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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references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 7102 == Outdated reference: A later version (-30) exists of draft-ietf-roll-unaware-leaves-18 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-40 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--).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: 8138 (if approved) Cisco Systems 5 Intended status: Standards Track 5 August 2020 6 Expires: 6 February 2021 8 A RPL DODAG Configuration Option for the 6LoWPAN Routing Header 9 draft-ietf-roll-turnon-rfc8138-10 11 Abstract 13 This document updates RFC 8138 by defining a bit in the RPL DODAG 14 Configuration Option to indicate whether compression is used within 15 the RPL Instance, and specify the behavior of RFC 8138-capable nodes 16 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 6 February 2021. 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. Requirements Language . . . . . . . . . . . . . . . . . . 4 56 3. The RPL DODAG Configuration Option . . . . . . . . . . . . . 4 57 4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 5 58 5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 5 59 5.1. Coexistence . . . . . . . . . . . . . . . . . . . . . . . 6 60 5.2. Inconsistent State While Migrating . . . . . . . . . . . 6 61 5.3. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 6 62 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 63 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 64 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 65 9. Normative References . . . . . . . . . . . . . . . . . . . . 8 66 10. Informative References . . . . . . . . . . . . . . . . . . . 9 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 69 1. Introduction 71 The packet compression technique defined in [RFC8138] can only be 72 activated in a RPL [RFC6550] network when all the nodes support it. 73 Otherwise, a non-capable node acting as leaf-only would fail to 74 communicate, and acting as a router it would drop the compressed 75 packets and black-hole a portion of the network. 77 The original idea was to use a flag day but that proved impractical 78 in a number of situations such as a large metering network that is 79 used in production and incurs financial losses when interrupted. 81 This specification is designed for the scenario where a live network 82 is upgraded to support [RFC8138]. During the migration, the 83 compression should remain inactive, until all nodes are upgraded. 84 This document complements [RFC8138] and dedicates a flag in the RPL 85 DODAG Configuration Option to indicate whether the [RFC8138] 86 compression should be used within the RPL DODAG. 88 The setting of this new flag is controlled by the Root and propagates 89 as is in the whole network as part of the normal RPL signaling. 91 The idea is to use the flag to maintain the compression inactive 92 during the migration phase. When the migration is complete (e.g., as 93 known by network management and/or inventory), the flag is set and 94 the compression is globally activated in the whole DODAG. 96 2. Terminology 98 2.1. References 100 The terminology used in this document is consistent with and 101 incorporates that described in "Terms Used in Routing for Low-Power 102 and Lossy Networks (LLNs)" [RFC7102]. Other terms in use in LLNs are 103 found in "Terminology for Constrained-Node Networks" [RFC7228]. 105 "RPL", the "RPL Packet Information" (RPI), and "RPL Instance" 106 (indexed by a RPLInstanceID) are defined in "RPL: IPv6 Routing 107 Protocol for Low-Power and Lossy Networks" [RFC6550]. The RPI is the 108 abstract information that RPL defines to be placed in data packets, 109 e.g., as the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. 110 By extension the term "RPI" is often used to refer to the RPL Option 111 itself. The DODAG Information Solicitation (DIS), Destination 112 Advertisement Object (DAO) and DODAG Information Object (DIO) 113 messages are also specified in [RFC6550]. 115 This document uses the terms RPL-Unaware Leaf (RUL) and RPL-Aware 116 Leaf (RAL) consistently with "Using RPI Option Type, Routing Header 117 for Source Routes and IPv6-in-IPv6 encapsulation in the RPL Data 118 Plane" [USEofRPLinfo]. The term RPL-Aware Node (RAN) refers to a 119 node that is either a RAL or a RPL Router. A RAN manages the 120 reachability of its addresses and prefixes by injecting them in RPL 121 by itself. In contrast, a RUL leverages "Registration Extensions for 122 IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor 123 Discovery" [RFC8505] to obtain reachability services from its parent 124 router(s) as specified in "Routing for RPL Leaves" [UNAWARE-LEAVES]. 126 2.2. Glossary 128 This document often uses the following acronyms: 130 6LoWPAN: IPv6 over Low-Power Wireless Personal Area Network 131 6LoRH: 6LoWPAN Routing Header 132 DIO: DODAG Information Object (a RPL message) 133 DODAG: Destination-Oriented Directed Acyclic Graph 134 LLN: Low-Power and Lossy Network 135 RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks 136 OF: RPL Objective Function 137 OCP: RPL Objective Code Point 138 MOP: RPL Mode of Operation 139 RPI: RPL Packet Information 140 RAL: RPL-Aware Leaf 141 RAN: RPL-Aware Node 142 RUL: RPL-Unaware Leaf 143 SRH: Source Routing Header 145 2.3. Requirements Language 147 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 148 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 149 "OPTIONAL" in this document are to be interpreted as described in BCP 150 14 [RFC2119][RFC8174] when, and only when, they appear in all 151 capitals, as shown here. 153 3. The RPL DODAG Configuration Option 155 The DODAG Configuration Option is defined in Section 6.7.6 of 156 [RFC6550]. 158 The RPL DODAG Configuration Option is typically placed in a DODAG 159 Information Object (DIO) message. The DIO message propagates down 160 the DODAG to form and then maintain its structure. The DODAG 161 Configuration Option is copied unmodified from parents to children. 163 As shown in Figure 1, the DODAG Configuration Option was designed 164 with 4 bit positions reserved for future use as Flags. 166 0 1 2 3 167 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 1 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 | Type = 0x04 |Opt Length = 14| Flags |A| ... | 170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 171 | ... | 173 Figure 1: DODAG Configuration Option (Partial View) 175 This specification defines a new flag "Enable RFC8138 Compression" 176 (T). The "T" flag is set to turn-on the use of the compression of 177 RPL artifacts with [RFC8138] within the DODAG. The new "T" flag is 178 encoded in the Flags field in the RPL DODAG Configuration Option. 179 The suggested bit position of the "T" flag is indicated in Section 6. 181 [RFC6550] states, when referring to the DODAG Configuration Option, 182 that "Nodes other than the DODAG Root MUST NOT modify this 183 information when propagating the DODAG Configuration option". 184 Therefore, a legacy parent propagates the "T" flag as set by the Root 185 whether it supports this specification or not. So when the "T" flag 186 is set, it is transparently flooded to all the nodes in the DODAG. 188 Section 6.3.1 of [RFC6550] defines a 3-bit Mode of Operation (MOP) in 189 the DIO Base Object. This specification applies to MOP values 0 to 190 6. For a MOP value of 7, the compression MUST be used by default 191 regardless of the setting of the "T" flag. 193 4. Updating RFC 8138 195 A node SHOULD source packets in the compressed form using [RFC8138] 196 if and only if the "T" flag is set. This behaviour can be overridden 197 by e.g., configuration or network management. Overriding may be 198 needed e.g., to cope with a legacy implementation of the Root that 199 supports [RFC8138] but not this specification and cannot set the "T" 200 flag. 202 The decision of using [RFC8138] is made by the originator of the 203 packet depending on its capabilities and its knowledge of the state 204 of the "T" flag. A router that encapsulates a packet is the 205 originator of the resulting packet and is responsible to compress the 206 outer headers with [RFC8138], but it MUST leave the encapsulated 207 packet as is. 209 An external target [USEofRPLinfo] is not expected to support 210 [RFC8138]. In most cases, packets from and to an external target are 211 tunneled back and forth between the border router (referred to as 212 6LR) that serves the external target and the Root, regardless of the 213 MOP used in the RPL DODAG. The inner packet is typically not 214 compressed with [RFC8138], so for outgoing packets, the border router 215 just needs to decapsulate the (compressed) outer header and forward 216 the (uncompressed) inner packet towards the external target. 218 A router MUST uncompress a packet that is to be forwarded to an 219 external target. Otherwise, the router MUST forward the packet in 220 the form that the source used, either compressed or uncompressed. 222 A RUL [UNAWARE-LEAVES] is both a leaf and an external target. A RUL 223 does not participate in RPL and depends on the parent router to 224 obtain connectivity. In the case of a RUL, forwarding towards an 225 external target actually means delivering the packet. 227 5. Transition Scenarios 229 A node that supports [RFC8138] but not this specification can only be 230 used in an homogeneous network. Enabling the [RFC8138] compression 231 without a turn-on signaling requires a "flag day"; all nodes must be 232 upgraded, and then the network can be rebooted with the [RFC8138] 233 compression turned on. 235 The intent for this specification is to perform a migration once and 236 for all without the need for a flag day. In particular it is not the 237 intention to undo the setting of the "T" flag. Though it is possible 238 to roll back (see Section 5.3), adding nodes that do not support 239 [RFC8138] after a roll back may be problematic if the roll back did 240 not fully complete. 242 5.1. Coexistence 244 A node that supports this specification can operate in a network with 245 the [RFC8138] compression turned on or off with the "T" flag set 246 accordingly and in a network in transition from off to on or on to 247 off (see Section 5.2). 249 A node that does not support [RFC8138] can interoperate with nodes 250 that do in a network with [RFC8138] compression turned off. If the 251 compression is turned on, all the RPL-Aware Nodes are expected to be 252 able to handle compressed packets in the compressed form. A node 253 that cannot do so may remain connected to the network as a RUL, but 254 how the node is modified to turn into a RUL is out of scope. 256 5.2. Inconsistent State While Migrating 258 When the "T" flag is turned on by the Root, the information slowly 259 percolates through the DODAG as the DIO gets propagated. Some nodes 260 will see the flag and start sourcing packets in the compressed form 261 while other nodes in the same RPL DODAG are still not aware of it. 262 In non-storing mode, the Root will start using [RFC8138] with a 263 Source Routing Header 6LoRH (SRH-6LoRH) that routes all the way to 264 the parent router or to the leaf. 266 To ensure that a packet is forwarded across the RPL DODAG in the form 267 in which it was generated, it is required that all the RPL nodes 268 support [RFC8138] at the time of the switch. 270 Setting the "T" flag is ultimately the responsibility of the Network 271 Administrator. The expectation is that the network management or 272 upgrading tools in place enable the Network Administrator to know 273 when all the nodes that may join a DODAG were migrated. In the case 274 of a RPL instance with multiple Roots, all nodes that participate to 275 the RPL Instance may potentially join any DODAG. The network MUST be 276 operated with the "T" flag reset until all nodes in the RPL Instance 277 are upgraded to support this specification. 279 5.3. Rolling Back 281 When turning [RFC8138] compression off in the network, the Network 282 Administrator MUST wait until all nodes have converged to the "T" 283 flag reset before allowing nodes that do not support the compression 284 in the network. 286 It is RECOMMENDED to only deploy nodes that support [RFC8138] in a 287 network where the compression is turned on. A node that does not 288 support [RFC8138] MUST only be used as a RUL. 290 6. IANA Considerations 292 IANA is requested to assign a new option flag from the Registry for 293 the "DODAG Configuration Option Flags" that was created for [RFC6550] 294 as follows: 296 +---------------+---------------------------------+-----------+ 297 | Bit Number | Capability Description | Reference | 298 +---------------+---------------------------------+-----------+ 299 | 2 (suggested) | Turn on RFC8138 Compression (T) | THIS RFC | 300 +---------------+---------------------------------+-----------+ 302 Table 1: New DODAG Configuration Option Flag 304 7. Security Considerations 306 First of all, it is worth noting that with [RFC6550], every node in 307 the LLN that is RPL-aware can inject any RPL-based attack in the 308 network. A trust model has to be put in place in an effort to 309 exclude rogue nodes from participating to the RPL and the 6LoWPAN 310 signaling, as well as from the data packet exchange. This trust 311 model could be at a minimum based on a Layer-2 Secure joining and the 312 Link-Layer security. This is a generic RPL and 6LoWPAN requirement, 313 see Req5.1 in Appendix of [RFC8505]. 315 Setting the "T" flag before all routers are upgraded may cause a loss 316 of packets. The new bit is protected as the rest of the 317 configuration so this is just one of the many attacks that can happen 318 if an attacker manages to inject a corrupted configuration. 320 Setting and resetting the "T" flag may create inconsistencies in the 321 network but as long as all nodes are upgraded to [RFC8138] support 322 they will be able to forward both forms. The source is responsible 323 for selecting whether the packet is compressed or not, and all 324 routers must use the format that the source selected. So the result 325 of an inconsistency is merely that both forms will be present in the 326 network, at an additional cost of bandwidth for packets in the 327 uncompressed form. 329 An attacker in the middle of the network may reset the "T" flag to 330 cause extra energy spending in its subDAG. Conversely it may set the 331 "T" flag, so that nodes located downstream would compress when that 332 it is not desired, potentially resulting in the loss of packets. In 333 a tree structure, the attacker would be in position to drop the 334 packets from and to the attacked nodes. So the attacks above would 335 be more complex and more visible than simply dropping selected 336 packets. The downstream node may have other parents and see both 337 settings, which could raise attention. 339 8. Acknowledgments 341 The authors wish to thank Carles Gomez, Alvaro Retana, Dominique 342 Barthel and Rahul Jadhav for their in-depth reviews and constructive 343 suggestions. 345 Also many thanks to Michael Richardson for being always helpful and 346 responsive when need comes. 348 9. Normative References 350 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 351 Requirement Levels", BCP 14, RFC 2119, 352 DOI 10.17487/RFC2119, March 1997, 353 . 355 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 356 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 357 May 2017, . 359 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 360 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 361 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 362 Low-Power and Lossy Networks", RFC 6550, 363 DOI 10.17487/RFC6550, March 2012, 364 . 366 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 367 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 368 2014, . 370 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 371 "IPv6 over Low-Power Wireless Personal Area Network 372 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 373 April 2017, . 375 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 376 Perkins, "Registration Extensions for IPv6 over Low-Power 377 Wireless Personal Area Network (6LoWPAN) Neighbor 378 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 379 . 381 [UNAWARE-LEAVES] 382 Thubert, P. and M. Richardson, "Routing for RPL Leaves", 383 Work in Progress, Internet-Draft, draft-ietf-roll-unaware- 384 leaves-18, 12 June 2020, . 387 10. Informative References 389 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 390 Power and Lossy Networks (RPL) Option for Carrying RPL 391 Information in Data-Plane Datagrams", RFC 6553, 392 DOI 10.17487/RFC6553, March 2012, 393 . 395 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 396 Constrained-Node Networks", RFC 7228, 397 DOI 10.17487/RFC7228, May 2014, 398 . 400 [USEofRPLinfo] 401 Robles, I., Richardson, M., and P. Thubert, "Using RPI 402 Option Type, Routing Header for Source Routes and IPv6-in- 403 IPv6 encapsulation in the RPL Data Plane", Work in 404 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-40, 405 25 June 2020, . 408 Authors' Addresses 410 Pascal Thubert (editor) 411 Cisco Systems, Inc 412 Building D 413 45 Allee des Ormes - BP1200 414 06254 MOUGINS - Sophia Antipolis 415 France 417 Phone: +33 497 23 26 34 418 Email: pthubert@cisco.com 420 Li Zhao 421 Cisco Systems, Inc 422 Xinsi Building 423 No. 926 Yi Shan Rd 424 SHANGHAI 425 200233 426 China 428 Email: liz3@cisco.com