idnits 2.17.1 draft-ietf-softwire-lw4over6-11.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** There are 2 instances of too long lines in the document, the longest one being 1 character in excess of 72. == There are 1 instance of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (October 14, 2014) is 3480 days in the past. 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-12) exists of draft-ietf-softwire-map-dhcp-09 == Outdated reference: A later version (-13) exists of draft-ietf-pcp-port-set-06 == Outdated reference: A later version (-13) exists of draft-ietf-softwire-map-11 == Outdated reference: A later version (-08) exists of draft-ietf-softwire-unified-cpe-01 Summary: 1 error (**), 0 flaws (~~), 6 warnings (==), 1 comment (--).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: April 17, 2015 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 October 14, 2014 16 Lightweight 4over6: An Extension to the DS-Lite Architecture 17 draft-ietf-softwire-lw4over6-11 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 April 17, 2015. 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 . . . . . . . . . . . 9 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 . . . . . . . . . . . . . . . 11 79 7. Additional IPv4 address and Port Set Provisioning 80 Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . 12 81 8. ICMP Processing . . . . . . . . . . . . . . . . . . . . . . . 13 82 8.1. ICMPv4 Processing by the lwAFTR . . . . . . . . . . . . . 13 83 8.2. ICMPv4 Processing by the lwB4 . . . . . . . . . . . . . . 14 84 9. Security Considerations . . . . . . . . . . . . . . . . . . . 14 85 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 86 11. Author List . . . . . . . . . . . . . . . . . . . . . . . . . 14 87 12. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 18 88 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 89 13.1. Normative References . . . . . . . . . . . . . . . . . . 18 90 13.2. Informative References . . . . . . . . . . . . . . . . . 19 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 is a solution designed specifically for complete 145 independence between IPv6 subnet prefix and IPv4 address with or 146 without IPv4 address sharing. This is accomplished by maintaining 147 state for each softwire (per-subscriber state) in the central lwAFTR 148 and a hub-and-spoke forwarding architecture. [I-D.ietf-softwire-map] 149 also offers these capabilities or, alternatively, allows for a 150 reduction of the amount of centralized state using rules to express 151 IPv4/IPv6 address mappings. This introduces an algorithmic 152 relationship between the IPv6 subnet and IPv4 address. This 153 relationship also allows the option of direct, meshed connectivity 154 between users. 156 The tunneling mechanism remains the same for DS-Lite and Lightweight 157 4over6. This document describes the changes to DS-Lite that are 158 necessary to implement Lightweight 4over6. These changes mainly 159 concern the configuration parameters and provisioning method 160 necessary for the functional elements. 162 Lightweight 4over6 features keeping per-subscriber state in the 163 service provider's network. It is categorized as Binding approach in 164 [I-D.ietf-softwire-unified-cpe] which defines a unified IPv4-in-IPv6 165 Softwire CPE. 167 This document is an extended case, which covers address sharing for 168 [RFC7040]. It is also a variant of A+P called Binding Table Mode 169 (see Section 4.4 of [RFC6346]). 171 This document focuses on architectural considerations and 172 particularly on the expected behavior of the involved functional 173 elements and their interfaces. Deployment-specific issues are 174 discussed in a companion document. As such, discussions about 175 redundancy and provisioning policy are out of scope. 177 2. Conventions 179 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 180 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 181 document are to be interpreted as described in [RFC2119]. 183 3. Terminology 185 The document defines the following terms: 187 Lightweight 4over6 (lw4o6): An IPv4-over-IPv6 hub and spoke 188 mechanism, which extends DS-Lite by 189 moving the IPv4 translation (NAPT44) 190 function from the AFTR to the B4. 192 Lightweight B4 (lwB4): A B4 element (Basic Bridging BroadBand 193 element [RFC6333]), which supports 194 Lightweight 4over6 extensions. An lwB4 195 is a function implemented on a dual- 196 stack capable node, (either a directly 197 connected device or a CPE), that 198 supports port-restricted IPv4 address 199 allocation, implements NAPT44 200 functionality and creates a tunnel to 201 an lwAFTR. 203 Lightweight AFTR (lwAFTR): An AFTR element (Address Family 204 Transition Router element [RFC6333]), 205 which supports Lightweight 4over6 206 extension. An lwAFTR is an IPv4-in- 207 IPv6 tunnel endpoint which maintains 208 per-subscriber address binding only and 209 does not perform a NAPT44 function. 211 Restricted Port-Set: A non-overlapping range of allowed 212 external ports allocated to the lwB4 to 213 use for NAPT44. Source ports of IPv4 214 packets sent by the B4 must belong to 215 the assigned port-set. The port set is 216 used for all port aware IP protocols 217 (TCP, UDP, SCTP etc.). 219 Port-restricted IPv4 Address: A public IPv4 address with a restricted 220 port-set. In Lightweight 4over6, 221 multiple B4s may share the same IPv4 222 address, however, their port-sets must 223 be non-overlapping. 225 Throughout the remainder of this document, the terms B4/AFTR should 226 be understood to refer specifically to a DS-Lite implementation. The 227 terms lwB4/lwAFTR refer to a Lightweight 4over6 implementation. 229 4. Lightweight 4over6 Architecture 231 The Lightweight 4over6 architecture is functionally similar to DS- 232 Lite. lwB4s and an lwAFTR are connected through an IPv6-enabled 233 network. Both approaches use an IPv4-in-IPv6 encapsulation scheme to 234 deliver IPv4 connectivity. The following figure shows the data plane 235 with the main functional change between DS-Lite and lw4o6: 237 +--------+ +---------+ IPv4-in-IPv6 +---------+ +-------------+ 238 |IPv4 LAN|---| B4 |==================|AFTR/NAPT|----|IPv4Internet| 239 +--------+ +---------+ +---------+ +-------------+ 240 DS-Lite NAPT model: all state in the AFTR 242 +--------+ +---------+ IPv4-in-IPv6 +------+ +-------------+ 243 |IPv4 LAN|---|lwB4/NAPT|==================|lwAFTR|----|IPv4 Internet| 244 +--------+ +---------+ +------+ +-------------+ 245 LW4over6 NAPT model: 246 subscriber state in the lwAFTR, NAPT state in lwB4 248 Figure 1 Comparison of DS-Lite and Lightweight 4over6 Data Plane 250 There are three main components in the Lightweight 4over6 251 architecture: 253 o The lwB4, which performs the NAPT function and encapsulation/de- 254 capsulation IPv4/IPv6. 256 o The lwAFTR, which performs the encapsulation/de-capsulation IPv4/ 257 IPv6. 259 o The provisioning system, which tells the lwB4 which IPv4 address 260 and port set to use. 262 The lwB4 differs from a regular B4 in that it now performs the NAPT 263 functionality. This means that it needs to be provisioned with the 264 public IPv4 address and port set it is allowed to use. This 265 information is provided though a provisioning mechanism such as DHCP, 266 PCP or TR-69. 268 The lwAFTR needs to know the binding between the IPv6 address of each 269 subscriber and the IPv4 address and port set allocated to that 270 subscriber. This information is used to perform ingress filtering 271 upstream and encapsulation downstream. Note that this is per- 272 subscriber state as opposed to per-flow state in the regular AFTR 273 case. 275 The consequence of this architecture is that the information 276 maintained by the provisioning mechanism and the one maintained by 277 the lwAFTR MUST be synchronized (See figure 2). The details of this 278 synchronization depend on the exact provisioning mechanism and will 279 be discussed in a companion document. 281 The solution specified in this document allows the assignment of 282 either a full or a shared IPv4 address requesting CPEs. [RFC7040] 283 provides a mechanism for assigning a full IPv4 address only. 285 +------------+ 286 /-------|Provisioning|<-----\ 287 | +------------+ | 288 | | 289 V V 290 +--------+ +---------+ IPv4/IPv6 +------+ +-------------+ 291 |IPv4 LAN|---|lwB4/NAPT|==================|lwAFTR|----|IPv4 Internet| 292 +--------+ +---------+ +------+ +-------------+ 294 Figure 2 Lightweight 4over6 Provisioning Synchronization 296 5. Lightweight B4 Behavior 298 5.1. Lightweight B4 Provisioning with DHCPv6 300 With DS-Lite, the B4 element only needs to be configured with a 301 single DS-Lite specific parameter so that it can set up the softwire 302 (the IPv6 address of the AFTR). Its IPv4 address can be taken from 303 the well-known range 192.0.0.0/29. 305 In lw4o6, a number of lw4o6 specific configuration parameters must be 306 provisioned to the lwB4. These are: 308 o IPv6 Address for the lwAFTR 310 o IPv4 External (Public) Address for NAPT44 312 o Restricted port-set to use for NAPT44 314 o IPv6 Binding Prefix 316 For DHCPv6 based configuration of these parameters, the lwB4 SHOULD 317 implement OPTION_S46_CONT_LW as described in section 5.3 of 318 [I-D.ietf-softwire-map-dhcp]. This means that the lifetime of the 319 softwire and the derived configuration information (e.g. IPv4 shared 320 address, IPv4 address) is bound to the lifetime of the DHCPv6 lease. 321 If stateful IPv4 configuration or additional IPv4 configuration 322 information is required, DHCP 4o6 [RFC7341] must be used. 324 Although it would be possible to extend lw4o6 to have more than one 325 active lw4o6 tunnel configured simultaneously, this document is only 326 concerned with the use of a single tunnel. 328 The IPv6 binding prefix field is provisioned so that the CE can 329 identify the correct prefix to use as the tunnel source. On receipt 330 of the necessary configuration parameters listed in Section 5.1 of 331 this document, the lwB4 performs a longest prefix match between the 332 IPv6 binding prefix and its currently active IPv6 prefixes. The 333 result forms the subnet to be used for sourcing the lw4o6 tunnel. 334 The full /128 address is then constructed in the same manner as 335 [I-D.ietf-softwire-map]. 337 0 1 2 3 338 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 1 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 340 | Operator Assigned Prefix | 341 . (64-bits) . 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 343 | Zero Padding | IPv4 Address | 344 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 345 | IPv4 Addr cont. | PSID | 346 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 348 Figure 3 Construction of the lw4o6 /128 Prefix 350 Operator Assigned Prefix: IPv6 prefix allocated to the client. If 351 the prefix length is less than 64, right padded with 352 zeros to 64-bits. 354 Padding: Padding (all zeros) 356 IPv4 Address: Public IPv4 address allocated to the client 358 PSID: Port Set ID allocated to the client, left padded with 359 zeros to 16-bits. If no PSID is provisioned, all 360 zeros. 362 In the event that the lwB4's IPv6 encapsulation source address is 363 changed for any reason (such as the DHCPv6 lease expiring), the 364 lwB4's dynamic provisioning process must be re-initiated. When the 365 lwB4's public IPv4 address or port set ID is changed for any reason, 366 the lwB4 must flush its NAPT table. 368 An lwB4 MUST support dynamic port-restricted IPv4 address 369 provisioning. The port set algorithm for provisioning this is 370 described in Section 5.1 of [I-D.ietf-softwire-map]. For lw4o6, the 371 number of a-bits SHOULD be 0, thus allocating a single contiguous 372 port set to each lwB4. 374 Unless an lwB4 is being allocated a full IPv4 address, it is 375 RECOMMENDED that PSIDs containing the well-known ports (0-1023) are 376 not allocated to lwB4s. 378 In the event that the lwB4 receives an ICMPv6 error message (type 1, 379 code 5) originating from the lwAFTR, the lwB4 SHOULD interpret this 380 to mean that no matching entry in the lwAFTR's binding table has been 381 found. The lwB4 MAY then re-initiate the dynamic port-restricted 382 provisioning process. The lwB4's re-initiation policy SHOULD be 383 configurable. 385 The DNS considerations described in Section 5.5 and Section 6.4 of 386 [RFC6333] SHOULD be followed. 388 5.2. Lightweight B4 Data Plane Behavior 390 Several sections of [RFC6333] provide background information on the 391 B4's data plane functionality and MUST be implemented by the lwB4 as 392 they are common to both solutions. The relevant sections are: 394 5.2 Encapsulation Covering encapsulation and de- 395 capsulation of tunneled traffic 397 5.3 Fragmentation and Reassembly Covering MTU and fragmentation 398 considerations (referencing 399 [RFC2473]), with the exception 400 noted below. 402 7.1 Tunneling Covering tunneling and traffic 403 class mapping between IPv4 and IPv6 404 (referencing [RFC2473] and 405 [RFC2983]) 407 The lwB4 element performs IPv4 address translation (NAPT44) as well 408 as encapsulation and de-capsulation. It runs standard NAPT44 409 [RFC3022] using the allocated port-restricted address as its external 410 IPv4 address and port numbers. 412 The working flow of the lwB4 is illustrated in figure 4. 414 +-------------+ 415 | lwB4 | 416 +--------+ IPv4 |------+------| IPv4-in-IPv6 +----------+ 417 |IPv4 LAN|------->| |Encap.|-------------->|Configured| 418 | |<-------| NAPT | or |<--------------| lwAFTR | 419 +--------+ | |Decap.| +----------+ 420 +------+------+ 422 Figure 4 Working Flow of the lwB4 424 Internally connected hosts source IPv4 packets with an [RFC1918] 425 address. When the lwB4 receives such an IPv4 packet, it performs a 426 NAPT44 function on the source address and port by using the public 427 IPv4 address and a port number from the allocated port-set. Then, it 428 encapsulates the packet with an IPv6 header. The destination IPv6 429 address is the lwAFTR's IPv6 address and the source IPv6 address is 430 the lwB4's IPv6 tunnel endpoint address. Finally, the lwB4 forwards 431 the encapsulated packet to the configured lwAFTR. 433 When the lwB4 receives an IPv4-in-IPv6 packet from the lwAFTR, it de- 434 capsulates the IPv4 packet from the IPv6 packet. Then, it performs 435 NAPT44 translation on the destination address and port, based on the 436 available information in its local NAPT44 table. 438 If the IPv6 source address does not match the configured lwAFTR 439 address, then the packet MUST be discarded. If the decapsulated IPv4 440 packet does not match the lwB4's configuration (i.e. invalid 441 destination IPv4 address or port) then the packet MUST be dropped. 442 An ICMPv4 error message (type 13 - Communication Administratively 443 Prohibited) message MAY be sent back to the lwAFTR. The ICMP policy 444 SHOULD be configurable. 446 The lwB4 is responsible for performing ALG functions (e.g., SIP, 447 FTP), and other NAPT traversal mechanisms (e.g., UPnP, NAPT-PMP, 448 manual binding configuration, PCP) for the internal hosts. This 449 requirement is typical for NAPT44 gateways available today. 451 It is possible that a lwB4 is co-located in a host. In this case, 452 the functions of NAPT44 and encapsulation/de-capsulation are 453 implemented inside the host. 455 5.2.1. Changes to RFC2473 and RFC6333 Fragmentation Behaviour 457 For TCP and UDP traffic the NAPT44 implemented in the lwB4 SHOULD 458 conform with the behaviour and best current practices documented in 459 [RFC4787], [RFC5508], and [RFC5382]. If the lwB4 supports DCCP, then 460 the requirements in [RFC5597] SHOULD be implemented. 462 The NAPT44 in the lwB4 MUST implement ICMP message handling behaviour 463 conforming to the best current practice documented in [RFC5508]. If 464 the lwB4 receives an ICMP error (for errors detected inside the IPv6 465 tunnel), the node should relay the ICMP error message to the original 466 source (the lwAFTR). 468 This behaviour SHOULD be implemented conforming to the section 8 of 469 [RFC2473]. 471 6. Lightweight AFTR Behavior 473 6.1. Binding Table Maintenance 475 The lwAFTR maintains an address binding table containing the binding 476 between the lwB4's IPv6 address, the allocated IPv4 address and 477 restricted port-set. Unlike the DS-Lite extended binding table 478 defined in section 6.6 of [RFC6333] which is a 5-tuple NAPT table, 479 each entry in the Lightweight 4over6 binding table contains the 480 following 3-tuples: 482 o IPv6 Address for a single lwB4 484 o Public IPv4 Address 486 o Restricted port-set 488 The entry has two functions: the IPv6 encapsulation of inbound IPv4 489 packets destined to the lwB4 and the validation of outbound IPv4-in- 490 IPv6 packets received from the lwB4 for de-capsulation. 492 The lwAFTR does not perform NAPT and so does not need session 493 entries. 495 The lwAFTR MUST synchronize the binding information with the port- 496 restricted address provisioning process. If the lwAFTR does not 497 participate in the port-restricted address provisioning process, the 498 binding MUST be synchronized through other methods (e.g. out-of-band 499 static update). 501 If the lwAFTR participates in the port-restricted provisioning 502 process, then its binding table MUST be created as part of this 503 process. 505 For all provisioning processes, the lifetime of binding table entries 506 MUST be synchronized with the lifetime of address allocations. 508 6.2. lwAFTR Data Plane Behavior 510 Several sections of [RFC6333] provide background information on the 511 AFTR's data plane functionality and MUST be implemented by the lwAFTR 512 as they are common to both solutions. The relevant sections are: 514 6.2 Encapsulation Covering encapsulation and de- 515 capsulation of tunneled traffic 517 6.3 Fragmentation and Reassembly Fragmentation and re-assembly 518 considerations (referencing 519 [RFC2473]) 521 7.1 Tunneling Covering tunneling and traffic 522 class mapping between IPv4 and IPv6 523 (referencing [RFC2473] and 524 [RFC2983]) 526 When the lwAFTR receives an IPv4-in-IPv6 packet from an lwB4, it de- 527 capsulates the IPv6 header and verifies the source addresses and port 528 in the binding table. If both the source IPv4 and IPv6 addresses 529 match a single entry in the binding table and the source port is in 530 the allowed port-set for that entry, the lwAFTR forwards the packet 531 to the IPv4 destination. 533 If no match is found (e.g., no matching IPv4 address entry, port out 534 of range, etc.), the lwAFTR MUST discard or implement a policy (such 535 as redirection) on the packet. An ICMPv6 type 1, code 5 (source 536 address failed ingress/egress policy) error message MAY be sent back 537 to the requesting lwB4. The ICMP policy SHOULD be configurable. 539 When the lwAFTR receives an inbound IPv4 packet, it uses the IPv4 540 destination address and port to lookup the destination lwB4's IPv6 541 address in its binding table. If a match is found, the lwAFTR 542 encapsulates the IPv4 packet. The source is the lwAFTR's IPv6 543 address and the destination is the lwB4's IPv6 address from the 544 matched entry. Then, the lwAFTR forwards the packet to the lwB4 545 natively over the IPv6 network. 547 If no match is found, the lwAFTR MUST discard the packet. An ICMPv4 548 type 3, code 1 (Destination unreachable, host unreachable) error 549 message MAY be sent back. The ICMP policy SHOULD be configurable. 551 The lwAFTR MUST support hairpinning of traffic between two lwB4s, by 552 performing de-capsulation and re-encapsulation of packets. The 553 hairpinning policy MUST be configurable. 555 7. Additional IPv4 address and Port Set Provisioning Mechanisms 557 In addition to the DHCPv6 based mechanism described in section 5.1, 558 several other IPv4 provisioning protocols have been suggested. These 559 protocols MAY be implemented. These alternatives include: 561 o DHCPv4 over DHCPv6: [RFC7341] describes implementing DHCPv4 562 messages over an IPv6 only service providers network. This 563 enables leasing of IPv4 addresses and makes DHCPv4 options 564 available to the DHCPv4 over DHCPv6 client. 566 o PCP[RFC6887]: an lwB4 MAY use [I-D.ietf-pcp-port-set] to retrieve 567 a restricted IPv4 address and a set of ports. 569 In a Lightweight 4over6 domain, the binding information MUST be 570 aligned between the lwB4s, the lwAFTRs and the provisioning server. 572 8. ICMP Processing 574 For both the lwAFTR and the lwB4, ICMPv6 MUST be handled as described 575 in [RFC2473]. 577 ICMPv4 does not work in an address sharing environment without 578 special handling [RFC6269]. Due to the port-set style address 579 sharing, Lightweight 4over6 requires specific ICMP message handling 580 not required by DS-Lite. 582 8.1. ICMPv4 Processing by the lwAFTR 584 For inbound ICMP messages The following behavior SHOULD be 585 implemented by the lwAFTR to provide ICMP error handling and basic 586 remote IPv4 service diagnostics for a port restricted CPE: 588 1. Check the ICMP Type field. 590 2. If the ICMP type is set to 0 or 8 (echo reply or request), then 591 the lwAFTR MUST take the value of the ICMP identifier field as 592 the source port, and use this value to lookup the binding table 593 for an encapsulation destination. If a match is found, the 594 lwAFTR forwards the ICMP packet to the IPv6 address stored in the 595 entry; otherwise it MUST discard the packet. 597 3. If the ICMP type field is set to any other value, then the lwAFTR 598 MUST use the method described in REQ-3 of [RFC5508] to locate the 599 source port within the transport layer header in ICMP packet's 600 data field. The destination IPv4 address and source port 601 extracted from the ICMP packet are then used to make a lookup in 602 the binding table. If a match is found, it MUST forward the ICMP 603 reply packet to the IPv6 address stored in the entry; otherwise 604 it MUST discard the packet. 606 Additionally, the lwAFTR MAY implement: 608 o Discarding of all inbound ICMP messages. 610 The ICMP policy SHOULD be configurable. 612 8.2. ICMPv4 Processing by the lwB4 614 The lwB4 SHOULD implement the requirements defined in [RFC5508] for 615 ICMP forwarding. For ICMP echo request packets originating from the 616 private IPv4 network, the lwB4 SHOULD implement the method described 617 in [RFC6346] and use an available port from its port-set as the ICMP 618 Identifier. 620 9. Security Considerations 622 As the port space for a subscriber shrinks due to address sharing, 623 the randomness for the port numbers of the subscriber is decreased 624 significantly. This means it is much easier for an attacker to guess 625 the port number used, which could result in attacks ranging from 626 throughput reduction to broken connections or data corruption. 628 The port-set for a subscriber can be a set of contiguous ports or 629 non-contiguous ports. Contiguous port-sets do not reduce this 630 threat. However, with non-contiguous port-set (which may be 631 generated in a pseudo-random way [RFC6431]), the randomness of the 632 port number is improved, provided that the attacker is outside the 633 Lightweight 4over6 domain and hence does not know the port-set 634 generation algorithm. 636 More considerations about IP address sharing are discussed in 637 Section 13 of [RFC6269], which is applicable to this solution. 639 10. IANA Considerations 641 This document does not include an IANA request. 643 11. Author List 645 The following are extended authors who contributed to the effort: 647 Jianping Wu 649 Tsinghua University 651 Department of Computer Science, Tsinghua University 653 Beijing 100084 655 P.R.China 657 Phone: +86-10-62785983 659 Email: jianping@cernet.edu.cn 660 Peng Wu 662 Tsinghua University 664 Department of Computer Science, Tsinghua University 666 Beijing 100084 668 P.R.China 670 Phone: +86-10-62785822 672 Email: pengwu.thu@gmail.com 674 Qi Sun 676 Tsinghua University 678 Beijing 100084 680 P.R.China 682 Phone: +86-10-62785822 684 Email: sunqi@csnet1.cs.tsinghua.edu.cn 686 Chongfeng Xie 688 China Telecom 690 Room 708, No.118, Xizhimennei Street 692 Beijing 100035 694 P.R.China 696 Phone: +86-10-58552116 698 Email: xiechf@ctbri.com.cn 700 Xiaohong Deng 701 France Telecom 703 Email: xiaohong.deng@orange.com 705 Cathy Zhou 707 Huawei Technologies 709 Section B, Huawei Industrial Base, Bantian Longgang 711 Shenzhen 518129 713 P.R.China 715 Email: cathyzhou@huawei.com 717 Alain Durand 719 Juniper Networks 721 1194 North Mathilda Avenue 723 Sunnyvale, CA 94089-1206 725 USA 727 Email: adurand@juniper.net 729 Reinaldo Penno 731 Cisco Systems, Inc. 733 170 West Tasman Drive 735 San Jose, California 95134 737 USA 739 Email: repenno@cisco.com 740 Axel Clauberg 742 Deutsche Telekom AG 744 CTO-ATI 746 Landgrabenweg 151 748 Bonn, 53227 750 Germany 752 Email: axel.clauberg@telekom.de 754 Lionel Hoffmann 756 Bouygues Telecom 758 TECHNOPOLE 760 13/15 Avenue du Marechal Juin 762 Meudon 92360 764 France 766 Email: lhoffman@bouyguestelecom.fr 768 Maoke Chen 770 FreeBit Co., Ltd. 772 13F E-space Tower, Maruyama-cho 3-6 774 Shibuya-ku, Tokyo 150-0044 776 Japan 778 Email: fibrib@gmail.com 780 12. Acknowledgement 782 The authors would like to thank Ole Troan, Ralph Droms and Suresh 783 Krishnan for their comments and feedback. 785 This document is a merge of three documents: 786 [I-D.cui-softwire-b4-translated-ds-lite], [I-D.zhou-softwire-b4-nat] 787 and [I-D.penno-softwire-sdnat]. 789 13. References 791 13.1. Normative References 793 [I-D.ietf-softwire-map-dhcp] 794 Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec, 795 W., Bao, C., leaf.yeh.sdo@gmail.com, l., and X. Deng, 796 "DHCPv6 Options for configuration of Softwire Address and 797 Port Mapped Clients", draft-ietf-softwire-map-dhcp-09 798 (work in progress), October 2014. 800 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 801 E. Lear, "Address Allocation for Private Internets", BCP 802 5, RFC 1918, February 1996. 804 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 805 Requirement Levels", BCP 14, RFC 2119, March 1997. 807 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 808 IPv6 Specification", RFC 2473, December 1998. 810 [RFC4787] Audet, F. and C. Jennings, "Network Address Translation 811 (NAT) Behavioral Requirements for Unicast UDP", BCP 127, 812 RFC 4787, January 2007. 814 [RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. 815 Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, 816 RFC 5382, October 2008. 818 [RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT 819 Behavioral Requirements for ICMP", BCP 148, RFC 5508, 820 April 2009. 822 [RFC5597] Denis-Courmont, R., "Network Address Translation (NAT) 823 Behavioral Requirements for the Datagram Congestion 824 Control Protocol", BCP 150, RFC 5597, September 2009. 826 [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- 827 Stack Lite Broadband Deployments Following IPv4 828 Exhaustion", RFC 6333, August 2011. 830 13.2. Informative References 832 [I-D.cui-softwire-b4-translated-ds-lite] 833 Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I. 834 Farrer, "Lightweight 4over6: An Extension to the DS-Lite 835 Architecture", draft-cui-softwire-b4-translated-ds-lite-11 836 (work in progress), February 2013. 838 [I-D.ietf-pcp-port-set] 839 Qiong, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, 840 T., and S. Perreault, "Port Control Protocol (PCP) 841 Extension for Port Set Allocation", draft-ietf-pcp-port- 842 set-06 (work in progress), July 2014. 844 [I-D.ietf-softwire-map] 845 Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S., 846 Murakami, T., and T. Taylor, "Mapping of Address and Port 847 with Encapsulation (MAP)", draft-ietf-softwire-map-11 848 (work in progress), October 2014. 850 [I-D.ietf-softwire-unified-cpe] 851 Boucadair, M., Farrer, I., Perreault, S., and S. 852 Sivakumar, "Unified IPv4-in-IPv6 Softwire CPE", draft- 853 ietf-softwire-unified-cpe-01 (work in progress), May 2013. 855 [I-D.penno-softwire-sdnat] 856 Penno, R., Durand, A., Hoffmann, L., and A. Clauberg, 857 "Stateless DS-Lite", draft-penno-softwire-sdnat-02 (work 858 in progress), March 2012. 860 [I-D.zhou-softwire-b4-nat] 861 Zhou, C., Boucadair, M., and X. Deng, "NAT offload 862 extension to Dual-Stack lite", draft-zhou-softwire- 863 b4-nat-04 (work in progress), October 2011. 865 [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC 866 2983, October 2000. 868 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 869 Address Translator (Traditional NAT)", RFC 3022, January 870 2001. 872 [RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P. 873 Roberts, "Issues with IP Address Sharing", RFC 6269, June 874 2011. 876 [RFC6346] Bush, R., "The Address plus Port (A+P) Approach to the 877 IPv4 Address Shortage", RFC 6346, August 2011. 879 [RFC6431] Boucadair, M., Levis, P., Bajko, G., Savolainen, T., and 880 T. Tsou, "Huawei Port Range Configuration Options for PPP 881 IP Control Protocol (IPCP)", RFC 6431, November 2011. 883 [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. 884 Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 885 2013. 887 [RFC7040] Cui, Y., Wu, J., Wu, P., Vautrin, O., and Y. Lee, "Public 888 IPv4-over-IPv6 Access Network", RFC 7040, November 2013. 890 [RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I. 891 Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport", RFC 892 7341, August 2014. 894 Authors' Addresses 896 Yong Cui 897 Tsinghua University 898 Beijing 100084 899 P.R.China 901 Phone: +86-10-62603059 902 Email: yong@csnet1.cs.tsinghua.edu.cn 904 Qiong Sun 905 China Telecom 906 Room 708, No.118, Xizhimennei Street 907 Beijing 100035 908 P.R.China 910 Phone: +86-10-58552936 911 Email: sunqiong@ctbri.com.cn 912 Mohamed Boucadair 913 France Telecom 914 Rennes 35000 915 France 917 Email: mohamed.boucadair@orange.com 919 Tina Tsou 920 Huawei Technologies 921 2330 Central Expressway 922 Santa Clara, CA 95050 923 USA 925 Phone: +1-408-330-4424 926 Email: tena@huawei.com 928 Yiu L. Lee 929 Comcast 930 One Comcast Center 931 Philadelphia, PA 19103 932 USA 934 Email: yiu_lee@cable.comcast.com 936 Ian Farrer 937 Deutsche Telekom AG 938 CTO-ATI, Landgrabenweg 151 939 Bonn, NRW 53227 940 Germany 942 Email: ian.farrer@telekom.de