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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reference to an Informational RFC: RFC 7102 ** Downref: Normative reference to an Informational RFC: RFC 7228 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-38 == Outdated reference: A later version (-30) exists of draft-ietf-roll-unaware-leaves-14 == Outdated reference: A later version (-09) exists of draft-ietf-roll-capabilities-02 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft L. Zhao 4 Updates: 6550, 8138 (if approved) Cisco Systems 5 Intended status: Standards Track 17 April 2020 6 Expires: 19 October 2020 8 A RPL Configuration Option for the 6LoWPAN Routing Header 9 draft-ietf-roll-turnon-rfc8138-07 11 Abstract 13 This document updates RFC 8138 and RFC 6550 by defining a bit in the 14 RPL configuration option to indicate whether RFC 8138 compression is 15 used within the RPL Instance, and specify the behavior of RFC 16 8138-capable nodes when the bit is set and reset. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at https://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on 19 October 2020. 35 Copyright Notice 37 Copyright (c) 2020 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 42 license-info) in effect on the date of publication of this document. 43 Please review these documents carefully, as they describe your rights 44 and restrictions with respect to this document. Code Components 45 extracted from this document must include Simplified BSD License text 46 as described in Section 4.e of the Trust Legal Provisions and are 47 provided without warranty as described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2.1. References . . . . . . . . . . . . . . . . . . . . . . . 3 54 2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2.3. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 4 57 4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 4 58 5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 5 59 5.1. Inconsistent State While Migrating . . . . . . . . . . . 6 60 5.2. Single RPL Instance Scenario . . . . . . . . . . . . . . 6 61 5.3. Double RPL Instances Scenario . . . . . . . . . . . . . . 7 62 5.4. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 8 63 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 64 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 65 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 66 9. Normative References . . . . . . . . . . . . . . . . . . . . 9 67 10. Informative References . . . . . . . . . . . . . . . . . . . 9 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 70 1. Introduction 72 The transition of a RPL [RFC6550] network to activate the compression 73 defined in [RFC8138] can only be done when all routers in the network 74 support it. Otherwise, a non-capable node acting as a router would 75 drop the compressed packets and black-hole its subDAG. In a mixed 76 case with both RFC8138-capable and non-capable nodes, the compression 77 may be turned on only if all the non-capable nodes act as Hosts and 78 their RPL parents handle the compression/decompression for them. 80 This document complements [RFC8138] and dedicates a flag in the RPL 81 configuration option to indicate whether [RFC8138] compression should 82 be used within the RPL Instance. The setting of this new flag is 83 controlled by the Root and propagates as is in the whole network. 84 When the bit is not set, source nodes that support [RFC8138] should 85 refrain from using the compression unless the information is 86 superseded by configuration. 88 With RPL, a leaf is an IPv6 Host, which implies that leaves do not 89 forward packets. This specification provides scenarios that force a 90 non-capable RPL-Aware Node (RAN) to become a leaf. The parent router 91 must know, e.g., by configuration, or leveraging "RPL Capabilities" 92 [CAPABILITIES], when a leaf does not support the compression defined 93 in [RFC8138]. This is implicitly the case for a RPL-Unaware Leaf 94 (RUL) but is not known for a RPL-Aware Leaf (RAL). The parent router 95 must uncompress the packets before delivering them to a non-capable 96 leaf and it must compress the traffic from the leaf. 98 2. Terminology 100 2.1. References 102 The Terminology used in this document is consistent with and 103 incorporates that described in "Terms Used in Routing for Low-Power 104 and Lossy Networks (LLNs)" [RFC7102]. Other terms in use in LLNs are 105 found in "Terminology for Constrained-Node Networks" [RFC7228]. 107 "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by 108 a RPLInstanceID) are defined in "RPL: IPv6 Routing Protocol for 109 Low-Power and Lossy Networks" [RFC6550]. The RPI is the abstract 110 information that RPL defines to be placed in data packets, e.g., as 111 the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. By 112 extension the term "RPI" is often used to refer to the RPL Option 113 itself. The DODAG Information Solicitation (DIS), Destination 114 Advertisement Object (DAO) and DODAG Information Object (DIO) 115 messages are also specified in [RFC6550]. 117 This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware 118 Leaf (RAL) consistently with "Using RPI Option Type, Routing Header 119 for Source Routes and IPv6-in-IPv6 encapsulation in the RPL Data 120 Plane" [USEofRPLinfo]. The term RPL-Aware Node (RAN) refers to a 121 node that is either a RAL or a RPL Router. A RAN manages the 122 reachability of its addresses and prefixes by injecting them in RPL 123 by itself. In contrast, a RUL leverages "Registration Extensions for 124 IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor 125 Discovery" [RFC8505] to obtain reachability services from its parent 126 router(s) as specified in "Routing for RPL Leaves" [UNAWARE-LEAVES]. 128 2.2. Glossary 130 This document often uses the following acronyms: 132 6LoWPAN: IPv6 over Low-Power Wireless Personal Area Network 133 6LoRH: 6LoWPAN Routing Header 134 DIO: DODAG Information Object (a RPL message) 135 DODAG: Destination-Oriented Directed Acyclic Graph 136 LLN: Low-Power and Lossy Network 137 RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks 138 OF: RPL Objective Function 139 OCP: RPL Objective Code Point 140 MOP: RPL Mode of Operation 141 RPI: RPL Packet Information 142 RAL: RPL-Aware Leaf 143 RAN: RPL-Aware Node 144 RUL: RPL-Unaware Leaf 145 SRH: Source Routing Header 147 2.3. BCP 14 149 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 150 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 151 "OPTIONAL" in this document are to be interpreted as described in BCP 152 14 [RFC2119][RFC8174] when, and only when, they appear in all 153 capitals, as shown here. 155 3. Updating RFC 6550 157 This specification defines a new flag "Enable RFC8138 Compression" 158 (T). The "T" flag is set to turn on the use of the compression of 159 RPL artifacts with [RFC8138] within a RPL Instance. If a RPL 160 Instance has multiple Roots then they must be coordinated to use the 161 same setting. 163 RPL defines a Configuration Option that is registered to IANA in 164 section 20.14. of [RFC6550]. The "T" flag is encoded in one of the 165 reserved control bits in the RPL Configuration Option. The bit 166 position of the "T" flag is indicated in Section 6. 168 Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) 169 in the DIO Base Object. The new "T" flag is defined only for MOP 170 value between 0 to 6. For a MOP value of 7 or above, the flag MAY 171 indicate something different and MUST NOT be interpreted as "Enable 172 RFC8138 Compression" unless the specification of the MOP indicates to 173 do so. 175 4. Updating RFC 8138 177 A node that supports this specification MUST source packets in the 178 compressed form using [RFC8138] if and only if the "T" flag is set. 179 This behaviour can be overridden by the configuration of the node in 180 order to cope with intermediate implementations of the Root that 181 support [RFC8138] but not this specification and cannot set the "T" 182 flag. 184 The decision of using [RFC8138] is made by the originator of the 185 packet depending on its capabilities and its knowledge of the state 186 of the "T" flag. A router that encapsulates a packet is the 187 originator of the resulting packet and decides whether to compress 188 the outer headers as indicated above. An external target 189 [USEofRPLinfo] is not expected to support [RFC8138]. An intermediate 190 router MUST forward the packet in the form that the source used, 191 either compressed or uncompressed, unless it is forwarding to an 192 external target or delivering to a leaf that is not known to support 193 [RFC8138], in which cases it MUST uncompress the packet. 195 5. Transition Scenarios 197 A node that supports [RFC8138] but not this specification can only be 198 used in an homogeneous network. Enabling the [RFC8138] compression 199 requires a "flag day"; all nodes must be upgraded, and then the 200 network can be rebooted with the [RFC8138] compression turned on. 202 A node that supports this specification can work in a network with 203 [RFC8138] compression turned on or off with the "T" flag set 204 accordingly and in a network in transition from off to on or on to 205 off (see Section 5.1). 207 A node that does not support [RFC8138] can interoperate with nodes 208 that do in a network with [RFC8138] compression turned off. If the 209 compression is turned on, the node cannot forward compressed packets 210 and therefore it cannot act as a router. It may remain connected to 211 that network as a leaf, generates uncompressed packets, and can 212 receive packets if they are delivered by the parent router in the 213 uncompressed form. Unless this is known by other means, the node 214 SHOULD join as a RUL as an indication that its parent router needs to 215 uncompress the packets before delivering. 217 [RFC6550] states that "Nodes other than the DODAG Root MUST NOT 218 modify this information when propagating the DODAG Configuration 219 option". Therefore, even a legacy parent propagates the "T" flag as 220 set by the Root whether it supports this specification or not. So 221 when the "T" flag is set, it is transparently flooded to all the 222 nodes in the RPL Instance. 224 Sections 8.5 and 9.2 of [RFC6550] also suggests that a RAN may only 225 attach to a DODAG as a leaf when it does not support the Mode of 226 Operation of a RPL Instance, the Objective Function (OF) as indicated 227 by the Objective Code Point (OCP) or some other parameters in the 228 configuration option. 230 This specification reiterates that a RAN that is configured to 231 operate in a RPL Instance but does not support a value for a known 232 parameter that is mandatory for routing, such as the OCP, MUST NOT 233 operate as a router but MAY still join as a leaf. Note that a legacy 234 RAN will not recognize when a reserved field is used and will not 235 turn to a leaf when the "T" flag is set. 237 The intent for this specification is to perform a migration once and 238 for all without the need for a flag day. In particular it is not the 239 intention to undo the setting of the "T" flag, and though it is 240 possible to roll back (see Section 5.4), adding nodes that do not 241 support [RFC8138] after a roll back may be problematic if the roll 242 back is not fully complete (see caveats in Section 5.2). 244 5.1. Inconsistent State While Migrating 246 When the "T" flag is turned on in the configuration option by the 247 Root, the information slowly percolates through the DODAG as the DIO 248 gets propagated. 250 Some nodes will see the flag and start sourcing packets in the 251 compressed form while other nodes in the same RPL Instance are still 252 not aware of it. Conversely, in non-storing mode, the Root will 253 start using [RFC8138] with a Source Routing Header 6LoRH (SRH-6LoRH) 254 that routes all the way to the parent router or to the leaf. 256 To ensure that a packet is forwarded across the RPL Instance in the 257 form in which it was generated, it is required that all the routers 258 support [RFC8138] at the time of the switch, and that all nodes that 259 do not support [RFC8138] only operate as leaves. 261 Setting the "T" flag is ultimately the responsibility of the network 262 administrator. In a case of upgrading a network to turn the 263 compression on, the network SHOULD be operated with the "T" flag 264 reset until all targeted nodes are upgraded to support this 265 specification. Section 5.2 and Section 5.3 provide possible 266 transition scenarios where this can be enforced. 268 5.2. Single RPL Instance Scenario 270 In a Single RPL Instance Scenario, nodes that support [RFC8138] are 271 configured with a new OCP, that may use the same OF operation or a 272 variation of it, while nodes that do not support [RFC8138] are not, 273 but are configured to join an unknown OCP. 275 The Root migrates to the new OCP before it sets the "T" flag, so that 276 nodes that do not support [RFC8138] are all attached as leaves when 277 the "T" flag is eventually set. 279 The parent router - which supports [RFC8138] - compresses the packets 280 originated from the leaf and uncompresses the packets going to the 281 leaf. This may be done on the fly by the parent of a non-capable 282 RAL, or as part of the tunneling operation between the parent and the 283 Root, if the leaf behaves as a RUL. This is described in section 7, 284 8, and 9 of [USEofRPLinfo]. 286 Note that though tunneling from the Root to the parent is the generic 287 case for RULs, on paper it is possible for the Root to avoid it for 288 the traffic that it originates. The Root SHOULD always use tunneling 289 to the parent of a RUL, even for its own packets, unless it knows 290 that the leaf supports [RFC8138]. 292 This scenario presents a number of caveats: 294 * The method consumes an extra OCP. It also forces nodes that do 295 not support [RFC8138] to operate as RULs, unless there is a method 296 to let the parent router know that it must uncompress the packet 297 for this RAL. 299 * If the RPL implementation of a node does not turn it to a leaf 300 when the OCP is changed to an unknown one, then the node may be 301 stalled. 303 * If the only possible parents of a node are nodes that do not 304 support [RFC8138], then that node will loose all its parent at the 305 time of the migration and it will be stalled until a parent is 306 deployed with the new capability. 308 5.3. Double RPL Instances Scenario 310 An alternative to the Single RPL Instance Scenario is to deploy an 311 additional RPL Instance for the nodes that support [RFC8138]. 313 The two RPL Instances operate independently as specified in 314 [RFC6550]. The preexisting RPL Instance does not use [RFC8138], 315 whereas the new RPL Instance does. This is signaled by the "T" flag 316 which is only set in the configuration option in DIO messages in the 317 new RPL Instance. 319 Nodes that support [RFC8138] participate in both Instances but favor 320 the new RPL Instance for the traffic that they source. By contrast, 321 nodes that only support the uncompressed format would either not be 322 configured for the new RPL Instance, or would be configured to join 323 it as leaves only. 325 This method eliminates the risks of nodes being stalled that are 326 described in Section 5.2 but requires implementations to support at 327 least two RPL Instances and demands management capabilities to 328 introduce new RPL Instances and deprecate old ones. 330 The 2 instances MUST be operated with the same security guarantees, 331 e.g., both "unsecured" with a lower layer security of a same 332 strength, both "preinstalled" or both "authenticated" security mode 333 (see section 3.2.3 of [RFC6550] for more details on those modes). 334 The latter mode could be use to enforce the segregation of updated 335 and non-updated nodes, by providing the keys for joining as routers 336 to the updated nodes only. 338 5.4. Rolling Back 340 After downgrading a network to turn the [RFC8138] compression off, 341 the administrator SHOULD make sure that all nodes have converged to 342 the "T" flag reset before allowing nodes that do not support the 343 compression in the network (see caveats in Section 5.2). 345 It is RECOMMENDED to only deploy nodes that support [RFC8138] in a 346 network where the compression is turned on. A node that does not 347 support [RFC8138] MUST only be used as a leaf. 349 6. IANA Considerations 351 This specification updates the Registry for the "DODAG Configuration 352 Option Flags" that was created for [RFC6550] as follows: 354 +------------+---------------------------------+-----------+ 355 | Bit Number | Capability Description | Reference | 356 +============+=================================+===========+ 357 | 2 | Turn on RFC8138 Compression (T) | THIS RFC | 358 +------------+---------------------------------+-----------+ 360 Table 1: New DODAG Configuration Option Flag 362 7. Security Considerations 364 First of all, it is worth noting that with [RFC6550], every node in 365 the LLN that is RPL-aware can inject any RPL-based attack in the 366 network. A trust model MUST be put in place so that rogue nodes are 367 excluded from participating to the RPL and the 6LowpAN signaling, and 368 from the data packet exchange. This trust model could be at a 369 minimum based on a Layer-2 Secure joining and the Link-Layer 370 security. This is a generic RPL and 6LoWPAN requirement, see Req5.1 371 in Appendix of [RFC8505]. 373 Setting the "T" flag before some routers are upgraded may cause a 374 loss of packets. The new bit is protected as the rest of the 375 configuration so this is just one of the many attacks that can happen 376 if an attacker manages to inject a corrupted configuration. 378 Setting and resetting the "T" flag may create inconsistencies in the 379 network but as long as all nodes are upgraded to [RFC8138] support 380 they will be able to forward both forms. The source is responsible 381 for selecting whether the packet is compressed or not, and all 382 routers must use the format that the source selected. So the result 383 of an inconsistency is merely that both forms will be present in the 384 network, at an additional cost of bandwidth for packets in the 385 uncompressed form. 387 8. Acknowledgments 389 The authors wish to thank Dominique Barthel and Rahul Jadhav for 390 their in-depth reviews and constructive suggestions. 392 9. Normative References 394 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 395 Requirement Levels", BCP 14, RFC 2119, 396 DOI 10.17487/RFC2119, March 1997, 397 . 399 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 400 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 401 May 2017, . 403 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 404 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 405 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 406 Low-Power and Lossy Networks", RFC 6550, 407 DOI 10.17487/RFC6550, March 2012, 408 . 410 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 411 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 412 2014, . 414 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 415 Constrained-Node Networks", RFC 7228, 416 DOI 10.17487/RFC7228, May 2014, 417 . 419 [USEofRPLinfo] 420 Robles, I., Richardson, M., and P. Thubert, "Using RPI 421 Option Type, Routing Header for Source Routes and IPv6-in- 422 IPv6 encapsulation in the RPL Data Plane", Work in 423 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-38, 424 23 March 2020, . 427 [UNAWARE-LEAVES] 428 Thubert, P. and M. Richardson, "Routing for RPL Leaves", 429 Work in Progress, Internet-Draft, draft-ietf-roll-unaware- 430 leaves-14, 11 April 2020, . 433 10. Informative References 435 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 436 Power and Lossy Networks (RPL) Option for Carrying RPL 437 Information in Data-Plane Datagrams", RFC 6553, 438 DOI 10.17487/RFC6553, March 2012, 439 . 441 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 442 "IPv6 over Low-Power Wireless Personal Area Network 443 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 444 April 2017, . 446 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 447 Perkins, "Registration Extensions for IPv6 over Low-Power 448 Wireless Personal Area Network (6LoWPAN) Neighbor 449 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 450 . 452 [CAPABILITIES] 453 Jadhav, R., Thubert, P., Richardson, M., and R. Sahoo, 454 "RPL Capabilities", Work in Progress, Internet-Draft, 455 draft-ietf-roll-capabilities-02, 11 March 2020, 456 . 459 Authors' Addresses 461 Pascal Thubert (editor) 462 Cisco Systems, Inc 463 Building D 464 45 Allee des Ormes - BP1200 465 06254 MOUGINS - Sophia Antipolis 466 France 468 Phone: +33 497 23 26 34 469 Email: pthubert@cisco.com 471 Li Zhao 472 Cisco Systems, Inc 473 Xinsi Building 474 No. 926 Yi Shan Rd 475 SHANGHAI 476 200233 477 China 479 Email: liz3@cisco.com