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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-rfc8138-01 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 Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP) 98 in the DIO Base Object. The new "T" flag is defined only for MOP 99 value between 0 to 6. For a MOP value of 7 or above, the flag MAY 100 indicate something different and MUST NOT be interpreted as "Enable 101 RFC8138 Compression" unless the specification of the MOP indicates to 102 do so. 104 4. Updating RFC 8138 106 This document specifies controls that enable and disable the use of 107 the [RFC8138] compression in a RPL Instance. Arguably, this could 108 have been done in [RFC8138] itself. 110 A node that supports this specification SHOULD source packets in the 111 compressed form using [RFC8138] if the new "T" flag is set in the RPL 112 configuration option from its parents. Failure to do so will result 113 in larger packets, yields higher risks of loss and may cause a 114 fragmentation. 116 A node that supports this specification SHOULD refrain from sourcing 117 packets in the compressed form using [RFC8138] if the "T" flag is 118 reset. This behaviour can be overridden by a configuration of the 119 node in order to cope with intermediate implementations of the root 120 that support [RFC8138] but not this specification and cannot set the 121 "T" flag. 123 The decision of using RFC 8138 to compress a packet is made at the 124 source depending on its capabilities and its knowledge of the state 125 of the "T" flag. A router MUST forward the packet in the form that 126 the source used, either compressed or uncompressed. A router that 127 encapsulates a packet is the source of the resulting packet and the 128 rules above apply to it in that case. 130 5. Transition Scenarios 132 A node that supports [RFC8138] but not this specification can only be 133 used in an homogeneous network and an upgrade requires a "flag day" 134 where all nodes are updated and then the network is rebooted with 135 implicitely RFC 8138 compression turned on with the "T" flag set on. 137 A node that supports this specification can work in a network with 138 RFC 8138 compression turned on or off with the "T" flag set 139 accordingly and in a network in transition from off to on or on to 140 off (see Section 5.1). 142 A node that does not support [RFC8138] can interoperate with a node 143 that supports this specification in a network with RFC 8138 144 compression turned off. But it cannot forward compressed packets and 145 therefore it cannot act as a router in a network with RFC 8138 146 compression turned on. It may remain connected to that network as a 147 leaf and generate uncompressed packets as long as imcoming packets 148 are decapsulated by the parent and delivered in uncompressed form. 150 [RFC6550] states that "Nodes other than the DODAG root MUST NOT 151 modify this information when propagating the DODAG Configuration 152 option". In other words, the configuration option is a way for the 153 root to configure the LLN nodes but it cannot be used by a parent to 154 advertise its capabilities down the DODAG. It results whether a 155 parent supports RFC 8138 is not known by the child with the current 156 level of specifications, and a child cannot favor a parent based on a 157 particular support. 159 Sections 8.5 and 9.2 of [RFC6550] also suggests that a RPL-aware node 160 may attach to a DODAG as a leaf node only, e.g., when a node does not 161 support the Mode of Operation of a RPL Instance, the Objective 162 Function (OF) as indicated by the Objective Code Point (OCP) or some 163 other parameters in the configuration option. But the node is also 164 free to refrain from joining an Instance when a parameter is not 165 suitable. This means that changing the OCP in a DODAG can be used to 166 force nodes that do not support a particular feature to join as leaf 167 only. This specification reiterates that a node that is configured 168 to operate in an Instance but does not support a value for a known 169 parameter that is mandatory for routing MUST NOT operate as a router 170 but MAY still joins as a leaf. Note that a legacy node will not 171 recognize when a reserved field is now used and will not turn to a 172 leaf when that happens. 174 The intent for this specification is to perform a migration once and 175 for all without the need for a flag day. In particular it is not the 176 intention to undo the setting of the "T" flag, and though it is 177 possible to roll back (see Section 5.4), adding nodes that do not 178 support [RFC8138] after a roll back may be problematic if the roll 179 back is not fully complete (see caveats in Section 5.2). 181 5.1. Inconsistent State While Migrating 183 When the "T" flag is turned on in the configuration option by the 184 root, the information slowly percolates through the DODAG as the DIO 185 gets propagated. Some nodes will see the flag and start sourcing 186 packets in the compressed form while other nodes in the same instance 187 are still not aware of it. Conversely, in non-storing mode, the root 188 will start using RFC 8138 with a SRH-6LoRH that routes all the way to 189 the last router or possibly to the leaf, if the leaf supports RFC 190 8138. 192 This is why it is required that all the routers in the Instance 193 support [RFC8138] at the time of the switch, and all nodes that do 194 not support [RFC8138] only operate as leaves. 196 Setting the "T" flag is ultimately the responsibility of the network 197 administrator. In a case of upgrading a network to turn the 198 compression on, the network SHOULD be operated with the "T" flag 199 reset until all targeted nodes are upgraded to support this 200 specification. Section 5.2 and Section 5.3 provide possible 201 transition scenarios where this can be enforced. 203 5.2. Single Instance Scenario 205 In a single instance scenario, nodes that support RFC 8138 are 206 configured with a new OCP, that may use the same OF operation or a 207 variation of it. when it finally sets the "T" flag, the root also 208 migrates to the new OCP. As a result, nodes that do not support RFC 209 8138 join as leaves and do not forward packets anymore. The leaves 210 generate packets without compression. The parents - which supports 211 RFC 8138 - may encapsulate the packets using RFC 8138 if needed. The 212 other way around, the root encapsulates packets to the leaves all the 213 way to the parent, which decapsulates and distribute the uncompresses 214 inner packet to the leaf. 216 This scenario presents a number of caveats: 218 o The method consumes an extra OCP. It also requires a means to 219 signal the capabilities of the leaf, e.g., using "RPL Mode of 220 Operation extension" [I-D.rahul-roll-mop-ext]. 222 o If an implementation does not move to a leaf mode when the OCP is 223 changed to an unknown one, then the node may be stalled. 225 o If the only possible parents of a node are nodes that do not 226 support RFC 8138, then that node will loose all its parent at the 227 time of the migration and it will be stalled until a parent is 228 deployed with the new capability. 230 o Nodes that only support RFC8138 for forwarding may not parse the 231 RPI in native form. If such nodes are present, the parent needs 232 to encapsulate with RFC8138. 234 5.3. Double Instance Scenario 236 An alternate to the Single Instance Scenario is to deploy an 237 additional Instance for the nodes that support [RFC8138]. The two 238 instances operate as ships-in-the-night as specified in [RFC6550]. 239 The preexisting Instance that does not use [RFC8138], whereas the new 240 Instance does. This is signaled by the "T" flag which is only set in 241 the configuration option in DIO messages in the new Instance. 243 Nodes that support RFC 8138 participate to both Instances but favor 244 the new Instance for the traffic that they source. On the other 245 hand, nodes that only support the uncompressed format would either 246 not be configured for the new instance, or would be configured to 247 join it as leaves only. 249 This method eliminates the risks of nodes being stalled that are 250 described in Section 5.2 but requires implementations to support at 251 least two RPL Instances and demands management capabilities to 252 introduce new Instances and deprecate old ones. 254 5.4. Rolling Back 256 After downgrading a network to turn the [RFC8138] compression off, 257 the administrator SHOULD make sure that all nodes have converged to 258 the "T" flag reset before allowing nodes that do not support the 259 compression in the network (see caveats in Section 5.2). 261 It is RECOMMENDED to only deploy nodes that support [RFC8138] in a 262 network where the compression is turned on. A node that does not 263 support [RFC8138] MUST only be used as a leaf. 265 6. IANA Considerations 267 This specification updates the "Registry for the DODAG Configuration 268 Option Flags" that was created for [RFC6550] as follows: 270 +---------------+---------------------------------+-----------------+ 271 | Bit Number | Meaning | Defining Spec | 272 +---------------+---------------------------------+-----------------+ 273 | 2 (suggested) | Turn on RFC8138 Compression | This | 274 | | (T) | | 275 +---------------+---------------------------------+-----------------+ 277 Table 1: New DODAG Configuration Option Flag 279 7. Security Considerations 281 No specific threat was identified with this specification. 283 8. Acknowledgments 284 9. References 286 9.1. Normative References 288 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 289 Requirement Levels", BCP 14, RFC 2119, 290 DOI 10.17487/RFC2119, March 1997, 291 . 293 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 294 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 295 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 296 Low-Power and Lossy Networks", RFC 6550, 297 DOI 10.17487/RFC6550, March 2012, 298 . 300 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 301 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 302 May 2017, . 304 9.2. Informative References 306 [I-D.rahul-roll-mop-ext] 307 Jadhav, R. and P. Thubert, "RPL Mode of Operation 308 extension", draft-rahul-roll-mop-ext-01 (work in 309 progress), June 2019. 311 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 312 "IPv6 over Low-Power Wireless Personal Area Network 313 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 314 April 2017, . 316 Authors' Addresses 318 Pascal Thubert (editor) 319 Cisco Systems, Inc 320 Building D 321 45 Allee des Ormes - BP1200 322 MOUGINS - Sophia Antipolis 06254 323 FRANCE 325 Phone: +33 497 23 26 34 326 Email: pthubert@cisco.com 327 Li Zhao 328 Cisco Systems, Inc 329 Xinsi Building 330 No. 926 Yi Shan Rd 331 SHANGHAI 200233 332 CHINA 334 Email: liz3@cisco.com