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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-03) exists of draft-ietf-v6ops-siit-dc-00 == Outdated reference: A later version (-03) exists of draft-ietf-v6ops-siit-eam-00 -- Obsolete informational reference (is this intentional?): RFC 6145 (Obsoleted by RFC 7915) Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 Operations T. Anderson 3 Internet-Draft Redpill Linpro 4 Intended status: Informational S. Steffann 5 Expires: December 30, 2015 S.J.M. Steffann Consultancy 6 June 28, 2015 8 SIIT-DC: Dual Translation Mode 9 draft-ietf-v6ops-siit-dc-2xlat-01 11 Abstract 13 This document describes an extension of the Stateless IP/ICMP 14 Translation for IPv6 Internet Data Centre Environments architecture 15 (SIIT-DC), which allows applications, protocols, or nodes that are 16 incompatible with IPv6, and/or Network Address Translation to operate 17 correctly in an SIIT-DC environment. This is accomplished by 18 introducing a new component called an SIIT-DC Edge Relay, which 19 reverses the translations made by an SIIT-DC Border Relay. The 20 application and/or node is thus provided with seemingly native IPv4 21 connectivity that provides end-to-end address transparency. 23 The reader is expected to be familiar with the SIIT-DC architecture 24 described in I-D.ietf-v6ops-siit-dc. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on December 30, 2015. 43 Copyright Notice 45 Copyright (c) 2015 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 3. Edge Relay Description . . . . . . . . . . . . . . . . . . . 4 63 3.1. Node-Based Edge Relay . . . . . . . . . . . . . . . . . . 5 64 3.2. Network-Based Edge Relay . . . . . . . . . . . . . . . . 6 65 3.2.1. Edge Router "On A Stick" . . . . . . . . . . . . . . 7 66 3.2.2. Edge Router that Bridges IPv6 Packets . . . . . . . . 8 67 4. Deployment Considerations . . . . . . . . . . . . . . . . . . 9 68 4.1. IPv6 Path MTU . . . . . . . . . . . . . . . . . . . . . . 9 69 4.2. IPv4 MTU . . . . . . . . . . . . . . . . . . . . . . . . 10 70 4.3. IPv4 Identification Header . . . . . . . . . . . . . . . 10 71 5. Intra-IDC IPv4 Communication . . . . . . . . . . . . . . . . 10 72 5.1. Hairpinning by the SIIT-DC Border Relay . . . . . . . . . 10 73 5.2. Additional EAMs Configured in Edge Relay . . . . . . . . 11 74 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 75 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 76 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 77 8.1. Address Spoofing . . . . . . . . . . . . . . . . . . . . 13 78 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 79 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 80 9.2. Informative References . . . . . . . . . . . . . . . . . 14 81 Appendix A. Examples: Network-Based IPv4 Connectivity . . . . . 15 82 A.1. Subnet with IPv4 Service Addresses . . . . . . . . . . . 15 83 A.2. Subnet with Unrouted IPv4 Addresses . . . . . . . . . . . 16 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 86 1. Introduction 88 SIIT-DC [I-D.ietf-v6ops-siit-dc] describes an architecture where 89 IPv4-only users can access IPv6-only services through a stateless 90 translator called an SIIT-DC Border Relay (BR). This approach has 91 certain limitations, however. In particular, the following cases 92 will work poorly or not at all: 94 o Application protocols that do not support NAT (i.e., the lack of 95 end-to-end transparency of IP addresses). 97 o Nodes that cannot connect to IPv6 networks at all, or that can 98 only connect such networks if they also provide IPv4 connectivity 99 (i.e., dual-stacked networks). 101 o Application software which makes use of legacy IPv4-only APIs, or 102 otherwise makes assumptions that IPv4 connectivity is available. 104 By extending the SIIT-DC architecture with a new component called an 105 Edge Relay (ER), all of the above can be made to work correctly in an 106 otherwise IPv6-only network environment using SIIT-DC. 108 The purpose of the ER is to reverse the IPv4-to-IPv6 packet 109 translations previously done by the BR for traffic arriving from IPv4 110 clients and forward this as "native" IPv4 to the node or application. 111 In the reverse direction, IPv4 packets transmitted by the node or 112 application are intercepted by the ER, which translates them to IPv6 113 before they are forwarded to the BR, which in turn will reverse the 114 translations and forward them to the IPv4 client. The node or 115 application is thus provided with "virtual" IPv4 Internet 116 connectivity that retains end-to-end transparency for the IPv4 117 addresses. 119 2. Terminology 121 This document makes use of the following terms: 123 SIIT-DC Border Relay (BR) 124 A device or a logical function that translates traffic between 125 IPv4 clients and IPv6 services. See [I-D.ietf-v6ops-siit-dc]. 127 SIIT-DC Edge Relay (ER) 128 A device or logical function that provides "native" IPv4 129 connectivity to IPv4-only nodes or applications. It functions in 130 the same way as a BR, but is located close to the IPv4-only nodes/ 131 applications it is supporting rather than on the network border. 133 IPv4 Service Address 134 An IPv4 address representing an IPv6 service, with which IPv4-only 135 clients communicates. It is coupled with an IPv6 Service Address 136 using an EAM. Packets sent to this address is translated to IPv6 137 by the BR and possibly back to IPv4 again by the ER, and vice 138 versa in the opposite direction. 140 IPv6 Service Address 141 An IPv6 address assigned to an application, node, or service; 142 either directly or indirectly (through an ER). It is coupled with 143 an IPv4 Service Address using an EAM. IPv4-only clients 144 communicates with the IPv6 Service Address through SIIT-DC. 146 Explicit Address Mapping (EAM) 147 A bi-directional coupling between an IPv4 Service Address and an 148 IPv6 Service Address configured in an BR/ER. When translating 149 between IPv4 and IPv6, the BR/ER changes the address fields in the 150 translated packet's IP header according to any matching EAM. The 151 EAM algorithm is specified in [I-D.ietf-v6ops-siit-eam]. 153 Translation Prefix 154 An IPv6 prefix into which the entire IPv4 address space is mapped, 155 according to the algorithm in [RFC6052]. The Translation Prefix 156 is routed to the BR's IPv6 interface. When translating between 157 IPv4 and IPv6, an BR/ER will insert/remove the Translation Prefix 158 into/from the address fields in the translated packet's IP header, 159 unless an EAM exists for the IP address that is being translated. 161 IPv4-converted IPv6 addresses 162 As defined in Section 1.3 of [RFC6052]. 164 IDC 165 Short for "Internet Data Centre"; a data centre whose main purpose 166 is to deliver services to the public Internet, the use case SIIT- 167 DC is primarily targeted at. IDCs are typically operated by 168 Internet Content Providers or Managed Services Providers. 170 SIIT 171 The Stateless IP/ICMP Translation algorithm, as specified in 172 [RFC6145]. 174 XLAT 175 Short for "Translation". Used in figures to indicate where a BR/ 176 ER uses SIIT [RFC6145] to translate IPv4 packets to IPv6 and vice 177 versa. 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. Edge Relay Description 185 An Edge Relay (ER) is at its core an implementation of the Stateless 186 IP/ICMP Translation algorithm [RFC6145] that supports Explicit 187 Address Mappings [I-D.ietf-v6ops-siit-eam]. It provides virtual IPv4 188 connectivity for nodes or applications which require this to operate 189 correctly in an SIIT-DC environment. 191 Packets from the IPv4 Internet destined for an IPv4 Service Address 192 is first translated to IPv6 by a BR. The resulting IPv6 packets are 193 subsequently forwarded to the ER that owns the IPv6 Service Address 194 the translated packets are addressed to. The ER then translates them 195 back to IPv4 before forwarding them to the IPv4 application or node. 196 In the other direction, the exact same translations happen, only in 197 reverse. This process provides end-to-end transparency of IPv4 198 addresses. 200 An ER may handle an arbitrary number of IPv4/IPv6 Service Addresses. 201 All the EAMs configured in the BR that involve the IPv4/IPv6 Service 202 Addresses handled by an ER MUST also be present in the ER's 203 configuration. 205 An ER may be implemented in two distinct ways; as a software-based 206 service residing inside an otherwise IPv6-only node, or as a network- 207 based service that provides an isolated IPv4 network segment to which 208 nodes that require IPv4 can connect. In both cases native IPv6 209 connectivity may be provided simultaneously with the virtual IPv4 210 connectivity. Thus, dual-stack connectivity is facilitated in case 211 the node or application support it. 213 The choice between a node- or network-based ER is made on a per- 214 service or per-node basis. An arbitrary number of each type of ER 215 may co-exist in an SIIT-DC architecture. 217 This section describes the different approaches and discusses which 218 approach fits best for the various use cases. 220 3.1. Node-Based Edge Relay 222 A Node-based Edge Relay 224 [IPv4 Internet] [IPv6 Internet] 225 | | 226 +-----|-----+ | 227 | (BR/XLAT) | | 228 +-----|-----+ | 229 | | +---------------+ 230 [IPv6-only IDC network] | +----------------+| 231 | | /--(ER/XLAT)--AF_INET Dual-stack || 232 \-------------------------+ | Application || 233 | \------------AF_INET6 Software || 234 | +----------------+| 235 +--------------------------------------+ 237 Figure 1 239 A node-based ER is typically implemented as a logical software 240 function that runs inside the operating system of an IPv6 node. It 241 provides applications running on the same node with IPv4 242 connectivity. Its IPv4 Service Address SHOULD be considered a 243 regular local address that allows application running on the same 244 node to use it with IPv4-only API calls, e.g., to create AF_INET 245 sockets that listen for and accept incoming connections to its IPv4 246 Service Address. An ER may accomplish this by creating a virtual 247 network adapter to which it assigns the IPv4 Service Address and 248 points a default IPv4 route. This approach is similar to the "Bump- 249 in-the-Stack" approach discussed in [RFC6535], however it does not 250 include an Extension Name Resolver. 252 As shown in Figure 1, if the application supports dual-stack 253 operation, IPv6 clients will be able to communicate with it directly 254 using native IPv6. Neither the BR nor the ER will intercept this 255 communication. Support for IPv6 in the application is however not a 256 requirement; the application may opt not to establish any IPv6 257 sockets. Foregoing IPv6 in this manner will simply preclude 258 connectivity to the service from IPv6-only clients; connectivity to 259 the service from IPv4 clients (through the BR) will continue work in 260 the same way. 262 The ER requires a dedicated IPv6 Service Address for each IPv4 263 Service Address it has configured. The IPv6 network MUST forward 264 traffic to these IPv6 Service Addresses to the node, whose operating 265 system MUST in turn forward them to the ER. This document does not 266 attempt to fully explore the multitude of ways this could be 267 accomplished, however considering that the IPv6 protocol is designed 268 for having multiple addresses assigned to a single node, one 269 particularly straight-forward way would be to assign the ER's IPv6 270 Service Addresses as secondary IPv6 addresses on the node itself so 271 that it the upstream router learns of their location using the IPv6 272 Neighbor Discovery Protocol [RFC4861]. 274 3.2. Network-Based Edge Relay 276 A Basic Network-based Edge Relay 278 [IPv4 Internet] [IPv6 Internet] 279 | | 280 +-----|-----+ | 281 | (BR/XLAT) | | 282 +-----|-----+ | 283 | | 284 [IPv6-only IDC network] +----+ 285 | | +----------------+| 286 +-----|-----+ [v4-only] | | IPv4-only || 287 | (ER/XLAT)-----[network]--------AF_INET Application || 288 +-----------+ [segment] | | Software || 289 | +----------------+| 290 +---------------------------+ 292 Figure 2 294 A network-based ER performs the exact same as a node-based ER does, 295 only that instead of assigning the IPv4 Service Addresses to an 296 internal-only virtual network adapter, traffic destined for them are 297 forwarded onto a network segment to which nodes that require IPv4 298 connectivity connect to. The ER also functions as the default IPv4 299 router for the nodes on this network segment. 301 Each node on the IPv4 network segment MUST acquire and assign an IPv4 302 Service Address to a local network interface. While this document 303 does not attempt to explore all the various methods by which this 304 could be accomplished, some examples are provided in Appendix A. 306 The basic ER illustrated in Figure 2 establishes an IPv4-only network 307 segment between itself and the IPv4-only nodes it serves. This is 308 fine if the nodes it provides IPv4 access have no support for IPv6 309 whatsoever; however if they are dual-stack capable, it is would not 310 be ideal to take away their IPv6 connectivity in this manner. While 311 it is RECOMMENDED to use a node-based ER in this case, appropriate 312 implementations of a node-based ER might not be available for every 313 node. If the application protocol in question does not work 314 correctly in a NAT environment, standard SIIT-DC cannot be used 315 either, which leaves a network-based ER is the only remaining 316 solution. The following subsections contains examples on how the ER 317 could be implemented in a way that provides IPv6 connectivity for 318 dual-stack capable nodes. 320 3.2.1. Edge Router "On A Stick" 322 A Network-based Edge Relay "On A Stick" 324 [IPv4 Internet] [IPv6 Internet] 325 | | 326 +-----|-----+ | 327 | (BR/XLAT) | | 328 +-----|-----+ | 329 | | 330 [IPv6-only IDC network] 331 | 332 | +-------------+ 333 | | _IPv6_ | 334 | | / \ | 335 +==== (ER/XLAT) | 336 | | \_ _/ | 337 | | IPv4 | +----+ 338 | +-------------+ | +----------------+| 339 | | /---AF_INET Dual-stack || 340 [Dual-stack network segment]----< | Application || 341 | \--AF_INET6 Software || 342 | +----------------+| 343 +----------------------------+ 345 Figure 3 347 The ER "On A Stick" approach illustrated in Figure 3 ensures that the 348 dual-stack capable node retains native IPv6 connectivity by 349 connecting the ER's IPv4 and IPv6 interfaces to the same network 350 segment, alternatively by using a single dual-stacked interface. 351 Native IPv6 traffic between the IDC network and the node bypasses the 352 ER entirely, while IPv4 traffic from the node will be routed directly 353 to the ER (because it acts as its default IPv4 router), where it is 354 translated to IPv6 before being transmitted to the upstream default 355 IPv6 router. The ER could attract inbound traffic to the IPv6 356 Service Addresses by responding to the upstream router's IPv6 357 Neighbor Discovery [RFC4861] messages for them. 359 3.2.2. Edge Router that Bridges IPv6 Packets 361 A Network-based Edge Relay containing an IPv6 Bridge 363 [IPv4 Internet] [IPv6 Internet] 364 | | 365 +-----|-----+ | 366 | (BR/XLAT) | | 367 +-----|-----+ | 368 | | 369 [IPv6-only IDC network] 370 | 371 +-----------|--------------+ 372 | ____/ \_IPv6_ | 373 | / \ | 374 | (IPv6 Bridge) (ER/XLAT) | 375 | \____ _ _/ | 376 | \ / IPv4 | +----+ 377 +-----------|--------------+ | +----------------+| 378 | | /---AF_INET Dual-stack || 379 [Dual-stack network segment]----< | Application || 380 | \--AF_INET6 Software || 381 | +----------------+| 382 +----------------------------+ 384 Figure 4 386 The ER illustrated in Figure 4 will transparently bridge IPv6 frames 387 between its upstream and downstream interfaces. IPv6 packets 388 addressed the ER's own IPv6 Service Addresses from the upstream IDC 389 network are intercepted (e.g., by responding to IPv6 Neighbor 390 Discovery [RFC4861] messages for them) and routed through the 391 translation function before being forwarded out its downstream 392 interface as IPv4 packets. The downstream network segment thus 393 becomes dual-stacked. 395 4. Deployment Considerations 397 4.1. IPv6 Path MTU 399 The IPv6 Path MTU between the ER and the BR will typically be larger 400 than the default value defined in Section 4 of [RFC6145] (1280), as 401 it will typically contained within a single administrative domain. 402 Therefore, it is RECOMMENDED that the IPv6 Path MTU configured in the 403 ER is raised accordingly. It is RECOMMENDED that the ER and the BR 404 use identical configured IPv6 Path MTU values. 406 4.2. IPv4 MTU 408 In order to avoid IPv6 fragmentation, an ER SHOULD ensure that the 409 IPv4 MTU used by applications or nodes is equal to the configured 410 IPv6 Path MTU - 20, so that an maximum-sized IPv4 packet can fit in 411 an unfragmented IPv6 packet. This ensures that the application may 412 do its part in avoiding IP-level fragmentation from occurring, e.g., 413 by segmenting/fragmenting outbound packets at the application layer, 414 and advertising the maximum size its peer may use for inbound packets 415 (e.g., through the use of the TCP MSS option). 417 A node-based ER could accomplish this by configuring this MTU value 418 on the virtual network adapter, while a network-based ER could do so 419 by advertising the MTU to its downstream nodes using the DHCPv4 420 Interface MTU Option [RFC2132]. 422 4.3. IPv4 Identification Header 424 If the generation of IPv6 Atomic Fragments is disabled, the value of 425 the IPv4 Identification header will be lost during the translation. 426 Conversely, enabling the generation of IPv6 Atomic Fragments will 427 ensure that the IPv4 Identification Header will carried end-to-end. 428 Note that for this to work bi-directionally, IPv6 Atomic Fragment 429 generation MUST be enabled on both the BR and the ER. 431 Apart from certain diagnostic tools, there are few (if any) 432 application protocols that make use of the IPv4 Identification 433 header. Therefore, the loss of the IPv4 Identification value will 434 therefore generally not cause any problems. 436 IPv6 Atomic Fragments and their impact on the IPv4 Identification 437 header is further discussed in Section 4.9.2 of 438 [I-D.ietf-v6ops-siit-dc]. 440 5. Intra-IDC IPv4 Communication 442 Although SIIT-DC is primarily intended to facilitate communication 443 between IPv4-only nodes on the Internet and services located in an 444 IPv6-only IDC network, an IPv4-only node or application located 445 behind an ER might need to communicate with other nodes or services 446 in the IDC. The IPv4-only node or application will need to so 447 through the ER, as it will typically be incapable to contact IPv6 448 destinations directly. The following subsections discusses various 449 methods on how to facilitate such communication. 451 5.1. Hairpinning by the SIIT-DC Border Relay 452 If the BR supports hairpinning as described in Section 4.2 of I-D 453 .ietf-v6ops-siit-eam [I-D.ietf-v6ops-siit-eam], the easiest solution 454 is to make the target service available through SIIT-DC in the normal 455 way, that is, by provisioning an EAM to the BR that assigns an IPv4 456 Service Address with the target service's IPv6 Service Address. 458 This allows the IPv4-only node or application to transmit packets 459 destined for the target service's IPv4 Service Address, which the ER 460 will then translate to a corresponding IPv4-converted IPv6 address by 461 inserting the Translation Prefix [RFC6052]. When this IPv6 packet 462 reaches the BR, it will be hairpinned and transmitted back to the 463 target service's IPv6 Service Address (where it could possibly pass 464 through another ER before reaching the target service). Return 465 traffic from the target service will be hairpinned in the same 466 fashion. 468 Hairpinned IPv4-IPv4 packet flow 470 +-[Pkt#1: IPv4]-+ +--[Pkt#2: IPv6]-------------+ 471 | SRC 192.0.2.1 | (XLAT#1) | SRC 2001:db8:a:: | 472 | DST 192.0.2.2 |--(@ ER A)-->| DST 2001:db8:46::192.0.2.2 |---\ 473 +---------------+ +----------------------------+ | 474 (XLAT#2) 475 +-[Pkt#4: IPv4]-+ +--[Pkt#3: IPv6]-------------+ ( @ BR ) 476 | SRC 192.0.2.1 | (XLAT#3) | SRC 2001:db8:46::192.0.2.1 | | 477 | DST 192.0.2.2 |<--(@ ER B)--| DST 2001:db8:b:: |<--/ 478 +---------------+ +----------------------------+ 480 Figure 5 482 Figure 5 illustrates the flow of a hairpinned packet sent from the 483 IPv4-only node/app behind ER A towards an IPv6-only node/app behind 484 ER B. ER A is configured with the EAM {192.0.2.1,2001:db8:a::}, ER B 485 with {192.0.2.2,2001:db8:b::}. The BR is configured with both EAMs, 486 and supports hairpinning. Note that if the target service had not 487 been located behind an ER, the third and final translation (XLAT#3) 488 would not have happened, i.e., the target service/node would have 489 received and responded to packet #3 directly. 491 If the IPv4-only nodes/services do not need connectivity with the 492 public IPv4 Internet, private IPv4 addresses [RFC1918] could be used 493 as their IPv4 Service Addresses in order to conserve the IDC 494 operator's pool of public IPv4 addresses. 496 5.2. Additional EAMs Configured in Edge Relay 498 If the BR does not support hairpinning, or if the hairpinning 499 solution is not desired for some other reason, intra-IDC IPv4 traffic 500 may be facilitated by configuring additional EAMs on the ER for each 501 service the IPv4-only node or application needs to communicate with. 502 This makes the IPv6 traffic between the ER and the target service's 503 IPv6 Service Address follow the direct path through the IPv6 network. 504 The traffic does not pass the BR, which means that this solution 505 might yield better latency than the hairpinning approach. 507 The additional EAM configured in the ER consists of the target's IPv6 508 Service Address and an IPv4 Service Address. The IPv4-only node or 509 application will contact the target's assigned IPv4 Service Address 510 using its own IPv4 Service Address as the source. The ER will then 511 proceed to translate this to an IPv6 packet with the local 512 application/node's own IPv6 Service Address as source and the target 513 service's IPv6 Service Address as the destination, and forward this 514 to the IPv6 network. Replies from the target service will undergo 515 these translations in reverse. 517 If the target service is also located behind another ER, that other 518 ER MUST also be provisioned with an additional EAM that contains the 519 origin IPv4-only application/node's IPv4 and IPv6 Service Addresses. 520 Otherwise, the target service's ER will be unable to translate the 521 source address of the incoming packets. 523 Non-hairpinned IPv4-IPv4 packet flow 525 +-[Pkt#1: IPv4]-+ +--[Pkt#2: IPv6]---+ 526 | SRC 192.0.2.1 | (XLAT#1) | SRC 2001:db8:a:: | 527 | DST 192.0.2.2 |--(@ ER A)-->| DST 2001:db8:b:: | 528 +---------------+ +------------------+ 529 | 530 +-[Pkt#3: IPv4]-+ | 531 | SRC 192.0.2.1 | (XLAT#2) | 532 | DST 192.0.2.2 |<-------(@ ER B)------/ 533 +---------------+ 535 Figure 6 537 Figure 6 illustrates the flow of a packet carrying intra-IDC IPv4 538 traffic between two IPv4-only nodes/applications that are both 539 located behind ERs. Both ER A and ER B are configured with two EAMs: 540 {192.0.2.1,2001:db8:a::} and {192.0.2.2,2001:db8:b::}. The packet 541 will follow the regular routing path through the IPv6 IDC network; 542 the BR is not involved and the packet will not be hairpinned. 544 The above approach is not mutually exclusive with the hairpinning 545 approach described in Section 5.1: If both EAMs above are also 546 configured on the BR, both 192.0.2.1 and 192.0.2.2 would be reachable 547 from other IPv4-only services/nodes using the hairpinning approach. 548 They would also be reachable from the IPv4 Internet. 550 Note that if the target service in this example was not located 551 behind an ER, but instead was a native IPv6 service listening on 552 2001:db8:b::, the second translation step in Figure 6 would not 553 occur; the target service would receive and respond to packet #2 554 directly. 556 As with the hairpinning approach, if the IPv4-only nodes/services do 557 not need connectivity to/from the public IPv4 Internet, private IPv4 558 addresses [RFC1918] could be used as their IPv4 Service Addresses. 559 Alternatively, in the case where the target service is on native 560 IPv6, the target's assigned IPv4 Service Address has only local 561 significance behind the ER. It could therefore be assigned from the 562 IPv4 Service Continuity Prefix [RFC7335]. 564 6. Acknowledgements 566 The author would like to especially thank the authors of 464XLAT 567 [RFC6877]: Masataka Mawatari, Masanobu Kawashima, and Cameron Byrne. 568 The architecture described by this document is merely an adaptation 569 of their work to a data centre environment, and could not have 570 happened without them. 572 The author would like also to thank the following individuals for 573 their contributions, suggestions, corrections, and criticisms: Fred 574 Baker, Tobias Brox, Ray Hunter, Shucheng LIU (Will), Andrew 575 Yourtchenko. 577 7. IANA Considerations 579 This draft makes no request of the IANA. The RFC Editor may remove 580 this section prior to publication. 582 8. Security Considerations 584 This section discusses security considerations specific to the use of 585 an ER. See the Security Considerations section in 586 [I-D.ietf-v6ops-siit-dc] for additional security considerations 587 applicable to the SIIT-DC architecture in general. 589 8.1. Address Spoofing 590 If the ER receives an IPv4 packet from the application/node from a 591 source address it does not have an EAM for, both the source and 592 destination addresses will be rewritten according to [RFC6052]. 593 After undergoing the reverse translation in the BR, the resulting 594 IPv4 packet routed to the IPv4 network will have a spoofed IPv4 595 source address. The ER SHOULD therefore ensure that ingress 596 filtering [RFC2827] is used on the ER's IPv4 interface, so that such 597 packets are immediately discarded. 599 If the ER receives an IPv6 packet with both the source and 600 destination address equal to one of its local IPv6 Service Addresses, 601 the resulting packet would appear to the IPv4-only application/node 602 as locally generated, as both the source address and the destination 603 address will be the same address. This could trick the application 604 into believing the packet came from a trusted source (itself). To 605 prevent this, the ER SHOULD discard any received IPv6 packets that 606 have a source address that is either 1) equal to any of its local 607 IPv6 Service Addresses, or 2) after translation from IPv6 to IPv4, 608 equal to any of its local IPv4 Service Addresses. 610 9. References 612 9.1. Normative References 614 [I-D.ietf-v6ops-siit-dc] 615 Anderson, T., "SIIT-DC: Stateless IP/ICMP Translation for 616 IPv6 Data Centre Environments", draft-ietf-v6ops-siit- 617 dc-00 (work in progress), December 2014. 619 [I-D.ietf-v6ops-siit-eam] 620 Anderson, T. and A. Leiva, "Explicit Address Mappings for 621 Stateless IP/ICMP Translation", draft-ietf-v6ops-siit- 622 eam-00 (work in progress), May 2015. 624 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 625 Requirement Levels", BCP 14, RFC 2119, March 1997. 627 9.2. Informative References 629 [RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or 630 converting network protocol addresses to 48.bit Ethernet 631 address for transmission on Ethernet hardware", STD 37, 632 RFC 826, November 1982. 634 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 635 E. Lear, "Address Allocation for Private Internets", BCP 636 5, RFC 1918, February 1996. 638 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 639 2131, March 1997. 641 [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor 642 Extensions", RFC 2132, March 1997. 644 [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: 645 Defeating Denial of Service Attacks which employ IP Source 646 Address Spoofing", BCP 38, RFC 2827, May 2000. 648 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 649 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 650 September 2007. 652 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 653 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 654 October 2010. 656 [RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation 657 Algorithm", RFC 6145, April 2011. 659 [RFC6535] Huang, B., Deng, H., and T. Savolainen, "Dual-Stack Hosts 660 Using "Bump-in-the-Host" (BIH)", RFC 6535, February 2012. 662 [RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown, 663 "Default Address Selection for Internet Protocol Version 6 664 (IPv6)", RFC 6724, September 2012. 666 [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: 667 Combination of Stateful and Stateless Translation", RFC 668 6877, April 2013. 670 [RFC7335] Byrne, C., "IPv4 Service Continuity Prefix", RFC 7335, 671 August 2014. 673 Appendix A. Examples: Network-Based IPv4 Connectivity 675 A.1. Subnet with IPv4 Service Addresses 676 One relatively straight-forward way to provide IPv4 connectivity 677 between the ER and the IPv4 node(s) it serves is to ensure the IPv4 678 Service Address(es) can be enclosed within a larger IPv4 prefix. The 679 ER may then claim one address in this prefix for itself, and use it 680 to provide an IPv4 default router address. The ER may then proceed 681 to assign the IPv4 Service Address(es) to its downstream node(s) 682 using DHCPv4 [RFC2131]. For example, if the IPv4 Service Addresses 683 are 192.0.2.26 and 192.0.2.27, the ER would configure the address 684 192.0.2.25/29 on its IPv4-facing interface and would add the two IPv4 685 Service Addresses to its DHCPv4 pool. 687 One disadvantage of this method is that IPv4 communication between 688 the IPv4 node(s) behind the ER and other services made available 689 through SIIT-DC becomes impossible, if those other services are 690 assigned IPv4 Service Addresses that also are covered by the same 691 IPv4 prefix (e.g., 192.0.2.28). This happens because the IPv4 nodes 692 will mistakenly believe they have an on-link route to the entire 693 prefix, and attempt to resolve the addresses using ARP [RFC0826], 694 instead of sending them to the ER for translation to IPv6. This 695 problem could however be overcome by avoiding assigning IPv4 Service 696 Addresses which overlaps with an IPv4 prefix handled by an ER (at the 697 expense of wasting some potential IPv4 Service Addresses), or by 698 ensuring that the overlapping IPv6 Service Addresses are only 699 assigned to services which do not need to communicate with the IPv4 700 node(s) behind the ER. A third way to avoid this problem is 701 discussed in Appendix A.2. 703 A.2. Subnet with Unrouted IPv4 Addresses 705 In order to avoid the problem discussed in Appendix A.1, a private 706 unrouted IPv4 network that does not encompass the IPv4 Service 707 Address(es) could be used to provide connectivity between the ER and 708 the IPv4-only node(s) it serves. An IPv4-only node must then assign 709 its IPv4 Service Address as secondary local address, while the ER 710 routes each of the IPv4 Service Addresses to its assigned node using 711 that node's private on-link IPv4 address as the next-hop. This 712 approach would ensure there are no overlaps with IPv4 Service 713 addresses elsewhere in the infrastructure, but on the other hand it 714 would preclude the use of DHCPv4 [RFC2131] for assigning the IPv4 715 Service Addresses. 717 This approach creates a need to ensure that the IPv4 application is 718 selecting the IPv4 Service Address (as opposed to its private on-link 719 IPv4 address) as its source address when initiating outbound 720 connections. This could be accomplished by altering the Default 721 Address Selection Policy Table [RFC6724] on the IPv4 node. 723 Authors' Addresses 725 Tore Anderson 726 Redpill Linpro 727 Vitaminveien 1A 728 0485 Oslo 729 Norway 731 Phone: +47 959 31 212 732 Email: tore@redpill-linpro.com 733 URI: http://www.redpill-linpro.com 735 Sander Steffann 736 S.J.M. Steffann Consultancy 737 Tienwoningenweg 46 738 Apeldoorn, Gelderland 7312 DN 739 The Netherlands 741 Email: sander@steffann.nl