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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: June 17, 2019 Individual 6 December 14, 2018 8 OSPFv3 Extensions for Segment Routing 9 draft-ietf-ospf-ospfv3-segment-routing-extensions-21 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", "NOT RECOMMENDED", "MAY", and 25 "OPTIONAL" in this document are to be interpreted as described in 26 BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all 27 capitals, as shown here. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on June 17, 2019. 46 Copyright Notice 48 Copyright (c) 2018 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (https://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 3. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 4 66 3.1. SID/Label Sub-TLV . . . . . . . . . . . . . . . . . . . . 4 67 4. Segment Routing Capabilities . . . . . . . . . . . . . . . . 5 68 5. OSPFv3 Extended Prefix Range TLV . . . . . . . . . . . . . . 5 69 6. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 7 70 7. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 11 71 7.1. Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 11 72 7.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 13 73 8. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 14 74 8.1. Intra-area Segment routing in OSPFv3 . . . . . . . . . . 14 75 8.2. Inter-area Segment routing in OSPFv3 . . . . . . . . . . 15 76 8.3. Segment Routing for External Prefixes . . . . . . . . . . 16 77 8.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 16 78 8.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 16 79 8.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 16 80 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 81 9.1. OSPFv3 Extended-LSA TLV Registry . . . . . . . . . . . . 17 82 9.2. OSPFv3 Extended-LSA Sub-TLV registry . . . . . . . . . . 17 83 10. Security Considerations . . . . . . . . . . . . . . . . . . . 17 84 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18 85 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 86 12.1. Normative References . . . . . . . . . . . . . . . . . . 19 87 12.2. Informative References . . . . . . . . . . . . . . . . . 20 88 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 90 1. Introduction 92 Segment Routing (SR) allows a flexible definition of end-to-end paths 93 within IGP topologies by encoding paths as sequences of topological 94 sub-paths, called "segments". These segments are advertised by the 95 link-state routing protocols (IS-IS and OSPF). Prefix segments 96 represent an ECMP-aware shortest-path to a prefix (or a node), as per 97 the state of the IGP topology. Adjacency segments represent a hop 98 over a specific adjacency between two nodes in the IGP. A prefix 99 segment is typically a multi-hop path while an adjacency segment, in 100 most cases, is a one-hop path. SR's control-plane can be applied to 101 both IPv6 and MPLS data-planes, and does not require any additional 102 signalling (other than IGP extensions). The IPv6 data plane is out 103 of the scope of this specification - OSPFv3 extension for SR with 104 IPv6 data plane will be specified in a separate document. When used 105 in MPLS networks, SR paths do not require any LDP or RSVP-TE 106 signalling. However, SR can interoperate in the presence of LSPs 107 established with RSVP or LDP. 109 This draft describes the OSPFv3 extensions required for Segment 110 Routing with MPLS data plane. 112 Segment Routing architecture is described in [RFC8402]. 114 Segment Routing use cases are described in [RFC7855]. 116 2. Terminology 118 This section lists some of the terminology used in this document: 120 ABR - Area Border Router 122 Adj-SID - Adjacency Segment Identifier 124 AS - Autonomous System 126 ASBR - Autonomous System Boundary Router 128 DR - Designated Router 130 IS-IS - Intermediate System to Intermediate System 132 LDP - Label Distribution Protocol 134 LSP - Label Switched Path 136 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 145 SR - Segment Routing 147 SRGB - Segment Routing Global Block 149 SRLB - Segment Routing Local Block 151 SRMS - Segment Routing Mapping Server 153 TLV - Type Length Value 155 3. Segment Routing Identifiers 157 Segment Routing defines various types of Segment Identifiers (SIDs): 158 Prefix-SID, Adjacency-SID, and LAN Adjacency SID. 160 3.1. SID/Label Sub-TLV 162 The SID/Label Sub-TLV appears in multiple TLVs or Sub-TLVs defined 163 later in this document. It is used to advertise the SID or label 164 associated with a prefix or adjacency. The SID/Label Sub-TLV has 165 following format: 167 0 1 2 3 168 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 1 169 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 170 | Type | Length | 171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 172 | SID/Label (variable) | 173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 175 where: 177 Type: 7 179 Length: Either 3 or 4 octets 181 SID/Label: If length is set to 3, then the 20 rightmost bits 182 represent a label. If length is set to 4, then the value 183 represents a 32-bit SID. 185 The receiving router MUST ignore the SID/Label Sub-TLV if the 186 length is other than 3 or 4. 188 4. Segment Routing Capabilities 190 Segment Routing requires some additional router capabilities to be 191 advertised to other routers in the area. 193 These SR capabilities are advertised in the OSPFv3 Router Information 194 Opaque LSA (defined in [RFC7770]) and specified in 195 [I-D.ietf-ospf-segment-routing-extensions]. 197 5. OSPFv3 Extended Prefix Range TLV 199 In some cases it is useful to advertise attributes for a range of 200 prefixes. The Segment Routing Mapping Server, which is described in 201 [I-D.ietf-spring-segment-routing-ldp-interop], is an example of where 202 a single advertisement is needed to advertise SIDs for multiple 203 prefixes from a contiguous address range. 205 The OSPFv3 Extended Prefix Range TLV is defined for this purpose. 207 The OSPFv3 Extended Prefix Range TLV is a top-level TLV of the 208 following LSAs defined in [RFC8362]: 210 E-Intra-Area-Prefix-LSA 212 E-Inter-Area-Prefix-LSA 214 E-AS-External-LSA 216 E-Type-7-LSA 218 Multiple OSPFv3 Extended Prefix Range TLVs MAY be advertised in each 219 LSA mentioned above. The OSPFv3 Extended Prefix Range TLV has the 220 following format: 222 0 1 2 3 223 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 1 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 | Type | Length | 226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 227 | Prefix Length | AF | Range Size | 228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 | Flags | Reserved | 230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 231 | Address Prefix (variable) | 232 | ... | 233 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 234 | Sub-TLVs (variable) | 235 +- -+ 236 | | 238 where: 240 Type: 9 242 Length: Variable, in octets, dependent on Sub-TLVs. 244 Prefix length: Length of prefix in bits. 246 AF: Address family for the prefix. 248 AF: 0 - IPv4 unicast 250 AF: 1 - IPv6 unicast 252 Range size: Represents the number of prefixes that are covered by 253 the advertisement. The Range Size MUST NOT exceed the number of 254 prefixes that could be satisfied by the prefix length without 255 including: 257 Addresses from the IPv4 multicast address range (224.0.0.0/3), 258 if the AF is IPv4 unicast 260 Addresses other than the IPv6 unicast addresses, if the AF is 261 IPv6 unicast 263 Flags: Reserved. MUST be zero when sent and are ignored when 264 received. 266 Reserved: SHOULD be set to 0 on transmission and MUST be ignored 267 on reception. 269 Address Prefix: 271 For the address family IPv4 unicast, the prefix itself is 272 encoded as a 32-bit value. The default route is represented by 273 a prefix of length 0. 275 For the address family IPv6 unicast, the prefix, encoded as an 276 even multiple of 32-bit words, padded with zeroed bits as 277 necessary. This encoding consumes ((PrefixLength + 31) / 32) 278 32-bit words. 280 Prefix encoding for other address families is beyond the scope 281 of this specification. 283 The range represents the contiguous set of prefixes with the same 284 prefix length as specified by the Prefix Length field. The set 285 starts with the prefix that is specified by the Address Prefix field. 286 The number of prefixes in the range is equal to the Range size. 288 If the OSPFv3 Extended Prefix Range TLVs advertising the exact same 289 range appears in multiple LSAs of the same type, originated by the 290 same OSPFv3 router, the LSA with the numerically smallest Instance ID 291 MUST be used and subsequent instances of the OSPFv3 Extended Prefix 292 Range TLVs MUST be ignored. 294 6. Prefix SID Sub-TLV 296 The Prefix SID Sub-TLV is a Sub-TLV of the following OSPFv3 TLVs as 297 defined in [RFC8362] and in Section 5: 299 Intra-Area Prefix TLV 301 Inter-Area Prefix TLV 303 External Prefix TLV 305 OSPFv3 Extended Prefix Range TLV 307 It MAY appear more than once in the parent TLV and has the following 308 format: 310 0 1 2 3 311 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 1 312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 313 | Type | Length | 314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 315 | Flags | Algorithm | Reserved | 316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 317 | SID/Index/Label (variable) | 318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 319 where: 321 Type: 4 323 Length: 7 or 8 octets, dependent on the V-flag 325 Flags: Single octet field. The following flags are defined: 327 0 1 2 3 4 5 6 7 328 +--+--+--+--+--+--+--+--+ 329 | |NP|M |E |V |L | | | 330 +--+--+--+--+--+--+--+--+ 331 where: 333 NP-Flag: No-PHP flag. If set, then the penultimate hop MUST 334 NOT pop the Prefix-SID before delivering packets to the node 335 that advertised the Prefix-SID. 337 M-Flag: Mapping Server Flag. If set, the SID was advertised by 338 a Segment Routing Mapping Server as described in 339 [I-D.ietf-spring-segment-routing-ldp-interop]. 341 E-Flag: Explicit-Null Flag. If set, any upstream neighbor of 342 the Prefix-SID originator MUST replace the Prefix-SID with the 343 Explicit-NULL label (0 for IPv4, 2 for IPv6) before forwarding 344 the packet. 346 V-Flag: Value/Index Flag. If set, then the Prefix-SID carries 347 an absolute value. If not set, then the Prefix-SID carries an 348 index. 350 L-Flag: Local/Global Flag. If set, then the value/index 351 carried by the Prefix-SID has local significance. If not set, 352 then the value/index carried by this Sub-TLV has global 353 significance. 355 Other bits: Reserved. These MUST be zero when sent and are 356 ignored when received. 358 Reserved: SHOULD be set to 0 on transmission and MUST be ignored 359 on reception. 361 Algorithm: Single octet identifying the algorithm the Prefix-SID 362 is associated with as defined in 363 [I-D.ietf-ospf-segment-routing-extensions]. 365 A router receiving a Prefix-SID from a remote node and with an 366 algorithm value that such remote node has not advertised in the 367 SR-Algorithm Sub-TLV [I-D.ietf-ospf-segment-routing-extensions] 368 MUST ignore the Prefix-SID Sub-TLV. 370 SID/Index/Label: According to the V-Flag and L-Flag, it contains: 372 V-flag is set to 0 and L-flag is set to 0: The SID/Index/Label 373 field is a 4 octet index defining the offset in the SID/Label 374 space advertised by this router 376 V-flag is set to 1 and L-flag is set to 1: The SID/Index/Label 377 field is a 3 octet local label where the 20 rightmost bits are 378 used for encoding the label value. 380 All other combinations of V-flag and L-flag are invalid and any 381 SID advertisement received with an invalid setting for V and L 382 flags MUST be ignored. 384 If an OSPFv3 router advertises multiple Prefix-SIDs for the same 385 prefix, topology, and algorithm, all of them MUST be ignored. 387 When calculating the outgoing label for the prefix, the router MUST 388 take into account, as described below, the E, NP, and M flags 389 advertised by the next-hop router if that router advertised the SID 390 for the prefix. This MUST be done regardless of whether the next-hop 391 router contributes to the best path to the prefix. 393 The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for 394 Prefix-SIDs allocated to prefixes that are propagated between areas 395 by an ABR based on intra-area or inter-area reachability, unless the 396 advertised prefix is directly attached to such ABR. 398 The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for 399 Prefix-SIDs allocated to redistributed prefixes, unless the 400 redistributed prefix is directly attached to the advertising ASBR. 402 If the NP-Flag is not set, then any upstream neighbor of the Prefix- 403 SID originator MUST pop the Prefix-SID. This is equivalent to the 404 penultimate hop popping mechanism used in the MPLS dataplane. If the 405 NP-flag is not set, then the received E-flag is ignored. 407 If the NP-flag is set then: 409 If the E-flag is not set, then any upstream neighbor of the 410 Prefix-SID originator MUST keep the Prefix-SID on top of the 411 stack. This is useful when the originator of the Prefix-SID needs 412 to stitch the incoming packet into a continuing MPLS LSP to the 413 final destination. This could occur at an ABR (prefix propagation 414 from one area to another) or at an ASBR (prefix propagation from 415 one domain to another). 417 If the E-flag is set, then any upstream neighbor of the Prefix-SID 418 originator MUST replace the Prefix-SID with an Explicit-NULL 419 label. This is useful, e.g., when the originator of the Prefix- 420 SID is the final destination for the related prefix and the 421 originator wishes to receive the packet with the original Traffic 422 Class field [RFC5462]. 424 When the M-Flag is set, the NP-flag and the E-flag MUST be ignored on 425 reception. 427 As the Mapping Server does not specify the originator of a prefix 428 advertisement, it is not possible to determine PHP behavior solely 429 based on the Mapping Server advertisement. However, PHP behavior 430 SHOULD be done in following cases: 432 The Prefix is intra-area type and the downstream neighbor is the 433 originator of the prefix. 435 The Prefix is inter-area type and the downstream neighbor is an 436 ABR, which is advertising prefix reachability and is setting the 437 LA-bit in the Prefix Options as described in [RFC8362]. 439 The Prefix is external type and the downstream neighbor is an 440 ASBR, which is advertising prefix reachability and is setting the 441 LA-bit in the Prefix Options as described in [RFC8362]. 443 When a Prefix-SID is advertised in the OSPFv3 Extended Prefix Range 444 TLV, then the value advertised in the Prefix SID Sub-TLV is 445 interpreted as a starting SID/Label value. 447 Example 1: If the following router addresses (loopback addresses) 448 need to be mapped into the corresponding Prefix SID indexes: 450 Router-A: 2001:DB8::1/128, Prefix-SID: Index 1 451 Router-B: 2001:DB8::2/128, Prefix-SID: Index 2 452 Router-C: 2001:DB8::3/128, Prefix-SID: Index 3 453 Router-D: 2001:DB8::4/128, Prefix-SID: Index 4 455 then the Address Prefix field in the OSPFv3 Extended Prefix Range TLV 456 would be set to 2001:DB8::1, the Prefix Length would be set to 128, 457 the Range Size would be set to 4, and the Index value in the Prefix- 458 SID Sub-TLV would be set to 1. 460 Example 2: If the following prefixes need to be mapped into the 461 corresponding Prefix-SID indexes: 463 2001:DB8:1::0/120, Prefix-SID: Index 51 464 2001:DB8:1::100/120, Prefix-SID: Index 52 465 2001:DB8:1::200/120, Prefix-SID: Index 53 466 2001:DB8:1::300/120, Prefix-SID: Index 54 467 2001:DB8:1::400/120, Prefix-SID: Index 55 468 2001:DB8:1::500/120, Prefix-SID: Index 56 469 2001:DB8:1::600/120, Prefix-SID: Index 57 471 then the Prefix field in the OSPFv3 Extended Prefix Range TLV would 472 be set to 2001:DB8:1::0, the Prefix Length would be set to 120, the 473 Range Size would be set to 7, and the Index value in the Prefix-SID 474 Sub-TLV would be set to 51. 476 7. Adjacency Segment Identifier (Adj-SID) 478 An Adjacency Segment Identifier (Adj-SID) represents a router 479 adjacency in Segment Routing. 481 7.1. Adj-SID Sub-TLV 483 The Adj-SID Sub-TLV is an optional Sub-TLV of the Router-Link TLV as 484 defined in [RFC8362]. It MAY appear multiple times in the Router- 485 Link TLV. The Adj-SID Sub-TLV has the following format: 487 0 1 2 3 488 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 1 489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 490 | Type | Length | 491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 492 | Flags | Weight | Reserved | 493 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 494 | SID/Label/Index (variable) | 495 +---------------------------------------------------------------+ 497 where: 499 Type: 5 501 Length: 7 or 8 octets, dependent on the V flag. 503 Flags: Single octet field containing the following flags: 505 0 1 2 3 4 5 6 7 506 +-+-+-+-+-+-+-+-+ 507 |B|V|L|G|P| | 508 +-+-+-+-+-+-+-+-+ 510 where: 512 B-Flag: Backup Flag. If set, the Adj-SID refers to an 513 adjacency that is eligible for protection (e.g., using IPFRR or 514 MPLS-FRR) as described in section 3.5 of [RFC8402]. 516 The V-Flag: Value/Index Flag. If set, then the Adj-SID carries 517 an absolute value. If not set, then the Adj-SID carries an 518 index. 520 The L-Flag: Local/Global Flag. If set, then the value/index 521 carried by the Adj-SID has local significance. If not set, 522 then the value/index carried by this Sub-TLV has global 523 significance. 525 The G-Flag: Group Flag. When set, the G-Flag indicates that 526 the Adj-SID refers to a group of adjacencies (and therefore MAY 527 be assigned to other adjacencies as well). 529 P-Flag. Persistent flag. When set, the P-Flag indicates that 530 the Adj-SID is persistently allocated, i.e., the Adj-SID value 531 remains the same across router restart and/or interface flap. 533 Other bits: Reserved. These MUST be zero when sent and are 534 ignored when received. 536 Reserved: SHOULD be set to 0 on transmission and MUST be ignored 537 on reception. 539 Weight: Weight used for load-balancing purposes. The use of the 540 weight is defined in [RFC8402]. 542 SID/Index/Label: as described in Section 6. 544 An SR-capable router MAY allocate an Adj-SID for each of its 545 adjacencies and set the B-Flag when the adjacency is eligible for 546 protection by an FRR mechanism (IP or MPLS) as described in 547 [RFC8402]. 549 An SR-capable router MAY allocate more than one Adj-SID to an 550 adjacency. 552 An SR-capable router MAY allocate the same Adj-SID to different 553 adjacencies. 555 When the P-flag is not set, the Adj-SID MAY be persistent. When the 556 P-flag is set, the Adj-SID MUST be persistent. 558 7.2. LAN Adj-SID Sub-TLV 560 The LAN Adj-SID Sub-TLV is an optional Sub-TLV of the Router-Link 561 TLV. It MAY appear multiple times in the Router-Link TLV. It is 562 used to advertise a SID/Label for an adjacency to a non-DR router on 563 a broadcast, NBMA, or hybrid [RFC6845] network. 565 0 1 2 3 566 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 1 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 | Type | Length | 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 570 | Flags | Weight | Reserved | 571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 572 | Neighbor ID | 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 | SID/Label/Index (variable) | 575 +---------------------------------------------------------------+ 577 where: 579 Type: 6 581 Length: 11 or 12 octets, dependent on V-flag. 583 Flags: same as in Section 7.1 585 Weight: Weight used for load-balancing purposes. The use of the 586 weight is defined in [RFC8402]. 588 Reserved: SHOULD be set to 0 on transmission and MUST be ignored 589 on reception. 591 Neighbor ID: The Router ID of the neighbor for which the LAN-Adj- 592 SID is advertised. 594 SID/Index/Label: as described in Section 6. 596 When the P-flag is not set, the LAN Adj-SID MAY be persistent. 597 When the P-flag is set, the LAN Adj-SID MUST be persistent. 599 8. Elements of Procedure 601 8.1. Intra-area Segment routing in OSPFv3 603 An OSPFv3 router that supports segment routing MAY advertise Prefix- 604 SIDs for any prefix to which it is advertising reachability (e.g., a 605 loopback IP address as described in Section 6). 607 A Prefix-SID can also be advertised by SR Mapping Servers (as 608 described in [I-D.ietf-spring-segment-routing-ldp-interop]). A 609 Mapping Server advertises Prefix-SIDs for remote prefixes that exist 610 in the OSPFv3 routing domain. Multiple Mapping Servers can advertise 611 Prefix-SIDs for the same prefix, in which case the same Prefix-SID 612 MUST be advertised by all of them. The SR Mapping Server could use 613 either area flooding scope or autonomous system flooding scope when 614 advertising Prefix SIDs for prefixes, based on the configuration of 615 the SR Mapping Server. Depending on the flooding scope used, the SR 616 Mapping Server chooses the OSPFv3 LSA type that will be used. If the 617 area flooding scope is needed, an E-Intra-Area-Prefix-LSA [RFC8362] 618 is used. If autonomous system flooding scope is needed, an E-AS- 619 External-LSA [RFC8362] is used. 621 When a Prefix-SID is advertised by the Mapping Server, which is 622 indicated by the M-flag in the Prefix-SID Sub-TLV (Section 6), the 623 route type as implied by the LSA type is ignored and the Prefix-SID 624 is bound to the corresponding prefix independent of the route type. 626 Advertisement of the Prefix-SID by the Mapping Server using an Inter- 627 Area Prefix TLV, External-Prefix TLV, or Intra-Area-Prefix TLV 628 [RFC8362] does not itself contribute to the prefix reachability. The 629 NU-bit [RFC5340] MUST be set in the PrefixOptions field of the LSA 630 which is used by the Mapping Server to advertise SID or SID Range, 631 which prevents the advertisement from contributing to prefix 632 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. Same rules 641 that are used for propagating prefixes between areas [RFC5340] are 642 used for the propagation of the prefix ranges. 644 8.2. Inter-area Segment routing in OSPFv3 646 In order to support SR in a multi-area environment, OSPFv3 MUST 647 propagate Prefix-SID information between areas. The following 648 procedure is used to propagate Prefix SIDs between areas. 650 When an OSPFv3 ABR advertises an Inter-Area-Prefix-LSA from an intra- 651 area prefix to all its connected areas, it will also include the 652 Prefix-SID Sub-TLV, as described in Section 6. The Prefix-SID value 653 will be set as follows: 655 The ABR will look at its best path to the prefix in the source 656 area and find the advertising router associated with the best path 657 to that prefix. 659 The ABR will then determine if such router advertised a Prefix-SID 660 for the prefix and use it when advertising the Prefix-SID to other 661 connected areas. 663 If no Prefix-SID was advertised for the prefix in the source area 664 by the router that contributes to the best path to the prefix, the 665 originating ABR will use the Prefix-SID advertised by any other 666 router when propagating the Prefix-SID for the prefix to other 667 areas. 669 When an OSPFv3 ABR advertises Inter-Area-Prefix-LSA LSAs from an 670 inter-area route to all its connected areas, it will also include the 671 Prefix-SID Sub-TLV, as described in Section 6. The Prefix-SID value 672 will be set as follows: 674 The ABR will look at its best path to the prefix in the backbone 675 area and find the advertising router associated with the best path 676 to that prefix. 678 The ABR will then determine if such router advertised a Prefix-SID 679 for the prefix and use it when advertising the Prefix-SID to other 680 connected areas. 682 If no Prefix-SID was advertised for the prefix in the backbone 683 area by the ABR that contributes to the best path to the prefix, 684 the originating ABR will use the Prefix-SID advertised by any 685 other router when propagating the Prefix-SID for the prefix to 686 other areas. 688 8.3. Segment Routing for External Prefixes 690 AS-External-LSAs are flooded domain wide. When an ASBR, which 691 supports SR, originates an E-AS-External-LSA, it SHOULD also include 692 a Prefix-SID Sub-TLV, as described in Section 6. The Prefix-SID 693 value will be set to the SID that has been reserved for that prefix. 695 When an NSSA [RFC3101] ABR translates an E-NSSA-LSA into an E-AS- 696 External-LSA, it SHOULD also advertise the Prefix-SID for the prefix. 697 The NSSA ABR determines its best path to the prefix advertised in the 698 translated E-NSSA-LSA and finds the advertising router associated 699 with that path. If the advertising router has advertised a Prefix- 700 SID for the prefix, then the NSSA ABR uses it when advertising the 701 Prefix-SID for the E-AS-External-LSA. Otherwise, the Prefix-SID 702 advertised by any other router will be used. 704 8.4. Advertisement of Adj-SID 706 The Adjacency Segment Routing Identifier (Adj-SID) is advertised 707 using the Adj-SID Sub-TLV as described in Section 7. 709 8.4.1. Advertisement of Adj-SID on Point-to-Point Links 711 An Adj-SID MAY be advertised for any adjacency on a P2P link that is 712 in neighbor state 2-Way or higher. If the adjacency on a P2P link 713 transitions from the FULL state, then the Adj-SID for that adjacency 714 MAY be removed from the area. If the adjacency transitions to a 715 state lower than 2-Way, then the Adj-SID advertisement MUST be 716 withdrawn from the area. 718 8.4.2. Adjacency SID on Broadcast or NBMA Interfaces 720 Broadcast, NBMA, or hybrid [RFC6845] networks in OSPFv3 are 721 represented by a star topology where the DR is the central point to 722 which all other routers on the broadcast, NBMA, or hybrid network 723 connect. As a result, routers on the broadcast, NBMA, or hybrid 724 network advertise only their adjacency to the DR. Routers that do 725 not act as DR do not form or advertise adjacencies with each other. 726 They do, however, maintain 2-Way adjacency state with each other and 727 are directly reachable. 729 When Segment Routing is used, each router on the broadcast, NBMA, or 730 hybrid network MAY advertise the Adj-SID for its adjacency to the DR 731 using the Adj-SID Sub-TLV as described in Section 7.1. 733 SR-capable routers MAY also advertise a LAN-Adj-SID for other 734 neighbors (e.g., BDR, DR-OTHER) on the broadcast, NBMA, or hybrid 735 network using the LAN-Adj-SID Sub-TLV as described in Section 7.2. 737 9. IANA Considerations 739 This specification updates several existing OSPFv3 registries. 741 9.1. OSPFv3 Extended-LSA TLV Registry 743 Following values are allocated: 745 o 9 - OSPFv3 Extended Prefix Range TLV 747 9.2. OSPFv3 Extended-LSA Sub-TLV registry 749 o 4 - Prefix SID Sub-TLV 751 o 5 - Adj-SID Sub-TLV 753 o 6 - LAN Adj-SID Sub-TLV 755 o 7 - SID/Label Sub-TLV 757 10. Security Considerations 759 With the OSPFv3 segment routing extensions defined herein, OSPFv3 760 will now program the MPLS data plane [RFC3031]. Previously, LDP 761 [RFC5036] or another label distribution mechanism was required to 762 advertise MPLS labels and program the MPLS data plane. 764 In general, the same types of attacks that can be carried out on the 765 IP control plane can be carried out on the MPLS control plane 766 resulting in traffic being misrouted in the respective data planes. 767 However, the latter can be more difficult to detect and isolate. 769 Existing security extensions as described in [RFC5340] and [RFC8362] 770 apply to these segment routing extensions. While OSPFv3 is under a 771 single administrative domain, there can be deployments where 772 potential attackers have access to one or more networks in the OSPFv3 773 routing domain. In these deployments, stronger authentication 774 mechanisms such as those specified in [RFC4552] or [RFC7166] SHOULD 775 be used. 777 Implementations MUST assure that malformed TLV and Sub-TLV defined in 778 this document are detected and do not provide a vulnerability for 779 attackers to crash the OSPFv3 router or routing process. Reception 780 of a malformed TLV or Sub-TLV SHOULD be counted and/or logged for 781 further analysis. Logging of malformed TLVs and Sub-TLVs SHOULD be 782 rate-limited to prevent a Denial of Service (DoS) attack (distributed 783 or otherwise) from overloading the OSPFv3 control plane. 785 11. Contributors 787 The following people gave a substantial contribution to the content 788 of this document and should be considered as co-authors: 790 Clarence Filsfils 791 Cisco Systems, Inc. 792 Brussels 793 Belgium 795 Email: cfilsfil@cisco.com 797 Hannes Gredler 798 RtBrick Inc. 799 Austria 801 Email: hannes@rtbrick.com 803 Rob Shakir 804 Google, Inc. 805 1600 Amphitheatre Parkway 806 Mountain View, CA 94043 807 US 809 Email: robjs@google.com 811 Wim Henderickx 812 Nokia 813 Copernicuslaan 50 814 Antwerp 2018 815 BE 817 Email: wim.henderickx@nokia.com 819 Jeff Tantsura 820 Nuage Networks 821 US 823 Email: jefftant.ietf@gmail.com 825 Thanks to Acee Lindem for his substantial contribution to the content 826 of this document. 828 We would like to thank Anton Smirnov for his contribution as well. 830 12. References 832 12.1. Normative References 834 [ALGOREG] "IGP Algorithm Types", . 837 [I-D.ietf-ospf-segment-routing-extensions] 838 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 839 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 840 Extensions for Segment Routing", draft-ietf-ospf-segment- 841 routing-extensions-27 (work in progress), December 2018. 843 [I-D.ietf-spring-segment-routing-ldp-interop] 844 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., and 845 S. Litkowski, "Segment Routing interworking with LDP", 846 draft-ietf-spring-segment-routing-ldp-interop-15 (work in 847 progress), September 2018. 849 [I-D.ietf-spring-segment-routing-mpls] 850 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 851 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 852 data plane", draft-ietf-spring-segment-routing-mpls-18 853 (work in progress), December 2018. 855 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 856 Requirement Levels", BCP 14, RFC 2119, 857 DOI 10.17487/RFC2119, March 1997, 858 . 860 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol 861 Label Switching Architecture", RFC 3031, 862 DOI 10.17487/RFC3031, January 2001, 863 . 865 [RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", 866 RFC 3101, DOI 10.17487/RFC3101, January 2003, 867 . 869 [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., 870 "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, 871 October 2007, . 873 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 874 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 875 . 877 [RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching 878 (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic 879 Class" Field", RFC 5462, DOI 10.17487/RFC5462, February 880 2009, . 882 [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast 883 and Point-to-Multipoint Interface Type", RFC 6845, 884 DOI 10.17487/RFC6845, January 2013, 885 . 887 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 888 S. Shaffer, "Extensions to OSPF for Advertising Optional 889 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 890 February 2016, . 892 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 893 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 894 May 2017, . 896 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 897 F. Baker, "OSPFv3 Link State Advertisement (LSA) 898 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 899 2018, . 901 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 902 Decraene, B., Litkowski, S., and R. Shakir, "Segment 903 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 904 July 2018, . 906 12.2. Informative References 908 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 909 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 910 . 912 [RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting 913 Authentication Trailer for OSPFv3", RFC 7166, 914 DOI 10.17487/RFC7166, March 2014, 915 . 917 [RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B., 918 Litkowski, S., Horneffer, M., and R. Shakir, "Source 919 Packet Routing in Networking (SPRING) Problem Statement 920 and Requirements", RFC 7855, DOI 10.17487/RFC7855, May 921 2016, . 923 Authors' Addresses 925 Peter Psenak (editor) 926 Cisco Systems, Inc. 927 Eurovea Centre, Central 3 928 Pribinova Street 10 929 Bratislava 81109 930 Slovakia 932 Email: ppsenak@cisco.com 934 Stefano Previdi (editor) 935 Individual 937 Email: stefano.previdi@net