ROLL S. Anamalamudi Internet-Draft SRM University-AP Intended status: Standards Track C. Perkins Expires: March 20, 2022 Lupin Lodge S.V.R.Anand Indian Institute of Science B. Liu Huawei Technologies September 16, 2021 Supporting Asymmetric Links in Low Power Networks: AODV-RPL draft-ietf-roll-aodv-rpl-11 Abstract Route discovery for symmetric and asymmetric Peer-to-Peer (P2P) traffic flows is a desirable feature in Low power and Lossy Networks (LLNs). For that purpose, this document specifies a reactive P2P route discovery mechanism for both hop-by-hop routing and source routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL protocol (AODV-RPL). Paired Instances are used to construct directional paths, for cases where there are asymmetric links between source and target nodes. 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 https://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 March 20, 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. Anamalamudi, et al. Expires March 20, 2022 [Page 1] Internet-Draft AODV-RPL September 2021 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6 4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 6 4.1. AODV-RPL RREQ Option . . . . . . . . . . . . . . . . . . 6 4.2. AODV-RPL RREP Option . . . . . . . . . . . . . . . . . . 8 4.3. AODV-RPL Target Option . . . . . . . . . . . . . . . . . 10 5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11 6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13 6.1. Route Request Generation . . . . . . . . . . . . . . . . 13 6.2. Receiving and Forwarding RREQ messages . . . . . . . . . 14 6.2.1. General Processing . . . . . . . . . . . . . . . . . 14 6.2.2. Additional Processing for Multiple Targets . . . . . 16 6.3. Generating Route Reply (RREP) at TargNode . . . . . . . . 16 6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 16 6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 17 6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 17 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 18 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 19 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 20 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 20 9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 21 10. Security Considerations . . . . . . . . . . . . . . . . . . . 21 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 12.1. Normative References . . . . . . . . . . . . . . . . . . 22 12.2. Informative References . . . . . . . . . . . . . . . . . 23 Appendix A. Example: Using ETX/RSSI Values to determine value of S bit . . . . . . . . . . . . . . . . . . . . . . . 24 Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 26 B.1. Changes from version 10 to version 11 . . . . . . . . . . 26 B.2. Changes from version 09 to version 10 . . . . . . . . . . 27 B.3. Changes from version 08 to version 09 . . . . . . . . . . 27 B.4. Changes from version 07 to version 08 . . . . . . . . . . 28 B.5. Changes from version 06 to version 07 . . . . . . . . . . 29 Anamalamudi, et al. Expires March 20, 2022 [Page 2] Internet-Draft AODV-RPL September 2021 B.6. Changes from version 05 to version 06 . . . . . . . . . . 29 B.7. Changes from version 04 to version 05 . . . . . . . . . . 29 B.8. Changes from version 03 to version 04 . . . . . . . . . . 29 B.9. Changes from version 02 to version 03 . . . . . . . . . . 29 Appendix C. Contributors . . . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 1. Introduction Routing Protocol for Low-Power and Lossy Networks (RPL) [RFC6550] is an IPv6 distance vector routing protocol designed to support multiple traffic flows through a root-based Destination-Oriented Directed Acyclic Graph (DODAG). Typically, a router does not have routing information for most other routers. Consequently, for traffic between routers within the DODAG (i.e., Peer-to-Peer (P2P) traffic) data packets either have to traverse the root in non-storing mode, or traverse a common ancestor in storing mode. Such P2P traffic is thereby likely to traverse longer routes and may suffer severe congestion near the root (for more information see [RFC6997], [RFC6998]). The network environment that is considered in this document is assumed to be the same as described in Section 1 of [RFC6550]. The route discovery process in AODV-RPL is modeled on the analogous procedure specified in AODV [RFC3561]. The on-demand nature of AODV route discovery is natural for the needs of peer-to-peer routing in RPL-based LLNs. AODV terminology has been adapted for use with AODV- RPL messages, namely RREQ for Route Request, and RREP for Route Reply. AODV-RPL currently omits some features compared to AODV -- in particular, flagging Route Errors, "blacklisting" unidirectional links ([RFC3561]), multihoming, and handling unnumbered interfaces. AODV-RPL reuses and extends the core RPL functionality to support routes with bidirectional asymmetric links. It retains RPL's DODAG formation, RPL Instance and the associated Objective Function (defined in [RFC6551]), trickle timers, and support for storing and non-storing modes. AODV-RPL adds basic messages RREQ and RREP as part of RPL DODAG Information Object (DIO) control message, which go in separate (paired) RPL instances. AODV-RPL does not utilize the Destination Advertisement Object (DAO) control message of RPL. AODV- RPL specifies a new Mode of Operation (MOP) running in a separate instance dedicated to discover P2P routes, which may differ from routes discoverable by native RPL. AODV-RPL can be operated whether or not native RPL is running otherwise. Anamalamudi, et al. Expires March 20, 2022 [Page 3] Internet-Draft AODV-RPL September 2021 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 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. AODV-RPL reuses names for messages and data structures, including Rank, DODAG and DODAGID, as defined in RPL [RFC6550]. AODV Ad Hoc On-demand Distance Vector Routing[RFC3561]. Asymmetric Route The route from the OrigNode to the TargNode can traverse different nodes than the route from the TargNode to the OrigNode. An asymmetric route may result from the asymmetry of links, such that only one direction of the series of links satisfies the Objective Function during route discovery. Bi-directional Asymmetric Link A link that can be used in both directions but with different link characteristics. DIO DODAG Information Object DODAG RREQ-Instance (or simply RREQ-Instance) RPL Instance built using the DIO with RREQ option; used for control message transmission from OrigNode to TargNode, thus enabling data transmission from TargNode to OrigNode. DODAG RREP-Instance (or simply RREP-Instance) RPL Instance built using the DIO with RREP option; used for control message transmission from TargNode to OrigNode thus enabling data transmission from OrigNode to TargNode. Downward Direction The direction from the OrigNode to the TargNode. Downward Route A route in the downward direction. hop-by-hop routing Routing when each node stores routing information about the next hop. Anamalamudi, et al. Expires March 20, 2022 [Page 4] Internet-Draft AODV-RPL September 2021 on-demand routing Routing in which a route is established only when needed. OrigNode The IPv6 router (Originating Node) initiating the AODV-RPL route discovery to obtain a route to TargNode. Paired DODAGs Two DODAGs for a single route discovery process between OrigNode and TargNode. P2P Peer-to-Peer -- in other words, not constrained a priori to traverse a common ancestor. reactive routing Same as "on-demand" routing. RREQ-DIO message An AODV-RPL MOP DIO message containing the RREQ option. The RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. The RREQ-DIO message has a secure variant as noted in [RFC6550]. RREP-DIO message An AODV-RPL MOP DIO message containing the RREP option. The RPLInstanceID in RREP-DIO MUST be paired to the one in the associated RREQ-DIO message as described in Section 6.3.2. The RREP-DIO message has a secure variant as noted in [RFC6550]. Source routing A mechanism by which the source supplies the complete route towards the target node along with each data packet [RFC6550]. Symmetric route The upstream and downstream routes traverse the same routers and over the same links. TargNode The IPv6 router (Target Node) for which OrigNode requires a route and initiates Route Discovery within the LLN network. Upward Direction The direction from the TargNode to the OrigNode. Upward Route A route in the upward direction. ART option Anamalamudi, et al. Expires March 20, 2022 [Page 5] Internet-Draft AODV-RPL September 2021 AODV-RPL Target option: a target option defined in this document. 3. Overview of AODV-RPL With AODV-RPL, routes from OrigNode to TargNode within the LLN network are established "on-demand". In other words, the route discovery mechanism in AODV-RPL is invoked reactively when OrigNode has data for delivery to the TargNode but existing routes do not satisfy the application's requirements. AODV-RPL is thus functional without requiring the use of RPL or any other routing protocol. The routes discovered by AODV-RPL are not constrained to traverse a common ancestor. AODV-RPL can enable asymmetric communication paths in networks with bidirectional asymmetric links. For this purpose, AODV-RPL enables discovery of two routes: namely, one from OrigNode to TargNode, and another from TargNode to OrigNode. When possible, AODV-RPL also enables symmetric route discovery along Paired DODAGs (see Section 5). In AODV-RPL, routes are discovered by first forming a temporary DAG rooted at the OrigNode. Paired DODAGs (Instances) are constructed according to the AODV-RPL Mode of Operation (MOP) during route formation between the OrigNode and TargNode. The RREQ-Instance is formed by route control messages from OrigNode to TargNode whereas the RREP-Instance is formed by route control messages from TargNode to OrigNode. Intermediate routers join the Paired DODAGs based on the Rank [RFC6550] as calculated from the DIO message. Henceforth in this document, the RREQ-DIO message means the AODV-RPL mode DIO message from OrigNode to TargNode, containing the RREQ option (see Section 4.1). Similarly, the RREP-DIO message means the AODV-RPL mode DIO message from TargNode to OrigNode, containing the RREP option (see Section 4.2). The route discovered in the RREQ-Instance is used for transmitting data from TargNode to OrigNode, and the route discovered in RREP-Instance is used for transmitting data from OrigNode to TargNode. 4. AODV-RPL DIO Options 4.1. AODV-RPL RREQ Option OrigNode selects one of its IPv6 addresses and sets it in the DODAGID field of the RREQ-DIO message. Exactly one RREQ option MUST be present in a RREQ-DIO message, otherwise the message MUST be dropped. Anamalamudi, et al. Expires March 20, 2022 [Page 6] Internet-Draft AODV-RPL September 2021 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 | Option Length |S|H|X| Compr | L | MaxRank | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Orig SeqNo | | +-+-+-+-+-+-+-+-+ | | | | | | Address Vector (Optional, Variable Length) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Format for AODV-RPL RREQ Option OrigNode supplies the following information in the RREQ option: Option Type TBD2 Option Length The length of the option in octets, excluding the Type and Length fields. Variable due to the presence of the address vector and the number of octets elided according to the Compr value. S Symmetric bit indicating a symmetric route from the OrigNode to the router transmitting this RREQ-DIO. See Section 5. H Set to one for a hop-by-hop route. Set to zero for a source route. This flag controls both the downstream route and upstream route. X Reserved. MUST be set to zero. Compr 4-bit unsigned integer. Number of prefix octets that are elided from the Address Vector. The octets elided are shared with the IPv6 address in the DODAGID. This field is only used in source routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be set to zero and ignored upon reception. L Anamalamudi, et al. Expires March 20, 2022 [Page 7] Internet-Draft AODV-RPL September 2021 2-bit unsigned integer determining the length of time that a node is able to belong to the RREQ-Instance (a temporary DAG including the OrigNode and the TargNode). Once the time is reached, a node MUST leave the RREQ-Instance and stop sending or receiving any more DIOs for the RREQ-Instance. This naturally depends on the node's ability to keep track of the time. * 0x00: No time limit imposed. * 0x01: 16 seconds * 0x02: 64 seconds * 0x03: 256 seconds L is independent from the route lifetime, which is defined in the DODAG configuration option. MaxRank This field indicates the upper limit on the integer portion of the Rank (calculated using the DAGRank() macro defined in [RFC6550]). A value of 0 in this field indicates the limit is infinity. Orig SeqNo Sequence Number of OrigNode. See Section 6.1. Address Vector A vector of IPv6 addresses representing the route that the RREQ- DIO has passed. It is only present when the H bit is set to 0. The prefix of each address is elided according to the Compr field. TargNode can join the RREQ instance at a Rank whose integer portion is less than or equal to the MaxRank. Other nodes MUST NOT join a RREQ instance if its own Rank would be equal to or higher than MaxRank. A router MUST discard a received RREQ if the integer part of the advertised Rank equals or exceeds the MaxRank limit. 4.2. AODV-RPL RREP Option TargNode sets one of its IPv6 addresses in the DODAGID field of the RREP-DIO message. Exactly one RREP option MUST be present in a RREP- DIO message, otherwise the message MUST be dropped. TargNode supplies the following information in the RREP option: Anamalamudi, et al. Expires March 20, 2022 [Page 8] Internet-Draft AODV-RPL September 2021 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 | Option Length |G|H|X| Compr | L | MaxRank | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Shift |X X| | +-+-+-+-+-+-+-+-+ | | | | | | Address Vector (Optional, Variable Length) | . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Format for AODV-RPL RREP option Option Type TBD3 Option Length The length of the option in octets, excluding the Type and Length fields. Variable due to the presence of the address vector and the number of octets elided according to the Compr value. G Gratuitous route (see Section 7). H The H bit in the RREP option MUST be set to be the same as the H bit in RREQ option. It requests either source routing (H=0) or hop-by-hop (H=1) for the downstream route. X Reserved. MUST be set to zero. Compr 4-bit unsigned integer. Same definition as in RREQ option. L 2-bit unsigned integer defined as in RREQ option. MaxRank Similarly to MaxRank in the RREQ message, this field indicates the upper limit on the integer portion of the Rank. A value of 0 in this field indicates the limit is infinity. Shift Anamalamudi, et al. Expires March 20, 2022 [Page 9] Internet-Draft AODV-RPL September 2021 6-bit unsigned integer. This field is used to recover the original RPLInstanceID (see Section 6.3.3); 0 indicates that the original RPLInstanceID is used. X X MUST be initialized to zero and ignored upon reception. Address Vector Only present when the H bit is set to 0. For an asymmetric route, the Address Vector represents the IPv6 addresses of the path through the network the RREP-DIO has passed. For a symmetric route, it is the Address Vector when the RREQ-DIO arrives at the TargNode, unchanged during the transmission to the OrigNode. 4.3. AODV-RPL Target Option The AODV-RPL Target (ART) Option is based on the Target Option in core RPL [RFC6550]. The Flags field is replaced by the Destination Sequence Number of the TargNode and the Prefix Length field is reduced to 7 bits so that the value is limited to be no greater than 127. A RREQ-DIO message MUST carry at least one ART Option. A RREP-DIO message MUST carry exactly one ART Option. Otherwise, the message MUST be dropped. OrigNode can include multiple TargNode addresses via multiple AODV- RPL Target Options in the RREQ-DIO, for routes that share the same requirement on metrics. This reduces the cost to building only one DODAG. 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 | Option Length | Dest SeqNo |X|Prefix Length| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + | | Target Prefix / Address (Variable Length) | . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: ART Option format for AODV-RPL MOP Option Type TBD4 Anamalamudi, et al. Expires March 20, 2022 [Page 10] Internet-Draft AODV-RPL September 2021 Option Length Length of the option in octets excluding the Type and Length fields. Dest SeqNo In RREQ-DIO, if nonzero, it is the Sequence Number for the last route that OrigNode stored to the TargNode for which a route is desired. In RREP-DIO, it is the destination sequence number associated to the route. Zero is used if there is no known information about the sequence number of TargNode, and not used otherwise. X A one-bit reserved field. This field MUST be initialized to zero by the sender and MUST be ignored by the receiver. Prefix Length 7-bit unsigned integer. Number of valid leading bits in the IPv6 Prefix. If Prefix Length is 0, then the value in the Target Prefix / Address field represents an IPv6 address, not a prefix. Target Prefix / Address (variable-length field) An IPv6 destination address or prefix. The Prefix Length field contains the number of valid leading bits in the prefix. The Target Prefix / Address field contains the least number of octets that can represent all of the bits of the Prefix, in other words Ceil(Prefix Length/8) octets. The initial bits in the Target Prefix / Address field preceding the prefix length (if any) MUST be set to zero on transmission and MUST be ignored on receipt. If Prefix Length is zero, the Address field is 128 bits for IPv6 addresses. 5. Symmetric and Asymmetric Routes Links are considered symmetric until indication to the contrary is received. In Figure 4 and Figure 5, BR is the Border Router, O is the OrigNode, each R is an intermediate router, and T is the TargNode. If the RREQ-DIO arrives over an interface that is known to be symmetric, and the S bit is set to 1, then it remains as 1, as illustrated in Figure 4. If an intermediate router sends out RREQ- DIO with the S bit set to 1, then each link en route from the OrigNode O to this router has met the requirements of route discovery, and the route can be used symmetrically. Anamalamudi, et al. Expires March 20, 2022 [Page 11] Internet-Draft AODV-RPL September 2021 BR /----+----\ / | \ / | \ R R R _/ \ | / \ / \ | / \ / \ | / \ R -------- R --- R ----- R -------- R / \ <--S=1--> / \ <--S=1--> / \ <--S=1--> \ / \ / <--S=1--> / \ / \ / \ O ---------- R ------ R------ R ----- R ----------- T / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ R ----- R ----------- R ----- R ----- R ----- R ---- R----- R >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< Figure 4: AODV-RPL with Symmetric Paired Instances Upon receiving a RREQ-DIO with the S bit set to 1, a node determines whether this link can be used symmetrically, i.e., both directions meet the requirements of data transmission. If the RREQ-DIO arrives over an interface that is not known to be symmetric, or is known to be asymmetric, the S bit is set to 0. If the S bit arrives already set to be '0', it is set to be '0' when the RREQ-DIO is propagated (Figure 5). For an asymmetric route, there is at least one hop which doesn't satisfy the Objective Function. Based on the S bit received in RREQ-DIO, TargNode T determines whether or not the route is symmetric before transmitting the RREP-DIO message upstream towards the OrigNode O. The criteria used to determine whether or not each link is symmetric is beyond the scope of the document. For instance, intermediate routers can use local information (e.g., bit rate, bandwidth, number of cells used in 6tisch [RFC9030]), a priori knowledge (e.g., link quality according to previous communication) or use averaging techniques as appropriate to the application. Other link metric information can be acquired before AODV-RPL operation, by executing evaluation procedures; for instance test traffic can be generated between nodes of the deployed network. During AODV-RPL operation, OAM techniques for evaluating link state (see [RFC7548], [RFC7276], [co-ioam]) MAY be used (at regular intervals appropriate for the LLN). The evaluation procedures are out of scope for AODV-RPL. Anamalamudi, et al. Expires March 20, 2022 [Page 12] Internet-Draft AODV-RPL September 2021 Appendix A describes an example method using the upstream Expected Number of Transmissions (ETX) and downstream Received Signal Strength Indicator (RSSI) to estimate whether the link is symmetric in terms of link quality using an averaging technique. BR /----+----\ / | \ / | \ R R R / \ | / \ / \ | / \ / \ | / \ R --------- R --- R ---- R --------- R / \ --S=1--> / \ --S=0--> / \ --S=1--> \ / \ / --S=0--> / \ / \ / \ O ---------- R ------ R------ R ----- R ----------- T / \ / \ / \ / \ / <--S=0-- / \ / \ / <--S=0-- / \ / \ / \ / \ R ----- R ----------- R ----- R ----- R ----- R ---- R----- R <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< Figure 5: AODV-RPL with Asymmetric Paired Instances As illustrated in Figure 5, an intermediate router determines the S bit value that the RREQ-DIO should carry using link asymmetry detection methods as discussed earlier in this section. In many cases the intermediate router has already made the link asymmetry decision by the time RREQ-DIO arrives. 6. AODV-RPL Operation 6.1. Route Request Generation The route discovery process is initiated when an application at the OrigNode has data to be transmitted to the TargNode, but does not have a route that satisfies the Objective Function for the target of the data transmission. In this case, the OrigNode builds a local RPLInstance and a DODAG rooted at itself. Then it transmits a DIO message containing exactly one RREQ option (see Section 4.1) via link-local multicast. The DIO MUST contain at least one ART Option (see Section 4.3). The required ART Option indicates the TargNode. The S bit in RREQ-DIO sent out by the OrigNode is set to 1. Anamalamudi, et al. Expires March 20, 2022 [Page 13] Internet-Draft AODV-RPL September 2021 Each node maintains a sequence number; the operation is specified in section 7.2 of [RFC6550]. When the OrigNode initiates a route discovery process, it MUST increase its own sequence number to avoid conflicts with previously established routes. The sequence number is carried in the Orig SeqNo field of the RREQ option. The address in the ART Option can be a unicast IPv6 address or a prefix. The OrigNode can initiate the route discovery process for multiple targets simultaneously by including multiple ART Options. Within a RREQ-DIO the requirements for the routes to different TargNodes MUST be the same. OrigNode can maintain different RPLInstances to discover routes with different requirements to the same targets. Using the RPLInstanceID pairing mechanism (see Section 6.3.3), route replies (RREP-DIOs) for different RPLInstances can be generated. The transmission of RREQ-DIO obeys the Trickle timer [RFC6206]. If the length of time specified by the L field has elapsed, the OrigNode MUST leave the DODAG and stop sending RREQ-DIOs in the related RPLInstance. 6.2. Receiving and Forwarding RREQ messages 6.2.1. General Processing Upon receiving a RREQ-DIO, a router goes through the steps below. If the router has not joined the RREQ-Instance, then the maximum useful rank (MaxUseRank) is MaxRank. Otherwise, MaxUseRank is set to be the Rank value that was stored when the router processed the best previous RREQ for the DODAG with the given RREQ-Instance. Step 1: The router MUST first determine whether to propagate the RREQ-DIO. It does this by determining whether or not the downstream direction of the incoming link satisfies the Objective Function (OF). If not the RREQ-DIO MUST be dropped, and the following steps are not processed. Otherwise, the router MUST join the RREQ-Instance and prepare to propagate the RREQ-DIO. The upstream neighbor router that transmitted the received RREQ-DIO is selected as the preferred parent. Step 2: If the H bit is set to 1, then the router (TargNode or intermediate) MUST build an upward route entry towards OrigNode which includes at least the following items: Source Address, Anamalamudi, et al. Expires March 20, 2022 [Page 14] Internet-Draft AODV-RPL September 2021 RPLInstanceID, Destination Address, Next Hop, Lifetime, and Sequence Number. The Destination Address and the RPLInstanceID respectively can be learned from the DODAGID and the RPLInstanceID of the RREQ-DIO, and the Source Address is the address used by the local router to send data to the Next Hop, i.e., the preferred parent. The lifetime is set according to DODAG configuration (not the L field) and can be extended when the route is actually used. The sequence number represents the freshness of the route entry, and it is copied from the Orig SeqNo field of the RREQ option. A route entry with the same source and destination address, same RPLInstanceID, but stale sequence number, MUST be deleted. Step 3: If the S bit of the incoming RREQ-DIO is 0, then the route cannot be symmetric, and the S bit of the RREQ-DIO to be transmitted is set to 0. Otherwise, the router MUST determine whether the downward (i.e., towards the TargNode) direction of the incoming link satisfies the OF. If so, the S bit of the RREQ-DIO to be transmitted is set to 1. Otherwise the S bit of the RREQ-DIO to be transmitted is set to 0. When a router joins the RREQ-Instance, it also associates within its data structure for the RREQ-Instance the information about whether or not the RREQ-DIO to be transmitted has the S-bit set to 1. This information associated to RREQ-Instance is known as the S-bit of the RREQ-Instance. It will be used later during the RREP-DIO message processing Section 6.3.2 for RPLInstance pairing as described in Section 6.4. Step 4: The router checks whether one of its addresses is included in one of the ART Options. If so, this router is one of the TargNodes. Otherwise, it is an intermediate router. If the router is an intermediate router, then it transmits the RREQ-DIO via link-local multicast; if the H bit is set to 0, the intermediate router MUST include the address of the interface receiving the RREQ-DIO into the address vector. Otherwise, the router is TargNode; if it was not already associated with the RREQ-Instance, it prepares and transmits a RREP-DIO (Section 6.3). If, on the other hand, TargNode was already associated with the RREQ-Instance, it takes no further action and does not send an RREP-DIO. Anamalamudi, et al. Expires March 20, 2022 [Page 15] Internet-Draft AODV-RPL September 2021 6.2.2. Additional Processing for Multiple Targets If the OrigNode tries to reach multiple TargNodes in a single RREQ- Instance, one of the TargNodes can be an intermediate router to the others, therefore it MUST continue sending RREQ-DIO to reach other targets. In this case, before transmitting the RREQ-DIO via link- local multicast, a TargNode MUST delete the Target Option encapsulating its own address, so that downstream routers with higher Rank values do not try to create a route to this TargNode. An intermediate router could receive several RREQ-DIOs from routers with lower Rank values in the same RREQ-Instance with different lists of Target Options. When transmitting the RREQ-DIO, the intersection of all received lists MUST be included. For example, suppose two RREQ-DIOs are received with the same RPLInstance and OrigNode. Suppose further that the first RREQ has (T1, T2) as the targets, and the second one has (T2, T4) as targets. Then only T2 needs to be included in the generated RREQ-DIO. If the intersection is empty, it means that all the targets have been reached, and the router MUST NOT transmit any RREQ-DIO. For the purposes of determining the intersection with previous incoming RREQ-DIOs, the intermediate router maintains a record of the targets that have been requested for a given RREQ-Instance. Any incoming RREQ-DIO message having multiple ART Options coming from a router with higher Rank than the Rank of the stored targets is ignored. 6.3. Generating Route Reply (RREP) at TargNode When H=1 in the incoming RREQ, the TargNode MUST NOT generate a RREP if one of its addresses is present in the Address Vector. If the implementation selects the symmetric route, and the L field is not 0, the TargNode MAY delay transmitting the RREP-DIO for duration RREP_WAIT_TIME to await a route with a lower Rank. The value of RREP_WAIT_TIME is set by default to 1/4 of the duration determined by the L field. For L == 0, RREP_WAIT_TIME is set by default to 0. Depending upon the application, RREP_WAIT_TIME may be set to other values. Smaller values enable quicker formation for the P2P route. Larger values enable formation of P2P routes with better Rank values. 6.3.1. RREP-DIO for Symmetric route If a RREQ-DIO arrives at TargNode with the S bit set to 1, there is a symmetric route both of whose directions satisfy the Objective Function. Other RREQ-DIOs might later provide better upward routes. The method of selection between a qualified symmetric route and an asymmetric route that might have better performance is implementation-specific and out of scope. Anamalamudi, et al. Expires March 20, 2022 [Page 16] Internet-Draft AODV-RPL September 2021 For a symmetric route, the RREP-DIO message is unicast to the next hop according to the accumulated address vector (H=0) or the route entry (H=1). Thus the DODAG in RREP-Instance does not need to be built. The RPLInstanceID in the RREP-Instance is paired as defined in Section 6.3.3. In case the H bit is set to 0, the address vector received in the RREQ-DIO MUST be included in the RREP-DIO. TargNode increments its current sequence number and uses the incremented result in the Dest SeqNo in the ART option of the RREQ-DIO. The address of the OrigNode MUST be encapsulated in the ART Option and included in this RREP-DIO message. 6.3.2. RREP-DIO for Asymmetric Route When a RREQ-DIO arrives at a TargNode with the S bit set to 0, the TargNode MUST build a DODAG in the RREP-Instance corresponding to the RREQ-DIO, rooted at itself in order to discover the downstream route from the OrigNode to the TargNode. The RREP-DIO message MUST be transmitted via link-local multicast until the OrigNode is reached or MaxRank is exceeded. The settings of the fields in RREP option and ART option are the same as for the symmetric route, except for the value of the S bit associated with the RREP-instance. 6.3.3. RPLInstanceID Pairing Since the RPLInstanceID is assigned locally (i.e., there is no coordination between routers in the assignment of RPLInstanceID), the tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely identify a discovered route. It is possible that multiple route discoveries with dissimilar Objective Functions are initiated simultaneously. Thus between the same pair of OrigNode and TargNode, there can be multiple AODV-RPL route discovery instances. To avoid any mismatch, the RREQ-Instance and the RREP-Instance in the same route discovery MUST be paired using the RPLInstanceID. When preparing the RREP-DIO, a TargNode could find the RPLInstanceID candidate for the RREP-Instance is already occupied by another RPL Instance from an earlier route discovery operation which is still active. This unlikely case might happen if two distinct OrigNodes need routes to the same TargNode, and they happen to use the same RPLInstanceID for RREQ-Instance. In such cases, the original RPLInstanceID of an already active RREP-Instance MUST NOT be used again for assigning RPLInstanceID for the later RREP-Instance. Reusing the same RPLInstanceID for two distinct DODAGs originated with the same DODAGID (TargNode address) would prevent intermediate routers to distinguish between these DODAGs (and their associated Objective Functions). Instead, the RPLInstanceID MUST be replaced by Anamalamudi, et al. Expires March 20, 2022 [Page 17] Internet-Draft AODV-RPL September 2021 another value so that the two RREP-instances can be distinguished. In RREP-DIO option, the Shift field of the RREP-DIO message(Figure 2) indicates the shift to be applied to original RPLInstanceID to obtain the replacement RPLInstanceID. When the new RPLInstanceID after shifting exceeds 255, it rolls over starting at 0. For example, if the original RPLInstanceID is 252, and shifted by 6, the new RPLInstanceID will be 2. Related operations can be found in Section 6.4. RPLInstanceID collisions do not occur across RREQ-DIOs; the DODAGID equals the OrigNode address and is sufficient to disambiguate between DODAGs. 6.4. Receiving and Forwarding Route Reply Upon receiving a RREP-DIO, a router performs the following steps: Step 1: If the Objective Function is not satisfied, the router MUST NOT join the DODAG; the router MUST discard the RREQ-DIO, and does not execute the remaining steps in this section. An Intermediate Router MUST NOT forward a RREP if one of its addresses is present in the Address Vector, and does not execute the remaining steps in this section. If the S bit of the associated RREQ-Instance is set to 1, the router MUST proceed to step 2. If the S-bit of the RREQ-Instance is set to 0, the router MUST determine whether the downward direction of the link (towards the TargNode) over which the RREP-DIO is received satisfies the Objective Function, and the router's Rank would not exceed the MaxRank limit. If so, the router joins the DODAG of the RREP- Instance. The router that transmitted the received RREP-DIO is selected as the preferred parent. Afterwards, other RREP-DIO messages can be received. Step 2: The router next checks if one of its addresses is included in the ART Option. If so, this router is the OrigNode of the route discovery. Otherwise, it is an intermediate router. Step 3: If the H bit is set to 1, then the router (OrigNode or intermediate) MUST build a downward route entry towards TargNode which includes at least the following items: OrigNode Address, RPLInstanceID, TargNode Address as destination, Next Hop, Lifetime Anamalamudi, et al. Expires March 20, 2022 [Page 18] Internet-Draft AODV-RPL September 2021 and Sequence Number. For a symmetric route, the Next Hop in the route entry is the router from which the RREP-DIO is received. For an asymmetric route, the Next Hop is the preferred parent in the DODAG of RREQ-Instance. The RPLInstanceID in the route entry MUST be the original RPLInstanceID (after subtracting the Shift field value). The source address is learned from the ART Option, and the destination address is learned from the DODAGID. The lifetime is set according to DODAG configuration (i.e., not the L field) and can be extended when the route is actually used. The sequence number represents the freshness of the route entry, and is copied from the Dest SeqNo field of the ART option of the RREP- DIO. A route entry with same source and destination address, same RPLInstanceID, but stale sequence number (i.e., incoming sequence number is less than the currently stored sequence number of the route entry), MUST be deleted. Step 4: If the receiver is the OrigNode, it can start transmitting the application data to TargNode along the path as provided in RREP- Instance, and processing for the RREP-DIO is complete. Otherwise, in case of an asymmetric route, the intermediate router MUST include the address of the interface receiving the RREP-DIO into the address vector, and then transmit the RREP-DIO via link-local multicast. In case of a symmetric route, the RREP-DIO message is unicast to the Next Hop according to the address vector in the RREP-DIO (H=0) or the local route entry (H=1). The RPLInstanceID in the transmitted RREP-DIO is the same as the value in the received RREP-DIO. The local knowledge for the TargNode's sequence number SHOULD be updated. Upon receiving a RREP-DIO, a router which already belongs to the RREP-Instance SHOULD drop the RREP-DIO. 7. Gratuitous RREP In some cases, an Intermediate router that receives a RREQ-DIO message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode instead of continuing to multicast the RREQ-DIO towards TargNode. The intermediate router effectively builds the RREP-Instance on behalf of the actual TargNode. The G bit of the RREP option is provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the Intermediate node from the RREP-DIO sent by TargNode (G=0). The gratuitous RREP-DIO can be sent out when an intermediate router receives a RREQ-DIO for a TargNode, and the router has a more recent (larger destination sequence number) pair of downward and upward routes to the TargNode which also satisfy the Objective Function. Anamalamudi, et al. Expires March 20, 2022 [Page 19] Internet-Draft AODV-RPL September 2021 In case of source routing, the intermediate router MUST unicast the received RREQ-DIO to TargNode including the address vector between the OrigNode and the router. Thus the TargNode can have a complete upward route address vector from itself to the OrigNode. Then the router MUST transmit the gratuitous RREP-DIO including the address vector from the router itself to the TargNode. In case of hop-by-hop routing, the intermediate router MUST unicast the received RREQ-DIO to the Next Hop on the route. The Next Hop router along the route MUST build new route entries with the related RPLInstanceID and DODAGID in the downward direction. The above process will happen recursively until the RREQ-DIO arrives at the TargNode. Then the TargNode MUST unicast recursively the RREP-DIO hop-by-hop to the intermediate router, and the routers along the route SHOULD build new route entries in the upward direction. Upon receiving the unicast RREP-DIO, the intermediate router sends the gratuitous RREP-DIO to the OrigNode as defined in Section 6.3. 8. Operation of Trickle Timer The trickle timer operation to control RREQ-Instance/RREP-Instance multicast uses [RFC6206] to control RREQ-DIO and RREP-DIO transmissions. The Trickle control of these DIO transmissions follow the procedures described in the Section 8.3 of [RFC6550] entitled "DIO Transmission". 9. IANA Considerations Note to RFC editor: The sentences "The parenthesized number 5 is only a suggestion." and "The parenthesized numbers are only suggestions." are to be removed prior publication. A Subregistry in this section refers to a named sub-registry of the "Routing Protocol for Low Power and Lossy Networks (RPL)" registry. 9.1. New Mode of Operation: AODV-RPL IANA is asked to assign a new Mode of Operation, named "AODV-RPL" for peer-to-peer hop-by-hop routing from the "Mode of Operation" Subregistry. The parenthesized number 5 is only a suggestion. Anamalamudi, et al. Expires March 20, 2022 [Page 20] Internet-Draft AODV-RPL September 2021 +-------------+---------------+---------------+ | Value | Description | Reference | +-------------+---------------+---------------+ | TBD1 (5) | AODV-RPL | This document | +-------------+---------------+---------------+ Figure 6: Mode of Operation 9.2. AODV-RPL Options: RREQ, RREP, and Target IANA is asked to assign three new AODV-RPL options "RREQ", "RREP" and "ART", as described in Figure 7 from the "RPL Control Message Options" Subregistry. The parenthesized numbers are only suggestions. +-------------+------------------------+---------------+ | Value | Meaning | Reference | +-------------+------------------------+---------------+ | TBD2 (0x0B) | RREQ Option | This document | +-------------+------------------------+---------------+ | TBD3 (0x0C) | RREP Option | This document | +-------------+------------------------+---------------+ | TBD4 (0x0D) | ART Option | This document | +-------------+------------------------+---------------+ Figure 7: AODV-RPL Options 10. Security Considerations The security considerations for the operation of AODV-RPL are similar to those for the operation of RPL (as described in Section 19 of the RPL specification [RFC6550]). Sections 6.1 and 10 of [RFC6550] describe RPL's optional security framework, which AODV-RPL relies on to provide data confidentiality, authentication, replay protection, and delay protection services. Additional analysis for the security threats to RPL can be found in [RFC7416]. A router can join a temporary DAG created for a secure AODV-RPL route discovery only if it can support the security configuration in use (see Section 6.1 of [RFC6550]), which also specifies the key in use. It does not matter whether the key is preinstalled or dynamically acquired. The router must have the key in use before it can join the DAG being created for secure route discovery. If a rogue router knows the key for the security configuration in use, it can join the secure AODV-RPL route discovery and cause various types of damage. Such a rogue router could advertise false information in its DIOs in order to include itself in the discovered Anamalamudi, et al. Expires March 20, 2022 [Page 21] Internet-Draft AODV-RPL September 2021 route(s). It could generate bogus RREQ-DIO, and RREP-DIO messages carrying bad routes or maliciously modify genuine RREP-DIO messages it receives. A rogue router acting as the OrigNode could launch denial-of-service attacks against the LLN deployment by initiating fake AODV-RPL route discoveries. When rogue routers might be present, RPL's preinstalled mode of operation, where the key to use for route discovery is preinstalled, SHOULD be used. When a RREQ-DIO message uses the source routing option by setting the H bit to 0, a rogue router may populate the Address Vector field with a set of addresses that may result in the RREP-DIO traveling in a routing loop. If a rogue router is able to forge a gratuitous RREP, significant damage might result. 11. Acknowledgements The authors thank Pascal Thubert, Rahul Jadhav, and Lijo Thomas for their support and valuable inputs. The authors specially thank Lavanya H.M for implementing AODV-RPl in Contiki and conducting extensive simulation studies. The authors would like to acknowledge the review, feedback and comments from the following people, in alphabetical order: Roman Danyliw, Lars Eggert, Benjamin Kaduk, Tero Kivinen, Erik Kline, Murray Kucherawy, Warren Kumari, Francesca Palombini, Alvaro Retana, Ines Robles, John Scudder, Meral Shirazipour, Peter Van der Stok, Eric Vyncke, and Robert Wilton. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206, March 2011, . Anamalamudi, et al. Expires March 20, 2022 [Page 22] Internet-Draft AODV-RPL September 2021 [RFC6550] Winter, T., Ed., Thubert, P., Ed., 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, DOI 10.17487/RFC6550, March 2012, . [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., and D. Barthel, "Routing Metrics Used for Path Calculation in Low-Power and Lossy Networks", RFC 6551, DOI 10.17487/RFC6551, March 2012, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 12.2. Informative References [co-ioam] Ballamajalu, Rashmi., S.V.R., Anand., and Malati Hegde, "Co-iOAM: In-situ Telemetry Metadata Transport for Resource Constrained Networks within IETF Standards Framework", 2018 10th International Conference on Communication Systems & Networks (COMSNETS) pp.573-576, Jan 2018. [contiki] Contiki contributors, "The Contiki Open Source OS for the Internet of Things (Contiki Version 2.7)", Nov 2013, . [Contiki-ng] Contiki-NG contributors, "Contiki-NG: The OS for Next Generation IoT Devices (Contiki-NG Version 4.6)", Dec 2020, . [cooja] Contiki/Cooja contributors, "Cooja Simulator for Wireless Sensor Networks (Contiki/Cooja Version 2.7)", Nov 2013, . [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- Demand Distance Vector (AODV) Routing", RFC 3561, DOI 10.17487/RFC3561, July 2003, . Anamalamudi, et al. Expires March 20, 2022 [Page 23] Internet-Draft AODV-RPL September 2021 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and J. Martocci, "Reactive Discovery of Point-to-Point Routes in Low-Power and Lossy Networks", RFC 6997, DOI 10.17487/RFC6997, August 2013, . [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, "A Mechanism to Measure the Routing Metrics along a Point- to-Point Route in a Low-Power and Lossy Network", RFC 6998, DOI 10.17487/RFC6998, August 2013, . [RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. Weingarten, "An Overview of Operations, Administration, and Maintenance (OAM) Tools", RFC 7276, DOI 10.17487/RFC7276, June 2014, . [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., and M. Richardson, Ed., "A Security Threat Analysis for the Routing Protocol for Low-Power and Lossy Networks (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, . [RFC7548] Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A. Sehgal, "Management of Networks with Constrained Devices: Use Cases", RFC 7548, DOI 10.17487/RFC7548, May 2015, . [RFC9030] Thubert, P., Ed., "An Architecture for IPv6 over the Time- Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)", RFC 9030, DOI 10.17487/RFC9030, May 2021, . Appendix A. Example: Using ETX/RSSI Values to determine value of S bit The combination of Received Signal Strength Indication(downstream) (RSSI) and Expected Number of Transmissions(upstream) (ETX) has been tested to determine whether a link is symmetric or asymmetric at intermediate nodes. We present two methods to obtain an ETX value from RSSI measurement. Method 1: In the first method, we constructed a table measuring RSSI vs ETX using the Cooja simulation [cooja] setup in the Contiki OS environment[contiki]. We used Contiki-2.7 running 6LoWPAN/RPL protocol stack for the simulations. For approximating the number of packet drops based on the RSSI values, we implemented simple logic that drops transmitted packets with certain pre-defined Anamalamudi, et al. Expires March 20, 2022 [Page 24] Internet-Draft AODV-RPL September 2021 ratios before handing over the packets to the receiver. The packet drop ratio is implemented as a table lookup of RSSI ranges mapping to different packet drop ratios with lower RSSI ranges resulting in higher values. While this table has been defined for the purpose of capturing the overall link behavior, it is highly recommended to conduct physical radio measurement experiments, in general. By keeping the receiving node at different distances, we let the packets experience different packet drops as per the described method. The ETX value computation is done by another module which is part of RPL Objective Function implementation. Since ETX value is reflective of the extent of packet drops, it allowed us to prepare a useful ETX vs RSSI table. ETX versus RSSI values obtained in this way may be used as explained below: Source---------->NodeA---------->NodeB------->Destination Figure 8: Communication link from Source to Destination +-------------------------+----------------------------------------+ | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA | +-------------------------+----------------------------------------+ | > -60 | 150 | | -70 to -60 | 192 | | -80 to -70 | 226 | | -90 to -80 | 662 | | -100 to -90 | 3840 | +-------------------------+----------------------------------------+ Table 1: Selection of S bit based on Expected ETX value Method 2: One could also make use of the function guess_etx_from_rssi() defined in the 6LoWPAN/RPL protocol stack of Contiki-ng OS [Contiki-ng] to obtain RSSI-ETX mapping. This function outputs ETX value ranging between 128 and 3840 for -60 <= rssi <= -89. The function description is beyond the scope of this document. We tested the operations in this specification by making the following experiment, using the above parameters. In our experiment, a communication link is considered as symmetric if the ETX value of NodeA->NodeB and NodeB->NodeA (see Figure 8) are within, say, a 1:3 ratio. This ratio should be understood as determining the link's symmetric/asymmetric nature. NodeA can typically know the ETX value in the direction of NodeA -> NodeB but it has no direct way of knowing the value of ETX from NodeB->NodeA. Using physical testbed experiments and realistic wireless channel propagation models, one can determine a relationship between RSSI and ETX representable as an expression or a mapping table. Such a relationship in turn can be Anamalamudi, et al. Expires March 20, 2022 [Page 25] Internet-Draft AODV-RPL September 2021 used to estimate ETX value at nodeA for link NodeB--->NodeA from the received RSSI from NodeB. Whenever nodeA determines that the link towards the nodeB is bi-directional asymmetric then the S bit is set to 0. Afterwards, the link from NodeA to Destination remains designated as asymmetric and the S bit remains set to 0. Appendix B. Changelog Note to the RFC Editor: please remove this section before publication. B.1. Changes from version 10 to version 11 o Numerous editorial improvements. o Replace Floor((7+(Prefix Length))/8) by Ceil(Prefix Length/8) for simplicity and ease of understanding. o Use "L field" instead of "L bit" since L is a two-bit field. o Improved the procedures in section 6.2.1. o Define the S bit of the data structure a node uses to represent whether or not the RREQ instance is for a symmetric or an asymmetric route. This replaces text in the document that was a holdover from earlier versions in which the RREP had an S bit for that purpose. o Quote terminology from AODV that has been identified as possibly originating in language reflecting various kinds of bias against certain cultures. o Clarified the relationship of AODV-RPL to RPL. o Eliminated the "Point-to-Point" terminology to avoid suggesting only a single link. o Modified certain passages to better reflect the possibility that a node might have multiple IP addresses. o "Rsv" replaced by "X X" for reserved field. o Added mandates for reserved fields, and replaces some ambiguous language phraseology by mandates. o Replaced "retransmit" terminology by more correct "propagate" terminology. Anamalamudi, et al. Expires March 20, 2022 [Page 26] Internet-Draft AODV-RPL September 2021 o Added text about determining link symmetry near Figure 5. o Mandated checking the Address Vector to avoid routing loops. o Improved specification for use of the Shift value in Section 6.3.3. o Corrected the wrong use of RREQ-Instance to be RREP-Instance. o Referred to Subregistry values instead of Registry values in Section 9. o Sharpened language in Section 10, eliminated misleading use of capitalization in the words "Security Configuration". o Added acknowledgements and contributors. B.2. Changes from version 09 to version 10 o Changed the title for brevity and to remove acronyms. o Added "Note to the RFC Editor" in Section 9. o Expanded DAO and P2MP in Section 1. o Reclassified [RFC6998] and [RFC7416] as Informational. o SHOULD changed to MUST in Section 4.1 and Section 4.2. o Several editorial improvements and clarifications. B.3. Changes from version 08 to version 09 o Removed section "Link State Determination" and put some of the relevant material into Section 5. o Cited security section of [RFC6550] as part of the RREP-DIO message description in Section 2. o SHOULD has been changed to MUST in Section 4.2. o Expanded the terms ETX and RSSI in Section 5. o Section 6.4 has been expanded to provide a more precise explanation of the handling of route reply. Anamalamudi, et al. Expires March 20, 2022 [Page 27] Internet-Draft AODV-RPL September 2021 o Added [RFC7416] in the Security Considerations (Section 10) for RPL security threats. Cited [RFC6550] for authenticated mode of operation. o Appendix A has been mostly re-written to describe methods to determine whether or not the S bit should be set to 1. o For consistency, adjusted several mandates from SHOULD to MUST and from SHOULD NOT to MUST NOT. o Numerous editorial improvements and clarifications. B.4. Changes from version 07 to version 08 o Instead of describing the need for routes to "fulfill the requirements", specify that routes need to "satisfy the Objective Function". o Removed all normative dependencies on [RFC6997] o Rewrote Section 10 to avoid duplication of language in cited specifications. o Added a new section "Link State Determination" with text and citations to more fully describe how implementations determine whether links are symmetric. o Modified text comparing AODV-RPL to other protocols to emphasize the need for AODV-RPL instead of the problems with the other protocols. o Clarified that AODV-RPL uses some of the base RPL specification but does not require an instance of RPL to run. o Improved capitalization, quotation, and spelling variations. o Specified behavior upon reception of a RREQ-DIO or RREP-DIO message for an already existing DODAGID (e.g, Section 6.4). o Fixed numerous language issues in IANA Considerations Section 9. o For consistency, adjusted several mandates from SHOULD to MUST and from SHOULD NOT to MUST NOT. o Numerous editorial improvements and clarifications. Anamalamudi, et al. Expires March 20, 2022 [Page 28] Internet-Draft AODV-RPL September 2021 B.5. Changes from version 06 to version 07 o Added definitions for all fields of the ART option (see Section 4.3). Modified definition of Prefix Length to prohibit Prefix Length values greater than 127. o Modified the language from [RFC6550] Target Option definition so that the trailing zero bits of the Prefix Length are no longer described as "reserved". o Reclassified [RFC3561] and [RFC6998] as Informative. o Added citation for [RFC8174] to Terminology section. B.6. Changes from version 05 to version 06 o Added Security Considerations based on the security mechanisms defined in [RFC6550]. o Clarified the nature of improvements due to P2P route discovery versus bidirectional asymmetric route discovery. o Editorial improvements and corrections. B.7. Changes from version 04 to version 05 o Add description for sequence number operations. o Extend the residence duration L in section 4.1. o Change AODV-RPL Target option to ART option. B.8. Changes from version 03 to version 04 o Updated RREP option format. Remove the T bit in RREP option. o Using the same RPLInstanceID for RREQ and RREP, no need to update [RFC6550]. o Explanation of Shift field in RREP. o Multiple target options handling during transmission. B.9. Changes from version 02 to version 03 o Include the support for source routing. Anamalamudi, et al. Expires March 20, 2022 [Page 29] Internet-Draft AODV-RPL September 2021 o Import some features from [RFC6997], e.g., choice between hop-by- hop and source routing, the L field which determines the duration of residence in the DAG, MaxRank, etc. o Define new target option for AODV-RPL, including the Destination Sequence Number in it. Move the TargNode address in RREQ option and the OrigNode address in RREP option into ADOV-RPL Target Option. o Support route discovery for multiple targets in one RREQ-DIO. o New RPLInstanceID pairing mechanism. Appendix C. Contributors Abdur Rashid Sangi Huaiyin Institute of Technology No.89 North Beijing Road, Qinghe District Huaian 223001 P.R. China Email: sangi_bahrian@yahoo.com Malati Hegde Indian Institute of Science Bangalore 560012 India Email: malati@iisc.ac.in Mingui Zhang Huawei Technologies No. 156 Beiqing Rd. Haidian District Beijing 100095 P.R. China Email: zhangmingui@huawei.com Authors' Addresses Satish Anamalamudi SRM University-AP Amaravati Campus Amaravati, Andhra Pradesh 522 502 India Email: satishnaidu80@gmail.com Anamalamudi, et al. Expires March 20, 2022 [Page 30] Internet-Draft AODV-RPL September 2021 Charles E. Perkins Lupin Lodge Los Gatos 95033 United States Email: charliep@computer.org S.V.R Anand Indian Institute of Science Bangalore 560012 India Email: anandsvr@iisc.ac.in Bing Liu Huawei Technologies No. 156 Beiqing Rd. Haidian District Beijing 100095 China Email: remy.liubing@huawei.com Anamalamudi, et al. Expires March 20, 2022 [Page 31]