Internet Engineering Task Force M. Goyal, Ed. Internet-Draft University of Wisconsin Intended status: Experimental Milwaukee Expires: November 6, 2012 E. Baccelli M. Philipp INRIA A. Brandt Sigma Designs J. Martocci Johnson Controls May 5, 2012 Reactive Discovery of Point-to-Point Routes in Low Power and Lossy Networks draft-ietf-roll-p2p-rpl-10 Abstract This document specifies a point-to-point route discovery mechanism, complementary to the RPL core functionality. This mechanism allows an IPv6 router to discover "on demand" routes to one or more IPv6 routers in the LLN such that the discovered routes meet specified metrics constraints. 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 November 6, 2012. Copyright Notice Copyright (c) 2012 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 Goyal, et al. Expires November 6, 2012 [Page 1] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. The Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Functional Overview . . . . . . . . . . . . . . . . . . . . . 6 6. P2P Route Discovery Mode Of Operation . . . . . . . . . . . . 9 6.1. Setting a P2P Mode DIO . . . . . . . . . . . . . . . . . . 9 7. New RPL Control Message Options . . . . . . . . . . . . . . . 11 7.1. P2P Route Discovery Option (P2P-RDO) . . . . . . . . . . . 12 7.2. Data Option . . . . . . . . . . . . . . . . . . . . . . . 15 8. The Discovery Reply Object (DRO) . . . . . . . . . . . . . . . 15 8.1. Secure DRO . . . . . . . . . . . . . . . . . . . . . . . . 17 8.2. Setting a P2P-RDO Carried in a Discovery Reply Object . . 18 9. P2P-RPL Route Discovery By Creating a Temporary DAG . . . . . 18 9.1. Joining a Temporary DAG . . . . . . . . . . . . . . . . . 18 9.2. Trickle Operation For P2P Mode DIOs . . . . . . . . . . . 19 9.3. Processing a P2P Mode DIO . . . . . . . . . . . . . . . . 20 9.4. Additional Processing of a P2P Mode DIO At An Intermediate Router . . . . . . . . . . . . . . . . . . . 21 9.5. Additional Processing of a P2P Mode DIO At The Target . . 22 9.6. Processing a DRO At An Intermediate Router . . . . . . . . 24 9.7. Processing a DRO At The Origin . . . . . . . . . . . . . . 25 10. The Discovery Reply Object Acknowledgement (DRO-ACK) . . . . . 26 11. Packet Forwarding Along a Route Discovered Using P2P-RPL . . . 27 12. Interoperability with Core RPL . . . . . . . . . . . . . . . . 28 13. Security Considerations . . . . . . . . . . . . . . . . . . . 28 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 14.1. Additions to DIO Mode of Operation . . . . . . . . . . . . 29 14.2. Additions to RPL Control Message Options . . . . . . . . . 29 14.3. Additions to RPL Control Codes . . . . . . . . . . . . . . 30 14.4. New Registry for Upper Layer Headers inside Data Option . 30 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31 16.1. Normative References . . . . . . . . . . . . . . . . . . . 31 16.2. Informative References . . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32 Goyal, et al. Expires November 6, 2012 [Page 2] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 1. Introduction Targeting Low power and Lossy Networks (LLNs), the RPL routing protocol [RFC6550] provides paths along a Directed Acyclic Graph (DAG) rooted at a single router in the network. Establishment and maintenance of a DAG is performed by routers in the LLN using DODAG Information Object (DIO) messages. When two arbitrary routers (neither of which is the DAG's root) need to communicate, the data packets are restricted to travel only along the links in the DAG. Such point-to-point (P2P) routing functionality may not be sufficient for several Home and Building Automation applications [RFC5826] [RFC5867] due to the following reasons: o The need to pre-establish routes: each potential destination in the network must declare itself as such ahead of the time a source needs to reach it. o The need to route only along the links in the DAG: A DAG is built to optimize the routing cost to reach the root. Restricting P2P routes to use only the in-DAG links may result in significantly suboptimal routes and severe traffic congestion near the DAG root. This document describes an extension to core RPL that enables an IPv6 router in the LLN to discover routes to one or more IPv6 routers in the LLN "on demand", such that the discovered routes meet the specified metrics constraints, without necessarily going along the links in an existing DAG. This reactive P2P route discovery mechanism is henceforth referred to as P2P-RPL. P2P-RPL does not guarantee discovery of a route. Also, the discovered routes may not be optimal. However, any discovered routes are guaranteed to satisfy the desired constraints in terms of the routing metrics and are thus considered "good enough" from the application's perspective. A mechanism to measure the end-to-end cost of an existing route is specified in [I-D.ietf-roll-p2p-measurement]. As discussed in Section 4, measuring the end-to-end cost of an existing route may help decide whether to initiate the discovery of a better route using P2P-RPL and the metric constraints to be used for this purpose. 2. The Use Cases One use case, common in home and commercial building environments, involves a device (say a remote control or an airduct controller) that suddenly needs to communicate with another device (say a lamp or a humidity sensor) to which it does not already have a route. In this case, the remote control (or the airduct controller) must be able to discover a route to the lamp (or the humidity sensor) "on Goyal, et al. Expires November 6, 2012 [Page 3] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 demand". Another use case, common in a commercial building environment, involves a large LLN deployment where P2P communication along a particular DAG among hundreds (or thousands) of routers creates severe traffic congestion near that DAG's root, and thus routes across this DAG are desirable. Other use cases involve scenarios where energy or latency constraints are not satisfied by the P2P routes along an existing DAG because they involve traversing many more intermediate routers than necessary to reach the destination. 3. 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 [RFC2119]. Additionally, this document uses terminology from [RFC6550]. This document introduces the following terms: Origin : The IPv6 router initiating the P2P-RPL route discovery. Target : The IPv6 router at the other end point of the P2P route(s) to be discovered. A P2P-RPL route discovery can discover routes to multiple Targets at the same time. Intermediate Router: An IPv6 router that is neither the Origin nor a Target. Forward direction: The direction from the Origin to the Target. Backward direction: The direction from the Target to the Origin. Forward Route: A route in the Forward direction. Backward Route: A route in the Backward direction. Bidirectional Route: A route that can be used in both Forward and Backward directions. Source Route: A complete and ordered list of routers that can be used by a packet to travel from a source to a destination node. Hop-by-hop Route: The route characterized by each router on the route Goyal, et al. Expires November 6, 2012 [Page 4] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 using its routing table to determine the next hop on the route. 4. Applicability A route discovery using P2P-RPL may be performed by an Origin when no route exists between itself and the Target(s) or when the existing routes do not satisfy the application requirements. P2P-RPL is designed to discover Hop-by-hop or Source Routes to one or more Targets such that the discovered routes meet the specified constraints. In some application contexts, the constraints that the discovered routes must satisfy are intrinsically known or can be specified by the application. For example, an Origin that expects its Targets to be less than 5 hops away may use "hop-count < 5" as the constraint. In other application contexts, the Origin may need to measure the cost of the existing route to a Target to determine the constraints. For example, an Origin that measures the total ETX along its current route to a Target to be 20 may use "ETX < x*20", where x is a fraction that the Origin decides, as the constraint. A mechanism to measure the cost of an existing route between two IPv6 routers is specified in [I-D.ietf-roll-p2p-measurement]. If there is no existing route between the Origin and the Target(s) or the cost measurement for the existing routes fails, the Origin will have to guess the constraints to be used in the initial route discovery. Once, the initial route discovery succeeds or fails, the Origin will have a better estimate for the constraints to be used in the subsequent route discovery. P2P-RPL may result in discovery of better P2P routes than the ones available along a global DAG designed to optimize routing cost to the DAG's root. The improvement in route quality depends on a number of factors including the network topology, the "distance" between the Origin and the Target (in terms of the routing metrics in use) and the prevalent conditions in the network. In general, a P2P-RPL route may be better than the one along a global DAG if the Origin and the Target are nearby. Similarly, a P2P-RPL route may not be much better than the one along a global DAG if the Origin and the Target are far apart. Note that, even when P2P-RPL routes are not much better than those along a global DAG, P2P-RPL routes may still be able to avoid congestion that might occur near the root if the routing takes place only along a global DAG. In general, the costs associated with a P2P-RPL route discovery (in terms of the control messages, mostly DIOs, generated) increases with the distance between the Origin and the Target. However, it is possible to limit the cost of route discovery by carefully setting the routing constraints, the Trickle parameters (that govern the DIO generation) and the lifetime of the temporary DAG created for the route discovery. A network designer may take into consideration both the benefits (potentially better Goyal, et al. Expires November 6, 2012 [Page 5] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 routes; no need to maintain routes proactively; avoid congestion near the global DAG's root) and costs when using P2P-RPL. The latency associated with a P2P-RPL route discovery again depends on the distance between the Origin and the Target and the Trickle parameters. Note that the participation in a P2P-RPL route discovery is limited to the routers with IPv6 addresses that are reachable in both Forward and Backward directions. 5. Functional Overview This section contains a high level description of P2P-RPL. A P2P-RPL route discovery takes place by forming a DAG rooted at the Origin. As is the case with core RPL, P2P-RPL uses IPv6 link-local multicast DIO messages to establish a DAG. However, unlike core RPL, this DAG is temporary in nature and routers in the DAG leave once the DAG's life time is over. The sole purpose of DAG creation is to discover routes to the Target(s) and DIOs serve as the route discovery messages. Each router joining the DAG determines a rank for itself in the DAG and ignores the subsequent DIOs received from lower (higher in numerical value) ranked neighbors. Thus, the route discovery messages propagate away from the Origin rather than return back to it. As in core RPL, DIO generation at a router is controlled by a Trickle timer [RFC6206] that allows a router to avoid generating unnecessary messages while providing protection against packet loss. P2P-RPL also uses the routing metrics [RFC6551], objective functions and packet forwarding framework [RFC6554][RFC6553] developed for core RPL. An Origin may use P2P-RPL to discover routes to one or more Targets identified by one or more unicast/multicast addresses. P2P-RPL allows for the discovery of one Hop-by-hop Route or up to four Source Routes per Target. P2P-RPL allows an Origin to piggyback time- critical application data on the DIO messages for delivery to the Target(s). P2P-RPL does not guarantee discovery of a route to a Target. Also, the discovered routes may not be the best available. However, any discovered routes are guaranteed to satisfy the desired constraints in terms of the routing metrics and are thus considered "good enough" from the application's perspective. A P2P-RPL route discovery takes place by forming a temporary DAG rooted at the Origin. The DIOs, used to create the temporary DAG, are identified by a new Mode of Operation (P2P Route Discovery mode defined in Section 6). The DIOs, listing the P2P Route Discovery mode as the Mode of Operation, are henceforth referred to as the P2P Goyal, et al. Expires November 6, 2012 [Page 6] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 mode DIOs. A P2P mode DIO always carries one P2P Route Discovery Option (defined in Section 7.1) in which the Origin specifies the following information: o The IPv6 address of a Target. This could be a unicast address or a multicast one. Any additional Targets may be specified by including one or more RPL Target Options [RFC6550] inside the DIO. o The nature of the route(s) to be discovered: hop-by-hop or Source Routes. This specification allows for the discovery of one Hop- by-hop Route or up to four Source Routes per Target. o The desired number of routes (if Source Routes are being discovered). o Whether the Target(s) should send Discovery Reply Object (DRO) messages (defined in Section 8) back to the Origin on receiving a DIO message. A DRO message carries a discovered Source Route back to the Origin or establishes a Hop-by-hop Route between the Origin and the Target. By not allowing the generation of DRO messages, an Origin can use P2P-RPL as purely a mechanism to deliver time- critical application data to the Target(s). A P2P Route Discovery Option also accumulates a route from the Origin to a Target as the routers join the temporary DAG. A P2P mode DIO MAY also carry: o One or more Metric Container Options to specify: * The relevant routing metrics. * The constraints that the discovered route must satisfy. These constraints also limit how far the DIOs message may travel. o One or more RPL Target options to specify additional unicast or multicast Targets. o One Data Option (defined in Section 7.2) to carry time-critical application-level data to be delivered to the Target(s). As the routers join the temporary DAG, they keep track of the best (partial) route(s) they have seen and advertise these routes, along with the corresponding routing metrics, in their P2P mode DIOs. A router, including the Target(s), discards a received P2P mode DIO if the aggregated routing metrics on the route advertised by the DIO do not satisfy the listed constraints. These constraints can be used to limit the propagation of P2P mode DIO messages. A router may also Goyal, et al. Expires November 6, 2012 [Page 7] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 discard a received P2P mode DIO if it does not wish to be a part of the discovered route due to limited resources or due to policy reasons. When a Target receives a P2P mode DIO, it forwards the data in the Data Option, if present, to the higher layer. The Target may remember the discovered route for use as a Source Route to reach the Origin. If the Origin has requested DRO messages to be sent back, the Target may select the route contained in the received DIO for further processing as described next. This document does not specify a particular method for the Target to use to select a route for further processing. Example methods include selecting any route that meets the constraints or selecting the best route(s) discovered over a certain time period. If one or more Source Routes are being discovered, the Target sends the selected Source Routes to the Origin via DRO messages with one DRO message carrying one discovered route. On receiving a DRO message, the Origin stores the discovered route in its memory. If a Hop-by-hop Route is being discovered, the Target sends a DRO message containing the selected route to the Origin. The DRO message travels back to the Origin along the selected route, establishing state for this route in the routers on the path. The Target may include a Data Option in a DRO message to deliver any time-critical application data to the Origin. The Target may request the Origin to acknowledge the receipt of a DRO message by sending back a DRO Acknowledgement (DRO-ACK) message (defined in Section 10). The Origin unicasts a DRO-ACK message to the Target. If the Target does not receive the requested DRO-ACK within a certain time interval of sending a DRO, it resends the DRO message (up to a certain number of times) carrying the same route as before. The use of trickle timers to delay the propagation of DIO messages may cause some nodes to generate these messages even when the desired routes have already been discovered. In order to preempt the generation of such unnecessary messages, the Target may set a "stop" flag in the DRO message to let the nodes in the LLN know about the completion of the route discovery process. The routers receiving such a DRO should not generate any more DIOs for this temporary DAG. Neither should they process any received DIOs for this temporary DAG in future. However, such routers must still process the DROs received for this temporary DAG. Goyal, et al. Expires November 6, 2012 [Page 8] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 6. P2P Route Discovery Mode Of Operation This section specifies a new RPL Mode of Operation (MOP), P2P Route Discovery mode (or P2P mode, for short), with value 4 (to be confirmed by IANA). A DIO message, listing P2P mode as the MOP, is identified as performing a P2P-RPL route discovery by creating a temporary DAG. A P2P mode DIO MUST carry one and only one P2P Route Discovery Option (specified in Section 7.1). 6.1. Setting a P2P Mode DIO The Base Object in a P2P mode DIO message MUST be set in the following manner: o RPLInstanceID: RPLInstanceID MUST be a local value as described in Section 5.1 of [RFC6550]. The Origin MUST NOT use the same RPLInstanceID in two or more concurrent route discoveries. When initiating a new route discovery to a particular Target, the Origin MUST NOT reuse the RPLInstanceID used in a previous route discovery to this Target if the previously discovered routes might still exist. The Default Lifetime and Lifetime Unit parameters in the DODAG Configuration Option specify the lifetime of the state the routers, including the Origin and the Target, maintain for a hop-by-hop or a Source Route discovered using P2P-RPL. Thus, an Origin can safely reuse an RPLInstanceID to discover a new route to a Target if the lifetime of all previously discovered routes to this Target using this RPLInstanceID is over. o Version Number: MUST be set to zero. The temporary DAG used for P2P-RPL route discovery does not exist long enough to have new versions. o Grounded (G) Flag: This flag MUST be set to one. Unlike a global RPL instance, the concept of a floating DAG, used to provide connectivity within a sub-DAG detached from a grounded DAG, does not apply to a local RPL instance. Hence, an Origin MUST always set the G flag to one when initiating a P2P-RPL route discovery. Further, clause 3 of Section 8.2.2.2 in [RFC6550] does not apply and a node MUST NOT initiate a new DAG if it does not have any parent left in a P2P-RPL DAG. o Mode of Operation (MOP): MUST be set to 4, corresponding to P2P Route Discovery mode. o DTSN: MUST be set to zero on transmission and ignored on reception. Goyal, et al. Expires November 6, 2012 [Page 9] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 o DODAGPreference (Prf): This field MUST be set to zero (least preferred). o DODAGID: This field MUST be set to an IPv6 address of the Origin. o The other fields in the DIO Base Object can be set in the desired fashion as per the rules described in [RFC6550]. The DODAG Configuration Option, inside a P2P mode DIO MUST be set in the following manner: o The Origin MUST set the MaxRankIncrease parameter to zero to disable local repair of the temporary DAG. o The Origin SHOULD set the Trickle parameters (DIOIntervalDoublings, DIOIntervalMin, DIORedundancyConstant) as recommended in Section 9.2. o The Origin sets the Default Lifetime and Lifetime Unit parameters to indicate the lifetime of the state the routers, including the Origin and the Target(s), maintain for a hop-by-hop or a Source Route discovered using P2P-RPL. o The Origin sets the other fields in the DODAG Configuration Option, including the OCP identifying the Objective function, in the desired fashion as per the rules described in [RFC6550]. o An Intermediate Router (or a Target) MUST set various fields in the DODAG Configuration Option in the outgoing P2P mode DIOs to the values they had in the incoming P2P mode DIOs for this DAG. A default DODAG Configuration Option comes in effect if a P2P mode DIO does not carry an explicit one. The default DODAG Configuration Option has the following parameter values: o Authentication Enabled: 0 o DIOIntervalMin: 6, which translates to 64ms as the value for Imin parameter in Trickle operation. o DIORedundancyConstant: 1 o MaxRankIncrease: 0 o Default Lifetime: 0xFF o Lifetime Unit: 0xFFFF Goyal, et al. Expires November 6, 2012 [Page 10] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 o Objective Code Point: 0, i.e., OF0 [RFC6552] is the default objective function. o The remaining parameters have default values as specified in [RFC6550]. The routing metrics and constraints [RFC6551] used in P2P-RPL route discovery are included in one or more Metric Container Options [RFC6550] inside the P2P mode DIO. Note that a DIO need not include a Metric Container if OF0 is the objective function in effect. In that case, a P2P mode DIO may still specify an upper limit on the maximum rank, that a router may have in the temporary DAG, inside the P2P Route Discovery Option (described in Section 7.1). A P2P mode DIO: o MUST carry one (and only one) P2P Route Discovery Option (described in Section 7.1). The P2P Route Discovery Option allows for the specification of one unicast or multicast address for the Target. o MAY carry one or more RPL Target Options to specify additional unicast/multicast addresses for the Target. o MAY carry one or more Metric Container Options to specify routing metrics and constraints. o MAY carry one Data Option (described in Section 7.2) containing time-critical application data to be delivered to the Target(s). o MAY carry one or more Route Information or Prefix Information Options (described in [RFC6550]). A router MUST discard a received P2P mode DIO if it violates any of the rules listed above. 7. New RPL Control Message Options This document defines two new RPL control message options: the P2P Route Discovery Option and the Data Option. Goyal, et al. Expires November 6, 2012 [Page 11] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 7.1. P2P Route Discovery Option (P2P-RDO) - 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 = 10 | Option Length |R|H| N | Compr | L |MaxRank/NH | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Target | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Address[1..n] | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Format of P2P Route Discovery Option (P2P-RDO) The format of a P2P Route Discovery Option (P2P-RDO) is illustrated in Figure 1. A P2P mode DIO and a DRO (defined in Section 8) message MUST carry one and at most one P2P-RDO. A P2P-RDO consists of the following fields: o Option Type: 0x0A (to be confirmed by IANA). o Option Length: 8-bit unsigned integer, representing the length in octets of the option, not including the Option Type and Option Length fields. o Reply (R): The Origin sets this flag to one to allow the Target(s) to send DRO messages back to the Origin. If this flag is zero, a Target MUST NOT generate any DRO message. o Hop-by-hop (H): This flag is valid only if the R flag is set to one. The Origin sets this flag to one if it desires Hop-by-hop Routes. The Origin sets this flag to zero if it desires Source Routes. This specification allows for the establishment of one hop-by-hop route or up to four Source Routes per Target. The Hop- by-hop Route is established in the Forward direction, i.e. from the Origin to the Target. This specification does not allow for the establishment of Hop-by-hop Routes in the Backward direction. o Number of Routes (N): This flag is valid only if the R flag is one and H flag is zero, i.e. the Targets are allowed to generate DRO Goyal, et al. Expires November 6, 2012 [Page 12] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 messages carrying discovered Source Routes back to the Origin. In this case, the value in the N field plus one indicates the number of Source Routes that each Target should convey to the Origin. When Hop-by-hop Routes are being discovered, the N field MUST be set to zero on transmission and ignored on reception. o Compr: 4-bit unsigned integer indicating the number of prefix octets that are elided from the Target field and the Address vector. For example, Compr value will be zero if full IPv6 addresses are carried in the Target field and the Address vector. o Life Time (L): A 2-bit field that indicates the minimum life time of the temporary DAG, i.e., the minimum duration a router joining the temporary DAG MUST maintain its membership in the DAG. The mapping between the values in this field and the life time of the temporary DAG is as follows: * 0x00: 1 second; * 0x01: 4 seconds; * 0x02: 16 seconds; * 0x03: 64 seconds; The Origin sets this field based on its expectation regarding the time required for the route discovery to complete, which includes the time required for the DIOs to reach the Target(s) and the DROs to travel back to the Origin. While deciding the temporary DAG's lifetime, the Origin should also take in account the fact that all nodes joining the temporary DAG would need to stay in the DAG for at least this much time. o MaxRank/NH: * When a P2P-RDO is included in a P2P mode DIO, this field indicates the upper limit on the integer portion of the rank (calculated using the DAGRank() macro defined in [RFC6550]) that a router may have in the temporary DAG being created. An Intermediate Router MUST NOT join a temporary DAG being created by a P2P mode DIO if the integer portion of its rank would be equal to or higher (in numerical value) than the MaxRank limit. A Target can join the temporary DAG at a rank whose integer portion is equal to the MaxRank. A router MUST discard a received P2P mode DIO if the integer part of the advertized rank equals or exceeds the MaxRank limit. A value 0 in this field indicates that the MaxRank is infinity. Goyal, et al. Expires November 6, 2012 [Page 13] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 * When a P2P-RDO is included in a DRO message, this field indicates the index of the next hop address inside the Address vector. o Target: An IPv6 address of the Target after eliding Compr number of prefix octets. When the P2P-RDO is included in a P2P mode DIO, this field may contain a unicast address or a multicast one. Any additional Target addresses can be specified by including one or more RPL Target Options [RFC6550] in the DIO. When the P2P-RDO is included in a DRO, this field MUST contain a unicast IPv6 address of the Target generating the DRO. o Address[1..n]: A vector of IPv6 addresses representing a (partial) route in the Forward direction: * Each element in the Address vector has size (16 - Compr) octets and MUST contain a valid IPv6 address with first Compr octets elided. * The total number of elements inside the Address vector is given by n = (Option Length - 2 - (16 - Compr))/(16 - Compr). * The IPv6 addresses in the Address vector MUST be reachable in both Forward and Backward directions. Reachability in the Backward direction allows a DRO message to use the route accumulated in the Address vector to travel from the Target to the Origin. * The Address vector MUST carry the accumulated route in the Forward direction, i.e., the first element in the Address vector must contain the IPv6 address of the router next to the Origin and so on. * The Origin and Target addresses MUST NOT be included in the Address vector. * A router adding its address to the vector MUST ensure that its address does not already exist in the vector. A router specifying a complete route in the Address vector MUST ensure that the vector does not contain any address more than once. * The Address vector MUST NOT contain any multicast addresses. Goyal, et al. Expires November 6, 2012 [Page 14] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 7.2. Data Option 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 = 11 | Option Length | SeqNo | Upper | Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+... Figure 2: Format of Data Option The format of a Data Option is illustrated in Figure 2. A P2P mode DIO and a DRO (defined in Section 8) message MAY carry one or more Data Options. A P2P-RDO consists of the following fields: o Option Type: 0x0B (to be confirmed by IANA). o Option Length: An 8-bit unsigned integer, representing the length in octets of the option, not including the Option Type and Option Length fields. o SeqNo: A 4-bit field representing the sequence number of the data carried by the Data Option. o Upper: A 4-bit field that identifies the upper layer protocol header with which the information in the Data field starts. A value 0x00 in this field identifies UDP as the upper layer protocol. The other values are reserved at present. o Data: If the Data Option is contained in a DIO, this field contains application data to be delivered to the Target(s). If the Data Option is contained in a DRO, this field contains application data to be delivered to the Origin. 8. The Discovery Reply Object (DRO) This section defines two new RPL Control Message types, the Discovery Reply Object (DRO), with code 0x04 (to be confirmed by IANA), and the Secure DRO, with code 0x84 (to be confirmed by IANA). A DRO serves one of the following functions: o Carry a discovered Source Route from a Target to the Origin; o Establish a Hop-by-hop Route as it travels from a Target to the Origin. A DRO message MAY serve the function of letting the routers in the Goyal, et al. Expires November 6, 2012 [Page 15] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 LLN know that a P2P-RPL route discovery is complete and no more DIO messages need to be generated for the corresponding temporary DAG. A DRO message MAY also carry time-critical application data from the Target to the Origin in a Data Option. A DRO message MUST carry one P2P-RDO whose Target field MUST contain a unicast IPv6 address of the Target that generated the DRO. A DRO message travels from the Target to the Origin via link-local multicast along the route specified inside the Address vector in the P2P-RDO. 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 |S|A|Seq| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | DODAGID | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option(s)... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+... Figure 3: Format of the base Discovery Reply Object (DRO) The format of the base Discovery Reply Object (DRO) is shown in Figure 3. A base DRO consists of the following fields: o RPLInstanceID: The RPLInstanceID of the temporary DAG used for route discovery. o Version: The Version of the temporary DAG used for route discovery. Since a temporary DAG always has value zero for the Version, this field MUST always be set to zero. o Stop (S): This flag, when set to one by a Target, indicates that the P2P-RPL route discovery is over. All the routers receiving such a DRO, including the ones not listed in the route carried inside P2P-RDO, * SHOULD NOT process any more DIOs received for this temporary DAG; * SHOULD NOT generate any more DIOs for this temporary DAG; * SHOULD cancel any pending DIO transmission for this temporary DAG. Goyal, et al. Expires November 6, 2012 [Page 16] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 Note that the stop flag serves to stop further DIO generation/ processing for a P2P-RPL route discovery but it does not affect the processing of DRO messages at either the Origin or the Intermediate Routers. In other words, a router (the Origin or an Intermediate Router) MUST continue to process the DRO messages even if an earlier DRO message (with the same RPLInstanceID and DODAGID fields) had the stop flag set to one. o Ack Required (A): This flag, when set to one by the Target, indicates that the Origin MUST unicast a DRO-ACK message (defined in Section 10) to the Target when it receives the DRO. o Sequence Number (Seq): This 2-bit field indicates the sequence number for the DRO. This field is relevant when the A flag is set to one, i.e., the Target requests an acknowledgement from the Origin for a received DRO. The Origin includes the RPLInstanceID, the DODAGID and the Sequence Number of the received DRO inside the DRO-ACK message it sends back to the Target. o Reserved: These bits are reserved for future use. These bits MUST be set to zero on transmission and MUST be ignored on reception. o DODAGID: The DODAGID of the temporary DAG used for route discovery. The DODAGID also identifies the Origin. The RPLInstanceID, the Version and the DODAGID together uniquely identify the temporary DAG used for route discovery and can be copied from the DIO message advertizing the temporary DAG. o Options: The DRO message: * MUST carry one P2P-RDO that MUST specify a complete route between the Target and the Origin; * MAY carry one or more Metric Container Options that contains the aggregated routing metrics values for the route specified in P2P-RDO; * MAY carry one Data Option to carry any time-critical application data to the Origin. 8.1. Secure DRO A Secure DRO message follows the format in Figure 7 of [RFC6550], where the base format is the base DRO shown in Figure 3. Goyal, et al. Expires November 6, 2012 [Page 17] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 8.2. Setting a P2P-RDO Carried in a Discovery Reply Object A Discovery Reply Object MUST carry one P2P-RDO, which MUST be set as defined in Section 7.1. Specifically, the following fields MUST be set as specified next: o Reply (R): This flag MUST be set to zero on transmission and ignored on reception. o Hop-by-Hop (H): The H flag in the P2P-RDO included in a DRO message MUST have the same value as the H flag in the P2P-RDO inside the corresponding DIO message. o Number of Routes (N): This field MUST be set to zero on transmission and ignored on reception. o Life Time (L): This field MUST be set to zero on transmission and ignored on reception. o MaxRank/NH: This field indicates the index of the next hop address in the Address vector. When a Target generates a DRO message, the NH field is set to n = (Option Length - 2 - (16 - Compr))/(16 - Compr). o Target: This field MUST contain a unicast IPv6 address of the Target generating the DRO. o Address[1..n]: The Address vector MUST contain a complete route between the Origin and the Target such that the first element in the vector contains the IPv6 address of the router next to the Origin and the last element contains the IPv6 address of the router next to the Target. 9. P2P-RPL Route Discovery By Creating a Temporary DAG This section details the P2P-RPL route discovery operation. 9.1. Joining a Temporary DAG All the routers participating in a P2P-RPL route discovery, including the Origin and the Target(s), MUST join the temporary DAG being created for the purpose. When a router joins a temporary DAG advertized by a P2P mode DIO, it SHOULD maintain its membership in the temporary DAG for the suggested Life Time duration listed in the P2P-RDO. The only purpose of a temporary DAG's existence is to facilitate the P2P-RPL route discovery process. The temporary DAG MUST NOT be used to route packets. A router SHOULD detach from the Goyal, et al. Expires November 6, 2012 [Page 18] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 temporary DAG once the duration of its membership in the DAG has exceeded the DAG's life time. After receiving a DRO with the stop flag set to one, a router SHOULD NOT send or receive any more DIOs for this temporary DAG and SHOULD also cancel any pending DIO transmission. 9.2. Trickle Operation For P2P Mode DIOs An RPL router uses a Trickle timer [RFC6206] to control DIO transmissions. The Trickle control of DIO transmissions provides quick resolution of any "inconsistency" while avoiding redundant DIO transmissions. The Trickle algorithm also imparts protection against loss of DIOs due to inherent lack of reliability in LLNs. When controlling the transmissions of a P2P mode DIO, a Trickle timer SHOULD follow the following rules: o The receipt of a P2P mode DIO, that allows the router to advertise a better route (in terms of the routing metrics and the OF in use) than before, is considered "inconsistent" and hence resets the Trickle timer. Note that the first receipt of a P2P mode DIO advertising a particular temporary DAG is always considered an "inconsistent" event. o The receipt of a P2P mode DIO from a parent in the temporary DAG is considered neither "consistent" nor "inconsistent" if it does not allow the router to advertise a better route than before. Thus, the receipt of such DIOs has no impact on the Trickle operation. Note that this document does not impose any requirements on how a router might choose its parents in the temporary DAG. o The receipt of a P2P mode DIO is considered "consistent" if the source of the DIO is not a parent in the temporary DAG and either of the following conditions is true: * The DIO advertises a better route than the router but does not allow the router to advertise a better route itself; or * The DIO advertises a route as good as the route (to be) advertised by the router. Note that Trickle algorithm's DIO suppression rules are in effect at all times. Hence, a P2P-RPL router may suppress a DIO transmission even if it has not made any DIO transmission yet. o The receipt of a P2P mode DIO, that advertises a worse route than what the router advertises (or would advertise when it gets a chance to generate its DIO), is considered neither "consistent" Goyal, et al. Expires November 6, 2012 [Page 19] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 nor "inconsistent", i.e., the receipt of such a DIO has no impact on the Trickle operation. o The Imin parameter SHOULD be set taking in account the connectivity within the network. For highly connected networks, a small Imin value (of the order of the typical transmission delay for a DIO) may lead to congestion in the network as a large number of routers reset their Trickle timers in response to the first receipt of a DIO from the Origin. These routers would generate their DIOs within Imin interval and cause additional routers to reset their trickle timers and generate more DIOs. Thus, for highly connected networks, the Imin parameter SHOULD be set to a value at least one order of magnitude larger than the typical transmission delay for a DIO. For sparsely connected networks, the Imin parameter can be set to a value that is a small multiple of the typical transmission delay for a DIO. Note that the Imin value has a direct impact on the time required for a P2P-RPL route discovery to complete. In general, the time required for a P2P- RPL route discovery would increase approximately linearly with the value of the Imin parameter. o The Imax parameter SHOULD be set to a large value (several orders of magnitude higher than the Imin value) and is unlikely to be critical for P2P-RPL operation. This is because the first receipt of a P2P mode DIO for a particular temporary DAG is considered an inconsistent event and would lead to resetting of Trickle timer duration to the Imin value. Given the temporary nature of the DAGs used in P2P-RPL, Trickle timer may not get a chance to increase much. o The recommended value of redundancy constant "k" is 1. With this value of "k", a DIO transmission will be suppressed if the router receives even a single "consistent" DIO during a timer interval. This setting for the redundancy constant is designed to reduce the number of messages generated during a route discovery process and is suitable for environments with low or moderate packet loss rates. In environments with high packet loss rates, a higher value for the redundancy constant may be more suitable. 9.3. Processing a P2P Mode DIO The rules for DIO processing and transmission, described in Section 8 of RPL [RFC6550], apply to P2P mode DIOs as well except as modified in this document. The following rules for processing a received P2P mode DIO apply to both Intermediate Routers and the Target. Goyal, et al. Expires November 6, 2012 [Page 20] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 A router SHOULD discard a received P2P mode DIO with no further processing if it does not have bidirectional reachability with the neighbor that generated the received DIO. Note that bidirectional reachability does not mean that the link must have the same values for a routing metric in both directions. A router SHOULD calculate the values of the link-level routing metrics included in the received DIO taking in account the metric's value in both forward and Backward directions. Bidirectional reachability along a discovered route allows the Target to use this route to reach the Origin. In particular, the DRO messages travel from the Target to the Origin along a discovered route. A router MUST discard a received P2P mode DIO with no further processing: o If the DIO advertises INFINITE_RANK as defined in [RFC6550]. o If the integer part of the rank advertised in the DIO equals or exceeds the MaxRank limit listed in the P2P Route Discovery Option. o If the router cannot evaluate the mandatory route constraints listed in the DIO or if the routing metric values do not satisfy one or more of the mandatory constraints. o If the router previously received a DRO message with the same RPLInstanceID and DODAGID as the received DIO and with the stop flag set to one. The router MUST check the Target addresses listed in the P2P-RDO and any RPL Target Options included in the received DIO. If one of its IPv6 addresses is listed as a Target address or if it belongs to the multicast group specified as one of the Target addresses, the router considers itself a Target and processes the received DIO as specified in Section 9.5. Otherwise, the router considers itself an Intermediate Router and processes the received DIO as specified in Section 9.4. 9.4. Additional Processing of a P2P Mode DIO At An Intermediate Router An Intermediate Router MUST discard a received P2P mode DIO with no further processing if the router cannot elide Compr (as specified in the P2P-RDO) prefix octets from its IPv6 address. On receiving a P2P mode DIO, an Intermediate Router MUST do the following: Goyal, et al. Expires November 6, 2012 [Page 21] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 o The router updates the Data Option to be carried in the router's DIOs if the one in the received DIO has a higher sequence number than what the router currently has (or if the router currently is not aware of any Data Option). o The router determines whether this DIO advertises a better route than the router itself and whether the receipt of the DIO would allow the router to advertise a better route than before. Accordingly, the router SHOULD consider this DIO as consistent/ inconsistent from Trickle perspective as described in Section 9.2. Note that the route comparison in a P2P-RPL route discovery is performed using the parent selection rules of the OF in use as specified in Section 14 of RPL [RFC6550]. If the received DIO would allow the router to advertise a better route, the router MUST remember the route advertised (inside the P2P-RDO) in the DIO (after adding its own IPv6 address to the route) for inclusion in its future DIOs. When an Intermediate Router adds itself to a route, it MUST ensure that the IPv6 address added to the route is reachable in both Forward and Backward directions. To improve the diversity of the routes being discovered, an Intermediate Router SHOULD keep track of multiple partial routes to be advertised in the P2P-RDO inside its DIO. When the router generates its DIO, it SHOULD randomly select the partial route to be included in the P2P-RDO. Note that the route accumulation in a P2P mode DIO MUST take place even if the Origin does not want any DRO messages to be generated (i.e., the R flag inside the P2P-RDO is set to zero). This is because the Target may still be able to use the accumulated route as a source route to reach the Origin. 9.5. Additional Processing of a P2P Mode DIO At The Target The Target MUST determine if the received DIO contains a Data Option and deliver the data to the specified upper layer protocol if the option's sequence number is higher than that of the options in the previously received DIOs for this route discovery (or if the DIOs received earlier did not have a Data Option). If this route discovery involves multiple Targets, the Target MUST remember the Data Option with highest sequence number for inclusion in its own DIOs. The Target MAY store the route contained in the P2P-RDO in the received DIO for use as a Source Route to reach the Origin. The lifetime of this Source Route is specified by the Default Lifetime and Lifetime Unit parameters inside the DODAG Configuration Option currently in effect. This lifetime can be extended (or shortened) appropriately following a hint from an upper-layer protocol. If the Reply flag inside the P2P-RDO in the received DIO is zero, the Goyal, et al. Expires November 6, 2012 [Page 22] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 Target MUST discard the received DIO with no further processing. Otherwise, the Target MAY select the route contained in the P2P-RDO to send a DRO message back to the Origin. If the H flag inside the P2P-RDO is one, the Target needs to select one route and send a DRO message along this route back to the Origin. If the H flag is zero, the number of routes to be selected (and the number of DRO messages to be sent back) is given by one plus the value of the N field in the P2P-RDO. This document does not prescribe a particular method for the Target to select the routes. Example methods include selecting each route that meets the specified routing constraints until the desired number have been selected or selecting the best routes discovered over a certain time period. If multiple routes are to be selected, the Target SHOULD avoid selecting routes that have large segments in common. If the Target selects the route contained in the P2P-RDO in the received DIO, it sends a DRO message back to the Origin (identified by the DODAGID field in the DIO). The DRO message MUST include a P2P-RDO that contains the selected route inside the Address vector. Various fields inside the P2P-RDO MUST be set as specified in Section 8.2. The Target MAY set the A flag inside the DRO message to one if it desires the Origin to send back a DRO-ACK message on receiving the DRO. In this case, the Target waits for DRO_ACK_WAIT_TIME duration for the DRO-ACK message to arrive. Failure to receive the DRO-ACK message within this time duration causes the Target to retransmit the DRO message. The Target MAY retransmit the DRO message in this fashion up to MAX_DRO_RETRANSMISSIONS times. Both DRO_ACK_WAIT_TIME and MAX_DRO_RETRANSMISSIONS are configurable parameters to be decided based on the characteristics of individual deployments. Note that all DRO transmissions and retransmissions MUST take place while the Target is still a part of the temporary DAG created for the route discovery. A Target MUST NOT transmit a DRO if it no longer belongs to this DAG. The Target MAY set the stop flag inside the DRO message to one if o this router is the only Target specified in the corresponding DIO, i.e., the corresponding DIO specified a unicast address of the router as the Target inside the P2P-RDO with no additional Targets specified via RPL Target Options; and o the Target has already selected the desired number of routes. The Target MAY include a Metric Container Option in the DRO message. This Metric Container contains the end-to-end routing metric values for the route specified in the P2P-RDO. The Target MAY include one Data Option in the DRO message to carry time-critical application Goyal, et al. Expires November 6, 2012 [Page 23] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 data for the Origin. Note that this Data Option is not same as the Data Option that the Target may include in the DIOs it generates for this route discovery (if the route discovery involves multiple Targets). The Target MUST transmit the DRO message via a link-local multicast. A Target MUST NOT forward a P2P mode DIO any further if no other Targets are to be discovered, i.e., if a unicast IPv6 address (of this Target) is specified as the Target inside the P2P-RDO and no additional Targets are specified via RPL Target Options inside the DIOs for this route discovery. Otherwise, the Target MUST generate DIOs for this route discovery as an Intermediate Router would. 9.6. Processing a DRO At An Intermediate Router If the DODAGID field in the received DRO does not list a router's own IPv6 address, the router considers itself an Intermediate Router and MUST process the received message in the following manner: o The router MUST discard the received DRO with no further processing if it does not belong to the temporary DAG identified by the RPLInstanceID and the DODAGID fields in the DRO. o If the stop flag inside the received DRO is set to one, the router SHOULD NOT send or receive any more DIOs for this temporary DAG and SHOULD cancel any pending DIO transmission. o The router MUST ignore any Metric Container and Data Options contained in the DRO message. o If Address[NH] element inside the P2P-RDO lists the router's own unicast IPv6 address, the router is a part of the route carried in the P2P-RDO. In this case, the router MUST do the following: * To prevent loops, the router MUST discard the DRO message with no further processing if the Address vector in the P2P-RDO includes multiple IPv6 addresses assigned to the router's interfaces and if such addresses do not appear back to back inside the Address vector. * If the H flag inside the P2P-RDO is one, the router MUST store the state for the forward hop-by-hop route carried inside the P2P-RDO. This state consists of: + The RPLInstanceID and the DODAGID fields of the DRO. + The route's destination, the Target (identified by Target field inside P2P-RDO). Goyal, et al. Expires November 6, 2012 [Page 24] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 + The IPv6 address of the next hop, Address[NH+1] (unless NH value equals the number of elements in the Address vector, in which case the Target itself is the next hop). This hop-by-hop routing state MUST expire at the end of the lifetime specified by the Default Lifetime and Lifetime Unit parameters inside the DODAG Configuration Option used in P2P mode DIOs for this route discovery. * If the router already maintains a hop-by-hop state listing the Target as the destination and carrying same RPLInstanceID and DODAGID fields as the received DRO and the next hop information in the state does not match the next hop indicated in the received DRO, the router MUST discard the DRO message with no further processing. * The router MUST decrement the NH field inside the P2P-RDO and send the DRO further via link-local multicast. 9.7. Processing a DRO At The Origin When a router receives a DRO message that lists its IPv6 address in the DODAGID field, the router recognizes itself as the Origin for the corresponding P2P-RPL route discovery and processes the message in the following manner: o The Origin MUST discard the received DRO with no further processing if it no longer belongs to the temporary DAG identified by the RPLInstanceID and the DODAGID fields in the DRO. o The Origin MUST check if the received DRO contains a Data Option with higher sequence number than what was received previously (or if this Data Option is the first one received). In that case, the Origin MUST deliver the data inside the Data Option to the upper layer protocol identified inside the Data Option. o If the stop flag inside the received DRO is set to one, the Origin SHOULD NOT generate any more DIOs for this temporary DAG and SHOULD cancel any pending DIO transmission. o If the P2P-RDO inside the DRO identifies the discovered route as a Source Route (H=0), the Origin MUST store in its memory the discovered route contained in the Address vector. The lifetime of this Source Route is specified by the Default Lifetime and Lifetime Unit parameters inside the DODAG Configuration Option in the P2P mode DIOs used for this route discovery. This lifetime could be extended (or shortened) appropriately following a hint from an upper-layer protocol. Goyal, et al. Expires November 6, 2012 [Page 25] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 o If the P2P-RDO inside the DRO identifies the discovered route as a Hop-by-hop Route (H=1), the Origin MUST store in its memory the state for the discovered route in the manner described in Section 9.6. This hop-by-hop routing state MUST expire at the end of the lifetime specified by the Default Lifetime and Lifetime Unit parameters inside the DODAG Configuration Option used in P2P mode DIOs for this route discovery. A future version of this document may consider specifying a signaling mechanism that will allow the Origin to extend (or shorten) the lifetime of a P2P-RPL Hop-by-hop Route following a suitable hint from an upper-layer protocol. o If the received DRO message contains one or more Metric Container Options, the Origin MAY store the values of the routing metrics associated with the discovered route in its memory. This information may be useful in formulating the constraints for any future P2P-RPL route discovery to the Target. o If the A flag is set to one in the received DRO message, the Origin MUST generate a DRO-ACK message as described in Section 10 and unicast the message to the Target (identified by the Target field inside the P2P-RDO). The Origin MAY use the route just discovered to send the DRO-ACK message to the Target. Section 11 describes how a packet may be forwarded along a source/Hop-by-hop Route discovered using P2P-RPL. 10. The Discovery Reply Object Acknowledgement (DRO-ACK) 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 |Seq| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | DODAGID | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Format of the base Discovery Reply Object Acknowledgement (DRO-ACK) A DRO message may fail to reach the Origin due to a number of reasons. Unlike the DIO messages that benefit from Trickle- controlled retransmissions, the DRO messages are prone to loss due to unreliable packet transmission in LLNs. Since a DRO message travels Goyal, et al. Expires November 6, 2012 [Page 26] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 via link-local multicast, it cannot use link-level acknowledgements to improve the reliability of its transmission. Also, an Intermediate Router may drop the DRO message (e.g., because of its inability to store the state for the Hop-by-hop Route the DRO is establishing). To protect against the potential failure of a DRO message to reach the Origin, the Target MAY request the Origin to send back a DRO Acknowledgement (DRO-ACK) message on receiving a DRO message. Failure to receive such an acknowledgement within the DRO_ACK_WAIT_TIME interval of sending the DRO message forces the Target to resend the message. This section defines two new RPL Control Message types: DRO Acknowledgement (DRO-ACK; with code 0x05; to be confirmed by IANA) and Secure DRO-ACK (with code 0x85; to be confirmed by IANA). A DRO- ACK message MUST travel as a unicast message from the Origin to the Target. The format of a base DRO-ACK message is shown in Figure 4. Various fields in a DRO-ACK message MUST have the same values as the corresponding fields in the DRO message. The field marked as "Reserved" MUST be set to zero on transmission and MUST be ignored on reception. A Secure DRO-ACK message follows the format in Figure 7 of [RFC6550], where the base format is same as the base DRO-ACK shown in Figure 4. 11. Packet Forwarding Along a Route Discovered Using P2P-RPL An Origin MAY use a Source Routing Header (SRH) [RFC6554] to send a packet along a Source Route discovered using P2P-RPL. Travel along a Hop-by-hop Route, established using P2P-RPL, requires specifying the RPLInstanceID and the DODAGID (of the temporary DAG used for the route discovery) to identify the route. This is because a P2P-RPL route discovery does not use globally unique RPLInstanceID values and hence both the RPLInstanceID (a local value assigned by the Origin) and the DODAGID (an IPv6 address of the Origin) are required to uniquely identify a P2P-RPL Hop-by-hop Route to a particular destination. An Origin MAY include an RPL option [RFC6553] inside the IPv6 hop-by- hop options header of a packet to send it along a Hop-by-hop Route established using P2P-RPL. For this purpose, the Origin MUST set the DODAGID of the temporary DAG used for the route discovery as the source IPv6 address of the packet. Further, the Origin MUST specify inside the RPL option the RPLInstanceID of the temporary DAG used for the route discovery and set the O flag inside the RPL option to one. On receiving this packet, an Intermediate Router checks the O flag and correctly infer the source IPv6 address of the packet as the DODAGID of the Hop-by-hop Route. The router then uses the DODAGID, Goyal, et al. Expires November 6, 2012 [Page 27] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 the RPLInstanceID and the destination address to identify the routing state to be used to forward the packet further. 12. Interoperability with Core RPL This section describes how RPL routers that implement P2P-RPL interact with RPL routers that do not. In general, P2P-RPL operation does not affect core RPL operation and vice versa. However, core RPL does allow a router to join a DAG as a leaf node even if it does not understand the Mode of Operation (MOP) used in the DAG. Thus, an RPL router that does not implement P2P-RPL may conceivably join a temporary DAG being created for a P2P-RPL route discovery as a leaf node and maintain its membership even though the DAG no longer exists. This may impose a drain on the router's memory. However, such RPL-only leaf nodes do not interfere with P2P-RPL route discovery since a leaf node may only generate a DIO advertising an INFINITE_RANK and all routers implementing P2P-RPL are required to discard such DIOs. Note that core RPL does not require a router to join a DAG whose MOP it does not understand. Moreover, RPL routers in a particular deployment may have strict restrictions on the DAGs they may join, thereby mitigating the problem. The P2P-RPL mechanism described in this document works best when all the RPL routers in the LLN implement P2P-RPL. In general, the ability to discover routes as well as the quality of discovered routes would deteriorate with the fraction of RPL routers that implement P2P-RPL. 13. Security Considerations A P2P-RPL deployment may be susceptible to denial of service attacks by rogue routers that initiate fake route discoveries. A rogue router could join a temporary DAG and advertise false information in its DIOs in order to include itself in the discovered route(s). It could generate bogus DRO messages carrying bad routes or maliciously modify genuine DRO messages it receives. In general, the security considerations for the operation of P2P-RPL are similar to the ones for the operation of RPL (as described in Section 19 of [RFC6550]). Section 10 of RPL specification [RFC6550] describes a variety of security mechanisms that provide data confidentiality, authentication, replay protection and delay protection services. Each RPL control message has a secure version that allows the specification of the level of security and the algorithms used to secure the message. The mechanism defined in this document is based on the use of DIOs to form a temporary DAG and Goyal, et al. Expires November 6, 2012 [Page 28] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 discover P2P routes. These DIOs can be used in their secure versions if desired. New RPL control messages defined in this document (DRO and DRO-ACK) have secure versions as well. In addition, a P2P-RPL deployment may use the security features provided by the link layer in use. Thus, a particular P2P-RPL deployment can analyze its security requirements and use the appropriate set of RPL (or link layer) security mechanisms that meet those requirements. Since a DRO message travels along a Source Route specified inside the message, some of the security concerns that led to the deprecation of Type 0 routing header [RFC5095] may apply. To avoid the possibility of a DRO message traveling in a routing loop, this document requires each Intermediate Router to confirm that the Source Route listed inside the message does not contain any routing loop involving itself before the router could forward the message further. As specified in Section 9.6, this check involves the router making sure that its IPv6 addresses do not appear multiple times inside the Source Route with one or more other IPv6 addresses in between. 14. IANA Considerations 14.1. Additions to DIO Mode of Operation IANA is requested to allocate a new value in the "DIO Mode of Operation" registry for the "P2P Route Discovery Mode" described in this document. +----------+-----------------------------------------+--------------+ | MOP | Description | Reference | | Value | | | +----------+-----------------------------------------+--------------+ | 4 | Reactive P2P route discovery mode of | This | | | operation | document | +----------+-----------------------------------------+--------------+ DIO Mode of Operation 14.2. Additions to RPL Control Message Options IANA is requested to allocate new values in the "RPL Control Message Options" registry for the "P2P Route Discovery Option" and the "Data Option" described in this document. Goyal, et al. Expires November 6, 2012 [Page 29] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 +-------+---------------------+---------------+ | Value | Meaning | Reference | +-------+---------------------+---------------+ | 10 | P2P Route Discovery | This document | | 11 | Data | This document | +-------+---------------------+---------------+ RPL Control Message Options 14.3. Additions to RPL Control Codes IANA is requested to allocate new code points in the "RPL Control Codes" registry for the "Discovery Reply Object" and "Discovery Reply Object Acknowledgement" (and their secure versions) described in this document. +------+--------------------------------------------+---------------+ | Code | Description | Reference | +------+--------------------------------------------+---------------+ | 0x04 | Discovery Reply Object | This document | | 0x05 | Discovery Reply Object Acknowledgement | This document | | 0x84 | Secure Discovery Reply Object | This document | | 0x85 | Secure Discovery Reply Object | This document | | | Acknowledgement | | +------+--------------------------------------------+---------------+ RPL Control Codes 14.4. New Registry for Upper Layer Headers inside Data Option This document creates a new IANA registry for the Upper Layer Header type inside the RPL Data Option, with the following initial content: +-------+-------------+---------------+ | Value | Description | Reference | +-------+-------------+---------------+ | 0x00 | UDP Header | This document | +-------+-------------+---------------+ Upper Layer Header Types inside RPL Data Option 15. Acknowledgements Authors gratefully acknowledge the contributions of the following individuals (in alphabetical order) in the development of this document: Dominique Barthel, Jakob Buron, Thomas Clausen, Richard Kelsey, Phil Levis, Zach Shelby, Pascal Thubert, Hristo Valev and JP Goyal, et al. Expires November 6, 2012 [Page 30] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 Vasseur. 16. References 16.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, "The Trickle Algorithm", RFC 6206, March 2011. [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. 16.2. Informative References [I-D.ietf-roll-p2p-measurement] Goyal, M., Baccelli, E., Brandt, A., and J. Martocci, "A Mechanism to Measure the Quality of a Point-to-point Route in a Low Power and Lossy Network", draft-ietf-roll-p2p-measurement-04 (work in progress), March 2012. [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation of Type 0 Routing Headers in IPv6", RFC 5095, December 2007. [RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation Routing Requirements in Low-Power and Lossy Networks", RFC 5826, April 2010. [RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen, "Building Automation Routing Requirements in Low-Power and Lossy Networks", RFC 5867, June 2010. [RFC6552] Thubert, P., "Objective Function Zero for the Routing Protocol for Low-Power and Lossy Networks (RPL)", RFC 6552, March 2012. [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- Goyal, et al. Expires November 6, 2012 [Page 31] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 Power and Lossy Networks (RPL) Option for Carrying RPL Information in Data-Plane Datagrams", RFC 6553, March 2012. [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 Routing Header for Source Routes with the Routing Protocol for Low-Power and Lossy Networks (RPL)", RFC 6554, March 2012. Authors' Addresses Mukul Goyal (editor) University of Wisconsin Milwaukee 3200 N Cramer St Milwaukee, WI 53201 USA Phone: +1 414 2295001 Email: mukul@uwm.edu Emmanuel Baccelli INRIA Phone: +33-169-335-511 Email: Emmanuel.Baccelli@inria.fr URI: http://www.emmanuelbaccelli.org/ Matthias Philipp INRIA Phone: +33-169-335-511 Email: Matthias.Philipp@inria.fr Anders Brandt Sigma Designs Emdrupvej 26A, 1. Copenhagen, Dk-2100 Denmark Phone: +45-29609501 Email: abr@sdesigns.dk Goyal, et al. Expires November 6, 2012 [Page 32] Internet-Draft draft-ietf-roll-p2p-rpl-10 May 2012 Jerald Martocci Johnson Controls 507 E Michigan St Milwaukee, WI 53202 USA Phone: +1 414-524-4010 Email: jerald.p.martocci@jci.com Goyal, et al. Expires November 6, 2012 [Page 33]