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Roy 5 L. Nguyen 6 P. Pillay-Esnault 7 Cisco Systems 8 March 29, 2005 10 Multi-Topology (MT) Routing in OSPF 11 draft-ietf-ospf-mt-03.txt 13 Status of this Memo 15 This document is an Internet-Draft and is subject to all provisions 16 of section 3 of RFC 3667. By submitting this Internet-Draft, each 17 author represents that any applicable patent or other IPR claims of 18 which he or she is aware have been or will be disclosed, and any of 19 which he or she become aware will be disclosed, in accordance with 20 RFC 3668. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that 24 other groups may also distribute working documents as 25 Internet-Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 38 This Internet-Draft will expire on September 27, 2005. 40 Copyright Notice 42 Copyright (C) The Internet Society (2005). 44 Abstract 46 This draft describes an extension to OSPF in order to define 47 independent IP topologies called Multi-Topologies (MTs). The MT 48 extension can be used for computing different paths for unicast 49 traffic, multicast traffic, different classes of service, or in-band 50 network management. [M-ISIS] describes a similar mechanism for ISIS. 51 An optional extension to exclude selected links from the default 52 topology is also described. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2.1 Requirements notation . . . . . . . . . . . . . . . . . . 4 59 2.2 Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 3. Base MT Functional Specifications . . . . . . . . . . . . . . 5 61 3.1 MT Area Boundary . . . . . . . . . . . . . . . . . . . . . 5 62 3.2 Adjacency for MTs . . . . . . . . . . . . . . . . . . . . 5 63 3.3 Sending OSPF control packets . . . . . . . . . . . . . . . 5 64 3.4 Advertising MT Adjacencies and the Corresponding IP 65 Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 3.4.1 Advertising MT Adjacencies and the Corresponding 67 IP Prefixes . . . . . . . . . . . . . . . . . . . . . 5 68 3.4.2 Inter-Area and External Routing . . . . . . . . . . . 6 69 3.5 Flushing MT Information . . . . . . . . . . . . . . . . . 6 70 3.6 MT SPF Computation . . . . . . . . . . . . . . . . . . . . 6 71 3.7 MT-ID Values . . . . . . . . . . . . . . . . . . . . . . . 7 72 3.8 Forwarding in MT . . . . . . . . . . . . . . . . . . . . . 7 73 4. Default Topology Link Exclusion Functional Specifications . . 8 74 4.1 Exclusion of Links in the Default Topology . . . . . . . . 8 75 4.2 New Area Data Structure Parameter . . . . . . . . . . . . 8 76 4.3 Adjacency Formation with Link Exclusion Capability . . . . 9 77 4.4 OSPF Control Packets Transmission Over Excluded Links . . 9 78 4.5 OSPF LSA Advertisement and SPF Computation for 79 Excluded Links . . . . . . . . . . . . . . . . . . . . . . 9 80 5. Interoperability between MT Capable and Non-MT Capable 81 Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 82 6. Migration from non-MT-Area to MT-area . . . . . . . . . . . . 12 83 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 84 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 85 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 86 9.1 Normative References . . . . . . . . . . . . . . . . . . . . 15 87 9.2 Informative References . . . . . . . . . . . . . . . . . . . 15 88 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15 89 A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 90 B. OSPF data formats . . . . . . . . . . . . . . . . . . . . . . 18 91 B.1 Router-LSAs . . . . . . . . . . . . . . . . . . . . . . . 18 92 B.2 Network-LSAs . . . . . . . . . . . . . . . . . . . . . . . 19 93 B.3 Summary-LSAs . . . . . . . . . . . . . . . . . . . . . . . 19 94 B.4 AS-External-LSAs . . . . . . . . . . . . . . . . . . . . . 20 95 B.5 NSSA-LSAs . . . . . . . . . . . . . . . . . . . . . . . . 21 96 Intellectual Property and Copyright Statements . . . . . . . . 22 98 1. Introduction 100 OSPF uses a fixed packet format, therefore it is not easy to 101 introduce any backward compatible extensions. However, the OSPF 102 specification [OSPF] introduced TOS metric in an earlier 103 specification [RFC1583] in order to announce a different link cost 104 based on TOS. TOS based routing as described in [RFC1583] was never 105 deployed and was subsequently deprecated. 107 We propose to reuse the TOS based metric fields. They have been 108 redefined as MT-ID and MT-ID Metric and are used to advertise 109 different topologies by advertising separate metrics for each of 110 them. 112 2. Terminology 114 2.1 Requirements notation 116 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 117 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 118 document are to be interpreted as described in RFC2119 [RFC2119]. 120 2.2 Terms 122 We define the following terminology in this document: 124 Non-MT router 125 Routers that do not have the MT capability 126 MT router 127 Routers that have MT capability as described in this document 128 MT-ID 129 Renamed TOS field in LSAs to represent multitopology ID. 130 Default topology 131 Topology that is built using the TOS 0 metric (default metric) 132 MT topology 133 Topology that is built using the corresponding MT-ID metric 134 MT 135 Shorthand notation for MT topology 136 MT#0 topology 137 Representation of TOS 0 metric in MT-ID format 138 Non-MT-Area 139 An area that contains only non-MT routers 140 MT-Area 141 An area that contains both non-MT routers and MT routers or only 142 MT routers 144 3. Base MT Functional Specifications 146 3.1 MT Area Boundary 148 Each OSPF interface belongs to a single area and all MTs sharing that 149 link need to belong to the same area. Therefore the area boundaries 150 for all MTs are the same but each MT's attachment to the area is 151 independent. 153 3.2 Adjacency for MTs 155 Each interface can be configured to belong to a set of topologies. A 156 single adjacency will be formed with neighbors on the interface even 157 if the interface is configured to participate in multiple topologies. 158 Furthermore, adjacency formation will be independent of the 159 topologies configured for the interface or neighbors on that 160 interface. 162 3.3 Sending OSPF control packets 164 OSPF control packets MUST be sent over the default topology. 166 OSPF control packets sent to the remote end-point of a virtual link 167 may need to traverse multiple hops. These control packets MUST be 168 correctly classified by the virtual link end-point routers as packets 169 belonging to the default topology. Even though the VL may belong to 170 one or more non-default topologies, OSPF control packets sent to the 171 remote end of a virtual link MUST be forwarded using the default 172 topology. 174 3.4 Advertising MT Adjacencies and the Corresponding IP Prefixes 176 We will reuse the TOS metric field in order to advertise a topology 177 and prefixes belonging to that topology. The TOS field is redefined 178 as MT-ID in the payload of Router-LSAs, Summary-LSAs, NSSA-LSAs, and 179 AS-External-LSAs (see Appendix A). 181 MT-ID metrics in LSAs SHOULD be in ascending order of MT-ID. If an 182 MT-ID exists in an LSA or router link multiple times, the metric in 183 the first MT-ID instance MUST be used. 185 3.4.1 Advertising MT Adjacencies and the Corresponding IP Prefixes 187 When a router establishes a FULL adjacency over a link that belongs 188 to a set of MTs, it will advertise the corresponding cost for each 189 MT-ID. 191 By default, all links are included in default topology and all 192 advertised prefixes belonging to the default topology will use the 193 TOS0 metric the same as in standard OSPF [OSPF]. 195 Each MT has its own MT-ID metric field. When a link is not part of a 196 given MT, the corresponding MT-ID metric is excluded from the LSA. 198 The Network-LSA does not contain any MT information since the DR is 199 shared by all MTs. Hence, there is no change to the Network-LSA. 201 3.4.2 Inter-Area and External Routing 203 In Summary-LSAs, NSSA-LSAs, and AS-External-LSAs, the TOS metric 204 fields are defined as MT-ID metric fields and are used in order to 205 advertise prefix and router reachability in the corresponding 206 topology. 208 When a router originates a Summary-LSA, NSSA-LSA, or AS-External-LSA 209 that belongs to a set of MTs, it will include the corresponding cost 210 for each MT-ID. By default, the router participates in the default 211 topology and uses the TOS0 metric for the default topology the same 212 as in standard OSPF [OSPF]. 214 Setting the P-bit in NSSA-LSAs is topology independent and pertains 215 to all MT-ID advertised in the body of the LSA. 217 3.5 Flushing MT Information 219 When a certain link or prefix that existed or was reachable in a 220 certain topology is no longer part of that topology or is unreachable 221 in that topology, a new version of the LSA must be originated 222 excluding metric information representing the link or prefix in that 223 topology. 225 The MT metric in the Router-LSA can also be set to the maximum 226 possible metric to enable the router to become a stub in a certain 227 topology [STUB]. 229 3.6 MT SPF Computation 231 By considering MT-ID metrics in the LSAs, OSPF will be able to 232 compute multiple topologies and find paths to IP prefixes for each MT 233 independently. A separate SPF will be computed for each MT-ID to 234 find independent paths to IP prefixes. Each nexthop computed during 235 the MT SPF MUST belong to the same MT. 237 Network-LSAs are used by all topologies during the SPF computation. 238 During the SPF for a given MT-ID, only the links and metrics for that 239 MT-ID will be considered. Entries in the Router Routing table will 240 be MT-ID specific. 242 During the SPF computation for the default topology only the TOS0 243 metric is considered during the SPF computation. 245 3.7 MT-ID Values 247 Since AS-External-LSAs use the high order bit in the MT-ID field (E 248 bit) for the external metric-type, only MT-IDs in the range [0-127] 249 are valid. The following MT-ID values are reserved: 251 0 - Reserved for advertising the metric associated with the 252 default topology (see Section 4.2) 254 1 - Reserved for advertising the metric associated with the 255 default multicast topology 257 MT-IDs [128-255] SHOULD be ignored. 259 3.8 Forwarding in MT 261 Forwarding assures that only routes belonging to a single topology 262 are used to forward a packet along its way from source to 263 destination. Therefore, user configuration MUST be consistently 264 applied throughout the network so that an incoming packet is 265 associated with the same topology through each hop end to end. It is 266 outside of the scope of this document to consider different methods 267 of associating an incoming packet to a corresponding topology. 269 4. Default Topology Link Exclusion Functional Specifications 271 The multi-topologies imply that all the routers participate in the 272 default topology. However, it can be useful to exclude some links 273 from the default topology and reserve them for some specific classes 274 of traffic. 276 The multi-topologies extension for default topology link or prefix 277 exclusion is described in the following subsections. 279 4.1 Exclusion of Links in the Default Topology 281 OSPF does not have the notion of an unreachable link. All links can 282 have a maximum metric of 0xFFFF advertised in the Router-LSA. The 283 link exclusion capability requires routers to ignore TOS0 metrics in 284 Router-LSAs in the default topology and to alternately use the 285 MT-ID#0 metric to advertise the metric associated with the default 286 topology. Hence, all routers within an area MUST agree on how the 287 metric for default topology will be advertised. 289 The unused T-bit is defined as the MT-bit in the option field in 290 order to assure that a multi-topology link-excluding capable router 291 will only form an adjacency with another similarly configured router. 293 +---+---+---+---+---+---+---+---+ 294 |DN |O |DC |EA |NP |MC |E |MT | 295 +---+---+---+---+---+---+---+---+ 297 MT-bit: This bit MUST be set in the Hello packet only if 298 MTRoutingExclusionCapability is enabled (see Section 4.2) 300 4.2 New Area Data Structure Parameter 302 We define a new parameter in the Area Data Structure: 304 MTRoutingExclusionCapability 305 This is a configurable parameter that will be used to facilitate 306 the introduction of MT routers in an area and ensure backward 307 compatibility. 309 When an area data structure is created the 310 MTRoutingExclusionCapability is disabled by default. 312 If MTRoutingExclusionCapability is disabled: 314 o The MT-bit MUST be cleared in Hello packets. 315 o If a link participates in a non-default topology, it is 316 automatically included in the default topology to support backward 317 compatibility between MT and non-MT routers. This is accomplished 318 through advertisement via the TOS0 metric field the same as in 319 standard OSPF [OSPF]. 321 If MTRoutingExclusionCapability is enabled: 323 o The MT-bit MUST be set in Hello packets 324 o The router will only accept a Hello if the MT-bit is set (see 325 Section 4.3) 327 When MTRoutingExclusionCapability is set to enabled a router is said 328 to be operating in MTRoutingExclusionCapability mode. 330 4.3 Adjacency Formation with Link Exclusion Capability 332 In order to have a smooth transition from a non-MT area to an 333 MT-area, an MT router with MTRoutingExclusionCapability disabled will 334 form adjacencies with non-MT routers and will include all links as 335 part of default topology. 337 A link may cease participating in default topology if 338 MTRoutingExclusionCapability is set to enabled. In this state, a 339 router will only form adjacency with routers that set the MT-bit in 340 their Hello packets. This will ensure that all routers have 341 MTRoutingExclusionCapability enabled before the default topology can 342 be disabled on a link. 344 Receiving OSPF Hello packets as defined in section 10.5 of [OSPF] is 345 modified as follows: 347 o If the MTRoutingExclusionCapability of the Area Data structure is 348 set to enabled, the Hello packets are discarded if the the 349 received Hello packet does not have the MT-bit in the hello 350 options set. 352 4.4 OSPF Control Packets Transmission Over Excluded Links 354 If MTRoutingExclusionCapability is enabled and the default topology 355 is not configured on an interface, connected routes MUST exist for 356 the default topology so that OSPF control packets can be sent and 357 received on that interface. 359 4.5 OSPF LSA Advertisement and SPF Computation for Excluded Links 361 When MTRoutingExclusionCapability is enabled and the link does not 362 participate in the default topology, the MT-ID#0 metric is not 363 advertised. The link's TOS0 metric is ignored during the default 364 topology SPF computation. 366 When MTRoutingExclusionCapability is enabled and a link participates 367 in the default topology, MT-ID#0 metric is used to advertise the 368 metric associated with the default topology. The link's TOS0 metric 369 is ignored during the default topology SPF computation. 371 Independent of the MTRoutingExclusionCapability setting, the TOS0 372 metric is used for Summary-LSAs, NSSA-LSAs, and AS-External-LSAs. 374 o If the prefix or router does not exist in the default topology, 375 the TOS0 metric is set to infinity (0xFFFFFF). 376 o If the prefix or router exists in default the topology, the TOS0 377 metric is used to advertise the metric in the default topology. 379 During the summary and external prefix calculation for the default 380 topology the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and 381 AS-External-LSAs. 383 5. Interoperability between MT Capable and Non-MT Capable Routers 385 The default metric field is mandatory in all LSAs (even when metric 386 value is 0). Even when a link or prefix does not exist in the 387 default topology, a non-MT router can consider the zero value in the 388 metric field as a valid metric and consider the link or prefix as 389 part of the default topology. 391 In order to prevent the above problem, an MT capable router will 392 include all links as part of the default topology. If links need to 393 be removed from the default topology, an MT capable router MUST be 394 configured in MTRoutingExclusionCapability mode. In this mode, 395 routers will assure that all other routers in the area are in the 396 MTRoutingExclusionCapability mode before considering the MT-ID#0 397 metric in the SPF calculation. Only then can the TOS0 metric field 398 in Router LSAs be safely ignored during the default topology SPF 399 computation. 401 Note that for any prefix or router to become reachable in a certain 402 topology, a contiguous path inside that topology must exist between 403 the calculating router and the destination prefix or router. 405 6. Migration from non-MT-Area to MT-area 407 Introducing MT-OSPF into a network can be done gradually to allow MT 408 routers and non-MT routers to participate in the default topology 409 while MT routers participate in other topologies. 411 If there is a requirement to exclude some links from the default 412 topology in an area, all routers in the area MUST be in 413 MTRoutingExclusionCapability mode. In this section we describe the 414 migration steps to consider while transitioning from a non-MT network 415 to an MT network. 417 Consider a network with a backbone area and a set of non-backbone 418 areas functioning in standard OSPF mode. We would like to migrate to 419 an MT network either partially or completely. 421 1. As required, part of an area is upgrade to be MT capable. The MT 422 routers will interact with non-MT routers in the default topology 423 and participate in other topologies as required. 424 2. If a new non-backbone area is created for MT routers, it may be 425 configured in MTRoutingExclusionCapability mode since there is no 426 interaction required with non-MT routers. In this mode, the 427 default topology can be excluded on links as required. 428 3. If there is more than one non-backbone areas where MT is being 429 used, it is desirable that the backbone area first be upgraded to 430 be MT capable so that inter-area routing is assured for MT 431 destinations in different areas. 432 4. Gradually the whole network can be made MT capable. 434 Note that inter-area routing for the MT-area still depends on the 435 backbone area. Therefore, if different areas configured for a given 436 topology need to communicate, the backbone area also needs to be 437 configured for this topology. 439 7. Security Considerations 441 This document does not raise any security issues that are not already 442 covered in [OSPF]. 444 8. IANA Considerations 446 The T-bit as defined in [RFC1583] for a router's TOS capability is 447 redefined as the MT-bit in this document. Similarly, the TOS field 448 for Router-LSAs, Summary-LSAs, NSSA-LSAs, and AS-External LSAs as 449 defined in [OSPF] is redefined as MT-ID in this document. 451 9. References 453 9.1 Normative References 455 [NSSA] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", 456 RFC 3101, January 2003. 458 [OSPF] Moy, J., "OSPF Version 2", RFC 2328, April 1998. 460 [RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994. 462 [RFC2119] Bradner, S., "Key words for use in RFC's to Indicate 463 Requirement Levels", RFC 2119, March 1997. 465 9.2 Informative References 467 [M-ISIS] Przygienda, T., Shen, N. and N. Sheth, "M-ISIS: Multi 468 Topology (MT) Routing in IS-IS", 469 draft-ietf-isis-wg-multi-topology-07.txt (work in 470 progress). 472 [STUB] Retana, A., Nguyen, L., White, R., Zinin, A. and D. 473 McPherson, "OSPF Stub Router Advertisement", RFC 3137, June 474 2001. 476 Authors' Addresses 478 Peter Psenak 479 Cisco Systems 480 Parc Pegasus, De Kleetlaan 6A 481 1831 Diegem 482 Belgium 484 EMail: ppsenak@cisco.com 486 Sina Mirtorabi 487 Cisco Systems 488 225 West Tasman Drive 489 San Jose, CA 95134 490 USA 492 EMail: sina@cisco.com 493 Abhay Roy 494 Cisco Systems 495 225 West Tasman Drive 496 San Jose, CA 95134 497 USA 499 EMail: akr@cisco.com 501 Liem Nguyen 502 Cisco Systems 503 7025 Kit Creek Road 504 Research Triangle Park, NC 27709 505 USA 507 EMail: lhnguyen@cisco.com 509 Padma Pillay-Esnault 510 Cisco Systems 511 225 West Tasman Drive 512 San Jose, CA 95134 513 USA 515 EMail: ppe@cisco.com 517 Appendix A. Acknowledgments 519 The authors would like to thank Scott Sturgess, Alvaro Retana, and 520 David Kushi for their comments on the document. Thanks to Acee 521 Lindem for review and editing. 523 Appendix B. OSPF data formats 525 LSA content defined in [OSPF] is modified to introduce the MT-ID. 527 B.1 Router-LSAs 529 Router-LSAs are the Type 1 LSAs. Each router in an area originates a 530 router-LSA. The LSA describes the state and cost of the router's 531 links (i.e., interfaces) to the area. All of the router's links to 532 the area must be described in a single router-LSA. For details 533 concerning the construction of router-LSAs, see Section 12.4.1 534 [OSPF]. 536 0 1 2 3 537 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 1 538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 539 | LS age | Options | 1 | 540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 541 | Link State ID | 542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 543 | Advertising Router | 544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 545 | LS sequence number | 546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 547 | LS checksum | length | 548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 549 |*|*|*|N|W|V|E|B| 0 | # links | 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 | Link ID | 552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 | Link Data | 554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 555 | Type | # MT-ID | metric | 556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 557 | MT-ID | 0 | MT-ID metric | 558 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 559 | ... | 560 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 561 | MT-ID | 0 | MT-ID metric | 562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 563 | Link ID | 564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 565 | Link Data | 566 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 567 | ... | 569 B.2 Network-LSAs 571 Network-LSAs are the Type 2 LSAs. A network-LSA is originated for 572 each broadcast and NBMA network in the area which supports two or 573 more routers. The network-LSA is originated by the network's 574 Designated Router. The LSA describes all routers attached to the 575 network, including the Designated Router itself. The LSA's Link 576 State ID field lists the IP interface address of the Designated 577 Router. 579 The distance from the network to all attached routers is zero. This 580 is why metric fields need not be specified in the network-LSA. For 581 details concerning the construction of network-LSAs, see Section 582 12.4.2 [OSPF]. 584 0 1 2 3 585 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 1 586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 587 | LS age | Options | 2 | 588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 589 | Link State ID | 590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 | Advertising Router | 592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 593 | LS sequence number | 594 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 595 | LS checksum | length | 596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 597 | Network Mask | 598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 599 | Attached Router | 600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 | ... | 603 Note that network LSA does not contain any MT-ID fields as the cost 604 of the network to the attached routers is 0 and DR is shared by all 605 topologies. 607 B.3 Summary-LSAs 609 Summary-LSAs are the Type 3 and 4 LSAs. These LSAs are originated by 610 area border routers. Summary-LSAs describe inter-area destinations. 611 For details concerning the construction of summary- LSAs, see Section 612 12.4.3 [OSPF]. 614 Type 3 summary-LSAs are used when the destination is an IP network. 615 In this case the LSA's Link State ID field is an IP network number 616 (if necessary, the Link State ID can also have one or more of the 617 network's "host" bits set; see Appendix E [OSPF] for details). When 618 the destination is an AS boundary router, a Type 4 summary-LSA is 619 used, and the Link State ID field is the AS boundary router's OSPF 620 Router ID. (To see why it is necessary to advertise the location of 621 each ASBR, consult Section 16.4 of [OSPF]). Other than the 622 difference in the Link State ID field, the format of Type 3 and 4 623 summary-LSAs is identical. 625 0 1 2 3 626 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 1 627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 628 | LS age | Options | 3 or 4 | 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 630 | Link State ID | 631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 632 | Advertising Router | 633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 634 | LS sequence number | 635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 636 | LS checksum | length | 637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 638 | Network Mask | 639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 640 | 0 | metric | 641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 642 | MT-ID | MT-ID metric | 643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 644 | ... | 645 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 646 | MT-ID | MT-ID metric | 647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 649 B.4 AS-External-LSAs 651 AS-external-LSAs are the Type 5 LSAs. These LSAs are originated by 652 AS boundary routers, and describe destinations external to the AS. 653 For details concerning the construction of AS-external-LSAs, see 654 Section 12.4.3 [OSPF]. 656 AS-external-LSAs usually describe a particular external destination. 657 For these LSAs the Link State ID field specifies an IP network number 658 (if necessary, the Link State ID can also have one or more of the 659 network's "host" bits set; see Appendix E [OSPF] for details). 660 AS-external-LSAs are also used to describe a default route. Default 661 routes are used when no specific route exists to the destination. 663 When describing a default route, the Link State ID is always set to 664 DefaultDestination (0.0.0.0) and the Network Mask is set to 0.0.0.0. 666 0 1 2 3 667 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 1 668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 669 | LS age | Options | 5 | 670 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 671 | Link State ID | 672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 673 | Advertising Router | 674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 675 | LS sequence number | 676 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 677 | LS checksum | length | 678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 679 | Network Mask | 680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 681 |E| 0 | metric | 682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 683 | Forwarding address | 684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 685 | External Route Tag | 686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 |E| MT-ID | MT-ID metric | 688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 689 | Forwarding address | 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 691 | External Route Tag | 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 | ... | 694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 695 |E| MT-ID | MT-ID metric | 696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 697 | Forwarding address | 698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 | External Route Tag | 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 702 B.5 NSSA-LSAs 704 NSSA-LSAs are the Type 7 LSAs. These LSAs are originated by AS 705 boundary routers local to an NSSA, and describe destinations external 706 to the AS. The changes to NSSA-LSAs are identical to those for 707 External-LSAs (Appendix A.4.5). For details concerning the 708 construction of NSSA-LSAs see Section 2.4 [NSSA]. 710 Intellectual Property Statement 712 The IETF takes no position regarding the validity or scope of any 713 Intellectual Property Rights or other rights that might be claimed to 714 pertain to the implementation or use of the technology described in 715 this document or the extent to which any license under such rights 716 might or might not be available; nor does it represent that it has 717 made any independent effort to identify any such rights. 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