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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Open Shortest Path First IGP P. Psenak, Ed. 3 Internet-Draft Cisco Systems, Inc. 4 Intended status: Standards Track S. Previdi, Ed. 5 Expires: May 24, 2019 Individual 6 November 20, 2018 8 OSPFv3 Extensions for Segment Routing 9 draft-ietf-ospf-ospfv3-segment-routing-extensions-19 11 Abstract 13 Segment Routing (SR) allows a flexible definition of end-to-end paths 14 within IGP topologies by encoding paths as sequences of topological 15 sub-paths, called "segments". These segments are advertised by the 16 link-state routing protocols (IS-IS and OSPF). 18 This draft describes the OSPFv3 extensions required for Segment 19 Routing with MPLS data plane. 21 Requirements Language 23 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 24 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 25 document are to be interpreted as described in [RFC2119]. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on May 24, 2019. 44 Copyright Notice 46 Copyright (c) 2018 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (https://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 3. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 4 64 3.1. SID/Label Sub-TLV . . . . . . . . . . . . . . . . . . . . 4 65 4. Segment Routing Capabilities . . . . . . . . . . . . . . . . 4 66 5. OSPFv3 Extended Prefix Range TLV . . . . . . . . . . . . . . 5 67 6. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 7 68 7. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 10 69 7.1. Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 10 70 7.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 12 71 8. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 13 72 8.1. Intra-area Segment routing in OSPFv3 . . . . . . . . . . 13 73 8.2. Inter-area Segment routing in OSPFv3 . . . . . . . . . . 14 74 8.3. Segment Routing for External Prefixes . . . . . . . . . . 15 75 8.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 15 76 8.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 15 77 8.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 16 78 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 79 9.1. OSPFv3 Extended-LSA TLV Registry . . . . . . . . . . . . 16 80 9.2. OSPFv3 Extended-LSA Sub-TLV registry . . . . . . . . . . 16 81 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 82 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17 83 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 84 12.1. Normative References . . . . . . . . . . . . . . . . . . 18 85 12.2. Informative References . . . . . . . . . . . . . . . . . 20 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 88 1. Introduction 90 Segment Routing (SR) allows a flexible definition of end-to-end paths 91 within IGP topologies by encoding paths as sequences of topological 92 sub-paths, called "segments". These segments are advertised by the 93 link-state routing protocols (IS-IS and OSPF). Prefix segments 94 represent an ECMP-aware shortest-path to a prefix (or a node), as per 95 the state of the IGP topology. Adjacency segments represent a hop 96 over a specific adjacency between two nodes in the IGP. A prefix 97 segment is typically a multi-hop path while an adjacency segment, in 98 most cases, is a one-hop path. SR's control-plane can be applied to 99 both IPv6 and MPLS data-planes, and does not require any additional 100 signalling (other than IGP extensions). The IPv6 data plane is out 101 of the scope of this specification - OSPFv3 extension for SR with 102 IPv6 data plane will be specified in a separate document. When used 103 in MPLS networks, SR paths do not require any LDP or RSVP-TE 104 signalling. However, SR can interoperate in the presence of LSPs 105 established with RSVP or LDP. 107 There are additional segment types, e.g., Binding SID defined in 108 [RFC8402]. 110 This draft describes the OSPFv3 extensions required for Segment 111 Routing with MPLS data plane. 113 Segment Routing architecture is described in [RFC8402]. 115 Segment Routing use cases are described in [RFC7855]. 117 2. Terminology 119 This section lists some of the terminology used in this document: 121 ABR - Area Border Router 123 Adj-SID - Adjacency Segment Identifier 125 AS - Autonomous System 127 ASBR - Autonomous System Boundary Router 129 IS-IS - Intermediate System to Intermediate System 131 LDP - Label Distribution Protocol 133 LSP - Label Switched Path 135 MPLS - Multi Protocol Label Switching 137 OSPF - Open Shortest Path First 139 SPF - Shortest Path First 141 RSVP - Resource Reservation Protocol 143 SID - Segment Identifier 144 SR - Segment Routing 146 SRGB - Segment Routing Global Block 148 SRLB - Segment Routing Local Block 150 SRMS - Segment Routing Mapping Server 152 TLV - Type Length Value 154 3. Segment Routing Identifiers 156 Segment Routing defines various types of Segment Identifiers (SIDs): 157 Prefix-SID, Adjacency-SID, LAN Adjacency SID, and Binding SID. 159 3.1. SID/Label Sub-TLV 161 The SID/Label Sub-TLV appears in multiple TLVs or Sub-TLVs defined 162 later in this document. It is used to advertise the SID or label 163 associated with a prefix or adjacency. The SID/Label Sub-TLV has 164 following format: 166 0 1 2 3 167 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 1 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 | Type | Length | 170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 171 | SID/Label (variable) | 172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 174 where: 176 Type: 7 178 Length: Either 3 or 4 octets 180 SID/Label: If length is set to 3, then the 20 rightmost bits 181 represent a label. If length is set to 4, then the value 182 represents a 32-bit SID. 184 The receiving router MUST ignore the SID/Label Sub-TLV if the 185 length is other than 3 or 4. 187 4. Segment Routing Capabilities 189 Segment Routing requires some additional router capabilities to be 190 advertised to other routers in the area. 192 These SR capabilities are advertised in the OSPFv3 Router Information 193 Opaque LSA (defined in [RFC7770]) and specified in 194 [I-D.ietf-ospf-segment-routing-extensions]. 196 5. OSPFv3 Extended Prefix Range TLV 198 In some cases it is useful to advertise attributes for a range of 199 prefixes. The Segment Routing Mapping Server, which is described in 200 [I-D.ietf-spring-segment-routing-ldp-interop], is an example of where 201 a single advertisement is needed to advertise SIDs for multiple 202 prefixes from a contiguous address range. 204 The OSPFv3 Extended Prefix Range TLV is defined for this purpose. 206 The OSPFv3 Extended Prefix Range TLV is a top-level TLV of the 207 following LSAs defined in [RFC8362]: 209 E-Intra-Area-Prefix-LSA 211 E-Inter-Area-Prefix-LSA 213 E-AS-External-LSA 215 E-Type-7-LSA 217 Multiple OSPFv3 Extended Prefix Range TLVs MAY be advertised in each 218 LSA mentioned above. The OSPFv3 Extended Prefix Range TLV has the 219 following format: 221 0 1 2 3 222 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 1 223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 224 | Type | Length | 225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 226 | Prefix Length | AF | Range Size | 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 228 | Flags | Reserved | 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | Address Prefix (variable) | 231 | ... | 232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 | Sub-TLVs (variable) | 234 +- -+ 235 | | 237 where: 239 Type: 9 240 Length: Variable, in octets, dependent on Sub-TLVs. 242 Prefix length: Length of prefix in bits. 244 AF: Address family for the prefix. 246 AF: 0 - IPv4 unicast 248 AF: 1 - IPv6 unicast 250 Range size: Represents the number of prefixes that are covered by 251 the advertisement. The Range Size MUST NOT exceed the number of 252 prefixes that could be satisfied by the prefix length without 253 including: 255 Addresses from the IPv4 multicast address range (224.0.0.0/3), 256 if the AF is IPv4 unicast 258 Addresses other than the IPv6 unicast addresses, if the AF is 259 IPv6 unicast 261 Flags: Reserved. MUST be zero when sent and are ignored when 262 received. 264 Reserved: SHOULD be set to 0 on transmission and MUST be ignored 265 on reception. 267 Address Prefix: 269 For the address family IPv4 unicast, the prefix itself is 270 encoded as a 32-bit value. The default route is represented by 271 a prefix of length 0. 273 For the address family IPv6 unicast, the prefix, encoded as an 274 even multiple of 32-bit words, padded with zeroed bits as 275 necessary. This encoding consumes ((PrefixLength + 31) / 32) 276 32-bit words. 278 Prefix encoding for other address families is beyond the scope 279 of this specification. 281 If the OSPFv3 Extended Prefix Range TLVs advertising the exact same 282 range appears in multiple LSAs of the same type, originated by the 283 same OSPFv3 router, the LSA with the numerically smallest Instance ID 284 MUST be used and subsequent instances of the OSPFv3 Extended Prefix 285 Range TLVs MUST be ignored. 287 6. Prefix SID Sub-TLV 289 The Prefix SID Sub-TLV is a Sub-TLV of the following OSPFv3 TLVs as 290 defined in [RFC8362] and in Section 5: 292 Intra-Area Prefix TLV 294 Inter-Area Prefix TLV 296 External Prefix TLV 298 OSPFv3 Extended Prefix Range TLV 300 It MAY appear more than once in the parent TLV and has the following 301 format: 303 0 1 2 3 304 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 1 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | Type | Length | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | Flags | Algorithm | Reserved | 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | SID/Index/Label (variable) | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 where: 314 Type: 4 316 Length: 7 or 8 octets, dependent on the V-flag 318 Flags: Single octet field. The following flags are defined: 320 0 1 2 3 4 5 6 7 321 +--+--+--+--+--+--+--+--+ 322 | |NP|M |E |V |L | | | 323 +--+--+--+--+--+--+--+--+ 324 where: 326 NP-Flag: No-PHP flag. If set, then the penultimate hop MUST 327 NOT pop the Prefix-SID before delivering packets to the node 328 that advertised the Prefix-SID. 330 M-Flag: Mapping Server Flag. If set, the SID was advertised by 331 a Segment Routing Mapping Server as described in 332 [I-D.ietf-spring-segment-routing-ldp-interop]. 334 E-Flag: Explicit-Null Flag. If set, any upstream neighbor of 335 the Prefix-SID originator MUST replace the Prefix-SID with the 336 Explicit-NULL label (0 for IPv4, 2 for IPv6) before forwarding 337 the packet. 339 V-Flag: Value/Index Flag. If set, then the Prefix-SID carries 340 an absolute value. If not set, then the Prefix-SID carries an 341 index. 343 L-Flag: Local/Global Flag. If set, then the value/index 344 carried by the Prefix-SID has local significance. If not set, 345 then the value/index carried by this Sub-TLV has global 346 significance. 348 Other bits: Reserved. These MUST be zero when sent and are 349 ignored when received. 351 Reserved: SHOULD be set to 0 on transmission and MUST be ignored 352 on reception. 354 Algorithm: Single octet identifying the algorithm the Prefix-SID 355 is associated with as defined in 356 [I-D.ietf-ospf-segment-routing-extensions]. 358 A router receiving a Prefix-SID from a remote node and with an 359 algorithm value that such remote node has not advertised in the 360 SR-Algorithm Sub-TLV [I-D.ietf-ospf-segment-routing-extensions] 361 MUST ignore the Prefix-SID Sub-TLV. 363 SID/Index/Label: According to the V-Fag, it contains either: 365 A 32-bit index defining the offset in the SID/Label space 366 advertised by this router. 368 A 24-bit label where the 20 rightmost bits are used for 369 encoding the label value. 371 If an OSPFv3 router advertises multiple Prefix-SIDs for the same 372 prefix, topology, and algorithm, all of them MUST be ignored. 374 When calculating the outgoing label for the prefix, the router MUST 375 take into account, as described below, the E, NP, and M flags 376 advertised by the next-hop router if that router advertised the SID 377 for the prefix. This MUST be done regardless of whether the next-hop 378 router contributes to the best path to the prefix. 380 The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for 381 Prefix-SIDs allocated to prefixes that are propagated between areas 382 by an ABR based on intra-area or inter-area reachability, unless the 383 advertised prefix is directly attached to such ABR. 385 The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for 386 Prefix-SIDs allocated to redistributed prefixes, unless the 387 redistributed prefix is directly attached to the advertising 388 Autonomous System Boundary Router (ASBR). 390 If the NP-Flag is not set, then any upstream neighbor of the Prefix- 391 SID originator MUST pop the Prefix-SID. This is equivalent to the 392 penultimate hop popping mechanism used in the MPLS dataplane. If the 393 NP-flag is not set, then the received E-flag is ignored. 395 If the NP-flag is set then: 397 If the E-flag is not set, then any upstream neighbor of the 398 Prefix-SID originator MUST keep the Prefix-SID on top of the 399 stack. This is useful when the originator of the Prefix-SID needs 400 to stitch the incoming packet into a continuing MPLS LSP to the 401 final destination. This could occur at an Area Border Router 402 (prefix propagation from one area to another) or at an AS Boundary 403 Router (prefix propagation from one domain to another). 405 If the E-flag is set, then any upstream neighbor of the Prefix-SID 406 originator MUST replace the Prefix-SID with an Explicit-NULL 407 label. This is useful, e.g., when the originator of the Prefix- 408 SID is the final destination for the related prefix and the 409 originator wishes to receive the packet with the original EXP 410 bits. 412 When the M-Flag is set, the NP-flag and the E-flag MUST be ignored on 413 reception. 415 As the Mapping Server does not specify the originator of a prefix 416 advertisement, it is not possible to determine PHP behavior solely 417 based on the Mapping Server advertisement. However, PHP behavior 418 SHOULD be done in following cases: 420 The Prefix is intra-area type and the downstream neighbor is the 421 originator of the prefix. 423 The Prefix is inter-area type and the downstream neighbor is an 424 ABR, which is advertising prefix reachability and is setting the 425 LA-bit in the Prefix Options as described in [RFC8362]. 427 The Prefix is external type and the downstream neighbor is an 428 ASBR, which is advertising prefix reachability and is setting the 429 LA-bit in the Prefix Options as described in [RFC8362]. 431 When a Prefix-SID is advertised in the OSPFv3 Extended Prefix Range 432 TLV, then the value advertised in the Prefix SID Sub-TLV is 433 interpreted as a starting SID/Label value. 435 Example 1: If the following router addresses (loopback addresses) 436 need to be mapped into the corresponding Prefix SID indexes: 438 Router-A: 2001:DB8::1/128, Prefix-SID: Index 1 439 Router-B: 2001:DB8::2/128, Prefix-SID: Index 2 440 Router-C: 2001:DB8::3/128, Prefix-SID: Index 3 441 Router-D: 2001:DB8::4/128, Prefix-SID: Index 4 443 then the Address Prefix field in the OSPFv3 Extended Prefix Range TLV 444 would be set to 2001:DB8::1, the Prefix Length would be set to 128, 445 the Range Size would be set to 4, and the Index value in the Prefix- 446 SID Sub-TLV would be set to 1. 448 Example 2: If the following prefixes need to be mapped into the 449 corresponding Prefix-SID indexes: 451 2001:DB8:1::0/120, Prefix-SID: Index 51 452 2001:DB8:1::100/120, Prefix-SID: Index 52 453 2001:DB8:1::200/120, Prefix-SID: Index 53 454 2001:DB8:1::300/120, Prefix-SID: Index 54 455 2001:DB8:1::400/120, Prefix-SID: Index 55 456 2001:DB8:1::500/120, Prefix-SID: Index 56 457 2001:DB8:1::600/120, Prefix-SID: Index 57 459 then the Prefix field in the OSPFv3 Extended Prefix Range TLV would 460 be set to 2001:DB8:1::0, the Prefix Length would be set to 120, the 461 Range Size would be set to 7, and the Index value in the Prefix-SID 462 Sub-TLV would be set to 51. 464 7. Adjacency Segment Identifier (Adj-SID) 466 An Adjacency Segment Identifier (Adj-SID) represents a router 467 adjacency in Segment Routing. 469 7.1. Adj-SID Sub-TLV 471 The Adj-SID Sub-TLV is an optional Sub-TLV of the Router-Link TLV as 472 defined in [RFC8362]. It MAY appear multiple times in the Router- 473 Link TLV. The Adj-SID Sub-TLV has the following format: 475 0 1 2 3 476 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 1 477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 478 | Type | Length | 479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 480 | Flags | Weight | Reserved | 481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 482 | SID/Label/Index (variable) | 483 +---------------------------------------------------------------+ 485 where: 487 Type: 5 489 Length: 7 or 8 octets, dependent on the V flag. 491 Flags: Single octet field containing the following flags: 493 0 1 2 3 4 5 6 7 494 +-+-+-+-+-+-+-+-+ 495 |B|V|L|G|P| | 496 +-+-+-+-+-+-+-+-+ 498 where: 500 B-Flag: Backup Flag. If set, the Adj-SID refers to an 501 adjacency that is eligible for protection (e.g., using IPFRR or 502 MPLS-FRR) as described in section 3.5 of [RFC8402]. 504 The V-Flag: Value/Index Flag. If set, then the Adj-SID carries 505 an absolute value. If not set, then the Adj-SID carries an 506 index. 508 The L-Flag: Local/Global Flag. If set, then the value/index 509 carried by the Adj-SID has local significance. If not set, 510 then the value/index carried by this Sub-TLV has global 511 significance. 513 The G-Flag: Group Flag. When set, the G-Flag indicates that 514 the Adj-SID refers to a group of adjacencies (and therefore MAY 515 be assigned to other adjacencies as well). 517 P-Flag. Persistent flag. When set, the P-Flag indicates that 518 the Adj-SID is persistently allocated, i.e., the Adj-SID value 519 remains the same across router restart and/or interface flap. 521 Other bits: Reserved. These MUST be zero when sent and are 522 ignored when received. 524 Reserved: SHOULD be set to 0 on transmission and MUST be ignored 525 on reception. 527 Weight: Weight used for load-balancing purposes. The use of the 528 weight is defined in [RFC8402]. 530 SID/Index/Label: According to the V-Flag, it contains either: 532 A 32-bit index defining the offset in the SID/Label space 533 advertised by this router. 535 A 24-bit label where the 20 rightmost bits are used for 536 encoding the label value. 538 An SR-capable router MAY allocate an Adj-SID for each of its 539 adjacencies and set the B-Flag when the adjacency is eligible for 540 protection by an FRR mechanism (IP or MPLS) as described in 541 [RFC8402]. 543 An SR-capable router MAY allocate more than one Adj-SID to an 544 adjacency. 546 An SR-capable router MAY allocate the same Adj-SID to different 547 adjacencies. 549 When the P-flag is not set, the Adj-SID MAY be persistent. When the 550 P-flag is set, the Adj-SID MUST be persistent. 552 7.2. LAN Adj-SID Sub-TLV 554 The LAN Adj-SID Sub-TLV is an optional Sub-TLV of the Router-Link 555 TLV. It MAY appear multiple times in the Router-Link TLV. It is 556 used to advertise a SID/Label for an adjacency to a non-DR router on 557 a broadcast, NBMA, or hybrid [RFC6845] network. 559 0 1 2 3 560 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 1 561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 562 | Type | Length | 563 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 564 | Flags | Weight | Reserved | 565 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 566 | Neighbor ID | 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 | SID/Label/Index (variable) | 569 +---------------------------------------------------------------+ 571 where: 573 Type: 6 575 Length: 11 or 12 octets, dependent on V-flag. 577 Flags: same as in Section 7.1 579 Weight: Weight used for load-balancing purposes. The use of the 580 weight is defined in [RFC8402]. 582 Reserved: SHOULD be set to 0 on transmission and MUST be ignored 583 on reception. 585 Neighbor ID: The Router ID of the neighbor for which the LAN-Adj- 586 SID is advertised. 588 SID/Index/Label: According to the V and L flags, it contains 589 either: 591 A 32-bit index defining the offset in the SID/Label space 592 advertised by this router. 594 A 24-bit label where the 20 rightmost bits are used for 595 encoding the label value. 597 When the P-flag is not set, the Adj-SID MAY be persistent. When 598 the P-flag is set, the Adj-SID MUST be persistent. 600 8. Elements of Procedure 602 8.1. Intra-area Segment routing in OSPFv3 604 An OSPFv3 router that supports segment routing MAY advertise Prefix- 605 SIDs for any prefix to which it is advertising reachability (e.g., a 606 loopback IP address as described in Section 6). 608 A Prefix-SID can also be advertised by SR Mapping Servers (as 609 described in [I-D.ietf-spring-segment-routing-ldp-interop]). A 610 Mapping Server advertises Prefix-SIDs for remote prefixes that exist 611 in the OSPFv3 routing domain. Multiple Mapping Servers can advertise 612 Prefix-SIDs for the same prefix, in which case the same Prefix-SID 613 MUST be advertised by all of them. The SR Mapping Server could use 614 either area flooding scope or autonomous system flooding scope when 615 advertising Prefix SIDs for prefixes, based on the configuration of 616 the SR Mapping Server. Depending on the flooding scope used, the SR 617 Mapping Server chooses the OSPFv3 LSA type that will be used. If the 618 area flooding scope is needed, an E-Intra-Area-Prefix-LSA [RFC8362] 619 is used. If autonomous system flooding scope is needed, an E-AS- 620 External-LSA [RFC8362] is used. 622 When a Prefix-SID is advertised by the Mapping Server, which is 623 indicated by the M-flag in the Prefix-SID Sub-TLV (Section 6), the 624 route type as implied by the LSA type is ignored and the Prefix-SID 625 is bound to the corresponding prefix independent of the route type. 627 Advertisement of the Prefix-SID by the Mapping Server using an Inter- 628 Area Prefix TLV, External-Prefix TLV, or Intra-Area-Prefix TLV 629 [RFC8362] does not itself contribute to the prefix reachability. The 630 NU-bit MUST be set in the PrefixOptions field of the LSA which is 631 used by the Mapping Server to advertise SID or SID Range, which 632 prevents the advertisement from contributing to prefix reachability. 634 An SR Mapping Server MUST use the OSPFv3 Extended Prefix Range TLVs 635 when advertising SIDs for prefixes. Prefixes of different route- 636 types can be combined in a single OSPFv3 Extended Prefix Range TLV 637 advertised by an SR Mapping Server. 639 Area-scoped OSPFv3 Extended Prefix Range TLVs are propagated between 640 areas. Similar to propagation of prefixes between areas, an ABR only 641 propagates the OSPFv3 Extended Prefix Range TLV that it considers to 642 be the best from the set it received. The rules used to pick the 643 best OSPFv3 Extended Prefix Range TLV are described in Section 5. 645 8.2. Inter-area Segment routing in OSPFv3 647 In order to support SR in a multi-area environment, OSPFv3 MUST 648 propagate Prefix-SID information between areas. The following 649 procedure is used to propagate Prefix SIDs between areas. 651 When an OSPFv3 ABR advertises an Inter-Area-Prefix-LSA from an intra- 652 area prefix to all its connected areas, it will also include the 653 Prefix-SID Sub-TLV, as described in Section 6. The Prefix-SID value 654 will be set as follows: 656 The ABR will look at its best path to the prefix in the source 657 area and find the advertising router associated with the best path 658 to that prefix. 660 The ABR will then determine if such router advertised a Prefix-SID 661 for the prefix and use it when advertising the Prefix-SID to other 662 connected areas. 664 If no Prefix-SID was advertised for the prefix in the source area 665 by the router that contributes to the best path to the prefix, the 666 originating ABR will use the Prefix-SID advertised by any other 667 router when propagating the Prefix-SID for the prefix to other 668 areas. 670 When an OSPFv3 ABR advertises Inter-Area-Prefix-LSA LSAs from an 671 inter-area route to all its connected areas, it will also include the 672 Prefix-SID Sub-TLV, as described in Section 6. The Prefix-SID value 673 will be set as follows: 675 The ABR will look at its best path to the prefix in the backbone 676 area and find the advertising router associated with the best path 677 to that prefix. 679 The ABR will then determine if such router advertised a Prefix-SID 680 for the prefix and use it when advertising the Prefix-SID to other 681 connected areas. 683 If no Prefix-SID was advertised for the prefix in the backbone 684 area by the ABR that contributes to the best path to the prefix, 685 the originating ABR will use the Prefix-SID advertised by any 686 other router when propagating the Prefix-SID for the prefix to 687 other areas. 689 8.3. Segment Routing for External Prefixes 691 AS-External-LSAs are flooded domain wide. When an ASBR, which 692 supports SR, originates an E-AS-External-LSA, it SHOULD also include 693 a Prefix-SID Sub-TLV, as described in Section 6. The Prefix-SID 694 value will be set to the SID that has been reserved for that prefix. 696 When an NSSA [RFC3101] ABR translates an E-NSSA-LSA into an E-AS- 697 External-LSA, it SHOULD also advertise the Prefix-SID for the prefix. 698 The NSSA ABR determines its best path to the prefix advertised in the 699 translated E-NSSA-LSA and finds the advertising router associated 700 with that path. If the advertising router has advertised a Prefix- 701 SID for the prefix, then the NSSA ABR uses it when advertising the 702 Prefix-SID for the E-AS-External-LSA. Otherwise, the Prefix-SID 703 advertised by any other router will be used. 705 8.4. Advertisement of Adj-SID 707 The Adjacency Segment Routing Identifier (Adj-SID) is advertised 708 using the Adj-SID Sub-TLV as described in Section 7. 710 8.4.1. Advertisement of Adj-SID on Point-to-Point Links 712 An Adj-SID MAY be advertised for any adjacency on a P2P link that is 713 in neighbor state 2-Way or higher. If the adjacency on a P2P link 714 transitions from the FULL state, then the Adj-SID for that adjacency 715 MAY be removed from the area. If the adjacency transitions to a 716 state lower than 2-Way, then the Adj-SID advertisement MUST be 717 withdrawn from the area. 719 8.4.2. Adjacency SID on Broadcast or NBMA Interfaces 721 Broadcast, NBMA, or hybrid [RFC6845] networks in OSPFv3 are 722 represented by a star topology where the Designated Router (DR) is 723 the central point to which all other routers on the broadcast, NBMA, 724 or hybrid network connect. As a result, routers on the broadcast, 725 NBMA, or hybrid network advertise only their adjacency to the DR. 726 Routers that do not act as DR do not form or advertise adjacencies 727 with each other. They do, however, maintain 2-Way adjacency state 728 with each other and are directly reachable. 730 When Segment Routing is used, each router on the broadcast, NBMA, or 731 hybrid network MAY advertise the Adj-SID for its adjacency to the DR 732 using the Adj-SID Sub-TLV as described in Section 7.1. 734 SR-capable routers MAY also advertise a LAN-Adj-SID for other 735 neighbors (e.g., BDR, DR-OTHER) on the broadcast, NBMA, or hybrid 736 network using the LAN-Adj-SID Sub-TLV as described in Section 7.2. 738 9. IANA Considerations 740 This specification updates several existing OSPFv3 registries. 742 9.1. OSPFv3 Extended-LSA TLV Registry 744 Following values are allocated: 746 o 9 - OSPFv3 Extended Prefix Range TLV 748 9.2. OSPFv3 Extended-LSA Sub-TLV registry 750 o 4 - Prefix SID Sub-TLV 752 o 5 - Adj-SID Sub-TLV 754 o 6 - LAN Adj-SID Sub-TLV 756 o 7 - SID/Label Sub-TLV 758 10. Security Considerations 760 With the OSPFv3 segment routing extensions defined herein, OSPFv3 761 will now program the MPLS data plane [RFC3031]. Previously, LDP 762 [RFC5036] or another label distribution mechanism was required to 763 advertise MPLS labels and program the MPLS data plane. 765 In general, the same types of attacks that can be carried out on the 766 IP control plane can be carried out on the MPLS control plane 767 resulting in traffic being misrouted in the respective data planes. 768 However, the latter can be more difficult to detect and isolate. 770 Existing security extensions as described in [RFC5340] and [RFC8362] 771 apply to these segment routing extensions. While OSPFv3 is under a 772 single administrative domain, there can be deployments where 773 potential attackers have access to one or more networks in the OSPFv3 774 routing domain. In these deployments, stronger authentication 775 mechanisms such as those specified in [RFC4552] or [RFC7166] SHOULD 776 be used. 778 Implementations MUST assure that malformed TLV and Sub-TLV defined in 779 this document are detected and do not provide a vulnerability for 780 attackers to crash the OSPFv3 router or routing process. Reception 781 of a malformed TLV or Sub-TLV SHOULD be counted and/or logged for 782 further analysis. Logging of malformed TLVs and Sub-TLVs SHOULD be 783 rate-limited to prevent a Denial of Service (DoS) attack (distributed 784 or otherwise) from overloading the OSPFv3 control plane. 786 11. Contributors 788 The following people gave a substantial contribution to the content 789 of this document and should be considered as co-authors: 791 Clarence Filsfils 792 Cisco Systems, Inc. 793 Brussels 794 Belgium 796 Email: cfilsfil@cisco.com 798 Hannes Gredler 799 RtBrick Inc. 800 Austria 802 Email: hannes@rtbrick.com 804 Rob Shakir 805 Google, Inc. 806 1600 Amphitheatre Parkway 807 Mountain View, CA 94043 808 US 810 Email: robjs@google.com 812 Wim Henderickx 813 Nokia 814 Copernicuslaan 50 815 Antwerp 2018 816 BE 818 Email: wim.henderickx@nokia.com 820 Jeff Tantsura 821 Nuage Networks 822 US 824 Email: jefftant.ietf@gmail.com 826 Thanks to Acee Lindem for his substantial contribution to the content 827 of this document. 829 We would like to thank Anton Smirnov for his contribution as well. 831 12. References 833 12.1. Normative References 835 [ALGOREG] "IGP Algorithm Types", . 838 [I-D.ietf-ospf-segment-routing-extensions] 839 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 840 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 841 Extensions for Segment Routing", draft-ietf-ospf-segment- 842 routing-extensions-25 (work in progress), April 2018. 844 [I-D.ietf-spring-segment-routing-ldp-interop] 845 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., and 846 S. Litkowski, "Segment Routing interworking with LDP", 847 draft-ietf-spring-segment-routing-ldp-interop-15 (work in 848 progress), September 2018. 850 [I-D.ietf-spring-segment-routing-mpls] 851 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 852 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 853 data plane", draft-ietf-spring-segment-routing-mpls-15 854 (work in progress), October 2018. 856 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 857 Requirement Levels", BCP 14, RFC 2119, 858 DOI 10.17487/RFC2119, March 1997, 859 . 861 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol 862 Label Switching Architecture", RFC 3031, 863 DOI 10.17487/RFC3031, January 2001, 864 . 866 [RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", 867 RFC 3101, DOI 10.17487/RFC3101, January 2003, 868 . 870 [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., 871 "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, 872 October 2007, . 874 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 875 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 876 . 878 [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast 879 and Point-to-Multipoint Interface Type", RFC 6845, 880 DOI 10.17487/RFC6845, January 2013, 881 . 883 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 884 S. Shaffer, "Extensions to OSPF for Advertising Optional 885 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 886 February 2016, . 888 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 889 F. Baker, "OSPFv3 Link State Advertisement (LSA) 890 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 891 2018, . 893 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 894 Decraene, B., Litkowski, S., and R. Shakir, "Segment 895 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 896 July 2018, . 898 12.2. Informative References 900 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 901 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 902 . 904 [RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting 905 Authentication Trailer for OSPFv3", RFC 7166, 906 DOI 10.17487/RFC7166, March 2014, 907 . 909 [RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B., 910 Litkowski, S., Horneffer, M., and R. Shakir, "Source 911 Packet Routing in Networking (SPRING) Problem Statement 912 and Requirements", RFC 7855, DOI 10.17487/RFC7855, May 913 2016, . 915 Authors' Addresses 917 Peter Psenak (editor) 918 Cisco Systems, Inc. 919 Eurovea Centre, Central 3 920 Pribinova Street 10 921 Bratislava 81109 922 Slovakia 924 Email: ppsenak@cisco.com 926 Stefano Previdi (editor) 927 Individual 929 Email: stefano.previdi@net