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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) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Pillay-Esnault 3 Internet-Draft Cisco Systems 4 Intended status: Standards Track P. Moyer 5 Expires: March 13, 2011 Pollere, Inc 6 J. Doyle 7 Jeff Doyle and Associates 8 E. Ertekin 9 M. Lundberg 10 Booz Allen Hamilton 11 September 9, 2010 13 OSPFv3 as a PE-CE routing protocol 14 draft-ietf-l3vpn-ospfv3-pece-06 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 March 13, 2011. 62 Copyright Notice 64 Copyright (c) 2010 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. OSPFv3 Route Extended Communities Attribute . . . . . . . 11 104 4.5. Loop Prevention Techniques . . . . . . . . . . . . . . . . 13 105 4.5.1. OSPFv3 Down Bit . . . . . . . . . . . . . . . . . . . 14 106 4.5.2. Other Possible Loops . . . . . . . . . . . . . . . . . 14 107 5. OSPFv3 Sham Links . . . . . . . . . . . . . . . . . . . . . . 14 108 5.1. Creating A Sham link . . . . . . . . . . . . . . . . . . . 15 109 5.2. OSPF Protocol On Sham link . . . . . . . . . . . . . . . . 16 110 5.3. OSPF Packet Forwarding On Sham Link . . . . . . . . . . . 16 111 6. Multiple Address Family Support . . . . . . . . . . . . . . . 17 112 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 113 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 114 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 an AS-External OSPFv3 LSAs. Instead, 193 it may be desirable to view these LSAs as inter-area-prefix LSAs. 194 For the encoding of OSPFv3 LSAs, a new OSPFv3 Route Extended 195 Community attribute is defined in Section 4.4. 197 Multiple instances over a link: 199 OSPFv3 operates on a per-link basis as opposed to OSPFv2, which 200 operates on a per-IP-subnet basis. The support of multiple OSPFv3 201 protocol instances on a link changes the architecture described in 202 [rfc4577]. [rfc4577] specifies that each interface belongs to no 203 more than one OSPF instance. For OSPFv3, multiple instances can 204 be established over a single interface, and associated with the 205 same VRF. 207 In addition to establishing multiple OSPFv3 instances over a 208 single PE-CE link, multiple OSPFv3 instances can also be 209 established across a sham link. This enables multiple OSPFv3 210 instances associated with a VRF to independently establish intra- 211 area connectivity to other OSPFv3 instances attached to a remote 212 PE VRF. Support for multiple OSPFv3 instances across the sham 213 link is described in Section 5. 215 4. BGP/OSPFv3 Interaction Procedures for PE Routers 217 4.1. VRFs and OSPFv3 Instances 219 The relationship between VRFs, interfaces, and OSPFv3 instances on a 220 PE router is described in the following section. 222 As defined in [rfc4364], a PE router can be configured with one or 223 more VRFs. Each VRF configured on the PE corresponds to a customer 224 VPN, and retains the destinations that are reachable within that VPN. 225 Each VRF may be associated with one or more interfaces, which allows 226 multiple sites to participate in the same VPN. If OSPFv3 is 227 instantiated on an interface associated with a VRF, the VRF will be 228 populated with OSPFv3 routing information. 230 As OSPFv3 supports multiple instances on a single interface, it is 231 therefore possible that multiple customer sites can connect to the 232 same interface of a PE router (e.g., through a layer 2 switch) using 233 distinct OSPFv3 instances. However, since a PE interface can be 234 associated with only one VRF, all OSPFv3 instances running on the 235 same interface MUST be associated with the same VRF. 237 4.1.1. Independent OSPFv3 Instances in PEs 239 Similar to [rfc4577], the PE must associate at least one OSPFv3 240 instance for each OSPFv3 domain to which it attaches, and each 241 instance of OSPFv3 MUST be associated with a single VRF. 243 The support of multiple PE-CE OSPFv3 instances per PE interface does 244 not change the paradigm that an OSPF instance can be associated with 245 only a single VRF. Furthermore, for each instance instantiated on 246 the interface, the PE establishes adjacencies with corresponding CEs 247 associated with the instance. Note that although multiple instances 248 may populate a common VRF, they do not leak routes to one another, 249 unless configured to do so. 251 4.1.2. OSPFv3 Domain Identifier 253 The OSPFv3 Domain ID describes the administrative domain of the OSPF 254 instance which originated the route. It has an AS wide significance 255 and is one of the parameters used to determine whether a VPN-IPv6 256 route should be translated as an Inter-area-prefix-LSA or External- 257 LSA. Each OSPFv3 instance MUST have a primary Domain ID which is 258 transported along with the VPN-IPv6 route in a BGP attribute over the 259 MPLS VPN backbone. Each OSPFv3 instance may have a set of secondary 260 Domain IDs which applies to other OSPFv3 instances within its 261 administrative domain. 263 The primary Domain ID may either be configured or may be set to a 264 value of NULL. The secondary Domain IDs are only allowed if a non- 265 null primary Domain ID is configured. The Domain ID MUST be 266 configured on a per-OSPFv3 instance basis. 268 The Domain ID is used to determine whether an incoming VPN-IPv6 route 269 belongs to the same domain as the receiving OSPFv3 instance. An 270 incoming VPN-IPv6 route is said to belong to the same domain if a 271 non-NULL incoming Domain ID matches either the local primary or one 272 of the secondary Domain IDs. If the local Domain ID and incoming 273 Domain ID are NULL, it is considered a match. 275 4.2. OSPFv3 Areas 277 Sections 4.1.4 and 4.2.3 of [rfc4577] describe the characteristics of 278 a PE router within an OSPFv2 domain. The mechanisms and expected 279 behavior described in [rfc4577] are applicable to an OSPFv3 domain. 281 4.3. VRFs and Routes 283 From the perspective of the CE, the PE appears as any other OSPFv3 284 neighbor. There is no requirement for the CE to support any 285 mechanisms of IPv6 BGP/MPLS VPNs or for the CE to have any awareness 286 of the VPNs, thereby enabling any OSPFv3 implementation to be used on 287 a CE. 289 Because the export and import policies might cause different routes 290 to be installed in different VRFs of the same OSPFv3 domain, the MPLS 291 VPN backbone cannot be considered as a single router from the 292 perspective of the domain's CEs. Rather, each CE should view its 293 connected PE as a separate router. 295 The PE uses OSPFv3 to distribute routes to CEs, and MP-BGP [rfc2858] 296 to distribute VPN-IPv6 routes to other (remote) PE routers as defined 297 in [rfc4659]. An IPv6 prefix installed in the VRF by OSPFv3 is 298 changed to a VPN-IPv6 prefix by the addition of an 8-octet Route 299 Distinguisher (RD) as discussed in Section 2 of [rfc4659]. This VPN- 300 IPv6 route can then be redistributed into MP-BGP according to an 301 export policy that adds a Route Target Extended Communities (RT) 302 attribute to the NLRI [rfc4360]. An IPv6 Address Specific BGP 303 Extended Communities attribute as described in [rfc5701] may also be 304 attached to the route. 306 Domain IDs are used to distinguish between OSPFv3 instances. When an 307 OSPFv3 distributed route is redistributed into MP-BGP, the Domain ID, 308 OSPFv3 Router ID, Area, OSPFv3 Route Type, and Options fields 309 (External Route Type) are also carried in an attribute of the MP-BGP 310 route. 312 A PE receiving a VPN-IPv6 NLRI from MP-BGP uses an import policy to 313 determine, based on the RT, whether the route is eligible to be 314 installed in one of its local VRFs. The BGP decision process selects 315 which of the eligible routes are to be installed in the associated 316 VRF, and the selected set of VPN-IPv6 routes are converted into IPv6 317 routes by removing the RD before installation. 319 An IPv6 route learned from MP-BGP and installed in a VRF might or 320 might not be redistributed into OSPFv3, depending on the local 321 configuration. For example, the PE might be configured to advertise 322 only a default route to CEs of a particular OSPFv3 instance. 323 Further, if the route is to be redistributed into multiple OSPFv3 324 instances, the route might be advertised using different LSA types in 325 different instances. 327 If an IPv6 route learned from MP-BGP is to be redistributed into a 328 particular OSPFv3 instance, the OSPFv3 Route Extended Community 329 attribute (Section 4.4) of the VPN-IPv6 route is used to determine 330 whether the OSPFv3 instance from which the route was learned is the 331 same as the OSPFv3 instance into which the route is to be 332 redistributed. 334 4.3.1. OSPFv3 Routes on PE 336 VRFs may be populated by both OSPFv3 routes from a CE or VPN-IPv6 337 routes from other PEs via MP-BGP. OSPFv3 routes are installed in a 338 VRF using the OSPFv3 decision process. As described in [rfc4577], 339 OSPFv2 routes installed in a VRF may be redistributed into BGP and 340 disseminated to other PEs participating in the VPN. At these remote 341 PEs, the VPN-IPv6 routes may be imported into a VRF and redistributed 342 into the OSPFv3 instance(s) associated with that VRF. 344 As specified in [rfc4659], routes imported and exported into a VRF 345 are controlled by the Route Target (RT) Extended Communities 346 attribute. OSPFv3 routes that are redistributed into BGP are given a 347 RT that corresponds to the VRF. This RT is examined at remote PEs. 348 In order to import a route, a VRF must have a RT that is identical to 349 the route's RT. For routes which are eligible to be imported into 350 the VRF, the standard BGP decision process is used to choose the 351 "best" route(s). 353 When a route is advertised from a CE to a PE via OSPFv3 and that 354 route is installed in the VRF associated with the CE, the route is 355 advertised to other locally attached CEs under normal OSPFv3 356 procedures. 358 The route is also redistributed into MP-BGP to be advertised to 359 remote PEs. The information necessary for accurate redistribution 360 back into OSPFv3 by the remote PEs is carried in an OSPFv3 Route 361 Extended Communities attribute (Section 4.4). The relevant local 362 OSPFv3 information encoded into the attribute is: 364 The Domain ID of the local OSPFv3 process. If no Domain ID is 365 configured, the NULL identifier is used. 367 The Area ID of the PE-CE link. 369 The PE's Router ID associated with the OSPFv3 instance. 371 The Route Type, as determined by the LSA type from which the route 372 was learned. 374 The Options fields (External metric-type) 376 A Multi-Exit-Discriminator (MED) attribute SHOULD also be set to the 377 value of the OSPFv3 distance associated with the route plus 1, when 378 the OSPFv3 route is redistributed into the MP-BGP. 380 4.3.2. VPN-IPv6 Routes Received from MP-BGP 382 When a PE receives a valid VPN-IPv6 route from MP-BGP and has 383 identified an association with a local VRF, it must determine: 385 Whether a route to the corresponding IPv6 prefix is to be 386 installed in the VRF; 388 Whether the installed IPv6 route is to be redistributed to one or 389 more local OSPFv3 instances; and 391 What OSPFv3 LSA type is to be used when advertising the route into 392 each OSPFv3 instance 394 An IPv6 route derived from a received VPN-IPv6 route is not installed 395 in the associated local VRF if: 397 The BGP decision process identifies a better route to the 398 destination NLRI 400 A configured import policy prohibits the installation of the route 402 The PE advertises the IPv6 route learned from MP-BGP to attached CEs 403 via OSPFv3 if: 405 No configured filtering prohibits redistributing the route to 406 OSPFv3 407 No configured policy blocks the route in favor of a less-specific 408 summary route 410 No OSPFv3 route to the same prefix exists in the VRF. 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 ABR 432 regardless of whether or not the route is being advertised into the 433 same area number from which the remote PE learned it (that is, 434 whether the VPN-IPv6 route carries the same or different area 435 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 453 The OSPFv3 domain from which the route was learned is the same as 454 the domain of the OSPFv3 instance into which it is redistributed 455 AND it was advertised to the remote PE in an AS-External (type 456 0x4005) or a Type-7 (type 0x2007, NSSA) LSA; OR 458 The route was not learned from an OSPFv3 instance 460 To determine if the learned route is from a different domain, the 461 Domain ID associated with the VPN-IPv6 route (in the OSPFv3 Route 462 Extended Communities attribute or attributes) is compared with the 463 local OSPFv3 Domain ID, if configured. Compared Domain IDs are 464 considered identical if: 466 1. All six bytes are identical; or 468 2. Both Domain IDs are NULL (all zeroes). 470 Note that if the VPN-IPv6 route does not have a Domain ID in its 471 attributes, or if the local OSPFv3 instance does not have a 472 configured Domain ID, in either case the route is considered to have 473 a NULL Domain ID. 475 An IPv6 route that is determined to be external might or might not be 476 advertised to a connected CE, depending on the type of area to which 477 the PE-CE link belongs and whether there is a configured policy 478 restricting its advertisement. 480 If there are multiple external routes to the same prefix, the 481 standard OSPFv3 decision process is used to select the "best" route. 483 If the external route is to be advertised and the area type of the 484 PE/CE link is NSSA, the PE advertises the route in a Type-7 (type 485 0x2007) LSA; otherwise the external route is advertised in an AS- 486 External (type 0x4005) LSA. 488 The DN bit of the LSA advertising the external route MUST be set, as 489 described in Section 4.5.1. 491 If the VPN-IPv6 route indicates a route type-1 metric, the PE 492 advertises the external route with that metric-type; otherwise the 493 metric-type of the external IPv6 route is set to type-2 by default. 495 4.4. OSPFv3 Route Extended Communities Attribute 497 OSPFv3 routes from one site are translated and delivered 498 transparently to the remote site as BGP VPN-IPv6 routes. The 499 original OSPFv3 routes carry OSPFv3 specific information which need 500 to be communicated to the remote PE to ensure transparency. BGP 501 extended communities are used to carry the needed information to 502 enable the receiving side to reconstruct a database just as in the 503 OSPFv2 case. 505 All OSPFv3 routes added to the VRF routing table on a PE router are 506 examined to create a corresponding VPN-IPv6 route in BGP. Each of 507 the OSPFv3 routes MUST have a corresponding BGP Extended Community 508 Attribute which contains and preserves the OSPFv3 information 509 attached to the original OSPFv3 route. 511 This document defines a new BGP attribute in the proposed "IPv6 512 Address Specific Extended Community" registry described in Section 3 513 of [rfc5701]. The OSPFv3 Route Extended Community Attribute has the 514 Sub-type value of 0x0004. It carries an OSPFv3 Domain ID, OSPFv3 515 Router ID, OSPFv3 Area ID, OSPFv3 Route type, and Options field. 517 0 1 2 3 518 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 1 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 | 0x00 | 4 | OSPF Domain ID | 522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 523 | OSPF Domain ID (Cont.) | 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 | OSPF Router ID | 526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 527 | Area ID | 528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 529 | Route Type | Options | UNUSED | 530 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 532 The OSPFv3 Route Extended Community Attribute 534 This attribute is MANDATORY for all OSPFv3 routes in a VRF instance 535 on a PE router. The fields of this new BGP Extended Community 536 attribute are described in the following sections. 538 OSPFv3 Domain IDs field : 6 bytes 540 Each OSPFv3 Instance within a VRF MUST have a Domain ID. The 541 Domain ID is configured per OSPFv3 Instance. The OSPFv3 Domain ID 542 is a 6-byte number and its default value is 0. 544 OSPFv3 Router ID field : 4 bytes 546 The OSPFv3 Router ID is a 32 bit number as in OSPFv2. Setting 547 this field is OPTIONAL and its default value is 0. 549 OSPFv3 Area ID : 4 bytes 551 The Area ID field indicates the 32-bit Area ID to which the route 552 belongs. 554 OSPFv3 Route Types : 1 byte 556 To accommodate OSPFv3 LSA types, the OSPF Route Type field is 557 encoded as follows: 559 Route Type Route Type LSA Type Description 560 Code 561 ----------------------------------------------------------- 562 0x30 Inter-area 0x2003 Inter-area-prefix-LSA 563 0x50 External 0x4005 AS-external-LSA 564 0x70 NSSA 0x2007 NSSA-LSA 565 0x90 Intra-area-prefix 0x2009 Intra-area-prefix-LSA 567 The OSPFv3 Route Type Field Encoding 569 OSPFv3 Route Options : 1 byte 571 The Options field indicates the options that are associated with 572 the OSPFv3 route. 574 8 7 6 5 4 3 2 1 575 +---+---+---+---+---+---+---+---+ 576 | | | | | | | | E | 577 +---+---+---+---+---+---+---+---+ 579 The OSPFv3 Route Options Field 581 The least significant bit (i.e., bit E) in this field designates 582 the external metric type. If the bit is clear, the route carries 583 a Type-1 external metric; if the bit is set, the route carries a 584 Type-2 external metric. 586 4.5. Loop Prevention Techniques 588 In some topologies, it is possible for routing loops to occur due to 589 the nature and manner of route reachability propagation. One such 590 example is the case of a dual homed CE router connected to two PEs; 591 those PE routers would receive this information both through their CE 592 and their peer PE. As there is transparent transport of OSPFv3 593 routes over the BGP/MPLS backbone, it is not possible for the PE 594 routers to determine whether they are within a loop. 596 The loop scenarios in OSPFv3 topologies are identical to those in the 597 OSPFv2 topologies described in Section 4.2.5.1 and Section 4.2.5.2 of 598 [rfc4577]. Of the two loop preventions mechanisms described in the 599 sections aforementioned, only the DN bit option will be supported in 600 the OSPFv3 implementation. 602 4.5.1. OSPFv3 Down Bit 604 Section 1 and Section 3 of [rfc4576] describe the usage of the DN-bit 605 for OSPFv2 and are applicable for OSPFv3 for inter-area-prefix LSAs, 606 NSSA LSAs and External LSAs. Similarly, the DN-bit MUST be set in 607 inter-area-prefix-LSAs, NSSA-LSAs and AS-External-LSAs, when these 608 are originated from a PE to a CE, to prevent those prefixes from 609 being re-advertised into BGP. As in [rfc4577], any LSA with the DN 610 bit set must not be used for route calculations. 612 The DN bit MUST be clear in all other LSA types. The OSPFv3 DN-bit 613 format is described in Appendix 4.1.1 of [rfc5340]. 615 4.5.2. Other Possible Loops 617 The mechanism described in Section 4.5.1 of this document is 618 sufficient to prevent looping if the DN bit information attached to a 619 prefix is preserved in the OSPF domain. As described in Section 620 4.2.5.3 of [rfc4576], caution must be exercised if mutual 621 redistribution is performed on a PE causing loss of loop prevention 622 information. 624 5. OSPFv3 Sham Links 626 This section modifies the specification of OSPFv2 sham links (defined 627 in Section 4.2.7 of [rfc4577]) to support OSPFv3. Support for OSPFv3 628 sham links is an OPTIONAL feature of this specification. 630 A sham link enables a VPN backbone to act as an intra-area link. It 631 is needed when two sites are connected by an intra-area "backdoor" 632 link and the inter-area MPLS VPN backbone route would be less 633 preferable due to OSPF route preference rules. The figure below 634 shows the instantiation of a sham link between two VPN sites. 636 (VPN backbone) 637 (site-1) <-------- sham link --------> (site-2) 638 CE1 -------- PE1 -------- P ---------- PE2 -------- CE2 639 | | 640 |___________________________________________________| 641 <------------ backdoor link --------------> 642 (OSPF intra-area link) 644 Sham Link 646 Much of the operation of sham links remains semantically identical to 647 what was previously specified. There are, however, several 648 differences that need to be defined to ensure the proper operation of 649 OSPFv3 sham links. 651 One of the primary differences between sham links for OSPFv3 and sham 652 links as specified in [rfc4577] are for configurations where multiple 653 OSPFv3 instances populate a VRF. It may be desirable to provide 654 separate intra-area links between these instances over the same sham 655 link. To achieve this, multiple OSPFv3 instances may be established 656 across the PE-PE sham link to provide intra-area connectivity between 657 PE-CE OSPFv3 instances. 659 Note that even though multiple OSPFv3 instances may be associated 660 with a VRF, a sham link is still thought of as a relation between two 661 VRFs. 663 Another modification to OSPFv2 sham links is that OSPFv3 sham links 664 are now identified by 128-bit endpoint addresses. Since sham links 665 end-point addresses are now 128-bits, they can no longer default to 666 the RouterID, which is a 32-bit number. Sham link endpoint addresses 667 MUST be configured. 669 Sham link endpoint addresses MUST be distributed by BGP as routeable 670 VPN IPv6 addresses whose IPv6 address prefix is 128 bits long. As 671 specified in section 4.2.7.1 of [rfc4577], these endpoint addresses 672 MUST NOT be advertised by OSPFv3; if there is no BGP route to the 673 sham link endpoint address, that address is to appear unreachable, so 674 that the sham link appears to be down. 676 If there is a BGP route to the remote sham link endpoint address, the 677 sham link appears to be up. Conversely, if there is no BGP route to 678 the sham link endpoint address, the sham link appears to be down. 680 5.1. Creating A Sham link 682 The procedures for creating an OSPFv3 sham link are identical to 683 those specified in Section 4.2.7.2 of [rfc4577]. Note that the 684 creation of OSPFv3 sham links requires the configuration of both 685 local and remote 128-bit sham link endpoint addresses. The local 686 Sham link endpoint address associated with a VRF MAY be used by all 687 OSPFv3 instances that are attached to that VRF. The OSPFv3 PE-PE 688 "link" Instance ID in the protocol packet header is used to 689 demultiplex multiple OSPFv3 instance protocol packets exchanged over 690 the sham link. 692 5.2. OSPF Protocol On Sham link 694 Much of the operation of OSPFv3 over a sham link is semantically the 695 same as the operation of OSPFv2 over a sham link, as described in 696 Section 4.2.7.3 of [rfc4577]. This includes the methodology for 697 sending and receiving OSPFv3 packets over sham links, as well as 698 Hello/Router Dead Intervals. Furthermore, the procedures associated 699 with the assignment of sham link metrics adhere to those set forth 700 for OSPFv2. OSPFv3 sham links are treated as on demand circuits. 702 Although the operation of the OSPFv3 protocol over the sham link is 703 the same as OSPFv2, multiple OSPFv3 instances may be instantiated 704 across this link. By instantiating multiple instances across the 705 sham link, distinct intra-area connections can be established between 706 PE-PE OSPFv3 instances associated with the endpoint addresses. 708 For example, if two OSPFv3 instances (O1, O2) attach to a VRF V1, and 709 on a remote PE, two other OSPFv3 instances (O3, O4) attach to a VRF 710 V2, it may be desirable to connect, O1 and O3 with an intra-area 711 link, and O2 and O4 with an intra-area link. This can be 712 accomplished by instantiating two OSPFv3 instances across the sham 713 link, which connects V1 and V2. O1 and O3 can be mapped to one of 714 the sham link OSPFv3 instances; O2 and O4 can be mapped to the other 715 sham link OSPFv3 instance. 717 5.3. OSPF Packet Forwarding On Sham Link 719 The rules associated with route redistribution, stated in Section 720 4.2.7.4 of [rfc4577], remain unchanged in this specification. 721 Specifically: 723 If the next hop interface for a particular route is a sham link, 724 then the PE SHOULD NOT redistribute that route into BGP as a VPN- 725 IPv6 route. 727 Any other route advertised in an LSA that is transmitted over a 728 sham link MUST also be redistributed (by the PE flooding the LSA 729 over the sham link) into BGP. 731 When redistributing these LSAs into BGP, they are encoded with the 732 OSPFv3 Route Extended Community, as defined in Section 4.4 of this 733 document. 735 When forwarding a packet, if the preferred route for that packet has 736 the sham link as its next hop interface, then the packet MUST be 737 forwarded according to the corresponding BGP route (as defined in 738 [rfc4364] and [rfc4659]). 740 6. Multiple Address Family Support 742 The support of multiple address families (AF) in OSPFv3 is described 743 in [RFC5838]. [RFC5838] differentiates between AF using reserved 744 ranges of Instance IDs for each AF. 746 The architecture described in this document is fully compatible with 747 [RFC5838]. The OSPFv3 PE-CE protocol can support multiple address 748 families across a MPLS VPN backbone. All AFs redistributed from 749 OSPFv3 into BGP on a PE MUST contain the OSPFv3 Route Extended 750 Community Attribute. 752 Note that since [RFC5838] does not support multiple AFs across 753 virtual links, this document only addresses support for unicast IPv6 754 addresses across the sham link. 756 7. Security Considerations 758 The extensions described in this document are specific to the use of 759 OSPFv3 as the PE-CE protocol and do not introduce any concerns 760 regarding the use of BGP as transport of IPv6 reachability over the 761 MPLS Backbone. The Security considerations for the transport of IPv6 762 reachability information using BGP are discussed in Section 11 of 763 [rfc4659] and are not altered. 765 The new extensions defined in this document do not introduce any new 766 security concerns other than those already defined in Section 6 of 767 [rfc4577]. 769 8. IANA Considerations 771 This document defines a new BGP attribute in the proposed "IPv6 772 Address Specific Extended Community" registry described in Section 3 773 of [rfc5701]. This document makes the following assignments in the 774 "IPv6 Address Specific Extended Community" registry. 776 Name Sub-type Value 777 ---- -------------- 778 OSPFv3 Route Attributes 0x0004 779 The OSPFv3 specific BGP Extended Community types 781 This document also defines a new "OSPFv3 Route Attribute Options" 782 registry. Represented by 8 bits, the new registry documents the 783 contents of the Options field in the OSPFv3 Route Attributes Extended 784 Community. This document makes the following assignment in the 785 "OSPFv3 Route Attribute Options" registry. 787 Value Description Reference 788 ----- ----------- --------- 789 0x01 External Metric Type [rfcThis] 791 OSPFv3 Route Attribute Options 793 Following the policies outlined in [RFC5226], the IANA policy for 794 assigning the remaining bits for the "OSPFv3 Route Attribute Options" 795 registry shall be "Standards Action": values are assigned only for 796 Standards Track RFCs approved by the IESG. 798 9. Contributors 800 Joe Lapolito 802 10. Acknowledgments 804 The authors would like to thank Kelvin Upson, Seiko Okano, Matthew 805 Everett, and Dr. Vineet Mehta for their support of this work. Thanks 806 to Peter Psenak, Abhay Roy and Acee Lindem for their last call 807 comments. 809 This document was produced using Marshall Rose's xml2rfc tool. 811 11. References 813 11.1. Normative References 815 [RFC2119] Bradner, S., "Key words for use in RFC's to Indicate 816 Requirement Levels", BCP 14, RFC 2119, March 1997. 818 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 819 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 820 May 2008. 822 [RFC5838] Mirtorabi, S., Roy, A., Barnes, M., Aggarwal, R., and A. 823 Lindem, "Support of address families in OSPFv3", 824 April 2010. 826 [rfc2328] Moy, J., "OSPF Version 2", RFC 2328, April 1998. 828 [rfc2858] Bates, T., Rehkter, Y., Chandra, R., and D. Katz, 829 "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000. 831 [rfc4360] Sangli, S., Tappan, D., and Y. Rehkter, "BGP Extended 832 Communities Attribute", RFC 4360, February 2006. 834 [rfc4364] Rosen, E. and Y. Rehkter, "BGP/MPLS IP Virtual Private 835 Networks (VPNs)", RFC 4364, February 2006. 837 [rfc4576] Rosen, E., Psenak, P., and P. Pillay-Esnault, "Using a 838 Link State Advertisement (LSA) Options Bit to Prevent 839 Looping in BGP/MPLS IP Virtual Private Networks (VPNs)", 840 RFC 4576, June 2006. 842 [rfc4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the 843 Provider/Customer Edge Protocol for BGP/MPLS IP Virtual 844 Private Networks (VPNs)", RFC 4577, June 2006. 846 [rfc4659] De Clercq, J., Ooms, D., Carugi, M., and F. Lefaucheur, 847 "BGP-MPLS IP Virtual Private Network (VPN) Extension for 848 IPv6 VPN", RFC 4659, September 2006. 850 [rfc5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 851 for IPv6", RFC 5340, July 2008. 853 [rfc5701] Rehkter, Y., "IPv6 Address Specific BGP Extended 854 Communities Attribute", November 2009. 856 11.2. Informative References 858 [rfc2547] Rosen, E. and Y. Rehkter, "BGP/MPLS VPNs", RFC 2547, 859 March 1999. 861 Authors' Addresses 863 Padma Pillay-Esnault 864 Cisco Systems 865 510 McCarty Blvd 866 Milpitas, CA 95035 867 USA 869 EMail: ppe@cisco.com 870 Peter Moyer 871 Pollere, Inc 872 325M Sharon Park Drive #214 873 Menlo Park, CA 94025 874 USA 876 EMail: pete@pollere.net 878 Jeff Doyle 879 Jeff Doyle and Associates 880 9878 Teller Ct. 881 Westminster, CO 80021 882 USA 884 EMail: jdoyle@doyleassociates.net 886 Emre Ertekin 887 Booz Allen Hamilton 888 5220 Pacific Concourse Drive 889 Los Angeles, CA 90045 890 USA 892 EMail: ertekin_emre@bah.com 894 Michael Lundberg 895 Booz Allen Hamilton 896 22 Batterymarch Street 897 Boston, MA 02109 898 USA 900 EMail: lundberg_michael@bah.com