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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 S. Previdi, Ed. 4 Intended status: Standards Track C. Filsfils 5 Expires: January 3, 2015 Cisco Systems, Inc. 6 H. Gredler 7 Juniper Networks, Inc. 8 R. Shakir 9 British Telecom 10 W. Henderickx 11 Alcatel-Lucent 12 J. Tantsura 13 Ericsson 14 July 2, 2014 16 OSPFv3 Extensions for Segment Routing 17 draft-psenak-ospf-segment-routing-ospfv3-extension-02 19 Abstract 21 Segment Routing (SR) allows for a flexible definition of end-to-end 22 paths within IGP topologies by encoding paths as sequences of 23 topological sub-paths, called "segments". These segments are 24 advertised by the link-state routing protocols (IS-IS and OSPF). 26 This draft describes the necessary OSPFv3 extensions that need to be 27 introduced for Segment Routing. 29 Requirements Language 31 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 32 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 33 document are to be interpreted as described in RFC 2119 [RFC2119]. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at http://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on January 3, 2015. 51 Copyright Notice 53 Copyright (c) 2014 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 69 2. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 3 70 2.1. SID/Label sub-TLV . . . . . . . . . . . . . . . . . . . . 3 71 3. Segment Routing Capabilities . . . . . . . . . . . . . . . . 4 72 3.1. SR-Algorithm TLV . . . . . . . . . . . . . . . . . . . . 4 73 3.2. SID/Label Range TLV . . . . . . . . . . . . . . . . . . . 5 74 4. Prefix SID Identifier . . . . . . . . . . . . . . . . . . . . 7 75 4.1. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . 7 76 4.2. SID/Label Binding sub-TLV . . . . . . . . . . . . . . . . 11 77 4.2.1. ERO Metric sub-TLV . . . . . . . . . . . . . . . . . 13 78 4.2.2. ERO sub-TLVs . . . . . . . . . . . . . . . . . . . . 13 79 5. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 19 80 5.1. Adj-SID sub-TLV . . . . . . . . . . . . . . . . . . . . . 20 81 5.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 21 82 6. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 23 83 6.1. Intra-area Segment routing in OSPFv3 . . . . . . . . . . 23 84 6.2. Inter-area Segment routing in OSPFv3 . . . . . . . . . . 24 85 6.3. SID for External Prefixes . . . . . . . . . . . . . . . . 25 86 6.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 25 87 6.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 25 88 6.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 25 89 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 90 7.1. OSPF Router Information (RI) TLVs Registry . . . . . . . 26 91 7.2. OSPFv3 Extend-LSA sub-TLV registry . . . . . . . . . . . 26 92 8. Security Considerations . . . . . . . . . . . . . . . . . . . 27 93 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27 94 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27 95 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 96 11.1. Normative References . . . . . . . . . . . . . . . . . . 27 97 11.2. Informative References . . . . . . . . . . . . . . . . . 27 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28 100 1. Introduction 102 Segment Routing (SR) allows for a flexible definition of end-to-end 103 paths within IGP topologies by encoding paths as sequences of 104 topological sub-paths, called "segments". These segments are 105 advertised by the link-state routing protocols (IS-IS and OSPF). 106 Prefix segments represent an ecmp-aware shortest-path to a prefix (or 107 a node), as per the state of the IGP topology. Adjacency segments 108 represent a hop over a specific adjacency between two nodes in the 109 IGP. A prefix segment is typically a multi-hop path while an 110 adjacency segment, in most of the cases, is a one-hop path. SR's 111 control-plane can be applied to both IPv6 and MPLS data-planes, and 112 do not require any additional signaling (other than the regular IGP). 113 For example, when used in MPLS networks, SR paths do not require any 114 LDP or RSVP-TE signaling. Still, SR can interoperate in the presence 115 of LSPs established with RSVP or LDP . 117 This draft describes the necessary OSPFv3 extensions that need to be 118 introduced for Segment Routing. 120 Segment Routing architecture is described in 121 [I-D.filsfils-rtgwg-segment-routing]. 123 Segment Routing use cases are described in 124 [I-D.filsfils-rtgwg-segment-routing-use-cases]. 126 2. Segment Routing Identifiers 128 Segment Routing defines various types of Segment Identifiers (SIDs): 129 Prefix-SID, Adjacency-SID, LAN Adjacency SID and Binding SID. 131 2.1. SID/Label sub-TLV 133 SID/Label sub-TLV appears in multiple TLVs or Sub-TLVs defined later 134 in this document. It is used to advertise SID or label associated 135 with the prefix or adjacency. SID/Label TLV has following format: 137 0 1 2 3 138 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 1 139 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 140 | Type | Length | 141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 142 | SID/Label (variable) | 143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 145 where: 147 Type: TBD, suggested value 1 149 Length: variable, 3 or 4 bytes 151 SID/Label: if length is set to 3, then the 20 rightmost bits 152 represent a label. If length is set to 4 then the value 153 represents a 32 bit SID. 155 The receiving router MUST ignore SID/Label sub-TLV if the length 156 is other then 3 or 4. 158 3. Segment Routing Capabilities 160 Segment Routing requires some additional capabilities of the router 161 to be advertised to other routers in the area. 163 These SR capabilities are advertised in OSPFv3 Router Information 164 Opaque LSA (defined in [RFC4970]). 166 3.1. SR-Algorithm TLV 168 SR-Algorithm TLV is a TLV of Router Information Opaque LSA (defined 169 in [RFC4970]). 171 Router may use various algorithms when calculating reachability to 172 other nodes in area or to prefixes attached to these nodes. Examples 173 of these algorithms are metric based Shortest Path First (SPF), 174 various sorts of Constrained SPF, etc. SR-Algorithm TLV allows a 175 router to advertise algorithms that router is currently using to 176 other routers in an area. SR-Algorithm TLV has following structure: 178 0 1 2 3 179 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 1 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 | Type | Length | 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 | Algorithm 1 | Algorithm... | Algorithm n | | 184 +- -+ 185 | | 186 + + 188 where: 190 Type: TBD, suggested value 8 192 Length: variable 194 Algorithm: one octet identifying the algorithm. The following 195 value has been defined: 197 0: IGP metric based SPT. 199 RI LSA can be advertised at any of the defined flooding scopes (link, 200 area, or autonomous system (AS)). For the purpose of the SR- 201 Algorithm TLV propagation area scope flooding is required. 203 3.2. SID/Label Range TLV 205 The SID/Label Range TLV is a TLV of Router Information Opaque LSA 206 (defined in [RFC4970]). 208 SID/Label Sub-TLV MAY appear multiple times and has following format: 210 0 1 2 3 211 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 1 212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 213 | Type | Length | 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 | Range Size | Reserved | 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | Sub-TLVs (variable) | 218 +- -+ 219 | | 220 + + 222 where: 224 Type: TBD, suggested value 9 225 Length: variable 227 Range Size: 3 octets of SID/label range 229 Currently the only supported Sub-TLV is the SID/Label TLV as defined 230 in Section 2.1. SID/Label advertised in SID/Label TLV represents the 231 first SID/Label from the advertised range. 233 Multiple occurrence of the SID/Label Range TLV MAY be advertised, in 234 order to advertise multiple ranges. In such case: 236 o The originating router MUST encode each range into a different 237 SID/Label Range TLV. 239 o The originating router decides in which order the set of SID/Label 240 Range TLVs are advertised inside Router Information Opaque LSA. 241 The originating router MUST ensure the order is same after a 242 graceful restart (using checkpointing, non-volatile storage or any 243 other mechanism) in order to guarantee the same order before and 244 after graceful restart. 246 o Receiving router must adhere to the order in which the ranges are 247 advertised when calculating a SID/label from the SID index. 249 o A router not supporting multiple occurrences SID/Label Range TLV 250 MUST take into consideration the first occurrence in the received 251 set. 253 Here follows an example of advertisement of multiple ranges: 255 The originating router advertises following ranges: 256 Range 1: [100, 199] 257 Range 2: [1000, 1099] 258 Range 3: [500, 599] 260 The receiving routers concatenate the ranges and build the SRGB 261 is as follows: 263 SRGB = [100, 199] 264 [1000, 1099] 265 [500, 599] 267 The indexes span multiple ranges: 269 index=0 means label 100 270 ... 271 index 99 means label 199 272 index 100 means label 1000 273 index 199 means label 1099 274 ... 275 index 200 means label 500 276 ... 278 RI LSA can be advertised at any of the defined flooding scopes (link, 279 area, or autonomous system (AS)). For the purpose of the SR- 280 Capability TLV propagation area scope flooding is required. 282 4. Prefix SID Identifier 284 A new extended OSPFv3 LSAs as defined in 285 [I-D.ietf-ospf-ospfv3-lsa-extend] are used to advertise SID or label 286 values associated with the prefix in OSPFv3. 288 4.1. Prefix SID Sub-TLV 290 The Prefix SID Sub-TLV is a Sub-TLV of the following OSPFv3 TLVs as 291 defined in [I-D.ietf-ospf-ospfv3-lsa-extend]: 293 Intra-Area Prefix TLV 295 Inter-Area Prefix TLV 297 External Prefix TLV 299 It MAY appear more than once and has following format: 301 0 1 2 3 302 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 1 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 304 | Type | Length | 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | Flags | Algorithm | Range Size | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | SID/Index/Label (variable) | 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 311 where: 313 Type: TBD, suggested value 2. 315 Length: variable 317 Flags: 1 octet field. The following flags are defined: 319 0 320 0 1 2 3 4 5 6 7 321 +-+-+-+-+-+-+-+-+ 322 |N|P|M|E|V|L| | 323 +-+-+-+-+-+-+-+-+ 325 where: 327 N-Flag: Node-SID flag. If set, then the Prefix-SID refers to 328 the router identified by the prefix. Typically, the N-Flag is 329 set on Prefix-SIDs attached to a router loopback address. The 330 N-Flag is set when the Prefix-SID is a Node- SID as described 331 in [I-D.filsfils-rtgwg-segment-routing]. 333 P-Flag: no-PHP flag. If set, then the penultimate hop MUST NOT 334 pop the Prefix-SID before delivering the packet to the node 335 that advertised the Prefix-SID. 337 M-Flag: Mapping Server Flag. If set, the SID is advertised 338 from the Segment Routing Mapping Server functionality as 339 described in [I-D.filsfils-rtgwg-segment-routing-use-cases]. 341 E-Flag: Explicit-Null Flag. If set, any upstream neighbor of 342 the Prefix-SID originator MUST replace the Prefix-SID with a 343 Prefix-SID having an Explicit-NULL value (0 for IPv4) before 344 forwarding the packet. 346 The V-Flag: Value/Index Flag. If set, then the Prefix-SID 347 carries an absolute value. If not set, then the Prefix-SID 348 carries an index. 350 The L-Flag: Local/Global Flag. If set, then the value/index 351 carried by the PrefixSID has local significance. If not set, 352 then the value/index carried by this subTLV has global 353 significance. 355 Other bits: MUST be zero when sent and ignored when received. 357 Algorithm: one octet identifying the algorithm the Prefix-SID is 358 associated with as defined in Section 3.1. 360 Range Size: this field provides the ability to specify a range of 361 addresses and their associated Prefix SIDs. It represents a 362 compression scheme to distribute a continuous Prefix and their 363 continuous, corresponding SID/Label Block. If a single SID is 364 advertised then the Range Size field MUST be set to 1. For range 365 advertisements > 1, Range Size represents the number of addresses 366 that need to be mapped into a Prefix-SID. 368 SID/Index/Label: label or index value depending on the V-bit 369 setting. 371 Examples: 373 A 32 bit global index defining the offset in the SID/Label 374 space advertised by this router - in this case the V and L 375 flags MUST be unset. 377 A 24 bit local label where the 20 rightmost bits are used 378 for encoding the label value - in this case the V and L 379 flags MUST be set. 381 If multiple Prefix-SIDs are advertised for the same prefix, the 382 receiving router MUST use the first encoded SID and MAY use the 383 subsequent ones. 385 When propagating Prefix-SIDs between areas, if multiple prefix-SIDs 386 are advertised for a prefix, an implementation SHOULD preserve the 387 original ordering, when advertising prefix-SIDs to other areas. This 388 allows implementations that only use single Prefix-SID to have a 389 consistent view across areas. 391 When calculating the outgoing label for the prefix, the router MUST 392 take into account E and P flags advertised by the next-hop router, if 393 next-hop router advertised the SID for the prefix. This MUST be done 394 regardless of next-hop router contributing to the best path to the 395 prefix or not. 397 P-Flag (no-PHP) MUST be set on the Prefix-SIDs allocated to inter- 398 area prefixes that are originated by the ABR based on intra-area or 399 inter-area reachability between areas. In case the inter-area prefix 400 is generated based on the prefix which is directly attached to the 401 ABR, P-Flag SHOULD NOT be set 403 P-Flag (no-PHP) MUST NOT be set on the Prefix-SIDs allocated to 404 redistributed prefixes, unless the redistributed prefix is directly 405 attached to ASBR, in which case the P-Flag SHOULD NOT be set. 407 If the P-flag is not set then any upstream neighbor of the Prefix-SID 408 originator MUST pop the Prefix-SID. This is equivalent to the 409 penultimate hop popping mechanism used in the MPLS dataplane. In 410 such case MPLS EXP bits of the Prefix-SID are not preserved to the 411 ultimate hop (the Prefix-SID being removed). If the P-flag is unset 412 the received E-flag is ignored. 414 If the P-flag is set then: 416 If the E-flag is not set then any upstream neighbor of the Prefix- 417 SID originator MUST keep the Prefix-SID on top of the stack. This 418 is useful when the originator of the Prefix-SID must stitch the 419 incoming packet into a continuing MPLS LSP to the final 420 destination. This could occur at an inter-area border router 421 (prefix propagation from one area to another) or at an inter- 422 domain border router (prefix propagation from one domain to 423 another). 425 If the E-flag is set then any upstream neighbor of the Prefix-SID 426 originator MUST replace the PrefixSID with a Prefix-SID having an 427 Explicit-NULL value. This is useful, e.g., when the originator of 428 the Prefix-SID is the final destination for the related prefix and 429 the originator wishes to receive the packet with the original EXP 430 bits. 432 When M-Flag is set, P-flag MUST be set and E-bit MUST NOT be set. 434 Example 1: if the following router addresses (loopback addresses) 435 need to be mapped into the corresponding Prefix SID indexes: 437 Router-A: 192::1/128, Prefix-SID: Index 1 438 Router-B: 192::2/128, Prefix-SID: Index 2 439 Router-C: 192::3/128, Prefix-SID: Index 3 440 Router-D: 192::4/128, Prefix-SID: Index 4 442 then the Address Prefix field in Intra-Area Prefix TLV, Inter-Area 443 Prefix TLV or External Prefix TLV is set to 192::1, Prefix Length in 444 these TLVs would be set to 128, Range Size in Prefix SID sub-TLV 445 would be set to 4 and Index value would be set to 1. 447 Example 2: If the following prefixes need to be mapped into the 448 corresponding Prefix-SID indexes: 450 10:1:1::0/120, Prefix-SID: Index 51 451 10:1:1::100/120, Prefix-SID: Index 52 452 10:1:1::200/120, Prefix-SID: Index 53 453 10:1:1::300/120, Prefix-SID: Index 54 454 10:1:1::400/120, Prefix-SID: Index 55 455 10:1:1::500/120, Prefix-SID: Index 56 456 10:1:1::600/120, Prefix-SID: Index 57 458 then the Address Prefix field in Intra-Area Prefix TLV, Inter-Area 459 Prefix TLV or External Prefix TLV is set to 10:1:1::0, Prefix Length 460 in these TLVs would be set to 120, Range Size in Prefix SID sub-TLV 461 would be set to 7 and Index value would be set to 51. 463 4.2. SID/Label Binding sub-TLV 465 SID/Label Binding sub-TLV is used to advertise SID/Label mapping for 466 a path to the prefix. 468 The SID/Label Binding TLV MAY be originated by any router in an 469 OSPFv3 domain. The router may advertise a SID/Label binding to a FEC 470 along with at least a single 'nexthop style' anchor. The protocol 471 supports more than one 'nexthop style' anchor to be attached to a 472 SID/Label binding, which results into a simple path description 473 language. In analogy to RSVP the terminology for this is called an 474 'Explicit Route Object' (ERO). Since ERO style path notation allows 475 to anchor SID/label bindings to both link and node IP addresses any 476 label switched path, can be described. Furthermore also SID/Label 477 Bindings from external protocols can get easily re-advertised. 479 The SID/Label Binding TLV may be used for advertising SID/Label 480 Bindings and their associated Primary and Backup paths. In one 481 single TLV either a primary ERO Path, a backup ERO Path or both are 482 advertised. If a router wants to advertise multiple parallel paths 483 then it can generate several TLVs for the same Prefix/FEC. Each 484 occurrence of a Binding TLV with respect with a given FEC Prefix has 485 accumulating and not canceling semantics. 487 SID/Label Binding sub-TLV is a sub-TLV of the following OSPFv3 TLVs, 488 as defined in [I-D.ietf-ospf-ospfv3-lsa-extend]: 490 Intra-Area Prefix TLV 491 Inter-Area Prefix TLV 493 External Prefix TLV 495 Multiple SID/Label Binding sub-TLVs can be present in above mentioned 496 TLVs. SID/Label Binding sub-TLV has following format: 498 0 1 2 3 499 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 1 500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 501 | Type | Length | 502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 503 | Flags | Weight | Range Size | 504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 505 | Sub-TLVs (variable) | 506 +- -+ 507 | | 509 where: 511 Type: TBD, suggested value 5 513 Length: variable 515 Flags: 1 octet field of following flags: 517 0 1 2 3 4 5 6 7 518 +-+-+-+-+-+-+-+-+ 519 |M| | 520 +-+-+-+-+-+-+-+-+ 522 where: 524 M-bit - When the bit is set the binding represents the 525 mirroring context as defined in 526 [I-D.minto-rsvp-lsp-egress-fast-protection]. 528 Weight: weight used for load-balancing purposes. The use of the 529 weight is defined in [I-D.filsfils-rtgwg-segment-routing]. 531 Range Size: usage is the same as described in Section 4.1 533 SID/Label Binding sub-TLV currently supports following Sub-TLVs: 535 SID/Label sub-TLV as described in Section 2.1. This sub-TLV MUST 536 appear in the SID/Label Binding Sub-TLV and it MUST only appear 537 once. 539 ERO Metric sub-TLV as defined in Section 4.2.1. 541 ERO sub-TLVs as defined in Section 4.2.2. 543 4.2.1. ERO Metric sub-TLV 545 ERO Metric sub-TLV is a Sub-TLV of the SID/Label Binding TLV. 547 The ERO Metric sub-TLV carries the cost of an ERO path. It is used 548 to compare the cost of a given source/destination path. A router 549 SHOULD advertise the ERO Metric sub-TLV. The cost of the ERO Metric 550 sub-TLV SHOULD be set to the cumulative IGP or TE path cost of the 551 advertised ERO. Since manipulation of the Metric field may attract 552 or distract traffic from and to the advertised segment it MAY be 553 manually overridden. 555 0 1 2 3 556 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 1 557 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 558 | Type | Length | 559 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 560 | Metric (4 octets) | 561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 563 ERO Metric sub-TLV format 565 where: 567 Type: TBD, suggested value 6 569 Length: 4 bytes 571 Metric: 4 bytes 573 4.2.2. ERO sub-TLVs 575 All 'ERO' information represents an ordered set which describes the 576 segments of a path. The last ERO sub-TLV describes the segment 577 closest to the egress point, contrary the first ERO sub-TLV describes 578 the first segment of a path. If a router extends or stitches a path 579 it MUST prepend the new segments path information to the ERO list. 581 The above similarly applies to backup EROs. 583 All ERO Sub-TLVs must immediately follow the (SID)/Label Sub-TLV. 585 All Backup ERO sub-TLVs must immediately follow last ERO Sub-TLV. 587 4.2.2.1. IPv4 ERO sub-TLV 589 IPv4 ERO sub-TLV is a sub-TLV of the SID/Label Binding sub-TLV. 591 The IPv4 ERO sub-TLV describes a path segment using IPv4 Address 592 style of encoding. Its semantics have been borrowed from [RFC3209]. 594 0 1 2 3 595 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 1 596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 597 | Type | Length | 598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 599 | Flags | Reserved | 600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 | IPv4 Address (4 octets) | 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 IPv4 ERO sub-TLV format 606 where: 608 Type: TBD, suggested value 7 610 Length: 8 bytes 612 Flags: 1 octet field of following flags: 614 0 1 2 3 4 5 6 7 615 +-+-+-+-+-+-+-+-+ 616 |L| | 617 +-+-+-+-+-+-+-+-+ 619 where: 621 L-bit - If the L bit is set, then the value of the attribute is 622 'loose.' Otherwise, the value of the attribute is 'strict.' 624 IPv4 Address - the address of the explicit route hop. 626 4.2.2.2. IPv6 ERO sub-TLV 628 IPv6 ERO sub-TLV is a sub-TLV of the SID/Label Binding sub-TLV. 630 The IPv6 ERO sub-TLV (Type TBA) describes a path segment using IPv6 631 Address style of encoding. Its semantics have been borrowed from 632 [RFC3209]. 634 0 1 2 3 635 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 1 636 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 637 | Type | Length | 638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 639 | Flags | Reserved | 640 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 641 | | 642 +- -+ 643 | | 644 +- IPv6 Address -+ 645 | | 646 +- -+ 647 | | 648 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 650 IPv6 ERO sub-TLV format 652 where: 654 Type: TBD, suggested value 8 656 Length: 8 bytes 658 Flags: 1 octet field of following flags: 660 0 1 2 3 4 5 6 7 661 +-+-+-+-+-+-+-+-+ 662 |L| | 663 +-+-+-+-+-+-+-+-+ 665 where: 667 L-bit - If the L bit is set, then the value of the attribute is 668 'loose.' Otherwise, the value of the attribute is 'strict.' 670 IPv6 Address - the address of the explicit route hop. 672 4.2.2.3. Unnumbered Interface ID ERO sub-TLV 674 Unnumbered Interface ID ERO sub-TLV is a sub-TLV of the SID/Label 675 Binding sub-TLV. 677 The appearance and semantics of the 'Unnumbered Interface ID' have 678 been borrowed from [RFC3477]. 680 The Unnumbered Interface-ID ERO sub-TLV describes a path segment that 681 spans over an unnumbered interface. Unnumbered interfaces are 682 referenced using the interface index. Interface indices are assigned 683 local to the router and therefore not unique within a domain. All 684 elements in an ERO path need to be unique within a domain and hence 685 need to be disambiguated using a domain unique Router-ID. 687 0 1 2 3 688 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 1 689 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 690 | Type | Length | 691 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 692 | Flags | Reserved | 693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 694 | Router ID | 695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 696 | Interface ID | 697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 where: 701 Unnumbered Interface ID ERO sub-TLV format 703 Type: TBD, suggested value 9 705 Length: 12 bytes 707 Flags: 1 octet field of following flags: 709 0 1 2 3 4 5 6 7 710 +-+-+-+-+-+-+-+-+ 711 |L| | 712 +-+-+-+-+-+-+-+-+ 714 where: 716 L-bit - If the L bit is set, then the value of the attribute is 717 'loose.' Otherwise, the value of the attribute is 'strict.' 719 Router-ID: Router-ID of the next-hop. 721 Interface ID: is the identifier assigned to the link by the router 722 specified by the Router-ID. 724 4.2.2.4. IPv4 Backup ERO sub-TLV 726 IPv4 Prefix Backup ERO sub-TLV is a sub-TLV of the SID/Label Binding 727 sub-TLV. 729 The IPv4 Backup ERO sub-TLV describes a path segment using IPv4 730 Address style of encoding. Its semantics have been borrowed from 731 [RFC3209]. 733 0 1 2 3 734 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 1 735 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 736 | Type | Length | 737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 738 | Flags | Reserved | 739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 740 | IPv4 Address (4 octets) | 741 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 743 IPv4 Backup ERO sub-TLV format 745 where: 747 Type: TBD, suggested value 10 749 Length: 8 bytes 751 Flags: 1 octet field of following flags: 753 0 1 2 3 4 5 6 7 754 +-+-+-+-+-+-+-+-+ 755 |L| | 756 +-+-+-+-+-+-+-+-+ 758 where: 760 L-bit - If the L bit is set, then the value of the attribute is 761 'loose.' Otherwise, the value of the attribute is 'strict.' 763 IPv4 Address - the address of the explicit route hop. 765 4.2.2.5. IPv6 Backup ERO sub-TLV 767 IPv6 ERO sub-TLV is a sub-TLV of the SID/Label Binding sub-TLV. 769 The IPv6 Backup ERO sub-TLV describes a Backup path segment using 770 IPv6 Address style of encoding. Its appearance and semantics have 771 been borrowed from [RFC3209]. 773 The 'L' bit in the Flags is a one-bit attribute. If the L bit is 774 set, then the value of the attribute is 'loose.' Otherwise, the 775 value of the attribute is 'strict.' 776 0 1 2 3 777 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 1 778 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 779 | Type | Length | 780 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 781 | Flags | Reserved | 782 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 783 | | 784 +- -+ 785 | | 786 +- IPv6 Address -+ 787 | | 788 +- -+ 789 | | 790 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 792 IPv6 Backup ERO sub-TLV format 794 where: 796 Type: TBD, suggested value 11 798 Length: 8 bytes 800 Flags: 1 octet field of following flags: 802 0 1 2 3 4 5 6 7 803 +-+-+-+-+-+-+-+-+ 804 |L| | 805 +-+-+-+-+-+-+-+-+ 807 where: 809 L-bit - If the L bit is set, then the value of the attribute is 810 'loose.' Otherwise, the value of the attribute is 'strict.' 812 IPv6 Address - the address of the explicit route hop. 814 4.2.2.6. Unnumbered Interface ID Backup ERO sub-TLV 816 Unnumbered Interface ID Backup sub-TLV is a sub-TLV of the SID/Label 817 Binding sub-TLV. 819 The appearance and semantics of the 'Unnumbered Interface ID' have 820 been borrowed from [RFC3477]. 822 The Unnumbered Interface-ID ERO sub-TLV describes a path segment that 823 spans over an unnumbered interface. Unnumbered interfaces are 824 referenced using the interface index. Interface indices are assigned 825 local to the router and therefore not unique within a domain. All 826 elements in an ERO path need to be unique within a domain and hence 827 need to be disambiguated using a domain unique Router-ID. 829 0 1 2 3 830 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 1 831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 832 | Type | Length | 833 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 834 | Flags | Reserved | 835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 836 | Router ID | 837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 838 | Interface ID | 839 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 841 Unnumbered Interface ID Backup ERO sub-TLV format 843 where: 845 Type: TBD, suggested value 12 847 Length: 12 bytes 849 Flags: 1 octet field of following flags: 851 0 1 2 3 4 5 6 7 852 +-+-+-+-+-+-+-+-+ 853 |L| | 854 +-+-+-+-+-+-+-+-+ 856 where: 858 L-bit - If the L bit is set, then the value of the attribute is 859 'loose.' Otherwise, the value of the attribute is 'strict.' 861 Router-ID: Router-ID of the next-hop. 863 Interface ID: is the identifier assigned to the link by the router 864 specified by the Router-ID. 866 5. Adjacency Segment Identifier (Adj-SID) 868 An Adjacency Segment Identifier (Adj-SID) represents a router 869 adjacency in Segment Routing. At the current stage of Segment 870 Routing architecture it is assumed that the Adj-SID value has local 871 significance (to the router). 873 5.1. Adj-SID sub-TLV 875 A new extended OSPFv3 LSAs, as defined in 876 [I-D.ietf-ospf-ospfv3-lsa-extend], are used to advertise prefix SID 877 in OSPFv3 879 Adj-SID sub-TLV is an optional sub-TLV of the Router-Link TLV as 880 defined in [I-D.ietf-ospf-ospfv3-lsa-extend]. It MAY appear multiple 881 times in Router-Link TLV. Examples where more than one Adj-SID may 882 be used per neighbor are described in 883 [I-D.filsfils-rtgwg-segment-routing-use-cases]. The structure of the 884 Adj-SID Sub-TLV is as follows: 886 0 1 2 3 887 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 1 888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 889 | Type | Length | 890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 891 | Flags | Weight | Reserved | 892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 893 | SID/Label/Index (variable) | 894 +---------------------------------------------------------------+ 896 where: 898 Type: TBD, suggested value 10. 900 Length: variable. 902 Flags. 1 octet field of following flags: 904 0 1 2 3 4 5 6 7 905 +-+-+-+-+-+-+-+-+ 906 |B|V|L|S| | 907 +-+-+-+-+-+-+-+-+ 909 where: 911 B-Flag: Backup-flag: set if the Adj-SID refer to an adjacency 912 being protected (e.g.: using IPFRR or MPLS-FRR) as described in 913 [I-D.filsfils-rtgwg-segment-routing-use-cases]. 915 The V-Flag: Value/Index Flag. If set, then the Prefix-SID 916 carries an absolute value. If not set, then the Prefix-SID 917 carries an index. 919 The L-Flag: Local/Global Flag. If set, then the value/index 920 carried by the PrefixSID has local significance. If not set, 921 then the value/index carried by this subTLV has global 922 significance. 924 The S-Flag. Set Flag. When set, the S-Flag indicates that the 925 Adj-SID refers to a set of adjacencies (and therefore MAY be 926 assigned to other adjacencies as well). 928 Other bits: MUST be zero when originated and ignored when 929 received. 931 Weight: weight used for load-balancing purposes. The use of the 932 weight is defined in [I-D.filsfils-rtgwg-segment-routing]. 934 SID/Index/Label: label or index value depending on the V-bit 935 setting. 937 Examples: 939 A 32 bit global index defining the offset in the SID/Label 940 space advertised by this router - in this case the V and L 941 flags MUST be unset. 943 A 24 bit local label where the 20 rightmost bits are used 944 for encoding the label value - in this case the V and L 945 flags MUST be set. 947 16 octet IPv6 address - in this case the V-flag MUST be set. 948 The L-flag MUST be set for link-local IPv6 address and MUST 949 be unset for IPv6 global unicast address. 951 A SR capable router MAY allocate an Adj-SID for each of its 952 adjacencies and set the B-Flag when the adjacency is protected by a 953 FRR mechanism (IP or MPLS) as described in 954 [I-D.filsfils-rtgwg-segment-routing-use-cases]. 956 5.2. LAN Adj-SID Sub-TLV 958 LAN Adj-SID is an optional sub-TLV of the Router-Link TLV. It MAY 959 appear multiple times in Router-Link TLV. It is used to advertise 960 SID/Label for adjacency to non-DR node on broadcast or NBMA network. 962 0 1 2 3 963 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 1 964 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 965 | Type | Length | 966 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 967 | Flags | Weight | Reserved | 968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 969 | Neighbor ID | 970 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 971 | SID/Label/Index (variable) | 972 +---------------------------------------------------------------+ 974 where: 976 Type: TBD, suggested value 11. 978 Length: variable. 980 Flags. 1 octet field of following flags: 982 0 1 2 3 4 5 6 7 983 +-+-+-+-+-+-+-+-+ 984 |B|V|L|S| | 985 +-+-+-+-+-+-+-+-+ 987 where: 989 B-Flag: Backup-flag: set if the LAN-Adj-SID refer to an 990 adjacency being protected (e.g.: using IPFRR or MPLS-FRR) as 991 described in [I-D.filsfils-rtgwg-segment-routing-use-cases]. 993 The V-Flag: Value/Index Flag. If set, then the Prefix-SID 994 carries an absolute value. If not set, then the Prefix-SID 995 carries an index. 997 The L-Flag: Local/Global Flag. If set, then the value/index 998 carried by the PrefixSID has local significance. If not set, 999 then the value/index carried by this subTLV has global 1000 significance. 1002 The S-Flag. Set Flag. When set, the S-Flag indicates that the 1003 Adj-SID refers to a set of adjacencies (and therefore MAY be 1004 assigned to other adjacencies as well). 1006 Other bits: MUST be zero when originated and ignored when 1007 received. 1009 Weight: weight used for load-balancing purposes. The use of the 1010 weight is defined in [I-D.filsfils-rtgwg-segment-routing]. 1012 SID/Index/Label: label or index value depending on the V-bit 1013 setting. 1015 Examples: 1017 A 32 bit global index defining the offset in the SID/Label 1018 space advertised by this router - in this case the V and L 1019 flags MUST be unset. 1021 A 24 bit local label where the 20 rightmost bits are used 1022 for encoding the label value - in this case the V and L 1023 flags MUST be set. 1025 16 octet IPv6 address - in this case the V-flag MUST be set. 1026 The L-flag MUST be set for link-local IPv6 address and MUST 1027 be unset for IPv6 global unicast address. 1029 6. Elements of Procedure 1031 6.1. Intra-area Segment routing in OSPFv3 1033 The OSPFv3 node that supports segment routing MAY advertise Prefix- 1034 SIDs for any prefix that it is advertising reachability for (e.g. 1035 loopback IP address) as described in Section 4.1. 1037 If multiple routers advertise Prefix-SID for the same prefix, then 1038 the Prefix-SID MUST be the same. This is required in order to allow 1039 traffic load-balancing if multiple equal cost paths to the 1040 destination exist in the network. 1042 Prefix-SID can also be advertised by the SR Mapping Servers (as 1043 described in [I-D.filsfils-rtgwg-segment-routing-use-cases]). The 1044 Mapping Server advertises Prefix-SID for remote prefixes that exist 1045 in the network. Multiple Mapping Servers can advertise Prefix-SID 1046 for the same prefix, in which case the same Prefix-SID MUST be 1047 advertised by all of them. SR Mapping Server could use either area 1048 scope or autonomous system flooding scope when advertising Prefix SID 1049 for prefixes, based on the configuration of the SR Mapping Server. 1050 Depending on the flooding scope used, SR Mapping Server chooses the 1051 LSA that will be used. If the area flooding scope is needed, E- 1052 Intra-Area-Prefix-LSA ([I-D.ietf-ospf-ospfv3-lsa-extend]) is used. 1053 If autonomous system flooding scope is needed, E-AS-External-LSA 1054 ([I-D.ietf-ospf-ospfv3-lsa-extend]) is used. 1056 When Prefix-SID is advertised by the Mapping Server, which is 1057 indicated by the M-flag in the Prefix-SID sub-TLV (Section 4.1), 1058 route-type as indicated by the LSA type which is being used for 1059 flooding is ignored. Prefix SID is bound to a prefix, in which case 1060 route-type becomes unimportant. 1062 Advertisement of the Prefix-SID by the Mapping Server using Inter- 1063 Area Prefix TLV, External Prefix TLV or Intra-Area-Prefix TLV 1064 ([I-D.ietf-ospf-ospfv3-lsa-extend]) does not itself contribute to the 1065 prefix reachability. NU-bit MUST be set in the PrefixOptions field 1066 of the LSA which is used by the Mapping Server to advertise SID or 1067 SID range, which prevents such advertisement to contribute to the 1068 prefix reachability. 1070 6.2. Inter-area Segment routing in OSPFv3 1072 In order to support SR in a multi-area environment, OSPFv3 must 1073 propagate Prefix-SID information between areas. The following 1074 procedure is used in order to propagate Prefix SIDs between areas. 1076 When an OSPFv3 ABR advertises a Inter-Area-Prefix-LSA from an intra- 1077 area prefix to all its connected areas, it will also include Prefix- 1078 SID sub-TLV, as described in Section 4.1. The Prefix-SID value will 1079 be set as follows: 1081 The ABR will look at its best path to the prefix in the source 1082 area and find out the advertising router associated with its best 1083 path to that prefix. 1085 If no Prefix-SID was advertised for the prefix in the source area 1086 by the router that contributes to the best path to the prefix, 1087 then the ABR will use the Prefix-SID advertised by any other 1088 router (e.g.: a Prefix-SID coming from an SR Mapping Server as 1089 defined in [I-D.filsfils-rtgwg-segment-routing-use-cases]) when 1090 propagating Prefix-SID for the prefix to other areas. 1092 When an OSPFv3 ABR advertises Inter-Area-Prefix-LSA LSAs from an 1093 inter-area route to all its connected areas it will also include 1094 Prefix-SID sub-TLV, as described in Section 4.1. The Prefix-SID 1095 value will be set as follows: 1097 The ABR will look at its best path to the prefix in the source 1098 area and find out the advertising router associated with its best 1099 path to that prefix. 1101 The ABR will then look if such router advertised a Prefix-SID for 1102 the prefix and use it when advertising the Prefix-SID to other 1103 connected areas. 1105 If no Prefix-SID was advertised for the prefix in the source area 1106 by the ABR that contributes to the best path to the prefix, the 1107 originating ABR will use the Prefix-SID advertised by any other 1108 router (e.g.: a Prefix-SID coming from an SR Mapping Server as 1109 defined in [I-D.filsfils-rtgwg-segment-routing-use-cases]) when 1110 propagating Prefix-SID for the prefix to other areas. 1112 6.3. SID for External Prefixes 1114 AS-External-LSAs are flooded domain wide. When an ASBR, which 1115 supports SR, generates AS-External-LSA, it should also include 1116 Prefix-SID sub-TLV, as described in Section 4.1 Prefix-SID value will 1117 be set to the SID that has been reserved for that prefix. 1119 When a NSSA ASBR translates NSSA-LSA into AS-External-LSA, it should 1120 also advertise the Prefix-SID for the prefix. The NSSA ABR 1121 determines its best path to the prefix advertised in the translated 1122 NSSA-LSA and finds the advertising router associated with such path. 1123 If such advertising router has advertised a Prefix-SID for the 1124 prefix, then the NSSA ASBR uses it when advertising the Prefix-SID in 1125 AS-External-LSA. Otherwise the Prefix-SID advertised by any other 1126 router will be used (e.g.: a Prefix-SID coming from an SR Mapping 1127 Server as defined in [I-D.filsfils-rtgwg-segment-routing-use-cases]). 1129 6.4. Advertisement of Adj-SID 1131 The Adjacency Segment Routing Identifier (Adj-SID) is advertised 1132 using the Adj-SID Sub-TLV as described in Section 5. 1134 6.4.1. Advertisement of Adj-SID on Point-to-Point Links 1136 Adj-SID MAY be advertised for any adjacency on p2p link that is in a 1137 state 2-Way or higher. If the adjacency on a p2p link transitions 1138 from the FULL state, then the Adj-SID for that adjacency MAY be 1139 removed from the area. If the adjacency transitions to a state lower 1140 then 2-Way, then the Adj-SID MUST be removed from the area. 1142 6.4.2. Adjacency SID on Broadcast or NBMA Interfaces 1144 Broadcast or NBMA networks in OSPFv3 are represented by a star 1145 topology where the Designated Router (DR) is the central point all 1146 other routers on the broadcast or NBMA network connect to. As a 1147 result, routers on the broadcast or NBMA network advertise only their 1148 adjacency to DR and BDR. Routers that are neither DR nor BDR do not 1149 form and do not advertise adjacencies between them. They, however, 1150 maintain a 2-Way adjacency state between them. 1152 When Segment Routing is used, each router on the broadcast or NBMA 1153 network MAY advertise the Adj-SID for its adjacency to DR using Adj- 1154 SID Sub-TLV as described in Section 5.1. 1156 SR capable router MAY also advertise Adj-SID for other neighbors 1157 (e.g. BDR, DR-OTHER) on broadcast or NBMA network using the LAN ADJ- 1158 SID Sub-TLV as described in section 5.1.1.2. Section 5.2. 1160 7. IANA Considerations 1162 This specification updates two existing OSPF registries. 1164 7.1. OSPF Router Information (RI) TLVs Registry 1166 o suggested value 8 - SR-Algorithm TLV 1168 o suggested value 9 - SID/Label Range TLV 1170 7.2. OSPFv3 Extend-LSA sub-TLV registry 1172 o suggested value 1 - SID/Label sub-TLV 1174 o suggested value 2 - Prefix SID sub-TLV 1176 o suggested value 3 - Adj-SID sub-TLV 1178 o suggested value 4 - LAN Adj-SID sub-TLV 1180 o suggested value 5 - SID/Label Binding sub-TLV 1182 o suggested value 6 - ERO Metric sub-TLV 1184 o suggested value 7 - IPv4 ERO sub-TLV 1186 o suggested value 8 - IPv6 ERO sub-TLV 1188 o suggested value 9 - Unnumbered Interface ID ERO sub-TLV 1190 o suggested value 10 - IPv4 Backup ERO sub-TLV 1192 o suggested value 11 - IPv6 Backup ERO sub-TLV 1194 o suggested value 12 - Unnumbered Interface ID Backup ERO sub-TLV 1196 8. Security Considerations 1198 Implementations must assure that malformed permutations of the newly 1199 defined sub-TLvs do not result in errors which cause hard OSPFv3 1200 failures. 1202 9. Contributors 1204 The following people gave a substantial contribution to the content 1205 of this document: Ahmed Bashandy, Martin Horneffer, Bruno Decraene, 1206 Stephane Litkowski, Igor Milojevic, Rob Shakir and Saku Ytti. 1208 10. Acknowledgements 1210 We would like to thank Anton Smirnov for his contribution. 1212 Many thanks to Yakov Rekhter, John Drake and Shraddha Hedge for their 1213 contribution on earlier incarnations of the "Binding / MPLS Label 1214 TLV" in [I-D.gredler-ospf-label-advertisement]. 1216 11. References 1218 11.1. Normative References 1220 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1221 Requirement Levels", BCP 14, RFC 2119, March 1997. 1223 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 1224 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 1225 Tunnels", RFC 3209, December 2001. 1227 [RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links 1228 in Resource ReSerVation Protocol - Traffic Engineering 1229 (RSVP-TE)", RFC 3477, January 2003. 1231 [RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S. 1232 Shaffer, "Extensions to OSPF for Advertising Optional 1233 Router Capabilities", RFC 4970, July 2007. 1235 11.2. Informative References 1237 [I-D.filsfils-rtgwg-segment-routing] 1238 Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 1239 Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., 1240 Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe, 1241 "Segment Routing Architecture", draft-filsfils-rtgwg- 1242 segment-routing-01 (work in progress), October 2013. 1244 [I-D.filsfils-rtgwg-segment-routing-use-cases] 1245 Filsfils, C., Francois, P., Previdi, S., Decraene, B., 1246 Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., 1247 Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E. 1248 Crabbe, "Segment Routing Use Cases", draft-filsfils-rtgwg- 1249 segment-routing-use-cases-02 (work in progress), October 1250 2013. 1252 [I-D.gredler-ospf-label-advertisement] 1253 Gredler, H., Amante, S., Scholl, T., and L. Jalil, 1254 "Advertising MPLS labels in OSPF", draft-gredler-ospf- 1255 label-advertisement-03 (work in progress), May 2013. 1257 [I-D.ietf-ospf-ospfv3-lsa-extend] 1258 Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 1259 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-03 1260 (work in progress), May 2014. 1262 [I-D.minto-rsvp-lsp-egress-fast-protection] 1263 Jeganathan, J., Gredler, H., and Y. Shen, "RSVP-TE LSP 1264 egress fast-protection", draft-minto-rsvp-lsp-egress-fast- 1265 protection-03 (work in progress), November 2013. 1267 Authors' Addresses 1269 Peter Psenak (editor) 1270 Cisco Systems, Inc. 1271 Apollo Business Center 1272 Mlynske nivy 43 1273 Bratislava 821 09 1274 Slovakia 1276 Email: ppsenak@cisco.com 1278 Stefano Previdi (editor) 1279 Cisco Systems, Inc. 1280 Via Del Serafico, 200 1281 Rome 00142 1282 Italy 1284 Email: sprevidi@cisco.com 1285 Clarence Filsfils 1286 Cisco Systems, Inc. 1287 Brussels 1288 Belgium 1290 Email: cfilsfil@cisco.com 1292 Hannes Gredler 1293 Juniper Networks, Inc. 1294 1194 N. Mathilda Ave. 1295 Sunnyvale, CA 94089 1296 US 1298 Email: hannes@juniper.net 1300 Rob Shakir 1301 British Telecom 1302 London 1303 UK 1305 Email: rob.shakir@bt.com 1307 Wim Henderickx 1308 Alcatel-Lucent 1309 Copernicuslaan 50 1310 Antwerp 2018 1311 BE 1313 Email: wim.henderickx@alcatel-lucent.com 1315 Jeff Tantsura 1316 Ericsson 1317 300 Holger Way 1318 San Jose, CA 95134 1319 US 1321 Email: Jeff.Tantsura@ericsson.com