wdiff draft-ietf-roll-dao-projection-00.txt draft-ietf-roll-dao-projection-01.txt

ROLL P. Thubert, Ed.
Internet-Draft J. Pylakutty
Intended status: Standards Track Cisco
Expires: June September 11, 2017 March 10, 2017 December 07, 2016

Root initiated routing state in RPL
draft-ietf-roll-dao-projection-00
draft-ietf-roll-dao-projection-01

Abstract

This document proposes a protocol extension to RPL that enables to
install a limited amount of centrally-computed routes in a RPL graph,
enabling loose source routing down a non-storing mode DODAG, or
transversal routes inside the DODAG. As opposed to the classical
route injection in RPL that are injected by DAO messages, the end devices, this
draft projects the routes from enables the root of the DODAG. DODAG to projects the routes that are
needed on the nodes where they should be installed.

Status of This Memo

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

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This Internet-Draft will expire on April 27, September 11, 2017.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. New RPL Control Message Options . . . . . . . . . . . . . . . 4 3
3.1. Via Information Option . . . . . . . . . . . . . . . . . 4
4. Projected DAO . . . . 4
4. . . . . . . . . . . . . . . . . . . . . 5
4.1. Non-storing Mode Projected DAO . . . . . . . . . . . . . 6
4.2. Storing-Mode Projected DAO . . . . . . . . . . . . . . . 8
5. Applications . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Loose Source Routing in Non-storing Mode . . . . . . . . . . 5
5. Centralized Computation of Optimized Peer-to-Peer 10
5.2. Transversal Routes in storing and non-storing modes . . 9 . 11
6. RPL Instances . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. 14
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9. 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.2. 14
10.2. Informative References . . . . . . . . . . . . . . . . . 13 15
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 15
A.1. Using storing mode P-DAO in non-storing mode MOP . . . . 16
A.2. Projecting a storing-mode transversal route . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 18

1. Introduction

The Routing Protocol for Low Power and Lossy Networks (LLN)(RPL)
[RFC6550] (LLN)
(RPL) specification defines is a generic Distance Vector protocol that is designed well suited
for very low energy consumption and adapted to application in a variety of LLNs. low energy Internet of Things (IoT)
networks. 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 Internet. The root is responsible to select
the RPL Instance that is used to forward a packet coming from the
Internet into the RPL domain and set the related RPL information in
the packets.

In the non-storing mode (NSM) of operation (MOP), the root also
computes routes down the DODAG towards the end device and leverages
source routing to get there, while the default route via the root is
used for routing upwards within the LLN and to the Internet at large.
NSM is the dominant MOP because because networks may get arbitrary
large and in Storing Mode, the amount of memory in nodes close to the
root may unexpectedly require memory beyond a node's capabilities.

But as a network gets deep, the size of the source routing header
that the root must add to all the downward packets may also become an
issue for far away target devices. In some use cases, a RPL network
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 has in non-storing mode.

Additionally, RPL storing mode is optimized or Point-to-Multipoint
(P2MP), root to leaves and Multipoint-to-Point (MP2P) leaves to root
operations, whereby routes are always installed along the RPL DODAG.
Transversal Peer to Peer (P2P) routes in a RPL network will generally
suffer from some stretch since routing between 2 peers always happens
via a common parent. In NSM, all peer-to-peer routes travel all the
way to the root, which adds a source routing header and forwards the
packet down to the destination, resulting in the longest stretch and
overload of the radio bandwidth near the root. A controller, for
instance collocated with the RPL root, with enough topological
awareness of the connectivity between nodes, would be able to compute
more direct routes, avoiding the vicinity of the root whenever
possible.

The 6TiSCH architecture [I-D.ietf-6tisch-architecture] leverages RPL
for its routing operation and considers the Deterministic Networking
Architecture [I-D.finn-detnet-architecture] [I-D.ietf-detnet-architecture] as one possible model
whereby the device resources and capabilities are exposed to an
external controller which installs routing states into the network
based on some objective functions that reside in that external
entity.

Based on heuristics of usage, path length, and knowledge of device
capacity and available resources such as battery levels and
reservable buffers, a Path Computation Element ([PCE]) with a global
visibility on the system could install additional P2P routes that are
more optimized for the current needs as expressed by the objective
function.

This draft enables a RPL root, with optionally the assistance of a
PCE, to install and maintain additional storing and non-storing mode
routes within the RPL domain, along a selected set of nodes and for a
selected duration, thus providing routes from more suitable than those
obtained
from with the distributed operation of RPL RPL. Those routes may be
installed in either storing and non-
storing modes. non-storing modes RPL instances,
resulting in potentially hybrid situations where the mode of the
projected routes is different from that of the other routes in the
instance.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

The Terminology used in this document is consistent with and
incorporates that described in `Terminology in Low power And Lossy
Networks' [RFC7102] and [RFC6550].

3. New RPL Control Message Options

Section 6.7 of [RFC6550] specifies Control Message Options (CMO) to
be placed in RPL messages such as the DAO Destination Advertisement
Object (DAO) message. The RPL Target Option and the Transit
Information Option (TIO) are such options; the former indicates a
node to be reached and the latter specifies a parent that can be used
to reach that node. Options may be factorized; one or more
contiguous TIOs apply to the one or more contiguous Target options
that immediately precede the TIOs in the RPL message.

This specification introduces a new Control Message Option, the Via
Information option (VIO). Like the TIO, the VIO MUST be preceded by
one or more RPL Target options to which it applies. Unlike the TIO,
the VIO are not factorized: multiple contiguous Via options indicate
an ordered sequence of hops routers to reach the target(s), presented in
the
same order as they would appear of the packet stream, source to destination, and in which a
routing header. state must be installed.

The Via Information option MUST contain at least one Via Address.

3.1. Via Information Option

The Via Information option MAY be present in DAO messages, and its
format is as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x0A | Option Length | Path Sequence | Path Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Next-Hop Via Address 1 .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .... .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Via Address n .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: Eliding the RPLInstanceID Via Information option format

Option Type: 0x0A (to be confirmed by IANA)

Option Length: Variable, In bytes; variable, depending on whether or not Parent Address
is present. the number of Via
Addresses.

Path Sequence: 8-bit unsigned integer. When a RPL Target option is
issued by the root of the DODAG (i.e. in a DAO message), that
root sets the Path Sequence and increments the Path Sequence
each time it issues a RPL Target option with updated
information. The indicated sequence deprecates any state for a
given Target that was learned from a previous sequence and adds
to any state that was learned for that sequence.

Path Lifetime: 8-bit unsigned integer. The length of time in
Lifetime Units (obtained from the Configuration option) that
the prefix is valid for route determination. The period starts
when a new Path Sequence is seen. A value of all one bits
(0xFF) represents infinity. A value of all zero bits (0x00)
indicates a loss of reachability. A DAO message that contains
a Via Information option with a Path Lifetime of 0x00 for a
Target is referred as a No-Path (for that Target) in this
document.

Next-Hop

Via Address: 8 or 16 bytes. IPv6 Address of the next hop towards the
destination(s) indicated in the target option that immediately
precede the VIO. The TBD: See how the /64 prefix can be elided if
it is the same as that of (all of) the target(s). In that
case, the Next-Hop Address is could be expressed as the 8-bytes
suffix only, otherwise it is expressed as 16 bytes.

4. Loose Source Routing in Non-storing Mode

A classical RPL implementation bytes, at least in a very constrained LLN uses the
non-storing mode of operation whereby 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 builds a path to a destination down the DODAG by
concatenating this information.

Figure 2: RPL non-storing operation

Nodes are not expected to store downward routing state via their
children, and the routing operates in strict source routing mode as
detailed in An IPv6 Routing Header for Source Routes with RPL
[RFC6554]

This draft proposes an addition adds a capability to RPL whereby the root projects a route
through an extended DAO message called a Projected-DAO (P-DAO) to an
arbitrary node router down the DODAG, indicating a child next hop or a direct sequence
of children routers via which a certain destination (target) indicated in the Target
Information option may be reached.

A P-DAO message MUST contain at least a Target Information option and
at least one VIA Information option following it.

Like a classical DAO message, a P-DAO is processed only if it is
"new" per section 9.2.2. "Generation of DAO Messages" of the RPL
specification [RFC6550]; this is determined using the Path Sequence
information from the VIO as opposed to a TIO. Also, a Path Lifetime
of 0 in a VIO indicates that a route is to be removed.

There are two kinds of P-DAO, the storing mode and the non-storing
mode ones.

The non-storing mode P-DAO discussed in section Section 4.1 has a
single VIO with one or more Via Addresses in it, the list of Via
Addresses indicating the source-routed path to the target to be
installed in the router that receives the message, which replies
to the root directly with a DAO-ACK message.

The storing mode P-DAO discussed in section Section 4.2 has at
least two Via Information options with one Via Address each, for
the ingress and the egress of the path, and more if there are
intermediate routers. The Via Addresses indicate the routers in
which the routing state to the target have to be installed via the
next Via Address in the sequence of VIO. In normal operations,
the P-DAO is propagated along the chain of Via Routers from the
egress router of the path till the ingress one, which confirms the
installation to the root with a DAO-ACK message. Note that the
root may be the ingress and it may be the egress of the path, that
it can also be neither but it cannot be both.

The root is expected to use the mechanism these mechanisms optimally and with
required parsimony to limit the state installed in the devices to fit
within
the device their resources, but how the root figures the amount of
resources that are is available in each device is out of scope. scope for this
document.

In particular, the draft expects that the root has enough information
about the capability for each node to store a number of routes, which
can be discovered for instance using a Network Management System
(NMS) and/or the RPL routing extensions specified in Routing for Path
Calculation in LLNs [RFC6551].

A route that is installed by a P-DAO is not necessarily installed
along the DODAG, though how the root and the optional PCE obtain the
additional topological information to compute other routes is out of
scope for this document

4.1. Non-storing Mode Projected DAO

As illustrated in Figure 2, the non-storing mode P-DAO enables the
root to install a source-routed path towards a target in any
particular router; with this path information the router can add a
source routed header reflecting the path to any packet for which the
current destination either is the said target or can be reached via
the target, for instance a loose source routed packet for which the
next loose hop is the target, or a packet for which the router has a
routing state to the final destination via the target.

LLN

Figure 2: Non-Storing with Projected routes

When Projecting a RPL domain operates in non-storing Mode route

A router that receives a non-storing P-DAO installs a source routed
path towards each of Operation (NS-MOP),
only the root possesses routing information about consecutive targets via a source route path
indicated in the whole network.
A following VIO.

When forwarding a packet to a destination for which the router
determines that is generated within routing happens via the domain first reaches target, the router inserts
the root,
which can then apply a source routing information header in the packet to reach the
destination. Similarly, a packet coming from target.

In order to do so, the outside of router encapsulates the
domain for a destination that is expected to be packet with an IP in
IP header and a RPL domain
reaches the root. non-storing mode source routing header (SRH)
[RFC6554].

In NS-MOP, the root, or some associated centralized computation
engine, can thus determine uncompressed form the amount source of packets that reach a the packet would be self, the
destination in would be the RPL domain, and thus first Via Address in the amount of energy and
bandwidth that is wasted for transmission, between itself VIO, and the
destination, as well as SRH
would contain the risk of fragmentation, any potential
delays because list of a paths longer than necessary (shorter paths exist
that would not traverse the root).

Additionally, remaining Via Addresses and then the DAG root knows
target.

In practice, the whole DAG topology, so when router will normally use the
source of a packet is also in IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch [RFC8025] to
compress the RPL domain, the root can determine artifacts as indicated in the common parent 6LoWPAN Routing Header
[I-D.ietf-roll-routing-dispatch] specification. In that would have been used case, the
router indicates self as encapsulator in storing mode, an IP-in-IP 6LoRH Header,
and thus places the list of nodes Via Addresses in the path between order of the common parent VIO and then
the
destination. For instance target in the below diagram, if SRH 6LoRH Header.

4.2. Storing-Mode Projected DAO

As illustrated in Figure 3, the source is 41 storing mode P-DAO enables the root
to install a routing state towards a target in the routers along a
segment between an ingress and an egress router; this enables the destination 52,
routers to forward along that segment any packet for which the common parent next
loose hop is the node 22. said target, for instance a loose source routed
packet for which the next loose hop is the target, or a packet for
which the router has a routing state to the final destination via the
target.

------+---------
| Internet
|
+-----+
| | Border Router
| | (RPL Root)
+-----+ | \ \____
/ \ \ ^ |
| | DAO | ACK |
o o 11 o 12 o 13
/ | / \ | | Loose
o 22 o 23 o 24 o 25
/ \ | \ \ o 31 o 32 o o o 35
/ / | \ ^ | \ Source
o o o o o 41 o 42 o o o 45 o 46 | | DAO | Route
o o o o o o o o o | \ ^ |
o 51 o 52 o 53 o o 55 o 56 o o v | DAO v
o o o o

LLN

Figure 3: Non-Storing with Projected routes

With this draft, the root can install routing states along a segment
that is either itself to the destination, or from one or more common
parents for a particular source/destination pair towards that
destination (in our example, this would be the segment made of nodes
22, 32, 42).

The draft expects that the root has enough information about the
capability for each node to store Projecting a number of routes, which can be
discovered for instance using a Network Management System (NMS) and/
or the RPL routing extensions specified in Routing for Path
Calculation in LLNs [RFC6551]. route

Based on that available topological, usage and capabilities node
information, the root or an associated PCE computes which segment
should be routed optimized and which relevant state should be installed in
which nodes. The algorithm is out of scope but it is envisaged that
the root could compute the ratio between the optimal path (existing
path not traversing the root, and the current path), the application SLA
service level agreement (SLA) for specific flows that could benefit
from shorter paths, the energy wasted in the network, local
congestion on various links that would benefit from having flows
routed along other alternate paths.

This draft introduces a new mode of operation for loose source
routing in

In order to install the LLN, relevant routing state along the Non-Storing with Projected routes MOP. With
this new MOP, segment
between an ingress and an egress routers, the root sends a unicast DAO
P-DAO message to the last node egress router of the routing segment that must
be installed. The DAO P-DAO message contains the ordered list of hops
along the segment as a list direct sequence of Via Information options
that are preceded by one or more RPL Target options to which they
relate. Each Via Information option contains a
lifetime Path Lifetime for
which the state is to be maintained.

The root sends the DAO P-DAO directly to the last egress node in of the segment,
which In that P-DAO, the destination IP address matches the Via
Address in the last VIO. This is how the egress recognizes its role.
In a similar fashion, the ingress node recognizes its role as it
matches Via Address in the first 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 targets target(s) on its own.

The last node in It may either be
the segment target, or may have another some existing information to reach the
target(s), such as a connected route or an already installed
projected route. If it does not have such a route then the node
should lookup the address on the relevant interfaces. If one of the targets cannot be located, the node
MUST answer to the root with a negative DAO-ACK listing the target(s)
that could not be located (suggested status 10), and continue the process for those targets
that could 10 to be located if any.

For confirmed by
IANA).

If the targets that could be located, last egress node in can reach all the segment
generates a DAO targets, then it forwards the
P-DAO with unchanged content to its loose predecessor in the segment
as indicated in the list of Via Information options.

The node strips the last Via Information option which corresponds to
self, options, and uses it as source address for recursively
the DAO to message is propagated unchanged along the sequence of routers
indicated in the P-DAO, but in the predecessor. reverse order, from egress to
ingress.

The address of the predecessor to be used as destination for of the
propagated DAO message is found in the now last Via Information option. The
predecessor is expected to have a route to option the
precedes the one that contain the address of the propagating node,
which is used as
source, either connected, installed previously as another source of the packet.

Upon receiving a propagated DAO, or
from other means.

The predecessor is expected to have an intermediate router as well as
the ingress router install a route to towards the address used as
source and DAO target(s) via its
successor in the P-DAO; the router locates the VIO that is his successor. If it does not contains its
address, and cannot locate uses as next hop the successor, address found in the predecessor node MUST answer Via Address
field in the following VIO. The router MAY install additional routes
towards the addresses that are located in VIOs that are after the
next one, if any, but in case of a conflict or a lack of resource, a
route to a target installed by the root has precedence.

The process recurses till the P-DAO is propagated to ingress router
of the segment, which answers with a
negative DAO-ACK indicating to the successor that could not be located.
The DAO-ACK contains root.

Also, the list of targets that could not path indicated in a P-DAO may be routed loose, in which case the
reachability to
(suggested status 11).

If the predecessor can route next hop has to be asserted. Each router along
the successor node, then it installs path indicated in a route P-DAO is expected to the targets via the successor. be able to reach its
successor, either with a connected route (direct neighbor), or by
routing, for instance following a route installed previously by a DAO
or a P-DAO message. If that route is not connected then a recursive
lookup will may take place at packet forwarding time to find the next hop
to reach the target(s). From there, If it does not and cannot reach the node strips next
router in the last Via Information
option and either answers P-DAO, the router MUST answer to the root with a positive
negative DAO-ACK that
contains indicating the list of targets successor that could be routed to, or propagates
the DAO is unreachable
(suggested status 11 to its own predecessor. be confirmed by IANA).

A NULL lifetime Path Lifetime of 0 in the a Via Information option along the segment is used to clean up
the state.

In The P-DAO is forwarded as described above, but the example below, say that there DAO is
interpreted as a lot No-Path DAO and results in cleaning up existing
state as opposed to refreshing an existing one or installing a new
one.

5. Applications

5.1. Loose Source Routing in Non-storing Mode

A RPL implementation operating in a very constrained LLN typically
uses the non-storing mode of traffic operation whereby a RPL node indicates a
parent-child relationship to nodes 55
and 56 the root, using a Destination
Advertisement Object (DAO) that is unicast from the node directly to
the root, and the root decides typically builds a source routed path to reduce a
destination down the size DODAG by recursively concatenating this
information.

Figure 4: RPL non-storing mode of routing headers to
those destinations. The 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 first send then apply a DAO source routing information to node 45
indicating target 55 and reach the destination
if the destination is also in the DODAG. Similarly, a Via segment (35, 45), 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 another
DAO to node 46 indicating target 56 and the risk of fragmentation, any
potential delays because of a Via segment (35, 46). This
will save one entry in 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 on both sides. The that
the root
may then send a DAO must add to node 35 indicating targets 55 all the downward packets becomes an issue for
nodes that are many hops away. In some use cases, a RPL network
forms long lines and 56 a Via
segment (13, 24, 35) limited amount of well-targeted routing state
would allow to fully optimize that path.

Alternatively, make the root may send a DAO source routing operation loose as opposed to node 45 indicating target
55 and a Via segment (13, 24, 35, 45)
strict, and then a DAO 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 46
indicating target 56 and is limited, the decision of which route
is installed where can only be optimized with a Via segment (13, 24, 35, 46), indicating global knowledge of
the same DAO Sequence.

5. Centralized Computation system, a knowledge that the root or an associated PCE may
possess by means that are outside of Optimized Peer-to-Peer Routes

With the initial specifications scope of RPL [RFC6550], this specification.

This specification enables to store source-routed or storing mode
state in intermediate routers, which enables to limit the P2P path from excursion
of the source route headers in deep networks. Once a P-DAO exchange
has taken place for a given target, if the root operates in non
storing mode, then it may elide the sequence of routers that is
installed in the network from its source route headers to a destination
that are reachable via that target, and the source route headers
effectively become loose.

5.2. Transversal Routes in storing and non-storing modes

RPL is often stretched, optimized for Point-to-Multipoint (P2MP), root to leaves and
Multipoint-to-Point (MP2P) leaves to root operations, whereby routes
are always installed along the RPL DODAG. Transversal Peer to Peer
(P2P) routes in a RPL network will generally suffer from some stretch
since routing between 2 peers always happens via a common parent, as
illustrated in
[RFC6550]:

- Figure 5:

o 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 a
Routing Header 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

o 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 DAO 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 additional P2P
routes, either if the RPL route present a stretch from shortest path,
or if the new route is engineered with a different objective.

Figure 4: 5: Routing Stretch between S and D via common parent X

It results that it is often beneficial to enable transversal P2P
routes, either if the RPL route presents a stretch from shortest
path, or if the new route is engineered with a different objective.
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.

Figure 6: Projected Transversal Route

This specification enables to store source-routed or storing mode
state in intermediate routers, which enables to limit the stretch of
a P2P route and maintain the characteristics within a given SLA. An
example of service using this mechanism oculd be a control loop that
would be installed in a network that uses classical RPL for
asynchronous data collection. In that case, the P2P path may be
installed in a different RPL Instance, with a different objective
function.

6. RPL Instances

It must be noted that RPL has a concept of instance but does not have
a concept of an administrative distance, which exists in certain
proprietary implementations to sort out conflicts between multiple
sources. This draft conforms the instance model as follows:

o if the PCE needs to influence a particular instance to add better
routes in conformance with the routing objectives in that
instance, it may do so. When the PCE modifies an existing
instance then the added routes must not create a loop in that
instance. This is achieved by always preferring a route obtained
from the PCE over a route that is learned via RPL.

o If the PCE installs a more specific (Traffic Engineering) route
between a particular pair of nodes then it should use a Local
Instance from the ingress node of that path. Only packets
associated with that instance will be routed along that path.

In all cases, the path is indicated by VIA options, a new Via Information option,
and the flow is similar to the flow used to obtain loose source
routing.

The root sends the DAO with the target option and the Via Option to
the lest router in the path; the last router removes the last Via
Option and passes the DAO to the previous hop.

Figure 5: Projected DAO from root

The process recurses till the destination which sends a DAO-ACK to
the root. In the example above, for target D, the list of via
options is S, A, B and C. The projected DAO is sent by the root to

Figure 6: Projected DAO-ACK to root

The process recurses till the destination which sends a DAO-ACK to
the root. In the example above, for target D, the list of via
options is S, A, B and C. The projected DAO is sent by the root to
------+---------
| Internet
|
+-----+
| | 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 7: Projected Transversal Route

7. Security Considerations

This draft uses messages that are already present in [RFC6550] 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.

8. IANA Considerations

This document updates the IANA registry for the Mode of Operation
(MOP)

4: Non-Storing with Projected routes [this]

This document updates IANA registry for the RPL Control Message
Options

0x0A: Via descriptor [this]

9. Acknowledgments

The authors wish to acknowledge JP Vasseur and Patrick Wetterwald for
their contributions to the ideas developed here.

10. References
9.1.

10.1. Normative References

[I-D.ietf-roll-routing-dispatch]
Thubert, P., Bormann, C., Toutain, L., and R. Cragie,
"6LoWPAN Routing Header", draft-ietf-roll-routing-
dispatch-05 (work in progress), October 2016.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC6550] 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,
<http://www.rfc-editor.org/info/rfc6550>.

[RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
and D. Barthel, "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks", RFC 6551,
DOI 10.17487/RFC6551, March 2012,
<http://www.rfc-editor.org/info/rfc6551>.

[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,
<http://www.rfc-editor.org/info/rfc6554>.

[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power

[RFC8025] Thubert, P., Ed. and
Lossy Networks", R. Cragie, "IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
RFC 7102, 8025, DOI 10.17487/RFC7102, January
2014, <http://www.rfc-editor.org/info/rfc7102>.

9.2. 10.17487/RFC8025, November 2016,
<http://www.rfc-editor.org/info/rfc8025>.

10.2. Informative References

[I-D.finn-detnet-architecture]
Finn, N. and P. Thubert, "Deterministic Networking
Architecture", draft-finn-detnet-architecture-08 (work in
progress), August 2016.

[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-10 draft-ietf-6tisch-architecture-11 (work
in progress), June January 2017.

[I-D.ietf-detnet-architecture]
Finn, N. and P. Thubert, "Deterministic Networking
Architecture", draft-ietf-detnet-architecture-00 (work in
progress), September 2016.

[PCE] IETF, "Path Computation Element",
<https://datatracker.ietf.org/doc/charter-ietf-pce/>.

[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,
<http://www.rfc-editor.org/info/rfc6997>.

[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <http://www.rfc-editor.org/info/rfc7102>.

Appendix A. Examples
A.1. Using storing mode P-DAO in non-storing mode MOP

In non-storing mode, the DAG root maintains the knowledge of the
whole DODAG topology, so when both the source and the destination of
a packet are in the DODAG, the root can determine the common parent
that would have been used in storing mode, and thus the list of nodes
in the path between the common parent and the destination. For
instance in the diagram shown in Figure 7, if the source is node 41
and the destination is node 52, then the common parent is node 22.

------+---------
| Internet
|
+-----+
| | Border Router
| | (RPL Root)
+-----+
| \ \____
/ \ \
o 11 o 12 o 13
/ | / \
o 22 o 23 o 24 o 25
/ \ | \ \
o 31 o 32 o o o 35
/ / | \ | \
o 41 o 42 o o o 45 o 46
| | | | \ |
o 51 o 52 o 53 o o 55 o 56

LLN

Figure 7: Example DODAG forming a logical tree topology

With this draft, the root can install a storing mode routing states
along a segment that is either from itself to the destination, or
from one or more common parents for a particular source/destination
pair towards that destination (in this particular example, this would
be the segment made of nodes 22, 32, 42).

In the example below, say that there is a lot of traffic to nodes 55
and 56 and the root decides to reduce the size of routing headers to
those destinations. The root can first send a DAO to node 45
indicating target 55 and a Via segment (35, 45), as well as another
DAO to node 46 indicating target 56 and a Via segment (35, 46). This
will save one entry in the routing header on both sides. The root
may then send a DAO to node 35 indicating targets 55 and 56 a Via
segment (13, 24, 35) to fully optimize that path.

Alternatively, the root may send a DAO to node 45 indicating target
55 and a Via segment (13, 24, 35, 45) and then a DAO to node 46
indicating target 56 and a Via segment (13, 24, 35, 46), indicating
the same DAO Sequence.

A.2. Projecting a storing-mode transversal route

In this example, say that a PCE determines that a path must be
installed between node S and node D via routers A, B and C, in order
to serve the needs of a particular application.

The root sends a P-DAO with a target option indicating the
destination D and a sequence Via Information option, one for S, which
is the ingress router of the segment, one for A and then for B, which
are an intermediate routers, and one for C, which is the egress
router.

Figure 8: Projected DAO from root

Upon reception of the P-DAO, C validates that it can reach D, e.g.
using IPv6 Neighbor Discovery, and if so, propagates the P-DAO
unchanged to B.

B checks that it can reach C and of so, installs a route towards D
via C. Then it propagates the P-DAO to A.

The process recurses till the P-DAO reaches S, the ingress of the
segment, which installs a route to D via A and sends a DAO-ACK to the
root.

Figure 9: Projected DAO-ACK to root

As a result, a transversal route is installed that does not need to
follow the DODAG structure.

Figure 10: Projected Transversal Route

Authors' Addresses
Pascal Thubert (editor)
Cisco Systems
Village d'Entreprises Green Side
400, Avenue de Roumanille
Batiment T3
Biot - Sophia Antipolis 06410
FRANCE

Phone: +33 4 97 23 26 34
Email: pthubert@cisco.com

James Pylakutty
Cisco Systems
Cessna Business Park
Kadubeesanahalli
Marathalli ORR
Bangalore, Karnataka 560087
INDIA

Phone: +91 80 4426 4140
Email: mundenma@cisco.com