 28.
Reserved: The Reserved field MUST initialized to zero by the sender
and MUST be ignored by the receiver
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5.3. Via Information Options
A VIO signals the ordered list of IPv6 Via Addresses that constitutes
the hops of either a Leg (using Non-Storing Mode) a Segment (using
storing mode) of a Track. A Storing Mode P-DAO contains one Storing
Mode VIO (SM-VIO) whereas a Non-Storing Mode P-DAO contains one Non-
Storing Mode VIO (NSM-VIO)
The duration of the validity of a VIO is indicated in a Segment
Lifetime field. A P-DAO message that contains a VIO with a Segment
Lifetime of zero is referred as a No-Path P-DAO.
The VIO contains one or more SRH-6LoRH header(s), each formed of a
SRH-6LoRH head and a collection of compressed Via Addresses, except
in the case of a Non-Storing Mode No-Path P-DAO where the SRH-6LoRH
header is not present.
In the case of a SM-VIO, or if [RFC8138] is not used in the data
packets, then the Root MUST use only one SRH-6LoRH per Via
Information Option, and the compression is the same forall the
addresses, as shown in Figure 12, 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 make the VIO globally shorter; this means that more
than one SRH-6LoRH may be present.
The format of the Via Information Options is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Option Length | Flags | P-RouteID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Segm. Sequence | Seg. Lifetime | SRH-6LoRH head |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Via Address 1 (compressed by RFC 8138) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .... .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Via Address n (compressed by RFC 8138) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Additional SRH-6LoRH Header(s) .
| |
. .... .
Figure 12: VIO format (uncompressed form)
Option Type: 0x0E for SM-VIO, 0x0F for NSM-VIO (to be confirmed by
IANA), see =Table 25
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.
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 Serial Track, i.e., made of a single segment/Leg.
In an SM-VIO, the P-RouteID indicates an actual Segment. In an an
NSM-VIO, it indicates a Leg, that is a serial subTrack that is
added to the overall topology of the Track.
Segment Sequence: 8-bit unsigned integer. The Segment Sequence
obeys the operation in section 7.2 of [RPL] and the lollipop
starts at 255.
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When the Root of the DODAG needs to refresh or update a Segment in
a Track, it increments the Segment Sequence individually for that
Segment.
The Segment information indicated in the VIO deprecates any state
for the Segment indicated by the P-RouteID within the indicated
Track and sets up the new information.
A VIO with a Segment Sequence that is not as fresh as the current
one is ignored.
A VIO for a given DODAGID with the same (TrackID, P-RouteID,
Segment Sequence) indicates a retry; it MUST NOT change the
Segment and MUST be propagated or answered as the first copy.
Segment Lifetime: 8-bit unsigned integer. The length of time in
Lifetime Units (obtained from the Configuration option) that the
Segment is usable.
The period starts when a new Segment Sequence is seen. The value
of 255 (0xFF) represents infinity. The value of zero (0x00)
indicates a loss of reachability.
SRH-6LoRH head: The first 2 bytes of the (first) SRH-6LoRH as shown
in Figure 6 of [RFC8138]. As an example, a 6LoRH Type of 4 means
that the VIA Addresses are provided in full with no compression.
Via Address: An IPv6 ULA or GUA of a node along the Segment. The
VIO contains one or more IPv6 Via Addresses listed in the datapath
order from Ingress to Egress. The list is expressed in a
compressed form as signaled by the preceding SRH-6LoRH header.
In a Storing Mode P-DAO that updates or removes a section of an
already existing Segment, the list in the SM-VIO may represent
only the section of the Segment that is being updated; at the
extreme, the SM-VIO updates only one node, in which case it
contains only one IPv6 address. In all other cases, the list in
the VIO MUST be complete.
In the case of an SM-VIO, the list indicates a sequential (strict)
path through direct neighbors, the complete list starts at Ingress
and ends at Egress, and the nodes listed in the VIO, including the
Egress, MAY be considered as implicit Targets.
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In the case of an NSM-VIO, the complete list can be loose and
excludes the Ingress node, starting at the first loose hop and
ending at a Track Egress; the Track Egress MUST be considered as
an implicit Target, so it MUST NOT be signaled in a RPL Target
Option.
5.4. Sibling Information Option
The Sibling Information Option (SIO) provides indication on siblings
that could be used by the Root to form P-Routes. One or more SIO(s)
may be placed in the DAO messages that are sent to the Root in Non-
Storing Mode.
To advertise a neighbor node, the router MUST have an active Address
Registration from that sibling using [RFC8505], for an address (ULA
or GUA) that serves as identifier for the node. If this router also
registers an address to that sibling, and the link has similar
properties in both directions, only the router with the lowest
Interface ID in its registered address needs report the SIO, and the
Root will assume symmetry.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Option Length |S| Flags |Comp.| Opaque |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Step of Rank | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Sibling DODAGID (if the D flag not set) .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Sibling Address .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Sibling Information Option Format
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Option Type: 0x10 for SIO (to be confirmed by IANA), see =Table 25
Option Length: 8-bit unsigned integer, representing the length in
octets of the option, not including the Option Type and Length
fields, see section 6.7.1. of [RPL].
Reserved for Flags: MUST be set to zero by the sender and MUST be
ignored by the receiver.
S: 1-bit flag that is set to indicate that sibling belongs to the
same DODAG. When not set, the Sibling DODAGID is indicated.
Flags: Reserved. The Flags field MUST initialized to zero by the
sender and MUST be ignored by the receiver
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. An industrial Alliance that
uses RPL for a particular use / environment MAY redefine the use
of this field to fit its needs.
Compression Type: 3-bit unsigned integer. This is the SRH-6LoRH
Type as defined in figure 7 in section 5.1 of [RFC8138] that
corresponds to the compression used for the Sibling Address and
its DODAGID if resent. The Compression reference is the Root of
the Main DODAG.
Step of Rank: 16-bit unsigned integer. This is the Step of Rank
[RPL] as computed by the Objective Function between this node and
the sibling.
Reserved: The Reserved field MUST initialized to zero by the sender
and MUST be ignored by the receiver
Sibling DODAGID: 2 to 16 bytes, the DODAGID of the sibling in a
[RFC8138] compressed form as indicated by the Compression Type
field. This field is present if and only if the D flag is not
set.
Sibling Address: 2 to 16 bytes, an IPv6 Address of the sibling, with
a scope that MUST be make it reachable from the Root, e.g., it
cannot be a Link Local Address. The IPv6 address is encoded in
the [RFC8138] compressed form indicated by the Compression Type
field.
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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. Requesting a Track
This specification introduces the PDR message, used by an LLN node to
request the formation of a new Track for which this node is Ingress.
Note that the namespace for the TrackID is owned by the Ingress node,
and in the absence of a PDR, there must be some procedure for the
Root to assign TrackIDs in that namespace while avoiding collisions,
more in Section 6.2.
The PDR signals the desired TrackID and the duration for which the
Track should be established. Upon a PDR, the Root MAY install the
Track as requested, in which case it answers with a PDR-ACK
indicating the granted Track Lifetime. All the Segments MUST be of a
same mode, either Storing or Non-Storing. All the Segments MUST be
created with the same TrackID and the same DODAGID signaled in the
P-DAO.
The Root designs the Track as it sees best, and updates / changes the
Segments overtime to serve the Track as needed. There is no
notification to the requesting node when those changes happen. The
Segment Lifetime in the P-DAO messages does not need to be aligned to
the Requested Lifetime in the PDR, or between P-DAO messages for
different Segments. The Root may use shorter lifetimes for the
Segments and renew them faster than the Track is, or longer lifetimes
in which case it will need to tear down the Segments if the Track is
not renewed.
When the Track Lifetime that was returned in the PDR-ACK is close to
elapse - vs. the trip time from the node to the Root, the requesting
node SHOULD resend a PDR using the TrackID in the PDR-ACK to extend
the lifetime of the Track, else the Track will time out and the Root
will tear down the whole structure.
If the Track fails and cannot be restored, the Root notifies the
requesting node asynchronously with a PDR-ACK with a Track Lifetime
of 0, indicating that the Track has failed, and a PDR-ACK Status
indicating the reason of the fault.
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6.2. Identifying a Track
RPL defines the concept of an Instance to signal an individual
routing topology, and multiple topologies can coexist in the same
network. The RPLInstanceID is tagged in the RPI of every packet to
signal which topology the packet actually follows.
This draft leverages the RPL Instance model as follows:
* The Root MAY use P-DAO messages to add better routes in the main
(Global) RPL Instance in conformance with the routing objectives
in that Instance.
To achieve this, the Root MAY install a Segment along a path down
the main Non-Storing Mode DODAG. This enables a loose source
routing and reduces the size of the Routing Header, see
Section 3.3.1. The Root MAY also install a Track Leg across the
Main DODAG to complement the routing topology.
When adding a P-Route to the RPL Main DODAG, the Root MUST set the
RPLInstanceID field of the P-DAO Base Object (see section 6.4.1.
of [RPL]) to the RPLInstanceID of the Main DODAG, and MUST NOT use
the DODAGID field. A P-Route provides a longer match to the
Target Address than the default route via the Root, so it is
preferred.
* The Root MAY also use P-DAO messages to install a Track as an
independent routing topology (say, Traffic Engineered) to achieve
particular routing characteristics from an Ingress to an Egress
Endpoints. To achieve this, the Root MUST set up a local RPL
Instance (see section 5 of [RPL]), and the Local RPLInstanceID
serves as TrackID. The TrackID MUST be unique for the IPv6 ULA or
GUA of the Track Ingress that serves as DODAGID for the Track.
This way, a Track is uniquely identified by the tuple (DODAGID,
TrackID) where the TrackID is always represented with the D flag
set to 0 (see also section 5.1. of [RPL]), indicating when used in
an RPI that the source address of the IPv6 packet signals the
DODAGID.
The P-DAO Base Object MUST indicate the tuple (DODAGID, TrackID)
that identifies the Track as shown in Figure 6, and the P-RouteID
that identifies the P-Route MUST be signaled in the VIO as shown
in Figure 12.
The Track Ingress is the root of the DODAG ID formed by the local
RPL Instance. It owns the namespace of its TrackIDs, so it can
pick any unused value to request a new Track with a PDR. In a
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particular deployment where PDR are not used, the namespace can be
delegated to the main Root, which can assign the TrackIDs for the
Tracks it creates without collision.
With this specification, the 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 Root and the Track
Ingress picking the same value at the same time, it is RECOMMENDED
that the Track Ingress starts allocating the ID value of the Local
RPLInstanceID (see section 5.1. of [RPL]) used as TrackIDs with
the value 0 incrementing, while the Root starts with 63
decrementing.
6.3. Installing a Track
A Serial Track 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-Leg Track. A
single-Leg 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 Serial Track.
A Complex Track can be installed as a collection of P-Routes with the
same DODAGID and Track ID. The Ingress of a Non-Storing Mode P-Route
is the owner and Root of the DODAGID. The Ingress of a Storing Mode
P-Route must be either the owner of the DODAGID, or a hop of a Leg of
the same Track. In the latter case, the Targets of the P-Route must
include the next hop of the Leg if there is one, to ensure forwarding
continuity. In the case of a Complex Track, each Segment is
maintained independently and asynchronously by the Root, with its own
lifetime that may be shorter, the same, or longer than that of the
Track.
A route along a Track for which the TrackID is not the RPLInstanceID
of the Main DODAG MUST be installed with a higher precedence than the
routes along the Main DODAG, meaning that:
* Longest match MUST be the prime comparison for routing.
* In case of equal length match, the route along the Track MUST be
preferred vs. the one along the Main DODAG.
* There SHOULD NOT be 2 different Tracks leading to the same Target
from same Ingress node, unless there's a policy for selecting
which packets use which Track; such policy is out of scope.
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* 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.
6.3.1. Signaling a Projected Route
This draft adds a capability whereby the Root of a main RPL DODAG
installs a Track as a collection of P-Routes, using a Projected-DAO
(P-DAO) message for each individual Track Leg or Segment. The P-DAO
signals a collection of Targets in the RPL Target Option(s) (RTO).
Those Targets can be reached via a sequence of routers indicated in a
VIO.
Like a classical DAO message, a P-DAO causes a change of state only
if it is "new" per section 9.2.2. "Generation of DAO Messages" of
the RPL specification [RPL]; this is determined using the Segment
Sequence information from the VIO as opposed to the Path Sequence
from a TIO. Also, a Segment Lifetime of 0 in a VIO indicates that
the P-Route associated to the Segment is to be removed. There are
two Modes of operation for the P-Routes, the Storing and the Non-
Storing Modes.
A P-DAO message MUST be sent from the address of the Root that serves
as DODAGID for the Main DODAG. It MUST contain either exactly one
sequence of one or more RTOs followed one VIO, or any number of
sequences of one or more RTOs followed by one or more TIOs. The
former is the normal expression for this specification, where as the
latter corresponds to the variation for lesser constrained
environments described in Section 7.2.
A P-DAO that creates or updates a Track Leg MUST be sent to a GUA or
a ULA of the Ingress of the Leg; it must contain the full list of
hops in the Leg unless the Leg is being removed. A P-DAO that
creates a new Track Segment MUST be sent to a GUA or a ULA of the
Segment Egress and MUST signal the full list of hops in Segment; a
P-DAO that updates (including deletes) a section of a Segment MUST be
sent to the first node after the modified Segment and signal the full
list of hops in the section starting at the node that immediately
precedes the modified section.
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In Non-Storing Mode, as discussed in Section 6.3.3, the Root sends
the P-DAO to the Track Ingress where the source-routing state is
applied, whereas in Storing Mode, the P-DAO is sent to the last node
on the installed path and forwarded in the reverse direction,
installing a Storing Mode state at each hop, as discussed in
Section 6.3.2. In both cases the Track Ingress is the owner of the
Track, and it generates the P-DAO-ACK when the installation is
successful.
If the 'K' Flag is present in the P-DAO, the P-DAO must be
acknowledged using a DAO-ACK that is sent back to the address of the
Root from which the P-DAO was received. In most cases, the first
node of the Leg, Segment, or updated section of the Segment is the
node that sends the acknowledgment. The exception to the rule is
when an intermediate node in a Segment fails to forward a Storing
Mode P-DAO to the previous node in the SM-VIO.
In a No-Path Non-Storing Mode P-DAO, the SRH-6LoRH MUST NOT be
present in the NSM-VIO; the state in the Ingress is erased
regardless. In all other cases, a VIO MUST contain at least one Via
Address, and a Via Address MUST NOT be present more than once, which
would create a loop.
A node that processes a VIO MAY verify whether one of these
conditions happen, and when so, it MUST ignore the P-DAO and reject
it with a RPL Rejection Status of "Error in VIO" in the DAO-ACK, see
Section 10.14.
Other errors than those discussed explicitely that prevent the
installing the route are acknowledged with a RPL Rejection Status of
"Unqualified Rejection" in the DAO-ACK.
6.3.2. Installing a Track Segment with a Storing Mode P-Route
As illustrated in Figure 14, a Storing Mode P-DAO installs a route
along the Segment signaled by the SM-VIO towards the Targets
indicated in the Target Options. The Segment is to be included in a
DODAG indicated by the P-DAO Base Object, that may be the one formed
by the RPL Main DODAG, or a Track associated with a local RPL
Instance.
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------+---------
| Internet
|
+-----+
| | Border router
| | (RPL Root)
+-----+ | ^ |
| | DAO | ACK |
o o o o | | |
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 o o o o o 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 14: Projecting a route
In order to install the relevant routing state along the Segment ,
the Root sends a unicast P-DAO message to the Track Egress router of
the routing Segment that is being installed. The P-DAO message
contains a SM-VIO with the strict sequence of Via Addresses. The SM-
VIO follows one or more RTOs indicating the Targets to which the
Track leads. The SM-VIO contains a Segment Lifetime for which the
state is to be maintained.
The Root sends the P-DAO directly to the Egress node of the Segment.
In that P-DAO, the destination IP address matches the last Via
Address in the SM-VIO. This is how the Egress recognizes its role.
In a similar fashion, the Segment Ingress node recognizes its role as
it matches first Via Address in the SM-VIO.
The Egress node of the Segment is the only node in the path that does
not install a route in response to the P-DAO; it is expected to be
already able to route to the Target(s) based on its existing tables.
If one of the Targets is not known, the node MUST answer to the Root
with a DAO-ACK listing the unreachable Target(s) in an RTO and a
rejection status of "Unreachable Target".
If the Egress node can reach all the Targets, then it forwards the
P-DAO with unchanged content to its predecessor in the Segment as
indicated in the list of Via Information options, and recursively the
message is propagated unchanged along the sequence of routers
indicated in the P-DAO, but in the reverse order, from Egress to
Ingress.
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The address of the predecessor to be used as destination of the
propagated DAO message is found in the Via Address the precedes the
one that contain the address of the propagating node, which is used
as source of the message.
Upon receiving a propagated DAO, all except the Egress router MUST
install a route towards the DAO Target(s) via their successor in the
SM-VIO. A router that cannot store the routes to all the Targets in
a P-DAO MUST reject the P-DAO by sending a DAO-ACK to the Root with a
Rejection Status of "Out of Resources" as opposed to forwarding the
DAO to its predecessor in the list. The router MAY install
additional routes towards the VIA Addresses that are the SM-VIO after
self, if any, but in case of a conflict or a lack of resource, the
route(s) to the Target(s) are the ones that must be installed in
priority.
If a router cannot reach its predecessor in the SM-VIO, the router
MUST send the DAO-ACK to the Root with a Rejection Status of
"Predecessor Unreachable".
The process continues till the P-DAO is propagated to Ingress router
of the Segment, which answers with a DAO-ACK to the Root. The Root
always expects a DAO-ACK, either from the Track Ingress with a
positive status or from any node along the segment with a negative
status. If the DAO-ACK is not received, the Root may retry the DAO
with the same TID, or tear down the route.
6.3.3. Installing a Track Leg with a Non-Storing Mode P-Route
As illustrated in Figure 15, a Non-Storing Mode P-DAO installs a
source-routed path within the Track indicated by the P-DAO Base
Object, towards the Targets indicated in the Target Options. The
source-routed path requires a Source-Routing header which implies an
IP-in-IP encapsulation to add the SRH to an existing packet. It is
sent to the Track Ingress which creates a tunnel associated with the
Track, and connected routes over the tunnel to the Targets in the
RTO. The tunnel encapsulation MUST incorporate a routing header via
the list addresses listed in the VIO in the same order. The content
of the NSM-VIO starting at the first SRH-6LoRH header MUST be used
verbatim by the Track Ingress when it encapsulates a packet to
forward it over the Track.
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------+---------
| Internet
|
+-----+
| | Border router
| | (RPL Root)
+-----+ | P ^ ACK
| Track | DAO |
o o o o Ingress X V | X
o o o o o o o X o X Source
o o o o o o o o X o o X Routed
o o ° o o o o X o X Segment
o o o o o o o o X Egress X
o o o o o |
Target
o o LLN o o
o o o o
Figure 15: 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 Leg(s) of
the same Track that use it, and stitched Segments must be installed
in order from the last that reaches to the Targets to the first.
If the next entry in the loose sequence is reachable over a Storing
Mode P-Route, it MUST be the Target of a Segment and the Ingress of a
next segment, both already setup; the segments are associated with
the same Track, which avoids the need of an additional encapsulation.
For instance, in Section 3.5.1.3, Segments A==>B-to-C and
C==>D==>E-to-F must be installed with Storing Mode P-DAO messages 1
and 2 before the Track A-->C-->E-to-F that joins them can be
installed with Non-Storing Mode P-DAO 3.
Conversely, if it is reachable over a Non-Storing Mode P-Route, the
next loose source-routed hop of the inner Track is a Target of a
previously installed Track and the Ingress of a next Track, which
requires a de- and a re-encapsulation when switching the outer Tracks
that join the loose hops. This is examplified in Section 3.5.2.3
where Non-Storing Mode P-DAO 1 and 2 install strict Tracks that Non-
Storing Mode P-DAO 3 joins as a super Track. In such a case, packets
are subject to double IP-in-IP encapsulation.
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6.4. Tearing Down a P-Route
A P-DAO with a lifetime of 0 is interpreted as a No-Path DAO and
results in cleaning up existing state as opposed to refreshing an
existing one or installing a new one. To tear down a Track, the Root
must tear down all the Track Segments and Legs that compose it one by
one.
Since the state about a Leg of a Track is located only the Ingress
Node, the Root cleans up the Leg by sending an NSM-VIO to the Ingress
indicating the TrackID and the P-RouteID of the Leg being removed, a
Segment Lifetime of 0 and a newer Segment Sequence. The SRH-6LoRH
with the Via Addresses in the NSM-VIO are not needed and MUST be
omitted. Upon that NSM-VIO, the Ingress node removes all state for
that Track if any, and replies positively anyway.
The Root cleans up a section of a Segment by sending an SM-VIO to the
last node of the Segment, with the TrackID and the P-RouteID of the
Segment being updated, a Segment Lifetime of zero (0) and a newer
Segment Sequence. The Via Addresses in the SM-VIO indicates the
section of the Segment being modified, from the first to the last
node that is impacted. This can be the whole Segment if it is
totally removed, or a sequence of one or more nodes that have been
bypassed by a Segment update.
The No-Path P-DAO is forwarded normally along the reverse list, even
if the intermediate node does not find a Segment state to clean up.
This results in cleaning up the existing Segment state if any, as
opposed to refreshing an existing one or installing a new one.
6.5. Maintaining a Track
Repathing a Track Segment or Leg may cause jitter and packet
misordering. For critical flows that require timely and/or in-order
delivery, it might be necessary to deploy the PAREO functions
[RAW-ARCHI] over a highly redundant Track. This specification allows
to use more than one Leg for a Track, and 1+N packet redundancy.
This section provides the steps to ensure that no packet is lost due
to the operation itself. This is ensured by installing the new
section from its last node to the first, so when an intermediate node
installs a route along the new section, all the downstream nodes in
the section have already installed their own. The disabled section
is removed when the packets in-flight are forwarded along the new
section as well.
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6.5.1. Maintaining a Track Segment
To modify a section of a Segment between a first node and a second,
downstream node (which can be the Ingress and Egress), while
conserving those nodes in the Segment, the Root sends an SM-VIO to
the second node indicating the sequence of nodes in the new section
of the Segment. The SM-VIO indicates the TrackID and the P-RouteID
of the Segment being updated, and a newer Segment Sequence. The
P-DAO is propagated from the second to the first node and on the way,
it updates the state on the nodes that are common to the old and the
new section of the Segment and creates a state in the new nodes.
When the state is updated in an intermediate node, that node might
still receive packets that were in flight from the Ingress to self
over the old section of the Segment. Since the remainder of the
Segment is already updated, the packets are forwarded along the new
version of the Segment from that node on.
After a reasonable time to enable the deprecated sections to empty,
the root tears down the remaining section(s) of the old segments are
teared down as described in Section 6.4.
6.5.2. Maintaining a Track Leg
This specification allows to add Legs to a Track by sending a Non-
Storing Mode P-DAO to the Ingress associated to the same TrackID, and
a new Segment ID. If the Leg is loose, then the Segments that join
the hops must be created first. It makes sense to add a new Leg
before removing one that is misbehaving, and switch to the new Leg
before removing the old.
It is also possible to update a Track Leg by sending a Non-Storing
Mode P-DAO to the Ingress with the same Segment ID, an incremented
Segment Sequence, and the new complete listy of hops in the NSM-VIO.
Updating a live Leg means changing one or more of the intermediate
loose hops, and involves laying out new Segments from and to the new
loose hops before the NSM-VIO for the new Leg is issued.
Packets that are in flight over the old version of the Track Leg
still follow the old source route path over the old Segments. After
a reasonable time to enable the deprecated Segments to empty, the
root tears down those Segments as described in Section 6.4.
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6.6. Encapsulating and Forwarding Along a Track
When forwarding a packet to a destination for which a router
determines that routing happens via a Track for which it is Ingress,
the router must encapsulated the packet using IP-in-IP to add the
Source Routing Header with the final destination set to the Track
Egress. Though fragmentation is possible in a 6LoWPAN LLN, e.g.,
using [6LoWPAN], [RFC8930], and/or [RFC8931], it is RECOMMENDED to
allow an MTU that is larger than 1280 in the main DODAG and allows
for the additional headers while exposing only 1280 to the 6LoWPAN
Nodes as indicated by section 4 of [6LoWPAN].
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
RPL Main DODAG, e.g., by setting the "T" flag [TURN-ON_RFC8138] in
the RPL configuration option.
The Track Ingress that places a packet in a Track encapsulates it
with an IP-in-IP header, a Routing Header, and an IPv6 Hop-by-Hop
Option Header that contains the RPL Packet Information (RPI) as
follows:
* In the uncompressed form the source of the packet is the address
that this router uses as DODAGID for the Track, the destination is
the first Via Address in the NSM-VIO, and the RH is a Source
Routing Header (SRH) [RFC6554] that contains the list of the
remaining Via Addresses terminating by the Track Egress.
* The preferred alternate in a network where 6LoWPAN Header
Compression [RFC6282] is used is to leverage "IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch"
[RFC8025] to compress the RPL artifacts as indicated in [RFC8138].
In that case, the source routed header is the exact copy of the
(chain of) SRH-6LoRH found in the NSM-VIO, also terminating by the
Track Egress. The RPI-6LoRH is appended next, followed by an IP-
in-IP 6LoRH Header that indicates the Ingress router in the
Encapsulator Address field, see as a similar case Figure 20 of
[TURN-ON_RFC8138].
To signal the Track in the packet, this specification leverages the
RPL Forwarding model follows:
* In the data packets, the Track DODAGID and the TrackID MUST be
respectively signaled as the IPv6 Source Address and the
RPLInstanceID field of the RPI that MUST be placed in the outer
chain of IPv6 Headers.
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The RPI carries a local RPLInstanceID called the TrackID, which,
in association with the DODAGID, indicates the Track along which
the packet is forwarded.
The D flag in the RPLInstanceID MUST be set to 0 to indicate that
the source address in the IPv6 header is set ot the DODAGID, more
in Section 6.2.
* This draft conforms to the principles of [RFC9008] with regards to
packet forwarding and encapsulation along a Track, as follows:
- With this draft, the Track is a RPL DODAG. From the
perspective of that DODAG, the Track Ingress is the Root, the
Track Egress is a RPL-Aware 6LR, and neighbors of the Track
Egress that can be reached via the Track, but are external to
it, are external destinations and treated as RPL-Unaware Leaves
(RULs). The encapsulation rules in [RFC9008] apply.
- If the Track Ingress is the originator of the packet and the
Track Egress is the destination of the packet, there is no need
for an encapsulation.
- So the Track Ingress must encapsulate the traffic that it did
not originate, and add an RPI.
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 as
discussed in more details Section 3.5.2.3. 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.
The forwarding of a packet along a track will fail if the Track
continuity is broken,e.g.:
* In the case of a strict path along a Segment, if the next strict
hop is not reachable, the packet is dropped.
* In the case of a loose source-routed path, when the loose next hop
is not a neighbor, there must be a Segment of the same Track to
that loose next hop. When that is the case the packet is
forwarded to the next hop along that segment, or a common neighbor
with the loose next hop, on which case the packet is forwarded to
that neighbor, or another Track to the loose next hop for which
this node or a neighbor is Ingress; in the last case, another
encapsulation takes place and the process possibly recurses;
otherwise the packet is dropped.
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* 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, or a Target of another Segment of
the same Track for which this node is Ingress, otherwise the
packet MUST be dropped.
In case of a failure forwarding a packet along a Segment, e.g., the
next hop is unreachable, the node that discovers the fault MUST send
an ICMPv6 Error message [RFC4443] to the Root, with a new Code "Error
in P-Route" (See Section 10.13). The Root can then repair by
updating the broken Segment and/or Tracks, and in the case of a
broken Segment, remove the leftover sections of the segment using SM-
VIOs with a lifetime of 0 indicating the section ot one or more nodes
being removed (See Section 6.5).
In case of a permanent forwarding error along a Source Route path,
the node that fails to forward SHOULD send an ICMP error with a code
"Error in Source Routing Header" back to the source of the packet, as
described in section 11.2.2.3. of [RPL]. Upon this message, the
encapsulating node SHOULD stop using the source route path for a
reasonable period of time which duration depends on the deployment,
and it SHOULD send an ICMP message with a Code "Error in P-Route" to
the Root. Failure to follow these steps may result in packet loss
and wasted resources along the source route path that is broken.
Either way, the ICMP message MUST be throttled in case of consecutive
occurrences. It MUST be sourced at the ULA or a GUA that is used in
this Track for the source node, so the Root can establish where the
error happened.
The portion of the invoking packet that is sent back in the ICMP
message SHOULD record at least up to the RH if one is present, and
this hop of the RH SHOULD be consumed by this node so that the
destination in the IPv6 header is the next hop that this node could
not reach. if a 6LoWPAN Routing Header (6LoRH) [RFC8138] is used to
carry the IPv6 routing information in the outer header then that
whole 6LoRH information SHOULD be present in the ICMP message.
6.7. Compression of the RPL Artifacts
When using [RFC8138] in the Main DODAG operated in Non-Storing Mode
in a 6LoWPAN LLN, a typical packet that circulates in the Main DODAG
is formatted as shown in Figure 16, representing the case where :
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+-+ ... -+- ... -+- ... -+-+- ... +-+-+-+ ... +-+-+ ... -+ ... +-...
|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 16: A Packet as Forwarded along the Main DODAG
Since there is no page switch between the encapsulated packet and the
encapsulation, the first octet of the compressed packet that acts as
page selector is actually removed at encapsulation, so the inner
packet used in the descriptions below start with the SRH-6LoRH, and
is verbatim the packet represented in Figure 16 from the second octet
on.
When encapsulating that inner packet to place it in the Track, the
first header that the Ingress appends at the head of the inner packet
is an IP-in-IP 6LoRH Header; in that header, the encapsulator
address, which maps to the IPv6 source address in the uncompressed
form, contains a GUA or ULA IPv6 address of the Ingress node that
serves as DODAG ID for the Track, expressed in the compressed form
and using the DODAGID of the Main DODAG as compression reference. If
the address is compressed to 2 bytes, the resulting value for the
Length field shown in Figure 17 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 17: The IP-in-IP 6LoRH Header
At the head of the resulting sequence of bytes, the track Ingress
then adds the RPI that carries the TrackID as RPLinstanceID as a P-
RPI-6LoRH Header, as illustrated in Figure 8, using the TrackID as
RPLInstanceID. Combined with the IP-in-IP 6LoRH Header, this allows
to identify the Track without ambiguity.
The SRH-6LoRH is then added at the head of the resulting sequence of
bytes as a verbatim copy of the content of the SR-VIO that signaled
the selected Track Leg.
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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 18: The SRH 6LoRH Header
The format of the resulting encapsulated packet in [RFC8138]
compressed form is illustrated in Figure 19:
+-+ ... -+-+-+- ... -+-+-+- ... -+-+-+-+-+- ... +-+-+-+-+-+-+- ...
| Page 1 | SRH-6LoRH | P-RPI-6LoRH | IP-in-IP 6LoRH | Inner Packet
+-+ ... -+-+-+- ... -+-+-+- ... -+-+-+-+-+- ... +-+-+-+-+-+-+- ...
Signals : Loose Hops : TrackID : Track DODAGID :
Figure 19: A Packet as Forwarded along a Track
7. Lesser Constrained Variations
7.1. Storing Mode Main DODAG
This specification expects that the Main DODAG is operated in Non-
Storing Mode. The reasons for that limitation are mostly related to
LLN operations, power and spectrum conservation:
* In Non-Storing Mode The Root already possesses the DODAG topology,
so the additional topological information is reduced to the
siblings.
* The downwards routes are updated with unicast messages to the
Root, which ensures that the Root can reach back to the LLN nodes
after a repair faster than in the case of Storing Mode. Also the
Root can control the use of the path diversity in the DODAG to
reach to 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 like OSPF, ISIS,
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EIGRP, BABEL or RIP at the expense of a route stretch vs. the
shortest path routes to a destination that those protocols compute.
P-Routes add the capability to install shortest and/or constrained
routes to special destinations such as discussed in section A.9.4. of
the ANIMA ACP [RFC8994].
In a powered and wired network, when enough memory to store the
needed routes is available, the RPL Storing Mode proposes a better
trade-off than the Non-Storing, as it reduces the route stretch and
lowers the load on the Root. In that case, the control path between
the Root and the LLN nodes is highly available compared to LLNs, and
the nodes can be reached to maintain the P-Routes at most times.
This section specifies the additions that are needed to support
Projected Routes when the Main DODAG is operated in Storing Mode. As
long as the RPI can be processed adequately by the dataplane, the
changes to this specification are limited to the DAO message. The
Track structure, routes and forwarding operations remain the same.
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 as Non-Storing DAO messages
are.
In the DAO message, the originating router advertises a set of
neighbor nodes using Sibling Information Options (SIO)s, regardless
of the relative position in the DODAG of the advertised node vs. this
router.
The DAO message MUST be formed as follows:
* The originating router is identified by the source address of the
DAO. That address MUST be the one that this router registers to
neighbor routers so the Root can correlate the DAOs from those
routers when they advertise this router as their neighbor. The
DAO contains one or more sequences of one Transit Information
Option and one or more Sibling Information Options. There is no
RPL Target Option so the Root is not confused into adding a
Storing Mode route to the Target.
* The TIO is formed as in Storing Mode, and the Parent Address is
not present. The Path Sequence and Path Lifetime fields are
aligned with the values used in the Address Registration of the
node(s) advertised in the SIO, as explained in Section 9.1. of
[RFC9010]. Having similar values in all nodes allows to factorise
the TIO for multiple SIOs as done with [RPL].
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* The TIO is followed by one or more SIOs that provide an address
(ULA or GUA) of the advertised neighbor node.
But the RPL routing information headers may not be supported on all
type of routed network infrastructures, especially not in high-speed
routers. When the RPI is not be supported in the dataplane, there
cannot be local RPL Instances and RPL can only operate as a single
topology (the Main DODAG). The RPL Instance is that of the Main
DODAG and the Ingress node that encapsulates is not the Root. The
routes along the Tracks are alternate routes to those available along
the Main DODAG. They MAY conflict with routes to children and MUST
take precedence in the routing table. The Targets MUST be adjacent
to the Track Egress to avoid loops that may form if the packet is
reinjected in the Main DODAG.
7.2. A Track as a Full DODAG
This specification builds parallel or crossing Track Legs 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 capability to store large amount of topological
information and compute complex paths:
* With this specification, the node in the LLN has no topological
awareness, and does not need to maintain dynamic information about
the link quality and availability.
* The Root has a complete topological information and statistical
metrics that allow it or its PCE to perform a global optimization
of all Tracks in its DODAG. Based on that information, the Root
computes the Track Leg and predigest the source route paths.
* The node merely selects one of the proposed paths and applies the
associated pre-computed routing header in the encapsulation. This
alleviates both the complexity of computing a path and the
compressed form of the routing header.
The "Reliable and Available Wireless (RAW) Architecture/Framework"
[RAW-ARCHI] actually expects the PSE at the Track Ingress to react to
changes in the forwarding conditions along the Track, and reroute
packets to maintain the required degree of reliability. To achieve
this, the PSE need the full richness of a DODAG to form any path that
could make meet the Service Level Objective (SLO).
This section specifies the additions that are needed to turn the
Track into a full DODAG and enable the main Root to provide the
necessary topological information to the Track Ingress. The
expectation is that the metrics that the PSE uses are of an order
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other than that of the PCE, because of the difference of time scale
between routing and forwarding, mor e in [RAW-ARCHI]. It follows
that the PSE will learn the metrics it needs from an alternate
source, e.g., OAM frames.
To pass the topological information to the Ingress, the Root uses a
P-DAO messages that contains sequences of Target and Transit
Information options that collectively represent the Track, expressed
in the same fashion as in classical Non-Storing Mode. The difference
as that the Root is the source as opposed to the destination, and can
report information on many Targets, possibly the full Track, with one
P-DAO.
Note that the Path Sequence and Lifetime in the TIO are selected by
the Root, and that the Target/Transit information tupples in the
P-DAO are not those received by the Root in the DAO messages about
the said Targets. The Track may follow sibling routes and does not
need to be congruent with the Main DODAG.
8. Profiles
This document provides a set of tools that may or may not be needed
by an implementation depending on the type of application it serves.
This sections described profiles that can be implemented separately
and can be used to discriminate what an implementation can and cannot
do. This section describes profiles that enable to implement only a
portion of this specification to meet a particular use case.
Profiles 0 to 2 operate in the Main RPL Instance and do not require
the support of local RPL Instances or the indication of the RPL
Instance in the data plane. Profile 3 and above leverage Local RPL
Instances to build arbitrary Tracks rooted at the Track Ingress and
using its namespace for TrackID.
Profiles 0 and 1 are REQUIRED by all implementations that may be used
in LLNs; this enables to use Storing Mode to reduce the size of the
Source Route Header in the most common LLN deployments. Profile 2 is
RECOMMENDED in high speed / wired environment to enable traffic
Engineering and network automation. All the other profile /
environment combinations are OPTIONAL.
Profile 0 Profile 0 is the Legacy support of [RPL] Non-Storing Mode,
with default routing Northwards (up) and strict source routing
Southwards (down the main DOAG). 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.
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Profile 1 (Storing Mode P-Route Segments along the Main DODAG) Profi
le 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) P
rofile 2 extends Profile 0 with Strict Source-Routing Non-Storing
Mode P-Routes along the Main DODAG, which is the same as Profile 1
but using NSM VIOs as opposed to SM VIOs. Profile 2 provides the
same capability to compress the SRH in packets down the Main DODAG
as Profile 1, but it require an encapsulation, in order to insert
an additional SRH between the loose source routing hops. In that
case, the Tracks MUST be installed as subTracks of the Main DODAG,
the main RPL Instance MUST be used as TrackID, and the Ingress
node that encapsulates is not the Root as it does not own the
DODAGID.
Profile 3 In order to form the best path possible, those Profiles
require the support of Sibling Information Option to inform the
Root of additional possible hops. Profile 3 extends Profile 1
with additional Storing Mode P-Routes that install segments that
do not follow the Main DODAG. If the Segment Ingress (in the SM-
VIO) is the same as the IPv6 Address of the Track Ingress (in the
projected DAO base Object), the P-DAO creates an implicit Track
between the Segment Ingress and the Segment Egress.
Profile 4 Profile 4 extends Profile 2 with Strict Source-Routing
Non-Storing Mode P-Routes to form East-West Tracks that are inside
the Main DODAG but do not necessarily follow it. A Track is
formed as one or more strict source source routed paths between
the Root that is the Track Ingress, and the Track Egress that is
the last node.
Profile 5 Profile 5 Combines Profile 4 with Profile 1 and enables to
loose source routing between the Ingress and the Egress of the
Track. As in Profile 1, Storing Mode P-Routes connect the dots in
the loose source route.
Profile 6 Profile 6 Combines Profile 4 with Profile 2 and also
enables to loose source routing between the Ingress and the Egress
of the Track.
Profile 7 Profile 7 implements profile 5 in a Main DODAG that is
operated in Storing Mode as presented in Section 7.1. As in
Profile 1 and 2, the TrackID is the RPLInstanceID of the Main
DODAG. Longest match rules decide whether a packet is sent along
the Main DODAG or rerouted in a track.
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Profile 8 Profile 8 is offered in preparation of the RAW work, and
for use cases where an arbitrary node in the network can afford
the same code complexity as the RPL Root in a traditional
deployment. It offers a full DODAG visibility to the Track
Ingress as specified in Section 7.2 in a Non-Storing Mode Main
DODAG.
Profile 9 Profile 9 combines profiles 7 and 8, operating the Track
as a full DODAG within a Storing Mode Main DODAG, using only the
Main DODAG RPLInstanceID as TrackID.
9. Security Considerations
It is worth noting that with [RPL], every node in the LLN is RPL-
aware and can inject any RPL-based attack in the network. This draft
uses messages that are already present in RPL [RPL] with optional
secured versions. The same secured versions may be used with this
draft, and whatever security is deployed for a given network also
applies to the flows in this draft.
The LLN nodes depend on the 6LBR and the RPL participants for their
operation. A trust model must be put in place to ensure that the
right devices are acting in these roles, so as to avoid threats such
as black-holing, (see [RFC7416] section 7). This trust model could
be at a minimum based on a Layer-2 Secure joining and the Link-Layer
security. This is a generic 6LoWPAN requirement, see Req5.1 in
Appendix B.5 of [RFC8505].
In a general manner, the Security Considerations in [RPL], and
[RFC7416] apply to this specification as well. The Link-Layer
security is needed in particular to prevent Denial-Of-Service attacks
whereby a rogue router creates a high churn in the RPL network by
constantly injected forged P-DAO messages and using up all the
available storage in the attacked routers.
Additionally, the trust model could include a role validation (e.g.,
using a role-based authorization) to ensure that the node that claims
to be a RPL Root is entitled to do so. That trust should propagate
from Egress to Ingress in the case of a Storing Mode P-DAO.
This specification suggests some validation of the VIO to prevent
basic loops by avoiding that a node appears twice. But that is only
a minimal protection. Arguably, an attacker tha can inject P-DAOs
can reroute any traffic and deplete critical resources such as
spectrum and battery in the LLN rapidly.
10. IANA Considerations
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10.1. New Elective 6LoWPAN Routing Header Type
This document updates the IANA registry titled "Elective 6LoWPAN
Routing Header Type" that was created for [RFC8138] and assigns the
following value:
+===============+=============+===============+
| Value | Description | Reference |
+===============+=============+===============+
| 8 (Suggested) | P-RPI-6LoRH | This document |
+---------------+-------------+---------------+
Table 21: New Elective 6LoWPAN Routing
Header Type
10.2. New Critical 6LoWPAN Routing Header Type
This document updates the IANA registry titled "Critical 6LoWPAN
Routing Header Type" that was created for [RFC8138] and assigns the
following value:
+===============+=============+===============+
| Value | Description | Reference |
+===============+=============+===============+
| 8 (Suggested) | P-RPI-6LoRH | This document |
+---------------+-------------+---------------+
Table 22: New Critical 6LoWPAN Routing
Header Type
10.3. New Subregistry For The RPL Option Flags
IANA is required to create a subregistry for the 8-bit RPL Option
Flags field, as detailed in Figure 7, under the "Routing Protocol for
Low Power and Lossy Networks (RPL)" registry. The bits are indexed
from 0 (leftmost) to 7. Each bit is Tracked with the following
qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Indication When Set
* Reference
Registration procedure is "Standards Action" [RFC8126]. The initial
allocation is as indicated in Table 26:
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+===============+======================+===============+
| Bit number | Indication When Set | Reference |
+===============+======================+===============+
| 0 | Down 'O' | [RFC6553] |
+---------------+----------------------+---------------+
| 1 | Rank-Error (R) | [RFC6553] |
+---------------+----------------------+---------------+
| 2 | Forwarding-Error (F) | [RFC6553] |
+---------------+----------------------+---------------+
| 3 (Suggested) | Projected-Route (P) | This document |
+---------------+----------------------+---------------+
Table 23: Initial PDR Flags
10.4. New RPL Control Codes
This document extends the IANA Subregistry created by RFC 6550 for
RPL Control Codes as indicated in Table 24:
+==================+=============================+===============+
| Code | Description | Reference |
+==================+=============================+===============+
| 0x09 (Suggested) | Projected DAO Request (PDR) | This document |
+------------------+-----------------------------+---------------+
| 0x0A (Suggested) | PDR-ACK | This document |
+------------------+-----------------------------+---------------+
Table 24: New RPL Control Codes
10.5. New RPL Control Message Options
This document extends the IANA Subregistry created by RFC 6550 for
RPL Control Message Options as indicated in Table 25:
+==================+=============================+===============+
| Value | Meaning | Reference |
+==================+=============================+===============+
| 0x0E (Suggested) | Stateful VIO (SM-VIO) | This document |
+------------------+-----------------------------+---------------+
| 0x0F (Suggested) | Source-Routed VIO (NSM-VIO) | This document |
+------------------+-----------------------------+---------------+
| 0x10 (Suggested) | Sibling Information option | This document |
+------------------+-----------------------------+---------------+
Table 25: RPL Control Message Options
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10.6. SubRegistry for the Projected DAO Request Flags
IANA is required to create a registry for the 8-bit Projected DAO
Request (PDR) Flags field. Each bit is Tracked with the following
qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Reference
Registration procedure is "Standards Action" [RFC8126]. The initial
allocation is as indicated in Table 26:
+============+========================+===============+
| Bit number | Capability description | Reference |
+============+========================+===============+
| 0 | PDR-ACK request (K) | This document |
+------------+------------------------+---------------+
| 1 | Requested path should | This document |
| | be redundant (R) | |
+------------+------------------------+---------------+
Table 26: Initial PDR Flags
10.7. SubRegistry for the PDR-ACK Flags
IANA is required to create an subregistry for the 8-bit PDR-ACK Flags
field. Each bit is Tracked with the following qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Reference
Registration procedure is "Standards Action" [RFC8126]. No bit is
currently defined for the PDR-ACK Flags.
10.8. Subregistry for the PDR-ACK Acceptance Status Values
IANA is requested to create a Subregistry for the PDR-ACK Acceptance
Status values.
* Possible values are 6-bit unsigned integers (0..63).
* Registration procedure is "Standards Action" [RFC8126].
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* Initial allocation is as indicated in Table 27:
+-------+------------------------+---------------+
| Value | Meaning | Reference |
+-------+------------------------+---------------+
| 0 | Unqualified Acceptance | This document |
+-------+------------------------+---------------+
Table 27: Acceptance values of the PDR-ACK Status
10.9. Subregistry for the PDR-ACK Rejection Status Values
IANA is requested to create a Subregistry for the PDR-ACK Rejection
Status values.
* Possible values are 6-bit unsigned integers (0..63).
* Registration procedure is "Standards Action" [RFC8126].
* Initial allocation is as indicated in Table 28:
+-------+-----------------------+---------------+
| Value | Meaning | Reference |
+-------+-----------------------+---------------+
| 0 | Unqualified Rejection | This document |
+-------+-----------------------+---------------+
| 1 | Transient Failure | This document |
+-------+-----------------------+---------------+
Table 28: Rejection values of the PDR-ACK Status
10.10. SubRegistry for the Via Information Options Flags
IANA is requested to create a Subregistry for the 5-bit Via
Information Options (Via Information Option) Flags field. Each bit
is Tracked with the following qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Reference
Registration procedure is "Standards Action" [RFC8126]. No bit is
currently defined for the Via Information Options (Via Information
Option) Flags.
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10.11. SubRegistry for the Sibling Information Option Flags
IANA is required to create a registry for the 5-bit Sibling
Information Option (SIO) Flags field. Each bit is Tracked with the
following qualities:
* Bit number (counting from bit 0 as the most significant bit)
* Capability description
* Reference
Registration procedure is "Standards Action" [RFC8126]. The initial
allocation is as indicated in Table 29:
+===============+========================+===========+
| Bit number | Capability description | Reference |
+===============+========================+===========+
| 0 (Suggested) | "S" flag: Sibling in | This |
| | same DODAG as Self | document |
+---------------+------------------------+-----------+
Table 29: Initial SIO Flags
10.12. New destination Advertisement Object Flag
This document modifies the "destination Advertisement Object (DAO)
Flags" registry initially created in Section 20.11 of [RPL] .
Section 4.1.1 also defines one new entry in the Registry as follows:
+---------------+------------------------+-----------+
| Bit Number | Capability Description | Reference |
+---------------+------------------------+-----------+
| 2 (Suggested) | Projected DAO (P) | THIS RFC |
+---------------+------------------------+-----------+
Table 30: New destination Advertisement Object
(DAO) Flag
10.13. New ICMPv6 Error Code
In some cases RPL will return an ICMPv6 error message when a message
cannot be forwarded along a P-Route.
IANA has defined an ICMPv6 "Code" Fields Registry for ICMPv6 Message
Types. ICMPv6 Message Type 1 describes "destination Unreachable"
codes. This specification requires that a new code is allocated from
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the ICMPv6 Code Fields Registry for ICMPv6 Message Type 1, for "Error
in P-Route", with a suggested code value of 8, to be confirmed by
IANA.
10.14. New RPL Rejection Status values
This specification updates the Subregistry for the "RPL Rejection
Status" values under the RPL registry, as follows:
+---------------+-------------------------+-----------+
| Value | Meaning | Reference |
+---------------+-------------------------+-----------+
| 2 (Suggested) | Out of Resources | THIS RFC |
+---------------+-------------------------+-----------+
| 3 (Suggested) | Error in VIO | THIS RFC |
+---------------+-------------------------+-----------+
| 4 (Suggested) | Predecessor Unreachable | THIS RFC |
+---------------+-------------------------+-----------+
| 5 (Suggested) | Unreachable Target | THIS RFC |
+---------------+-------------------------+-----------+
| 6..63 | Unassigned | |
+---------------+-------------------------+-----------+
Table 31: Rejection values of the RPL Status
11. Acknowledgments
The authors wish to acknowledge JP Vasseur, Remy Liubing, James
Pylakutty, and Patrick Wetterwald for their contributions to the
ideas developed here. Many thanks to Dominique Barthel and SVR Anand
for their global contribution to 6TiSCH, RAW and this document, as
well as text suggestions that were incorporated, and to Michael
Richardson for his useful recommendations based on his global view of
the system. Also special thanks Toerless Eckert for his deep review,
with many excellent suggestions that improved the readability and
well as the content of the specification.
12. Normative References
[INT-ARCHI]
Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
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[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
13. Informative References
[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>.
[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>.
[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>.
[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>.
[6TiSCH-ARCHI]
Thubert, P., Ed., "An Architecture for IPv6 over the Time-
Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)",
RFC 9030, DOI 10.17487/RFC9030, May 2021,
<https://www.rfc-editor.org/info/rfc9030>.
[RAW-ARCHI]
Thubert, P., Papadopoulos, G. Z., and L. Berger, "Reliable
and Available Wireless Architecture/Framework", Work in
Progress, Internet-Draft, draft-ietf-raw-architecture-01,
28 July 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-raw-architecture-01>.
[USE-CASES]
Papadopoulos, G. Z., Thubert, P., Theoleyre, F., and C. J.
Bernardos, "RAW use cases", Work in Progress, Internet-
Draft, draft-ietf-raw-use-cases-02, 12 July 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-raw-use-
cases-02>.
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[TURN-ON_RFC8138]
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>.
[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[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>.
[I-D.irtf-panrg-path-properties]
Enghardt, T. and C. Krähenbühl, "A Vocabulary of Path
Properties", Work in Progress, Internet-Draft, draft-irtf-
panrg-path-properties-03, 9 July 2021,
<https://datatracker.ietf.org/doc/html/draft-irtf-panrg-
path-properties-03>.
[PCE] IETF, "Path Computation Element",
<https://dataTracker.ietf.org/doc/charter-ietf-pce/>.
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 Mougins - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Rahul Arvind Jadhav
Huawei Tech
Kundalahalli Village, Whitefield,
Bangalore 560037
Karnataka
India
Phone: +91-080-49160700
Email: rahul.ietf@gmail.com
Matthew Gillmore
Itron, Inc
Building D
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2111 N Molter Road
Liberty Lake, 99019
United States
Phone: +1.800.635.5461
Email: matthew.gillmore@itron.com
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