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Farrer 5 Expires: November 14, 2013 Deutsche Telekom AG 6 May 13, 2013 8 Provisioning IPv4 Configuration Over IPv6 Only Networks 9 draft-ietf-dhc-v4configuration-00 11 Abstract 13 As IPv6 becomes more widely adopted, some service providers are 14 taking the approach of deploying IPv6 only networks, without dual- 15 stack functionality for IPv4. However, access to IPv4 based services 16 is still an ongoing requirement and approaches such as IPv4-in-IPv6 17 softwire tunnels are being developed to meet this need. 19 In order to provision end-user's hosts with the necessary IPv4 20 configuration, a number of different mechanisms have been proposed. 21 This memo discusses the benefits and drawbacks of each, with the aim 22 of recommending a single approach as the basis for future work. 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 November 14, 2013. 47 Copyright Notice 48 Copyright (c) 2013 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. Overview of IPv4 Parameter Configuration Approaches . . . 3 65 1.2. DHCPv4o6 Based Provisioning - Functional Overview . . . . 4 66 1.3. DHCPv6 Based Provisioning - Functional Overview . . . . . 5 67 1.4. DHCPv4oSW Based Provisioning - Functional Overview . . . 5 68 1.5. DHCPv4oDHCPv6 Based Provisioning - Functional Overview . 6 69 2. Requirements for the Solution Evaluation . . . . . . . . . . 7 70 3. Comparison of the Four Approaches . . . . . . . . . . . . . . 8 71 3.1. Pros and Cons of the Different Approaches . . . . . . . . 8 72 3.1.1. DHCPv4o6 Based Provisioning . . . . . . . . . . . . . 8 73 3.1.2. DHCPv6 Based Provisioning . . . . . . . . . . . . . . 9 74 3.2. DHCPv4oSW Based Provisioning . . . . . . . . . . . . . . 10 75 3.2.1. Pros . . . . . . . . . . . . . . . . . . . . . . . . 10 76 3.2.2. Cons . . . . . . . . . . . . . . . . . . . . . . . . 10 77 3.3. DHCPv4oDHCPv6 Based Provisioning . . . . . . . . . . . . 11 78 3.3.1. Pros . . . . . . . . . . . . . . . . . . . . . . . . 11 79 3.3.2. Cons . . . . . . . . . . . . . . . . . . . . . . . . 11 80 4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 11 81 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 82 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 83 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 84 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 85 8.1. Normative References . . . . . . . . . . . . . . . . . . 12 86 8.2. Informative References . . . . . . . . . . . . . . . . . 12 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 89 1. Introduction 91 A service provider with an IPv6-only network must also be able to 92 provide customers with access to the Internet and other services over 93 IPv4. Softwire based IPv4-in-IPv6 tunneling mechanisms are an 94 obvious example of this, such as the ones described in: 96 o [I-D.ietf-softwire-lw4over6] 98 o [I-D.ietf-softwire-map] 100 o [I-D.ietf-softwire-unified-cpe] 102 A general trend here is to relocate NAT44 functionality and IPv4 103 address sharing from the centralized tunnel concentrator to the CPE 104 in order to achieve better scalability. This results in the need to 105 provision a number of configuration parameters to the CPE, such as 106 the external public IPv4 address and a restricted port-range to use 107 for NAT. 109 In order to configure customer's devices for softwire functionality, 110 a dynamic provisioning mechanism is necessary. In IPv4 only 111 networks, DHCPv4 has often been used to provide configuration, but in 112 an IPv6 only network, DHCPv4 messages cannot be transported natively. 114 Although softwire mechanisms are currently the only use-case for dhcp 115 based configuration of IPv4 parameters in IPv6 only networks, a 116 suitable approach must not be limited to only supporting softwire 117 configuration. 119 This document compares four different approaches which have been 120 proposed for resolving this problem. 122 1.1. Overview of IPv4 Parameter Configuration Approaches 124 In order to resolve the problem described above, the following 125 approaches for transporting IPv4 configuration parameters have been 126 suggested: 128 1. Adapt DHCPv4 format messages to be transported over IPv6 as 129 described in [I-D.ietf-dhc-dhcpv4-over-ipv6]. For brevity, this 130 is referred to as DHCPv4o6. 132 2. Extend DHCPv6 with new options for IPv4 configuration, such as 133 [I-D.ietf-softwire-map-dhcp] describes. 135 3. Use DHCPv6 as above for external IPv4 address and source port 136 configuration. Use DHCPv4 over IPv4 messages within an IPv6 137 softwire for configuring additional parameters. This is referred 138 to as DHCPv4oSW. 140 4. Use DHCPv4 format messages, transporting them within a new DHCPv6 141 message type as described in [I-D.scskf-dhc-dhcpv4-over-dhcpv6]. 142 This is referred to as DHCPv4oDHCPv6. 144 At the time of writing, working examples of the first two approaches 145 have been developed and successfully tested in several different 146 operators networks. The third and fourth methods are still 147 theoretical. 149 The following sections provide more detail for each approach. 151 1.2. DHCPv4o6 Based Provisioning - Functional Overview 153 In order to receive IPv4 configuration parameters, IPv4-only clients 154 initiate and exchange DHCPv4 messages with the DHCPv4 server. In 155 order adapt this to an IPv6-only network, an existing DHCPv4 client 156 implements a 'Client Relay' (CRA) function, which takes DHCPv4 157 messages and puts them into UDPv6 and IPv6. 159 As the mechanism involves unicast based communications, the IPv6 160 address of the server must be provisioned to the client. This option 161 is described in [I-D.mrugalski-softwire-dhcpv4-over-v6-option]. 163 The DHCPv4o6 server must either provide an IPv6 interface to the 164 client, or an intermediary 'Transport Relay Agent' device can act as 165 the gateway between the IPv4 and IPv6 domains. 167 For the dynamic allocation of IPv4 addresses, the DHCPv4o6 server 168 needs to be extended to support the new functionality, such as 169 storing the IPv6 address of DHCPv4o6 clients. The CRA6ADDR option 170 must also be implemented. 172 This approach currently uses functional elements for ingress and 173 egress of the IPv6-only transport domain--the CRA on the host and the 174 TRA or TSV on the server. As a result, this approach has sometimes 175 been referred to as a tunneling approach. However, relay agent 176 encapsulation is not a tunnel, since it carries only DHCP traffic; it 177 would be more accurate to describe it as an encapsulation. 179 It is worth noting that there is no technical reason for using relay 180 encapsulation for DHCPv4o6; this approach was taken because the 181 authors of the draft originally imagined that it might be used to 182 provide configuration information for an unmodified DHCPv4 client. 183 However, this turns out not to be a viable approach: in order for 184 this to work, there would have to be IPv4 routing on the local link 185 to which the client is connected. In that case, there's no need for 186 DHCPv4o6. 188 Given that this is the case, there is no technical reason why 189 DHCPv4o6 can't simply use the IPv6 transport directly, without any 190 relay encapsulation. This would greatly simplify the specification 191 and the implementation, and would still address the requirements 192 stated in this document. 194 [I-D.ietf-dhc-dhcpv4-over-ipv6] decribes this solution in detail. 196 The protocol stack is as follows: 198 DHCPv4/UDPv6/IPv6 200 1.3. DHCPv6 Based Provisioning - Functional Overview 202 In this approach, DHCPv6 would be extended with new DHCPv6 options 203 for configuring all IPv4 based services and functions. Any DHCPv4 204 options needed by IPv4 clients connected to the IPV6 network are 205 updated as new DHCPv6 native options carrying IPv4 configuration 206 parameters. 208 At the time of writing, it is not known how many such options would 209 need to be ported from DHCPv4 to DHCPv6. 211 An example of this approach is described in 212 [I-D.ietf-softwire-map-dhcp], where a DHCPv6 message is used to 213 convey the parameters necessary for IPv4 in IPv6 softwire 214 configuration. 216 The protocol stack is as follows: 218 DHCPv6/UDPv6/IPv6 220 1.4. DHCPv4oSW Based Provisioning - Functional Overview 222 In this approach, the configuration of IPv4 address and source ports 223 (if required) is carried out using DHCPv6 as described in section 1.3 224 above. Any additional IPv4 configuration parameters which are 225 required are then provisioned using a DHCPv4 messages transported 226 within IPv6 in the configured softwire in the same manner as any 227 other IPv4 based traffic. 229 On receipt at the tunnel concentrator (e.g. MAP Border Router or a 230 Lightweight 4over6 lwAFTR), the DHCPv4 message removed from the 231 softwire and forwarded to the DHCPv4 server in the same way as any 232 other IPv4 packet is handled. 234 As the client is already configured with its external IPv4 address 235 and source ports (using DHCPv6), the messages exchanged between the 236 DHCPv4 client and server would be strictly DHCPINFORM/DHCPACK 237 messages, for the configuration of additional IPv4 parameters. 238 Broadcast based DHCPDISCOVER messages can not be transported as they 239 are not compatible with the softwire architecture. 241 For this approach to function, a mechanism for the DHCPv4 client to 242 learn the IPv4 address of the DHCPv4 server is needed. This could be 243 done by defining a well-known IPv4 address for the DHCPv4 server, 244 implementing a DHCPv4 relay function within the tunnel concentrator 245 or other configuration methods. 247 From a transport perspective, the key difference between this method 248 and DHCPv4o6 (described above) is that here, the DHCPv4 message is 249 put into UDPv4 and IPv4 and then put into the IPv6 softwire, instead 250 of directly placing the DHCPv4 message into UDPv6 and IPv6. 252 Currently, this approach is only theoretical and does not have a 253 corresponding Internet Draft providing more detail. 255 The protocol stack that would be used for obtaining additional IPv4 256 configuraion is as follows: 258 DHCPv4/UDPv4/IPv4/IPv6 260 1.5. DHCPv4oDHCPv6 Based Provisioning - Functional Overview 262 [I-D.scskf-dhc-dhcpv4-over-dhcpv6] describes the transport of DHCPv4 263 messages within two new DHCPv6 messages types: BOOTREQUESTV6 and 264 BOOTREPLYV6. These messages types must be implemented in both the 265 DHCPv4oDHCPv6 client and server. 267 In this approach, the configuration of stateless IPv4 addresses and 268 source ports (if required) is carried out using DHCPv6 as described 269 in section 1.3 above. Dynamic IPv4 addressing, and/or any additional 270 IPv4 configuration, is provided using DHCPv4 messages carried 271 (without IPv4/UDPv4 headers) within a new OPTION_BOOTP_MSG DHCPv6 272 option. 274 OPTION_BOOTP_MSG enables the client and server to send BOOTP/DHCPv4 275 messages verbatim across the IPv6 network. When a DHCPv4oDHCPv6 276 server receives a DHCPv6 request containing OPTION_BOOT_MSG within a 277 BOOTREQUESTV6 message, it passes it to the DHCPv4 server engine. 278 Likewise, the DHCPv4 server place its DHCPv4 response in the payload 279 of OPTION_BOOTP_MSG and puts this into a BOOTPRPLYV6 message. 281 As the DHCPv4 messages are carried within DHCPv6 multicast messages, 282 using the All_DHCP_Relay_Agents_and_Servers, they can be relayed in 283 exactly the same way as any other DHCPv6 multicasted message. 285 Optionally, DHCPv6 relays could be updated so that they forward the 286 BOOTREQUESTV6 message to a different destination address, allowing 287 for the separation of DHCPv4 and DHCPv4 provisioning infrastructure. 289 The protocol stack used for obtaining dynamic v4 addressing or 290 additional IPv4 configuraion is as follows: 292 DHCPv4/DHCPv6/UDPv6/IPv6 294 2. Requirements for the Solution Evaluation 296 The following requirements have been defined for the evalution of the 297 different approaches: 299 1. Minimize the amount of work necessary to implement the solution 300 through re-use of existing standards and implementations as much 301 as possible. 303 2. Provide a method of supporting all existing DHCPv4 options so 304 that they can be utilised without the need for further 305 standardation. 307 3. Allow for the dynamic leasing of IPv4 addresses to clients. This 308 allows for more efficient use of limited IPv4 resources. 310 4. Enable the separation of IPv4 and IPv6 host configuration. 312 5. Avoid leaving legacy IPv4 options in DHCPv6. 314 6. Provide a flexible architecture to give operators the option of 315 only deploying the functional elements necessary for their 316 specific requirements. 318 3. Comparison of the Four Approaches 320 The table below shows a comparison of the different approaches 321 against the solution requirements described above. 323 +----------+----------+--------+-----------+---------------+ 324 | Req. No. | DHCPv4o6 | DHCPv6 | DHCPv4oSW | DHCPv4oDHCPv6 | 325 +----------+----------+--------+-----------+---------------+ 326 | 1 | No | Yes | Yes | Yes | 327 | 2 | Yes | No | Yes | Yes | 328 | 3 | Yes | No | No | Yes | 329 | 4 | Yes | No | Yes | Yes | 330 | 5 | Yes | No | Yes | Yes | 331 | 6 | Yes | No | Yes | Yes | 332 +----------+----------+--------+-----------+---------------+ 334 Table 1: Approach Comparison 336 3.1. Pros and Cons of the Different Approaches 338 The following sections of the document provide more details of the 339 pros and cons relevant to each of the approaches. 341 3.1.1. DHCPv4o6 Based Provisioning 343 3.1.1.1. Pros 345 1. Once implemented, all existing DHCPv4 options will be available 346 with no further ongoing development work necessary. 348 2. IPv4 and IPv6 based provisioning can be separated from each other 349 if required, allowing flexibility in network design. 351 3. Easy to implement through minor adaptation of existing DHCPv4 352 client/server code. 354 4. Simple, in that no additional functional elements are necessary 355 except the DHCPv4o6 client and server. The Transport Relay Agent 356 is completely optional. 358 5. Suitable for the provisioning of dynamic IPv4 configuration as 359 the existing DHCPv4 leasing mechanism can be used. 361 6. Implementations already exist, proving that the approach works. 363 3.1.1.2. Cons 364 1. More complex, in that there are more new functional elements 365 (CRA, DHCPv4o6 server and optionally TRA) within the architecture 366 than are necessary in DHCPv6 based provisioning. 368 2. A new DHCPv6 option is necessary in order to provision the IPv6 369 address of the DHCPv4 server to the end device. 371 3. For a Host CRA (HCRA), DHCPv4 client host needs to be updated to 372 implement the IPv6 encapsulation and decapsulation function. 373 Otherwise a physically separate On-Link CRA (LCRA) functional 374 element must be deployed. 376 4. A DHCPv4 server must be deployed and maintained. 378 5. The DHCPv4 server needs to be updated to implement new DHCPv4o6 379 functionality. 381 3.1.2. DHCPv6 Based Provisioning 383 3.1.2.1. Pros 385 1. Simpler, in that no additional functional elements are required 386 except the DHCPv6 client and server. 388 2. A single protocol is used to deliver configuration information 389 for IPv4 and IPv6. 391 3. A single provisioning point for all configuration parameters. 393 4. Implementations already exist, proving that the approach works. 395 3.1.2.2. Cons 397 1. Any required DHCPv4 options must be ported to DHCPv6, which will 398 require re-development work for each option. All functional 399 elements in the DHCPv6 implementation (clients, servers, relays) 400 would need to be updated for each change. 402 2. Means that DHCPv4 'legacy' options, which will be of decreasing 403 relevance in the future will remain in DHCPv6 for the lifetime of 404 the protocol. 406 3. Each time that a DHCPv4 option is ported to DHCPv6, all clients 407 and servers would need to be updated to implement the new option. 409 4. Does not provide an architecture for keeping IPv4 and IPv6 410 domains separated. 412 5. Does not provide a mechanism for dynamic IPv4 address leasing. A 413 DHCPv4 lease lifetime mechanism would need to be added to DHCPv6 414 for this. 416 3.2. DHCPv4oSW Based Provisioning 418 3.2.1. Pros 420 1. Once implemented, all existing DHCPv4 options will be be 421 available with no further ongoing development work necessary. 423 2. Uses the existing DHCPv4 and DHCPv6 architectures in order to 424 provide IPv4 configuration in an IPv6 only environment. 426 3. DHCPv4 and DHCPv6 based provisioning can be separated from each 427 other if required, allowing flexibility in network design. 429 3.2.2. Cons 431 1. More complex, in that there are more new functional elements 432 within the architecture than are necessary in DHCPv6 based 433 provisioning. 435 2. IPv4 over IPv6 softwire approaches which distribute NAT to the 436 CPE and allow for IP address sharing (MAP-E & LW4o6) forbid the 437 use of reserved TCP/UDP ports (e.g. 0-1024). Every DHCPv4 438 client sharing the same address needs to have a UDP listener 439 running on UDP port 68. To resolve this would require 440 significant rework to either the softwire mechanisms and/or the 441 DHCPv4 client implementation. 443 3. From the current specification, DHCPINFORM is not suitable for 444 use over a softwire. Additional work, such as the development of 445 'shims' would be necessary 447 4. The current DHCPINFORM specification has a number of unclear 448 points, such as those described in 449 [I-D.ietf-dhc-dhcpinform-clarify]. Substantial work would be 450 required to resolve this. 452 5. Links the deployment of IPv4 configuration over IPv6 to a 453 softwire implementation (e.g. requiring a softwire concentrator 454 to act as a DHCPv4 relay). Whilst softwires are the only 455 application for this functionality at the moment, this may not 456 always be the case. 458 6. A new mechanism must be defined in order to provide the DHCPv4 459 client with the IPv4 address of the DHCPv4 server so that unicast 460 DHCPINFORM messages can be sent. 462 7. As only DHCPINFORM/DHCPACK DHCPv4 message types are supported, 463 dynamic IPv4 address leasing (using DHCPDISCOVER messages) can 464 not be used. 466 8. The approach is unproven as no existing implementations exist. 468 3.3. DHCPv4oDHCPv6 Based Provisioning 470 3.3.1. Pros 472 1. Once implemented, all existing DHCPv4 options will be be 473 available with no further ongoing development work necessary. 475 2. Uses the existing DHCPv4 and DHCPv6 architectures in order to 476 provide IPv4 configuration in an IPv6 only environment. 478 3. DHCPv4 and DHCPv6 based provisioning can be separated from each 479 other if required, allowing flexibility in network design. 481 4. Suitable for the provisioning of dynamic IPv4 configuration as 482 the existing DHCPv4 leasing mechanism can be used. 484 3.3.2. Cons 486 1. More complex, in that there are more new functional elements 487 within the architecture than are necessary in DHCPv6 based 488 provisioning. 490 2. DHCPv6 clients needs to be updated to implement the new DHCPv6 491 message types. 493 3. The DHCPv6 server needs to be updated to implement new 494 DHCPv4oDHCPv6 message types and functionality. 496 4. If separation of DHCPv4 and DHCPv4 provisioning infrastructure is 497 required, DHCPv6 relay agents need to be updated to implement 498 dedicated forwarding destinations based on message type. 500 5. The approach is currently unproven as no existing implementations 501 exist. 503 4. Conclusion 504 Discussion: This chapter will be updated to reflect the consensus 505 of the DHC Working Group. 507 5. IANA Considerations 509 This document makes no request of IANA. 511 Note to RFC Editor: this section may be removed on publication as an 512 RFC. 514 6. Security Considerations 516 7. Acknowledgements 518 Thanks to Ted Lemon and Tomek Mrugalski for their input and reviews. 520 8. References 522 8.1. Normative References 524 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 525 Requirement Levels", BCP 14, RFC 2119, March 1997. 527 8.2. Informative References 529 [I-D.ietf-dhc-dhcpinform-clarify] 530 Hankins, D., "Dynamic Host Configuration Protocol 531 DHCPINFORM Message Clarifications", draft-ietf-dhc- 532 dhcpinform-clarify-06 (work in progress), October 2011. 534 [I-D.ietf-dhc-dhcpv4-over-ipv6] 535 Cui, Y., Wu, P., Wu, J., and T. Lemon, "DHCPv4 over IPv6 536 Transport", draft-ietf-dhc-dhcpv4-over-ipv6-06 (work in 537 progress), March 2013. 539 [I-D.ietf-softwire-lw4over6] 540 Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 541 Farrer, "Lightweight 4over6: An Extension to the DS-Lite 542 Architecture", draft-ietf-softwire-lw4over6-00 (work in 543 progress), April 2013. 545 [I-D.ietf-softwire-map-dhcp] 546 Mrugalski, T., Troan, O., Dec, W., Bao, C., 547 leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options 548 for Mapping of Address and Port", draft-ietf-softwire-map- 549 dhcp-03 (work in progress), February 2013. 551 [I-D.ietf-softwire-map] 552 Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S., 553 Murakami, T., and T. Taylor, "Mapping of Address and Port 554 with Encapsulation (MAP)", draft-ietf-softwire-map-06 555 (work in progress), May 2013. 557 [I-D.ietf-softwire-unified-cpe] 558 Boucadair, M. and I. Farrer, "Unified IPv4-in-IPv6 559 Softwire CPE", draft-ietf-softwire-unified-cpe-00 (work in 560 progress), March 2013. 562 [I-D.mrugalski-softwire-dhcpv4-over-v6-option] 563 Mrugalski, T. and P. Wu, "Dynamic Host Configuration 564 Protocol for IPv6 (DHCPv6) Option for DHCPv4 over IPv6 565 Endpoint", draft-mrugalski-softwire- 566 dhcpv4-over-v6-option-01 (work in progress), September 567 2012. 569 [I-D.scskf-dhc-dhcpv4-over-dhcpv6] 570 Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I. 571 Farrer, "DHCPv4 over DHCPv6 Transport", draft-scskf-dhc- 572 dhcpv4-over-dhcpv6-01 (work in progress), April 2013. 574 Authors' Addresses 576 Branimir Rajtar 577 Hrvatski Telekom 578 Zagreb 579 Croatia 581 Email: branimir.rajtar@t.ht.hr 583 Ian Farrer 584 Deutsche Telekom AG 585 Bonn 586 Germany 588 Email: ian.farrer@telekom.de