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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references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 7102 == Outdated reference: A later version (-30) exists of draft-ietf-roll-unaware-leaves-18 == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-40 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). 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 18 September 2020 6 Expires: 22 March 2021 8 A RPL DODAG Configuration Option for the 6LoWPAN Routing Header 9 draft-ietf-roll-turnon-rfc8138-15 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 unset. 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 22 March 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. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 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 design of Low Power and Lossy Networks (LLNs) is generally 72 focused on saving energy, which is the most constrained resource of 73 all. The routing optimizations in the "Routing Protocol for Low 74 Power and Lossy Networks" [RFC6550] (RPL) such as routing along a 75 Destination-Oriented Directed Acyclic Graph (DODAG) to a Root Node 76 and the associated routing header compression and forwarding 77 technique specified in [RFC8138] derive from that primary concern. 79 Enabling [RFC8138] on a running network requires a Flag Day where the 80 network is upgraded and rebooted. Otherwise, if acting as a Leaf, a 81 node that does not support the compression would fail to communicate; 82 if acting as a router it would drop the compressed packets and black- 83 hole a portion of the network. This specification enables a hot 84 upgrade where a live network is migrated. During the migration, the 85 compression remains inactive, until all nodes are upgraded. 87 This document complements [RFC8138] and signals whether it should be 88 used within a RPL DODAG with a new flag in the RPL DODAG 89 Configuration Option. The setting of this new flag is controlled by 90 the Root and propagates as is in the whole network as part of the 91 normal RPL signaling. 93 The flag is cleared to maintain the compression inactive during the 94 migration phase. When the migration is complete (e.g., as known by 95 network management and/or inventory), the flag is set and the 96 compression is globally activated in the whole DODAG. 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), and "RPL Instance" 108 (indexed by a RPLInstanceID) are defined in "RPL: IPv6 Routing 109 Protocol for Low-Power and Lossy Networks" [RFC6550]. The RPI is the 110 abstract information that RPL defines to be placed in data packets, 111 e.g., as the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. 112 By 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 SubDAG: A DODAG rooted at a node which is a child of that node and a 139 subset of a larger DAG 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. Requirements Language 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 The DODAG Configuration Option is defined in Section 6.7.6 of 158 [RFC6550]. Its purpose is extended to distribute configuration 159 information affecting the construction and maintenance of the DODAG, 160 as well as operational parameters for RPL on the DODAG, through the 161 DODAG. As shown in Figure 1, the Option was originally designed with 162 4 bit positions reserved for future use as Flags. 164 0 1 2 3 165 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 1 166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 | Type = 0x04 |Opt Length = 14| | |T| |A| ... | 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 170 Figure 1: DODAG Configuration Option (Partial View) 172 This specification defines a new flag "Enable RFC8138 Compression" 173 (T). The "T" flag is set to turn-on the use of [RFC8138] within the 174 DODAG. The "T" flag is encoded in position 2 of the reserved Flags 175 in the DODAG Configuration Option (counting from bit 0 as the most 176 significant bit) and set to 0 in legacy implementations as specified 177 respectively in Sections 20.14 and 6.7.6 of [RFC6550]. 179 The RPL DODAG Configuration Option is typically placed in a DODAG 180 Information Object (DIO) message. The DIO message propagates down 181 the DODAG to form and then maintain its structure. The DODAG 182 Configuration Option is copied unmodified from parents to children. 184 Section 6.3.1 of [RFC6550] defines a 3-bit Mode of Operation (MOP) in 185 the DIO Base Object. This specification applies to MOP values 0 to 186 6. For a MOP value of 7, the bit in position 2 is considered 187 unallocated and [RFC8138] MUST be used by default. 189 [RFC6550] states that "Nodes other than the DODAG Root MUST NOT 190 modify this information when propagating the DODAG Configuration 191 option". Therefore, a legacy parent propagates the "T" flag as set 192 by the Root whether it supports this specification or not. So when 193 the "T" flag is set, it is transparently flooded to all the nodes in 194 the DODAG. 196 4. Updating RFC 8138 198 A node SHOULD generate packets in the compressed form using [RFC8138] 199 if and only if the "T" flag is set. This behavior can be overridden 200 by configuration or network management. Overriding may be needed 201 e.g., to turn on the compression in a network where all nodes support 202 [RFC8138] but the Root does not support this specification and cannot 203 set the "T" flag, or to disable it locally in case of a problem. 205 The decision to use [RFC8138] is made by the originator of the packet 206 depending on its capabilities and its knowledge of the state of the 207 "T" flag. A router encapsulating a packet is the originator of the 208 resulting packet and is responsible for compressing the outer headers 209 with [RFC8138], but it MUST leave the encapsulated packet as is. 211 An external target [USEofRPLinfo] is not expected to support 212 [RFC8138]. In most cases, packets to and from an external target are 213 tunneled back and forth between the border router (referred to as 214 6LR) that serves the external target and the Root, regardless of the 215 MOP used in the RPL DODAG. The inner packet is typically not 216 compressed with [RFC8138], so for outgoing packets, the border router 217 just needs to decapsulate the (compressed) outer header and forward 218 the (uncompressed) inner packet towards the external target. 220 A router MUST uncompress a packet that is to be forwarded to an 221 external target. Otherwise, the router MUST forward the packet in 222 the form that the source used, either compressed or uncompressed. 224 A RUL [UNAWARE-LEAVES] is both a leaf and an external target. A RUL 225 does not participate in RPL and depends on the parent router to 226 obtain connectivity. In the case of a RUL, forwarding towards an 227 external target actually means delivering the packet. 229 5. Transition Scenarios 231 A node that supports [RFC8138] but not this specification can only be 232 used in a homogeneous network. Enabling the [RFC8138] compression 233 without a turn-on signaling method requires a "flag day"; by which 234 time all nodes must be upgraded, and at which point the network can 235 be rebooted with the [RFC8138] compression turned on. 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. Though it is possible 240 to roll back (see Section 5.3), the roll back operation SHOULD be 241 complete before the network operator adds nodes that do not support 242 [RFC8138]. 244 5.1. Coexistence 246 A node that supports this specification can operate in a network with 247 the [RFC8138] compression turned on or off with the "T" flag set 248 accordingly and in a network in transition from off to on or on to 249 off (see Section 5.2). 251 A node that does not support [RFC8138] can interoperate with nodes 252 that do in a network with [RFC8138] compression turned off. If the 253 compression is turned on, all the RPL-Aware Nodes are expected to be 254 able to handle compressed packets in the compressed form. A node 255 that cannot do so may remain connected to the network as a RUL as 256 described in [UNAWARE-LEAVES]. 258 5.2. Inconsistent State While Migrating 260 When the "T" flag is turned on by the Root, the information slowly 261 percolates through the DODAG as the DIO gets propagated. Some nodes 262 will see the flag and start sourcing packets in the compressed form 263 while other nodes in the same RPL DODAG are still not aware of it. 264 In non-storing mode, the Root will start using [RFC8138] with a 265 Source Routing Header 6LoRH (SRH-6LoRH) that routes all the way to 266 the parent router or to the leaf. 268 To ensure that a packet is forwarded across the RPL DODAG in the form 269 in which it was generated, it is required that all the RPL nodes 270 support [RFC8138] at the time of the switch. 272 Setting the "T" flag is ultimately the responsibility of the Network 273 Administrator. The expectation is that the network management or 274 upgrading tools in place enable the Network Administrator to know 275 when all the nodes that may join a DODAG were migrated. In the case 276 of a RPL instance with multiple Roots, all nodes that participate to 277 the RPL Instance may potentially join any DODAG. The network MUST be 278 operated with the "T" flag unset until all nodes in the RPL Instance 279 are upgraded to support this specification. 281 5.3. Rolling Back 283 When turning [RFC8138] compression off in the network, the Network 284 Administrator MUST wait until all nodes have converged to the "T" 285 flag unset before allowing nodes that do not support the compression 286 in the network. To that effect, whether the compression is active in 287 a node SHOULD be exposed the node's management interface. 289 Nodes that do not support [RFC8138] SHOULD NOT be deployed in a 290 network where the compression is turned on. If that is done, the 291 node can only operate as a RUL. 293 6. IANA Considerations 295 IANA is requested to assign a new option flag from the Registry for 296 the "DODAG Configuration Option Flags" that was created for [RFC6550] 297 as follows: 299 +---------------+---------------------------------+-----------+ 300 | Bit Number | Capability Description | Reference | 301 +---------------+---------------------------------+-----------+ 302 | 2 (suggested) | Turn on RFC8138 Compression (T) | THIS RFC | 303 +---------------+---------------------------------+-----------+ 305 Table 1: New DODAG Configuration Option Flag 307 7. Security Considerations 309 It is worth noting that in RPL [RFC6550], every node in the LLN that 310 is RPL-aware and has access to the RPL domain can inject any RPL- 311 based attack in the network, more in [RFC7416]. This document 312 applies typically to an existing deployment and does not change its 313 security requirements and operations. It is assumed that the 314 security mechanisms as defined for RPL are followed. 316 Setting the "T" flag before all routers are upgraded may cause a loss 317 of packets. The new bit is protected as the rest of the 318 configuration so this is just one of the many attacks that can happen 319 if an attacker manages to inject a corrupted configuration. 321 Setting and unsetting the "T" flag may create inconsistencies in the 322 network but as long as all nodes are upgraded to [RFC8138] support 323 they will be able to forward both forms. The source is responsible 324 for selecting whether the packet is compressed or not, and all 325 routers must use the format that the source selected. So the result 326 of an inconsistency is merely that both forms will be present in the 327 network, at an additional cost of bandwidth for packets in the 328 uncompressed form. 330 An attacker may unset the "T" flag to force additional energy 331 consumption of child or descendant nodes in its subDAG. Conversely 332 it may set the "T" flag, so that nodes located downstream would 333 compress when that it is not desired, potentially resulting in the 334 loss of packets. In a tree structure, the attacker would be in 335 position to drop the packets from and to the attacked nodes. So the 336 attacks above would be more complex and more visible than simply 337 dropping selected packets. The downstream node may have other 338 parents and see both settings, which could raise attention. 340 8. Acknowledgments 342 The authors wish to thank Murray Kucherawy, Meral Shirazipour, Barry 343 Leiba, Tirumaleswar Reddy, Nagendra Kumar Nainar, Stewart Bryant, 344 Carles Gomez, Eric Vyncke, Roman Danyliw, and especially Benjamin 345 Kaduk, Alvaro Retana, Dominique Barthel and Rahul Jadhav for their 346 in-depth reviews and constructive suggestions. 348 Also many thanks to Michael Richardson for being always helpful and 349 responsive when need comes. 351 9. Normative References 353 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 354 Requirement Levels", BCP 14, RFC 2119, 355 DOI 10.17487/RFC2119, March 1997, 356 . 358 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 359 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 360 May 2017, . 362 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 363 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 364 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 365 Low-Power and Lossy Networks", RFC 6550, 366 DOI 10.17487/RFC6550, March 2012, 367 . 369 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 370 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 371 2014, . 373 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 374 "IPv6 over Low-Power Wireless Personal Area Network 375 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 376 April 2017, . 378 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 379 Perkins, "Registration Extensions for IPv6 over Low-Power 380 Wireless Personal Area Network (6LoWPAN) Neighbor 381 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 382 . 384 [UNAWARE-LEAVES] 385 Thubert, P. and M. Richardson, "Routing for RPL Leaves", 386 Work in Progress, Internet-Draft, draft-ietf-roll-unaware- 387 leaves-18, 12 June 2020, . 390 10. Informative References 392 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 393 Power and Lossy Networks (RPL) Option for Carrying RPL 394 Information in Data-Plane Datagrams", RFC 6553, 395 DOI 10.17487/RFC6553, March 2012, 396 . 398 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 399 Constrained-Node Networks", RFC 7228, 400 DOI 10.17487/RFC7228, May 2014, 401 . 403 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 404 and M. Richardson, Ed., "A Security Threat Analysis for 405 the Routing Protocol for Low-Power and Lossy Networks 406 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 407 . 409 [USEofRPLinfo] 410 Robles, I., Richardson, M., and P. Thubert, "Using RPI 411 Option Type, Routing Header for Source Routes and IPv6-in- 412 IPv6 encapsulation in the RPL Data Plane", Work in 413 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-40, 414 25 June 2020, . 417 Authors' Addresses 419 Pascal Thubert (editor) 420 Cisco Systems, Inc 421 Building D 422 45 Allee des Ormes - BP1200 423 06254 MOUGINS - Sophia Antipolis 424 France 426 Phone: +33 497 23 26 34 427 Email: pthubert@cisco.com 428 Li Zhao 429 Cisco Systems, Inc 430 Xinsi Building 431 No. 926 Yi Shan Rd 432 SHANGHAI 433 200233 434 China 436 Email: liz3@cisco.com