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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-12) exists of draft-ietf-softwire-map-dhcp-06 == Outdated reference: A later version (-09) exists of draft-ietf-dhc-dhcpv4-over-dhcpv6-04 == Outdated reference: A later version (-13) exists of draft-ietf-pcp-port-set-04 == Outdated reference: A later version (-13) exists of draft-ietf-softwire-map-10 == Outdated reference: A later version (-08) exists of draft-ietf-softwire-unified-cpe-01 Summary: 0 errors (**), 0 flaws (~~), 7 warnings (==), 1 comment (--). 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 10, 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 6, 2014 16 Lightweight 4over6: An Extension to the DS-Lite Architecture 17 draft-ietf-softwire-lw4over6-04 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 10, 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 . . . . . . . . . . . . . . . . . . 10 77 6.1. Binding Table Maintenance . . . . . . . . . . . . . . . . 10 78 6.2. lwAFTR Data Plane Behavior . . . . . . . . . . . . . . . 11 79 7. Additional IPv4 address and Port Set Provisioning 80 Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . 12 81 8. ICMP Processing . . . . . . . . . . . . . . . . . . . . . . . 12 82 8.1. ICMPv4 Processing by the lwAFTR . . . . . . . . . . . . . 13 83 8.2. ICMPv4 Processing by the lwB4 . . . . . . . . . . . . . . 13 84 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 85 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 86 11. Author List . . . . . . . . . . . . . . . . . . . . . . . . . 14 87 12. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 17 88 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 89 13.1. Normative References . . . . . . . . . . . . . . . . . . 17 90 13.2. Informative References . . . . . . . . . . . . . . . . . 18 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 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 services. The following figure shows the 229 data plane 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_SW46_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 the /64 prefix assigned to the WAN interface 320 (learned via SLAAC, DHCPv6 or manual configuration) and suffixing 321 64-bits for the interface identifier. The /128 prefix is constructed 322 as follows: 324 0 1 2 3 325 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 1 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | Operator assigned (64-bits) | 328 | | 329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 330 | Zero Padding | IPv4 Address | 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 | IPv4 Addr cont. | PSID | 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 Figure 3 Construction of the lw4o6 /128 Prefix 337 Padding: Padding (all zeros) 339 IPv4 Address: Public IPv4 address allocated to the client 341 PSID: Port Set ID allocated to the client, left padded with 342 zeros to 16-bits. If no PSID is provisioned, all 343 zeros. 345 In the event that the lwB4's encapsulation source address is changed 346 for any reason (such as the DHCPv6 lease expiring), the lwB4's 347 dynamic provisioning process must be re-initiated. 349 An lwB4 MUST support dynamic port-restricted IPv4 address 350 provisioning. The port set algorithm for provisioning this is 351 described in Section 5.1 of [I-D.ietf-softwire-map]. For lw4o6, the 352 number of a-bits SHOULD be 0. 354 In the event that the lwB4 receives and ICMPv6 error message (type 1, 355 code 5) originating from the lwAFTR, the lwB4 SHOULD interpret this 356 to mean that no matching entry in the lwAFTR's binding table has been 357 found. The lwB4 MAY then re-initiate the dynamic port-restricted 358 provisioning process. The lwB4's re-initiation policy SHOULD be 359 configurable. 361 The DNS considerations described in Section 5.5 and Section 6.4 of 362 [RFC6333] SHOULD be followed. 364 5.2. Lightweight B4 Data Plane Behavior 366 Several sections of [RFC6333] provide background information on the 367 B4's data plane functionality and MUST be implemented by the lwB4 as 368 they are common to both solutions. The relevant sections are: 370 5.2 Encapsulation Covering encapsulation and de- 371 capsulation of tunneled traffic 373 5.3 Fragmentation and Reassembly Covering MTU and fragmentation 374 considerations (referencing 375 [RFC2473]), with the exception 376 noted below. 378 7.1 Tunneling Covering tunneling and traffic 379 class mapping between IPv4 and IPv6 380 (referencing [RFC2473] and 381 [RFC4213]) 383 The lwB4 element performs IPv4 address translation (NAPT44) as well 384 as encapsulation and de-capsulation. It runs standard NAPT44 385 [RFC3022] using the allocated port-restricted address as its external 386 IPv4 address and port numbers. 388 The working flow of the lwB4 is illustrated in figure 3. 390 +-------------+ 391 | lwB4 | 392 +--------+ IPv4 |------+------| IPv4-in-IPv6 +----------+ 393 |IPv4 LAN|------->| |Encap.|-------------->|Configured| 394 | |<-------| NAPT | or |<--------------| lwAFTR | 395 +--------+ | |Decap.| +----------+ 396 +------+------+ 398 Figure 4 Working Flow of the lwB4 400 Internally connected hosts source IPv4 packets with an [RFC1918] 401 address. When the lwB4 receives such an IPv4 packet, it performs a 402 NAPT44 function on the source address and port by using the public 403 IPv4 address and a port number from the allocated port-set. Then, it 404 encapsulates the packet with an IPv6 header. The destination IPv6 405 address is the lwAFTR's IPv6 address and the source IPv6 address is 406 the lwB4's IPv6 tunnel endpoint address. Finally, the lwB4 forwards 407 the encapsulated packet to the configured lwAFTR. 409 When the lwB4 receives an IPv4-in-IPv6 packet from the lwAFTR, it de- 410 capsulates the IPv4 packet from the IPv6 packet. Then, it performs 411 NAPT44 translation on the destination address and port, based on the 412 available information in its local NAPT44 table. 414 If the IPv6 source address does not match the configured lwAFTR 415 address, then the packet MUST be discarded. If the decapsulated IPv4 416 packet does not match the lwB4's configuration (i.e. invalid 417 destination IPv4 address or port) then the packet MUST be dropped. 418 An ICMPv4 error message (type 13 - Communication Administratively 419 Prohibited) message MAY be sent back to the lwAFTR. The ICMP policy 420 SHOULD be configurable. 422 The lwB4 is responsible for performing ALG functions (e.g., SIP, 423 FTP), and other NAPT traversal mechanisms (e.g., UPnP, NAPT-PMP, 424 manual binding configuration, PCP) for the internal hosts. This 425 requirement is typical for NAPT44 gateways available today. 427 It is possible that a lwB4 is co-located in a host. In this case, 428 the functions of NAPT44 and encapsulation/de-capsulation are 429 implemented inside the host. 431 5.2.1. Changes to RFC2473 and RFC6333 Fragmentation Behaviour 433 On receiving an encapsulated packet containing an IPv4 fragment, the 434 lwB4 SHOULD wait until all other fragments have been received and de- 435 capsulated. The original packet is then re-assembled before 436 performing NAPT. This is necessary because layer-4 protocol 437 information is only present in the first fragment. However, as this 438 provides a potential security flaw (as discussed in [RFC4459] 439 Section 5) it is RECOMMENDED that the lwB4 implements mechanisms to 440 prevent buffer memory exhaustion. 442 When an lwB4 receives an IPv4 packet from a connected host that 443 exceeds the IPv6 MTU size after encapsulation, the lwB4 SHOULD 444 fragment the IPv4 packet before encapsulation. This lwB4 behavior 445 will not result IPv6 fragmentation so that lwAFTR is not required to 446 re- assemble fragmented IPv6 packets. If the the Don't Fragment (DF) 447 bit is set in the IPv4 packet header (e.g. for PMTUD discovery), then 448 the IPv4 packet is dropped by the lwB4 and an ICMP Fragmentation 449 Needed (Type 3, Code 4) with the correct tunnel MTU is sent. 451 6. Lightweight AFTR Behavior 453 6.1. Binding Table Maintenance 455 The lwAFTR maintains an address binding table containing the binding 456 between the lwB4's IPv6 address, the allocated IPv4 address and 457 restricted port-set. Unlike the DS-Lite extended binding table 458 defined in section 6.6 of [RFC6333] which is a 5-tuple NAPT table, 459 each entry in the Lightweight 4over6 binding table contains the 460 following 3-tuples: 462 o IPv6 Address for a single lwB4 464 o Public IPv4 Address 466 o Restricted port-set 467 The entry has two functions: the IPv6 encapsulation of inbound IPv4 468 packets destined to the lwB4 and the validation of outbound IPv4-in- 469 IPv6 packets received from the lwB4 for de-capsulation. 471 The lwAFTR does not perform NAPT and so does not need session 472 entries. 474 The lwAFTR MUST synchronize the binding information with the port- 475 restricted address provisioning process. If the lwAFTR does not 476 participate in the port-restricted address provisioning process, the 477 binding MUST be synchronized through other methods (e.g. out-of-band 478 static update). 480 If the lwAFTR participates in the port-restricted provisioning 481 process, then its binding table MUST be created as part of this 482 process. 484 For all provisioning processes, the lifetime of binding table entries 485 MUST be synchronized with the lifetime of address allocations. 487 6.2. lwAFTR Data Plane Behavior 489 Several sections of [RFC6333] provide background information on the 490 AFTR's data plane functionality and MUST be implemented by the lwAFTR 491 as they are common to both solutions. The relevant sections are: 493 6.2 Encapsulation Covering encapsulation and de- 494 capsulation of tunneled traffic 496 6.3 Fragmentation and Reassembly Fragmentation and re-assembly 497 considerations (referencing 498 [RFC2473]) 500 7.1 Tunneling Covering tunneling and traffic 501 class mapping between IPv4 and IPv6 502 (referencing [RFC2473] and 503 [RFC4213]) 505 When the lwAFTR receives an IPv4-in-IPv6 packet from an lwB4, it de- 506 capsulates the IPv6 header and verifies the source addresses and port 507 in the binding table. If both the source IPv4 and IPv6 addresses 508 match a single entry in the binding table and the source port is in 509 the allowed port-set for that entry, the lwAFTR forwards the packet 510 to the IPv4 destination. 512 If no match is found (e.g., no matching IPv4 address entry, port out 513 of range, etc.), the lwAFTR MUST discard or implement a policy (such 514 as redirection) on the packet. An ICMPv6 type 1, code 5 (source 515 address failed ingress/egress policy) error message MAY be sent back 516 to the requesting lwB4. The ICMP policy SHOULD be configurable. 518 When the lwAFTR receives an inbound IPv4 packet, it uses the IPv4 519 destination address and port to lookup the destination lwB4's IPv6 520 address in its binding table. If a match is found, the lwAFTR 521 encapsulates the IPv4 packet. The source is the lwAFTR's IPv6 522 address and the destination is the lwB4's IPv6 address from the 523 matched entry. Then, the lwAFTR forwards the packet to the lwB4 524 natively over the IPv6 network. 526 If no match is found, the lwAFTR MUST discard the packet. An ICMPv4 527 type 3, code 1 (Destination unreachable, host unreachable) error 528 message MAY be sent back. The ICMP policy SHOULD be configurable. 530 The lwAFTR MUST support hairpinning of traffic between two lwB4s, by 531 performing de-capsulation and re-encapsulation of packets. The 532 hairpinning policy MUST be configurable. 534 7. Additional IPv4 address and Port Set Provisioning Mechanisms 536 In addition to the DHCPv6 based mechanism described in section 5.1, 537 several other IPv4 provisioning protocols have been suggested. These 538 protocols MAY be implemented. These alternatives include: 540 o DHCPv4 over DHCPv6: [I-D.ietf-dhc-dhcpv4-over-dhcpv6] describes 541 implementing DHCPv4 messages over an IPv6 only service providers 542 network. This enables leasing of IPv4 addresses and makes DHCPv4 543 options available to the DHCPv4 over DHCPv6 client. 545 o PCP[RFC6887]: an lwB4 MAY use [I-D.ietf-pcp-port-set] to retrieve 546 a restricted IPv4 address and a set of ports. 548 In a Lightweight 4over6 domain, the binding information MUST be 549 aligned between the lwB4s, the lwAFTRs and the provisioning server. 551 8. ICMP Processing 553 For both the lwAFTR and the lwB4, ICMPv6 MUST be handled as described 554 in [RFC2473]. 556 ICMPv4 does not work in an address sharing environment without 557 special handling [RFC6269]. Due to the port-set style address 558 sharing, Lightweight 4over6 requires specific ICMP message handling 559 not required by DS-Lite. 561 8.1. ICMPv4 Processing by the lwAFTR 563 For inbound ICMP messages The following behavior SHOULD be 564 implemented by the lwAFTR to provide ICMP error handling and basic 565 remote IPv4 service diagnostics for a port restricted CPE: 567 1. Check the ICMP Type field. 569 2. If the ICMP type is set to 0 or 8 (echo reply or request), then 570 the lwAFTR MUST take the value of the ICMP identifier field as 571 the source port, and use this value to lookup the binding table 572 for an encapsulation destination. If a match is found, the 573 lwAFTR forwards the ICMP packet to the IPv6 address stored in the 574 entry; otherwise it MUST discard the packet. 576 3. If the ICMP type field is set to any other value, then the lwAFTR 577 MUST use the method described in REQ-3 of [RFC5508] to locate the 578 source port within the transport layer header in ICMP packet's 579 data field. The destination IPv4 address and source port 580 extracted from the ICMP packet are then used to make a lookup in 581 the binding table. If a match is found, it MUST forward the ICMP 582 reply packet to the IPv6 address stored in the entry; otherwise 583 it MUST discard the packet. 585 Additionally, the lwAFTR MAY implement: 587 o Discarding of all inbound ICMP messages. 589 The ICMP policy SHOULD be configurable. 591 8.2. ICMPv4 Processing by the lwB4 593 The lwB4 SHOULD implement the requirements defined in [RFC5508] for 594 ICMP forwarding. For ICMP echo request packets originating from the 595 private IPv4 network, the lwB4 SHOULD implement the method described 596 in [RFC6346] and use an available port from its port-set as the ICMP 597 Identifier. 599 9. Security Considerations 601 As the port space for a subscriber shrinks due to address sharing, 602 the randomness for the port numbers of the subscriber is decreased 603 significantly. This means it is much easier for an attacker to guess 604 the port number used, which could result in attacks ranging from 605 throughput reduction to broken connections or data corruption. 607 The port-set for a subscriber can be a set of contiguous ports or 608 non-contiguous ports. Contiguous port-sets do not reduce this 609 threat. However, with non-contiguous port-set (which may be 610 generated in a pseudo-random way [RFC6431]), the randomness of the 611 port number is improved, provided that the attacker is outside the 612 Lightweight 4over6 domain and hence does not know the port-set 613 generation algorithm. 615 More considerations about IP address sharing are discussed in 616 Section 13 of [RFC6269], which is applicable to this solution. 618 10. IANA Considerations 620 This document does not include an IANA request. 622 11. Author List 624 The following are extended authors who contributed to the effort: 626 Jianping Wu 628 Tsinghua University 630 Department of Computer Science, Tsinghua University 632 Beijing 100084 634 P.R.China 636 Phone: +86-10-62785983 638 Email: jianping@cernet.edu.cn 640 Peng Wu 642 Tsinghua University 644 Department of Computer Science, Tsinghua University 646 Beijing 100084 648 P.R.China 650 Phone: +86-10-62785822 652 Email: pengwu.thu@gmail.com 653 Qi Sun 655 Tsinghua University 657 Beijing 100084 659 P.R.China 661 Phone: +86-10-62785822 663 Email: sunqi@csnet1.cs.tsinghua.edu.cn 665 Chongfeng Xie 667 China Telecom 669 Room 708, No.118, Xizhimennei Street 671 Beijing 100035 673 P.R.China 675 Phone: +86-10-58552116 677 Email: xiechf@ctbri.com.cn 679 Xiaohong Deng 681 France Telecom 683 Email: xiaohong.deng@orange.com 685 Cathy Zhou 687 Huawei Technologies 689 Section B, Huawei Industrial Base, Bantian Longgang 691 Shenzhen 518129 693 P.R.China 694 Email: cathyzhou@huawei.com 696 Alain Durand 698 Juniper Networks 700 1194 North Mathilda Avenue 702 Sunnyvale, CA 94089-1206 704 USA 706 Email: adurand@juniper.net 708 Reinaldo Penno 710 Cisco Systems, Inc. 712 170 West Tasman Drive 714 San Jose, California 95134 716 USA 718 Email: repenno@cisco.com 720 Alex Clauberg 722 Deutsche Telekom AG 724 GTN-FM4 726 Landgrabenweg 151 728 Bonn, CA 53227 730 Germany 732 Email: axel.clauberg@telekom.de 733 Lionel Hoffmann 735 Bouygues Telecom 737 TECHNOPOLE 739 13/15 Avenue du Marechal Juin 741 Meudon 92360 743 France 745 Email: lhoffman@bouyguestelecom.fr 747 Maoke Chen 749 FreeBit Co., Ltd. 751 13F E-space Tower, Maruyama-cho 3-6 753 Shibuya-ku, Tokyo 150-0044 755 Japan 757 Email: fibrib@gmail.com 759 12. Acknowledgement 761 The authors would like to thank Ole Troan, Ralph Droms and Suresh 762 Krishnan for their comments and feedback. 764 This document is a merge of three documents: 765 [I-D.cui-softwire-b4-translated-ds-lite], [I-D.zhou-softwire-b4-nat] 766 and [I-D.penno-softwire-sdnat]. 768 13. References 770 13.1. Normative References 772 [I-D.ietf-softwire-map-dhcp] 773 Mrugalski, T., Troan, O., Dec, W., Bao, C., 774 leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options 775 for configuration of Softwire Address and Port Mapped 776 Clients", draft-ietf-softwire-map-dhcp-06 (work in 777 progress), November 2013. 779 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 780 E. Lear, "Address Allocation for Private Internets", BCP 781 5, RFC 1918, February 1996. 783 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 784 Requirement Levels", BCP 14, RFC 2119, March 1997. 786 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 787 2131, March 1997. 789 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 790 IPv6 Specification", RFC 2473, December 1998. 792 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 793 for IPv6 Hosts and Routers", RFC 4213, October 2005. 795 [RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT 796 Behavioral Requirements for ICMP", BCP 148, RFC 5508, 797 April 2009. 799 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 800 Stack Lite Broadband Deployments Following IPv4 801 Exhaustion", RFC 6333, August 2011. 803 13.2. Informative References 805 [I-D.cui-softwire-b4-translated-ds-lite] 806 Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 807 Farrer, "Lightweight 4over6: An Extension to the DS-Lite 808 Architecture", draft-cui-softwire-b4-translated-ds-lite-11 809 (work in progress), February 2013. 811 [I-D.ietf-dhc-dhcpv4-over-dhcpv6] 812 Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I. 813 Farrer, "DHCPv4 over DHCPv6 Transport", draft-ietf-dhc- 814 dhcpv4-over-dhcpv6-04 (work in progress), January 2014. 816 [I-D.ietf-pcp-port-set] 817 Qiong, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, 818 T., and S. Perreault, "Port Control Protocol (PCP) 819 Extension for Port Set Allocation", draft-ietf-pcp-port- 820 set-04 (work in progress), November 2013. 822 [I-D.ietf-softwire-map-dhcp] 823 Mrugalski, T., Troan, O., Dec, W., Bao, C., 824 leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options 825 for configuration of Softwire Address and Port Mapped 826 Clients", draft-ietf-softwire-map-dhcp-06 (work in 827 progress), November 2013. 829 [I-D.ietf-softwire-map] 830 Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S., 831 Murakami, T., and T. Taylor, "Mapping of Address and Port 832 with Encapsulation (MAP)", draft-ietf-softwire-map-10 833 (work in progress), January 2014. 835 [I-D.ietf-softwire-unified-cpe] 836 Boucadair, M., Farrer, I., Perreault, S., and S. 837 Sivakumar, "Unified IPv4-in-IPv6 Softwire CPE", draft- 838 ietf-softwire-unified-cpe-01 (work in progress), May 2013. 840 [I-D.penno-softwire-sdnat] 841 Penno, R., Durand, A., Hoffmann, L., and A. Clauberg, 842 "Stateless DS-Lite", draft-penno-softwire-sdnat-02 (work 843 in progress), March 2012. 845 [I-D.zhou-softwire-b4-nat] 846 Zhou, C., Boucadair, M., and X. Deng, "NAT offload 847 extension to Dual-Stack lite", draft-zhou- 848 softwire-b4-nat-04 (work in progress), October 2011. 850 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 851 Address Translator (Traditional NAT)", RFC 3022, January 852 2001. 854 [RFC4459] Savola, P., "MTU and Fragmentation Issues with In-the- 855 Network Tunneling", RFC 4459, April 2006. 857 [RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P. 858 Roberts, "Issues with IP Address Sharing", RFC 6269, June 859 2011. 861 [RFC6346] Bush, R., "The Address plus Port (A+P) Approach to the 862 IPv4 Address Shortage", RFC 6346, August 2011. 864 [RFC6431] Boucadair, M., Levis, P., Bajko, G., Savolainen, T., and 865 T. Tsou, "Huawei Port Range Configuration Options for PPP 866 IP Control Protocol (IPCP)", RFC 6431, November 2011. 868 [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. 869 Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 870 2013. 872 [RFC7040] Cui, Y., Wu, J., Wu, P., Vautrin, O., and Y. Lee, "Public 873 IPv4-over-IPv6 Access Network", RFC 7040, November 2013. 875 Authors' Addresses 877 Yong Cui 878 Tsinghua University 879 Beijing 100084 880 P.R.China 882 Phone: +86-10-62603059 883 Email: yong@csnet1.cs.tsinghua.edu.cn 885 Qiong Sun 886 China Telecom 887 Room 708, No.118, Xizhimennei Street 888 Beijing 100035 889 P.R.China 891 Phone: +86-10-58552936 892 Email: sunqiong@ctbri.com.cn 894 Mohamed Boucadair 895 France Telecom 896 Rennes 35000 897 France 899 Email: mohamed.boucadair@orange.com 901 Tina Tsou 902 Huawei Technologies 903 2330 Central Expressway 904 Santa Clara, CA 95050 905 USA 907 Phone: +1-408-330-4424 908 Email: tena@huawei.com 909 Yiu L. Lee 910 Comcast 911 One Comcast Center 912 Philadelphia, PA 19103 913 USA 915 Email: yiu_lee@cable.comcast.com 917 Ian Farrer 918 Deutsche Telekom AG 919 CTO-ATI, Landgrabenweg 151 920 Bonn, NRW 53227 921 Germany 923 Email: ian.farrer@telekom.de