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'Ref15') (Obsoleted by RFC 2373) ** Obsolete normative reference: RFC 1885 (ref. 'Ref16') (Obsoleted by RFC 2463) ** Obsolete normative reference: RFC 1970 (ref. 'Ref17') (Obsoleted by RFC 2461) ** Obsolete normative reference: RFC 1981 (ref. 'Ref18') (Obsoleted by RFC 8201) ** Obsolete normative reference: RFC 1826 (ref. 'Ref19') (Obsoleted by RFC 2402) -- Possible downref: Non-RFC (?) normative reference: ref. 'Ref20' Summary: 24 errors (**), 0 flaws (~~), 13 warnings (==), 9 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: May 1997 D. Ferguson 5 File name: draft-ietf-ospf-ospfv6-03.txt Juniper Networks 6 Network Working Group J. Moy 7 Internet Draft Cascade Communications Corp. 8 November 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 ................................. 8 70 2.7 Packet format changes .................................. 8 71 2.8 LSA format changes ..................................... 9 72 2.9 Handling unknown LSA types ............................ 11 73 2.10 Stub area support ..................................... 11 74 2.11 Identifying neighbors by Router ID .................... 12 75 2.12 Removal of TOS ........................................ 12 76 3 Implementation details ................................ 12 77 3.1 Protocol data structures .............................. 14 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 ............................ 17 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 ........................... 22 88 3.3.1 Routing table lookup .................................. 23 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 ................... 39 102 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 ..................... 46 110 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 IPv6 link-local addresses are for use on a single link, for 268 purposes of neighbor discovery, auto-configuration, etc. IPv6 269 routers do not forward IPv6 datagrams having link-local source 270 addresses [Ref15]. Link-local unicast addresses are assigned 271 from the IPv6 address range FF80/10. 273 OSPF for IPv6 assumes that each router has been assigned link- 274 local unicast addresses on each of the router's attached 275 physical segments. On all OSPF interfaces except virtual links, 276 OSPF packets are sent using the interface's associated link- 277 local unicast address as source. A router learns the link-local 278 addresses of all other routers attached to its links, and uses 279 these addresses as next hop information during packet 280 forwarding. 282 On virtual links, global scope or site-local IP addresses must 283 be used as the source for OSPF protocol packets. 285 Link-local addresses appear in OSPF Link-LSAs (see Section 286 3.4.3.6). However, link-local addresses are not allowed in other 287 OSPF LSA types. In particular, link-local addresses cannot be 288 advertised in inter-area-prefix-LSAs (Section 3.4.3.3), AS- 289 external-LSAs (Section 3.4.3.5) or intra-area-prefix-LSAs 290 (Section 3.4.3.7). 292 2.6. Authentication changes 294 In OSPF for IPv6, authentication has been removed from OSPF 295 itself. The "AuType" and "Authentication" fields have been 296 removed from the OSPF packet header, and all authentication 297 related fields have been removed from the OSPF area and 298 interface structures. 300 When running over IPv6, OSPF relies on the IP Authentication 301 Header (see [Ref19]) and the IP Encapsulating Security Payload 302 (see [Ref20]) to ensure integrity and 303 authentication/confidentiality of routing exchanges. 305 2.7. Packet format changes 307 OSPF for IPv6 runs directly over IPv6. Aside from this, all 308 addressing semantics have been removed from the OSPF packet 309 headers, making it essentially "network-protocol independent". 310 All addressing information is now contained in the various LSA 311 types only. 313 In detail, changes in OSPF packet format consist of the 314 following: 316 o The OSPF version number has been increased from 2 to 3. 318 o The Options field in Hello Packets and Database description 319 Packets has been expanded to 24-bits. 321 o The Authentication and AuType fields have been removed from 322 the OSPF packet header (see Section 2.6). 324 o The Hello packet now contains no address information at all, 325 and includes a Interface ID which the originating router has 326 assigned to uniquely identify (among its own interfaces) its 327 interface to the link. This Interface ID becomes the 328 Network-LSA's Link State ID, should the router become 329 Designated Router on the link. 331 o Two options bits, the "R-bit" and the "V6-bit", have been 332 added to the Options field for processing Router-LSAs during 333 the SPF calculation (see Section A.2). If the "R-bit" is 334 clear an OSPF speaker can participate in OSPF topology 335 distribution without being used to forward transit traffic; 336 this can be used in multi-homed hosts that want to 337 participate in the routing protocol. The V6-bit specializes 338 the R-bit; if the V6-bit is clear an OSPF speaker can 339 participate in OSPF topology distribution without being used 340 to forward IPv6 datagrams. If the R-bit is set and the V6- 341 bit is clear, IPv6 datagrams are not forwarded but datagrams 342 belonging to another protocol family may be forwarded. 344 o The OSPF packet header now includes an "Instance ID" which 345 allows multiple OSPF protocol instances to be run on a 346 single link (see Section 2.4). 348 2.8. LSA format changes 350 All addressing semantics have been removed from the LSA header, 351 and from Router-LSAs and Network-LSAs. These two LSAs now 352 describe the routing domain's topology in a network-protocol 353 independent manner. New LSAs have been added to distribute IPv6 354 address information, and data required for next hop resolution. 355 The names of some of IPv4's LSAs have been changed to be more 356 consistent with each other. 358 In detail, changes in LSA format consist of the following: 360 o The Options field has been removed from the LSA header, 361 expanded to 24 bits, and moved into the body of Router-LSAs, 362 Network-LSAs, Inter-Area-Router-LSAs and Link-LSAs. See 363 Section A.2 for details. 365 o The LSA Type field has been expanded (into the former 366 Options space) to 16 bits, with the upper three bits 367 encoding flooding scope and the handling of unknown LSA 368 types (see Section 2.9). 370 o Addresses in LSAs are now expressed as [prefix, prefix 371 length] instead of [address, mask] (see Section A.4.1). The 372 default route is expressed as a prefix with length 0. 374 o The Router and Network LSAs now have no address information, 375 and are network-protocol-independent. 377 o Router interface information may be spread across multiple 378 Router LSAs. Receivers must concatenate all the Router-LSAs 379 originated by a given router when running the SPF 380 calculation. 382 o A new LSA called the Link-LSA has been introduced. The LSAs 383 have local-link flooding scope; they are never flooded 384 beyond the link that they are associated with. Link-LSAs 385 have three purposes: 1) they provide the router's link-local 386 address to all other routers attached to the link and 2) 387 they inform other routers attached to the link of a list of 388 IPv6 prefixes to associate with the link and 3) they allow 389 the router to assert a collection of Options bits to 390 associate with the Network-LSA that will be originated for 391 the link. See Section A.4.8 for details. 393 In IPv4, the router-LSA carries a router's IPv4 interface 394 addresses, the IPv4 equivalent of link-local addresses. 395 These are only used when calculating next hops during the 396 OSPF routing calculation (see Section 16.1.1 of [Ref1]), so 397 they do not need to be flooded past the local link; hence 398 using link-LSAs to distribute these addresses is more 399 efficient. Note that link-local addresses cannot be learned 400 through the reception of Hellos in all cases: on NBMA links 401 next hop routers do not necessarily exchange hellos, but 402 rather learn of each other's existence by way of the 403 Designated Router. 405 o The Options field in the Network LSA is set to the logical 406 OR of the Options that each router on the link advertises in 407 its Link-LSA. 409 o Type-3 summary-LSAs have been renamed "Inter-Area-Prefix- 410 LSAs". Type-4 summary LSAs have been renamed "Inter-Area- 411 Router-LSAs". 413 o The Link State ID in Inter-Area-Prefix-LSAs, Inter-Area- 414 Router-LSAs and AS-external-LSAs has lost its addressing 415 semantics, and now serves solely to identify individual 416 pieces of the Link State Database. All addresses or Router 417 IDs that formerly were expressed by the Link State ID are 418 now carried in the LSA bodies. 420 o Network-LSAs and Link-LSAs are the only LSAs whose Link 421 State ID carries additional meaning. For these LSAs, the 422 Link State ID is always the Interface ID of the originating 423 router on the link being described. For this reason, 424 Network-LSAs and Link-LSAs are now the only LSAs that cannot 425 be broken into arbitrarily small pieces. 427 o A new LSA called the Intra-Area-Prefix-LSA has been 428 introduced. This LSA carries all IPv6 prefix information 429 that in IPv4 is included in Router-LSAs and Network-LSAs. 430 See Section A.4.9 for details. 432 o Inclusion of a forwarding address in AS-external-LSAs is now 433 optional, as is the inclusion of an external route tag (see 435 [Ref5]). In addition, AS-external-LSAs can now reference 436 another LSA, for inclusion of additional route attributes 437 that are outside the scope of the OSPF protocol itself. For 438 example, this can be used to attach BGP path attributes to 439 external routes as proposed in [Ref10]. 441 2.9. Handling unknown LSA types 443 Handling of unknown LSA types has been made more flexible so 444 that, based on LS type, unknown LSA types are either treated as 445 having link-local flooding scope, or are stored and flooded as 446 if they were understood (desirable for things like the proposed 447 External Attributes LSA in [Ref10]). This behavior is explicitly 448 coded in the LSA Handling bit of the link state header's LS type 449 field (see Section A.4.2.1). 451 The IPv4 OSPF behavior of simply discarding unknown types is 452 unsupported due to the desire to mix router capabilities on a 453 single link. Discarding unknown types causes problems when the 454 Designated Router supports fewer options than the other routers 455 on the link. 457 2.10. Stub area support 459 In OSPF for IPv4, stub areas were designed to minimize link- 460 state database and routing table sizes for the areas' internal 461 routers. This allows routers with minimal resources to 462 participate in even very large OSPF routing domains. 464 In OSPF for IPv6, the concept of stub areas is retained. In 465 IPv6, of the mandatory LSA types, stub areas carry only router- 466 LSAs, network-LSAs, Inter-Area-Prefix-LSAs, Link-LSAs, and 467 Intra-Area-Prefix-LSAs. This is the IPv6 equivalent of the LSA 468 types carried in IPv4 stub areas: router-LSAs, network-LSAs and 469 type 3 summary-LSAs. 471 However, unlike in IPv4, IPv6 allows LSAs with unrecognized LS 472 types to be labeled "Store and flood the LSA, as if type 473 understood" (see the U-bit in Section A.4.2.1). Uncontrolled 474 introduction of such LSAs could cause a stub area's link-state 475 database to grow larger than it's component routers' capacities. 476 To guard against this, the following rules regarding stub areas 477 have been established: 479 (1) No LSAs with AS flooding scope can be flooded into/within 480 stub areas. This generalizes the rule that AS-external-LSAs 481 are not flooded into/throughout stub areas. 483 (2) No LSAs with U-bit set to 1 (flood even when LS type 484 unrecognized) should be flooded into/within stub areas. 486 Note that a router internal to a stub area may still get 487 unrecognized LSA types in its database, but only when both a) 488 the LSAs have link-local or area flooding scope, and b) the 489 router shares a network segment with another router that does 490 understand the LSA's type. 492 2.11. Identifying neighbors by Router ID 494 In OSPF for IPv6, neighboring routers on a given link are always 495 identified by their OSPF Router ID. This contrasts with the IPv4 496 behavior where neighbors on point-to-point networks and virtual 497 links are identified by their Router IDs, and neighbors on 498 broadcast, NBMA and Point-to-MultiPoint links are identified by 499 their IPv4 interface addresses. 501 This change affects the reception of OSPF packets (see Section 502 8.2 of [Ref1]), the lookup of neighbors (Section 10 of [Ref1]) 503 and the reception of Hello Packets in particular (Section 10.5 504 of [Ref1]). 506 The Router ID of 0.0.0.0 is reserved, and should not be used. 508 2.12. Removal of TOS 510 The semantics of IPv4 TOS have not been moved forward to IPv6. 511 Therefore, support for TOS in OSPF for IPv6 has been removed. 512 This affects both LSA formats and routing calculations. 514 The IPv6 header does have a 24-bit Flow Label field which may be 515 used by a source to label those packets for which it requests 516 special handling by IPv6 routers, such as non-default quality of 517 service or "real-time" service. The OSPF LSAs for IPv6 have been 518 organized so that future extensions to support routing based on 519 Flow Label are possible. 521 3. Implementation details 523 When going from IPv4 to IPv6, the basic OSPF mechanisms remain 524 unchanged from those documented in [Ref1]. These mechanisms are 525 briefly outlined in Section 4 of [Ref1]. Both IPv6 and IPv4 have a 526 link-state database composed of LSAs and synchronized between 527 adjacent routers. Initial synchronization is performed through the 528 Database Exchange process, through the exchange of Database 529 Description, Link State Request and Link State Update packets. 530 Thereafter database synchronization is maintained via flooding, 531 utilizing Link State Update and Link State Acknowledgment packets. 532 Both IPv6 and IPv4 use OSPF Hello Packets to disover and maintain 533 neighbor relationships, and to elect Designated Routers and Backup 534 Designated Routers on broadcast and NBMA links. The decision as to 535 which neighbor relationships become adjacencies, along with the 536 basic ideas behind inter-area routing, importing external 537 information in AS-external-LSAs and the various routing calculations 538 are also the same. 540 In particular, the following IPv4 OSPF functionality described in 541 [Ref1] remains completely unchanged for IPv6: 543 o Both IPv4 and IPv6 use OSPF packet types described in Section 544 4.3 of [Ref1], namely: Hello, Database Description, Link State 545 Request, Link State Update and Link State Acknowledgment 546 packets. While in some cases (e.g., Hello packets) their format 547 has changed somewhat, the functions of the various packet types 548 remains the same. 550 o The system requirements for an OSPF implementation remain 551 unchanged, although OSPF for IPv6 requires an IPv6 protocol 552 stack (from the network layer on down) since it runs directly 553 over the IPv6 network layer. 555 o The discovery and maintenance of neighbor relationships, and the 556 selection and establishment of adjacencies remain the same. This 557 includes election of the Designated Router and Backup Designated 558 Router on broadcast and NBMA links. These mechanisms are 559 described in Sections 7, 7.1, 7.2, 7.3, 7.4 and 7.5 of [Ref1]. 561 o The link types (or equivalently, interface types) supported by 562 OSPF remain unchanged, namely: point-to-point, broadcast, NBMA, 563 Point-to-MultiPoint and virtual links. 565 o The interface state machine, including the list of OSPF 566 interface states and events, and the Designated Router and 567 Backup Designated Router election algorithm, remain unchanged. 568 These are described in Sections 9.1, 9.2, 9.3 and 9.4 of [Ref1]. 570 o The neighbor state machine, including the list of OSPF neighbor 571 states and events, remain unchanged. These are described in 572 Sections 10.1, 10.2, 10.3 and 10.4 of [Ref1]. 574 o Aging of the link-state database, as well as flushing LSAs from 575 the routing domain through the premature aging process, remains 576 unchanged from the description in Sections 14 and 14.1 of 577 [Ref1]. 579 However, some OSPF protocol mechanisms have changed, as outlined in 580 Section 2 above. These changes are explained in detail in the 581 following subsections, making references to the appropriate sections 582 of [Ref1]. 584 The following subsections provide a recipe for turning an IPv4 OSPF 585 implementation into an IPv6 OSPF implementation. 587 3.1. Protocol data structures 589 The major OSPF data structures are the same for both IPv4 and 590 IPv6: areas, interfaces, neighbors, the link-state database and 591 the routing table. The top-level data structures for IPv6 remain 592 those listed in Section 5 of [Ref1], with the following 593 modifications: 595 o All LSAs with known LS type and AS flooding scope appear in 596 the top-level data structure, instead of belonging to a 597 specific area or link. AS-external-LSAs are the only LSAs 598 defined by this specification which have AS flooding scope. 599 LSAs with unknown LS type, U-bit set to 1 (flood even when 600 unrecognized) and AS flooding scope also appear in the top- 601 level data structure. 603 o Since IPv6 does not have the concept of TOS, "TOS 604 capability" is not a part of the OSPF fro IPv6 605 specification. 607 3.1.1. The Area Data structure 609 The IPv6 area data structure contains all elements defined 610 for IPv4 areas in Section 6 of [Ref1]. In addition, all LSAs 611 of known type which have area flooding scope are contained 612 in the IPv6 area data structure. This always includes the 613 following LSA types: router-LSAs, network-LSAs, inter-area- 614 prefix-LSAs, inter-area-router-LSAs and intra-area-prefix- 615 LSAs. LSAs with unknown LS type, U-bit set to 1 (flood even 616 when unrecognized) and area scope also appear in the area 617 data structure. IPv6 routers implementing MOSPF add group- 618 membership-LSAs to the area data structure. Type-7-LSAs 619 belong to an NSSA area's data structure. 621 3.1.2. The Interface Data structure 623 In OSPF for IPv6, an interface connects a router to a link. 624 The IPv6 interface structure modifies the IPv4 interface 625 structure (as defined in Section 9 of [Ref1]) as follows: 627 Interface ID 628 Every interface is assigned an Interface ID, which 629 uniquely identifies the interface with the router. For 630 example, some implementations may be able to use the 631 MIB-II IfIndex as Interface ID. The Interface ID appears 632 in Hello packets sent out the interface, the link- 633 local-LSA originated by router for the attached link, 634 and the router-LSA originated by the router-LSA for the 635 associated area. It will also serve as the Link State ID 636 for the network-LSA that the router will originate for 637 the link if the router is elected Designated Router. 639 Instance ID 640 Every interface is assigned an Instance ID. This should 641 default to 0, and is only necessary to assign 642 differently on those links that will contain multiple 643 separate communities of OSPF Routers. For example, 644 suppose that there are two communities of routers on a 645 given ethernet segment that you wish to keep separate. 646 The first community is given an Instance ID of 0, by 647 assigning 0 as the Instance ID of all its routers' 648 interfaces to the ethernet. An Instance ID of 1 is 649 assigned to the other routers' interface to the 650 ethernet. The OSPF transmit and receive processing (see 651 Section 3.2) will then keep the two communities 652 separate. 654 List of LSAs with link-local scope 655 All LSAs with link-local scope and which were 656 originated/flooded on the link belong to the interface 657 structure which connects to the link. This includes the 658 collection of the link's link-LSAs. 660 List of LSAs with unknown LS type 661 All LSAs with unknown LS type and U-bit set to 0 (if 662 unrecognized, treat the LSA as if it had link-local 663 flooding scope) are kept in data structure for the 664 interface that received the LSA. 666 IP interface address 667 For IPv6, the IPv6 address appearing in the source of 668 OSPF packets sent out the interface is almost always a 669 link-local address. The one exception is for virtual 670 links, which must use one of the router's own site-local 671 or global IPv6 addresses as IP interface address. 673 List of link prefixes 674 A list of IPv6 prefixes can be configured for the 675 attached link. These will be advertised by the router in 676 link-LSAs, so that they can be advertised by the link's 677 Designated Router in intra-area-prefix-LSAs. 679 There is only a single interface output cost, as IPv6 has no 680 concept of TOS. In addition, OSPF for IPv6 relies on the IP 681 Authentication Header (see [Ref19]) and the IP Encapsulating 682 Security Payload (see [Ref20]) to ensure integrity and 683 authentication/confidentiality of routing exchanges. For 684 that reason, AuType and Authentication key are not 685 associated with IPv6 OSPF interfaces. 687 Interface states, events, and the interface state machine 688 remain unchanged from IPv4, and are documented in Sections 689 9.1, 9.2 and 9.3 of [Ref1] respectively. The Designated 690 Router and Backup Designated Router election algorithm also 691 remains unchanged from the IPv4 election in Section 9.4 of 692 [Ref1]. 694 3.1.3. The Neighbor Data Structure 696 The neighbor structure performs the same function in both 697 IPv6 and IPv4. Namely, it collects all information required 698 to form an adjacency between two routers, if an adjacency 699 becomes necessary. Each neighbor structure is bound to a 700 single OSPF interface. The differences between the IPv6 701 neighbor structure and the neighbor structure defined for 702 IPv4 in Section 10 of [Ref1] are: 704 Neighbor's Interface ID 705 The Interface ID that the neighbor advertises in its 706 Hello Packets must be recorded in the neighbor 707 structure. The router will include the neighbor's 708 Interface ID in the router's router-LSA when either a) 709 advertising a point-to-point link to the neighbor or b) 710 advertising a link to a network where the neighbor has 711 become Designated Router. 713 Neighbor IP address 714 Except on virtual links, the neighbor's IP address will 715 be an IPv6 link-local address. 717 Neighbor's Designated Router 718 The neighbor's choice of Designated Router is now 719 encoded as Router ID, instead of as an IP address. 721 Neighbor's Backup Designated Router 722 The neighbor's choice of Designated Router is now 723 encoded as Router ID, instead of as an IP address. 725 Neighbor states, events, and the neighbor state machine 726 remain unchanged from IPv4, and are documented in Sections 727 10.1, 10.2 and 10.3 of [Ref1] respectively. The decision as 728 to which adjacencies to form also remains unchanged from the 729 IPv4 logic documented in Section 10.4 of [Ref1]. 731 3.2. Protocol Packet Processing 733 OSPF for IPv6 runs directly over IPv6's network layer. As such, 734 it is encapsulated in one or more IPv6 headers, with the Next 735 Header field of the immediately encapsulating IPv6 header set to 736 the value 89. OSPF protocol packets should be given precedence 737 over regular IPv6 data traffic, in both sending and receiving. 738 as an aid towards accomplishing this precedence, OSPF routing 739 protocol packets are sent with IPv6 Priority field set to 7 740 (internet control traffic). 742 As for IPv4, in IPv6 OSPF routing protocol packets are sent 743 along adjacencies only (with the exception of Hello packets, 744 which are used to discover the adjacencies). OSPF packet types 745 and functions are the same in both IPv4 and IPv4, encoded by the 746 Type field of the standard OSPF packet header. 748 3.2.1. Sending protocol packets 750 When an IPv6 router sends an OSPF routing protocol packet, 751 it fills in the fields of the standard OSPF for IPv6 packet 752 header (see Section A.3.1) as follows: 754 Version # 755 Set to 3, the version number of the protocol as 756 documented in this specification. 758 Type 759 The type of OSPF packet, such as Link state Update or 760 Hello Packet. 762 Packet length 763 The length of the entire OSPF packet in bytes, including 764 the standard OSPF packet header. 766 Router ID 767 The identity of the router itself (who is originating 768 the packet). 770 Area ID 771 The OSPF area that the packet is being sent into. 773 Instance ID 774 The OSPF Instance ID associated with the interface that 775 the packet is being sent out of. 777 Checksum 778 The standard IP 16-bit one's complement checksum of the 779 entire OSPF packet. 781 Selection of OSPF routing protocol packets' IPv6 source and 782 destination addresses is performed identically to the IPv4 783 logic in Section 8.1 of [Ref1]. The IPv6 destination address 784 is chosen from among the addresses AllSPFRouters, 785 AllDRouters and the Neighbor IP address associated with the 786 other end of the adjacency (which in IPv6, for all links 787 except virtual links, is an IPv6 link-local address). 789 The sending of Link State Request Packets and Link State 790 Acknowledgment Packets remains unchanged from the IPv4 791 procedures documented in Sections 10.9 and 13.5 of [Ref1] 792 respectively. Sending Hello Packets is documented in Section 793 3.2.1.1, and the sending of Database Description Packets in 794 Section 3.2.1.2. The sending of Link State Update Packets is 795 documented in Section 3.5.2. 797 3.2.1.1. Sending Hello packets 799 IPv6 changes the way OSPF Hello packets are sent in the 800 following ways (compare to Section 9.5 of [Ref1]): 802 o Before the Hello Packet is sent out an interface, 803 the interface's Interface ID must be copied into the 804 Hello Packet. 806 o The Hello Packet no longer contains an IP network 807 mask, as OSPF for IPv6 runs per-link instead of 808 per-subnet. 810 o The choice of Designated Router and Backup 811 Designated Router are now indicated within Hellos by 812 their Router IDs, instead of by their IP interface 813 addresses. Advertising the Designated Router (or 814 Backup Designated Router) as 0.0.0.0 indicates that 815 the Designated Router (or Backup Designated Router) 816 has not yet been chosen. 818 o The Options field within Hello packets has moved 819 around, getting larger in the process. More options 820 bits are now possible. Those that must be set 821 correctly in Hello packets are: The E-bit is set if 822 and only if the interface attaches to a non-stub 823 area, the N-bit is set if and only if the interface 824 attaches to an NSSA area (see [Ref9]), and the DC- 825 bit is set if and only if the router wishes to 826 suppress the sending of future Hellos over the 827 interface (see [Ref11]). Unrecognized bits in the 828 Hello Packet's Options field should be cleared. 830 Sending Hello packets on NBMA networks proceeds for IPv6 831 in exactly the same way as for IPv4, as documented in 832 Section 9.5.1 of [Ref1]. 834 3.2.1.2. Sending Database Description Packets 836 The sending of Database Description packets differs from 837 Section 10.8 of [Ref1] in the following ways: 839 o The Options field within Database Description 840 packets has moved around, getting larger in the 841 process. More options bits are now possible. Those 842 that must be set correctly in Database Description 843 packets are: The MC-bit is set if and only if the 844 router is forwarding multicast datagrams according 845 to the MOSPF specification in [Ref7]. Unrecognized 846 bits in the Database Description Packet's Options 847 field should be cleared. 849 3.2.2. Receiving protocol packets 851 Whenever an OSPF protocol packet is received by the router 852 it is marked with the interface it was received on. For 853 routers that have virtual links configured, it may not be 854 immediately obvious which interface to associate the packet 855 with. For example, consider the Router RT11 depicted in 856 Figure 6 of [Ref1]. If RT11 receives an OSPF protocol 857 packet on its interface to Network N8, it may want to 858 associate the packet with the interface to Area 2, or with 859 the virtual link to Router RT10 (which is part of the 860 backbone). In the following, we assume that the packet is 861 initially associated with the non-virtual link. 863 In order for the packet to be passed to OSPF for processing, 864 the following tests must be performed on the encapsulating 865 IPv6 headers: 867 o The packet's IP destination address must be one of the 868 IPv6 unicast addresses associated with the receiving 869 interface (this includes link-local addresses), or one 870 of the IP multicast addresses AllSPFRouters or 871 AllDRouters. 873 o The Next Header field of the immediately encapsulating 874 IPv6 header must specify the OSPF protocol (89). 876 o Any encapsulating IP Authentication Headers (see 877 [Ref19]) and the IP Encapsulating Security Payloads (see 878 [Ref20]) must be processed and/or verified to ensure 879 integrity and authentication/confidentiality of OSPF 880 routing exchanges. 882 o Locally originated packets should not be passed on to 883 OSPF. That is, the source IPv6 address should be 884 examined to make sure this is not a multicast packet 885 that the router itself generated. 887 After processing the encapsulating IPv6 headers, the OSPF 888 packet header is processed. The fields specified in the 889 header must match those configured for the receiving 890 interface. If they do not, the packet should be discarded: 892 o The version number field must specify protocol version 893 3. 895 o The standard IP 16-bit one's complement checksum of the 896 entire OSPF packet must be verified. 898 o The Area ID found in the OSPF header must be verified. 899 If both of the following cases fail, the packet should 900 be discarded. The Area ID specified in the header must 901 either: 903 (1) Match the Area ID of the receiving interface. In 904 this case, unlike for IPv4, the IPv6 source address 905 is not restricted to lie on the same IP subnet as 906 the receiving interface. IPv6 OSPF runs per-link, 907 instead of per-IP-subnet. 909 (2) Indicate the backbone. In this case, the packet has 910 been sent over a virtual link. The receiving router 911 must be an area border router, and the Router ID 912 specified in the packet (the source router) must be 913 the other end of a configured virtual link. The 914 receiving interface must also attach to the virtual 915 link's configured Transit area. If all of these 916 checks succeed, the packet is accepted and is from 917 now on associated with the virtual link (and the 918 backbone area). 920 o The Instance ID specified in the OSPF header must match 921 the receiving interface's Instance ID. 923 o Packets whose IP destination is AllDRouters should only 924 be accepted if the state of the receiving interface is 925 DR or Backup (see Section 9.1). 927 After header processing, the packet is further processed 928 according to it OSPF packet type. OSPF packet types and 929 functions are the same for both IPv4 and IPv6. 931 If the packet type is Hello, it should then be further 932 processed by the Hello Protocol. All other packet types are 933 sent/received only on adjacencies. This means that the 934 packet must have been sent by one of the router's active 935 neighbors. The neighbor is identified by the Router ID 936 appearing the the received packet's OSPF header. Packets not 937 matching any active neighbor are discarded. 939 The receive processing of Database Description Packets, Link 940 State Request Packets and Link State Acknowledgment Packets 941 remains unchanged from the IPv4 procedures documented in 942 Sections 10.6, 10.7 and 13.7 of [Ref1] respectively. The 943 receiving of Hello Packets is documented in Section 3.2.2.1, 944 and the receiving of Link State Update Packets is documented 945 in Section 3.5.1. 947 3.2.2.1. Receiving Hello Packets 949 The receive processing of Hello Packets differs from 950 Section 10.5 of [Ref1] in the following ways: 952 o On all link types (e.g., broadcast, NBMA, point-to- 953 point, etc), neighbors are identified solely by 954 their OSPF Router ID. For all link types except 955 virtual links, the Neighbor IP address is set to the 956 IPv6 source address in the IPv6 header of the 957 received OSPF Hello packet. 959 o There is no longer a Network Mask field in the Hello 960 Packet. 962 o The neighbor's choice of Designated Router and 963 Backup Designated Router is now encoded as an OSPF 964 Router ID instead of an IP interface address. 966 3.3. The Routing table Structure 968 The routing table used by OSPF for IPv4 is defined in Section 11 969 of [Ref1]. For IPv6 there are analogous routing table entries: 970 there are routing table entries for IPv6 address prefixes, and 971 also for AS boundary routers. The latter routing table entries 972 are only used to hold intermediate results during the routing 973 table build process (see Section 3.8). 975 Also, to hold the intermediate results during the shortest-path 976 calculation for each area, there is a separate routing table for 977 each area holding the following entries: 979 o An entry for each router in the area. Routers are identified 980 by their OSPF router ID. These routing table entries hold 981 the set of shortest paths through a given area to a given 982 router, which in turn allows calculation of paths to the 983 IPv6 prefixes advertised by that router in Intra-area- 984 prefix-LSAs. If the router is also an area-border router, 985 these entries are also used to calculate paths for inter- 986 area address prefixes. If in addition the router is the 987 other endpoint of a virtual link, the routing table entry 988 describes the cost and viability of the virtual link. 990 o An entry for each transit link in the area. Transit links 991 have associated network-LSAs. Both the transit link and the 992 network-LSA are identified by a combination of the 993 Designated Router's Interface ID on the link and the 994 Designated Router's OSPF Router ID. These routing table 995 entries allow later calculation of paths to IP prefixes 996 advertised for the transit link in intra-area-prefix-LSAs. 998 Since IPv6 does not support the concept of Type of Service 999 (TOS), there are no longer separate sets of paths for each TOS. 1000 The rest of the fields in the IPv4 OSPF routing table (see 1001 Section 11 of [Ref1]) remain valid for IPv6: Optional 1002 capabilities (routers only), path type, cost, type 2 cost, link 1003 state origin, and for each of the equal cost paths to the 1004 destination, the next hop and advertising router (inter-area and 1005 AS external paths only). 1007 For IPv6, the link-state origin field in the routing table entry 1008 is the router-LSA or network-LSA that has directly or indirectly 1009 produced the routing table entry. For example, if the routing 1010 table entry describes a route to an IPv6 prefix, the link state 1011 origin is the router-LSA or network-LSA that is listed in the 1012 body of the intra-area-prefix-LSA that has produced the route 1013 (see Section A.4.9). 1015 3.3.1. Routing table lookup 1017 Routing table lookup (i.e., determining the best matching 1018 routing table entry during IP forwarding) is the same for 1019 IPv6 as for IPv4, except that Type of Service is not taken 1020 into account. The lookup consists of the first three steps 1021 of Section 11.1 in [Ref1], ignoring the last step that 1022 concerns only TOS. 1024 3.4. Link State Advertisements 1026 For IPv6, the OSPF LSA header has changed slightly, with the LS 1027 type field expanding and the Options field being moved into the 1028 body of appropriate LSAs. Also, the formats of some LSAs have 1029 changed somewhat (namely router-LSAs, network-LSAs and AS- 1030 external-LSAs), while the names of other LSAs have been changed 1031 (type 3 and 4 summary-LSAs are now inter-area-prefix-LSAs and 1032 inter-area-router-LSAs respectively) and additional LSAs have 1033 been added (Link-LSAs and Intra-Area-Prefix-LSAs). Since IPv6 1034 does not support TOS, TOS is no longer encoded within LSAs. 1036 These changes will be described in detail in the following 1037 subsections. 1039 3.4.1. The LSA Header 1041 In both IPv4 and IPv6, all OSPF LSAs begin with a standard 1042 20 byte LSA header. However, the contents of this 20 byte 1043 header have changed in IPv6. The LS age, Advertising Router, 1044 LS Sequence Number, LS checksum and length fields within the 1045 LSA header remain unchanged, as documented in Sections 1046 12.1.1, 12.1.5, 12.1.6, 12.1.7 and A.4.1 of [Ref1] 1047 respectively. However, the following fields have changed 1048 for IPv6: 1050 Options 1051 The Options field has been removed from the standard 20 1052 byte LSA header, and into the body of router-LSAs, 1053 network-LSAs, inter-area-router-LSAs and link-LSAs. The 1054 size of the Options field has increased from 8 to 24 1055 bits, and some of the bit definitions have changed (see 1056 Section A.2). In addition a separate PrefixOptions 1057 field, 8 bits in length, is attached to each prefix 1058 advertised within the body of an LSA. 1060 LS type 1061 The size of the LS type field has increased from 8 to 16 1062 bits, with the top two bits encoding flooding scope and 1063 the next bit encoding the handling of unknown LS types. 1064 See Section A.4.2.1 for the current coding of the LS 1065 type field. 1067 Link State ID 1068 Link State ID remains at 32 bits in length, but except 1069 for network-LSAs and link-LSAs, Link State ID has shed 1070 any addressing semantics. For example, an IPv6 router 1071 originating multiple AS-external-LSAs could start by 1072 assigning the first a Link State ID of 0.0.0.1, the 1073 second a Link State ID of 0.0.0.2, and so on. Instead of 1074 the IPv4 behavior of encoding the network number within 1075 the AS-external-LSA's Link State ID, the IPv6 Link State 1076 ID simply serves as a way to differentiate multiple LSAs 1077 originated by the same router. 1079 For network-LSAs, the Link State ID is set to the 1080 Designated Router's Interface ID on the link. When a 1081 router originates a Link-LSA for a given link, its Link 1082 State ID is set equal to the router's Interface ID on 1083 the link. 1085 3.4.2. The link-state database 1087 In IPv6, as in IPv4, individual LSAs are identified by a 1088 combination of their LS type, Link State ID and Advertising 1089 Router fields. Given two instances of an LSA, the most 1090 recent instance is determined by examining the LSAs' LS 1091 Sequence Number, using LS checksum and LS age as tiebreakers 1092 (see Section 13.1 of [Ref1]). 1094 In IPv6, the link-state database is split across three 1095 separate data structures. LSAs with AS flooding scope are 1096 contained within the top-level OSPF data structure (see 1097 Section 3.1) as long as either their LS type is known or 1098 their U-bit is 1 (flood even when unrecognized); this 1099 includes the AS-external-LSAs. LSAs with area flooding scope 1100 are contained within the appropriate area structure (see 1101 Section 3.1.1) as long as either their LS type is known or 1102 their U-bit is 1 (flood even when unrecognized); this 1103 includes router-LSAs, network-LSAs, inter-area-prefix-LSAs, 1104 inter-area-router-LSAs, and intra-area-prefix-LSAs. LSAs 1105 with unknown LS type and U-bit set to 0 and/or link-local 1106 flooding scope are contained within the appropriate 1107 interface structure (see Section 3.1.2); this includes 1108 link-LSAs. 1110 To lookup or install an LSA in the database, you first 1111 examine the LS type and the LSA's context (i.e., to which 1112 area or link does the LSA belong). This information allows 1113 you to find the correct list of LSAs, all of the same LS 1114 type, where you then search based on the LSA's Link State ID 1115 and Advertising Router. 1117 3.4.3. Originating LSAs 1119 The process of reoriginating an LSA in IPv6 is the same as 1120 in IPv4: the LSA's LS sequence number is incremented, its 1121 LS age is set to 0, its LS checksum is calculated, and the 1122 LSA is added to the link state database and flooded out the 1123 appropriate interfaces. 1125 To the list of events causing LSAs to be reoriginated, which 1126 for IPv4 is given in Section 12.4 of [Ref1], the following 1127 events are added for IPv6: 1129 o The Interface ID of a neighbor changes. This may cause a 1130 new instance of a router-LSA to be originated for the 1131 associated area. 1133 o A new prefix is added to an attached link, or a prefix 1134 is deleted (both through configuration). This causes the 1135 router to reoriginate its link-LSA for the link, or, if 1136 it is the only router attached to the link, causes the 1137 router to reoriginate an intra-area-prefix-LSA. 1139 o A new link-LSA is received, causing the link's 1140 collection of prefixes to change. If the router is 1141 Designated Router for the link, it originates a new 1142 intra-area-prefix-LSA. 1144 Detailed construction of the seven required IPv6 LSA types 1145 is supplied by the following subsections. In order to 1146 display example LSAs, the network map in Figure 15 of [Ref1] 1147 has been reworked to show IPv6 addressing, resulting in 1148 Figure 1. The OSPF cost of each interface is has been 1149 displayed in Figure 1. The assignment of IPv6 prefixes to 1150 network links is shown in Table 1. A single area address 1151 range has been configured for Area 1, so that outside of 1152 Area 1 all of its prefixes are covered by a single route to 1153 5f00:0000:c001::/48. The OSPF interface IDs and the link- 1154 local addresses for the router interfaces in Figure 1 are 1155 given in Table 2. 1157 Network IPv6 prefix 1158 __________________________________ 1159 N1 5f00:0000:0c01:0200::/56 1160 N2 5f00:0000:0c01:0300::/56 1161 N3 5f00:0000:0c01:0100::/56 1162 N4 5f00:0000:0c01:0400::/56 1164 Table 1: IPv6 link prefixes for sample network 1166 .......................................... 1167 . Area 1. 1168 . + . 1169 . | . 1170 . | 3+---+1 . 1171 . N1 |--|RT1|-----+ . 1172 . | +---+ \ . 1173 . | \ ______ . 1174 . + \/ \ 1+---+ 1175 . * N3 *------|RT4|------ 1176 . + /\_______/ +---+ 1177 . | / | . 1178 . | 3+---+1 / | . 1179 . N2 |--|RT2|-----+ 1| . 1180 . | +---+ +---+ . 1181 . | |RT3|---------------- 1182 . + +---+ . 1183 . |2 . 1184 . | . 1185 . +------------+ . 1186 . N4 . 1187 .......................................... 1189 Figure 1: Area 1 with IP addresses shown 1190 Router interface Interface ID link-local address 1191 ______________________________________________________ 1192 RT1 to N1 1 fe80:0001::RT1 1193 to N3 2 fe80:0002::RT1 1194 RT2 to N2 1 fe80:0001::RT2 1195 to N3 2 fe80:0002::RT2 1196 RT3 to N3 1 fe80:0001::RT3 1197 to N4 2 fe80:0002::RT3 1198 RT4 to N3 1 fe80:0001::RT4 1200 Table 2: OSPF Interface IDs and link-local addresses 1202 3.4.3.1. Router-LSAs 1204 The LS type of a router-LSA is set to the value 0x2001. 1205 Router-LSAs have area flooding scope. A router may 1206 originate one or more router-LSAs for a given area. 1207 Taken together, the collection of router-LSAs originated 1208 by the router for an area describes the collected states 1209 of all the router's interface to the area. When multiple 1210 router-LSAs are used, they are distinguished by their 1211 Link State ID fields. 1213 The Options field in the router-LSA should be coded as 1214 follows. The V6-bit should be set. The E-bit should be 1215 clear if and only if the area is an OSPF stub area. The 1216 MC-bit should be set if and only if the router is 1217 running MOSPF (see [Ref8]). The N-bit should be set if 1218 and only if the area is an OSPF NSSA area. The R-bit 1219 should be set. The DC-bit should be set if and only if 1220 the router can correctly process the DoNotAge bit when 1221 it appears in the LS age field of LSAs (see [Ref11]). 1222 All unrecognized bits in the Options field should be 1223 cleared 1225 To the left of the Options field, the router capability 1226 bits V, E and B should be coded according to Section 1227 12.4.1 of [Ref1]. Bit W should be coded according to 1228 [Ref8]. 1230 Each of the router's interfaces to the area are then 1231 described by appending "link descriptions" to the 1232 router-LSA. Each link description is 16 bytes long, 1233 consisting of 5 fields: (link) Type, Metric, Interface 1234 ID, Neighbor Interface ID and Neighbor Router ID (see 1235 Section A.4.3). Interfaces in state "Down" or "Loopback" 1236 are not described (although looped back interfaces can 1237 contribute prefixes to Intra-Area-Prefix-LSAs). Nor are 1238 interfaces without any full adjacencies described. All 1239 other interfaces to the area add zero, one or more link 1240 descriptions, the number and content of which depend on 1241 the interface type. Within each link description, the 1242 Metric field is always set the interface's output cost 1243 and the Interface ID field is set to the interface's 1244 OSPF Interface ID. 1246 Point-to-point interfaces 1247 If the neighboring router is fully adjacent, add a 1248 Type 1 link description (point-to-point). The 1249 Neighbor Interface ID field is set to the Interface 1250 ID advertised by the neighbor in its Hello packets, 1251 and the Neighbor Router ID field is set to the 1252 neighbor's Router ID. 1254 Broadcast and NBMA interfaces 1255 If the router is fully adjacent to the link's 1256 Designated Router, or if the router itself is 1257 Designated Router and is fully adjacent to at least 1258 one other router, add a single Type 2 link 1259 description (transit network). The Neighbor 1260 Interface ID field is set to the Interface ID 1261 advertised by the Designated Router in its Hello 1262 packets, and the Neighbor Router ID field is set to 1263 the Designated Router's Router ID. 1265 Virtual links 1266 If the neighboring router is fully adjacent, add a 1267 Type 4 link description (virtual). The Neighbor 1268 Interface ID field is set to the Interface ID 1269 advertised by the neighbor in its Hello packets, and 1270 the Neighbor Router ID field is set to the 1271 neighbor's Router ID. Note that the output cost of a 1272 virtual link is calculated during the routing table 1273 calculation (see Section 3.7). 1275 Point-to-MultiPoint interfaces 1276 For each fully adjacent neighbor associated with the 1277 interface, add a separate Type 1 link description 1278 (point-to-point) with Neighbor Interface ID field 1279 set to the Interface ID advertised by the neighbor 1280 in its Hello packets, and Neighbor Router ID field 1281 set to the neighbor's Router ID. 1283 As an example, consider the router-LSA that router RT3 1284 would originate for Area 1 in Figure 1. Only a single 1285 interface must be described, namely that which connects 1286 to the transit network N3. It assumes that RT4 has bee 1287 elected Designated Router of Network N3. 1289 ; RT3's router-LSA for Area 1 1291 LS age = 0 ;newly (re)originated 1292 LS type = 0x2001 ;router-LSA 1293 Link State ID = 0 ;first fragment 1294 Advertising Router = 192.1.1.3 ;RT3's Router ID 1295 bit E = 0 ;not an AS boundary router 1296 bit B = 1 ;area border router 1297 Options = (V6-bit|E-bit|R-bit) 1298 Type = 2 ;connects to N3 1299 Metric = 1 ;cost to N3 1300 Interface ID = 1 ;RT3's Interface ID on N3 1301 Neighbor Interface ID = 1 ;RT4's Interface ID on N3 1302 Neighbor Router ID = 192.1.1.4 ; RT4's Router ID 1304 If for example another router was added to Network N4, 1305 RT3 would have to advertise a second link description 1306 for its connection to (the now transit) network N4. This 1307 could be accomplished by reoriginating the above 1308 router-LSA, this time with two link descriptions. Or, a 1309 separate router-LSA could be originated with a separate 1310 Link State ID (e.g., using a Link State ID of 1) to 1311 describe the connection to N4. 1313 Host routes no longer appear in the router-LSA, but are 1314 instead included in intra-area-prefix-LSAs. 1316 3.4.3.2. Network-LSAs 1318 The LS type of a network-LSA is set to the value 0x2002. 1319 Network-LSAs have area flooding scope. A network-LSA is 1320 originated for every transit broadcast or NBMA link, by 1321 the link's Designated Router. Transit links are those 1322 that have two or more attached routers. The network-LSA 1323 lists all routers attached to the link. 1325 The procedure for originating network-LSAs in IPv6 is 1326 the same as the IPv4 procedure documented in Section 1327 12.4.2 of [Ref1], with the following exceptions: 1329 o An IPv6 network-LSA's Link State ID is set to the 1330 Interface ID of the Designated Router on the link. 1332 o IPv6 network-LSAs do not contain a Network Mask. All 1333 addressing information formerly contained in the 1334 IPv4 network-LSA has now been consigned to intra- 1335 Area-Prefix-LSAs. 1337 o The Options field in the network-LSA is set to the 1338 logical OR of the Options fields contained within 1339 the link's associated link-LSAs. In this way, the 1340 network link exhibits a capability when at least one 1341 of the link's routers requests that the capability 1342 be asserted. 1344 As an example, assuming that Router RT4 has been elected 1345 Designated Router of Network N3 in Figure 1, the 1346 following network-LSA is originated: 1348 ; Network-LSA for Network N3 1350 LS age = 0 ;newly (re)originated 1351 LS type = 0x2002 ;network-LSA 1352 Link State ID = 1 ;RT4's Interface ID on N3 1353 Advertising Router = 192.1.1.4 ;RT4's Router ID 1354 Options = (V6-bit|E-bit|R-bit) 1355 Attached Router = 192.1.1.4 ;Router ID 1356 Attached Router = 192.1.1.1 ;Router ID 1357 Attached Router = 192.1.1.2 ;Router ID 1358 Attached Router = 192.1.1.3 ;Router ID 1360 3.4.3.3. Inter-Area-Prefix-LSAs 1362 The LS type of an inter-area-prefix-LSA is set to the 1363 value 0x2003. Inter-area-prefix-LSAs have area flooding 1364 scope. In IPv4, inter-area-prefix-LSAs were called type 1365 3 summary-LSAs. Each inter-area-prefix-LSA describes a 1366 prefix external to the area, yet internal to the 1367 Autonomous System. 1369 The procedure for originating inter-area-prefix-LSAs in 1370 IPv6 is the same as the IPv4 procedure documented in 1371 Sections 12.4.3 and 12.4.3.1 of [Ref1], with the 1372 following exceptions: 1374 o The Link State ID of an inter-area-prefix-LSA has 1375 lost all of its addressing semantics, and instead 1376 simply serves to distinguish multiple inter-area- 1377 prefix-LSAs that are originated by the same router. 1379 o The prefix is described by the PrefixLength, 1380 PrefixOptions and Address Prefix fields embedded 1381 within the LSA body. Network Mask is no longer 1382 specified. 1384 o The NU-bit in the PrefixOptions field should be 1385 clear. The coding of the MC-bit depends upon 1386 whether, and if so how, MOSPF is operating in the 1387 routing domain (see [Ref8]). 1389 o Link-local addresses can never be advertised in 1390 inter-area-prefix-LSAs. 1392 As an example, the following shows the inter-area- 1393 prefix-LSA that Router RT4 originates into the OSPF 1394 backbone area, condensing all of Area 1's prefixes into 1395 the single prefix 5f00:0000:c001::/48. The cost is set 1396 to 4, which is the maximum cost to all of the prefix' 1397 individual components. The prefix is padded out to an 1398 even number of 32-bit words, so that it consumes 64-bits 1399 of space instead of 48 bits. 1401 ; Inter-area-prefix-LSA for Area 1 addresses 1402 ; originated by Router RT4 into the backbone 1404 LS age = 0 ;newly (re)originated 1405 LS type = 0x2003 ;inter-area-prefix-LSA 1406 Advertising Router = 192.1.1.4 ;RT4's ID 1407 Metric = 4 ;maximum to components 1408 PrefixLength = 48 1409 PrefixOptions = 0 1410 Address Prefix = 5f00:0000:c001 ;padded to 64-bits 1412 3.4.3.4. Inter-Area-Router-LSAs 1414 The LS type of an inter-area-router-LSA is set to the 1415 value 0x2004. Inter-area-router-LSAs have area flooding 1416 scope. In IPv4, inter-area-router-LSAs were called type 1417 4 summary-LSAs. Each inter-area-router-LSA describes a 1418 path to a destination OSPF router (an ASBR) that is 1419 external to the area, yet internal to the Autonomous 1420 System. 1422 The procedure for originating inter-area-router-LSAs in 1423 IPv6 is the same as the IPv4 procedure documented in 1424 Section 12.4.3 of [Ref1], with the following exceptions: 1426 o The Link State ID of an inter-area-router-LSA is no 1427 longer the destination router's OSPF Router ID, but 1428 instead simply serves to distinguish multiple 1429 inter-area-router-LSAs that are originated by the 1430 same router. The destination router's Router ID is 1431 now found in the body of the LSA. 1433 o The Options field in an inter-area-router-LSA should 1434 be set equal to the Options field contained in the 1435 destination router's own router-LSA. The Options 1436 field thus describes the capabilities supported by 1437 the destination router. 1439 As an example, consider the OSPF Autonomous System 1440 depicted in Figure 6 of [Ref1]. Router RT4 would 1441 originate into Area 1 the following inter-area-router- 1442 LSA for destination router RT7. 1444 ; inter-area-router-LSA for AS boundary router RT7 1445 ; originated by Router RT4 into Area 1 1447 LS age = 0 ;newly (re)originated 1448 LS type = 0x2004 ;inter-area-router-LSA 1449 Advertising Router = 192.1.1.4 ;RT4's ID 1450 Options = (V6-bit|E-bit|R-bit) ;RT7's capabilities 1451 Metric = 14 ;cost to RT7 1452 Destination Router ID = Router RT7's ID 1454 3.4.3.5. AS-external-LSAs 1456 The LS type of an AS-external-LSA is set to the value 1457 0x4005. AS-external-LSAs have AS flooding scope. Each 1458 AS-external-LSA describes a path to a prefix external to 1459 the Autonomous System. 1461 The procedure for originating AS-external-LSAs in IPv6 1462 is the same as the IPv4 procedure documented in Section 1463 12.4.4 of [Ref1], with the following exceptions: 1465 o The Link State ID of an AS-external-LSA has lost all 1466 of its addressing semantics, and instead simply 1467 serves to distinguish multiple AS-external-LSAs that 1468 are originated by the same router. 1470 o The prefix is described by the PrefixLength, 1471 PrefixOptions and Address Prefix fields embedded 1472 within the LSA body. Network Mask is no longer 1473 specified. 1475 o The NU-bit in the PrefixOptions field should be 1476 clear. The coding of the MC-bit depends upon 1477 whether, and if so how, MOSPF is operating in the 1478 routing domain (see [Ref8]). 1480 o Link-local addresses can never be advertised in AS- 1481 external-LSAs. 1483 o The forwarding address is present in the AS- 1484 external-LSA if and only if the AS-external-LSA's 1485 bit F is set. 1487 o The external route tag is present in the AS- 1488 external-LSA if and only if the AS-external-LSA's 1489 bit T is set. 1491 o The capability for an AS-external-LSA to reference 1492 another LSA has been included, by inclusion of the 1493 Referenced LS Type field and the optional Referenced 1494 Link State ID field (the latter present if and only 1495 if Referenced LS Type is non-zero). This capability 1496 is for future use; for now Referenced LS Type should 1497 be set to 0. 1499 As an example, consider the OSPF Autonomous System 1500 depicted in Figure 6 of [Ref1]. Assume that RT7 has 1501 learned its route to N12 via BGP, and that it wishes to 1502 advertise a Type 2 metric into the AS. Further assume 1503 the the IPv6 prefix for N12 is the value 1504 5f00:0000:0a00::/40. RT7 would then originate the 1505 following AS-external-LSA for the external network N12. 1506 Note that within the AS-external-LSA, N12's prefix 1507 occupies 64 bits of space, to maintain 32-bit alignment. 1509 ; AS-external-LSA for Network N12, 1510 ; originated by Router RT7 1512 LS age = 0 ;newly (re)originated 1513 LS type = 0x4005 ;AS-external-LSA 1514 Link State ID = 123 ;or something else 1515 Advertising Router = Router RT7's ID 1516 bit E = 1 ;Type 2 metric 1517 bit F = 0 ;no forwarding address 1518 bit T = 1 ;external route tag included 1519 Metric = 2 1520 PrefixLength = 40 1521 PrefixOptions = 0 1522 Referenced LS Type = 0 ;no Referenced Link State ID 1523 Address Prefix = 5f00:0000:0a00 ;padded to 64-bits 1524 External Route Tag = as per BGP/OSPF interaction 1526 3.4.3.6. Link-LSAs 1528 The LS type of a Link-LSA is set to the value 0x0008. 1529 Link-LSAs have link-local flooding scope. A router 1530 originates a separate Link-LSA for each attached link 1531 that supports 2 or more (including the originating 1532 router itself) routers. 1534 Link-LSAs have three purposes: 1) they provide the 1535 router's link-local address to all other routers 1536 attached to the link and 2) they inform other routers 1537 attached to the link of a list of IPv6 prefixes to 1538 associate with the link and 3) they allow the router to 1539 assert a collection of Options bits in the Network-LSA 1540 that will be originated for the link. 1542 A Link-LSA for a given Link L is built in the following 1543 fashion: 1545 o The Link State ID is set to the router's Interface 1546 ID on Link L. 1548 o The Router Priority of the router's interface to 1549 Link L is inserted into the Link-LSA. 1551 o The Link-LSA's Options field is set to those bits 1552 that the router wishes set in Link L's Network LSA. 1554 o The router inserts its link-local address on Link L 1555 into the Link-LSA. This information will be used 1556 when the other routers on Link L do their next hop 1557 calculations (see Section 3.8.1.1). 1559 o Each IPv6 address prefix that has been configured 1560 into the router for Link L is added to the Link-LSA, 1561 by specifying values for PrefixLength, 1562 PrefixOptions, and Address Prefix fields. 1564 After building a Link-LSA for a given link, the router 1565 installs the link-LSA into the associate interface data 1566 structure and floods the Link-LSA onto the link. All 1567 other routers on the link will receive the Link-LSA, but 1568 it will go no further. 1570 As an example, consider the Link-LSA that RT3 will build 1571 for N3 in Figure 1. Suppose that the prefix 1572 5f00:0000:0c01:0100::/56 has been configured within RT3 1573 for N3. This will give rise to the following Link-LSA, 1574 which RT3 will flood onto N3, but nowhere else. Note 1575 that not all routers on N3 need be configured with the 1576 prefix; those not configured will learn the prefix when 1577 receiving RT3's Link-LSA. 1579 ; RT3's Link-LSA for N3 1581 LS age = 0 ;newly (re)originated 1582 LS type = 0x0008 ;Link-LSA 1583 Link State ID = 1 ;RT3's Interface ID on N3 1584 Advertising Router = 192.1.1.3 ;RT3's Router ID 1585 Rtr Pri = 1 ;RT3's N3 Router Priority 1586 Options = (V6-bit|E-bit|R-bit) 1587 Link-local Interface Address = fe80:0001::RT3 1588 # prefixes = 1 1589 PrefixLength = 56 1590 PrefixOptions = 0 1591 Address Prefix = 5f00:0000:c001:0100 ;pad to 64-bits 1593 3.4.3.7. Intra-Area-Prefix-LSAs 1595 The LS type of an intra-area-prefix-LSA is set to the 1596 value 0x2009. Intra-area-prefix-LSAs have area flooding 1597 scope. An intra-area-prefix-LSA has one of two 1598 functions. It associates a list of IPv6 address prefixes 1599 with a transit network link by referencing a network- 1600 LSA, or associates a list of IPv6 address prefixes with 1601 a router by referencing a router-LSA. A sub network 1602 link's prefixes are associated with its attached router. 1604 A router may originate multiple intra-area-prefix-LSAs 1605 for a given area, distinguished by their Link State ID 1606 fields. 1608 A network link's Designated Router originates an intra- 1609 area-prefix-LSA to advertise the link's prefixes 1610 throughout the area. For a link L, L's Designated Router 1611 builds an intra-area-prefix-LSA in the following 1612 fashion: 1614 o In order to indicate that the prefixes are to be 1615 associated with the Link L, the fields Referenced LS 1616 type, Referenced Link State ID, and Referenced 1617 Advertising Router are set to the corresponding 1618 fields in Link L's Network LSA (namely LS type, Link 1619 State ID, and Advertising Router respectively). This 1620 means that Referenced LS Type is set to 0x2002, 1621 Referenced Link State ID is set to the Designated 1622 Router's Interface ID on Link L, and Referenced 1623 Advertising Router is set to the Designated Router's 1624 Router ID. 1626 o Each Link-LSA associated with Link L is examined 1627 (these are in the Designated Router's interface 1628 structure for Link L). If the Link-LSA's Advertising 1629 Router is fully adjacent to the Designated Router, 1630 the list of prefixes in the Link-LSA is copied into 1631 the intra-area-prefix-LSA that is being built. 1632 Prefixes having the NU-bit and/or LA-bit set in 1633 their Options field should not be copied, nor should 1634 link-local addresses be copied. Each prefix is 1635 described by the PrefixLength, PrefixOptions, and 1636 Address Prefix fields. Multiple prefixes having the 1637 same PrefixLength and Address Prefix are considered 1638 to be duplicates; in this case their Prefix Options 1639 fields should be merged by logically OR'ing the 1640 fields together, and a single resulting prefix 1641 should be copied into the intra-area-prefix-LSA. The 1642 Metric field for all prefixes is set to 0. 1644 o The "# prefixes" field is set to the number of 1645 prefixes that the router has copied into the LSA. If 1646 necessary, the list of prefixes can be spread across 1647 multiple intra-area-prefix-LSAs in order to keep the 1648 LSA size small. 1650 A router builds an intra-area-prefix-LSA to advertise 1651 its own prefixes, and those of its attached stub network 1652 links. A Router RTX would build its intra-area-prefix- 1653 LSA in the following fashion: 1655 o In order to indicate that the prefixes are to be 1656 associated with the Router RTX itself, RTX sets 1657 Referenced LS type to 0x2001, Referenced Link State 1658 ID to 0, and Referenced Advertising Router to RTX's 1659 own Router ID. 1661 o Router RTX examines its list of interfaces to the 1662 area. If the interface is in state Down, its 1663 prefixes are not included. If the interface has been 1664 reported in RTX's router-LSA as a Type 2 link 1665 description (link to transit network), its prefixes 1666 are not included (they will be included in the 1667 intra-area-prefix-LSA for the link instead). If the 1668 interface type is point-to-point or Point-to- 1669 MultiPoint, or the interface is in state Loopback, 1670 the site-local and global scope IPv6 addresses 1671 associated with the interface (if any) are copied 1672 into the intra-area-prefix-LSA, setting the LA-bit 1673 in the PrefixOptions field, and setting the 1674 PrefixLength to 128 and the Metric to 0. Otherwise, 1675 the list of site-local and global prefixes 1676 configured in RTX for the link are copied into the 1677 intra-area-prefix-LSA by specifying the 1678 PrefixLength, PrefixOptions, and Address Prefix 1679 fields. The Metric field for each of these prefixes 1680 is set to the interface's output cost. 1682 o RTX adds the IPv6 prefixes for any directly attached 1683 hosts (see Section C.7) to the intra-area-prefix- 1684 LSA. 1686 o If RTX has one or more virtual links configured 1687 through the area, it includes one of its site-local 1688 or global scope IPv6 interface addresses in the LSA 1689 (if it hasn't already), setting the LA-bit in the 1690 PrefixOptions field, and setting the PrefixLength to 1691 128 and the Metric to 0. This information will be 1692 used later in the routing calculation so that the 1693 two ends of the virtual link can discover each 1694 other's IPv6 addresses. 1696 o The "# prefixes" field is set to the number of 1697 prefixes that the router has copied into the LSA. If 1698 necessary, the list of prefixes can be spread across 1699 multiple intra-area-prefix-LSAs in order to keep the 1700 LSA size small. 1702 For example, the intra-area-prefix-LSA originated by RT4 1703 for Network N3 (assuming that RT4 is N3's Designated 1704 Router), and the intra-area-prefix-LSA originated into 1705 Area 1 by Router RT3 for its own prefixes, are pictured 1706 below. 1708 ; Intra-area-prefix-LSA 1709 ; for network link N3 1711 LS age = 0 ;newly (re)originated 1712 LS type = 0x2009 ;Link-LSA 1713 Link State ID = 5 ;or something 1714 Advertising Router = 192.1.1.4 ;RT4's Router ID 1715 # prefixes = 1 1716 Referenced LS type = 0x2002 ;network-LSA reference 1717 Referenced Link State ID = 1 1718 Referenced Advertising Router = 192.1.1.4 1719 PrefixLength = 56 ;N3's prefix 1720 PrefixOptions = 0 1721 Metric = 0 1722 Address Prefix = 5f00:0000:c001:0100 ;pad 1724 ; RT3's Intra-area-prefix-LSA 1725 ; for its own prefixes 1727 LS age = 0 ;newly (re)originated 1728 LS type = 0x2009 ;Link-LSA 1729 Link State ID = 177 ;or something 1730 Advertising Router = 192.1.1.3 ;RT3's Router ID 1731 # prefixes = 1 1732 Referenced LS type = 0x2001 ;router-LSA reference 1733 Referenced Link State ID = 0 1734 Referenced Advertising Router = 192.1.1.3 1735 PrefixLength = 56 ;N4's prefix 1736 PrefixOptions = 0 1737 Metric = 2 ;N4 interface cost 1738 Address Prefix = 5f00:0000:c001:0400 ;pad 1740 3.5. Flooding 1742 Most of the flooding algorithm remains unchanged from the IPv4 1743 flooding mechanisms described in Section 13 of [Ref1]. In 1744 particular, the processes for determining which LSA instance is 1745 newer (Section 13.1 of [Ref1]), responding to updates of self- 1746 originated LSAs (Section 13.4 of [Ref1]), sending Link State 1747 Acknowledgment packets (Section 13.5 of [Ref1]), retransmitting 1748 LSAs (Section 13.6 of [Ref1]) and receiving Link State 1749 Acknowledgment packets (Section 13.7 of [Ref1]) are exactly the 1750 same for IPv6 and IPv4. 1752 However, the addition of flooding scope and handling options for 1753 unrecognized LSA types (see Section A.4.2.1) has caused some 1754 changes in the OSPF flooding algorithm: the reception of Link 1755 State Updates (Section 13 in [Ref1]) and the sending of Link 1756 State Updates (Section 13.3 of [Ref1]) must take into account 1757 the LSA's scope and U-bit setting. Also, installation of LSAs 1758 into the OSPF database (Section 13.2 of [Ref1]) causes different 1759 events in IPv6, due to the reorganization of LSA types and 1760 contents in IPv6. These changes are described in detail below. 1762 3.5.1. Receiving Link State Update packets 1764 The encoding of flooding scope in the LS type and the need 1765 to process unknown LS types causes modifications to the 1766 processing of received Link State Update packets. As in 1767 IPv4, each LSA in a received Link State Update packet is 1768 examined. In IPv4, eight steps are executed for each LSA, as 1769 described in Section 13 of [Ref1]. For IPv6, all the steps 1770 are the same, except that Steps 2 and 3 are modified as 1771 follows: 1773 (2) Examine the LSA's LS type. If the LS type is unknown, 1774 the area has been configured as a stub area, and either 1775 the LSA's flooding scope is set to "AS flooding scope" 1776 or the U-bit of the LS type is set to 1 (flood even when 1777 unrecognized), then discard the LSA and get the next one 1778 from the Link State Update Packet. This generalizes the 1779 IPv4 behavior where AS-external-LSAs are not flooding 1780 into/throughout stub areas. See Section 2.10 for more 1781 details. 1783 (3) Else if the flooding scope of the LSA is set to 1784 "reserved", discard the LSA and get the next one from 1785 the Link State Update Packet. 1787 Steps 5b (sending Link State Update packets) and 5d 1788 (installing LSAs in the link state database) in Section 13 1789 of [Ref1] are also somewhat different for IPv6, as described 1790 in Sections 3.5.2 and 3.5.3 below. 1792 3.5.2. Sending Link State Update packets 1794 The sending of Link State Update packets is described in 1795 Section 13.3 of [Ref1]. For IPv4 and IPv6, the steps for 1796 sending a Link State Update packet are the same (steps 1 1797 through 5 of Section 13.3 in [Ref1]). However, the list of 1798 eligible interfaces out which to flood the LSA is different. 1799 For IPv6, the eligible interfaces are selected based on the 1800 following factors: 1802 o The LSA's flooding scope. 1804 o For LSAs with area or link-local flooding scoping, the 1805 particular area or interface that the LSA is associated 1806 with. 1808 o Whether the LSA has a recognized LS type. 1810 o The setting of the U-bit in the LS type. If the U-bit is 1811 set to 0, unrecognized LS types are treated as having 1812 link-local scope. If set to 1, unrecognized LS types are 1813 stored and flooded as if they were recognized. 1815 Choosing the set of eligible interfaces then breaks into the 1816 following cases: 1818 Case 1 1819 The LSA's LS type is recognized. In this case, the set 1820 of eligible interfaces is set depending on the flooding 1821 scope encoded in the LS type. If the flooding scope is 1822 "AS flooding scope", the eligible interfaces are all 1823 router interfaces excepting virtual links and those 1824 connecting to stub areas. If the flooding scope is "area 1825 flooding scope", the set of eligible interfaces are 1826 those interfaces connecting to the LSA's associated 1827 area. If the flooding scope is "link-local flooding 1828 scope", then there is a single eligible interface, the 1829 one connecting to the LSA's associated link (which, when 1830 the LSA is received in a Link State Update packet, is 1831 also the interface the LSA was received on). 1833 Case 2 1834 The LS type is unrecognized, and the U-bit in the LS 1835 Type is set to 0 (treat the LSA as if it had link-local 1836 flooding scope). In this case there is a single eligible 1837 interface, namely, the interface on which the LSA was 1838 received. 1840 Case 3 1841 The LS type is unrecognized, and the U-bit in the LS 1842 Type is set to 1 (store and flood the LSA, as if type 1843 understood). In this case, select the eligible 1844 interfaces based on the encoded flooding scope as in 1845 Case 1 above. However, in this case interfaces attaching 1846 to stub areas are excluded regardless of flooding scope. 1848 A further decision must sometimes be made before adding an 1849 LSA to a given neighbor's link-state retransmission list 1850 (Step 1d in Section 13.3 of [Ref1]). If the LS type is 1851 recognized by the router, but not by the neighbor (as can be 1852 determined by examining the Options field that the neighbor 1853 advertised in its Database Description packet) and the LSA's 1854 U-bit is set to 0, then the LSA should be added to the 1855 neighbor's link-state retransmission list if and only if 1856 that neighbor is the Designated Router or Backup Designated 1857 Router for the attached link. The LS types described in 1858 detail by this memo, namely router-LSAs (LS type 0x2001), 1859 network-LSAs (0x2002), Inter-Area-Prefix-LSAs (0x2003), 1860 Inter-Area-Router-LSAs (0x2004), AS-External-LSAs (0x4005), 1861 Link-LSAs (0x0008) and Intra-Area-Prefix-LSAs (0x2009) are 1862 assumed to be understood by all routers. However, as an 1863 example the group-membership-LSA (0x2006) is understood only 1864 by MOSPF routers and since it has its U-bit set to 0, it 1865 should only be forwarded to a non-MOSPF neighbor (determined 1866 by examining the MC-bit in the neighbor's Database 1867 Description packets' Options field) when the neighbor is 1868 Designated Router or Backup Designated Router for the 1869 attached link. 1871 The previous paragraph solves a problem in IPv4 OSPF 1872 extensions such as MOSPF, which require that the Designated 1873 Router support the extension in order to have the new LSA 1874 types flooded across broadcast and NBMA networks (see 1875 Section 10.2 of [Ref8]). 1877 3.5.3. Installing LSAs in the database 1879 There are three separate places to store LSAs, depending on 1880 their flooding scope. LSAs with AS flooding scope are stored 1881 in the global OSPF data structure (see Section 3.1) as long 1882 as their LS type is known or their U-bit is 1. LSAs with 1883 area flooding scope are stored in the appropriate area data 1884 structure (see Section 3.1.1) as long as their LS type is 1885 known or their U-bit is 1. LSAs with link-local flooding 1886 scope, and those LSAs with unknown LS type and U-bit set to 1887 0 (treat the LSA as if it had link-local flooding scope) are 1888 stored in the appropriate interface structure. 1890 When storing the LSA into the link-state database, a check 1891 must be made to see whether the LSA's contents have changed. 1892 Changes in contents are indicated exactly as in Section 13.2 1893 of [Ref1]. When an LSA's contents have been changed, the 1894 following parts of the routing table must be recalculated, 1895 based on the LSA's LS type: 1897 Router-LSAs, Network-LSAs and Intra-Area-Prefix-LSAs 1898 The entire routing table is recalculated, starting with 1899 the shortest path calculation for each area (see Section 1900 3.8). 1902 Link-LSAs 1903 The next hop of some of the routing table's entries, 1904 which is always an IPv6 link-local address, may need to 1905 be recalculated. Link-local LSAs provide the OSPF Router 1906 ID to link-local address mapping used in the next hop 1907 calculation. See Section 3.8.1.1 for details. 1909 Inter-Area-Prefix-LSAs and Inter-Area-Router-LSAs 1910 The best route to the destination described by the LSA 1911 must be recalculated (see Section 16.5 in [Ref1]). If 1912 this destination is an AS boundary router, it may also 1913 be necessary to re-examine all the AS-external-LSAs. 1915 AS-external-LSAs 1916 The best route to the destination described by the AS- 1917 external-LSA must be recalculated (see Section 16.6 in 1918 [Ref1]). 1920 As in IPv4, any old instance of the LSA must be removed from 1921 the database when the new LSA is installed. This old 1922 instance must also be removed from all neighbors' Link state 1923 retransmission lists. 1925 3.6. Definition of self-originated LSAs 1927 In IPv6 the definition of a self-originated LSA has been 1928 simplified from the IPv4 definition appearing in Sections 13.4 1929 and 14.1 of [Ref1]. For IPv6, self-originated LSAs are those 1930 LSAs whose Advertising Router is equal to the router's own 1931 Router ID. 1933 3.7. Virtual links 1935 OSPF virtual links for IPv4 are described in Section 15 of 1936 [Ref1]. Virtual links are the same in IPv6, with the following 1937 exceptions: 1939 o LSAs having AS flooding scope are never flooded over virtual 1940 adjacencies, nor are LSAs with AS flooding scope summarized 1941 over virtual adjacencies during the Database Exchange 1942 process. This is a generalization of the IPv4 treatment of 1943 AS-external-LSAs. 1945 o The IPv6 interface address of a virtual link must be an IPv6 1946 address having site-local or global scope, instead of the 1947 link-local addresses used by other interface types. This 1948 address is used as the IPv6 source for OSPF protocol packets 1949 sent over the virtual link. 1951 o Likewise, the virtual neighbor's IPv6 address is an IPv6 1952 address with site-local or global scope. To enable the 1953 discovery of a virtual neighbor's IPv6 address during the 1954 routing calculation, the neighbor advertises its virtual 1955 link's IPv6 interface address in an Intra-Area-Prefix-LSA 1956 originated for the virtual link's transit area (see Sections 1957 3.4.3.7 and 3.8.1). 1959 o Like all other IPv6 OSPF interfaces, virtual links are 1960 assigned unique (within the router) Interface IDs. These are 1961 advertised in Hellos sent over the virtual link, and in the 1962 router's router-LSAs. 1964 o IPv6 has no concept of TOS, so all discussions of TOS in 1965 Section 15 of [Ref1] are not applicable to OSPF for IPv6. 1967 3.8. Routing table calculation 1969 The IPv6 OSPF routing calculation proceeds along the same lines 1970 as the IPv4 OSPF routing calculation, following the five steps 1971 specified by Section 16 of [Ref1]. High level differences 1972 between the IPv6 and IPv4 calculations include: 1974 o Prefix information has been removed from router-LSAs, and 1975 now is advertised in intra-area-prefix-LSAs. Whenever [Ref1] 1976 specifies that stub networks within router-LSAs be examined, 1977 IPv6 will instead examine prefixes within intra-area- 1978 prefix-LSAs. 1980 o Type 3 and 4 summary-LSAs have been renamed inter-area- 1981 prefix-LSAs and inter-area-router-LSAs (respectively). 1983 o Addressing information is no longer encoded in Link State 1984 IDs, and must instead be found within the body of LSAs. 1986 o In IPv6, a router can originate multiple router-LSAs within 1987 a single area, distinguished by Link State ID. These 1988 router-LSAs must be treated as a single aggregate by the 1989 area's shortest path calculation (see Section 3.8.1). 1991 o IPv6 has no concept of TOS; all TOS routing calculations in 1992 [Ref1] are inapplicable to OSPF for IPv6. In particular, 1993 Section 16.9 of [Ref1] can be ignored for IPv6. 1995 For each area, routing table entries have been created for the 1996 area's routers and transit links, in order to store the results 1997 of the area's shortest-path tree calculation (see Section 1998 3.8.1). These entries are then used when processing intra-area- 1999 prefix-LSAs, inter-area-prefix-LSAs and inter-area-router-LSAs, 2000 as described in Section 3.8.2. 2002 Events generated as a result of routing table changes (Section 2003 16.7 of [Ref1]), and the equal-cost multipath logic (Section 2004 16.8 of [Ref1]) are identical for both IPv4 and IPv6. 2006 3.8.1. Calculating the shortest path tree for an area 2008 The IPv4 shortest path calculation is contained in Section 2009 16.1 of [Ref1]. The graph used by the shortest-path tree 2010 calculation is identical for both IPv4 and IPv6. The graph's 2011 vertices are routers and transit links, represented by 2012 router-LSAs and network-LSAs respectively. A router is 2013 identified by its OSPF Router ID, while a transit link is 2014 identified by its Designated Router's Interface ID and OSPF 2015 Router ID. Both routers and transit links have associated 2016 routing table entries within the area (see Section 3.3). 2018 Section 16.1 of [Ref1] splits up the shortest path 2019 calculations into two stages. First the Dijkstra calculation 2020 is performed, and then the stub links are added onto the 2021 tree as leaves. The IPv6 calculation maintains this split. 2023 The Dijkstra calculation for IPv6 is identical to that 2024 specified for IPv4, with the following exceptions 2025 (referencing the steps from the Dijkstra calculation as 2026 described in Section 16.1 of [Ref1]): 2028 o The Vertex ID for a router is the OSPF Router ID. The 2029 Vertex ID for a transit network is a combination of the 2030 Interface ID and OSPF Router ID of the network's 2031 Designated Router. 2033 o In Step 2, when a router Vertex V has just been added to 2034 the shortest path tree, there may be multiple LSAs 2035 associated with the router. All Router-LSAs with 2036 Advertising Router set to V's OSPF Router ID must 2037 processed as an aggregate, treating them as fragments of 2038 a single large router-LSA. The Options field and the 2039 router type bits (bits W, V, E and B) should always be 2040 taken from "fragment" with the smallest Link State ID. 2042 o Step 2a is not needed in IPv6, as there are no longer 2043 stub network links in router-LSAs. 2045 o In Step 2b, if W is a router, there may again be 2046 multiple LSAs associated with the router. All Router- 2047 LSAs with Advertising Router set to W's OSPF Router ID 2048 must processed as an aggregate, treating them as 2049 fragments of a single large router-LSA. 2051 o In Step 4, there are now per-area routing table entries 2052 for each of an area's routers, instead of just the area 2053 border routers. These entries subsume all the 2054 functionality of IPv4's area border router routing table 2055 entries, including the maintenance of virtual links. 2056 When the router added to the area routing table in this 2057 step is the other end of a virtual link, the virtual 2058 neighbor's IP address is set as follows: The collection 2059 of intra-area-prefix-LSAs originated by the virtual 2060 neighbor is examined, with the virtual neighbor's IP 2061 address being set to the first prefix encountered having 2062 the "LA-bit" set. 2064 o Routing table entries for transit networks, which are no 2065 longer associated with IP networks, are also modified in 2066 Step 4. 2068 The next stage of the shortest path calculation proceeds 2069 similarly to the two steps of the second stage of Section 2070 16.1 in [Ref1]. However, instead of examining the stub links 2071 within router-LSAs, the list of the area's intra-area- 2072 prefix-LSAs is examined. A prefix advertisement whose "NU- 2073 bit" is set should not be included in the routing 2074 calculation. The cost of any advertised prefix is the sum of 2075 the prefix' advertised metric plus the cost to the transit 2076 vertex (either router or transit network) identified by 2077 intra-area-prefix-LSA's Referenced LS type, Referenced Link 2078 State ID and Referenced Advertising Router fields. This 2079 latter cost is stored in the transit vertex' routing table 2080 entry for the area. 2082 3.8.1.1. The next hop calculation 2084 In IPv6, the calculation of the next hop's IPv6 address 2085 (which will be a link-local address) proceeds along the 2086 same lines as the IPv4 next hop calculation (see Section 2087 16.1.1 of [Ref1]). The only difference is in calculating 2088 the next hop IPv6 address for a router (call it Router 2089 X) which shares a link with the calculating router. In 2090 this case the calculating router assigns the next hop 2091 IPv6 address to be the link-local interface address 2092 contained in Router X's Link-LSA (see Section A.4.8) for 2093 the link. This procedure is necessary since on some 2094 links, such as NBMA links, the two routers need not be 2095 neighbors, and therefore might not be exchanging OSPF 2096 Hellos. 2098 3.8.2. Calculating the inter-area routes 2100 Calculation of inter-area routes for IPv6 proceeds along the 2101 same lines as the IPv4 calculation in Section 16.2 of 2102 [Ref1], with the following modifications: 2104 o The names of the Type 3 summary-LSAs and Type 4 2105 summary-LSAs have been changed to inter-area-prefix-LSAs 2106 and inter-area-router-LSAs respectively. 2108 o The Link State ID of the above LSA types no longer 2109 encodes the network or router described by the LSA. 2110 Instead, an address prefix is contained in the body of 2111 an inter-area-prefix-LSA, and a described router's OSPF 2112 Router ID is carried in the body of an inter-area- 2113 router-LSA. 2115 o Prefixes having the "NU-bit" set in their Prefix Options 2116 field should be ignored by the inter-area route 2117 calculation. 2119 When a single inter-area-prefix-LSA or inter-area-router-LSA 2120 has changed, the incremental calculations outlined in 2121 Section 16.5 of [Ref1] can be performed instead of 2122 recalculating the entire routing table. 2124 3.8.3. Examining transit areas' summary-LSAs 2126 Examination of transit areas' summary-LSAs in IPv6 proceeds 2127 along the same lines as the IPv4 calculation in Section 16.3 2128 of [Ref1], modified in the same way as the IPv6 inter-area 2129 route calculation in Section 3.8.2. 2131 3.8.4. Calculating AS external routes 2133 The IPv6 AS external route calculation proceeds along the 2134 same lines as the IPv4 calculation in Section 16.4 of 2135 [Ref1], with the following exceptions: 2137 o The Link State ID of the AS-external-LSA types no longer 2138 encodes the network described by the LSA. Instead, an 2139 address prefix is contained in the body of an AS- 2140 external-LSA. 2142 o The default route is described by AS-external-LSAs which 2143 advertise zero length prefixes. 2145 o Instead of comparing the AS-external-LSA's Forwarding 2146 address field to 0.0.0.0 to see whether a forwarding 2147 address has been used, bit F of the external-LSA is 2148 examined. A forwarding address is in use if and only if 2149 bit F is set. 2151 o Prefixes having the "NU-bit" set in their Prefix Options 2152 field should be ignored by the inter-area route 2153 calculation. 2155 When a single AS-external-LSA has changed, the incremental 2156 calculations outlined in Section 16.6 of [Ref1] can be 2157 performed instead of recalculating the entire routing table. 2159 References 2161 [Ref1] Moy, J., "OSPF Version 2", Internet Draft, , Cascade, September 1996. 2164 [Ref2] McKenzie, A., "ISO Transport Protocol specification ISO DP 2165 8073", RFC 905, ISO, April 1984. 2167 [Ref3] McCloghrie, K., and M. Rose, "Management Information Base 2168 for network management of TCP/IP-based internets: MIB-II", 2169 STD 17, RFC 1213, Hughes LAN Systems, Performance Systems 2170 International, March 1991. 2172 [Ref4] Fuller, V., T. Li, J. Yu, and K. Varadhan, "Classless 2173 Inter-Domain Routing (CIDR): an Address Assignment and 2174 Aggregation Strategy", RFC1519, BARRNet, cisco, MERIT, 2175 OARnet, September 1993. 2177 [Ref5] Varadhan, K., S. Hares and Y. Rekhter, "BGP4/IDRP for IP--- 2178 OSPF Interaction", RFC1745, December 1994 2180 [Ref6] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 2181 1700, USC/Information Sciences Institute, October 1994. 2183 [Ref7] deSouza, O., and M. Rodrigues, "Guidelines for Running OSPF 2184 Over Frame Relay Networks", RFC 1586, March 1994. 2186 [Ref8] Moy, J., "Multicast Extensions to OSPF", RFC 1584, Proteon, 2187 Inc., March 1994. 2189 [Ref9] Coltun, R. and V. Fuller, "The OSPF NSSA Option", RFC 1587, 2190 RainbowBridge Communications, Stanford University, March 2191 1994. 2193 [Ref10] Ferguson, D., "The OSPF External Attributes LSA", 2194 unpublished. 2196 [Ref11] Moy, J., "Extending OSPF to Support Demand Circuits", RFC 2197 1793, Cascade, April 1995. 2199 [Ref12] Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191, 2200 DECWRL, Stanford University, November 1990. 2202 [Ref13] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP- 2203 4)", RFC 1771, T.J. Watson Research Center, IBM Corp., cisco 2204 Systems, March 1995. 2206 [Ref14] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2207 (IPv6) Specification", RFC 1883, Xerox PARC, Ipsilon 2208 Networks, December 1995. 2210 [Ref15] Deering, S. and R. Hinden, "IP Version 6 Addressing 2211 Architecture", RFC 1884, Xerox PARC, Ipsilon Networks, 2212 December 1995. 2214 [Ref16] Conta, A. and S. Deering, "Internet Control Message Protocol 2215 (ICMPv6) for the Internet Protocol Version 6 (IPv6) 2216 Specification" RFC 1885, Digital Equipment Corporation, 2217 Xerox PARC, December 1995. 2219 [Ref17] Narten, T., E. Nordmark and W. Simpson, "Neighbor Discovery 2220 for IP Version 6 (IPv6)", RFC 1970, August 1996. 2222 [Ref18] McCann, J., S. Deering and J. Mogul, "Path MTU Discovery for 2223 IP version 6", RFC 1981, August 1996. 2225 [Ref19] Atkinson, R., "IP Authentication Header", RFC 1826, Naval 2226 Research Laboratory, August 1995. 2228 [Ref20] Atkinson, R., "IP Encapsulating Security Payload (ESP)", RFC 2229 1827, Naval Research Laboratory, August 1995. 2231 A. OSPF data formats 2233 This appendix describes the format of OSPF protocol packets and OSPF 2234 LSAs. The OSPF protocol runs directly over the IPv6 network layer. 2235 Before any data formats are described, the details of the OSPF 2236 encapsulation are explained. 2238 Next the OSPF Options field is described. This field describes 2239 various capabilities that may or may not be supported by pieces of 2240 the OSPF routing domain. The OSPF Options field is contained in OSPF 2241 Hello packets, Database Description packets and in OSPF LSAs. 2243 OSPF packet formats are detailed in Section A.3. 2245 A description of OSPF LSAs appears in Section A.4. This section 2246 describes how IPv6 address prefixes are represented within LSAs, 2247 details the standard LSA header, and then provides formats for each 2248 of the specific LSA types. 2250 A.1 Encapsulation of OSPF packets 2252 OSPF runs directly over the IPv6's network layer. OSPF packets are 2253 therefore encapsulated solely by IPv6 and local data-link headers. 2255 OSPF does not define a way to fragment its protocol packets, and 2256 depends on IPv6 fragmentation when transmitting packets larger than 2257 the link MTU. If necessary, the length of OSPF packets can be up to 2258 65,535 bytes. The OSPF packet types that are likely to be large 2259 (Database Description Packets, Link State Request, Link State 2260 Update, and Link State Acknowledgment packets) can usually be split 2261 into several separate protocol packets, without loss of 2262 functionality. This is recommended; IPv6 fragmentation should be 2263 avoided whenever possible. Using this reasoning, an attempt should 2264 be made to limit the sizes of OSPF packets sent over virtual links 2265 to 576 bytes unless Path MTU Discovery is being performed. 2267 The other important features of OSPF's IPv6 encapsulation are: 2269 o Use of IPv6 multicast. Some OSPF messages are multicast, when 2270 sent over broadcast networks. Two distinct IP multicast 2271 addresses are used. Packets sent to these multicast addresses 2272 should never be forwarded; they are meant to travel a single hop 2273 only. As such, the multicast addresses have been chosen with 2274 link-local scope, and packets sent to these addresses should 2275 have their IPv6 Hop Limit set to 1. 2277 AllSPFRouters 2278 This multicast address has been assigned the value FF02::5. 2280 All routers running OSPF should be prepared to receive 2281 packets sent to this address. Hello packets are always sent 2282 to this destination. Also, certain OSPF protocol packets 2283 are sent to this address during the flooding procedure. 2285 AllDRouters 2286 This multicast address has been assigned the value FF02::6. 2287 Both the Designated Router and Backup Designated Router must 2288 be prepared to receive packets destined to this address. 2289 Certain OSPF protocol packets are sent to this address 2290 during the flooding procedure. 2292 o OSPF is IP protocol 89. This number should be inserted in the 2293 Next Header field of the encapsulating IPv6 header. 2295 o Routing protocol packets are sent with IPv6 Priority field set 2296 to 7 (internet control traffic). OSPF protocol packets should 2297 be given precedence over regular IPv6 data traffic, in both 2298 sending and receiving. 2300 A.2 The Options field 2302 The 24-bit OSPF Options field is present in OSPF Hello packets, 2303 Database Description packets and certain LSAs (router-LSAs, 2304 network-LSAs, inter-area-router-LSAs and link-LSAs). The Options 2305 field enables OSPF routers to support (or not support) optional 2306 capabilities, and to communicate their capability level to other 2307 OSPF routers. Through this mechanism routers of differing 2308 capabilities can be mixed within an OSPF routing domain. 2310 An option mismatch between routers can cause a variety of behaviors, 2311 depending on the particular option. Some option mismatches prevent 2312 neighbor relationships from forming (e.g., the E-bit below); these 2313 mismatches are discovered through the sending and receiving of Hello 2314 packets. Some option mismatches prevent particular LSA types from 2315 being flooded across adjacencies (e.g., the MC-bit below); these are 2316 discovered through the sending and receiving of Database Description 2317 packets. Some option mismatches prevent routers from being included 2318 in one or more of the various routing calculations because of their 2319 reduced functionality (again the MC-bit is an example); these 2320 mismatches are discovered by examining LSAs. 2322 Six bits of the OSPF Options field have been assigned. Each bit is 2323 described briefly below. Routers should reset (i.e. clear) 2324 unrecognized bits in the Options field when sending Hello packets or 2325 Database Description packets and when originating LSAs. Conversely, 2326 routers encountering unrecognized Option bits in received Hello 2327 Packets, Database Description packets or LSAs should ignore the 2328 capability and process the packet/LSA normally. 2330 1 2 2331 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+--+--+--+--+ 2333 | | | | | | | | | | | | | | | | | | |DC| R| N|MC| E|V6| 2334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+--+--+--+--+ 2336 The Options field 2338 V6-bit 2339 If this bit is clear, the router/link should be excluded from 2340 IPv6 routing calculations. See Section 3.8 of this memo. 2342 E-bit 2343 This bit describes the way AS-external-LSAs are flooded, as 2344 described in Sections 3.6, 9.5, 10.8 and 12.1.2 of [Ref1]. 2346 MC-bit 2347 This bit describes whether IP multicast datagrams are forwarded 2348 according to the specifications in [Ref7]. 2350 N-bit 2351 This bit describes the handling of Type-7 LSAs, as specified in 2352 [Ref8]. 2354 R-bit 2355 This bit (the `Router' bit) indicates whether the originator is 2356 an active router. If the router bit is clear routes which 2357 transit the advertising node cannot be computed. Clearing the 2358 router bit would be appropriate for a multi-homed host that 2359 wants to participate in routing, but does not want to forward 2360 non-locally addressed packets. 2362 DC-bit 2363 This bit describes the router's handling of demand circuits, as 2364 specified in [Ref10]. 2366 A.3 OSPF Packet Formats 2368 There are five distinct OSPF packet types. All OSPF packet types 2369 begin with a standard 16 byte header. This header is described 2370 first. Each packet type is then described in a succeeding section. 2371 In these sections each packet's division into fields is displayed, 2372 and then the field definitions are enumerated. 2374 All OSPF packet types (other than the OSPF Hello packets) deal with 2375 lists of LSAs. For example, Link State Update packets implement the 2376 flooding of LSAs throughout the OSPF routing domain. The format of 2377 LSAs is described in Section A.4. 2379 The receive processing of OSPF packets is detailed in Section 3.2.2. 2380 The sending of OSPF packets is explained in Section 3.2.1. 2382 A.3.1 The OSPF packet header 2384 Every OSPF packet starts with a standard 16 byte header. Together 2385 with the encapsulating IPv6 headers, the OSPF header contains all 2386 the information necessary to determine whether the packet should be 2387 accepted for further processing. This determination is described in 2388 Section 3.2.2 of this memo. 2390 0 1 2 3 2391 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 2392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2393 | Version # | Type | Packet length | 2394 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2395 | Router ID | 2396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2397 | Area ID | 2398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2399 | Checksum | Instance ID | 0 | 2400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2402 Version # 2403 The OSPF version number. This specification documents version 3 2404 of the OSPF protocol. 2406 Type 2407 The OSPF packet types are as follows. See Sections A.3.2 through 2408 A.3.6 for details. 2410 Type Description 2411 ________________________________ 2412 1 Hello 2413 2 Database Description 2414 3 Link State Request 2415 4 Link State Update 2416 5 Link State Acknowledgment 2418 Packet length 2419 The length of the OSPF protocol packet in bytes. This length 2420 includes the standard OSPF header. 2422 Router ID 2423 The Router ID of the packet's source. 2425 Area ID 2426 A 32 bit number identifying the area that this packet belongs 2427 to. All OSPF packets are associated with a single area. Most 2428 travel a single hop only. Packets travelling over a virtual 2429 link are labelled with the backbone Area ID of 0. 2431 Checksum 2432 The standard IP checksum of the entire contents of the packet, 2433 starting with the OSPF packet header. This checksum is 2434 calculated as the 16-bit one's complement of the one's 2435 complement sum of all the 16-bit words in the packet. If the 2436 packet's length is not an integral number of 16-bit words, the 2437 packet is padded with a byte of zero before checksumming. 2439 Instance ID 2440 Enables multiple instances of OSPF to be run over a single link. 2441 Each protocol instance would be assigned a separate Instance ID; 2442 the Instance ID has local link significance only. Received 2443 packets whose Instance ID is not equal to the receiving 2444 interface's Instance ID are discarded. 2446 0 These fields are reserved. They must be 0. 2448 A.3.2 The Hello packet 2450 Hello packets are OSPF packet type 1. These packets are sent 2451 periodically on all interfaces (including virtual links) in order to 2452 establish and maintain neighbor relationships. In addition, Hello 2453 Packets are multicast on those links having a multicast or broadcast 2454 capability, enabling dynamic discovery of neighboring routers. 2456 All routers connected to a common link must agree on certain 2457 parameters (HelloInterval and RouterDeadInterval). These parameters 2458 are included in Hello packets, so that differences can inhibit the 2459 forming of neighbor relationships. The Hello packet also contains 2460 fields used in Designated Router election (Designated Router ID and 2461 Backup Designated Router ID), and fields used to detect bi- 2462 directionality (the Router IDs of all neighbors whose Hellos have 2463 been recently received). 2465 0 1 2 3 2466 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 2467 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2468 | 3 | 1 | Packet length | 2469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2470 | Router ID | 2471 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2472 | Area ID | 2473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2474 | Checksum | Instance ID | 0 | 2475 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2476 | Interface ID | 2477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2478 | Rtr Pri | Options | 2479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2480 | HelloInterval | RouterDeadInterval | 2481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2482 | Designated Router ID | 2483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2484 | Backup Designated Router ID | 2485 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2486 | Neighbor ID | 2487 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2488 | ... | 2490 Interface ID 2491 32-bit number uniquely identifying this interface among the 2492 collection of this router's interfaces. For example, in some 2493 implementations it may be possible to use the MIB-II IfIndex. 2495 Rtr Pri 2496 This router's Router Priority. Used in (Backup) Designated 2497 Router election. If set to 0, the router will be ineligible to 2498 become (Backup) Designated Router. 2500 Options 2501 The optional capabilities supported by the router, as documented 2502 in Section A.2. 2504 HelloInterval 2505 The number of seconds between this router's Hello packets. 2507 RouterDeadInterval 2508 The number of seconds before declaring a silent router down. 2510 Designated Router ID 2511 The identity of the Designated Router for this network, in the 2512 view of the sending router. The Designated Router is identified 2513 by its Router ID. Set to 0.0.0.0 if there is no Designated 2514 Router. 2516 Backup Designated Router ID 2517 The identity of the Backup Designated Router for this network, 2518 in the view of the sending router. The Backup Designated Router 2519 is identified by its IP Router ID. Set to 0.0.0.0 if there is 2520 no Backup Designated Router. 2522 Neighbor ID 2523 The Router IDs of each router from whom valid Hello packets have 2524 been seen recently on the network. Recently means in the last 2525 RouterDeadInterval seconds. 2527 A.3.3 The Database Description packet 2529 Database Description packets are OSPF packet type 2. These packets 2530 are exchanged when an adjacency is being initialized. They describe 2531 the contents of the link-state database. Multiple packets may be 2532 used to describe the database. For this purpose a poll-response 2533 procedure is used. One of the routers is designated to be the 2534 master, the other the slave. The master sends Database Description 2535 packets (polls) which are acknowledged by Database Description 2536 packets sent by the slave (responses). The responses are linked to 2537 the polls via the packets' DD sequence numbers. 2539 0 1 2 3 2540 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 2541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2542 | 3 | 2 | Packet length | 2543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2544 | Router ID | 2545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2546 | Area ID | 2547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2548 | Checksum | Instance ID | 0 | 2549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2550 |0|0|0|0|0|I|M|MS Options | 2551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2552 | DD sequence number | 2553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2554 | | 2555 +- -+ 2556 | | 2557 +- An LSA Header -+ 2558 | | 2559 +- -+ 2560 | | 2561 +- -+ 2562 | | 2563 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2564 | ... | 2566 The format of the Database Description packet is very similar to 2567 both the Link State Request and Link State Acknowledgment packets. 2568 The main part of all three is a list of items, each item describing 2569 a piece of the link-state database. The sending of Database 2570 Description Packets is documented in Section 10.8 of [Ref1]. The 2571 reception of Database Description packets is documented in Section 2572 10.6 of [Ref1]. 2574 I-bit 2575 The Init bit. When set to 1, this packet is the first in the 2576 sequence of Database Description Packets. 2578 M-bit 2579 The More bit. When set to 1, it indicates that more Database 2580 Description Packets are to follow. 2582 MS-bit 2583 The Master/Slave bit. When set to 1, it indicates that the 2584 router is the master during the Database Exchange process. 2585 Otherwise, the router is the slave. 2587 Options 2588 The optional capabilities supported by the router, as documented 2589 in Section A.2. 2591 DD sequence number 2592 Used to sequence the collection of Database Description Packets. 2593 The initial value (indicated by the Init bit being set) should 2594 be unique. The DD sequence number then increments until the 2595 complete database description has been sent. 2597 The rest of the packet consists of a (possibly partial) list of the 2598 link-state database's pieces. Each LSA in the database is described 2599 by its LSA header. The LSA header is documented in Section A.4.1. 2600 It contains all the information required to uniquely identify both 2601 the LSA and the LSA's current instance. 2603 A.3.4 The Link State Request packet 2605 Link State Request packets are OSPF packet type 3. After exchanging 2606 Database Description packets with a neighboring router, a router may 2607 find that parts of its link-state database are out-of-date. The 2608 Link State Request packet is used to request the pieces of the 2609 neighbor's database that are more up-to-date. Multiple Link State 2610 Request packets may need to be used. 2612 A router that sends a Link State Request packet has in mind the 2613 precise instance of the database pieces it is requesting. Each 2614 instance is defined by its LS sequence number, LS checksum, and LS 2615 age, although these fields are not specified in the Link State 2616 Request Packet itself. The router may receive even more recent 2617 instances in response. 2619 The sending of Link State Request packets is documented in Section 2620 10.9 of [Ref1]. The reception of Link State Request packets is 2621 documented in Section 10.7 of [Ref1]. 2623 0 1 2 3 2624 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 2625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2626 | 3 | 3 | Packet length | 2627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2628 | Router ID | 2629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2630 | Area ID | 2631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2632 | Checksum | Instance ID | 0 | 2633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2634 | 0 | LS type | 2635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2636 | Link State ID | 2637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2638 | Advertising Router | 2639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2640 | ... | 2642 Each LSA requested is specified by its LS type, Link State ID, and 2643 Advertising Router. This uniquely identifies the LSA, but not its 2644 instance. Link State Request packets are understood to be requests 2645 for the most recent instance (whatever that might be). 2647 A.3.5 The Link State Update packet 2649 Link State Update packets are OSPF packet type 4. These packets 2650 implement the flooding of LSAs. Each Link State Update packet 2651 carries a collection of LSAs one hop further from their origin. 2652 Several LSAs may be included in a single packet. 2654 Link State Update packets are multicast on those physical networks 2655 that support multicast/broadcast. In order to make the flooding 2656 procedure reliable, flooded LSAs are acknowledged in Link State 2657 Acknowledgment packets. If retransmission of certain LSAs is 2658 necessary, the retransmitted LSAs are always carried by unicast Link 2659 State Update packets. For more information on the reliable flooding 2660 of LSAs, consult Section 3.5. 2662 0 1 2 3 2663 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 2664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2665 | 3 | 4 | Packet length | 2666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2667 | Router ID | 2668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2669 | Area ID | 2670 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2671 | Checksum | Instance ID | 0 | 2672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2673 | # LSAs | 2674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2675 | | 2676 +- +-+ 2677 | LSAs | 2678 +- +-+ 2679 | ... | 2681 # LSAs 2682 The number of LSAs included in this update. 2684 The body of the Link State Update packet consists of a list of LSAs. 2685 Each LSA begins with a common 20 byte header, described in Section 2686 A.4.2. Detailed formats of the different types of LSAs are described 2687 in Section A.4. 2689 A.3.6 The Link State Acknowledgment packet 2691 Link State Acknowledgment Packets are OSPF packet type 5. To make 2692 the flooding of LSAs reliable, flooded LSAs are explicitly 2693 acknowledged. This acknowledgment is accomplished through the 2694 sending and receiving of Link State Acknowledgment packets. The 2695 sending of Link State Acknowledgement packets is documented in 2696 Section 13.5 of [Ref1]. The reception of Link State Acknowledgement 2697 packets is documented in Section 13.7 of [Ref1]. 2699 Multiple LSAs can be acknowledged in a single Link State 2700 Acknowledgment packet. Depending on the state of the sending 2701 interface and the sender of the corresponding Link State Update 2702 packet, a Link State Acknowledgment packet is sent either to the 2703 multicast address AllSPFRouters, to the multicast address 2704 AllDRouters, or as a unicast (see Section 13.5 of [Ref1] for 2705 details). 2707 The format of this packet is similar to that of the Data Description 2708 packet. The body of both packets is simply a list of LSA headers. 2710 0 1 2 3 2711 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 2712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2713 | 3 | 5 | Packet length | 2714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2715 | Router ID | 2716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2717 | Area ID | 2718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2719 | Checksum | Instance ID | 0 | 2720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2721 | | 2722 +- -+ 2723 | | 2724 +- An LSA Header -+ 2725 | | 2726 +- -+ 2727 | | 2728 +- -+ 2729 | | 2730 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2731 | ... | 2733 Each acknowledged LSA is described by its LSA header. The LSA 2734 header is documented in Section A.4.2. It contains all the 2735 information required to uniquely identify both the LSA and the LSA's 2736 current instance. 2738 A.4 LSA formats 2740 This memo defines seven distinct types of LSAs. Each LSA begins 2741 with a standard 20 byte LSA header. This header is explained in 2742 Section A.4.2. Succeeding sections then diagram the separate LSA 2743 types. 2745 Each LSA describes a piece of the OSPF routing domain. Every router 2746 originates a router-LSA. A network-LSA is advertised for each link 2747 by its Designated Router. A router's link-local addresses are 2748 advertised to its neighbors in link-LSAs. IPv6 prefixes are 2749 advertised in intra-area-prefix-LSAs, inter-area-prefix-LSAs and 2750 AS-external-LSAs. Location of specific routers can be advertised 2751 across area boundaries in inter-area-router-LSAs. All LSAs are then 2752 flooded throughout the OSPF routing domain. The flooding algorithm 2753 is reliable, ensuring that all routers have the same collection of 2754 LSAs. (See Section 3.5 for more information concerning the flooding 2755 algorithm). This collection of LSAs is called the link-state 2756 database. 2758 From the link state database, each router constructs a shortest path 2759 tree with itself as root. This yields a routing table (see Section 2760 11 of [Ref1]). For the details of the routing table build process, 2761 see Section 3.8. 2763 A.4.1 IPv6 Prefix Representation 2765 IPv6 addresses are bit strings of length 128. IPv6 routing 2766 algorithms, and OSPF for IPv6 in particular, advertise IPv6 address 2767 prefixes. IPv6 address prefixes are bit strings whose length ranges 2768 between 0 and 128 bits (inclusive). 2770 Within OSPF, IPv6 address prefixes are always represented by a 2771 combination of three fields: PrefixLength, PrefixOptions, and 2772 Address Prefix. PrefixLength is the length in bits of the prefix. 2773 PrefixOptions is an 8-bit field describing various capabilities 2774 associated with the prefix (see Section A.4.2). Address Prefix is an 2775 encoding of the prefix itself as an even multiple of 32-bit words, 2776 padding with zero bits as necessary; this encoding consumes 2777 (PrefixLength + 31) / 32) 32-bit words. 2779 The default route is represented by a prefix of length 0. 2781 Examples of IPv6 Prefix representation in OSPF can be found in 2782 Sections A.4.5, A.4.7, A.4.8 and A.4.9. 2784 A.4.1.1 Prefix Options 2786 Each prefix is advertised along with an 8-bit field of capabilities. 2787 These serve as input to the various routing calculations, allowing, 2788 for example, certain prefixes to be ignored in some cases, or to be 2789 marked as not readvertisable in others. 2791 0 1 2 3 4 5 6 7 2792 +--+--+--+--+--+--+--+--+ 2793 | | | | | P|MC|LA|NU| 2794 +--+--+--+--+--+--+--+--+ 2796 The Prefix Options field 2798 NU-bit 2799 The "no unicast" capability bit. If set, the prefix should be 2800 excluded from IPv6 unicast calculations, otherwise it should be 2801 included. 2803 LA-bit 2804 The "local address" capability bit. If set, the prefix is 2805 actually an IPv6 interface address of the advertising router. 2807 MC-bit 2808 The "multicast" capability bit. If set, the prefix should be 2809 included in IPv6 multicast routing calculations, otherwise it 2810 should be excluded. 2812 P-bit 2813 The "propagate" bit. Set on NSSA area prefixes that should be 2814 readvertised at the NSSA area border. 2816 A.4.2 The LSA header 2818 All LSAs begin with a common 20 byte header. This header contains 2819 enough information to uniquely identify the LSA (LS type, Link State 2820 ID, and Advertising Router). Multiple instances of the LSA may 2821 exist in the routing domain at the same time. It is then necessary 2822 to determine which instance is more recent. This is accomplished by 2823 examining the LS age, LS sequence number and LS checksum fields that 2824 are also contained in the LSA header. 2826 0 1 2 3 2827 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 2828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2829 | LS age | LS type | 2830 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2831 | Link State ID | 2832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2833 | Advertising Router | 2834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2835 | LS sequence number | 2836 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2837 | LS checksum | length | 2838 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2840 LS age 2841 The time in seconds since the LSA was originated. 2843 LS type 2844 The LS type field indicates the function performed by the LSA. 2845 The high-order three bits of LS type encode generic properties 2846 of the LSA, while the remainder (called LSA function code) 2847 indicate the LSA's specific functionality. See Section A.4.2.1 2848 for a detailed description of LS type. 2850 Link State ID 2851 Together with LS type and Advertising Router, uniquely 2852 identifies the LSA in the link-state database. 2854 Advertising Router 2855 The Router ID of the router that originated the LSA. For 2856 example, in network-LSAs this field is equal to the Router ID of 2857 the network's Designated Router. 2859 LS sequence number 2860 Detects old or duplicate LSAs. Successive instances of an LSA 2861 are given successive LS sequence numbers. See Section 12.1.6 in 2862 [Ref1] for more details. 2864 LS checksum 2865 The Fletcher checksum of the complete contents of the LSA, 2866 including the LSA header but excluding the LS age field. See 2867 Section 12.1.7 in [Ref1] for more details. 2869 length 2870 The length in bytes of the LSA. This includes the 20 byte LSA 2871 header. 2873 A.4.2.1 LS type 2875 The LS type field indicates the function performed by the LSA. The 2876 high-order three bits of LS type encode generic properties of the 2877 LSA, while the remainder (called LSA function code) indicate the 2878 LSA's specific functionality. The format of the LS type is as 2879 follows: 2881 1 2882 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2883 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 2884 |U |S2|S1| LSA Function Code | 2885 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 2887 The U bit indicates how the LSA should be handled by a router which 2888 does not recognize the LSA's function code. Its values are: 2890 U-bit LSA Handling 2891 ____________________________________________________________ 2892 0 Treat the LSA as if it had link-local flooding scope 2893 1 Store and flood the LSA, as if type understood 2895 The S1 and S2 bits indicate the flooding scope of the LSA. The 2896 values are: 2898 _______________________________________________________________________ 2899 0 0 Link-Local Scoping. Flooded only on link it is originated on. 2900 0 1 Area Scoping. Flooded to all routers in the originating area 2901 1 0 AS Scoping. Flooded to all routers in the AS 2902 1 1 Reserved 2904 The LSA function codes are defined as follows. The origination and 2905 processing of these LSA function codes are defined elsewhere in this 2906 memo, except for the group-membership-LSA (see [Ref7]) and the 2907 Type-7-LSA (see [Ref8]). Each LSA function code also implies a 2908 specific setting for the U, S1 and S2 bits, as shown below. 2910 LSA function code LS Type Description 2911 ___________________________________________________ 2912 1 0x2001 Router-LSA 2913 2 0x2002 Network-LSA 2914 3 0x2003 Inter-Area-Prefix-LSA 2915 4 0x2004 Inter-Area-Router-LSA 2916 5 0x4005 AS-External-LSA 2917 6 0x2006 Group-membership-LSA 2918 7 0x2007 Type-7-LSA 2919 8 0x0008 Link-LSA 2920 9 0x2009 Intra-Area-Prefix-LSA 2921 A.4.3 Router-LSAs 2923 Router-LSAs have LS type equal to 0x2001. Each router in an area 2924 originates one or more router-LSAs. The complete collection of 2925 router-LSAs originated by the router describe the state and cost of 2926 the router's interfaces to the area. For details concerning the 2927 construction of router-LSAs, see Section 3.4.3.1. Router-LSAs are 2928 flooded throughout a single area only. 2930 0 1 2 3 2931 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 2932 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2933 | LS age |0|0|1| 1 | 2934 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2935 | Link State ID | 2936 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2937 | Advertising Router | 2938 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2939 | LS sequence number | 2940 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2941 | LS checksum | length | 2942 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2943 | 0 |W|V|E|B| Options | 2944 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2945 | Type | 0 | Metric | 2946 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2947 | Interface ID | 2948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2949 | Neighbor Interface ID | 2950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2951 | Neighbor Router ID | 2952 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2953 | ... | 2954 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2955 | Type | 0 | Metric | 2956 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2957 | Interface ID | 2958 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2959 | Neighbor Interface ID | 2960 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2961 | Neighbor Router ID | 2962 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2963 | ... | 2965 A single router may originate one or more Router LSAs, distinguished 2966 by their Link-State IDs (which are chosen arbitrarily by the 2967 originating router). The Options field and V, E and B bits should 2968 be the same in all Router LSAs from a single originator. However, 2969 in the case of a mismatch the values in the LSA with the lowest Link 2970 State ID take precedence. When more than one Router LSA is received 2971 from a single router, the links are processed as if concatenated 2972 into a single LSA. 2974 bit V 2975 When set, the router is an endpoint of one or more fully 2976 adjacent virtual links having the described area as Transit area 2977 (V is for virtual link endpoint). 2979 bit E 2980 When set, the router is an AS boundary router (E is for 2981 external). 2983 bit B 2984 When set, the router is an area border router (B is for border). 2986 bit W 2987 When set, the router is a wild-card multicast receiver. When 2988 running MOSPF, these routers receive all multicast datagrams, 2989 regardless of destination. See Sections 3, 4 and A.2 of [Ref8] 2990 for details. 2992 Options 2993 The optional capabilities supported by the router, as documented 2994 in Section A.2. 2996 The following fields are used to describe each router interface. 2997 The Type field indicates the kind of interface being described. It 2998 may be an interface to a transit network, a point-to-point 2999 connection to another router or a virtual link. The values of all 3000 the other fields describing a router interface depend on the 3001 interface's Type field. 3003 Type 3004 The kind of interface being described. One of the following: 3006 Type Description 3007 __________________________________________________ 3008 1 Point-to-point connection to another router 3009 2 Connection to a transit network 3010 3 Reserved 3011 4 Virtual link 3013 Metric 3014 The cost of using this router interface, for outbound traffic. 3016 Interface ID 3017 The Interface ID assigned to the interface being described. See 3018 Sections 3.1.2 and C.3. 3020 Neighbor Interface ID 3021 The Interface ID the neighbor router (or the attached link's 3022 Designated Router, for Type 2 interfaces) has been advertising 3023 in hello packets sent on the attached link. 3025 Neighbor Router ID 3026 The Router ID the neighbor router (or the attached link's 3027 Designated Router, for Type 2 interfaces). 3029 For Type 2 links, the combination of Neighbor Interface ID and 3030 Neighbor Router ID allows the network-LSA for the attached link 3031 to be found in the link-state database. 3033 A.4.4 Network-LSAs 3035 Network-LSAs have LS type equal to 0x2002. A network-LSA is 3036 originated for each broadcast and NBMA link in the area which 3037 supports two or more routers. The network-LSA is originated by the 3038 link's Designated Router. The LSA describes all routers attached to 3039 the link, including the Designated Router itself. The LSA's Link 3040 State ID field is set to the Interface ID that the Designated Router 3041 has been advertising in Hello packets on the link. 3043 The distance from the network to all attached routers is zero. This 3044 is why the metric fields need not be specified in the network-LSA. 3045 For details concerning the construction of network-LSAs, see Section 3046 3.4.3.2. 3048 0 1 2 3 3049 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 3050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3051 | LS age |0|0|1| 2 | 3052 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3053 | Link State ID | 3054 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3055 | Advertising Router | 3056 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3057 | LS sequence number | 3058 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3059 | LS checksum | length | 3060 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3061 | 0 | Options | 3062 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3063 | Attached Router | 3064 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3065 | ... | 3067 Attached Router 3068 The Router IDs of each of the routers attached to the link. 3069 Actually, only those routers that are fully adjacent to the 3070 Designated Router are listed. The Designated Router includes 3071 itself in this list. The number of routers included can be 3072 deduced from the LSA header's length field. 3074 A.4.5 Inter-Area-Prefix-LSAs 3076 Inter-Area-Prefix-LSAs have LS type equal to 0x2003. These LSAs are 3077 are the IPv6 equivalent of OSPF for IPv4's type 3 summary-LSAs (see 3078 Section 12.4.3 of [Ref1]). Originated by area border routers, they 3079 describe routes to IPv6 address prefixes that belong to other areas. 3080 A separate Inter-Area-Prefix-LSA is originated for each IPv6 address 3081 prefix. For details concerning the construction of Inter-Area- 3082 Prefix-LSAs, see Section 3.4.3.3. 3084 For stub areas, Inter-Area-Prefix-LSAs can also be used to describe 3085 a (per-area) default route. Default summary routes are used in stub 3086 areas instead of flooding a complete set of external routes. When 3087 describing a default summary route, the Inter-Area-Prefix-LSA's 3088 PrefixLength is set to 0. 3090 0 1 2 3 3091 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 3092 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3093 | LS age |0|0|1| 3 | 3094 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3095 | Link State ID | 3096 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3097 | Advertising Router | 3098 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3099 | LS sequence number | 3100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3101 | LS checksum | length | 3102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3103 | 0 | Metric | 3104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3105 | PrefixLength | PrefixOptions | (0) | 3106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3107 | Address Prefix | 3108 | ... | 3109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3111 Metric 3112 The cost of this route. Expressed in the same units as the 3113 interface costs in the router-LSAs. When the Inter-Area-Prefix- 3114 LSA is describing a route to a range of addresses (see Section 3115 C.2) the cost is set to the maximum cost to any reachable 3116 component of the address range. 3118 PrefixLength, PrefixOptions and Address Prefix 3119 Representation of the IPv6 address prefix, as described in 3120 Section A.4.1. 3122 A.4.6 Inter-Area-Router-LSAs 3124 Inter-Area-Router-LSAs have LS type equal to 0x2004. These LSAs are 3125 are the IPv6 equivalent of OSPF for IPv4's type 4 summary-LSAs (see 3126 Section 12.4.3 of [Ref1]). Originated by area border routers, they 3127 describe routes to routers in other areas. (To see why it is 3128 necessary to advertise the location of each ASBR, consult Section 3129 16.4 in [Ref1].) Each LSA describes a route to a single router. For 3130 details concerning the construction of Inter-Area-Router-LSAs, see 3131 Section 3.4.3.4. 3133 0 1 2 3 3134 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 3135 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3136 | LS age |0|0|1| 4 | 3137 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3138 | Link State ID | 3139 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3140 | Advertising Router | 3141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3142 | LS sequence number | 3143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3144 | LS checksum | length | 3145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3146 | 0 | Options | 3147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3148 | 0 | Metric | 3149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3150 | Destination Router ID | 3151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3153 Options 3154 The optional capabilities supported by the router, as documented 3155 in Section A.2. 3157 Metric 3158 The cost of this route. Expressed in the same units as the 3159 interface costs in the router-LSAs. 3161 Destination Router ID 3162 The Router ID of the router being described by the LSA. 3164 A.4.7 AS-external-LSAs 3166 AS-external-LSAs have LS type equal to 0x4005. These LSAs are 3167 originated by AS boundary routers, and describe destinations 3168 external to the AS. Each LSA describes a route to a single IPv6 3169 address prefix. For details concerning the construction of AS- 3170 external-LSAs, see Section 3.4.3.5. 3172 AS-external-LSAs can be used to describe a default route. Default 3173 routes are used when no specific route exists to the destination. 3174 When describing a default route, the AS-external-LSA's PrefixLength 3175 is set to 0. 3177 0 1 2 3 3178 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 3179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3180 | LS age |0|1|0| 5 | 3181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3182 | Link State ID | 3183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3184 | Advertising Router | 3185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3186 | LS sequence number | 3187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3188 | LS checksum | length | 3189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3190 | |E|F|T| Metric | 3191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3192 | PrefixLength | PrefixOptions | Referenced LS Type | 3193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3194 | Address Prefix | 3195 | ... | 3196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3197 | | 3198 +- -+ 3199 | | 3200 +- Forwarding Address (Optional) -+ 3201 | | 3202 +- -+ 3203 | | 3204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3205 | External Route Tag (Optional) | 3206 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3207 | Referenced Link State ID (Optional) | 3208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3210 bit E 3211 The type of external metric. If bit E is set, the metric 3212 specified is a Type 2 external metric. This means the metric is 3213 considered larger than any intra-AS path. If bit E is zero, the 3214 specified metric is a Type 1 external metric. This means that 3215 it is expressed in the same units as the link state metric 3216 (i.e., the same units as interface cost). 3218 bit F 3219 If set, a Forwarding Address has been included in the LSA. 3221 bit T 3222 If set, an External Route Tag has been included in the LSA. 3224 Metric 3225 The cost of this route. Interpretation depends on the external 3226 type indication (bit E above). 3228 PrefixLength, PrefixOptions and Address Prefix 3229 Representation of the IPv6 address prefix, as described in 3230 Section A.4.1. 3232 Referenced LS type 3233 If non-zero, an LSA with this LS type is to be associated with 3234 this LSA (see Referenced Link State ID below). 3236 Forwarding address 3237 A fully qualified IPv6 address (128 bits). Included in the LSA 3238 if and only if bit F has been set. If included, Data traffic 3239 for the advertised destination and TOS will be forwarded to this 3240 address. Must not be set to the IPv6 Unspecified Address 3241 (0:0:0:0:0:0:0:0). 3243 External Route Tag 3244 A 32-bit field which may be used to communicate additional 3245 information between AS boundary routers; see [Ref5] for example 3246 usage. Included in the LSA if and only if bit T has been set. 3248 Referenced Link State ID 3249 Included if and only if Reference LS Type is non-zero. If 3250 included, additional information concerning the advertised 3251 external route can be found in the LSA having LS type equal to 3252 "Referenced LS Type", Link State ID equal to "Referenced Link 3253 State ID" and Advertising Router the same as that specified in 3254 the AS-external-LSA's link state header. This additional 3255 information is not used by the OSPF protocol itself. It may be 3256 used to communicate information between AS boundary routers; the 3257 precise nature of such information is outside the scope of this 3258 specification. 3260 All, none or some of the fields labeled Forwarding address, External 3261 Route Tag and Referenced Link State ID may be present in the AS- 3262 external-LSA (as indicated by the setting of bit F, bit T and 3263 Referenced LS type respectively). However, when present Forwarding 3264 Address always comes first, with External Route Tag always preceding 3265 Referenced Link State ID. 3267 A.4.8 Link-LSAs 3269 Link-LSAs have LS type equal to 0x0008. A router originates a 3270 separate Link-LSA for each link it is attached to. These LSAs have 3271 local-link flooding scope; they are never flooded beyond the link 3272 that they are associated with. Link-LSAs have three purposes: 1) 3273 they provide the router's link-local address to all other routers 3274 attached to the link and 2) they inform other routers attached to 3275 the link of a list of IPv6 prefixes to associate with the link and 3276 3) they allow the router to assert a collection of Options bits to 3277 associate with the Network-LSA that will be originated for the link. 3279 A link-LSA's Link State ID is set equal to the originating router's 3280 Interface ID on the link. 3281 0 1 2 3 3282 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 3283 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3284 | LS age |0|0|0| 8 | 3285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3286 | Link State ID | 3287 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3288 | Advertising Router | 3289 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3290 | LS sequence number | 3291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3292 | LS checksum | length | 3293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3294 | Rtr Pri | Options | 3295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3296 | | 3297 +- -+ 3298 | | 3299 +- Link-local Interface Address -+ 3300 | | 3301 +- -+ 3302 | | 3303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3304 | # prefixes | 3305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3306 | PrefixLength | PrefixOptions | (0) | 3307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3308 | Address Prefix | 3309 | ... | 3310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3311 | ... | 3312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3313 | PrefixLength | PrefixOptions | (0) | 3314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3315 | Address Prefix | 3316 | ... | 3317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3319 Rtr Pri 3320 The Router Priority of the interface attaching the originating 3321 router to the link. 3323 Options 3324 The set of Options bits that the router would like set in the 3325 Network-LSA that will be originated for the link. 3327 Link-local Interface Address 3328 The originating router's link-local interface address on the 3329 link. 3331 # prefixes 3332 The number of IPv6 address prefixes contained in the LSA. 3334 The rest of the link-LSA contains a list of IPv6 prefixes to be 3335 associated with the link. 3337 PrefixLength, PrefixOptions and Address Prefix 3338 Representation of an IPv6 address prefix, as described in 3339 Section A.4.1. 3341 A.4.9 Intra-Area-Prefix-LSAs 3343 Intra-Area-Prefix-LSAs have LS type equal to 0x2009. A router uses 3344 Intra-Area-Prefix-LSAs to advertise one or more IPv6 address 3345 prefixes that are associated with a) the router itself, b) an 3346 attached stub network segment or c) an attached transit network 3347 segment. In IPv4, a) and b) were accomplished via the router's 3348 router-LSA, and c) via a network-LSA. However, in OSPF for IPv6 all 3349 addressing information has been removed from router-LSAs and 3350 network-LSAs, leading to the introduction of the Intra-Area-Prefix- 3351 LSA. 3353 A router can originate multiple Intra-Area-Prefix-LSAs for each 3354 router or transit network; each such LSA is distinguished by its 3355 Link State ID. 3357 0 1 2 3 3358 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 3359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3360 | LS age |0|0|1| 9 | 3361 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3362 | Link State ID | 3363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3364 | Advertising Router | 3365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3366 | LS sequence number | 3367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3368 | LS checksum | length | 3369 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3370 | # prefixes | Referenced LS type | 3371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3372 | Referenced Link State ID | 3373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3374 | Referenced Advertising Router | 3375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3376 | PrefixLength | PrefixOptions | Metric | 3377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3378 | Address Prefix | 3379 | ... | 3380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3381 | ... | 3382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3383 | PrefixLength | PrefixOptions | Metric | 3384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3385 | Address Prefix | 3386 | ... | 3387 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3389 # prefixes 3390 The number of IPv6 address prefixes contained in the LSA. 3392 Referenced LS type, Referenced Link State ID and Referenced 3393 Advertising Router 3394 Identifies the router-LSA or network-LSA with which the IPv6 3395 address prefixes should be associated. If Referenced LS type is 3396 1, the prefixes are associated with a router-LSA, Referenced 3397 Link State ID should be 0 and Referenced Advertising Router 3398 should be the originating router's Router ID. If Referenced LS 3399 type is 2, the prefixes are associated with a network-LSA, 3400 Referenced Link State ID should be the Interface ID of the 3401 link's Designated Router and Referenced Advertising Router 3402 should be the Designated Router's Router ID. 3404 The rest of the Intra-Area-Prefix-LSA contains a list of IPv6 3405 prefixes to be associated with the router or transit link, together 3406 with the cost of each prefix. 3408 PrefixLength, PrefixOptions and Address Prefix 3409 Representation of an IPv6 address prefix, as described in 3410 Section A.4.1. 3412 Metric 3413 The cost of this prefix. Expressed in the same units as the 3414 interface costs in the router-LSAs. 3416 B. Architectural Constants 3418 Architectural constants for the OSPF protocol are defined in 3419 Appendix C of [Ref1]. The only difference for OSPF for IPv6 is that 3420 DefaultDestination is encoded as a prefix of length 0 (see Section 3421 A.4.1). 3423 C. Configurable Constants 3425 The OSPF protocol has quite a few configurable parameters. These 3426 parameters are listed below. They are grouped into general 3427 functional categories (area parameters, interface parameters, etc.). 3428 Sample values are given for some of the parameters. 3430 Some parameter settings need to be consistent among groups of 3431 routers. For example, all routers in an area must agree on that 3432 area's parameters, and all routers attached to a network must agree 3433 on that network's HelloInterval and RouterDeadInterval. 3435 Some parameters may be determined by router algorithms outside of 3436 this specification (e.g., the address of a host connected to the 3437 router via a SLIP line). From OSPF's point of view, these items are 3438 still configurable. 3440 C.1 Global parameters 3442 In general, a separate copy of the OSPF protocol is run for each 3443 area. Because of this, most configuration parameters are 3444 defined on a per-area basis. The few global configuration 3445 parameters are listed below. 3447 Router ID 3448 This is a 32-bit number that uniquely identifies the router 3449 in the Autonomous System. If a router's OSPF Router ID is 3450 changed, the router's OSPF software should be restarted 3451 before the new Router ID takes effect. Before restarting in 3452 order to change its Router ID, the router should flush its 3453 self-originated LSAs from the routing domain (see Section 3454 14.1 of [Ref1]), or they will persist for up to MaxAge 3455 minutes. 3457 Because the size of the Router ID is smaller than an IPv6 3458 address, it cannot be set to one of the router's IPv6 3459 addresses (as is commonly done for IPv4). Possible Router ID 3460 assignment procedures for IPv6 include: a) assign the IPv6 3461 Router ID as one of the router's IPv4 addresses or b) assign 3462 IPv6 Router IDs through some local administrative procedure 3463 (similar to procedures used by manufacturers to assign 3464 product serial numbers). 3466 The Router ID of 0.0.0.0 is reserved, and should not be 3467 used. 3469 C.2 Area parameters 3471 All routers belonging to an area must agree on that area's 3472 configuration. Disagreements between two routers will lead to 3473 an inability for adjacencies to form between them, with a 3474 resulting hindrance to the flow of routing protocol and data 3475 traffic. The following items must be configured for an area: 3477 Area ID 3478 This is a 32-bit number that identifies the area. The Area 3479 ID of 0 is reserved for the backbone. 3481 List of address ranges 3482 Address ranges control the advertisement of routes across 3483 area boundaries. Each address range consists of the 3484 following items: 3486 [IPv6 prefix, prefix length] 3487 Describes the collection of IPv6 addresses contained 3488 in the address range. 3490 Status Set to either Advertise or DoNotAdvertise. Routing 3491 information is condensed at area boundaries. 3492 External to the area, at most a single route is 3493 advertised (via a inter-area-prefix-LSA) for each 3494 address range. The route is advertised if and only 3495 if the address range's Status is set to Advertise. 3496 Unadvertised ranges allow the existence of certain 3497 networks to be intentionally hidden from other 3498 areas. Status is set to Advertise by default. 3500 ExternalRoutingCapability 3501 Whether AS-external-LSAs will be flooded into/throughout the 3502 area. If AS-external-LSAs are excluded from the area, the 3503 area is called a "stub". Internal to stub areas, routing to 3504 external destinations will be based solely on a default 3505 inter-area route. The backbone cannot be configured as a 3506 stub area. Also, virtual links cannot be configured through 3507 stub areas. For more information, see Section 3.6 of 3508 [Ref1]. 3510 StubDefaultCost 3511 If the area has been configured as a stub area, and the 3512 router itself is an area border router, then the 3513 StubDefaultCost indicates the cost of the default inter- 3514 area-prefix-LSA that the router should advertise into the 3515 area. See Section 12.4.3.1 of [Ref1] for more information. 3517 C.3 Router interface parameters 3519 Some of the configurable router interface parameters (such as 3520 Area ID, HelloInterval and RouterDeadInterval) actually imply 3521 properties of the attached links, and therefore must be 3522 consistent across all the routers attached to that link. The 3523 parameters that must be configured for a router interface are: 3525 IPv6 link-local address 3526 The IPv6 link-local address associated with this interface. 3527 May be learned through auto-configuration. 3529 Area ID 3530 The OSPF area to which the attached link belongs. 3532 Instance ID 3533 The OSPF protocol instance associated with this OSPF 3534 interface. Defaults to 0. 3536 Interface ID 3537 32-bit number uniquely identifying this interface among the 3538 collection of this router's interfaces. For example, in some 3539 implementations it may be possible to use the MIB-II 3540 IfIndex. 3542 IPv6 prefixes 3543 The list of IPv6 prefixes to associate with the link. These 3544 will be advertised in intra-area-prefix-LSAs. 3546 Interface output cost(s) 3547 The cost of sending a packet on the interface, expressed in 3548 the link state metric. This is advertised as the link cost 3549 for this interface in the router's router-LSA. The interface 3550 output cost must always be greater than 0. 3552 RxmtInterval 3553 The number of seconds between LSA retransmissions, for 3554 adjacencies belonging to this interface. Also used when 3555 retransmitting Database Description and Link State Request 3556 Packets. This should be well over the expected round-trip 3557 delay between any two routers on the attached link. The 3558 setting of this value should be conservative or needless 3559 retransmissions will result. Sample value for a local area 3560 network: 5 seconds. 3562 InfTransDelay 3563 The estimated number of seconds it takes to transmit a Link 3564 State Update Packet over this interface. LSAs contained in 3565 the update packet must have their age incremented by this 3566 amount before transmission. This value should take into 3567 account the transmission and propagation delays of the 3568 interface. It must be greater than 0. Sample value for a 3569 local area network: 1 second. 3571 Router Priority 3572 An 8-bit unsigned integer. When two routers attached to a 3573 network both attempt to become Designated Router, the one 3574 with the highest Router Priority takes precedence. If there 3575 is still a tie, the router with the highest Router ID takes 3576 precedence. A router whose Router Priority is set to 0 is 3577 ineligible to become Designated Router on the attached link. 3578 Router Priority is only configured for interfaces to 3579 broadcast and NBMA networks. 3581 HelloInterval 3582 The length of time, in seconds, between the Hello Packets 3583 that the router sends on the interface. This value is 3584 advertised in the router's Hello Packets. It must be the 3585 same for all routers attached to a common link. The smaller 3586 the HelloInterval, the faster topological changes will be 3587 detected; however, more OSPF routing protocol traffic will 3588 ensue. Sample value for a X.25 PDN: 30 seconds. Sample 3589 value for a local area network (LAN): 10 seconds. 3591 RouterDeadInterval 3592 After ceasing to hear a router's Hello Packets, the number 3593 of seconds before its neighbors declare the router down. 3594 This is also advertised in the router's Hello Packets in 3595 their RouterDeadInterval field. This should be some 3596 multiple of the HelloInterval (say 4). This value again 3597 must be the same for all routers attached to a common link. 3599 C.4 Virtual link parameters 3601 Virtual links are used to restore/increase connectivity of the 3602 backbone. Virtual links may be configured between any pair of 3603 area border routers having interfaces to a common (non-backbone) 3604 area. The virtual link appears as an unnumbered point-to-point 3605 link in the graph for the backbone. The virtual link must be 3606 configured in both of the area border routers. 3608 A virtual link appears in router-LSAs (for the backbone) as if 3609 it were a separate router interface to the backbone. As such, 3610 it has most of the parameters associated with a router interface 3611 (see Section C.3). Virtual links do not have link-local 3612 addresses, but instead use one of the router's global-scope or 3613 site-local IPv6 addresses as the IP source in OSPF protocol 3614 packets it sends along the virtual link. Router Priority is not 3615 used on virtual links. Interface output cost is not configured 3616 on virtual links, but is dynamically set to be the cost of the 3617 intra-area path between the two endpoint routers. The parameter 3618 RxmtInterval must be configured, and should be well over the 3619 expected round-trip delay between the two routers. This may be 3620 hard to estimate for a virtual link; it is better to err on the 3621 side of making it too large. 3623 A virtual link is defined by the following two configurable 3624 parameters: the Router ID of the virtual link's other endpoint, 3625 and the (non-backbone) area through which the virtual link runs 3626 (referred to as the virtual link's Transit area). Virtual links 3627 cannot be configured through stub areas. 3629 C.5 NBMA network parameters 3631 OSPF treats an NBMA network much like it treats a broadcast 3632 network. Since there may be many routers attached to the 3633 network, a Designated Router is selected for the network. This 3634 Designated Router then originates a network-LSA, which lists all 3635 routers attached to the NBMA network. 3637 However, due to the lack of broadcast capabilities, it may be 3638 necessary to use configuration parameters in the Designated 3639 Router selection. These parameters will only need to be 3640 configured in those routers that are themselves eligible to 3641 become Designated Router (i.e., those router's whose Router 3642 Priority for the network is non-zero), and then only if no 3643 automatic procedure for discovering neighbors exists: 3645 List of all other attached routers 3646 The list of all other routers attached to the NBMA network. 3647 Each router is configured with its Router ID and IPv6 link- 3648 local address on the network. Also, for each router listed, 3649 that router's eligibility to become Designated Router must 3650 be defined. When an interface to a NBMA network comes up, 3651 the router sends Hello Packets only to those neighbors 3652 eligible to become Designated Router, until the identity of 3653 the Designated Router is discovered. 3655 PollInterval 3656 If a neighboring router has become inactive (Hello Packets 3657 have not been seen for RouterDeadInterval seconds), it may 3658 still be necessary to send Hello Packets to the dead 3659 neighbor. These Hello Packets will be sent at the reduced 3660 rate PollInterval, which should be much larger than 3661 HelloInterval. Sample value for a PDN X.25 network: 2 3662 minutes. 3664 C.6 Point-to-MultiPoint network parameters 3666 On Point-to-MultiPoint networks, it may be necessary to 3667 configure the set of neighbors that are directly reachable over 3668 the Point-to-MultiPoint network. Each neighbor is configured 3669 with its Router ID and IPv6 link-local address on the network. 3670 Designated Routers are not elected on Point-to-MultiPoint 3671 networks, so the Designated Router eligibility of configured 3672 neighbors is undefined. 3674 C.7 Host route parameters 3676 Host routes are advertised in intra-area-prefix-LSAs as fully 3677 qualified IPv6 prefixes (i.e., prefix length set equal to 128 3678 bits). They indicate either router interfaces to point-to-point 3679 networks, looped router interfaces, or IPv6 hosts that are 3680 directly connected to the router (e.g., via a PPP connection). 3681 For each host directly connected to the router, the following 3682 items must be configured: 3684 Host IPv6 address 3685 The IPv6 address of the host. 3687 Cost of link to host 3688 The cost of sending a packet to the host, in terms of the 3689 link state metric. However, since the host probably has only 3690 a single connection to the internet, the actual configured 3691 cost(s) in many cases is unimportant (i.e., will have no 3692 effect on routing). 3694 Area ID 3695 The OSPF area to which the host belongs. 3697 Security Considerations 3699 When running over IPv6, OSPF relies on the IP Authentication Header 3700 (see [Ref19]) and the IP Encapsulating Security Payload (see 3701 [Ref20]) to ensure integrity and authentication/confidentiality of 3702 routing exchanges. 3704 Authors Addresses 3706 Rob Coltun 3707 FORE Systems 3708 Phone: (301) 571-2521 3709 Email: rcoltun@fore.com 3711 Dennis Ferguson 3712 Juniper Networks 3713 101 University Avenue, Suite 240 3714 Palo Alto, CA 94301 3715 Phone: (415) 614-4143 3716 Email: dennis@jnx.com 3718 John Moy 3719 Cascade Communications Corp. 3720 5 Carlisle Road 3721 Westford, MA 01886 3722 Phone: (508) 952-1367 3723 Fax: (508) 392-9250 3724 Email: jmoy@casc.com 3726 This document expires in May 1997.