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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (February 1, 2013) is 4095 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 6145 (Obsoleted by RFC 7915) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Cheng 3 Internet-Draft Huawei Technologies 4 Intended status: Informational M. Boucadair 5 Expires: August 5, 2013 France Telecom 6 A. Retana 7 Cisco Systems 8 February 1, 2013 10 Routing for IPv4-embedded IPv6 Packets 11 draft-ietf-ospf-ipv4-embedded-ipv6-routing-07 13 Abstract 15 This document describes routing packets destined to IPv4-embedded 16 IPv6 addresses across an IPv6 core using OSPFv3 with a separate 17 routing table. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on August 5, 2013. 36 Copyright Notice 38 Copyright (c) 2013 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 1.1. The Scenario . . . . . . . . . . . . . . . . . . . . . . . 3 55 1.2. Routing Solution per RFC5565 . . . . . . . . . . . . . . . 4 56 1.3. An Alternative Routing Solution with OSPFv3 . . . . . . . 4 57 1.4. OSPFv3 Routing with a Specific Topology . . . . . . . . . 6 58 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 7 59 3. Provisioning . . . . . . . . . . . . . . . . . . . . . . . . . 7 60 3.1. Deciding the IPv4-embedded IPv6 Topology . . . . . . . . . 7 61 3.2. Maintaining a Dedicated IPv4-embedded IPv6 Routing 62 Table . . . . . . . . . . . . . . . . . . . . . . . . . . 8 63 3.3. OSPFv3 Topology with a Separate Instance ID . . . . . . . 8 64 3.4. OSPFv3 Topology with the Default Instance . . . . . . . . 8 65 4. IP Packets Translation . . . . . . . . . . . . . . . . . . . . 9 66 4.1. Address Translation . . . . . . . . . . . . . . . . . . . 9 67 5. Advertising IPv4-embedded IPv6 Routes . . . . . . . . . . . . 10 68 5.1. Advertising IPv4-embedded IPv6 Routes through an IPv6 69 Transit Network . . . . . . . . . . . . . . . . . . . . . 10 70 5.1.1. Routing Metrics . . . . . . . . . . . . . . . . . . . 10 71 5.1.2. Forwarding Address . . . . . . . . . . . . . . . . . . 10 72 5.2. Advertising IPv4 Addresses into Client Networks . . . . . 11 73 6. Aggregation on IPv4 Addresses and Prefixes . . . . . . . . . . 11 74 7. Forwarding . . . . . . . . . . . . . . . . . . . . . . . . . . 11 75 8. Backdoor Connections . . . . . . . . . . . . . . . . . . . . . 12 76 9. Prevention of Loops . . . . . . . . . . . . . . . . . . . . . 12 77 10. MTU Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 12 78 11. Security Considerations . . . . . . . . . . . . . . . . . . . 13 79 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 80 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 81 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 82 14.1. Normative References . . . . . . . . . . . . . . . . . . . 14 83 14.2. Informative References . . . . . . . . . . . . . . . . . . 14 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 86 1. Introduction 88 This document describes a routing scenario where IPv4 packets are 89 transported over an IPv6 network, based on [RFC6145] and [RFC6052], 90 along with a separate OSPFv3 routing table for IPv4-embedded IPv6 91 routes in the IPv6 network. This document does not introduce any new 92 IPv6 transition mechanism. 94 In this document the following terminology is used: 96 o An IPv4-embedded IPv6 address denotes an IPv6 address which 97 contains an embedded 32-bit IPv4 address constructed according to 98 the rules defined in [RFC6052]. 100 o IPv4-embedded IPv6 packets are packets of which destination 101 addresses are IPv4-embedded IPv6 addresses. 103 o AFBR (Address Family Border Router, [RFC5565]) refers to an edge 104 router, which supports both IPv4 and IPv6 address families, but 105 the backbone network it connects to only supports either the IPv4 106 or IPv6 address family. 108 o AFXLBR (Address Family Translation Border Router) is defined in 109 this document. It refers to a border router that supports both 110 IPv4 and IPv6 address families, located on the boundary of an 111 IPv4-only network and an IPv6-only network, and is capable of 112 performing IP header translation between IPv4 and IPv6 according 113 to [RFC6145]. 115 1.1. The Scenario 117 Due to exhaustion of public IPv4 addresses, there has been a 118 continuing effort within the IETF on IPv6 transitional techniques. 119 In the course of the transition, it is certain that networks based on 120 IPv4 and IPv6 technologies respectively, will co-exist at least for 121 some time. One scenario of this co-existence is the inter-connection 122 of IPv4-only and IPv6-only networks, and in particular, when an IPv6- 123 only network serves as inter-connection between several segregated 124 IPv4-only networks. In this scenario, IPv4 packets are transported 125 over the IPv6 network between IPv4 networks. In order to forward an 126 IPv4 packet from a source IPv4 network to the destination IPv4 127 network, IPv4 reachability information must be exchanged between the 128 IPv4 networks by some mechanism. 130 In general, running an IPv6-only network would reduce OPEX and 131 optimize the operation compared to IPv4-IPv6 dual-stack environment. 132 Some solutions have been proposed to allow delivery of IPv4 services 133 over an IPv6-only network. This document focuses on an engineering 134 technique which aims to separate the routing table dedicated to IPv4- 135 embedded IPv6 destinations from native IPv6 ones. 137 Maintaining a separate routing table for IPv4-embedded IPv6 routes 138 optimizes IPv4 packets forwarding. It also prevents overload of the 139 native IPv6 routing tables. A separate routing table can be 140 generated from a separate routing instance or a separate routing 141 topology. 143 1.2. Routing Solution per RFC5565 145 The aforementioned scenario is described in [RFC5565], i.e., IPv4- 146 over-IPv6 scenario, where the network core is IPv6-only, and the 147 inter-connected IPv4 networks are called IPv4 client networks. The P 148 routers in the core only support IPv6 but the AFBRs (Address Family 149 Border Routers) support IPv4 on interfaces facing IPv4 client 150 networks, and IPv6 on interfaces facing the core. The routing 151 solution defined in [RFC5565] for this scenario is to run i-BGP among 152 AFBRs to exchange IPv4 routing information in the core, and the IPv4 153 packets are forwarded from one IPv4 client network to the other 154 through a softwire using tunneling technology such as MPLS LSP, GRE, 155 L2TPv3, etc. 157 1.3. An Alternative Routing Solution with OSPFv3 159 In this document, we propose an alternative routing solution for the 160 scenario described in Section 1.1, where several segregated IPv4 161 networks, called IPv4 client networks, are interconnected by an IPv6 162 network. We refer to the border node on the boundary of an IPv4 163 client network and the IPv6 network as an Address Family Translation 164 Border Router (AFXLBR), which supports both the IPv4 and IPv6 address 165 families, and is capable of translating an IPv4 packet to an IPv6 166 packet, and vice versa, according to [RFC6145]. The described 167 scenario is illustrated in Figure 1. 169 +--------+ +--------+ 170 | IPv4 | | IPv4 | 171 | Client | | Client | 172 | Network| | Network| 173 +--------+ +--------+ 174 | \ / | 175 | \ / | 176 | \ / | 177 | X | 178 | / \ | 179 | / \ | 180 | / \ | 181 +--------+ +--------+ 182 | AFXLBR | | AFXLBR | 183 +--| IPv4/6 |---| IPv4/6 |--+ 184 | +--------+ +--------+ | 185 +--------+ | | +--------+ 186 | IPv6 | | | | IPv6 | 187 | Client |----| |----| Client | 188 | Network| | IPv6 | | Network| 189 +--------+ | only | +--------+ 190 | | 191 | +--------+ +--------+ | 192 +--| AFXLBR |---| AFXLBR |--+ 193 | IPv4/6 | | IPv4/6 | 194 +--------+ +--------+ 195 | \ / | 196 | \ / | 197 | \ / | 198 | X | 199 | / \ | 200 | / \ | 201 | / \ | 202 +--------+ +--------+ 203 | IPv4 | | IPv4 | 204 | Client | | Client | 205 | Network| | Network| 206 +--------+ +--------+ 208 Figure 1: Segregated IPv4 Networks Inter-connected by an IPv6 Network 210 Since the scenario occurs most commonly in a single Autonomous 211 System, an IPv6 prefix can be locally allocated and used by AFXLBRs 212 to construct IPv4-embedded IPv6 addresses according to [RFC6052]. 213 The embedded IPv4 address or prefix belongs to an IPv4 client network 214 that is connected to the AFXLBR. An AFXLBR injects IPv4-embedded 215 IPv6 addresses and prefixes into the IPv6 network using OSPFv3, and 216 it also installs IPv4-embedded IPv6 routes advertised by other 217 AFXLBRs. 219 When an AFXLBR receives an IPv4 packet from a locally connected IPv4 220 client network and destined to a remote IPv4 client network, it 221 translates the IPv4 header to the relevant IPv6 header according to 222 [RFC6145], and in that process, source and destination IPv4 address 223 are translated into IPv4-embedded IPv6 addresses, respectively, 224 according to [RFC6052]. The resulting IPv6 packet is then forwarded 225 to the AFXLBR that connects to the destination IPv4 client network. 226 The remote AFXLBR derives the IPv4 source and destination addresses 227 from the IPv4-embedded IPv6 addresses, respectively, according to 228 [RFC6052], and translates the header of the received IPv6 packet to 229 the relevant IPv4 header according to [RFC6145]. The resulting IPv4 230 packet is then forwarded according to the IPv4 routing table 231 maintained on the AFXLBR. 233 There are use cases where the proposed routing solution is useful. 234 One case is that some border nodes do not participate in i-BGP for 235 routes exchange, or i-BGP is not used at all. Another case is when 236 tunnels are not deployed in the IPv6 network, or native IPv6 237 forwarding is preferred. Note that with this routing solution, the 238 IPv4 and IPv6 header translation performed in both directions by the 239 AFXLBR is stateless. 241 1.4. OSPFv3 Routing with a Specific Topology 243 In general, IPv4-embedded IPv6 packets can be forwarded just like 244 native IPv6 packets with OSPFv3 running in the IPv6 network. 245 However, this would require IPv4-embedded IPv6 routes to be flooded 246 throughout the entire IPv6 network and stored on every router. This 247 is not desirable from the scaling perspective. Moreover, since all 248 IPv6 routes are stored in the same routing table, it would be 249 inconvenient to manage the resource required for routing and 250 forwarding based on traffic category, if so desired. 252 To improve the situation, a separate OSPFv3 routing table can be 253 constructed that is dedicated to the IPv4-embedded IPv6 topology, and 254 that table is solely used for routing IPv4-embedded IPv6 packets in 255 the IPv6 network. The IPv4-embedded IPv6 topology includes all the 256 participating AFXLBR routers and a set of P routers providing 257 redundant connectivity with alternate routing paths. 259 There are two methods to build a separate OSPFv3 routing table for 260 IPv4-embedded IPv6 routes: 262 o The first one is to run a separate OSPFv3 instance for IPv4- 263 embedded IPv6 topology in the IPv6 network according to [RFC5838]. 265 o The second one is to stay with the existing OSPFv3 instance that 266 already operates in the IPv6 network, but maintain a separate 267 IPv4-embedded IPv6 topology, according to 268 [I-D.ietf-ospf-mt-ospfv3]. 270 With either method, there would be a dedicated IPv4-embedded IPv6 271 topology that is maintained on all participating AFXLBR and P 272 routers, along with a dedicated IPv4-embedded IPv6 routing table. 273 This routing table is then used solely in the IPv6 network for IPv4- 274 embedded IPv6 packets. 276 It would be an operator's preference as which method is to be used. 277 This document elaborates on how configuration is done for each method 278 and related routing issues that are common to both. 280 This document only focuses on unicast routing for IPv4-embedded IPv6 281 packets using OSPFv3. 283 2. Requirements Language 285 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 286 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 287 document are to be interpreted as described in [RFC2119]. 289 3. Provisioning 291 3.1. Deciding the IPv4-embedded IPv6 Topology 293 Before deploying configurations that use a separate OSPFv3 routing 294 table for IPv4-embedded IPv6 addresses and prefixes, a decision must 295 be made on the set of routers and their interfaces in the IPv6 296 network that should be part of the IPv4-embedded IPv6 topology. 298 For the purpose of this IPv4-embedded IPv6 topology, all AFXLBRs that 299 connect to IPv4 client networks MUST be members of this topology, and 300 also at least some of their network core facing interfaces along with 301 some P routers in the IPv6 network. 303 The IPv4-embedded IPv6 topology is a sub-topology of the entire IPv6 304 network, and if all routers (including AFXLBRs and P-routers) and all 305 their interfaces are included, the two topologies converge. In 306 general, as more P routers and their interfaces are configured on 307 this sub-topology, it would increase the inter-connectivity and 308 potentially, there would be more routing paths across the network 309 from one IPv4 client network to the other, at the cost of more 310 routers needing to participate in IPv4-embedded IPv6 routing. In any 311 case, the IPv4-embedded IPv6 topology MUST be continuous with no 312 partitions. 314 3.2. Maintaining a Dedicated IPv4-embedded IPv6 Routing Table 316 In an IPv6 network, in order to maintain a separate IPv6 routing 317 table that contains routes for IPv4-embedded IPv6 destinations only, 318 OSPFv3 needs to use the mechanism defined either in [RFC5838] or in 319 [I-D.ietf-ospf-mt-ospfv3] with the required configuration, as 320 described in the following sub-sections. 322 3.3. OSPFv3 Topology with a Separate Instance ID 324 It is assumed that the scenario described in this document is under a 325 single Autonomous System and, as such, an OSPFv3 instance ID (IID) is 326 allocated locally and used for OSPFv3 operation dedicated to unicast 327 IPv4-embedded IPv6 routing in an IPv6 network. This IID is 328 configured on OSPFv3 router interfaces that participate in the IPv4- 329 embedded IPv6 topology. 331 The range for a locally configured OSPFv3 IID is from 192 to 255, 332 inclusive, and this IID must be used to encode the "Instance ID" 333 field in the packet header of OSPFv3 packets associated with the 334 OSPFv3 instance. 336 In addition, the "AF" bit in the OSPFv3 Option field MUST be set. 338 During Hello packet processing, an adjacency may only be established 339 when the received Hello packet contains the same Instance ID as 340 configured on the receiving OSPFv3 interface. This insures that only 341 interfaces configured as part of the OSPFv3 unicast IPv4-embedded 342 IPv6 topology are used for IPv4-embedded IPv6 unicast routing. 344 For more details, the reader is referred to [RFC5838]. 346 3.4. OSPFv3 Topology with the Default Instance 348 Similar to that as described in the previous section, an OSPFv3 349 multi-topology ID (MT-ID) is locally allocated and used for an OSPFv3 350 operation including unicast IPv4-embedded IPv6 routing in an IPv6 351 network. This MTID is configured on each OSPFv3 router interface 352 that participates in this routing topology. 354 The range for a locally configured OSPFv3 MT-ID is from 32 to 255, 355 inclusive, and this MT-ID must be used to encode the "MT-ID" field 356 included in extended Link State Advertisements (LSAs) for the IPv4- 357 embedded IPv6 unicast topology as documented in 358 [I-D.ietf-ospf-mt-ospfv3]. 360 In addition, the MT bit in the OSPFv3 Option field must be set. 362 For more details, the reader is referred to 363 [I-D.ietf-ospf-mt-ospfv3]. 365 4. IP Packets Translation 367 When transporting IPv4 packets across an IPv6 network with the 368 mechanism described above, an IPv4 packet is translated to an IPv6 369 packet at the ingress AFXLBR, and the IPv6 packet is translated back 370 to an IPv4 packet at the egress AFXLBR. The IP packet header 371 translation is accomplished in stateless manner according to rules 372 specified in [RFC6145], with the address translation details 373 explained in the next sub-section. 375 4.1. Address Translation 377 Prior to address translation, an IPv6 prefix is allocated by the 378 Autonomous System and it is used to form IPv4-embedded IPv6 379 addresses. 381 The IPv6 prefix can either be the well-known IPv6 prefix (WKP) 64: 382 ff9b::/96, or a network-specific prefix that is unique to the 383 Autonomous System; and for the latter case, the IPv6 prefix length 384 may be 32, 40, 48, 56 or 64. In either case, this IPv6 prefix is 385 used during the address translation between an IPv4 address and an 386 IPv4-embedded IPv6 address, as described in [RFC6052]. 388 During translation from an IPv4 header to an IPv6 header at an 389 ingress AFXLBR, the source IPv4 address and destination IPv4 address 390 are translated into the corresponding IPv6 source address and 391 destination IPv6 address, respectively, and during translation from 392 an IPv6 header to an IPv4 header at an egress AFXLBR, the source IPv6 393 address and destination IPv6 address are translated into the 394 corresponding IPv4 source address and destination IPv4 address, 395 respectively. Note that the address translation is accomplished in a 396 stateless manner. 398 When a well-known IPv6 prefix (WKP) is used, [RFC6052] allows only 399 global IPv4 addresses to be embedded in the IPv6 address. An AFXLBR 400 MUST NOT translate packets in which an address is composed of the WKP 401 and a non-global IPv4 address; they MUST drop these packets. 403 In the case where both the IPv4 client networks and the IPv6 transit 404 network belong to the same organization, non-global IPv4 addresses 405 may be used with a network-specific prefix [RFC6052]. 407 5. Advertising IPv4-embedded IPv6 Routes 409 In order to forward IPv4 packets to the proper destination across an 410 IPv6 network, IPv4 reachability needs to be disseminated throughout 411 the IPv6 network and this is performed by AFXLBRs that connect to 412 IPv4 client networks using OSPFv3. 414 With the scenario described in this document, i.e., a set of AFXLBRs 415 that inter-connect a bunch of IPv4 client networks with an IPv6 416 network, the IPv4 networks and IPv6 networks belong to separate and 417 independent Autonomous Systems, and as such, these AFXLBRs behave as 418 AS Boundary Routers (ASBRs). 420 5.1. Advertising IPv4-embedded IPv6 Routes through an IPv6 Transit 421 Network 423 IPv4 addresses and prefixes in an IPv4 client network are translated 424 into IPv4-embedded IPv6 addresses and prefixes, respectively, using 425 the IPv6 prefix allocated by the Autonomous System and the method 426 specified in [RFC6052]. These routes are then advertised by one or 427 more attached ASBRs into the IPv6 transit network using AS-External- 428 LSAs [RFC5340], i.e., with advertising scope comprising the entire 429 Autonomous System. 431 5.1.1. Routing Metrics 433 By default, the metric in an AS-External-LSA that carries an IPv4- 434 embedded IPv6 address or prefixes is a Type 1 external metric, which 435 is comparable to the link state metric and we assume that in most 436 cases, OSPFv2 is used in client IPv4 networks. This metric is added 437 to the metric of the intra-AS path to the ASBR during the OSPFv3 438 route calculation. Through ASBR configuration, the metric can be set 439 to a Type 2 external metric, which is considered much larger than the 440 metric for any intra-AS path. Refer to the OSPFv3 specification 441 [RFC5340] for more detail. In either case, an external metric may 442 take the same value as in an IPv4 network (using OSPFv2 or another 443 routing protocol), but may also be specified based on some routing 444 policy; the details of which are outside of the scope of this 445 document. 447 5.1.2. Forwarding Address 449 If the "Forwarding Address" field of an OSPFv3 AS-External-LSA is 450 used to carry an IPv6 address, that must also be an IPv4-embedded 451 IPv6 address where the embedded IPv4 address is the destination 452 address in an IPv4 client network. However, since an AFXLBR sits on 453 the border of an IPv4 network and an IPv6 network, it is RECOMMENDED 454 that the "Forwarding Address" field is not used, so that the AFXLBR 455 can make the forwarding decision based on its own IPv4 routing table. 457 5.2. Advertising IPv4 Addresses into Client Networks 459 IPv4-embedded IPv6 routes injected into the IPv6 network from one 460 IPv4 client network MAY be advertised into another IPv4 client 461 network, after the associated destination addresses and prefixes are 462 translated back to IPv4 addresses and prefixes, respectively. This 463 operation is similar to normal OSPFv3 operation, wherein an AS- 464 External-LSA can be advertised in a non-backbone area by default. 466 An IPv4 client network can limit which advertisements it receives 467 through configuration. 469 For the purpose of this document, IPv4-embedded IPv6 routes MUST NOT 470 be advertised into any IPv6 client networks that also connected to 471 the IPv6 transit network. 473 6. Aggregation on IPv4 Addresses and Prefixes 475 In order to reduce the amount of LSAs that are injected to the IPv6 476 network, an implementation should provide mechanisms to aggregate 477 IPv4 addresses and prefixes at AFXLBR prior to advertisement as IPv4- 478 embedded IPv6 addresses and prefixes. In general, the aggregation 479 practice should be based on routing policy, which is outside of the 480 scope of this document. 482 7. Forwarding 484 There are three cases in forwarding IP packets in the scenario 485 described in this document: 487 1. On an AFXLBR, if an IPv4 packet that is received on an interface 488 connecting to an IPv4 client network with a destination IPv4 489 address belonging to another IPv4 client network, the header of 490 the packet is translated to the corresponding IPv6 header as 491 described in Section 4, and the packet is then forwarded to the 492 destination AFXLBR that advertised the IPv4-embedded IPv6 address 493 into the IPv6 network. 495 2. On an AFXLBR, if an IPv4-embedded IPv6 packet is received and the 496 embedded destination IPv4 address is in its IPv4 routing table, 497 the header of the packet is translated to the corresponding IPv4 498 header as described in Section 4, and the packet is then 499 forwarded accordingly. 501 3. On any router that is within the IPv4-embedded IPv6 topology 502 subset of the IPv6 network, if an IPv4-embedded IPv6 packet is 503 received and a route is found in the IPv4-embedded IPv6 routing 504 table, the packet is forwarded to the IPv6 next-hop just like the 505 handling for a normal IPv6 packet, without any translation. 507 The classification of IPv4-embedded IPv6 packet is according to the 508 IPv6 prefix of the destination address, which is either the Well 509 Known Prefix (i.e., 64:ff9b::/96) or locally allocated as defined in 510 [RFC6052]. 512 8. Backdoor Connections 514 In some deployments, IPv4 client networks are inter-connected across 515 the IPv6 network, but also directly connected to each other. The 516 "backdoor" connections between IPv4 client networks can certainly be 517 used to transport IPv4 packets between IPv4 client networks. In 518 general, backdoor connections are preferred over the IPv6 network, 519 since there requires no address family translation. 521 9. Prevention of Loops 523 If an LSA sent from an AFXLBR into a client network could then be 524 received by another AFXLBR, it would be possible for routing loops to 525 occur. To prevent loops, an AFXLBR MUST set the DN-bit [RFC4576] in 526 any LSA that it sends to a client network. The AFXLBR MUST also 527 ignore any LSA received from a client network that already has the 528 DN-bit sent. 530 10. MTU Issues 532 In the IPv6 network, there are no new MTU issues introduced by this 533 document. If a separate OSPFv3 instance (per [RFC5838]) is used for 534 IPv4-embedded IPv6 routing, the MTU handling in the IPv6 network is 535 the same as that of the default OSPFv3 instance. If a separate 536 OSPFv3 topology (according to [I-D.ietf-ospf-mt-ospfv3]) is used for 537 IPv4-embedded IPv6 routing, the MTU handling in the IPv6 network is 538 the same as that of the default OSPFv3 topology. 540 However, the MTU in the IPv6 network may be different than that of 541 IPv4 client networks. Since an IPv6 router will never fragment a 542 packet, the packet size of any IPv4-embedded IPv6 packet entering the 543 IPv6 network must be equal to or less than the MTU of the IPv6 544 network. In order to achieve this requirement, it is recommended 545 that AFXLBRs perform IPv6 path discovery among themselves and the 546 resulting MTU, after taking into account of the difference between 547 the IPv4 header length and the IPv6 header length, must be 548 "propagated" into IPv4 client networks, e.g., included in the OSPFv2 549 Database Description packet. 551 The details of passing the proper MTU into IPv4 client networks are 552 beyond the scope of this document. 554 11. Security Considerations 556 There are several security aspects that require attention in the 557 deployment practice described in this document. 559 In the OSPFv3 transit network, the security considerations for OSPFv3 560 are covered in [RFC5340], and in particular, IPsec can be used for 561 OSPFv3 authentication and confidentiality as suggested in [RFC5838]. 563 When a separate OSPFv3 instance is used to support IPv4-embedded IPv6 564 routing, the same Security Association (SA) (refer to [RFC4552] ) 565 must be used by the embedded IPv4 address instance as other instances 566 utilizing the same link as specified in [RFC5838]. 568 Security considerations as currently documented in [RFC6052] must 569 also be thought through with proper implementation in this 570 engineering practice including the following: 572 o The IPv6 prefix that is used to carry an embedded IPv4 address 573 (refer to Section 4.1) must be configured by the authorized 574 operator on all participating AFXLBRs in a secure manner. This is 575 to help prevent an malicious attack resulting in network 576 disruption, denial of service, and possible information 577 disclosure. 579 o Effective mechanisms (such as reverse path checking) must be 580 implemented in the IPv6 transit network (including AFXLIBR nodes) 581 to prevent spoofing on embedded IPv4 addresses, which, otherwise, 582 might be used as source addresses of malicious packets. 584 o If firewalls are used in IPv4 and/or IPv6 networks, the 585 configuration on the routers must be consistent so there are no 586 holes in the IPv4 address filtering. 588 The details of security handling for this engineering practice are 589 beyond the scope of this document. 591 12. IANA Considerations 593 No new IANA assignments are required for this document. 595 13. Acknowledgements 597 Many thanks to Acee Lindem, Dan Wing, Joel Halpern, Mike Shand and 598 Brian Carpenter for their comments. 600 14. References 602 14.1. Normative References 604 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 605 Requirement Levels", BCP 14, RFC 2119, March 1997. 607 [RFC4576] Rosen, E., Psenak, P., and P. Pillay-Esnault, "Using a 608 Link State Advertisement (LSA) Options Bit to Prevent 609 Looping in BGP/MPLS IP Virtual Private Networks (VPNs)", 610 RFC 4576, June 2006. 612 [RFC5565] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh 613 Framework", RFC 5565, June 2009. 615 [RFC5838] Lindem, A., Mirtorabi, S., Roy, A., Barnes, M., and R. 616 Aggarwal, "Support of Address Families in OSPFv3", 617 RFC 5838, April 2010. 619 [RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation 620 Algorithm", RFC 6145, April 2011. 622 14.2. Informative References 624 [I-D.ietf-ospf-mt-ospfv3] 625 Mirtorabi, S. and A. Roy, "Multi-topology routing in 626 OSPFv3 (MT-OSPFv3)", draft-ietf-ospf-mt-ospfv3-03 (work in 627 progress), July 2007. 629 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 630 for OSPFv3", RFC 4552, June 2006. 632 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 633 for IPv6", RFC 5340, July 2008. 635 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 636 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 637 October 2010. 639 Authors' Addresses 641 Dean Cheng 642 Huawei Technologies 643 2330 Central Expressway 644 Santa Clara, California 95050 645 USA 647 Email: dean.cheng@huawei.com 649 Mohamed Boucadair 650 France Telecom 651 Rennes, 35000 652 France 654 Email: mohamed.boucadair@orange.com 656 Alvaro Retana 657 Cisco Systems 658 7025 Kit Creek Rd. 659 Research Triangle Park, North Carolina 27709 660 USA 662 Email: aretana@cisco.com