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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 5226 (Obsoleted by RFC 8126) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Softwire WG M. Boucadair 3 Internet-Draft Orange 4 Intended status: Standards Track I. Farrer 5 Expires: March 17, 2017 Deutsche Telekom 6 September 13, 2016 8 Unified IPv4-in-IPv6 Softwire CPE 9 draft-ietf-softwire-unified-cpe-06 11 Abstract 13 In IPv6-only provider networks, transporting IPv4 packets 14 encapsulated in IPv6 is a common solution to the problem of IPv4 15 service continuity. A number of differing functional approaches have 16 been developed for this, each having their own specific 17 characteristics. As these approaches share a similar functional 18 architecture and use the same data plane mechanisms, this memo 19 specifies a DHCPv6 option whereby a single CPE can interwork with all 20 of the standardized and proposed approaches to providing encapsulated 21 IPv4 in IPv6 services. 23 Requirements Language 25 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 26 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 27 document are to be interpreted as described in RFC 2119 [RFC2119]. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on March 17, 2017. 46 Copyright Notice 48 Copyright (c) 2016 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 64 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 65 1.2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 4 66 1.3. DHCPv6 S46 Priority Option . . . . . . . . . . . . . . . 4 67 1.4. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . 5 68 1.5. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . 6 69 2. Operator Deployment Considerations for Deploying Multiple 70 Sotfwire Mechanisms . . . . . . . . . . . . . . . . . . . . . 6 71 2.1. Client Address Planning . . . . . . . . . . . . . . . . . 6 72 2.2. Backwards Compatability with Existing Softwire Clients . 7 73 3. Security Considerations . . . . . . . . . . . . . . . . . . . 7 74 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 75 4.1. S46 Mechanisms and their Identifying Option Codes . . . . 7 76 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 77 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 78 6.1. Normative References . . . . . . . . . . . . . . . . . . 8 79 6.2. Informative References . . . . . . . . . . . . . . . . . 9 80 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 82 1. Introduction 84 IPv4 service continuity is one of the major technical challenges 85 which must be considered during IPv6 migration. Over the past few 86 years, a number of different approaches have been developed to assist 87 with this problem (e.g., [RFC6333], [RFC7596], or [RFC7597]). These 88 approaches, referred to as 'S46 mechanisms' in this document, exist 89 in order to meet the particular deployment, scaling, addressing and 90 other requirements of different service provider's networks. 92 A common feature shared between all of the differing modes is the 93 integration of softwire tunnel end-point functionality into the 94 Customer Premise Equipment (CPE) router. Due to this inherent data 95 plane similarity, a single CPE may be capable of supporting several 96 different approaches. Users may also wish to configure a specific 97 mode of operation. 99 A service provider's network may also have more than one S46 100 mechanism enabled in order to support a diverse CPE population with 101 differing client functionality, such as during a migration between 102 mechanisms, or where services require specific supporting softwire 103 architectures. 105 For softwire based services to be successfully established, it is 106 essential that the customer end-node, the service provider end-node 107 and provisioning systems are able to indicate their capabilities and 108 preferred mode of operation. 110 A number of DHCPv6 options for the provisioning of softwires have 111 been standardized: 113 RFC6334 Defines DHCPv6 option 64 for configuring Basic Bridging 114 BroadBand (B4, [RFC6333]) elements with the IPv6 address of 115 the Address Family Transition Router (AFTR, [RFC6333]). 116 RFC7341 Defines DHCPv6 option 88 for configuring the address of a 117 DHCPv4 over DHCPv6 server, which can then be used by a 118 softwire client for obtaining further configuration. 119 RFC7598 Defines DHCPv6 options 94, 95 and 96 for provisioning Mapping 120 of Address and Port with Encapsulation (MAP-E, [RFC7597]), 121 Mapping of Address and Port using Translation (MAP-T, 122 [RFC7599]), and Lightweight 4over6 [RFC7596] respectively. 124 This document describes a DHCPv6 based prioritization method whereby 125 a CPE which supports several S46 mechanisms and receives 126 configuration for more than one can prioritise which mechanism to 127 use. The method requires no server side logic to be implemented and 128 only uses a simple S46 mechanism prioritization to be implemented in 129 the CPE. 131 The prioritization method as described here does not provide 132 redundancy between S46 mechanisms for the client. I.e. If the 133 highest priority S46 mechanism which has been provisioned to the 134 client is not available for any reason, the means for identifying 135 this and falling back to the S46 mechanism with the next highest 136 priority is not in the scope of this document. 138 1.1. Terminology 140 This document makes use of the following terms: 142 o Address Family Transition Router (AFTR): is the IPv4-in-IPv6 143 tunnel termination point and the NAT44 function deployed in the 144 operator's network [RFC6333]. 145 o Border Relay (BR): a MAP-enabled router managed by the service 146 provider at the edge of a MAP domain. A BR has at least an 147 IPv6-enabled interface and an IPv4 interface connected to the 148 native IPv4 network [RFC7597]. 149 o Customer Premise Equipment (CPE): denotes the equipment at the 150 customer edge that terminates the customer end of an IPv6 151 transitional tunnel. In some documents (e.g., [RFC7597]), this 152 functional entity is called CE (Customer Edge). 154 1.2. Rationale 156 The following rationale has been adopted for this document: 158 (1) Simplify solution migration paths: Define unified CPE behavior, 159 allowing for smooth migration between the different s46 160 mechanisms. 161 (2) Deterministic CPE co-existence behavior: Specify the behavior 162 when several S46 mechanisms co-exist in the CPE. 163 (3) Deterministic service provider co-existence behavior: Specify 164 the behavior when several modes co-exist in the service 165 providers network. 166 (4) Re-usability: Maximize the re-use of existing functional blocks 167 including tunnel end-points, port restricted NAPT44, forwarding 168 behavior, etc. 169 (5) Solution agnostic: Adopt neutral terminology and avoid (as far 170 as possible) overloading the document with solution-specific 171 terms. 172 (6) Flexibility: Allow operators to compile CPE software only for 173 the mode(s) necessary for their chosen deployment context(s). 174 (7) Simplicity: Provide a model that allows operators to only 175 implement the specific mode(s) that they require without the 176 additional complexity of unneeded modes. 178 1.3. DHCPv6 S46 Priority Option 180 The S46 Priority Option is used to convey a priority order of IPv4 181 service continuity mechanisms. Figure 1 shows the format of the S46 182 Priority Option. 184 0 1 2 3 185 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 | OPTION_S46_PRIORITY | option-length | 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 | s46-option-code | s46-option-code | 190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 191 | ... | s46-option-code | 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 194 Figure 1: S46 Priority Option 196 o option-code: OPTION_S46_PRIORITY (TBD) 197 o option-length: >=2 and a multiple of 2, in octets. 198 o s46-option-code: 16-bits long IANA registered option code of the 199 DHCPv6 option which is used to identify the softwire mechanism. 200 S46 mechanism are prioritized in the appearance order in the S46 201 Priority Option. 203 Each defined s46_option_code MUST NOT appear more than once within 204 the list of S46 option codes. The option MUST contain at least one 205 s46-option-code. 207 1.4. DHCPv6 Client Behavior 209 Clients MAY request option OPTION_S46_PRIORITY, as defined in 210 [RFC3315], Sections 17.1.1, 18.1.1, 18.1.3, 18.1.4, 18.1.5, and 22.7. 211 As a convenience to the reader, we mention here that the client 212 includes requested option codes in the Option Request Option. 214 Upon receipt of a DHCPv6 Advertise message from the server containing 215 OPTION_S46_PRIORITY the client performs the following steps: 217 1. Check the contents of the DHCPv6 message for options containing 218 valid S46 mechanism configuration. A candidate list of possible 219 S46 mechanisms is created from these option codes. 220 2. Check the contents of OPTION_S46_PRIORITY for the DHCPv6 option 221 codes contained in the included s46-option-code fields. From 222 this, an S46 mechanism priority list is created, ordered from 223 highest to lowest following the appearance order. 224 3. Sequentially check the priority list against the candidate list 225 until a match is found. 226 4. When a match is found, the client MUST configure the resulting 227 S46 mechanism. 229 In the event that no match is found between the priority list and the 230 candidate list, the client MAY proceed with configuring one or more 231 of the provisioned S46 softwire mechanism(s). In this case, which 232 mechanism(s) are chosen by the client is implementation-specific and 233 not defined here. 235 If an invalid OPTION_S46_PRIORITY option is received, the client MAY 236 proceed with configuring the provisioned S46 mechanisms as if 237 OPTION_S46_PRIORITY had not been received. 239 If an unknown option code is received in OPTION_S46_PRIORITY option, 240 the client MUST skip it and continue processing other listed option 241 codes if they exist. The initial option codes that are allowed to be 242 included in a OPTION_S46_PRIORITY option are listed in Section 4.1. 244 1.5. DHCPv6 Server Behavior 246 Sections 17.2.2 and 18.2 of [RFC3315] govern server operation in 247 regards to option assignment. As a convenience to the reader, we 248 mention here that the server will send a particular option code only 249 if configured with specific values for that option code and if the 250 client requested it. 252 Option OPTION_S46_PRIORITY is a singleton. Servers MUST NOT send 253 more than one instance of the OPTION_S46_PRIORITY option. 255 2. Operator Deployment Considerations for Deploying Multiple Sotfwire 256 Mechanisms 258 The following sub-sections describe some considerations for operators 259 who are planning on implementing multiple softwire mechanisms in 260 their network (e.g., during a migration between mechanisms). 262 2.1. Client Address Planning 264 As an operator's available IPv4 resources are likely to be limited, 265 it may be desirable to use a common range of IPv4 addresses across 266 all of the active Softwire mechanisms. However, this is likely to 267 result in difficulties in routing ingress IPv4 traffic to the correct 268 Border Relay (BR)/AFTR instance which is actively serving a given CE. 269 For example, a client which is configured to use MAP-E may send its 270 traffic to the MAP-E BR, but on the return path, the ingress IP 271 traffic gets routed to a MAP-T BR. The resulting translated packet 272 that gets forwarded to the MAP-E client will be dropped. 274 Therefore, operators are advised to use separate IPv4 pools for each 275 of the different mechanisms to simplify planning and IPv4 routing. 277 For IPv6 planning there is less of a constraint as the BR/AFTR 278 elements for the different mechanisms can contain configuration for 279 overlapping client's IPv6 addresses, providing only one mechanism is 280 actively serving a given client at a time. However, the IPv6 address 281 that is used as the tunnel concentrator's endpoint (BR/AFTR address) 282 needs to be different for each mechanisms to ensure correct 283 operation. 285 2.2. Backwards Compatability with Existing Softwire Clients 287 Deployed clients which can support multiple softwire mechanisms, but 288 do not implement the prioritization mechanism described here may 289 require additional planning. In this scenario, the CPE would request 290 configuration for all of the supported softwire mechanisms in its 291 DHCPv6 Option Request Option (ORO), but would not request 292 OPTION_S46_PRIORITY. By default, the DHCPv6 server will respond with 293 configuration for all of the requested mechanisms which could result 294 in unpredictable and unwanted client configuration. 296 In this scenario, it may be necessary for the operator to implement 297 logic within the DHCPv6 server to identify such clients and only 298 provision them with configuration for a single softwire mechanism. 299 It should be noted that this can lead to complexity and reduced 300 scalability in the DHCPv6 server implementation due to the addition 301 DHCPv6 message processing overhead. 303 3. Security Considerations 305 Security considerations discussed in [RFC6334] and [RFC7598] apply 306 for this document. 308 Misbehaving intermediate nodes may alter the content of the S46 309 Priority Option. This may lead to setting a different IPv4 service 310 continuity mechanism than the one initially preferred by the network 311 side. 313 4. IANA Considerations 315 IANA is kindly requested to allocate the following DHCPv6 option 316 code: 318 TBD for OPTION_S46_PRIORITY 320 All values should be added to the DHCPv6 option code space defined in 321 Section 24.3 of [RFC3315]. 323 4.1. S46 Mechanisms and their Identifying Option Codes 325 This document requests that IANA create a new registry entitled 326 "Option Codes permitted in the S46 Priority Option". This registry 327 will enumerate the set of DHCPv6 Option Codes that can be included in 328 OPTION_S46_PRIORITY option. Options may be added to this list using 329 the IETF Review process described in Section 4.1 of [RFC5226]. 331 The following table shows the option codes which are currently 332 defined and the S46 mechanisms which they represent. The contents of 333 this table shows the format and the initial values for the new 334 registry. Option codes that have not been requested to be added 335 according to the stated procedure should not be mentioned at all in 336 the table, and should not be listed as "reserved" or "unassigned". 337 The valid range of values for the registry is the range of DHCPv6 338 Option Codes (1-65535). 340 +-------------+--------------------+-----------+ 341 | Option Code | S46 Mechanism | Reference | 342 +-------------+--------------------+-----------+ 343 | 64 | DS-Lite | [RFC6334] | 344 | 88 | DHCPv4 over DHCPv6 | [RFC7341] | 345 | 94 | MAP-E | [RFC7598] | 346 | 95 | MAP-T | [RFC7598] | 347 | 96 | Lightweight 4over6 | [RFC7598] | 348 +-------------+--------------------+-----------+ 350 Table 1: DHCPv6 Option to S46 Mechanism Mappings 352 5. Acknowledgements 354 Many thanks to O. Troan, S. Barth. A. Yourtchenko, B. Volz, T. 355 Mrugalski, J. Scudder, P. Kyzivat, and F. Baker for their input 356 and suggestions. 358 6. References 360 6.1. Normative References 362 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 363 Requirement Levels", BCP 14, RFC 2119, 364 DOI 10.17487/RFC2119, March 1997, 365 . 367 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 368 C., and M. Carney, "Dynamic Host Configuration Protocol 369 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 370 2003, . 372 [RFC6334] Hankins, D. and T. Mrugalski, "Dynamic Host Configuration 373 Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite", 374 RFC 6334, DOI 10.17487/RFC6334, August 2011, 375 . 377 [RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I. 378 Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport", 379 RFC 7341, DOI 10.17487/RFC7341, August 2014, 380 . 382 [RFC7598] Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec, 383 W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for 384 Configuration of Softwire Address and Port-Mapped 385 Clients", RFC 7598, DOI 10.17487/RFC7598, July 2015, 386 . 388 6.2. Informative References 390 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 391 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 392 DOI 10.17487/RFC5226, May 2008, 393 . 395 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 396 Stack Lite Broadband Deployments Following IPv4 397 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, 398 . 400 [RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 401 Farrer, "Lightweight 4over6: An Extension to the Dual- 402 Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596, 403 July 2015, . 405 [RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S., 406 Murakami, T., and T. Taylor, Ed., "Mapping of Address and 407 Port with Encapsulation (MAP-E)", RFC 7597, 408 DOI 10.17487/RFC7597, July 2015, 409 . 411 [RFC7599] Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S., 412 and T. Murakami, "Mapping of Address and Port using 413 Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599, July 414 2015, . 416 Authors' Addresses 418 Mohamed Boucadair 419 Orange 420 Rennes 421 France 423 Email: mohamed.boucadair@orange.com 424 Ian Farrer 425 Deutsche Telekom 426 Germany 428 Email: ian.farrer@telekom.de