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Zhao 4 Updates: 6550, 8138 (if approved) Cisco Systems 5 Intended status: Standards Track 12 December 2019 6 Expires: 14 June 2020 8 Configuration option for RFC 8138 9 draft-ietf-roll-turnon-rfc8138-02 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 14 June 2020. 34 Copyright Notice 36 Copyright (c) 2019 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 . . . . . . . . . . . 4 56 5.2. Single Instance Scenario . . . . . . . . . . . . . . . . 5 57 5.3. Double Instance 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 . . . . . . . . . . . . . . . . . . . 7 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 an homogeneous network and an upgrade requires a "flag day" 133 where all nodes are updated and then the network is rebooted with 134 implicitely 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 as long as imcoming packets 147 are decapsulated by the parent and delivered in uncompressed form. 149 [RFC6550] states that "Nodes other than the DODAG root MUST NOT 150 modify this information when propagating the DODAG Configuration 151 option". In other words, the configuration option is a way for the 152 root to configure the LLN nodes but it cannot be used by a parent to 153 advertise its capabilities down the DODAG. It results whether a 154 parent supports RFC 8138 is not known by the child with the current 155 level of specifications, and a child cannot favor a parent based on a 156 particular support. 158 Sections 8.5 and 9.2 of [RFC6550] also suggests that a RPL-aware node 159 may attach to a DODAG as a leaf node only, e.g., when a node does not 160 support the Mode of Operation of a RPL Instance, the Objective 161 Function (OF) as indicated by the Objective Code Point (OCP) or some 162 other parameters in the configuration option. But the node is also 163 free to refrain from joining an Instance when a parameter is not 164 suitable. This means that changing the OCP in a DODAG can be used to 165 force nodes that do not support a particular feature to join as leaf 166 only. This specification reiterates that a node that is configured 167 to operate in an Instance but does not support a value for a known 168 parameter that is mandatory for routing MUST NOT operate as a router 169 but MAY still joins as a leaf. Note that a legacy node will not 170 recognize when a reserved field is now used and will not turn to a 171 leaf when that happens. 173 The intent for this specification is to perform a migration once and 174 for all without the need for a flag day. In particular it is not the 175 intention to undo the setting of the "T" flag, and though it is 176 possible to roll back (see Section 5.4), adding nodes that do not 177 support [RFC8138] after a roll back may be problematic if the roll 178 back is not fully complete (see caveats in Section 5.2). 180 5.1. Inconsistent State While Migrating 182 When the "T" flag is turned on in the configuration option by the 183 root, the information slowly percolates through the DODAG as the DIO 184 gets propagated. Some nodes will see the flag and start sourcing 185 packets in the compressed form while other nodes in the same instance 186 are still not aware of it. Conversely, in non-storing mode, the root 187 will start using RFC 8138 with a SRH-6LoRH that routes all the way to 188 the last router or possibly to the leaf, if the leaf supports RFC 189 8138. 191 This is why it is required that all the routers in the Instance 192 support [RFC8138] at the time of the switch, and all nodes that do 193 not support [RFC8138] only operate as leaves. 195 Setting the "T" flag is ultimately the responsibility of the network 196 administrator. In a case of upgrading a network to turn the 197 compression on, the network SHOULD be operated with the "T" flag 198 reset until all targeted nodes are upgraded to support this 199 specification. Section 5.2 and Section 5.3 provide possible 200 transition scenarios where this can be enforced. 202 5.2. Single Instance Scenario 204 In a single instance scenario, nodes that support RFC 8138 are 205 configured with a new OCP, that may use the same OF operation or a 206 variation of it. when it finally sets the "T" flag, the root also 207 migrates to the new OCP. As a result, nodes that do not support RFC 208 8138 join as leaves and do not forward packets anymore. The leaves 209 generate packets without compression. The parents - which supports 210 RFC 8138 - may encapsulate the packets using RFC 8138 if needed. The 211 other way around, the root encapsulates packets to the leaves all the 212 way to the parent, which decapsulates and distribute the uncompresses 213 inner packet to the leaf. 215 This scenario presents a number of caveats: 217 * The method consumes an extra OCP. It also requires a means to 218 signal the capabilities of the leaf, e.g., using "RPL Mode of 219 Operation extension" [MOP-EXT]. 221 * If an implementation does not move to a leaf mode when the OCP is 222 changed to an unknown one, then the node may be stalled. 224 * If the only possible parents of a node are nodes that do not 225 support RFC 8138, then that node will loose all its parent at the 226 time of the migration and it will be stalled until a parent is 227 deployed with the new capability. 229 * Nodes that only support RFC8138 for forwarding may not parse the 230 RPI in native form. If such nodes are present, the parent needs 231 to encapsulate with RFC8138. 233 5.3. Double Instance Scenario 235 An alternate to the Single Instance Scenario is to deploy an 236 additional Instance for the nodes that support [RFC8138]. The two 237 instances operate as ships-in-the-night as specified in [RFC6550]. 238 The preexisting Instance that does not use [RFC8138], whereas the new 239 Instance does. This is signaled by the "T" flag which is only set in 240 the configuration option in DIO messages in the new Instance. 242 Nodes that support RFC 8138 participate to both Instances but favor 243 the new Instance for the traffic that they source. On the other 244 hand, nodes that only support the uncompressed format would either 245 not be configured for the new instance, or would be configured to 246 join it as leaves only. 248 This method eliminates the risks of nodes being stalled that are 249 described in Section 5.2 but requires implementations to support at 250 least two RPL Instances and demands management capabilities to 251 introduce new Instances and deprecate old ones. 253 5.4. Rolling Back 255 After downgrading a network to turn the [RFC8138] compression off, 256 the administrator SHOULD make sure that all nodes have converged to 257 the "T" flag reset before allowing nodes that do not support the 258 compression in the network (see caveats in Section 5.2). 260 It is RECOMMENDED to only deploy nodes that support [RFC8138] in a 261 network where the compression is turned on. A node that does not 262 support [RFC8138] MUST only be used as a leaf. 264 6. IANA Considerations 266 This specification updates the Registry for the "DODAG Configuration 267 Option Flags" that was created for [RFC6550] as follows: 269 +------------+---------------------------------+-----------+ 270 | Bit Number | Capability Description | Reference | 271 +============+=================================+===========+ 272 | 2 | Turn on RFC8138 Compression (T) | THIS RFC | 273 +------------+---------------------------------+-----------+ 275 Table 1: New DODAG Configuration Option Flag 277 7. Security Considerations 279 Turning the "T" flag on before some routers are upgraded may cause a 280 loss of packets. The new bit is protected as the rest of the 281 configuration so this is just one of the many attacks that can happen 282 if an attacker manages to inject a corrupted configuration. 284 Turning the "T" flag on and off may create inconsistencies in the 285 network but as long as all nodes are upgraded to RFC 8138 support 286 they will be able to forward both forms. The draft insists that the 287 source is responsible for selecting whether the packet is compressed 288 or not, and all routers must use the format that the source selected. 289 So the result of an inconsistency is merely that both forms will be 290 present in the network, at an additional cost of bandwidth for 291 packets in the uncompressed form. 293 8. Acknowledgments 295 9. Normative References 297 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 298 Requirement Levels", BCP 14, RFC 2119, 299 DOI 10.17487/RFC2119, March 1997, 300 . 302 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 303 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 304 May 2017, . 306 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 307 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 308 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 309 Low-Power and Lossy Networks", RFC 6550, 310 DOI 10.17487/RFC6550, March 2012, 311 . 313 10. Informative References 315 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 316 "IPv6 over Low-Power Wireless Personal Area Network 317 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 318 April 2017, . 320 [MOP-EXT] Jadhav, R., Thubert, P., and M. Richardson, "Mode of 321 Operation extension and Capabilities", Work in Progress, 322 Internet-Draft, draft-ietf-roll-mopex-cap-01, 2 November 323 2019, . 326 Authors' Addresses 328 Pascal Thubert (editor) 329 Cisco Systems, Inc 330 Building D, 45 Allee des Ormes - BP1200 331 06254 MOUGINS - Sophia Antipolis 332 France 334 Phone: +33 497 23 26 34 335 Email: pthubert@cisco.com 337 Li Zhao 338 Cisco Systems, Inc 339 Xinsi Building, No. 926 Yi Shan Rd 340 SHANGHAI 341 200233 342 China 344 Email: liz3@cisco.com