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'Ref1' ** Downref: Normative reference to an Unknown state RFC: RFC 905 (ref. 'Ref2') ** Obsolete normative reference: RFC 1519 (ref. 'Ref4') (Obsoleted by RFC 4632) ** Downref: Normative reference to an Historic RFC: RFC 1745 (ref. 'Ref5') ** Obsolete normative reference: RFC 1700 (ref. 'Ref6') (Obsoleted by RFC 3232) ** Downref: Normative reference to an Informational RFC: RFC 1586 (ref. 'Ref7') -- Possible downref: Non-RFC (?) normative reference: ref. 'Ref8' ** Obsolete normative reference: RFC 1587 (ref. 'Ref9') (Obsoleted by RFC 3101) -- Possible downref: Non-RFC (?) normative reference: ref. 'Ref10' ** Obsolete normative reference: RFC 1771 (ref. 'Ref13') (Obsoleted by RFC 4271) ** Obsolete normative reference: RFC 2460 (ref. 'Ref14') (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 2373 (ref. 'Ref15') (Obsoleted by RFC 3513) ** Obsolete normative reference: RFC 2463 (ref. 'Ref16') (Obsoleted by RFC 4443) ** Obsolete normative reference: RFC 2461 (ref. 'Ref17') (Obsoleted by RFC 4861) ** Obsolete normative reference: RFC 1981 (ref. 'Ref18') (Obsoleted by RFC 8201) ** Obsolete normative reference: RFC 2402 (ref. 'Ref19') (Obsoleted by RFC 4302, RFC 4305) -- Possible downref: Non-RFC (?) normative reference: ref. 'Ref20' Summary: 20 errors (**), 0 flaws (~~), 14 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group R. Coltun 2 Internet Draft Siara Systems 3 Expiration Date: December 1999 D. Ferguson 4 File name: draft-ietf-ospf-ospfv6-06.txt Juniper Networks 5 Network Working Group J. Moy 6 Internet Draft Sycamore Networks 7 June 1999 9 OSPF for IPv6 11 Status of this Memo 13 This document is an Internet-Draft and is in full conformance with 14 all provisions of Section 10 of RFC2026. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six 22 months and may be updated, replaced, or obsoleted by other documents 23 at any time. It is inappropriate to use Internet- Drafts as 24 reference material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 Abstract 34 This document describes the modifications to OSPF to support version 35 6 of the Internet Protocol (IPv6). The fundamental mechanisms of 36 OSPF (flooding, DR election, area support, SPF calculations, etc.) 37 remain unchanged. However, some changes have been necessary, either 38 due to changes in protocol semantics between IPv4 and IPv6, or 39 simply to handle the increased address size of IPv6. 41 Changes between OSPF for IPv4 and this document include the 42 following. Addressing semantics have been removed from OSPF packets 43 and the basic LSAs. New LSAs have been created to carry IPv6 44 addresses and prefixes. OSPF now runs on a per-link basis, instead 45 of on a per-IP-subnet basis. Flooding scope for LSAs has been 46 generalized. Authentication has been removed from the OSPF protocol 47 itself, instead relying on IPv6's Authentication Header and 48 Encapsulating Security Payload. 50 Most packets in OSPF for IPv6 are almost as compact as those in OSPF 51 for IPv4, even with the larger IPv6 addresses. Most field- and 52 packet-size limitations present in OSPF for IPv4 have been relaxed. 53 In addition, option handling has been made more flexible. 55 All of OSPF for IPv4's optional capabilities, including on-demand 56 circuit support, NSSA areas, and the multicast extensions to OSPF 57 (MOSPF) are also supported in OSPF for IPv6. 59 Please send comments to ospf@discuss.microsoft.com. 61 Table of Contents 63 1 Introduction ........................................... 5 64 1.1 Terminology ............................................ 5 65 2 Differences from OSPF for IPv4 ......................... 5 66 2.1 Protocol processing per-link, not per-subnet ........... 5 67 2.2 Removal of addressing semantics ........................ 6 68 2.3 Addition of Flooding scope ............................. 6 69 2.4 Explicit support for multiple instances per link ....... 7 70 2.5 Use of link-local addresses ............................ 7 71 2.6 Authentication changes ................................. 8 72 2.7 Packet format changes .................................. 8 73 2.8 LSA format changes ..................................... 9 74 2.9 Handling unknown LSA types ............................ 11 75 2.10 Stub area support ..................................... 11 76 2.11 Identifying neighbors by Router ID .................... 12 77 3 Implementation details ................................ 12 78 3.1 Protocol data structures .............................. 13 79 3.1.1 The Area Data structure ............................... 14 80 3.1.2 The Interface Data structure .......................... 14 81 3.1.3 The Neighbor Data Structure ........................... 16 82 3.2 Protocol Packet Processing ............................ 16 83 3.2.1 Sending protocol packets .............................. 17 84 3.2.1.1 Sending Hello packets ................................. 18 85 3.2.1.2 Sending Database Description Packets .................. 18 86 3.2.2 Receiving protocol packets ............................ 19 87 3.2.2.1 Receiving Hello Packets ............................... 21 88 3.3 The Routing table Structure ........................... 21 89 3.3.1 Routing table lookup .................................. 22 90 3.4 Link State Advertisements ............................. 22 91 3.4.1 The LSA Header ........................................ 23 92 3.4.2 The link-state database ............................... 24 93 3.4.3 Originating LSAs ...................................... 24 94 3.4.3.1 Router-LSAs ........................................... 27 95 3.4.3.2 Network-LSAs .......................................... 29 96 3.4.3.3 Inter-Area-Prefix-LSAs ................................ 30 97 3.4.3.4 Inter-Area-Router-LSAs ................................ 31 98 3.4.3.5 AS-external-LSAs ...................................... 32 99 3.4.3.6 Link-LSAs ............................................. 34 100 3.4.3.7 Intra-Area-Prefix-LSAs ................................ 35 101 3.5 Flooding .............................................. 39 102 3.5.1 Receiving Link State Update packets ................... 39 103 3.5.2 Sending Link State Update packets ..................... 40 104 3.5.3 Installing LSAs in the database ....................... 42 105 3.6 Definition of self-originated LSAs .................... 42 106 3.7 Virtual links ......................................... 43 107 3.8 Routing table calculation ............................. 43 108 3.8.1 Calculating the shortest path tree for an area ........ 44 109 3.8.1.1 The next hop calculation .............................. 46 110 3.8.2 Calculating the inter-area routes ..................... 46 111 3.8.3 Examining transit areas' summary-LSAs ................. 46 112 3.8.4 Calculating AS external routes ........................ 47 113 3.9 Multiple interfaces to a single link .................. 47 114 References ............................................ 49 115 A OSPF data formats ..................................... 51 116 A.1 Encapsulation of OSPF packets ......................... 51 117 A.2 The Options field ..................................... 52 118 A.3 OSPF Packet Formats ................................... 55 119 A.3.1 The OSPF packet header ................................ 56 120 A.3.2 The Hello packet ...................................... 58 121 A.3.3 The Database Description packet ....................... 60 122 A.3.4 The Link State Request packet ......................... 62 123 A.3.5 The Link State Update packet .......................... 63 124 A.3.6 The Link State Acknowledgment packet .................. 64 125 A.4 LSA formats ........................................... 66 126 A.4.1 IPv6 Prefix Representation ............................ 67 127 A.4.1.1 Prefix Options ........................................ 68 128 A.4.2 The LSA header ........................................ 69 129 A.4.2.1 LS type ............................................... 71 130 A.4.3 Router-LSAs ........................................... 73 131 A.4.4 Network-LSAs .......................................... 76 132 A.4.5 Inter-Area-Prefix-LSAs ................................ 77 133 A.4.6 Inter-Area-Router-LSAs ................................ 79 134 A.4.7 AS-external-LSAs ...................................... 80 135 A.4.8 Link-LSAs ............................................. 83 136 A.4.9 Intra-Area-Prefix-LSAs ................................ 85 137 B Architectural Constants ............................... 87 138 C Configurable Constants ................................ 87 139 C.1 Global parameters ..................................... 87 140 C.2 Area parameters ....................................... 88 141 C.3 Router interface parameters ........................... 89 142 C.4 Virtual link parameters ............................... 90 143 C.5 NBMA network parameters ............................... 91 144 C.6 Point-to-MultiPoint network parameters ................ 92 145 C.7 Host route parameters ................................. 92 146 Security Considerations ............................... 93 147 Authors' Addresses .................................... 93 148 1. Introduction 150 This document describes the modifications to OSPF to support version 151 6 of the Internet Protocol (IPv6). The fundamental mechanisms of 152 OSPF (flooding, DR election, area support, SPF calculations, etc.) 153 remain unchanged. However, some changes have been necessary, either 154 due to changes in protocol semantics between IPv4 and IPv6, or 155 simply to handle the increased address size of IPv6. 157 This document is organized as follows. Section 2 describes the 158 differences between OSPF for IPv4 and OSPF for IPv6 in detail. 159 Section 3 provides implementation details for the changes. Appendix 160 A gives the OSPF for IPv6 packet and LSA formats. Appendix B lists 161 the OSPF architectural constants. Appendix C describes configuration 162 parameters. 164 1.1. Terminology 166 This document attempts to use terms from both the OSPF for IPv4 167 specification ([Ref1]) and the IPv6 protocol specifications 168 ([Ref14]). This has produced a mixed result. Most of the terms 169 used both by OSPF and IPv6 have roughly the same meaning (e.g., 170 interfaces). However, there are a few conflicts. IPv6 uses 171 "link" similarly to IPv4 OSPF's "subnet" or "network". In this 172 case, we have chosen to use IPv6's "link" terminology. "Link" 173 replaces OSPF's "subnet" and "network" in most places in this 174 document, although OSPF's Network-LSA remains unchanged (and 175 possibly unfortunately, a new Link-LSA has also been created). 177 The names of some of the OSPF LSAs have also changed. See 178 Section 2.8 for details. 180 2. Differences from OSPF for IPv4 182 Most of the algorithms from OSPF for IPv4 [Ref1] have preserved in 183 OSPF for IPv6. However, some changes have been necessary, either due 184 to changes in protocol semantics between IPv4 and IPv6, or simply to 185 handle the increased address size of IPv6. 187 The following subsections describe the differences between this 188 document and [Ref1]. 190 2.1. Protocol processing per-link, not per-subnet 192 IPv6 uses the term "link" to indicate "a communication facility 193 or medium over which nodes can communicate at the link layer" 194 ([Ref14]). "Interfaces" connect to links. Multiple IP subnets 195 can be assigned to a single link, and two nodes can talk 196 directly over a single link, even if they do not share a common 197 IP subnet (IPv6 prefix). 199 For this reason, OSPF for IPv6 runs per-link instead of the IPv4 200 behavior of per-IP-subnet. The terms "network" and "subnet" used 201 in the IPv4 OSPF specification ([Ref1]) should generally be 202 relaced by link. Likewise, an OSPF interface now connects to a 203 link instead of an IP subnet, etc. 205 This change affects the receiving of OSPF protocol packets, and 206 the contents of Hello Packets and Network-LSAs. 208 2.2. Removal of addressing semantics 210 In OSPF for IPv6, addressing semantics have been removed from 211 the OSPF protocol packets and the main LSA types, leaving a 212 network-protocol-independent core. In particular: 214 o IPv6 Addresses are not present in OSPF packets, except in 215 LSA payloads carried by the Link State Update Packets. See 216 Section 2.7 for details. 218 o Router-LSAs and Network-LSAs no longer contain network 219 addresses, but simply express topology information. See 220 Section 2.8 for details. 222 o OSPF Router IDs, Area IDs and LSA Link State IDs remain at 223 the IPv4 size of 32-bits. They can no longer be assigned as 224 (IPv6) addresses. 226 o Neighboring routers are now always identified by Router ID, 227 where previously they had been identified by IP address on 228 broadcast and NBMA "networks". 230 2.3. Addition of Flooding scope 232 Flooding scope for LSAs has been generalized and is now 233 explicitly coded in the LSA's LS type field. There are now three 234 separate flooding scopes for LSAs: 236 o Link-local scope. LSA is flooded only on the local link, and 237 no further. Used for the new Link-LSA (see Section A.4.8). 239 o Area scope. LSA is flooded throughout a single OSPF area 240 only. Used for Router-LSAs, Network-LSAs, Inter-Area-Prefix- 241 LSAs, Inter-Area-Router-LSAs and Intra-Area-Prefix-LSAs. 243 o AS scope. LSA is flooded throughout the routing domain. Used 244 for AS-external-LSAs. 246 2.4. Explicit support for multiple instances per link 248 OSPF now supports the ability to run multiple OSPF protocol 249 instances on a single link. For example, this may be required on 250 a NAP segment shared between several providers -- providers may 251 be running separate OSPF routing domains that want to remain 252 separate even though they have one or more physical network 253 segments (i.e., links) in common. In OSPF for IPv4 this was 254 supported in a haphazard fashion using the authentication fields 255 in the OSPF for IPv4 header. 257 Another use for running multiple OSPF instances is if you want, 258 for one reason or another, to have a single link belong to two 259 or more OSPF areas. 261 Support for multiple protocol instances on a link is 262 accomplished via an "Instance ID" contained in the OSPF packet 263 header and OSPF interface structures. Instance ID solely affects 264 the reception of OSPF packets. 266 2.5. Use of link-local addresses 268 IPv6 link-local addresses are for use on a single link, for 269 purposes of neighbor discovery, auto-configuration, etc. IPv6 270 routers do not forward IPv6 datagrams having link-local source 271 addresses [Ref15]. Link-local unicast addresses are assigned 272 from the IPv6 address range FF80/10. 274 OSPF for IPv6 assumes that each router has been assigned link- 275 local unicast addresses on each of the router's attached 276 physical segments. On all OSPF interfaces except virtual links, 277 OSPF packets are sent using the interface's associated link- 278 local unicast address as source. A router learns the link-local 279 addresses of all other routers attached to its links, and uses 280 these addresses as next hop information during packet 281 forwarding. 283 On virtual links, global scope or site-local IP addresses must 284 be used as the source for OSPF protocol packets. 286 Link-local addresses appear in OSPF Link-LSAs (see Section 287 3.4.3.6). However, link-local addresses are not allowed in other 288 OSPF LSA types. In particular, link-local addresses cannot be 289 advertised in inter-area-prefix-LSAs (Section 3.4.3.3), AS- 290 external-LSAs (Section 3.4.3.5) or intra-area-prefix-LSAs 291 (Section 3.4.3.7). 293 2.6. Authentication changes 295 In OSPF for IPv6, authentication has been removed from OSPF 296 itself. The "AuType" and "Authentication" fields have been 297 removed from the OSPF packet header, and all authentication 298 related fields have been removed from the OSPF area and 299 interface structures. 301 When running over IPv6, OSPF relies on the IP Authentication 302 Header (see [Ref19]) and the IP Encapsulating Security Payload 303 (see [Ref20]) to ensure integrity and 304 authentication/confidentiality of routing exchanges. 306 Protection of OSPF packet exchanges against accidental data 307 corruption is provided by the standard IPv6 16-bit one's 308 complement checksum, covering the entire OSPF packet and 309 prepended IPv6 pseudo-header (see Section A.3.1). 311 2.7. Packet format changes 313 OSPF for IPv6 runs directly over IPv6. Aside from this, all 314 addressing semantics have been removed from the OSPF packet 315 headers, making it essentially "network-protocol-independent". 316 All addressing information is now contained in the various LSA 317 types only. 319 In detail, changes in OSPF packet format consist of the 320 following: 322 o The OSPF version number has been increased from 2 to 3. 324 o The Options field in Hello Packets and Database description 325 Packets has been expanded to 24-bits. 327 o The Authentication and AuType fields have been removed from 328 the OSPF packet header (see Section 2.6). 330 o The Hello packet now contains no address information at all, 331 and includes an Interface ID which the originating router 332 has assigned to uniquely identify (among its own interfaces) 333 its interface to the link. This Interface ID becomes the 334 Network-LSA's Link State ID, should the router become 335 Designated Router on the link. 337 o Two options bits, the "R-bit" and the "V6-bit", have been 338 added to the Options field for processing Router-LSAs during 339 the SPF calculation (see Section A.2). If the "R-bit" is 340 clear an OSPF speaker can participate in OSPF topology 341 distribution without being used to forward transit traffic; 342 this can be used in multi-homed hosts that want to 343 participate in the routing protocol. The V6-bit specializes 344 the R-bit; if the V6-bit is clear an OSPF speaker can 345 participate in OSPF topology distribution without being used 346 to forward IPv6 datagrams. If the R-bit is set and the 347 V6-bit is clear, IPv6 datagrams are not forwarded but 348 datagrams belonging to another protocol family may be 349 forwarded. 351 o The OSPF packet header now includes an "Instance ID" which 352 allows multiple OSPF protocol instances to be run on a 353 single link (see Section 2.4). 355 2.8. LSA format changes 357 All addressing semantics have been removed from the LSA header, 358 and from Router-LSAs and Network-LSAs. These two LSAs now 359 describe the routing domain's topology in a network-protocol- 360 independent manner. New LSAs have been added to distribute IPv6 361 address information, and data required for next hop resolution. 362 The names of some of IPv4's LSAs have been changed to be more 363 consistent with each other. 365 In detail, changes in LSA format consist of the following: 367 o The Options field has been removed from the LSA header, 368 expanded to 24 bits, and moved into the body of Router-LSAs, 369 Network-LSAs, Inter-Area-Router-LSAs and Link-LSAs. See 370 Section A.2 for details. 372 o The LSA Type field has been expanded (into the former 373 Options space) to 16 bits, with the upper three bits 374 encoding flooding scope and the handling of unknown LSA 375 types (see Section 2.9). 377 o Addresses in LSAs are now expressed as [prefix, prefix 378 length] instead of [address, mask] (see Section A.4.1). The 379 default route is expressed as a prefix with length 0. 381 o The Router and Network LSAs now have no address information, 382 and are network-protocol-independent. 384 o Router interface information may be spread across multiple 385 Router LSAs. Receivers must concatenate all the Router-LSAs 386 originated by a given router when running the SPF 387 calculation. 389 o A new LSA called the Link-LSA has been introduced. The LSAs 390 have local-link flooding scope; they are never flooded 391 beyond the link that they are associated with. Link-LSAs 392 have three purposes: 1) they provide the router's link-local 393 address to all other routers attached to the link, 2) they 394 inform other routers attached to the link of a list of IPv6 395 prefixes to associate with the link and 3) they allow the 396 router to assert a collection of Options bits to associate 397 with the Network-LSA that will be originated for the link. 398 See Section A.4.8 for details. 400 In IPv4, the router-LSA carries a router's IPv4 interface 401 addresses, the IPv4 equivalent of link-local addresses. 402 These are only used when calculating next hops during the 403 OSPF routing calculation (see Section 16.1.1 of [Ref1]), so 404 they do not need to be flooded past the local link; hence 405 using link-LSAs to distribute these addresses is more 406 efficient. Note that link-local addresses cannot be learned 407 through the reception of Hellos in all cases: on NBMA links 408 next hop routers do not necessarily exchange hellos, but 409 rather learn of each other's existence by way of the 410 Designated Router. 412 o The Options field in the Network LSA is set to the logical 413 OR of the Options that each router on the link advertises in 414 its Link-LSA. 416 o Type-3 summary-LSAs have been renamed "Inter-Area-Prefix- 417 LSAs". Type-4 summary LSAs have been renamed "Inter-Area- 418 Router-LSAs". 420 o The Link State ID in Inter-Area-Prefix-LSAs, Inter-Area- 421 Router-LSAs and AS-external-LSAs has lost its addressing 422 semantics, and now serves solely to identify individual 423 pieces of the Link State Database. All addresses or Router 424 IDs that were formerly expressed by the Link State ID are 425 now carried in the LSA bodies. 427 o Network-LSAs and Link-LSAs are the only LSAs whose Link 428 State ID carries additional meaning. For these LSAs, the 429 Link State ID is always the Interface ID of the originating 430 router on the link being described. For this reason, 431 Network-LSAs and Link-LSAs are now the only LSAs whose size 432 cannot be limited: a Network-LSA must list all routers 433 connected to the link, and a Link-LSA must list all of a 434 router's addresses on the link. 436 o A new LSA called the Intra-Area-Prefix-LSA has been 437 introduced. This LSA carries all IPv6 prefix information 438 that in IPv4 is included in Router-LSAs and Network-LSAs. 439 See Section A.4.9 for details. 441 o Inclusion of a forwarding address in AS-external-LSAs is now 442 optional, as is the inclusion of an external route tag (see 443 [Ref5]). In addition, AS-external-LSAs can now reference 444 another LSA, for inclusion of additional route attributes 445 that are outside the scope of the OSPF protocol itself. For 446 example, this can be used to attach BGP path attributes to 447 external routes as proposed in [Ref10]. 449 2.9. Handling unknown LSA types 451 Handling of unknown LSA types has been made more flexible so 452 that, based on LS type, unknown LSA types are either treated as 453 having link-local flooding scope, or are stored and flooded as 454 if they were understood (desirable for things like the proposed 455 External-Attributes-LSA in [Ref10]). This behavior is explicitly 456 coded in the LSA Handling bit of the link state header's LS type 457 field (see Section A.4.2.1). 459 The IPv4 OSPF behavior of simply discarding unknown types is 460 unsupported due to the desire to mix router capabilities on a 461 single link. Discarding unknown types causes problems when the 462 Designated Router supports fewer options than the other routers 463 on the link. 465 2.10. Stub area support 467 In OSPF for IPv4, stub areas were designed to minimize link- 468 state database and routing table sizes for the areas' internal 469 routers. This allows routers with minimal resources to 470 participate in even very large OSPF routing domains. 472 In OSPF for IPv6, the concept of stub areas is retained. In 473 IPv6, of the mandatory LSA types, stub areas carry only router- 474 LSAs, network-LSAs, Inter-Area-Prefix-LSAs, Link-LSAs, and 475 Intra-Area-Prefix-LSAs. This is the IPv6 equivalent of the LSA 476 types carried in IPv4 stub areas: router-LSAs, network-LSAs and 477 type 3 summary-LSAs. 479 However, unlike in IPv4, IPv6 allows LSAs with unrecognized LS 480 types to be labeled "Store and flood the LSA, as if type 481 understood" (see the U-bit in Section A.4.2.1). Uncontrolled 482 introduction of such LSAs could cause a stub area's link-state 483 database to grow larger than its component routers' capacities. 485 To guard against this, the following rule regarding stub areas 486 has been established: an LSA whose LS type is unrecognized is 487 not flooded into/throughout stub areas if either a) the unknown 488 LSA has AS flooding scope or b) the unknown LSA has U-bit set to 489 1 (flood even when LS type unrecognized). See Section 3.5 for 490 details. 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 (Section 10.5 of [Ref1]). 505 The Router ID of 0.0.0.0 is reserved, and should not be used. 507 3. Implementation details 509 When going from IPv4 to IPv6, the basic OSPF mechanisms remain 510 unchanged from those documented in [Ref1]. These mechanisms are 511 briefly outlined in Section 4 of [Ref1]. Both IPv6 and IPv4 have a 512 link-state database composed of LSAs and synchronized between 513 adjacent routers. Initial synchronization is performed through the 514 Database Exchange process, through the exchange of Database 515 Description, Link State Request and Link State Update packets. 516 Thereafter database synchronization is maintained via flooding, 517 utilizing Link State Update and Link State Acknowledgment packets. 518 Both IPv6 and IPv4 use OSPF Hello Packets to discover and maintain 519 neighbor relationships, and to elect Designated Routers and Backup 520 Designated Routers on broadcast and NBMA links. The decision as to 521 which neighbor relationships become adjacencies, along with the 522 basic ideas behind inter-area routing, importing external 523 information in AS-external-LSAs and the various routing calculations 524 are also the same. 526 In particular, the following IPv4 OSPF functionality described in 527 [Ref1] remains completely unchanged for IPv6: 529 o Both IPv4 and IPv6 use OSPF packet types described in Section 530 4.3 of [Ref1], namely: Hello, Database Description, Link State 531 Request, Link State Update and Link State Acknowledgment 532 packets. While in some cases (e.g., Hello packets) their format 533 has changed somewhat, the functions of the various packet types 534 remains the same. 536 o The system requirements for an OSPF implementation remain 537 unchanged, although OSPF for IPv6 requires an IPv6 protocol 538 stack (from the network layer on down) since it runs directly 539 over the IPv6 network layer. 541 o The discovery and maintenance of neighbor relationships, and the 542 selection and establishment of adjacencies remain the same. This 543 includes election of the Designated Router and Backup Designated 544 Router on broadcast and NBMA links. These mechanisms are 545 described in Sections 7, 7.1, 7.2, 7.3, 7.4 and 7.5 of [Ref1]. 547 o The link types (or equivalently, interface types) supported by 548 OSPF remain unchanged, namely: point-to-point, broadcast, NBMA, 549 Point-to-MultiPoint and virtual links. 551 o The interface state machine, including the list of OSPF 552 interface states and events, and the Designated Router and 553 Backup Designated Router election algorithm, remain unchanged. 554 These are described in Sections 9.1, 9.2, 9.3 and 9.4 of [Ref1]. 556 o The neighbor state machine, including the list of OSPF neighbor 557 states and events, remain unchanged. These are described in 558 Sections 10.1, 10.2, 10.3 and 10.4 of [Ref1]. 560 o Aging of the link-state database, as well as flushing LSAs from 561 the routing domain through the premature aging process, remains 562 unchanged from the description in Sections 14 and 14.1 of 563 [Ref1]. 565 However, some OSPF protocol mechanisms have changed, as outlined in 566 Section 2 above. These changes are explained in detail in the 567 following subsections, making references to the appropriate sections 568 of [Ref1]. 570 The following subsections provide a recipe for turning an IPv4 OSPF 571 implementation into an IPv6 OSPF implementation. 573 3.1. Protocol data structures 575 The major OSPF data structures are the same for both IPv4 and 576 IPv6: areas, interfaces, neighbors, the link-state database and 577 the routing table. The top-level data structures for IPv6 remain 578 those listed in Section 5 of [Ref1], with the following 579 modifications: 581 o All LSAs with known LS type and AS flooding scope appear in 582 the top-level data structure, instead of belonging to a 583 specific area or link. AS-external-LSAs are the only LSAs 584 defined by this specification which have AS flooding scope. 585 LSAs with unknown LS type, U-bit set to 1 (flood even when 586 unrecognized) and AS flooding scope also appear in the top- 587 level data structure. 589 3.1.1. The Area Data structure 591 The IPv6 area data structure contains all elements defined 592 for IPv4 areas in Section 6 of [Ref1]. In addition, all LSAs 593 of known type which have area flooding scope are contained 594 in the IPv6 area data structure. This always includes the 595 following LSA types: router-LSAs, network-LSAs, inter-area- 596 prefix-LSAs, inter-area-router-LSAs and intra-area-prefix- 597 LSAs. LSAs with unknown LS type, U-bit set to 1 (flood even 598 when unrecognized) and area scope also appear in the area 599 data structure. IPv6 routers implementing MOSPF add group- 600 membership-LSAs to the area data structure. Type-7-LSAs 601 belong to an NSSA area's data structure. 603 3.1.2. The Interface Data structure 605 In OSPF for IPv6, an interface connects a router to a link. 606 The IPv6 interface structure modifies the IPv4 interface 607 structure (as defined in Section 9 of [Ref1]) as follows: 609 Interface ID 610 Every interface is assigned an Interface ID, which 611 uniquely identifies the interface with the router. For 612 example, some implementations may be able to use the 613 MIB-II IfIndex as Interface ID. The Interface ID appears 614 in Hello packets sent out the interface, the link-local- 615 LSA originated by router for the attached link, and the 616 router-LSA originated by the router-LSA for the 617 associated area. It will also serve as the Link State ID 618 for the network-LSA that the router will originate for 619 the link if the router is elected Designated Router. 621 Instance ID 622 Every interface is assigned an Instance ID. This should 623 default to 0, and is only necessary to assign 624 differently on those links that will contain multiple 625 separate communities of OSPF Routers. For example, 626 suppose that there are two communities of routers on a 627 given ethernet segment that you wish to keep separate. 628 The first community is given an Instance ID of 0, by 629 assigning 0 as the Instance ID of all its routers' 630 interfaces to the ethernet. An Instance ID of 1 is 631 assigned to the other routers' interfaces to the 632 ethernet. The OSPF transmit and receive processing (see 633 Section 3.2) will then keep the two communities 634 separate. 636 List of LSAs with link-local scope 637 All LSAs with link-local scope and which were 638 originated/flooded on the link belong to the interface 639 structure which connects to the link. This includes the 640 collection of the link's link-LSAs. 642 List of LSAs with unknown LS type 643 All LSAs with unknown LS type and U-bit set to 0 (if 644 unrecognized, treat the LSA as if it had link-local 645 flooding scope) are kept in the data structure for the 646 interface that received the LSA. 648 IP interface address 649 For IPv6, the IPv6 address appearing in the source of 650 OSPF packets sent out the interface is almost always a 651 link-local address. The one exception is for virtual 652 links, which must use one of the router's own site-local 653 or global IPv6 addresses as IP interface address. 655 List of link prefixes 656 A list of IPv6 prefixes can be configured for the 657 attached link. These will be advertised by the router in 658 link-LSAs, so that they can be advertised by the link's 659 Designated Router in intra-area-prefix-LSAs. 661 In OSPF for IPv6, each router interface has a single metric, 662 representing the cost of sending packets out the interface. 663 In addition, OSPF for IPv6 relies on the IP Authentication 664 Header (see [Ref19]) and the IP Encapsulating Security 665 Payload (see [Ref20]) to ensure integrity and 666 authentication/confidentiality of routing exchanges. For 667 that reason, AuType and Authentication key are not 668 associated with IPv6 OSPF interfaces. 670 Interface states, events, and the interface state machine 671 remain unchanged from IPv4, and are documented in Sections 672 9.1, 9.2 and 9.3 of [Ref1] respectively. The Designated 673 Router and Backup Designated Router election algorithm also 674 remains unchanged from the IPv4 election in Section 9.4 of 675 [Ref1]. 677 3.1.3. The Neighbor Data Structure 679 The neighbor structure performs the same function in both 680 IPv6 and IPv4. Namely, it collects all information required 681 to form an adjacency between two routers, if an adjacency 682 becomes necessary. Each neighbor structure is bound to a 683 single OSPF interface. The differences between the IPv6 684 neighbor structure and the neighbor structure defined for 685 IPv4 in Section 10 of [Ref1] are: 687 Neighbor's Interface ID 688 The Interface ID that the neighbor advertises in its 689 Hello Packets must be recorded in the neighbor 690 structure. The router will include the neighbor's 691 Interface ID in the router's router-LSA when either a) 692 advertising a point-to-point link to the neighbor or b) 693 advertising a link to a network where the neighbor has 694 become Designated Router. 696 Neighbor IP address 697 Except on virtual links, the neighbor's IP address will 698 be an IPv6 link-local address. 700 Neighbor's Designated Router 701 The neighbor's choice of Designated Router is now 702 encoded as a Router ID, instead of as an IP address. 704 Neighbor's Backup Designated Router 705 The neighbor's choice of Designated Router is now 706 encoded as a Router ID, instead of as an IP address. 708 Neighbor states, events, and the neighbor state machine 709 remain unchanged from IPv4, and are documented in Sections 710 10.1, 10.2 and 10.3 of [Ref1] respectively. The decision as 711 to which adjacencies to form also remains unchanged from the 712 IPv4 logic documented in Section 10.4 of [Ref1]. 714 3.2. Protocol Packet Processing 716 OSPF for IPv6 runs directly over IPv6's network layer. As such, 717 it is encapsulated in one or more IPv6 headers, with the Next 718 Header field of the immediately encapsulating IPv6 header set to 719 the value 89. 721 As for IPv4, in IPv6 OSPF routing protocol packets are sent 722 along adjacencies only (with the exception of Hello packets, 723 which are used to discover the adjacencies). OSPF packet types 724 and functions are the same in both IPv4 and IPv4, encoded by the 725 Type field of the standard OSPF packet header. 727 3.2.1. Sending protocol packets 729 When an IPv6 router sends an OSPF routing protocol packet, 730 it fills in the fields of the standard OSPF for IPv6 packet 731 header (see Section A.3.1) as follows: 733 Version # 734 Set to 3, the version number of the protocol as 735 documented in this specification. 737 Type 738 The type of OSPF packet, such as Link state Update or 739 Hello Packet. 741 Packet length 742 The length of the entire OSPF packet in bytes, including 743 the standard OSPF packet header. 745 Router ID 746 The identity of the router itself (who is originating 747 the packet). 749 Area ID 750 The OSPF area that the packet is being sent into. 752 Instance ID 753 The OSPF Instance ID associated with the interface that 754 the packet is being sent out of. 756 Checksum 757 The standard IPv6 16-bit one's complement checksum, 758 covering the entire OSPF packet and prepended IPv6 759 pseudo-header (see Section A.3.1). 761 Selection of OSPF routing protocol packets' IPv6 source and 762 destination addresses is performed identically to the IPv4 763 logic in Section 8.1 of [Ref1]. The IPv6 destination address 764 is chosen from among the addresses AllSPFRouters, 765 AllDRouters and the Neighbor IP address associated with the 766 other end of the adjacency (which in IPv6, for all links 767 except virtual links, is an IPv6 link-local address). 769 The sending of Link State Request Packets and Link State 770 Acknowledgment Packets remains unchanged from the IPv4 771 procedures documented in Sections 10.9 and 13.5 of [Ref1] 772 respectively. Sending Hello Packets is documented in Section 773 3.2.1.1, and the sending of Database Description Packets in 774 Section 3.2.1.2. The sending of Link State Update Packets is 775 documented in Section 3.5.2. 777 3.2.1.1. Sending Hello packets 779 IPv6 changes the way OSPF Hello packets are sent in the 780 following ways (compare to Section 9.5 of [Ref1]): 782 o Before the Hello Packet is sent out an interface, 783 the interface's Interface ID must be copied into the 784 Hello Packet. 786 o The Hello Packet no longer contains an IP network 787 mask, as OSPF for IPv6 runs per-link instead of per- 788 subnet. 790 o The choice of Designated Router and Backup 791 Designated Router are now indicated within Hellos by 792 their Router IDs, instead of by their IP interface 793 addresses. Advertising the Designated Router (or 794 Backup Designated Router) as 0.0.0.0 indicates that 795 the Designated Router (or Backup Designated Router) 796 has not yet been chosen. 798 o The Options field within Hello packets has moved 799 around, getting larger in the process. More options 800 bits are now possible. Those that must be set 801 correctly in Hello packets are: The E-bit is set if 802 and only if the interface attaches to a non-stub 803 area, the N-bit is set if and only if the interface 804 attaches to an NSSA area (see [Ref9]), and the DC- 805 bit is set if and only if the router wishes to 806 suppress the sending of future Hellos over the 807 interface (see [Ref11]). Unrecognized bits in the 808 Hello Packet's Options field should be cleared. 810 Sending Hello packets on NBMA networks proceeds for IPv6 811 in exactly the same way as for IPv4, as documented in 812 Section 9.5.1 of [Ref1]. 814 3.2.1.2. Sending Database Description Packets 816 The sending of Database Description packets differs from 817 Section 10.8 of [Ref1] in the following ways: 819 o The Options field within Database Description 820 packets has moved around, getting larger in the 821 process. More options bits are now possible. Those 822 that must be set correctly in Database Description 823 packets are: The MC-bit is set if and only if the 824 router is forwarding multicast datagrams according 825 to the MOSPF specification in [Ref7], and the DC-bit 826 is set if and only if the router wishes to suppress 827 the sending of Hellos over the interface (see 828 [Ref11]). Unrecognized bits in the Database 829 Description Packet's Options field should be 830 cleared. 832 3.2.2. Receiving protocol packets 834 Whenever an OSPF protocol packet is received by the router 835 it is marked with the interface it was received on. For 836 routers that have virtual links configured, it may not be 837 immediately obvious which interface to associate the packet 838 with. For example, consider the Router RT11 depicted in 839 Figure 6 of [Ref1]. If RT11 receives an OSPF protocol 840 packet on its interface to Network N8, it may want to 841 associate the packet with the interface to Area 2, or with 842 the virtual link to Router RT10 (which is part of the 843 backbone). In the following, we assume that the packet is 844 initially associated with the non-virtual link. 846 In order for the packet to be passed to OSPF for processing, 847 the following tests must be performed on the encapsulating 848 IPv6 headers: 850 o The packet's IP destination address must be one of the 851 IPv6 unicast addresses associated with the receiving 852 interface (this includes link-local addresses), or one 853 of the IP multicast addresses AllSPFRouters or 854 AllDRouters. 856 o The Next Header field of the immediately encapsulating 857 IPv6 header must specify the OSPF protocol (89). 859 o Any encapsulating IP Authentication Headers (see 860 [Ref19]) and the IP Encapsulating Security Payloads (see 861 [Ref20]) must be processed and/or verified to ensure 862 integrity and authentication/confidentiality of OSPF 863 routing exchanges. 865 o Locally originated packets should not be passed on to 866 OSPF. That is, the source IPv6 address should be 867 examined to make sure this is not a multicast packet 868 that the router itself generated. 870 After processing the encapsulating IPv6 headers, the OSPF 871 packet header is processed. The fields specified in the 872 header must match those configured for the receiving 873 interface. If they do not, the packet should be discarded: 875 o The version number field must specify protocol version 876 3. 878 o The standard IPv6 16-bit one's complement checksum, 879 covering the entire OSPF packet and prepended IPv6 880 pseudo-header, must be verified (see Section A.3.1). 882 o The Area ID found in the OSPF header must be verified. 883 If both of the following cases fail, the packet should 884 be discarded. The Area ID specified in the header must 885 either: 887 (1) Match the Area ID of the receiving interface. In 888 this case, unlike for IPv4, the IPv6 source 889 address is not restricted to lie on the same IP 890 subnet as the receiving interface. IPv6 OSPF runs 891 per-link, instead of per-IP-subnet. 893 (2) Indicate the backbone. In this case, the packet 894 has been sent over a virtual link. The receiving 895 router must be an area border router, and the 896 Router ID specified in the packet (the source 897 router) must be the other end of a configured 898 virtual link. The receiving interface must also 899 attach to the virtual link's configured Transit 900 area. If all of these checks succeed, the packet 901 is accepted and is from now on associated with 902 the virtual link (and the backbone area). 904 o The Instance ID specified in the OSPF header must match 905 the receiving interface's Instance ID. 907 o Packets whose IP destination is AllDRouters should only 908 be accepted if the state of the receiving interface is 909 DR or Backup (see Section 9.1). 911 After header processing, the packet is further processed 912 according to it OSPF packet type. OSPF packet types and 913 functions are the same for both IPv4 and IPv6. 915 If the packet type is Hello, it should then be further 916 processed by the Hello Protocol. All other packet types are 917 sent/received only on adjacencies. This means that the 918 packet must have been sent by one of the router's active 919 neighbors. The neighbor is identified by the Router ID 920 appearing the the received packet's OSPF header. Packets not 921 matching any active neighbor are discarded. 923 The receive processing of Database Description Packets, Link 924 State Request Packets and Link State Acknowledgment Packets 925 remains unchanged from the IPv4 procedures documented in 926 Sections 10.6, 10.7 and 13.7 of [Ref1] respectively. The 927 receiving of Hello Packets is documented in Section 3.2.2.1, 928 and the receiving of Link State Update Packets is documented 929 in Section 3.5.1. 931 3.2.2.1. Receiving Hello Packets 933 The receive processing of Hello Packets differs from 934 Section 10.5 of [Ref1] in the following ways: 936 o On all link types (e.g., broadcast, NBMA, point-to- 937 point, etc), neighbors are identified solely by 938 their OSPF Router ID. For all link types except 939 virtual links, the Neighbor IP address is set to the 940 IPv6 source address in the IPv6 header of the 941 received OSPF Hello packet. 943 o There is no longer a Network Mask field in the Hello 944 Packet. 946 o The neighbor's choice of Designated Router and 947 Backup Designated Router is now encoded as an OSPF 948 Router ID instead of an IP interface address. 950 3.3. The Routing table Structure 952 The routing table used by OSPF for IPv4 is defined in Section 11 953 of [Ref1]. For IPv6 there are analogous routing table entries: 954 there are routing table entries for IPv6 address prefixes, and 955 also for AS boundary routers. The latter routing table entries 956 are only used to hold intermediate results during the routing 957 table build process (see Section 3.8). 959 Also, to hold the intermediate results during the shortest-path 960 calculation for each area, there is a separate routing table for 961 each area holding the following entries: 963 o An entry for each router in the area. Routers are identified 964 by their OSPF router ID. These routing table entries hold 965 the set of shortest paths through a given area to a given 966 router, which in turn allows calculation of paths to the 967 IPv6 prefixes advertised by that router in Intra-area- 968 prefix-LSAs. If the router is also an area-border router, 969 these entries are also used to calculate paths for inter- 970 area address prefixes. If in addition the router is the 971 other endpoint of a virtual link, the routing table entry 972 describes the cost and viability of the virtual link. 974 o An entry for each transit link in the area. Transit links 975 have associated network-LSAs. Both the transit link and the 976 network-LSA are identified by a combination of the 977 Designated Router's Interface ID on the link and the 978 Designated Router's OSPF Router ID. These routing table 979 entries allow later calculation of paths to IP prefixes 980 advertised for the transit link in intra-area-prefix-LSAs. 982 The fields in the IPv4 OSPF routing table (see Section 11 of 983 [Ref1]) remain valid for IPv6: Optional capabilities (routers 984 only), path type, cost, type 2 cost, link state origin, and for 985 each of the equal cost paths to the destination, the next hop 986 and advertising router. 988 For IPv6, the link-state origin field in the routing table entry 989 is the router-LSA or network-LSA that has directly or indirectly 990 produced the routing table entry. For example, if the routing 991 table entry describes a route to an IPv6 prefix, the link state 992 origin is the router-LSA or network-LSA that is listed in the 993 body of the intra-area-prefix-LSA that has produced the route 994 (see Section A.4.9). 996 3.3.1. Routing table lookup 998 Routing table lookup (i.e., determining the best matching 999 routing table entry during IP forwarding) is the same for 1000 IPv6 as for IPv4. 1002 3.4. Link State Advertisements 1004 For IPv6, the OSPF LSA header has changed slightly, with the LS 1005 type field expanding and the Options field being moved into the 1006 body of appropriate LSAs. Also, the formats of some LSAs have 1007 changed somewhat (namely router-LSAs, network-LSAs and AS- 1008 external-LSAs), while the names of other LSAs have been changed 1009 (type 3 and 4 summary-LSAs are now inter-area-prefix-LSAs and 1010 inter-area-router-LSAs respectively) and additional LSAs have 1011 been added (Link-LSAs and Intra-Area-Prefix-LSAs). Type of 1012 Service (TOS) has been removed from the OSPFv2 specification 1013 [Ref1], and is not encoded within OSPF for IPv6's LSAs. 1015 These changes will be described in detail in the following 1016 subsections. 1018 3.4.1. The LSA Header 1020 In both IPv4 and IPv6, all OSPF LSAs begin with a standard 1021 20 byte LSA header. However, the contents of this 20 byte 1022 header have changed in IPv6. The LS age, Advertising Router, 1023 LS Sequence Number, LS checksum and length fields within the 1024 LSA header remain unchanged, as documented in Sections 1025 12.1.1, 12.1.5, 12.1.6, 12.1.7 and A.4.1 of [Ref1] 1026 respectively. However, the following fields have changed 1027 for IPv6: 1029 Options 1030 The Options field has been removed from the standard 20 1031 byte LSA header, and into the body of router-LSAs, 1032 network-LSAs, inter-area-router-LSAs and link-LSAs. The 1033 size of the Options field has increased from 8 to 24 1034 bits, and some of the bit definitions have changed (see 1035 Section A.2). In addition a separate PrefixOptions 1036 field, 8 bits in length, is attached to each prefix 1037 advertised within the body of an LSA. 1039 LS type 1040 The size of the LS type field has increased from 8 to 16 1041 bits, with the top two bits encoding flooding scope and 1042 the next bit encoding the handling of unknown LS types. 1043 See Section A.4.2.1 for the current coding of the LS 1044 type field. 1046 Link State ID 1047 Link State ID remains at 32 bits in length, but except 1048 for network-LSAs and link-LSAs, Link State ID has shed 1049 any addressing semantics. For example, an IPv6 router 1050 originating multiple AS-external-LSAs could start by 1051 assigning the first a Link State ID of 0.0.0.1, the 1052 second a Link State ID of 0.0.0.2, and so on. Instead of 1053 the IPv4 behavior of encoding the network number within 1054 the AS-external-LSA's Link State ID, the IPv6 Link State 1055 ID simply serves as a way to differentiate multiple LSAs 1056 originated by the same router. 1058 For network-LSAs, the Link State ID is set to the 1059 Designated Router's Interface ID on the link. When a 1060 router originates a Link-LSA for a given link, its Link 1061 State ID is set equal to the router's Interface ID on 1062 the link. 1064 3.4.2. The link-state database 1066 In IPv6, as in IPv4, individual LSAs are identified by a 1067 combination of their LS type, Link State ID and Advertising 1068 Router fields. Given two instances of an LSA, the most 1069 recent instance is determined by examining the LSAs' LS 1070 Sequence Number, using LS checksum and LS age as tiebreakers 1071 (see Section 13.1 of [Ref1]). 1073 In IPv6, the link-state database is split across three 1074 separate data structures. LSAs with AS flooding scope are 1075 contained within the top-level OSPF data structure (see 1076 Section 3.1) as long as either their LS type is known or 1077 their U-bit is 1 (flood even when unrecognized); this 1078 includes the AS-external-LSAs. LSAs with area flooding scope 1079 are contained within the appropriate area structure (see 1080 Section 3.1.1) as long as either their LS type is known or 1081 their U-bit is 1 (flood even when unrecognized); this 1082 includes router-LSAs, network-LSAs, inter-area-prefix-LSAs, 1083 inter-area-router-LSAs, and intra-area-prefix-LSAs. LSAs 1084 with unknown LS type and U-bit set to 0 and/or link-local 1085 flooding scope are contained within the appropriate 1086 interface structure (see Section 3.1.2); this includes link- 1087 LSAs. 1089 To lookup or install an LSA in the database, you first 1090 examine the LS type and the LSA's context (i.e., to which 1091 area or link does the LSA belong). This information allows 1092 you to find the correct list of LSAs, all of the same LS 1093 type, where you then search based on the LSA's Link State ID 1094 and Advertising Router. 1096 3.4.3. Originating LSAs 1098 The process of reoriginating an LSA in IPv6 is the same as 1099 in IPv4: the LSA's LS sequence number is incremented, its LS 1100 age is set to 0, its LS checksum is calculated, and the LSA 1101 is added to the link state database and flooded out the 1102 appropriate interfaces. 1104 To the list of events causing LSAs to be reoriginated, which 1105 for IPv4 is given in Section 12.4 of [Ref1], the following 1106 events and/or actions are added for IPv6: 1108 o The state of one of the router's interfaces changes. The 1109 router may need to (re)originate or flush its Link-LSA 1110 and one or more router-LSAs and/or intra-area-prefix- 1111 LSAs. 1113 o The identity of a link's Designated Router changes. The 1114 router may need to (re)originate or flush the link's 1115 network-LSA and one or more router-LSAs and/or intra- 1116 area-prefix-LSAs. 1118 o A neighbor transitions to/from "Full" state. The router 1119 may need to (re)originate or flush the link's network- 1120 LSA and one or more router-LSAs and/or intra-area- 1121 prefix-LSAs. 1123 o The Interface ID of a neighbor changes. This may cause a 1124 new instance of a router-LSA to be originated for the 1125 associated area, and the reorigination of one or more 1126 intra-area-prefix-LSAs. 1128 o A new prefix is added to an attached link, or a prefix 1129 is deleted (both through configuration). This causes the 1130 router to reoriginate its link-LSA for the link, or, if 1131 it is the only router attached to the link, causes the 1132 router to reoriginate an intra-area-prefix-LSA. 1134 o A new link-LSA is received, causing the link's 1135 collection of prefixes to change. If the router is 1136 Designated Router for the link, it originates a new 1137 intra-area-prefix-LSA. 1139 Detailed construction of the seven required IPv6 LSA types 1140 is supplied by the following subsections. In order to 1141 display example LSAs, the network map in Figure 15 of [Ref1] 1142 has been reworked to show IPv6 addressing, resulting in 1143 Figure 1. The OSPF cost of each interface is has been 1144 displayed in Figure 1. The assignment of IPv6 prefixes to 1145 network links is shown in Table 1. A single area address 1146 range has been configured for Area 1, so that outside of 1147 Area 1 all of its prefixes are covered by a single route to 1148 5f00:0000:c001::/48. The OSPF interface IDs and the link- 1149 local addresses for the router interfaces in Figure 1 are 1150 given in Table 2. 1152 .......................................... 1153 . Area 1. 1154 . + . 1155 . | . 1156 . | 3+---+1 . 1157 . N1 |--|RT1|-----+ . 1158 . | +---+ \ . 1159 . | \ ______ . 1160 . + \/ \ 1+---+ 1161 . * N3 *------|RT4|------ 1162 . + /\_______/ +---+ 1163 . | / | . 1164 . | 3+---+1 / | . 1165 . N2 |--|RT2|-----+ 1| . 1166 . | +---+ +---+ . 1167 . | |RT3|---------------- 1168 . + +---+ . 1169 . |2 . 1170 . | . 1171 . +------------+ . 1172 . N4 . 1173 .......................................... 1175 Figure 1: Area 1 with IP addresses shown 1177 Network IPv6 prefix 1178 ----------------------------------- 1179 N1 5f00:0000:c001:0200::/56 1180 N2 5f00:0000:c001:0300::/56 1181 N3 5f00:0000:c001:0100::/56 1182 N4 5f00:0000:c001:0400::/56 1184 Table 1: IPv6 link prefixes for sample network 1185 Router interface Interface ID link-local address 1186 ------------------------------------------------------- 1187 RT1 to N1 1 fe80:0001::RT1 1188 to N3 2 fe80:0002::RT1 1189 RT2 to N2 1 fe80:0001::RT2 1190 to N3 2 fe80:0002::RT2 1191 RT3 to N3 1 fe80:0001::RT3 1192 to N4 2 fe80:0002::RT3 1193 RT4 to N3 1 fe80:0001::RT4 1195 Table 2: OSPF Interface IDs and link-local addresses 1197 3.4.3.1. Router-LSAs 1199 The LS type of a router-LSA is set to the value 0x2001. 1200 Router-LSAs have area flooding scope. A router may 1201 originate one or more router-LSAs for a given area. Each 1202 router-LSA contains an integral number of interface 1203 descriptions; taken together, the collection of router- 1204 LSAs originated by the router for an area describes the 1205 collected states of all the router's interfaces to the 1206 area. When multiple router-LSAs are used, they are 1207 distinguished by their Link State ID fields. 1209 The Options field in the router-LSA should be coded as 1210 follows. The V6-bit should be set. The E-bit should be 1211 clear if and only if the attached area is an OSPF stub 1212 area. The MC-bit should be set if and only if the router 1213 is running MOSPF (see [Ref8]). The N-bit should be set 1214 if and only if the attached area is an OSPF NSSA area. 1215 The R-bit should be set. The DC-bit should be set if and 1216 only if the router can correctly process the DoNotAge 1217 bit when it appears in the LS age field of LSAs (see 1218 [Ref11]). All unrecognized bits in the Options field 1219 should be cleared 1221 To the left of the Options field, the router capability 1222 bits V, E and B should be coded according to Section 1223 12.4.1 of [Ref1]. Bit W should be coded according to 1224 [Ref8]. 1226 Each of the router's interfaces to the area are then 1227 described by appending "link descriptions" to the 1228 router-LSA. Each link description is 16 bytes long, 1229 consisting of 5 fields: (link) Type, Metric, Interface 1230 ID, Neighbor Interface ID and Neighbor Router ID (see 1231 Section A.4.3). Interfaces in state "Down" or "Loopback" 1232 are not described (although looped back interfaces can 1233 contribute prefixes to Intra-Area-Prefix-LSAs). Nor are 1234 interfaces without any full adjacencies described. All 1235 other interfaces to the area add zero, one or more link 1236 descriptions, the number and content of which depend on 1237 the interface type. Within each link description, the 1238 Metric field is always set the interface's output cost 1239 and the Interface ID field is set to the interface's 1240 OSPF Interface ID. 1242 Point-to-point interfaces 1243 If the neighboring router is fully adjacent, add a 1244 Type 1 link description (point-to-point). The 1245 Neighbor Interface ID field is set to the Interface 1246 ID advertised by the neighbor in its Hello packets, 1247 and the Neighbor Router ID field is set to the 1248 neighbor's Router ID. 1250 Broadcast and NBMA interfaces 1251 If the router is fully adjacent to the link's 1252 Designated Router, or if the router itself is 1253 Designated Router and is fully adjacent to at least 1254 one other router, add a single Type 2 link 1255 description (transit network). The Neighbor 1256 Interface ID field is set to the Interface ID 1257 advertised by the Designated Router in its Hello 1258 packets, and the Neighbor Router ID field is set to 1259 the Designated Router's Router ID. 1261 Virtual links 1262 If the neighboring router is fully adjacent, add a 1263 Type 4 link description (virtual). The Neighbor 1264 Interface ID field is set to the Interface ID 1265 advertised by the neighbor in its Hello packets, and 1266 the Neighbor Router ID field is set to the 1267 neighbor's Router ID. Note that the output cost of a 1268 virtual link is calculated during the routing table 1269 calculation (see Section 3.7). 1271 Point-to-MultiPoint interfaces 1272 For each fully adjacent neighbor associated with the 1273 interface, add a separate Type 1 link description 1274 (point-to-point) with Neighbor Interface ID field 1275 set to the Interface ID advertised by the neighbor 1276 in its Hello packets, and Neighbor Router ID field 1277 set to the neighbor's Router ID. 1279 As an example, consider the router-LSA that router RT3 1280 would originate for Area 1 in Figure 1. Only a single 1281 interface must be described, namely that which connects 1282 to the transit network N3. It assumes that RT4 has been 1283 elected Designated Router of Network N3. 1285 ; RT3's router-LSA for Area 1 1287 LS age = 0 ;newly (re)originated 1288 LS type = 0x2001 ;router-LSA 1289 Link State ID = 0 ;first fragment 1290 Advertising Router = 192.1.1.3 ;RT3's Router ID 1291 bit E = 0 ;not an AS boundary router 1292 bit B = 1 ;area border router 1293 Options = (V6-bit|E-bit|R-bit) 1294 Type = 2 ;connects to N3 1295 Metric = 1 ;cost to N3 1296 Interface ID = 1 ;RT3's Interface ID on N3 1297 Neighbor Interface ID = 1 ;RT4's Interface ID on N3 1298 Neighbor Router ID = 192.1.1.4 ; RT4's Router ID 1300 If for example another router was added to Network N4, 1301 RT3 would have to advertise a second link description 1302 for its connection to (the now transit) network N4. This 1303 could be accomplished by reoriginating the above router- 1304 LSA, this time with two link descriptions. Or, a 1305 separate router-LSA could be originated with a separate 1306 Link State ID (e.g., using a Link State ID of 1) to 1307 describe the connection to N4. 1309 Host routes no longer appear in the router-LSA, but are 1310 instead included in intra-area-prefix-LSAs. 1312 3.4.3.2. Network-LSAs 1314 The LS type of a network-LSA is set to the value 0x2002. 1315 Network-LSAs have area flooding scope. A network-LSA is 1316 originated for every transit broadcast or NBMA link, by 1317 the link's Designated Router. Transit links are those 1318 that have two or more attached routers. The network-LSA 1319 lists all routers attached to the link. 1321 The procedure for originating network-LSAs in IPv6 is 1322 the same as the IPv4 procedure documented in Section 1323 12.4.2 of [Ref1], with the following exceptions: 1325 o An IPv6 network-LSA's Link State ID is set to the 1326 Interface ID of the Designated Router on the link. 1328 o IPv6 network-LSAs do not contain a Network Mask. All 1329 addressing information formerly contained in the 1330 IPv4 network-LSA has now been consigned to intra- 1331 Area-Prefix-LSAs. 1333 o The Options field in the network-LSA is set to the 1334 logical OR of the Options fields contained within 1335 the link's associated link-LSAs. In this way, the 1336 network link exhibits a capability when at least one 1337 of the link's routers requests that the capability 1338 be asserted. 1340 As an example, assuming that Router RT4 has been elected 1341 Designated Router of Network N3 in Figure 1, the 1342 following network-LSA is originated: 1344 ; Network-LSA for Network N3 1346 LS age = 0 ;newly (re)originated 1347 LS type = 0x2002 ;network-LSA 1348 Link State ID = 1 ;RT4's Interface ID on N3 1349 Advertising Router = 192.1.1.4 ;RT4's Router ID 1350 Options = (V6-bit|E-bit|R-bit) 1351 Attached Router = 192.1.1.4 ;Router ID 1352 Attached Router = 192.1.1.1 ;Router ID 1353 Attached Router = 192.1.1.2 ;Router ID 1354 Attached Router = 192.1.1.3 ;Router ID 1356 3.4.3.3. Inter-Area-Prefix-LSAs 1358 The LS type of an inter-area-prefix-LSA is set to the 1359 value 0x2003. Inter-area-prefix-LSAs have area flooding 1360 scope. In IPv4, inter-area-prefix-LSAs were called type 1361 3 summary-LSAs. Each inter-area-prefix-LSA describes a 1362 prefix external to the area, yet internal to the 1363 Autonomous System. 1365 The procedure for originating inter-area-prefix-LSAs in 1366 IPv6 is the same as the IPv4 procedure documented in 1367 Sections 12.4.3 and 12.4.3.1 of [Ref1], with the 1368 following exceptions: 1370 o The Link State ID of an inter-area-prefix-LSA has 1371 lost all of its addressing semantics, and instead 1372 simply serves to distinguish multiple inter-area- 1373 prefix-LSAs that are originated by the same router. 1375 o The prefix is described by the PrefixLength, 1376 PrefixOptions and Address Prefix fields embedded 1377 within the LSA body. Network Mask is no longer 1378 specified. 1380 o The NU-bit in the PrefixOptions field should be 1381 clear. The coding of the MC-bit depends upon 1382 whether, and if so how, MOSPF is operating in the 1383 routing domain (see [Ref8]). 1385 o Link-local addresses can never be advertised in 1386 inter-area-prefix-LSAs. 1388 As an example, the following shows the inter-area- 1389 prefix-LSA that Router RT4 originates into the OSPF 1390 backbone area, condensing all of Area 1's prefixes into 1391 the single prefix 5f00:0000:c001::/48. The cost is set 1392 to 4, which is the maximum cost to all of the prefix' 1393 individual components. The prefix is padded out to an 1394 even number of 32-bit words, so that it consumes 64-bits 1395 of space instead of 48 bits. 1397 ; Inter-area-prefix-LSA for Area 1 addresses 1398 ; originated by Router RT4 into the backbone 1400 LS age = 0 ;newly (re)originated 1401 LS type = 0x2003 ;inter-area-prefix-LSA 1402 Advertising Router = 192.1.1.4 ;RT4's ID 1403 Metric = 4 ;maximum to components 1404 PrefixLength = 48 1405 PrefixOptions = 0 1406 Address Prefix = 5f00:0000:c001 ;padded to 64-bits 1408 3.4.3.4. Inter-Area-Router-LSAs 1410 The LS type of an inter-area-router-LSA is set to the 1411 value 0x2004. Inter-area-router-LSAs have area flooding 1412 scope. In IPv4, inter-area-router-LSAs were called type 1413 4 summary-LSAs. Each inter-area-router-LSA describes a 1414 path to a destination OSPF router (an ASBR) that is 1415 external to the area, yet internal to the Autonomous 1416 System. 1418 The procedure for originating inter-area-router-LSAs in 1419 IPv6 is the same as the IPv4 procedure documented in 1420 Section 12.4.3 of [Ref1], with the following exceptions: 1422 o The Link State ID of an inter-area-router-LSA is no 1423 longer the destination router's OSPF Router ID, but 1424 instead simply serves to distinguish multiple inter- 1425 area-router-LSAs that are originated by the same 1426 router. The destination router's Router ID is now 1427 found in the body of the LSA. 1429 o The Options field in an inter-area-router-LSA should 1430 be set equal to the Options field contained in the 1431 destination router's own router-LSA. The Options 1432 field thus describes the capabilities supported by 1433 the destination router. 1435 As an example, consider the OSPF Autonomous System 1436 depicted in Figure 6 of [Ref1]. Router RT4 would 1437 originate into Area 1 the following inter-area-router- 1438 LSA for destination router RT7. 1440 ; inter-area-router-LSA for AS boundary router RT7 1441 ; originated by Router RT4 into Area 1 1443 LS age = 0 ;newly (re)originated 1444 LS type = 0x2004 ;inter-area-router-LSA 1445 Advertising Router = 192.1.1.4 ;RT4's ID 1446 Options = (V6-bit|E-bit|R-bit) ;RT7's capabilities 1447 Metric = 14 ;cost to RT7 1448 Destination Router ID = Router RT7's ID 1450 3.4.3.5. AS-external-LSAs 1452 The LS type of an AS-external-LSA is set to the value 1453 0x4005. AS-external-LSAs have AS flooding scope. Each 1454 AS-external-LSA describes a path to a prefix external to 1455 the Autonomous System. 1457 The procedure for originating AS-external-LSAs in IPv6 1458 is the same as the IPv4 procedure documented in Section 1459 12.4.4 of [Ref1], with the following exceptions: 1461 o The Link State ID of an AS-external-LSA has lost all 1462 of its addressing semantics, and instead simply 1463 serves to distinguish multiple AS-external-LSAs that 1464 are originated by the same router. 1466 o The prefix is described by the PrefixLength, 1467 PrefixOptions and Address Prefix fields embedded 1468 within the LSA body. Network Mask is no longer 1469 specified. 1471 o The NU-bit in the PrefixOptions field should be 1472 clear. The coding of the MC-bit depends upon 1473 whether, and if so how, MOSPF is operating in the 1474 routing domain (see [Ref8]). 1476 o Link-local addresses can never be advertised in AS- 1477 external-LSAs. 1479 o The forwarding address is present in the AS- 1480 external-LSA if and only if the AS-external-LSA's 1481 bit F is set. 1483 o The external route tag is present in the AS- 1484 external-LSA if and only if the AS-external-LSA's 1485 bit T is set. 1487 o The capability for an AS-external-LSA to reference 1488 another LSA has been included, by inclusion of the 1489 Referenced LS Type field and the optional Referenced 1490 Link State ID field (the latter present if and only 1491 if Referenced LS Type is non-zero). This capability 1492 is for future use; for now Referenced LS Type should 1493 be set to 0. 1495 As an example, consider the OSPF Autonomous System 1496 depicted in Figure 6 of [Ref1]. Assume that RT7 has 1497 learned its route to N12 via BGP, and that it wishes to 1498 advertise a Type 2 metric into the AS. Further assume 1499 the the IPv6 prefix for N12 is the value 1500 5f00:0000:0a00::/40. RT7 would then originate the 1501 following AS-external-LSA for the external network N12. 1502 Note that within the AS-external-LSA, N12's prefix 1503 occupies 64 bits of space, to maintain 32-bit alignment. 1505 ; AS-external-LSA for Network N12, 1506 ; originated by Router RT7 1508 LS age = 0 ;newly (re)originated 1509 LS type = 0x4005 ;AS-external-LSA 1510 Link State ID = 123 ;or something else 1511 Advertising Router = Router RT7's ID 1512 bit E = 1 ;Type 2 metric 1513 bit F = 0 ;no forwarding address 1514 bit T = 1 ;external route tag included 1515 Metric = 2 1516 PrefixLength = 40 1517 PrefixOptions = 0 1518 Referenced LS Type = 0 ;no Referenced Link State ID 1519 Address Prefix = 5f00:0000:0a00 ;padded to 64-bits 1520 External Route Tag = as per BGP/OSPF interaction 1522 3.4.3.6. Link-LSAs 1524 The LS type of a Link-LSA is set to the value 0x0008. 1525 Link-LSAs have link-local flooding scope. A router 1526 originates a separate Link-LSA for each attached link 1527 that supports 2 or more (including the originating 1528 router itself) routers. 1530 Link-LSAs have three purposes: 1) they provide the 1531 router's link-local address to all other routers 1532 attached to the link and 2) they inform other routers 1533 attached to the link of a list of IPv6 prefixes to 1534 associate with the link and 3) they allow the router to 1535 assert a collection of Options bits in the Network-LSA 1536 that will be originated for the link. 1538 A Link-LSA for a given Link L is built in the following 1539 fashion: 1541 o The Link State ID is set to the router's Interface 1542 ID on Link L. 1544 o The Router Priority of the router's interface to 1545 Link L is inserted into the Link-LSA. 1547 o The Link-LSA's Options field is set to those bits 1548 that the router wishes set in Link L's Network LSA. 1550 o The router inserts its link-local address on Link L 1551 into the Link-LSA. This information will be used 1552 when the other routers on Link L do their next hop 1553 calculations (see Section 3.8.1.1). 1555 o Each IPv6 address prefix that has been configured 1556 into the router for Link L is added to the Link-LSA, 1557 by specifying values for PrefixLength, 1558 PrefixOptions, and Address Prefix fields. 1560 After building a Link-LSA for a given link, the router 1561 installs the link-LSA into the associate interface data 1562 structure and floods the Link-LSA onto the link. All 1563 other routers on the link will receive the Link-LSA, but 1564 it will go no further. 1566 As an example, consider the Link-LSA that RT3 will build 1567 for N3 in Figure 1. Suppose that the prefix 1568 5f00:0000:c001:0100::/56 has been configured within RT3 1569 for N3. This will give rise to the following Link-LSA, 1570 which RT3 will flood onto N3, but nowhere else. Note 1571 that not all routers on N3 need be configured with the 1572 prefix; those not configured will learn the prefix when 1573 receiving RT3's Link-LSA. 1575 ; RT3's Link-LSA for N3 1577 LS age = 0 ;newly (re)originated 1578 LS type = 0x0008 ;Link-LSA 1579 Link State ID = 1 ;RT3's Interface ID on N3 1580 Advertising Router = 192.1.1.3 ;RT3's Router ID 1581 Rtr Pri = 1 ;RT3's N3 Router Priority 1582 Options = (V6-bit|E-bit|R-bit) 1583 Link-local Interface Address = fe80:0001::RT3 1584 # prefixes = 1 1585 PrefixLength = 56 1586 PrefixOptions = 0 1587 Address Prefix = 5f00:0000:c001:0100 ;pad to 64-bits 1589 3.4.3.7. Intra-Area-Prefix-LSAs 1591 The LS type of an intra-area-prefix-LSA is set to the 1592 value 0x2009. Intra-area-prefix-LSAs have area flooding 1593 scope. An intra-area-prefix-LSA has one of two 1594 functions. It associates a list of IPv6 address prefixes 1595 with a transit network link by referencing a network- 1596 LSA, or associates a list of IPv6 address prefixes with 1597 a router by referencing a router-LSA. A stub link's 1598 prefixes are associated with its attached router. 1600 A router may originate multiple intra-area-prefix-LSAs 1601 for a given area, distinguished by their Link State ID 1602 fields. Each intra-area-prefix-LSA contains an integral 1603 number of prefix descriptions. 1605 A link's Designated Router originates one or more intra- 1606 area-prefix-LSAs to advertise the link's prefixes 1607 throughout the area. For a link L, L's Designated Router 1608 builds an intra-area-prefix-LSA in the following 1609 fashion: 1611 o In order to indicate that the prefixes are to be 1612 associated with the Link L, the fields Referenced LS 1613 type, Referenced Link State ID, and Referenced 1614 Advertising Router are set to the corresponding 1615 fields in Link L's network-LSA (namely LS type, Link 1616 State ID, and Advertising Router respectively). This 1617 means that Referenced LS Type is set to 0x2002, 1618 Referenced Link State ID is set to the Designated 1619 Router's Interface ID on Link L, and Referenced 1620 Advertising Router is set to the Designated Router's 1621 Router ID. 1623 o Each Link-LSA associated with Link L is examined 1624 (these are in the Designated Router's interface 1625 structure for Link L). If the Link-LSA's Advertising 1626 Router is fully adjacent to the Designated Router, 1627 the list of prefixes in the Link-LSA is copied into 1628 the intra-area-prefix-LSA that is being built. 1629 Prefixes having the NU-bit and/or LA-bit set in 1630 their Options field should not be copied, nor should 1631 link-local addresses be copied. Each prefix is 1632 described by the PrefixLength, PrefixOptions, and 1633 Address Prefix fields. Multiple prefixes having the 1634 same PrefixLength and Address Prefix are considered 1635 to be duplicates; in this case their Prefix Options 1636 fields should be merged by logically OR'ing the 1637 fields together, and a single resulting prefix 1638 should be copied into the intra-area-prefix-LSA. The 1639 Metric field for all prefixes is set to 0. 1641 o The "# prefixes" field is set to the number of 1642 prefixes that the router has copied into the LSA. If 1643 necessary, the list of prefixes can be spread across 1644 multiple intra-area-prefix-LSAs in order to keep the 1645 LSA size small. 1647 A router builds an intra-area-prefix-LSA to advertise 1648 its own prefixes, and those of its attached stub links. 1649 A Router RTX would build its intra-area-prefix-LSA in 1650 the following fashion: 1652 o In order to indicate that the prefixes are to be 1653 associated with the Router RTX itself, RTX sets 1654 Referenced LS type to 0x2001, Referenced Link State 1655 ID to 0, and Referenced Advertising Router to RTX's 1656 own Router ID. 1658 o Router RTX examines its list of interfaces to the 1659 area. If the interface is in state Down, its 1660 prefixes are not included. If the interface has been 1661 reported in RTX's router-LSA as a Type 2 link 1662 description (link to transit network), its prefixes 1663 are not included (they will be included in the 1664 intra-area-prefix-LSA for the link instead). If the 1665 interface type is Point-to-MultiPoint, or the 1666 interface is in state Loopback, or the interface 1667 connects to a point-to-point link which has not been 1668 assigned a prefix, then the site-local and global 1669 scope IPv6 addresses associated with the interface 1670 (if any) are copied into the intra-area-prefix-LSA, 1671 setting the LA-bit in the PrefixOptions field, and 1672 setting the PrefixLength to 128 and the Metric to 0. 1673 Otherwise, the list of site-local and global 1674 prefixes configured in RTX for the link are copied 1675 into the intra-area-prefix-LSA by specifying the 1676 PrefixLength, PrefixOptions, and Address Prefix 1677 fields. The Metric field for each of these prefixes 1678 is set to the interface's output cost. 1680 o RTX adds the IPv6 prefixes for any directly attached 1681 hosts belonging to the area (see Section C.7) to the 1682 intra-area-prefix-LSA. 1684 o If RTX has one or more virtual links configured 1685 through the area, it includes one of its site-local 1686 or global scope IPv6 interface addresses in the LSA 1687 (if it hasn't already), setting the LA-bit in the 1688 PrefixOptions field, and setting the PrefixLength to 1689 128 and the Metric to 0. This information will be 1690 used later in the routing calculation so that the 1691 two ends of the virtual link can discover each 1692 other's IPv6 addresses. 1694 o The "# prefixes" field is set to the number of 1695 prefixes that the router has copied into the LSA. If 1696 necessary, the list of prefixes can be spread across 1697 multiple intra-area-prefix-LSAs in order to keep the 1698 LSA size small. 1700 For example, the intra-area-prefix-LSA originated by RT4 1701 for Network N3 (assuming that RT4 is N3's Designated 1702 Router), and the intra-area-prefix-LSA originated into 1703 Area 1 by Router RT3 for its own prefixes, are pictured 1704 below. 1706 ; Intra-area-prefix-LSA 1707 ; for network link N3 1709 LS age = 0 ;newly (re)originated 1710 LS type = 0x2009 ;Intra-area-prefix-LSA 1711 Link State ID = 5 ;or something 1712 Advertising Router = 192.1.1.4 ;RT4's Router ID 1713 # prefixes = 1 1714 Referenced LS type = 0x2002 ;network-LSA reference 1715 Referenced Link State ID = 1 1716 Referenced Advertising Router = 192.1.1.4 1717 PrefixLength = 56 ;N3's prefix 1718 PrefixOptions = 0 1719 Metric = 0 1720 Address Prefix = 5f00:0000:c001:0100 ;pad 1722 ; RT3's Intra-area-prefix-LSA 1723 ; for its own prefixes 1725 LS age = 0 ;newly (re)originated 1726 LS type = 0x2009 ;Intra-area-prefix-LSA 1727 Link State ID = 177 ;or something 1728 Advertising Router = 192.1.1.3 ;RT3's Router ID 1729 # prefixes = 1 1730 Referenced LS type = 0x2001 ;router-LSA reference 1731 Referenced Link State ID = 0 1732 Referenced Advertising Router = 192.1.1.3 1733 PrefixLength = 56 ;N4's prefix 1734 PrefixOptions = 0 1735 Metric = 2 ;N4 interface cost 1736 Address Prefix = 5f00:0000:c001:0400 ;pad 1738 When network conditions change, it may be necessary for 1739 a router to move prefixes from one intra-area-prefix-LSA 1740 to another. For example, if the router is Designated 1741 Router for a link but the link has no other attached 1742 routers, the link's prefixes are advertised in an intra- 1743 area-prefix-LSA referring to the Designated Router's 1744 router-LSA. When additional routers appear on the link, 1745 a network-LSA is originated for the link and the link's 1746 prefixes are moved to an intra-area-prefix-LSA referring 1747 to the network-LSA. 1749 Note that in the intra-area-prefix-LSA, the "Referenced 1750 Advertising Router" is always equal to the router that 1751 is originating the intra-area-prefix-LSA (i.e., the 1752 LSA's Advertising Router). The reason that the 1753 Referenced Advertising Router field appears is that, 1754 even though it is currently redundant, it may not be in 1755 the future. We may sometime want to use the same LSA 1756 format to advertise address prefixes for other protocol 1757 suites. In that event, the Designated Router may not be 1758 running the other protocol suite, and so another of the 1759 link's routers may need to send out the prefix-LSA. In 1760 that case, "Referenced Advertising Router" and 1761 "Advertising Router" would be different. 1763 3.5. Flooding 1765 Most of the flooding algorithm remains unchanged from the IPv4 1766 flooding mechanisms described in Section 13 of [Ref1]. In 1767 particular, the processes for determining which LSA instance is 1768 newer (Section 13.1 of [Ref1]), responding to updates of self- 1769 originated LSAs (Section 13.4 of [Ref1]), sending Link State 1770 Acknowledgment packets (Section 13.5 of [Ref1]), retransmitting 1771 LSAs (Section 13.6 of [Ref1]) and receiving Link State 1772 Acknowledgment packets (Section 13.7 of [Ref1]) are exactly the 1773 same for IPv6 and IPv4. 1775 However, the addition of flooding scope and handling options for 1776 unrecognized LSA types (see Section A.4.2.1) has caused some 1777 changes in the OSPF flooding algorithm: the reception of Link 1778 State Updates (Section 13 in [Ref1]) and the sending of Link 1779 State Updates (Section 13.3 of [Ref1]) must take into account 1780 the LSA's scope and U-bit setting. Also, installation of LSAs 1781 into the OSPF database (Section 13.2 of [Ref1]) causes different 1782 events in IPv6, due to the reorganization of LSA types and 1783 contents in IPv6. These changes are described in detail below. 1785 3.5.1. Receiving Link State Update packets 1787 The encoding of flooding scope in the LS type and the need 1788 to process unknown LS types causes modifications to the 1789 processing of received Link State Update packets. As in 1790 IPv4, each LSA in a received Link State Update packet is 1791 examined. In IPv4, eight steps are executed for each LSA, as 1792 described in Section 13 of [Ref1]. For IPv6, all the steps 1793 are the same, except that Steps 2 and 3 are modified as 1794 follows: 1796 (2) Examine the LSA's LS type. If the LS type is 1797 unknown, the area has been configured as a stub area, 1798 and either the LSA's flooding scope is set to "AS 1799 flooding scope" or the U-bit of the LS type is set to 1800 1 (flood even when unrecognized), then discard the 1801 LSA and get the next one from the Link State Update 1802 Packet. This generalizes the IPv4 behavior where AS- 1803 external-LSAs are not flooded into/throughout stub 1804 areas. 1806 (3) Else if the flooding scope of the LSA is set to 1807 "reserved", discard the LSA and get the next one from 1808 the Link State Update Packet. 1810 Steps 5b (sending Link State Update packets) and 5d 1811 (installing LSAs in the link state database) in Section 13 1812 of [Ref1] are also somewhat different for IPv6, as described 1813 in Sections 3.5.2 and 3.5.3 below. 1815 3.5.2. Sending Link State Update packets 1817 The sending of Link State Update packets is described in 1818 Section 13.3 of [Ref1]. For IPv4 and IPv6, the steps for 1819 sending a Link State Update packet are the same (steps 1 1820 through 5 of Section 13.3 in [Ref1]). However, the list of 1821 eligible interfaces out which to flood the LSA is different. 1822 For IPv6, the eligible interfaces are selected based on the 1823 following factors: 1825 o The LSA's flooding scope. 1827 o For LSAs with area or link-local flooding scoping, the 1828 particular area or interface that the LSA is associated 1829 with. 1831 o Whether the LSA has a recognized LS type. 1833 o The setting of the U-bit in the LS type. If the U-bit is 1834 set to 0, unrecognized LS types are treated as having 1835 link-local scope. If set to 1, unrecognized LS types are 1836 stored and flooded as if they were recognized. 1838 Choosing the set of eligible interfaces then breaks into the 1839 following cases: 1841 Case 1 1842 The LSA's LS type is recognized. In this case, the set 1843 of eligible interfaces is set depending on the flooding 1844 scope encoded in the LS type. If the flooding scope is 1845 "AS flooding scope", the eligible interfaces are all 1846 router interfaces excepting virtual links. In addition, 1847 AS-external-LSAs are not flooded out interfaces 1848 connecting to stub areas. If the flooding scope is "area 1849 flooding scope", the set of eligible interfaces are 1850 those interfaces connecting to the LSA's associated 1851 area. If the flooding scope is "link-local flooding 1852 scope", then there is a single eligible interface, the 1853 one connecting to the LSA's associated link (which, when 1854 the LSA is received in a Link State Update packet, is 1855 also the interface the LSA was received on). 1857 Case 2 1858 The LS type is unrecognized, and the U-bit in the LS 1859 Type is set to 0 (treat the LSA as if it had link-local 1860 flooding scope). In this case there is a single eligible 1861 interface, namely, the interface on which the LSA was 1862 received. 1864 Case 3 1865 The LS type is unrecognized, and the U-bit in the LS 1866 Type is set to 1 (store and flood the LSA, as if type 1867 understood). In this case, select the eligible 1868 interfaces based on the encoded flooding scope as in 1869 Case 1 above. However, in this case interfaces attached 1870 to stub areas are always excluded. 1872 A further decision must sometimes be made before adding an 1873 LSA to a given neighbor's link-state retransmission list 1874 (Step 1d in Section 13.3 of [Ref1]). If the LS type is 1875 recognized by the router, but not by the neighbor (as can be 1876 determined by examining the Options field that the neighbor 1877 advertised in its Database Description packet) and the LSA's 1878 U-bit is set to 0, then the LSA should be added to the 1879 neighbor's link-state retransmission list if and only if 1880 that neighbor is the Designated Router or Backup Designated 1881 Router for the attached link. The LS types described in 1882 detail by this memo, namely router-LSAs (LS type 0x2001), 1883 network-LSAs (0x2002), Inter-Area-Prefix-LSAs (0x2003), 1884 Inter-Area-Router-LSAs (0x2004), AS-External-LSAs (0x4005), 1885 Link-LSAs (0x0008) and Intra-Area-Prefix-LSAs (0x2009) are 1886 assumed to be understood by all routers. However, as an 1887 example the group-membership-LSA (0x2006) is understood only 1888 by MOSPF routers and since it has its U-bit set to 0, it 1889 should only be forwarded to a non-MOSPF neighbor (determined 1890 by examining the MC-bit in the neighbor's Database 1891 Description packets' Options field) when the neighbor is 1892 Designated Router or Backup Designated Router for the 1893 attached link. 1895 The previous paragraph solves a problem in IPv4 OSPF 1896 extensions such as MOSPF, which require that the Designated 1897 Router support the extension in order to have the new LSA 1898 types flooded across broadcast and NBMA networks (see 1899 Section 10.2 of [Ref8]). 1901 3.5.3. Installing LSAs in the database 1903 There are three separate places to store LSAs, depending on 1904 their flooding scope. LSAs with AS flooding scope are stored 1905 in the global OSPF data structure (see Section 3.1) as long 1906 as their LS type is known or their U-bit is 1. LSAs with 1907 area flooding scope are stored in the appropriate area data 1908 structure (see Section 3.1.1) as long as their LS type is 1909 known or their U-bit is 1. LSAs with link-local flooding 1910 scope, and those LSAs with unknown LS type and U-bit set to 1911 0 (treat the LSA as if it had link-local flooding scope) are 1912 stored in the appropriate interface structure. 1914 When storing the LSA into the link-state database, a check 1915 must be made to see whether the LSA's contents have changed. 1916 Changes in contents are indicated exactly as in Section 13.2 1917 of [Ref1]. When an LSA's contents have been changed, the 1918 following parts of the routing table must be recalculated, 1919 based on the LSA's LS type: 1921 Router-LSAs, Network-LSAs, Intra-Area-Prefix-LSAs and Link- 1922 LSAs 1923 The entire routing table is recalculated, starting with 1924 the shortest path calculation for each area (see Section 1925 3.8). 1927 Inter-Area-Prefix-LSAs and Inter-Area-Router-LSAs 1928 The best route to the destination described by the LSA 1929 must be recalculated (see Section 16.5 in [Ref1]). If 1930 this destination is an AS boundary router, it may also 1931 be necessary to re-examine all the AS-external-LSAs. 1933 AS-external-LSAs 1934 The best route to the destination described by the AS- 1935 external-LSA must be recalculated (see Section 16.6 in 1936 [Ref1]). 1938 As in IPv4, any old instance of the LSA must be removed from 1939 the database when the new LSA is installed. This old 1940 instance must also be removed from all neighbors' Link state 1941 retransmission lists. 1943 3.6. Definition of self-originated LSAs 1945 In IPv6 the definition of a self-originated LSA has been 1946 simplified from the IPv4 definition appearing in Sections 13.4 1947 and 14.1 of [Ref1]. For IPv6, self-originated LSAs are those 1948 LSAs whose Advertising Router is equal to the router's own 1949 Router ID. 1951 3.7. Virtual links 1953 OSPF virtual links for IPv4 are described in Section 15 of 1954 [Ref1]. Virtual links are the same in IPv6, with the following 1955 exceptions: 1957 o LSAs having AS flooding scope are never flooded over virtual 1958 adjacencies, nor are LSAs with AS flooding scope summarized 1959 over virtual adjacencies during the Database Exchange 1960 process. This is a generalization of the IPv4 treatment of 1961 AS-external-LSAs. 1963 o The IPv6 interface address of a virtual link must be an IPv6 1964 address having site-local or global scope, instead of the 1965 link-local addresses used by other interface types. This 1966 address is used as the IPv6 source for OSPF protocol packets 1967 sent over the virtual link. 1969 o Likewise, the virtual neighbor's IPv6 address is an IPv6 1970 address with site-local or global scope. To enable the 1971 discovery of a virtual neighbor's IPv6 address during the 1972 routing calculation, the neighbor advertises its virtual 1973 link's IPv6 interface address in an Intra-Area-Prefix-LSA 1974 originated for the virtual link's transit area (see Sections 1975 3.4.3.7 and 3.8.1). 1977 o Like all other IPv6 OSPF interfaces, virtual links are 1978 assigned unique (within the router) Interface IDs. These are 1979 advertised in Hellos sent over the virtual link, and in the 1980 router's router-LSAs. 1982 3.8. Routing table calculation 1984 The IPv6 OSPF routing calculation proceeds along the same lines 1985 as the IPv4 OSPF routing calculation, following the five steps 1986 specified by Section 16 of [Ref1]. High level differences 1987 between the IPv6 and IPv4 calculations include: 1989 o Prefix information has been removed from router-LSAs, and 1990 now is advertised in intra-area-prefix-LSAs. Whenever [Ref1] 1991 specifies that stub networks within router-LSAs be examined, 1992 IPv6 will instead examine prefixes within intra-area-prefix- 1993 LSAs. 1995 o Type 3 and 4 summary-LSAs have been renamed inter-area- 1996 prefix-LSAs and inter-area-router-LSAs (respectively). 1998 o Addressing information is no longer encoded in Link State 1999 IDs, and must instead be found within the body of LSAs. 2001 o In IPv6, a router can originate multiple router-LSAs within 2002 a single area, distinguished by Link State ID. These router- 2003 LSAs must be treated as a single aggregate by the area's 2004 shortest path calculation (see Section 3.8.1). 2006 For each area, routing table entries have been created for the 2007 area's routers and transit links, in order to store the results 2008 of the area's shortest-path tree calculation (see Section 2009 3.8.1). These entries are then used when processing intra-area- 2010 prefix-LSAs, inter-area-prefix-LSAs and inter-area-router-LSAs, 2011 as described in Section 3.8.2. 2013 Events generated as a result of routing table changes (Section 2014 16.7 of [Ref1]), and the equal-cost multipath logic (Section 2015 16.8 of [Ref1]) are identical for both IPv4 and IPv6. 2017 3.8.1. Calculating the shortest path tree for an area 2019 The IPv4 shortest path calculation is contained in Section 2020 16.1 of [Ref1]. The graph used by the shortest-path tree 2021 calculation is identical for both IPv4 and IPv6. The graph's 2022 vertices are routers and transit links, represented by 2023 router-LSAs and network-LSAs respectively. A router is 2024 identified by its OSPF Router ID, while a transit link is 2025 identified by its Designated Router's Interface ID and OSPF 2026 Router ID. Both routers and transit links have associated 2027 routing table entries within the area (see Section 3.3). 2029 Section 16.1 of [Ref1] splits up the shortest path 2030 calculations into two stages. First the Dijkstra calculation 2031 is performed, and then the stub links are added onto the 2032 tree as leaves. The IPv6 calculation maintains this split. 2034 The Dijkstra calculation for IPv6 is identical to that 2035 specified for IPv4, with the following exceptions 2036 (referencing the steps from the Dijkstra calculation as 2037 described in Section 16.1 of [Ref1]): 2039 o The Vertex ID for a router is the OSPF Router ID. The 2040 Vertex ID for a transit network is a combination of the 2041 Interface ID and OSPF Router ID of the network's 2042 Designated Router. 2044 o In Step 2, when a router Vertex V has just been added to 2045 the shortest path tree, there may be multiple LSAs 2046 associated with the router. All Router-LSAs with 2047 Advertising Router set to V's OSPF Router ID must 2048 processed as an aggregate, treating them as fragments of 2049 a single large router-LSA. The Options field and the 2050 router type bits (bits W, V, E and B) should always be 2051 taken from "fragment" with the smallest Link State ID. 2053 o Step 2a is not needed in IPv6, as there are no longer 2054 stub network links in router-LSAs. 2056 o In Step 2b, if W is a router, there may again be 2057 multiple LSAs associated with the router. All Router- 2058 LSAs with Advertising Router set to W's OSPF Router ID 2059 must processed as an aggregate, treating them as 2060 fragments of a single large router-LSA. 2062 o In Step 4, there are now per-area routing table entries 2063 for each of an area's routers, instead of just the area 2064 border routers. These entries subsume all the 2065 functionality of IPv4's area border router routing table 2066 entries, including the maintenance of virtual links. 2067 When the router added to the area routing table in this 2068 step is the other end of a virtual link, the virtual 2069 neighbor's IP address is set as follows: The collection 2070 of intra-area-prefix-LSAs originated by the virtual 2071 neighbor is examined, with the virtual neighbor's IP 2072 address being set to the first prefix encountered having 2073 the "LA-bit" set. 2075 o Routing table entries for transit networks, which are no 2076 longer associated with IP networks, are also modified in 2077 Step 4. 2079 The next stage of the shortest path calculation proceeds 2080 similarly to the two steps of the second stage of Section 2081 16.1 in [Ref1]. However, instead of examining the stub links 2082 within router-LSAs, the list of the area's intra-area- 2083 prefix-LSAs is examined. A prefix advertisement whose "NU- 2084 bit" is set should not be included in the routing 2085 calculation. The cost of any advertised prefix is the sum of 2086 the prefix' advertised metric plus the cost to the transit 2087 vertex (either router or transit network) identified by 2088 intra-area-prefix-LSA's Referenced LS type, Referenced Link 2089 State ID and Referenced Advertising Router fields. This 2090 latter cost is stored in the transit vertex' routing table 2091 entry for the area. 2093 3.8.1.1. The next hop calculation 2095 In IPv6, the calculation of the next hop's IPv6 address 2096 (which will be a link-local address) proceeds along the 2097 same lines as the IPv4 next hop calculation (see Section 2098 16.1.1 of [Ref1]). The only difference is in calculating 2099 the next hop IPv6 address for a router (call it Router 2100 X) which shares a link with the calculating router. In 2101 this case the calculating router assigns the next hop 2102 IPv6 address to be the link-local interface address 2103 contained in Router X's Link-LSA (see Section A.4.8) for 2104 the link. This procedure is necessary since on some 2105 links, such as NBMA links, the two routers need not be 2106 neighbors, and therefore might not be exchanging OSPF 2107 Hellos. 2109 3.8.2. Calculating the inter-area routes 2111 Calculation of inter-area routes for IPv6 proceeds along the 2112 same lines as the IPv4 calculation in Section 16.2 of 2113 [Ref1], with the following modifications: 2115 o The names of the Type 3 summary-LSAs and Type 4 summary- 2116 LSAs have been changed to inter-area-prefix-LSAs and 2117 inter-area-router-LSAs respectively. 2119 o The Link State ID of the above LSA types no longer 2120 encodes the network or router described by the LSA. 2121 Instead, an address prefix is contained in the body of 2122 an inter-area-prefix-LSA, and a described router's OSPF 2123 Router ID is carried in the body of an inter-area- 2124 router-LSA. 2126 o Prefixes having the "NU-bit" set in their Prefix Options 2127 field should be ignored by the inter-area route 2128 calculation. 2130 When a single inter-area-prefix-LSA or inter-area-router-LSA 2131 has changed, the incremental calculations outlined in 2132 Section 16.5 of [Ref1] can be performed instead of 2133 recalculating the entire routing table. 2135 3.8.3. Examining transit areas' summary-LSAs 2137 Examination of transit areas' summary-LSAs in IPv6 proceeds 2138 along the same lines as the IPv4 calculation in Section 16.3 2139 of [Ref1], modified in the same way as the IPv6 inter-area 2140 route calculation in Section 3.8.2. 2142 3.8.4. Calculating AS external routes 2144 The IPv6 AS external route calculation proceeds along the 2145 same lines as the IPv4 calculation in Section 16.4 of 2146 [Ref1], with the following exceptions: 2148 o The Link State ID of the AS-external-LSA types no longer 2149 encodes the network described by the LSA. Instead, an 2150 address prefix is contained in the body of an AS- 2151 external-LSA. 2153 o The default route is described by AS-external-LSAs which 2154 advertise zero length prefixes. 2156 o Instead of comparing the AS-external-LSA's Forwarding 2157 address field to 0.0.0.0 to see whether a forwarding 2158 address has been used, bit F of the external-LSA is 2159 examined. A forwarding address is in use if and only if 2160 bit F is set. 2162 o Prefixes having the "NU-bit" set in their Prefix Options 2163 field should be ignored by the inter-area route 2164 calculation. 2166 When a single AS-external-LSA has changed, the incremental 2167 calculations outlined in Section 16.6 of [Ref1] can be 2168 performed instead of recalculating the entire routing table. 2170 3.9. Multiple interfaces to a single link 2172 In OSPF for IPv6, a router may have multiple interfaces to a 2173 single link. All interfaces are involved in the reception and 2174 transmission of data traffic, however only a single interface 2175 sends and receives OSPF control traffic. In more detail: 2177 o Each of the multiple interfaces are assigned different 2178 Interface IDs. In this way the router can automatically 2179 detect when multiple interfaces attach to the same link, 2180 when receiving Hellos from its own Router ID but with an 2181 Interface ID other than the receiving interface's. 2183 o The router turns off the sending and receiving of OSPF 2184 packets (that is, control traffic) on all but one of the 2185 interfaces to the link. The choice of interface to send and 2186 receive control traffic is implementation dependent; as one 2187 example, the interface with the highest Interface ID could 2188 be chosen. If the router is elected DR, it will be this 2189 interface's Interface ID that will be used as the network- 2190 LSA's Link State ID. 2192 o All the multiple interfaces to the link will however appear 2193 in the router-LSA. In addition, a Link-LSA will be generated 2194 for each of the multiple interfaces. In this way, all 2195 interfaces will be included in OSPF's routing calculations. 2197 o If the interface which is responsible for sending and 2198 receiving control traffic fails, another will have to take 2199 over, reforming all neighbor adjacencies from scratch. This 2200 failure can be detected by the router itself, when the other 2201 interfaces to the same link cease to hear the router's own 2202 Hellos. 2204 References 2206 [Ref1] Moy, J., "OSPF Version 2", STD 54, RFC 2328, Ascend 2207 Communications, Inc., April 1998. 2209 [Ref2] McKenzie, A., "ISO Transport Protocol specification ISO DP 2210 8073", RFC 905, ISO, April 1984. 2212 [Ref3] McCloghrie, K., and M. Rose, "Management Information Base 2213 for network management of TCP/IP-based internets: MIB-II", 2214 STD 17, RFC 1213, Hughes LAN Systems, Performance Systems 2215 International, March 1991. 2217 [Ref4] Fuller, V., T. Li, J. Yu, and K. Varadhan, "Classless Inter- 2218 Domain Routing (CIDR): an Address Assignment and Aggregation 2219 Strategy", RFC1519, BARRNet, cisco, MERIT, OARnet, September 2220 1993. 2222 [Ref5] Varadhan, K., S. Hares and Y. Rekhter, "BGP4/IDRP for 2223 IP---OSPF Interaction", RFC1745, December 1994 2225 [Ref6] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 2226 1700, USC/Information Sciences Institute, October 1994. 2228 [Ref7] deSouza, O., and M. Rodrigues, "Guidelines for Running OSPF 2229 Over Frame Relay Networks", RFC 1586, March 1994. 2231 [Ref8] Moy, J., "Multicast Extensions to OSPF", RFC 1584, Proteon, 2232 Inc., March 1994. 2234 [Ref9] Coltun, R. and V. Fuller, "The OSPF NSSA Option", RFC 1587, 2235 RainbowBridge Communications, Stanford University, March 2236 1994. 2238 [Ref10] Ferguson, D., "The OSPF External Attributes LSA", 2239 unpublished. 2241 [Ref11] Moy, J., "Extending OSPF to Support Demand Circuits", RFC 2242 1793, Cascade, April 1995. 2244 [Ref12] Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191, 2245 DECWRL, Stanford University, November 1990. 2247 [Ref13] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 2248 (BGP-4)", RFC 1771, T.J. Watson Research Center, IBM Corp., 2249 cisco Systems, March 1995. 2251 [Ref14] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2252 (IPv6) Specification", RFC 2460, Cisco, Nokia, December 2253 1998. 2255 [Ref15] Hinden R. and S. Deering, "IP Version 6 Addressing 2256 Architecture", RFC 2373, Nokia, Cisco Systems, July 1998. 2258 [Ref16] Conta, A. and S. Deering, "Internet Control Message Protocol 2259 (ICMPv6) for the Internet Protocol Version 6 (IPv6) 2260 Specification" RFC 2463, Lucent, Cisco Systems, December 2261 1998. 2263 [Ref17] Narten, T., E. Nordmark and W. Simpson, "Neighbor Discovery 2264 for IP Version 6 (IPv6)", RFC 2461, December 1998. 2266 [Ref18] McCann, J., S. Deering and J. Mogul, "Path MTU Discovery for 2267 IP version 6", RFC 1981, August 1996. 2269 [Ref19] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2270 2402, BBN Corp, @Home Network, November 1998. 2272 [Ref20] Kent S. and R. Atkinson, "IP Encapsulating Security Payload 2273 (ESP)", RFC 2406, BBN Corp, @Home Network, November 1998. 2275 A. OSPF data formats 2277 This appendix describes the format of OSPF protocol packets and OSPF 2278 LSAs. The OSPF protocol runs directly over the IPv6 network layer. 2279 Before any data formats are described, the details of the OSPF 2280 encapsulation are explained. 2282 Next the OSPF Options field is described. This field describes 2283 various capabilities that may or may not be supported by pieces of 2284 the OSPF routing domain. The OSPF Options field is contained in OSPF 2285 Hello packets, Database Description packets and in OSPF LSAs. 2287 OSPF packet formats are detailed in Section A.3. 2289 A description of OSPF LSAs appears in Section A.4. This section 2290 describes how IPv6 address prefixes are represented within LSAs, 2291 details the standard LSA header, and then provides formats for each 2292 of the specific LSA types. 2294 A.1 Encapsulation of OSPF packets 2296 OSPF runs directly over the IPv6's network layer. OSPF packets are 2297 therefore encapsulated solely by IPv6 and local data-link headers. 2299 OSPF does not define a way to fragment its protocol packets, and 2300 depends on IPv6 fragmentation when transmitting packets larger than 2301 the link MTU. If necessary, the length of OSPF packets can be up to 2302 65,535 bytes. The OSPF packet types that are likely to be large 2303 (Database Description Packets, Link State Request, Link State 2304 Update, and Link State Acknowledgment packets) can usually be split 2305 into several separate protocol packets, without loss of 2306 functionality. This is recommended; IPv6 fragmentation should be 2307 avoided whenever possible. Using this reasoning, an attempt should 2308 be made to limit the sizes of OSPF packets sent over virtual links 2309 to 1280 bytes unless Path MTU Discovery is being performed [Ref14]. 2311 The other important features of OSPF's IPv6 encapsulation are: 2313 o Use of IPv6 multicast. Some OSPF messages are multicast, when 2314 sent over broadcast networks. Two distinct IP multicast 2315 addresses are used. Packets sent to these multicast addresses 2316 should never be forwarded; they are meant to travel a single hop 2317 only. As such, the multicast addresses have been chosen with 2318 link-local scope, and packets sent to these addresses should 2319 have their IPv6 Hop Limit set to 1. 2321 AllSPFRouters 2322 This multicast address has been assigned the value FF02::5. 2324 All routers running OSPF should be prepared to receive 2325 packets sent to this address. Hello packets are always sent 2326 to this destination. Also, certain OSPF protocol packets 2327 are sent to this address during the flooding procedure. 2329 AllDRouters 2330 This multicast address has been assigned the value FF02::6. 2331 Both the Designated Router and Backup Designated Router must 2332 be prepared to receive packets destined to this address. 2333 Certain OSPF protocol packets are sent to this address 2334 during the flooding procedure. 2336 o OSPF is IP protocol 89. This number should be inserted in the 2337 Next Header field of the encapsulating IPv6 header. 2339 A.2 The Options field 2341 The 24-bit OSPF Options field is present in OSPF Hello packets, 2342 Database Description packets and certain LSAs (router-LSAs, network- 2343 LSAs, inter-area-router-LSAs and link-LSAs). The Options field 2344 enables OSPF routers to support (or not support) optional 2345 capabilities, and to communicate their capability level to other 2346 OSPF routers. Through this mechanism routers of differing 2347 capabilities can be mixed within an OSPF routing domain. 2349 An option mismatch between routers can cause a variety of behaviors, 2350 depending on the particular option. Some option mismatches prevent 2351 neighbor relationships from forming (e.g., the E-bit below); these 2352 mismatches are discovered through the sending and receiving of Hello 2353 packets. Some option mismatches prevent particular LSA types from 2354 being flooded across adjacencies (e.g., the MC-bit below); these are 2355 discovered through the sending and receiving of Database Description 2356 packets. Some option mismatches prevent routers from being included 2357 in one or more of the various routing calculations because of their 2358 reduced functionality (again the MC-bit is an example); these 2359 mismatches are discovered by examining LSAs. 2361 Six bits of the OSPF Options field have been assigned. Each bit is 2362 described briefly below. Routers should reset (i.e. clear) 2363 unrecognized bits in the Options field when sending Hello packets or 2364 Database Description packets and when originating LSAs. Conversely, 2365 routers encountering unrecognized Option bits in received Hello 2366 Packets, Database Description packets or LSAs should ignore the 2367 capability and process the packet/LSA normally. 2369 1 2 2370 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+--+--+--+--+ 2372 | | | | | | | | | | | | | | | | | | |DC| R| N|MC| E|V6| 2373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+--+--+--+--+ 2375 The Options field 2377 V6-bit 2378 If this bit is clear, the router/link should be excluded from 2379 IPv6 routing calculations. See Section 3.8 of this memo. 2381 E-bit 2382 This bit describes the way AS-external-LSAs are flooded, as 2383 described in Sections 3.6, 9.5, 10.8 and 12.1.2 of [Ref1]. 2385 MC-bit 2386 This bit describes whether IP multicast datagrams are forwarded 2387 according to the specifications in [Ref7]. 2389 N-bit 2390 This bit describes the handling of Type-7 LSAs, as specified in 2391 [Ref8]. 2393 R-bit 2394 This bit (the `Router' bit) indicates whether the originator is 2395 an active router. If the router bit is clear routes which 2396 transit the advertising node cannot be computed. Clearing the 2397 router bit would be appropriate for a multi-homed host that 2398 wants to participate in routing, but does not want to forward 2399 non-locally addressed packets. 2401 DC-bit 2402 This bit describes the router's handling of demand circuits, as 2403 specified in [Ref10]. 2405 A.3 OSPF Packet Formats 2407 There are five distinct OSPF packet types. All OSPF packet types 2408 begin with a standard 16 byte header. This header is described 2409 first. Each packet type is then described in a succeeding section. 2410 In these sections each packet's division into fields is displayed, 2411 and then the field definitions are enumerated. 2413 All OSPF packet types (other than the OSPF Hello packets) deal with 2414 lists of LSAs. For example, Link State Update packets implement the 2415 flooding of LSAs throughout the OSPF routing domain. The format of 2416 LSAs is described in Section A.4. 2418 The receive processing of OSPF packets is detailed in Section 3.2.2. 2419 The sending of OSPF packets is explained in Section 3.2.1. 2421 A.3.1 The OSPF packet header 2423 Every OSPF packet starts with a standard 16 byte header. Together 2424 with the encapsulating IPv6 headers, the OSPF header contains all 2425 the information necessary to determine whether the packet should be 2426 accepted for further processing. This determination is described in 2427 Section 3.2.2 of this memo. 2429 0 1 2 3 2430 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 2431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2432 | Version # | Type | Packet length | 2433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2434 | Router ID | 2435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2436 | Area ID | 2437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2438 | Checksum | Instance ID | 0 | 2439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2441 Version # 2442 The OSPF version number. This specification documents version 3 2443 of the OSPF protocol. 2445 Type 2446 The OSPF packet types are as follows. See Sections A.3.2 through 2447 A.3.6 for details. 2449 Type Description 2450 --------------------------------- 2451 1 Hello 2452 2 Database Description 2453 3 Link State Request 2454 4 Link State Update 2455 5 Link State Acknowledgment 2457 Packet length 2458 The length of the OSPF protocol packet in bytes. This length 2459 includes the standard OSPF header. 2461 Router ID 2462 The Router ID of the packet's source. 2464 Area ID 2465 A 32 bit number identifying the area that this packet belongs 2466 to. All OSPF packets are associated with a single area. Most 2467 travel a single hop only. Packets travelling over a virtual 2468 link are labelled with the backbone Area ID of 0. 2470 Checksum 2471 OSPF uses the standard checksum calculation for IPv6 2472 applications: The 16-bit one's complement of the one's 2473 complement sum of the entire contents of the packet, starting 2474 with the OSPF packet header, and prepending a "pseudo-header" of 2475 IPv6 header fields, as specified in [Ref14, section 8.1]. The 2476 "Upper-Layer Packet Length" in the pseudo-header is set to value 2477 of the OSPF packet header's length field. The Next Header value 2478 used in the pseudo-header is 89. If the packet's length is not 2479 an integral number of 16-bit words, the packet is padded with a 2480 byte of zero before checksumming. Before computing the checksum, 2481 the checksum field in the OSPF packet header is set to 0. 2483 Instance ID 2484 Enables multiple instances of OSPF to be run over a single link. 2485 Each protocol instance would be assigned a separate Instance ID; 2486 the Instance ID has local link significance only. Received 2487 packets whose Instance ID is not equal to the receiving 2488 interface's Instance ID are discarded. 2490 0 These fields are reserved. They must be 0. 2492 A.3.2 The Hello packet 2494 Hello packets are OSPF packet type 1. These packets are sent 2495 periodically on all interfaces (including virtual links) in order to 2496 establish and maintain neighbor relationships. In addition, Hello 2497 Packets are multicast on those links having a multicast or broadcast 2498 capability, enabling dynamic discovery of neighboring routers. 2500 All routers connected to a common link must agree on certain 2501 parameters (HelloInterval and RouterDeadInterval). These parameters 2502 are included in Hello packets, so that differences can inhibit the 2503 forming of neighbor relationships. The Hello packet also contains 2504 fields used in Designated Router election (Designated Router ID and 2505 Backup Designated Router ID), and fields used to detect bi- 2506 directionality (the Router IDs of all neighbors whose Hellos have 2507 been recently received). 2509 0 1 2 3 2510 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 2511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2512 | 3 | 1 | Packet length | 2513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2514 | Router ID | 2515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2516 | Area ID | 2517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2518 | Checksum | Instance ID | 0 | 2519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2520 | Interface ID | 2521 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2522 | Rtr Pri | Options | 2523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2524 | HelloInterval | RouterDeadInterval | 2525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2526 | Designated Router ID | 2527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2528 | Backup Designated Router ID | 2529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2530 | Neighbor ID | 2531 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2532 | ... | 2534 Interface ID 2535 32-bit number uniquely identifying this interface among the 2536 collection of this router's interfaces. For example, in some 2537 implementations it may be possible to use the MIB-II IfIndex. 2539 Rtr Pri 2540 This router's Router Priority. Used in (Backup) Designated 2541 Router election. If set to 0, the router will be ineligible to 2542 become (Backup) Designated Router. 2544 Options 2545 The optional capabilities supported by the router, as documented 2546 in Section A.2. 2548 HelloInterval 2549 The number of seconds between this router's Hello packets. 2551 RouterDeadInterval 2552 The number of seconds before declaring a silent router down. 2554 Designated Router ID 2555 The identity of the Designated Router for this network, in the 2556 view of the sending router. The Designated Router is identified 2557 by its Router ID. Set to 0.0.0.0 if there is no Designated 2558 Router. 2560 Backup Designated Router ID 2561 The identity of the Backup Designated Router for this network, 2562 in the view of the sending router. The Backup Designated Router 2563 is identified by its IP Router ID. Set to 0.0.0.0 if there is 2564 no Backup Designated Router. 2566 Neighbor ID 2567 The Router IDs of each router from whom valid Hello packets have 2568 been seen recently on the network. Recently means in the last 2569 RouterDeadInterval seconds. 2571 A.3.3 The Database Description packet 2573 Database Description packets are OSPF packet type 2. These packets 2574 are exchanged when an adjacency is being initialized. They describe 2575 the contents of the link-state database. Multiple packets may be 2576 used to describe the database. For this purpose a poll-response 2577 procedure is used. One of the routers is designated to be the 2578 master, the other the slave. The master sends Database Description 2579 packets (polls) which are acknowledged by Database Description 2580 packets sent by the slave (responses). The responses are linked to 2581 the polls via the packets' DD sequence numbers. 2583 0 1 2 3 2584 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 2585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2586 | 3 | 2 | Packet length | 2587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2588 | Router ID | 2589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2590 | Area ID | 2591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2592 | Checksum | Instance ID | 0 | 2593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2594 | 0 | Options | 2595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2596 | Interface MTU | 0 |0|0|0|0|0|I|M|MS 2597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2598 | DD sequence number | 2599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2600 | | 2601 +- -+ 2602 | | 2603 +- An LSA Header -+ 2604 | | 2605 +- -+ 2606 | | 2607 +- -+ 2608 | | 2609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2610 | ... | 2612 The format of the Database Description packet is very similar to 2613 both the Link State Request and Link State Acknowledgment packets. 2614 The main part of all three is a list of items, each item describing 2615 a piece of the link-state database. The sending of Database 2616 Description Packets is documented in Section 10.8 of [Ref1]. The 2617 reception of Database Description packets is documented in Section 2618 10.6 of [Ref1]. 2620 Options 2621 The optional capabilities supported by the router, as documented 2622 in Section A.2. 2624 Interface MTU 2625 The size in bytes of the largest IPv6 datagram that can be sent 2626 out the associated interface, without fragmentation. The 2627 MTUs of common Internet link types can be found in Table 2628 7-1 of [Ref12]. Interface MTU should be set to 0 in Database 2629 Description packets sent over virtual links. 2631 I-bit 2632 The Init bit. When set to 1, this packet is the first in the 2633 sequence of Database Description Packets. 2635 M-bit 2636 The More bit. When set to 1, it indicates that more Database 2637 Description Packets are to follow. 2639 MS-bit 2640 The Master/Slave bit. When set to 1, it indicates that the 2641 router is the master during the Database Exchange process. 2642 Otherwise, the router is the slave. 2644 DD sequence number 2645 Used to sequence the collection of Database Description Packets. 2646 The initial value (indicated by the Init bit being set) should 2647 be unique. The DD sequence number then increments until the 2648 complete database description has been sent. 2650 The rest of the packet consists of a (possibly partial) list of the 2651 link-state database's pieces. Each LSA in the database is described 2652 by its LSA header. The LSA header is documented in Section A.4.1. 2653 It contains all the information required to uniquely identify both 2654 the LSA and the LSA's current instance. 2656 A.3.4 The Link State Request packet 2658 Link State Request packets are OSPF packet type 3. After exchanging 2659 Database Description packets with a neighboring router, a router may 2660 find that parts of its link-state database are out-of-date. The 2661 Link State Request packet is used to request the pieces of the 2662 neighbor's database that are more up-to-date. Multiple Link State 2663 Request packets may need to be used. 2665 A router that sends a Link State Request packet has in mind the 2666 precise instance of the database pieces it is requesting. Each 2667 instance is defined by its LS sequence number, LS checksum, and LS 2668 age, although these fields are not specified in the Link State 2669 Request Packet itself. The router may receive even more recent 2670 instances in response. 2672 The sending of Link State Request packets is documented in Section 2673 10.9 of [Ref1]. The reception of Link State Request packets is 2674 documented in Section 10.7 of [Ref1]. 2676 0 1 2 3 2677 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 2678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2679 | 3 | 3 | Packet length | 2680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2681 | Router ID | 2682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2683 | Area ID | 2684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2685 | Checksum | Instance ID | 0 | 2686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2687 | 0 | LS type | 2688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2689 | Link State ID | 2690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2691 | Advertising Router | 2692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2693 | ... | 2695 Each LSA requested is specified by its LS type, Link State ID, and 2696 Advertising Router. This uniquely identifies the LSA, but not its 2697 instance. Link State Request packets are understood to be requests 2698 for the most recent instance (whatever that might be). 2700 A.3.5 The Link State Update packet 2702 Link State Update packets are OSPF packet type 4. These packets 2703 implement the flooding of LSAs. Each Link State Update packet 2704 carries a collection of LSAs one hop further from their origin. 2705 Several LSAs may be included in a single packet. 2707 Link State Update packets are multicast on those physical networks 2708 that support multicast/broadcast. In order to make the flooding 2709 procedure reliable, flooded LSAs are acknowledged in Link State 2710 Acknowledgment packets. If retransmission of certain LSAs is 2711 necessary, the retransmitted LSAs are always carried by unicast Link 2712 State Update packets. For more information on the reliable flooding 2713 of LSAs, consult Section 3.5. 2715 0 1 2 3 2716 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 2717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2718 | 3 | 4 | Packet length | 2719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2720 | Router ID | 2721 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2722 | Area ID | 2723 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2724 | Checksum | Instance ID | 0 | 2725 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2726 | # LSAs | 2727 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2728 | | 2729 +- +-+ 2730 | LSAs | 2731 +- +-+ 2732 | ... | 2734 # LSAs 2735 The number of LSAs included in this update. 2737 The body of the Link State Update packet consists of a list of LSAs. 2738 Each LSA begins with a common 20 byte header, described in Section 2739 A.4.2. Detailed formats of the different types of LSAs are described 2740 in Section A.4. 2742 A.3.6 The Link State Acknowledgment packet 2744 Link State Acknowledgment Packets are OSPF packet type 5. To make 2745 the flooding of LSAs reliable, flooded LSAs are explicitly 2746 acknowledged. This acknowledgment is accomplished through the 2747 sending and receiving of Link State Acknowledgment packets. The 2748 sending of Link State Acknowledgement packets is documented in 2749 Section 13.5 of [Ref1]. The reception of Link State Acknowledgement 2750 packets is documented in Section 13.7 of [Ref1]. 2752 Multiple LSAs can be acknowledged in a single Link State 2753 Acknowledgment packet. Depending on the state of the sending 2754 interface and the sender of the corresponding Link State Update 2755 packet, a Link State Acknowledgment packet is sent either to the 2756 multicast address AllSPFRouters, to the multicast address 2757 AllDRouters, or as a unicast (see Section 13.5 of [Ref1] for 2758 details). 2760 The format of this packet is similar to that of the Data Description 2761 packet. The body of both packets is simply a list of LSA headers. 2763 0 1 2 3 2764 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 2765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2766 | 3 | 5 | Packet length | 2767 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2768 | Router ID | 2769 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2770 | Area ID | 2771 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2772 | Checksum | Instance ID | 0 | 2773 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2774 | | 2775 +- -+ 2776 | | 2777 +- An LSA Header -+ 2778 | | 2779 +- -+ 2780 | | 2781 +- -+ 2782 | | 2783 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2784 | ... | 2786 Each acknowledged LSA is described by its LSA header. The LSA 2787 header is documented in Section A.4.2. It contains all the 2788 information required to uniquely identify both the LSA and the LSA's 2789 current instance. 2791 A.4 LSA formats 2793 This memo defines seven distinct types of LSAs. Each LSA begins 2794 with a standard 20 byte LSA header. This header is explained in 2795 Section A.4.2. Succeeding sections then diagram the separate LSA 2796 types. 2798 Each LSA describes a piece of the OSPF routing domain. Every router 2799 originates a router-LSA. A network-LSA is advertised for each link 2800 by its Designated Router. A router's link-local addresses are 2801 advertised to its neighbors in link-LSAs. IPv6 prefixes are 2802 advertised in intra-area-prefix-LSAs, inter-area-prefix-LSAs and AS- 2803 external-LSAs. Location of specific routers can be advertised 2804 across area boundaries in inter-area-router-LSAs. All LSAs are then 2805 flooded throughout the OSPF routing domain. The flooding algorithm 2806 is reliable, ensuring that all routers have the same collection of 2807 LSAs. (See Section 3.5 for more information concerning the flooding 2808 algorithm). This collection of LSAs is called the link-state 2809 database. 2811 From the link state database, each router constructs a shortest path 2812 tree with itself as root. This yields a routing table (see Section 2813 11 of [Ref1]). For the details of the routing table build process, 2814 see Section 3.8. 2816 A.4.1 IPv6 Prefix Representation 2818 IPv6 addresses are bit strings of length 128. IPv6 routing 2819 algorithms, and OSPF for IPv6 in particular, advertise IPv6 address 2820 prefixes. IPv6 address prefixes are bit strings whose length ranges 2821 between 0 and 128 bits (inclusive). 2823 Within OSPF, IPv6 address prefixes are always represented by a 2824 combination of three fields: PrefixLength, PrefixOptions, and 2825 Address Prefix. PrefixLength is the length in bits of the prefix. 2826 PrefixOptions is an 8-bit field describing various capabilities 2827 associated with the prefix (see Section A.4.2). Address Prefix is an 2828 encoding of the prefix itself as an even multiple of 32-bit words, 2829 padding with zero bits as necessary; this encoding consumes 2830 (PrefixLength + 31) / 32) 32-bit words. 2832 The default route is represented by a prefix of length 0. 2834 Examples of IPv6 Prefix representation in OSPF can be found in 2835 Sections A.4.5, A.4.7, A.4.8 and A.4.9. 2837 A.4.1.1 Prefix Options 2839 Each prefix is advertised along with an 8-bit field of capabilities. 2840 These serve as input to the various routing calculations, allowing, 2841 for example, certain prefixes to be ignored in some cases, or to be 2842 marked as not readvertisable in others. 2844 0 1 2 3 4 5 6 7 2845 +--+--+--+--+--+--+--+--+ 2846 | | | | | P|MC|LA|NU| 2847 +--+--+--+--+--+--+--+--+ 2849 The Prefix Options field 2851 NU-bit 2852 The "no unicast" capability bit. If set, the prefix should be 2853 excluded from IPv6 unicast calculations, otherwise it should be 2854 included. 2856 LA-bit 2857 The "local address" capability bit. If set, the prefix is 2858 actually an IPv6 interface address of the advertising router. 2860 MC-bit 2861 The "multicast" capability bit. If set, the prefix should be 2862 included in IPv6 multicast routing calculations, otherwise it 2863 should be excluded. 2865 P-bit 2866 The "propagate" bit. Set on NSSA area prefixes that should be 2867 readvertised at the NSSA area border. 2869 A.4.2 The LSA header 2871 All LSAs begin with a common 20 byte header. This header contains 2872 enough information to uniquely identify the LSA (LS type, Link State 2873 ID, and Advertising Router). Multiple instances of the LSA may 2874 exist in the routing domain at the same time. It is then necessary 2875 to determine which instance is more recent. This is accomplished by 2876 examining the LS age, LS sequence number and LS checksum fields that 2877 are also contained in the LSA header. 2879 0 1 2 3 2880 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 2881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2882 | LS age | LS type | 2883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2884 | Link State ID | 2885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2886 | Advertising Router | 2887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2888 | LS sequence number | 2889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2890 | LS checksum | length | 2891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2893 LS age 2894 The time in seconds since the LSA was originated. 2896 LS type 2897 The LS type field indicates the function performed by the LSA. 2898 The high-order three bits of LS type encode generic properties 2899 of the LSA, while the remainder (called LSA function code) 2900 indicate the LSA's specific functionality. See Section A.4.2.1 2901 for a detailed description of LS type. 2903 Link State ID 2904 Together with LS type and Advertising Router, uniquely 2905 identifies the LSA in the link-state database. 2907 Advertising Router 2908 The Router ID of the router that originated the LSA. For 2909 example, in network-LSAs this field is equal to the Router ID of 2910 the network's Designated Router. 2912 LS sequence number 2913 Detects old or duplicate LSAs. Successive instances of an LSA 2914 are given successive LS sequence numbers. See Section 12.1.6 in 2915 [Ref1] for more details. 2917 LS checksum 2918 The Fletcher checksum of the complete contents of the LSA, 2919 including the LSA header but excluding the LS age field. See 2920 Section 12.1.7 in [Ref1] for more details. 2922 length 2923 The length in bytes of the LSA. This includes the 20 byte LSA 2924 header. 2926 A.4.2.1 LS type 2928 The LS type field indicates the function performed by the LSA. The 2929 high-order three bits of LS type encode generic properties of the 2930 LSA, while the remainder (called LSA function code) indicate the 2931 LSA's specific functionality. The format of the LS type is as 2932 follows: 2934 1 2935 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2936 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 2937 |U |S2|S1| LSA Function Code | 2938 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 2940 The U bit indicates how the LSA should be handled by a router which 2941 does not recognize the LSA's function code. Its values are: 2943 U-bit LSA Handling 2944 ------------------------------------------------------------- 2945 0 Treat the LSA as if it had link-local flooding scope 2946 1 Store and flood the LSA, as if type understood 2948 The S1 and S2 bits indicate the flooding scope of the LSA. The 2949 values are: 2951 S2 S1 Flooding Scope 2952 ------------------------------------------------------------------------ 2953 0 0 Link-Local Scoping. Flooded only on link it is originated on. 2954 0 1 Area Scoping. Flooded to all routers in the originating area 2955 1 0 AS Scoping. Flooded to all routers in the AS 2956 1 1 Reserved 2958 The LSA function codes are defined as follows. The origination and 2959 processing of these LSA function codes are defined elsewhere in this 2960 memo, except for the group-membership-LSA (see [Ref7]) and the 2961 Type-7-LSA (see [Ref8]). Each LSA function code also implies a 2962 specific setting for the U, S1 and S2 bits, as shown below. 2964 LSA function code LS Type Description 2965 ---------------------------------------------------- 2966 1 0x2001 Router-LSA 2967 2 0x2002 Network-LSA 2968 3 0x2003 Inter-Area-Prefix-LSA 2969 4 0x2004 Inter-Area-Router-LSA 2970 5 0x4005 AS-External-LSA 2971 6 0x2006 Group-membership-LSA 2972 7 0x2007 Type-7-LSA 2973 8 0x0008 Link-LSA 2974 9 0x2009 Intra-Area-Prefix-LSA 2975 A.4.3 Router-LSAs 2977 Router-LSAs have LS type equal to 0x2001. Each router in an area 2978 originates one or more router-LSAs. The complete collection of 2979 router-LSAs originated by the router describe the state and cost of 2980 the router's interfaces to the area. For details concerning the 2981 construction of router-LSAs, see Section 3.4.3.1. Router-LSAs are 2982 flooded throughout a single area only. 2984 0 1 2 3 2985 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 2986 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2987 | LS age |0|0|1| 1 | 2988 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2989 | Link State ID | 2990 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2991 | Advertising Router | 2992 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2993 | LS sequence number | 2994 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2995 | LS checksum | length | 2996 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2997 | 0 |W|V|E|B| Options | 2998 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2999 | Type | 0 | Metric | 3000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3001 | Interface ID | 3002 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3003 | Neighbor Interface ID | 3004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3005 | Neighbor Router ID | 3006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3007 | ... | 3008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3009 | Type | 0 | Metric | 3010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3011 | Interface ID | 3012 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3013 | Neighbor Interface ID | 3014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3015 | Neighbor Router ID | 3016 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3017 | ... | 3019 A single router may originate one or more Router LSAs, distinguished 3020 by their Link-State IDs (which are chosen arbitrarily by the 3021 originating router). The Options field and V, E and B bits should 3022 be the same in all Router LSAs from a single originator. However, 3023 in the case of a mismatch the values in the LSA with the lowest Link 3024 State ID take precedence. When more than one Router LSA is received 3025 from a single router, the links are processed as if concatenated 3026 into a single LSA. 3028 bit V 3029 When set, the router is an endpoint of one or more fully 3030 adjacent virtual links having the described area as Transit area 3031 (V is for virtual link endpoint). 3033 bit E 3034 When set, the router is an AS boundary router (E is for 3035 external). 3037 bit B 3038 When set, the router is an area border router (B is for border). 3040 bit W 3041 When set, the router is a wild-card multicast receiver. When 3042 running MOSPF, these routers receive all multicast datagrams, 3043 regardless of destination. See Sections 3, 4 and A.2 of [Ref8] 3044 for details. 3046 Options 3047 The optional capabilities supported by the router, as documented 3048 in Section A.2. 3050 The following fields are used to describe each router interface. 3051 The Type field indicates the kind of interface being described. It 3052 may be an interface to a transit network, a point-to-point 3053 connection to another router or a virtual link. The values of all 3054 the other fields describing a router interface depend on the 3055 interface's Type field. 3057 Type 3058 The kind of interface being described. One of the following: 3060 Type Description 3061 --------------------------------------------------- 3062 1 Point-to-point connection to another router 3063 2 Connection to a transit network 3064 3 Reserved 3065 4 Virtual link 3067 Metric 3068 The cost of using this router interface, for outbound traffic. 3070 Interface ID 3071 The Interface ID assigned to the interface being described. See 3072 Sections 3.1.2 and C.3. 3074 Neighbor Interface ID 3075 The Interface ID the neighbor router (or the attached link's 3076 Designated Router, for Type 2 interfaces) has been advertising 3077 in hello packets sent on the attached link. 3079 Neighbor Router ID 3080 The Router ID the neighbor router (or the attached link's 3081 Designated Router, for Type 2 interfaces). 3083 For Type 2 links, the combination of Neighbor Interface ID and 3084 Neighbor Router ID allows the network-LSA for the attached link 3085 to be found in the link-state database. 3087 A.4.4 Network-LSAs 3089 Network-LSAs have LS type equal to 0x2002. A network-LSA is 3090 originated for each broadcast and NBMA link in the area which 3091 supports two or more routers. The network-LSA is originated by the 3092 link's Designated Router. The LSA describes all routers attached to 3093 the link, including the Designated Router itself. The LSA's Link 3094 State ID field is set to the Interface ID that the Designated Router 3095 has been advertising in Hello packets on the link. 3097 The distance from the network to all attached routers is zero. This 3098 is why the metric fields need not be specified in the network-LSA. 3099 For details concerning the construction of network-LSAs, see Section 3100 3.4.3.2. 3102 0 1 2 3 3103 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 3104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3105 | LS age |0|0|1| 2 | 3106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3107 | Link State ID | 3108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3109 | Advertising Router | 3110 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3111 | LS sequence number | 3112 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3113 | LS checksum | length | 3114 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3115 | 0 | Options | 3116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3117 | Attached Router | 3118 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3119 | ... | 3121 Attached Router 3122 The Router IDs of each of the routers attached to the link. 3123 Actually, only those routers that are fully adjacent to the 3124 Designated Router are listed. The Designated Router includes 3125 itself in this list. The number of routers included can be 3126 deduced from the LSA header's length field. 3128 A.4.5 Inter-Area-Prefix-LSAs 3130 Inter-Area-Prefix-LSAs have LS type equal to 0x2003. These LSAs are 3131 are the IPv6 equivalent of OSPF for IPv4's type 3 summary-LSAs (see 3132 Section 12.4.3 of [Ref1]). Originated by area border routers, they 3133 describe routes to IPv6 address prefixes that belong to other areas. 3134 A separate Inter-Area-Prefix-LSA is originated for each IPv6 address 3135 prefix. For details concerning the construction of Inter-Area- 3136 Prefix-LSAs, see Section 3.4.3.3. 3138 For stub areas, Inter-Area-Prefix-LSAs can also be used to describe 3139 a (per-area) default route. Default summary routes are used in stub 3140 areas instead of flooding a complete set of external routes. When 3141 describing a default summary route, the Inter-Area-Prefix-LSA's 3142 PrefixLength is set to 0. 3144 0 1 2 3 3145 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 3146 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3147 | LS age |0|0|1| 3 | 3148 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3149 | Link State ID | 3150 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3151 | Advertising Router | 3152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3153 | LS sequence number | 3154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3155 | LS checksum | length | 3156 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3157 | 0 | Metric | 3158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3159 | PrefixLength | PrefixOptions | (0) | 3160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3161 | Address Prefix | 3162 | ... | 3163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3165 Metric 3166 The cost of this route. Expressed in the same units as the 3167 interface costs in the router-LSAs. When the Inter-Area-Prefix- 3168 LSA is describing a route to a range of addresses (see Section 3169 C.2) the cost is set to the maximum cost to any reachable 3170 component of the address range. 3172 PrefixLength, PrefixOptions and Address Prefix 3173 Representation of the IPv6 address prefix, as described in 3174 Section A.4.1. 3176 A.4.6 Inter-Area-Router-LSAs 3178 Inter-Area-Router-LSAs have LS type equal to 0x2004. These LSAs are 3179 are the IPv6 equivalent of OSPF for IPv4's type 4 summary-LSAs (see 3180 Section 12.4.3 of [Ref1]). Originated by area border routers, they 3181 describe routes to routers in other areas. (To see why it is 3182 necessary to advertise the location of each ASBR, consult Section 3183 16.4 in [Ref1].) Each LSA describes a route to a single router. For 3184 details concerning the construction of Inter-Area-Router-LSAs, see 3185 Section 3.4.3.4. 3187 0 1 2 3 3188 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 3189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3190 | LS age |0|0|1| 4 | 3191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3192 | Link State ID | 3193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3194 | Advertising Router | 3195 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3196 | LS sequence number | 3197 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3198 | LS checksum | length | 3199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3200 | 0 | Options | 3201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3202 | 0 | Metric | 3203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3204 | Destination Router ID | 3205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3207 Options 3208 The optional capabilities supported by the router, as documented 3209 in Section A.2. 3211 Metric 3212 The cost of this route. Expressed in the same units as the 3213 interface costs in the router-LSAs. 3215 Destination Router ID 3216 The Router ID of the router being described by the LSA. 3218 A.4.7 AS-external-LSAs 3220 AS-external-LSAs have LS type equal to 0x4005. These LSAs are 3221 originated by AS boundary routers, and describe destinations 3222 external to the AS. Each LSA describes a route to a single IPv6 3223 address prefix. For details concerning the construction of AS- 3224 external-LSAs, see Section 3.4.3.5. 3226 AS-external-LSAs can be used to describe a default route. Default 3227 routes are used when no specific route exists to the destination. 3228 When describing a default route, the AS-external-LSA's PrefixLength 3229 is set to 0. 3231 0 1 2 3 3232 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 3233 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3234 | LS age |0|1|0| 5 | 3235 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3236 | Link State ID | 3237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3238 | Advertising Router | 3239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3240 | LS sequence number | 3241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3242 | LS checksum | length | 3243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3244 | |E|F|T| Metric | 3245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3246 | PrefixLength | PrefixOptions | Referenced LS Type | 3247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3248 | Address Prefix | 3249 | ... | 3250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3251 | | 3252 +- -+ 3253 | | 3254 +- Forwarding Address (Optional) -+ 3255 | | 3256 +- -+ 3257 | | 3258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3259 | External Route Tag (Optional) | 3260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3261 | Referenced Link State ID (Optional) | 3262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3264 bit E 3265 The type of external metric. If bit E is set, the metric 3266 specified is a Type 2 external metric. This means the metric is 3267 considered larger than any intra-AS path. If bit E is zero, the 3268 specified metric is a Type 1 external metric. This means that 3269 it is expressed in the same units as the link state metric 3270 (i.e., the same units as interface cost). 3272 bit F 3273 If set, a Forwarding Address has been included in the LSA. 3275 bit T 3276 If set, an External Route Tag has been included in the LSA. 3278 Metric 3279 The cost of this route. Interpretation depends on the external 3280 type indication (bit E above). 3282 PrefixLength, PrefixOptions and Address Prefix 3283 Representation of the IPv6 address prefix, as described in 3284 Section A.4.1. 3286 Referenced LS type 3287 If non-zero, an LSA with this LS type is to be associated with 3288 this LSA (see Referenced Link State ID below). 3290 Forwarding address 3291 A fully qualified IPv6 address (128 bits). Included in the LSA 3292 if and only if bit F has been set. If included, Data traffic 3293 for the advertised destination will be forwarded to this 3294 address. Must not be set to the IPv6 Unspecified Address 3295 (0:0:0:0:0:0:0:0). 3297 External Route Tag 3298 A 32-bit field which may be used to communicate additional 3299 information between AS boundary routers; see [Ref5] for example 3300 usage. Included in the LSA if and only if bit T has been set. 3302 Referenced Link State ID 3303 Included if and only if Reference LS Type is non-zero. If 3304 included, additional information concerning the advertised 3305 external route can be found in the LSA having LS type equal to 3306 "Referenced LS Type", Link State ID equal to "Referenced Link 3307 State ID" and Advertising Router the same as that specified in 3308 the AS-external-LSA's link state header. This additional 3309 information is not used by the OSPF protocol itself. It may be 3310 used to communicate information between AS boundary routers; the 3311 precise nature of such information is outside the scope of this 3312 specification. 3314 All, none or some of the fields labeled Forwarding address, External 3315 Route Tag and Referenced Link State ID may be present in the AS- 3316 external-LSA (as indicated by the setting of bit F, bit T and 3317 Referenced LS type respectively). However, when present Forwarding 3318 Address always comes first, with External Route Tag always preceding 3319 Referenced Link State ID. 3321 A.4.8 Link-LSAs 3323 Link-LSAs have LS type equal to 0x0008. A router originates a 3324 separate Link-LSA for each link it is attached to. These LSAs have 3325 local-link flooding scope; they are never flooded beyond the link 3326 that they are associated with. Link-LSAs have three purposes: 1) 3327 they provide the router's link-local address to all other routers 3328 attached to the link and 2) they inform other routers attached to 3329 the link of a list of IPv6 prefixes to associate with the link and 3330 3) they allow the router to assert a collection of Options bits to 3331 associate with the Network-LSA that will be originated for the link. 3333 A link-LSA's Link State ID is set equal to the originating router's 3334 Interface ID on the link. 3335 0 1 2 3 3336 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 3337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3338 | LS age |0|0|0| 8 | 3339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3340 | Link State ID | 3341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3342 | Advertising Router | 3343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3344 | LS sequence number | 3345 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3346 | LS checksum | length | 3347 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3348 | Rtr Pri | Options | 3349 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3350 | | 3351 +- -+ 3352 | | 3353 +- Link-local Interface Address -+ 3354 | | 3355 +- -+ 3356 | | 3357 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3358 | # prefixes | 3359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3360 | PrefixLength | PrefixOptions | (0) | 3361 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3362 | Address Prefix | 3363 | ... | 3364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3365 | ... | 3366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3367 | PrefixLength | PrefixOptions | (0) | 3368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3369 | Address Prefix | 3370 | ... | 3371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3373 Rtr Pri 3374 The Router Priority of the interface attaching the originating 3375 router to the link. 3377 Options 3378 The set of Options bits that the router would like set in the 3379 Network-LSA that will be originated for the link. 3381 Link-local Interface Address 3382 The originating router's link-local interface address on the 3383 link. 3385 # prefixes 3386 The number of IPv6 address prefixes contained in the LSA. 3388 The rest of the link-LSA contains a list of IPv6 prefixes to be 3389 associated with the link. 3391 PrefixLength, PrefixOptions and Address Prefix 3392 Representation of an IPv6 address prefix, as described in 3393 Section A.4.1. 3395 A.4.9 Intra-Area-Prefix-LSAs 3397 Intra-Area-Prefix-LSAs have LS type equal to 0x2009. A router uses 3398 Intra-Area-Prefix-LSAs to advertise one or more IPv6 address 3399 prefixes that are associated with a) the router itself, b) an 3400 attached stub network segment or c) an attached transit network 3401 segment. In IPv4, a) and b) were accomplished via the router's 3402 router-LSA, and c) via a network-LSA. However, in OSPF for IPv6 all 3403 addressing information has been removed from router-LSAs and 3404 network-LSAs, leading to the introduction of the Intra-Area-Prefix- 3405 LSA. 3407 A router can originate multiple Intra-Area-Prefix-LSAs for each 3408 router or transit network; each such LSA is distinguished by its 3409 Link State ID. 3411 0 1 2 3 3412 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 3413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3414 | LS age |0|0|1| 9 | 3415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3416 | Link State ID | 3417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3418 | Advertising Router | 3419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3420 | LS sequence number | 3421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3422 | LS checksum | length | 3423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3424 | # prefixes | Referenced LS type | 3425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3426 | Referenced Link State ID | 3427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3428 | Referenced Advertising Router | 3429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3430 | PrefixLength | PrefixOptions | Metric | 3431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3432 | Address Prefix | 3433 | ... | 3434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3435 | ... | 3436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3437 | PrefixLength | PrefixOptions | Metric | 3438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3439 | Address Prefix | 3440 | ... | 3441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3443 # prefixes 3444 The number of IPv6 address prefixes contained in the LSA. 3446 Router 3447 Referenced LS type, Referenced Link State ID and Referenced 3448 Advertising 3449 Identifies the router-LSA or network-LSA with which the IPv6 3450 address prefixes should be associated. If Referenced LS type is 3451 1, the prefixes are associated with a router-LSA, Referenced 3452 Link State ID should be 0 and Referenced Advertising Router 3453 should be the originating router's Router ID. If Referenced LS 3454 type is 2, the prefixes are associated with a network-LSA, 3455 Referenced Link State ID should be the Interface ID of the 3456 link's Designated Router and Referenced Advertising Router 3457 should be the Designated Router's Router ID. 3459 The rest of the Intra-Area-Prefix-LSA contains a list of IPv6 3460 prefixes to be associated with the router or transit link, together 3461 with the cost of each prefix. 3463 PrefixLength, PrefixOptions and Address Prefix 3464 Representation of an IPv6 address prefix, as described in 3465 Section A.4.1. 3467 Metric 3468 The cost of this prefix. Expressed in the same units as the 3469 interface costs in the router-LSAs. 3471 B. Architectural Constants 3473 Architectural constants for the OSPF protocol are defined in 3474 Appendix B of [Ref1]. The only difference for OSPF for IPv6 is that 3475 DefaultDestination is encoded as a prefix of length 0 (see Section 3476 A.4.1). 3478 C. Configurable Constants 3480 The OSPF protocol has quite a few configurable parameters. These 3481 parameters are listed below. They are grouped into general 3482 functional categories (area parameters, interface parameters, etc.). 3483 Sample values are given for some of the parameters. 3485 Some parameter settings need to be consistent among groups of 3486 routers. For example, all routers in an area must agree on that 3487 area's parameters, and all routers attached to a network must agree 3488 on that network's HelloInterval and RouterDeadInterval. 3490 Some parameters may be determined by router algorithms outside of 3491 this specification (e.g., the address of a host connected to the 3492 router via a SLIP line). From OSPF's point of view, these items are 3493 still configurable. 3495 C.1 Global parameters 3497 In general, a separate copy of the OSPF protocol is run for each 3498 area. Because of this, most configuration parameters are 3499 defined on a per-area basis. The few global configuration 3500 parameters are listed below. 3502 Router ID 3503 This is a 32-bit number that uniquely identifies the router 3504 in the Autonomous System. If a router's OSPF Router ID is 3505 changed, the router's OSPF software should be restarted 3506 before the new Router ID takes effect. Before restarting in 3507 order to change its Router ID, the router should flush its 3508 self-originated LSAs from the routing domain (see Section 3509 14.1 of [Ref1]), or they will persist for up to MaxAge 3510 minutes. 3512 Because the size of the Router ID is smaller than an IPv6 3513 address, it cannot be set to one of the router's IPv6 3514 addresses (as is commonly done for IPv4). Possible Router ID 3515 assignment procedures for IPv6 include: a) assign the IPv6 3516 Router ID as one of the router's IPv4 addresses or b) assign 3517 IPv6 Router IDs through some local administrative procedure 3518 (similar to procedures used by manufacturers to assign 3519 product serial numbers). 3521 The Router ID of 0.0.0.0 is reserved, and should not be 3522 used. 3524 C.2 Area parameters 3526 All routers belonging to an area must agree on that area's 3527 configuration. Disagreements between two routers will lead to 3528 an inability for adjacencies to form between them, with a 3529 resulting hindrance to the flow of routing protocol and data 3530 traffic. The following items must be configured for an area: 3532 Area ID 3533 This is a 32-bit number that identifies the area. The Area 3534 ID of 0 is reserved for the backbone. 3536 List of address ranges 3537 Address ranges control the advertisement of routes across 3538 area boundaries. Each address range consists of the 3539 following items: 3541 [IPv6 prefix, prefix length] 3542 Describes the collection of IPv6 addresses contained 3543 in the address range. 3545 Status Set to either Advertise or DoNotAdvertise. Routing 3546 information is condensed at area boundaries. 3547 External to the area, at most a single route is 3548 advertised (via a inter-area-prefix-LSA) for each 3549 address range. The route is advertised if and only 3550 if the address range's Status is set to Advertise. 3551 Unadvertised ranges allow the existence of certain 3552 networks to be intentionally hidden from other 3553 areas. Status is set to Advertise by default. 3555 ExternalRoutingCapability 3556 Whether AS-external-LSAs will be flooded into/throughout the 3557 area. If AS-external-LSAs are excluded from the area, the 3558 area is called a "stub". Internal to stub areas, routing to 3559 external destinations will be based solely on a default 3560 inter-area route. The backbone cannot be configured as a 3561 stub area. Also, virtual links cannot be configured through 3562 stub areas. For more information, see Section 3.6 of 3563 [Ref1]. 3565 StubDefaultCost 3566 If the area has been configured as a stub area, and the 3567 router itself is an area border router, then the 3568 StubDefaultCost indicates the cost of the default inter- 3569 area-prefix-LSA that the router should advertise into the 3570 area. See Section 12.4.3.1 of [Ref1] for more information. 3572 C.3 Router interface parameters 3574 Some of the configurable router interface parameters (such as 3575 Area ID, HelloInterval and RouterDeadInterval) actually imply 3576 properties of the attached links, and therefore must be 3577 consistent across all the routers attached to that link. The 3578 parameters that must be configured for a router interface are: 3580 IPv6 link-local address 3581 The IPv6 link-local address associated with this interface. 3582 May be learned through auto-configuration. 3584 Area ID 3585 The OSPF area to which the attached link belongs. 3587 Instance ID 3588 The OSPF protocol instance associated with this OSPF 3589 interface. Defaults to 0. 3591 Interface ID 3592 32-bit number uniquely identifying this interface among the 3593 collection of this router's interfaces. For example, in some 3594 implementations it may be possible to use the MIB-II 3595 IfIndex. 3597 IPv6 prefixes 3598 The list of IPv6 prefixes to associate with the link. These 3599 will be advertised in intra-area-prefix-LSAs. 3601 Interface output cost(s) 3602 The cost of sending a packet on the interface, expressed in 3603 the link state metric. This is advertised as the link cost 3604 for this interface in the router's router-LSA. The interface 3605 output cost must always be greater than 0. 3607 RxmtInterval 3608 The number of seconds between LSA retransmissions, for 3609 adjacencies belonging to this interface. Also used when 3610 retransmitting Database Description and Link State Request 3611 Packets. This should be well over the expected round-trip 3612 delay between any two routers on the attached link. The 3613 setting of this value should be conservative or needless 3614 retransmissions will result. Sample value for a local area 3615 network: 5 seconds. 3617 InfTransDelay 3618 The estimated number of seconds it takes to transmit a Link 3619 State Update Packet over this interface. LSAs contained in 3620 the update packet must have their age incremented by this 3621 amount before transmission. This value should take into 3622 account the transmission and propagation delays of the 3623 interface. It must be greater than 0. Sample value for a 3624 local area network: 1 second. 3626 Router Priority 3627 An 8-bit unsigned integer. When two routers attached to a 3628 network both attempt to become Designated Router, the one 3629 with the highest Router Priority takes precedence. If there 3630 is still a tie, the router with the highest Router ID takes 3631 precedence. A router whose Router Priority is set to 0 is 3632 ineligible to become Designated Router on the attached link. 3633 Router Priority is only configured for interfaces to 3634 broadcast and NBMA networks. 3636 HelloInterval 3637 The length of time, in seconds, between the Hello Packets 3638 that the router sends on the interface. This value is 3639 advertised in the router's Hello Packets. It must be the 3640 same for all routers attached to a common link. The smaller 3641 the HelloInterval, the faster topological changes will be 3642 detected; however, more OSPF routing protocol traffic will 3643 ensue. Sample value for a X.25 PDN: 30 seconds. Sample 3644 value for a local area network (LAN): 10 seconds. 3646 RouterDeadInterval 3647 After ceasing to hear a router's Hello Packets, the number 3648 of seconds before its neighbors declare the router down. 3649 This is also advertised in the router's Hello Packets in 3650 their RouterDeadInterval field. This should be some 3651 multiple of the HelloInterval (say 4). This value again 3652 must be the same for all routers attached to a common link. 3654 C.4 Virtual link parameters 3656 Virtual links are used to restore/increase connectivity of the 3657 backbone. Virtual links may be configured between any pair of 3658 area border routers having interfaces to a common (non-backbone) 3659 area. The virtual link appears as an unnumbered point-to-point 3660 link in the graph for the backbone. The virtual link must be 3661 configured in both of the area border routers. 3663 A virtual link appears in router-LSAs (for the backbone) as if 3664 it were a separate router interface to the backbone. As such, 3665 it has most of the parameters associated with a router interface 3666 (see Section C.3). Virtual links do not have link-local 3667 addresses, but instead use one of the router's global-scope or 3668 site-local IPv6 addresses as the IP source in OSPF protocol 3669 packets it sends along the virtual link. Router Priority is not 3670 used on virtual links. Interface output cost is not configured 3671 on virtual links, but is dynamically set to be the cost of the 3672 intra-area path between the two endpoint routers. The parameter 3673 RxmtInterval must be configured, and should be well over the 3674 expected round-trip delay between the two routers. This may be 3675 hard to estimate for a virtual link; it is better to err on the 3676 side of making it too large. 3678 A virtual link is defined by the following two configurable 3679 parameters: the Router ID of the virtual link's other endpoint, 3680 and the (non-backbone) area through which the virtual link runs 3681 (referred to as the virtual link's Transit area). Virtual links 3682 cannot be configured through stub areas. 3684 C.5 NBMA network parameters 3686 OSPF treats an NBMA network much like it treats a broadcast 3687 network. Since there may be many routers attached to the 3688 network, a Designated Router is selected for the network. This 3689 Designated Router then originates a network-LSA, which lists all 3690 routers attached to the NBMA network. 3692 However, due to the lack of broadcast capabilities, it may be 3693 necessary to use configuration parameters in the Designated 3694 Router selection. These parameters will only need to be 3695 configured in those routers that are themselves eligible to 3696 become Designated Router (i.e., those router's whose Router 3697 Priority for the network is non-zero), and then only if no 3698 automatic procedure for discovering neighbors exists: 3700 List of all other attached routers 3701 The list of all other routers attached to the NBMA network. 3702 Each router is configured with its Router ID and IPv6 link- 3703 local address on the network. Also, for each router listed, 3704 that router's eligibility to become Designated Router must 3705 be defined. When an interface to a NBMA network comes up, 3706 the router sends Hello Packets only to those neighbors 3707 eligible to become Designated Router, until the identity of 3708 the Designated Router is discovered. 3710 PollInterval 3711 If a neighboring router has become inactive (Hello Packets 3712 have not been seen for RouterDeadInterval seconds), it may 3713 still be necessary to send Hello Packets to the dead 3714 neighbor. These Hello Packets will be sent at the reduced 3715 rate PollInterval, which should be much larger than 3716 HelloInterval. Sample value for a PDN X.25 network: 2 3717 minutes. 3719 C.6 Point-to-MultiPoint network parameters 3721 On Point-to-MultiPoint networks, it may be necessary to 3722 configure the set of neighbors that are directly reachable over 3723 the Point-to-MultiPoint network. Each neighbor is configured 3724 with its Router ID and IPv6 link-local address on the network. 3725 Designated Routers are not elected on Point-to-MultiPoint 3726 networks, so the Designated Router eligibility of configured 3727 neighbors is undefined. 3729 C.7 Host route parameters 3731 Host prefixes are advertised in intra-area-prefix-LSAs. They 3732 indicate either internal router addresses, router interfaces to 3733 point-to-point networks, looped router interfaces, or IPv6 hosts 3734 that are directly connected to the router (e.g., via a PPP 3735 connection). For each host directly connected to the router, 3736 the following items must be configured: 3738 Host IPv6 prefix 3739 The IPv6 prefix belonging to the host. 3741 Cost of link to host 3742 The cost of sending a packet to the host, in terms of the 3743 link state metric. However, since the host probably has only 3744 a single connection to the internet, the actual configured 3745 cost(s) in many cases is unimportant (i.e., will have no 3746 effect on routing). 3748 Area ID 3749 The OSPF area to which the host's prefix belongs. 3751 Security Considerations 3753 When running over IPv6, OSPF relies on the IP Authentication Header 3754 (see [Ref19]) and the IP Encapsulating Security Payload (see 3755 [Ref20]) to ensure integrity and authentication/confidentiality of 3756 routing exchanges. 3758 Authors Addresses 3760 Rob Coltun 3761 Siara Systems 3762 300 Ferguson Drive 3763 Mountain View, CA 94043 3764 Phone: (650) 390-9030 3765 Email: rcoltun@siara.com 3767 Dennis Ferguson 3768 Juniper Networks 3769 385 Ravendale Drive 3770 Mountain View, CA 94043 3771 Phone: +1 650 526 8004 3772 Email: dennis@juniper.com 3774 John Moy 3775 Sycamore Networks, Inc. 3776 10 Elizabeth Drive 3777 Chelmsford, MA 01824 3778 Phone: (978) 250-2975 3779 Fax: (978) 256-3434 3780 Email: jmoy@sycamorenet.com 3782 This document expires in December 1999.