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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 4919 ** Downref: Normative reference to an Informational RFC: RFC 6606 == Outdated reference: A later version (-23) exists of draft-ietf-6lo-ap-nd-12 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-31 == Outdated reference: A later version (-18) exists of draft-ietf-roll-efficient-npdao-17 -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Updates: 6550, 8505 (if approved) M. Richardson 5 Intended status: Standards Track Sandelman 6 Expires: 3 May 2020 31 October 2019 8 Eliding and Querying RPL Information 9 draft-ietf-roll-unaware-leaves-05 11 Abstract 13 This specification extends RFC6550 and RFC8505 to provide unicast and 14 multicast routing services in a RPL domain to 6LNs that are plain 15 hosts and do not participate to RPL. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on 3 May 2020. 34 Copyright Notice 36 Copyright (c) 2019 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 41 license-info) in effect on the date of publication of this document. 42 Please review these documents carefully, as they describe your rights 43 and restrictions with respect to this document. Code Components 44 extracted from this document must include Simplified BSD License text 45 as described in Section 4.e of the Trust Legal Provisions and are 46 provided without warranty as described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 52 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 2.2. References . . . . . . . . . . . . . . . . . . . . . . . 4 54 2.3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5 55 3. 6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . . 6 56 3.1. RFC 6775 . . . . . . . . . . . . . . . . . . . . . . . . 7 57 3.2. RFC 8505 Extended ARO . . . . . . . . . . . . . . . . . . 7 58 3.2.1. R Flag . . . . . . . . . . . . . . . . . . . . . . . 8 59 3.2.2. TID, I Field and Opaque Fields . . . . . . . . . . . 8 60 3.2.3. ROVR . . . . . . . . . . . . . . . . . . . . . . . . 8 61 3.3. RFC 8505 Extended DAR/DAC . . . . . . . . . . . . . . . . 9 62 4. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 9 63 5. Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . . 10 64 6. 6LN Requirements to be a RPL-Unware Leaf . . . . . . . . . . 10 65 6.1. Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . . 10 66 6.2. External Routes and RPL Artifacts . . . . . . . . . . . . 11 67 6.2.1. Support of the HbH Header . . . . . . . . . . . . . . 12 68 6.2.2. Support of the Routing Header . . . . . . . . . . . . 12 69 6.2.3. Support of IPv6 Encapsulation . . . . . . . . . . . . 12 70 7. Updated RPL Status . . . . . . . . . . . . . . . . . . . . . 12 71 8. Updated RPL Target option . . . . . . . . . . . . . . . . . . 13 72 9. Protocol Operations for Unicast Addresses . . . . . . . . . . 14 73 9.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 14 74 9.1.1. In RPL Non-Storing-Mode . . . . . . . . . . . . . . . 15 75 9.1.2. In RPL Storing-Mode . . . . . . . . . . . . . . . . . 18 76 9.2. Operation . . . . . . . . . . . . . . . . . . . . . . . . 18 77 9.2.1. By the 6LN . . . . . . . . . . . . . . . . . . . . . 19 78 9.2.2. By the 6LR . . . . . . . . . . . . . . . . . . . . . 20 79 9.2.3. By the RPL Root . . . . . . . . . . . . . . . . . . . 22 80 9.2.4. By the 6LBR . . . . . . . . . . . . . . . . . . . . . 23 81 10. Protocol Operations for Multicast Addresses . . . . . . . . . 23 82 11. Implementation Status . . . . . . . . . . . . . . . . . . . . 25 83 12. Security Considerations . . . . . . . . . . . . . . . . . . . 25 84 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 85 13.1. RPL Target Option Flags . . . . . . . . . . . . . . . . 26 86 13.2. New Subsubregistry for the RPL Non-Rejection Status 87 values . . . . . . . . . . . . . . . . . . . . . . . . . 26 88 13.3. New Subsubregistry for the RPL Rejection Status 89 values . . . . . . . . . . . . . . . . . . . . . . . . . 26 90 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26 91 15. Normative References . . . . . . . . . . . . . . . . . . . . 27 92 16. Informative References . . . . . . . . . . . . . . . . . . . 29 93 Appendix A. Example Compression . . . . . . . . . . . . . . . . 30 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 96 1. Introduction 98 The design of Low Power and Lossy Networks (LLNs) is generally 99 focused on saving energy, which is the most constrained resource of 100 all. Other design constraints, such as a limited memory capacity, 101 duty cycling of the LLN devices and low-power lossy transmissions, 102 derive from that primary concern. 104 The IETF produced the "Routing Protocol for Low Power and Lossy 105 Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services 106 within such constraints. RPL is a Distance-Vector protocol, which, 107 compared to link-state protocols, limits the amount of topological 108 knowledge that needs to be installed and maintained in each node. In 109 order to operate in constrained networks, RPL allows a Routing 110 Stretch (see [RFC6687]), whereby routing is only performed along a 111 DODAG as opposed to straight along a shortest path between 2 peers, 112 whatever that would mean in a given LLN. This trades the quality of 113 peer-to-peer (P2P) paths for a vastly reduced amount of control 114 traffic and routing state that would be required to operate a any-to- 115 any shortest path protocol. Finally, broken routes may be fixed 116 lazily and on-demand, based on dataplane inconsistency discovery, 117 which avoids wasting energy in the proactive repair of unused paths. 119 In order to cope with lossy transmissions, RPL forms Direction- 120 Oriented Directed Acyclic Graphs (DODAGs) using DODAG Information 121 Solicitation (DIS) and DODAG Information Object (DIO) messages. For 122 most of the nodes, though not all, a DODAG provides multiple 123 forwarding solutions towards the Root of the topology via so-called 124 parents. RPL is designed to adapt to fuzzy connectivity, whereby the 125 physical topology cannot be expected to reach a stable state, with a 126 lazy control that creates routes proactively but only fixes them when 127 they are used by actual traffic. The result is that RPL provides 128 reachability for most of the LLN nodes, most of the time, but may not 129 really converge in the classical sense. RPL provides unicast and 130 multicast routing services back to RPL-Aware nodes (RANs). A RAN 131 will inject routes to itself using Destination Advertisement Object 132 (DAO) messages sent to either parent-nodes in Storing Mode or to the 133 Root indicating their parent in Non-Storing Mode. This process 134 effectively forms a DODAG back to the device that is a subset of the 135 DODAG to the Root with all links reversed. 137 When a routing protocol such as RPL is used to maintain reachability 138 within a Non-Broadcast Multi-Access (NBMA) subnet, some nodes may act 139 as routers and participate to the routing operations whereas others 140 may be plain hosts. In [RFC6550] terms, a host that is reachable 141 over the RPL network is called a Leaf. 143 "When to use RFC 6553, 6554 and IPv6-in-IPv6" [USEofRPLinfo] 144 introduces the term RPL-Aware-Leaf (RAL) for a leaf that injects 145 routes in RPL to manage the reachability of its own IPv6 addresses. 146 In contrast, a RPL-Unaware Leaf (RUL) designates a leaf does not 147 participate to RPL at all. In that case, the 6LN is a plain host 148 that needs an interface to its RPL router to obtain routing services 149 over the LLN. This specification enables a RPL-Unaware Leaf (RUL) to 150 announce itself as a host and request that 6LRs that accept the 151 registration also inject the relevant routing information for the 152 Registered Address in the RPL domain on its behalf. The unicast 153 packet forwarding operation by the 6LR serving a Leaf 6LN is 154 described in [USEofRPLinfo]. 156 Examples of routing-agnostic 6LN may include lightly-powered sensors 157 such as window smash sensor (alarm system), or the kinetically 158 powered light switch. Other application of this specification may 159 include a smart grid network that controls appliances - such as 160 washing machines or the heating system - in the home. Applicances 161 may not participate to the RPL protocol operated in the smart grid 162 network but can still receive control packet from the smart grid. 164 2. Terminology 166 2.1. BCP 14 168 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 169 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 170 "OPTIONAL" in this document are to be interpreted as described in BCP 171 14 [RFC2119][RFC8174] when, and only when, they appear in all 172 capitals, as shown here. 174 2.2. References 176 The Terminology used in this document is consistent with and 177 incorporates that described in Terms Used in Routing for Low-Power 178 and Lossy Networks (LLNs). [RFC7102]. 180 A glossary of classical 6LoWPAN acronyms is given in Section 2.3. 182 The term "byte" is used in its now customary sense as a synonym for 183 "octet". 185 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 186 a RPLInstanceID)are defined in "RPL: IPv6 Routing Protocol for 187 Low-Power and Lossy Networks" [RFC6550] . The DODAG Information 188 Solicitation (DIS), Destination Advertisement Object (DAO) and DODAG 189 Information Object (DIO) messages are also specified in [RFC6550]. 191 The Destination Cleanup Object (DCO) message is defined in 192 [EFFICIENT-NPDAO]. 194 This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware 195 Leaf (RAL) consistently with [USEofRPLinfo]. The term RPL-Aware Node 196 (RAN) is introduced to refer to a node that is either a RAL or a RPL 197 router. As opposed to a RUL, a RAN manages the reachability of its 198 addresses and prefixes by injecting them in RPL by itself. 200 Other terms in use in LLNs are found in Terminology for 201 Constrained-Node Networks [RFC7228]. 203 Readers are expected to be familiar with all the terms and concepts 204 that are discussed in 206 * "Neighbor Discovery for IP version 6" [RFC4861], 208 * "IPv6 Stateless Address Autoconfiguration" [RFC4862], 210 * "Problem Statement and Requirements for IPv6 over Low-Power 211 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], 213 * "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 214 Overview, Assumptions, Problem Statement, and Goals" [RFC4919], 216 * "Neighbor Discovery Optimization for Low-power and Lossy Networks" 217 [RFC6775], and 219 * "Registration Extensions for IPv6 over Low-Power Wireless Personal 220 Area Network (6LoWPAN) Neighbor Discovery" [RFC8505]. 222 2.3. Glossary 224 This document often uses the following acronyms: 226 AR: Address Resolution (aka Address Lookup) 228 6LBR: 6LoWPAN Border Router 230 6LN: 6LoWPAN Node (a Low Power host or router) 232 6LR: 6LoWPAN Router 234 6CIO: Capability Indication Option 236 (E)ARO: (Extended) Address Registration Option 237 (E)DAR: (Extended) Duplicate Address Request 239 (E)DAC: (Extended) Duplicate Address Confirmation 241 DAD: Duplicate Address Detection 243 DAO: Destination Advertisement Object 245 DCO: Destination Cleanup Object 247 DIS: DODAG Information Solicitation 249 DIO: DODAG Information Object 251 DODAG: Destination-Oriented Directed Acyclic Graph 253 LLN: Low-Power and Lossy Network 255 NA: Neighbor Advertisement 257 NCE: Neighbor Cache Entry 259 ND: Neighbor Discovery 261 NDP: Neighbor Discovery Protocol 263 NS: Neighbor Solicitation 265 RA: Router Advertisement 267 ROVR: Registration Ownership Verifier 269 RPI: RPL Packet Information (an Option in the Hop-By_Hop Header) 271 RAL: RPL-Aware Leaf 273 RAN: RPL-Aware Node (either a RPL router or a RPL-Aware Leaf) 275 RUL: RPL-Unaware Leaf 277 TID: Transaction ID (a sequence counter in the EARO) 279 3. 6LoWPAN Neighbor Discovery 280 3.1. RFC 6775 282 The "IPv6 Neighbor Discovery (IPv6 ND) Protocol" (NDP) suite 283 [RFC4861] [RFC4862] was defined for transit media such a Ethernet, 284 and relies heavily on multicast operations for address discovery and 285 duplicate address detection (DAD). 287 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 288 (6LoWPAN ND) adapts IPv6 ND for operations over energy-constrained 289 LLNs. In particular, 6LoWPAN ND introduces a unicast host address 290 registration mechanism that contributes to reducing the use of 291 multicast messages that are present in the classical IPv6 ND 292 protocol. 6LoWPAN ND defines a new Address Registration Option (ARO) 293 that is carried in the unicast Neighbor Solicitation (NS) and 294 Neighbor Advertisement (NA) messages between the 6LoWPAN Node (6LN) 295 and the 6LoWPAN Router (6LR). 297 6LoWPAN ND also defines the Duplicate Address Request (DAR) and 298 Duplicate Address Confirmation (DAC) messages between the 6LR and the 299 6LoWPAN Border Router (6LBR). In an LLN, the 6LBR is the central 300 repository of all the Registered Addresses in its domain. 302 The main functions of [RFC6775] are to proactively establish the 303 Neighbor Cache Entry in the 6LR and to avoid address duplication. 304 There is no concept of registering the address for an external 305 service such as RPL routing. That feature is introduced with 306 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]. 308 3.2. RFC 8505 Extended ARO 310 [RFC8505] updates the behavior of RFC 6775 to enable a generic 311 registration to services such as routing, and defines an Extended 312 Address Registration Option (EARO). The format of the EARO is shown 313 in Figure 1: 315 0 1 2 3 316 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 1 317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 318 | Type | Length | Status | Opaque | 319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 320 | Rsvd | I |R|T| TID | Registration Lifetime | 321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 322 | | 323 ... Registration Ownership Verifier ... 324 | | 325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 Figure 1: EARO Option Format 329 3.2.1. R Flag 331 [RFC8505] introduces the R flag in the EARO. The Registering Node 332 sets the R flag to indicate whether the 6LR should ensure 333 reachability for the Registered Address, e.g., by means of routing or 334 proxying ND. If the R flag is not set, then the Registering Node is 335 expected to be a RAN that handles the reachability of the Registered 336 Address by itself. 338 This document specifies how the R flag is used in the context of RPL. 339 A 6LN operates as a RUL for an IPv6 address iff it sets the R flag in 340 the NS(EARO) used to register the address. The RPL router generates 341 a DAO message for the Registered Address upon an NS(EARO) iff the R 342 flag in the EARO is set. Conversely, this document specifies a 343 behavior of a RPL router acting as 6LR for the registration 6LR that 344 depends on the setting of the R flag in the NS(EARO). 346 3.2.2. TID, I Field and Opaque Fields 348 The EARO also includes a sequence counter called Transaction ID 349 (TID), which maps to the Path Sequence Field found in Transit Options 350 in RPL DAO messages. This is the reason why the support of [RFC8505] 351 by the RUL as opposed to only [RFC6775] is a prerequisite for this 352 specification (more in Section 6.1). The EARO also transports an 353 Opaque field and an "I" field that describes what the Opaque field 354 transports and how to use it. Section 9.2.1 specifies the use of the 355 "I" field and of the Opaque field by a RUL. 357 3.2.3. ROVR 359 Section 5.3. of [RFC8505] introduces the Registration Ownership 360 Verifier (ROVR) field of a variable length from 64 to 256 bits. The 361 ROVR is a replacement of the EUI-64 field in the ARO [RFC6775] that 362 was used to identify uniquely a registration based on the Link-Layer 363 address of the owner but provided no protection against spoofing. 365 "Address Protected Neighbor Discovery for Low-power and Lossy 366 Networks" [AP-ND] leverages the ROVR field as a cryptographic proof 367 of ownership to prevent a rogue third party from misusing the 368 address. [AP-ND] adds a challenge/response exchange to the [RFC8505] 369 registration and enables Source Address Validation by a 6LR that will 370 drop packets with a spoofed address. 372 This specification does not address how the protection by [AP-ND] 373 could be extended to RPL. On the other hand, it adds the ROVR to the 374 DAO to build the proxied EDAR at the Root, which means that nodes 375 that are aware of the host route to the 6LN are now aware of the 376 associated ROVR as well. 378 3.3. RFC 8505 Extended DAR/DAC 380 [RFC8505] updates the periodic DAR/DAC exchange that takes place 381 between the 6LR and the 6LBR using Extended DAR/DAC messages. The 382 Extended Duplicate Address messages can carry the ROVR field of 383 variable size. The periodic EDAR/EDAC exchange is triggered by a 384 NS(EARO) message and is intended to create and then refresh the 385 corresponding state in the 6LBR for a lifetime that is indicated by 386 the 6LN. Conversely, RPL [RFC6550] specifies a periodic DAO from the 387 6LN all the way to the Root that maintains the routing state in the 388 RPL network for a lifetime that is indicated by the source of the 389 DAO. This means that there are two periodic messages that traverse 390 the whole network to indicate that an address is still reachable, one 391 to the Root and one to the 6LBR. This represents a waste of 392 bandwidth and energy that can be undesirable in an LLN. 394 This specification saves the support of RPL in a 6LN called a RUL and 395 avoids an extraneous periodic flow across the LLN. The RUL only 396 needs to perform a [RFC8505] registration to the 6LR. The 6LR turns 397 it into a DAO message to the Root on behalf of the RUL. Upon the new 398 DAO, the Root proxies the EDAR exchange to the 6LBR on behalf of the 399 6LR. This is illustrated in Figure 5. 401 4. Updating RFC 6550 403 This document specifies a new behavior whereby a 6LR injects DAO 404 messages for unicast addresses (see Section 9) and multicast 405 addresses (see Section 10) on behalf of leaves that are not aware of 406 RPL. The Targets are exposed as External addresses. An IP-in-IP 407 encapsulation that terminates at the border 6LR is used to remove RPL 408 artifacts and compression techniques that may not be processed 409 correctly outside of the RPL domain. 411 This document synchronizes the liveness monitoring at the Root and 412 the 6LBR. A same value of lifetime is used for both, and a single 413 keep alive message, the RPL DAO, traverses the RPL network. A new 414 behavior is introduced whereby the RPL Root proxies the EDAR message 415 to the 6LBR on behalf of the 6LR (more in Section 5). 417 The RPL Status defined in section 6.5.1. of [RFC6550] for use in the 418 DAO-Ack message is extended to be used in the DCO messages 419 [EFFICIENT-NPDAO] as well. Furthermore, this specification enables 420 to use a RPL status to transport the IPv6 ND status defined for use 421 in the EARO, more in Section 7. 423 Section 6.7. of [RFC6550] introduces the RPL Control Message Options 424 such as the RPL Target Option that can be included in a RPL Control 425 Message such as the DAO. Section 8 updates the RPL Target Option to 426 optionally transport the ROVR used in the IPv6 Registration (see 427 Section 3.2.3) so the RPL Root can generate a full EDAR Message. 429 5. Updating RFC 8505 431 This document updates [RFC8505] to introduce a keep-alive EDAR 432 message and a keep-alive NS(EARO) message. The keep-alive messages 433 are used for backward compatibility, when the DAO does not transport 434 a ROVR as specified in Section 8. The keep-alive messages have a 435 zero ROVR field and can only be used to refresh a pre-existing state 436 associated to the Registered Address. More specifically, a keep- 437 alive message can only increase the lifetime and/or increment the TID 438 of the existing state in a 6LBR. 440 Upon the renewal of a 6LoWPAN ND registration, this specification 441 changes the behavior of a RPL router acting as 6LR for the 442 registration as follows. If the Root indicates the capability to 443 proxy the EDAR/EDAC exchange to the 6LBR then the 6LR refrains from 444 sending an EDAR message; if the Root is separated from the 6LBR, the 445 Root regenerates the EDAR message to the 6LBR upon a DAO message that 446 signals the liveliness of the Address. 448 6. 6LN Requirements to be a RPL-Unware Leaf 450 This document provides RPL routing for a RUL, that is a 6LN acting as 451 a plain host and not aware of RPL. Still, a minimal RPL-independent 452 functionality is expected from the 6LN in order to obtain routing 453 services from the 6LR. 455 6.1. Support of 6LoWPAN ND 457 A RUL MUST implement [RFC8505] and set the R flag in the EARO option. 458 A 6LN is considered to be a RUL if and only if it sets the R flag in 459 the EARO. 461 A RUL MUST register to all the 6LRs from which it expects to get 462 routing services. The registrations SHOULD be performed in a rapid 463 sequence, using the exact same EARO for a same Address. Gaps between 464 the registrations will invalidate some of the routes till the 465 registration finally shows on those routes as well. 467 [RFC8505] introduces error Status values in the NA(EARO) which can be 468 received synchronously upon an NS(EARO) or asynchronously. The RUL 469 MUST support both cases and refrain from using the Registered Address 470 as specified by [RFC8505] depending on the Status value. 472 A RUL SHOULD support [AP-ND] to protect the ownership of its 473 addresses. 475 6.2. External Routes and RPL Artifacts 477 Section 4.1. of [USEofRPLinfo] provides a set of rules that MUST be 478 followed when forwarding packets over an external route: 480 RPL data packets are often encapsulated using IP-in-IP and in Non- 481 Storing Mode, packets going down will carry an SRH as well. RPL data 482 packets also typically carry a Hop-by-Hop Header to transport a RPL 483 Packet Information (RPI) [RFC6550]. These additional headers are 484 called RPL artifacts. When IP-in-IP is used and the outer headers 485 terminate at a 6LR down the path (see Figure 9 for the compressed 486 format in Storing Mode), then the 6LR decapsulates the IP-in-IP and 487 the packet that is forwarded to the external destination is free of 488 RPL artifacts - but possibly an RPI if packet was generated by a RAN 489 in the same RPL domain as the destination RUL. 491 Non-Storing Mode DAO messages are used to signal external routes to 492 the Root, even if the DODAG is operated in Storing Mode. This 493 enables to advertise the 6LR that injects the route for use as tunnel 494 endpoint in the data path. For all external routes, the Root should 495 use an IP-in-IP tunnel to that 6LR, with the RPL artifacts in the 496 outer header to be stripped by the 6LR. The IP-in-IP encapsulation 497 may be avoided in Storing Mode if the path to the external 498 destination beyond the 6LR is known to handle or ignore the RPL 499 artifacts properly [RFC8200]. A RUL is an example of a destination 500 that is reachable via an external (host) route for which IP-in-IP 501 tunneling may be avoided as it ignores the RPI and the consumed SRH 502 artifacts. The use of non-Storing Mode signaling in Storing Mode and 503 the associated IP-in-IP encapsulation are transparent to intermediate 504 routers that only see packets back and forth between the Root and the 505 6LR and do not need a special support for external routes. 507 A RUL may not support IP-in-IP tunneling [RFC8504], so if IP-in-IP is 508 used, and unless the Root as a better knowledge, the tunnel should 509 terminate at the 6LR that injected the external route to the RUL. 511 Additionally, the RUL is not expected to support the compression 512 method defined in [RFC8138]. The 6LR that injected the route should 513 uncompress the packet before forwarding over an external route, even 514 when delivering to a RUL, even when it is not the destination in the 515 outer header of the incoming packet. 517 6.2.1. Support of the HbH Header 519 A RUL is expected to process an unknown Option Type in a Hop-by-Hop 520 Header as prescribed by section 4.2 of [RFC8200]. This means in 521 particular that an RPI with an Option Type of 0x23 [USEofRPLinfo] is 522 ignored when not understood. 524 6.2.2. Support of the Routing Header 526 A RUL is expected to process an unknown Routing Header Type as 527 prescribed by section 4.4 of [RFC8200]. This means in particular 528 that Routing Header with a Routing Type of 3 [RFC6553] is ignored 529 when the Segments Left is zero, and dropped otherwise. 531 6.2.3. Support of IPv6 Encapsulation 533 Section 2.1 of [USEofRPLinfo] sets the rules for forwarding IP-in-IP 534 either to the final 6LN or to a parent 6LR. In order to enable IP- 535 in-IP to the 6LN in Non-Storing Mode, the 6LN must be able to 536 decapsulate the tunneled packet and either drop the inner packet if 537 it is not the final destination, or pass it to the upper layer for 538 further processing. Unless it is aware that the RUL can handle IP- 539 in-IP properly, the Root that encapsulates a packet to a RUL 540 terminates the IP-in-IP tunnel at the parent 6LR . For that reason, 541 it is beneficial but not necessary for a RUL to support IP-in-IP. 543 7. Updated RPL Status 545 The RPL Status is defined in section 6.5.1. of [RFC6550] for use in 546 the DAO-Ack message and values are assigned as follows: 548 +---------+--------------------------------+ 549 | Range | Meaning | 550 +=========+================================+ 551 | 0 | Success/Unqualified acceptance | 552 +---------+--------------------------------+ 553 | 1-127 | Not an outright rejection | 554 +---------+--------------------------------+ 555 | 128-255 | Rejection | 556 +---------+--------------------------------+ 558 Table 1: RPL Status per RFC 6550 560 This specification extends the scope of the RPL status to be used in 561 RPL DCO messages. Furthermore, this specification enables to carry 562 the status values defined for use in the IPv6 ND Extended Address 563 Registration Option (EARO) and listed in table 1 of [RFC8505] in a 564 RPL status. Only EARO status values in the range 0-63 can be 565 transported. 567 The resulting RPL status is as follows: 569 0 570 0 1 2 3 4 5 6 7 571 +-+-+-+-+-+-+-+-+ 572 |E|A| Value | 573 +-+-+-+-+-+-+-+-+ 575 Figure 2: RPL status Format 577 RPL Status subfields: 579 E: 1-bit flag. Set to indicate a rejection. When not set, a value 580 of 0 indicates Success/Unqualified acceptance and other values 581 indicate "not an outright rejection" as per RFC 6550. 583 A: 1-bit flag. Indicates the type of the status value. 585 Status Value: 6-bit unsigned integer. If the 'A' flag is set this 586 field transports a status value defined for IPv6 ND EARO. When 587 the 'A' flag is not set, the status value is defined in a RPL 588 extension. 590 When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a DAC 591 message, the RPL Root MUST copy the ARO status unchanged in a RPL 592 status with the 'A' bit set. Conversely the 6LR MUST copy the value 593 of the RPL status unchanged in the EARO of an NA message that is 594 built upon a RPL status with the 'A' bit set in a DCO or a DAO-ACK 595 message. 597 8. Updated RPL Target option 599 This specification updates the RPL Target option to transport the 600 ROVR as illustrated in Figure 3. This enables the RPL Root to 601 generate a full EDAR Message as opposed to a keep-alive EDAR that has 602 restricted properties. The Target Prefix MUST be aligned to the next 603 4-byte boundary after the size indicated by the Prefix Length. if 604 necessary it is padded with zeros. The size of the ROVR is indicated 605 in a new ROVR Type field that is encoded to map the CodePfx in the 606 EDAR message (see section 4.2 of [RFC8505]). With this specification 607 the ROVR is the remainder of the RPL Target Option. 609 0 1 2 3 610 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 1 611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 612 | Type = 0x05 | Option Length |ROVRsz | Flags | Prefix Length | 613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 614 | | 615 + + 616 | Target Prefix (Variable Length) | 617 . Aligned to 4-byte boundary . 618 . . 619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 620 | | 621 ... Registration Ownership Verifier (ROVR) ... 622 | | 623 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 625 Figure 3: Updated Target Option 627 New fields: 629 RVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4, 630 denoting a ROVR size of 64, 128, 192, or 256 bits, respectively. 632 Registration Ownership Verifier (ROVR): This is the same field as in 633 the EARO, see [RFC8505] 635 9. Protocol Operations for Unicast Addresses 637 9.1. General Flow 639 This specification enables to save the exchange of Extended Duplicate 640 Address messages, EDAR and EDAC, from a 6LN all the way to the 6LBR 641 across a RPL mesh, for the sole purpose of refreshing an existing 642 state in the 6LBR. Instead, the EDAR/EDAC exchange is proxied by the 643 RPL Root upon a DAO message that refreshes the RPL routing state. To 644 achieve this, the lifetimes and sequence counters in 6LoWPAN ND and 645 RPL are aligned. In other words, the Path Sequence and the Path 646 Lifetime in the DAO message are taken from the Transaction ID and the 647 registration lifetime in the NS(EARO) message from the 6LN. 649 In that flow, the RPL Root acts as a proxy to refresh the state in 650 the 6LBR. The proxy operation applies to both RUL and RAN. This 651 means that in a RPL network where the function is enabled, refreshing 652 the state in the 6LBR is the responsibility of the Root. 653 Consequently, only addresses that are injected in RPL will be kept 654 alive by the RPL Root. If an additional routing protocol is deployed 655 on a same network, that additional routing protocol may need to 656 handle the keep alive procedure for the addresses that it serves. 658 From the perspective of the 6LN, the registration flow happens 659 transparently; it is not delayed by the proxy RPL operation, so the 660 device does not need to change the amount of time it waits based upon 661 whether RPL proxy operation happens or not. 663 On the first registration, illustrated in Figure 4, from the 664 perspective of the 6LR in Non-Storing Mode, the Extended Duplicate 665 Address message takes place as prescribed by [RFC8505]. When 666 successful, the flow creates a Neighbor Cache Entry (NCE) in the 6LR, 667 and the 6LR injects the Registered Address in RPL using DAO/DAO-ACK 668 exchanges all the way to the RPL DODAG Root. The protocol does not 669 carry a specific information that the Extended Duplicate Address 670 messages were already exchanged, so the Root proxies them anyway. 672 Note that any of the functions 6LR, Root and 6LBR might be collapsed 673 in a single node, in which case the flow above happens internally, 674 and possibly through internal API calls as opposed to messaging. 676 9.1.1. In RPL Non-Storing-Mode 678 In Non-Storing Mode, the flows can be nested as illustrated in 679 Figure 4 and it is possible to carry information such as an updated 680 lifetime from the 6LBR all the way to the 6LN. 682 6LN 6LR Root 6LBR 683 | | | | 684 | NS(EARO) | | | 685 |--------------->| | 686 | | Extended DAR | 687 | |-------------------------------->| 688 | | | 689 | | Extended DAC | 690 | |<--------------------------------| 691 | | DAO | | 692 | |-------------->| | 693 | | | keep-alive EDAR | 694 | | |---------------->| 695 | | | EDAC | 696 | | |<----------------| 697 | | DAO-ACK | | 698 | |<--------------| | 699 | NA(EARO) | | 700 |<---------------| | | 701 | | | | 702 (in case if an Error not reported in DAO-ACK) 703 | | | | 704 | | DCO | | 705 | |<--------------| | 706 | NA(EARO) | | | 707 |<---------------| | | 708 | | | | 710 Figure 4: First Registration Flow in Non-Storing Mode 712 A re-registration is performed by the 6LN to maintain the NCE in the 713 6LR alive before lifetime expires. Upon a re-registration, as 714 illustrated in Figure 5, the 6LR redistributes the Registered Address 715 NS(EARO) in RPL. 717 This causes the RPL DODAG Root to refresh the state in the 6LBR with 718 a keep-alive EDAC message. The keep-alive EDAC lacks the 719 Registration Ownership Verifier (ROVR) information, since it is not 720 present in RPL DAO messages, but the EDAC message sent in response by 721 the 6LBR contains the actual value of the ROVR field for that 722 registration. 724 6LN 6LR Root 6LBR 725 | | | | 726 | | | | 727 | NS(EARO) | | | 728 |--------------->| | | 729 | | DAO | | 730 | |-------------->| | 731 | | | keep-alive EDAR | 732 | | |---------------->| 733 | | | EDAC | 734 | | |<----------------| 735 | | DAO-ACK | | 736 | |<--------------| | 737 | NA(EARO) | | 738 |<---------------| | | 739 | | | | 740 | | | | 742 Figure 5: Next Registration Flow in Non-Storing Mode 744 In case of an error on the keep-alive EDAR flow, the error SHOULD be 745 returned in the DAO-ACK - if one was requested - using the mapping of 746 RPL Status and 6LoWPAN Status values discussed in Section 4. 748 If the Root could not return the negative Status in the DAO-ACK then 749 it sends an asynchronous Destination Cleanup Object (DCO) message 750 [EFFICIENT-NPDAO] to the 6LR placing the negative Status in the RPL 751 status with the 'A' flag set. Note that if both are used in a short 752 interval of time, the DAO-ACK and DCO messages are not guaranteed to 753 arrive in the same order at the 6LR. So the 6LR must still expect a 754 DAO-ACK even if it received a DCO while it was waiting for an 755 acknowledgement for a short period of time, but the negative status 756 in the DCO supercedes a positive status in the DAO-ACK regardless of 757 the order in which they are received. 759 Upon the DAO-ACK - or the DCO if it arrives first - the 6LR responds 760 to the RUL with a NA(EARO) and the 6LoWPAN ND Status value that is 761 copied from the RPL status in the RPL message. An asynchronous DCO 762 is also translated in an asynchronous NA(EARO) to the RUL with a 763 copied Status value. The RPL Status values that are copied with 764 6LoWPAN ND are in the range 128 to 192 and listed in the same order 765 (see Table 2). A RPL Status Value of 128 maps to 6LoWPAN ND Status 766 Code of 1 and so on. 768 9.1.2. In RPL Storing-Mode 770 In Storing Mode, the DAO-ACK is optional. When it is used, it is 771 generated by the RPL parent, which does not need to wait for the 772 grand-parent to send the acknowledgement. A successful DAO-ACK is 773 not a guarantee that the DAO has yet reached the Root or that the 774 keep-alive EDAR has succeeded. 776 If the keep alive fails, the path is cleaned up asynchronously using 777 a DCO message [EFFICIENT-NPDAO] as illustrated in Figure 6 and 778 described in further details in Section 9.2.3. 780 6LN 6LR 6LR Root 6LBR 781 | | | | | 782 | NS(EARO) | | | | 783 |-------------->| | | | 784 | NA(EARO) | | | | 785 |<--------------| | | | 786 | | | | | 787 | | DAO | | | 788 | |-------------->| | | 789 | | DAO-ACK | | | 790 | |<--------------| | | 791 | | | | | 792 | | | DAO | | 793 | | |-------------->| | 794 | | | DAO-ACK | | 795 | | |<--------------| | 796 | | | | | 797 | | | | keep-alive EDAR | 798 | | | |---------------->| 799 | | | | EDAC(ROVR) | 800 | | | |<----------------| 801 | | | | | 802 (in case if an Error) 803 | | | | | 804 | | DCO | | 805 | |<------------------------------| | 806 | NA(EARO) | | | | 807 |<--------------| | | | 808 | | | | | 810 Figure 6: Next Registration Flow in Storing Mode 812 9.2. Operation 813 9.2.1. By the 6LN 815 This specification does not alter the operation of a 6LoWPAN ND- 816 compliant 6LN, and a RUL is expected to operate as follows: 818 * The 6LN obtains an IPv6 global address, for instance using 819 autoconfiguration [RFC4862] based on a Prefix Information Option 820 (PIO) [RFC4861] found in a Router Advertisement message or by some 821 other means such as DHCPv6 [RFC3315]. 823 * Once it has formed an address, the 6LN (re)registers its address 824 periodically, within the Lifetime of the previous registration, as 825 prescribed by [RFC6775]. 827 * A 6LN acting as a RUL sets the R flag in the EARO whereas a 6LN 828 acting as a RAN does not set the R flag as prescribed by [RFC8505] 829 section 5.1. 831 * Upon each consecutive registration, the 6LN increases the TID 832 field in the EARO, as prescribed by [RFC8505] section 5.2. 834 * The 6LN can register to more than one 6LR at the same time. In 835 that case, a same value of TID is used for each registration. 837 * The 6LN may use any of the 6LRs to which it register to forward 838 its packets. Using a 6LR to which the 6LN is not registered may 839 result in packets dropped by a Source Address Validation function. 841 Even without support for RPL, a RUL may be aware of opaque values to 842 be provided to the routing protocol. If the RUL has a knowledge of 843 the RPL Instance the packet should be injected into, then it SHOULD 844 set the Opaque field in the EARO to the RPLInstanceID, else it MUST 845 leave the Opaque field to zero. In any fashion the 6LN MUST set the 846 "I" field to zero to indicate that topological information to be 847 passed to a routing process as specified in [RFC8505] section 5.1. 849 A RUL is not expected to produce RPL artifacts in the data packets, 850 but it MAY do so. for instance, if the RUL has a minimal awareness of 851 the RPL Instance and can build an RPI. A RUL that places an RPI in a 852 data packet MUST indicate the RPLInstanceID that corresponds to the 853 RPL Instance the packet should be injected into. All the flags and 854 the Rank field are set to zero as specified by section 11.2 of 855 [RFC6550]. 857 9.2.2. By the 6LR 859 Also as prescribed by [RFC8505], the 6LR generates a DAR message upon 860 reception of a valid NS(EARO) message for the registration of a new 861 IPv6 Address by a 6LN. If the Duplicate Address exchange succeeds, 862 then the 6LR installs a Neighbor Cache Entry (NCE). If the R flag 863 was set in the EARO of the NS message, and this 6LR can manage the 864 reachability of Registered Address, then the 6LR sets the R flag in 865 the EARO of the NA message that is sent in response. 867 From then on, the 6LN periodically sends a new NS(EARO) to refresh 868 the NCE state before the lifetime indicated in the EARO expires, with 869 TID that is incremented each time till it wraps in a lollipop fashion 870 (see section 5.2.1 of [RFC8505] which is fully compatible with 871 section 7.2 of [RFC6550]). As long as the R flag is set and this 872 router can still manage the reachability of Registered Address, the 873 6LR keeps setting the R flag in the EARO of the response NA message, 874 but the exchange of Extended Duplicate Address messages is skipped. 876 The Opaque field in the EARO hints the 6LR on the RPL Instance that 877 should be used for the DAO advertisements, and for the forwarding of 878 packets sourced at the registered address when there is no RPL Packet 879 Information (RPI) in the packet, in which case the 6LR SHOULD add one 880 to the packet. if the "I" field is not zero, then the 6LR MUST 881 consider that the Opaque field is zero. If the Opaque field is not 882 set to zero, then it should carry a RPLInstanceID for the Instance 883 suggested by the 6LN. If the 6LR does not participate to the 884 associated Instance, then the 6LR MUST consider that the Opaque field 885 is empty. If the Opaque field is empty, the 6LR is free to use the 886 default Instance (zero) for the registered address or to select an 887 Instance of its choice; else, that is if the 6LR participates to the 888 suggested Instance, then the 6LR SHOULD use that Instance for the 889 registered address. 891 Upon a successful NS/NA(EARO) exchange: if the R flag was set in the 892 EARO of the NS message, then the 6LR SHOULD inject the Registered 893 Address in RPL by sending a DAO message on behalf of the 6LN; else 894 the 6LR MUST NOT inject the Registered Address into RPL. 896 The DAO message advertising the Registered Address MUST be 897 constructed as follows: 899 * The Registered Address is placed in a RPL Target Option in the DAO 900 message as the Target Prefix, and the Prefix Length is set to 128; 902 * the External 'E' flag in the Transit Information Option (TIO) 903 associated to the Target Option is set to indicate that the 6LR 904 redistributes an external target into the RPL network. When the 905 Root has to use an IP-in-IP [USEofRPLinfo], then this flag 906 indicates the IP-in-IP should be addressed to this node; 908 * the Path Lifetime in the TIO is computed from the Lifetime in the 909 EARO Option to adapt it to the Lifetime Units used in the RPL 910 operation. Note that if the lifetime is 0, then the 6LR generates 911 a No-Path DAO message that cleans up the routes down to the 912 Address of the 6LN; 914 * the Path Sequence in the TIO is set to the TID value found in the 915 EARO option; 917 * Additionally, in Non-Storing Mode the 6LR indicates one of its 918 global IPv6 unicast addresses as the Parent Address in the TIO. 920 If a DAO-ACK is not requested, or has a Status that is less than 128, 921 indicating the DAO was accepted, respectively by a parent in Storing 922 Mode or by the Root in non-Storing Mode,, the 6LR replies with a 923 NA(EARO) to the RUL with a status of 0 (Success). 925 In case of a DAO-ACK or a DCO with a status of 132 (Validation 926 Requested) the 6LR challenges the 6LN for ownership of the address, 927 as described in section 6.1 of [RFC8505]. If the challenge succeeds 928 then the operations continue as normal. In particular a DAO message 929 is generated upon the NS(EARO) that proves the ownership of the 930 address. If the challenge failed the 6LR MUST refrain from injecting 931 the address in RPL and may take actions to protect itself against DoS 932 attacks by a rogue 6LN, see Section 12 934 Other status values above 128 indicate that the 6LR failed to inject 935 the address into the RPL network. In that case the the 6LR MUST send 936 a NA(EARO) to the RUL with the copied Status value. If for any other 937 reason the 6LR fails to inject the address into the RPL network, the 938 6LR SHOULD send a NA(EARO) to the RUL with a status of 2 (Out of 939 Storage) which indicates a possibility to retry later. 941 If a 6LR receives a valid NS(EARO) message with the R flag reset and 942 the 6LR was redistributing the Registered Address due to previous 943 NS(EARO) messages with the flag set, then it MUST stop injecting the 944 address. It is up to the Registering Node to maintain the 945 corresponding route from then on, either keeping it active by sending 946 further DAO messages, or destroying it using a No-Path DAO. 948 Upon a DCO message indicating that the address of a RUL should be 949 removed from the routing table, the 6LR issues an asynchronous 950 NA(EARO) to the RUL with the copied Status value. 952 9.2.3. By the RPL Root 954 In RPL Storing Mode of Operation (MOP), the DAO message is propagated 955 from child to parent all the way to the Root along the DODAG, 956 populating routing state as it goes. In Non-Storing Mode, The DAO 957 message is sent directly to the RPL Root. Upon reception of a DAO 958 message, for each RPL Target option that creates or updates an 959 existing RPL state: 961 * the Root notifies the 6LBR using an internal API if they are co- 962 located, or performs an EDAR/EDAC exchange on behalf of the 6LR if 963 they are separated. If the Target option transports a ROVR, then 964 the Root MUST use it to build a full EDAR message as the 6LR 965 would. Else, a keep-alive EDAR is used with the ROVR field set to 966 zero. 968 An EDAR message MUST be constructed as follows: 970 * The Target IPv6 address from in the RPL Target Option is placed in 971 the Registered Address field of the EDAR message and in the Target 972 field of the NS message, respectively; 974 * the Registration Lifetime is adapted from the Path Lifetime in the 975 TIO by converting the Lifetime Units used in RPL into units of 60 976 seconds used in the 6LoWPAN ND messages; 978 * the RPL Root indicates its own MAC Address as Source Link Layer 979 Address (SLLA) in the NS(EARO); 981 * the TID value is set to the Path Sequence in the TIO and indicated 982 with an ICMP code of 1 in the EDAR message; 984 * when present in the RPL Target option, the ROVR field is used as 985 is in the EDAR and the ICMP Code Suffix is set to the appropriate 986 value as shown in Table 4 of [RFC8505] depending on the length of 987 the ROVR field. If it is not present the ROVR field in the EDAR 988 is set to zero indicating that this is a keep-alive EDAR. The 989 actual value of the ROVR for that registration is expected from 990 the 6LBR in the response EDAC. 992 Upon a Status value in an EDAC message that is not "Success", the 993 Root SHOULD destroy the formed paths using either a DAO-ACK (in Non- 994 Storing Mode) or a DCO downwards as specified in [EFFICIENT-NPDAO]. 995 Failure to destroy the former path would result in Stale routing 996 state and local black holes if the address belongs to another party 997 elsewhere in the network. The RPL Status value that maps the 6LowpAN 998 ND status value MUST be placed in the DCO. 1000 9.2.4. By the 6LBR 1002 Upon reception of an EDAR message with the ROVR field is set to zero 1003 indicating a keep-alive EDAR, the 6LBR checks whether an entry exists 1004 for the and computes whether the TID in the DAR message is fresher 1005 than that in the entry as prescribed in section 4.2.1. of [RFC8505]. 1007 If the entry does not exist, the 6LBR does not create the entry, and 1008 answers with a Status "Removed" in the EDAC message. 1010 If the entry exists but is not fresher, the 6LBR does not update the 1011 entry, and answers with a Status "Success" in the EDAC message. 1013 If the entry exists and the TID in the DAR message is fresher, the 1014 6LBR updates the TID in the entry, and if the lifetime of the entry 1015 is extended by the Registration Lifetime in the DAR message, it also 1016 updates the lifetime of the entry. In that case, the 6LBR replies 1017 with a Status "Success" in the DAC message. 1019 The EDAC that is constructed is the same as if the keep-alive EDAR 1020 was a full EDAR, and includes the ROVR that is associated to the 1021 registration. 1023 10. Protocol Operations for Multicast Addresses 1025 Section 12 of [RFC6550] details the RPL support for multicast flows. 1026 This support is not source-specific and only operates as an extension 1027 to the Storing Mode of Operation for unicast packets. Note that it 1028 is the RPL model that the multicast packet is passed as a Layer-2 1029 unicast to each if the interested children. This remains true when 1030 forwarding between the 6LR and the listener 6LN. 1032 "Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its 1033 updated version "Multicast Listener Discovery Version 2 (MLDv2) for 1034 IPv6" [RFC3810] provide an interface for a listener to register to 1035 multicast flows. MLDv2 is backwards compatible with MLD, and adds in 1036 particular the capability to filter the sources via black lists and 1037 white lists. In the MLD model, the router is a "querier" and the 1038 host is a multicast listener that registers to the querier to obtain 1039 copies of the particular flows it is interested in. 1041 On the first registration, as illustrated in Figure 7, the 6LN, as an 1042 MLD listener, sends an unsolicited Report to the 6LR in order to 1043 start receiving the flow immediately. Since multicast Layer-2 1044 messages are avoided, it is important that the asynchronous messages 1045 for unsolicited Report and Done are sent reliably, for instance using 1046 an Layer-2 acknoledgement, or attempted multiple times. 1048 The 6LR acts as a generic MLD querier and generates a DAO for the 1049 multicast target. The lifetime of the DAO is set to be in the order 1050 of the Query Interval, yet larger to account for variable propagation 1051 delays. 1053 The Root proxies the MLD echange as listener with the 6LBR acting as 1054 the querier, so as to get packets from a source external to the RPL 1055 domain. Upon a DAO with a multicast target, the RPL Root checks if 1056 it is already registered as a listener for that address, and if not, 1057 it performs its own unsolicited Report for the multicast target. 1059 6LN 6LR Root 6LBR 1060 | | | | 1061 | unsolicited Report | | | 1062 |------------------->| | | 1063 | | | | 1064 | | DAO | | 1065 | |-------------->| | 1066 | | DAO-ACK | | 1067 | |<--------------| | 1068 | | | | 1069 | | | unsolicited Report | 1070 | | |------------------->| 1071 | | | | 1072 | | | | 1074 Figure 7: First Multicast Registration Flow 1076 A re-registration is pulled by 6LR acting as querier. Note that the 1077 message may sent unicast to all the known individual listeners. Upon 1078 a time out of the Query Interval, the 6LR sends a Query to each of 1079 its listeners, and gets a Report back that is mapped into a DAO, as 1080 illustrated in Figure 8, 1081 6LN 6LR Root 6LBR 1082 | | | | 1083 | Query | | | 1084 |<-------------------| | | 1085 | Report | | | 1086 |------------------->| | | 1087 | | DAO | | 1088 | |-------------->| | 1089 | | DAO-ACK | | 1090 | |<--------------| | 1091 | | | | 1092 | | | Query | 1093 | | |<-------------------| 1094 | | | Report | 1095 | | |------------------->| 1096 | | | | 1097 | | | | 1099 Figure 8: Next Registration Flow 1101 Note that any of the functions 6LR, Root and 6LBR might be collapsed 1102 in a single node, in which case the flow above happens internally, 1103 and possibly through internal API calls as opposed to messaging. 1105 11. Implementation Status 1107 12. Security Considerations 1109 The LLN nodes depend on the 6LBR and the RPL participants for their 1110 operation. A trust model must be put in place to ensure that the 1111 right devices are acting in these roles, so as to avoid threats such 1112 as black-holing, (see [RFC7416] section 7) or bombing attack whereby 1113 an impersonated 6LBR would destroy state in the network by using the 1114 "Removed" Status code. This trust model could be at a minimum based 1115 on a Layer-2 access control, or could provide role validation as 1116 well. This is a generic 6LoWPAN requirement, see Req5.1 in 1117 Appendix of [RFC8505]. 1119 The keep-alive EDAR message does not carry a valid Registration 1120 Unique ID [RFC8505] and it cannot be used to create a binding state 1121 in the 6LBR. The 6LBR MUST NOT create an entry based on a keep-alive 1122 EDAR that does not match an existing entry. All it can do is refresh 1123 the lifetime and the TID of an existing entry. 1125 At the time of this writing RPL does not have a zerotrust model 1126 whereby the it is possible to validate the origin of an address that 1127 is injected in a DAO. This specification makes a first step in that 1128 direction by allowing the Root to challenge the RUL by the 6LR that 1129 serves it. 1131 13. IANA Considerations 1133 13.1. RPL Target Option Flags 1135 Section 20.15 of [RFC6550] creates a registry for the 8-bit RPL 1136 Target Option Flags field. This specification reduces the field to 4 1137 bits. The IANA is requested to reduce the size of the registry 1138 accordingly. 1140 13.2. New Subsubregistry for the RPL Non-Rejection Status values 1142 This specification creates a new subsubregistry for the RPL Non- 1143 Rejection Status values for use in RPL DAO-ACK and RCO Messages, 1144 under the ICMPv6 parameters registry. 1146 * Possible values are 6-bit unsigned integers (0..63). 1148 * Registration procedure is "Standards Action" [RFC8126]. 1150 * Initial allocation is as indicated in Table 2: 1152 +-------+------------------------+---------------+ 1153 | Value | Meaning | Defining Spec | 1154 +=======+========================+===============+ 1155 | 0 | Unqualified acceptance | RFC 6550 | 1156 +-------+------------------------+---------------+ 1158 Table 2: Status values of the RPL DAO-ACK Message 1160 13.3. New Subsubregistry for the RPL Rejection Status values 1162 This specification creates a new subsubregistry for the RPL Non- 1163 Rejection Status values for use in RPL DAO-ACK and RCO Messages, 1164 under the ICMPv6 parameters registry. 1166 * Possible values are 6-bit unsigned integers (0..63). 1168 * Registration procedure is "Standards Action" [RFC8126]. 1170 * There is no initial allocation 1172 14. Acknowledgments 1174 The authors wish to thank Georgios Papadopoulos for their early 1175 reviews of and contributions to this document 1177 15. Normative References 1179 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1180 Requirement Levels", BCP 14, RFC 2119, 1181 DOI 10.17487/RFC2119, March 1997, 1182 . 1184 [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast 1185 Listener Discovery (MLD) for IPv6", RFC 2710, 1186 DOI 10.17487/RFC2710, October 1999, 1187 . 1189 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1190 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1191 DOI 10.17487/RFC3810, June 2004, 1192 . 1194 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1195 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1196 Overview, Assumptions, Problem Statement, and Goals", 1197 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1198 . 1200 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1201 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1202 DOI 10.17487/RFC4861, September 2007, 1203 . 1205 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1206 Address Autoconfiguration", RFC 4862, 1207 DOI 10.17487/RFC4862, September 2007, 1208 . 1210 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1211 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1212 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1213 Low-Power and Lossy Networks", RFC 6550, 1214 DOI 10.17487/RFC6550, March 2012, 1215 . 1217 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1218 Power and Lossy Networks (RPL) Option for Carrying RPL 1219 Information in Data-Plane Datagrams", RFC 6553, 1220 DOI 10.17487/RFC6553, March 2012, 1221 . 1223 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 1224 Statement and Requirements for IPv6 over Low-Power 1225 Wireless Personal Area Network (6LoWPAN) Routing", 1226 RFC 6606, DOI 10.17487/RFC6606, May 2012, 1227 . 1229 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1230 Bormann, "Neighbor Discovery Optimization for IPv6 over 1231 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1232 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1233 . 1235 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1236 Writing an IANA Considerations Section in RFCs", BCP 26, 1237 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1238 . 1240 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 1241 "IPv6 over Low-Power Wireless Personal Area Network 1242 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 1243 April 2017, . 1245 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1246 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1247 May 2017, . 1249 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1250 (IPv6) Specification", STD 86, RFC 8200, 1251 DOI 10.17487/RFC8200, July 2017, 1252 . 1254 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1255 Perkins, "Registration Extensions for IPv6 over Low-Power 1256 Wireless Personal Area Network (6LoWPAN) Neighbor 1257 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1258 . 1260 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 1261 "Address Protected Neighbor Discovery for Low-power and 1262 Lossy Networks", Work in Progress, Internet-Draft, draft- 1263 ietf-6lo-ap-nd-12, 10 April 2019, 1264 . 1266 [USEofRPLinfo] 1267 Robles, I., Richardson, M., and P. Thubert, "Using RPL 1268 Option Type, Routing Header for Source Routes and IPv6-in- 1269 IPv6 encapsulation in the RPL Data Plane", Work in 1270 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-31, 1271 7 August 2019, . 1274 [EFFICIENT-NPDAO] 1275 Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient 1276 Route Invalidation", Work in Progress, Internet-Draft, 1277 draft-ietf-roll-efficient-npdao-17, 30 October 2019, 1278 . 1281 16. Informative References 1283 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 1284 C., and M. Carney, "Dynamic Host Configuration Protocol 1285 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 1286 2003, . 1288 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1289 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1290 DOI 10.17487/RFC6282, September 2011, 1291 . 1293 [RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur, 1294 Ed., "Performance Evaluation of the Routing Protocol for 1295 Low-Power and Lossy Networks (RPL)", RFC 6687, 1296 DOI 10.17487/RFC6687, October 2012, 1297 . 1299 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1300 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1301 2014, . 1303 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1304 Constrained-Node Networks", RFC 7228, 1305 DOI 10.17487/RFC7228, May 2014, 1306 . 1308 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1309 and M. Richardson, Ed., "A Security Threat Analysis for 1310 the Routing Protocol for Low-Power and Lossy Networks 1311 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1312 . 1314 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 1315 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 1316 RFC 8025, DOI 10.17487/RFC8025, November 2016, 1317 . 1319 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node 1320 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, 1321 January 2019, . 1323 Appendix A. Example Compression 1325 Figure 9 illustrates the case in Storing Mode where the packet is 1326 received from the Internet, then the Root encapsulates the packet to 1327 insert the RPI and deliver to the 6LR that is the parent and last hop 1328 to the final destination, which is not known to support [RFC8138]. 1329 The difference with the format presented in Figure 19 of [RFC8138] is 1330 the addition of a SRH-6LoRH before the RPI-6LoRH to transport the 1331 destination address of the outer IPv6 header. 1333 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1334 |11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP 1335 |Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1336 +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-... 1337 <-4bytes-> <- RFC 6282 -> 1338 No RPL artifact 1340 Figure 9: Encapsulation to Parent 6LR in Storing Mode 1342 In Figure 9, the source of the IP-in-IP encapsulation is the Root, so 1343 it is elided in the IP-in-IP 6LoRH. The destination is the parent 1344 6LR of the destination of the inner packet so it cannot be elided. 1345 In Storing Mode, it is placed as the single entry in an SRH-6LoRH as 1346 the first 6LoRH. Since there is a single entry so the SRH-6LoRH Size 1347 is 0. In this particular example, the 6LR address can be compressed 1348 to 2 bytes so a Type of 1 is used. It results that the total length 1349 of the SRH-6LoRH is 4 bytes. 1351 In Non-Storing Mode, the encapsulation from the Root would be similar 1352 to that represented in Figure 9 with possibly more hops in the SRH- 1353 6LoRH and possibly multiple SRH-6LoRHs if the various addresses in 1354 the routing header are not compressed to the same format. Note that 1355 on the last hop to the parent 6LR, the RH3 is consumed and removed 1356 from the compressed form, so the use of Non-Storing Mode vs. Storing 1357 Mode is indistinguishable from the packet format. 1359 Follows the RPI-6LoRH and then the IP-in-IP 6LoRH. When the IP-in-IP 1360 6LoRH is removed, all the router headers that precede it are also 1361 removed. 1363 The Paging Dispatch [RFC8025] may also be removed if there was no 1364 previous Page change to a Page other than 0 or 1, since the 1365 LOWPAN_IPHC is encoded in the same fashion in the default Page 0 and 1366 in Page 1. The resulting packet to the destination is the inner 1367 packet compressed with [RFC6282]. 1369 Authors' Addresses 1370 Pascal Thubert (editor) 1371 Cisco Systems, Inc 1372 Building D, 45 Allee des Ormes - BP1200 1373 06254 Mougins - Sophia Antipolis 1374 France 1376 Phone: +33 497 23 26 34 1377 Email: pthubert@cisco.com 1379 Michael C. Richardson 1380 Sandelman Software Works 1382 Email: mcr+ietf@sandelman.ca 1383 URI: http://www.sandelman.ca/