Recommendations for Efficient Implementation of RPL
draft-gnawali-roll-rpl-recommendations-00

Abstract

RPL is a flexible routing protocol applicable to a wide range of Low Power and Lossy Networks. To enable this wide applicability, RPL provides many configuration options and gives implementers choices on how to implement various components of RPL. Drawing on our experiences, we distill the design choices and configuration parameters that lead to efficient RPL implementations and operations.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Set the Minimum Trickle Interval with Care
• 4. Use Large Maximum Trickle Interval
• 5. Poison Route Sparingly
• 6. Preserve Neighbor Information
• 7. Slow-Down Datapath Traffic During Path Inconsistency
• 8. Acknowledgements
• 9. IANA Considerations
• 10. Security Considerations
• 11. References
• 11.1. Normative References
• 11.2. Informative References
• Authors' Addresses

1. Introduction

RPL [I-D.ietf-roll-rpl] is a routing protocol that is applicable in a wide range of settings in networks characterized by low power and lossy links (LLN). Because RPL is designed to work in a wide range of settings, it offers many configuration parameters and choices in how different mechanisms are implemented. This flexibility is essential to ensure the wide applicability of this protocol.

One can take advantage of this flexibility to implement and configure RPL in the most efficient way for a given network. However, it is easy to inadvertently configure RPL to work inefficiently in the network. These design choices must be made carefully drawing on implementation and operational experiences.

In this document, we describe aspects of configuration and mechanisms that impact the performance of RPL. We hope these descriptions serve as guidelines and best practices for RPL implementers and enables them to understand why certain design and configuration choices are favored over others.

2. Terminology

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 [RFC2119].

This terminology used in this document is consistent with the terminologies described in [I-D.ietf-roll-terminology], [I-D.ietf-roll-rpl], and [I-D.ietf-roll-routing-metrics].

This document does not introduce new terms.

3. Set the Minimum Trickle Interval with Care

The minimum Trickle interval determines the fastest rate at which RPL will send DIOs. It is not useful to have multiple DIOs in the transmit queue at a given node. The information in the older DIOs is likely already stale when the new DIO is generated. In systems that cannot cancel the packets that are already in the queue, it is advisable to set the minimum interval to be much larger than the minimum link layer packet time.

4. Use Large Maximum Trickle Interval

The maximum Trickle interval determines the slowest rate at which RPL will send DIOs. It is recommended that the maximum interval is set to several hours. A large interval does not necessarily make RPL less agile or the routing information stale. Trickle will operate at a rate between the minimum and maximum interval depending on the dynamics in the network.

5. Poison Route Sparingly

It is often not necessary for a node to poison a route explicitly by advertising a rank of INFINITY. With datapath validation, it is easy to detect a loop and coupled with adaptive beaconing, the routes can be repaired quickly without additional explicit mechanism for route poisoning. Poisoning the route does not prevent loops.

6. Preserve Neighbor Information

The neighborhood information is useful even when a node detects that it has lost a route. It is recommended that the nodes not flush the entire or subset of the neighbor table even when a node loses its route or detects a loop. It is sufficient to mark the nodes in the table with the updated information that resulted in route loss or loops, e.g., marking the particular parent with a rank of INFINITY.

7. Slow-Down Datapath Traffic During Path Inconsistency

When a node detects that a path is inconsistent through datapath validation, it tasks the control plane to repair the topology and make it consistent. During this time, although the route is available, it is advisable that the data packets are sent at lower rates to reduce contention with the control packets.

8. Acknowledgements

We will acknowledge people who contribute their experiences.

9. IANA Considerations

None.

10. Security Considerations

Security considerations to be developed in accordance to the output of the WG.

11. References

11.1. Normative References

11.2. Informative References

Authors' Addresses