ROLL R. Jadhav, Ed. Internet-Draft Huawei Intended status: Standards Track P. Thubert Expires: March 30, 2019 Cisco R. Sahoo Z. Cao Huawei September 26, 2018 Efficient Route Invalidation draft-ietf-roll-efficient-npdao-06 Abstract This document describes the problems associated with the use of NPDAO messaging in RPL and signaling changes to improve route invalidation efficiency. 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 30, 2019. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (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 Jadhav, et al. Expires March 30, 2019 [Page 1] Internet-Draft Efficient Route Invalidation September 2018 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language and Terminology . . . . . . . . . . 3 1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 3 1.3. Why NPDAO is important? . . . . . . . . . . . . . . . . . 4 2. Problems with current NPDAO messaging . . . . . . . . 5 2.1. Lost NPDAO due to link break to the previous parent . . . 5 2.2. Invalidate routes to dependent nodes . . . . . . . . . . 5 2.3. Possible route downtime caused by async operation of NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 5 3. Requirements for the NPDAO Optimization . . . . . . . . . . . 5 3.1. Req#1: Tolerant to link failures to the previous parents . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Req#2: Dependent nodes route invalidation on parent switching . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Req#3: Route invalidation should not impact data traffic 6 4. Proposed changes to RPL signaling . . . . . . . . . . . . . . 6 4.1. Change in RPL route invalidation semantics . . . . . . . 6 4.2. Transit Information Option changes . . . . . . . . . . . 7 4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 8 4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 9 4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 9 4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 9 4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 9 4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 10 4.4. Other considerations . . . . . . . . . . . . . . . . . . 11 4.4.1. Dependent Nodes invalidation . . . . . . . . . . . . 11 4.4.2. NPDAO and DCO in the same network . . . . . . . . . . 11 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . 12 Appendix A. Example DCO Messaging . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction RPL [RFC6550] specifies a proactive distance-vector based routing scheme. RPL has an optional messaging in the form of DAO messages using which the 6LBR can learn route towards the nodes. In storing mode, DAO messages would result in routing entries been created on Jadhav, et al. Expires March 30, 2019 [Page 2] Internet-Draft Efficient Route Invalidation September 2018 all intermediate hops from the node's parent all the way towards the 6LBR. RPL allows use of No-Path DAO (NPDAO) messaging to invalidate a routing path corresponding to the given target, thus releasing resources utilized on that path. A NPDAO is a DAO message with route lifetime of zero, originates at the target node and always flows upstream towards the 6LBR. This document explains the problems associated with the current use of NPDAO messaging and also discusses the requirements for an optimized route invalidation messaging scheme. Further a new pro-active route invalidation message called as "Destination Cleanup Object (DCO)" is specified which fulfills requirements of an optimized route invalidation messaging. 1.1. Requirements Language and Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. The document only caters to the RPL's storing mode of operation (MOP). The non-storing MOP does not require use of NPDAO for route invalidation since routing entries are not maintained on 6LRs. Common Ancestor node: 6LR node which is the first common node on the old and new path for the child node. NPDAO: No-Path DAO. A DAO message which has target with lifetime 0. DCO: Destination Cleanup Object, A new RPL control message type defined by this draft. Regular DAO: A DAO message with non-zero lifetime. LLN: Low Power and Lossy Networks. Target Node: The node switching its parent whose routing adjacencies are updated (created/removed). This document also uses terminology described in [RFC6550]. 1.2. Current NPDAO messaging RPL uses NPDAO messaging in the storing mode so that the node changing it routing adjacencies can invalidate the previous route. This is needed so that nodes along previous path can release any resources (such as the routing entry) it maintains on behalf of target node. Jadhav, et al. Expires March 30, 2019 [Page 3] Internet-Draft Efficient Route Invalidation September 2018 For the rest of this document consider the following topology: (6LBR) | | | (A) / \ / \ / \ (G) (H) | | | | | | (B) (C) \ ; \ ; \ ; (D) / \ / \ / \ (E) (F) Figure 1: Sample topology Node (D) is connected via preferred parent (B). (D) has an alternate path via (C) towards the BR. Node (A) is the common ancestor for (D) for paths through (B)-(G) and (C)-(H). When (D) switches from (B) to (C), RPL allows sending NPDAO to (B) and regular DAO to (C). 1.3. Why NPDAO is important? Nodes in LLNs may be resource constrained. There is limited memory available and routing entry records are one of the primary elements occupying dynamic memory in the nodes. Route invalidation helps 6LR nodes to decide which entries could be discarded to better achieve resource utilization. Thus it becomes necessary to have efficient route invalidation mechanism. Also note that a single parent switch may result in a "sub-tree" switching from one parent to another. Thus the route invalidation needs to be done on behalf of the sub- tree and not the switching node alone. In the above example, when Node (D) switches parent, the route invalidation needs to be done for (D), (E) and (F). Thus without efficient route invalidation, a 6LR may have to hold a lot of stale route entries. Jadhav, et al. Expires March 30, 2019 [Page 4] Internet-Draft Efficient Route Invalidation September 2018 2. Problems with current NPDAO messaging 2.1. Lost NPDAO due to link break to the previous parent When a node switches its parent, the NPDAO is to be sent to its previous parent and a regular DAO to its new parent. In cases where the node switches its parent because of transient or permanent parent link/node failure then the NPDAO message is bound to fail. 2.2. Invalidate routes to dependent nodes RPL does not specify how route invalidation will work for dependent nodes rooted at switching node, resulting in stale routing entries of the dependent nodes. The only way for 6LR to invalidate the route entries for dependent nodes would be to use route lifetime expiry which could be substantially high for LLNs. In the example topology, when Node (D) switches its parent, Node (D) generates an NPDAO on its behalf. There is no NPDAO generated by these child nodes through the previous path resulting in stale entries on nodes (B) and (G) for nodes (E) and (F). 2.3. Possible route downtime caused by async operation of NPDAO and DAO A switching node may generate both an NPDAO and DAO via two different paths at almost the same time. There is a possibility that an NPDAO generated may invalidate the previous route and the regular DAO sent via the new path gets lost on the way. This may result in route downtime impacting downward traffic for the switching node. In the example topology, consider Node (D) switches from parent (B) to (C). An NPDAO sent from previous route may invalidate the existing route whereas there is no way to determine whether the new DAO has successfully updated the route entries on the new path. 3. Requirements for the NPDAO Optimization 3.1. Req#1: Tolerant to link failures to the previous parents When the switching node sends the NPDAO message to the previous parent, it is normal that the link to the previous parent is prone to failure. Therefore, it is required that the NPDAO message must be tolerant to the link failure. The link referred here represents the link between the node and its previous parent (from whom the node is now disassociating). Jadhav, et al. Expires March 30, 2019 [Page 5] Internet-Draft Efficient Route Invalidation September 2018 3.2. Req#2: Dependent nodes route invalidation on parent switching It should be possible to do route invalidation for dependent nodes rooted at the switching node. 3.3. Req#3: Route invalidation should not impact data traffic While sending the NPDAO and DAO messages, it is possible that the NPDAO successfully invalidates the previous path, while the newly sent DAO gets lost (new path not set up successfully). This will result in downstream unreachability to the node switching paths. Therefore, it is desirable that the route invalidation is synchronized with the DAO to avoid the risk of route downtime. 4. Proposed changes to RPL signaling 4.1. Change in RPL route invalidation semantics As described in Section 1.2, the NPDAO originates at the node switching the parent and traverses upstream towards the root. In order to solve the problems as mentioned in Section 2, the draft adds new pro-active route invalidation message called as "Destination Cleanup Object" (DCO) that originates at a common ancestor node between the new and old path. The common ancestor node generates a DCO in response to the change in the next-hop on receiving a regular DAO for the target. In Figure 1, when node D decides to switch the path from B to C, it sends a regular DAO to node C with reachability information containing target as address of D and a incremented path sequence number. Node C will update the routing table based on the reachability information in DAO and in turn generate another DAO with the same reachability information and forward it to H. Node H also follows the same procedure as Node C and forwards it to node A. When node A receives the regular DAO, it finds that it already has a routing table entry on behalf of the target address of node D. It finds however that the next hop information for reaching node D has changed i.e. the node D has decided to change the paths. In this case, Node A which is the common ancestor node for node D along the two paths (previous and new), may generate a DCO which traverses downwards in the network. The document in the subsequent section will explain the message format changes to handle this downward flow of NPDAO. Jadhav, et al. Expires March 30, 2019 [Page 6] Internet-Draft Efficient Route Invalidation September 2018 4.2. Transit Information Option changes Every RPL message is divided into base message fields and additional Options. The base fields apply to the message as a whole and options are appended to add message/use-case specific attributes. As an example, a DAO message may be attributed by one or more "RPL Target" options which specifies the reachability information for the given targets. Similarly, a Transit Information option may be associated with a set of RPL Target options. The draft proposes a change in Transit Information option to contain "Invalidate previous route" (I) bit. This I-bit signals the common ancestor node to generate a DCO on behalf of the target node. The I-bit is carried in the transit information option which augments the reachability information for a given set of RPL Target(s). 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 = 0x06 | Option Length |E|I| Flags | Path Control | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Path Sequence | Path Lifetime | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + | | + Parent Address* + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Updated Transit Information Option (New I flag added) I (Invalidate previous route) bit: 1 bit flag. The 'I' flag is set by the target node to indicate that it wishes to invalidate the previous route by a common ancestor node between the two paths. The common ancestor node SHOULD generate a DCO message in response to this I-bit when it sees that the routing adjacencies have changed for the target. I-bit governs the ownership of the DCO message in a way that the target node is still in control of its own route invalidation. Jadhav, et al. Expires March 30, 2019 [Page 7] Internet-Draft Efficient Route Invalidation September 2018 4.3. Destination Cleanup Object (DCO) A new ICMPv6 RPL control message type is defined by this specification called as "Destination Cleanup Object" (DCO), which is used for proactive cleanup of state and routing information held on behalf of the target node by 6LRs. The DCO message always traverses downstream and cleans up route information and other state information associated with the given target. 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 |K|D| Flags | Reserved | DCOSequence | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + DODAGID(optional) + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option(s)... +-+-+-+-+-+-+-+-+ Figure 3: DCO base object RPLInstanceID: 8-bit field indicating the topology instance associated with the DODAG, as learned from the DIO. K: The 'K' flag indicates that the recipient is expected to send a DCO-ACK back. D: The 'D' flag indicates that the DODAGID field is present. This flag MUST be set when a local RPLInstanceID is used. Flags: The 6 bits remaining unused in the Flags field are reserved for future use. These bits MUST be initialized to zero by the sender and MUST be ignored by the receiver. Reserved: 8-bit unused field. The field MUST be initialized to zero by the sender and MUST be ignored by the receiver. DCOSequence: Incremented at each unique DCO message from a node and echoed in the DCO-ACK message. DODAGID (optional): 128-bit unsigned integer set by a DODAG root that uniquely identifies a DODAG. This field is only present when the 'D' Jadhav, et al. Expires March 30, 2019 [Page 8] Internet-Draft Efficient Route Invalidation September 2018 flag is set. This field is typically only present when a local RPLInstanceID is in use, in order to identify the DODAGID that is associated with the RPLInstanceID. When a global RPLInstanceID is in use, this field need not be present. Unassigned bits of the DCO Base are reserved. They MUST be set to zero on transmission and MUST be ignored on reception. 4.3.1. Secure DCO A Secure DCO message follows the format in [RFC6550] figure 7, where the base message format is the DCO message shown in Figure 3. 4.3.2. DCO Options The DCO message MAY carry valid options. This specification allows for the DCO message to carry the following options: 0x00 Pad1 0x01 PadN 0x05 RPL Target 0x06 Transit Information 0x09 RPL Target Descriptor The DCO carries a Target option and an associated Transit Information option with a lifetime of 0x00000000 to indicate a loss of reachability to that Target. 4.3.3. Path Sequence number in the DCO A DCO message may contain a Path Sequence in the transit information option to identify the freshness of the DCO message. The Path Sequence in the DCO MUST use the same Path Sequence number present in the regular DAO message when the DCO is generated in response to DAO message. 4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) The DCO-ACK message may be sent as a unicast packet by a DCO recipient in response to a unicast DCO message. Jadhav, et al. Expires March 30, 2019 [Page 9] Internet-Draft Efficient Route Invalidation September 2018 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 |D| Reserved | DCOSequence | Status | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + DODAGID(optional) + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: DCO-ACK base object RPLInstanceID: 8-bit field indicating the topology instance associated with the DODAG, as learned from the DIO. D: The 'D' flag indicates that the DODAGID field is present. This flag MUST be set when a local RPLInstanceID is used. Reserved: 7-bit unused field. The field MUST be initialized to zero by the sender and MUST be ignored by the receiver. DCOSequence: Incremented at each unique DCO message from a node and echoed in the DCO-ACK message. Status: Indicates the completion. Status 0 is defined as unqualified acceptance in this specification. The remaining status values are reserved as rejection codes. DODAGID (optional): 128-bit unsigned integer set by a DODAG root that uniquely identifies a DODAG. This field is only present when the 'D' flag is set. This field is typically only present when a local RPLInstanceID is in use, in order to identify the DODAGID that is associated with the RPLInstanceID. When a global RPLInstanceID is in use, this field need not be present. Unassigned bits of the DCO-Ack Base are reserved. They MUST be set to zero on transmission and MUST be ignored on reception. 4.3.5. Secure DCO-ACK A Secure DCO-ACK message follows the format in [RFC6550] figure 7, where the base message format is the DCO-ACK message shown in Figure 4. Jadhav, et al. Expires March 30, 2019 [Page 10] Internet-Draft Efficient Route Invalidation September 2018 4.4. Other considerations 4.4.1. Dependent Nodes invalidation Current RPL [RFC6550] does not provide a mechanism for route invalidation for dependent nodes. This document allows the dependent nodes invalidation. Dependent nodes will generate their respective DAOs to update their paths, and the previous route invalidation for those nodes should work in the similar manner described for switching node. The dependent node may set the I-bit in the transit information option as part of regular DAO so as to request invalidation of previous route from the common ancestor node. 4.4.2. NPDAO and DCO in the same network Even with the changed semantics, the current NPDAO mechanism in [RFC6550] can still be used. There are certain scenarios where current NPDAO signalling may still be used, for example, when the route lifetime expiry of the target happens or when the node simply decides to gracefully terminate the RPL session on graceful node shutdown. Moreover a deployment can have a mix of nodes supporting the proposed DCO and the existing NPDAO mechanism. 5. Acknowledgements Many thanks to Cenk Gundogan, Simon Duquennoy, Georgios Papadopoulous, Peter Van Der Stok for their review and comments. 6. IANA Considerations IANA is requested to allocate new ICMPv6 RPL control codes in RPL [RFC6550] for DCO and DCO-ACK messages. +------+---------------------------------------------+--------------+ | Code | Description | Reference | +------+---------------------------------------------+--------------+ | 0x04 | Destination Cleanup Object | This | | | | document | | 0x05 | Destination Cleanup Object Acknowledgement | This | | | | document | | 0x84 | Secure Destination Cleanup Object | This | | | | document | | 0x85 | Secure Destination Cleanup Object | This | | | Acknowledgement | document | +------+---------------------------------------------+--------------+ Jadhav, et al. Expires March 30, 2019 [Page 11] Internet-Draft Efficient Route Invalidation September 2018 IANA is requested to allocate bit 18 in the Transit Information Option defined in RPL [RFC6550] section 6.7.8 for Invalidate route 'I' flag. 7. Security Considerations This document handles security considerations inline to base RPL. Secure versions of DCO and DCO-ACK are added similar to other RPL messages. For general RPL security considerations, see [RFC6550]. 8. References 8.1. 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, . [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, . 8.2. Informative References [I-D.ietf-6tisch-architecture] Thubert, P., "An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4", draft-ietf-6tisch-architecture-14 (work in progress), April 2018. Appendix A. Example DCO Messaging In Figure 1, node (D) switches its parent from (B) to (C). The sequence of actions is as follows: 1. Node D switches its parent from node B to node C 2. D sends a regular DAO(tgt=D,pathseq=x+1,I_flag=1) in the updated path to C 3. C checks for routing entry on behalf of D, since it cannot find an entry on behalf of D it creates a new routing entry and forwards the reachability information of the target D to H in a DAO. 4. Similar to C, node H checks for routing entry on behalf of D, cannot find an entry and hence creates a new routing entry and Jadhav, et al. Expires March 30, 2019 [Page 12] Internet-Draft Efficient Route Invalidation September 2018 forwards the reachability information of the target D to H in a DAO. 5. Node A receives the DAO, and checks for routing entry on behalf of D. It finds a routing entry but checks that the next hop for target D is now changed. Node A checks the I_flag and generates DCO(tgt=D,pathseq=pathseq(DAO)) to previous next hop for target D which is G. Subsequently, A updates the routing entry and forwards the reachability information of target D upstream DAO(tgt=D,pathseq=x+1,I_flag=x) (the I_flag carries no significance henceforth). 6. Node G receives the DCO and invalidates routing entry of target D and forwards the (un)reachability information downstream to B. 7. Similarly, B processes the DCO by invalidating the routing entry of target D and forwards the (un)reachability information downstream to D. 8. D ignores the DCO since the target is itself. 9. The propagation of the DCO will stop at any node where the node does not have an routing information associated with the target. If the routing information is present and the pathseq associated is not older, then still the DCO is dropped. Authors' Addresses Rahul Arvind Jadhav (editor) Huawei Kundalahalli Village, Whitefield, Bangalore, Karnataka 560037 India Phone: +91-080-49160700 Email: rahul.ietf@gmail.com Pascal Thubert Cisco Systems, Inc Building D 45 Allee des Ormes - BP1200 MOUGINS - Sophia Antipolis 06254 France Phone: +33 497 23 26 34 Email: pthubert@cisco.com Jadhav, et al. Expires March 30, 2019 [Page 13] Internet-Draft Efficient Route Invalidation September 2018 Rabi Narayan Sahoo Huawei Kundalahalli Village, Whitefield, Bangalore, Karnataka 560037 India Phone: +91-080-49160700 Email: rabinarayans@huawei.com Zhen Cao Huawei W Chang'an Ave Beijing China Email: zhencao.ietf@gmail.com Jadhav, et al. Expires March 30, 2019 [Page 14]