idnits 2.17.1 draft-ietf-ospf-ipv4-embedded-ipv6-routing-14.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 2 instances of lines with non-RFC3849-compliant IPv6 addresses in the document. If these are example addresses, they should be changed. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (June 11, 2013) is 3971 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 6145 (Obsoleted by RFC 7915) -- Obsolete informational reference (is this intentional?): RFC 6506 (Obsoleted by RFC 7166) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). 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: December 13, 2013 France Telecom 6 A. Retana 7 Cisco Systems 8 June 11, 2013 10 Routing for IPv4-embedded IPv6 Packets 11 draft-ietf-ospf-ipv4-embedded-ipv6-routing-14 13 Abstract 15 This document describes a routing scenario where IPv4 packets are 16 transported over an IPv6 network, based on RFCs 6145 and 6052, along 17 with a separate OSPFv3 routing table for IPv4-embedded IPv6 routes in 18 the IPv6 network. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on December 13, 2013. 37 Copyright Notice 39 Copyright (c) 2013 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 1.1. The Scenario . . . . . . . . . . . . . . . . . . . . . . 3 56 1.2. Routing Solution per RFC5565 . . . . . . . . . . . . . . 4 57 1.3. An Alternative Routing Solution with OSPFv3 . . . . . . . 4 58 1.4. OSPFv3 Routing with a Specific Topology . . . . . . . . . 6 59 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 6 60 3. Provisioning . . . . . . . . . . . . . . . . . . . . . . . . 6 61 3.1. Deciding the IPv4-embedded IPv6 Topology . . . . . . . . 6 62 3.2. Maintaining a Dedicated IPv4-embedded IPv6 Routing Table 7 63 4. IP Packets Translation . . . . . . . . . . . . . . . . . . . 8 64 4.1. Address Translation . . . . . . . . . . . . . . . . . . . 8 65 5. Advertising IPv4-embedded IPv6 Routes . . . . . . . . . . . . 8 66 5.1. Advertising IPv4-embedded IPv6 Routes through an IPv6 67 Transit Network . . . . . . . . . . . . . . . . . . . . . 9 68 5.1.1. Routing Metrics . . . . . . . . . . . . . . . . . . . 9 69 5.1.2. Forwarding Address . . . . . . . . . . . . . . . . . 9 70 5.2. Advertising IPv4 Addresses into Client Networks . . . . . 9 71 6. Aggregation on IPv4 Addresses and Prefixes . . . . . . . . . 10 72 7. Forwarding . . . . . . . . . . . . . . . . . . . . . . . . . 10 73 8. Backdoor Connections . . . . . . . . . . . . . . . . . . . . 11 74 9. Prevention of Loops . . . . . . . . . . . . . . . . . . . . . 11 75 10. MTU Issues . . . . . . . . . . . . . . . . . . . . . . . . . 11 76 11. Security Considerations . . . . . . . . . . . . . . . . . . . 11 77 12. Operational Considerations . . . . . . . . . . . . . . . . . 12 78 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 79 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 80 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 81 15.1. Normative References . . . . . . . . . . . . . . . . . . 13 82 15.2. Informative References . . . . . . . . . . . . . . . . . 14 83 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 85 1. Introduction 87 This document describes a routing scenario where IPv4 packets are 88 transported over an IPv6 network, based on [RFC6145] and [RFC6052], 89 along with a separate OSPFv3 routing table for IPv4-embedded IPv6 90 routes in the IPv6 network. This document does not introduce any new 91 IPv6 transition mechanism. 93 In this document the following terminology is used: 95 o An IPv4-embedded IPv6 address denotes an IPv6 address which 96 contains an embedded 32-bit IPv4 address constructed according to 97 the rules defined in [RFC6052]. 99 o IPv4-embedded IPv6 packets are packets of which destination 100 addresses are IPv4-embedded IPv6 addresses. 102 o AFBR (Address Family Border Router, [RFC5565]) refers to an edge 103 router, which supports both IPv4 and IPv6 address families, but 104 the backbone network it connects to only supports either the IPv4 105 or IPv6 address family. 107 o AFXLBR (Address Family Translation Border Router) is defined in 108 this document. It refers to a border router that supports both 109 IPv4 and IPv6 address families, located on the boundary of an 110 IPv4-only network and an IPv6-only network, and is capable of 111 performing IP header translation between IPv4 and IPv6 according 112 to [RFC6145]. 114 1.1. The Scenario 116 Due to exhaustion of public IPv4 addresses, there has been a 117 continuing effort within the IETF on IPv6 transitional techniques. 118 In the course of the transition, it is certain that networks based on 119 IPv4 and IPv6 technologies respectively, will co-exist at least for 120 some time. One scenario of this co-existence is the inter-connection 121 of IPv4-only and IPv6-only networks, and in particular, when an 122 IPv6-only network serves as inter-connection between several 123 segregated IPv4-only networks. In this scenario, IPv4 packets are 124 transported over the IPv6 network between IPv4 networks. In order to 125 forward an IPv4 packet from a source IPv4 network to the destination 126 IPv4 network, IPv4 reachability information must be exchanged between 127 the IPv4 networks by some mechanism. 129 In general, running an IPv6-only network would reduce operational 130 expenditure and optimize the operation compared to IPv4-IPv6 dual- 131 stack environment. Some solutions have been proposed to allow 132 delivery of IPv4 services over an IPv6-only network. This document 133 specifies an engineering technique that separates the routing table 134 dedicated to IPv4-embedded IPv6 destinations from the routing table 135 used for native IPv6 destinations. 137 OSPFv3 is designed to support multiple instances. Maintaining a 138 separate routing table for IPv4-embedded IPv6 routes would simplify 139 the implementation, trouble shooting and operation; it also prevents 140 overload of the native IPv6 routing table. A separate routing table 141 can be generated from a separate routing instance. 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 148 P(rovider) Routers in the core only support IPv6 but the AFBRs 149 (Address Family Border Routers) support IPv4 on interfaces facing 150 IPv4 client networks, and IPv6 on interfaces facing the core. The 151 routing solution defined in [RFC5565] for this scenario is to run 152 i-BGP among AFBRs to exchange IPv4 routing information in the core, 153 and the IPv4 packets are forwarded from one IPv4 client network to 154 the other through a softwire using tunneling technology such as MPLS 155 LSP, GRE, 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 inter-connected by an IPv6 162 network. The IPv6 network and the inter-connected IPv4 networks may 163 or may not belong to the same Autonomous System. We refer to the 164 border node on the boundary of an IPv4 client network and the IPv6 165 network as an Address Family Translation Border Router (AFXLBR), 166 which supports both the IPv4 and IPv6 address families, and is 167 capable of translating an IPv4 packet to an IPv6 packet, and vice 168 versa, according to [RFC6145]. The described scenario is illustrated 169 in Figure 1. 171 +--------+ +--------+ 172 | IPv4 | | IPv4 | 173 | Client | | Client | 174 | Network| | Network| 175 +--------+ +--------+ 176 | \ / | 177 | \ / | 178 | \ / | 179 | X | 180 | / \ | 181 | / \ | 182 | / \ | 183 +--------+ +--------+ 184 | AFXLBR | | AFXLBR | 185 +--| IPv4/6 |---| IPv4/6 |--+ 186 | +--------+ +--------+ | 187 +--------+ | | +--------+ 188 | IPv6 | | | | IPv6 | 189 | Client |----| |----| Client | 190 | Network| | IPv6 | | Network| 191 +--------+ | only | +--------+ 192 | | 193 | +--------+ +--------+ | 194 +--| AFXLBR |---| AFXLBR |--+ 195 | IPv4/6 | | IPv4/6 | 196 +--------+ +--------+ 197 | \ / | 198 | \ / | 199 | \ / | 200 | X | 201 | / \ | 202 | / \ | 203 | / \ | 204 +--------+ +--------+ 205 | IPv4 | | IPv4 | 206 | Client | | Client | 207 | Network| | Network| 208 +--------+ +--------+ 210 Figure 1: Segregated IPv4 Networks Inter-connected by an IPv6 Network 212 Since the scenario occurs most commonly within an organization, an 213 IPv6 prefix can be locally allocated and used by AFXLBRs to construct 214 IPv4-embedded IPv6 addresses according to [RFC6052]. The embedded 215 IPv4 address or prefix belongs to an IPv4 client network that is 216 connected to the AFXLBR. An AFXLBR injects IPv4-embedded IPv6 217 addresses and prefixes into the IPv6 network using OSPFv3, and it 218 also installs IPv4-embedded IPv6 routes advertised by other AFXLBRs. 220 When an AFXLBR receives an IPv4 packet from a locally connected IPv4 221 client network and destined to a remote IPv4 client network, it 222 translates the IPv4 header to the relevant IPv6 header according to 223 [RFC6145], and in that process, source and destination IPv4 address 224 are translated into IPv4-embedded IPv6 addresses, respectively, 225 according to [RFC6052]. The resulting IPv6 packet is then forwarded 226 to the AFXLBR that connects to the destination IPv4 client network. 227 The remote AFXLBR derives the IPv4 source and destination addresses 228 from the IPv4-embedded IPv6 addresses, respectively, according to 229 [RFC6052], and translates the header of the received IPv6 packet to 230 the relevant IPv4 header according to [RFC6145]. The resulting IPv4 231 packet is then forwarded according to the IPv4 routing table 232 maintained on the AFXLBR. 234 There are use cases where the proposed routing solution is useful. 235 One case is that some border nodes do not participate in i-BGP for 236 routes exchange, or i-BGP is not used at all. Another case is when 237 tunnels are not deployed in the IPv6 network, or native IPv6 238 forwarding is preferred. Note that with this routing solution, the 239 IPv4 and IPv6 header translation performed in both directions by the 240 AFXLBR is stateless. 242 1.4. OSPFv3 Routing with a Specific Topology 244 In general, IPv4-embedded IPv6 packets can be forwarded just like 245 native IPv6 packets with OSPFv3 running in the IPv6 network. 246 However, this would require IPv4-embedded IPv6 routes be flooded 247 throughout the entire IPv6 network and stored on every router. This 248 is not desirable from the scaling perspective. Moreover, since all 249 IPv6 routes are stored in the same routing table, it would be 250 inconvenient to manage the resource required for routing and 251 forwarding based on traffic category, if so desired. 253 To improve the situation, a separate OSPFv3 routing table can be 254 constructed that is dedicated to the IPv4-embedded IPv6 topology, and 255 that table is solely used for routing IPv4-embedded IPv6 packets in 256 the IPv6 network. The IPv4-embedded IPv6 topology includes all the 257 participating AFXLBR routers and a set of P Routers providing 258 redundant connectivity with alternate routing paths. 260 To realize this, a separate OSPFv3 instance is configured in the IPv6 261 network according to [RFC5838]. This instance operates on all 262 participating AFXLBR and a set of P routers that inter-connecting 263 them. As a result, there would be a dedicated IPv4-embedded IPv6 264 topology that is maintained on all these routers along with a 265 dedicated IPv4-embedded IPv6 routing table. This routing table in 266 the IPv6 network is solely for forwarding IPv4-embedded IPv6 packets. 268 This document elaborates on how configuration is done with this 269 method and related routing issues. 271 This document only focuses on unicast routing for IPv4-embedded IPv6 272 packets using OSPFv3. 274 2. Requirements Language 276 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 277 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 278 document are to be interpreted as described in [RFC2119]. 280 3. Provisioning 282 3.1. Deciding the IPv4-embedded IPv6 Topology 283 Before deploying configurations that use a separate OSPFv3 routing 284 table for IPv4-embedded IPv6 addresses and prefixes, a decision must 285 be made on the set of routers and their interfaces in the IPv6 286 network that should be part of the IPv4-embedded IPv6 topology. 288 For the purpose of this IPv4-embedded IPv6 topology, all AFXLBRs that 289 connect to IPv4 client networks MUST be members of this topology. An 290 AFXLBR MUST have at least one connection with a P Router in the IPv6 291 network or another AFXLBR. 293 The IPv4-embedded IPv6 topology is a sub-topology of the entire IPv6 294 network, and if all routers (including AFXLBRs and P routers) and all 295 their interfaces are included, the two topologies converge. 296 Generally speaking, when this sub-topology contains more inter- 297 connected P Routers, there would be more routing paths across the 298 IPv6 network from one IPv4 client network to the other; however, this 299 requires more routers in the IPv6 network to participate in 300 IPv4-embedded IPv6 routing. In any case, the IPv4-embedded IPv6 301 topology MUST be continuous with no partitions. 303 3.2. Maintaining a Dedicated IPv4-embedded IPv6 Routing Table 305 In an IPv6 network, in order to maintain a separate IPv6 routing 306 table that contains routes for IPv4-embedded IPv6 destinations only, 307 OSPFv3 needs to use the mechanism defined in [RFC5838]. 309 It is assumed that the IPv6 network that is inter-connected with IPv4 310 networks in this document is under one administration and as such, an 311 OSPFv3 instance ID (IID) is allocated locally and used for OSPFv3 312 operation dedicated to unicast IPv4-embedded IPv6 routing in an IPv6 313 network. This IID is configured on OSPFv3 router interfaces that 314 participate in the IPv4-embedded IPv6 topology. 316 The range for a locally configured OSPFv3 IID is allocated from 192 317 to 255, inclusive, as "Private Use" per 318 [I-D.ietf-ospf-ospfv3-iid-registry-update]. This IID must be used to 319 encode the "Instance ID" field in the packet header of OSPFv3 packets 320 associated with the OSPFv3 instance. 322 In addition, the "AF" bit in the OSPFv3 Option field MUST be set. 324 During Hello packet processing, an adjacency may only be established 325 when the received Hello packet contains the same Instance ID as 326 configured on the receiving OSPFv3 interface. This insures that only 327 interfaces configured as part of the OSPFv3 unicast IPv4-embedded 328 IPv6 topology are used for IPv4-embedded IPv6 unicast routing. 330 For more details, the reader is referred to [RFC5838]. 332 4. IP Packets Translation 334 When transporting IPv4 packets across an IPv6 network with the 335 mechanism described above (Section 3.2), an IPv4 packet is translated 336 to an IPv6 packet at the ingress AFXLBR, and the IPv6 packet is 337 translated back to an IPv4 packet at the egress AFXLBR. The IP 338 packet header translation is accomplished in stateless manner 339 according to rules specified in [RFC6145], with the address 340 translation details explained in the next sub-section. 342 4.1. Address Translation 344 Prior to address translation, an IPv6 prefix is allocated by the 345 operator and it is used to form IPv4-embedded IPv6 addresses. 347 The IPv6 prefix can either be the well-known IPv6 prefix (WKP) 348 64:ff9b::/96, or a network-specific prefix that is unique to the 349 organization; and for the latter case, the IPv6 prefix length may be 350 32, 40, 48, 56 or 64. In either case, this IPv6 prefix is used 351 during the address translation between an IPv4 address and an 352 IPv4-embedded IPv6 address, as described in [RFC6052]. 354 During translation from an IPv4 header to an IPv6 header at an 355 ingress AFXLBR, the source IPv4 address and destination IPv4 address 356 are translated into the corresponding IPv6 source address and 357 destination IPv6 address, respectively, and during translation from 358 an IPv6 header to an IPv4 header at an egress AFXLBR, the source IPv6 359 address and destination IPv6 address are translated into the 360 corresponding IPv4 source address and destination IPv4 address, 361 respectively. Note that the address translation is accomplished in a 362 stateless manner. 364 When a well-known IPv6 prefix (WKP) is used, [RFC6052] allows only 365 global IPv4 addresses to be embedded in the IPv6 address. An IPv6 366 address composed with a WKP and a non-global IPv4 address is hence 367 invalid, and packets that contain such address received by an AFXLBR 368 are dropped. 370 In the case where both the IPv4 client networks and the IPv6 transit 371 network belong to the same organization, non-global IPv4 addresses 372 may be used with a network-specific prefix [RFC6052]. 374 5. Advertising IPv4-embedded IPv6 Routes 376 In order to forward IPv4 packets to the proper destination across an 377 IPv6 network, IPv4 reachability needs to be disseminated throughout 378 the IPv6 network and this is performed by AFXLBRs that connect to 379 IPv4 client networks using OSPFv3. 381 With the scenario described in this document, i.e., a set of AFXLBRs 382 that inter-connect a bunch of IPv4 client networks with an IPv6 383 network, the IPv4 networks and IPv6 networks belong to the same or 384 separate Autonomous Systems, and as such, these AFXLBRs behave as AS 385 Boundary Routers (ASBRs). 387 5.1. Advertising IPv4-embedded IPv6 Routes through an IPv6 Transit 388 Network 390 IPv4 addresses and prefixes in an IPv4 client network are translated 391 into IPv4-embedded IPv6 addresses and prefixes, respectively, using 392 the IPv6 prefix allocated by the operator and the method specified in 393 [RFC6052]. These routes are then advertised by one or more attached 394 ASBRs into the IPv6 transit network using AS-External-LSAs [RFC5340], 395 i.e., with advertising scope comprising the entire Autonomous System. 397 5.1.1. Routing Metrics 399 By default, the metric in an AS-External-LSA that carries an 400 IPv4-embedded IPv6 address or prefixes is a Type 1 external metric, 401 which is comparable to the link state metric and we assume that in 402 most cases, OSPFv2 is used in client IPv4 networks. This metric is 403 added to the metric of the intra-AS path to the ASBR during the 404 OSPFv3 route calculation. Through ASBR configuration, the metric can 405 be set to a Type 2 external metric, which is considered much larger 406 than the metric for any intra-AS path. Refer to the OSPFv3 407 specification [RFC5340] for more detail. In either case, an external 408 metric may take the same value as in an IPv4 network (using OSPFv2 or 409 another routing protocol), but may also be specified based on some 410 routing policy; the details of which are outside of the scope of this 411 document. 413 5.1.2. Forwarding Address 415 If the "Forwarding Address" field of an OSPFv3 AS-External-LSA is 416 used to carry an IPv6 address, that must also be an IPv4-embedded 417 IPv6 address where the embedded IPv4 address is the destination 418 address in an IPv4 client network. However, since an AFXLBR sits on 419 the border of an IPv4 network and an IPv6 network, it is RECOMMENDED 420 that the "Forwarding Address" field is not used, so that the AFXLBR 421 can make the forwarding decision based on its own IPv4 routing table. 423 5.2. Advertising IPv4 Addresses into Client Networks 425 IPv4-embedded IPv6 routes injected into the IPv6 network from one 426 IPv4 client network MAY be advertised into another IPv4 client 427 network, after the associated destination addresses and prefixes are 428 translated back to IPv4 addresses and prefixes, respectively. This 429 operation is similar to normal OSPFv3 operation, wherein an AS- 430 External-LSA can be advertised in a non-backbone area by default. 432 An IPv4 client network can limit which advertisements it receives 433 through configuration. 435 For the purpose of this document, IPv4-embedded IPv6 routes MUST NOT 436 be advertised into any IPv6 client networks that also connected to 437 the IPv6 transit network. 439 6. Aggregation on IPv4 Addresses and Prefixes 441 In order to reduce the amount of LSAs that are injected to the IPv6 442 network, an implementation should provide mechanisms to aggregate 443 IPv4 addresses and prefixes at AFXLBR prior to advertisement as 444 IPv4-embedded IPv6 addresses and prefixes. In general, the 445 aggregation practice should be based on routing policy, which is 446 outside of the scope of this document. 448 7. Forwarding 450 There are three cases in forwarding IP packets in the scenario 451 described in this document: 453 1. On an AFXLBR, if an IPv4 packet that is received on an interface 454 connecting to an IPv4 segregated client network with a 455 destination IPv4 address belonging to another IPv4 client 456 network, the header of the packet is translated to the 457 corresponding IPv6 header as described in Section 4, and the 458 packet is then forwarded to the destination AFXLBR that 459 advertised the IPv4-embedded IPv6 address into the IPv6 network. 461 2. On an AFXLBR, if an IPv4-embedded IPv6 packet is received and the 462 embedded destination IPv4 address is in its IPv4 routing table, 463 the header of the packet is translated to the corresponding IPv4 464 header as described in Section 4, and the packet is then 465 forwarded accordingly. 467 3. On any router that is within the IPv4-embedded IPv6 topology 468 subset of the IPv6 network, if an IPv4-embedded IPv6 packet is 469 received and a route is found in the IPv4-embedded IPv6 routing 470 table, the packet is forwarded to the IPv6 next-hop just like the 471 handling for a normal IPv6 packet, without any translation. 473 The classification of IPv4-embedded IPv6 packet is according to the 474 IPv6 prefix of the destination address, which is either the Well 475 Known Prefix (i.e., 64:ff9b::/96) or locally allocated as defined in 476 [RFC6052]. 478 8. Backdoor Connections 480 In some deployments, IPv4 client networks are inter-connected across 481 the IPv6 network, but also directly connected to each other. The 482 direct connections between IPv4 client networks, as sometimes called 483 "backdoor" connections, can certainly be used to transport IPv4 484 packets between IPv4 client networks. In general, backdoor 485 connections are preferred over the IPv6 network since there requires 486 no address family translation. 488 9. Prevention of Loops 490 If an LSA sent from an AFXLBR into a client network could then be 491 received by another AFXLBR, it would be possible for routing loops to 492 occur. To prevent loops, an AFXLBR MUST set the DN-bit [RFC4576] in 493 any LSA that it sends to a client network. The AFXLBR MUST also 494 ignore any LSA received from a client network that already has the 495 DN-bit sent. 497 10. MTU Issues 499 In the IPv6 network, there are no new MTU issues introduced by this 500 document. If a separate OSPFv3 instance (per [RFC5838]) is used for 501 IPv4-embedded IPv6 routing, the MTU handling in the IPv6 network is 502 the same as that of the default OSPFv3 instance. 504 However, the MTU in the IPv6 network may be different than that of 505 IPv4 client networks. Since an IPv6 router will never fragment a 506 packet, the packet size of any IPv4-embedded IPv6 packet entering the 507 IPv6 network must be equal to or less than the MTU of the IPv6 508 network. In order to achieve this requirement, it is recommended 509 that AFXLBRs perform IPv6 path discovery among themselves and the 510 resulting MTU, after taking into account of the difference between 511 the IPv4 header length and the IPv6 header length, must be 512 "propagated" into IPv4 client networks, e.g., included in the OSPFv2 513 Database Description packet. 515 The details of passing the proper MTU into IPv4 client networks are 516 beyond the scope of this document. 518 11. Security Considerations 520 There are several security aspects that require attention in the 521 deployment practice described in this document. 523 In the OSPFv3 transit network, the security considerations for OSPFv3 524 are handled as usual, and in particular, authentication mechanisms 525 described in [RFC6506] can be deployed. 527 When a separate OSPFv3 instance is used to support IPv4-embedded IPv6 528 routing, the same Security Association (SA) (refer to [RFC4552] ) 529 MUST be used by the embedded IPv4 address instance as other instances 530 utilizing the same link as specified in [RFC5838]. 532 Security considerations as documented in [RFC6052] must also be 533 thought through with proper implementation including the following: 535 o The IPv6 prefix that is used to carry an embedded IPv4 address 536 (refer to Section 4.1) must be configured by the authorized 537 operator on all participating AFXLBRs in a secure manner. This is 538 to help prevent an malicious attack resulting in network 539 disruption, denial of service, and possible information 540 disclosure. 542 o Effective mechanisms (such as reverse path checking) must be 543 implemented in the IPv6 transit network (including AFXLIBR nodes) 544 to prevent spoofing on embedded IPv4 addresses, which, otherwise, 545 might be used as source addresses of malicious packets. 547 o If firewalls are used in IPv4 and/or IPv6 networks, the 548 configuration on the routers must be consistent so there are no 549 holes in the IPv4 address filtering. 551 The details of security handling are beyond the scope of this 552 document. 554 12. Operational Considerations 556 This document puts together some mechanisms based on existing 557 technologies developed by IETF as an integrated solution to transport 558 IPv4 packets over an IPv6 network using a separate OSPFv3 routing 559 table. There are several aspects that require attention for the 560 deployment and operation. 562 The tunnel-based solution documented in [RFC5565] and the solution 563 proposed in this document are both used for transporting IPv4 packets 564 over an IPv6 network, with different mechanisms. The two methods are 565 not related to each other, and they can co-exist in the same network 566 if so deployed, without any conflict. 568 If one approach is to be deployed, it is the operator's decision for 569 the choice. Note that each approach has its own characteristics and 570 requirements. E.g., the tunnel-based solution requires a mesh of 571 inter-AFBR softwires (tunnels) spanning the IPv6 network, as well as 572 iBGP to exchange routes between AFBRs ([RFC5565]); the approach in 573 this document requires AFXLBR capable of performing IPv4-IPv6 packet 574 header translation per [RFC6145]. 576 To deploy the solution as documented here, there requires some 577 configurations. An IPv6 prefix must first be chosen that is used to 578 form all the IPv4-embedded IPv6 addresses and prefixes advertised by 579 AFXLBR in the IPv6 network; the detail is referred to Section 4.1. 580 The IPv4-embedded IPv6 routing table is created by using a separate 581 OSPFv3 instance in the IPv6 network, the configuration is 582 accomplished according to [RFC5838], as described in Section 3.2. 584 Note this document does not change any behavior of OSPFv3, and the 585 existing or common practice should apply, in the context of 586 scalability. For example, the amount of routes that are advertised 587 by OSPFv3 is one key concern. With the solution as described in this 588 document, IPv4-embedded IPv6 addresses and prefixes will be injected 589 by AFXLBR into some part of the IPv6 network (see Section 3.1 for 590 details), and a separate routing table will be used for IPv4-embedded 591 IPv6 routing. Care must be taken during the network design, such 592 that 1) aggregation are performed on IPv4 addresses and prefixes 593 before being advertised in the IPv6 network as described in 594 Section 6, and 2) estimates are made as the amount of IPv4-embedded 595 IPv6 routes that would be disseminated in the IPv6 network, and the 596 size of the separate OSPFv3 routing table. 598 13. IANA Considerations 600 No new IANA assignments are required for this document. 602 14. Acknowledgements 604 Many thanks to Acee Lindem, Dan Wing, Joel Halpern, Mike Shand and 605 Brian Carpenter for their comments. 607 15. References 609 15.1. Normative References 611 [I-D.ietf-ospf-ospfv3-iid-registry-update] 612 Retana, A. and D. Cheng, "OSPFv3 Instance ID Registry 613 Update", draft-ietf-ospf-ospfv3-iid-registry-update-04 614 (work in progress), April 2013. 616 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 617 Requirement Levels", BCP 14, RFC 2119, March 1997. 619 [RFC4576] Rosen, E., Psenak, P., and P. Pillay-Esnault, "Using a 620 Link State Advertisement (LSA) Options Bit to Prevent 621 Looping in BGP/MPLS IP Virtual Private Networks (VPNs)", 622 RFC 4576, June 2006. 624 [RFC5565] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh 625 Framework", RFC 5565, June 2009. 627 [RFC5838] Lindem, A., Mirtorabi, S., Roy, A., Barnes, M., and R. 628 Aggarwal, "Support of Address Families in OSPFv3", RFC 629 5838, April 2010. 631 [RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation 632 Algorithm", RFC 6145, April 2011. 634 15.2. Informative References 636 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 637 for OSPFv3", RFC 4552, June 2006. 639 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 640 for IPv6", RFC 5340, July 2008. 642 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 643 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 644 October 2010. 646 [RFC6506] Bhatia, M., Manral, V., and A. Lindem, "Supporting 647 Authentication Trailer for OSPFv3", RFC 6506, February 648 2012. 650 Authors' Addresses 652 Dean Cheng 653 Huawei Technologies 654 2330 Central Expressway 655 Santa Clara, California 95050 656 USA 658 Email: dean.cheng@huawei.com 660 Mohamed Boucadair 661 France Telecom 662 Rennes 35000 663 France 665 Email: mohamed.boucadair@orange.com 666 Alvaro Retana 667 Cisco Systems 668 7025 Kit Creek Rd. 669 Research Triangle Park, North Carolina 27709 670 USA 672 Email: aretana@cisco.com