6MAN J. Hui Internet-Draft Arch Rock Corporation Intended status: Standards Track JP. Vasseur Expires: April 14, 2012 Cisco Systems, Inc October 12, 2011 RPL Option for Carrying RPL Information in Data-Plane Datagrams draft-ietf-6man-rpl-option-04 Abstract The RPL protocol requires data-plane datagrams to carry RPL routing information that is processed by RPL routers when forwarding those datagrams. This document describes the RPL Option for use within a RPL domain. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 14, 2012. Copyright Notice Copyright (c) 2011 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. Hui & Vasseur Expires April 14, 2012 [Page 1] Internet-Draft RPL Option October 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Format of the RPL Option . . . . . . . . . . . . . . . . . . . 5 4. RPL Router Behavior . . . . . . . . . . . . . . . . . . . . . 7 5. RPL Border Router Behavior . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 9. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 10.1. Normative References . . . . . . . . . . . . . . . . . . . 13 10.2. Informative References . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Hui & Vasseur Expires April 14, 2012 [Page 2] Internet-Draft RPL Option October 2011 1. Introduction RPL is a distance vector IPv6 routing protocol designed for Low power and Lossy Networks (LLNs) [I-D.ietf-roll-rpl]. Such networks are typically constrained in energy and/or channel capacity. To conserve precious resources, a routing protocol must generate control traffic sparingly. However, this is at odds with the need to quickly propagate any new routing information to resolve routing inconsistencies quickly. To help minimize resource consumption, RPL uses a slow proactive process to construct and maintain a routing topology but a reactive and dynamic process to resolving routing inconsistencies. In the steady state, RPL maintains the routing topology using a low-rate beaconing process. However, when RPL detects inconsistencies that may prevent proper datagram delivery, RPL temporarily increases the beacon rate to quickly resolve those inconsistencies. This dynamic rate control operation is governed by the use of dynamic timers also referred to as "Trickle" timers and defined in [I-D.ietf-roll-trickle]. In contrast to other routing protocols (e.g OSPF [RFC2328]), RPL detects routing inconsistencies using data-path verification, by including routing information within the datagram itself. In doing so, repair mechanisms operate only as needed, allowing the control and data planes to operate on similar time scales. The main motivation for data path verification in LLNs is that control plane traffic should be carefully bounded with respect to the data traffic. Intuitively, there is no need to solve routing issues (which may be temporary) in the absence of data traffic. The RPL protocol constructs a Directed Acyclic Graph (DAG) that attempts to minimize path costs to the DAG root according to a set of metric and objective functions. There are circumstances where loops may occur, and RPL is designed to use a data-path loop detection method. This is one of the known requirements of RPL and other data- path usage might be defined in the future. To that end, this document proposes a new IPv6 option, called the RPL Option, to be carried within the IPv6 Hop-by-Hop header. The RPL Option is only for use within a RPL domain. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Hui & Vasseur Expires April 14, 2012 [Page 3] Internet-Draft RPL Option October 2011 2. Overview Datagrams sent between nodes within a RPL domain MUST include a RPL Option or RPL Source Route Header (SRH) and MAY include both. When a RPL Border Router inserts a RPL Option, it MUST do so by using IPv6- in-IPv6 tunneling, as specified in [RFC2473]. Use of tunneling ensures that the datagram is delivered unmodified and that ICMP errors return to the RPL Option source rather than the source of the original datagram. Hui & Vasseur Expires April 14, 2012 [Page 4] Internet-Draft RPL Option October 2011 3. Format of the RPL Option The RPL Option is carried in an IPv6 Hop-by-Hop Options header, immediately following the IPv6 header. This option has an alignment requirement of 2n. The option has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Opt Data Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |O|R|F|0|0|0|0|0| RPLInstanceID | SenderRank | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (sub-TLVs) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: RPL Option Option Type: TBD by IANA. Opt Data Len: 8-bit field indicating the length of the option, in octets, excluding the Option Type and Opt Data Len fields. Down 'O': 1-bit flag as defined in Section 11.2 of [I-D.ietf-roll-rpl]. The processing shall follow the rules described in Section 11.2 of [I-D.ietf-roll-rpl]. Rank-Error 'R': 1-bit flag as defined in Section 11.2 of [I-D.ietf-roll-rpl]. The processing shall follow the rules described in Section 11.2 of [I-D.ietf-roll-rpl]. Forwarding-Error 'F': 1-bit flag as defined in Section 11.2 of [I-D.ietf-roll-rpl]. The processing shall follow the rules described in Section 11.2 of [I-D.ietf-roll-rpl]. RPLInstanceID: 8-bit field as defined in Section 11.2 of [I-D.ietf-roll-rpl]. The processing shall follow the rules described in Section 11.2 of [I-D.ietf-roll-rpl]. SenderRank: 16-bit field as defined in Section 11.2 of [I-D.ietf-roll-rpl]. The processing shall follow the rules described in Section 11.2 of [I-D.ietf-roll-rpl]. Values within the RPL Option are expected to change en-route. Nodes that do not understand the RPL Option MUST discard the packet. Thus, according to [RFC2460] the two high order bits of the Option Type must be equal set to '01' and the third bit is equal to '1'. The RPL Option Data Length is variable. Hui & Vasseur Expires April 14, 2012 [Page 5] Internet-Draft RPL Option October 2011 The action taken by using the RPL Option and the potential set of sub-TLVs carried within the RPL Option MUST be specified by the RFC of the protocol that use that option. No TLVs are defined in this document. A RPL device MUST skip over any unrecognized sub-TLVs and attempt to process any additional sub-TLVs that may appear after. Hui & Vasseur Expires April 14, 2012 [Page 6] Internet-Draft RPL Option October 2011 4. RPL Router Behavior To deliver an IPv6 datagram to its destination, a router may need to insert a new RPL Option. Routers MUST use IPv6-in-IPv6 tunneling, as specified in [RFC2473] to include a new RPL Option in datagrams that are sourced by other nodes. Using IPv6-in-IPv6 tunneling ensures that the delivered datagram remains unmodified and that ICMPv6 errors generated by inserting the RPL Option are sent back to the router that generated the routing header. To avoid fragmentation, it is desirable to employ MTU sizes that allow for the header expansion (i.e. at least 1280 + 40 (outer IP header) + RPL_OPTION_MAX_SIZE), where RPL_OPTION_MAX_SIZE is the maximum RPL Option header size for a given RPL network. To take advantage of this, however, the communicating endpoints need to be aware of the MTU along the path (i.e. through Path MTU Discovery). Unfortunately, the larger MTU size may not be available on all links (e.g. 1280 octets on 6LoWPAN links). However, it is expected that much of the traffic on these types of networks consists of much smaller messages than the MTU, so performance degradation through fragmentation would be limited. Hui & Vasseur Expires April 14, 2012 [Page 7] Internet-Draft RPL Option October 2011 5. RPL Border Router Behavior RPL Border Routers (referred to as LBRs in [I-D.ietf-roll-terminology]) are responsible for ensuring that a RPL Option is only used within a RPL domain. For datagrams destined to the RPL Border Router, the router processes the packet in the usual way. For instance, if the RPL Option was included using tunneled mode and the RPL Border Router serves as the tunnel endpoint, the router removes the outer IPv6 header, at the same time removing the RPL Option as well. Datagrams destined elsewhere within the same RPL domain are forwarded to the correct interface. Datagrams destined to nodes outside the RPL domain are dropped if the outer-most IPv6 header contains a RPL Option. Hui & Vasseur Expires April 14, 2012 [Page 8] Internet-Draft RPL Option October 2011 6. Security Considerations This option may be used to mount several potential attacks since routers may be flooded by bogus datagrams containing the RPL Option. In particular, an inconsistent Rank value can cause a RPL router to reset its DIO Trickle timer. In order to avoid any unacceptable impact on network operations, an implementation MAY limit the number of triggers caused by receiving a RPL Option to no greater than MAX_RPL_OPTION_TRIGGERS per hour. A RECOMMENDED value for MAX_RPL_OPTION_TRIGGERS is 20. Hui & Vasseur Expires April 14, 2012 [Page 9] Internet-Draft RPL Option October 2011 7. IANA Considerations IANA is requested to reserve a new value in the Destination Options and Hop-by-Hop Options registry. The proposed value to be confirmed by IANA is: Hex Value Binary Value act chg rest Description Reference --------- --- --- ------- ----------------- ---------- TBD 01 1 TBD RPL Option [RFCthis] As specified in [RFC2460], the first two bits indicate that the IPv6 node MUST discard the packet if it doesn't recognize the option type, and the third bit indicates that the Option Data may change en-route. The remaining bits serve as the option type and are TBD by IANA. IANA is requested to create a registry called RPL-option-TLV, for the TLVs carried in the RPL Option header. New codes may be allocated only by IETF Review [RFC5226]. The type field is an 8-bit field whose value be between 0 and 255, inclusive. Hui & Vasseur Expires April 14, 2012 [Page 10] Internet-Draft RPL Option October 2011 8. Acknowledgements The authors thank Jari Arkko, Richard Kelsey, Suresh Krishnan, Vishwas Manral, Erik Nordmark, Pascal Thubert, and Tim Winter, for their comments and suggestions that helped shape this document. Hui & Vasseur Expires April 14, 2012 [Page 11] Internet-Draft RPL Option October 2011 9. Changes (This section to be removed by the RFC editor.) Draft 04: - Clarify when the RPL Option is used. - Updated text on recommendations for avoiding fragmentation. - Specify skip-over-and-continue policy for unrecognized sub-TLVs. - Change use of IPv6-in-IPv6 tunneling from SHOULD to MUST. - Specify RPL Border Router operations in terms of forwarding decision outcomes. - Expand security section. Draft 03: - Removed any presumed values that are TBD by IANA. Hui & Vasseur Expires April 14, 2012 [Page 12] Internet-Draft RPL Option October 2011 10. References 10.1. Normative References [I-D.ietf-roll-rpl] Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J., Kelsey, R., Levis, P., Pister, K., Struik, R., and J. Vasseur, "RPL: IPv6 Routing Protocol for Low power and Lossy Networks", draft-ietf-roll-rpl-19 (work in progress), March 2011. [I-D.ietf-roll-trickle] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, "The Trickle Algorithm", draft-ietf-roll-trickle-08 (work in progress), January 2011. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 Specification", RFC 2473, December 1998. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. 10.2. Informative References [I-D.hui-6man-rpl-headers] Hui, J., Thubert, P., and J. Vasseur, "Using RPL Headers Without IP-in-IP", draft-hui-6man-rpl-headers-00 (work in progress), July 2010. [I-D.ietf-roll-terminology] Vasseur, J., "Terminology in Low power And Lossy Networks", draft-ietf-roll-terminology-06 (work in progress), September 2011. Hui & Vasseur Expires April 14, 2012 [Page 13] Internet-Draft RPL Option October 2011 Authors' Addresses Jonathan W. Hui Arch Rock Corporation 501 2nd St. Ste. 410 San Francisco, California 94107 USA Phone: +415 692 0828 Email: jhui@archrock.com JP Vasseur Cisco Systems, Inc 11, Rue Camille Desmoulins Issy Les Moulineaux, 92782 France Email: jpv@cisco.com Hui & Vasseur Expires April 14, 2012 [Page 14]