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Zhao 4 Updates: 6550, 8138 (if approved) Cisco Systems 5 Intended status: Standards Track 22 January 2020 6 Expires: 25 July 2020 8 Configuration option for RFC 8138 9 draft-ietf-roll-turnon-rfc8138-03 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 25 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 . . . . . . . . . . . . . . . . . . . . . . 2 53 4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 3 54 5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 3 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 to [RFC8138] in a network can only be done when all 69 nodes support the specification. In a mixed case with both 70 RFC8138-capable and non-capable nodes, the compression should be 71 turned off. 73 This document complements RFC 8138 and dedicates a bit in the RPL 74 configuration option to indicate whether RFC 8138 compression should 75 be used within the RPL Instance. When the bit is not set, source 76 nodes that support RFC 8138 should refrain from using the compression 77 unless the information is superseded by configuration. 79 2. BCP 14 81 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 82 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 83 "OPTIONAL" in this document are to be interpreted as described in BCP 84 14 [RFC2119][RFC8174] when, and only when, they appear in all 85 capitals, as shown here. 87 3. Updating RFC 6550 89 RPL defines a configuration option that is registered to IANA in 90 section 20.14. of [RFC6550]. This specification defines a new flag 91 "Enable RFC8138 Compression" (T) that is encoded in one of the 92 reserved control bits in the option. The new flag is set to turn on 93 the use of the compression of RPL artifacts with RFC 8138. The bit 94 position of the "T" flag is indicated in Section 6. 96 Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) 97 in the DIO Base Object. The new "T" flag is defined only for MOP 98 value between 0 to 6. For a MOP value of 7 or above, the flag MAY 99 indicate something different and MUST NOT be interpreted as "Enable 100 RFC8138 Compression" unless the specification of the MOP indicates to 101 do so. 103 4. Updating RFC 8138 105 This document specifies controls that enable and disable the use of 106 the [RFC8138] compression in a RPL Instance. Arguably, this could 107 have been done in [RFC8138] itself. 109 A node that supports this specification SHOULD source packets in the 110 compressed form using [RFC8138] if the new "T" flag is set in the RPL 111 configuration option from its parents. Failure to do so will result 112 in larger packets, yields higher risks of loss and may cause a 113 fragmentation. 115 A node that supports this specification SHOULD refrain from sourcing 116 packets in the compressed form using [RFC8138] if the "T" flag is 117 reset. This behaviour can be overridden by a configuration of the 118 node in order to cope with intermediate implementations of the root 119 that support [RFC8138] but not this specification and cannot set the 120 "T" flag. 122 The decision of using RFC 8138 to compress a packet is made at the 123 source depending on its capabilities and its knowledge of the state 124 of the "T" flag. A router MUST forward the packet in the form that 125 the source used, either compressed or uncompressed. A router that 126 encapsulates a packet is the source of the resulting packet and the 127 rules above apply to it in that case. 129 5. Transition Scenarios 131 A node that supports [RFC8138] but not this specification can only be 132 used in a homogeneous network and an upgrade requires a "flag day" 133 where all nodes are updated and then the network is rebooted with 134 implicitly RFC 8138 compression turned on with the "T" flag set on. 136 A node that supports this specification can work in a network with 137 RFC 8138 compression turned on or off with the "T" flag set 138 accordingly and in a network in transition from off to on or on to 139 off (see Section 5.1). 141 A node that does not support [RFC8138] can interoperate with a node 142 that supports this specification in a network with RFC 8138 143 compression turned off. But it cannot forward compressed packets and 144 therefore it cannot act as a router in a network with RFC 8138 145 compression turned on. It may remain connected to that network as a 146 leaf and generate uncompressed packets. The leaf can receive packets 147 if they are delivered by the parent 6LR in the uncompressed form. 148 This requires a knowledge by the 6LR that the leaf does not support 149 RFC 8138. A RPL-Unaware-Leaf (RUL) [USEofRPLinfo] is an external 150 target and by default is not expected to support RFC 8138. 152 [RFC6550] states that "Nodes other than the DODAG root MUST NOT 153 modify this information when propagating the DODAG Configuration 154 option". In other words, the configuration option is a way for the 155 root to configure the LLN nodes but it cannot be used by a parent to 156 advertise its capabilities down the DODAG. A parent propagates the 157 "T" flag as set whether it supports RFC 8138 or not. The setting of 158 the "T" flag can thus not be used as an indication of the support by 159 the sender, and a child cannot favor a parent based on it. 161 Sections 8.5 and 9.2 of [RFC6550] also suggests that a RPL-aware node 162 may attach to a DODAG as a leaf node only, e.g., when a node does not 163 support the Mode of Operation of a RPL Instance, the Objective 164 Function (OF) as indicated by the Objective Code Point (OCP) or some 165 other parameters in the configuration option. [USEofRPLinfo] 166 indicates that the node may also join as a RUL, in which case it 167 refrains from participating to RPL and depends on the 6LR to ensure 168 connectivity regardless on the way the RPL network is operated. 170 This means that changing the OCP in a DODAG can be used to force 171 nodes that do not support a particular feature to join as leaf only. 172 This specification reiterates that a node that is configured to 173 operate in a RPL Instance but does not support a value for a known 174 parameter that is mandatory for routing MUST NOT operate as a router 175 but MAY still join as a leaf. Note that a legacy node will not 176 recognize when a reserved field is now used and will not turn to a 177 leaf when that happens. 179 The intent for this specification is to perform a migration once and 180 for all without the need for a flag day. In particular it is not the 181 intention to undo the setting of the "T" flag, and though it is 182 possible to roll back (see Section 5.4), adding nodes that do not 183 support [RFC8138] after a roll back may be problematic if the roll 184 back is not fully complete (see caveats in Section 5.2). 186 5.1. Inconsistent State While Migrating 188 When the "T" flag is turned on in the configuration option by the 189 root, the information slowly percolates through the DODAG as the DIO 190 gets propagated. Some nodes will see the flag and start sourcing 191 packets in the compressed form while other nodes in the same RPL 192 Instance are still not aware of it. Conversely, in non-storing mode, 193 the root will start using RFC 8138 with a SRH-6LoRH that routes all 194 the way to the last router or possibly to the leaf, if the leaf 195 supports RFC 8138. 197 This is why it is required that all the routers in the RPL Instance 198 support [RFC8138] at the time of the switch, and all nodes that do 199 not support [RFC8138] only operate as leaves. 201 Setting the "T" flag is ultimately the responsibility of the network 202 administrator. In a case of upgrading a network to turn the 203 compression on, the network SHOULD be operated with the "T" flag 204 reset until all targeted nodes are upgraded to support this 205 specification. Section 5.2 and Section 5.3 provide possible 206 transition scenarios where this can be enforced. 208 5.2. Single RPL Instance Scenario 210 In a Single RPL Instance Scenario, nodes that support RFC 8138 are 211 configured with a new OCP, that may use the same OF operation or a 212 variation of it. The root sets the "T" flag at the time it migrates 213 to the new OCP. As a result, nodes that do not support RFC 8138 join 214 as leaves and do not forward packets anymore. The leaves generate 215 packets without compression. The parents - which supports RFC 8138 - 216 may encapsulate the packets using RFC 8138 if needed. The other way 217 around, the root encapsulates packets to the leaves all the way to 218 the parent, which decapsulates and distribute the uncompressed inner 219 packet to the leaf. 221 This scenario presents a number of caveats: 223 * The method consumes an extra OCP. It also requires a means to 224 signal the capabilities of the leaf, e.g., using "RPL Mode of 225 Operation extension" [MOP-EXT]. 227 * If an implementation does not move to a leaf mode when the OCP is 228 changed to an unknown one, then the node may be stalled. 230 * If the only possible parents of a node are nodes that do not 231 support RFC 8138, then that node will loose all its parent at the 232 time of the migration and it will be stalled until a parent is 233 deployed with the new capability. 235 * Nodes that only support RFC8138 for forwarding may not parse the 236 RPI in native form. If such nodes are present, the parent needs 237 to encapsulate with RFC8138. 239 5.3. Double RPL Instances Scenario 241 An alternate to the Single RPL Instance Scenario is to deploy an 242 additional RPL Instance for the nodes that support [RFC8138]. The 243 two RPL Instances operate independently as specified in [RFC6550]. 244 The preexisting RPL Instance that does not use [RFC8138], whereas the 245 new RPL Instance does. This is signaled by the "T" flag which is 246 only set in the configuration option in DIO messages in the new RPL 247 Instance. 249 Nodes that support RFC 8138 participate to both Instances but favor 250 the new RPL Instance for the traffic that they source. On the other 251 hand, nodes that only support the uncompressed format would either 252 not be configured for the new RPL Instance, or would be configured to 253 join it as leaves only. 255 This method eliminates the risks of nodes being stalled that are 256 described in Section 5.2 but requires implementations to support at 257 least two RPL Instances and demands management capabilities to 258 introduce new RPL Instances and deprecate old ones. 260 5.4. Rolling Back 262 After downgrading a network to turn the [RFC8138] compression off, 263 the administrator SHOULD make sure that all nodes have converged to 264 the "T" flag reset before allowing nodes that do not support the 265 compression in the network (see caveats in Section 5.2). 267 It is RECOMMENDED to only deploy nodes that support [RFC8138] in a 268 network where the compression is turned on. A node that does not 269 support [RFC8138] MUST only be used as a leaf. 271 6. IANA Considerations 273 This specification updates the Registry for the "DODAG Configuration 274 Option Flags" that was created for [RFC6550] as follows: 276 +------------+---------------------------------+-----------+ 277 | Bit Number | Capability Description | Reference | 278 +============+=================================+===========+ 279 | 2 | Turn on RFC8138 Compression (T) | THIS RFC | 280 +------------+---------------------------------+-----------+ 282 Table 1: New DODAG Configuration Option Flag 284 7. Security Considerations 286 Turning the "T" flag on before some routers are upgraded may cause a 287 loss of packets. The new bit is protected as the rest of the 288 configuration so this is just one of the many attacks that can happen 289 if an attacker manages to inject a corrupted configuration. 291 Turning the "T" flag on and off may create inconsistencies in the 292 network but as long as all nodes are upgraded to RFC 8138 support 293 they will be able to forward both forms. The draft insists that the 294 source is responsible for selecting whether the packet is compressed 295 or not, and all routers must use the format that the source selected. 296 So the result of an inconsistency is merely that both forms will be 297 present in the network, at an additional cost of bandwidth for 298 packets in the uncompressed form. 300 8. Acknowledgments 302 9. Normative References 304 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 305 Requirement Levels", BCP 14, RFC 2119, 306 DOI 10.17487/RFC2119, March 1997, 307 . 309 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 310 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 311 May 2017, . 313 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 314 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 315 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 316 Low-Power and Lossy Networks", RFC 6550, 317 DOI 10.17487/RFC6550, March 2012, 318 . 320 [USEofRPLinfo] 321 Robles, I., Richardson, M., and P. Thubert, "Using RPI 322 Option Type, Routing Header for Source Routes and IPv6-in- 323 IPv6 encapsulation in the RPL Data Plane", Work in 324 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-34, 325 20 January 2020, . 328 10. Informative References 330 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 331 "IPv6 over Low-Power Wireless Personal Area Network 332 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 333 April 2017, . 335 [MOP-EXT] Jadhav, R., Thubert, P., and M. Richardson, "Mode of 336 Operation extension and Capabilities", Work in Progress, 337 Internet-Draft, draft-ietf-roll-mopex-cap-01, 2 November 338 2019, . 341 Authors' Addresses 343 Pascal Thubert (editor) 344 Cisco Systems, Inc 345 Building D 346 45 Allee des Ormes - BP1200 347 06254 MOUGINS - Sophia Antipolis 348 France 350 Phone: +33 497 23 26 34 351 Email: pthubert@cisco.com 353 Li Zhao 354 Cisco Systems, Inc 355 Xinsi Building 356 No. 926 Yi Shan Rd 357 SHANGHAI 358 200233 359 China 361 Email: liz3@cisco.com