Internet DRAFT - draft-thubert-dao-projection
draft-thubert-dao-projection
ROLL P. Thubert, Ed.
Internet-Draft J. Pylakutty
Intended status: Standards Track Cisco
Expires: December 31, 2015 June 29, 2015
Root initiated routing state in RPL
draft-thubert-dao-projection-00
Abstract
This document proposes a root-initiated protocol extension to RPL
that enables to install a limited amount of downward routes in non-
storing mode. This enables loose source routing down the DODAG.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 31, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Thubert & Pylakutty Expires December 31, 2015 [Page 1]
Internet-Draft Root initiated routing state in RPL June 2015
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. New RPL Control Message Options . . . . . . . . . . . . . . . 4
3.1. Via Information . . . . . . . . . . . . . . . . . . . . . 5
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Routing Protocol for Low Power and Lossy Networks [RFC6550]
(LLN)(RPL) specification defines a generic Distance Vector protocol
that is indeed designed for very low energy consumption and adapted
to a variety of LLNs. RPL forms Destination Oriented Directed
Acyclic Graphs (DODAGs) which 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.
A classical RPL implementation 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.
Thubert & Pylakutty Expires December 31, 2015 [Page 2]
Internet-Draft Root initiated routing state in RPL June 2015
------+---------
| Internet
|
+-----+
| | 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 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]
The non-storing mode of operation (MOP) is largely utilized because
networks can get very large and the amount of memory in nodes close
to the root may become prohibitive in storing mode. 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 as well. In
some cases, RPL network form long lines and a limited number of well-
targeted routes would enable a loose source routing operation and
save packet size, energy, and eventually fragmentation which is
highly detrimental to the LLN operation.
This draft proposes an addition whereby the root projects a route
through an extended DAO to an arbitrary node down the DODAG,
indicating a child or a direct sequence of children via which a
certain destination (target) may be reached. The root is expected to
use the mechanism optimally and with required parsimony to fit within
the device resources, but how the root figures the amount of
resources that are available is out of scope.
Thubert & Pylakutty Expires December 31, 2015 [Page 3]
Internet-Draft Root initiated routing state in RPL June 2015
------+---------
| Internet
|
+-----+
| | Border Router
| | (RPL Root)
+-----+ | ^ |
| | DAO | ACK |
o o o o | | | Loose
o o o o o o o o o | ^ | Source
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 o o
LLN
Figure 2: Non-Storing with Projected routes
The 6TiSCH architecture [I-D.ietf-6tisch-architecture] leverages the
Deterministic Networking Architecture [I-D.finn-detnet-architecture]
as one possible model whereby the device resources and capabilities
are exposed to an external entity (a Path Computation Element [PCE]),
which installs routing states into the network based on some
objective functions that reside in that external entity.
Based on non-specified heuristics of usage, path length, and
knowledge of device capacity, this draft enables a RPL root to
install and maintain a local and temporary storing mode path within
the RPL domain, along a selected set of nodes and for a selected
duration, thus advantageously modifying the mode of operation of RPL
in non-storing mode.
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 message. The RPL Target
option indicates a node to be reached and the Transit Information
Option specifies a parent that can be used to reach that node.
Thubert & Pylakutty Expires December 31, 2015 [Page 4]
Internet-Draft Root initiated routing state in RPL June 2015
This specification introduces a new Control Message Option, the Via
Information option. One or more Via Information options MUST be
preceded by one or more RPL Target options, and the Via options
indicate an ordered sequence of hops to reach the target(s),
presented in the same order as they would in a routing header.
3.1. Via Information
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Child Address .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Eliding the RPLInstanceID
Option Type: 0x0A (to be confirmed by IANA)
Option Length: Variable, depending on whether or not Parent Address
is present.
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
Thubert & Pylakutty Expires December 31, 2015 [Page 5]
Internet-Draft Root initiated routing state in RPL June 2015
Target is referred as a No-Path (for that Target) in this
document.
Child Address: 8 or 16 bytes. IPv6 Address of the child of the node
that is a next hop towards the destination(s) indicated in the
target option. If the /64 prefix is the same as that of (all
of) the target(s) then the prefix can be elided and the address
is expressed as the 8-bytes suffix only.
4. Operation
When a RPL domain operates in non-storing Mode of Operation (NS-MOP),
only the root possesses routing information about the whole network.
A packet that is generated within the domain first reaches the root,
which can then apply a source routing information to reach the
destination. 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.
In NS-MOP, the root, or some associated centralized computation
engine, can thus 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).
Additionally, the DAG root knows the whole DAG topology, so when the
source of a packet is also in the RPL domain, 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 below diagram, if the source is 41
and the destination 52, the common parent is the node 22.
Thubert & Pylakutty Expires December 31, 2015 [Page 6]
Internet-Draft Root initiated routing state in RPL June 2015
------+---------
| 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 2: 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 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]. Based on that information, the root
computes which segment should be routed 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 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
paths.
This draft introduces a new mode of operation for loose source
routing in the LLN, the Non-Storing with Projected routes MOP. With
this new MOP, the root sends a unicast DAO message to the last node
of the routing segment that must be installed. The DAO message
contains the ordered list of hops along the segment as a list of Via
Information options that are preceded by one or more RPL Target
Thubert & Pylakutty Expires December 31, 2015 [Page 7]
Internet-Draft Root initiated routing state in RPL June 2015
options to which they relate. Each Via Information option contains a
lifetime for which state is to be maintained.
The root sends the DAO directly to the last node in the segment,
which is expected to be able to route to the targets on its own.
The last node in the segment may have another 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 be located if any.
For the targets that could be located, last node in the segment
generates a DAO 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, and uses it as source address for the DAO to the predecessor.
The address of the predecessor to be used as destination for the DAO
message is found in the now last Via Information option. The
predecessor is expected to have a route to the address used as
source, either connected, installed previously as another DAO, or
from other means.
The predecessor is expected to have a route to the address used as
source and that is his successor. If it does not and cannot locate
the successor, the predecessor node MUST answer to the root with a
negative DAO-ACK indicating the successor that could not be located.
The DAO-ACK contains the list of targets that could not be routed to
(suggested status 11).
If the predecessor can route to the successor node, then it installs
a route to the targets via the successor. If that route is not
connected then a recursive lookup will take place to reach the
target(s). From there, the node strips the last Via Information
option and either answers to the root with a positive DAO-ACK that
contains the list of targets that could be routed to, or propagates
the DAO to its own predecessor.
A NULL lifetime in the Via Information option along the segment is
used to clean up the state.
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
Thubert & Pylakutty Expires December 31, 2015 [Page 8]
Internet-Draft Root initiated routing state in RPL June 2015
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.
5. 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.
6. 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]
7. Acknowledgements
The authors wish to acknowledge JP Vasseur and Patrick Wetterwald for
their contributions to the ideas developed here.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6550] Winter, T., Thubert, P., 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, March 2012.
Thubert & Pylakutty Expires December 31, 2015 [Page 9]
Internet-Draft Root initiated routing state in RPL June 2015
[RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D.
Barthel, "Routing Metrics Used for Path Calculation in
Low-Power and Lossy Networks", RFC 6551, March 2012.
[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, March
2012.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, January 2014.
8.2. Informative References
[I-D.finn-detnet-architecture]
Finn, N., Thubert, P., and M. Teener, "Deterministic
Networking Architecture", draft-finn-detnet-
architecture-01 (work in progress), March 2015.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-08 (work
in progress), May 2015.
[PCE] IETF, "Path Computation Element",
<https://datatracker.ietf.org/doc/charter-ietf-pce/>.
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
Thubert & Pylakutty Expires December 31, 2015 [Page 10]
Internet-Draft Root initiated routing state in RPL June 2015
James Pylakutty
Cisco Systems
Cessna Business Park
Kadubeesanahalli
Marathalli ORR
Bangalore, Karnataka 560087
INDIA
Phone: +91 80 4426 4140
Email: mundenma@cisco.com
Thubert & Pylakutty Expires December 31, 2015 [Page 11]
