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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Softwire Working Group Y. Cui 3 Internet-Draft Tsinghua University 4 Intended status: Standards Track Q. Sun 5 Expires: August 18, 2014 China Telecom 6 M. Boucadair 7 France Telecom 8 T. Tsou 9 Huawei Technologies 10 Y. Lee 11 Comcast 12 I. Farrer 13 Deutsche Telekom AG 14 February 14, 2014 16 Lightweight 4over6: An Extension to the DS-Lite Architecture 17 draft-ietf-softwire-lw4over6-07 19 Abstract 21 Dual-Stack Lite (RFC 6333) describes an architecture for transporting 22 IPv4 packets over an IPv6 network. This document specifies an 23 extension to DS-Lite called Lightweight 4over6 which moves the 24 Network Address and Port Translation (NAPT) function from the 25 centralized DS-Lite tunnel concentrator to the tunnel client located 26 in the Customer Premises Equipment (CPE). This removes the 27 requirement for a Carrier Grade NAT function in the tunnel 28 concentrator and reduces the amount of centralized state that must be 29 held to a per-subscriber level. In order to delegate the NAPT 30 function and make IPv4 Address sharing possible, port-restricted IPv4 31 addresses are allocated to the CPEs. 33 Status of This Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at http://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on August 18, 2014. 50 Copyright Notice 52 Copyright (c) 2014 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 68 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 4. Lightweight 4over6 Architecture . . . . . . . . . . . . . . . 5 71 5. Lightweight B4 Behavior . . . . . . . . . . . . . . . . . . . 7 72 5.1. Lightweight B4 Provisioning with DHCPv6 . . . . . . . . . 7 73 5.2. Lightweight B4 Data Plane Behavior . . . . . . . . . . . 8 74 5.2.1. Changes to RFC2473 and RFC6333 Fragmentation 75 Behaviour . . . . . . . . . . . . . . . . . . . . . . 10 76 6. Lightweight AFTR Behavior . . . . . . . . . . . . . . . . . . 11 77 6.1. Binding Table Maintenance . . . . . . . . . . . . . . . . 11 78 6.2. lwAFTR Data Plane Behavior . . . . . . . . . . . . . . . 12 79 7. Additional IPv4 address and Port Set Provisioning 80 Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . 13 81 8. ICMP Processing . . . . . . . . . . . . . . . . . . . . . . . 13 82 8.1. ICMPv4 Processing by the lwAFTR . . . . . . . . . . . . . 14 83 8.2. ICMPv4 Processing by the lwB4 . . . . . . . . . . . . . . 14 84 9. Security Considerations . . . . . . . . . . . . . . . . . . . 14 85 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 86 11. Author List . . . . . . . . . . . . . . . . . . . . . . . . . 15 87 12. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 18 88 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 89 13.1. Normative References . . . . . . . . . . . . . . . . . . 18 90 13.2. Informative References . . . . . . . . . . . . . . . . . 19 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 93 1. Introduction 95 Dual-Stack Lite (DS-Lite, [RFC6333]) defines a model for providing 96 IPv4 access over an IPv6 network using two well-known technologies: 98 IP in IP [RFC2473] and Network Address Translation (NAT). The DS- 99 Lite architecture defines two major functional elements as follows: 101 Basic Bridging BroadBand element: A B4 element is a function 102 implemented on a dual-stack capable 103 node, either a directly connected 104 device or a CPE, that creates a 105 tunnel to an AFTR. 107 Address Family Transition Router: An AFTR element is the combination 108 of an IPv4-in-IPv6 tunnel endpoint 109 and an IPv4-IPv4 NAT implemented on 110 the same node. 112 As the AFTR performs the centralized NAT44 function, it dynamically 113 assigns public IPv4 addresses and ports to requesting host's traffic 114 (as described in [RFC3022]). To achieve this, the AFTR must 115 dynamically maintain per-flow state in the form of active NAPT 116 sessions. For service providers with a large number of B4 clients, 117 the size and associated costs for scaling the AFTR can quickly become 118 prohibitive. It can also place a large NAPT logging overhead upon 119 the service provider in countries where legal requirements mandate 120 this. 122 This document describes a mechanism called Lightweight 4 over 6 123 (lw4o6), which provides a solution for these problems. By relocating 124 the NAPT functionality from the centralized AFTR to the distributed 125 B4s, a number of benefits can be realised: 127 o NAPT44 functionality is already widely supported and used in 128 today's CPE devices. Lw4o6 uses this to provide private<->public 129 NAPT44, meaning that the service provider does not need a 130 centralized NAT44 function. 132 o The amount of state that must be maintained centrally in the AFTR 133 can be reduced from per-flow to per-subscriber. This reduces the 134 amount of resources (memory and processing power) necessary in the 135 AFTR. 137 o The reduction of maintained state results in a greatly reduced 138 logging overhead on the service provider. 140 Operator's IPv6 and IPv4 addressing architectures remain independent 141 of each other. Therefore, flexible IPv4/IPv6 addressing schemes can 142 be deployed. 144 Lightweight 4over6 provides a solution for a hub-and-spoke softwire 145 architecture only. It does not offer direct, meshed IPv4 146 connectivity between subscribers without packets traversing the AFTR. 147 If this type of meshed interconnectivity is required, 148 [I-D.ietf-softwire-map] provides a suitable solution. 150 The tunneling mechanism remains the same for DS-Lite and Lightweight 151 4over6. This document describes the changes to DS-Lite that are 152 necessary to implement Lightweight 4over6. These changes mainly 153 concern the configuration parameters and provisioning method 154 necessary for the functional elements. 156 Lightweight 4over6 features keeping per-subscriber state in the 157 service provider's network. It is categorized as Binding approach in 158 [I-D.ietf-softwire-unified-cpe] which defines a unified IPv4-in-IPv6 159 Softwire CPE. 161 This document is an extended case, which covers address sharing for 162 [RFC7040]. It is also a variant of A+P called Binding Table Mode 163 (see Section 4.4 of [RFC6346]). 165 This document focuses on architectural considerations and 166 particularly on the expected behavior of the involved functional 167 elements and their interfaces. Deployment-specific issues are 168 discussed in a companion document. As such, discussions about 169 redundancy and provisioning policy are out of scope. 171 2. Conventions 173 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 174 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 175 document are to be interpreted as described in [RFC2119]. 177 3. Terminology 179 The document defines the following terms: 181 Lightweight 4over6 (lw4o6): An IPv4-over-IPv6 hub and spoke 182 mechanism, which extends DS-Lite by 183 moving the IPv4 translation (NAPT44) 184 function from the AFTR to the B4. 186 Lightweight B4 (lwB4): A B4 element (Basic Bridging BroadBand 187 element [RFC6333]), which supports 188 Lightweight 4over6 extensions. An lwB4 189 is a function implemented on a dual- 190 stack capable node, (either a directly 191 connected device or a CPE), that 192 supports port-restricted IPv4 address 193 allocation, implements NAPT44 194 functionality and creates a tunnel to 195 an lwAFTR 197 Lightweight AFTR (lwAFTR): An AFTR element (Address Family 198 Transition Router element [RFC6333]), 199 which supports Lightweight 4over6 200 extension. An lwAFTR is an IPv4-in- 201 IPv6 tunnel endpoint which maintains 202 per-subscriber address binding only and 203 does not perform a NAPT44 function. 205 Restricted Port-Set: A non-overlapping range of allowed 206 external ports allocated to the lwB4 to 207 use for NAPT44. Source ports of IPv4 208 packets sent by the B4 must belong to 209 the assigned port-set. The port set is 210 used for all port aware IP protocols 211 (TCP, UDP, SCTP etc.) 213 Port-restricted IPv4 Address: A public IPv4 address with a restricted 214 port-set. In Lightweight 4over6, 215 multiple B4s may share the same IPv4 216 address, however, their port-sets must 217 be non-overlapping. 219 Throughout the remainder of this document, the terms B4/AFTR should 220 be understood to refer specifically to a DS-Lite implementation. The 221 terms lwB4/lwAFTR refer to a Lightweight 4over6 implementation. 223 4. Lightweight 4over6 Architecture 225 The Lightweight 4over6 architecture is functionally similar to DS- 226 Lite. lwB4s and an lwAFTR are connected through an IPv6-enabled 227 network. Both approaches use an IPv4-in-IPv6 encapsulation scheme to 228 deliver IPv4 connectivity. The following figure shows the data plane 229 with the main functional change between DS-Lite and lw4o6: 231 +--------+ +---------+ IPv4-in-IPv6 +------+ +-------------+ 232 |IPv4 LAN|---|lwB4/NAPT|==================|lwAFTR|----|IPv4 Internet| 233 +--------+ +---------+ +------+ +-------------+ 234 ^ | 235 +-------------------------+ 236 NAPT function relocated 237 to lwB4 in lw4o6 239 Figure 1 Lightweight 4over6 Data Plane Overview 240 There are three main components in the Lightweight 4over6 241 architecture: 243 o The lwB4, which performs the NAPT function and encapsulation/de- 244 capsulation IPv4/IPv6. 246 o The lwAFTR, which performs the encapsulation/de-capsulation IPv4/ 247 IPv6. 249 o The provisioning system, which tells the lwB4 which IPv4 address 250 and port set to use. 252 The lwB4 differs from a regular B4 in that it now performs the NAPT 253 functionality. This means that it needs to be provisioned with the 254 public IPv4 address and port set it is allowed to use. This 255 information is provided though a provisioning mechanism such as DHCP, 256 PCP or TR-69. 258 The lwAFTR needs to know the binding between the IPv6 address of each 259 subscriber and the IPv4 address and port set allocated to that 260 subscriber. This information is used to perform ingress filtering 261 upstream and encapsulation downstream. Note that this is per- 262 subscriber state as opposed to per-flow state in the regular AFTR 263 case. 265 The consequence of this architecture is that the information 266 maintained by the provisioning mechanism and the one maintained by 267 the lwAFTR MUST be synchronized (See figure 2). The details of this 268 synchronization depend on the exact provisioning mechanism and will 269 be discussed in a companion document. 271 The solution specified in this document allows the assignment of 272 either a full or a shared IPv4 address requesting CPEs. [RFC7040] 273 provides a mechanism for assigning a full IPv4 address only. 275 +------------+ 276 /-------|Provisioning|<-----\ 277 | +------------+ | 278 | | 279 V V 280 +--------+ +---------+ IPv4/IPv6 +------+ +-------------+ 281 |IPv4 LAN|---|lwB4/NAPT|==================|lwAFTR|----|IPv4 Internet| 282 +--------+ +---------+ +------+ +-------------+ 284 Figure 2 Lightweight 4over6 Provisioning Synchronization 286 5. Lightweight B4 Behavior 288 5.1. Lightweight B4 Provisioning with DHCPv6 290 With DS-Lite, the B4 element only needs to be configured with a 291 single DS-Lite specific parameter so that it can set up the softwire 292 (the IPv6 address of the AFTR). Its IPv4 address can be taken from 293 the well-known range 192.0.0.0/29. 295 In lw4o6, due to the distributed nature of the NAPT function, a 296 number of lw4o6 specific configuration parameters must be provisioned 297 to the lwB4. These are: 299 o IPv6 Address for the lwAFTR 301 o IPv4 External (Public) Address for NAPT44 303 o Restricted port-set to use for NAPT44 305 For DHCPv6 based configuration of these parameters, the lwB4 SHOULD 306 implement OPTION_S46_CONT_LW as described in section 6.3 of 307 [I-D.ietf-softwire-map-dhcp]. This means that the lifetime of the 308 softwire and the derived configuration information (e.g. IPv4 shared 309 address, IPv4 address) is bound to the lifetime of the DHCPv6 lease. 310 If stateful IPv4 configuration or additional IPv4 configuration 311 information is required, DHCPv4 [RFC2131] must be used. 313 Some other mechanisms which may be adapted for the provisioning of 314 IPv4 addresses and port-sets are described in section 7 below. 316 An IPv6 address from an assigned prefix is also required for the lwB4 317 to use as the encapsulation source address for the softwire. In 318 order to enable end-to-end provisioning, the IPv6 address is 319 constructed by taking a /64 prefix assigned to the WAN interface and 320 suffixing 64-bits for the interface identifier. As there may be 321 multiple WAN prefixes, of which only one can be used for lw4o6, the 322 CPE creates a new WAN prefix specifically for use as the tunnel 323 source address. The /128 prefix is then constructed in the same 324 manner as [I-D.ietf-softwire-map]: 326 0 1 2 3 327 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 1 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | Operator assigned (64-bits) | 330 | | 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 | Zero Padding | IPv4 Address | 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 | IPv4 Addr cont. | PSID | 335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 337 Figure 3 Construction of the lw4o6 /128 Prefix 339 Padding: Padding (all zeros) 341 IPv4 Address: Public IPv4 address allocated to the client 343 PSID: Port Set ID allocated to the client, left padded with 344 zeros to 16-bits. If no PSID is provisioned, all 345 zeros. 347 In the event that the lwB4's encapsulation source address is changed 348 for any reason (such as the DHCPv6 lease expiring), the lwB4's 349 dynamic provisioning process must be re-initiated. 351 An lwB4 MUST support dynamic port-restricted IPv4 address 352 provisioning. The port set algorithm for provisioning this is 353 described in Section 5.1 of [I-D.ietf-softwire-map]. For lw4o6, the 354 number of a-bits SHOULD be 0. 356 In the event that the lwB4 receives an ICMPv6 error message (type 1, 357 code 5) originating from the lwAFTR, the lwB4 SHOULD interpret this 358 to mean that no matching entry in the lwAFTR's binding table has been 359 found. The lwB4 MAY then re-initiate the dynamic port-restricted 360 provisioning process. The lwB4's re-initiation policy SHOULD be 361 configurable. 363 The DNS considerations described in Section 5.5 and Section 6.4 of 364 [RFC6333] SHOULD be followed. 366 5.2. Lightweight B4 Data Plane Behavior 368 Several sections of [RFC6333] provide background information on the 369 B4's data plane functionality and MUST be implemented by the lwB4 as 370 they are common to both solutions. The relevant sections are: 372 5.2 Encapsulation Covering encapsulation and de- 373 capsulation of tunneled traffic 375 5.3 Fragmentation and Reassembly Covering MTU and fragmentation 376 considerations (referencing 377 [RFC2473]), with the exception 378 noted below. 380 7.1 Tunneling Covering tunneling and traffic 381 class mapping between IPv4 and IPv6 382 (referencing [RFC2473] and 383 [RFC4213]) 385 The lwB4 element performs IPv4 address translation (NAPT44) as well 386 as encapsulation and de-capsulation. It runs standard NAPT44 387 [RFC3022] using the allocated port-restricted address as its external 388 IPv4 address and port numbers. 390 The working flow of the lwB4 is illustrated in figure 4. 392 +-------------+ 393 | lwB4 | 394 +--------+ IPv4 |------+------| IPv4-in-IPv6 +----------+ 395 |IPv4 LAN|------->| |Encap.|-------------->|Configured| 396 | |<-------| NAPT | or |<--------------| lwAFTR | 397 +--------+ | |Decap.| +----------+ 398 +------+------+ 400 Figure 4 Working Flow of the lwB4 402 Internally connected hosts source IPv4 packets with an [RFC1918] 403 address. When the lwB4 receives such an IPv4 packet, it performs a 404 NAPT44 function on the source address and port by using the public 405 IPv4 address and a port number from the allocated port-set. Then, it 406 encapsulates the packet with an IPv6 header. The destination IPv6 407 address is the lwAFTR's IPv6 address and the source IPv6 address is 408 the lwB4's IPv6 tunnel endpoint address. Finally, the lwB4 forwards 409 the encapsulated packet to the configured lwAFTR. 411 When the lwB4 receives an IPv4-in-IPv6 packet from the lwAFTR, it de- 412 capsulates the IPv4 packet from the IPv6 packet. Then, it performs 413 NAPT44 translation on the destination address and port, based on the 414 available information in its local NAPT44 table. 416 If the IPv6 source address does not match the configured lwAFTR 417 address, then the packet MUST be discarded. If the decapsulated IPv4 418 packet does not match the lwB4's configuration (i.e. invalid 419 destination IPv4 address or port) then the packet MUST be dropped. 420 An ICMPv4 error message (type 13 - Communication Administratively 421 Prohibited) message MAY be sent back to the lwAFTR. The ICMP policy 422 SHOULD be configurable. 424 The lwB4 is responsible for performing ALG functions (e.g., SIP, 425 FTP), and other NAPT traversal mechanisms (e.g., UPnP, NAPT-PMP, 426 manual binding configuration, PCP) for the internal hosts. This 427 requirement is typical for NAPT44 gateways available today. 429 It is possible that a lwB4 is co-located in a host. In this case, 430 the functions of NAPT44 and encapsulation/de-capsulation are 431 implemented inside the host. 433 5.2.1. Changes to RFC2473 and RFC6333 Fragmentation Behaviour 435 5.2.1.1. Processing of Incoming IPv4 Fragments Encapsulated in IPv6 437 The following process for handling fragmented packets is taken from 438 Section 3.4 of [RFC6146], adapted for use with fragmentation of 439 encapsulated IPv4 tunnel traffic and NAT44. 441 On receiving an encapsulated packet containing an IPv4 fragment, then 442 more processing may be needed than for non-fragmented payloads. This 443 specification leaves open the exact details of how the lwB4 handles 444 incoming encapsulated IPv6 packets containing IPv4 fragments, and 445 simply requires that the external behavior of the lwB4 be compliant 446 with the following conditions: 448 The lwB4 MUST handle encapsulated IPv4 fragments. In particular, the 449 lwB4 MUST handle fragments arriving out of order, conditional on the 450 following: 452 o The lwB4 MUST limit the amount of resources devoted to the storage 453 of fragmented packets in order to protect from DoS attacks. 455 o As long as the lwB4 has available resources, the lwB4 MUST allow 456 the fragments to arrive over a time interval. The time interval 457 SHOULD be configurable and the default value MUST be of at least 458 FRAGMENT_MIN. 460 o The lwB4 MAY require that the UDP, TCP, or ICMP header be 461 completely contained within the fragment that contains fragment 462 offset equal to zero. 464 For incoming packets carrying TCP or UDP IPv4 fragments with a non- 465 zero checksum, after de-capsulation, the lwB4 MAY elect to queue the 466 fragments as they arrive and perform NAPT44 on all fragments at the 467 same time. In this case, the incoming 5-tuple is determined by 468 extracting the appropriate fields from the received packet, as 469 described in [RFC2473]. Alternatively, a lwB4 MAY translate the de- 470 capsulated fragments as they arrive, by storing information that 471 allows it to compute the 5-tuple for fragments other than the first. 473 In the latter case, subsequent fragments may arrive before the first, 474 and the rules (in the bulleted list above) about how the lwB4 handles 475 (out-of-order) fragments apply. 477 For incoming de-capsulated IPv4 packets carrying UDP packets with a 478 zero checksum, if the lwB4 has enough resources, the lwB4 MUST 479 reassemble the packets and MUST calculate the checksum. If the lwB4 480 does not have enough resources, then it MUST silently discard the 481 packets. The handling of fragmented and un-fragmented UDP packets 482 with a zero checksum as specified above deviates from that specified 483 in [RFC6145]. 485 Implementers of an lwB4 should be aware that there are a number of 486 well-known attacks against IP fragmentation; see [RFC1858] and 487 [RFC3128]. Implementers should also be aware of additional issues 488 with reassembling packets at high rates, described in [RFC4963]. 490 5.2.1.2. Processing of Outbound IPv4 Packets Requiring Fragmentation 491 for Encapsulation 493 When an lwB4 receives an IPv4 packet from a connected host that 494 exceeds the IPv6 MTU size after encapsulation, the lwB4 SHOULD 495 fragment the IPv4 packet before encapsulation. This lwB4 behavior 496 avoids IPv6 fragmentation, so that the lwAFTR is not required to re- 497 assemble fragmented IPv6 packets. If the the Don't Fragment (DF) bit 498 is set in the IPv4 packet header (e.g. for PMTUD discovery), then the 499 IPv4 packet is dropped by the lwB4 and an ICMP Fragmentation Needed 500 (Type 3, Code 4) with the correct tunnel MTU is sent. 502 6. Lightweight AFTR Behavior 504 6.1. Binding Table Maintenance 506 The lwAFTR maintains an address binding table containing the binding 507 between the lwB4's IPv6 address, the allocated IPv4 address and 508 restricted port-set. Unlike the DS-Lite extended binding table 509 defined in section 6.6 of [RFC6333] which is a 5-tuple NAPT table, 510 each entry in the Lightweight 4over6 binding table contains the 511 following 3-tuples: 513 o IPv6 Address for a single lwB4 515 o Public IPv4 Address 517 o Restricted port-set 518 The entry has two functions: the IPv6 encapsulation of inbound IPv4 519 packets destined to the lwB4 and the validation of outbound IPv4-in- 520 IPv6 packets received from the lwB4 for de-capsulation. 522 The lwAFTR does not perform NAPT and so does not need session 523 entries. 525 The lwAFTR MUST synchronize the binding information with the port- 526 restricted address provisioning process. If the lwAFTR does not 527 participate in the port-restricted address provisioning process, the 528 binding MUST be synchronized through other methods (e.g. out-of-band 529 static update). 531 If the lwAFTR participates in the port-restricted provisioning 532 process, then its binding table MUST be created as part of this 533 process. 535 For all provisioning processes, the lifetime of binding table entries 536 MUST be synchronized with the lifetime of address allocations. 538 6.2. lwAFTR Data Plane Behavior 540 Several sections of [RFC6333] provide background information on the 541 AFTR's data plane functionality and MUST be implemented by the lwAFTR 542 as they are common to both solutions. The relevant sections are: 544 6.2 Encapsulation Covering encapsulation and de- 545 capsulation of tunneled traffic 547 6.3 Fragmentation and Reassembly Fragmentation and re-assembly 548 considerations (referencing 549 [RFC2473]) 551 7.1 Tunneling Covering tunneling and traffic 552 class mapping between IPv4 and IPv6 553 (referencing [RFC2473] and 554 [RFC4213]) 556 When the lwAFTR receives an IPv4-in-IPv6 packet from an lwB4, it de- 557 capsulates the IPv6 header and verifies the source addresses and port 558 in the binding table. If both the source IPv4 and IPv6 addresses 559 match a single entry in the binding table and the source port is in 560 the allowed port-set for that entry, the lwAFTR forwards the packet 561 to the IPv4 destination. 563 If no match is found (e.g., no matching IPv4 address entry, port out 564 of range, etc.), the lwAFTR MUST discard or implement a policy (such 565 as redirection) on the packet. An ICMPv6 type 1, code 5 (source 566 address failed ingress/egress policy) error message MAY be sent back 567 to the requesting lwB4. The ICMP policy SHOULD be configurable. 569 When the lwAFTR receives an inbound IPv4 packet, it uses the IPv4 570 destination address and port to lookup the destination lwB4's IPv6 571 address in its binding table. If a match is found, the lwAFTR 572 encapsulates the IPv4 packet. The source is the lwAFTR's IPv6 573 address and the destination is the lwB4's IPv6 address from the 574 matched entry. Then, the lwAFTR forwards the packet to the lwB4 575 natively over the IPv6 network. 577 If no match is found, the lwAFTR MUST discard the packet. An ICMPv4 578 type 3, code 1 (Destination unreachable, host unreachable) error 579 message MAY be sent back. The ICMP policy SHOULD be configurable. 581 The lwAFTR MUST support hairpinning of traffic between two lwB4s, by 582 performing de-capsulation and re-encapsulation of packets. The 583 hairpinning policy MUST be configurable. 585 7. Additional IPv4 address and Port Set Provisioning Mechanisms 587 In addition to the DHCPv6 based mechanism described in section 5.1, 588 several other IPv4 provisioning protocols have been suggested. These 589 protocols MAY be implemented. These alternatives include: 591 o DHCPv4 over DHCPv6: [I-D.ietf-dhc-dhcpv4-over-dhcpv6] describes 592 implementing DHCPv4 messages over an IPv6 only service providers 593 network. This enables leasing of IPv4 addresses and makes DHCPv4 594 options available to the DHCPv4 over DHCPv6 client. 596 o PCP[RFC6887]: an lwB4 MAY use [I-D.ietf-pcp-port-set] to retrieve 597 a restricted IPv4 address and a set of ports. 599 In a Lightweight 4over6 domain, the binding information MUST be 600 aligned between the lwB4s, the lwAFTRs and the provisioning server. 602 8. ICMP Processing 604 For both the lwAFTR and the lwB4, ICMPv6 MUST be handled as described 605 in [RFC2473]. 607 ICMPv4 does not work in an address sharing environment without 608 special handling [RFC6269]. Due to the port-set style address 609 sharing, Lightweight 4over6 requires specific ICMP message handling 610 not required by DS-Lite. 612 8.1. ICMPv4 Processing by the lwAFTR 614 For inbound ICMP messages The following behavior SHOULD be 615 implemented by the lwAFTR to provide ICMP error handling and basic 616 remote IPv4 service diagnostics for a port restricted CPE: 618 1. Check the ICMP Type field. 620 2. If the ICMP type is set to 0 or 8 (echo reply or request), then 621 the lwAFTR MUST take the value of the ICMP identifier field as 622 the source port, and use this value to lookup the binding table 623 for an encapsulation destination. If a match is found, the 624 lwAFTR forwards the ICMP packet to the IPv6 address stored in the 625 entry; otherwise it MUST discard the packet. 627 3. If the ICMP type field is set to any other value, then the lwAFTR 628 MUST use the method described in REQ-3 of [RFC5508] to locate the 629 source port within the transport layer header in ICMP packet's 630 data field. The destination IPv4 address and source port 631 extracted from the ICMP packet are then used to make a lookup in 632 the binding table. If a match is found, it MUST forward the ICMP 633 reply packet to the IPv6 address stored in the entry; otherwise 634 it MUST discard the packet. 636 Additionally, the lwAFTR MAY implement: 638 o Discarding of all inbound ICMP messages. 640 The ICMP policy SHOULD be configurable. 642 8.2. ICMPv4 Processing by the lwB4 644 The lwB4 SHOULD implement the requirements defined in [RFC5508] for 645 ICMP forwarding. For ICMP echo request packets originating from the 646 private IPv4 network, the lwB4 SHOULD implement the method described 647 in [RFC6346] and use an available port from its port-set as the ICMP 648 Identifier. 650 9. Security Considerations 652 As the port space for a subscriber shrinks due to address sharing, 653 the randomness for the port numbers of the subscriber is decreased 654 significantly. This means it is much easier for an attacker to guess 655 the port number used, which could result in attacks ranging from 656 throughput reduction to broken connections or data corruption. 658 The port-set for a subscriber can be a set of contiguous ports or 659 non-contiguous ports. Contiguous port-sets do not reduce this 660 threat. However, with non-contiguous port-set (which may be 661 generated in a pseudo-random way [RFC6431]), the randomness of the 662 port number is improved, provided that the attacker is outside the 663 Lightweight 4over6 domain and hence does not know the port-set 664 generation algorithm. 666 More considerations about IP address sharing are discussed in 667 Section 13 of [RFC6269], which is applicable to this solution. 669 10. IANA Considerations 671 This document does not include an IANA request. 673 11. Author List 675 The following are extended authors who contributed to the effort: 677 Jianping Wu 679 Tsinghua University 681 Department of Computer Science, Tsinghua University 683 Beijing 100084 685 P.R.China 687 Phone: +86-10-62785983 689 Email: jianping@cernet.edu.cn 691 Peng Wu 693 Tsinghua University 695 Department of Computer Science, Tsinghua University 697 Beijing 100084 699 P.R.China 701 Phone: +86-10-62785822 703 Email: pengwu.thu@gmail.com 704 Qi Sun 706 Tsinghua University 708 Beijing 100084 710 P.R.China 712 Phone: +86-10-62785822 714 Email: sunqi@csnet1.cs.tsinghua.edu.cn 716 Chongfeng Xie 718 China Telecom 720 Room 708, No.118, Xizhimennei Street 722 Beijing 100035 724 P.R.China 726 Phone: +86-10-58552116 728 Email: xiechf@ctbri.com.cn 730 Xiaohong Deng 732 France Telecom 734 Email: xiaohong.deng@orange.com 736 Cathy Zhou 738 Huawei Technologies 740 Section B, Huawei Industrial Base, Bantian Longgang 742 Shenzhen 518129 744 P.R.China 745 Email: cathyzhou@huawei.com 747 Alain Durand 749 Juniper Networks 751 1194 North Mathilda Avenue 753 Sunnyvale, CA 94089-1206 755 USA 757 Email: adurand@juniper.net 759 Reinaldo Penno 761 Cisco Systems, Inc. 763 170 West Tasman Drive 765 San Jose, California 95134 767 USA 769 Email: repenno@cisco.com 771 Alex Clauberg 773 Deutsche Telekom AG 775 GTN-FM4 777 Landgrabenweg 151 779 Bonn, CA 53227 781 Germany 783 Email: axel.clauberg@telekom.de 784 Lionel Hoffmann 786 Bouygues Telecom 788 TECHNOPOLE 790 13/15 Avenue du Marechal Juin 792 Meudon 92360 794 France 796 Email: lhoffman@bouyguestelecom.fr 798 Maoke Chen 800 FreeBit Co., Ltd. 802 13F E-space Tower, Maruyama-cho 3-6 804 Shibuya-ku, Tokyo 150-0044 806 Japan 808 Email: fibrib@gmail.com 810 12. Acknowledgement 812 The authors would like to thank Ole Troan, Ralph Droms and Suresh 813 Krishnan for their comments and feedback. 815 This document is a merge of three documents: 816 [I-D.cui-softwire-b4-translated-ds-lite], [I-D.zhou-softwire-b4-nat] 817 and [I-D.penno-softwire-sdnat]. 819 13. References 821 13.1. Normative References 823 [I-D.ietf-softwire-map-dhcp] 824 Mrugalski, T., Troan, O., Dec, W., Bao, C., 825 leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options 826 for configuration of Softwire Address and Port Mapped 827 Clients", draft-ietf-softwire-map-dhcp-06 (work in 828 progress), November 2013. 830 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 831 E. Lear, "Address Allocation for Private Internets", BCP 832 5, RFC 1918, February 1996. 834 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 835 Requirement Levels", BCP 14, RFC 2119, March 1997. 837 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 838 2131, March 1997. 840 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 841 IPv6 Specification", RFC 2473, December 1998. 843 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 844 for IPv6 Hosts and Routers", RFC 4213, October 2005. 846 [RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT 847 Behavioral Requirements for ICMP", BCP 148, RFC 5508, 848 April 2009. 850 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 851 Stack Lite Broadband Deployments Following IPv4 852 Exhaustion", RFC 6333, August 2011. 854 13.2. Informative References 856 [I-D.cui-softwire-b4-translated-ds-lite] 857 Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 858 Farrer, "Lightweight 4over6: An Extension to the DS-Lite 859 Architecture", draft-cui-softwire-b4-translated-ds-lite-11 860 (work in progress), February 2013. 862 [I-D.ietf-dhc-dhcpv4-over-dhcpv6] 863 Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I. 864 Farrer, "DHCPv4 over DHCPv6 Transport", draft-ietf-dhc- 865 dhcpv4-over-dhcpv6-04 (work in progress), January 2014. 867 [I-D.ietf-pcp-port-set] 868 Qiong, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, 869 T., and S. Perreault, "Port Control Protocol (PCP) 870 Extension for Port Set Allocation", draft-ietf-pcp-port- 871 set-04 (work in progress), November 2013. 873 [I-D.ietf-softwire-map-dhcp] 874 Mrugalski, T., Troan, O., Dec, W., Bao, C., 875 leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options 876 for configuration of Softwire Address and Port Mapped 877 Clients", draft-ietf-softwire-map-dhcp-06 (work in 878 progress), November 2013. 880 [I-D.ietf-softwire-map] 881 Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S., 882 Murakami, T., and T. Taylor, "Mapping of Address and Port 883 with Encapsulation (MAP)", draft-ietf-softwire-map-10 884 (work in progress), January 2014. 886 [I-D.ietf-softwire-unified-cpe] 887 Boucadair, M., Farrer, I., Perreault, S., and S. 888 Sivakumar, "Unified IPv4-in-IPv6 Softwire CPE", draft- 889 ietf-softwire-unified-cpe-01 (work in progress), May 2013. 891 [I-D.penno-softwire-sdnat] 892 Penno, R., Durand, A., Hoffmann, L., and A. Clauberg, 893 "Stateless DS-Lite", draft-penno-softwire-sdnat-02 (work 894 in progress), March 2012. 896 [I-D.zhou-softwire-b4-nat] 897 Zhou, C., Boucadair, M., and X. Deng, "NAT offload 898 extension to Dual-Stack lite", draft-zhou- 899 softwire-b4-nat-04 (work in progress), October 2011. 901 [RFC1858] Ziemba, G., Reed, D., and P. Traina, "Security 902 Considerations for IP Fragment Filtering", RFC 1858, 903 October 1995. 905 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 906 Address Translator (Traditional NAT)", RFC 3022, January 907 2001. 909 [RFC3128] Miller, I., "Protection Against a Variant of the Tiny 910 Fragment Attack (RFC 1858)", RFC 3128, June 2001. 912 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 913 Errors at High Data Rates", RFC 4963, July 2007. 915 [RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation 916 Algorithm", RFC 6145, April 2011. 918 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 919 NAT64: Network Address and Protocol Translation from IPv6 920 Clients to IPv4 Servers", RFC 6146, April 2011. 922 [RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P. 923 Roberts, "Issues with IP Address Sharing", RFC 6269, June 924 2011. 926 [RFC6346] Bush, R., "The Address plus Port (A+P) Approach to the 927 IPv4 Address Shortage", RFC 6346, August 2011. 929 [RFC6431] Boucadair, M., Levis, P., Bajko, G., Savolainen, T., and 930 T. Tsou, "Huawei Port Range Configuration Options for PPP 931 IP Control Protocol (IPCP)", RFC 6431, November 2011. 933 [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. 934 Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 935 2013. 937 [RFC7040] Cui, Y., Wu, J., Wu, P., Vautrin, O., and Y. Lee, "Public 938 IPv4-over-IPv6 Access Network", RFC 7040, November 2013. 940 Authors' Addresses 942 Yong Cui 943 Tsinghua University 944 Beijing 100084 945 P.R.China 947 Phone: +86-10-62603059 948 Email: yong@csnet1.cs.tsinghua.edu.cn 950 Qiong Sun 951 China Telecom 952 Room 708, No.118, Xizhimennei Street 953 Beijing 100035 954 P.R.China 956 Phone: +86-10-58552936 957 Email: sunqiong@ctbri.com.cn 959 Mohamed Boucadair 960 France Telecom 961 Rennes 35000 962 France 964 Email: mohamed.boucadair@orange.com 965 Tina Tsou 966 Huawei Technologies 967 2330 Central Expressway 968 Santa Clara, CA 95050 969 USA 971 Phone: +1-408-330-4424 972 Email: tena@huawei.com 974 Yiu L. Lee 975 Comcast 976 One Comcast Center 977 Philadelphia, PA 19103 978 USA 980 Email: yiu_lee@cable.comcast.com 982 Ian Farrer 983 Deutsche Telekom AG 984 CTO-ATI, Landgrabenweg 151 985 Bonn, NRW 53227 986 Germany 988 Email: ian.farrer@telekom.de