idnits 2.17.1 draft-ietf-behave-address-format-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** You're using the IETF Trust Provisions' Section 6.b License Notice from 12 Sep 2009 rather than the newer Notice from 28 Dec 2009. (See https://trustee.ietf.org/license-info/) 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 lines with non-RFC3849-compliant IPv6 addresses in the document. If these are example addresses, they should be changed. -- The draft header indicates that this document obsoletes RFC2765, but the abstract doesn't seem to mention this, which it should. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: IPv4-Translatable IPv6 addresses SHOULD follow the IPv6 address architecture and SHOULD be compatible with the IPv4 address architecture. The first IPv4-translatable address is the subnet-router anycast address in IPv6 and network identifier in IPv4, the last IPv4-translatable address is the subnet broadcast addresses in IPv4. Both of them SHOULD not be used for IPv6 nodes. In addition, the minimum IPv4 subnet can be used for hosts is /30 (the router interface needs a valid address for the same subnet) and this rule SHOULD also be applied to the corresponding subnet of the IPv4-translatable addresses. -- The document date (March 14, 2010) is 5155 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-11) exists of draft-ietf-behave-dns64-04 == Outdated reference: A later version (-10) exists of draft-ietf-behave-v6v4-framework-03 -- Obsolete informational reference (is this intentional?): RFC 3330 (Obsoleted by RFC 5735) -- Obsolete informational reference (is this intentional?): RFC 3484 (Obsoleted by RFC 6724) Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Bao 3 Internet-Draft CERNET Center/Tsinghua University 4 Obsoletes: 2765 (if approved) C. Huitema 5 Intended status: Standards Track Microsoft Corporation 6 Expires: September 15, 2010 M. Bagnulo 7 UC3M 8 M. Boucadair 9 France Telecom 10 X. Li 11 CERNET Center/Tsinghua University 12 March 14, 2010 14 IPv6 Addressing of IPv4/IPv6 Translators 15 draft-ietf-behave-address-format-05.txt 17 Abstract 19 This document discusses the algorithmic translation of an IPv6 20 address to a corresponding IPv4 address, and vice versa, using only 21 statically configured information. It defines a well-known prefix 22 for use in algorithmic translations, while allowing organizations to 23 also use network-specific prefixes when appropriate. Algorithmic 24 translation is used in IPv4/IPv6 translators, as well as other types 25 of proxies and gateways (e.g., for DNS) used in IPv4/IPv6 scenarios. 27 Status of this Memo 29 This Internet-Draft is submitted to IETF in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF), its areas, and its working groups. Note that 34 other groups may also distribute working documents as Internet- 35 Drafts. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 The list of current Internet-Drafts can be accessed at 43 http://www.ietf.org/ietf/1id-abstracts.txt. 45 The list of Internet-Draft Shadow Directories can be accessed at 46 http://www.ietf.org/shadow.html. 48 This Internet-Draft will expire on September 15, 2010. 50 Copyright Notice 52 Copyright (c) 2010 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 BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 68 1.1. Applicability Scope . . . . . . . . . . . . . . . . . . . 3 69 1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4 70 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 71 2. IPv4-Embedded IPv6 Address Format . . . . . . . . . . . . . . 4 72 2.1. Address Translation Algorithms . . . . . . . . . . . . . . 6 73 2.2. Text Representation . . . . . . . . . . . . . . . . . . . 6 74 3. Deployment Guidelines and Choices . . . . . . . . . . . . . . 7 75 3.1. Restrictions on the use of the Well-Known Prefix . . . . . 7 76 3.2. Impact on Inter-Domain Routing . . . . . . . . . . . . . . 8 77 3.3. Choice of Prefix for Stateless Translation Deployments . . 8 78 3.4. Choice of Prefix for Stateful Translation Deployments . . 11 79 3.5. Choice of Suffix . . . . . . . . . . . . . . . . . . . . . 11 80 3.6. Choice of the Well-Known Prefix . . . . . . . . . . . . . 12 81 4. Security Considerations . . . . . . . . . . . . . . . . . . . 13 82 4.1. Protection Against Spoofing . . . . . . . . . . . . . . . 13 83 4.2. Secure Configuration . . . . . . . . . . . . . . . . . . . 14 84 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 85 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 86 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14 87 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 88 8.1. Normative References . . . . . . . . . . . . . . . . . . . 16 89 8.2. Informative References . . . . . . . . . . . . . . . . . . 16 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 92 1. Introduction 94 This document is part of a series of IPv4/IPv6 translation documents. 95 A framework for IPv4/IPv6 translation is discussed in 96 [I-D.ietf-behave-v6v4-framework], including a taxonomy of scenarios 97 that will be used in this document. Other documents specify the 98 behavior of various types of translators and gateways, including 99 mechanisms for translating between IP headers and other types of 100 messages that include IP addresses. This document specifies how an 101 individual IPv6 address is translated to a corresponding IPv4 102 address, and vice versa, in cases where an algorithmic mapping is 103 used. While specific types of devices are used herein as examples, 104 it is the responsibility of the specification of such devices to 105 reference this document for algorithmic mapping of the addresses 106 themselves. 108 This document reserves a "Well-Known Prefix" for use in an 109 algorithmic mapping. The value of this IPv6 prefix is: 111 64:FF9B::/96 113 Section 2 describes the format of "IPv4-Embedded IPv6 addresses", 114 i.e., IPv6 addresses in which 32 bits contain an IPv4 address. This 115 format is common to both "IPv4-Converted" and "IPv4-Translatable" 116 IPv6 addresses. This section also defines the algorithms for 117 translating addresses, and the text representation of IPv4-Embedded 118 IPv6 addresses. 120 Section 3 discusses the choice of prefixes, the conditions of use of 121 the Well-Known Prefix and Network-Specific Prefixes, and the use of 122 IPv4-Embedded IPv6 addresses with stateless and stateful translation. 124 Section 4 discusses security concerns. 126 In some scenarios, a dual-stack host will unnecessarily send its 127 traffic through an IPv6/IPv4 translator. This can be caused by 128 host's default address selection algorithm [RFC3484], referrals, or 129 other reasons. Optimizing these scenarios for dual-stack hosts is 130 for future study. 132 1.1. Applicability Scope 134 This document is part of a series defining address translation 135 services. We understand that the address format could also be used 136 by other interconnection methods between IPv6 and IPv4, e.g., methods 137 based on encapsulation. If encapsulation methods are developed by 138 the IETF, we expect that their descriptions will document their 139 specific use of IPv4-Embedded IPv6 addresses. 141 1.2. Conventions 143 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 144 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 145 document are to be interpreted as described in RFC 2119 [RFC2119]. 147 1.3. Terminology 149 This document makes use of the following terms: 151 IPv4/IPv6 translator: an entity that translates IPv4 packets to IPv6 152 packets, and vice versa. It may do "stateless" translation, 153 meaning that there is no per-flow state required, or "stateful" 154 translation where per-flow state is created when the first packet 155 in a flow is received. 156 Address translator: any entity that has to derive an IPv4 address 157 from an IPv6 address or vice versa. This applies not only to 158 devices that do IPv4/IPv6 packet translation, but also to other 159 entities that manipulate addresses, such as name resolution 160 proxies (e.g. DNS64 [I-D.ietf-behave-dns64]) and possibly other 161 types of Application Layer Gateways (ALGs). 162 Well-Known Prefix: the IPv6 prefix defined in this document for use 163 in an algorithmic mapping. 164 Network-Specific Prefix: an IPv6 prefix assigned by an organization 165 for use in algorithmic mapping. Options for the Network Specific 166 Prefix are discussed in Section 3.3 and Section 3.4. 167 IPv4-Embedded IPv6 addresses: IPv6 addresses in which 32 bits 168 contain an IPv4 address. Their format is described in Section 2. 169 IPv4-Converted IPv6 addresses: IPv6 addresses used to represent IPv4 170 nodes in an IPv6 network. They are a variant of IPv4-Embedded 171 IPv6 addresses, and follow the format described in Section 2. 172 IPv4-Translatable IPv6 addresses: IPv6 addresses assigned to IPv6 173 nodes for use with stateless translation. They are a variant of 174 IPv4-Embedded IPv6 addresses, and follow the format described in 175 Section 2. 177 2. IPv4-Embedded IPv6 Address Format 179 IPv4-Converted IPv6 addresses and IPv4-Translatable IPv6 addresses 180 follow the same format, described here as the IPv4-Embedded IPv6 181 address Format. IPv4-Embedded IPv6 addresses are composed of a 182 variable length prefix, the embedded IPv4 address, and a variable 183 length suffix, as presented in the following diagram, in which PL 184 designates the prefix length: 186 +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 187 |PL| 0-------------32--40--48--56--64--72--80--88--96--104-112-120-| 188 +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 189 |32| prefix |v4(32) | u | suffix | 190 +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 191 |40| prefix |v4(24) | u |(8)| suffix | 192 +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 193 |48| prefix |v4(16) | u | (16) | suffix | 194 +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 195 |56| prefix |(8)| u | v4(24) | suffix | 196 +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 197 |64| prefix | u | v4(32) | suffix | 198 +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 199 |96| prefix | v4(32) | 200 +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 202 Figure 1 204 In these addresses, the prefix shall be either the "Well-Known 205 Prefix", or a "Network-Specific Prefix" unique to the organization 206 deploying the address translators. (The Well-Known prefic is 96 bits 207 long, and can only be used in the last form of the table.) 209 Various deployments justify different prefix lengths with Network- 210 Specific prefixes. The tradeoff between different prefix lengths are 211 discussed in Section 3.3 and Section 3.4. 213 Bits 64 to 71 of the address are reserved for compatibility with the 214 host identifier format defined in the IPv6 addressing architecture 215 [RFC4291]. These bits MUST be set to zero. When using a /96 216 Network-Specific Prefix, the administrators MUST ensure that the bits 217 64 to 71 are set to zero. A simple way to achieve that is to 218 construct the /96 Network-Specific Prefix by picking a /64 prefix, 219 and then adding four octets set to zero. 221 The IPv4 address is encoded following the prefix, most significant 222 bits first. Depending of the prefix length, the 4 octets of the 223 address may be separated by the reserved octet "u", whose 8 bits MUST 224 be set to zero. In particular: 225 o When the prefix is 32 bits long, the IPv4 address is encoded in 226 positions 32 to 63. 227 o When the prefix is 40 bits long, 24 bits of the IPv4 address are 228 encoded in positions 40 to 63, with the remaining 8 bits in 229 position 72 to 79. 230 o When the prefix is 48 bits long, 16 bits of the IPv4 address are 231 encoded in positions 48 to 63, with the remaining 16 bits in 232 position 72 to 87. 234 o When the prefix is 56 bits long, 8 bits of the IPv4 address are 235 encoded in positions 56 to 63, with the remaining 24 bits in 236 position 72 to 95. 237 o When the prefix is 64 bits long, the IPv4 address is encoded in 238 positions 72 to 103. 239 o When the prefix is 96 bits long, the IPv4 address is encoded in 240 positions 96 to 127. 242 There are no remaining bits, and thus no suffix, if the prefix is 96 243 bits long. In the other cases, the remaining bits of the address 244 constitute the suffix. These bits are reserved for future 245 extensions, and SHOULD be set to zero. 247 2.1. Address Translation Algorithms 249 IPv4-Embedded IPv6 addresses are composed according to the following 250 algorithm: 251 o Concatenate the prefix, the 32 bits of the IPv4 address and the 252 null suffix if needed to obtain a 128 bit address. 253 o If the prefix length is less than 96 bits, remove the last octet 254 and insert the null octet "u" at the appropriate position, as 255 documented in Figure 1. 257 The IPv4 addresses are extracted from the IPv4-Embedded IPv6 258 addresses according to the following algorithm: 259 o If the prefix is 96 bit long, extract the last 32 bits of the IPv6 260 address; 261 o for the other prefix lengths, extract the "u" octet to obtain a 262 120 bit sequence, then extract the 32 bits following the prefix. 264 2.2. Text Representation 266 IPv4-Embedded IPv6 addresses will be represented in text in 267 conformity with section 2.2 of [RFC4291]. IPv4-Embedded IPv6 268 addresses constructed using the Well-Known Prefix or a /96 Network- 269 Specific Prefix may be represented using the alternative form 270 presented in section 2.2 of [RFC4291], with the embedded IPv4 address 271 represented in dotted decimal notation. Examples of such 272 representations are presented in Table 1 and Table 2. 274 +-----------------------+------------+------------------------------+ 275 | Network-Specific | IPv4 | IPv4-Embedded IPv6 address | 276 | Prefix | address | | 277 +-----------------------+------------+------------------------------+ 278 | 2001:DB8::/32 | 192.0.2.33 | 2001:DB8:C000:221:: | 279 | 2001:DB8:100::/40 | 192.0.2.33 | 2001:DB8:1C0:2:21:: | 280 | 2001:DB8:122::/48 | 192.0.2.33 | 2001:DB8:122:C000:2:2100:: | 281 | 2001:DB8:122:300::/56 | 192.0.2.33 | 2001:DB8:122:3C0:0:221:: | 282 | 2001:DB8:122:344::/64 | 192.0.2.33 | 2001:DB8:122:344:C0:2:2100:: | 283 | 2001:DB8:122:344::/96 | 192.0.2.33 | 2001:DB8:122:344::192.0.2.33 | 284 +-----------------------+------------+------------------------------+ 286 Table 1: Text representation of IPv4-Embedded IPv6 addresses using 287 Network-Specific Prefixes 289 +-------------------+--------------+----------------------------+ 290 | Well Known Prefix | IPv4 address | IPv4-Embedded IPv6 address | 291 +-------------------+--------------+----------------------------+ 292 | 64:FF9B::/96 | 192.0.2.33 | 64:FF9B::192.0.2.33 | 293 +-------------------+--------------+----------------------------+ 295 Table 2: Text representation of IPv4-Embedded IPv6 addresses using 296 the Well-Known Prefix 298 The Network-Specific Prefix examples in Table 1 are derived from the 299 IPv6 prefix reserved for documentation in [RFC3849]. The IPv4 300 address 192.0.2.33 is part of the subnet 192.0.2.0/24 reserved for 301 documentation in [RFC3330]. 303 3. Deployment Guidelines and Choices 305 3.1. Restrictions on the use of the Well-Known Prefix 307 The Well-Known Prefix MAY be used by organizations deploying 308 translation services, as explained in Section 3.4. 310 The Well-Known Prefix SHOULD NOT be used to construct IPv4- 311 Translatable addresses. The nodes served by IPv4-Translatable IPv6 312 addresses should be able to receive global IPv6 traffic bound to 313 their IPv4-Translatable IPv6 address without incurring intermediate 314 protocol translation. This is only possible if the specific prefix 315 used to build the IPv4-Translatable IPv6 addresses is advertized in 316 inter-domain routing, but the advertisement of more specific prefixes 317 derived from the Well-Known Prefix is not supported, as explained in 318 Section 3.2. Network-Specific Prefixes SHOULD be used in these 319 scenarios, as explained in Section 3.3. 321 The Well-Known Prefix MUST NOT be used to represent non global IPv4 322 addresses, such as those defined in [RFC1918]. 324 3.2. Impact on Inter-Domain Routing 326 The Well-Known Prefix MAY appear in inter-domain routing tables, if 327 service providers decide to provide IPv6-IPv4 interconnection 328 services to peers. Advertisement of the Well-Known Prefix SHOULD be 329 controlled either by upstream and/or downstream service providers 330 owing to inter-domain routing policies, e.g., through configuration 331 of BGP [RFC4271]. Organizations that advertize the Well-Known Prefix 332 in inter-domain routing MUST be able to provide IPv4/IPv6 translation 333 service. 335 When the IPv4/IPv6 translation relies on the Well-Known Prefix, 336 embedded IPv6 prefixes longer than the Well-Known Prefix MUST NOT be 337 advertised in BGP (especially e-BGP) [RFC4271] because this leads to 338 importing the IPv4 routing table into the IPv6 one and therefore 339 induces scalability issues to the global IPv6 routing table. 340 Administrators of BGP nodes SHOULD configure filters that discard 341 advertisements of embedded IPv6 prefixes longer than the Well-Known 342 Prefix. 344 When the IPv4/IPv6 translation service relies on Network-Specific 345 Prefixes, the IPv4-Translatable IPv6 prefixes used in stateless 346 translation MUST be advertised with proper aggregation to the IPv6 347 Internet. Similarly, if translators are configured with multiple 348 Network-Specific Prefixes,these prefixes MUST be advertised to the 349 IPv6 Internet with proper aggregation. 351 3.3. Choice of Prefix for Stateless Translation Deployments 353 Organizations may deploy translation services using stateless 354 translation. In these deployments, internal IPv6 nodes are addressed 355 using IPv4-Translatable IPv6 addresses, which enable them to be 356 accessed by IPv4 nodes. The addresses of these external IPv4 nodes 357 are then represented in IPv4-Converted IPv6 addresses. 359 Organizations deploying stateless IPv4/IPv6 translation SHOULD assign 360 a Network-Specific Prefix to their IPv4/IPv6 translation service. 361 IPv4-Translatable and IPv4-Converted IPv6 addresses MUST be 362 constructed as specified in Section 2. IPv4-Translatable IPv6 363 addresses MUST use the selected Network-Specific Prefix. Both IPv4- 364 Translatable IPv6 addresses and IPv4-Converted IPv6 addresses SHOULD 365 use the same prefix. 367 Using the same prefix ensures that IPv6 nodes internal to the 368 organization will use the most efficient paths to reach the nodes 369 served by IPv4-Translatable IPv6 addresses. Specifically, if a node 370 learns the IPv4 address of a target internal node without knowing 371 that this target is in fact located behind the same translator that 372 the node also uses, translation rules will ensure that the IPv6 373 address constructed with the Network-Specific prefix is the same as 374 the IPv4-Translatable IPv6 address assigned to the target. Standard 375 routing preference (more specific wins) will then ensure that the 376 IPv6 packets are delivered directly, without requiring "hair-pinning" 377 at the translator. 379 The intra-domain routing protocol must be able to deliver packets to 380 the nodes served by IPv4-Translatable IPv6 addresses. This may 381 require routing on some or all of the embedded IPv4 address bits. 382 Security considerations detailed in Section 4 require that routers 383 check the validity of the IPv4-Translatable IPv6 source addresses, 384 using some form of reverse path check. 386 The management of stateless address translation can be illustrated 387 with a small example. We will consider an IPv6 network with the 388 prefix 2001:DB8:122::/48. The network administrator has selected the 389 Network-Specific prefix 2001:DB8:122:344::/64 for managing stateless 390 IPv4/IPv6 translation. The IPv4-Translatable address block is 2001: 391 DB8:122:344:C0:2::/96 and this block is visible in IPv4 as the subnet 392 192.0.2.0/24. In this network, the host A is assigned the IPv4- 393 Translatable IPv6 address 2001:DB8:122:344:C0:2:2100::, which 394 corresponds to the IPv4 address 192.0.2.33. Host A's address is 395 configured either manually or through DHCPv6. 397 In this example, host A is not directly connected to the translator, 398 but instead to a link managed by a router R. The router R is 399 configured to forward to A the packets bound to 2001:DB8:122:344:C0: 400 2:2100::. To receive these packets, R will advertise reachability of 401 the prefix 2001:DB8:122:344:C0:2:2100::/104 in the intra-domain 402 routing protocol -- or perhaps a shorter prefix if many hosts on link 403 have IPv4-Translatable IPv6 addresses derived from the same IPv4 404 subnet. If a packet bound to 192.0.2.33 reaches the translator, the 405 destination address will be translated to 2001:DB8:122:344:C0:2: 406 2100::, and the packet will be routed towards R and then to A. 408 Let's suppose now that a host B of the same domain learns the IPv4 409 address of A, maybe through an application-specific referral. If B 410 has translation-aware software, B can compose a destination address 411 by combining the Network-Specific Prefix 2001:DB8:122:344::/64 and 412 the IPv4 address 192.0.2.33, resulting in the address 2001:DB8:122: 413 344:C0:2:2100::. The packet sent by B will be forwarded towards R, 414 and then to A, avoiding protocol translation. 416 Forwarding, and reverse path checks, should be performed on the 417 combination of the prefix and the IPv4 address. In theory, routers 418 should be able to route on prefixes of any length. However, routing 419 on prefixes larger than 64 bits may be slower on some routers. But 420 routing efficiency is not the only consideration in the choice of a 421 prefix length. Organizations also need to consider the availability 422 of prefixes, and the potential impact of all-zeroes identifiers. 424 If a /32 prefix is used, all the routing bits are contained in the 425 top 64 bits of the IPv6 address, leading to excellent routing 426 properties. These prefixes may however be hard to obtain, and 427 allocation of a /32 to a small set of IPv4-Translatable IPv6 428 addresses may be seen as wasteful. In addition, the /32 prefix and a 429 zero suffix leads to an all-zeroes interface identifier, an issue 430 that we discuss in Section 3.5. 432 Intermediate prefix lengths such as /40, /48 or /56 appear as 433 compromises. Only some of the IPv4 bits are part of the /64 434 prefixes. Reverse path checks, in particular, may have a limited 435 efficiency. Reverse path checks limited to the most significant bits 436 of the IPv4 address will reduce the possibility of spoofing external 437 IPv4 addresses, but would allow IPv6 nodes to spoof internal IPv4- 438 Translatable IPv6 addresses. 440 We propose here a compromise, based on using no more than 1/256th of 441 an organization's allocation of IPv6 addresses for the IPv4/IPv6 442 translation service. For example, if the organization is an Internet 443 Service Provider with an allocated IPv6 prefix /32 or shorter, the 444 ISP could dedicate a /40 prefix to the translation service. An end 445 site with a /48 allocation could dedicate a /56 prefix to the 446 translation service, or possibly a /96 prefix if all IPv4- 447 Translatable IPv6 addresses are located on the same link. 449 The recommended prefix length is also a function of the deployment 450 scenario. The stateless translation can be used for Scenario 1, 451 Scenario 2, Scenario 5, and Scenario 6 defined in 452 [I-D.ietf-behave-v6v4-framework]. For different scenarios, the 453 prefix length recommendations are: 454 o For scenario 1 (an IPv6 network to the IPv4 Internet) and scenario 455 2 (the IPv4 Internet to an IPv6 network), we recommend using a /40 456 prefix for an ISP holding a /32 allocation, and a /56 prefix for a 457 site holding a /48 allocation. 458 o For scenario 5 (an IPv6 network to an IPv4 network) and scenario 6 459 (an IPv4 network to an IPv6 network), we recommend using a /64 or 460 a /96 prefix. 462 IPv4-Translatable IPv6 addresses SHOULD follow the IPv6 address 463 architecture and SHOULD be compatible with the IPv4 address 464 architecture. The first IPv4-translatable address is the subnet- 465 router anycast address in IPv6 and network identifier in IPv4, the 466 last IPv4-translatable address is the subnet broadcast addresses in 467 IPv4. Both of them SHOULD not be used for IPv6 nodes. In addition, 468 the minimum IPv4 subnet can be used for hosts is /30 (the router 469 interface needs a valid address for the same subnet) and this rule 470 SHOULD also be applied to the corresponding subnet of the IPv4- 471 translatable addresses. 473 3.4. Choice of Prefix for Stateful Translation Deployments 475 Organizations may deploy translation services based on stateful 476 translation technology. An organization may decide to use either a 477 Network-Specific Prefix or the Well-Known Prefix for its stateful 478 IPv4/IPv6 translation service. 480 When these services are used, IPv6 nodes are addressed through 481 standard IPv6 addresses, while IPv4 nodes are represented by IPv4- 482 Converted IPv6 addresses, as specified in Section 2. 484 The stateful nature of the translation creates a potential stability 485 issue when the organization deploys multiple translators. If several 486 translators use the same prefix, there is a risk that packets 487 belonging to the same connection may be routed to different 488 translators as the internal routing state changes. This issue can be 489 avoided either by assigning different prefixes to different 490 translators, or by ensuring that all translators using same prefix 491 coordinate their state. 493 Stateful translation can be used in scenarios defined in 494 [I-D.ietf-behave-v6v4-framework]. The Well Known Prefix SHOULD be 495 used in these scenarios, with two exceptions: 496 o In all scenarios, the translation MAY use a Network-Specific 497 Prefix, if deemed appropriate for management reasons. 498 o The Well-Known Prefix MUST NOT be used for scenario 3 (the IPv6 499 Internet to an IPv4 network), as this would lead to using the 500 Well-Known Prefix with non-global IPv4 addresses. That means a 501 Network-Specific Prefix MUST be used in that scenario, for example 502 a /96 prefix compatible with the Well-Known prefix format. 504 3.5. Choice of Suffix 506 The address format described in Section 2 recommends a zero suffix. 507 Before making this recommendation, we considered different options: 508 checksum neutrality; the encoding of a port range; and a value 509 different than 0. 511 In the case of stateless translation, there would be no need for the 512 translator to recompute a one's complement checksum if both the IPv4- 513 Translatable and the IPv4-Converted IPv6 addresses were constructed 514 in a "checksum-neutral" manner, that is if the IPv6 addresses would 515 have the same one's complement checksum as the embedded IPv4 address. 516 In the case of stateful translation, checksum neutrality does not 517 eliminate checksum computation during translation, as only one of the 518 two addresses would be checksum neutral. We considered reserving 16 519 bits in the suffix to guarantee checksum neutrality, but declined 520 because it would not help with stateful translation, and because 521 checksum neutrality can also be achieved by an appropriate choice of 522 the Network-Specific Prefix, as was done for example with the Well- 523 Known Prefix. 525 There have been proposals to complement stateless translation with a 526 port-range feature. Instead of mapping an IPv4 address to exactly 527 one IPv6 prefix, the options would allow several IPv6 nodes to share 528 an IPv4 address, with each node managing a different range of ports. 529 If a port range extension is needed, it could be defined later, using 530 bits currently reserved as null in the suffix. 532 When a /32 prefix is used, an all-zero suffix results in an all-zero 533 interface identifier. We understand the conflict with Section 2.6.1 534 of RFC4291, which specifies that all zeroes are used for the subnet- 535 router anycast address. However, in our specification, there would 536 be only one node with an IPv4-Translatable IPv6 address in the /64 537 subnet, and the anycast semantic would not create confusion. We thus 538 decided to keep the null suffix for now. This issue does not exist 539 for prefixes larger than 32 bits, such as the /40, /56, /64 and /96 540 prefixes that we recommend in Section 3.3. 542 3.6. Choice of the Well-Known Prefix 544 Before making our recommendation of the Well-Known Prefix, we were 545 faced with three choices: 546 o reuse the IPv4-mapped prefix, ::FFFF:0:0/96, as specified in RFC 547 2765 Section 2.1; 548 o request IANA to allocate a /32 prefix, 549 o or request allocation of a new /96 prefix. 551 We weighted the pros and cons of these choices before settling on the 552 recommended /96 Well-Known Prefix. 554 The main advantage of the existing IPv4-mapped prefix is that it is 555 already defined. Reusing that prefix would require minimal 556 standardization efforts. However, being already defined is not just 557 an advantage, as there may be side effects of current 558 implementations. When presented with the IPv4-mapped prefix, current 559 versions of Windows and MacOS generate IPv4 packets, but will not 560 send IPv6 packets. If we used the IPv4-mapped prefix, these nodes 561 would not be able to support translation without modification. This 562 will defeat the main purpose of the translation techniques. We thus 563 eliminated the first choice, and decided to not reuse the IPv4-mapped 564 prefix, ::FFFF:0:0/96. 566 A /32 prefix would have allowed the embedded IPv4 address to fit 567 within the top 64 bits of the IPv6 address. This would have 568 facilitated routing and load balancing when an organization deploys 569 several translators. However, such destination-address based load 570 balancing may not be desirable. It is not compatible with STUN in 571 the deployments involving multiple stateful translators, each one 572 having a different pool of IPv4 addresses. STUN compatibility would 573 only be achieved if the translators managed the same pool of IPv4 574 addresses and were able to coordinate their translation state, in 575 which case there is no big advantage to using a /32 prefix rather 576 than a /96 prefix. 578 According to Section 2.2 of [RFC4291], in the legal textual 579 representations of IPv6 addresses, dotted decimal can only appear at 580 the end. The /96 prefix is compatible with that requirement. It 581 enables the dotted decimal notation without requiring an update to 582 [RFC4291]. This representation makes the address format easier to 583 use, and log files easier to read. 585 The prefix that we recommend has the particularity of being "checksum 586 neutral". The sum of the hexadecimal numbers "0064" and "FF9B" is 587 "FFFF", i.e. a value equal to zero in one's complement arithmetic. 588 An IPv4-Embedded IPv6 address constructed with this prefix will have 589 the same one's complement checksum as the embedded IPv4 address. 591 4. Security Considerations 593 4.1. Protection Against Spoofing 595 By and large, IPv4/IPv6 translators can be modeled as special 596 routers, are subject to the same risks, and can implement the same 597 mitigations. There is however a particular risk that directly 598 derives from the practice of embedding IPv4 addresses in IPv6: 599 address spoofing. 601 An attacker could use an IPv4-Embedded IPv6 address as the source 602 address of malicious packets. After translation, the packets will 603 appear as IPv4 packets from the specified source, and the attacker 604 may be hard to track. If left without mitigation, the attack would 605 allow malicious IPv6 nodes to spoof arbitrary IPv4 addresses. 607 The mitigation is to implement reverse path checks, and to verify 608 throughout the network that packets are coming from an authorized 609 location. 611 4.2. Secure Configuration 613 The prefixes and formats need to be the configured consistently among 614 multiple devices in the same network (e.g., nodes that need to prefer 615 native over translated addresses, DNS gateways, and IPv4/IPv6 616 translators). As such, the means by which they are learned/ 617 configured MUST be secure. Specifying a default prefix and/or format 618 in implementations provides one way to configure them securely. Any 619 alternative means of configuration is responsible for specifying how 620 to do so securely. 622 5. IANA Considerations 624 The Well Known Prefix falls into the range ::/8 reserved by the IETF. 625 The prefix definition does not require an IANA action. 627 6. Acknowledgements 629 Many people in the Behave WG have contributed to the discussion that 630 led to this document, including Andrew Sullivan, Andrew Yourtchenko, 631 Brian Carpenter, Dan Wing, Ed Jankiewicz, Fred Baker, Hiroshi Miyata, 632 Iljitsch van Beijnum, John Schnizlein, Keith Moore, Kevin Yin, Magnus 633 Westerlund, Margaret Wasserman, Masahito Endo, Phil Roberts, Philip 634 Matthews, Remi Denis-Courmont, Remi Despres and William Waites. 636 Marcelo Bagnulo is partly funded by Trilogy, a research project 637 supported by the European Commission under its Seventh Framework 638 Program. 640 7. Contributors 642 The following individuals co-authored drafts from which text has been 643 incorporated, and are listed in alphabetical order. 645 Congxiao Bao 646 CERNET Center/Tsinghua University 647 Room 225, Main Building, Tsinghua University 648 Beijing, 100084 649 China 650 Phone: +86 62785983 651 Email: congxiao@cernet.edu.cn 653 Dave Thaler 654 Microsoft Corporation 655 One Microsoft Way 656 Redmond, WA 98052 657 USA 658 Phone: +1 425 703 8835 659 Email: dthaler@microsoft.com 661 Fred Baker 662 Cisco Systems 663 Santa Barbara, California 93117 664 USA 665 Phone: +1-408-526-4257 666 Fax: +1-413-473-2403 667 Email: fred@cisco.com 669 Hiroshi Miyata 670 Yokogawa Electric Corporation 671 2-9-32 Nakacho 672 Musashino-shi, Tokyo 180-8750 673 JAPAN 674 Email: h.miyata@jp.yokogawa.com 676 Marcelo Bagnulo 677 Universidad Carlos III de Madrid 678 Av. Universidad 30 679 Leganes, Madrid 28911 680 ESPANA 681 Email: marcelo@it.uc3m.es 683 Xing Li 684 CERNET Center/Tsinghua University 685 Room 225, Main Building, Tsinghua University 686 Beijing, 100084 687 China 688 Phone: +86 62785983 689 Email: xing@cernet.edu.cn 691 8. References 693 8.1. Normative References 695 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 696 Requirement Levels", BCP 14, RFC 2119, March 1997. 698 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 699 Architecture", RFC 4291, February 2006. 701 8.2. Informative References 703 [I-D.ietf-behave-dns64] 704 Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum, 705 "DNS64: DNS extensions for Network Address Translation 706 from IPv6 Clients to IPv4 Servers", 707 draft-ietf-behave-dns64-04 (work in progress), 708 December 2009. 710 [I-D.ietf-behave-v6v4-framework] 711 Baker, F., Li, X., Bao, C., and K. Yin, "Framework for 712 IPv4/IPv6 Translation", 713 draft-ietf-behave-v6v4-framework-03 (work in progress), 714 October 2009. 716 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 717 E. Lear, "Address Allocation for Private Internets", 718 BCP 5, RFC 1918, February 1996. 720 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 721 September 2002. 723 [RFC3484] Draves, R., "Default Address Selection for Internet 724 Protocol version 6 (IPv6)", RFC 3484, February 2003. 726 [RFC3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix 727 Reserved for Documentation", RFC 3849, July 2004. 729 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 730 Protocol 4 (BGP-4)", RFC 4271, January 2006. 732 Authors' Addresses 734 Congxiao Bao 735 CERNET Center/Tsinghua University 736 Room 225, Main Building, Tsinghua University 737 Beijing, 100084 738 China 740 Phone: +86 10-62785983 741 Email: congxiao@cernet.edu.cn 743 Christian Huitema 744 Microsoft Corporation 745 One Microsoft Way 746 Redmond, WA 98052-6399 747 U.S.A. 749 Email: huitema@microsoft.com 751 Marcelo Bagnulo 752 UC3M 753 Av. Universidad 30 754 Leganes, Madrid 28911 755 Spain 757 Phone: +34-91-6249500 758 Fax: 759 Email: marcelo@it.uc3m.es 760 URI: http://www.it.uc3m.es/marcelo 762 Mohamed Boucadair 763 France Telecom 764 3, Av Francois Chateaux 765 Rennes 350000 766 France 768 Email: mohamed.boucadair@orange-ftgroup.com 769 Xing Li 770 CERNET Center/Tsinghua University 771 Room 225, Main Building, Tsinghua University 772 Beijing, 100084 773 China 775 Phone: +86 10-62785983 776 Email: xing@cernet.edu.cn