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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT J. De Clercq 3 Alcatel 4 D. Ooms 5 OneSparrow 6 S. Prevost 7 BTexact 8 F. Le Faucheur 9 Cisco 10 May, 2005 11 Expires November, 2005 13 Connecting IPv6 Islands over IPv4 MPLS 14 using IPv6 Provider Edge Routers (6PE) 16 Status of this Memo 18 By submitting this Internet-Draft, each author represents that any 19 applicable patent or other IPR claims of which he or she is aware 20 have been or will be disclosed, and any of which he or she becomes 21 aware will be disclosed, in accordance with Section 6 of BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF), its areas, and its working groups. Note that 25 other groups may also distribute working documents as Internet- 26 Drafts. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 The list of current Internet-Drafts can be accessed at 34 http://www.ietf.org/ietf/1id-abstracts.txt 36 The list of Internet-Draft Shadow Directories can be accessed at 37 http://www.ietf.org/shadow.html 39 Abstract 41 This document explains how to interconnect IPv6 islands over a 42 Multi-Protocol Label Switching (MPLS)-enabled IPv4 cloud. This 43 approach relies on IPv6 Provider Edge routers (6PE) which are Dual 44 Stack in order to connect to IPv6 islands and to the MPLS core which 45 is only required to run IPv4 MPLS. The 6PE routers exchange the IPv6 46 reachability information transparently over the core using the 47 Multi-Protocol Border Gateway Protocol (MP-BGP) over IPv4. In doing 48 so, the BGP Next Hop field is used to convey the IPv4 address of the 49 6PE router so that dynamically established IPv4-signaled MPLS Label 50 Switched Paths (LSPs) can be used without explicit tunnel 51 configuration. 53 Requirements 55 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 56 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 57 document are to be interpreted as described in RFC 2119 [KEYWRD]. 59 1. Introduction 61 There are several approaches for providing IPv6 connectivity over an 62 MPLS core network [ISPSCEN] including (i) requiring that MPLS 63 networks support setting up IPv6-signaled LSPs and set up IPv6 64 connectivity by using those, (ii) use only configured tunneling over 65 IPv4-signaled LSPs, or (iii) use the IPv6 Provider Edge (6PE) 66 approach. 68 This document specifies operations of the 6PE approach for 69 interconnection of IPv6 islands over an IPv4 MPLS cloud. The approach 70 requires the edge routers that are connected to IPv6 islands to be 71 Dual Stack MP-BGP-speaking routers while the core routers are only 72 required to run IPv4 MPLS. The approach uses MP-BGP over IPv4, relies 73 on identification of the 6PE routers by their IPv4 address and uses 74 IPv4-signaled MPLS LSPs that don't require any explicit tunnel 75 configuration. 77 Throughout this document, the terminology of [IPV6] and [VPN] is 78 used. 80 In this document an 'IPv6 island' is a network running native IPv6 as 81 per [IPv6]. A typical example of an IPv6 island would be a customer's 82 IPv6 site connected via its IPv6 Customer Edge (CE) router to one (or 83 more) Dual Stack Provider Edge router(s) of a Service Provider. These 84 IPv6 Provider Edge routers (6PE) are connected to an IPv4 MPLS core 85 network. 87 +--------+ 88 |site A CE---+ +-----------------+ 89 +--------+ | | | +--------+ 90 6PE-+ IPv4 MPLS core +-6PE--CE site C | 91 +--------+ | | | +--------+ 92 |site B CE---+ +-----------------+ 93 +--------+ 95 IPv6 islands IPv4 cloud IPv6 island 96 <-------------><---------------------><--------------> 98 The interconnection method described in this document typically 99 applies to an ISP that has an IPv4 MPLS network and is familiar with 100 BGP (possibly already offering BGP/MPLS VPN services) and that wants 101 to offer IPv6 services to some of its customers. However, the ISP 102 may not (yet) want to upgrade its network core to IPv6 nor use only 103 IPv6-over-IPv4 tunnelling. With the 6PE approach described here, the 104 provider only has to upgrade some Provider Edge (PE) routers to Dual 105 Stack operations so they behave as 6PE routers (and route reflectors 106 if those are used for exchange of IPv6 reachability among 6PE 107 routers) while leaving the IPv4 MPLS core routers untouched. These 108 6PE routers provide connectivity to IPv6 islands. They may also 109 provide other services simultaneously (IPv4 connectivity, IPv4 L3VPN 110 services, L2VPN services, etc.). Also with the 6PE approach, no 111 tunnels need to be explicitly configured, and no IPv4 headers need to 112 be inserted in front of the IPv6 packets. 114 The ISP obtains IPv6 connectivity to its peers and upstreams using 115 means outside of the scope of this memo, and its 6PE routers 116 readvertise it over the IPv4 MPLS core with MP-BGP. 118 The interface between the edge router of the IPv6 island (Customer 119 Edge (CE) router) and the 6PE router is a native IPv6 interface which 120 can be physical or logical. A routing protocol (IGP or EGP) may run 121 between the CE router and the 6PE router for the distribution of IPv6 122 reachability information. Alternatively, static routes and/or a 123 default route may be used on the 6PE router and the CE router to 124 control reachability. An IPv6 island may connect to the provider 125 network over more than one interface. 127 The 6PE approach described in this document can be used for customers 128 that already have an IPv4 service from the network provider and 129 additionally require an IPv6 service, as well as for customers that 130 require only IPv6 connectivity. 132 The scenario is also described in [ISPSCEN]. 134 Note that the 6PE approach specified in this document provides global 135 IPv6 reachability. Support of IPv6 VPNs is not within the scope of 136 this document and is addressed in [V6VPN]. 138 2. Protocol Overview 140 Each IPv6 site is connected to at least one Provider Edge router that 141 is located on the border of the IPv4 MPLS cloud. We call such a 142 router a 6PE router. The 6PE router MUST be dual stack IPv4 and IPv6. 143 The 6PE router MUST be configurable with at least one IPv4 address on 144 the IPv4 side and at least one IPv6 address on the IPv6 side. The 145 configured IPv4 address needs to be routable in the IPv4 cloud, and 146 there needs to be a label bound via an IPv4 label distribution 147 protocol to this IPv4 route. 149 As a result of this, every considered 6PE router knows which MPLS 150 label to use to send packets to any other 6PE router. Note that an 151 MPLS network offering BGP/MPLS IP VPN services already fulfills these 152 requirements. 154 No extra routes need to be injected in the IPv4 cloud. 156 We call the 6PE router receiving IPv6 packets from an IPv6 site an 157 Ingress 6PE router (relative to these IPv6 packets). We call a 6PE 158 router forwarding IPv6 packets to an IPv6 site an Egress 6PE router 159 (relative to these IPv6 packets). 161 Interconnecting IPv6 islands over an IPv4 MPLS cloud takes place 162 through the following steps: 164 (1) Exchange IPv6 reachability information among 6PE routers with 165 MP-BGP [MP-BGP-v6]: 167 The 6PE routers MUST exchange the IPv6 prefixes over MP-BGP 168 sessions as per [MP-BGP-v6] running over IPv4. The MP-BGP AFI used 169 MUST be IPv6 (value 2). In doing so, the 6PE routers convey their 170 IPv4 address as the BGP Next Hop for the advertised IPv6 prefixes. 171 Since MP-BGP assumes that the BGP Next Hop is of the same address 172 family as the NLRI, the IPv4 address needs to be embedded in an 173 IPv6 format. The IPv4-mapped IPv6 address is defined in [V6ADDR] 174 as an "address type used to represent the addresses of IPv4 nodes 175 as IPv6 addresses" which precisely fits the above purpose. 176 Therefore, the IPv4 address of the egress 6PE router MUST be 177 encoded as an IPv4-mapped IPv6 address in the BGP Next Hop field. 178 In addition, the 6PE MUST bind a label to the IPv6 prefix as per 179 [LABEL]. The SAFI used in MP-BGP MUST be the "label" SAFI (value 180 4) as defined in [LABEL]. Rationale for this and label allocation 181 policies are discussed in section 3. 183 (2) Transport IPv6 packets from Ingress 6PE router to Egress 6PE 184 router over IPv4-signaled LSPs: 186 The Ingress 6PE router MUST forward IPv6 data over the IPv4- 187 signaled LSP towards the Egress 6PE router identified by the IPv4 188 address advertised in the IPv4-mapped IPv6 address of the BGP Next 189 Hop for the corresponding IPv6 prefix. 191 As required by BGP specification, PE routers form a full peering mesh 192 unless Route Reflectors are used. 194 3. Transport over IPv4-signaled LSPs and IPv6 label binding 196 In this approach, the IPv4-mapped IPv6 addresses allow a 6PE router 197 that has to forward an IPv6 packet to automatically determine the 198 IPv4-signaled LSP to use for a particular IPv6 destination by looking 199 at the MP-BGP routing information. 201 The IPv4-signaled LSPs can be established using any existing 202 technique (LDP, RSVP-TE, ...). 204 When tunneling IPv6 packets over the IPv4 MPLS backbone, rather than 205 successively prepend an IPv4 header and then perform label imposition 206 based on the IPv4 header, the ingress 6PE Router MUST directly 207 perform label imposition of the IPv6 header without prepending any 208 IPv4 header. The (outer) label imposed MUST correspond to the IPv4- 209 signaled LSP starting on the ingress 6PE Router and ending on the 210 egress 6PE Router. 212 While this approach could conceptually operate in some situations 213 using a single level of labels, there are significant advantages in 214 using a second level of labels which are bound to IPv6 prefixes via 215 MP-BGP advertisements in accordance with [LABEL]. 217 For instance, use of a second level label allows Penultimate Hop 218 Popping (PHP) on the IPv4 Label Switch Router (LSR) upstream of the 219 egress 6PE router without any IPv6 capabilities/upgrade on the 220 penultimate router; this is because it still transmits MPLS packets 221 even after the PHP (instead of having to transmit IPv6 packets and 222 encapsulate them appropriately). 224 Also, an existing IPv4-signaled LSP which is using "IPv4 Explicit 225 NULL label" over the last hop (say because that LSP is already used 226 to transport IPv4 traffic with the Pipe Diff-Serv Tunneling Model as 227 defined in [MPLS-DS]) could not be used to carry IPv6 with a single 228 label since the "IPv4 Explicit NULL label" can not be used to carry 229 native IPv6 traffic (see [MPLS-STACK]), while it could be used to 230 carry labeled IPv6 traffic (see [EXP-NULL]). 232 This is why a second label is always used with the 6PE approach. 234 The label bound by MP-BGP to the IPv6 prefix indicates to the Egress 235 6PE Router that the packet is an IPv6 packet. This label advertised 236 by the Egress 6PE Router with MP-BGP MAY be an arbitrary label value 237 which identifies an IPv6 routing context or outgoing interface to 238 send the packet to, or MAY be the IPv6 Explicit Null Label. An 239 Ingress 6PE Router MUST be able to accept any such advertised label. 241 4. Crossing Multiple IPv4 Autonomous Systems 243 This section discusses the case where two IPv6 islands are connected 244 to different Autonomous Systems. 246 Like in the case of multi-AS backbone operations for IPv4 VPNs 247 described in section 10 of [VPN], three main approaches can be 248 distinguished: 250 (a) EBGP redistribution of IPv6 routes from AS to neighboring AS 252 This approach is the equivalent for exchange of IPv6 routes to 253 procedure (a) described in section 10 of [VPN] for the exchange of 254 VPN-IPv4 routes. 256 In this approach, the 6PE routers use IBGP (according to [MP-BGP-v6] 257 and [LABEL] and as described in this document for the single-AS 258 situation) to redistribute labeled IPv6 routes either to an 259 Autonomous System Border Router (ASBR) 6PE router, or to a route 260 reflector of which an ASBR 6PE router is a client. The ASBR then uses 261 EBGP to redistribute the (non-labeled) IPv6 routes to an ASBR in 262 another AS, which in turn distributes them to the 6PE routers in that 263 AS as described earlier in this specification, or perhaps to another 264 ASBR which in turn distributes them etc. 266 There may be one, or multiple, ASBR interconnection(s) across any two 267 ASes. IPv6 needs to be activated on the inter-ASBR links and each 268 ASBR 6PE router has at least one IPv6 address on the interface to 269 that link. 271 No inter-AS LSPs are used. There is effectively a separate mesh of 272 LSPs across the 6PE routers within each AS. 274 In this approach, the ASBR exchanging IPv6 routes may peer over IPv6 275 or over IPv4. The exchange of IPv6 routes MUST be carried out as per 276 [MP-BGP-v6]. 278 Note that the peering ASBR in the neighboring AS to which the IPv6 279 routes were distributed with EBGP, should in its turn redistribute 280 these routes to the 6PEs in its AS using IBGP and encoding its own 281 IPv4 address as the IPv4-mapped IPv6 BGP Next Hop. 283 (b) EBGP redistribution of labeled IPv6 routes from AS to neighboring 284 AS 286 This approach is the equivalent for exchange of IPv6 routes to 287 procedure (b) described in section 10 of [VPN] for the exchange of 288 VPN-IPv4 routes. 290 In this approach, the 6PE routers use IBGP (as described earlier in 291 this document for the single-AS situation) to redistribute labeled 292 IPv6 routes either to an Autonomous System Border Router (ASBR) 6PE 293 router, or to a route reflector of which an ASBR 6PE router is a 294 client. The ASBR then uses EBGP to redistribute the labeled IPv6 295 routes to an ASBR in another AS, which in turn distributes them to 296 the 6PE routers in that AS as described earlier in this 297 specification, or perhaps to another ASBR which in turn distributes 298 them etc. 300 There may be one, or multiple, ASBR interconnection(s) across any two 301 ASes. IPv6 may or may not be activated on the inter-ASBR links. 303 This approach requires that there be label switched paths established 304 across ASes. Hence the corresponding considerations described for 305 procedure (b) in section 10 of [VPN] apply equally to this approach 306 for IPv6. 308 In this approach, the ASBR exchanging IPv6 routes may peer over IPv4 309 or IPv6 (in which case, IPv6 obviously needs to be activated on the 310 inter-ASBR link). When peering over IPv6, the exchange of labeled 311 IPv6 routes MUST be carried out as per [MP-BGP-v6] and [LABEL]. When 312 peering over IPv4, the exchange of labeled IPv6 routes MUST be 313 carried out as per [MP-BGP-v6] and [LABEL] with encoding of the IPv4 314 address of the ASBR as an IPv4-mapped IPv6 address in the BGP Next 315 Hop field. 317 (c) Multihop EBGP redistribution of labeled IPv6 routes between 318 source and destination ASes, with EBGP redistribution of labeled IPv4 319 routes from AS to neighboring AS. 321 This approach is the equivalent for exchange of IPv6 routes to 322 procedure (c) described in section 10 of [VPN] for exchange of VPN- 323 IPv4 routes. 325 In this approach, IPv6 routes are neither maintained nor distributed 326 by the ASBR routers. The ASBR routers need not be dual stack and may 327 be IPv4/MPLS-only routers. An ASBR needs to maintain labeled IPv4 /32 328 routes to the 6PE routers within its AS. It uses EBGP to distribute 329 these routes to other ASes. ASBRs in any transit ASes will also have 330 to use EBGP to pass along the labled IPv4 /32 routes. This results in 331 the creation of an IPv4 label switched path from the ingress 6PE 332 router to the egress 6PE router. Now 6PE routers in different ASes 333 can establish multi-hop EBGP connections to each other over IPv4, and 334 can exchange labeled IPv6 routes (with an IPv4-mapped IPv6 BGP Next 335 Hop) over those connections. 337 IPv6 need not be activated on the inter-ASBR links. 339 The considerations described for procedure (c) in section 10 of [VPN] 340 with respect to possible use of multi-hop EBGP connections via 341 route-reflectors in different ASes, as well as with respect to the 342 use of a third label in case the IPv4 /32 routes for the (6)PE 343 routers are NOT made known to the P routers, apply equally to this 344 approach for IPv6. 346 This approach requires that there be IPv4 label switched paths 347 established across the ASes leading form a packet's ingress 6PE 348 router to its egress 6PE router. Hence, the considerations described 349 for procedure (c) in section 10 of [VPN] with respect to LSPs 350 spanning multiple ASes apply equally to this approach for IPv6. 352 Note also that the exchange of IPv6 routes can only start after BGP 353 has created IPv4 connectivity between the ASes. 355 5. Security Considerations 357 The extensions defined in this document allow BGP to propagate 358 reachability information about IPv6 routes over an MPLS IPv4 core 359 network. As such, no new security issues are raised beyond those that 360 already exist in BGP-4 and use of MP-BGP for IPv6. 362 The security features of BGP and corresponding security policy 363 defined in the ISP domain are applicable. 365 For the inter-AS distribution of IPv6 routes according to case (a) of 366 section 4 of this document, no new security issues are raised beyond 367 those that already exist in the use of EBGP for IPv6 [MP-BGP-v6]. 369 For the inter-AS distribution of IPv6 routes according to case (b) 370 and (c) of section 4 of this document, the procedures require that 371 there be label switched paths established across the AS boundaries. 372 Hence the appropriate trust relationships must exist between and 373 among the set of ASes along the path. Care must be taken to avoid 374 "label spoofing". To this end an ASBR 6PE SHOULD only accept labeled 375 packets from its peer ASBR 6PE if the topmost label is a label that 376 it has explicitly signaled to that peer ASBR 6PE. 378 Note that for the inter-AS distribution of IPv6 routes according to 379 case (c) of section 4 of this document, label spoofing may be more 380 difficult to prevent. Indeed, the MPLS label distributed with the 381 IPv6 routes via multi-hop EBGP is directly sent from the egress 6PE 382 to ingress 6PEs in an other AS (or through route reflectors). This 383 label is advertised transparently through the AS boundaries. When the 384 egress 6PE that sent the labeled IPv6 routes receives a data packet 385 that has this particular label on top of its stack, it may not be 386 able to verify whether the label was pushed on the stack by an 387 ingress 6PE that is allowed to do so. As such one AS may be 388 vulnerable to label spoofing in a different AS. The same issue 389 equally applies to the option (c) of section 10 of [VPN]. Just like 390 it is the case for [VPN], addressing this particular security issue 391 is for further study. 393 IANA Considerations 395 This document has no actions for IANA. 397 Acknowledgements 399 We wish to thank Gerard Gastaud and Eric Levy-Abegnoli who 400 contributed to this document, and we wish to thank Tri T. Nguyen who 401 initiated this document, but who unfortunately passed away much too 402 soon. We also thank Pekka Savola for his valuable comments and 403 suggestions. 405 Normative References 407 [IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6 408 (IPv6) Specification", RFC2460. 410 [KEYWRD] S. Bradner, Key words for use in RFCs to Indicate 411 Requirement Levels, RFC2119, March 1997. 413 [LABEL] Rekhter Y., E. Rosen, "Carrying Label Information in 414 BGP-4", RFC 3107, May 2001. 416 [MP-BGP] T. Bates, R. Chandra, D. Katz, Y. Rekhter, "Multiproto- 417 col Extensions for BGP-4", RFC 2858. 419 [MP-BGP-v6] Marques P., et al., "Use of BGP-4 Multiprotocol Exten- 420 sions for IPv6 Inter-Domain Routing", RFC 2545. 422 [V6ADDR] Deering, S., and R. Hinden, "IP Version 6 Addressing 423 Architecture", RFC 3513 425 [MPLS-STACK] Rosen E., et al., "MPLS Label Stack Encoding", RFC 3032. 427 Informative References 429 [ISPSCEN] Lind M., et al., "Scenarios and Analysis for Introducing 430 IPv6 into ISP Networks", draft-ietf-v6ops-isp- 431 scenarios-analysis, (work in progress) 433 [EXP-NULL] Rosen, E., et al., "Removing a Restriction on the use of 434 MPLS Explicit NULL", draft-rosen-mpls-explicit-null- 435 01.txt, work in progress 437 [MPLS-DS] Le Faucheur et al., "MPLS Support for DiffServ", RFC 438 3270 440 [V6VPN] De Clercq J., Ooms D., Carugi M., Le Faucheur F., "BGP- 441 MPLS VPN extension for IPv6 VPN over an IPv4 infrastruc- 442 ture", draft-ietf-l3vpn-bgp-ipv6 (work in progress). 444 [VPN] Rosen E., Rekhter Y., Brannon S., Chase C., De Clercq 445 J., Hitchin P., Marshall , Srinivasan V., "BGP/MPLS 446 VPNs", draft-ietf-l3vpn-rfc2547bis (work in progress). 448 Authors' Addresses 450 Jeremy De Clercq 451 Alcatel 452 Fr. Wellesplein 1, 2018 Antwerpen, Belgium 453 E-mail: jeremy.de_clercq@alcatel.be 455 Dirk Ooms 456 OneSparrow 457 Belegstraat 13, 2018 Antwerpen, Belgium 458 E-mail: dirk@onesparrow.com 460 Stuart Prevost 461 BTexact Technologies 462 Room 136 Polaris House, Adastral Park, 463 Martlesham Heath, Ipswich, Suffolk IP5 3RE, England 464 E-mail: stuart.prevost@bt.com 466 Francois Le Faucheur 467 Cisco Systems 468 Domaine Green Side, 400, Avenue de Roumanille, Batiment T3 469 06 410 BIOT, SOPHIA ANTIPOLIS, FRANCE 470 E-mail: flefauch@cisco.com 472 APPENDIX A 474 [RFC-editor note: remove before publication] 476 Changes 477 ngtrans history (draft-ietf-ngtrans-bgp-tunnel-0x.txt) 478 00->01: editorial changes 479 extended section 4 480 01->02: editorial changes 481 added tunnel-specific considerations 482 added case of multiple IPv4 domains between IPv6 islands 483 added discussion on v6[v4]addresses in appendix A 484 02->03: complete rewrite: it turned out that two interpretations 485 of the previous drafts existed, the two different 486 interpretations are described explicitly in this version 487 03->04: renaming of the two approaches 488 editorial changes 489 clearly indicate which part requires standards track 490 04->05: added 5.1.3 to clarify how DS-BGP routers agree on tunnel 491 type 493 v6ops history (draft-ooms-v6ops-bgp-tunnel-0x.txt) 494 05->00 individual submission: no changes. The document passed 495 ngtrans last call early 2002, but the transfer to the IESG 496 was postponed because of the reorg and closing down of 497 ngtrans. 498 00->01 no changes 499 01->02 according to v6ops mailing list discussion, the scope of 500 the document was restricted to the "MP-BGP over IPv4 using 501 LSPs" approach. 502 02->03 adopted various comments 503 03->04 clean-up of the requirements terminology 504 clarification of section 4 506 Intellectual Property Statement 508 The IETF takes no position regarding the validity or scope of any 509 Intellectual Property Rights or other rights that might be claimed to 510 pertain to the implementation or use of the technology described in 511 this document or the extent to which any license under such rights 512 might or might not be available; nor does it represent that it has 513 made any independent effort to identify any such rights. 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