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Zhao 4 Updates: 6550, 8138 (if approved) Cisco Systems 5 Intended status: Standards Track 24 January 2020 6 Expires: 27 July 2020 8 Configuration option for RFC 8138 9 draft-ietf-roll-turnon-rfc8138-04 11 Abstract 13 This document complements RFC 8138 and dedicates a bit in the RPL 14 configuration option defined in RFC 6550 to indicate whether RFC 8138 15 compression is used within the RPL Instance. 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 27 July 2020. 34 Copyright Notice 36 Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 51 2. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 52 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 3 53 4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 3 54 5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 4 55 5.1. Inconsistent State While Migrating . . . . . . . . . . . 5 56 5.2. Single RPL Instance Scenario . . . . . . . . . . . . . . 5 57 5.3. Double RPL Instances Scenario . . . . . . . . . . . . . . 6 58 5.4. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 6 59 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 60 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 61 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 62 9. Normative References . . . . . . . . . . . . . . . . . . . . 7 63 10. Informative References . . . . . . . . . . . . . . . . . . . 8 64 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 66 1. Introduction 68 The transition of a RPL [RFC6550] network to activate the compression 69 defined in [RFC8138] can only be done when all routers in the network 70 support it. A non-capable node acting as a router would drop the 71 compressed packets and black-hole its subDAG. In a mixed case with 72 both RFC8138-capable and non-capable nodes, the compression may be 73 turned on only if all the non-capable nodes act as leaves and their 74 RPL parents handle the compression/decompression on their behalf. 76 This document complements RFC 8138 and dedicates a flag in the RPL 77 configuration option to indicate whether RFC 8138 compression should 78 be used within the RPL Instance. The setting of new flag is 79 controlled by the Root and propagates as is in the whole network. 80 When the bit is not set, source nodes that support RFC 8138 should 81 refrain from using the compression unless the information is 82 superseded by configuration. 84 This specification provides scenarios that force a legacy node to 85 become a RPL-Aware-Leaf (RAL). In that case, the 6LR must be aware 86 by means out of scope that it must uncompress the packets before 87 delivering to the RAL. 89 2. BCP 14 91 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 92 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 93 "OPTIONAL" in this document are to be interpreted as described in BCP 94 14 [RFC2119][RFC8174] when, and only when, they appear in all 95 capitals, as shown here. 97 3. Updating RFC 6550 99 This specification defines a new flag "Enable RFC8138 Compression" 100 (T). The "T" flag is set to turn on the use of the compression of 101 RPL artifacts with [RFC8138] within a RPL Instance. If a RPL 102 Instance has multiple Roots then they must be coordinated to use the 103 same setting. 105 RPL defines a Configuration Option that is registered to IANA in 106 section 20.14. of [RFC6550]. The "T" flag is encoded in one of the 107 reserved control bits in the RPL Configuration Option. The bit 108 position of the "T" flag is indicated in Section 6. 110 Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) 111 in the DIO Base Object. The new "T" flag is defined only for MOP 112 value between 0 to 6. For a MOP value of 7 or above, the flag MAY 113 indicate something different and MUST NOT be interpreted as "Enable 114 RFC8138 Compression" unless the specification of the MOP indicates to 115 do so. 117 4. Updating RFC 8138 119 A node that supports this specification MUST source packets in the 120 compressed form using [RFC8138] if and only if the "T" flag is set. 121 This behaviour can be overridden by a configuration of the node in 122 order to cope with intermediate implementations of the root that 123 support [RFC8138] but not this specification and cannot set the "T" 124 flag. 126 The decision of using [RFC8138] is made by the originator of the 127 packet depending on its capabilities and its knowledge of the state 128 of the "T" flag. A router that encapsulates a packet is the 129 originator of the resulting packet and decides whether to compress 130 the outer headers as indicated above. An external target 131 [USEofRPLinfo] is not expected to support [RFC8138]. An intermediate 132 router MUST forward the packet in the form that the source used, 133 either compressed or uncompressed, unless it is either forwarding to 134 an external target or delivering to a leaf that is not known to 135 support RFC 8138, in which cases it MUST uncompress the packet. 137 A RPL-Unaware Leaf (RUL) [UNAWARE-LEAVES] is both a leaf and an 138 external target. A RUL does not participate to RPL and depends on 139 the 6LR to ensure its connectivity. Packets from/to a RUL are 140 tunneled back and forth to the Root regardless of the MOP used in the 141 RPL Instance. A node that supports this specification but does not 142 support [RFC8138] SHOULD join as a RUL to ensure that the 6LR is 143 aware it needs to uncompress the packets before delivering. 145 5. Transition Scenarios 147 A node that supports [RFC8138] but not this specification can only be 148 used in a homogeneous network and an upgrade requires a "flag day" 149 where all nodes are updated and then the network is rebooted with 150 implicitly RFC 8138 compression turned on with the "T" flag set on. 152 A node that supports this specification can work in a network with 153 RFC 8138 compression turned on or off with the "T" flag set 154 accordingly and in a network in transition from off to on or on to 155 off (see Section 5.1). 157 A node that does not support [RFC8138] can interoperate with nodes 158 that do in a network with RFC 8138 compression turned off. If the 159 compression is turned on, the node cannot forward compressed packets 160 and therefore it cannot act as a router. It may remain connected to 161 that network as a leaf, in which case it generates uncompressed 162 packets and can receive packets if they are delivered by the parent 163 6LR in the uncompressed form. 165 [RFC6550] states that "Nodes other than the DODAG root MUST NOT 166 modify this information when propagating the DODAG Configuration 167 option". Therefore, even a legacy parent propagates the "T" flag as 168 set by the Root whether it supports this specification or not. So 169 when the "T" flag is set, it is transparently flooded to all the 170 nodes in the RPL Instance. 172 Sections 8.5 and 9.2 of [RFC6550] also suggests that a RPL-aware node 173 may only attach to a DODAG as a leaf node when the node does not 174 support the Mode of Operation of a RPL Instance, the Objective 175 Function (OF) as indicated by the Objective Code Point (OCP) or some 176 other parameters in the configuration option. 178 Per the above, changing the OCP in a DODAG can be used to force nodes 179 that do not support a particular feature to join as leaf only. This 180 specification reiterates that a node that is configured to operate in 181 a RPL Instance but does not support a value for a known parameter 182 that is mandatory for routing MUST NOT operate as a router but MAY 183 still join as a leaf. Note that a legacy node will not recognize 184 when a reserved field is now used and will not turn to a leaf when 185 the "T" flag is set. 187 The intent for this specification is to perform a migration once and 188 for all without the need for a flag day. In particular it is not the 189 intention to undo the setting of the "T" flag, and though it is 190 possible to roll back (see Section 5.4), adding nodes that do not 191 support [RFC8138] after a roll back may be problematic if the roll 192 back is not fully complete (see caveats in Section 5.2). 194 5.1. Inconsistent State While Migrating 196 When the "T" flag is turned on in the configuration option by the 197 root, the information slowly percolates through the DODAG as the DIO 198 gets propagated. Some nodes will see the flag and start sourcing 199 packets in the compressed form while other nodes in the same RPL 200 Instance are still not aware of it. Conversely, in non-storing mode, 201 the root will start using RFC 8138 with a SRH-6LoRH that routes all 202 the way to the last router or possibly to the leaf, if the leaf 203 supports RFC 8138. 205 This is why it is required that all the routers in the RPL Instance 206 support [RFC8138] at the time of the switch, and all nodes that do 207 not support [RFC8138] only operate as leaves. 209 Setting the "T" flag is ultimately the responsibility of the network 210 administrator. In a case of upgrading a network to turn the 211 compression on, the network SHOULD be operated with the "T" flag 212 reset until all targeted nodes are upgraded to support this 213 specification. Section 5.2 and Section 5.3 provide possible 214 transition scenarios where this can be enforced. 216 5.2. Single RPL Instance Scenario 218 In a Single RPL Instance Scenario, nodes that support RFC 8138 are 219 configured with a new OCP, that may use the same OF operation or a 220 variation of it. The root sets the "T" flag at the time it migrates 221 to the new OCP. As a result, nodes that do not support RFC 8138 join 222 as leaves and do not forward packets anymore. The leaves generate 223 packets without compression. The parents - which supports RFC 8138 - 224 may encapsulate the packets using RFC 8138 if needed. The other way 225 around, the root encapsulates packets to the leaves all the way to 226 the parent, which decapsulates and distribute the uncompressed inner 227 packet to the leaf. 229 This scenario presents a number of caveats: 231 * The method consumes an extra OCP. It also requires a means to 232 signal the capabilities of the leaf, e.g., using "RPL Mode of 233 Operation extension" [MOP-EXT]. 235 * If an implementation does not move to a leaf mode when the OCP is 236 changed to an unknown one, then the node may be stalled. 238 * If the only possible parents of a node are nodes that do not 239 support RFC 8138, then that node will loose all its parent at the 240 time of the migration and it will be stalled until a parent is 241 deployed with the new capability. 243 * Nodes that only support RFC8138 for forwarding may not parse the 244 RPI in native form. If such nodes are present, the parent needs 245 to encapsulate with RFC8138. 247 5.3. Double RPL Instances Scenario 249 An alternate to the Single RPL Instance Scenario is to deploy an 250 additional RPL Instance for the nodes that support [RFC8138]. The 251 two RPL Instances operate independently as specified in [RFC6550]. 252 The preexisting RPL Instance that does not use [RFC8138], whereas the 253 new RPL Instance does. This is signaled by the "T" flag which is 254 only set in the configuration option in DIO messages in the new RPL 255 Instance. 257 Nodes that support RFC 8138 participate to both Instances but favor 258 the new RPL Instance for the traffic that they source. On the other 259 hand, nodes that only support the uncompressed format would either 260 not be configured for the new RPL Instance, or would be configured to 261 join it as leaves only. 263 This method eliminates the risks of nodes being stalled that are 264 described in Section 5.2 but requires implementations to support at 265 least two RPL Instances and demands management capabilities to 266 introduce new RPL Instances and deprecate old ones. 268 5.4. Rolling Back 270 After downgrading a network to turn the [RFC8138] compression off, 271 the administrator SHOULD make sure that all nodes have converged to 272 the "T" flag reset before allowing nodes that do not support the 273 compression in the network (see caveats in Section 5.2). 275 It is RECOMMENDED to only deploy nodes that support [RFC8138] in a 276 network where the compression is turned on. A node that does not 277 support [RFC8138] MUST only be used as a leaf. 279 6. IANA Considerations 281 This specification updates the Registry for the "DODAG Configuration 282 Option Flags" that was created for [RFC6550] as follows: 284 +------------+---------------------------------+-----------+ 285 | Bit Number | Capability Description | Reference | 286 +============+=================================+===========+ 287 | 2 | Turn on RFC8138 Compression (T) | THIS RFC | 288 +------------+---------------------------------+-----------+ 290 Table 1: New DODAG Configuration Option Flag 292 7. Security Considerations 294 Setting the "T" flag before some routers are upgraded may cause a 295 loss of packets. The new bit is protected as the rest of the 296 configuration so this is just one of the many attacks that can happen 297 if an attacker manages to inject a corrupted configuration. 299 Setting and resetting the "T" flag may create inconsistencies in the 300 network but as long as all nodes are upgraded to RFC 8138 support 301 they will be able to forward both forms. The draft insists that the 302 source is responsible for selecting whether the packet is compressed 303 or not, and all routers must use the format that the source selected. 304 So the result of an inconsistency is merely that both forms will be 305 present in the network, at an additional cost of bandwidth for 306 packets in the uncompressed form. 308 8. Acknowledgments 310 The authors wish to thank Rahul Jadhav for his in-depth review and 311 constructive suggestions. 313 9. Normative References 315 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 316 Requirement Levels", BCP 14, RFC 2119, 317 DOI 10.17487/RFC2119, March 1997, 318 . 320 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 321 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 322 May 2017, . 324 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 325 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 326 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 327 Low-Power and Lossy Networks", RFC 6550, 328 DOI 10.17487/RFC6550, March 2012, 329 . 331 [USEofRPLinfo] 332 Robles, I., Richardson, M., and P. Thubert, "Using RPI 333 Option Type, Routing Header for Source Routes and IPv6-in- 334 IPv6 encapsulation in the RPL Data Plane", Work in 335 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-34, 336 20 January 2020, . 339 [UNAWARE-LEAVES] 340 Thubert, P. and M. Richardson, "Routing for RPL Leaves", 341 Work in Progress, Internet-Draft, draft-ietf-roll-unaware- 342 leaves-08, 16 December 2019, . 345 10. Informative References 347 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 348 "IPv6 over Low-Power Wireless Personal Area Network 349 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 350 April 2017, . 352 [MOP-EXT] Jadhav, R., Thubert, P., and M. Richardson, "Mode of 353 Operation extension and Capabilities", Work in Progress, 354 Internet-Draft, draft-ietf-roll-mopex-cap-01, 2 November 355 2019, . 358 Authors' Addresses 360 Pascal Thubert (editor) 361 Cisco Systems, Inc 362 Building D 363 45 Allee des Ormes - BP1200 364 06254 MOUGINS - Sophia Antipolis 365 France 367 Phone: +33 497 23 26 34 368 Email: pthubert@cisco.com 370 Li Zhao 371 Cisco Systems, Inc 372 Xinsi Building 373 No. 926 Yi Shan Rd 374 SHANGHAI 375 200233 376 China 377 Email: liz3@cisco.com