RFC 6550

RFC 6550
Title	RFC 6550
Type	Request for Comments
Number	6550
Status	Internet Standard
Authors	Jonathan Hui, Amin Vahdat, David Culler, et al.
Year	2012
Pages	84
Organization	Internet Engineering Task Force

RFC 6550

RFC 6550 specifies the RPL (Routing Protocol for Low-Power and Lossy Networks), an IP routing protocol designed for constrained devices and networks. It defines how nodes form directed acyclic graphs for upward and downward traffic, addresses metrics and objective functions, and describes maintenance, multicast, and security considerations. The document standardizes behaviors for deployments such as smart metering, building automation, and environmental sensing.

Introduction

RPL was developed within the Internet Engineering Task Force ROLL Working Group to serve environments characterized by low bandwidth, high loss, constrained processing, and variable link quality. The specification provides mechanisms for constructing Destination-Oriented Directed Acyclic Graphs using IPv6 addressing and supports both point-to-point and multipoint-to-point traffic patterns. RFC 6550 aligns with related standards from the IETF Routing Area and complements other protocols from bodies like the IEEE Standards Association and the 3rd Generation Partnership Project.

Background and Motivation

Motivation for RPL arose from requirements articulated by stakeholders such as utility companies deploying Advanced Metering Infrastructure, municipal initiatives like Smart City pilots, and research platforms at institutions including the University of California, Berkeley and the Massachusetts Institute of Technology. Prior protocols such as legacy ad hoc routing efforts and specifications from the Internet Architecture Board lacked optimizations for constrained nodes common in projects funded by agencies like the National Science Foundation and the European Commission. Use cases from industrial automation influenced design goals recorded in IETF workshops and drafts produced by contributors affiliated with organizations such as Cisco Systems, ARM Holdings, and Silicon Labs.

Protocol Overview

RPL organizes nodes into one or more DODAGs rooted at one or more border routers or gateways. It leverages IPv6 mechanisms standardized by the Internet Engineering Task Force and integrates with header compression approaches championed by proponents in the 6LoWPAN Working Group. Core components include objective functions that map metrics and constraints to ranks, control messages for topology maintenance, and facilities for loop avoidance and local repair. RPL supports both storing and non-storing modes for maintaining downward routes, and accommodates multicast via interaction with protocols standardized by the Multicast Extensions Working Group.

Message Formats and Routing

Control-plane messages are encoded in ICMPv6 formats defined by IETF documents and include DIO, DAO, DIS, and DAO-ACK message types. DIOs convey configuration and rank information; DAOs enable downward route propagation toward roots, with optional sequence and lifetime semantics. The protocol specifies the use of metrics such as ETX and hop count and recommends objective functions like OF0 and MRHOF to select preferred parents. Interactions with link-layer technologies from standards bodies such as the IEEE 802.15.4 Working Group and adaptations for constrained networks from industry players like ARM Limited are described to ensure compatibility across deployments.

Security Considerations

RFC 6550 incorporates security modes that reference IETF security frameworks and leverages mechanisms compatible with protocols from the Internet Key Exchange family and key management practices advocated by organizations like the Internet Society. Threats addressed include outsider and insider attacks, spoofing, and replay, with options for authenticated control messages and secure direct keying. Operational recommendations reflect deployments in regulated sectors such as Smart Grid and prescribe interaction with policy frameworks promoted by agencies like the Federal Communications Commission and the European Telecommunications Standards Institute.

Implementation and Deployment

Multiple open-source and commercial implementations exist, originating from projects at research centers such as the INRIA and companies including Contiki OS maintainers and vendors like Silicon Labs and Texas Instruments. Field deployments have been reported in utility trials led by entities such as Itron and municipal programs in cities that partnered with consortiums including Echelon Corporation and academic testbeds like FIT IoT-LAB. Interoperability testing and certification efforts have involved standards organizations and industry forums including the IETF Interop Workshop and vendor alliances promoting IPv6-based sensor networks.

Extensions and Related Work

Subsequent work and extensions to RPL address areas such as secure bootstrap, route optimization, multipath routing, and adaptations for mobility; these efforts are documented in IETF follow-on drafts and referenced experimental RFCs. Related protocols and frameworks include link-layer specifications from the IEEE 802 family, routing approaches from the IETF MANET Working Group, and application-layer architectures promoted by consortia such as the Open Connectivity Foundation and the Zigbee Alliance. Research continuations at institutions like the University of Cambridge and ETH Zurich explore performance in large-scale deployments and interactions with emerging technologies standardized by entities like the 3GPP.

Category:Internet standards