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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Unexpected draft version: The latest known version of draft-rekhter-v6-ext-communities is -02, but you're referring to -03. Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Pillay-Esnault 3 Internet-Draft Cisco Systems 4 Intended status: Standards Track P. Moyer 5 Expires: May 28, 2010 Pollere, Inc 6 J. Doyle 7 Jeff Doyle and Associates 8 E. Ertekin 9 M. Lundberg 10 Booz Allen Hamilton 11 November 24, 2009 13 OSPFv3 as a PE-CE routing protocol 14 draft-ietf-l3vpn-ospfv3-pece-04 16 This document may contain material from IETF Documents or IETF 17 Contributions published or made publicly available before November 18 10, 2008. The person(s) controlling the copyright in some of this 19 material may not have granted the IETF Trust the right to allow 20 modifications of such material outside the IETF Standards Process. 21 Without obtaining an adequate license from the person(s) controlling 22 the copyright in such materials, this document may not be modified 23 outside the IETF Standards Process, and derivative works of it may 24 not be created outside the IETF Standards Process, except to format 25 it for publication as an RFC or to translate it into languages other 26 than English. 28 Abstract 30 Many Service Providers (SPs) offer Virtual Private Network (VPN) 31 services to their customers using a technique in which Customer Edge 32 (CE) routers are routing peers of Provider Edge (PE) routers. The 33 Border Gateway Protocol (BGP) is used to distribute the customer's 34 routes across the provider's IP backbone network, and Multiprotocol 35 Label Switching (MPLS) is used to tunnel customer packets across the 36 provider's backbone. This is known as a "BGP/MPLS IP VPN". 37 Originally only IPv4 was supported and it was later extended to 38 support IPv6 VPNs as well. Extensions were later added for the 39 support of the Open Shortest Path First protocol version 2 (OSPFv2) 40 as a PE-CE routing protocol for the IPv4 VPNs. This document extends 41 those specifications to support OSPF version 3 (OSPFv3) as a PE-CE 42 routing protocol. The OSPFv3 PE-CE functionality is identical to 43 that of OSPFv2 except for the differences described in this document. 45 Status of This Memo 47 This Internet-Draft is submitted to IETF in full conformance with the 48 provisions of BCP 78 and BCP 79. 50 Internet-Drafts are working documents of the Internet Engineering 51 Task Force (IETF), its areas, and its working groups. Note that 52 other groups may also distribute working documents as Internet- 53 Drafts. 55 Internet-Drafts are draft documents valid for a maximum of six months 56 and may be updated, replaced, or obsoleted by other documents at any 57 time. It is inappropriate to use Internet-Drafts as reference 58 material or to cite them other than as "work in progress." 60 The list of current Internet-Drafts can be accessed at 61 http://www.ietf.org/ietf/1id-abstracts.txt. 63 The list of Internet-Draft Shadow Directories can be accessed at 64 http://www.ietf.org/shadow.html. 66 This Internet-Draft will expire on May 28, 2010. 68 Copyright Notice 70 Copyright (c) 2009 IETF Trust and the persons identified as the 71 document authors. All rights reserved. 73 This document is subject to BCP 78 and the IETF Trust's Legal 74 Provisions Relating to IETF Documents 75 (http://trustee.ietf.org/license-info) in effect on the date of 76 publication of this document. Please review these documents 77 carefully, as they describe your rights and restrictions with respect 78 to this document. Code Components extracted from this document must 79 include Simplified BSD License text as described in Section 4.e of 80 the Trust Legal Provisions and are provided without warranty as 81 described in the BSD License. 83 This document may contain material from IETF Documents or IETF 84 Contributions published or made publicly available before November 85 10, 2008. The person(s) controlling the copyright in some of this 86 material may not have granted the IETF Trust the right to allow 87 modifications of such material outside the IETF Standards Process. 88 Without obtaining an adequate license from the person(s) controlling 89 the copyright in such materials, this document may not be modified 90 outside the IETF Standards Process, and derivative works of it may 91 not be created outside the IETF Standards Process, except to format 92 it for publication as an RFC or to translate it into languages other 93 than English. 95 Table of Contents 97 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 98 2. Specification of Requirements . . . . . . . . . . . . . . . . 4 99 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 100 3.1. OSPFv3 Specificities . . . . . . . . . . . . . . . . . . . 5 101 4. BGP/OSPFv3 Interaction Procedures for PE Routers . . . . . . . 6 102 4.1. VRFs and OSPFv3 Instances . . . . . . . . . . . . . . . . 6 103 4.1.1. Independent OSPFv3 Instances in PEs . . . . . . . . . 6 104 4.1.2. OSPFv3 Domain and PE-PE Link Instance Identifiers . . 7 105 4.2. OSPFv3 Areas . . . . . . . . . . . . . . . . . . . . . . . 8 106 4.3. VRFs and Routes . . . . . . . . . . . . . . . . . . . . . 8 107 4.3.1. OSPFv3 Routes on PE . . . . . . . . . . . . . . . . . 9 108 4.3.2. VPN-IPv6 Routes Received from MP-BGP . . . . . . . . . 10 109 4.4. OSPFv3 Route Extended Communities Attribute . . . . . . . 12 110 4.5. Loop Prevention Techniques . . . . . . . . . . . . . . . . 14 111 4.5.1. OSPFv3 Down Bit . . . . . . . . . . . . . . . . . . . 15 112 4.5.2. Other Possible Loops . . . . . . . . . . . . . . . . . 15 113 5. OSPFv3 Sham Links . . . . . . . . . . . . . . . . . . . . . . 15 114 5.1. Creating A Sham link . . . . . . . . . . . . . . . . . . . 16 115 5.2. OSPF Protocol On Sham link . . . . . . . . . . . . . . . . 16 116 5.3. OSPF Packet Forwarding On Sham Link . . . . . . . . . . . 17 117 6. Multiple Address Family Support . . . . . . . . . . . . . . . 18 118 7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 119 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 120 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 18 121 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 122 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 123 11.1. Normative References . . . . . . . . . . . . . . . . . . . 19 124 11.2. Informative References . . . . . . . . . . . . . . . . . . 20 126 1. Introduction 128 [rfc4364] offers Service Providers (SPs) a method for providing 129 Layer-3 Virtual Private Network (VPN) services to subtending customer 130 networks. Using the procedures defined in [rfc4364], provider edge 131 (PE) routers separate customer VPN routing information into Virtual 132 Routing and Forwarding (VRF) tables. The Border Gateway Protocol 133 (BGP) is used to disseminate customer network VPN routes between PE 134 VRFs configured in the same VPN. 136 The initial BGP/MPLS IP VPN specification enabled PE routers to learn 137 routes within customer sites through static routing, or through a 138 dynamic routing protocol instantiated on the PE-CE link. 139 Specifically, [rfc4364] (and its predecessor, [rfc2547]) included 140 support for dynamic routing protocols such as BGP, RIP, and OSPFv2. 141 The OSPFv2 as the Provider/Customer Edge Protocol for BGP/MPLS IP 142 Virtual Private Networks specification [rfc4577] further updates the 143 operation of OSPFv2 as the PE-CE routing protocol by detailing 144 additional extensions to enable intra-domain routing connectivity 145 between OSPFv2-based customer sites. 147 While [rfc4364] was defined for IPv4 based networks, [rfc4659] 148 extends the BGP/MPLS IP VPN framework to support IPv6 VPNs. This 149 includes the capability to connect IPv6 based sites over an IPv4 or 150 IPv6 SP backbone. It is expected that OSPFv3 will be used as the IGP 151 for some IPv6 VPNs just as the OSPFv2 was used for IPv4 VPNs. The 152 advantages of using OSPFv3 as a PE-CE protocol are the same as for 153 the IPv4 VPN deployment. 155 This document defines the mechanisms required to enable the operation 156 of OSPFv3 as the PE-CE Routing Protocol in BGP MPLS/IP VPNs. In 157 doing so, it reuses, and extends where necessary, the "BGP/MPLS IP 158 VPN" method for IPv6 VPNs defined in [rfc4659], and OSPFv2 as the 159 PE-CE routing protocol defined in [rfc4577]. This document also 160 includes the specifications for maintaining intra-domain routing 161 connectivity between OSPFv3-based customer sites across a SP 162 backbone. 164 We presuppose familiarity with the contents of [rfc4364], [rfc4659], 165 [rfc4577], [rfc4576], [rfc5340] and [rfc2328]. 167 2. Specification of Requirements 169 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 170 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 171 document are to be interpreted as described in [RFC2119]. 173 3. Requirements 175 The benefits and considerations associated with deploying OSPFv3 as 176 the PE-CE routing protocol are similar to those described in 177 [rfc4577]. The requirements described in Section 3 of [rfc4577] 178 remain semantically identical for the deployment of OSPFv3. 180 [rfc5340] describes the modifications required to OSPF to support 181 IPv6. In that specification, many of the fundamental mechanisms 182 associated with OSPFv2 remain unchanged for OSPFv3. Consequently, 183 the operation of OSPFv3 as the PE-CE routing protocol is very similar 184 to OSPFv2 as the PE-CE protocol. 186 3.1. OSPFv3 Specificities 188 Section 2.0 of [rfc5340] describes differences between OSPFv3 and 189 OSPFv2. Several of these changes will require modifications to the 190 architecture described in [rfc4577]. These differences and their 191 corresponding impact to [rfc4577] are described below: 193 New LSA types: 195 For an IPv6 MPLS/VPN architecture where customers interface to 196 providers through OSPFv3, traditional BGP/OSPF interactions 197 specify that VPN-IPv6 reachability information redistributed into 198 OSPFv3 will be expressed as an AS-External OSPFv3 LSAs. Instead, 199 it may be desirable to view these LSAs as AS-internal (inter-area- 200 prefix, and intra-area-prefix) LSAs. For the encoding of OSPFv3 201 LSAs, a new OSPFv3 Route Extended Community attribute is defined 202 in Section 4.4. 204 Multiple instances over a link: 206 OSPFv3 operates on a per-link basis as opposed to OSPFv2, which 207 operates on a per-IP-subnet basis. The support of multiple OSPFv3 208 protocol instances on a link changes the architecture described in 209 [rfc4577]. [rfc4577] specifies that each interface belongs to no 210 more than one OSPF instance. For OSPFv3, multiple instances can 211 be established over a single interface, and associated with the 212 same VRF. To distinguish between routes originated from different 213 OSPFv3 instances, an Instance ID field is carried in a newly- 214 defined OSPFv3 Route Extended Community attribute. 216 In addition to establishing multiple OSPFv3 instances over a 217 single PE-CE link, multiple OSPFv3 instances can also be 218 established across a sham link. This enables multiple OSPFv3 219 instances associated with a VRF to independently establish intra- 220 area connectivity to other OSPFv3 instances attached to a remote 221 PE VRF. Support for multiple OSPFv3 instances across the sham 222 link is described in Section 5. 224 4. BGP/OSPFv3 Interaction Procedures for PE Routers 226 4.1. VRFs and OSPFv3 Instances 228 The relationship between VRFs, interfaces, and OSPFv3 instances on a 229 PE router is described in the following section. 231 As defined in [rfc4364], a PE router can be configured with one or 232 more VRFs. Each VRF configured on the PE corresponds to a customer 233 VPN, and retains the destinations that are reachable within that VPN. 234 Each VRF may be associated with one or more interfaces, which allows 235 multiple sites to participate in the same VPN. If OSPFv3 is 236 instantiated on an interface associated with a VRF, the VRF will be 237 populated with OSPFv3 routing information. 239 As OSPFv3 supports multiple instances on a single interface, it is 240 therefore possible that multiple customer sites can connect to the 241 same interface of a PE router (e.g., through a layer 2 switch) using 242 distinct OSPFv3 instances. However, since a PE interface can be 243 associated with only one VRF, all OSPFv3 instances running on the 244 same interface MUST be associated with the same VRF. 246 Since multiple OSPFv3 instances can be associated with a single VRF, 247 an additional mechanism is needed to demultiplex routes across these 248 instances. When a PE supports multiple OSPFv3 instances in a VRF, a 249 local Instance ID is assigned to the "link" that spans over the MPLS 250 VPN backbone (PE-PE). As specified in [rfc5340], the Instance ID has 251 link-local significance only. Therefore, the Instance IDs assigned 252 to the PE-PE "link" need not be the same as the Instance IDs assigned 253 to the PE-CE links. By default, this Instance ID is set to NULL. 254 The OSPFv3 Domain ID and local Instance ID associated with the MPLS 255 backbone may be used to demultiplex routes for multiple instances. 256 Further details on Domain IDs and Instance IDs are provided in 257 Section 4.1.2. 259 4.1.1. Independent OSPFv3 Instances in PEs 261 Similar to [rfc4577], the PE must associate at least one OSPFv3 262 instance for each OSPFv3 domain to which it attaches, and each 263 instance of OSPFv3 MUST be associated with a single VRF. 265 The support of multiple PE-CE OSPFv3 instances per PE interface does 266 not change the paradigm that an OSPF instance can be associated with 267 only a single VRF. Furthermore, for each instance instantiated on 268 the interface, the PE establishes adjacencies with corresponding CEs 269 associated with the instance. Note that although multiple instances 270 may populate a common VRF, they do not leak routes to one another, 271 unless configured to do so. 273 4.1.2. OSPFv3 Domain and PE-PE Link Instance Identifiers 275 The OSPFv3 Domain ID describes the administrative domain of the OSPF 276 instance which originated the route. It has an AS wide significance 277 and is one of the parameters used to determine whether a VPN-IPv6 278 route should be translated as an Inter-area-prefix-LSA or External- 279 LSA. Each OSPFv3 instance MUST have a primary Domain ID which is 280 transported along with the VPN-IPv6 route in a BGP attribute over the 281 MPLS VPN backbone. Each OSPFv3 instance may have a set of secondary 282 Domain IDs which applies to other OSPFv3 instances within its 283 administrative domain. 285 The primary Domain ID may either be configured or may be set to a 286 value of NULL. The secondary Domain IDs are only allowed if a non- 287 null primary Domain ID is configured. The Domain ID may be 288 configured on a per-OSPFv3 instance basis or per-VRF. If the Domain 289 ID is configured on the VRF level, consequently all OSPFv3 instances 290 associated with the VRF will share the same Domain ID. 292 The OSPFv3 PE-PE "link" Instance ID has local significance for the 293 PE-PE "link" over the MPLS VPN backbone within a VRF. This link 294 Instance ID is used for the support of multiple OSPFv3 instances 295 within the same VRF and it is also transported along with the VPN- 296 IPv6 route in a BGP attribute over the MPLS VPN backbone. A PE-PE 297 "link" Instance ID is needed only if multiple OSPFv3 instances are 298 supported, otherwise it is set to NULL. When multiple instances are 299 associated with a VRF, each instance should have a unique PE-PE 300 "link" Instance ID. 302 The tuple is used to determine whether an 303 incoming VPN-IPv6 route belongs to the same domain as the receiving 304 OSPFv3 instance. An incoming VPN-IPv6 route is said to belong to the 305 same domain if both conditions below are met 307 1. A non-NULL incoming Domain ID matches either the local primary or 308 one of the secondary Domain IDs. If the local Domain ID and 309 incoming Domain ID are NULL, it is considered a match. 311 2. A non-NULL incoming Instance ID matches the local Instance ID. 312 If the local Instance ID and incoming Instance ID are NULL, it is 313 considered a match. 315 4.2. OSPFv3 Areas 317 Sections 4.1.4 and 4.2.3 of [rfc4577] describe the characteristics of 318 a PE router within an OSPFv2 domain. The mechanisms and expected 319 behavior described in [rfc4577] are applicable to an OSPFv3 domain. 321 4.3. VRFs and Routes 323 From the perspective of the CE, the PE appears as any other OSPFv3 324 neighbor. There is no requirement for the CE to support any 325 mechanisms of IPv6 BGP/MPLS VPNs or for the CE to have any awareness 326 of the VPNs, thereby enabling any OSPFv3 implementation to be used on 327 a CE. 329 Because the export and import policies might cause different routes 330 to be installed in different VRFs of the same OSPFv3 domain, the MPLS 331 VPN backbone cannot be considered as a single router from the 332 perspective of the domain's CEs. Rather, each CE should view its 333 connected PE as a separate router. 335 The PE uses OSPFv3 to distribute routes to CEs, and MP-BGP [rfc2858] 336 to distribute VPN-IPv6 routes to other (remote) PE routers as defined 337 in [rfc4659]. An IPv6 prefix installed in the VRF by OSPFv3 is 338 changed to a VPN-IPv6 prefix by the addition of an 8-octet Route 339 Distinguisher (RD) as discussed in Section 2 of [rfc4659]. This VPN- 340 IPv6 route can then be redistributed into MP-BGP according to an 341 export policy that adds a Route Target Extended Communities (RT) 342 attribute to the NLRI [rfc4360]. An IPv6 Address Specific BGP 343 Extended Communities attribute as described in [BGP-EXTCOMM-IPV6] may 344 also be attached to the route. 346 Domain IDs and Instance IDs are used to distinguish between OSPFv3 347 instances. When an OSPFv3-distributed route is redistributed into 348 MP-BGP, the Domain ID, OSPFv3 Router ID, Area, OSPFv3 Route Type, 349 External Route Type, Options fields, and Instance ID are also carried 350 in an attribute of the MP-BGP route. 352 A PE receiving a VPN-IPv6 NLRI from MP-BGP uses an import policy to 353 determine, based on the RT, whether the route is eligible to be 354 installed in one of its local VRFs. The BGP decision process selects 355 which of the eligible routes are to be installed in the associated 356 VRF, and the selected set of VPN-IPv6 routes are converted into IPv6 357 routes by removing the RD before installation. 359 An IPv6 route learned from MP-BGP and installed in a VRF might or 360 might not be redistributed into OSPFv3, depending on the local 361 configuration. For example, the PE might be configured to advertise 362 only a default route to CEs of a particular OSPFv3 instance. 364 Further, if the route is to be redistributed into multiple OSPFv3 365 instances, the route might be advertised using different LSA types in 366 different instances. 368 If an IPv6 route learned from MP-BGP is to be redistributed into a 369 particular OSPFv3 instance, the OSPFv3 Route Extended Community 370 attribute (Section 4.4) of the VPN-IPv6 route is used to determine 371 whether the OSPFv3 instance from which the route was learned is the 372 same as the OSPFv3 instance into which the route is to be 373 redistributed. 375 4.3.1. OSPFv3 Routes on PE 377 VRFs may be populated by both OSPFv3 routes from a CE or VPN-IPv6 378 routes from other PEs via MP-BGP. OSPFv3 routes are installed in a 379 VRF using the OSPFv3 decision process. As described in [rfc4577], 380 OSPFv2 routes installed in a VRF may be redistributed into BGP and 381 disseminated to other PEs participating in the VPN. At these remote 382 PEs, the VPN-IPv6 routes may be imported into a VRF and redistributed 383 into the OSPFv3 instance(s) associated with that VRF. 385 As specified in [rfc4659], routes imported and exported into a VRF 386 are controlled by the Route Target (RT) Extended Communities 387 attribute. OSPFv3 routes that are redistributed into BGP are given a 388 RT that corresponds to the VRF. This RT is examined at remote PEs. 389 In order to import a route, a VRF must have a RT that is identical to 390 the route's RT. For routes which are eligible to be imported into 391 the VRF, the standard BGP decision process is used to choose the 392 "best" route(s). 394 When a route is advertised from a CE to a PE via OSPFv3 and that 395 route is installed in the VRF associated with the CE, the route is 396 advertised to other locally attached CEs under normal OSPFv3 397 procedures. 399 The route is also redistributed into MP-BGP to be advertised to 400 remote PEs. The information necessary for accurate redistribution 401 back into OSPFv3 by the remote PEs is carried in an OSPFv3 Route 402 Extended Communities attribute (Section 4.4). The relevant local 403 OSPFv3 information encoded into the attribute is: 405 The Domain ID of the local OSPFv3 process. If no Domain ID is 406 configured, the NULL identifier is used. 408 The Instance ID of the PE-PE "link" 410 The Area ID of the PE-CE link. 412 The PE's Router ID associated with the OSPFv3 instance. 414 The Route Type, as determined by the LSA type from which the route 415 was learned. 417 The Options fields (External metric-type) 419 A Multi-Exit-Discriminator (MED) attribute SHOULD also be set to the 420 value of the OSPFv3 distance associated with the route plus 1, when 421 the OSPFv3 route is redistributed into the MP-BGP. 423 4.3.2. VPN-IPv6 Routes Received from MP-BGP 425 When a PE receives a valid VPN-IPv6 route from MP-BGP and has 426 identified an association with a local VRF, it must determine: 428 Whether a route to the corresponding IPv6 prefix is to be 429 installed in the VRF; 431 Whether the installed IPv6 route is to be redistributed to one or 432 more local OSPFv3 instances; and 434 What OSPFv3 LSA type is to be used when advertising the route into 435 each OSPFv3 instance 437 An IPv6 route derived from a received VPN-IPv6 route is not installed 438 in the associated local VRF if: 440 The BGP decision process identifies a better route to the 441 destination NLRI 443 A configured import policy prohibits the installation of the route 445 The PE advertises the IPv6 route learned from MP-BGP to attached CEs 446 via OSPFv3 if: 448 No configured filtering prohibits redistributing the route to 449 OSPFv3 451 No configured policy blocks the route in favor of a less-specific 452 summary route 454 No OSPFv3 route to the same prefix exists in the VRF. 456 The subsequent sections discuss the advertisement of routes learned 457 from MP-BGP, and the rules for determining what LSA types and what 458 CEs to advertise the routes to. 460 When the PE sends an LSA to a CE, it sets the DN bit in the LSA to 461 prevent looping. The DN bit is discussed in Section 4.5.1. 463 4.3.2.1. OSPF Inter-Area Routes 465 A PE advertises an IPv6 route using an Inter-Area-Prefix (type 466 0x2003) LSA under the following circumstances: 468 The OSPFv3 domain from which the IPv6 route was learned is the 469 same (as determined by the tuple) as the 470 domain of the OSPFv3 instance into which it is to be 471 redistributed; AND 473 The IPv6 route was advertised to a remote PE in an Intra-Area- 474 Prefix (type 0x2009) OR an Inter-Area-Prefix (type 0x2003) LSA. 476 Note that under these rules the PE represents itself as an ABR 477 regardless of whether or not the route is being advertised into the 478 same area number from which the remote PE learned it (that is, 479 whether the VPN-IPv6 route carries the same or different area 480 numbers). 482 4.3.2.2. OSPF Intra-Area Route 484 A route is advertised from a PE to a CE as an intra-area route using 485 an Intra-Area-Prefix (type 0x2009) LSA only when sham links are used, 486 as described in Section 5. Otherwise routes are advertised as either 487 inter-area (Section 4.3.2.1) or external (Sections 4.3.2.3) routes. 489 4.3.2.3. OSPF External Routes And NSSA Routes 491 A PE considers an IPv6 route to be external under the following 492 circumstances: 494 The OSPFv3 domain from which the route was learned is different 495 (as determined by the tuple) from the 496 domain of the OSPFv3 instance into which it is redistributed; OR 498 The OSPFv3 domain from which the route was learned is the same as 499 the domain of the OSPFv3 instance into which it is redistributed 500 AND it was advertised to the remote PE in an AS-External (type 501 0x4005) or a Type-7 (type 0x2007, NSSA) LSA; OR 503 The route was not learned from an OSPFv3 instance 505 To determine if the learned route is from a different domain, the 506 tuple associated with the VPN-IPv6 route (in 507 the OSPFv3 Route Extended Communities attribute or attributes) is 508 compared with the local OSPFv3 Domain ID and Instance ID, if 509 configured. Compared Domain IDs are considered identical if: 511 1. All six bytes are identical; or 513 2. Both Domain IDs are NULL (all zeroes). 515 Note that if the VPN-IPv6 route does not have a Domain ID in its 516 attributes, or if the local OSPFv3 instance does not have a 517 configured Domain ID, in either case the route is considered to have 518 a NULL Domain ID. 520 An IPv6 route that is determined to be external might or might not be 521 advertised to a connected CE, depending on the type of area to which 522 the PE-CE link belongs and whether there is a configured policy 523 restricting its advertisement. 525 If there are multiple external routes to the same prefix, the 526 standard OSPFv3 decision process is used to select the "best" route. 528 If the external route is to be advertised and the area type of the 529 PE/CE link is NSSA, the PE advertises the route in a Type-7 (type 530 0x2007) LSA; otherwise the external route is advertised in an AS- 531 External (type 0x4005) LSA. 533 The DN bit of the LSA advertising the external route MUST be set, as 534 described in Section 4.5.1. 536 If the VPN-IPv6 route indicates a route type-1 metric, the PE 537 advertises the external route with that metric-type; otherwise the 538 metric-type of the external IPv6 route is set to type-2 by default. 540 4.4. OSPFv3 Route Extended Communities Attribute 542 OSPFv3 routes from one site are translated and delivered 543 transparently to the remote site as BGP VPN-IPv6 routes. The 544 original OSPFv3 routes carry OSPFv3 specific information which need 545 to be communicated to the remote PE to ensure transparency. BGP 546 extended communities are used to carry the needed information to 547 enable the receiving side to reconstruct a database just as in the 548 OSPFv2 case. 550 All OSPFv3 routes added to the VRF routing table on a PE router are 551 examined to create a corresponding VPN-IPv6 route in BGP. Each of 552 the OSPFv3 routes MUST have a corresponding BGP Extended Community 553 Attribute which contains and preserves the OSPFv3 information 554 attached to the original OSPFv3 route. 556 This document defines a new BGP attribute in the proposed "IPv6 557 Address Specific Extended Community" registry described in Section 3 558 of [BGP-EXTCOMM-IPV6]. The OSPFv3 Route Extended Community Attribute 559 has the Sub-type value of 0x0004. It carries an OSPFv3 Domain ID, 560 OSPFv3 Router ID, OSPFv3 Area ID, OSPFv3 Route type, Options, and an 561 OSPFv3 Instance ID field. 563 0 1 2 3 564 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 566 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 567 | 0x00 | 4 | OSPF Domain ID | 568 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 569 | OSPF Domain ID (Cont.) | 570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 571 | OSPF Router ID | 572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 573 | Area ID | 574 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 575 | Route Type | Options |OSPF InstanceID| UNUSED | 576 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 578 The OSPFv3 Route Extended Community Attribute 580 This attribute is MANDATORY for all OSPFv3 routes in a VRF instance 581 on a PE router. The fields of this new BGP Extended Community 582 attribute are described in the following sections. 584 OSPFv3 Domain IDs field : 6 bytes 586 Each OSPFv3 Instance within a VRF MUST have a Domain ID. The 587 Domain ID may be configured at the VRF level or at the OSPFv3 588 Instance level. The OSPFv3 Domain ID is a 6-byte number and its 589 default value is 0. 591 OSPFv3 Router ID field : 4 bytes 593 The OSPFv3 Router ID is a 32 bit number as in OSPFv2. Setting 594 this field is OPTIONAL and its default value is 0. 596 OSPFv3 Area ID : 4 bytes 598 The Area ID field indicates the 32-bit Area ID to which the route 599 belongs. 601 OSPFv3 Route Types : 1 byte 603 To accommodate OSPFv3 LSA types, the OSPF Route Type field is 604 encoded as follows: 606 Route Type Route Type LSA Type Description 607 Code 608 ----------------------------------------------------------- 609 0x30 Inter-area 0x2003 Inter-area-prefix-LSA 610 0x50 External 0x2005 AS-external-LSA 611 0x70 NSSA 0x2007 NSSA-LSA 612 0x90 Intra-area-prefix 0x2009 Intra-area-prefix-LSA 614 The OSPFv3 Route Type Field Encoding 616 OSPFv3 Options : 1 byte 618 The Options field indicates if the route carries a type-1 or 619 type-2 metric. Setting the least significant bit in the field 620 indicates that the route carries a External type-2 metric. 622 OSPFv3 Instance ID field : 1 byte 624 The OSPFv3 Instance ID field is defined to carry the OSPFv3 625 Instance ID which is a one-byte number. The OSPFv3 Instance ID is 626 configured for the "link" simulated by the MPLS VPN backbone. 627 This attribute MAY be present whether several OSPFv3 instances are 628 defined or not. The Instance ID default value is 0. 630 4.5. Loop Prevention Techniques 632 In some topologies, it is possible for routing loops to occur due to 633 the nature and manner of route reachability propagation. One such 634 example is the case of a dual homed CE router connected to two PEs; 635 those PE routers would receive this information both through their CE 636 and their peer PE. As there is transparent transport of OSPFv3 637 routes over the BGP/MPLS backbone, it is not possible for the PE 638 routers to determine whether they are within a loop. 640 The loop scenarios in OSPFv3 topologies are identical to those in the 641 OSPFv2 topologies described in Section 4.2.5.1 and Section 4.2.5.2 of 642 [rfc4577]. Of the two loop preventions mechanisms described in the 643 sections aforementioned, only the DN bit option will be supported in 644 the OSPFv3 implementation. 646 4.5.1. OSPFv3 Down Bit 648 Section 1 and Section 3 of [rfc4576] describe the usage of the DN-bit 649 for OSPFv2 and are applicable for OSPFv3 for inter-area-prefix LSAs, 650 NSSA LSAs and External LSAs. Similarly, the DN-bit must be set in 651 inter-area-prefix-LSAs, NSSA-LSAs and AS-External-LSAs, when these 652 are originated from a PE to a CE, to prevent those prefixes from 653 being re-advertised into BGP. As in [rfc4577], any LSA with the DN 654 bit set must not be used for route calculations. 656 The DN bit MUST be clear in all other LSA types. The OSPFv3 DN-bit 657 format is described in Appendix 4.1.1 of [rfc5340]. 659 4.5.2. Other Possible Loops 661 The mechanism described in Section 4.5.1 of this document is 662 sufficient to prevent looping if the DN bit information attached to a 663 prefix is preserved in the OSPF domain. As described in Section 664 4.2.5.3 of [rfc4576], caution must be exercised if mutual 665 redistribution is performed on a PE causing loss of loop prevention 666 information. 668 5. OSPFv3 Sham Links 670 This section modifies the specification of OSPFv2 sham links (defined 671 in Section 4.2.7 of [rfc4577]) to support OSPFv3. Support for OSPFv3 672 sham links is an OPTIONAL feature of this specification. 674 A sham link enables a VPN backbone to act as an intra-area link. It 675 is needed when two sites are connected by an intra-area "backdoor" 676 link and the inter-area MPLS VPN backbone route would be less 677 preferable due to OSPF route preference rules. The figure below 678 shows the instantiation of a sham link between two VPN sites. 680 (VPN backbone) 681 (site-1) <-------- sham link --------> (site-2) 682 CE1 -------- PE1 -------- P ---------- PE2 -------- CE2 683 | | 684 |___________________________________________________| 685 <------------ backdoor link --------------> 686 (OSPF intra-area link) 688 Sham Link 690 Much of the operation of sham links remains semantically identical to 691 what was previously specified. There are, however, several 692 differences that need to be defined to ensure the proper operation of 693 OSPFv3 sham links. 695 One of the primary differences between sham links for OSPFv3 and sham 696 links as specified in [rfc4577] are for configurations where multiple 697 OSPFv3 instances populate a VRF. It may be desirable to provide 698 separate intra-area links between these instances over the same sham 699 link. To achieve this, multiple OSPFv3 instances may be established 700 across the PE-PE sham link to provide intra-area connectivity between 701 PE-CE OSPFv3 instances. 703 Note that even though multiple OSPFv3 instances may be associated 704 with a VRF, a sham link is still thought of as a relation between two 705 VRFs. 707 Another modification to OSPFv2 sham links is that OSPFv3 sham links 708 are now identified by 128-bit endpoint addresses. Since sham links 709 end-point addresses are now 128-bits, they can no longer default to 710 the RouterID, which is a 32-bit number. Sham link endpoint addresses 711 MUST be configured. 713 Sham link endpoint addresses MUST be distributed by BGP as routeable 714 VPN IPv6 addresses whose IPv6 address prefix is 128 bits long. As 715 specified in [rfc4577], these endpoint addresses MUST NOT be 716 advertised by OSPFv3. 718 If there is a BGP route to the remote sham link endpoint address, the 719 sham link appears to be up. Conversely, if there is no BGP route to 720 the sham link endpoint address, the sham link appears to be down. 722 5.1. Creating A Sham link 724 The procedures for creating an OSPFv3 sham link are identical to 725 those specified in Section 4.2.7.2 of [rfc4577]. Note that the 726 creation of OSPFv3 sham links requires the configuration of both 727 local and remote 128-bit sham link endpoint addresses. The local 728 Sham link endpoint address associated with a VRF MAY be used by all 729 OSPFv3 instances that are attached to that VRF. The OSPFv3 PE-PE 730 "link" Instance ID is used to demultiplex multiple OSPFv3 instance 731 protocol packets exchanged over the sham link. 733 5.2. OSPF Protocol On Sham link 735 Much of the operation of OSPFv3 over a sham link is semantically the 736 same as the operation of OSPFv2 over a sham link, as described in 737 Section 4.2.7.3 of [rfc4577]. This includes the methodology for 738 sending and receiving OSPFv3 packets over sham links, as well as 739 Hello/Router Dead Intervals. Furthermore, the procedures associated 740 with the assignment of sham link metrics adhere to those set forth 741 for OSPFv2. OSPFv3 sham links are treated as on demand circuits. 743 Although the operation of the OSPFv3 protocol over the sham link is 744 the same as OSPFv2, multiple OSPFv3 instances may be instantiated 745 across this link. By instantiating multiple instances across the 746 sham link, distinct intra-area connections can be established between 747 PE-PE OSPFv3 instances associated with the endpoint addresses. 749 For example, if two OSPFv3 instances (O1, O2) attach to a VRF V1, and 750 on a remote PE, two other OSPFv3 instances (O3, O4) attach to a VRF 751 V2, it may be desirable to connect, O1 and O3 with an intra-area 752 link, and O2 and O4 with an intra-area link. This can be 753 accomplished by instantiating two OSPFv3 instances across the sham 754 link, which connects V1 and V2. O1 and O3 can be mapped to one of 755 the sham link OSPFv3 instances; O2 and O4 can be mapped to the other 756 sham link OSPFv3 instance. 758 One difference from Section 4.2.7.3 of [rfc4577] is the addition of 759 Type 0x2009 intra-area-prefix LSAs, and the flooding of these LSAs 760 across the sham link. Furthermore, where prefixes associated with 761 OSPFv2 sham links are advertised in Type-1 LSAs, prefixes associated 762 with OSPFv3 sham links are advertised as OSPFv3 Type 0x2009 LSAs. 763 This change is required based on [rfc5340], which states that 764 loopback interfaces are advertised in intra-area-prefix LSAs. 766 5.3. OSPF Packet Forwarding On Sham Link 768 The rules associated with route redistribution, stated in Section 769 4.2.7.4 of [rfc4577], remain unchanged in this specification. 770 Specifically: 772 If the next hop interface for a particular route is a sham link, 773 then the PE SHOULD NOT redistribute that route into BGP as a VPN- 774 IPv6 route. 776 Any other route advertised in an LSA that is transmitted over a 777 sham link MUST also be redistributed (by the PE flooding the LSA 778 over the sham link) into BGP. 780 When redistributing these LSAs into BGP, they are encoded with the 781 OSPFv3 Route Extended Community, as defined in Section 4.4 of this 782 document. 784 When forwarding a packet, if the preferred route for that packet has 785 the sham link as its next hop interface, then the packet MUST be 786 forwarded according to the corresponding BGP route (as defined in 787 [rfc4364] and [rfc4659]). 789 6. Multiple Address Family Support 791 The support of multiple address families (AF) in OSPFv3 is described 792 in [OSPF-AF-ALT]. [OSPF-AF-ALT] differentiates between AF using 793 reserved ranges of Instance IDs for each AF. 795 The architecture described in this document is fully compatible with 796 [OSPF-AF-ALT]. The OSPFv3 PE-CE protocol can support multiple 797 address families across a MPLS VPN backbone. All AFs redistributed 798 from OSPFv3 into BGP on a PE MUST contain the OSPFv3 Route Extended 799 Community Attribute. 801 Note that since [OSPF-AF-ALT] does not support multiple AFs across 802 virtual links, this document only addresses support for unicast IPv6 803 addresses across the sham link. 805 7. Security Considerations 807 The extensions described in this document are specific to the use of 808 OSPFv3 as the PE-CE protocol and do not introduce any concerns 809 regarding the use of BGP as transport of IPv6 reachability over the 810 MPLS Backbone. The Security considerations for the transport of IPv6 811 reachability information using BGP are discussed in Section 11 of 812 [rfc4659] and are not altered. 814 The new extensions defined in this document do not introduce any new 815 security concerns other than those already defined in Section 6 of 816 [rfc4577]. 818 8. IANA Considerations 820 This document defines a new BGP attribute in the proposed "IPv6 821 Address Specific Extended Community" registry described in Section 3 822 of [BGP-EXTCOMM-IPV6]. This document makes the following assignments 823 in the "IPv6 Address Specific Extended Community" registry. 825 Name Sub-type Value 826 ---- -------------- 827 OSPFv3 Route Attributes 0x0004 829 The OSPFv3 specific BGP Extended Community types 831 9. Contributors 833 Joe Lapolito 835 10. Acknowledgments 837 The authors would like to thank Kelvin Upson, Seiko Okano, Matthew 838 Everett, and Dr. Vineet Mehta for their support of this work. 840 This document was produced using Marshall Rose's xml2rfc tool. 842 11. References 844 11.1. Normative References 846 [RFC2119] Bradner, S., "Key words for use in RFC's to 847 Indicate Requirement Levels", BCP 14, RFC 2119, 848 March 1997. 850 [rfc2328] Moy, J., "OSPF Version 2", RFC 2328, April 1998. 852 [rfc2858] Bates, T., Rehkter, Y., Chandra, R., and D. Katz, 853 "Multiprotocol Extensions for BGP-4", RFC 2858, 854 June 2000. 856 [rfc4360] Sangli, S., Tappan, D., and Y. Rehkter, "BGP 857 Extended Communities Attribute", RFC 4360, 858 February 2006. 860 [rfc4364] Rosen, E. and Y. Rehkter, "BGP/MPLS IP Virtual 861 Private Networks (VPNs)", RFC 4364, 862 February 2006. 864 [rfc4576] Rosen, E., Psenak, P., and P. Pillay-Esnault, 865 "Using a Link State Advertisement (LSA) Options 866 Bit to Prevent Looping in BGP/MPLS IP Virtual 867 Private Networks (VPNs)", RFC 4576, June 2006. 869 [rfc4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, 870 "OSPF as the Provider/Customer Edge Protocol for 871 BGP/MPLS IP Virtual Private Networks (VPNs)", 872 RFC 4577, June 2006. 874 [rfc4659] De Clercq, J., Ooms, D., Carugi, M., and F. 875 Lefaucheur, "BGP-MPLS IP Virtual Private Network 876 (VPN) Extension for IPv6 VPN", RFC 4659, 877 September 2006. 879 [rfc5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, 880 "OSPF for IPv6", RFC 5340, July 2008. 882 11.2. Informative References 884 [BGP-EXTCOMM-IPV6] Rehkter, Y., "IPv6 Address Specific BGP Extended 885 Communities Attribute", October 2008, . 889 [OSPF-AF-ALT] Mirtorabi, S., Roy, A., Barnes, M., Aggarwal, R., 890 and A. Lindem, "Support of address families in 891 OSPFv3", October 2008, . 894 [rfc2547] Rosen, E. and Y. Rehkter, "BGP/MPLS VPNs", 895 RFC 2547, March 1999. 897 Authors' Addresses 899 Padma Pillay-Esnault 900 Cisco Systems 901 510 McCarty Blvd 902 Milpitas, CA 95035 903 USA 905 EMail: ppe@cisco.com 907 Peter Moyer 908 Pollere, Inc 909 325M Sharon Park Drive #214 910 Menlo Park, CA 94025 911 USA 913 EMail: pete@pollere.net 915 Jeff Doyle 916 Jeff Doyle and Associates 917 9878 Teller Ct. 918 Westminster, CO 80021 919 USA 921 EMail: jdoyle@doyleassociates.net 922 Emre Ertekin 923 Booz Allen Hamilton 924 5220 Pacific Concourse Drive 925 Los Angeles, CA 90045 926 USA 928 EMail: ertekin_emre@bah.com 930 Michael Lundberg 931 Booz Allen Hamilton 932 22 Batterymarch Street 933 Boston, MA 02109 934 USA 936 EMail: lundberg_michael@bah.com