idnits 2.17.1 draft-ietf-softwire-unified-cpe-07.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (September 28, 2016) is 2766 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. 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 (==), 3 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: April 1, 2017 Deutsche Telekom 6 September 28, 2016 8 Unified IPv4-in-IPv6 Softwire CPE: A DHCPv6-based Prioritization 9 Mechanism 10 draft-ietf-softwire-unified-cpe-07 12 Abstract 14 In IPv6-only provider networks, transporting IPv4 packets 15 encapsulated in IPv6 is a common solution to the problem of IPv4 16 service continuity. A number of differing functional approaches have 17 been developed for this, each having their own specific 18 characteristics. As these approaches share a similar functional 19 architecture and use the same data plane mechanisms, this memo 20 specifies a DHCPv6 option whereby a single CPE can interwork with all 21 of the standardized and proposed approaches to providing encapsulated 22 IPv4 in IPv6 services by providing a prioritization mechanism. 24 Requirements Language 26 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 27 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 28 document are to be interpreted as described in RFC 2119 [RFC2119]. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 1, 2017. 47 Copyright Notice 49 Copyright (c) 2016 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 66 1.2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 4 67 1.3. DHCPv6 S46 Priority Option . . . . . . . . . . . . . . . 4 68 1.4. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . 5 69 1.5. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . 6 70 2. Operator Deployment Considerations for Deploying Multiple 71 Sotfwire Mechanisms . . . . . . . . . . . . . . . . . . . . . 6 72 2.1. Client Address Planning . . . . . . . . . . . . . . . . . 6 73 2.2. Backwards Compatability with Existing Softwire Clients . 7 74 3. Security Considerations . . . . . . . . . . . . . . . . . . . 7 75 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 76 4.1. S46 Mechanisms and their Identifying Option Codes . . . . 8 77 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 78 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 79 6.1. Normative References . . . . . . . . . . . . . . . . . . 8 80 6.2. Informative References . . . . . . . . . . . . . . . . . 9 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 83 1. Introduction 85 IPv4 service continuity is one of the major technical challenges 86 which must be considered during IPv6 migration. Over the past few 87 years, a number of different approaches have been developed to assist 88 with this problem (e.g., [RFC6333], [RFC7596], or [RFC7597]). These 89 approaches, referred to as 'S46 mechanisms' in this document, exist 90 in order to meet the particular deployment, scaling, addressing and 91 other requirements of different service provider's networks. 93 A common feature shared between all of the differing modes is the 94 integration of softwire tunnel end-point functionality into the 95 Customer Premise Equipment (CPE) router. Due to this inherent data 96 plane similarity, a single CPE may be capable of supporting several 97 different approaches. Users may also wish to configure a specific 98 mode of operation. 100 A service provider's network may also have more than one S46 101 mechanism enabled in order to support a diverse CPE population with 102 differing client functionality, such as during a migration between 103 mechanisms, or where services require specific supporting softwire 104 architectures. 106 For softwire based services to be successfully established, it is 107 essential that the customer end-node, the service provider end-node 108 and provisioning systems are able to indicate their capabilities and 109 preferred mode of operation. 111 A number of DHCPv6 options for the provisioning of softwires have 112 been standardized: 114 RFC6334 Defines DHCPv6 option 64 for configuring Basic Bridging 115 BroadBand (B4, [RFC6333]) elements with the IPv6 address of 116 the Address Family Transition Router (AFTR, [RFC6333]). 117 RFC7341 Defines DHCPv6 option 88 for configuring the address of a 118 DHCPv4 over DHCPv6 server, which can then be used by a 119 softwire client for obtaining further configuration. 120 RFC7598 Defines DHCPv6 options 94, 95 and 96 for provisioning Mapping 121 of Address and Port with Encapsulation (MAP-E, [RFC7597]), 122 Mapping of Address and Port using Translation (MAP-T, 123 [RFC7599]), and Lightweight 4over6 [RFC7596] respectively. 125 This document describes a DHCPv6 based prioritization method whereby 126 a CPE which supports several S46 mechanisms and receives 127 configuration for more than one can prioritise which mechanism to 128 use. The method requires no server side logic to be implemented and 129 only uses a simple S46 mechanism prioritization to be implemented in 130 the CPE. 132 The prioritization method as described here does not provide 133 redundancy between S46 mechanisms for the client. I.e. If the 134 highest priority S46 mechanism which has been provisioned to the 135 client is not available for any reason, the means for identifying 136 this and falling back to the S46 mechanism with the next highest 137 priority is not in the scope of this document. 139 1.1. Terminology 141 This document makes use of the following terms: 143 o Address Family Transition Router (AFTR): is the IPv4-in-IPv6 144 tunnel termination point and the NAT44 function deployed in the 145 operator's network [RFC6333]. 146 o Border Relay (BR): a MAP-enabled router managed by the service 147 provider at the edge of a MAP domain. A BR has at least an 148 IPv6-enabled interface and an IPv4 interface connected to the 149 native IPv4 network [RFC7597]. 150 o Customer Premise Equipment (CPE): denotes the equipment at the 151 customer edge that terminates the customer end of an IPv6 152 transitional tunnel. In some documents (e.g., [RFC7597]), this 153 functional entity is called CE (Customer Edge). 155 1.2. Rationale 157 The following rationale has been adopted for this document: 159 (1) Simplify solution migration paths: Define unified CPE behavior, 160 allowing for smooth migration between the different s46 161 mechanisms. 162 (2) Deterministic CPE co-existence behavior: Specify the behavior 163 when several S46 mechanisms co-exist in the CPE. 164 (3) Deterministic service provider co-existence behavior: Specify 165 the behavior when several modes co-exist in the service 166 providers network. 167 (4) Re-usability: Maximize the re-use of existing functional blocks 168 including tunnel end-points, port restricted NAPT44, forwarding 169 behavior, etc. 170 (5) Solution agnostic: Adopt neutral terminology and avoid (as far 171 as possible) overloading the document with solution-specific 172 terms. 173 (6) Flexibility: Allow operators to compile CPE software only for 174 the mode(s) necessary for their chosen deployment context(s). 175 (7) Simplicity: Provide a model that allows operators to only 176 implement the specific mode(s) that they require without the 177 additional complexity of unneeded modes. 179 1.3. DHCPv6 S46 Priority Option 181 The S46 Priority Option is used to convey a priority order of IPv4 182 service continuity mechanisms. Figure 1 shows the format of the S46 183 Priority Option. 185 0 1 2 3 186 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 1 187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 188 | OPTION_S46_PRIORITY | option-length | 189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 190 | s46-option-code | s46-option-code | 191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 192 | ... | s46-option-code | 193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 195 Figure 1: S46 Priority Option 197 o option-code: OPTION_S46_PRIORITY (TBD) 198 o option-length: >=2 and a multiple of 2, in octets. 199 o s46-option-code: 16-bits long IANA registered option code of the 200 DHCPv6 option which is used to identify the softwire mechanism. 201 S46 mechanism are prioritized in the appearance order in the S46 202 Priority Option. 204 Each defined s46_option_code MUST NOT appear more than once within 205 the list of S46 option codes. The option MUST contain at least one 206 s46-option-code. 208 1.4. DHCPv6 Client Behavior 210 Clients MAY request option OPTION_S46_PRIORITY, as defined in 211 [RFC3315], Sections 17.1.1, 18.1.1, 18.1.3, 18.1.4, 18.1.5, and 22.7. 212 As a convenience to the reader, we mention here that the client 213 includes requested option codes in the Option Request Option. 215 Upon receipt of a DHCPv6 Advertise message from the server containing 216 OPTION_S46_PRIORITY the client performs the following steps: 218 1. Check the contents of the DHCPv6 message for options containing 219 valid S46 mechanism configuration. A candidate list of possible 220 S46 mechanisms is created from these option codes. 221 2. Check the contents of OPTION_S46_PRIORITY for the DHCPv6 option 222 codes contained in the included s46-option-code fields. From 223 this, an S46 mechanism priority list is created, ordered from 224 highest to lowest following the appearance order. 225 3. Sequentially check the priority list against the candidate list 226 until a match is found. 227 4. When a match is found, the client MUST configure the resulting 228 S46 mechanism. 230 In the event that no match is found between the priority list and the 231 candidate list, the client MAY proceed with configuring one or more 232 of the provisioned S46 softwire mechanism(s). In this case, which 233 mechanism(s) are chosen by the client is implementation-specific and 234 not defined here. 236 If an invalid OPTION_S46_PRIORITY option is received, the client MAY 237 proceed with configuring the provisioned S46 mechanisms as if 238 OPTION_S46_PRIORITY had not been received. 240 If an unknown option code is received in OPTION_S46_PRIORITY option, 241 the client MUST skip it and continue processing other listed option 242 codes if they exist. The initial option codes that are allowed to be 243 included in a OPTION_S46_PRIORITY option are listed in Section 4.1. 245 1.5. DHCPv6 Server Behavior 247 Sections 17.2.2 and 18.2 of [RFC3315] govern server operation in 248 regards to option assignment. As a convenience to the reader, we 249 mention here that the server will send a particular option code only 250 if configured with specific values for that option code and if the 251 client requested it. 253 Option OPTION_S46_PRIORITY is a singleton. Servers MUST NOT send 254 more than one instance of the OPTION_S46_PRIORITY option. 256 2. Operator Deployment Considerations for Deploying Multiple Sotfwire 257 Mechanisms 259 The following sub-sections describe some considerations for operators 260 who are planning on implementing multiple softwire mechanisms in 261 their network (e.g., during a migration between mechanisms). 263 2.1. Client Address Planning 265 As an operator's available IPv4 resources are likely to be limited, 266 it may be desirable to use a common range of IPv4 addresses across 267 all of the active Softwire mechanisms. However, this is likely to 268 result in difficulties in routing ingress IPv4 traffic to the correct 269 Border Relay (BR)/AFTR instance which is actively serving a given CE. 270 For example, a client which is configured to use MAP-E may send its 271 traffic to the MAP-E BR, but on the return path, the ingress IP 272 traffic gets routed to a MAP-T BR. The resulting translated packet 273 that gets forwarded to the MAP-E client will be dropped. 275 Therefore, operators are advised to use separate IPv4 pools for each 276 of the different mechanisms to simplify planning and IPv4 routing. 278 For IPv6 planning there is less of a constraint as the BR/AFTR 279 elements for the different mechanisms can contain configuration for 280 overlapping client's IPv6 addresses, providing only one mechanism is 281 actively serving a given client at a time. However, the IPv6 address 282 that is used as the tunnel concentrator's endpoint (BR/AFTR address) 283 needs to be different for each mechanisms to ensure correct 284 operation. 286 2.2. Backwards Compatability with Existing Softwire Clients 288 Deployed clients which can support multiple softwire mechanisms, but 289 do not implement the prioritization mechanism described here may 290 require additional planning. In this scenario, the CPE would request 291 configuration for all of the supported softwire mechanisms in its 292 DHCPv6 Option Request Option (ORO), but would not request 293 OPTION_S46_PRIORITY. By default, the DHCPv6 server will respond with 294 configuration for all of the requested mechanisms which could result 295 in unpredictable and unwanted client configuration. 297 In this scenario, it may be necessary for the operator to implement 298 logic within the DHCPv6 server to identify such clients and only 299 provision them with configuration for a single softwire mechanism. 300 It should be noted that this can lead to complexity and reduced 301 scalability in the DHCPv6 server implementation due to the addition 302 DHCPv6 message processing overhead. 304 3. Security Considerations 306 Security considerations discussed in [RFC6334] and [RFC7598] apply 307 for this document. 309 Misbehaving intermediate nodes may alter the content of the S46 310 Priority Option. This may lead to setting a different IPv4 service 311 continuity mechanism than the one initially preferred by the network 312 side. Also, a misbehaving node may alter the content of the S46 313 Priority Option and other DHCPv6 options (e.g., DHCPv6 Option #64 or 314 #90) so that the traffic is intercepted by an illegitimate node. 315 Those attacks are not unique to the S46 Priority Option but are 316 applicable to any DHCPv6 option that can be altered by a misbehaving 317 intermediate node. 319 4. IANA Considerations 321 IANA is kindly requested to allocate the following DHCPv6 option 322 code: 324 TBD for OPTION_S46_PRIORITY 326 All values should be added to the DHCPv6 option code space defined in 327 Section 24.3 of [RFC3315]. 329 4.1. S46 Mechanisms and their Identifying Option Codes 331 This document requests that IANA create a new registry entitled 332 "Option Codes permitted in the S46 Priority Option". This registry 333 will enumerate the set of DHCPv6 Option Codes that can be included in 334 OPTION_S46_PRIORITY option. Options may be added to this list using 335 the IETF Review process described in Section 4.1 of [RFC5226]. 337 The following table shows the option codes which are currently 338 defined and the S46 mechanisms which they represent. The contents of 339 this table shows the format and the initial values for the new 340 registry. Option codes that have not been requested to be added 341 according to the stated procedure should not be mentioned at all in 342 the table, and should not be listed as "reserved" or "unassigned". 343 The valid range of values for the registry is the range of DHCPv6 344 Option Codes (1-65535). 346 +-------------+--------------------+-----------+ 347 | Option Code | S46 Mechanism | Reference | 348 +-------------+--------------------+-----------+ 349 | 64 | DS-Lite | [RFC6334] | 350 | 88 | DHCPv4 over DHCPv6 | [RFC7341] | 351 | 94 | MAP-E | [RFC7598] | 352 | 95 | MAP-T | [RFC7598] | 353 | 96 | Lightweight 4over6 | [RFC7598] | 354 +-------------+--------------------+-----------+ 356 Table 1: DHCPv6 Option to S46 Mechanism Mappings 358 5. Acknowledgements 360 Many thanks to O. Troan, S. Barth. A. Yourtchenko, B. Volz, T. 361 Mrugalski, J. Scudder, P. Kyzivat, F. Baker, and B. Campbell for 362 their input and suggestions. 364 6. References 366 6.1. Normative References 368 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 369 Requirement Levels", BCP 14, RFC 2119, 370 DOI 10.17487/RFC2119, March 1997, 371 . 373 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 374 C., and M. Carney, "Dynamic Host Configuration Protocol 375 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 376 2003, . 378 [RFC6334] Hankins, D. and T. Mrugalski, "Dynamic Host Configuration 379 Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite", 380 RFC 6334, DOI 10.17487/RFC6334, August 2011, 381 . 383 [RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I. 384 Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport", 385 RFC 7341, DOI 10.17487/RFC7341, August 2014, 386 . 388 [RFC7598] Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec, 389 W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for 390 Configuration of Softwire Address and Port-Mapped 391 Clients", RFC 7598, DOI 10.17487/RFC7598, July 2015, 392 . 394 6.2. Informative References 396 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 397 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 398 DOI 10.17487/RFC5226, May 2008, 399 . 401 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 402 Stack Lite Broadband Deployments Following IPv4 403 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, 404 . 406 [RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 407 Farrer, "Lightweight 4over6: An Extension to the Dual- 408 Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596, 409 July 2015, . 411 [RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S., 412 Murakami, T., and T. Taylor, Ed., "Mapping of Address and 413 Port with Encapsulation (MAP-E)", RFC 7597, 414 DOI 10.17487/RFC7597, July 2015, 415 . 417 [RFC7599] Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S., 418 and T. Murakami, "Mapping of Address and Port using 419 Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599, July 420 2015, . 422 Authors' Addresses 424 Mohamed Boucadair 425 Orange 426 Rennes 427 France 429 Email: mohamed.boucadair@orange.com 431 Ian Farrer 432 Deutsche Telekom 433 Germany 435 Email: ian.farrer@telekom.de