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'Ref15') (Obsoleted by RFC 2373) ** Obsolete normative reference: RFC 1885 (ref. 'Ref16') (Obsoleted by RFC 2463) -- Possible downref: Non-RFC (?) normative reference: ref. 'Ref17' -- Possible downref: Non-RFC (?) normative reference: ref. 'Ref18' ** Obsolete normative reference: RFC 1826 (ref. 'Ref19') (Obsoleted by RFC 2402) -- Possible downref: Non-RFC (?) normative reference: ref. 'Ref20' Summary: 22 errors (**), 0 flaws (~~), 14 warnings (==), 11 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Coltun 3 Internet Draft FORE Systems 4 Expiration Date: December 1996 D. Ferguson 5 File name: draft-ietf-ospf-ospfv6-02.txt Juniper Networks 6 Network Working Group J. Moy 7 Internet Draft Cascade Communications Corp. 8 June 1996 10 OSPF for IPv6 12 Status of this Memo 14 This document is an Internet-Draft. Internet-Drafts are working 15 documents of the Internet Engineering Task Force (IETF), its areas, 16 and its working groups. Note that other groups may also distribute 17 working documents as Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six 20 months and may be updated, replaced, or obsoleted by other documents 21 at any time. It is inappropriate to use Internet- Drafts as 22 reference material or to cite them other than as "work in progress". 24 To learn the current status of any Internet-Draft, please check the 25 "1id-abstracts.txt" listing contained in the Internet- Drafts Shadow 26 Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), 27 munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or 28 ftp.isi.edu (US West Coast). 30 Abstract 32 This document describes the modifications to OSPF to support version 33 6 of the Internet Protocol (IPv6). The fundamental mechanisms of 34 OSPF (flooding, DR election, area support, SPF calculations, etc.) 35 remain unchanged. However, some changes have been necessary, either 36 due to changes in protocol semantics between IPv4 and IPv6, or 37 simply to handle the increased address size of IPv6. 39 Changes between OSPF for IPv4 and this document include the 40 following. Addressing semantics have been removed from OSPF packets 41 and the basic LSAs. New LSAs have been created to carry IPv6 42 addresses and prefixes. OSPF now runs on a per-link basis, instead 43 of on a per-IP-subnet basis. Flooding scope for LSAs has been 44 generalized. Authentication has been removed from the OSPF protocol 45 itself, instead relying on IPv6's Authentication Header and 46 Encapsulating Security Payload. 48 Most packets in OSPF for IPv6 are almost as compact as those in OSPF 49 for IPv4, even with the larger IPv6 addresses. Most field- and 50 packet-size limitations present in OSPF for IPv4 have been relaxed. 51 In addition, option handling has been made more flexible. 53 All of OSPF for IPv4's optional capabilities, including on-demand 54 circuit support, NSSA areas, and the multicast extensions to OSPF 55 (MOSPF) are also supported in OSPF for IPv6. 57 Please send comments to ospf@gated.cornell.edu. 59 Table of Contents 61 1 Introduction ........................................... 5 62 1.1 Terminology ............................................ 5 63 2 Differences from OSPF for IPv4 ......................... 5 64 2.1 Protocol processing per-link, not per-subnet ........... 5 65 2.2 Removal of addressing semantics ........................ 6 66 2.3 Addition of Flooding scope ............................. 6 67 2.4 Explicit support for multiple instances per link ....... 7 68 2.5 Use of link-local addresses ............................ 7 69 2.6 Authentication changes ................................. 7 70 2.7 Packet format changes .................................. 8 71 2.8 LSA format changes ..................................... 8 72 2.9 Handling unknown LSA types ............................ 10 73 2.10 Stub area support ..................................... 11 74 2.11 Identifying neighbors by Router ID .................... 11 75 2.12 Removal of TOS ........................................ 12 76 3 Implementation details ................................ 12 77 3.1 Protocol data structures .............................. 13 78 3.1.1 The Area Data structure ............................... 14 79 3.1.2 The Interface Data structure .......................... 14 80 3.1.3 The Neighbor Data Structure ........................... 16 81 3.2 Protocol Packet Processing ............................ 16 82 3.2.1 Sending protocol packets .............................. 17 83 3.2.1.1 Sending Hello packets ................................. 18 84 3.2.1.2 Sending Database Description Packets .................. 19 85 3.2.2 Receiving protocol packets ............................ 19 86 3.2.2.1 Receiving Hello Packets ............................... 21 87 3.3 The Routing table Structure ........................... 21 88 3.3.1 Routing table lookup .................................. 22 89 3.4 Link State Advertisements ............................. 23 90 3.4.1 The LSA Header ........................................ 23 91 3.4.2 The link-state database ............................... 24 92 3.4.3 Originating LSAs ...................................... 25 93 3.4.3.1 Router-LSAs ........................................... 27 94 3.4.3.2 Network-LSAs .......................................... 29 95 3.4.3.3 Inter-Area-Prefix-LSAs ................................ 30 96 3.4.3.4 Inter-Area-Router-LSAs ................................ 31 97 3.4.3.5 AS-external-LSAs ...................................... 32 98 3.4.3.6 Link-LSAs ............................................. 34 99 3.4.3.7 Intra-Area-Prefix-LSAs ................................ 35 100 3.5 Flooding .............................................. 38 101 3.5.1 Receiving Link State Update packets ................... 38 102 3.5.2 Sending Link State Update packets ..................... 39 103 3.5.3 Installing LSAs in the database ....................... 41 104 3.6 Definition of self-originated LSAs .................... 42 105 3.7 Virtual links ......................................... 42 106 3.8 Routing table calculation ............................. 43 107 3.8.1 Calculating the shortest path tree for an area ........ 44 108 3.8.1.1 The next hop calculation .............................. 45 109 3.8.2 Calculating the inter-area routes ..................... 45 110 3.8.3 Examining transit areas' summary-LSAs ................. 46 111 3.8.4 Calculating AS external routes ........................ 46 112 References ............................................ 48 113 A OSPF data formats ..................................... 50 114 A.1 Encapsulation of OSPF packets ......................... 50 115 A.2 The Options field ..................................... 52 116 A.3 OSPF Packet Formats ................................... 54 117 A.3.1 The OSPF packet header ................................ 55 118 A.3.2 The Hello packet ...................................... 57 119 A.3.3 The Database Description packet ....................... 59 120 A.3.4 The Link State Request packet ......................... 61 121 A.3.5 The Link State Update packet .......................... 62 122 A.3.6 The Link State Acknowledgment packet .................. 63 123 A.4 LSA formats ........................................... 65 124 A.4.1 IPv6 Prefix Representation ............................ 66 125 A.4.1.1 Prefix Options ........................................ 67 126 A.4.2 The LSA header ........................................ 68 127 A.4.2.1 LS type ............................................... 70 128 A.4.3 Router-LSAs ........................................... 72 129 A.4.4 Network-LSAs .......................................... 75 130 A.4.5 Inter-Area-Prefix-LSAs ................................ 76 131 A.4.6 Inter-Area-Router-LSAs ................................ 78 132 A.4.7 AS-external-LSAs ...................................... 79 133 A.4.8 Link-LSAs ............................................. 82 134 A.4.9 Intra-Area-Prefix-LSAs ................................ 84 135 B Architectural Constants ............................... 86 136 C Configurable Constants ................................ 86 137 C.1 Global parameters ..................................... 86 138 C.2 Area parameters ....................................... 87 139 C.3 Router interface parameters ........................... 88 140 C.4 Virtual link parameters ............................... 89 141 C.5 NBMA network parameters ............................... 90 142 C.6 Point-to-MultiPoint network parameters ................ 91 143 C.7 Host route parameters ................................. 91 144 Security Considerations ............................... 92 145 Authors' Addresses .................................... 92 146 1. Introduction 148 This document describes the modifications to OSPF to support version 149 6 of the Internet Protocol (IPv6). The fundamental mechanisms of 150 OSPF (flooding, DR election, area support, SPF calculations, etc.) 151 remain unchanged. However, some changes have been necessary, either 152 due to changes in protocol semantics between IPv4 and IPv6, or 153 simply to handle the increased address size of IPv6. 155 This document is organized as follows. Section 2 describes the 156 differences between OSPF for IPv4 and OSPF for IPv6 in detail. 157 Section 3 provides implementation details for the changes. Appendix 158 A gives the OSPF for IPv6 packet and LSA formats. Appendix B lists 159 the OSPF architectural constants. Appendix C describes configuration 160 parameters. 162 1.1. Terminology 164 This document attempts to use terms from both the OSPF for IPv4 165 specification ([Ref1]) and the IPv6 protocol specifications 166 ([Ref14]). This has produced a mixed result. Most of the terms 167 used both by OSPF and IPv6 have roughly the same meaning (e.g., 168 interfaces). However, there are a few conflicts. IPv6 uses 169 "link" similarly to IPv4 OSPF's "subnet" or "network". In this 170 case, we have chosen to use IPv6's "link" terminology. "Link" 171 replaces OSPF's "subnet" and "network" in most places in this 172 document, although OSPF's Network-LSA remains unchanged (and 173 possibly unfortunately, a new Link-LSA has also been created). 175 The names of some of the OSPF LSAs have also changed. See 176 Section 2.8 for details. 178 2. Differences from OSPF for IPv4 180 Most of the algorithms from OSPF for IPv4 [Ref1] have preserved in 181 OSPF for IPv6. However, some changes have been necessary, either due 182 to changes in protocol semantics between IPv4 and IPv6, or simply to 183 handle the increased address size of IPv6. 185 The following subsections describe the differences between this 186 document and [Ref1]. 188 2.1. Protocol processing per-link, not per-subnet 190 IPv6 uses the term "link" to indicate "a communication facility 191 or medium over which nodes can communicate at the link layer" 192 ([Ref14]). "Interfaces" connect to links. Multiple IP subnets 193 can be assigned to a single link, and two nodes can talk 194 directly over a single link, even if they do not share a common 195 IP subnet (IPv6 prefix). 197 For this reason, OSPF for IPv6 runs per-link instead of the IPv4 198 behavior of per-IP-subnet. The terms "network" and "subnet" used 199 in the IPv4 OSPF specification ([Ref1]) should generally be 200 relaced by link. Likewise, an OSPF interface now connects to a 201 link instead of an IP subnet, etc. 203 This change affects the receiving of OSPF protocol packets, and 204 the contents of Hello Packets and Network-LSAs. 206 2.2. Removal of addressing semantics 208 In OSPF for IPv6, addressing semantics have been removed from 209 the OSPF protocol packets and the main LSA types, leaving a 210 network-protocol-independent core. In particular: 212 o IPv6 Addresses are not present in OSPF packets, except for 213 in LSA payloads carried by the Link State Update Packets. 214 See Section 2.7 for details. 216 o Router-LSAs and Network-LSAs no longer contain network 217 addresses, but simply express topology information. See 218 Section 2.8 for details. 220 o OSPF Router IDs, Area IDs and LSA Link State IDs remain at 221 the IPv4 size of 32-bits. They can no longer be assigned as 222 (IPv6) addresses. 224 o Neighboring routers are now always identified by Router ID, 225 where previously they had been identified by IP address on 226 broadcast and NBMA "networks". 228 2.3. Addition of Flooding scope 230 Flooding scope for LSAs has been generalized and is now 231 explicitly coded in the LSA's LS type field. There are now three 232 separate flooding scopes for LSAs: 234 o Link-local scope. LSA is flooded only on the local link, and 235 no further. Used for the new Link-LSA (see Section A.4.8). 237 o Area scope. LSA is flooded throughout a single OSPF area 238 only. Used for Router-LSAs, Network-LSAs, Inter-Area- 239 Prefix-LSAs, Inter-Area-Router-LSAs and Intra-Area-Prefix- 240 LSAs. 242 o AS scope. LSA is flooded throughout the routing domain. Used 243 for AS-external-LSAs. 245 2.4. Explicit support for multiple instances per link 247 OSPF now supports the ability to run multiple OSPF protocol 248 instances on a single link. For example, this may be required on 249 a NAP segment shared between several providers -- providers may 250 be running a separate OSPF routing domains that want to remain 251 separate even though they have one or more physical network 252 segments (i.e., links) in common. In OSPF for IPv4 this was 253 supported in a haphazard fashion using the authentication fields 254 in the OSPF for IPv4 header. 256 Another use for running multiple OSPF instances is if you want, 257 for one reason or another, to have a single link belong to two 258 or more OSPF areas. 260 Support for multiple protocol instances on a link is 261 accomplished via an "Instance ID" contained in the OSPF packet 262 header and OSPF interface structures. Instance ID solely affects 263 the reception of OSPF packets. 265 2.5. Use of link-local addresses 267 On all interfaces except virtual links, OSPF packets are sent 268 using the link-local interface address as source. A router 269 learns the link-local interface addresses of all other routers 270 attached to its links, and uses these addresses as next hop 271 information for packet forwarding. 273 On virtual links, global scope or site-local IP addresses must 274 be used as the source for OSPF protocol packets. 276 2.6. Authentication changes 278 In OSPF for IPv6, authentication has been removed from OSPF 279 itself. The "Autype" and "Authentication" fields have been 280 removed from the OSPF packet header, and all authentication 281 related fields have been removed from the OSPF area and 282 interface structures. 284 When running over IPv6, OSPF relies on the IP Authentication 285 Header (see [Ref19]) and the IP Encapsulating Security Payload 286 (see [Ref20]) to ensure integrity and 287 authentication/confidentiality of routing exchanges. 289 2.7. Packet format changes 291 OSPF for IPv6 runs directly over IPv6. Aside from this, all 292 addressing semantics have been removed from the OSPF packet 293 headers, making it essentially "network-protocol independent". 294 All addressing information is now contained in the various LSA 295 types only. 297 In detail, changes in OSPF packet format consist of the 298 following: 300 o The OSPF version number has been increased from 2 to 3. 302 o The Options field in Hello Packets and Database description 303 Packets has been expanded to 24-bits. 305 o The Authentication and AuType fields have been removed from 306 the OSPF packet header (see Section 2.6). 308 o The Hello packet now contains no address information at all, 309 and includes a Interface ID which the originating router has 310 assigned to uniquely identify (among its own interfaces) its 311 interface to the link. This Interface ID becomes the 312 Network-LSA's Link State ID, should the router become 313 Designated Router on the link. 315 o Two options bits, the "R-bit" and the "V6-bit", have been 316 added to the Options field for processing Router-LSAs during 317 the SPF calculation (see Section A.2). If the "R-bit" is 318 clear an OSPF speaker can participate in OSPF topology 319 distribution without being used to forward transit traffic; 320 this can be used in multi-homed hosts that want to 321 participate in the routing protocol. The V6-bit specializes 322 the R-bit; if the V6-bit is clear an OSPF speaker can 323 participate in OSPF topology distribution without being used 324 to forward IPv6 datagrams. If the R-bit is set and the V6- 325 bit is clear, IPv6 datagrams are not forwarded but datagrams 326 belonging to another protocol family may be forwarded. 328 o The OSPF packet header now includes an "Instance ID" which 329 allows multiple OSPF protocol instances to be run on a 330 single link (see Section 2.4). 332 2.8. LSA format changes 334 All addressing semantics have been removed from the LSA header, 335 and from Router-LSAs and Network-LSAs. These two LSAs now 336 describe the routing domain's topology in a network-protocol 337 independent manner. New LSAs have been added to distribute IPv6 338 address information, and data required for next hop resolution. 339 The names of some of IPv4's LSAs have been changed to be more 340 consistent with each other. 342 In detail, changes in LSA format consist of the following: 344 o The Options field has been removed from the LSA header, 345 expanded to 24 bits, and moved into the body of Router-LSAs, 346 Network-LSAs, Inter-Area-Router-LSAs and Link-LSAs. See 347 Section A.2 for details. 349 o The LSA Type field has been expanded (into the former 350 Options space) to 16 bits, with the upper three bits 351 encoding flooding scope and the handling of unknown LSA 352 types (see Section 2.9). 354 o Addresses in LSAs are now expressed as [prefix, prefix 355 length] instead of [address, mask] (see Section A.4.1). The 356 default route is expressed as a prefix with length 0. 358 o The Router and Network LSAs now have no address information, 359 and are network-protocol-independent. 361 o Router interface information may be spread across multiple 362 Router LSAs. Receivers must concatenate all the Router-LSAs 363 originated by a given router when running the SPF 364 calculation. 366 o A new LSA called the Link-LSA has been introduced. The LSAs 367 have local-link flooding scope; they are never flooded 368 beyond the link that they are associated with. Link-LSAs 369 have three purposes: 1) they provide the router's link-local 370 address to all other routers attached to the link and 2) 371 they inform other routers attached to the link of a list of 372 IPv6 prefixes to associate with the link and 3) they allow 373 the router to assert a collection of Options bits to 374 associate with the Network-LSA that will be originated for 375 the link. See Section A.4.8 for details. 377 In IPv4, the router-LSA carries a router's IPv4 interface 378 addresses, the IPv4 equivalent of link-local addresses. 379 These are only used when calculating next hops during the 380 OSPF routing calculation (see Section 16.1.1 of [Ref1]), so 381 they do not need to be flooded past the local link; hence 382 using link-LSAs to distribute these addresses is more 383 efficient. Note that link-local addresses cannot be learned 384 through the reception of Hellos in all cases: on NBMA links 385 next hop routers do not necessarily exchange hellos, but 386 rather learn of each other's existence by way of the 387 Designated Router. 389 o The Options field in the Network LSA is set to the logical 390 OR of the Options that each router on the link advertises in 391 its Link-LSA. 393 o Type-3 summary-LSAs have been renamed "Inter-Area-Prefix- 394 LSAs". Type-4 summary LSAs have been renamed "Inter-Area- 395 Router-LSAs". 397 o The Link State ID in Inter-Area-Prefix-LSAs, Inter-Area- 398 Router-LSAs and AS-external-LSAs has lost its addressing 399 semantics, and now serves solely to identify individual 400 pieces of the Link State Database. All addresses or Router 401 IDs that formerly were expressed by the Link State ID are 402 now carried in the LSA bodies. 404 o Network-LSAs and Link-LSAs are the only LSAs whose Link 405 State ID carries additional meaning. For these LSAs, the 406 Link State ID is always the Interface ID of the originating 407 router on the link being described. For this reason, 408 Network-LSAs and Link-LSAs are now the only LSAs that cannot 409 be broken into arbitrarily small pieces. 411 o A new LSA called the Intra-Area-Prefix-LSA has been 412 introduced. This LSA carries all IPv6 prefix information 413 that in IPv4 is included in Router-LSAs and Network-LSAs. 414 See Section A.4.9 for details. 416 o Inclusion of a forwarding address in AS-external-LSAs is now 417 optional, as is the inclusion of an external route tag (see 418 [Ref5]). In addition, AS-external-LSAs can now reference 419 another LSA, for inclusion of additional route attributes 420 that are outside the scope of the OSPF protocol itself. For 421 example, this can be used to attach BGP path attributes to 422 external routes as proposed in [Ref10]. 424 2.9. Handling unknown LSA types 426 Handling of unknown LSA types has been made more flexible so 427 that, based on LS type, unknown LSA types are either treated as 428 having link-local flooding scope, or are stored and flooded as 429 if they were understood (desirable for things like the proposed 430 External Attributes LSA in [Ref10]). This behavior is explicitly 431 coded in the LSA Handling bit of the link state header's LS type 432 field (see Section A.4.2.1). 434 The IPv4 OSPF behavior of simply discarding unknown types is 435 unsupported due to the desire to mix router capabilities on a 436 single link. Discarding unknown types causes problems when the 437 Designated Router supports fewer options than the other routers 438 on the link. 440 2.10. Stub area support 442 In OSPF for IPv4, stub areas were designed to minimize link- 443 state database and routing table sizes for the areas' internal 444 routers. This allows routers with minimal resources to 445 participate in even very large OSPF routing domains. 447 In OSPF for IPv6, the concept of stub areas is retained. In 448 IPv6, of the mandatory LSA types, stub areas carry only router- 449 LSAs, network-LSAs, Inter-Area-Prefix-LSAs, Link-LSAs, and 450 Intra-Area-Prefix-LSAs. This is the IPv6 equivalent of the LSA 451 types carried in IPv4 stub areas: router-LSAs, network-LSAs and 452 type 3 summary-LSAs. 454 However, unlike in IPv4, IPv6 allows LSAs with unrecognized LS 455 types to be labeled "Store and flood the LSA, as if type 456 understood" (see the U-bit in Section A.4.2.1). Uncontrolled 457 introduction of such LSAs could cause a stub area's link-state 458 database to grow larger than it's component routers' capacities. 459 To guard against this, the following rules regarding stub areas 460 have been established: 462 (1) No LSAs with AS flooding scope can be flooded into/within 463 stub areas. This generalizes the rule that AS-external-LSAs 464 are not flooded into/throughout stub areas. 466 (2) No LSAs with U-bit set to 1 (flood even when LS type 467 unrecognized) should be flooded into/within stub areas. 469 Note that a router internal to a stub area may still get 470 unrecognized LSA types in its database, but only when both a) 471 the LSAs have link-local or area flooding scope, and b) the 472 router shares a network segment with another router that does 473 understand the LSA's type. 475 2.11. Identifying neighbors by Router ID 477 In OSPF for IPv6, neighboring routers on a given link are always 478 identified by their OSPF Router ID. This contrasts with the IPv4 479 behavior where neighbors on point-to-point networks and virtual 480 links are identified by their Router IDs, and neighbors on 481 broadcast, NBMA and Point-to-MultiPoint links are identified by 482 their IPv4 interface addresses. 484 This change affects the reception of OSPF packets (see Section 485 8.2 of [Ref1]), the lookup of neighbors (Section 10 of [Ref1]) 486 and the reception of Hello Packets in particular (Section 10.5 487 of [Ref1]). 489 The Router ID of 0.0.0.0 is reserved, and should not be used. 491 2.12. Removal of TOS 493 The semantics of IPv4 TOS have not been moved forward to IPv6. 494 Therefore, support for TOS in OSPF for IPv6 has been removed. 495 This affects both LSA formats and routing calculations. 497 The IPv6 header does have a 24-bit Flow Label field which may be 498 used by a source to label those packets for which it requests 499 special handling by IPv6 routers, such as non-default quality of 500 service or "real-time" service. The OSPF LSAs for IPv6 have been 501 organized so that future extensions to support routing based on 502 Flow Label are possible. 504 3. Implementation details 506 When going from IPv4 to IPv6, the basic OSPF mechanisms remain 507 unchanged from those documented in [Ref1]. These mechanisms are 508 briefly outlined in Section 4 of [Ref1]. Both IPv6 and IPv4 have a 509 link-state database composed of LSAs and synchronized between 510 adjacent routers. Initial synchronization is performed through the 511 Database Exchange process, through the exchange of Database 512 Description, Link State Request and Link State Update packets. 513 Thereafter database synchronization is maintained via flooding, 514 utilizing Link State Update and Link State Acknowledgment packets. 515 Both IPv6 and IPv4 use OSPF Hello Packets to disover and maintain 516 neighbor relationships, and to elect Designated Routers and Backup 517 Designated Routers on broadcast and NBMA links. The decision as to 518 which neighbor relationships become adjacencies, along with the 519 basic ideas behind inter-area routing, importing external 520 information in AS-external-LSAs and the various routing calculations 521 are also the same. 523 In particular, the following IPv4 OSPF functionality described in 524 [Ref1] remains completely unchanged for IPv6: 526 o Both IPv4 and IPv6 use OSPF packet types described in Section 527 4.3 of [Ref1], namely: Hello, Database Description, Link State 528 Request, Link State Update and Link State Acknowledgment 529 packets. While in some cases (e.g., Hello packets) their format 530 has changed somewhat, the functions of the various packet types 531 remains the same. 533 o The system requirements for an OSPF implementation remain 534 unchanged, although OSPF for IPv6 requires an IPv6 protocol 535 stack (from the network layer on down) since it runs directly 536 over the IPv6 network layer. 538 o The discovery and maintenance of neighbor relationships, and the 539 selection and establishment of adjacencies remain the same. This 540 includes election of the Designated Router and Backup Designated 541 Router on broadcast and NBMA links. These mechanisms are 542 described in Sections 7, 7.1, 7.2, 7.3, 7.4 and 7.5 of [Ref1]. 544 o The link types (or equivalently, interface types) supported by 545 OSPF remain unchanged, namely: point-to-point, broadcast, NBMA, 546 Point-to-MultiPoint and virtual links. 548 o The interface state machine, including the list of OSPF 549 interface states and events, and the Designated Router and 550 Backup Designated Router election algorithm, remain unchanged. 551 These are described in Sections 9.1, 9.2, 9.3 and 9.4 of [Ref1]. 553 o The neighbor state machine, including the list of OSPF neighbor 554 states and events, remain unchanged. These are described in 555 Sections 10.1, 10.2, 10.3 and 10.4 of [Ref1]. 557 o Aging of the link-state database, as well as flushing LSAs from 558 the routing domain through the premature aging process, remains 559 unchanged from the description in Sections 14 and 14.1 of 560 [Ref1]. 562 However, some OSPF protocol mechanisms have changed, as outlined in 563 Section 2 above. These changes are explained in detail in the 564 following subsections, making references to the appropriate sections 565 of [Ref1]. 567 The following subsections provide a recipe for turning an IPv4 OSPF 568 implementation into an IPv6 OSPF implementation. 570 3.1. Protocol data structures 572 The major OSPF data structures are the same for both IPv4 and 573 IPv6: areas, interfaces, neighbors, the link-state database and 574 the routing table. The top-level data structures for IPv6 remain 575 those listed in Section 5 of [Ref1], with the following 576 modifications: 578 o All LSAs with known LS type and AS flooding scope appear in 579 the top-level data structure, instead of belonging to a 580 specific area or link. AS-external-LSAs are the only LSAs 581 defined by this specification which have AS flooding scope. 582 LSAs with unknown LS type, U-bit set to 1 (flood even when 583 unrecognized) and AS flooding scope also appear in the top- 584 level data structure. 586 o Since IPv6 does not have the concept of TOS, "TOS 587 capability" is not a part of the OSPF fro IPv6 588 specification. 590 3.1.1. The Area Data structure 592 The IPv6 area data structure contains all elements defined 593 for IPv4 areas in Section 6 of [Ref1]. In addition, all LSAs 594 of known type which have area flooding scope are contained 595 in the IPv6 area data structure. This always includes the 596 following LSA types: router-LSAs, network-LSAs, inter-area- 597 prefix-LSAs, inter-area-router-LSAs and intra-area-prefix- 598 LSAs. LSAs with unknown LS type, U-bit set to 1 (flood even 599 when unrecognized) and area scope also appear in the area 600 data structure. IPv6 routers implementing MOSPF add group- 601 membership-LSAs to the area data structure. Type-7-LSAs 602 belong to an NSSA area's data structure. 604 3.1.2. The Interface Data structure 606 In OSPF for IPv6, an interface connects a router to a link. 607 The IPv6 interface structure modifies the IPv4 interface 608 structure (as defined in Section 9 of [Ref1]) as follows: 610 Interface ID 611 Every interface is assigned an Interface ID, which 612 uniquely identifies the interface with the router. For 613 example, some implementations may be able to use the 614 MIB-II IfIndex as Interface ID. The Interface ID appears 615 in Hello packets sent out the interface, the link- 616 local-LSA originated by router for the attached link, 617 and the router-LSA originated by the router-LSA for the 618 associated area. It will also serve as the Link State ID 619 for the network-LSA that the router will originate for 620 the link if the router is elected Designated Router. 622 Instance ID 623 Every interface is assigned an Instance ID. This should 624 default to 0, and is only necessary to assign 625 differently on those links that will contain multiple 626 separate communities of OSPF Routers. For example, 627 suppose that there are two communities of routers on a 628 given ethernet segment that you wish to keep separate. 629 The first community is given an Instance ID of 0, by 630 assigning 0 as the Instance ID of all its routers' 631 interfaces to the ethernet. An Instance ID of 1 is 632 assigned to the other routers' interface to the 633 ethernet. The OSPF transmit and receive processing (see 634 Section 3.2) will then keep the two communities 635 separate. 637 List of LSAs with link-local scope 638 All LSAs with link-local scope and which were 639 originated/flooded on the link belong to the interface 640 structure which connects to the link. This includes the 641 collection of the link's link-LSAs. 643 List of LSAs with unknown LS type 644 All LSAs with unknown LS type and U-bit set to 0 (if 645 unrecognized, treat the LSA as if it had link-local 646 flooding scope) are kept in data structure for the 647 interface that received the LSA. 649 IP interface address 650 For IPv6, the IPv6 address appearing in the source of 651 OSPF packets sent out the interface is almost always a 652 link-local address. The one exception is for virtual 653 links, which must use one of the router's own site-local 654 or global IPv6 addresses as IP interface address. 656 List of link prefixes 657 A list of IPv6 prefixes can be configured for the 658 attached link. These will be advertised by the router in 659 link-LSAs, so that they can be advertised by the link's 660 Designated Router in intra-area-prefix-LSAs. 662 There is only a single interface output cost, as IPv6 has no 663 concept of TOS. In addition, OSPF for IPv6 relies on the IP 664 Authentication Header (see [Ref19]) and the IP Encapsulating 665 Security Payload (see [Ref20]) to ensure integrity and 666 authentication/confidentiality of routing exchanges. For 667 that reason, AuType and Authentication key are not 668 associated with IPv6 OSPF interfaces. 670 Interface states, events, and the interface state machine 671 remain unchanged from IPv4, and are documented in Sections 672 9.1, 9.2 and 9.3 of [Ref1] respectively. The Designated 673 Router and Backup Designated Router election algorithm also 674 remains unchanged from the IPv4 election in Section 9.4 of 675 [Ref1]. 677 3.1.3. The Neighbor Data Structure 679 The neighbor structure performs the same function in both 680 IPv6 and IPv4. Namely, it collects all information required 681 to form an adjacency between two routers, if an adjacency 682 becomes necessary. Each neighbor structure is bound to a 683 single OSPF interface. The differences between the IPv6 684 neighbor structure and the neighbor structure defined for 685 IPv4 in Section 10 of [Ref1] are: 687 Neighbor's Interface ID 688 The Interface ID that the neighbor advertises in its 689 Hello Packets must be recorded in the neighbor 690 structure. The router will include the neighbor's 691 Interface ID in the router's router-LSA when either a) 692 advertising a point-to-point link to the neighbor or b) 693 advertising a link to a network where the neighbor has 694 become Designated Router. 696 Neighbor IP address 697 Except on virtual links, the neighbor's IP address will 698 be an IPv6 link-local address. 700 Neighbor's Designated Router 701 The neighbor's choice of Designated Router is now 702 encoded as Router ID, instead of as an IP address. 704 Neighbor's Backup Designated Router 705 The neighbor's choice of Designated Router is now 706 encoded as Router ID, instead of as an IP address. 708 Neighbor states, events, and the neighbor state machine 709 remain unchanged from IPv4, and are documented in Sections 710 10.1, 10.2 and 10.3 of [Ref1] respectively. The decision as 711 to which adjacencies to form also remains unchanged from the 712 IPv4 logic documented in Section 10.4 of [Ref1]. 714 3.2. Protocol Packet Processing 716 OSPF for IPv6 runs directly over IPv6's network layer. As such, 717 it is encapsulated in one or more IPv6 headers, with the Next 718 Header field of the immediately encapsulating IPv6 header set to 719 the value 89. OSPF protocol packets should be given precedence 720 over regular IPv6 data traffic, in both sending and receiving. 721 as an aid towards accomplishing this precedence, OSPF routing 722 protocol packets are sent with IPv6 Priority field set to 7 723 (internet control traffic). 725 As for IPv4, in IPv6 OSPF routing protocol packets are sent 726 along adjacencies only (with the exception of Hello packets, 727 which are used to discover the adjacencies). OSPF packet types 728 and functions are the same in both IPv4 and IPv4, encoded by the 729 Type field of the standard OSPF packet header. 731 3.2.1. Sending protocol packets 733 When an IPv6 router sends an OSPF routing protocol packet, 734 it fills in the fields of the standard OSPF for IPv6 packet 735 header (see Section A.3.1) as follows: 737 Version # 738 Set to 3, the version number of the protocol as 739 documented in this specification. 741 Type 742 The type of OSPF packet, such as Link state Update or 743 Hello Packet. 745 Packet length 746 The length of the entire OSPF packet in bytes, including 747 the standard OSPF packet header. 749 Router ID 750 The identity of the router itself (who is originating 751 the packet). 753 Area ID 754 The OSPF area that the packet is being sent into. 756 Instance ID 757 The OSPF Instance ID associated with the interface that 758 the packet is being sent out of. 760 Checksum 761 The standard IP 16-bit one's complement checksum of the 762 entire OSPF packet. 764 Selection of OSPF routing protocol packets' IPv6 source and 765 destination addresses is performed identically to the IPv4 766 logic in Section 8.1 of [Ref1]. The IPv6 destination address 767 is chosen from among the addresses AllSPFRouters, 768 AllDRouters and the Neighbor IP address associated with the 769 other end of the adjacency (which in IPv6, for all links 770 except virtual links, is an IPv6 link-local address). 772 The sending of Link State Request Packets and Link State 773 Acknowledgment Packets remains unchanged from the IPv4 774 procedures documented in Sections 10.9 and 13.5 of [Ref1] 775 respectively. Sending Hello Packets is documented in Section 776 3.2.1.1, and the sending of Database Description Packets in 777 Section 3.2.1.2. The sending of Link State Update Packets is 778 documented in Section 3.5.2. 780 3.2.1.1. Sending Hello packets 782 IPv6 changes the way OSPF Hello packets are sent in the 783 following ways (compare to Section 9.5 of [Ref1]): 785 o Before the Hello Packet is sent out an interface, 786 the interface's Interface ID must be copied into the 787 Hello Packet. 789 o The Hello Packet no longer contains an IP network 790 mask, as OSPF for IPv6 runs per-link instead of 791 per-subnet. 793 o The choice of Designated Router and Backup 794 Designated Router are now indicated within Hellos by 795 their Router IDs, instead of by their IP interface 796 addresses. Advertising the Designated Router (or 797 Backup Designated Router) as 0.0.0.0 indicates that 798 the Designated Router (or Backup Designated Router) 799 has not yet been chosen. 801 o The Options field within Hello packets has moved 802 around, getting larger in the process. More options 803 bits are now possible. Those that must be set 804 correctly in Hello packets are: The E-bit is set if 805 and only if the interface attaches to a non-stub 806 area, the N-bit is set if and only if the interface 807 attaches to an NSSA area (see [Ref9]), and the DC- 808 bit is set if and only if the router wishes to 809 suppress the sending of future Hellos over the 810 interface (see [Ref11]). Unrecognized bits in the 811 Hello Packet's Options field should be cleared. 813 Sending Hello packets on NBMA networks proceeds for IPv6 814 in exactly the same way as for IPv4, as documented in 815 Section 9.5.1 of [Ref1]. 817 3.2.1.2. Sending Database Description Packets 819 The sending of Database Description packets differs from 820 Section 10.8 of [Ref1] in the following ways: 822 o The Options field within Database Description 823 packets has moved around, getting larger in the 824 process. More options bits are now possible. Those 825 that must be set correctly in Database Description 826 packets are: The MC-bit is set if and only if the 827 router is forwarding multicast datagrams according 828 to the MOSPF specification in [Ref7]. Unrecognized 829 bits in the Database Description Packet's Options 830 field should be cleared. 832 3.2.2. Receiving protocol packets 834 Whenever an OSPF protocol packet is received by the router 835 it is marked with the interface it was received on. For 836 routers that have virtual links configured, it may not be 837 immediately obvious which interface to associate the packet 838 with. For example, consider the Router RT11 depicted in 839 Figure 6 of [Ref1]. If RT11 receives an OSPF protocol 840 packet on its interface to Network N8, it may want to 841 associate the packet with the interface to Area 2, or with 842 the virtual link to Router RT10 (which is part of the 843 backbone). In the following, we assume that the packet is 844 initially associated with the non-virtual link. 846 In order for the packet to be passed to OSPF for processing, 847 the following tests must be performed on the encapsulating 848 IPv6 headers: 850 o The packet's IP destination address must be one of the 851 IPv6 unicast addresses associated with the receiving 852 interface (this includes link-local addresses), or one 853 of the IP multicast addresses AllSPFRouters or 854 AllDRouters. 856 o The Next Header field of the immediately encapsulating 857 IPv6 header must specify the OSPF protocol (89). 859 o Any encapsulating IP Authentication Headers (see 860 [Ref19]) and the IP Encapsulating Security Payloads (see 861 [Ref20]) must be processed and/or verified to ensure 862 integrity and authentication/confidentiality of OSPF 863 routing exchanges. 865 o Locally originated packets should not be passed on to 866 OSPF. That is, the source IPv6 address should be 867 examined to make sure this is not a multicast packet 868 that the router itself generated. 870 After processing the encapsulating IPv6 headers, the OSPF 871 packet header is processed. The fields specified in the 872 header must match those configured for the receiving 873 interface. If they do not, the packet should be discarded: 875 o The version number field must specify protocol version 876 3. 878 o The standard IP 16-bit one's complement checksum of the 879 entire OSPF packet must be verified. 881 o The Area ID found in the OSPF header must be verified. 882 If both of the following cases fail, the packet should 883 be discarded. The Area ID specified in the header must 884 either: 886 (1) Match the Area ID of the receiving interface. In 887 this case, unlike for IPv4, the IPv6 source address 888 is not restricted to lie on the same IP subnet as 889 the receiving interface. IPv6 OSPF runs per-link, 890 instead of per-IP-subnet. 892 (2) Indicate the backbone. In this case, the packet has 893 been sent over a virtual link. The receiving router 894 must be an area border router, and the Router ID 895 specified in the packet (the source router) must be 896 the other end of a configured virtual link. The 897 receiving interface must also attach to the virtual 898 link's configured Transit area. If all of these 899 checks succeed, the packet is accepted and is from 900 now on associated with the virtual link (and the 901 backbone area). 903 o The Instance ID specified in the OSPF header must match 904 the receiving interface's Instance ID. 906 o Packets whose IP destination is AllDRouters should only 907 be accepted if the state of the receiving interface is 908 DR or Backup (see Section 9.1). 910 After header processing, the packet is further processed 911 according to it OSPF packet type. OSPF packet types and 912 functions are the same for both IPv4 and IPv6. 914 If the packet type is Hello, it should then be further 915 processed by the Hello Protocol. All other packet types are 916 sent/received only on adjacencies. This means that the 917 packet must have been sent by one of the router's active 918 neighbors. The neighbor is identified by the Router ID 919 appearing the the received packet's OSPF header. Packets not 920 matching any active neighbor are discarded. 922 The receive processing of Database Description Packets, Link 923 State Request Packets and Link State Acknowledgment Packets 924 remains unchanged from the IPv4 procedures documented in 925 Sections 10.6, 10.7 and 13.7 of [Ref1] respectively. The 926 receiving of Hello Packets is documented in Section 3.2.2.1, 927 and the receiving of Link State Update Packets is documented 928 in Section 3.5.1. 930 3.2.2.1. Receiving Hello Packets 932 The receive processing of Hello Packets differs from 933 Section 10.5 of [Ref1] in the following ways: 935 o On all link types (e.g., broadcast, NBMA, point-to- 936 point, etc), neighbors are identified solely by 937 their OSPF Router ID. For all link types except 938 virtual links, the Neighbor IP address is set to the 939 IPv6 source address in the IPv6 header of the 940 received OSPF Hello packet. 942 o There is no longer a Network Mask field in the Hello 943 Packet. 945 o The neighbor's choice of Designated Router and 946 Backup Designated Router is now encoded as an OSPF 947 Router ID instead of an IP interface address. 949 3.3. The Routing table Structure 951 The routing table used by OSPF for IPv4 is defined in Section 11 952 of [Ref1]. For IPv6 there are analogous routing table entries: 953 there are routing table entries for IPv6 address prefixes, and 954 also for AS boundary routers. The latter routing table entries 955 are only used to hold intermediate results during the routing 956 table build process (see Section 3.8). 958 Also, to hold the intermediate results during the shortest-path 959 calculation for each area, there is a separate routing table for 960 each area holding the following entries: 962 o An entry for each router in the area. Routers are identified 963 by their OSPF router ID. These routing table entries hold 964 the set of shortest paths through a given area to a given 965 router, which in turn allows calculation of paths to the 966 IPv6 prefixes advertised by that router in Intra-area- 967 prefix-LSAs. If the router is also an area-border router, 968 these entries are also used to calculate paths for inter- 969 area address prefixes. If in addition the router is the 970 other endpoint of a virtual link, the routing table entry 971 describes the cost and viability of the virtual link. 973 o An entry for each transit link in the area. Transit links 974 have associated network-LSAs. Both the transit link and the 975 network-LSA are identified by a combination of the 976 Designated Router's Interface ID on the link and the 977 Designated Router's OSPF Router ID. These routing table 978 entries allow later calculation of paths to IP prefixes 979 advertised for the transit link in intra-area-prefix-LSAs. 981 Since IPv6 does not support the concept of Type of Service 982 (TOS), there are no longer separate sets of paths for each TOS. 983 The rest of the fields in the IPv4 OSPF routing table (see 984 Section 11 of [Ref1]) remain valid for IPv6: Optional 985 capabilities (routers only), path type, cost, type 2 cost, link 986 state origin, and for each of the equal cost paths to the 987 destination, the next hop and advertising router (inter-area and 988 AS external paths only). 990 For IPv6, the link-state origin field in the routing table entry 991 is the router-LSA or network-LSA that has directly or indirectly 992 produced the routing table entry. For example, if the routing 993 table entry describes a route to an IPv6 prefix, the link state 994 origin is the router-LSA or network-LSA that is listed in the 995 body of the intra-area-prefix-LSA that has produced the route 996 (see Section A.4.9). 998 3.3.1. Routing table lookup 1000 Routing table lookup (i.e., determining the best matching 1001 routing table entry during IP forwarding) is the same for 1002 IPv6 as for IPv4, except that Type of Service is not taken 1003 into account. The lookup consists of the first three steps 1004 of Section 11.1 in [Ref1], ignoring the last step that 1005 concerns only TOS. 1007 3.4. Link State Advertisements 1009 For IPv6, the OSPF LSA header has changed slightly, with the LS 1010 type field expanding and the Options field being moved into the 1011 body of appropriate LSAs. Also, the formats of some LSAs have 1012 changed somewhat (namely router-LSAs, network-LSAs and AS- 1013 external-LSAs), while the names of other LSAs have been changed 1014 (type 3 and 4 summary-LSAs are now inter-area-prefix-LSAs and 1015 inter-area-router-LSAs respectively) and additional LSAs have 1016 been added (Link-LSAs and Intra-Area-Prefix-LSAs). Since IPv6 1017 does not support TOS, TOS is no longer encoded within LSAs. 1019 These changes will be described in detail in the following 1020 subsections. 1022 3.4.1. The LSA Header 1024 In both IPv4 and IPv6, all OSPF LSAs begin with a standard 1025 20 byte LSA header. However, the contents of this 20 byte 1026 header have changed in IPv6. The LS age, Advertising Router, 1027 LS Sequence Number, LS checksum and length fields within the 1028 LSA header remain unchanged, as documented in Sections 1029 12.1.1, 12.1.5, 12.1.6, 12.1.7 and A.4.1 of [Ref1] 1030 respectively. However, the following fields have changed 1031 for IPv6: 1033 Options 1034 The Options field has been removed from the standard 20 1035 byte LSA header, and into the body of router-LSAs, 1036 network-LSAs, inter-area-router-LSAs and link-LSAs. The 1037 size of the Options field has increased from 8 to 24 1038 bits, and some of the bit definitions have changed (see 1039 Section A.2). In addition a separate PrefixOptions 1040 field, 8 bits in length, is attached to each prefix 1041 advertised within the body of an LSA. 1043 LS type 1044 The size of the LS type field has increased from 8 to 16 1045 bits, with the top two bits encoding flooding scope and 1046 the next bit encoding the handling of unknown LS types. 1047 See Section A.4.2.1 for the current coding of the LS 1048 type field. 1050 Link State ID 1051 Link State ID remains at 32 bits in length, but except 1052 for network-LSAs and link-LSAs, Link State ID has shed 1053 any addressing semantics. For example, an IPv6 router 1054 originating multiple AS-external-LSAs could start by 1055 assigning the first a Link State ID of 0.0.0.1, the 1056 second a Link State ID of 0.0.0.2, and so on. Instead of 1057 the IPv4 behavior of encoding the network number within 1058 the AS-external-LSA's Link State ID, the IPv6 Link State 1059 ID simply serves as a way to differentiate multiple LSAs 1060 originated by the same router. 1062 For network-LSAs, the Link State ID is set to the 1063 Designated Router's Interface ID on the link. When a 1064 router originates a Link-LSA for a given link, its Link 1065 State ID is set equal to the router's Interface ID on 1066 the link. 1068 3.4.2. The link-state database 1070 In IPv6, as in IPv4, individual LSAs are identified by a 1071 combination of their LS type, Link State ID and Advertising 1072 Router fields. Given two instances of an LSA, the most 1073 recent instance is determined by examining the LSAs' LS 1074 Sequence Number, using LS checksum and LS age as tiebreakers 1075 (see Section 13.1 of [Ref1]). 1077 In IPv6, the link-state database is split across three 1078 separate data structures. LSAs with AS flooding scope are 1079 contained within the top-level OSPF data structure (see 1080 Section 3.1) as long as either their LS type is known or 1081 their U-bit is 1 (flood even when unrecognized); this 1082 includes the AS-external-LSAs. LSAs with area flooding scope 1083 are contained within the appropriate area structure (see 1084 Section 3.1.1) as long as either their LS type is known or 1085 their U-bit is 1 (flood even when unrecognized); this 1086 includes router-LSAs, network-LSAs, inter-area-prefix-LSAs, 1087 inter-area-router-LSAs, and intra-area-prefix-LSAs. LSAs 1088 with unknown LS type and U-bit set to 0 and/or link-local 1089 flooding scope are contained within the appropriate 1090 interface structure (see Section 3.1.2); this includes 1091 link-LSAs. 1093 To lookup or install an LSA in the database, you first 1094 examine the LS type and the LSA's context (i.e., to which 1095 area or link does the LSA belong). This information allows 1096 you to find the correct list of LSAs, all of the same LS 1097 type, where you then search based on the LSA's Link State ID 1098 and Advertising Router. 1100 3.4.3. Originating LSAs 1102 The process of reoriginating an LSA in IPv6 is the same as 1103 in IPv4: the LSA's LS sequence number is incremented, its 1104 LS age is set to 0, its LS checksum is calculated, and the 1105 LSA is added to the link state database and flooded out the 1106 appropriate interfaces. 1108 To the list of events causing LSAs to be reoriginated, which 1109 for IPv4 is given in Section 12.4 of [Ref1], the following 1110 events are added for IPv6: 1112 o The Interface ID of a neighbor changes. This may cause a 1113 new instance of a router-LSA to be originated for the 1114 associated area. 1116 o A new prefix is added to an attached link, or a prefix 1117 is deleted (both through configuration). This causes the 1118 router to reoriginate its link-LSA for the link, or, if 1119 it is the only router attached to the link, causes the 1120 router to reoriginate an intra-area-prefix-LSA. 1122 o A new link-LSA is received, causing the link's 1123 collection of prefixes to change. If the router is 1124 Designated Router for the link, it originates a new 1125 intra-area-prefix-LSA. 1127 Detailed construction of the seven required IPv6 LSA types 1128 is supplied by the following subsections. In order to 1129 display example LSAs, the network map in Figure 15 of [Ref1] 1130 has been reworked to show IPv6 addressing, resulting in 1131 Figure 1. The OSPF cost of each interface is has been 1132 displayed in Figure 1. The assignment of IPv6 prefixes to 1133 network links is shown in Table 1. A single area address 1134 range has been configured for Area 1, so that outside of 1135 Area 1 all of its prefixes are covered by a single route to 1136 5f00:0000:c001::/48. The OSPF interface IDs and the link- 1137 local addresses for the router interfaces in Figure 1 are 1138 given in Table 2. 1140 .......................................... 1141 . Area 1. 1142 . + . 1143 . | . 1144 . | 3+---+1 . 1145 . N1 |--|RT1|-----+ . 1146 . | +---+ \ . 1147 . | \ ______ . 1148 . + \/ \ 1+---+ 1149 . * N3 *------|RT4|------ 1150 . + /\_______/ +---+ 1151 . | / | . 1152 . | 3+---+1 / | . 1153 . N2 |--|RT2|-----+ 1| . 1154 . | +---+ +---+ . 1155 . | |RT3|---------------- 1156 . + +---+ . 1157 . |2 . 1158 . | . 1159 . +------------+ . 1160 . N4 . 1161 .......................................... 1163 Figure 1: Area 1 with IP addresses shown 1165 Network IPv6 prefix 1166 __________________________________ 1167 N1 5f00:0000:0c01:0200::/56 1168 N2 5f00:0000:0c01:0300::/56 1169 N3 5f00:0000:0c01:0100::/56 1170 N4 5f00:0000:0c01:0400::/56 1172 Table 1: IPv6 link prefixes for sample network 1173 Router interface Interface ID link-local address 1174 ______________________________________________________ 1175 RT1 to N1 1 fe80:0001::RT1 1176 to N3 2 fe80:0002::RT1 1177 RT2 to N2 1 fe80:0001::RT2 1178 to N3 2 fe80:0002::RT2 1179 RT3 to N3 1 fe80:0001::RT3 1180 to N4 2 fe80:0002::RT3 1181 RT4 to N3 1 fe80:0001::RT4 1183 Table 2: OSPF Interface IDs and link-local addresses 1185 3.4.3.1. Router-LSAs 1187 The LS type of a router-LSA is set to the value 0x2001. 1188 Router-LSAs have area flooding scope. A router may 1189 originate one or more router-LSAs for a given area. 1190 Taken together, the collection of router-LSAs originated 1191 by the router for an area describes the collected states 1192 of all the router's interface to the area. When multiple 1193 router-LSAs are used, they are distinguished by their 1194 Link State ID fields. 1196 The Options field in the router-LSA should be coded as 1197 follows. The V6-bit should be set. The E-bit should be 1198 clear if and only if the area is an OSPF stub area. The 1199 MC-bit should be set if and only if the router is 1200 running MOSPF (see [Ref8]). The N-bit should be set if 1201 and only if the area is an OSPF NSSA area. The R-bit 1202 should be set. The DC-bit should be set if and only if 1203 the router can correctly process the DoNotAge bit when 1204 it appears in the LS age field of LSAs (see [Ref11]). 1205 All unrecognized bits in the Options field should be 1206 cleared 1208 To the left of the Options field, the router capability 1209 bits V, E and B should be coded according to Section 1210 12.4.1 of [Ref1]. Bit W should be coded according to 1211 [Ref8]. 1213 Each of the router's interfaces to the area are then 1214 described by appending "link descriptions" to the 1215 router-LSA. Each link description is 16 bytes long, 1216 consisting of 5 fields: (link) Type, Metric, Interface 1217 ID, Neighbor Interface ID and Neighbor Router ID (see 1218 Section A.4.3). Interfaces in state "Down" or "Loopback" 1219 are not described (although looped back interfaces can 1220 contribute prefixes to Intra-Area-Prefix-LSAs). Nor are 1221 interfaces without any full adjacencies described. All 1222 other interfaces to the area add zero, one or more link 1223 descriptions, the number and content of which depend on 1224 the interface type. Within each link description, the 1225 Metric field is always set the interface's output cost 1226 and the Interface ID field is set to the interface's 1227 OSPF Interface ID. 1229 Point-to-point interfaces 1230 If the neighboring router is fully adjacent, add a 1231 Type 1 link description (point-to-point). The 1232 Neighbor Interface ID field is set to the Interface 1233 ID advertised by the neighbor in its Hello packets, 1234 and the Neighbor Router ID field is set to the 1235 neighbor's Router ID. 1237 Broadcast and NBMA interfaces 1238 If the router is fully adjacent to the link's 1239 Designated Router, or if the router itself is 1240 Designated Router and is fully adjacent to at least 1241 one other router, add a single Type 2 link 1242 description (transit network). The Neighbor 1243 Interface ID field is set to the Interface ID 1244 advertised by the Designated Router in its Hello 1245 packets, and the Neighbor Router ID field is set to 1246 the Designated Router's Router ID. 1248 Virtual links 1249 If the neighboring router is fully adjacent, add a 1250 Type 4 link description (virtual). The Neighbor 1251 Interface ID field is set to the Interface ID 1252 advertised by the neighbor in its Hello packets, and 1253 the Neighbor Router ID field is set to the 1254 neighbor's Router ID. Note that the output cost of a 1255 virtual link is calculated during the routing table 1256 calculation (see Section 3.7). 1258 Point-to-MultiPoint interfaces 1259 For each fully adjacent neighbor associated with the 1260 interface, add a separate Type 1 link description 1261 (point-to-point) with Neighbor Interface ID field 1262 set to the Interface ID advertised by the neighbor 1263 in its Hello packets, and Neighbor Router ID field 1264 set to the neighbor's Router ID. 1266 As an example, consider the router-LSA that router RT3 1267 would originate for Area 1 in Figure 1. Only a single 1268 interface must be described, namely that which connects 1269 to the transit network N3. It assumes that RT4 has bee 1270 elected Designated Router of Network N3. 1272 ; RT3's router-LSA for Area 1 1274 LS age = 0 ;newly (re)originated 1275 LS type = 0x2001 ;router-LSA 1276 Link State ID = 0 ;first fragment 1277 Advertising Router = 192.1.1.3 ;RT3's Router ID 1278 bit E = 0 ;not an AS boundary router 1279 bit B = 1 ;area border router 1280 Options = (V6-bit|E-bit|R-bit) 1281 Type = 2 ;connects to N3 1282 Metric = 1 ;cost to N3 1283 Interface ID = 1 ;RT3's Interface ID on N3 1284 Neighbor Interface ID = 1 ;RT4's Interface ID on N3 1285 Neighbor Router ID = 192.1.1.4 ; RT4's Router ID 1287 If for example another router was added to Network N4, 1288 RT3 would have to advertise a second link description 1289 for its connection to (the now transit) network N4. This 1290 could be accomplished by reoriginating the above 1291 router-LSA, this time with two link descriptions. Or, a 1292 separate router-LSA could be originated with a separate 1293 Link State ID (e.g., using a Link State ID of 1) to 1294 describe the connection to N4. 1296 Host routes no longer appear in the router-LSA, but are 1297 instead included in intra-area-prefix-LSAs. 1299 3.4.3.2. Network-LSAs 1301 The LS type of a network-LSA is set to the value 0x2002. 1302 Network-LSAs have area flooding scope. A network-LSA is 1303 originated for every transit broadcast or NBMA link, by 1304 the link's Designated Router. Transit links are those 1305 that have two or more attached routers. The network-LSA 1306 lists all routers attached to the link. 1308 The procedure for originating network-LSAs in IPv6 is 1309 the same as the IPv4 procedure documented in Section 1310 12.4.2 of [Ref1], with the following exceptions: 1312 o An IPv6 network-LSA's Link State ID is set to the 1313 Interface ID of the Designated Router on the link. 1315 o IPv6 network-LSAs do not contain a Network Mask. All 1316 addressing information formerly contained in the 1317 IPv4 network-LSA has now been consigned to intra- 1318 Area-Prefix-LSAs. 1320 o The Options field in the network-LSA is set to the 1321 logical OR of the Options fields contained within 1322 the link's associated link-LSAs. In this way, the 1323 network link exhibits a capability when at least one 1324 of the link's routers requests that the capability 1325 be asserted. 1327 As an example, assuming that Router RT4 has been elected 1328 Designated Router of Network N3 in Figure 1, the 1329 following network-LSA is originated: 1331 ; Network-LSA for Network N3 1333 LS age = 0 ;newly (re)originated 1334 LS type = 0x2002 ;network-LSA 1335 Link State ID = 1 ;RT4's Interface ID on N3 1336 Advertising Router = 192.1.1.4 ;RT4's Router ID 1337 Options = (V6-bit|E-bit|R-bit) 1338 Attached Router = 192.1.1.4 ;Router ID 1339 Attached Router = 192.1.1.1 ;Router ID 1340 Attached Router = 192.1.1.2 ;Router ID 1341 Attached Router = 192.1.1.3 ;Router ID 1343 3.4.3.3. Inter-Area-Prefix-LSAs 1345 The LS type of an inter-area-prefix-LSA is set to the 1346 value 0x2003. Inter-area-prefix-LSAs have area flooding 1347 scope. In IPv4, inter-area-prefix-LSAs were called type 1348 3 summary-LSAs. Each inter-area-prefix-LSA describes a 1349 prefix external to the area, yet internal to the 1350 Autonomous System. 1352 The procedure for originating inter-area-prefix-LSAs in 1353 IPv6 is the same as the IPv4 procedure documented in 1354 Sections 12.4.3 and 12.4.3.1 of [Ref1], with the 1355 following exceptions: 1357 o The Link State ID of an inter-area-prefix-LSA has 1358 lost all of its addressing semantics, and instead 1359 simply serves to distinguish multiple inter-area- 1360 prefix-LSAs that are originated by the same router. 1362 o The prefix is described by the PrefixLength, 1363 PrefixOptions and Address Prefix fields embedded 1364 within the LSA body. Network Mask is no longer 1365 specified. 1367 o The NU-bit in the PrefixOptions field should be 1368 clear. The coding of the MC-bit depends upon 1369 whether, and if so how, MOSPF is operating in the 1370 routing domain (see [Ref8]). 1372 As an example, the following shows the inter-area- 1373 prefix-LSA that Router RT4 originates into the OSPF 1374 backbone area, condensing all of Area 1's prefixes into 1375 the single prefix 5f00:0000:c001::/48. The cost is set 1376 to 4, which is the maximum cost to all of the prefix' 1377 individual components. The prefix is padded out to an 1378 even number of 32-bit words, so that it consumes 64-bits 1379 of space instead of 48 bits. 1381 ; Inter-area-prefix-LSA for Area 1 addresses 1382 ; originated by Router RT4 into the backbone 1384 LS age = 0 ;newly (re)originated 1385 LS type = 0x2003 ;inter-area-prefix-LSA 1386 Advertising Router = 192.1.1.4 ;RT4's ID 1387 Metric = 4 ;maximum to components 1388 PrefixLength = 48 1389 PrefixOptions = 0 1390 Address Prefix = 5f00:0000:c001 ;padded to 64-bits 1392 3.4.3.4. Inter-Area-Router-LSAs 1394 The LS type of an inter-area-router-LSA is set to the 1395 value 0x2004. Inter-area-router-LSAs have area flooding 1396 scope. In IPv4, inter-area-router-LSAs were called type 1397 4 summary-LSAs. Each inter-area-router-LSA describes a 1398 path to a destination OSPF router (an ASBR) that is 1399 external to the area, yet internal to the Autonomous 1400 System. 1402 The procedure for originating inter-area-router-LSAs in 1403 IPv6 is the same as the IPv4 procedure documented in 1404 Section 12.4.3 of [Ref1], with the following exceptions: 1406 o The Link State ID of an inter-area-router-LSA is no 1407 longer the destination router's OSPF Router ID, but 1408 instead simply serves to distinguish multiple 1409 inter-area-router-LSAs that are originated by the 1410 same router. The destination router's Router ID is 1411 now found in the body of the LSA. 1413 o The Options field in an inter-area-router-LSA should 1414 be set equal to the Options field contained in the 1415 destination router's own router-LSA. The Options 1416 field thus describes the capabilities supported by 1417 the destination router. 1419 As an example, consider the OSPF Autonomous System 1420 depicted in Figure 6 of [Ref1]. Router RT4 would 1421 originate into Area 1 the following inter-area-router- 1422 LSA for destination router RT7. 1424 ; inter-area-router-LSA for AS boundary router RT7 1425 ; originated by Router RT4 into Area 1 1427 LS age = 0 ;newly (re)originated 1428 LS type = 0x2004 ;inter-area-router-LSA 1429 Advertising Router = 192.1.1.4 ;RT4's ID 1430 Options = (V6-bit|E-bit|R-bit) ;RT7's capabilities 1431 Metric = 14 ;cost to RT7 1432 Destination Router ID = Router RT7's ID 1434 3.4.3.5. AS-external-LSAs 1436 The LS type of an AS-external-LSA is set to the value 1437 0x4005. AS-external-LSAs have AS flooding scope. Each 1438 AS-external-LSA describes a path to a prefix external to 1439 the Autonomous System. 1441 The procedure for originating AS-external-LSAs in IPv6 1442 is the same as the IPv4 procedure documented in Section 1443 12.4.4 of [Ref1], with the following exceptions: 1445 o The Link State ID of an AS-external-LSA has lost all 1446 of its addressing semantics, and instead simply 1447 serves to distinguish multiple AS-external-LSAs that 1448 are originated by the same router. 1450 o The prefix is described by the PrefixLength, 1451 PrefixOptions and Address Prefix fields embedded 1452 within the LSA body. Network Mask is no longer 1453 specified. 1455 o The NU-bit in the PrefixOptions field should be 1456 clear. The coding of the MC-bit depends upon 1457 whether, and if so how, MOSPF is operating in the 1458 routing domain (see [Ref8]). 1460 o The forwarding address is present in the AS- 1461 external-LSA if and only if the AS-external-LSA's 1462 bit F is set. 1464 o The external route tag is present in the AS- 1465 external-LSA if and only if the AS-external-LSA's 1466 bit T is set. 1468 o The capability for an AS-external-LSA to reference 1469 another LSA has been included, by inclusion of the 1470 Referenced LS Type field and the optional Referenced 1471 Link State ID field (the latter present if and only 1472 if Referenced LS Type is non-zero). This capability 1473 is for future use; for now Referenced LS Type should 1474 be set to 0. 1476 As an example, consider the OSPF Autonomous System 1477 depicted in Figure 6 of [Ref1]. Assume that RT7 has 1478 learned its route to N12 via BGP, and that it wishes to 1479 advertise a Type 2 metric into the AS. Further assume 1480 the the IPv6 prefix for N12 is the value 1481 5f00:0000:0a00::/40. RT7 would then originate the 1482 following AS-external-LSA for the external network N12. 1483 Note that within the AS-external-LSA, N12's prefix 1484 occupies 64 bits of space, to maintain 32-bit alignment. 1486 ; AS-external-LSA for Network N12, 1487 ; originated by Router RT7 1489 LS age = 0 ;newly (re)originated 1490 LS type = 0x4005 ;AS-external-LSA 1491 Link State ID = 123 ;or something else 1492 Advertising Router = Router RT7's ID 1493 bit E = 1 ;Type 2 metric 1494 bit F = 0 ;no forwarding address 1495 bit T = 1 ;external route tag included 1496 Metric = 2 1497 PrefixLength = 40 1498 PrefixOptions = 0 1499 Referenced LS Type = 0 ;no Referenced Link State ID 1500 Address Prefix = 5f00:0000:0a00 ;padded to 64-bits 1501 External Route Tag = as per BGP/OSPF interaction 1502 3.4.3.6. Link-LSAs 1504 The LS type of a Link-LSA is set to the value 0x0008. 1505 Link-LSAs have link-local flooding scope. A router 1506 originates a separate Link-LSA for each attached link 1507 that supports 2 or more (including the originating 1508 router itself) routers. 1510 Link-LSAs have three purposes: 1) they provide the 1511 router's link-local address to all other routers 1512 attached to the link and 2) they inform other routers 1513 attached to the link of a list of IPv6 prefixes to 1514 associate with the link and 3) they allow the router to 1515 assert a collection of Options bits in the Network-LSA 1516 that will be originated for the link. 1518 A Link-LSA for a given Link L is built in the following 1519 fashion: 1521 o The Link State ID is set to the router's Interface 1522 ID on Link L. 1524 o The Router Priority of the router's interface to 1525 Link L is inserted into the Link-LSA. 1527 o The Link-LSA's Options field is set to those bits 1528 that the router wishes set in Link L's Network LSA. 1530 o The router inserts its link-local address on Link L 1531 into the Link-LSA. This information will be used 1532 when the other routers on Link L do their next hop 1533 calculations (see Section 3.8.1.1). 1535 o Each IPv6 address prefix that has been configured 1536 into the router for Link L is added to the Link-LSA, 1537 by specifying values for PrefixLength, 1538 PrefixOptions, and Address Prefix fields. 1540 After building a Link-LSA for a given link, the router 1541 installs the link-LSA into the associate interface data 1542 structure and floods the Link-LSA onto the link. All 1543 other routers on the link will receive the Link-LSA, but 1544 it will go no further. 1546 As an example, consider the Link-LSA that RT3 will build 1547 for N3 in Figure 1. Suppose that the prefix 1548 5f00:0000:0c01:0100::/56 has been configured within RT3 1549 for N3. This will give rise to the following Link-LSA, 1550 which RT3 will flood onto N3, but nowhere else. Note 1551 that not all routers on N3 need be configured with the 1552 prefix; those not configured will learn the prefix when 1553 receiving RT3's Link-LSA. 1555 ; RT3's Link-LSA for N3 1557 LS age = 0 ;newly (re)originated 1558 LS type = 0x0008 ;Link-LSA 1559 Link State ID = 1 ;RT3's Interface ID on N3 1560 Advertising Router = 192.1.1.3 ;RT3's Router ID 1561 Rtr Pri = 1 ;RT3's N3 Router Priority 1562 Options = (V6-bit|E-bit|R-bit) 1563 Link-local Interface Address = fe80:0001::RT3 1564 # prefixes = 1 1565 PrefixLength = 56 1566 PrefixOptions = 0 1567 Address Prefix = 5f00:0000:c001:0100 ;pad to 64-bits 1569 3.4.3.7. Intra-Area-Prefix-LSAs 1571 The LS type of an intra-area-prefix-LSA is set to the 1572 value 0x2009. Intra-area-prefix-LSAs have area flooding 1573 scope. An intra-area-prefix-LSA has one of two 1574 functions. It associates a list of IPv6 address prefixes 1575 with a transit network link by referencing a network- 1576 LSA, or associates a list of IPv6 address prefixes with 1577 a router by referencing a router-LSA. A sub network 1578 link's prefixes are associated with its attached router. 1580 A router may originate multiple intra-area-prefix-LSAs 1581 for a given area, distinguished by their Link State ID 1582 fields. 1584 A network link's Designated Router originates an intra- 1585 area-prefix-LSA to advertise the link's prefixes 1586 throughout the area. For a link L, L's Designated Router 1587 builds an intra-area-prefix-LSA in the following 1588 fashion: 1590 o In order to indicate that the prefixes are to be 1591 associated with the Link L, the fields Referenced LS 1592 type, Referenced Link State ID, and Referenced 1593 Advertising Router are set to the corresponding 1594 fields in Link L's Network LSA (namely LS type, Link 1595 State ID, and Advertising Router respectively). This 1596 means that Referenced LS Type is set to 0x2002, 1597 Referenced Link State ID is set to the Designated 1598 Router's Interface ID on Link L, and Referenced 1599 Advertising Router is set to the Designated Router's 1600 Router ID. 1602 o Each Link-LSA associated with Link L is examined 1603 (these are in the Designated Router's interface 1604 structure for Link L). If the Link-LSA's Advertising 1605 Router is fully adjacent to the Designated Router, 1606 the list of prefixes in the Link-LSA is copied into 1607 the intra-area-prefix-LSA that is being built. 1608 Prefixes having the NU-bit and/or LA-bit set in 1609 their Options field should not be copied. Each 1610 prefix is described by the PrefixLength, 1611 PrefixOptions, and Address Prefix fields. Multiple 1612 prefixes having the same PrefixLength and Address 1613 Prefix are considered to be duplicates; in this case 1614 their Prefix Options fields should be merged by 1615 logically OR'ing the fields together, and a single 1616 resulting prefix should be copied into the intra- 1617 area-prefix-LSA. The Metric field for all prefixes 1618 is set to 0. 1620 o The "# prefixes" field is set to the number of 1621 prefixes that the router has copied into the LSA. If 1622 necessary, the list of prefixes can be spread across 1623 multiple intra-area-prefix-LSAs in order to keep the 1624 LSA size small. 1626 A router builds an intra-area-prefix-LSA to advertise 1627 its won prefixes, and those of its attached stub network 1628 links. A Router RTX would build its intra-area-prefix- 1629 LSA in the following fashion: 1631 o In order to indicate that the prefixes are to be 1632 associated with the Router RTX itself, RTX sets 1633 Referenced LS type to 0x2001, Referenced Link State 1634 ID to 0, and Referenced Advertising Router to RTX's 1635 own Router ID. 1637 o Router RTX examines its list of interfaces to the 1638 area. If the interface is in state Down, its 1639 prefixes are not included. If the interface has been 1640 reported in RTX's router-LSA as a Type 2 link 1641 description (link to transit network), its prefixes 1642 are not included (they will be included in the 1643 intra-area-prefix-LSA for the link instead). If the 1644 interface type is point-to-point or Point-to- 1645 MultiPoint, or the interface is in state Loopback, 1646 the site-local and global scope IPv6 addresses 1647 associated with the interface (if any) are copied 1648 into the intra-area-prefix-LSA, setting the LA-bit 1649 in the PrefixOptions field, and setting the 1650 PrefixLength to 128 and the Metric to 0. Otherwise, 1651 the list of prefixes configured in RTX for the link 1652 are copied into the intra-area-prefix-LSA by 1653 specifying the PrefixLength, PrefixOptions, and 1654 Address Prefix fields. The Metric field for each of 1655 these prefixes is set to the interface's output 1656 cost. 1658 o RTX adds the IPv6 prefixes for any directly attached 1659 hosts (see Section C.7) to the intra-area-prefix- 1660 LSA. 1662 o If RTX has one or more virtual links configured 1663 through the area, it includes one of its site-local 1664 or global scope IPv6 interface addresses in the LSA 1665 (if it hasn't already), setting the LA-bit in the 1666 PrefixOptions field, and setting the PrefixLength to 1667 128 and the Metric to 0. This information will be 1668 used later in the routing calculation so that the 1669 two ends of the virtual link can discover each 1670 other's IPv6 addresses. 1672 o The "# prefixes" field is set to the number of 1673 prefixes that the router has copied into the LSA. If 1674 necessary, the list of prefixes can be spread across 1675 multiple intra-area-prefix-LSAs in order to keep the 1676 LSA size small. 1678 For example, the intra-area-prefix-LSA originated by RT4 1679 for Network N3 (assuming that RT4 is N3's Designated 1680 Router), and the intra-area-prefix-LSA originated into 1681 Area 1 by Router RT3 for its own prefixes, are pictured 1682 below. 1684 ; Intra-area-prefix-LSA 1685 ; for network link N3 1687 LS age = 0 ;newly (re)originated 1688 LS type = 0x2009 ;Link-LSA 1689 Link State ID = 5 ;or something 1690 Advertising Router = 192.1.1.4 ;RT4's Router ID 1691 # prefixes = 1 1692 Referenced LS type = 0x2002 ;network-LSA reference 1693 Referenced Link State ID = 1 1694 Referenced Advertising Router = 192.1.1.4 1695 PrefixLength = 56 ;N3's prefix 1696 PrefixOptions = 0 1697 Metric = 0 1698 Address Prefix = 5f00:0000:c001:0100 ;pad 1700 ; RT3's Intra-area-prefix-LSA 1701 ; for its own prefixes 1703 LS age = 0 ;newly (re)originated 1704 LS type = 0x2009 ;Link-LSA 1705 Link State ID = 177 ;or something 1706 Advertising Router = 192.1.1.3 ;RT3's Router ID 1707 # prefixes = 1 1708 Referenced LS type = 0x2001 ;router-LSA reference 1709 Referenced Link State ID = 0 1710 Referenced Advertising Router = 192.1.1.3 1711 PrefixLength = 56 ;N4's prefix 1712 PrefixOptions = 0 1713 Metric = 2 ;N4 interface cost 1714 Address Prefix = 5f00:0000:c001:0400 ;pad 1716 3.5. Flooding 1718 Most of the flooding algorithm remains unchanged from the IPv4 1719 flooding mechanisms described in Section 13 of [Ref1]. In 1720 particular, the processes for determining which LSA instance is 1721 newer (Section 13.1 of [Ref1]), responding to updates of self- 1722 originated LSAs (Section 13.4 of [Ref1]), sending Link State 1723 Acknowledgment packets (Section 13.5 of [Ref1]), retransmitting 1724 LSAs (Section 13.6 of [Ref1]) and receiving Link State 1725 Acknowledgment packets (Section 13.7 of [Ref1]) are exactly the 1726 same for IPv6 and IPv4. 1728 However, the addition of flooding scope and handling options for 1729 unrecognized LSA types (see Section A.4.2.1) has caused some 1730 changes in the OSPF flooding algorithm: the reception of Link 1731 State Updates (Section 13 in [Ref1]) and the sending of Link 1732 State Updates (Section 13.3 of [Ref1]) must take into account 1733 the LSA's scope and U-bit setting. Also, installation of LSAs 1734 into the OSPF database (Section 13.2 of [Ref1]) causes different 1735 events in IPv6, due to the reorganization of LSA types and 1736 contents in IPv6. These changes are described in detail below. 1738 3.5.1. Receiving Link State Update packets 1740 The encoding of flooding scope in the LS type and the need 1741 to process unknown LS types causes modifications to the 1742 processing of received Link State Update packets. As in 1743 IPv4, each LSA in a received Link State Update packet is 1744 examined. In IPv4, eight steps are executed for each LSA, as 1745 described in Section 13 of [Ref1]. For IPv6, all the steps 1746 are the same, except that Steps 2 and 3 are modified as 1747 follows: 1749 (2) Examine the LSA's LS type. If the LS type is unknown, 1750 the area has been configured as a stub area, and either 1751 the LSA's flooding scope is set to "AS flooding scope" 1752 or the U-bit of the LS type is set to 1 (flood even when 1753 unrecognized), then discard the LSA and get the next one 1754 from the Link State Update Packet. This generalizes the 1755 IPv4 behavior where AS-external-LSAs are not flooding 1756 into/throughout stub areas. See Section 2.10 for more 1757 details. 1759 (3) Else if the flooding scope of the LSA is set to 1760 "reserved", discard the LSA and get the next one from 1761 the Link State Update Packet. 1763 Steps 5b (sending Link State Update packets) and 5d 1764 (installing LSAs in the link state database) in Section 13 1765 of [Ref1] are also somewhat different for IPv6, as described 1766 in Sections 3.5.2 and 3.5.3 below. 1768 3.5.2. Sending Link State Update packets 1770 The sending of Link State Update packets is described in 1771 Section 13.3 of [Ref1]. For IPv4 and IPv6, the steps for 1772 sending a Link State Update packet are the same (steps 1 1773 through 5 of Section 13.3 in [Ref1]). However, the list of 1774 eligible interfaces out which to flood the LSA is different. 1775 For IPv6, the eligible interfaces are selected based on the 1776 following factors: 1778 o The LSA's flooding scope. 1780 o For LSAs with area or link-local flooding scoping, the 1781 particular area or interface that the LSA is associated 1782 with. 1784 o Whether the LSA has a recognized LS type. 1786 o The setting of the U-bit in the LS type. If the U-bit is 1787 set to 0, unrecognized LS types are treated as having 1788 link-local scope. If set to 1, unrecognized LS types are 1789 stored and flooded as if they were recognized. 1791 Choosing the set of eligible interfaces then breaks into the 1792 following cases: 1794 Case 1 1795 The LSA's LS type is recognized. In this case, the set 1796 of eligible interfaces is set depending on the flooding 1797 scope encoded in the LS type. If the flooding scope is 1798 "AS flooding scope", the eligible interfaces are all 1799 router interfaces excepting virtual links and those 1800 connecting to stub areas. If the flooding scope is "area 1801 flooding scope", the set of eligible interfaces are 1802 those interfaces connecting to the LSA's associated 1803 area. If the flooding scope is "link-local flooding 1804 scope", then there is a single eligible interface, the 1805 one connecting to the LSA's associated link (which, when 1806 the LSA is received in a Link State Update packet, is 1807 also the interface the LSA was received on). 1809 Case 2 1810 The LS type is unrecognized, and the U-bit in the LS 1811 Type is set to 0 (treat the LSA as if it had link-local 1812 flooding scope). In this case there is a single eligible 1813 interface, namely, the interface on which the LSA was 1814 received. 1816 Case 3 1817 The LS type is unrecognized, and the U-bit in the LS 1818 Type is set to 1 (store and flood the LSA, as if type 1819 understood). In this case, select the eligible 1820 interfaces based on the encoded flooding scope as in 1821 Case 1 above. However, in this case interfaces attaching 1822 to stub areas are excluded regardless of flooding scope. 1824 A further decision must sometimes be made before adding an 1825 LSA to a given neighbor's link-state retransmission list 1826 (Step 1d in Section 13.3 of [Ref1]). If the LS type is 1827 recognized by the router, but not by the neighbor (as can be 1828 determined by examining the Options field that the neighbor 1829 advertised in its Database Description packet) and the LSA's 1830 U-bit is set to 0, then the LSA should be added to the 1831 neighbor's link-state retransmission list if and only if 1832 that neighbor is the Designated Router or Backup Designated 1833 Router for the attached link. The LS types described in 1834 detail by this memo, namely router-LSAs (LS type 0x2001), 1835 network-LSAs (0x2002), Inter-Area-Prefix-LSAs (0x2003), 1836 Inter-Area-Router-LSAs (0x2004), AS-External-LSAs (0x4005), 1837 Link-LSAs (0x0008) and Intra-Area-Prefix-LSAs (0x2009) are 1838 assumed to be understood by all routers. However, as an 1839 example the group-membership-LSA (0x2006) is understood only 1840 by MOSPF routers and since it has its U-bit set to 0, it 1841 should only be forwarded to a non-MOSPF neighbor (determined 1842 by examining the MC-bit in the neighbor's Database 1843 Description packets' Options field) when the neighbor is 1844 Designated Router or Backup Designated Router for the 1845 attached link. 1847 The previous paragraph solves a problem in IPv4 OSPF 1848 extensions such as MOSPF, which require that the Designated 1849 Router support the extension in order to have the new LSA 1850 types flooded across broadcast and NBMA networks (see 1851 Section 10.2 of [Ref8]). 1853 3.5.3. Installing LSAs in the database 1855 There are three separate places to store LSAs, depending on 1856 their flooding scope. LSAs with AS flooding scope are stored 1857 in the global OSPF data structure (see Section 3.1) as long 1858 as their LS type is known or their U-bit is 1. LSAs with 1859 area flooding scope are stored in the appropriate area data 1860 structure (see Section 3.1.1) as long as their LS type is 1861 known or their U-bit is 1. LSAs with link-local flooding 1862 scope, and those LSAs with unknown LS type and U-bit set to 1863 0 (treat the LSA as if it had link-local flooding scope) are 1864 stored in the appropriate interface structure. 1866 When storing the LSA into the link-state database, a check 1867 must be made to see whether the LSA's contents have changed. 1868 Changes in contents are indicated exactly as in Section 13.2 1869 of [Ref1]. When an LSA's contents have been changed, the 1870 following parts of the routing table must be recalculated, 1871 based on the LSA's LS type: 1873 Router-LSAs, Network-LSAs and Intra-Area-Prefix-LSAs 1874 The entire routing table is recalculated, starting with 1875 the shortest path calculation for each area (see Section 1876 3.8). 1878 Link-LSAs 1879 The next hop of some of the routing table's entries, 1880 which is always an IPv6 link-local address, may need to 1881 be recalculated. Link-local LSAs provide the OSPF Router 1882 ID to link-local address mapping used in the next hop 1883 calculation. See Section 3.8.1.1 for details. 1885 Inter-Area-Prefix-LSAs and Inter-Area-Router-LSAs 1886 The best route to the destination described by the LSA 1887 must be recalculated (see Section 16.5 in [Ref1]). If 1888 this destination is an AS boundary router, it may also 1889 be necessary to re-examine all the AS-external-LSAs. 1891 AS-external-LSAs 1892 The best route to the destination described by the AS- 1893 external-LSA must be recalculated (see Section 16.6 in 1894 [Ref1]). 1896 As in IPv4, any old instance of the LSA must be removed from 1897 the database when the new LSA is installed. This old 1898 instance must also be removed from all neighbors' Link state 1899 retransmission lists. 1901 3.6. Definition of self-originated LSAs 1903 In IPv6 the definition of a self-originated LSA has been 1904 simplified from the IPv4 definition appearing in Sections 13.4 1905 and 14.1 of [Ref1]. For IPv6, self-originated LSAs are those 1906 LSAs whose Advertising Router is equal to the router's own 1907 Router ID. 1909 3.7. Virtual links 1911 OSPF virtual links for IPv4 are described in Section 15 of 1912 [Ref1]. Virtual links are the same in IPv6, with the following 1913 exceptions: 1915 o LSAs having AS flooding scope are never flooded over virtual 1916 adjacencies, nor are LSAs with AS flooding scope summarized 1917 over virtual adjacencies during the Database Exchange 1918 process. This is a generalization of the IPv4 treatment of 1919 AS-external-LSAs. 1921 o The IPv6 interface address of a virtual link must be an IPv6 1922 address having site-local or global scope, instead of the 1923 link-local addresses used by other interface types. This 1924 address is used as the IPv6 source for OSPF protocol packets 1925 sent over the virtual link. 1927 o Likewise, the virtual neighbor's IPv6 address is an IPv6 1928 address with site-local or global scope. To enable the 1929 discovery of a virtual neighbor's IPv6 address during the 1930 routing calculation, the neighbor advertises its virtual 1931 link's IPv6 interface address in an Intra-Area-Prefix-LSA 1932 originated for the virtual link's transit area (see Sections 1933 3.4.3.7 and 3.8.1). 1935 o Like all other IPv6 OSPF interfaces, virtual links are 1936 assigned unique (within the router) Interface IDs. These are 1937 advertised in Hellos sent over the virtual link, and in the 1938 router's router-LSAs. 1940 o IPv6 has no concept of TOS, so all discussions of TOS in 1941 Section 15 of [Ref1] are not applicable to OSPF for IPv6. 1943 3.8. Routing table calculation 1945 The IPv6 OSPF routing calculation proceeds along the same lines 1946 as the IPv4 OSPF routing calculation, following the five steps 1947 specified by Section 16 of [Ref1]. High level differences 1948 between the IPv6 and IPv4 calculations include: 1950 o Prefix information has been removed from router-LSAs, and 1951 now is advertised in intra-area-prefix-LSAs. Whenever [Ref1] 1952 specifies that stub networks within router-LSAs be examined, 1953 IPv6 will instead examine prefixes within intra-area- 1954 prefix-LSAs. 1956 o Type 3 and 4 summary-LSAs have been renamed inter-area- 1957 prefix-LSAs and inter-area-router-LSAs (respectively). 1959 o Addressing information is no longer encoded in Link State 1960 IDs, and must instead be found within the body of LSAs. 1962 o In IPv6, a router can originate multiple router-LSAs within 1963 a single area, distinguished by Link State ID. These 1964 router-LSAs must be treated as a single aggregate by the 1965 area's shortest path calculation (see Section 3.8.1). 1967 o IPv6 has no concept of TOS; all TOS routing calculations in 1968 [Ref1] are inapplicable to OSPF for IPv6. In particular, 1969 Section 16.9 of [Ref1] can be ignored for IPv6. 1971 For each area, routing table entries have been created for the 1972 area's routers and transit links, in order to store the results 1973 of the area's shortest-path tree calculation (see Section 1974 3.8.1). These entries are then used when processing intra-area- 1975 prefix-LSAs, inter-area-prefix-LSAs and inter-area-router-LSAs, 1976 as described in Section 3.8.2. 1978 Events generated as a result of routing table changes (Section 1979 16.7 of [Ref1]), and the equal-cost multipath logic (Section 1980 16.8 of [Ref1]) are identical for both IPv4 and IPv6. 1982 3.8.1. Calculating the shortest path tree for an area 1984 The IPv4 shortest path calculation is contained in Section 1985 16.1 of [Ref1]. The graph used by the shortest-path tree 1986 calculation is identical for both IPv4 and IPv6. The graph's 1987 vertices are routers and transit links, represented by 1988 router-LSAs and network-LSAs respectively. A router is 1989 identified by its OSPF Router ID, while a transit link is 1990 identified by its Designated Router's Interface ID and OSPF 1991 Router ID. Both routers and transit links have associated 1992 routing table entries within the area (see Section 3.3). 1994 Section 16.1 of [Ref1] splits up the shortest path 1995 calculations into two stages. First the Dijkstra calculation 1996 is performed, and then the stub links are added onto the 1997 tree as leaves. The IPv6 calculation maintains this split. 1999 The Dijkstra calculation for IPv6 is identical to that 2000 specified for IPv4, with the following exceptions 2001 (referencing the steps from the Dijkstra calculation as 2002 described in Section 16.1 of [Ref1]): 2004 o The Vertex ID for a router is the OSPF Router ID. The 2005 Vertex ID for a transit network is a combination of the 2006 Interface ID and OSPF Router ID of the network's 2007 Designated Router. 2009 o In Step 2, when a router Vertex V has just been added to 2010 the shortest path tree, there may be multiple LSAs 2011 associated with the router. All Router-LSAs with 2012 Advertising Router set to V's OSPF Router ID must 2013 processed as an aggregate, treating them as fragments of 2014 a single large router-LSA. The Options field and the 2015 router type bits (bits W, V, E and B) should always be 2016 taken from "fragment" with the smallest Link State ID. 2018 o Step 2a is not needed in IPv6, as there are no longer 2019 stub network links in router-LSAs. 2021 o In Step 2b, if W is a router, there may again be 2022 multiple LSAs associated with the router. All Router- 2023 LSAs with Advertising Router set to W's OSPF Router ID 2024 must processed as an aggregate, treating them as 2025 fragments of a single large router-LSA. 2027 o In Step 4, there are now per-area routing table entries 2028 for each of an area's routers, instead of just the area 2029 border routers. These entries subsume all the 2030 functionality of IPv4's area border router routing table 2031 entries, including the maintenance of virtual links. 2032 When the router added to the area routing table in this 2033 step is the other end of a virtual link, the virtual 2034 neighbor's IP address is set as follows: The collection 2035 of intra-area-prefix-LSAs originated by the virtual 2036 neighbor is examined, with the virtual neighbor's IP 2037 address being set to the first prefix encountered having 2038 the "LA-bit" set. 2040 o Routing table entries for transit networks, which are no 2041 longer associated with IP networks, are also modified in 2042 Step 4. 2044 The next stage of the shortest path calculation proceeds 2045 similarly to the two steps of the second stage of Section 2046 16.1 in [Ref1]. However, instead of examining the stub links 2047 within router-LSAs, the list of the area's intra-area- 2048 prefix-LSAs is examined. A prefix advertisement whose "NU- 2049 bit" is set should not be included in the routing 2050 calculation. The cost of any advertised prefix is the sum of 2051 the prefix' advertised metric plus the cost to the transit 2052 vertex (either router or transit network) identified by 2053 intra-area-prefix-LSA's Referenced LS type, Referenced Link 2054 State ID and Referenced Advertising Router fields. This 2055 latter cost is stored in the transit vertex' routing table 2056 entry for the area. 2058 3.8.1.1. The next hop calculation 2060 In IPv6, the calculation of the next hop's IPv6 address 2061 (which will be a link-local address) proceeds along the 2062 same lines as the IPv4 next hop calculation (see Section 2063 16.1.1 of [Ref1]). The only difference is in calculating 2064 the next hop IPv6 address for a router (call it Router 2065 X) which shares a link with the calculating router. In 2066 this case the calculating router assigns the next hop 2067 IPv6 address to be the link-local interface address 2068 contained in Router X's Link-LSA (see Section A.4.8) for 2069 the link. This procedure is necessary since on some 2070 links, such as NBMA links, the two routers need not be 2071 neighbors, and therefore might not be exchanging OSPF 2072 Hellos. 2074 3.8.2. Calculating the inter-area routes 2076 Calculation of inter-area routes for IPv6 proceeds along the 2077 same lines as the IPv4 calculation in Section 16.2 of 2079 [Ref1], with the following modifications: 2081 o The names of the Type 3 summary-LSAs and Type 4 2082 summary-LSAs have been changed to inter-area-prefix-LSAs 2083 and inter-area-router-LSAs respectively. 2085 o The Link State ID of the above LSA types no longer 2086 encodes the network or router described by the LSA. 2087 Instead, an address prefix is contained in the body of 2088 an inter-area-prefix-LSA, and a described router's OSPF 2089 Router ID is carried in the body of an inter-area- 2090 router-LSA. 2092 o Prefixes having the "NU-bit" set in their Prefix Options 2093 field should be ignored by the inter-area route 2094 calculation. 2096 When a single inter-area-prefix-LSA or inter-area-router-LSA 2097 has changed, the incremental calculations outlined in 2098 Section 16.5 of [Ref1] can be performed instead of 2099 recalculating the entire routing table. 2101 3.8.3. Examining transit areas' summary-LSAs 2103 Examination of transit areas' summary-LSAs in IPv6 proceeds 2104 along the same lines as the IPv4 calculation in Section 16.3 2105 of [Ref1], modified in the same way as the IPv6 inter-area 2106 route calculation in Section 3.8.2. 2108 3.8.4. Calculating AS external routes 2110 The IPv6 AS external route calculation proceeds along the 2111 same lines as the IPv4 calculation in Section 16.4 of 2112 [Ref1], with the following exceptions: 2114 o The Link State ID of the AS-external-LSA types no longer 2115 encodes the network described by the LSA. Instead, an 2116 address prefix is contained in the body of an AS- 2117 external-LSA. 2119 o The default route is described by AS-external-LSAs which 2120 advertise zero length prefixes. 2122 o Instead of comparing the AS-external-LSA's Forwarding 2123 address field to 0.0.0.0 to see whether a forwarding 2124 address has been used, bit F of the external-LSA is 2125 examined. A forwarding address is in use if and only if 2126 bit F is set. 2128 o Prefixes having the "NU-bit" set in their Prefix Options 2129 field should be ignored by the inter-area route 2130 calculation. 2132 When a single AS-external-LSA has changed, the incremental 2133 calculations outlined in Section 16.6 of [Ref1] can be 2134 performed instead of recalculating the entire routing table. 2136 References 2138 [Ref1] Moy, J., "OSPF Version 2", Internet Draft, , Cascade, June 1996. 2141 [Ref2] McKenzie, A., "ISO Transport Protocol specification ISO DP 2142 8073", RFC 905, ISO, April 1984. 2144 [Ref3] McCloghrie, K., and M. Rose, "Management Information Base 2145 for network management of TCP/IP-based internets: MIB-II", 2146 STD 17, RFC 1213, Hughes LAN Systems, Performance Systems 2147 International, March 1991. 2149 [Ref4] Fuller, V., T. Li, J. Yu, and K. Varadhan, "Classless 2150 Inter-Domain Routing (CIDR): an Address Assignment and 2151 Aggregation Strategy", RFC1519, BARRNet, cisco, MERIT, 2152 OARnet, September 1993. 2154 [Ref5] Varadhan, K., S. Hares and Y. Rekhter, "BGP4/IDRP for IP--- 2155 OSPF Interaction", RFC1745, December 1994 2157 [Ref6] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 2158 1700, USC/Information Sciences Institute, October 1994. 2160 [Ref7] deSouza, O., and M. Rodrigues, "Guidelines for Running OSPF 2161 Over Frame Relay Networks", RFC 1586, March 1994. 2163 [Ref8] Moy, J., "Multicast Extensions to OSPF", RFC 1584, Proteon, 2164 Inc., March 1994. 2166 [Ref9] Coltun, R. and V. Fuller, "The OSPF NSSA Option", RFC 1587, 2167 RainbowBridge Communications, Stanford University, March 2168 1994. 2170 [Ref10] Ferguson, D., "The OSPF External Attributes LSA", 2171 unpublished. 2173 [Ref11] Moy, J., "Extending OSPF to Support Demand Circuits", RFC 2174 1793, Cascade, April 1995. 2176 [Ref12] Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191, 2177 DECWRL, Stanford University, November 1990. 2179 [Ref13] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP- 2180 4)", RFC 1771, T.J. Watson Research Center, IBM Corp., cisco 2181 Systems, March 1995. 2183 [Ref14] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2184 (IPv6) Specification", RFC 1883, Xerox PARC, Ipsilon 2185 Networks, December 1995. 2187 [Ref15] Deering, S. and R. Hinden, "IP Version 6 Addressing 2188 Architecture", RFC 1884, Xerox PARC, Ipsilon Networks, 2189 December 1995. 2191 [Ref16] Conta, A. and S. Deering, "Internet Control Message Protocol 2192 (ICMPv6) for the Internet Protocol Version 6 (IPv6) 2193 Specification" RFC 1885, Digital Equipment Corporation, 2194 Xerox PARC, December 1995. 2196 [Ref17] Narten, T., E. Nordmark and W. A. Simpson, "Neighbor 2197 Discovery for IP Version 6 (IPv6)", IBM, Sun Microsystems, 2198 work in progress. 2200 [Ref18] McCann, J. and S. Deering, "Path MTU Discovery for IP 2201 version 6", Digital Equipment Corporation, Xerox PARC, work 2202 in progress. 2204 [Ref19] Atkinson, R., "IP Authentication Header", RFC 1826, Naval 2205 Research Laboratory, August 1995. 2207 [Ref20] Atkinson, R., "IP Encapsulating Security Payload (ESP)", RFC 2208 1827, Naval Research Laboratory, August 1995. 2210 A. OSPF data formats 2212 This appendix describes the format of OSPF protocol packets and OSPF 2213 LSAs. The OSPF protocol runs directly over the IPv6 network layer. 2214 Before any data formats are described, the details of the OSPF 2215 encapsulation are explained. 2217 Next the OSPF Options field is described. This field describes 2218 various capabilities that may or may not be supported by pieces of 2219 the OSPF routing domain. The OSPF Options field is contained in OSPF 2220 Hello packets, Database Description packets and in OSPF LSAs. 2222 OSPF packet formats are detailed in Section A.3. 2224 A description of OSPF LSAs appears in Section A.4. This section 2225 describes how IPv6 address prefixes are represented within LSAs, 2226 details the standard LSA header, and then provides formats for each 2227 of the specific LSA types. 2229 A.1 Encapsulation of OSPF packets 2231 OSPF runs directly over the IPv6's network layer. OSPF packets are 2232 therefore encapsulated solely by IPv6 and local data-link headers. 2234 OSPF does not define a way to fragment its protocol packets, and 2235 depends on IPv6 fragmentation when transmitting packets larger than 2236 the link MTU. If necessary, the length of OSPF packets can be up to 2237 65,535 bytes. The OSPF packet types that are likely to be large 2238 (Database Description Packets, Link State Request, Link State 2239 Update, and Link State Acknowledgment packets) can usually be split 2240 into several separate protocol packets, without loss of 2241 functionality. This is recommended; IPv6 fragmentation should be 2242 avoided whenever possible. Using this reasoning, an attempt should 2243 be made to limit the sizes of OSPF packets sent over virtual links 2244 to 576 bytes unless Path MTU Discovery is being performed. 2246 The other important features of OSPF's IPv6 encapsulation are: 2248 o Use of IPv6 multicast. Some OSPF messages are multicast, when 2249 sent over broadcast networks. Two distinct IP multicast 2250 addresses are used. Packets sent to these multicast addresses 2251 should never be forwarded; they are meant to travel a single hop 2252 only. As such, the multicast addresses have been chosen with 2253 link-local scope, and packets sent to these addresses should 2254 have their IPv6 Hop Limit set to 1. 2256 AllSPFRouters 2257 This multicast address has been assigned the value FF02::5. 2259 All routers running OSPF should be prepared to receive 2260 packets sent to this address. Hello packets are always sent 2261 to this destination. Also, certain OSPF protocol packets 2262 are sent to this address during the flooding procedure. 2264 AllDRouters 2265 This multicast address has been assigned the value FF02::6. 2266 Both the Designated Router and Backup Designated Router must 2267 be prepared to receive packets destined to this address. 2268 Certain OSPF protocol packets are sent to this address 2269 during the flooding procedure. 2271 o OSPF is IP protocol 89. This number should be inserted in the 2272 Next Header field of the encapsulating IPv6 header. 2274 o Routing protocol packets are sent with IPv6 Priority field set 2275 to 7 (internet control traffic). OSPF protocol packets should 2276 be given precedence over regular IPv6 data traffic, in both 2277 sending and receiving. 2279 A.2 The Options field 2281 The 24-bit OSPF Options field is present in OSPF Hello packets, 2282 Database Description packets and certain LSAs (router-LSAs, 2283 network-LSAs, inter-area-router-LSAs and link-LSAs). The Options 2284 field enables OSPF routers to support (or not support) optional 2285 capabilities, and to communicate their capability level to other 2286 OSPF routers. Through this mechanism routers of differing 2287 capabilities can be mixed within an OSPF routing domain. 2289 An option mismatch between routers can cause a variety of behaviors, 2290 depending on the particular option. Some option mismatches prevent 2291 neighbor relationships from forming (e.g., the E-bit below); these 2292 mismatches are discovered through the sending and receiving of Hello 2293 packets. Some option mismatches prevent particular LSA types from 2294 being flooded across adjacencies (e.g., the MC-bit below); these are 2295 discovered through the sending and receiving of Database Description 2296 packets. Some option mismatches prevent routers from being included 2297 in one or more of the various routing calculations because of their 2298 reduced functionality (again the MC-bit is an example); these 2299 mismatches are discovered by examining LSAs. 2301 Six bits of the OSPF Options field have been assigned. Each bit is 2302 described briefly below. Routers should reset (i.e. clear) 2303 unrecognized bits in the Options field when sending Hello packets or 2304 Database Description packets and when originating LSAs. Conversely, 2305 routers encountering unrecognized Option bits in received Hello 2306 Packets, Database Description packets or LSAs should ignore the 2307 capability and process the packet/LSA normally. 2309 1 2 2310 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+--+--+--+--+ 2312 | | | | | | | | | | | | | | | | | | |DC| R| N|MC| E|V6| 2313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+--+--+--+--+ 2315 The Options field 2317 V6-bit 2318 If this bit is clear, the router/link should be excluded from 2319 IPv6 routing calculations. See Section 3.8 of this memo. 2321 E-bit 2322 This bit describes the way AS-external-LSAs are flooded, as 2323 described in Sections 3.6, 9.5, 10.8 and 12.1.2 of [Ref1]. 2325 MC-bit 2326 This bit describes whether IP multicast datagrams are forwarded 2327 according to the specifications in [Ref7]. 2329 N-bit 2330 This bit describes the handling of Type-7 LSAs, as specified in 2331 [Ref8]. 2333 R-bit 2334 This bit (the `Router' bit) indicates whether the originator is 2335 an active router. If the router bit is clear routes which 2336 transit the advertising node cannot be computed. Clearing the 2337 router bit would be appropriate for a multi-homed host that 2338 wants to participate in routing, but does not want to forward 2339 non-locally addressed packets. 2341 DC-bit 2342 This bit describes the router's handling of demand circuits, as 2343 specified in [Ref10]. 2345 A.3 OSPF Packet Formats 2347 There are five distinct OSPF packet types. All OSPF packet types 2348 begin with a standard 16 byte header. This header is described 2349 first. Each packet type is then described in a succeeding section. 2350 In these sections each packet's division into fields is displayed, 2351 and then the field definitions are enumerated. 2353 All OSPF packet types (other than the OSPF Hello packets) deal with 2354 lists of LSAs. For example, Link State Update packets implement the 2355 flooding of LSAs throughout the OSPF routing domain. The format of 2356 LSAs is described in Section A.4. 2358 The receive processing of OSPF packets is detailed in Section 3.2.2. 2359 The sending of OSPF packets is explained in Section 3.2.1. 2361 A.3.1 The OSPF packet header 2363 Every OSPF packet starts with a standard 16 byte header. Together 2364 with the encapsulating IPv6 headers, the OSPF header contains all 2365 the information necessary to determine whether the packet should be 2366 accepted for further processing. This determination is described in 2367 Section 3.2.2 of this memo. 2369 0 1 2 3 2370 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 2371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2372 | Version # | Type | Packet length | 2373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2374 | Router ID | 2375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2376 | Area ID | 2377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2378 | Checksum | Instance ID | 0 | 2379 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2381 Version # 2382 The OSPF version number. This specification documents version 3 2383 of the OSPF protocol. 2385 Type 2386 The OSPF packet types are as follows. See Sections A.3.2 through 2387 A.3.6 for details. 2389 Type Description 2390 ________________________________ 2391 1 Hello 2392 2 Database Description 2393 3 Link State Request 2394 4 Link State Update 2395 5 Link State Acknowledgment 2397 Packet length 2398 The length of the OSPF protocol packet in bytes. This length 2399 includes the standard OSPF header. 2401 Router ID 2402 The Router ID of the packet's source. 2404 Area ID 2405 A 32 bit number identifying the area that this packet belongs 2406 to. All OSPF packets are associated with a single area. Most 2407 travel a single hop only. Packets travelling over a virtual 2408 link are labelled with the backbone Area ID of 0. 2410 Checksum 2411 The standard IP checksum of the entire contents of the packet, 2412 starting with the OSPF packet header. This checksum is 2413 calculated as the 16-bit one's complement of the one's 2414 complement sum of all the 16-bit words in the packet. If the 2415 packet's length is not an integral number of 16-bit words, the 2416 packet is padded with a byte of zero before checksumming. 2418 Instance ID 2419 Enables multiple instances of OSPF to be run over a single link. 2420 Each protocol instance would be assigned a separate Instance ID; 2421 the Instance ID has local link significance only. Received 2422 packets whose Instance ID is not equal to the receiving 2423 interface's Instance ID are discarded. 2425 0 These fields are reserved. They must be 0. 2427 A.3.2 The Hello packet 2429 Hello packets are OSPF packet type 1. These packets are sent 2430 periodically on all interfaces (including virtual links) in order to 2431 establish and maintain neighbor relationships. In addition, Hello 2432 Packets are multicast on those links having a multicast or broadcast 2433 capability, enabling dynamic discovery of neighboring routers. 2435 All routers connected to a common link must agree on certain 2436 parameters (HelloInterval and RouterDeadInterval). These parameters 2437 are included in Hello packets, so that differences can inhibit the 2438 forming of neighbor relationships. The Hello packet also contains 2439 fields used in Designated Router election (Designated Router ID and 2440 Backup Designated Router ID), and fields used to detect bi- 2441 directionality (the Router IDs of all neighbors whose Hellos have 2442 been recently received). 2444 0 1 2 3 2445 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 2446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2447 | 3 | 1 | Packet length | 2448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2449 | Router ID | 2450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2451 | Area ID | 2452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2453 | Checksum | Instance ID | 0 | 2454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2455 | Interface ID | 2456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2457 | Rtr Pri | Options | 2458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2459 | HelloInterval | RouterDeadInterval | 2460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2461 | Designated Router ID | 2462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2463 | Backup Designated Router ID | 2464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2465 | Neighbor ID | 2466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2467 | ... | 2469 Interface ID 2470 32-bit number uniquely identifying this interface among the 2471 collection of this router's interfaces. For example, in some 2472 implementations it may be possible to use the MIB-II IfIndex. 2474 Rtr Pri 2475 This router's Router Priority. Used in (Backup) Designated 2476 Router election. If set to 0, the router will be ineligible to 2477 become (Backup) Designated Router. 2479 Options 2480 The optional capabilities supported by the router, as documented 2481 in Section A.2. 2483 HelloInterval 2484 The number of seconds between this router's Hello packets. 2486 RouterDeadInterval 2487 The number of seconds before declaring a silent router down. 2489 Designated Router ID 2490 The identity of the Designated Router for this network, in the 2491 view of the sending router. The Designated Router is identified 2492 by its Router ID. Set to 0.0.0.0 if there is no Designated 2493 Router. 2495 Backup Designated Router ID 2496 The identity of the Backup Designated Router for this network, 2497 in the view of the sending router. The Backup Designated Router 2498 is identified by its IP Router ID. Set to 0.0.0.0 if there is 2499 no Backup Designated Router. 2501 Neighbor ID 2502 The Router IDs of each router from whom valid Hello packets have 2503 been seen recently on the network. Recently means in the last 2504 RouterDeadInterval seconds. 2506 A.3.3 The Database Description packet 2508 Database Description packets are OSPF packet type 2. These packets 2509 are exchanged when an adjacency is being initialized. They describe 2510 the contents of the link-state database. Multiple packets may be 2511 used to describe the database. For this purpose a poll-response 2512 procedure is used. One of the routers is designated to be the 2513 master, the other the slave. The master sends Database Description 2514 packets (polls) which are acknowledged by Database Description 2515 packets sent by the slave (responses). The responses are linked to 2516 the polls via the packets' DD sequence numbers. 2518 0 1 2 3 2519 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 2520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2521 | 3 | 2 | Packet length | 2522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2523 | Router ID | 2524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2525 | Area ID | 2526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2527 | Checksum | Instance ID | 0 | 2528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2529 |0|0|0|0|0|I|M|MS Options | 2530 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2531 | DD sequence number | 2532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2533 | | 2534 +- -+ 2535 | | 2536 +- An LSA Header -+ 2537 | | 2538 +- -+ 2539 | | 2540 +- -+ 2541 | | 2542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2543 | ... | 2545 The format of the Database Description packet is very similar to 2546 both the Link State Request and Link State Acknowledgment packets. 2547 The main part of all three is a list of items, each item describing 2548 a piece of the link-state database. The sending of Database 2549 Description Packets is documented in Section 10.8 of [Ref1]. The 2550 reception of Database Description packets is documented in Section 2551 10.6 of [Ref1]. 2553 I-bit 2554 The Init bit. When set to 1, this packet is the first in the 2555 sequence of Database Description Packets. 2557 M-bit 2558 The More bit. When set to 1, it indicates that more Database 2559 Description Packets are to follow. 2561 MS-bit 2562 The Master/Slave bit. When set to 1, it indicates that the 2563 router is the master during the Database Exchange process. 2564 Otherwise, the router is the slave. 2566 Options 2567 The optional capabilities supported by the router, as documented 2568 in Section A.2. 2570 DD sequence number 2571 Used to sequence the collection of Database Description Packets. 2572 The initial value (indicated by the Init bit being set) should 2573 be unique. The DD sequence number then increments until the 2574 complete database description has been sent. 2576 The rest of the packet consists of a (possibly partial) list of the 2577 link-state database's pieces. Each LSA in the database is described 2578 by its LSA header. The LSA header is documented in Section A.4.1. 2579 It contains all the information required to uniquely identify both 2580 the LSA and the LSA's current instance. 2582 A.3.4 The Link State Request packet 2584 Link State Request packets are OSPF packet type 3. After exchanging 2585 Database Description packets with a neighboring router, a router may 2586 find that parts of its link-state database are out-of-date. The 2587 Link State Request packet is used to request the pieces of the 2588 neighbor's database that are more up-to-date. Multiple Link State 2589 Request packets may need to be used. 2591 A router that sends a Link State Request packet has in mind the 2592 precise instance of the database pieces it is requesting. Each 2593 instance is defined by its LS sequence number, LS checksum, and LS 2594 age, although these fields are not specified in the Link State 2595 Request Packet itself. The router may receive even more recent 2596 instances in response. 2598 The sending of Link State Request packets is documented in Section 2599 10.9 of [Ref1]. The reception of Link State Request packets is 2600 documented in Section 10.7 of [Ref1]. 2602 0 1 2 3 2603 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 2604 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2605 | 3 | 3 | Packet length | 2606 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2607 | Router ID | 2608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2609 | Area ID | 2610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2611 | Checksum | Instance ID | 0 | 2612 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2613 | 0 | LS type | 2614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2615 | Link State ID | 2616 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2617 | Advertising Router | 2618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2619 | ... | 2621 Each LSA requested is specified by its LS type, Link State ID, and 2622 Advertising Router. This uniquely identifies the LSA, but not its 2623 instance. Link State Request packets are understood to be requests 2624 for the most recent instance (whatever that might be). 2626 A.3.5 The Link State Update packet 2628 Link State Update packets are OSPF packet type 4. These packets 2629 implement the flooding of LSAs. Each Link State Update packet 2630 carries a collection of LSAs one hop further from their origin. 2631 Several LSAs may be included in a single packet. 2633 Link State Update packets are multicast on those physical networks 2634 that support multicast/broadcast. In order to make the flooding 2635 procedure reliable, flooded LSAs are acknowledged in Link State 2636 Acknowledgment packets. If retransmission of certain LSAs is 2637 necessary, the retransmitted LSAs are always carried by unicast Link 2638 State Update packets. For more information on the reliable flooding 2639 of LSAs, consult Section 3.5. 2641 0 1 2 3 2642 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 2643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2644 | 3 | 4 | Packet length | 2645 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2646 | Router ID | 2647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2648 | Area ID | 2649 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2650 | Checksum | Instance ID | 0 | 2651 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2652 | # LSAs | 2653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2654 | | 2655 +- +-+ 2656 | LSAs | 2657 +- +-+ 2658 | ... | 2660 # LSAs 2661 The number of LSAs included in this update. 2663 The body of the Link State Update packet consists of a list of LSAs. 2664 Each LSA begins with a common 20 byte header, described in Section 2665 A.4.2. Detailed formats of the different types of LSAs are described 2666 in Section A.4. 2668 A.3.6 The Link State Acknowledgment packet 2670 Link State Acknowledgment Packets are OSPF packet type 5. To make 2671 the flooding of LSAs reliable, flooded LSAs are explicitly 2672 acknowledged. This acknowledgment is accomplished through the 2673 sending and receiving of Link State Acknowledgment packets. The 2674 sending of Link State Acknowledgement packets is documented in 2675 Section 13.5 of [Ref1]. The reception of Link State Acknowledgement 2676 packets is documented in Section 13.7 of [Ref1]. 2678 Multiple LSAs can be acknowledged in a single Link State 2679 Acknowledgment packet. Depending on the state of the sending 2680 interface and the sender of the corresponding Link State Update 2681 packet, a Link State Acknowledgment packet is sent either to the 2682 multicast address AllSPFRouters, to the multicast address 2683 AllDRouters, or as a unicast (see Section 13.5 of [Ref1] for 2684 details). 2686 The format of this packet is similar to that of the Data Description 2687 packet. The body of both packets is simply a list of LSA headers. 2689 0 1 2 3 2690 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 2691 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2692 | 3 | 5 | Packet length | 2693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2694 | Router ID | 2695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2696 | Area ID | 2697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2698 | Checksum | Instance ID | 0 | 2699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2700 | | 2701 +- -+ 2702 | | 2703 +- An LSA Header -+ 2704 | | 2705 +- -+ 2706 | | 2707 +- -+ 2708 | | 2709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2710 | ... | 2712 Each acknowledged LSA is described by its LSA header. The LSA 2713 header is documented in Section A.4.2. It contains all the 2714 information required to uniquely identify both the LSA and the LSA's 2715 current instance. 2717 A.4 LSA formats 2719 This memo defines seven distinct types of LSAs. Each LSA begins 2720 with a standard 20 byte LSA header. This header is explained in 2721 Section A.4.2. Succeeding sections then diagram the separate LSA 2722 types. 2724 Each LSA describes a piece of the OSPF routing domain. Every router 2725 originates a router-LSA. A network-LSA is advertised for each link 2726 by its Designated Router. A router's link-local addresses are 2727 advertised to its neighbors in link-LSAs. IPv6 prefixes are 2728 advertised in intra-area-prefix-LSAs, inter-area-prefix-LSAs and 2729 AS-external-LSAs. Location of specific routers can be advertised 2730 across area boundaries in inter-area-router-LSAs. All LSAs are then 2731 flooded throughout the OSPF routing domain. The flooding algorithm 2732 is reliable, ensuring that all routers have the same collection of 2733 LSAs. (See Section 3.5 for more information concerning the flooding 2734 algorithm). This collection of LSAs is called the link-state 2735 database. 2737 From the link state database, each router constructs a shortest path 2738 tree with itself as root. This yields a routing table (see Section 2739 11 of [Ref1]). For the details of the routing table build process, 2740 see Section 3.8. 2742 A.4.1 IPv6 Prefix Representation 2744 IPv6 addresses are bit strings of length 128. IPv6 routing 2745 algorithms, and OSPF for IPv6 in particular, advertise IPv6 address 2746 prefixes. IPv6 address prefixes are bit strings whose length ranges 2747 between 0 and 128 bits (inclusive). 2749 Within OSPF, IPv6 address prefixes are always represented by a 2750 combination of three fields: PrefixLength, PrefixOptions, and 2751 Address Prefix. PrefixLength is the length in bits of the prefix. 2752 PrefixOptions is an 8-bit field describing various capabilities 2753 associated with the prefix (see Section A.4.2). Address Prefix is an 2754 encoding of the prefix itself as an even multiple of 32-bit words, 2755 padding with zero bits as necessary; this encoding consumes 2756 (PrefixLength + 31) / 32) 32-bit words. 2758 The default route is represented by a prefix of length 0. 2760 Examples of IPv6 Prefix representation in OSPF can be found in 2761 Sections A.4.5, A.4.7, A.4.8 and A.4.9. 2763 A.4.1.1 Prefix Options 2765 Each prefix is advertised along with an 8-bit field of capabilities. 2766 These serve as input to the various routing calculations, allowing, 2767 for example, certain prefixes to be ignored in some cases, or to be 2768 marked as not readvertisable in others. 2770 0 1 2 3 4 5 6 7 2771 +--+--+--+--+--+--+--+--+ 2772 | | | | | P|MC|LA|NU| 2773 +--+--+--+--+--+--+--+--+ 2775 The Prefix Options field 2777 NU-bit 2778 The "no unicast" capability bit. If set, the prefix should be 2779 excluded from IPv6 unicast calculations, otherwise it should be 2780 included. 2782 LA-bit 2783 The "local address" capability bit. If set, the prefix is 2784 actually an IPv6 interface address of the advertising router. 2786 MC-bit 2787 The "multicast" capability bit. If set, the prefix should be 2788 included in IPv6 multicast routing calculations, otherwise it 2789 should be excluded. 2791 P-bit 2792 The "propagate" bit. Set on NSSA area prefixes that should be 2793 readvertised at the NSSA area border. 2795 A.4.2 The LSA header 2797 All LSAs begin with a common 20 byte header. This header contains 2798 enough information to uniquely identify the LSA (LS type, Link State 2799 ID, and Advertising Router). Multiple instances of the LSA may 2800 exist in the routing domain at the same time. It is then necessary 2801 to determine which instance is more recent. This is accomplished by 2802 examining the LS age, LS sequence number and LS checksum fields that 2803 are also contained in the LSA header. 2805 0 1 2 3 2806 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 2807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2808 | LS age | LS type | 2809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2810 | Link State ID | 2811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2812 | Advertising Router | 2813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2814 | LS sequence number | 2815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2816 | LS checksum | length | 2817 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2819 LS age 2820 The time in seconds since the LSA was originated. 2822 LS type 2823 The LS type field indicates the function performed by the LSA. 2824 The high-order three bits of LS type encode generic properties 2825 of the LSA, while the remainder (called LSA function code) 2826 indicate the LSA's specific functionality. See Section A.4.2.1 2827 for a detailed description of LS type. 2829 Link State ID 2830 Together with LS type and Advertising Router, uniquely 2831 identifies the LSA in the link-state database. 2833 Advertising Router 2834 The Router ID of the router that originated the LSA. For 2835 example, in network-LSAs this field is equal to the Router ID of 2836 the network's Designated Router. 2838 LS sequence number 2839 Detects old or duplicate LSAs. Successive instances of an LSA 2840 are given successive LS sequence numbers. See Section 12.1.6 in 2841 [Ref1] for more details. 2843 LS checksum 2844 The Fletcher checksum of the complete contents of the LSA, 2845 including the LSA header but excluding the LS age field. See 2846 Section 12.1.7 in [Ref1] for more details. 2848 length 2849 The length in bytes of the LSA. This includes the 20 byte LSA 2850 header. 2852 A.4.2.1 LS type 2854 The LS type field indicates the function performed by the LSA. The 2855 high-order three bits of LS type encode generic properties of the 2856 LSA, while the remainder (called LSA function code) indicate the 2857 LSA's specific functionality. The format of the LS type is as 2858 follows: 2860 1 2861 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2862 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 2863 |U |S2|S1| LSA Function Code | 2864 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 2866 The U bit indicates how the LSA should be handled by a router which 2867 does not recognize the LSA's function code. Its values are: 2869 U-bit LSA Handling 2870 ____________________________________________________________ 2871 0 Treat the LSA as if it had link-local flooding scope 2872 1 Store and flood the LSA, as if type understood 2874 The S1 and S2 bits indicate the flooding scope of the LSA. The 2875 values are: 2877 _______________________________________________________________________ 2878 0 0 Link-Local Scoping. Flooded only on link it is originated on. 2879 0 1 Area Scoping. Flooded to all routers in the originating area 2880 1 0 AS Scoping. Flooded to all routers in the AS 2881 1 1 Reserved 2883 The LSA function codes are defined as follows. The origination and 2884 processing of these LSA function codes are defined elsewhere in this 2885 memo, except for the group-membership-LSA (see [Ref7]) and the 2886 Type-7-LSA (see [Ref8]). Each LSA function code also implies a 2887 specific setting for the U, S1 and S2 bits, as shown below. 2889 LSA function code LS Type Description 2890 ___________________________________________________ 2891 1 0x2001 Router-LSA 2892 2 0x2002 Network-LSA 2893 3 0x2003 Inter-Area-Prefix-LSA 2894 4 0x2004 Inter-Area-Router-LSA 2895 5 0x4005 AS-External-LSA 2896 6 0x2006 Group-membership-LSA 2897 7 0x2007 Type-7-LSA 2898 8 0x0008 Link-LSA 2899 9 0x2009 Intra-Area-Prefix-LSA 2900 A.4.3 Router-LSAs 2902 Router-LSAs have LS type equal to 0x2001. Each router in an area 2903 originates one or more router-LSAs. The complete collection of 2904 router-LSAs originated by the router describe the state and cost of 2905 the router's interfaces to the area. For details concerning the 2906 construction of router-LSAs, see Section 3.4.3.1. Router-LSAs are 2907 flooded throughout a single area only. 2909 0 1 2 3 2910 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 2911 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2912 | LS age |0|0|1| 1 | 2913 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2914 | Link State ID | 2915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2916 | Advertising Router | 2917 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2918 | LS sequence number | 2919 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2920 | LS checksum | length | 2921 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2922 | 0 |W|V|E|B| Options | 2923 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2924 | Type | 0 | Metric | 2925 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2926 | Interface ID | 2927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2928 | Neighbor Interface ID | 2929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2930 | Neighbor Router ID | 2931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2932 | ... | 2933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2934 | Type | 0 | Metric | 2935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2936 | Interface ID | 2937 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2938 | Neighbor Interface ID | 2939 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2940 | Neighbor Router ID | 2941 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2942 | ... | 2944 A single router may originate one or more Router LSAs, distinguished 2945 by their Link-State IDs (which are chosen arbitrarily by the 2946 originating router). The Options field and V, E and B bits should 2947 be the same in all Router LSAs from a single originator. However, 2948 in the case of a mismatch the values in the LSA with the lowest Link 2949 State ID take precedence. When more than one Router LSA is received 2950 from a single router, the links are processed as if concatenated 2951 into a single LSA. 2953 bit V 2954 When set, the router is an endpoint of one or more fully 2955 adjacent virtual links having the described area as Transit area 2956 (V is for virtual link endpoint). 2958 bit E 2959 When set, the router is an AS boundary router (E is for 2960 external). 2962 bit B 2963 When set, the router is an area border router (B is for border). 2965 bit W 2966 When set, the router is a wild-card multicast receiver. When 2967 running MOSPF, these routers receive all multicast datagrams, 2968 regardless of destination. See Sections 3, 4 and A.2 of [Ref8] 2969 for details. 2971 Options 2972 The optional capabilities supported by the router, as documented 2973 in Section A.2. 2975 The following fields are used to describe each router interface. 2976 The Type field indicates the kind of interface being described. It 2977 may be an interface to a transit network, a point-to-point 2978 connection to another router or a virtual link. The values of all 2979 the other fields describing a router interface depend on the 2980 interface's Type field. 2982 Type 2983 The kind of interface being described. One of the following: 2985 Type Description 2986 __________________________________________________ 2987 1 Point-to-point connection to another router 2988 2 Connection to a transit network 2989 3 Reserved 2990 4 Virtual link 2992 Metric 2993 The cost of using this router interface, for outbound traffic. 2995 Interface ID 2996 The Interface ID assigned to the interface being described. See 2997 Sections 3.1.2 and C.3. 2999 Neighbor Interface ID 3000 The Interface ID the neighbor router (or the attached link's 3001 Designated Router, for Type 2 interfaces) has been advertising 3002 in hello packets sent on the attached link. 3004 Neighbor Router ID 3005 The Router ID the neighbor router (or the attached link's 3006 Designated Router, for Type 2 interfaces). 3008 For Type 2 links, the combination of Neighbor Interface ID and 3009 Neighbor Router ID allows the network-LSA for the attached link 3010 to be found in the link-state database. 3012 A.4.4 Network-LSAs 3014 Network-LSAs have LS type equal to 0x2002. A network-LSA is 3015 originated for each broadcast and NBMA link in the area which 3016 supports two or more routers. The network-LSA is originated by the 3017 link's Designated Router. The LSA describes all routers attached to 3018 the link, including the Designated Router itself. The LSA's Link 3019 State ID field is set to the Interface ID that the Designated Router 3020 has been advertising in Hello packets on the link. 3022 The distance from the network to all attached routers is zero. This 3023 is why the metric fields need not be specified in the network-LSA. 3024 For details concerning the construction of network-LSAs, see Section 3025 3.4.3.2. 3027 0 1 2 3 3028 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 3029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3030 | LS age |0|0|1| 2 | 3031 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3032 | Link State ID | 3033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3034 | Advertising Router | 3035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3036 | LS sequence number | 3037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3038 | LS checksum | length | 3039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3040 | 0 | Options | 3041 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3042 | Attached Router | 3043 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3044 | ... | 3046 Attached Router 3047 The Router IDs of each of the routers attached to the link. 3048 Actually, only those routers that are fully adjacent to the 3049 Designated Router are listed. The Designated Router includes 3050 itself in this list. The number of routers included can be 3051 deduced from the LSA header's length field. 3053 A.4.5 Inter-Area-Prefix-LSAs 3055 Inter-Area-Prefix-LSAs have LS type equal to 0x2003. These LSAs are 3056 are the IPv6 equivalent of OSPF for IPv4's type 3 summary-LSAs (see 3057 Section 12.4.3 of [Ref1]). Originated by area border routers, they 3058 describe routes to IPv6 address prefixes that belong to other areas. 3059 A separate Inter-Area-Prefix-LSA is originated for each IPv6 address 3060 prefix. For details concerning the construction of Inter-Area- 3061 Prefix-LSAs, see Section 3.4.3.3. 3063 For stub areas, Inter-Area-Prefix-LSAs can also be used to describe 3064 a (per-area) default route. Default summary routes are used in stub 3065 areas instead of flooding a complete set of external routes. When 3066 describing a default summary route, the Inter-Area-Prefix-LSA's 3067 PrefixLength is set to 0. 3069 0 1 2 3 3070 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 3071 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3072 | LS age |0|0|1| 3 | 3073 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3074 | Link State ID | 3075 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3076 | Advertising Router | 3077 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3078 | LS sequence number | 3079 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3080 | LS checksum | length | 3081 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3082 | 0 | Metric | 3083 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3084 | PrefixLength | PrefixOptions | (0) | 3085 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3086 | Address Prefix | 3087 | ... | 3088 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3090 Metric 3091 The cost of this route. Expressed in the same units as the 3092 interface costs in the router-LSAs. When the Inter-Area-Prefix- 3093 LSA is describing a route to a range of addresses (see Section 3094 C.2) the cost is set to the maximum cost to any reachable 3095 component of the address range. 3097 PrefixLength, PrefixOptions and Address Prefix 3098 Representation of the IPv6 address prefix, as described in 3099 Section A.4.1. 3101 A.4.6 Inter-Area-Router-LSAs 3103 Inter-Area-Router-LSAs have LS type equal to 0x2004. These LSAs are 3104 are the IPv6 equivalent of OSPF for IPv4's type 4 summary-LSAs (see 3105 Section 12.4.3 of [Ref1]). Originated by area border routers, they 3106 describe routes to routers in other areas. (To see why it is 3107 necessary to advertise the location of each ASBR, consult Section 3108 16.4 in [Ref1].) Each LSA describes a route to a single router. For 3109 details concerning the construction of Inter-Area-Router-LSAs, see 3110 Section 3.4.3.4. 3112 0 1 2 3 3113 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 3114 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3115 | LS age |0|0|1| 4 | 3116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3117 | Link State ID | 3118 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3119 | Advertising Router | 3120 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3121 | LS sequence number | 3122 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3123 | LS checksum | length | 3124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3125 | 0 | Options | 3126 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3127 | 0 | Metric | 3128 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3129 | Destination Router ID | 3130 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3132 Options 3133 The optional capabilities supported by the router, as documented 3134 in Section A.2. 3136 Metric 3137 The cost of this route. Expressed in the same units as the 3138 interface costs in the router-LSAs. 3140 Destination Router ID 3141 The Router ID of the router being described by the LSA. 3143 A.4.7 AS-external-LSAs 3145 AS-external-LSAs have LS type equal to 0x4005. These LSAs are 3146 originated by AS boundary routers, and describe destinations 3147 external to the AS. Each LSA describes a route to a single IPv6 3148 address prefix. For details concerning the construction of AS- 3149 external-LSAs, see Section 3.4.3.5. 3151 AS-external-LSAs can be used to describe a default route. Default 3152 routes are used when no specific route exists to the destination. 3153 When describing a default route, the AS-external-LSA's PrefixLength 3154 is set to 0. 3156 0 1 2 3 3157 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 3158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3159 | LS age |0|1|0| 5 | 3160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3161 | Link State ID | 3162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3163 | Advertising Router | 3164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3165 | LS sequence number | 3166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3167 | LS checksum | length | 3168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3169 | |E|F|T| Metric | 3170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3171 | PrefixLength | PrefixOptions | Referenced LS Type | 3172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3173 | Address Prefix | 3174 | ... | 3175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3176 | | 3177 +- -+ 3178 | | 3179 +- Forwarding Address (Optional) -+ 3180 | | 3181 +- -+ 3182 | | 3183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3184 | External Route Tag (Optional) | 3185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3186 | Referenced Link State ID (Optional) | 3187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3189 bit E 3190 The type of external metric. If bit E is set, the metric 3191 specified is a Type 2 external metric. This means the metric is 3192 considered larger than any intra-AS path. If bit E is zero, the 3193 specified metric is a Type 1 external metric. This means that 3194 it is expressed in the same units as the link state metric 3195 (i.e., the same units as interface cost). 3197 bit F 3198 If set, a Forwarding Address has been included in the LSA. 3200 bit T 3201 If set, an External Route Tag has been included in the LSA. 3203 Metric 3204 The cost of this route. Interpretation depends on the external 3205 type indication (bit E above). 3207 PrefixLength, PrefixOptions and Address Prefix 3208 Representation of the IPv6 address prefix, as described in 3209 Section A.4.1. 3211 Referenced LS type 3212 If non-zero, an LSA with this LS type is to be associated with 3213 this LSA (see Referenced Link State ID below). 3215 Forwarding address 3216 A fully qualified IPv6 address (128 bits). Included in the LSA 3217 if and only if bit F has been set. If included, Data traffic 3218 for the advertised destination and TOS will be forwarded to this 3219 address. Must not be set to the IPv6 Unspecified Address 3220 (0:0:0:0:0:0:0:0). 3222 External Route Tag 3223 A 32-bit field which may be used to communicate additional 3224 information between AS boundary routers; see [Ref5] for example 3225 usage. Included in the LSA if and only if bit T has been set. 3227 Referenced Link State ID 3228 Included if and only if Reference LS Type is non-zero. If 3229 included, additional information concerning the advertised 3230 external route can be found in the LSA having LS type equal to 3231 "Referenced LS Type", Link State ID equal to "Referenced Link 3232 State ID" and Advertising Router the same as that specified in 3233 the AS-external-LSA's link state header. This additional 3234 information is not used by the OSPF protocol itself. It may be 3235 used to communicate information between AS boundary routers; the 3236 precise nature of such information is outside the scope of this 3237 specification. 3239 All, none or some of the fields labeled Forwarding address, External 3240 Route Tag and Referenced Link State ID may be present in the AS- 3241 external-LSA (as indicated by the setting of bit F, bit T and 3242 Referenced LS type respectively). However, when present Forwarding 3243 Address always comes first, with External Route Tag always preceding 3244 Referenced Link State ID. 3246 A.4.8 Link-LSAs 3248 Link-LSAs have LS type equal to 0x0008. A router originates a 3249 separate Link-LSA for each link it is attached to. These LSAs have 3250 local-link flooding scope; they are never flooded beyond the link 3251 that they are associated with. Link-LSAs have three purposes: 1) 3252 they provide the router's link-local address to all other routers 3253 attached to the link and 2) they inform other routers attached to 3254 the link of a list of IPv6 prefixes to associate with the link and 3255 3) they allow the router to assert a collection of Options bits to 3256 associate with the Network-LSA that will be originated for the link. 3258 A link-LSA's Link State ID is set equal to the originating router's 3259 Interface ID on the link. 3260 0 1 2 3 3261 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 3262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3263 | LS age |0|0|0| 8 | 3264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3265 | Link State ID | 3266 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3267 | Advertising Router | 3268 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3269 | LS sequence number | 3270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3271 | LS checksum | length | 3272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3273 | Rtr Pri | Options | 3274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3275 | | 3276 +- -+ 3277 | | 3278 +- Link-local Interface Address -+ 3279 | | 3280 +- -+ 3281 | | 3282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3283 | # prefixes | 3284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3285 | PrefixLength | PrefixOptions | (0) | 3286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3287 | Address Prefix | 3288 | ... | 3289 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3290 | ... | 3291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3292 | PrefixLength | PrefixOptions | (0) | 3293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3294 | Address Prefix | 3295 | ... | 3296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3298 Rtr Pri 3299 The Router Priority of the interface attaching the originating 3300 router to the link. 3302 Options 3303 The set of Options bits that the router would like set in the 3304 Network-LSA that will be originated for the link. 3306 Link-local Interface Address 3307 The originating router's link-local interface address on the 3308 link. 3310 # prefixes 3311 The number of IPv6 address prefixes contained in the LSA. 3313 The rest of the link-LSA contains a list of IPv6 prefixes to be 3314 associated with the link. 3316 PrefixLength, PrefixOptions and Address Prefix 3317 Representation of an IPv6 address prefix, as described in 3318 Section A.4.1. 3320 A.4.9 Intra-Area-Prefix-LSAs 3322 Intra-Area-Prefix-LSAs have LS type equal to 0x2009. A router uses 3323 Intra-Area-Prefix-LSAs to advertise one or more IPv6 address 3324 prefixes that are associated with a) the router itself, b) an 3325 attached stub network segment or c) an attached transit network 3326 segment. In IPv4, a) and b) were accomplished via the router's 3327 router-LSA, and c) via a network-LSA. However, in OSPF for IPv6 all 3328 addressing information has been removed from router-LSAs and 3329 network-LSAs, leading to the introduction of the Intra-Area-Prefix- 3330 LSA. 3332 A router can originate multiple Intra-Area-Prefix-LSAs for each 3333 router or transit network; each such LSA is distinguished by its 3334 Link State ID. 3336 0 1 2 3 3337 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 3338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3339 | LS age |0|0|1| 9 | 3340 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3341 | Link State ID | 3342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3343 | Advertising Router | 3344 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3345 | LS sequence number | 3346 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3347 | LS checksum | length | 3348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3349 | # prefixes | Referenced LS type | 3350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3351 | Referenced Link State ID | 3352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3353 | Referenced Advertising Router | 3354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3355 | PrefixLength | PrefixOptions | Metric | 3356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3357 | Address Prefix | 3358 | ... | 3359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3360 | ... | 3361 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3362 | PrefixLength | PrefixOptions | Metric | 3363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3364 | Address Prefix | 3365 | ... | 3366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3368 # prefixes 3369 The number of IPv6 address prefixes contained in the LSA. 3371 Referenced LS type, Referenced Link State ID and Referenced 3372 Advertising Router 3373 Identifies the router-LSA or network-LSA with which the IPv6 3374 address prefixes should be associated. If Referenced LS type is 3375 1, the prefixes are associated with a router-LSA, Referenced 3376 Link State ID should be 0 and Referenced Advertising Router 3377 should be the originating router's Router ID. If Referenced LS 3378 type is 2, the prefixes are associated with a network-LSA, 3379 Referenced Link State ID should be the Interface ID of the 3380 link's Designated Router and Referenced Advertising Router 3381 should be the Designated Router's Router ID. 3383 The rest of the Intra-Area-Prefix-LSA contains a list of IPv6 3384 prefixes to be associated with the router or transit link, together 3385 with the cost of each prefix. 3387 PrefixLength, PrefixOptions and Address Prefix 3388 Representation of an IPv6 address prefix, as described in 3389 Section A.4.1. 3391 Metric 3392 The cost of this prefix. Expressed in the same units as the 3393 interface costs in the router-LSAs. 3395 B. Architectural Constants 3397 Architectural constants for the OSPF protocol are defined in 3398 Appendix C of [Ref1]. The only difference for OSPF for IPv6 is that 3399 DefaultDestination is encoded as a prefix of length 0 (see Section 3400 A.4.1). 3402 C. Configurable Constants 3404 The OSPF protocol has quite a few configurable parameters. These 3405 parameters are listed below. They are grouped into general 3406 functional categories (area parameters, interface parameters, etc.). 3407 Sample values are given for some of the parameters. 3409 Some parameter settings need to be consistent among groups of 3410 routers. For example, all routers in an area must agree on that 3411 area's parameters, and all routers attached to a network must agree 3412 on that network's HelloInterval and RouterDeadInterval. 3414 Some parameters may be determined by router algorithms outside of 3415 this specification (e.g., the address of a host connected to the 3416 router via a SLIP line). From OSPF's point of view, these items are 3417 still configurable. 3419 C.1 Global parameters 3421 In general, a separate copy of the OSPF protocol is run for each 3422 area. Because of this, most configuration parameters are 3423 defined on a per-area basis. The few global configuration 3424 parameters are listed below. 3426 Router ID 3427 This is a 32-bit number that uniquely identifies the router 3428 in the Autonomous System. If a router's OSPF Router ID is 3429 changed, the router's OSPF software should be restarted 3430 before the new Router ID takes effect. Before restarting in 3431 order to change its Router ID, the router should flush its 3432 self-originated LSAs from the routing domain (see Section 3433 14.1 of [Ref1]), or they will persist for up to MaxAge 3434 minutes. 3436 Because the size of the Router ID is smaller than an IPv6 3437 address, it cannot be set to one of the router's IPv6 3438 addresses (as is commonly done for IPv4). Possible Router ID 3439 assignment procedures for IPv6 include: a) assign the IPv6 3440 Router ID as one of the router's IPv4 addresses or b) assign 3441 IPv6 Router IDs through some local administrative procedure 3442 (similar to procedures used by manufacturers to assign 3443 product serial numbers). 3445 The Router ID of 0.0.0.0 is reserved, and should not be 3446 used. 3448 C.2 Area parameters 3450 All routers belonging to an area must agree on that area's 3451 configuration. Disagreements between two routers will lead to 3452 an inability for adjacencies to form between them, with a 3453 resulting hindrance to the flow of routing protocol and data 3454 traffic. The following items must be configured for an area: 3456 Area ID 3457 This is a 32-bit number that identifies the area. The Area 3458 ID of 0 is reserved for the backbone. 3460 List of address ranges 3461 Address ranges control the advertisement of routes across 3462 area boundaries. Each address range consists of the 3463 following items: 3465 [IPv6 prefix, prefix length] 3466 Describes the collection of IPv6 addresses contained 3467 in the address range. 3469 Status Set to either Advertise or DoNotAdvertise. Routing 3470 information is condensed at area boundaries. 3471 External to the area, at most a single route is 3472 advertised (via a inter-area-prefix-LSA) for each 3473 address range. The route is advertised if and only 3474 if the address range's Status is set to Advertise. 3475 Unadvertised ranges allow the existence of certain 3476 networks to be intentionally hidden from other 3477 areas. Status is set to Advertise by default. 3479 ExternalRoutingCapability 3480 Whether AS-external-LSAs will be flooded into/throughout the 3481 area. If AS-external-LSAs are excluded from the area, the 3482 area is called a "stub". Internal to stub areas, routing to 3483 external destinations will be based solely on a default 3484 inter-area route. The backbone cannot be configured as a 3485 stub area. Also, virtual links cannot be configured through 3486 stub areas. For more information, see Section 3.6 of 3487 [Ref1]. 3489 StubDefaultCost 3490 If the area has been configured as a stub area, and the 3491 router itself is an area border router, then the 3492 StubDefaultCost indicates the cost of the default inter- 3493 area-prefix-LSA that the router should advertise into the 3494 area. See Section 12.4.3.1 of [Ref1] for more information. 3496 C.3 Router interface parameters 3498 Some of the configurable router interface parameters (such as 3499 Area ID, HelloInterval and RouterDeadInterval) actually imply 3500 properties of the attached links, and therefore must be 3501 consistent across all the routers attached to that link. The 3502 parameters that must be configured for a router interface are: 3504 IPv6 link-local address 3505 The IPv6 link-local address associated with this interface. 3506 May be learned through auto-configuration. 3508 Area ID 3509 The OSPF area to which the attached link belongs. 3511 Instance ID 3512 The OSPF protocol instance associated with this OSPF 3513 interface. Defaults to 0. 3515 Interface ID 3516 32-bit number uniquely identifying this interface among the 3517 collection of this router's interfaces. For example, in some 3518 implementations it may be possible to use the MIB-II 3519 IfIndex. 3521 IPv6 prefixes 3522 The list of IPv6 prefixes to associate with the link. These 3523 will be advertised in intra-area-prefix-LSAs. 3525 Interface output cost(s) 3526 The cost of sending a packet on the interface, expressed in 3527 the link state metric. This is advertised as the link cost 3528 for this interface in the router's router-LSA. The interface 3529 output cost must always be greater than 0. 3531 RxmtInterval 3532 The number of seconds between LSA retransmissions, for 3533 adjacencies belonging to this interface. Also used when 3534 retransmitting Database Description and Link State Request 3535 Packets. This should be well over the expected round-trip 3536 delay between any two routers on the attached link. The 3537 setting of this value should be conservative or needless 3538 retransmissions will result. Sample value for a local area 3539 network: 5 seconds. 3541 InfTransDelay 3542 The estimated number of seconds it takes to transmit a Link 3543 State Update Packet over this interface. LSAs contained in 3544 the update packet must have their age incremented by this 3545 amount before transmission. This value should take into 3546 account the transmission and propagation delays of the 3547 interface. It must be greater than 0. Sample value for a 3548 local area network: 1 second. 3550 Router Priority 3551 An 8-bit unsigned integer. When two routers attached to a 3552 network both attempt to become Designated Router, the one 3553 with the highest Router Priority takes precedence. If there 3554 is still a tie, the router with the highest Router ID takes 3555 precedence. A router whose Router Priority is set to 0 is 3556 ineligible to become Designated Router on the attached link. 3557 Router Priority is only configured for interfaces to 3558 broadcast and NBMA networks. 3560 HelloInterval 3561 The length of time, in seconds, between the Hello Packets 3562 that the router sends on the interface. This value is 3563 advertised in the router's Hello Packets. It must be the 3564 same for all routers attached to a common link. The smaller 3565 the HelloInterval, the faster topological changes will be 3566 detected; however, more OSPF routing protocol traffic will 3567 ensue. Sample value for a X.25 PDN: 30 seconds. Sample 3568 value for a local area network (LAN): 10 seconds. 3570 RouterDeadInterval 3571 After ceasing to hear a router's Hello Packets, the number 3572 of seconds before its neighbors declare the router down. 3573 This is also advertised in the router's Hello Packets in 3574 their RouterDeadInterval field. This should be some 3575 multiple of the HelloInterval (say 4). This value again 3576 must be the same for all routers attached to a common link. 3578 C.4 Virtual link parameters 3580 Virtual links are used to restore/increase connectivity of the 3581 backbone. Virtual links may be configured between any pair of 3582 area border routers having interfaces to a common (non-backbone) 3583 area. The virtual link appears as an unnumbered point-to-point 3584 link in the graph for the backbone. The virtual link must be 3585 configured in both of the area border routers. 3587 A virtual link appears in router-LSAs (for the backbone) as if 3588 it were a separate router interface to the backbone. As such, 3589 it has most of the parameters associated with a router interface 3590 (see Section C.3). Virtual links do not have link-local 3591 addresses, but instead use one of the router's global-scope or 3592 site-local IPv6 addresses as the IP source in OSPF protocol 3593 packets it sends along the virtual link. Router Priority is not 3594 used on virtual links. Interface output cost is not configured 3595 on virtual links, but is dynamically set to be the cost of the 3596 intra-area path between the two endpoint routers. The parameter 3597 RxmtInterval must be configured, and should be well over the 3598 expected round-trip delay between the two routers. This may be 3599 hard to estimate for a virtual link; it is better to err on the 3600 side of making it too large. 3602 A virtual link is defined by the following two configurable 3603 parameters: the Router ID of the virtual link's other endpoint, 3604 and the (non-backbone) area through which the virtual link runs 3605 (referred to as the virtual link's Transit area). Virtual links 3606 cannot be configured through stub areas. 3608 C.5 NBMA network parameters 3610 OSPF treats an NBMA network much like it treats a broadcast 3611 network. Since there may be many routers attached to the 3612 network, a Designated Router is selected for the network. This 3613 Designated Router then originates a network-LSA, which lists all 3614 routers attached to the NBMA network. 3616 However, due to the lack of broadcast capabilities, it may be 3617 necessary to use configuration parameters in the Designated 3618 Router selection. These parameters will only need to be 3619 configured in those routers that are themselves eligible to 3620 become Designated Router (i.e., those router's whose Router 3621 Priority for the network is non-zero), and then only if no 3622 automatic procedure for discovering neighbors exists: 3624 List of all other attached routers 3625 The list of all other routers attached to the NBMA network. 3626 Each router is configured with its Router ID and IPv6 link- 3627 local address on the network. Also, for each router listed, 3628 that router's eligibility to become Designated Router must 3629 be defined. When an interface to a NBMA network comes up, 3630 the router sends Hello Packets only to those neighbors 3631 eligible to become Designated Router, until the identity of 3632 the Designated Router is discovered. 3634 PollInterval 3635 If a neighboring router has become inactive (Hello Packets 3636 have not been seen for RouterDeadInterval seconds), it may 3637 still be necessary to send Hello Packets to the dead 3638 neighbor. These Hello Packets will be sent at the reduced 3639 rate PollInterval, which should be much larger than 3640 HelloInterval. Sample value for a PDN X.25 network: 2 3641 minutes. 3643 C.6 Point-to-MultiPoint network parameters 3645 On Point-to-MultiPoint networks, it may be necessary to 3646 configure the set of neighbors that are directly reachable over 3647 the Point-to-MultiPoint network. Each neighbor is configured 3648 with its Router ID and IPv6 link-local address on the network. 3649 Designated Routers are not elected on Point-to-MultiPoint 3650 networks, so the Designated Router eligibility of configured 3651 neighbors is undefined. 3653 C.7 Host route parameters 3655 Host routes are advertised in intra-area-prefix-LSAs as fully 3656 qualified IPv6 prefixes (i.e., prefix length set equal to 128 3657 bits). They indicate either router interfaces to point-to-point 3658 networks, looped router interfaces, or IPv6 hosts that are 3659 directly connected to the router (e.g., via a PPP connection). 3660 For each host directly connected to the router, the following 3661 items must be configured: 3663 Host IPv6 address 3664 The IPv6 address of the host. 3666 Cost of link to host 3667 The cost of sending a packet to the host, in terms of the 3668 link state metric. However, since the host probably has only 3669 a single connection to the internet, the actual configured 3670 cost(s) in many cases is unimportant (i.e., will have no 3671 effect on routing). 3673 Area ID 3674 The OSPF area to which the host belongs. 3676 Security Considerations 3678 When running over IPv6, OSPF relies on the IP Authentication Header 3679 (see [Ref19]) and the IP Encapsulating Security Payload (see 3680 [Ref20]) to ensure integrity and authentication/confidentiality of 3681 routing exchanges. 3683 Authors Addresses 3685 Rob Coltun 3686 FORE Systems 3687 Phone: (301) 571-2521 3688 Email: rcoltun@fore.com 3690 Dennis Ferguson 3691 Juniper Networks 3692 101 University Avenue, Suite 240 3693 Palo Alto, CA 94301 3694 Phone: (415) 614-4143 3695 Email: dennis@jnx.com 3697 John Moy 3698 Cascade Communications Corp. 3699 5 Carlisle Road 3700 Westford, MA 01886 3701 Phone: (508) 952-1367 3702 Fax: (508) 392-9250 3703 Email: jmoy@casc.com 3705 This document expires in December 1996.