Networking Working Group O. Gnawali Internet-Draft University of Houston Intended status: BCP P. Levis Expires: September 15, 2013 Stanford University March 14, 2013 Recommendations for Efficient Implementation of RPL draft-gnawali-roll-rpl-recommendations-05 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. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 15, 2013. 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. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. Gnawali & Levis Expires September 15, 2013 [Page 1] Internet-Draft draft-gnawali-roll-rpl-recommendations March 2013 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 BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Set the Minimum Trickle Interval with Care . . . . . . . . . . 3 4. Use Large Maximum Trickle Interval . . . . . . . . . . . . . . 4 5. Use Small Trickle Redundancy Constant . . . . . . . . . . . . . 4 6. Poison Route Sparingly . . . . . . . . . . . . . . . . . . . . 4 7. Preserve Neighbor Information . . . . . . . . . . . . . . . . . 4 8. Slow-Down Datapath Traffic During Path Inconsistency . . . . . 4 9. Choose Better Path Cost Over Route Stability . . . . . . . . . 5 10. Consider State Overhead While Running Storing Mode . . . . . . 5 11. Prevent Situations That Make Nodes a Leaf . . . . . . . . . . . 5 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 14. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 15.1. Normative References . . . . . . . . . . . . . . . . . . . 6 15.2. Informative References . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Gnawali & Levis Expires September 15, 2013 [Page 2] Internet-Draft draft-gnawali-roll-rpl-recommendations March 2013 1. Introduction RPL [RFC6550] 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], [RFC6550], and [RFC6551]. 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. Gnawali & Levis Expires September 15, 2013 [Page 3] Internet-Draft draft-gnawali-roll-rpl-recommendations March 2013 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. Use Small Trickle Redundancy Constant If a node receives more DIOs than the redundancy constant, it does not transmit, i.e., suppresses, its DIO. The rationale for this suppression is that the additional DIOs do not help discover new or better paths if certain number of DIOs have already been transmitted in the neighborhood of a node. In general, the smaller this number the more energy-efficient the route discovery. But setting this value too small can lead to network partitioning as many nodes will suppress their DIOs and will not be discovered. A constant of 3-5 has been found adequate in deployments. 6. 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 because the control packet can get dropped on the lossy link. 7. 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. 8. 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 Gnawali & Levis Expires September 15, 2013 [Page 4] Internet-Draft draft-gnawali-roll-rpl-recommendations March 2013 available, it is advisable that the data packets are sent at lower rates to reduce contention with the control packets. This slow-down can increase data packet latency or lead to queue overflow. 9. Choose Better Path Cost Over Route Stability With bursty links, a link metric designed to reflect link quality accurately can change rapidly. Other link metrics may also change rapidly. As a result, the path cost computed using these agile metrics can change rapidly. Selecting the best path then implies frequent parent changes. Route flapping is not detrimental to the performance of many network protocols such as sensor data collection over UDP. Hence, oftentimes, it is better to optimize for path cost than for path stability. 10. Consider State Overhead While Running Storing Mode A naive implementation of storing mode will have large state overhead, especially in large networks. However, it may be possible for storing mode to use RAM more efficiently by state aggregation, compression, and other techniques. The extent to which these techniques reduce the memory overhead, although promising based on experiences with other protocols, has not been evaluated for RPL state overhead. TinyOS open source implementation on TelosB, which has 10KB of RAM, is known to limit the routing table size to 30. An implementation on Contiki on MSP430F5438-based platform with has 16K of RAM is reported (in a private email to the authors) to support 100 entries. 11. Prevent Situations That Make Nodes a Leaf When different nodes in a single network run different OFs, have incompatible metrics, or run a mix of storing and non-storing modes[I-D.ko-roll-mix-network-pathology], the nodes may not join the DODAG or join as leaf nodes which do not extend DODAG connectivity as described in Section 8.5 of [RFC6550]. Thus, operating as a leaf node in the middle of a network can lead to network partitioning even though the network is physically connected. Generally avoid configurations that force some nodes to operate as leaf nodes even though the leaf nodes are at the physical edge of the network. 12. Acknowledgements Thanks to Ulrich Herberg, Mukul Goyal, C Chauvenet, JP Vasseur, and Gnawali & Levis Expires September 15, 2013 [Page 5] Internet-Draft draft-gnawali-roll-rpl-recommendations March 2013 Joakim Eriksson for their valuable comments. 13. IANA Considerations None. 14. Security Considerations There are no security implications related to this draft. 15. References 15.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. Alexander, "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks", RFC 6550, March 2012. [RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D. Barthel, "Routing Metrics Used for Path Calculation in Low-Power and Lossy Networks", RFC 6551, March 2012. 15.2. Informative References [I-D.ietf-roll-terminology] Vasseur, J., "Terminology in Low power And Lossy Networks", draft-ietf-roll-terminology-12 (work in progress), March 2013. [I-D.ko-roll-mix-network-pathology] Ko, J., Jeong, J., Park, J., Jun, J., Kim, N., and O. Gnawali, "RPL Routing Pathology In a Network With a Mix of Nodes Operating in Storing and Non-Storing Modes", draft-ko-roll-mix-network-pathology-02 (work in progress), February 2013. Gnawali & Levis Expires September 15, 2013 [Page 6] Internet-Draft draft-gnawali-roll-rpl-recommendations March 2013 Authors' Addresses Omprakash Gnawali University of Houston 577 Philip G. Hoffman Hall Houston, TX 77204 USA Phone: +1 713 743 3356 Email: gnawali@cs.uh.edu Philip Levis Stanford University 412 Gates Hall, Stanford University Stanford, CA 94305 USA Email: pal@cs.stanford.edu Gnawali & Levis Expires September 15, 2013 [Page 7]