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Low power and Lossy Networks (LLNs) are a class of network in which both the routers and their interconnect are constrained: LLN routers typically operate with constraints on (any subset of) processing power, memory and energy (battery), and their interconnects are characterized by (any subset of) high loss rates, low data rates and instability. LLNs are comprised of anything from a few dozen and up to thousands of routers, and support point-to-point traffic (between devices inside the LLN), point-to-multipoint traffic (from a central control point to a subset of devices inside the LLN) and multipoint-to-point traffic (from devices inside the LLN towards a central control point). This document specifies the IPv6 Routing Protocol for LLNs (RPL), which provides a mechanism whereby multipoint-to-point traffic from devices inside the LLN towards a central control point, as well as point-to-multipoint traffic from the central control point to the devices inside the LLN, is supported. Support for point-to-point traffic is also available.
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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 November 29, 2010.
Copyright (c) 2010 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.
1.
Introduction
1.1.
Design Principles
1.2.
Expectations of Link Layer Type
2.
Terminology
3.
Protocol Overview
3.1.
Topology
3.1.1.
Topology Identifiers
3.2.
Instances, DODAGs, and DODAG Versions
3.3.
Upward Routes and DODAG Construction
3.3.1.
DAG Repair
3.3.2.
Grounded and Floating DODAGs
3.3.3.
Administrative Preference
3.3.4.
Objective Function (OF)
3.3.5.
Distributed Algorithm Operation
3.4.
Downward Routes and Destination Advertisement
3.5.
Routing Metrics and Constraints Used By RPL
3.5.1.
Loop Avoidance
3.5.2.
Rank Properties
3.6.
Traffic Flows Supported by RPL
3.6.1.
Multipoint-to-Point Traffic
3.6.2.
Point-to-Multipoint Traffic
3.6.3.
Point-to-Point Traffic
4.
RPL Instance
4.1.
RPL Instance ID
5.
ICMPv6 RPL Control Message
5.1.
RPL Security Fields
5.2.
DODAG Information Solicitation (DIS)
5.2.1.
Format of the DIS Base Object
5.2.2.
Secure DIS
5.2.3.
DIS Options
5.3.
DODAG Information Object (DIO)
5.3.1.
Format of the DIO Base Object
5.3.2.
Secure DIO
5.3.3.
DIO Options
5.4.
Destination Advertisement Object (DAO)
5.4.1.
Format of the DAO Base Object
5.4.2.
Secure DAO
5.4.3.
DAO Options
5.5.
Destination Advertisement Object Acknowledgement (DAO-ACK)
5.5.1.
Format of the DAO-ACK Base Object
5.5.2.
Secure DAO-ACK
5.5.3.
DAO-ACK Options
5.6.
RPL Control Message Options
5.6.1.
RPL Control Message Option Generic Format
5.6.2.
Pad1
5.6.3.
PadN
5.6.4.
Metric Container
5.6.5.
Route Information
5.6.6.
DODAG Configuration
5.6.7.
RPL Target
5.6.8.
Transit Information
5.6.9.
Solicited Information
5.6.10.
Prefix Information
6.
Upward Routes
6.1.
DIO Base Rules
6.2.
Upward Route Discovery and Maintenance
6.2.1.
Neighbors and Parents within a DODAG Version
6.2.2.
Neighbors and Parents across DODAG Versions
6.2.3.
DIO Message Communication
6.3.
DIO Transmission
6.3.1.
Trickle Parameters
6.4.
DODAG Selection
6.5.
Operation as a Leaf Node
6.6.
Administrative Rank
7.
Downward Routes
7.1.
Downward Route Discovery and Maintenance
7.1.1.
Overview
7.1.2.
Mode of Operation
7.1.3.
Destination Advertisement Parents
7.1.4.
DAO Operation on Storing Nodes
7.1.5.
Operation of DAO Non-storing Nodes
7.1.6.
Scheduling to Send DAO (or No-Path)
7.1.7.
Triggering DAO Message from the Sub-DODAG
7.1.8.
Sending DAO Messages to DAO Parents
7.1.9.
Multicast Destination Advertisement Messages
8.
Packet Forwarding and Loop Avoidance/Detection
8.1.
Suggestions for Packet Forwarding
8.2.
Loop Avoidance and Detection
8.2.1.
Source Node Operation
8.2.2.
Router Operation
9.
Multicast Operation
10.
Maintenance of Routing Adjacency
11.
Guidelines for Objective Functions
11.1.
Objective Function Behavior
12.
RPL Constants and Variables
13.
Manageability Considerations
13.1.
Control of Function and Policy
13.1.1.
Initialization Mode
13.1.2.
DIO Base option
13.1.3.
Trickle Timers
13.1.4.
DAG Version Number Increment
13.1.5.
Destination Advertisement Timers
13.1.6.
Policy Control
13.1.7.
Data Structures
13.2.
Information and Data Models
13.3.
Liveness Detection and Monitoring
13.3.1.
Candidate Neighbor Data Structure
13.3.2.
Directed Acyclic Graph (DAG) Table
13.3.3.
Routing Table
13.3.4.
Other RPL Monitoring Parameters
13.3.5.
RPL Trickle Timers
13.4.
Verifying Correct Operation
13.5.
Requirements on Other Protocols and Functional Components
13.6.
Impact on Network Operation
14.
Security Considerations
14.1.
Overview
14.2.
Functional Description of Packet Protection
14.2.1.
Transmission of Outgoing Packets
14.2.2.
Reception of Incoming Packets
14.2.3.
Cryptographic Mode of Operation
14.3.
Protecting RPL ICMPv6 messages
14.4.
Security State Machine
15.
IANA Considerations
15.1.
RPL Control Message
15.2.
New Registry for RPL Control Codes
15.3.
New Registry for the Mode of Operation (MOP) DIO Control Field
15.4.
RPL Control Message Option
16.
Acknowledgements
17.
Contributors
18.
References
18.1.
Normative References
18.2.
Informative References
Appendix A.
Requirements
A.1.
Protocol Properties Overview
A.1.1.
IPv6 Architecture
A.1.2.
Typical LLN Traffic Patterns
A.1.3.
Constraint Based Routing
A.2.
Deferred Requirements
Appendix B.
Outstanding Issues
B.1.
Additional Support for P2P Routing
B.2.
Address / Header Compression
B.3.
Managing Multiple Instances
§
Authors' Addresses
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Low power and Lossy Networks (LLNs) consist of largely of constrained nodes (with limited processing power, memory, and sometimes energy when they are battery operated). These routers are interconnected by lossy links, typically supporting only low data rates, that are usually unstable with relatively low packet delivery rates. Another characteristic of such networks is that the traffic patterns are not simply point-to-point, but in many cases point-to-multipoint or multipoint-to-point. Furthermore such networks may potentially comprise up to thousands of nodes. These characteristics offer unique challenges to a routing solution: the IETF ROLL Working Group has defined application-specific routing requirements for a Low power and Lossy Network (LLN) routing protocol, specified in [I‑D.ietf‑roll‑building‑routing‑reqs] (Martocci, J., Riou, N., Mil, P., and W. Vermeylen, “Building Automation Routing Requirements in Low Power and Lossy Networks,” January 2010.), [RFC5826] (Brandt, A., Buron, J., and G. Porcu, “Home Automation Routing Requirements in Low-Power and Lossy Networks,” April 2010.), [RFC5673] (Pister, K., Thubert, P., Dwars, S., and T. Phinney, “Industrial Routing Requirements in Low-Power and Lossy Networks,” October 2009.), and [RFC5548] (Dohler, M., Watteyne, T., Winter, T., and D. Barthel, “Routing Requirements for Urban Low-Power and Lossy Networks,” May 2009.).
This document specifies the IPv6 Routing Protocol for Low power and lossy networks (RPL). Note that although RPL was specified according to the requirements set forth in the aforementioned requirement documents, its use is in no way limited to these applications.
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RPL was designed with the objective to meet the requirements spelled out in [I‑D.ietf‑roll‑building‑routing‑reqs] (Martocci, J., Riou, N., Mil, P., and W. Vermeylen, “Building Automation Routing Requirements in Low Power and Lossy Networks,” January 2010.), [RFC5826] (Brandt, A., Buron, J., and G. Porcu, “Home Automation Routing Requirements in Low-Power and Lossy Networks,” April 2010.), [RFC5673] (Pister, K., Thubert, P., Dwars, S., and T. Phinney, “Industrial Routing Requirements in Low-Power and Lossy Networks,” October 2009.), and [RFC5548] (Dohler, M., Watteyne, T., Winter, T., and D. Barthel, “Routing Requirements for Urban Low-Power and Lossy Networks,” May 2009.).
A network may run multiple instances of RPL concurrently. Each such instance may serve different and potentially antagonistic constraints or performance criteria. This document defines how a single instance operates.
In order to be useful in a wide range of LLN application domains, RPL separates packet processing and forwarding from the routing optimization objective. Examples of such objectives include minimizing energy, minimizing latency, or satisfying constraints. This document describes the mode of operation of RPL. Other companion documents specify routing objective functions. A RPL implementation, in support of a particular LLN application, will include the necessary objective function(s) as required by the application.
A set of companion documents to this specification will provide further guidance in the form of applicability statements specifying a set of operating points appropriate to the Building Automation, Home Automation, Industrial, and Urban application scenarios.
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In compliance with the layered architecture of IP, RPL does not rely on any particular features of a specific link layer technology. RPL is designed to be able to operate over a variety of different link layers, including but not limited to, low power wireless or PLC (Power Line Communication) technologies.
Implementers may find [RFC3819] (Karn, P., Bormann, C., Fairhurst, G., Grossman, D., Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. Wood, “Advice for Internet Subnetwork Designers,” July 2004.) a useful reference when designing a link layer interface between RPL and a particular link layer technology.
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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 RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].
Additionally, this document uses terminology from [I‑D.ietf‑roll‑terminology] (Vasseur, J., “Terminology in Low power And Lossy Networks,” March 2010.), and introduces the following terminology:
- DAG:
- Directed Acyclic Graph. A directed graph having the property that all edges are oriented in such a way that no cycles exist. All edges are contained in paths oriented toward and terminating at one or more root nodes.
- DAG root:
- A DAG root is a node within the DAG that has no outgoing edges. Because the graph is acyclic, by definition all DAGs must have at least one DAG root and all paths terminate at a DAG root.
- Destination Oriented DAG (DODAG):
- A DAG rooted at a single destination, i.e. at a single DAG root (the DODAG root) with no outgoing edges.
- DODAG root:
- A DODAG root is the DAG root of a DODAG.
- Rank:
- The rank of a node in a DAG identifies the nodes position with respect to a DODAG root. The farther away a node is from a DODAG root, the higher is the rank of that node. The rank of a node may be a simple topological distance, or may more commonly be calculated as a function of other properties as described later.
- DODAG parent:
- A parent of a node within a DODAG is one of the immediate successors of the node on a path towards the DODAG root. The DODAG parent of a node will have a lower rank than the node itself. (See Section 3.5.2.1 (Rank Comparison (DAGRank()))).
- DODAG sibling:
- A sibling of a node within a DODAG is defined in this specification to be any neighboring node which is located at the same rank within a DODAG. Note that siblings defined in this manner do not necessarily share a common DODAG parent. (See Section 3.5.2.1 (Rank Comparison (DAGRank()))).
- Sub-DODAG
- The sub-DODAG of a node is the set of other nodes in the DODAG that might use a path towards the DODAG root that contains that node. Nodes in the sub-DODAG of a node have a greater rank than that node itself (although not all nodes of greater rank are necessarily in the sub-DODAG of that node). (See Section 3.5.2.1 (Rank Comparison (DAGRank()))).
- DODAGID:
- The identifier of a DODAG root. The DODAGID must be unique within the scope of a RPL Instance in the LLN.
- DODAG Version:
- A specific sequence number iteration ("version") of a DODAG with a given DODAGID.
- RPL Instance:
- A set of possibly multiple DODAGs. A network may have more than one RPL Instance, and a RPL node can participate in multiple RPL Instances. Each RPL Instance operates independently of other RPL Instances. This document describes operation within a single RPL Instance. In RPL, a node can belong to at most one DODAG per RPL Instance. The tuple (RPLInstanceID, DODAGID) uniquely identifies a DODAG.
- RPLInstanceID:
- Unique identifier of a RPL Instance.
- DODAGVersionNumber:
- A sequential counter that is incremented by the root to form a new Version of a DODAG. A DODAG Version is identified uniquely by the (RPLInstanceID, DODAGID, DODAGVersionNumber) tuple.
- Up:
- Up refers to the direction from leaf nodes towards DODAG roots, following the orientation of the edges within the DODAG. This follows the common terminology used in graphs and depth-first-search, where vertices further from the root are "deeper," or "down," and vertices closer to the root are "shallower," or "up."
- Down:
- Down refers to the direction from DODAG roots towards leaf nodes, going against the orientation of the edges within the DODAG. This follows the common terminology used in graphs and depth-first-search, where vertices further from the root are "deeper," or "down," and vertices closer to the root are "shallower," or "up."
- Objective Code Point (OCP):
- An identifier, used to indicate which Objective Function is in use for forming a DODAG. The Objective Code Point is further described in [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.).
- Objective Function (OF):
- Defines which routing metrics, optimization objectives, and related functions are in use in a DODAG.
- Goal:
- The Goal is a host or set of hosts that satisfy a particular application objective (OF). Whether or not a DODAG can provide connectivity to a goal is a property of the DODAG. For example, a goal might be a host serving as a data collection point, or a gateway providing connectivity to an external infrastructure.
- Grounded:
- A DODAG is said to be grounded, when the root can reach the Goal of the objective function.
- Floating:
- A DODAG is floating if is not Grounded. A floating DODAG is not expected to reach the Goal defined for the OF. Typically, a DAG that is only intended to provide inner connectivity is a Floating DAG.
As they form networks, LLN devices often mix the roles of 'host' and 'router' when compared to traditional IP networks. In this document, 'host' refers to an LLN device that can generate but does not forward RPL traffic, 'router' refers to an LLN device that can forward as well as generate RPL traffic, and 'node' refers to any RPL device, either a host or a router.
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The aim of this section is to describe RPL in the spirit of [RFC4101] (Rescorla, E. and IAB, “Writing Protocol Models,” June 2005.). Protocol details can be found in further sections.
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This section describes how the basic RPL topologies, and the rules by which these are constructed, i.e. the rules governing DODAG formation.
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RPL uses four identifiers to maintain the topology:
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Each RPL Instance constructs a routing topology optimized for a certain Objective Function (OF) and routing metrics [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.). A RPL Instance may provide routes to certain destination prefixes, reachable via the DODAG roots or alternate paths within the DODAG. A single RPL Instance contains one or more Destination Oriented DAG (DODAG) roots. These roots may operate independently, or may coordinate over a non-LLN backchannel.
Each root has a unique identifier, the DODAGID.
A RPL Instance may comprise:
Traffic is bound to a specific RPL Instance by meta-data that is carried with the packet and associates the packet to a particular RPLInstanceID (Section 8.2 (Loop Avoidance and Detection)). The provisioning or automated discovery of a mapping between a RPLInstanceID and a type or service of application traffic is beyond the scope of this specification.
An example of a RPL Instance comprising a number of DODAGs is depicted in Figure 1 (RPL Instance). Revision of a DODAG Version (two iterations of the same DODAG) is depicted in Figure 2 (DODAG Version).
+----------------------------------------------------------------+
| |
| +--------------+ |
| | | |
| | (R1) | (R2) (Rn) |
| | / \ | /| \ / | \ |
| | / \ | / | \ / | \ |
| | (A) (B) | (C) | (D) ... (F) (G) (H) |
| | /|\ |\ | / | |\ | | | |
| | : : : : : | : (E) : : : : : |
| | | / \ |
| +--------------+ : : |
| DODAG |
| |
+----------------------------------------------------------------+
RPL Instance
| Figure 1: RPL Instance |
+----------------+ +----------------+
| | | |
| (R1) | | (R1) |
| / \ | | / |
| / \ | | / |
| (A) (B) | \ | (A) |
| /|\ |\ | ------\ | /|\ |
| : : (C) : : | \ | : : (C) |
| | / | \ |
| | ------/ | \ |
| | / | (B) |
| | | |\ |
| | | : : |
| | | |
+----------------+ +----------------+
Version N Version N+1
| Figure 2: DODAG Version |
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RPL provisions routes up towards DODAG roots, forming a DODAG optimized according to the Objective Function (OF) and routing metrics/constraints in use. RPL nodes construct and maintain these DODAGs through exchange of DODAG Information Object (DIO) messages. Undirected links between siblings are also identified during this process, which can be used to provide additional diversity.
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RPL supports global repair over the DODAG. A DODAG Root may increment the DODAG Version Number, thereby initiating a new DODAG version. This institutes a global repair operation, revising the DODAG and allowing nodes to choose an arbitrary new position within the new DODAG version. Global repair can be seen as a global reoptimization mechanism.
RPL also supports mechanisms which may be used for local repair within the DODAG version. The DIO message specifies the necessary parameters as configured from the DODAG root, as controlled by policy at the root.
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DODAGs can be grounded or floating. A grounded DODAG offers connectivity to reach a goal. A floating DODAG offers no such connectivity, and provides routes only to nodes within the DODAG. Floating DODAGs may be used, for example, to preserve inner connectivity during repair.
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An implementation/deployment may specify that some DODAG roots should be used over others through an administrative preference. Administrative preference offers a way to control traffic and engineer DODAG formation in order to better support application requirements or needs.
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The Objective Function (OF) implements the optimization objectives of route selection within the RPL Instance. The OF is identified by an Objective Code Point (OCP) within the DIO. The OF also specifies the procedure used to select parents and compute rank within a DODAG version along with potentially other DODAG characteristics. Further details may be found in Section 11 (Guidelines for Objective Functions), [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.), [I‑D.ietf‑roll‑of0] (Thubert, P., “RPL Objective Function 0,” February 2010.), and related companion specifications.
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A high level overview of the distributed algorithm, which constructs the DODAG, is as follows:
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RPL constructs and maintains DODAGs with DIO messages to establish upward routes: it uses Destination Advertisement Object (DAO) messages to establish downward routes along the DODAG as well as other P2P routes. DAO messages are an optional feature for applications that require P2MP or P2P traffic, in either storing (fully stateful) or non-storing (fully source routed [I‑D.hui‑6man‑rpl‑routing‑header] (Hui, J., Vasseur, J., and D. Culler, “A Source Routing Header for RPL,” May 2010.)) mode.
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Routing metrics are used by routing protocols to compute shortest paths. Interior Gateway Protocols (IGPs) such as IS-IS ([RFC5120] (Przygienda, T., Shen, N., and N. Sheth, “M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs),” February 2008.)) and OSPF ([RFC4915] (Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, “Multi-Topology (MT) Routing in OSPF,” June 2007.)) use static link metrics. Such link metrics can simply reflect the bandwidth or can also be computed according to a polynomial function of several metrics defining different link characteristics. Some routing protocols support more than one metric: in the vast majority of the cases, one metric is used per (sub)topology. Less often, a second metric may be used as a tie-breaker in the presence of Equal Cost Multiple Paths (ECMP). The optimization of multiple metrics is known as an NP complete problem and is sometimes supported by some centralized path computation engine.
In contrast, LLNs do require the support of both static and dynamic metrics. Furthermore, both link and node metrics are required. In the case of RPL, it is virtually impossible to define one metric, or even a composite metric, that will satisfy all use cases.
In addition, RPL supports constrained-based routing where constraints may be applied to both link and nodes. If a link or a node does not satisfy a required constraint, it is 'pruned' from the candidate list, thus leading to a constrained shortest path.
The set of supported link/node constraints and metrics is specified in [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.).
An Objective Function specifies constraints in use, and how these are used, in addition to the objectives used to compute the (constrained) path. Upstream and Downstream metrics may be merged or advertised separately depending on the OF and the metrics. When they are advertised separately, it may happen that the set of DIO parents is different from the set of DAO parents (a DAO parent is a node to which unicast DAO messages are sent). Yet, all are DODAG parents with regards to the rules for Rank computation.
- Example 1:
- Shortest path: path offering the shortest end-to-end delay
- Example 2:
- Constrained shortest path: the path that does not traverse any battery-operated node and that optimizes the path reliability
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RPL guarantees neither loop free path selection nor tight delay convergence times. In order to reduce control overhead, however, such as the cost of the count-to-infinity problem, RPL avoids creating loops when undergoing topology changes. Furthermore, RPL includes rank-based datapath validation mechanisms for detecting loops when they do occur. RPL uses this loop detection to ensure that packets make forward progress within the DODAG version and trigger repairs when necessary.
| TOC |
A node is greedy if it attempts to move deeper in the DODAG version, in order to increase the size of the parent set or improve some other metric. Moving deeper in within a DODAG version in this manner could result in instability and be detrimental to other nodes.
Once a node has joined a DODAG version, RPL disallows certain behaviors, including greediness, in order to prevent resulting instabilities in the DODAG version.
Suppose a node is willing to receive and process a DIO messages from a node in its own sub-DODAG, and in general a node deeper than itself. In this case, a possibility exists that a feedback loop is created, wherein two or more nodes continue to try and move in the DODAG version while attempting to optimize against each other. In some cases, this will result in instability. It is for this reason that RPL limits the cases where a node may process DIO messages from deeper nodes to some forms of local repair. This approach creates an 'event horizon', whereby a node cannot be influenced beyond some limit into an instability by the action of nodes that may be in its own sub-DODAG.
| TOC |
A DODAG loop may occur when a node detaches from the DODAG and reattaches to a device in its prior sub-DODAG. This may happen in particular when DIO messages are missed. Strict use of the DODAG Version Number can eliminate this type of loop, but this type of loop may possibly be encountered when using some local repair mechanisms.
| TOC |
A DAO loop may occur when the parent has a route installed upon receiving and processing a DAO message from a child, but the child has subsequently cleaned up the related DAO state. This loop happens when a No-Path (a DAO message that invalidates a previously announced prefix) was missed and persists until all state has been cleaned up. RPL includes an optional mechanism to acknowledge DAO messages, which may mitigate the impact of a single DAO message being missed. RPL includes loop detection mechanisms that may mitigate the impact of DAO loops and trigger their repair.
In the case where stateless DAO operation is used, i.e. source routing specifies the down routes, then DAO Loops should not occur on the stateless portions of the path.
| TOC |
Sibling loops could occur if a group of siblings kept choosing amongst themselves as successors such that a packet does not make forward progress. This specification limits the number of times that sibling forwarding may be used at a given rank, in order to prevent sibling loops.
| TOC |
The rank of a node is a scalar representation of the location of that node within a DODAG version. The rank is used to avoid and detect loops, and as such must demonstrate certain properties. The exact calculation of the rank is left to the Objective Function, and may depend on parents, link metrics, and the node configuration and policies.
The rank is not a cost metric, although its value can be derived from and influenced by metrics. The rank has properties of its own that are not necessarily those of all metrics:
- Type:
- The rank is an abstract decimal value.
- Function:
- The rank is the expression of a relative position within a DODAG version with regard to neighbors and is not necessarily a good indication or a proper expression of a distance or a cost to the root.
- Stability:
- The stability of the rank determines the stability of the routing topology. Some dampening or filtering might be applied to keep the topology stable, and thus the rank does not necessarily change as fast as some physical metrics would. A new DODAG version would be a good opportunity to reconcile the discrepancies that might form over time between metrics and ranks within a DODAG version.
- Granularity:
- The portion of the rank that is used to define a node's position in the DAG, DAGRank(node), is coarse grained. A fine granularity would make the selection of siblings difficult, since siblings must have the exact same rank value.
- Properties:
- The rank is strictly monotonic, and can be used to validate a progression from or towards the root. A metric, like bandwidth or jitter, does not necessarily exhibit this property.
- Abstract:
- The rank does not have a physical unit, but rather a range of increment per hop, where the assignment of each increment is to be determined by the Objective Function.
The rank value feeds into DODAG parent selection, according to the RPL loop-avoidance strategy. Once a parent has been added, and a rank value for the node within the DODAG has been advertised, the nodes further options with regard to DODAG parent selection and movement within the DODAG are restricted in favor of loop avoidance.
| TOC |
Rank may be thought of as a fixed point number, where the position of the decimal point between the integer part and the fractional part is determined by MinHopRankIncrease. MinHopRankIncrease is the minimum increase in rank between a node and any of its DODAG parents. When an objective function computes rank, the objective function operates on the entire (i.e. 16-bit) rank quantity. When rank is compared, e.g. for determination of parent/sibling relationships or loop detection, the integer portion of the rank is to be used. The integer portion of the Rank is computed by the DAGRank() macro as follows:
DAGRank(rank) = floor(rank/MinHopRankIncrease)
MinHopRankIncrease is provisioned at the DODAG Root and propagated in the DIO message. For efficient implementation the MinHopRankIncrease MUST be a power of 2. An implementation may configure a value MinHopRankIncrease as appropriate to balance between the loop avoidance logic of RPL (i.e. selection of eligible parents and siblings) and the metrics in use.
By convention in this document, using the macro DAGRank(node) may be interpreted as DAGRank(node.rank), where node.rank is the rank value as maintained by the node.
A node A has a rank less than the rank of a node B if DAGRank(A) is less than DAGRank(B).
A node A has a rank equal to the rank of a node B if DAGRank(A) is equal to DAGRank(B).
A node A has a rank greater than the rank of a node B if DAGRank(A) is greater than DAGRank(B).
| TOC |
The computation of the rank MUST be done in such a way so as to maintain the following properties for any nodes M and N that are neighbors in the LLN:
- DAGRank(M) is less than DAGRank(N):
- In this case, the position of M is closer to the DODAG root than the position of N. Node M may safely be a DODAG parent for Node N without risk of creating a loop. Further, for a node N, all parents in the DODAG parent set must be of rank less than DAGRank(N). In other words, the rank presented by a node N MUST be greater than that presented by any of its parents.
- DAGRank(M) equals DAGRank(N):
- In this case the positions of M and N within the DODAG and with respect to the DODAG root are similar (identical). In some cases, Node M may be used as a successor by Node N, which however entails the chance of creating a loop (which must be detected and resolved by some other means).
- DAGRank(M) is greater than DAGRank(N):
- In this case, the position of M is farther from the DODAG root than the position of N. Further, Node M may in fact be in the sub-DODAG of Node N. If node N selects node M as DODAG parent there is a risk to create a loop.
As an example, the rank could be computed in such a way so as to closely track ETX (Expected Transmission Count, a fairly common routing metric used in LLN and defined in [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.)) when the objective function is to minimize ETX, or latency when the objective function is to minimize latency, or in a more complicated way as appropriate to the objective function being used within the DODAG.
| TOC |
| TOC |
Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN applications ([I‑D.ietf‑roll‑building‑routing‑reqs] (Martocci, J., Riou, N., Mil, P., and W. Vermeylen, “Building Automation Routing Requirements in Low Power and Lossy Networks,” January 2010.), [RFC5826] (Brandt, A., Buron, J., and G. Porcu, “Home Automation Routing Requirements in Low-Power and Lossy Networks,” April 2010.), [RFC5673] (Pister, K., Thubert, P., Dwars, S., and T. Phinney, “Industrial Routing Requirements in Low-Power and Lossy Networks,” October 2009.), [RFC5548] (Dohler, M., Watteyne, T., Winter, T., and D. Barthel, “Routing Requirements for Urban Low-Power and Lossy Networks,” May 2009.)). The destinations of MP2P flows are designated nodes that have some application significance, such as providing connectivity to the larger Internet or core private IP network. RPL supports MP2P traffic by allowing MP2P destinations to be reached via DODAG roots.
| TOC |
Point-to-multipoint (P2MP) is a traffic pattern required by several LLN applications ([I‑D.ietf‑roll‑building‑routing‑reqs] (Martocci, J., Riou, N., Mil, P., and W. Vermeylen, “Building Automation Routing Requirements in Low Power and Lossy Networks,” January 2010.), [RFC5826] (Brandt, A., Buron, J., and G. Porcu, “Home Automation Routing Requirements in Low-Power and Lossy Networks,” April 2010.), [RFC5673] (Pister, K., Thubert, P., Dwars, S., and T. Phinney, “Industrial Routing Requirements in Low-Power and Lossy Networks,” October 2009.), [RFC5548] (Dohler, M., Watteyne, T., Winter, T., and D. Barthel, “Routing Requirements for Urban Low-Power and Lossy Networks,” May 2009.)). RPL supports P2MP traffic by using a destination advertisement mechanism that provisions routes toward destination prefixes and away from roots. Destination advertisements can update routing tables as the underlying DODAG topology changes.
| TOC |
RPL DODAGs provide a basic structure for point-to-point (P2P) traffic. For a RPL network to support P2P traffic, a root must be able to route packets to a destination. Nodes within the network may also have routing tables to destinations. A packet flows towards a root until it reaches an ancestor that has a known route to the destination. As pointed out later in this document, in the most constrained case (when nodes cannot store routes), that common ancestor may be the DODAG root. In other cases it may be a node closer to both the source and destination.
RPL also supports the case where a P2P destination is a 'one-hop' neighbor.
RPL neither specifies nor precludes additional mechanisms for computing and installing potentially more optimal routes to support arbitrary P2P traffic.
| TOC |
Within a given LLN, there may be multiple, logically independent RPL instances. This document describes how a single instance behaves.
A node may belong to multiple RPL Instances.
An instance can be either local to a root or global. When the instance is local, the DAG is a single DODAG that is rooted at the node that owns the DODAGID. This is used in particular for the construction of a temporary DODAG in support of P2P traffic optimization between the root and some other nodes.
Control and Data Packets that traverse a RPL network MUST be tagged in such a fashion that the instance is unambiguously identified (TBD flow label or RPL Hop-by-hop option ([I‑D.hui‑6man‑rpl‑option] (Hui, J. and J. Vasseur, “RPL Option for Carrying RPL Information in Data-Plane Datagrams,” March 2010.))). The identifiers include the RPLInstanceID and the DODAGID for local instances.
| TOC |
A global RPLInstanceID MUST be unique to the whole LLN. Mechanisms for allocating and provisioning global RPLInstanceID are out of scope for this document. There can be up to 128 global instance in the whole network, and up 64 local instances per DODAGID.
A global RPLinstanceID is encoded in a RPLinstanceID field as
follows:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|0| ID | Global RPLinstanceID in 0..127
+-+-+-+-+-+-+-+-+
| Figure 3: RPL Instance ID field format for global instances |
A local RPLInstanceID is autoconfigured by the node that owns the DODAGID and it MUST be unique for that DODAGID. In that case, the DODAGID MUST be a valid address of the root that is used as an endpoint of all communications within that instance.
A local RPLinstanceID is encoded in a RPLinstanceID field as
follows:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1|D| ID | Local RPLInstanceID in 0..63
+-+-+-+-+-+-+-+-+
| Figure 4: RPL Instance ID field format for local instances |
The D flag in a Local RPLInstanceID is always set to 0 in RPL control messages. It is used in data packets to indicate whether the DODAGID is the source or the destination of the packet. If the D flag is set to 1 then the destination address of the IPv6 packet MUST be the DODAGID. If the D flag is clear then the source address of the IPv6 packet MUST be the DODAGID.
| TOC |
This document defines the RPL Control Message, a new ICMPv6 message. A RPL Control Message is identified by a code, and composed of a base that depends on the code, and a series of options.
A RPL Control Message has the scope of a link. The source address is a link local address. The destination address is either all routers multicast address (FF02::2) or a link local address.
In accordance with [RFC4443] (Conta, A., Deering, S., and M. Gupta, “Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification,” March 2006.), the RPL Control Message consists of an ICMPv6 header followed by a message body. The message body is comprised of a message base and possibly a number of options as illustrated in Figure 5 (RPL Control Message).
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Base .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Option(s) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Figure 5: RPL Control Message |
The RPL Control message is an ICMPv6 information message with a requested Type of 155 (to be confirmed by IANA).
The Code field identifies the type of RPL Control Message. This document defines codes for the following RPL Control Message types (all codes are to be confirmed by the IANA Section 15.2 (New Registry for RPL Control Codes)):
The high order bit (0x80) of the code denotes whether the RPL message has security enabled. Secure versions of RPL messages have a modified format to support confidentiality and integrity, illustrated in Figure Figure 6 (Secure RPL Control Message).
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Security .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Base .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Option(s) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Figure 6: Secure RPL Control Message |
The remainder of this section describes the currently defined RPL Control Message Base formats followed by the currently defined RPL Control Message Options.
| TOC |
Each RPL message has a secure version. The secure versions provide integrity and confidentiality. Because security covers the base message as well as options, in secured messages the security information lies between the checksum and base, as shown in Figure Figure 6 (Secure RPL Control Message).
The format of the security section 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|C|KIM| LVL | |
+-+-+-+-+-+-+-+-+ +
| Counter |
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Key Identifier .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Security |
All fields are considered as packet payload from a security processing perspective. The exact placement and format of message integrity/authentication codes has not yet been determined.
Use of the Security section is further detailed in Section 14 (Security Considerations).
- Security Control Field:
- The Security Control Field has one flag and two fields:
- Counter Compression (C):
- If the Counter Compression flag is set then the Counter field is compressed from 4 bytes into 1 byte. If the Counter Compression flag is clear then the Counter field is 4 bytes and uncompressed.
- Key Identifier Mode (KIM):
- The Key Identifier Mode field indicates whether the key used for packet protection is determined implicitly or explicitly and indicates the particular representation of the Key Identifier field. The Key Identifier Mode is set one of the non-reserved values from the table below:
+------+-----+-----------------------------+------------+ | Mode | KIM | Meaning | Key | | | | | Identifier | | | | | Length | | | | | (octets) | +------+-----+-----------------------------+------------+ | 0 | 00 | Peer-to-peer key determined | 0 | | | | implicitly from originator | | | | | and recipient of packet. | | | | | | | | | | Key Source is not present. | | | | | Key Index is not present. | | +------+-----+-----------------------------+------------+ | 1 | 01 | Group key determined | 1 | | | | implicitly from Key Index | | | | | and side information. | | | | | | | | | | Key Source is not present. | | | | | Key Index is present. | | +------+-----+-----------------------------+------------+ | 2 | 10 | Signature key used; group | 0/9 | | | | key determined explicitly | | | | | if encryption used. | | | | | | | | | | Key Source may be present. | | | | | Key Index may be present. | | +------+-----+-----------------------------+------------+ | 3 | 11 | Group key determined | 9 | | | | explicitly from Key Source | | | | | Identifier and Key Index. | | | | | | | | | | Key Source is present. | | | | | Key Index is present. | | +------+-----+-----------------------------+------------+ Key Identifier Mode (KIM) Encoding- Security Level (LVL):
- The Security Level field indicates the provided packet protection. This value can be adapted on a per-packet basis and allows for varying levels of data authenticity and, optionally, for data confidentiality. When nontrivial protection is provided, replay protection is always provided. The Security Level is set to one of the non-reserved values in the table below:
+--------------------+-------------------+ | Without Signatures | With Signatures | +----+-----+-------------+------+-------------+-----+ | ID | LVL | Attributes | Auth | Attributes | Sig | | | | | Len | | Len | +----+-----+-------------+------+-------------+-----+ | 0 | 000 | None | 0 | None | 37 | | 1 | 001 | MIC-32 | 4 | Sign-32 | 37 | | 2 | 010 | MIC-64 | 8 | Sign-64 | 45 | | 3 | 011 | Rsvd | N/A | Rsvd | N/A | | 4 | 100 | ENC | 0 | ENC | 37 | | 5 | 101 | ENC-MIC-32 | 4 | ENC-Sign-32 | 41 | | 6 | 110 | ENC-MIC-64 | 8 | ENC-Sign-64 | 45 | | 7 | 111 | Rsvd | N/A | Reserved | N/A | +----+-----+-------------+------+-------------+-----+ Security Level (LVL) Encoding- Counter:
- The Counter field indicates the non-repeating value (nonce) used with the cryptographic mechanism that implements packet protection and allows for the provision of semantic security. This value is compressed from 4 octets to 1 octet if the Counter Compression field of the Security Control Field is set to one.
- Key Identifier:
- The Key Identifier field indicates which key was used to protect the packet. This field provides various levels of granularity of packet protection, including peer-to-peer keys, group keys, and signature keys. This field is represented as indicated by the Key Identifier Mode field and is formatted 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Key Source . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Key Index . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Key Identifier
- Key Source:
- The Key Source field, when present, indicates the logical identifier of the originator of a group key. When present this field is 8 bytes in length.
- Key Index:
- The Key Index field, when present, allows unique identification of different keys with the same originator. It is the responsibility of each key originator to make sure that actively used keys that it issues have distinct key indices and that all key indices have a value unequal to 0x00. When present this field is 1 byte in length.
Unassigned bits of the Security section are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
| TOC |
The DODAG Information Solicitation (DIS) message may be used to solicit a DODAG Information Object from a RPL node. Its use is analogous to that of a Router Solicitation as specified in IPv6 Neighbor Discovery; a node may use DIS to probe its neighborhood for nearby DODAGs. Section 6.3 (DIO Transmission) describes how nodes respond to a DIS.
| TOC |
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Figure 7: The DIS Base Object |
Unassigned bits of the DIS Base are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
| TOC |
A Secure DIS message follows the format in Figure Figure 6 (Secure RPL Control Message), where the base format is the DIS message shown in Figure Figure 7 (The DIS Base Object).
| TOC |
The DIS message MAY carry valid options.
This specification allows for the DIS message to carry the following options:
0x00 Pad1
0x01 PadN
0x05 RPL Target
0x07 Solicited Information
| TOC |
The DODAG Information Object carries information that allows a node to discover a RPL Instance, learn its configuration parameters, select a DODAG parent set, and maintain the upward routing topology.
| TOC |
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | Version | Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G|A|T|MOP| Prf | DTSN | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
| Figure 8: The DIO Base Object |
- Control Field:
- The DAG Control Field has three flags and two fields:
- Grounded (G):
- The Grounded (G) flag indicates whether the upward routes this node advertises provide connectivity to the set of addresses which are application-defined goals. If the flag is set, the DODAG is grounded and provides such connectivity. If the flag is cleared, the DODAG is floating and may not provide such connectivity.
- Destination Advertisement Supported (A):
- The Destination Advertisement Supported (A) flag indicates whether the root of this DODAG can collect and use downward route state. If the flag is set, nodes in the network are enabled to exchange destination advertisements messages to build downward routes (Section 7 (Downward Routes)). If the flag is cleared, destination advertisement messages are disabled and the DODAG maintains only upward routes.
- Destination Advertisement Trigger (T):
- The Destination Advertisement Trigger (T) flag indicates a complete refresh of downward routes. If the flag is set, then a refresh of downward route state is to take place over the entire DODAG. If the flag is cleared, the downward route maintenance is in its normal mode of operation. The further details of this process are described in Section 7 (Downward Routes).
- Mode of Operation (MOP):
- The Mode of Operation (MOP) field identifies the mode of operation of the RPL Instance as administratively provisioned at and distributed by the DODAG Root. All nodes who join the DODAG must be able to honor the MOP in order to fully participate as a router, or else they must only join as a leaf. MOP is encoded as in the table below:
+-----+-------------------------------------------------+ | MOP | Meaning | +-----+-------------------------------------------------+ | 00 | Non-storing | | 01 | Storing | | 10 | Reserved for future specification of mixed-mode | | 11 | Reserved | +-----+-------------------------------------------------+
Mode of Operation (MOP) Encoding
- DODAGPreference (Prf):
- A 3-bit unsigned integer that defines how preferable the root of this DODAG is compared to other DODAG roots within the instance. DAGPreference ranges from 0x00 (least preferred) to 0x07 (most preferred). The default is 0 (least preferred). Section 6.2 (Upward Route Discovery and Maintenance) describes how DAGPreference affects DIO processing.
- Version Number:
- 8-bit unsigned integer set by the DODAG root. Section 6.2 (Upward Route Discovery and Maintenance) describes the rules for version numbers and how they affect DIO processing.
- Rank:
- 16-bit unsigned integer indicating the DODAG rank of the node sending the DIO message. Section 6.2 (Upward Route Discovery and Maintenance) describes how Rank is set and how it affects DIO processing.
- RPLInstanceID:
- 8-bit field set by the DODAG root that indicates which RPL Instance the DODAG is part of.
- Destination Advertisement Trigger Sequence Number (DTSN):
- 8-bit unsigned integer set by the node issuing the DIO message. The Destination Advertisement Trigger Sequence Number (DTSN) flag is used as part of the procedure to maintain downward routes. The details of this process are described in Section 7 (Downward Routes).
- DODAGID:
- 128-bit unsigned integer set by a DODAG root which uniquely identifies a DODAG. Possibly derived from the IPv6 address of the DODAG root.
Unassigned bits of the DIO Base are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
| TOC |
A Secure DIO message follows the format in Figure Figure 6 (Secure RPL Control Message), where the base format is the DIS message shown in Figure Figure 8 (The DIO Base Object).
| TOC |
The DIO message MAY carry valid options.
This specification allows for the DIO message to carry the following options:
0x00 Pad1
0x01 PadN
0x02 Metric Container
0x03 Routing Information
0x04 DODAG Configuration
0x09 Prefix Information
| TOC |
The Destination Advertisement Object (DAO) is used to propagate destination information upwards along the DODAG. The DAO message is unicast by the child to the selected parent(s). The DAO message may optionally, upon explicit request or error, be acknowledged by the parent with a Destination Advertisement Acknowledgement (DAO-ACK) message back to the child.
| TOC |
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |K|D| Reserved | DAOSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID* +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
| Figure 9: The DAO Base Object |
- RPLInstanceID:
- 8-bit field indicating the topology instance associated with the DODAG, as learned from the DIO.
- K:
- The 'K' flag indicates that the parent is expected to send a DAO-ACK back.
- D:
- The 'D' flag indicates that the DODAGID field is present. This would typically only be set when a local RPLInstanceID is used.
- DAOSequence:
- Incremented at each unique DAO message, echoed in the DAO-ACK message.
- DODAGID*:
- 128-bit unsigned integer set by a DODAG root which uniquely identifies a DODAG. This field is only present when the 'D' flag is set. This field is typically only present when a local RPLInstanceID is in use, in order to identify the DODAGID that is associated with the RPLInstanceID. When a global RPLInstanceID is in use this field need not be present.
Unassigned bits of the DAO Base are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
| TOC |
A Secure DAO message follows the format in Figure Figure 6 (Secure RPL Control Message), where the base format is the DAO message shown in Figure Figure 9 (The DAO Base Object).
| TOC |
The DAO message MAY carry valid options.
This specification allows for the DAO message to carry the following options:
0x00 Pad1
0x01 PadN
0x05 RPL Target
0x06 Transit Information
A special case of the DAO message, termed a No-Path, is used to clear downward routing state that has been provisioned through DAO operation. The No-Path carries a RPL Transit Information option, which identifies the destination to which the DAO is associated, with a lifetime of 0x00000000 to indicate a loss of reachability.
| TOC |
The DAO-ACK message is sent as a unicast packet by a DAO parent in response to a unicast DAO message from a child.
| TOC |
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | Reserved | DAOSequence | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
| Figure 10: The DAO ACK Base Object |
- RPLInstanceID:
- 8-bit field indicating the topology instance associated with the DODAG, as learned from the DIO.
- DAOSequence:
- Incremented at each DAO message from a given child, echoed in the DAO-ACK by the parent. The DAOSequence serves in the parent-child communication and is not to be confused with the Transit Information option Sequence that is associated to a given target down the DODAG.
- Status:
- Indicates the completion. 0 is unqualified acceptance, above 128 are rejection code indicating that the node should select an alternate parent.
Unassigned bits of the DAO-ACK Base are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
| TOC |
A Secure DAO-ACK message follows the format in Figure Figure 6 (Secure RPL Control Message), where the base format is the DAO-ACK message shown in Figure Figure 10 (The DAO ACK Base Object).
| TOC |
This specification does not define any options to be carried by the DAO-ACK message.
| TOC |
| TOC |
RPL Control Message Options all follow this format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Option Type | Option Length | Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Figure 11: RPL Option Generic Format |
- Option Type:
- 8-bit identifier of the type of option. The Option Type values are to be confirmed by the IANA Section 15.4 (RPL Control Message Option).
- Option Length:
- 8-bit unsigned integer, representing the length in octets of the option, not including the Option Type and Length fields.
- Option Data:
- A variable length field that contains data specific to the option.
When processing a RPL message containing an option for which the Option Type value is not recognized by the receiver, the receiver MUST silently ignore the unrecognized option and continue to process the following option, correctly handling any remaining options in the message.
RPL message options may have alignment requirements. Following the convention in IPv6, options with alignment requirements are aligned in a packet such that multi-octet values within the Option Data field of each option fall on natural boundaries (i.e., fields of width n octets are placed at an integer multiple of n octets from the start of the header, for n = 1, 2, 4, or 8).
| TOC |
The Pad1 option may be present in DIS, DIO, DAO, and DAO-ACK messages, and its format is as follows:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Type = 0 |
+-+-+-+-+-+-+-+-+
| Figure 12: Format of the Pad 1 Option |
The Pad1 option is used to insert one or two octets of padding into the message to enable options alignment. If more than one octet of padding is required, the PadN option should be used rather than multiple Pad1 options.
NOTE! the format of the Pad1 option is a special case - it has neither Option Length nor Option Data fields.
| TOC |
The PadN option may be present in DIS, DIO, DAO, and DAO-ACK messages, and 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Type = 1 | Option Length | 0x00 Padding...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Figure 13: Format of the Pad N Option |
The PadN option is used to insert two or more octets of padding into the message to enable options alignment. PadN Option data MUST be ignored by the receiver.
- Option Type:
- 0x01 (to be confirmed by IANA)
- Option Length:
- For N (N > 1) octets of padding, the Option Length field contains the value N-2.
- Option Data:
- For N (N > 1) octets of padding, the Option Data consists of N-2 zero-valued octets.
| TOC |
The Metric Container option may be present in DIO messages, and 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Type = 2 | Option Length | Metric Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Figure 14: Format of the Metric Container Option |
The Metric Container is used to report metrics along the DODAG. The Metric Container may contain a number of discrete node, link, and aggregate path metrics and constraints specified in [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.) as chosen by the implementer.
The processing and propagation of the Metric Container is governed by implementation specific policy functions.
- Option Type:
- 0x02 (to be confirmed by IANA)
- Option Length:
- The Option Length field contains the length in octets of the Metric Data.
- Metric Data:
- The order, content, and coding of the Metric Container data is as specified in [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.).
| TOC |
The Route Information option may be present in DIO messages, and is equivalent in function to the IPv6 ND Route Information option as defined in [RFC4191] (Draves, R. and D. Thaler, “Default Router Preferences and More-Specific Routes,” November 2005.). The format of the option is modified slightly (Type, Length) in order to be carried as a RPL option 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 = 3 | Option Length | Prefix Length |Resvd|Prf|Resvd|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Prefix (Variable Length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Figure 15: Format of the Route Information Option |
The Route Information option is used to indicate that connectivity to the specified destination prefix is available from the DODAG root.
In the event that a RPL Control Message may need to specify connectivity to more than one destination, the Route Information option may be repeated.
[RFC4191] (Draves, R. and D. Thaler, “Default Router Preferences and More-Specific Routes,” November 2005.) should be consulted as the authoritative reference with respect to the Route Information option. The field descriptions are transcribed here for convenience:
- Option Type:
- 0x03 (to be confirmed by IANA)
- Option Length:
- Variable, length of the option in octets excluding the Type and Length fields. Note that this length is expressed in units of single-octets, unlike in IPv6 ND.
- Prefix Length
- 8-bit unsigned integer. The number of leading bits in the Prefix that are valid. The value ranges from 0 to 128. The Prefix field is 0, 8, or 16 octets depending on Length.
- Prf:
- 2-bit signed integer. The Route Preference indicates whether to prefer the router associated with this prefix over others, when multiple identical prefixes (for different routers) have been received. If the Reserved (10) value is received, the Route Information Option MUST be ignored.
- Resvd:
- Two 3-bit unused fields. They MUST be initialized to zero by the sender and MUST be ignored by the receiver.
- Route Lifetime
- 32-bit unsigned integer. The length of time in seconds (relative to the time the packet is sent) that the prefix is valid for route determination. A value of all one bits (0xffffffff) represents infinity.
- Prefix
- Variable-length field containing an IP address or a prefix of an IP address. The Prefix Length field contains the number of valid leading bits in the prefix. The bits in the prefix after the prefix length (if any) are reserved and MUST be initialized to zero by the sender and ignored by the receiver.
Unassigned bits of the Route Information option are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
| TOC |
The DODAG Configuration option may be present in DIO 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 = 4 | Option Length | Resvd | PCS | DIOIntDoubl. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DIOIntMin. | DIORedun. | MaxRankIncrease |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MinHopRankIncrease |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Figure 16: Format of the DODAG Configuration Option |
The DODAG Configuration option is used to distribute configuration information for DODAG Operation through the DODAG.
The information communicated in this option is generally static and unchanging within the DODAG, therefore it is not necessary to include in every DIO. This information is configured at the DODAG Root and distributed throughout the DODAG with the DODAG Configuration Option. Nodes other than the DODAG Root MUST NOT modify this information when propagating the DODAG Configuration option. This option MAY be included occasionally by the DODAG Root (as determined by the DODAG Root), and MUST be included in response to a unicast request, e.g. a unicast DODAG Information Solicitation (DIS) message.
- Option Type:
- 0x04 (to be confirmed by IANA)
- Option Length:
- 8 bytes
- Path Control Size (PCS):
- 3-bit unsigned integer used to configure the number of bits that may be allocated to the Path Control field (see Section 7.1.4.2 (Storing Mode DAO Message and Path Control)).
- DIOIntervalDoublings:
- 8-bit unsigned integer used to configure Imax of the DIO trickle timer (see Section 6.3.1 (Trickle Parameters)).
- DIOIntervalMin:
- 8-bit unsigned integer used to configure Imin of the DIO trickle timer (see Section 6.3.1 (Trickle Parameters)).
- DIORedundancyConstant:
- 8-bit unsigned integer used to configure k of the DIO trickle timer (see Section 6.3.1 (Trickle Parameters)).
- MaxRankIncrease:
- 16-bit unsigned integer used to configure DAGMaxRankIncrease, the allowable increase in rank in support of local repair. If DAGMaxRankIncrease is 0 then this mechanism is disabled.
- MinHopRankInc
- 16-bit unsigned integer used to configure MinHopRankIncrease as described in Section 3.5.2.1 (Rank Comparison (DAGRank())).
| TOC |
The RPL Target 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 = 5 | Option Length | Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Target Prefix (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Figure 17: Format of the RPL Target Option |
The RPL Target Option is used to indicate a target IPv6 address, prefix, or multicast group that is reachable or queried along the DODAG. It is used in DIO to identify a resource that the root is trying to reach, and in a DAO to indicate reachability. It is used in a DAO message to indicate reachability. A set of one or more Transit Information options MAY directly follow the Target option in a DAO message in support of constructing source routes in a non-storing mode of operation [I‑D.hui‑6man‑rpl‑routing‑header] (Hui, J., Vasseur, J., and D. Culler, “A Source Routing Header for RPL,” May 2010.). When the same set of Transit Information options apply equally to a set of DODAG Target options, the group of Target options MUST appear first, followed by the Transit Information options which apply to those Targets.
The RPL Target option may be repeated as necessary to indicate multiple targets.
- Option Type:
- 0x05 (to be confirmed by IANA)
- Option Length:
- Variable, length of the option in octets excluding the Type and Length fields.
- Prefix Length:
- 8-bit unsigned integer. Number of valid leading bits in the IPv6 Prefix.
- Target Prefix:
- Variable-length field identifying an IPv6 destination address, prefix, or multicast group. The Prefix Length field contains the number of valid leading bits in the prefix. The bits in the prefix after the prefix length (if any) are reserved and MUST be set to zero on transmission and MUST be ignored on receipt.
| TOC |
The Transit 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 = 6 | Option Length | Path Sequence | Path Control |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Parent Address* +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Figure 18: Format of the Transit Information option |
The Transit Information option is used for a node to indicate attributes for a path to one or more destinations. The destinations are indicated as by one or more Target options that immediately precede the Transit Information option(s).
The Transit Information option can used for a node to indicate its DODAG parents to an ancestor that is collecting DODAG routing information, typically for the purpose of constructing source routes. In the non-storing mode of operation this ancestor will be the DODAG Root, and this option is carried by the DAO message. The option length is used to determine whether the Parent Address is present or not.
A non-storing node that has more than one DAO parent MAY include a Transit Information option for each DAO parent as part of the non-storing Destination Advertisement operation. The node may code the Path Control field in order to signal a preference among parents.
One or more Transit Information options MUST be preceded by one or more RPL Target options. In this manner the RPL Target option indicates the child node, and the Transit Information option(s) enumerate the DODAG parents.
A typical non-storing node will use multiple Transit Information options, and it will send the DAO thus formed to only one parent that will forward it to the root. A typical storing node with use one Transit Information option with no parent field, and will send the DAO thus formed to multiple parents.
- Option Type:
- 0x06 (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 node that owns the Target Prefix (i.e. in a DAO message), that node sets the Path-Sequence and increments the Path-Sequence each time it issues a RPL Target option.
- Path Control:
- 8-bit bitfield. The Path Control field limits the number of DAO-Parents to which a DAO message advertising connectivity to a specific destination may be sent, as well as providing some indication of relative preference. The limit provides some bound on overall DAO fan-out in the LLN. The leftmost bit is associated with a path that contains a most-preferred link, and the subsequent bits are ordered down to the rightmost bit which is least preferred.
- Path Lifetime:
- 32-bit unsigned integer. The length of time in seconds (relative to the time the packet is sent) that the prefix is valid for route determination. A value of all one bits (0xFFFFFFFF) represents infinity. A value of all zero bits (0x00000000) indicates a loss of reachability. This is referred as a No-Path in this document.
- Parent Address (optional):
- IPv6 Address of the DODAG Parent of the node originally issuing the Transit Information Option. This field may not be present, as according to the DODAG Mode of Operation and indicated by the Transit Information option length.
Unassigned bits of the Transit Information option are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
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The Solicited Information option may be present in DIS 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 = 7 | Option Length | RPLInstanceID |V|I|D| Rsvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version |
+-+-+-+-+-+-+-+-+
| Figure 19: Format of the Solicited Information Option |
The Solicited Information option is used for a node to request a subset of neighboring nodes that meet the specified criteria to respond to a DIS message.
The Solicited Information option may specify a number of predicate criteria to be matched by a receiving node. If a node receiving a multicast DIS message containing a Solicited Information option matches ALL of the predicates, then it MUST reset its trickle timer in order to trigger a DIO response to the DIS message. When a node receives a DIS message containing a Solicited information option, and the DIS message is unicast OR the node does not match ALL the predicates, then the node MUST NOT reset the trickle timer.
- Option Type:
- 0x07 (to be confirmed by IANA)
- Option Length:
- 19 bytes
- Control Field:
- The Solicited Information option Control Field has three flags:
- V:
- If the V flag is set then the Version field is valid and a node should only respond if its DODAGVersionNumber matches the requested version. If the V flag is clear then the Version field is not valid and the Version field MUST be set to zero on transmission and ignored upon receipt.
- I:
- If the I flag is set then the RPLInstanceID field is valid and a node should only respond if it matches the requested RPLInstanceID. If the I flag is clear then the RPLInstanceID field is not valid and the RPLInstanceID field MUST be set to zero on transmission and ignored upon receipt.
- D:
- If the D flag is set then the DODAGID field is valid and a node should only respond if it matches the requested DODAGID. If the D flag is clear then the DODAGID field is not valid and the DODAGID field MUST be set to zero on transmission and ignored upon receipt.
- Version:
- 8-bit unsigned integer containing the DODAG Version number that is being solicited when valid.
- RPLInstanceID:
- 8-bit unsigned integer containing the RPLInstanceID that is being solicited when valid.
- DODAGID:
- 128-bit unsigned integer containing the DODAGID that is being solicited when valid.
Unassigned bits of the Solicited Information option are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
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The Prefix Information option may be present in DIO messages, and is equivalent in function to the IPv6 ND Prefix Information option as defined in [RFC4861] (Narten, T., Nordmark, E., Simpson, W., and H. Soliman, “Neighbor Discovery for IP version 6 (IPv6),” September 2007.). The format of the option is modified slightly (Type, Length) in order to be carried as a RPL option 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 = 8 | Option Length | Prefix Length |L|A| Reserved1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Figure 20: Format of the Prefix Information Option |
The Prefix Information option may be used to distribute the prefix in use inside the DODAG, e.g. for address autoconfiguration.
[RFC4861] (Narten, T., Nordmark, E., Simpson, W., and H. Soliman, “Neighbor Discovery for IP version 6 (IPv6),” September 2007.) should be consulted as the authoritative reference with respect to the Prefix Information option. The field descriptions are transcribed here for convenience:
- Option Type:
- 0x08 (to be confirmed by IANA)
- Option Length:
- 30. Note that this length is expressed in units of single-octets, unlike in IPv6 ND.
- Prefix Length
- 8-bit unsigned integer. The number of leading bits in the Prefix that are valid. The value ranges from 0 to 128. The prefix length field provides necessary information for on-link determination (when combined with the L flag in the prefix information option). It also assists with address autoconfiguration as specified in [RFC4862] (Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” September 2007.), for which there may be more restrictions on the prefix length.
- L
- 1-bit on-link flag. When set, indicates that this prefix can be used for on-link determination. When not set the advertisement makes no statement about on-link or off-link properties of the prefix. In other words, if the L flag is not set a host MUST NOT conclude that an address derived from the prefix is off-link. That is, it MUST NOT update a previous indication that the address is on-link.
- A
- 1-bit autonomous address-configuration flag. When set indicates that this prefix can be used for stateless address configuration as specified in [RFC4862] (Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” September 2007.).
- Reserved1
- 6-bit unused field. It MUST be initialized to zero by the sender and MUST be ignored by the receiver.
- Valid Lifetime
- 32-bit unsigned integer. The length of time in seconds (relative to the time the packet is sent) that the prefix is valid for the purpose of on-link determination. A value of all one bits (0xffffffff) represents infinity. The Valid Lifetime is also used by [RFC4862] (Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” September 2007.).
- Preferred Lifetime
- 32-bit unsigned integer. The length of time in seconds (relative to the time the packet is sent) that addresses generated from the prefix via stateless address autoconfiguration remain preferred [RFC4862] (Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” September 2007.). A value of all one bits (0xffffffff) represents infinity. See [RFC4862] (Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” September 2007.). Note that the value of this field MUST NOT exceed the Valid Lifetime field to avoid preferring addresses that are no longer valid.
- Reserved2
- This field is unused. It MUST be initialized to zero by the sender and MUST be ignored by the receiver.
- Prefix
- An IP address or a prefix of an IP address. The Prefix Length field contains the number of valid leading bits in the prefix. The bits in the prefix after the prefix length are reserved and MUST be initialized to zero by the sender and ignored by the receiver. A router SHOULD NOT send a prefix option for the link-local prefix and a host SHOULD ignore such a prefix option.
Unassigned bits of the Prefix Information option are reserved. They MUST be set to zero on transmission and MUST be ignored on reception.
| TOC |
This section describes how RPL discovers and maintains upward routes. It describes the use of DODAG Information Objects (DIOs), the messages used to discover and maintain these routes. It specifies how RPL generates and responds to DIOs. It also describes DODAG Information Solicitation (DIS) messages, which are used to trigger DIO transmissions.
| TOC |
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Upward route discovery allows a node to join a DODAG by discovering neighbors that are members of the DODAG of interest and identifying a set of parents. The exact policies for selecting neighbors and parents is implementation-dependent and driven by the OF. This section specifies the set of rules those policies must follow for interoperability.
| TOC |
RPL's upward route discovery algorithms and processing are in terms of three logical sets of link-local nodes. First, the candidate neighbor set is a subset of the nodes that can be reached via link-local multicast. The selection of this set is implementation-dependent and OF-dependent. Second, the parent set is a restricted subset of the candidate neighbor set. Finally, the preferred parent, a set of size one, is an element of the parent set that is the preferred next hop in upward routes.
More precisely:
These rules ensure that there is a consistent partial order on nodes within the DODAG. As long as node ranks do not change, following the above rules ensures that every node's route to a DODAG root is loop-free, as rank decreases on each hop to the root. The OF can guide candidate neighbor set and parent set selection, as discussed in [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.) and [I‑D.ietf‑roll‑of0] (Thubert, P., “RPL Objective Function 0,” February 2010.).
| TOC |
The above rules govern a single DODAG version. The rules in this section define how RPL operates when there are multiple DODAG versions:
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Within a particular implementation, a DODAG root may increment the DODAGVersionNumber periodically, at a rate that depends on the deployment, in order to trigger a global reoptimization of the DODAG. In other implementations, loop detection may be considered sufficient to solve routing issues by triggering local repair mechanisms, and the DODAG root may increment the DODAGVersionNumber only upon administrative intervention. Another possibility is that nodes within the LLN have some means by which they can signal detected routing inconsistencies or suboptimalities to the DODAG root, in order to request an on-demand DODAGVersionNumber increment (i.e. request a global repair of the DODAG). Note that such a mechanism is for further study and out of the scope of this document.
When the DODAG parent set becomes empty on a node that is not a root, (i.e. the last parent has been removed, causing the node to no longer be associated with that DODAG), then the DODAG information should not be suppressed until after the expiration of an implementation-specific local timer in order to observe if the DODAGVersionNumber has been incremented, should any new parents appear for the DODAG. This will help protect against the possibility of loops that may occur of that node were to inadvertently rejoin the old DODAG version in its own prior sub-DODAG.
As the DODAGVersionNumber is incremented, a new DODAG Version spreads outward from the DODAG root. Thus a parent that advertises the new DODAGVersionNumber cannot possibly belong to the sub-DODAG of a node that still advertises an older DODAGVersionNumber. A node may safely add such a parent, without risk of forming a loop, without regard to its relative rank in the prior DODAG Version. This is equivalent to jumping to a different DODAG.
As a node transitions to new DODAG Versions as a consequence of following these rules, the node will be unable to advertise the previous DODAG Version (prior DODAGVersionNumber) once it has committed to advertising the new DODAG Version.
During transition to a new DODAG Version, a node may decide to forward packets via 'future parents' that belong to the same DODAG (same RPLInstanceID and DODAGID), but are observed to advertise a more recent (incremented) DODAGVersionNumber. In that case, the node MUST act as a leaf with regard to the new version for the purpose of loop detection as specified in Section 8.2 (Loop Avoidance and Detection).
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An LLN node that is a goal for the Objective Function is the root of its own grounded DODAG, at rank ROOT_RANK.
In a deployment that uses a backbone link to federate a number of LLN roots, it is possible to run RPL over that backbone and use one router as a "backbone root". The backbone root is the virtual root of the DODAG, and exposes a rank of BASE_RANK over the backbone. All the LLN roots that are parented to that backbone root, including the backbone root if it also serves as LLN root itself, expose a rank of ROOT_RANK to the LLN, and are part of the same DODAG, coordinating DODAGVersionNumber and other DODAG root determined parameters with the virtual root over the backbone.
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The DODAGPreference (Prf) provides an administrative mechanism to engineer the self-organization of the LLN, for example indicating the most preferred LBR. If a node has the option to join a more preferred DODAG while still meeting other optimization objectives, then the node will generally seek to join the more preferred DODAG as determined by the OF. All else being equal, it is left to the implementation to determine which DODAG is most preferred, possibly based on additional criteria beyond Prf and the OF.
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Conceptually, an implementation is maintaining a DODAG parent set within the DODAG Version. Movement entails changes to the DODAG parent set. Moving up does not present the risk to create a loop but moving down might, so that operation is subject to additional constraints.
When a node migrates to the next DODAG Version, the DODAG parent and sibling sets need to be rebuilt for the new version. An implementation could defer to migrate for some reasonable amount of time, to see if some other neighbors with potentially better metrics but higher rank announce themselves. Similarly, when a node jumps into a new DODAG it needs to construct new DODAG parent/sibling sets for this new DODAG.
When a node moves to improve its position, it must conceptually abandon all DODAG parents and siblings with a rank larger than itself. As a consequence of the movement it may also add new siblings. Such a movement may occur at any time to decrease the rank, as per the calculation indicated by the OF. Maintenance of the parent and sibling sets occurs as the rank of candidate neighbors is observed as reported in their DIOs.
If a node needs to move down a DODAG that it is attached to, causing the rank to increase, then it MAY poison its routes and delay before moving as described in Section 6.2.2.5 (Poisoning a Broken Path).
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An implementation may choose to employ this poisoning mechanism when a node loses all of its current parents, i.e. the set of DODAG parents becomes depleted, and it can not jump to an alternate DODAG. An alternate mechanism is to form a floating DODAG.
The motivation for delaying announcement of the revised route through multiple DIO events is to (i) increase tolerance to DIO loss, (ii) allow time for the poisoning action to propagate, and (iii) to develop an accurate assessment of its new rank. Such gains are obtained at the expense of potentially increasing the delay before portions of the network are able to re-establish upwards routes. Path redundancy in the DODAG reduces the significance of either effect, since children with alternate parents should be able to utilize those alternates and retain their rank while the detached parent re-establishes its rank.
Although an implementation may advertise INFINITE_RANK for the purposes of poisoning, it is not expected to be equivalent to setting the rank to INFINITE_RANK, and an implementation would likely retain its rank value prior to the poisoning in some form, for purpose of maintaining its effective position within (L + DAGMaxRankIncrease).
| TOC |
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A DODAG parent may have moved, migrated to the next DODAG Version, or jumped to a different DODAG. A node should give some preference to remaining in the current DODAG, if possible via an alternate parent, but ought to follow the parent if there are no other options.
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When an DIO message is received, the receiving node must first determine whether or not the DIO message should be accepted for further processing, and subsequently present the DIO message for further processing if eligible.
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As DIO messages are received from candidate neighbors, the neighbors may be promoted to DODAG parents by following the rules of DODAG discovery as described in Section 6.2 (Upward Route Discovery and Maintenance). When a node places a neighbor into the DODAG parent set, the node becomes attached to the DODAG through the new DODAG parent node.
The most preferred parent should be used to restrict which other nodes may become DODAG parents. Some nodes in the DODAG parent set may be of a rank less than or equal to the most preferred DODAG parent. (This case may occur, for example, if an energy constrained device is at a lesser rank but should be avoided as per an optimization objective, resulting in a more preferred parent at a greater rank).
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RPL nodes transmit DIOs using a Trickle timer ([I‑D.ietf‑roll‑trickle] (Levis, P., Clausen, T., Hui, J., and J. Ko, “The Trickle Algorithm,” April 2010.)). A DIO from a sender with a lower DAGRank that causes no changes to the recipient's parent set, preferred parent, or Rank SHOULD be considered consistent with respect to the Trickle timer.
The following packets and events MUST be considered inconsistencies with respect to the Trickle timer, and cause the Trickle timer to reset:
Note that this list is not exhaustive, and an implementation MAY consider other messages or events to be inconsistencies.
If a node receives a unicast DIS message whose constraints (Solicited Information) it satisfies, it MUST unicast a DIO in response, and this DIO MUST include the RPL instance's DODAG Configuration object.
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The configuration parameters of the trickle timer are specified as follows:
- Imin:
- learned from the DIO message as (2^DIOIntervalMin)ms. The default value of DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN.
- Imax:
- learned from the DIO message as DIOIntervalDoublings. The default value of DIOIntervalDoublings is DEFAULT_DIO_INTERVAL_DOUBLINGS.
- k:
- learned from the DIO message as DIORedundancyConstant. The default value of DIORedundancyConstant is DEFAULT_DIO_REDUNDANCY_CONSTANT. In RPL, when k has the value of 0x00 this is to be treated as a redundancy constant of infinity in RPL, i.e. Trickle never suppresses messages.
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The DODAG selection is implementation and OF dependent. Nodes SHOULD prefer to join DODAGs for RPLInstanceIDs advertising OCPs and destinations compatible with their implementation specific objectives. In order to limit erratic movements, and all metrics being equal, nodes SHOULD keep their previous selection. Also, nodes SHOULD provide a means to filter out a parent whose availability is detected as fluctuating, at least when more stable choices are available.
When connection to a grounded DODAG is not possible or preferable for security or other reasons, scattered DODAGs MAY aggregate as much as possible into larger DODAGs in order to allow connectivity within the LLN.
A node SHOULD verify that bidirectional connectivity and adequate link quality is available with a candidate neighbor before it considers that candidate as a DODAG parent.
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In some cases a RPL node may attach to a DODAG as a leaf node only. One example of such a case is when a node does not understand the RPL Instance's OF or advertised path metric. A leaf node does not extend DODAG connectivity but still needs to advertise its presence using DIOs. A node operating as a leaf node must obey the following rules:
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In some cases it might be beneficial to adjust the rank advertised by a node beyond that computed by the OF based on some implementation specific policy and properties of the node. For example, a node that has limited battery should be a leaf unless there is no other choice, and may then augment the rank computation specified by the OF in order to expose an exaggerated rank.
| TOC |
This section describes how RPL discovers and maintains downward routes. The use of messages containing the Destination Advertisement Object (DAO), used to construct downward routes, are described. The downward routes are necessary in support of P2MP flows, from the DODAG roots toward the leaves. It specifies non-storing and storing behavior of nodes with respect to DAO messaging and DAO routing table entries. Nodes, as according to their resources and the implementation, may selectively store routing table entries learned from DAO messages, or may instead propagate the DAO information upwards and independently source local topology information in a new DAO message. information. A further optimization is described whereby DAO messages may be used to populate routing table entries for the '1-hop' neighbors, which may be useful in some cases as a shortcut for P2P flows.
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Destination Advertisement operation produces DAO messages that flow up the DODAG, provisioning downward routing state for destination prefixes available in the sub-DODAG of the DODAG root, and possibly other nodes. The routing state provisioned with this mechanism is in the form of soft-state routing table entries. DAO operation is presently defined in two distinct modes of operation, non-storing and storing, and allowance is made for future expansion.
Destination Advertisement may or may not be enabled over a DODAG rooted at a DODAG root. This is an a priori configuration determined by the implementation/deployment and not generally changed during the operation of the RPL LLN.
Destination Advertisement may be configured to operate in either a storing or non-storing mode, as reported in the MOP in the DIO message. Every node in the network participating in Destination Advertisement must behave consistently with that configured mode of operation, or alternately behave only as a leaf node. Hybrid or mixed-mode operation is not currently specified.
When Destination Advertisement is enabled:
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A DAO Routing Table Entry conceptually contains the following elements:
The DAO Routing Table Entry is logically associated with the following states:
- CONNECTED
- This entry is 'owned' by the node - it is manually configured and is considered as a 'self' entry for DAO Operation
- REACHABLE
- This entry has been reported from a neighbor of the node. This state includes the following substates:
- CONFIRMED
- This entry is active, newly validated, and usable
- PENDING
- This entry is active, awaiting validation, and usable. A Retry Counter is associated with this substate
- UNREACHABLE
- This entry is being cleaned up. This entry may be suppressed when the cleanup process is complete.
When an attempt is to be made to report the DAO entry to DAO Parents, the DAO Entry record is logically marked to indicate that an attempt has not yet been made for each parent. As the unicast attempts are completed for each parent, this mark may be cleared. This mechanism may serve to limit DAO entry updates for each parent to a subset that needs to be reported.
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+---------------------------------+
| |
| REACHABLE | +-------------+
| | | |
| +-----------+ | | CONNECTED |
(*)----------->| |-------+ | | |
| | Confirmed | | | +-------------+
| +-->| |---+ | |
| | +-----------+ | | |
| | | | |
| | | | |
| | | | |
| | +-----------+ | | | +-------------+
| | | |<--+ +-------->| |
| +---| Pending | | | UNREACHABLE |
| | |---------------->| |--->(*)
| +-----------+ | +-------------+
| |
+---------------------------------+
| DAO Routing Table Entry FSM |
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In the storing mode of operation, a DAO message from a node will contain one or more Target Options, each Target Option specifying either a CONNECTED destination or a destination in the sub-DODAG of the node.
For each attempt made to report the DAO entry to a set of DAO parents, the Path Control field will be constructed as follows:
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Triggering DAO messages from the Sub-DODAG occurs by using the following control fields with the rules described below:
The DTSN field from the DIO is a sequence number that is part of the mechanism to trigger DAO messages. The motivation to use a sequence number is to provide some means of reliable signaling to the sub-DODAG. Whereas a control flag that is activated for a short time may be unobserved by the sub-DODAG if the triggering DIO messages are lost, the DTSN increment may be observed later even if some intervening DIO messages have been lost.
The 'T' flag provides a way to signal the refresh of DAO information over the entire DODAG version. Whereas a DTSN increment may only trigger a DAO refresh as far as the next storing node (because a storing node will not increment its own DTSN in response, as described in the rules below), the assertion of the 'T' flag in conjunction with an incremented DTSN will result in a DAO refresh from the entire DODAG.
The control fields are used to trigger DAO messages as follows:
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A special case of DAO operation, distinct from unicast DAO operation, is multicast DAO operation which may be used to populate '1-hop' routing table entries.
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When forwarding a packet to a destination, precedence is given to selection of a next-hop successor as follows:
TTL must be decremented when forwarding. If the packet is being forwarded via a sibling, then the TTL may be decremented more aggressively (by more than one) to limit the impact of possible loops.
Note that the chosen successor MUST NOT be the neighbor that was the predecessor of the packet (split horizon), except in the case where it is intended for the packet to change from an up to an down flow, such as switching from DIO routes to DAO routes as the destination is neared.
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RPL loop avoidance mechanisms are kept simple and designed to minimize churn and states. Loops may form for a number of reasons, from control packet loss to sibling forwarding. RPL includes a reactive loop detection technique that protects from meltdown and triggers repair of broken paths.
RPL loop detection uses information that is placed into the packet. A future version of this specification will detail how this information is carried with the packet (e.g. a hop-by-hop option ([I‑D.hui‑6man‑rpl‑option] (Hui, J. and J. Vasseur, “RPL Option for Carrying RPL Information in Data-Plane Datagrams,” March 2010.)) or summarized somehow into the flow label). For the purpose of RPL operations, the information carried with a packet is constructed 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|S|R|F|0|0|0|0| RPLInstanceID | SenderRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPL Packet Information |
- Down 'O' bit:
- 1-bit flag indicating whether the packet is expected to progress up or down. A router sets the 'O' bit when the packet is expect to progress down (using DAO routes), and resets it when forwarding towards the root of the DODAG version. A host or RPL leaf node MUST set the bit to 0.
- Sibling 'S' bit:
- 1-bit flag indicating whether the packet has been forwarded via a sibling at the present rank, and denotes a risk of a sibling loop. A host or RPL leaf node MUST set the bit to 0.
- Rank-Error 'R' bit:
- 1-bit flag indicating whether a rank error was detected. A rank error is detected when there is a mismatch in the relative ranks and the direction as indicated in the 'O' bit. A host or RPL leaf node MUST set the bit to 0.
- Forwarding-Error 'F' bit:
- 1-bit flag indicating that this node can not forward the packet further towards the destination. The 'F' bit might be set by sibling that can not forward to a parent a packet with the Sibling 'S' bit set, or by a child node that does not have a route to destination for a packet with the down 'O' bit set. A host or RPL leaf node MUST set the bit to 0.
- RPLInstanceID:
- 8-bit field indicating the DODAG instance along which the packet is sent.
- SenderRank:
- 16-bit field set to zero by the source and to DAGRank(rank) by a router that forwards inside the RPL network.
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If the source is aware of the RPLInstanceID that is preferred for the packet, then it MUST set the RPLInstanceID field associated with the packet accordingly, otherwise it MUST set it to the RPL_DEFAULT_INSTANCE.
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Instance IDs are used to avoid loops between DODAGs from different origins. DODAGs that constructed for antagonistic constraints might contain paths that, if mixed together, would yield loops. Those loops are avoided by forwarding a packet along the DODAG that is associated to a given instance.
The RPLInstanceID is associated by the source with the packet. This RPLInstanceID MUST match the RPL Instance onto which the packet is placed by any node, be it a host or router. For traffic originating outside of the RPL domain there may be a mapping occurring at the gateway into the RPL domain, possibly based on an encoding within the flow label. This aspect of RPL operation is to be clarified in a future version of this specification.
When a router receives a packet that specifies a given RPLInstanceID and the node can forward the packet along the DODAG associated to that instance, then the router MUST do so and leave the RPLInstanceID value unchanged.
If any node can not forward a packet along the DODAG associated to the RPLInstanceID, then the node SHOULD discard the packet and send an ICMP error message.
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The DODAG is inconsistent if the direction of a packet does not match the rank relationship. A receiver detects an inconsistency if it receives a packet with either:
the 'O' bit set (to down) from a node of a higher rank.
the 'O' bit reset (for up) from a node of a lesser rank.
the 'S' bit set (to sibling) from a node of a different rank.
When the DODAG root increments the DODAGVersionNumber a temporary rank discontinuity may form between the next version and the prior version, in particular if nodes are adjusting their rank in the next version and deferring their migration into the next version. A router that is still a member of the prior version may choose to forward a packet to a (future) parent that is in the next version. In some cases this could cause the parent to detect an inconsistency because the rank-ordering in the prior version is not necessarily the same as in the next version and the packet may be judged to not be making forward progress. If the sending router is aware that the chosen successor has already joined the next version, then the sending router MUST update the SenderRank to INFINITE_RANK as it forwards the packets across the discontinuity into the next DODAG version in order to avoid a false detection of rank inconsistency.
One inconsistency along the path is not considered as a critical error and the packet may continue. But a second detection along the path of a same packet should not occur and the packet is dropped.
This process is controlled by the Rank-Error bit associated with the packet. When an inconsistency is detected on a packet, if the Rank-Error bit was not set then the Rank-Error bit is set. If it was set the packet is discarded and the trickle timer is reset.
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When a packet is forwarded along siblings, it cannot be checked for forward progress and may loop between siblings. Experimental evidence has shown that one sibling hop can be very useful and is generally sufficient to avoid loops. Based on that evidence, this specification enforces the simple rule that a packet may not make 2 sibling hops in a row.
When a host issues a packet or when a router forwards a packet to a non-sibling, the Sibling bit in the packet must be reset. When a router forwards to a sibling: if the Sibling bit was not set then the Sibling bit is set. If the Sibling bit was set then then the router SHOULD return the packet to the sibling that that passed it with the Forwarding-Error 'F' bit set and the 'S' bit left untouched.
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A DAO inconsistency happens when router that has an down DAO route via a child that is a remnant from an obsolete state that is not matched in the child. With DAO inconsistency loop recovery, a packet can be used to recursively explore and cleanup the obsolete DAO states along a sub-DODAG.
In a general manner, a packet that goes down should never go up again. If DAO inconsistency loop recovery is applied, then the router SHOULD send the packet back to the parent that passed it with the Forwarding-Error 'F' bit set and the 'O' bit left untouched. Otherwise the router MUST silently discard the packet.
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Upon receiving a packet with a Forwarding-Error bit set, the node MUST remove the routing states that caused forwarding to that neighbor, clear the Forwarding-Error bit and attempt to send the packet again. The packet may be sent to an alternate neighbor. If that alternate neighbor still has an inconsistent DAO state via this node, the process will recurse, this node will set the Forwarding-Error 'F' bit and the routing state in the alternate neighbor will be cleaned up as well.
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This section describes further the multicast routing operations over an IPv6 RPL network, and specifically how unicast DAOs can be used to relay group registrations up. Wherever the following text mentions Multicast Listener Discovery (MLD), one can read MLDv1 ([RFC2710] (Deering, S., Fenner, W., and B. Haberman, “Multicast Listener Discovery (MLD) for IPv6,” October 1999.)) or MLDv2 ([RFC3810] (Vida, R. and L. Costa, “Multicast Listener Discovery Version 2 (MLDv2) for IPv6,” June 2004.)).
As is traditional, a listener uses a protocol such as MLD with a router to register to a multicast group.
Along the path between the router and the DODAG root, MLD requests are mapped and transported as DAO messages within the RPL protocol; each hop coalesces the multiple requests for a same group as a single DAO message to the parent(s), in a fashion similar to proxy IGMP, but recursively between child router and parent up to the root.
A router might select to pass a listener registration DAO message to its preferred parent only, in which case multicast packets coming back might be lost for all of its sub-DODAG if the transmission fails over that link. Alternatively the router might select to copy additional parents as it would do for DAO messages advertising unicast destinations, in which case there might be duplicates that the router will need to prune.
As a result, multicast routing states are installed in each router on the way from the listeners to the root, enabling the root to copy a multicast packet to all its children routers that had issued a DAO message including a DAO for that multicast group, as well as all the attached nodes that registered over MLD.
For unicast traffic, it is expected that the grounded root of an DODAG terminates RPL and MAY redistribute the RPL routes over the external infrastructure using whatever routing protocol is used in the other routing domain. For multicast traffic, the root MAY proxy MLD for all the nodes attached to the RPL domain (this would be needed if the multicast source is located in the external infrastructure). For such a source, the packet will be replicated as it flows down the DODAG based on the multicast routing table entries installed from the DAO message.
For a source inside the DODAG, the packet is passed to the preferred parents, and if that fails then to the alternates in the DODAG. The packet is also copied to all the registered children, except for the one that passed the packet. Finally, if there is a listener in the external infrastructure then the DODAG root has to further propagate the packet into the external infrastructure.
As a result, the DODAG Root acts as an automatic proxy Rendezvous Point for the RPL network, and as source towards the Internet for all multicast flows started in the RPL LLN. So regardless of whether the root is actually attached to the Internet, and regardless of whether the DODAG is grounded or floating, the root can serve inner multicast streams at all times.
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The selection of successors, along the default paths up along the DODAG, or along the paths learned from destination advertisements down along the DODAG, leads to the formation of routing adjacencies that require maintenance.
In IGPs such as OSPF [RFC4915] (Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, “Multi-Topology (MT) Routing in OSPF,” June 2007.) or IS-IS [RFC5120] (Przygienda, T., Shen, N., and N. Sheth, “M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs),” February 2008.), the maintenance of a routing adjacency involves the use of Keepalive mechanisms (Hellos) or other protocols such as BFD ([I‑D.ietf‑bfd‑base] (Katz, D. and D. Ward, “Bidirectional Forwarding Detection,” January 2010.)) and MANET Neighborhood Discovery Protocol (NHDP [I‑D.ietf‑manet‑nhdp] (Clausen, T., Dearlove, C., and J. Dean, “Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP),” March 2010.)). Unfortunately, such an approach is not desirable in constrained environments such as LLN and would lead to excessive control traffic in light of the data traffic with a negative impact on both link loads and nodes resources. Overhead to maintain the routing adjacency should be minimized. Furthermore, it is not always possible to rely on the link or transport layer to provide information of the associated link state. The network layer needs to fall back on its own mechanism.
Thus RPL makes use of a different approach consisting of probing the neighbor using a Neighbor Solicitation message (see [RFC4861] (Narten, T., Nordmark, E., Simpson, W., and H. Soliman, “Neighbor Discovery for IP version 6 (IPv6),” September 2007.)). The reception of a Neighbor Advertisement (NA) message with the "Solicited Flag" set is used to verify the validity of the routing adjacency. Such mechanism MAY be used prior to sending a data packet. This allows for detecting whether or not the routing adjacency is still valid, and should it not be the case, select another feasible successor to forward the packet.
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An Objective Function (OF) allows for the selection of a DODAG to join, and a number of peers in that DODAG as parents. The OF is used to compute an ordered list of parents. The OF is also responsible to compute the rank of the device within the DODAG version.
The Objective Function is indicated in the DIO message using an Objective Code Point (OCP), as specified in [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.), and indicates the method that must be used to construct the DODAG. The Objective Code Points are specified in [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.), [I‑D.ietf‑roll‑of0] (Thubert, P., “RPL Objective Function 0,” February 2010.), and related companion specifications.
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Most Objective Functions are expected to follow the same abstract behavior:
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Following is a summary of RPL constants and variables.
- BASE_RANK
- This is the rank for a virtual root that might be used to coordinate multiple roots. BASE_RANK has a value of 0.
- ROOT_RANK
- This is the rank for a DODAG root. ROOT_RANK has a value of MinHopRankIncrease (as advertised by the DODAG root), such that DAGRank(ROOT_RANK) is 1.
- INFINITE_RANK
- This is the constant maximum for the rank. INFINITE_RANK has a value of 0xFFFF.
- RPL_DEFAULT_INSTANCE
- This is the RPLInstanceID that is used by this protocol by a node without any overriding policy. RPL_DEFAULT_INSTANCE has a value of 0.
- DEFAULT_PATH_CONTROL_SIZE
- TBD (To be determined)
- DEFAULT_DIO_INTERVAL_MIN
- TBD (To be determined)
- DEFAULT_DIO_INTERVAL_DOUBLINGS
- TBD (To be determined)
- DEFAULT_DIO_REDUNDANCY_CONSTANT
- TBD (To be determined)
- DEFAULT_MIN_HOP_RANK_INCREASE
- TBD a power of two (To be determined)
- DIO Timer
- One instance per DODAG that a node is a member of. Expiry triggers DIO message transmission. Trickle timer with variable interval in [0, DIOIntervalMin..2^DIOIntervalDoublings]. See Section 6.3.1 (Trickle Parameters)
- DAG Version Increment Timer
- Up to one instance per DODAG that the node is acting as DODAG root of. May not be supported in all implementations. Expiry triggers increment of DODAGVersionNumber, causing a new series of updated DIO message to be sent. Interval should be chosen appropriate to propagation time of DODAG and as appropriate to application requirements (e.g. response time vs. overhead).
- DelayDAO Timer
- Up to one instance per DAO parent (the subset of DODAG parents chosen to receive destination advertisements) per DODAG. Expiry triggers sending of DAO message to the DAO parent. See Section 7.1.6 (Scheduling to Send DAO (or No-Path))
- RemoveTimer
- Up to one instance per DAO entry per neighbor (i.e. those neighbors that have given DAO messages to this node as a DODAG parent) Expiry triggers a change in state for the DAO entry, setting up to do unreachable (No-Path) advertisements or immediately deallocating the DAO entry if there are no DAO parents. See Section 7.1.4.1.1.3 (Operation in the UNREACHABLE state)
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The aim of this section is to give consideration to the manageability of RPL, and how RPL will be operated in LLN beyond the use of a MIB module. The scope of this section is to consider the following aspects of manageability: fault management, configuration, accounting and performance.
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When a node is first powered up, it may either choose to stay silent and not send any multicast DIO message until it has joined a DODAG, or to immediately root a transient DODAG and start sending multicast DIO messages. A RPL implementation SHOULD allow configuring whether the node should stay silent or should start advertising DIO messages.
Furthermore, the implementation SHOULD to allow configuring whether or not the node should start sending an DIS message as an initial probe for nearby DODAGs, or should simply wait until it received DIO messages from other nodes that are part of existing DODAGs.
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RPL specifies a number of protocol parameters.
A RPL implementation SHOULD allow configuring the following routing protocol parameters, which are further described in Section 5.3 (DODAG Information Object (DIO)):
- DAGPreference
- RPLInstanceID
- DAGObjectiveCodePoint
- DODAGID
- Routing Information
- Prefix Information
- DIOIntervalDoublings
- DIOIntervalMin
- DIORedundancyConstant
- DAG Root behavior:
- In some cases, a node may not want to permanently act as a DODAG root if it cannot join a grounded DODAG. For example a battery-operated node may not want to act as a DODAG root for a long period of time. Thus a RPL implementation MAY support the ability to configure whether or not a node could act as a DODAG root for a configured period of time.
- DODAG Table Entry Suppression
- A RPL implementation SHOULD provide the ability to configure a timer after the expiration of which logical equivalent of the DODAG table that contains all the records about a DODAG is suppressed, to be invoked if the DODAG parent set becomes empty.
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A RPL implementation makes use of trickle timer to govern the sending of DIO message. Such an algorithm is determined a by a set of configurable parameters that are then advertised by the DODAG root along the DODAG in DIO messages.
For each DODAG, a RPL implementation MUST allow for the monitoring of the following parameters, further described in Section 6.3.1 (Trickle Parameters):
- I
- T
- C
- I_min
- I_doublings
A RPL implementation SHOULD provide a command (for example via API, CLI, or SNMP MIB) whereby any procedure that detects an inconsistency may cause the trickle timer to reset.
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A RPL implementation may allow by configuration at the DODAG root to refresh the DODAG states by updating the DODAGVersionNumber. A RPL implementation SHOULD allow configuring whether or not periodic or event triggered mechanism are used by the DODAG root to control DODAGVersionNumber change.
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The following set of parameters of the DAO messages SHOULD be configurable:
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DAG discovery enables nodes to implement different policies for selecting their DODAG parents.
A RPL implementation SHOULD allow configuring the set of acceptable or preferred Objective Functions (OF) referenced by their Objective Codepoints (OCPs) for a node to join a DODAG, and what action should be taken if none of a node's candidate neighbors advertise one of the configured allowable Objective Functions.
A node in an LLN may learn routing information from different routing protocols including RPL. It is in this case desirable to control via administrative preference which route should be favored. An implementation SHOULD allow for specifying an administrative preference for the routing protocol from which the route was learned.
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Some RPL implementation may limit the size of the candidate neighbor list in order to bound the memory usage, in which case some otherwise viable candidate neighbors may not be considered and simply dropped from the candidate neighbor list.
A RPL implementation MAY provide an indicator on the size of the candidate neighbor list.
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The information and data models necessary for the operation of RPL will be defined in a separate document specifying the RPL SNMP MIB.
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The aim of this section is to describe the various RPL mechanisms specified to monitor the protocol.
As specified in Section 3.1 (Topology), an implementation is expected to maintain a set of data structures in support of DODAG discovery:
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A node in the candidate neighbor list is a node discovered by the some means and qualified to potentially become of neighbor or a sibling (with high enough local confidence). A RPL implementation SHOULD provide a way monitor the candidate neighbors list with some metric reflecting local confidence (the degree of stability of the neighbors) measured by some metrics.
A RPL implementation MAY provide a counter reporting the number of times a candidate neighbor has been ignored, should the number of candidate neighbors exceeds the maximum authorized value.
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For each DAG, a RPL implementation is expected to keep track of the following DODAG table values:
The set of DODAG parents structure is itself a table with the following entries:
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For each route provisioned by RPL operation, a RPL implementation MUST keep track of the following:
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A RPL implementation SHOULD provide a counter reporting the number of a times the node has detected an inconsistency with respect to a DODAG parent, e.g. if the DODAGID has changed.
A RPL implementation MAY log the reception of a malformed DIO message along with the neighbor identification if avialable.
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A RPL implementation operating on a DODAG root MUST allow for the configuration of the following trickle parameters:
A RPL implementation MAY provide a counter reporting the number of times an inconsistency (and thus the trickle timer has been reset).
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This section has to be completed in further revision of this document to list potential Operations and Management (OAM) tools that could be used for verifying the correct operation of RPL.
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RPL does not have any impact on the operation of existing protocols.
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To be completed.
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+----------------------------------------------------------------+ | | | TBD | | Under Construction | | Deference given to Security Design Team | | | +----------------------------------------------------------------+
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From a security perspective, RPL networks are no different from any other network. They are vulnerable to passive eavesdropping attacks and potentially even active tampering when physical access to a wire is not required to participate in communications. The very nature of ad hoc networks and their cost objectives impose additional security constraints, which perhaps make these networks the most difficult environments to secure. Devices are low-cost and have limited capabilities in terms of computing power, available storage, and power drain; and it cannot always be assumed they have neither a trusted computing base nor a high-quality random number generator aboard. Communications cannot rely on the online availability of a fixed infrastructure and might involve short-term relationships between devices that may never have communicated before. These constraints might severely limit the choice of cryptographic algorithms and protocols and influence the design of the security architecture because the establishment and maintenance of trust relationships between devices need to be addressed with care. In addition, battery lifetime and cost constraints put severe limits on the security overhead these networks can tolerate, something that is of far less concern with higher bandwidth networks. Most of these security architectural elements can be implemented at higher layers and may, therefore, be considered to be outside the scope of this standard. Special care, however, needs to be exercised with respect to interfaces to these higher layers.
The security mechanisms in this standard are based on symmetric-key and public-key cryptography and use keys that are to be provided by higher layer processes. The establishment and maintenance of these keys are outside the scope of this standard. The mechanisms assume a secure implementation of cryptographic operations and secure and authentic storage of keying material.
The security mechanisms specified provide particular combinations of the following security services:
- Data confidentiality:
- Assurance that transmitted information is only disclosed to parties for which it is intended.
- Data authenticity:
- Assurance of the source of transmitted information (and, hereby, that information was not modified in transit).
- Replay protection:
- Assurance that a duplicate of transmitted information is detected.
- Timeliness (delay protection):
- Assurance that transmitted information was received in a timely manner.
The actual protection provided can be adapted on a per-packet basis and allows for varying levels of data authenticity (to minimize security overhead in transmitted packets where required) and for optional data confidentiality. When nontrivial protection is required, replay protection is always provided.
Replay protection is provided via the use of a non-repeating value (nonce) in the packet protection process and storage of some status information for each originating device on the receiving device, which allows detection of whether this particular nonce value was used previously by the originating device. In addition, so-called delay protection is provided amongst those devices that have a loosely synchronized clock on board. The acceptable time delay can be adapted on a per-packet basis and allows for varying latencies (to facilitate longer latencies in packets transmitted over a multi-hop communication path).
Cryptographic protection may use a key shared between two peer devices (link key) or a key shared among a group of devices (group key), thus allowing some flexibility and application-specific tradeoffs between key storage and key maintenance costs versus the cryptographic protection provided. If a group key is used for peer-to-peer communication, protection is provided only against outsider devices and not against potential malicious devices in the key-sharing group.
Data authenticity may be provided using symmetric-key based or public-key based techniques. With public-key based techniques (via signatures), one corroborates evidence as to the unique originator of transmitted information, whereas with symmetric-key based techniques data authenticity is only provided relative to devices in a key-sharing group. Thus, public-key based authentication may be useful in scenarios that require a more fine-grained authentication than can be provided with symmetric-key based authentication techniques alone, such as with group communications (broadcast, multicast), or in scenarios that require non-repudiation.
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This section describes the transmission of secured RPL control packets. Give an outgoing RPL control packet and required security protection, this section describes how RPL generates the secured packet to transmit. It describes the order of cryptographic operations to provide the required protection.
A RPL node MUST set the security section in the RPL packet to describes the required protection level.
The Counter field of the security header MUST be an increment of the last Counter field transmitted.
If the RPL packet is not a response to a Consistency Check message, the node MAY set the Counter Compression field of the security option. If the packet is a response to a Consistency Check message, the node MUST clear the Counter Compression field.
A node sets the Key Identifier Mode (KIM) of the packet based on its understanding of what keys destinations have.
A node MUST replaced the original packet payload with that payload encrypted using the security protection, key, and nonce specified in the security section.
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This section describes the reception of a secured RPL packet. Given an incoming RPL packet, this section describes now RPL generates an unencrypted version of the packet and validates its integrity.
The receiver uses the security control field of the security section to determine what processing to do. If the described level of security does not meet locally maintained security policies, a node MAY discard the packet without further processing. These policies can include security levels, keys used, or source identifiers.
Using a nonce derived from the Counter field and other information (as described in Section Figure 21 (CCM* Nonce)), the receiver checks the integrity of the packet by comparing the received MAC with the computed MAC. If this integrity check does not pass, a node MUST discard the packet.
RPL uses the key information described in a RPL message to decrypt its contents as necessary. Once a message has passed its integrity checks and been successfully decrypted, the node can update its local security information, such as the source's expected counter value for counter compression. A node MUST NOT update security information on receipt of a message that fails security policy checks, integrity checks, or decryption.
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The cryptographic mode of operation used is based on the CCM mode of operation specified with [TBDREF] and the block-cipher AES-128 [TBDREF]. This mode of operation is widely supported by existing implementations and coincides with the CCM* mode of operation specified with [TBDREF].
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The so-called nonce is constructed 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Reserved | LVL |
+-+-+-+-+-+-+-+-+
| Figure 21: CCM* Nonce |
- Source Identifier:
- 8 bytes. Source Identifier is set to the logical identifier of the originator of the protected packet.
- Counter:
- 4 bytes. Counter is set to the (uncompressed) value of the corresponding field in the Security option of the RPL control message.
- Security Level (LVL):
- 3 bits. Security Level is set to the value of the corresponding field in the Security option of the RPL control message.
Unassigned bits of the nonce are reserved. They MUST be set to zero when constructing the nonce.
All fields of the nonce shall be represented is most-significant-octet and most-significant-bit first order.
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For a RPL ICMPv6 message, the entire packet is within the scope of RPL security. The message authentication code is calculated over the entire IPv6 packet. This calculation is done before any compression that lower layers may apply. The IPv6 and ICMPv6 headers are never encrypted. The body of the RPL ICMPv6 message MAY be encrypted, starting from the first byte after the security information and continuing to the end of the packet.
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A DAG root starting a DODAG sets the RPL routing security policy for the entire DODAG.
A member of a secure DODAG MUST conform to the policy set by the DAG root. When starting a secure DODAG, the DAG root will send secure DIO messages. A node attempting to join the DODAG will send a secure Authentication Request (AREQ) to the DAG root. Nodes that are not authenticated in a secure DODAG will be unable to generate properly constructed secured RPL packets. These nodes are in state "unauthenticated". A member of a secure DODAG MUST forward an AREQ packet to the DAG root, and MUST NOT forward any other type of packet from an unauthenticated node.
The DAG root may choose to respond to the AREQ with an ARSP packet. This packet will provide the authenticating node with the cryptographic materials necessary to participate in RPL routing. Some authentication flows may involve the exchange of more than one AREQ or ARSP packets.
The simplest authentication flow will involve the use of a single pre-installed network-wide authentication key. The installation of this key is out of scope of this document. The authenticating node will use the pre-installed key to calculate a MIC for the AREQ packet. The DODAG root will verify the authenticity of the authenticating node using the same key. The DODAG root, having previously chosen a single random instance-wide shared key, will send this key, encrypted and authenticated with the pre-installed key, in the ARSP packet. The authenticating node, decoding this packet with the pre-installed key, will verify the authenticity of the DODAG root.
It is assumed that additional authentication and key exchange mechanisms will be included in future drafts of the document.
Periodic key updates will use the secure KU packet code. The responsibility for initiating key update will reside with the DODAG root, and is out of scope of this document.
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The RPL Control Message is an ICMP information message type that is to be used carry DODAG Information Objects, DODAG Information Solicitations, and Destination Advertisement Objects in support of RPL operation.
IANA has defined an ICMPv6 Type Number Registry. The suggested type value for the RPL Control Message is 155, to be confirmed by IANA.
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IANA is requested to create a registry, RPL Control Codes, for the Code field of the ICMPv6 RPL Control Message.
New codes may be allocated only by an IETF Consensus action. Each code should be tracked with the following qualities:
Three codes are currently defined:
| Code | Description | Reference |
|---|---|---|
| 0x00 | DODAG Information Solicitation | This document |
| 0x01 | DODAG Information Object | This document |
| 0x02 | Destination Advertisement Object | This document |
| 0x80 | Secure DODAG Information Solicitation | This document |
| 0x81 | Secure DODAG Information Object | This document |
| 0x82 | Secure Destination Advertisement Object | This document |
| 0x83 | Secure Destination Advertisement Object Acknowledgment | This document |
| RPL Control Codes |
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IANA is requested to create a registry for the Mode of Operation (MOP) DIO Control Field, which is contained in the DIO Base.
New fields may be allocated only by an IETF Consensus action. Each field should be tracked with the following qualities:
Two values are currently defined:
| MOP | Description | Reference |
|---|---|---|
| 00 | Non-Storing mode of operation | This document |
| 01 | Storing mode of operation | This document |
| DIO Base Flags |
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IANA is requested to create a registry for the RPL Control Message Options
| Value | Meaning | Reference |
|---|---|---|
| 0 | Pad1 | This document |
| 1 | PadN | This document |
| 2 | DAG Metric Container | This Document |
| 3 | Routing Information | This Document |
| 4 | DAG Timer Configuration | This Document |
| 5 | RPL Target | This Document |
| 6 | Transit Information | This Document |
| 7 | Solicited Information | This Document |
| 8 | Prefix Information | This Document |
| RPL Control Message Options |
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The authors would like to acknowledge the review, feedback, and comments from Roger Alexander, Emmanuel Baccelli, Dominique Barthel, Yusuf Bashir, Phoebus Chen, Mathilde Durvy, Manhar Goindi, Mukul Goyal, Anders Jagd, JeongGil (John) Ko, Quentin Lampin, Jerry Martocci, Matteo Paris, Alexandru Petrescu, Joseph Reddy, and Don Sturek.
The authors would like to acknowledge the guidance and input provided by the ROLL Chairs, David Culler and JP Vasseur.
The authors would like to acknowledge prior contributions of Robert Assimiti, Mischa Dohler, Julien Abeille, Ryuji Wakikawa, Teco Boot, Patrick Wetterwald, Bryan Mclaughlin, Carlos J. Bernardos, Thomas Watteyne, Zach Shelby, Caroline Bontoux, Marco Molteni, Billy Moon, and Arsalan Tavakoli, which have provided useful design considerations to RPL.
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RPL is the result of the contribution of the following members of the RPL Author Team, including the editors, and additional contributors as listed below:
JP Vasseur Cisco Systems, Inc 11, Rue Camille Desmoulins Issy Les Moulineaux, 92782 France Email: jpv@cisco.com Thomas Heide Clausen LIX, Ecole Polytechnique, France Phone: +33 6 6058 9349 EMail: T.Clausen@computer.org URI: http://www.ThomasClausen.org/ Philip Levis Stanford University 358 Gates Hall, Stanford University Stanford, CA 94305-9030 USA Email: pal@cs.stanford.edu Richard Kelsey Ember Corporation Boston, MA USA Phone: +1 617 951 1225 Email: kelsey@ember.com Jonathan W. Hui Arch Rock Corporation 501 2nd St. Ste. 410 San Francisco, CA 94107 USA Email: jhui@archrock.com Kris Pister Dust Networks 30695 Huntwood Ave. Hayward, 94544 USA Email: kpister@dustnetworks.com Anders Brandt Sigma Designs Emdrupvej 26A, 1. Copenhagen, DK-2100 Denmark Email: abr@sdesigns.dk Stephen Dawson-Haggerty UC Berkeley Soda Hall, UC Berkeley Berkeley, CA 94720 USA Email: stevedh@cs.berkeley.edu
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| [RFC2119] | Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). |
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| [I-D.hui-6man-rpl-option] | Hui, J. and J. Vasseur, “RPL Option for Carrying RPL Information in Data-Plane Datagrams,” draft-hui-6man-rpl-option-00 (work in progress), March 2010 (TXT). |
| [I-D.hui-6man-rpl-routing-header] | Hui, J., Vasseur, J., and D. Culler, “A Source Routing Header for RPL,” draft-hui-6man-rpl-routing-header-00 (work in progress), May 2010 (TXT). |
| [I-D.ietf-bfd-base] | Katz, D. and D. Ward, “Bidirectional Forwarding Detection,” draft-ietf-bfd-base-11 (work in progress), January 2010 (TXT). |
| [I-D.ietf-manet-nhdp] | Clausen, T., Dearlove, C., and J. Dean, “Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP),” draft-ietf-manet-nhdp-12 (work in progress), March 2010 (TXT). |
| [I-D.ietf-roll-building-routing-reqs] | Martocci, J., Riou, N., Mil, P., and W. Vermeylen, “Building Automation Routing Requirements in Low Power and Lossy Networks,” draft-ietf-roll-building-routing-reqs-09 (work in progress), January 2010 (TXT). |
| [I-D.ietf-roll-of0] | Thubert, P., “RPL Objective Function 0,” draft-ietf-roll-of0-01 (work in progress), February 2010 (TXT). |
| [I-D.ietf-roll-routing-metrics] | Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” draft-ietf-roll-routing-metrics-06 (work in progress), April 2010 (TXT). |
| [I-D.ietf-roll-terminology] | Vasseur, J., “Terminology in Low power And Lossy Networks,” draft-ietf-roll-terminology-03 (work in progress), March 2010 (TXT). |
| [I-D.ietf-roll-trickle] | Levis, P., Clausen, T., Hui, J., and J. Ko, “The Trickle Algorithm,” draft-ietf-roll-trickle-01 (work in progress), April 2010 (TXT). |
| [RFC1982] | Elz, R. and R. Bush, “Serial Number Arithmetic,” RFC 1982, August 1996 (TXT). |
| [RFC2710] | Deering, S., Fenner, W., and B. Haberman, “Multicast Listener Discovery (MLD) for IPv6,” RFC 2710, October 1999 (TXT). |
| [RFC3810] | Vida, R. and L. Costa, “Multicast Listener Discovery Version 2 (MLDv2) for IPv6,” RFC 3810, June 2004 (TXT). |
| [RFC3819] | Karn, P., Bormann, C., Fairhurst, G., Grossman, D., Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. Wood, “Advice for Internet Subnetwork Designers,” BCP 89, RFC 3819, July 2004 (TXT). |
| [RFC4101] | Rescorla, E. and IAB, “Writing Protocol Models,” RFC 4101, June 2005 (TXT). |
| [RFC4191] | Draves, R. and D. Thaler, “Default Router Preferences and More-Specific Routes,” RFC 4191, November 2005 (TXT). |
| [RFC4443] | Conta, A., Deering, S., and M. Gupta, “Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification,” RFC 4443, March 2006 (TXT). |
| [RFC4861] | Narten, T., Nordmark, E., Simpson, W., and H. Soliman, “Neighbor Discovery for IP version 6 (IPv6),” RFC 4861, September 2007 (TXT). |
| [RFC4862] | Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” RFC 4862, September 2007 (TXT). |
| [RFC4915] | Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, “Multi-Topology (MT) Routing in OSPF,” RFC 4915, June 2007 (TXT). |
| [RFC5120] | Przygienda, T., Shen, N., and N. Sheth, “M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs),” RFC 5120, February 2008 (TXT). |
| [RFC5548] | Dohler, M., Watteyne, T., Winter, T., and D. Barthel, “Routing Requirements for Urban Low-Power and Lossy Networks,” RFC 5548, May 2009 (TXT). |
| [RFC5673] | Pister, K., Thubert, P., Dwars, S., and T. Phinney, “Industrial Routing Requirements in Low-Power and Lossy Networks,” RFC 5673, October 2009 (TXT). |
| [RFC5826] | Brandt, A., Buron, J., and G. Porcu, “Home Automation Routing Requirements in Low-Power and Lossy Networks,” RFC 5826, April 2010 (TXT). |
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RPL demonstrates the following properties, consistent with the requirements specified by the application-specific requirements documents.
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RPL is strictly compliant with layered IPv6 architecture.
Further, RPL is designed with consideration to the practical support and implementation of IPv6 architecture on devices which may operate under severe resource constraints, including but not limited to memory, processing power, energy, and communication. The RPL design does not presume high quality reliable links, and operates over lossy links (usually low bandwidth with low packet delivery success rate).
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Multipoint-to-Point (MP2P) and Point-to-multipoint (P2MP) traffic flows from nodes within the LLN from and to egress points are very common in LLNs. Low power and lossy network Border Router (LBR) nodes may typically be at the root of such flows, although such flows are not exclusively rooted at LBRs as determined on an application-specific basis. In particular, several applications such as building or home automation do require P2P (Point-to-Point) communication.
As required by the aforementioned routing requirements documents, RPL supports the installation of multiple paths. The use of multiple paths include sending duplicated traffic along diverse paths, as well as to support advanced features such as Class of Service (CoS) based routing, or simple load balancing among a set of paths (which could be useful for the LLN to spread traffic load and avoid fast energy depletion on some, e.g. battery powered, nodes). Conceptually, multiple instances of RPL can be used to send traffic along different topology instances, the construction of which is governed by different Objective Functions (OF). Details of RPL operation in support of multiple instances are beyond the scope of the present specification.
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The RPL design supports constraint based routing, based on a set of routing metrics and constraints. The routing metrics and constraints for links and nodes with capabilities supported by RPL are specified in a companion document to this specification, [I‑D.ietf‑roll‑routing‑metrics] (Vasseur, J., Kim, M., Networks, D., and H. Chong, “Routing Metrics used for Path Calculation in Low Power and Lossy Networks,” April 2010.). RPL signals the metrics, constraints, and related Objective Functions (OFs) in use in a particular implementation by means of an Objective Code Point (OCP). Both the routing metrics, constraints, and the OF help determine the construction of the Directed Acyclic Graphs (DAG) using a distributed path computation algorithm.
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NOTE: RPL is still a work in progress. At this time there remain several unsatisfied application requirements, but these are to be addressed as RPL is further specified.
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This section enumerates some outstanding issues that are to be addressed in future revisions of the RPL specification.
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In some situations the baseline mechanism to support arbitrary P2P traffic, by flowing upwards along the DODAG until a common ancestor is reached and then flowing down, may not be suitable for all application scenarios. A related scenario may occur when the down paths setup along the DODAG by the destination advertisement mechanism are not the most desirable downward paths for the specific application scenario (in part because the DODAG links may not be symmetric). It may be desired to support within RPL the discovery and installation of more direct routes 'across' the DAG. Such mechanisms need to be investigated.
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In order to minimize overhead within the LLN it is desirable to perform some sort of address and/or header compression, perhaps via labels, addresses aggregation, or some other means. This is still under investigation.
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A network may run multiple instances of RPL concurrently. Such a network will require methods for assigning and otherwise managing RPLInstanceIDs. This will likely be addressed in a separate document.
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| Tim Winter (editor) | |
| Email: | wintert@acm.org |
| Pascal Thubert (editor) | |
| Cisco Systems | |
| Village d'Entreprises Green Side | |
| 400, Avenue de Roumanille | |
| Batiment T3 | |
| Biot - Sophia Antipolis 06410 | |
| FRANCE | |
| Phone: | +33 497 23 26 34 |
| Email: | pthubert@cisco.com |
| RPL Author Team | |
| IETF ROLL WG | |
| Email: | rpl-authors@external.cisco.com |