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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 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: January 13, 2012 Pollere, Inc 6 J. Doyle 7 Jeff Doyle and Associates 8 E. Ertekin 9 M. Lundberg 10 Booz Allen Hamilton 11 July 12, 2011 13 OSPFv3 as a PE-CE routing protocol 14 draft-ietf-l3vpn-ospfv3-pece-08 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 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). Note that other groups may also distribute 52 working documents as Internet-Drafts. The list of current Internet- 53 Drafts is at http://datatracker.ietf.org/drafts/current/. 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 This Internet-Draft will expire on January 13, 2012. 62 Copyright Notice 64 Copyright (c) 2011 IETF Trust and the persons identified as the 65 document authors. All rights reserved. 67 This document is subject to BCP 78 and the IETF Trust's Legal 68 Provisions Relating to IETF Documents 69 (http://trustee.ietf.org/license-info) in effect on the date of 70 publication of this document. Please review these documents 71 carefully, as they describe your rights and restrictions with respect 72 to this document. Code Components extracted from this document must 73 include Simplified BSD License text as described in Section 4.e of 74 the Trust Legal Provisions and are provided without warranty as 75 described in the Simplified BSD License. 77 This document may contain material from IETF Documents or IETF 78 Contributions published or made publicly available before November 79 10, 2008. The person(s) controlling the copyright in some of this 80 material may not have granted the IETF Trust the right to allow 81 modifications of such material outside the IETF Standards Process. 82 Without obtaining an adequate license from the person(s) controlling 83 the copyright in such materials, this document may not be modified 84 outside the IETF Standards Process, and derivative works of it may 85 not be created outside the IETF Standards Process, except to format 86 it for publication as an RFC or to translate it into languages other 87 than English. 89 Table of Contents 91 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 92 2. Specification of Requirements . . . . . . . . . . . . . . . . 4 93 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 94 3.1. OSPFv3 Specificities . . . . . . . . . . . . . . . . . . . 5 95 4. BGP/OSPFv3 Interaction Procedures for PE Routers . . . . . . . 6 96 4.1. VRFs and OSPFv3 Instances . . . . . . . . . . . . . . . . 6 97 4.1.1. Independent OSPFv3 Instances in PEs . . . . . . . . . 6 98 4.1.2. OSPFv3 Domain Identifier . . . . . . . . . . . . . . . 6 99 4.2. OSPFv3 Areas . . . . . . . . . . . . . . . . . . . . . . . 7 100 4.3. VRFs and Routes . . . . . . . . . . . . . . . . . . . . . 7 101 4.3.1. OSPFv3 Routes on PE . . . . . . . . . . . . . . . . . 8 102 4.3.2. VPN-IPv6 Routes Received from MP-BGP . . . . . . . . . 9 103 4.4. BGP Extended Communities Attribute . . . . . . . . . . . . 12 104 4.5. Loop Prevention Techniques . . . . . . . . . . . . . . . . 14 105 4.5.1. OSPFv3 Down Bit . . . . . . . . . . . . . . . . . . . 14 106 4.5.2. Other Possible Loops . . . . . . . . . . . . . . . . . 15 107 5. OSPFv3 Sham Links . . . . . . . . . . . . . . . . . . . . . . 15 108 5.1. Creating A Sham link . . . . . . . . . . . . . . . . . . . 16 109 5.2. OSPF Protocol On Sham link . . . . . . . . . . . . . . . . 16 110 5.3. OSPF Packet Forwarding On Sham Link . . . . . . . . . . . 17 111 6. Multiple Address Family Support . . . . . . . . . . . . . . . 17 112 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 113 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 114 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 18 115 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 116 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 117 11.1. Normative References . . . . . . . . . . . . . . . . . . . 18 118 11.2. Informative References . . . . . . . . . . . . . . . . . . 19 120 1. Introduction 122 [rfc4364] offers Service Providers (SPs) a method for providing 123 Layer-3 Virtual Private Network (VPN) services to subtending customer 124 networks. Using the procedures defined in [rfc4364], provider edge 125 (PE) routers separate customer VPN routing information into Virtual 126 Routing and Forwarding (VRF) tables. The Border Gateway Protocol 127 (BGP) is used to disseminate customer network VPN routes between PE 128 VRFs configured in the same VPN. 130 The initial BGP/MPLS IP VPN specification enabled PE routers to learn 131 routes within customer sites through static routing, or through a 132 dynamic routing protocol instantiated on the PE-CE link. 133 Specifically, [rfc4364] (and its predecessor, [rfc2547]) included 134 support for dynamic routing protocols such as BGP, RIP, and OSPFv2. 135 The OSPFv2 as the Provider/Customer Edge Protocol for BGP/MPLS IP 136 Virtual Private Networks specification [rfc4577] further updates the 137 operation of OSPFv2 as the PE-CE routing protocol by detailing 138 additional extensions to enable intra-domain routing connectivity 139 between OSPFv2-based customer sites. 141 While [rfc4364] was defined for IPv4 based networks, [rfc4659] 142 extends the BGP/MPLS IP VPN framework to support IPv6 VPNs. This 143 includes the capability to connect IPv6 based sites over an IPv4 or 144 IPv6 SP backbone. It is expected that OSPFv3 will be used as the IGP 145 for some IPv6 VPNs just as the OSPFv2 was used for IPv4 VPNs. The 146 advantages of using OSPFv3 as a PE-CE protocol are the same as for 147 the IPv4 VPN deployment. 149 This document defines the mechanisms required to enable the operation 150 of OSPFv3 as the PE-CE Routing Protocol in BGP MPLS/IP VPNs. In 151 doing so, it reuses, and extends where necessary, the "BGP/MPLS IP 152 VPN" method for IPv6 VPNs defined in [rfc4659], and OSPFv2 as the 153 PE-CE routing protocol defined in [rfc4577]. This document also 154 includes the specifications for maintaining intra-domain routing 155 connectivity between OSPFv3-based customer sites across a SP 156 backbone. 158 We presuppose familiarity with the contents of [rfc4364], [rfc4659], 159 [rfc4577], [rfc4576], [rfc5340] and [rfc2328]. 161 2. Specification of Requirements 163 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 164 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 165 document are to be interpreted as described in [RFC2119]. 167 3. Requirements 169 The benefits and considerations associated with deploying OSPFv3 as 170 the PE-CE routing protocol are similar to those described in 171 [rfc4577]. The requirements described in Section 3 of [rfc4577] 172 remain semantically identical for the deployment of OSPFv3. 174 [rfc5340] describes the modifications required to OSPF to support 175 IPv6. In that specification, many of the fundamental mechanisms 176 associated with OSPFv2 remain unchanged for OSPFv3. Consequently, 177 the operation of OSPFv3 as the PE-CE routing protocol is very similar 178 to OSPFv2 as the PE-CE protocol. 180 3.1. OSPFv3 Specificities 182 Section 2.0 of [rfc5340] describes differences between OSPFv3 and 183 OSPFv2. Several of these changes will require modifications to the 184 architecture described in [rfc4577]. These differences and their 185 corresponding impact to [rfc4577] are described below: 187 New LSA types: 189 For an IPv6 MPLS/VPN architecture where customers interface to 190 providers through OSPFv3, traditional BGP/OSPF interactions 191 specify that VPN-IPv6 reachability information redistributed into 192 OSPFv3 will be expressed as AS-External OSPFv3 LSAs. Instead, it 193 may be desirable to view these LSAs as inter-area-prefix LSAs. 194 The OSPF Route Type Extended Communities attribute defined in 195 [rfc4577] is extended to include OSPFv3 route types. These new 196 encodings are defined in Section 4.4. 198 Multiple instances over a link: 200 OSPFv3 operates on a per-link basis as opposed to OSPFv2, which 201 operates on a per-IP-subnet basis. The support of multiple OSPFv3 202 protocol instances on a link changes the architecture described in 203 [rfc4577]. [rfc4577] specifies that each interface belongs to no 204 more than one OSPF instance. For OSPFv3, multiple instances can 205 be established over a single interface, and associated with the 206 same VRF. 208 In addition to establishing multiple OSPFv3 instances over a 209 single PE-CE link, multiple OSPFv3 instances can also be 210 established across a sham link. This enables multiple OSPFv3 211 instances associated with a VRF to independently establish intra- 212 area connectivity to other OSPFv3 instances attached to a remote 213 PE VRF. Support for multiple OSPFv3 instances across the sham 214 link is described in Section 5. 216 4. BGP/OSPFv3 Interaction Procedures for PE Routers 218 4.1. VRFs and OSPFv3 Instances 220 The relationship between VRFs, interfaces, and OSPFv3 instances on a 221 PE router is described in the following section. 223 As defined in [rfc4364], a PE router can be configured with one or 224 more VRFs. Each VRF configured on the PE corresponds to a customer 225 VPN, and retains the destinations that are reachable within that VPN. 226 Each VRF may be associated with one or more interfaces, which allows 227 multiple sites to participate in the same VPN. If OSPFv3 is 228 instantiated on an interface associated with a VRF, the VRF will be 229 populated with OSPFv3 routing information. 231 As OSPFv3 supports multiple instances on a single interface, it is 232 therefore possible that multiple customer sites can connect to the 233 same interface of a PE router (e.g., through a layer 2 switch) using 234 distinct OSPFv3 instances. However, since a PE interface can be 235 associated with only one VRF, all OSPFv3 instances running on the 236 same interface MUST be associated with the same VRF. 238 4.1.1. Independent OSPFv3 Instances in PEs 240 Similar to [rfc4577], the PE must associate at least one OSPFv3 241 instance for each OSPFv3 domain to which it attaches, and each 242 instance of OSPFv3 MUST be associated with a single VRF. 244 The support of multiple PE-CE OSPFv3 instances per PE interface does 245 not change the paradigm that an OSPF instance can be associated with 246 only a single VRF. Furthermore, for each instance instantiated on 247 the interface, the PE establishes adjacencies with corresponding CEs 248 associated with the instance. Note that although multiple instances 249 may populate a common VRF, they do not leak routes to one another, 250 unless configured to do so. 252 4.1.2. OSPFv3 Domain Identifier 254 The OSPFv3 Domain ID describes the administrative domain of the OSPF 255 instance which originated the route. It has an AS wide significance 256 and is one of the parameters used to determine whether a VPN-IPv6 257 route should be translated as an Inter-area-prefix-LSA or External- 258 LSA. Each OSPFv3 instance MUST have a primary Domain ID which is 259 transported along with the VPN-IPv6 route in a BGP attribute over the 260 MPLS VPN backbone. Each OSPFv3 instance may have a set of secondary 261 Domain IDs which applies to other OSPFv3 instances within its 262 administrative domain. 264 The primary Domain ID may either be configured or may be set to a 265 value of NULL. The secondary Domain IDs are only allowed if a non- 266 null primary Domain ID is configured. The Domain ID MUST be 267 configured on a per-OSPFv3 instance basis. 269 The Domain ID is used to determine whether an incoming VPN-IPv6 route 270 belongs to the same domain as the receiving OSPFv3 instance. An 271 incoming VPN-IPv6 route is said to belong to the same domain if a 272 non-NULL incoming Domain ID matches either the local primary or one 273 of the secondary Domain IDs. If the local Domain ID and incoming 274 Domain ID are NULL, it is considered a match. 276 4.2. OSPFv3 Areas 278 Sections 4.1.4 and 4.2.3 of [rfc4577] describe the characteristics of 279 a PE router within an OSPFv2 domain. The mechanisms and expected 280 behavior described in [rfc4577] are applicable to an OSPFv3 domain. 282 4.3. VRFs and Routes 284 From the perspective of the CE, the PE appears as any other OSPFv3 285 neighbor. There is no requirement for the CE to support any 286 mechanisms of IPv6 BGP/MPLS VPNs or for the CE to have any awareness 287 of the VPNs, thereby enabling any OSPFv3 implementation to be used on 288 a CE. 290 Because the export and import policies might cause different routes 291 to be installed in different VRFs of the same OSPFv3 domain, the MPLS 292 VPN backbone cannot be considered as a single router from the 293 perspective of the domain's CEs. Rather, each CE should view its 294 connected PE as a separate router. 296 The PE uses OSPFv3 to distribute routes to CEs, and MP-BGP [rfc2858] 297 to distribute VPN-IPv6 routes to other (remote) PE routers as defined 298 in [rfc4659]. An IPv6 prefix installed in the VRF by OSPFv3 is 299 changed to a VPN-IPv6 prefix by the addition of an 8-octet Route 300 Distinguisher (RD) as discussed in Section 2 of [rfc4659]. This VPN- 301 IPv6 route can then be redistributed into MP-BGP according to an 302 export policy that adds a Route Target Extended Communities (RT) 303 attribute to the NLRI [rfc4360]. 305 Domain IDs are used to distinguish between OSPFv3 instances. When an 306 OSPFv3 distributed route is redistributed into MP-BGP, the Domain ID, 307 OSPFv3 Router ID, Area, OSPFv3 Route Type, and Options fields 308 (External Route Type) are also carried in Extended Community 309 Attributes of the MP-BGP route. 311 A PE receiving a VPN-IPv6 NLRI from MP-BGP uses an import policy to 312 determine, based on the RT, whether the route is eligible to be 313 installed in one of its local VRFs. The BGP decision process selects 314 which of the eligible routes are to be installed in the associated 315 VRF, and the selected set of VPN-IPv6 routes are converted into IPv6 316 routes by removing the RD before installation. 318 An IPv6 route learned from MP-BGP and installed in a VRF might or 319 might not be redistributed into OSPFv3, depending on the local 320 configuration. For example, the PE might be configured to advertise 321 only a default route to CEs of a particular OSPFv3 instance. 322 Further, if the route is to be redistributed into multiple OSPFv3 323 instances, the route might be advertised using different LSA types in 324 different instances. 326 If an IPv6 route learned from MP-BGP is to be redistributed into a 327 particular OSPFv3 instance, the OSPF Domain Identifier Extended 328 Communities attribute of the VPN-IPv6 route is used to determine 329 whether the OSPFv3 instance from which the route was learned is the 330 same as the OSPFv3 instance into which the route is to be 331 redistributed. 333 4.3.1. OSPFv3 Routes on PE 335 VRFs may be populated by both OSPFv3 routes from a CE or VPN-IPv6 336 routes from other PEs via MP-BGP. OSPFv3 routes are installed in a 337 VRF using the OSPFv3 decision process. They may be redistributed 338 into BGP and disseminated to other PEs participating in the VPN. At 339 these remote PEs, the VPN-IPv6 routes may be imported into a VRF and 340 redistributed into the OSPFv3 instance(s) associated with that VRF. 342 As specified in [rfc4659], routes imported and exported into a VRF 343 are controlled by the Route Target (RT) Extended Communities 344 attribute. OSPFv3 routes that are redistributed into BGP are given a 345 RT that corresponds to the VRF. This RT is examined at remote PEs. 346 In order to import a route, a VRF must have an import RT that is 347 identical to the route's RT. For routes which are eligible to be 348 imported into the VRF, the standard BGP decision process is used to 349 choose the "best" route(s). 351 When a route is advertised from a CE to a PE via OSPFv3 and that 352 route is installed in the VRF associated with the CE, the route is 353 advertised to other locally attached CEs under normal OSPFv3 354 procedures. 356 The route is also redistributed into MP-BGP to be advertised to 357 remote PEs. The information necessary for accurate redistribution 358 back into OSPFv3 by the remote PEs is carried in the OSPF Route Type, 359 OSPF Domain ID, and OSPF Router ID Extended Communities attributes 360 (Section 4.4). The relevant local OSPFv3 information encoded into 361 these attributes are: 363 The Area ID of the PE-CE link. 365 The Route Type, as determined by the LSA type from which the route 366 was learned. 368 The Options fields (External metric-type) 370 The Domain ID of the OSPFv3 process. If no Domain ID is 371 configured, the NULL identifier is used. 373 The PE's Router ID associated with the OSPFv3 instance. 375 A Multi-Exit-Discriminator (MED) attribute SHOULD also be set to the 376 value of the OSPFv3 metric associated with the route plus 1, when the 377 OSPFv3 route is redistributed into the MP-BGP. 379 4.3.2. VPN-IPv6 Routes Received from MP-BGP 381 When a PE receives a valid VPN-IPv6 route from MP-BGP and has 382 identified an association with a local VRF, it must determine: 384 Whether a route to the corresponding IPv6 prefix is to be 385 installed in the VRF; 387 Whether the installed IPv6 route is to be redistributed to one or 388 more local OSPFv3 instances; and 390 What OSPFv3 LSA type is to be used when advertising the route into 391 each OSPFv3 instance 393 An IPv6 route derived from a received VPN-IPv6 route is not installed 394 in the associated local VRF if: 396 The BGP decision process identifies a better route to the 397 destination NLRI 399 A configured import policy prohibits the installation of the route 401 The PE advertises the IPv6 route learned from MP-BGP to attached CEs 402 via OSPFv3 if: 404 No configured filtering prohibits redistributing the route to 405 OSPFv3 406 No configured policy blocks the route in favor of a less-specific 407 summary route 409 Redistribution of a BGP learned IPv6 route into OSPF is based on 410 local policy. 412 The subsequent sections discuss the advertisement of routes learned 413 from MP-BGP, and the rules for determining what LSA types and what 414 CEs to advertise the routes to. 416 When the PE sends an LSA to a CE, it sets the DN bit in the LSA to 417 prevent looping. The DN bit is discussed in Section 4.5.1. 419 4.3.2.1. OSPF Inter-Area Routes 421 A PE advertises an IPv6 route using an Inter-Area-Prefix (type 422 0x2003) LSA under the following circumstances: 424 The OSPFv3 domain from which the IPv6 route was learned is the 425 same (as determined by the Domain ID) as the domain of the OSPFv3 426 instance into which it is to be redistributed; AND 428 The IPv6 route was advertised to a remote PE in an Intra-Area- 429 Prefix (type 0x2009) OR an Inter-Area-Prefix (type 0x2003) LSA. 431 Note that under these rules the PE represents itself as an Area 432 Border Router (ABR) regardless of whether or not the route is being 433 advertised into the same area number from which the remote PE learned 434 it (that is, whether the VPN-IPv6 route carries the same or different 435 area numbers). 437 4.3.2.2. OSPF Intra-Area Route 439 A route is advertised as an intra-area route using an Intra-Area- 440 Prefix (type 0x2009) LSA only when sham links are used, as described 441 in Section 5. Otherwise routes are advertised as either inter-area 442 (Section 4.3.2.1) or external/NSSA (Sections 4.3.2.3) routes. 444 4.3.2.3. OSPF External Routes And NSSA Routes 446 A PE considers an IPv6 route to be external under the following 447 circumstances: 449 The OSPFv3 domain from which the route was learned is different 450 (as determined by the Domain ID) from the domain of the OSPFv3 451 instance into which it is redistributed; OR 452 The OSPFv3 domain from which the route was learned is the same as 453 the domain of the OSPFv3 instance into which it is redistributed 454 AND it was advertised to the remote PE in an AS-External (type 455 0x4005) or a Type-7 (type 0x2007, NSSA) LSA; OR 457 The route was not learned from an OSPFv3 instance 459 To determine if the learned route is from a different domain, the 460 Domain ID associated with the VPN-IPv6 route (in the OSPF Domain ID 461 Extended Communities attribute or attributes) is compared with the 462 local OSPFv3 Domain ID, if configured. Compared Domain IDs are 463 considered identical if: 465 1. All eight bytes are identical; or 467 2. Both Domain IDs are NULL (all zeroes). 469 Note that if the VPN-IPv6 route does not have a Domain ID in its 470 attributes, or if the local OSPFv3 instance does not have a 471 configured Domain ID, in either case the route is considered to have 472 a NULL Domain ID. 474 An IPv6 route that is determined to be external might or might not be 475 advertised to a connected CE, depending on the type of area to which 476 the PE-CE link belongs and whether there is a configured policy 477 restricting its advertisement. 479 If there are multiple external routes to the same prefix, the 480 standard OSPFv3 decision process is used to select the "best" route. 482 If the external route is to be advertised and the area type of the 483 PE-CE link is NSSA, the PE advertises the route in a Type-7 (type 484 0x2007) LSA; otherwise the external route is advertised in an AS- 485 External (type 0x4005) LSA. 487 The DN bit of the LSA advertising the external route MUST be set, as 488 described in Section 4.5.1. 490 If the VPN-IPv6 route indicates a route type-1 metric, the PE should 491 advertise the external route with that metric-type; otherwise the 492 metric-type of the external IPv6 route is set to type-2 by default. 493 Note that by default, a PE should advertise an external route with a 494 type-2 metric if the IPv6 route's Domain ID is different than the 495 local OSPFv3 instance, unless specified otherwise by local policy. 497 4.4. BGP Extended Communities Attribute 499 OSPFv3 routes from one site are translated and delivered 500 transparently to the remote site as BGP VPN-IPv6 routes. The 501 original OSPFv3 routes carry OSPFv3 specific information which need 502 to be communicated to the remote PE to ensure transparency. BGP 503 Extended Communities are used to carry the needed information to 504 enable the receiving side to reconstruct a database just as in the 505 OSPFv2 case. 507 All OSPFv3 routes added to the VRF routing table on a PE router are 508 examined to create a corresponding VPN-IPv6 route in BGP. Each of 509 the OSPFv3 routes MUST have corresponding the BGP Extended 510 Communities Attributes which contain and preserve the OSPFv3 511 information of the original OSPFv3 route. The BGP Extended 512 Communities attributes defined in [rfc4577] are reused for 513 convenience. 515 OSPF Domain Identifier Extended Communities Attribute 517 Each OSPFv3 Instance within a VRF MUST have a Domain ID. The Domain 518 ID is configured per OSPFv3 Instance. The OSPFv3 Domain ID is a 519 6-byte number and its default value is 0. This attribute has a two 520 byte type field, encoded with a value of 0x0005, 0x0105, or 0x0205. 522 0 1 2 3 523 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 1 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 | Type Value | Domain Identifier | 526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 527 | Domain Identifier Cont. | 528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 The OSPF Domain Identifier Extended Communities Attribute 532 OSPFv3 Domain IDs field : 6 bytes 534 Each OSPFv3 Instance within a VRF MUST have a Domain ID and its 535 default value (if none is configured) is 0. The Domain ID is 536 configured per OSPFv3 Instance. 538 OSPF Router ID Extended Communities Attribute 540 The OSPFv3 Router ID is a 32-bit number as in OSPFv2. This attribute 541 has a two byte type field, encoded with a value of 0x0107. 543 0 1 2 3 544 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 1 545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 546 | Type Value | Router ID | 547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 548 | Router ID Cont. | UNUSED | 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 The OSPF Router ID Extended Communities Attribute 553 OSPFv3 Router ID field : 4 bytes 555 The OSPFv3 Router ID is a 32 bit number as in OSPFv2. Setting 556 this field is OPTIONAL and its default value is 0. 558 OSPF Route Type Extended Communities Attribute 560 The OSPF Route Type Extended Communities attribute MUST be present. 561 It contains a two byte type field, encoded with a value of 0x0306. 562 The remaining six bytes are divided into three fields, an Area 563 Number, a Route Type, and an Options field 565 0 1 2 3 566 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 1 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 | Type Value | Area Number | 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 570 | Area Number Cont. | Route Type | Options | 571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 573 The OSPF Route Type Extended Communities Attribute 575 Area Number : 4 bytes 577 The area number indicates the 32-bit Area ID to which the route 578 belongs. 580 Route Types : 1 byte 582 To accommodate OSPFv3 LSA types, the Route Type field is encoded 583 as follows: 585 Route Type Route Type LSA Type Description 586 Code 587 ----------------------------------------------------------- 588 3 Inter-area 0x2003 Inter-area-prefix-LSA 589 5 External 0x4005 AS-external-LSA 590 7 NSSA 0x2007 NSSA-LSA 591 1 or 2 Intra-area-prefix 0x2009 Intra-area-prefix-LSA 593 Route Type Field Encoding 595 Options : 1 byte 597 The Options field indicates the options that are associated with 598 the OSPFv3 route. 600 8 7 6 5 4 3 2 1 601 +---+---+---+---+---+---+---+---+ 602 | | | | | | | | E | 603 +---+---+---+---+---+---+---+---+ 605 The OSPFv3 Route Options Field 607 The least significant bit (i.e., bit E) in this field designates 608 the external metric type. If the bit is clear, the route carries 609 a Type-1 external metric; if the bit is set, the route carries a 610 Type-2 external metric. 612 4.5. Loop Prevention Techniques 614 In some topologies, it is possible for routing loops to occur due to 615 the nature and manner of route reachability propagation. One such 616 example is the case of a dual homed CE router connected to two PEs; 617 those PE routers would receive reachability information both through 618 their CE and their peer PE. As there is transparent transport of 619 OSPFv3 routes over the BGP/MPLS backbone, it is not possible for the 620 PE routers to determine whether they are within a loop. 622 The loop scenarios in OSPFv3 topologies are identical to those in the 623 OSPFv2 topologies described in Section 4.2.5.1 and Section 4.2.5.2 of 624 [rfc4577]. Of the two loop preventions mechanisms described in the 625 sections aforementioned, only the DN bit option will be supported in 626 the OSPFv3 implementation. 628 4.5.1. OSPFv3 Down Bit 630 Section 1 and Section 3 of [rfc4576] describe the usage of the DN-bit 631 for OSPFv2 and are applicable for OSPFv3 for inter-area-prefix LSAs, 632 NSSA LSAs and External LSAs. Similarly, the DN-bit MUST be set in 633 inter-area-prefix-LSAs, NSSA-LSAs and AS-External-LSAs, when these 634 are originated from a PE to a CE, to prevent those prefixes from 635 being re-advertised into BGP. As in [rfc4577], any LSA with the DN 636 bit set must not be used for route calculations on PE routers. 638 The DN bit MUST be clear in all other LSA types. The OSPFv3 DN-bit 639 format is described in Appendix 4.1.1 of [rfc5340]. 641 4.5.2. Other Possible Loops 643 The mechanism described in Section 4.5.1 of this document is 644 sufficient to prevent looping if the DN bit information attached to a 645 prefix is preserved in the OSPF domain. As described in Section 646 4.2.5.3 of [rfc4576], caution must be exercised if mutual 647 redistribution is performed on a PE causing loss of loop prevention 648 information. 650 5. OSPFv3 Sham Links 652 This section modifies the specification of OSPFv2 sham links (defined 653 in Section 4.2.7 of [rfc4577]) to support OSPFv3. Support for OSPFv3 654 sham links is an OPTIONAL feature of this specification. 656 A sham link enables a VPN backbone to act as an intra-area link. It 657 is needed when two sites are connected by an intra-area "backdoor" 658 link and the inter-area MPLS VPN backbone route would be less 659 preferable due to OSPF route preference rules. The figure below 660 shows the instantiation of a sham link between two VPN sites. 662 (VPN backbone) 663 (site-1) <-------- sham link --------> (site-2) 664 CE1 -------- PE1 -------- P ---------- PE2 -------- CE2 665 | | 666 |___________________________________________________| 667 <------------ backdoor link --------------> 668 (OSPF intra-area link) 670 Sham Link 672 Much of the operation of sham links remains semantically identical to 673 what was previously specified. There are, however, several 674 differences that need to be defined to ensure the proper operation of 675 OSPFv3 sham links. 677 One of the primary differences between sham links for OSPFv3 and sham 678 links as specified in [rfc4577] are for configurations where multiple 679 OSPFv3 instances populate a VRF. It may be desirable to provide 680 separate intra-area links between these instances over the same sham 681 link. To achieve this, multiple OSPFv3 instances may be established 682 across the PE-PE sham link to provide intra-area connectivity between 683 PE-CE OSPFv3 instances. 685 Note that even though multiple OSPFv3 instances may be associated 686 with a VRF, a sham link is still thought of as a relation between two 687 VRFs. 689 Another modification to OSPFv2 sham links is that OSPFv3 sham links 690 are now identified by 128-bit endpoint addresses. Since sham links 691 end-point addresses are now 128-bits, they can no longer default to 692 the RouterID, which is a 32-bit number. Sham link endpoint addresses 693 MUST be configured. 695 Sham link endpoint addresses MUST be distributed by BGP as routeable 696 VPN IPv6 addresses whose IPv6 address prefix is 128 bits long. As 697 specified in section 4.2.7.1 of [rfc4577], these endpoint addresses 698 MUST NOT be advertised by OSPFv3; if there is no BGP route to the 699 sham link endpoint address, that address is to appear unreachable, so 700 that the sham link appears to be down. 702 If there is a BGP route to the remote sham link endpoint address, the 703 sham link appears to be up. Conversely, if there is no BGP route to 704 the sham link endpoint address, the sham link appears to be down. 706 5.1. Creating A Sham link 708 The procedures for creating an OSPFv3 sham link are identical to 709 those specified in Section 4.2.7.2 of [rfc4577]. Note that the 710 creation of OSPFv3 sham links requires the configuration of both 711 local and remote 128-bit sham link endpoint addresses. The local 712 Sham link endpoint address associated with a VRF MAY be used by all 713 OSPFv3 instances that are attached to that VRF. The OSPFv3 PE-PE 714 "link" Instance ID in the protocol packet header is used to 715 demultiplex multiple OSPFv3 instance protocol packets exchanged over 716 the sham link. 718 5.2. OSPF Protocol On Sham link 720 Much of the operation of OSPFv3 over a sham link is semantically the 721 same as the operation of OSPFv2 over a sham link, as described in 722 Section 4.2.7.3 of [rfc4577]. This includes the methodology for 723 sending and receiving OSPFv3 packets over sham links, as well as 724 Hello/Router Dead Intervals. Furthermore, the procedures associated 725 with the assignment of sham link metrics adhere to those set forth 726 for OSPFv2. OSPFv3 sham links are treated as on demand circuits. 728 Although the operation of the OSPFv3 protocol over the sham link is 729 the same as OSPFv2, multiple OSPFv3 instances may be instantiated 730 across this link. By instantiating multiple instances across the 731 sham link, distinct intra-area connections can be established between 732 PE-PE OSPFv3 instances associated with the endpoint addresses. 734 For example, if two OSPFv3 instances (O1, O2) attach to a VRF V1, and 735 on a remote PE, two other OSPFv3 instances (O3, O4) attach to a VRF 736 V2, it may be desirable to connect, O1 and O3 with an intra-area 737 link, and O2 and O4 with an intra-area link. This can be 738 accomplished by instantiating two OSPFv3 instances across the sham 739 link, which connects V1 and V2. O1 and O3 can be mapped to one of 740 the sham link OSPFv3 instances; O2 and O4 can be mapped to the other 741 sham link OSPFv3 instance. 743 5.3. OSPF Packet Forwarding On Sham Link 745 The rules associated with route redistribution, stated in Section 746 4.2.7.4 of [rfc4577], remain unchanged in this specification. 747 Specifically: 749 If the next hop interface for a particular route is a sham link, 750 then the PE SHOULD NOT redistribute that route into BGP as a VPN- 751 IPv6 route. 753 Any other route advertised in an LSA that is transmitted over a 754 sham link MUST also be redistributed (by the PE flooding the LSA 755 over the sham link) into BGP. 757 When redistributing these LSAs into BGP, they are encoded with the 758 BGP Extended Communities Attributes, as defined in Section 4.4 of 759 this document. 761 When forwarding a packet, if the preferred route for that packet has 762 the sham link as its next hop interface, then the packet MUST be 763 forwarded according to the corresponding BGP route (as defined in 764 [rfc4364] and [rfc4659]). 766 6. Multiple Address Family Support 768 The support of multiple address families (AF) in OSPFv3 is described 769 in [RFC5838]. [RFC5838] differentiates between AF using reserved 770 ranges of Instance IDs for each AF. 772 The architecture described in this document is fully compatible with 773 [RFC5838]. The OSPFv3 PE-CE protocol can support multiple address 774 families across a MPLS VPN backbone. All AFs redistributed from 775 OSPFv3 into BGP on a PE MUST contain the BGP Extended Communities 776 Attributes as described in Section 4.4. 778 7. Security Considerations 780 The extensions described in this document are specific to the use of 781 OSPFv3 as the PE-CE protocol and do not introduce any concerns 782 regarding the use of BGP as transport of IPv6 reachability over the 783 MPLS Backbone. The Security considerations for the transport of IPv6 784 reachability information using BGP are discussed in Section 11 of 785 [rfc4659] and are not altered. 787 The new extensions defined in this document do not introduce any new 788 security concerns other than those already defined in Section 6 of 789 [rfc4577]. 791 8. IANA Considerations 793 The BGP Extended Communities Attributes in this document are already 794 referenced in IANA. 796 9. Contributors 798 Joe Lapolito 800 10. Acknowledgments 802 The authors would like to thank Kelvin Upson, Seiko Okano, Matthew 803 Everett, Dr. Vineet Mehta, Paul Wells and Marek Karasek for their 804 support of this work. Thanks to Peter Psenak, Abhay Roy, Acee 805 Lindem, Nick Weeds and Robert Hanzl for their last call comments. 807 This document was produced using Marshall Rose's xml2rfc tool. 809 11. References 811 11.1. Normative References 813 [RFC2119] Bradner, S., "Key words for use in RFC's to Indicate 814 Requirement Levels", BCP 14, RFC 2119, March 1997. 816 [RFC5838] Mirtorabi, S., Roy, A., Barnes, M., Aggarwal, R., and A. 817 Lindem, "Support of address families in OSPFv3", 818 April 2010. 820 [rfc2328] Moy, J., "OSPF Version 2", RFC 2328, April 1998. 822 [rfc2858] Bates, T., Rehkter, Y., Chandra, R., and D. Katz, 823 "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000. 825 [rfc4360] Sangli, S., Tappan, D., and Y. Rehkter, "BGP Extended 826 Communities Attribute", RFC 4360, February 2006. 828 [rfc4364] Rosen, E. and Y. Rehkter, "BGP/MPLS IP Virtual Private 829 Networks (VPNs)", RFC 4364, February 2006. 831 [rfc4576] Rosen, E., Psenak, P., and P. Pillay-Esnault, "Using a 832 Link State Advertisement (LSA) Options Bit to Prevent 833 Looping in BGP/MPLS IP Virtual Private Networks (VPNs)", 834 RFC 4576, June 2006. 836 [rfc4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the 837 Provider/Customer Edge Protocol for BGP/MPLS IP Virtual 838 Private Networks (VPNs)", RFC 4577, June 2006. 840 [rfc4659] De Clercq, J., Ooms, D., Carugi, M., and F. Lefaucheur, 841 "BGP-MPLS IP Virtual Private Network (VPN) Extension for 842 IPv6 VPN", RFC 4659, September 2006. 844 [rfc5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 845 for IPv6", RFC 5340, July 2008. 847 11.2. Informative References 849 [rfc2547] Rosen, E. and Y. Rehkter, "BGP/MPLS VPNs", RFC 2547, 850 March 1999. 852 Authors' Addresses 854 Padma Pillay-Esnault 855 Cisco Systems 856 510 McCarty Blvd 857 Milpitas, CA 95035 858 USA 860 EMail: ppe@cisco.com 862 Peter Moyer 863 Pollere, Inc 864 325M Sharon Park Drive #214 865 Menlo Park, CA 94025 866 USA 868 EMail: pete@pollere.net 869 Jeff Doyle 870 Jeff Doyle and Associates 871 9878 Teller Ct. 872 Westminster, CO 80021 873 USA 875 EMail: jdoyle@doyleassociates.net 877 Emre Ertekin 878 Booz Allen Hamilton 879 5220 Pacific Concourse Drive 880 Los Angeles, CA 90045 881 USA 883 EMail: ertekin_emre@bah.com 885 Michael Lundberg 886 Booz Allen Hamilton 887 22 Batterymarch Street 888 Boston, MA 02109 889 USA 891 EMail: lundberg_michael@bah.com