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Zhao 4 Updates: 6550,8138 (if approved) Cisco Systems 5 Intended status: Standards Track December 12, 2019 6 Expires: June 14, 2020 8 Configuration option for RFC 8138 9 draft-ietf-roll-turnon-rfc8138-00 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 June 14, 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 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 53 3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 2 54 4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 3 55 5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 3 56 5.1. Inconsistent State While Migrating . . . . . . . . . . . 4 57 5.2. Single Instance Scenario . . . . . . . . . . . . . . . . 5 58 5.3. Double Instance Scenario . . . . . . . . . . . . . . . . 5 59 5.4. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 6 60 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 61 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 62 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 63 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 64 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 65 9.2. Informative References . . . . . . . . . . . . . . . . . 7 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 68 1. Introduction 70 The transition to [RFC8138] in a network can only be done when all 71 nodes support the specification. In a mixed case with both 72 RFC8138-capable and non-capable nodes, the compression should be 73 turned off. 75 This document complements RFC 8138 and dedicates a bit in the RPL 76 configuration option to indicate whether RFC 8138 compression should 77 be used within the RPL instance. When the bit is not set, source 78 nodes that support RFC 8138 should refrain from using the compression 79 unless the information is superseded by configuration. 81 2. BCP 14 83 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 84 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 85 "OPTIONAL" in this document are to be interpreted as described in BCP 86 14 [RFC2119][RFC8174] when, and only when, they appear in all 87 capitals, as shown here. 89 3. Updating RFC 6550 91 RPL defines a configuration option that is registered to IANA in 92 section 20.14. of [RFC6550]. This specification defines a new flag 93 "Enable RFC8138 Compression" (T) that is encoded in one of the 94 reserved control bits in the option. The new flag is set to turn on 95 the use of the compression of RPL artifacts with RFC 8138. 97 4. Updating RFC 8138 99 This document specifies controls that enable and disable the use of 100 the [RFC8138] compression in a RPL Instance. Arguably, this could 101 have been done in [RFC8138] itself. 103 A node that supports this specification SHOULD source packets in the 104 compressed form using [RFC8138] if the new "T" flag is set in the RPL 105 configuration option from its parents. Failure to do so will result 106 in larger packets, yields higher risks of loss and may cause a 107 fragmentation. 109 A node that supports this specification SHOULD refrain from sourcing 110 packets in the compressed form using [RFC8138] if the "T" flag is 111 reset. This behavior can be overridden by a configuration of the 112 node in order to cope with intermediate implementations of the root 113 that support [RFC8138] but not this specification and cannot set the 114 "T" flag. 116 The decision of using RFC 8138 to compress a packet is made at the 117 source depending on its capabilities and its knowledge of the state 118 of the "T" flag. A router MUST forward the packet in the form that 119 the source used, either compressed or uncompressed. A router that 120 encapsulates a packet is the source of the resulting packet and the 121 rules above apply to it in that case. 123 5. Transition Scenarios 125 It is RECOMMENDED to only deploy nodes that support [RFC8138] in a 126 network where the compression is turned on. A node that does not 127 support [RFC8138] MUST only be used as a leaf in that network. 129 [RFC6550] states that "Nodes other than the DODAG root MUST NOT 130 modify this information when propagating the DODAG Configuration 131 option". In other words, the configuration option is a way for the 132 root to configure the LLN nodes but it cannot be used by a parent to 133 advertise its capabilities down the DODAG. It results whether a 134 parent supports RFC 8138 is not known by the child with the current 135 level of specifications, and a child cannot favor a parent based on a 136 particular support. 138 Sections 8.5 and 9.2 of [RFC6550] also suggests that a RPL-aware node 139 may attach to a DODAG as a leaf node only, e.g., when a node does not 140 support the Mode of Operation of a RPL Instance, the Objective 141 Function (OF) as indicated by the Objective Code Point (OCP) or some 142 other parameters in the configuration option. But the node is also 143 free to refrain from joining an Instance when a parameter is not 144 suitable. This means that changing the OCP in a DODAG can be used to 145 force nodes that do not support a particular feature to join as leaf 146 only. This specification reiterates that a node that is configured 147 to operate in an Instance but does not support a value for a known 148 parameter that is mandatory for routing MUST NOT operate as a router 149 but MAY still joins as a leaf. Note that a legacy node will not 150 recognize when a reserved field is now used and will not turn to a 151 leaf when that happens. 153 A node that supports [RFC8138] but not this specification can only be 154 used in an homogeneous network and an upgrade requires a "flag day" 155 where all nodes are updated and then the network is rebooted with 156 implicitely RFC 8138 compression turned on with the "T" flag set on. 158 A node that supports this specification can work in a network with 159 RFC 8138 compression turned on or off with the "T" flag set 160 accordingly and in a network in transition from off to on or on to 161 off (see Section 5.1). 163 A node that does not support [RFC8138] can interoperate with a node 164 that supports this specification in a network with RFC 8138 165 compression turned off. But it cannot forward compressed packets and 166 therefore it cannot act as a router in a network with RFC 8138 167 compression turned on. It may remain connected to that network as a 168 leaf and generate uncompressed packets as long as imcoming packets 169 are decapsulated by the parent and delivered in uncompressed form. 171 The intent for this specification is to perform a migration once and 172 for all without the need for a flag day. In particular it is not the 173 intention to undo the setting of the "T" flag, and though it is 174 possible to roll back (see Section 5.4), adding nodes that do not 175 support [RFC8138] after a roll back may be problematic if the roll 176 back is not fully complete (see caveats in Section 5.2). 178 5.1. Inconsistent State While Migrating 180 When the "T" flag is turned on in the configuration option by the 181 root, the information slowly percolates through the DODAG as the DIO 182 gets propagated. Some nodes will see the flag and start sourcing 183 packets in the compressed form while other nodes in the same instance 184 are still not aware of it. Conversely, in non-storing mode, the root 185 will start using RFC 8138 with a SRH-6LoRH that routes all the way to 186 the last router or possibly to the leaf, if the leaf supports RFC 187 8138. 189 This is why it is required that all the routers in the Instance 190 support [RFC8138] at the time of the switch, and all nodes that do 191 not support [RFC8138] only operate as leaves. 193 Setting the "T" flag is ultimately the responsibility of the network 194 administrator. In a case of upgrading a network to turn the 195 compression on, the network SHOULD be operated with the "T" flag 196 reset until all targeted nodes are upgraded to support this 197 specification. Section 5.2 and Section 5.3 provide possible 198 transition scenarios where this can be enforced. 200 5.2. Single Instance Scenario 202 In a single instance scenario, nodes that support RFC 8138 are 203 configured with a new OCP, that may use the same OF operation or a 204 variation of it. when it finally sets the "T" flag, the root also 205 migrates to the new OCP. As a result, nodes that do not support RFC 206 8138 join as leaves and do not forward packets anymore. The leaves 207 generate packets without compression. The parents - which supports 208 RFC 8138 - may encapsulate the packets using RFC 8138 if needed. The 209 other way around, the root encapsulates packets to the leaves all the 210 way to the parent, which decapsulates and distribute the uncompresses 211 inner packet to the leaf, as illustrated in Section 4.3 of 212 [I-D.ietf-roll-useofrplinfo] 214 This scenario presents a number of caveats: 216 o The method consumes an extra OCP. It also requires a means to 217 signal the capabilities of the leaf, e.g., using "RPL Mode of 218 Operation extension" [I-D.rahul-roll-mop-ext]. 220 o If an implementation does not move to a leaf mode when the OCP is 221 changed to an unknown one, then the node may be stalled. 223 o If the only possible parents of a node are nodes that do not 224 support RFC 8138, then that node will loose all its parent at the 225 time of the migration and it will be stalled until a parent is 226 deployed with the new capability. 228 o Nodes that only support RFC8138 for forwarding may not parse the 229 RPI in native form. If such nodes are present, the parent needs 230 to encapsulate with RFC8138. 232 5.3. Double Instance Scenario 234 An alternate to the Single Instance Scenario is to deploy an 235 additional Instance for the nodes that support [RFC8138]. The two 236 instances operate as ships-in-the-night as specified in [RFC6550]. 237 The preexisting Instance that does not use [RFC8138], whereas the new 238 Instance does. This is signaled by the "T" flag which is only set in 239 the configuration option in DIO messages in the new Instance. 241 The legacy nodes would not be configured to participate to the second 242 instance, and islands that are only connected via legacy nodes would 243 not be reachable over the second instance. 245 Nodes that support RFC 8138 participate to both Instances but favor 246 the new Instance for the traffic that they source. On the other 247 hand, nodes that only support the uncompressed format would either 248 not be configured for the new instance, or would be configured to 249 join it as leaves only. 251 This method eliminates the risks of nodes being stalled that are 252 described in Section 5.2 but requires implementations to support at 253 least two RPL Instances and demands management capabilities to 254 introduce new Instances and deprecate old ones. 256 5.4. Rolling Back 258 After downgrading a network to turn the [RFC8138] compression off, 259 the administrator SHOULD make sure that all nodes have converged to 260 the "T" flag reset before allowing nodes that do not support the 261 compression in the network (see caveats in Section 5.2). This also 262 requires a means to signal the current state of the setting of the 263 logic that controls the compression in the node, also using 264 [I-D.rahul-roll-mop-ext]. 266 6. IANA Considerations 268 This specification updates the "Registry for the DODAG Configuration 269 Option Flags" that was created for [RFC6550] as follows: 271 +---------------+---------------------------------+-----------------+ 272 | Bit Number | Meaning | Defining Spec | 273 +---------------+---------------------------------+-----------------+ 274 | 2 (suggested) | Turn on RFC8138 Compression | This | 275 | | (T) | | 276 +---------------+---------------------------------+-----------------+ 278 Table 1: New DODAG Configuration Option Flag 280 7. Security Considerations 282 No specific threat was identified with this specification. 284 8. Acknowledgments 285 9. References 287 9.1. Normative References 289 [I-D.ietf-roll-useofrplinfo] 290 Robles, I., Richardson, M., and P. Thubert, "Using RPL 291 Option Type, Routing Header for Source Routes and IPv6-in- 292 IPv6 encapsulation in the RPL Data Plane", draft-ietf- 293 roll-useofrplinfo-32 (work in progress), November 2019. 295 [I-D.rahul-roll-mop-ext] 296 Jadhav, R. and P. Thubert, "RPL Mode of Operation 297 extension", draft-rahul-roll-mop-ext-01 (work in 298 progress), June 2019. 300 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 301 Requirement Levels", BCP 14, RFC 2119, 302 DOI 10.17487/RFC2119, March 1997, 303 . 305 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 306 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 307 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 308 Low-Power and Lossy Networks", RFC 6550, 309 DOI 10.17487/RFC6550, March 2012, 310 . 312 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 313 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 314 May 2017, . 316 9.2. Informative References 318 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 319 "IPv6 over Low-Power Wireless Personal Area Network 320 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 321 April 2017, . 323 Authors' Addresses 324 Pascal Thubert (editor) 325 Cisco Systems, Inc 326 Building D 327 45 Allee des Ormes - BP1200 328 MOUGINS - Sophia Antipolis 06254 329 FRANCE 331 Phone: +33 497 23 26 34 332 Email: pthubert@cisco.com 334 Li Zhao 335 Cisco Systems, Inc 336 Xinsi Building 337 No. 926 Yi Shan Rd 338 SHANGHAI 200233 339 CHINA 341 Email: liz3@cisco.com