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'ISO10589' ** Obsolete normative reference: RFC 8919 (Obsoleted by RFC 9479) ** Obsolete normative reference: RFC 8920 (Obsoleted by RFC 9492) == Outdated reference: A later version (-13) exists of draft-ietf-rtgwg-segment-routing-ti-lfa-05 Summary: 3 errors (**), 0 flaws (~~), 4 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Psenak, Ed. 3 Internet-Draft Cisco Systems 4 Intended status: Standards Track S. Hegde 5 Expires: August 23, 2021 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Individual 11 February 19, 2021 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-14 16 Abstract 18 IGP protocols traditionally compute best paths over the network based 19 on the IGP metric assigned to the links. Many network deployments 20 use RSVP-TE based or Segment Routing based Traffic Engineering to 21 steer traffic over a path that is computed using different metrics or 22 constraints than the shortest IGP path. This document proposes a 23 solution that allows IGPs themselves to compute constraint-based 24 paths over the network. This document also specifies a way of using 25 Segment Routing (SR) Prefix-SIDs and SRv6 locators to steer packets 26 along the constraint-based paths. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on August 23, 2021. 45 Copyright Notice 47 Copyright (c) 2021 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 64 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 4. Flexible Algorithm . . . . . . . . . . . . . . . . . . . . . 5 66 5. Flexible Algorithm Definition Advertisement . . . . . . . . . 6 67 5.1. ISIS Flexible Algorithm Definition Sub-TLV . . . . . . . 6 68 5.2. OSPF Flexible Algorithm Definition TLV . . . . . . . . . 8 69 5.3. Common Handling of Flexible Algorithm Definition TLV . . 9 70 6. Sub-TLVs of ISIS FAD Sub-TLV . . . . . . . . . . . . . . . . 10 71 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV . . . 10 72 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV . 11 73 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV . 12 74 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV . . . . 12 75 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 13 76 7. Sub-TLVs of OSPF FAD TLV . . . . . . . . . . . . . . . . . . 14 77 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV . . . 14 78 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV . 14 79 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV . 15 80 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV . . . . 15 81 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 16 82 8. ISIS Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . . 17 83 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . . 18 84 10. OSPF Flexible Algorithm ASBR Reachability Advertisement . . . 19 85 10.1. OSPFv2 Extended Inter-Area ASBR LSA . . . . . . . . . . 19 86 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV . . . . . . . . 21 87 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV . . . . . . 21 88 10.3. OSPFv2 EIA-ASBR LSA Advertisement and Processing . . . . 22 89 11. Advertisement of Node Participation in a Flex-Algorithm . . . 23 90 11.1. Advertisement of Node Participation for Segment Routing 24 91 11.2. Advertisement of Node Participation for Other 92 Applications . . . . . . . . . . . . . . . . . . . . . . 24 94 12. Advertisement of Link Attributes for Flex-Algorithm . . . . . 24 95 13. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 25 96 13.1. Multi-area and Multi-domain Considerations . . . . . . . 27 97 14. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 29 98 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 29 99 14.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 29 100 14.3. Other Applications' Forwarding for Flex-Algorithm . . . 30 101 15. Operational Considerations . . . . . . . . . . . . . . . . . 31 102 15.1. Inter-area Considerations . . . . . . . . . . . . . . . 31 103 15.2. Usage of SRLG Exclude Rule with Flex-Algorithm . . . . . 31 104 15.3. Max-metric consideration . . . . . . . . . . . . . . . . 32 105 16. Backward Compatibility . . . . . . . . . . . . . . . . . . . 32 106 17. Security Considerations . . . . . . . . . . . . . . . . . . . 33 107 18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 108 18.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 33 109 18.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 33 110 18.1.2. IGP Metric-Type Registry . . . . . . . . . . . . . . 33 111 18.2. Flexible Algorithm Definition Flags Registry . . . . . . 34 112 18.3. ISIS IANA Considerations . . . . . . . . . . . . . . . . 34 113 18.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 34 114 18.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 35 115 18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 116 TLV . . . . . . . . . . . . . . . . . . . . . . . . 35 117 18.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 36 118 18.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 36 119 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 36 120 18.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 36 121 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits . . . . . . . 37 122 18.4.5. OSPF Opaque LSA Option Types . . . . . . . . . . . . 37 123 18.4.6. OSPFv2 Externded Inter-Area ASBR TLVs . . . . . . . 37 124 18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs . . . . . . . . . . 37 125 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV 126 Registry . . . . . . . . . . . . . . . . . . . . . . 38 127 18.4.9. Link Attribute Applications Registry . . . . . . . . 39 128 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 39 129 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 40 130 20.1. Normative References . . . . . . . . . . . . . . . . . . 40 131 20.2. Informative References . . . . . . . . . . . . . . . . . 42 132 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 134 1. Introduction 136 An IGP-computed path based on the shortest IGP metric is often be 137 replaced by a traffic-engineered path due to the traffic requirements 138 which are not reflected by the IGP metric. Some networks engineer 139 the IGP metric assignments in a way that the IGP metric reflects the 140 link bandwidth or delay. If, for example, the IGP metric is 141 reflecting the bandwidth on the link and the application traffic is 142 delay sensitive, the best IGP path may not reflect the best path from 143 such an application's perspective. 145 To overcome this limitation, various sorts of traffic engineering 146 have been deployed, including RSVP-TE and SR-TE, in which case the TE 147 component is responsible for computing paths based on additional 148 metrics and/or constraints. Such paths need to be installed in the 149 forwarding tables in addition to, or as a replacement for, the 150 original paths computed by IGPs. Tunnels are often used to represent 151 the engineered paths and mechanisms like one described in [RFC3906] 152 are used to replace the native IGP paths with such tunnel paths. 154 This document specifies a set of extensions to ISIS, OSPFv2, and 155 OSPFv3 that enable a router to advertise TLVs that identify (a) 156 calculation-type, (b) specify a metric-type, and (c) describe a set 157 of constraints on the topology, that are to be used to compute the 158 best paths along the constrained topology. A given combination of 159 calculation-type, metric-type, and constraints is known as a 160 "Flexible Algorithm Definition". A router that sends such a set of 161 TLVs also assigns a Flex-Algorithm value to the specified combination 162 of calculation-type, metric-type, and constraints. 164 This document also specifies a way for a router to use IGPs to 165 associate one or more SR Prefix-SIDs or SRv6 locators with a 166 particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then 167 represents a path that is computed according to the identified Flex- 168 Algorithm. 170 2. Requirements Language 172 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 173 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 174 "OPTIONAL" in this document are to be interpreted as described in 175 [BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all 176 capitals, as shown here. 178 3. Terminology 180 This section defines terms that are often used in this document. 182 Flexible Algorithm Definition (FAD) - the set consisting of (a) 183 calculation-type, (b) metric-type, and (c) a set of constraints. 185 Flexible Algorithm - a numeric identifier in the range 128-255 that 186 is associated via configuration with the Flexible-Algorithm 187 Definition. 189 Local Flexible Algorithm Definition - Flexible Algorithm Definition 190 defined locally on the node. 192 Remote Flexible Algorithm Definition - Flexible Algorithm Definition 193 received from other nodes via IGP flooding. 195 Flexible Algorithm Participation - per application configuration 196 state that expresses whether the node is participating in a 197 particular Flexible Algorithm. 199 IGP Algorithm - value from the the "IGP Algorithm Types" registry 200 defined under "Interior Gateway Protocol (IGP) Parameters" IANA 201 registries. IGP Algorithms represents the triplet (Calculation Type, 202 Metric, Constraints), where the second and third elements of the 203 triple MAY be unspecified. 205 ABR - Area Border Router. In ISIS terminology it is also known as 206 L1/L2 router. 208 ASBR - Autonomous System Border Router. 210 4. Flexible Algorithm 212 Many possible constraints may be used to compute a path over a 213 network. Some networks are deployed as multiple planes. A simple 214 form of constraint may be to use a particular plane. A more 215 sophisticated form of constraint can include some extended metric as 216 described in [RFC8570]. Constraints which restrict paths to links 217 with specific affinities or avoid links with specific affinities are 218 also possible. Combinations of these are also possible. 220 To provide maximum flexibility, we want to provide a mechanism that 221 allows a router to (a) identify a particular calculation-type, (b) 222 metric-type, (c) describe a particular set of constraints, and (d) 223 assign a numeric identifier, referred to as Flex-Algorithm, to the 224 combination of that calculation-type, metric-type, and those 225 constraints. We want the mapping between the Flex-Algorithm and its 226 meaning to be flexible and defined by the user. As long as all 227 routers in the domain have a common understanding as to what a 228 particular Flex-Algorithm represents, the resulting routing 229 computation is consistent and traffic is not subject to any looping. 231 The set consisting of (a) calculation-type, (b) metric-type, and (c) 232 a set of constraints is referred to as a Flexible-Algorithm 233 Definition. 235 Flexible-Algorithm is a numeric identifier in the range 128-255 that 236 is associated via configuratin with the Flexible-Algorithm 237 Definition. 239 IANA "IGP Algorithm Types" registry defines the set of values for IGP 240 Algorithms. We propose to allocate the following values for Flex- 241 Algorithms from this registry: 243 128-255 - Flex-Algorithms 245 5. Flexible Algorithm Definition Advertisement 247 To guarantee the loop-free forwarding for paths computed for a 248 particular Flex-Algorithm, all routers that (a) are configured to 249 participate in a particular Flex-Algorithm, and (b) are in the same 250 Flex-Algorithm definition advertisement scope MUST agree on the 251 definition of the Flex-Algorithm. 253 5.1. ISIS Flexible Algorithm Definition Sub-TLV 255 The ISIS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used 256 to advertise the definition of the Flex-Algorithm. 258 The ISIS FAD Sub-TLV is advertised as a Sub-TLV of the ISIS Router 259 Capability TLV-242 that is defined in [RFC7981]. 261 ISIS FAD Sub-TLV has the following format: 263 0 1 2 3 264 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 1 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 | Type | Length |Flex-Algorithm | Metric-Type | 267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 268 | Calc-Type | Priority | 269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 270 | Sub-TLVs | 271 + + 272 | ... | 274 | | 275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 where: 279 Type: 26 281 Length: variable, dependent on the included Sub-TLVs 282 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 284 Metric-Type: Type of metric to be used during the calculation. 285 Following values are defined: 287 0: IGP Metric 289 1: Min Unidirectional Link Delay as defined in [RFC8570], 290 section 4.2, encoded as application specific link attribute as 291 specified in [RFC8919] and Section 12 of this document. 293 2: Traffic Engineering Default Metric as defined in [RFC5305], 294 section 3.7, encoded as application specific link attribute as 295 specified in [RFC8919] and Section 12 of this document. 297 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 298 Types" registry defined under "Interior Gateway Protocol (IGP) 299 Parameters" IANA registries. IGP algorithms in the range of 0-127 300 have a defined triplet (Calculation Type, Metric, Constraints). 301 When used to specify the Calc-Type in the FAD Sub-TLV, only the 302 Calculation Type defined for the specified IGP Algorithm is used. 303 The Metric/Constraints MUST NOT be inherited. If the required 304 calculation type is Shortest Path First, the value 0 SHOULD appear 305 in this field. 307 Priority: Value between 0 and 255 inclusive that specifies the 308 priority of the advertisement. 310 Sub-TLVs - optional sub-TLVs. 312 The ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a 313 router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given 314 Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs 315 for a given Flexible-Algorithm from the same originator SHOULD select 316 the first advertisement in the lowest numbered LSP. 318 The ISIS FAD Sub-TLV has an area scope. The Router Capability TLV in 319 which the FAD Sub-TLV is present MUST have the S-bit clear. 321 ISIS L1/L2 router MAY be configured to re-generate the winning FAD 322 from level 2, without any modification to it, to level 1 area. The 323 re-generation of the FAD Sub-TLV from level 2 to level 1 is 324 determined by the L1/L2 router, not by the originator of the FAD 325 advertisement in the level 2. In such case, the re-generated FAD 326 Sub-TLV will be advertised in the level 1 Router Capability TLV 327 originated by the L1/L2 router. 329 L1/L2 router MUST NOT re-generate any FAD Sub-TLV from level 1 to 330 level 2. 332 5.2. OSPF Flexible Algorithm Definition TLV 334 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 335 defined in [RFC7770]. 337 OSPF FAD TLV has the following format: 339 0 1 2 3 340 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 1 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 342 | Type | Length | 343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 344 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 345 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 346 | Sub-TLVs | 347 + + 348 | ... | 350 | | 351 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 353 where: 355 Type: 16 357 Length: variable, dependent on the included Sub-TLVs 359 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 360 inclusive. 362 Metric-Type: Type of metric to be used during the calculation. 363 Following values are defined: 365 0: IGP Metric 367 1: Min Unidirectional Link Delay as defined in [RFC7471], 368 section 4.2, encoded as application specific link attribute as 369 specified in [RFC8920] and Section 12 of this document. 371 2: Traffic Engineering metric as defined in [RFC3630], section 372 2.5.5, encoded as application specific link attribute as 373 specified in [RFC8920] and Section 12 of this document. 375 Calc-Type: as described in Section 5.1 376 Priority: as described in Section 5.1 378 Sub-TLVs - optional sub-TLVs. 380 When multiple OSPF FAD TLVs, for the same Flexible-Algorithm, are 381 received from a given router, the receiver MUST use the first 382 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 383 TLV, for the same Flex-Algorithm, appears in multiple Router 384 Information LSAs that have different flooding scopes, the OSPF FAD 385 TLV in the Router Information LSA with the area-scoped flooding scope 386 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 387 in multiple Router Information LSAs that have the same flooding 388 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 389 numerically smallest Instance ID MUST be used and subsequent 390 instances of the OSPF FAD TLV MUST be ignored. 392 The RI LSA can be advertised at any of the defined opaque flooding 393 scopes (link, area, or Autonomous System (AS)). For the purpose of 394 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 395 Autonomous System flooding scope SHOULD NOT be used by default unless 396 local configuration policy on the originating router indicates domain 397 wide flooding. 399 5.3. Common Handling of Flexible Algorithm Definition TLV 401 This section describes the protocol-independent handling of the FAD 402 TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in 403 this section, even though in case of ISIS it is a Sub-TLV. 405 The value of the Flex-Algorithm MUST be between 128 and 255 406 inclusive. If it is not, the FAD TLV MUST be ignored. 408 Only a subset of the routers participating in the particular Flex- 409 Algorithm need to advertise the definition of the Flex-Algorithm. 411 Every router, that is configured to participate in a particular Flex- 412 Algorithm, MUST select the Flex-Algorithm definition based on the 413 following ordered rules. This allows for the consistent Flex- 414 Algorithm definition selection in cases where different routers 415 advertise different definitions for a given Flex-Algorithm: 417 1. From the advertisements of the FAD in the area (including both 418 locally generated advertisements and received advertisements) 419 select the one(s) with the highest priority value. 421 2. If there are multiple advertisements of the FAD with the same 422 highest priority, select the one that is originated from the 423 router with the highest System-ID, in the case of ISIS, or Router 424 ID, in the case of OSPFv2 and OSPFv3. For ISIS, the System-ID is 425 described in [ISO10589]. For OSPFv2 and OSPFv3, standard Router 426 ID is described in [RFC2328] and [RFC5340] respectively. 428 A router that is not configured to participate in a particular Flex- 429 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 430 Algorithm. 432 A router that is not participating in a particular Flex-Algorithm is 433 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 434 MUST consider FAD advertisement regardless of the Flex-Algorithm 435 participation of the FAD originator. 437 Any change in the Flex-Algorithm definition may result in temporary 438 disruption of traffic that is forwarded based on such Flex-Algorithm 439 paths. The impact is similar to any other event that requires 440 network-wide convergence. 442 If a node is configured to participate in a particular Flexible- 443 Algorithm, but the selected Flex-Algorithm definition includes 444 calculation-type, metric-type, constraint, flag, or Sub-TLV that is 445 not supported by the node, it MUST stop participating in such 446 Flexible-Algorithm. That implies that it MUST NOT announce 447 participation for such Flexible-Algorithm as specified in Section 11 448 and it MUST remove any forwarding state associated with it. 450 Flex-Algorithm definition is topology independent. It applies to all 451 topologies that a router participates in. 453 6. Sub-TLVs of ISIS FAD Sub-TLV 455 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV 457 The Flexible Algorithm definition can specify 'colors' that are used 458 by the operator to exclude links during the Flex-Algorithm path 459 computation. 461 The ISIS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 462 advertise the exclude rule that is used during the Flex-Algorithm 463 path calculation as specified in Section 13. 465 The ISIS Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub- 466 TLV) is a Sub-TLV of the ISIS FAD Sub-TLV. It has the following 467 format: 469 0 1 2 3 470 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 1 471 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 472 | Type | Length | 473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 474 | Extended Admin Group | 475 +- -+ 476 | ... | 477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 478 where: 480 Type: 1 482 Length: variable, dependent on the size of the Extended Admin 483 Group. MUST be a multiple of 4 octets. 485 Extended Administrative Group: Extended Administrative Group as 486 defined in [RFC7308]. 488 The ISIS FAEAG Sub-TLV MUST NOT appear more then once in an ISIS FAD 489 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 490 ignored by the receiver. 492 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV 494 The Flexible Algorithm definition can specify 'colors' that are used 495 by the operator to include links during the Flex-Algorithm path 496 computation. 498 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used 499 to advertise include-any rule that is used during the Flex-Algorithm 500 path calculation as specified in Section 13. 502 The format of the ISIS Flexible Algorithm Include-Any Admin Group 503 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 504 Section 6.1. 506 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 507 2. 509 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 510 appear more then once in an ISIS FAD Sub-TLV. If it appears more 511 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 513 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV 515 The Flexible Algorithm definition can specify 'colors' that are used 516 by the operator to include link during the Flex-Algorithm path 517 computation. 519 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used 520 to advertise include-all rule that is used during the Flex-Algorithm 521 path calculation as specified in Section 13. 523 The format of the ISIS Flexible Algorithm Include-All Admin Group 524 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 525 Section 6.1. 527 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 528 3. 530 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 531 appear more then once in an ISIS FAD Sub-TLV. If it appears more 532 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 534 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV 536 The ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 537 is a Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 539 0 1 2 3 540 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 1 541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 542 | Type | Length | 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 544 | Flags | 545 +- -+ 546 | ... | 547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 548 where: 550 Type: 4 552 Length: variable, non-zero number of octets of the Flags field 554 Flags: 556 0 1 2 3 4 5 6 7... 557 +-+-+-+-+-+-+-+-+... 558 |M| | | ... 559 +-+-+-+-+-+-+-+-+... 561 M-flag: when set, the Flex-Algorithm specific prefix metric 562 MUST be used, if advertised with the prefix. This flag is not 563 applicable to prefixes advertised as SRv6 locators. 565 Bits are defined/sent starting with Bit 0 defined above. Additional 566 bit definitions that may be defined in the future SHOULD be assigned 567 in ascending bit order so as to minimize the number of bits that will 568 need to be transmitted. 570 Undefined bits MUST be transmitted as 0. 572 Bits that are NOT transmitted MUST be treated as if they are set to 0 573 on receipt. 575 The ISIS FADF Sub-TLV MUST NOT appear more then once in an ISIS FAD 576 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 577 ignored by the receiver. 579 If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV, 580 all the bits are assumed to be set to 0. 582 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV 584 The Flexible Algorithm definition can specify Shared Risk Link Groups 585 (SRLGs) that the operator wants to exclude during the Flex-Algorithm 586 path computation. 588 The ISIS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used to 589 advertise the exclude rule that is used during the Flex-Algorithm 590 path calculation as specified in Section 13. 592 The ISIS FAESRLG Sub-TLV is a Sub-TLV of the ISIS FAD Sub-TLV. It 593 has the following format: 595 0 1 2 3 596 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 1 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 | Type | Length | 599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 600 | Shared Risk Link Group Value | 601 +- -+ 602 | ... | 603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 where: 606 Type: 5 607 Length: variable, dependent on number of SRLG values. MUST be a 608 multiple of 4 octets. 610 Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. 612 The ISIS FAESRLG Sub-TLV MUST NOT appear more then once in an ISIS 613 FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST 614 be ignored by the receiver. 616 7. Sub-TLVs of OSPF FAD TLV 618 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 620 The Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is 621 a Sub-TLV of the OSPF FAD TLV. It's usage is described in 622 Section 6.1. It has the following format: 624 0 1 2 3 625 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 1 626 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 627 | Type | Length | 628 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 629 | Extended Admin Group | 630 +- -+ 631 | ... | 632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 633 where: 635 Type: 1 637 Length: variable, dependent on the size of the Extended Admin 638 Group. MUST be a multiple of 4 octets. 640 Extended Administrative Group: Extended Administrative Group as 641 defined in [RFC7308]. 643 The OSPF FAEAG Sub-TLV MUST NOT appear more then once in an OSPF FAD 644 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 645 by the receiver. 647 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 649 The usage of this Sub-TLVs is described in Section 6.2. 651 The format of the OSPF Flexible Algorithm Include-Any Admin Group 652 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 653 Section 7.1. 655 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 656 2. 658 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 659 appear more then once in an OSPF FAD TLV. If it appears more then 660 once, the OSPF FAD TLV MUST be ignored by the receiver. 662 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 664 The usage of this Sub-TLVs is described in Section 6.3. 666 The format of the OSPF Flexible Algorithm Include-Any Admin Group 667 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 668 Section 7.1. 670 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 671 3. 673 The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 674 appear more then once in an OSPF FAD TLV. If it appears more then 675 once, the OSPF FAD TLV MUST be ignored by the receiver. 677 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 679 The OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 680 is a Sub-TLV of the OSPF FAD TLV. It has the following format: 682 0 1 2 3 683 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 1 684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 685 | Type | Length | 686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 | Flags | 688 +- -+ 689 | ... | 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 691 where: 693 Type: 4 695 Length: variable, dependent on the size of the Flags field. MUST 696 be a multiple of 4 octets. 698 Flags: 700 0 1 2 3 4 5 6 7... 701 +-+-+-+-+-+-+-+-+... 702 |M| | | ... 703 +-+-+-+-+-+-+-+-+... 705 M-flag: when set, the Flex-Algorithm specific prefix metric 706 MUST be used, if advertised with the prefix. This flag is not 707 applicable to prefixes advertised as SRv6 locators. 709 Bits are defined/sent starting with Bit 0 defined above. Additional 710 bit definitions that may be defined in the future SHOULD be assigned 711 in ascending bit order so as to minimize the number of bits that will 712 need to be transmitted. 714 Undefined bits MUST be transmitted as 0. 716 Bits that are NOT transmitted MUST be treated as if they are set to 0 717 on receipt. 719 The OSPF FADF Sub-TLV MUST NOT appear more then once in an OSPF FAD 720 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 721 by the receiver. 723 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 724 the bits are assumed to be set to 0. 726 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV 728 The OSPF Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG Sub-TLV) is 729 a Sub-TLV of the OSPF FAD TLV. Its usage is described in 730 Section 6.5. It has the following format: 732 0 1 2 3 733 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 1 734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 735 | Type | Length | 736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 737 | Shared Risk Link Group Value | 738 +- -+ 739 | ... | 740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 741 where: 743 Type: 5 745 Length: variable, dependent on the number of SRLGs. MUST be a 746 multiple of 4 octets. 748 Shared Risk Link Group Value: SRLG value as defined in [RFC4203]. 750 The OSPF FAESRLG Sub-TLV MUST NOT appear more then once in an OSPF 751 FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be 752 ignored by the receiver. 754 8. ISIS Flexible Algorithm Prefix Metric Sub-TLV 756 The ISIS Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the 757 advertisement of a Flex-Algorithm specific prefix metric associated 758 with a given prefix advertisement. 760 The ISIS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 and 761 has the following format: 763 0 1 2 3 764 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 1 765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 766 | Type | Length |Flex-Algorithm | 767 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 768 | Metric | 769 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 770 where: 772 Type: 6 774 Length: 5 octets 776 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 778 Metric: 4 octets of metric information 780 The ISIS FAPM Sub-TLV MAY appear multiple times in its parent TLV. 781 If it appears more then once with the same Flex-Algorithm value, the 782 first instance MUST be used and any subsequent instances MUST be 783 ignored. 785 If a prefix is advertised with a Flex-Algorithm prefix metric larger 786 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 787 considered during the Flexible-Algorithm computation. 789 The usage of the Flex-Algorithm prefix metric is described in 790 Section 13. 792 The ISIS FAPM Sub-TLV MUST NOT be advertised as a sub-TLV of the ISIS 793 SRv6 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. The ISIS SRv6 794 Locator TLV includes the Algorithm and Metric fields which MUST be 795 used instead. If the FAPM Sub-TLV is present as a sub-TLV of the 796 ISIS SRv6 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be 797 ignored. 799 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV 801 The OSPF Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the 802 advertisement of a Flex-Algorithm specific prefix metric associated 803 with a given prefix advertisement. 805 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV is a Sub-TLV of 806 the: 808 - OSPFv2 Extended Prefix TLV [RFC7684] 810 - Following OSPFv3 TLVs as defined in [RFC8362]: 812 Intra-Area Prefix TLV 814 Inter-Area Prefix TLV 816 External Prefix TLV 818 OSPF FAPM Sub-TLV has the following format: 820 0 1 2 3 821 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 1 822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 823 | Type | Length | 824 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 825 |Flex-Algorithm | Flags | Reserved | 826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 827 | Metric | 828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 830 where: 832 Type: 3 for OSPFv2, 26 for OSPFv3 834 Length: 8 octets 836 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 838 Flags: single octet value 840 0 1 2 3 4 5 6 7 841 +-+-+-+-+-+-+-+-+ 842 |E| | 843 +-+-+-+-+-+-+-+-+ 845 E bit : position 0: The type of external metric. If bit is 846 set, the metric specified is a Type 2 external metric. This 847 bit is applicable only to OSPF External and NSSA external 848 prefixes. This is semantically the same as E bit in section 849 A.4.5 of [RFC2328] and section A.4.7 of [RFC5340] for OSPFv2 850 and OSPFv3 respectively. 852 Bits 1 through 7: MUST be cleared by sender and ignored by 853 receiver. 855 Reserved: Must be set to 0, ignored at reception. 857 Metric: 4 octets of metric information 859 The OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. 860 If it appears more then once with the same Flex-Algorithm value, the 861 first instance MUST be used and any subsequent instances MUST be 862 ignored. 864 The usage of the Flex-Algorithm prefix metric is described in 865 Section 13. 867 10. OSPF Flexible Algorithm ASBR Reachability Advertisement 869 An OSPF ABR advertises the reachability of ASBRs in its attached 870 areas to enable routers within that area to perform route 871 calculations for external prefixes advertised by the ASBRs. OSPF 872 extensions for advertisement of Flex-Algorithm specific reachability 873 and metric for ASBRs is similarly required for Flex-Algorithm 874 external prefix computations as described further in Section 13.1. 876 10.1. OSPFv2 Extended Inter-Area ASBR LSA 878 The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) LSA is an OSPF Opaque 879 LSA [RFC5250] that is used to advertise additional attributes related 880 to the reachability of the OSPFv2 ASBR that is external to the area 881 yet internal to the OSPF domain. Semantically, the OSPFv2 EIA-ASBR 882 LSA is equivalent to the fixed format Type 4 Summary LSA [RFC2328]. 883 Unlike the Type 4 Summary LSA, the LSID of the EIA-ASBR LSA does not 884 carry the ASBR Router-ID - the ASBR Router-ID is carried in the body 885 of the LSA. OSPFv2 EIA-ASBR LSA is advertised by an OSPFv2 ABR and 886 its flooding is defined to be area-scoped only. 888 An OSPFv2 ABR MUST NOT advertise the EIA-ASBR LSA for an ASBR for 889 which it is not advertising the Type 4 Summary LSA. The OSPFv2 EIA- 890 ASBR LSA MUST be ignored by an OSPFv2 router in the absence of the 891 Type 4 Summary LSA for that ASBR from the same advertising ABR. 893 The OSPFv2 EIA-ASBR LSA has the following format: 895 0 1 2 3 896 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 1 897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 898 | LS age | Options | LS Type | 899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 900 | Opaque Type | Opaque ID | 901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 902 | Advertising Router | 903 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 904 | LS sequence number | 905 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 906 | LS checksum | Length | 907 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 908 | | 909 +- TLVs -+ 910 | ... | 912 The Opaque Type used by the OSPFv2 EIA-ASBR LSA is TBD (suggested 913 value 11). The Opaque Type is used to differentiate the various 914 types of OSPFv2 Opaque LSAs and is described in Section 3 of 915 [RFC5250]. The LS Type MUST be 10, indicating that the Opaque LSA 916 flooding scope is area-local [RFC5250]. The LSA Length field 917 [RFC2328] represents the total length (in octets) of the Opaque LSA, 918 including the LSA header and all TLVs (including padding). 920 The Opaque ID field is an arbitrary value used to maintain multiple 921 OSPFv2 EIA-ASBR LSAs. For OSPFv2 EIA-ASBR LSAs, the Opaque ID has no 922 semantic significance other than to differentiate OSPFv2 EIA-ASBR 923 LSAs originated by the same OSPFv2 ABR. If multiple OSPFv2 EIA-ASBR 924 LSAs specify the same ASBR, the attributes from the Opaque LSA with 925 the lowest Opaque ID SHOULD be used. 927 The format of the TLVs within the body of the OSPFv2 EIA-ASBR LSA is 928 the same as the format used by the Traffic Engineering Extensions to 929 OSPFv2 [RFC3630]. The variable TLV section consists of one or more 930 nested TLV tuples. Nested TLVs are also referred to as sub- TLVs. 931 The Length field defines the length of the value portion in octets 932 (thus, a TLV with no value portion would have a length of 0). The 933 TLV is padded to 4-octet alignment; padding is not included in the 934 Length field (so a 3-octet value would have a length of 3, but the 935 total size of the TLV would be 8 octets). Nested TLVs are also 936 32-bit aligned. For example, a 1-byte value would have the Length 937 field set to 1, and 3 octets of padding would be added to the end of 938 the value portion of the TLV. The padding is composed of zeros. 940 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV 942 The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) TLV is a top-level TLV 943 of the OSPFv2 EIA-ASBR LSA and is used to advertise additional 944 attributes associated with the reachability of an ASBR. 946 The OSPFv2 EIA-ASBR TLV has the following format: 948 0 1 2 3 949 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 1 950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 951 | Type | Length | 952 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 953 | ASBR Router ID | 954 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 955 . . 956 . Sub-TLVs . 957 . . 958 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 960 where: 962 Type: 1 964 Length: variable 966 ASBR Router ID: four octets carrying the OSPF Router ID of the 967 ASBR whose information is being carried. 969 Sub-TLVs : variable 971 Only a single OSPFv2 EIA-ASBR TLV MUST be advertised in each OSPFv2 972 EIA-ASBR LSA and the receiver MUST ignore all instances of this TLV 973 other than the first one in an LSA. 975 OSPFv2 EIA-ASBR TLV MUST be present inside the OSPFv2 EIA-ASBR LSA. 976 If the OSPFv2 EIA-ASBR TLV is not present inside the OSPFv2 EIA-ASBR 977 LSA, the OSPFv2 EIA-ASBR MUST be ignored by the receiver. 979 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV 981 The OSPF Flexible Algorithm ASBR Metric (FAAM) Sub-TLV supports the 982 advertisement of a Flex-Algorithm specific metric associated with a 983 given ASBR reachability advertisement by an ABR. 985 The OSPF Flex-Algorithm ASBR Metric (FAAM) Sub-TLV is a Sub-TLV of 986 the: 988 - OSPFv2 Extended Inter-Area ASBR TLV as defined in Section 10.1.1 990 - OSPFv3 Inter-Area-Router TLV defined in [RFC8362] 992 OSPF FAAM Sub-TLV has the following format: 994 0 1 2 3 995 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 1 996 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 997 | Type | Length | 998 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 999 |Flex-Algorithm | Reserved | 1000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1001 | Metric | 1002 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1004 where: 1006 Type: 1 for OSPFv2, TBD (suggested value 28) for OSPFv3 1008 Length: 8 octets 1010 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 1012 Reserved: Must be set to 0, ignored at reception. 1014 Metric: 4 octets of metric information 1016 The OSPF FAAM Sub-TLV MAY appear multiple times in its parent TLV. 1017 If it appears more then once with the same Flex-Algorithm value, the 1018 first instance MUST be used and any subsequent instances MUST be 1019 ignored. 1021 The OSPF Flex-Algorithm ASBR metric is used by the ABR to advertise 1022 its reachability and its Flex-Algorithm specific metric towards the 1023 specific ASBR. This metric is used during the Flex-Algorithm 1024 specific route calculation for external and NSSA external OSPF 1025 prefixes by OSPF routers. It is similar to how the metric in the 1026 Type 4 Summary LSA for OSPFv2 and in the E-Inter-Area-Router LSA for 1027 OSPFv3 are used for the external and NSSA external route calculation. 1028 More details on the usage of the Flex-Algorithm ASBR metric can be 1029 found in Section 13.1. 1031 10.3. OSPFv2 EIA-ASBR LSA Advertisement and Processing 1033 OSPFv2 EIA-ASBR LSA is used by OSPFv2 ABR to advertise reachability 1034 of the ASBR between areas in the context of the specific Flex- 1035 Algorithm(s). 1037 OSPFv2 EIA-ASBR LSA MUST be used by ABR to advertise reachability of 1038 the ASBR between areas for those Flex-Algorithm(s) for which the 1039 winning FAD(s) includes the M-flag. 1041 OSPFv2 EIA-ASBR LSA MUST NOT be used by ABR to advertised the 1042 reachability of the ASBR for those Flex-Algorithm(s) for which the 1043 winning FAD(s) does not include the M-flag. 1045 Any previously generated OSPFv2 EIA-ASBR LSAs originated by the ABR 1046 MUST be flushed by the ABR if there is no more Flex-algorithm(s), in 1047 which the ABR participates, for which the winning FAD includes the 1048 M-flag. 1050 The advertisement of the ASBR reachability inside the OSPFv2 EIA-ASBR 1051 LSA follows the section 12.4.3. of [RFC2328]. The reachability of 1052 the ASBR is evaluated in the context of the specific Flex-Algorithm. 1054 OSPFv2 router MUST use the OSPFv2 EIA-ASBR LSAs to calculate the 1055 reachability of the ASBRs if the winning FAD for the specific Flex- 1056 Algorithm includes the M-flag. 1058 OSPFv2 router MUST NOT use the OSPFv2 EIA-ASBR LSAs to calculate the 1059 reachability of the ASBRs for the specific Flex-Algorithm if the 1060 winning FAD for such Flex-Algorithm does not include the M-flag. 1061 Type 4 Summary LSAs MUST be used instead as specified in section 1062 16.2. of [RFC2328]. 1064 The processing of the new or changed OSPFv2 EIA-ASBR LSA triggers the 1065 processing of the External routes similar to what is described in 1066 section 16.5. of the [RFC2328]. The External route calculation 1067 should be limited to Flex-Algorithm(s) for which the winning FAD(s) 1068 includes the M-flag. 1070 Processing of the OSPFv2 EIA-ASBR LSA does not require the existence 1071 of the equivalent Type 4 Summary LSA advertised the same ABR inside 1072 the area. When the OSPFv2 EIA-ASBR LSA is advertised by the ABR for 1073 a specific ASBR, it is expected that the same ABR would advertise the 1074 reachability of the same ASBR in the equivalent Type 4 Summary LSA. 1075 The presence of such Type 4 Summary LSA is not mandatory for the 1076 usage of the OSPFv2 EIA-ASBR LSA. This means that the order in which 1077 these LSAs are received is not significant. 1079 11. Advertisement of Node Participation in a Flex-Algorithm 1081 When a router is configured to support a particular Flex-Algorithm, 1082 we say it is participating in that Flex-Algorithm. 1084 Paths computed for a specific Flex-Algorithm MAY be used by various 1085 applications, each potentially using its own specific data plane for 1086 forwarding traffic over such paths. To guarantee the presence of the 1087 application specific forwarding state associated with a particular 1088 Flex-Algorithm, a router MUST advertise its participation for a 1089 particular Flex-Algorithm for each application specifically. 1091 11.1. Advertisement of Node Participation for Segment Routing 1093 [RFC8667], [RFC8665], and [RFC8666] (IGP Segment Routing extensions) 1094 describe how the SR-Algorithm is used to compute the IGP best path. 1096 Routers advertise the support for the SR-Algorithm as a node 1097 capability as described in the above mentioned IGP Segment Routing 1098 extensions. To advertise participation for a particular Flex- 1099 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 1100 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 1101 (OSPF) or sub-TLV (ISIS). 1103 Segment Routing Flex-Algorithm participation advertisement is 1104 topology independent. When a router advertises participation in an 1105 SR-Algorithm, the participation applies to all topologies in which 1106 the advertising node participates. 1108 11.2. Advertisement of Node Participation for Other Applications 1110 This section describes considerations related to how other 1111 applications can advertise their participation in a specific Flex- 1112 Algorithm. 1114 Application-specific Flex-Algorithm participation advertisements MAY 1115 be topology specific or MAY be topology independent, depending on the 1116 application itself. 1118 Application-specific advertisement for Flex-Algorithm participation 1119 MUST be defined for each application and is outside of the scope of 1120 this document. 1122 12. Advertisement of Link Attributes for Flex-Algorithm 1124 Various link attributes may be used during the Flex-Algorithm path 1125 calculation. For example, include or exclude rules based on link 1126 affinities can be part of the Flex-Algorithm definition as defined in 1127 Section 6 and Section 7. 1129 Link attribute advertisements that are to be used during Flex- 1130 Algorithm calculation MUST use the Application-Specific Link 1131 Attribute (ASLA) advertisements defined in [RFC8919] or [RFC8920], 1132 unless, in the case of IS-IS, the L-Flag is set in the ASLA 1133 advertisement. If the L-Flag is set, as defined in [RFC8919] 1134 Section 4.2 subject to the constraints discussed in Section 6 of the 1135 [[RFC8919], then legacy advertisements are to be used instead. 1137 The mandatory use of ASLA advertisements applies to link attributes 1138 specifically mentioned in this document (Min Unidirectional Link 1139 Delay, TE Default Metric, Administrative Group, Extended 1140 Administrative Group and Shared Risk Link Group) and any other link 1141 attributes that may be used in support of Flex-Algorithm in the 1142 future. 1144 A new Application Identifier Bit is defined to indicate that the ASLA 1145 advertisement is associated with the Flex-Algorithm application. 1146 This bit is set in the Standard Application Bit Mask (SABM) defined 1147 in [RFC8919] or [RFC8920]: 1149 Bit-3: Flexible Algorithm (X-bit) 1151 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 1152 Application MAY use either the Administrative Group or Extended 1153 Administrative Group encodings. If the Administrative Group encoding 1154 is used, then the first 32 bits of the corresponding FAD sub-TLVs are 1155 mapped to the link attribute advertisements as specified in RFC 7308. 1157 13. Calculation of Flexible Algorithm Paths 1159 A router MUST be configured to participate in a given Flex-Algorithm 1160 K and MUST select the FAD based on the rules defined in Section 5.3 1161 before it can compute any path for that Flex-Algorithm. 1163 As described in Section 11, participation for any particular Flex- 1164 Algorithm MUST be advertised on a per-application basis. Calculation 1165 of the paths for any particular Flex-Algorithm MUST be application 1166 specific. 1168 The way applications handle nodes that do not participate in 1169 Flexible-Algorithm is application specific. If the application only 1170 wants to consider participating nodes during the Flex-Algorithm 1171 calculation, then when computing paths for a given Flex-Algorithm, 1172 all nodes that do not advertise participation for that Flex-Algorithm 1173 in their application-specific advertisements MUST be pruned from the 1174 topology. Segment Routing, including both SR MPLS and SRv6, are 1175 applications that MUST use such pruning when computing Flex-Algorithm 1176 paths. 1178 When computing the path for a given Flex-Algorithm, the metric-type 1179 that is part of the Flex-Algorithm definition (Section 5) MUST be 1180 used. 1182 When computing the path for a given Flex-Algorithm, the calculation- 1183 type that is part of the Flex-Algorithm definition (Section 5) MUST 1184 be used. 1186 Various link include or exclude rules can be part of the Flex- 1187 Algorithm definition. To refer to a particular bit within an AG or 1188 EAG we uses term 'color'. 1190 Rules, in the order as specified below, MUST be used to prune links 1191 from the topology during the Flex-Algorithm computation. 1193 For all links in the topology: 1195 1. Check if any exclude rule is part of the Flex-Algorithm 1196 definition. If such exclude rule exists, check if any color that 1197 is part of the exclude rule is also set on the link. If such a 1198 color is set, the link MUST be pruned from the computation. 1200 2. Check if any exclude SRLG rule is part of the Flex-Algorithm 1201 definition. If such exclude rule exists, check if the link is 1202 part of any SRLG that is also part of the SRLG exclude rule. If 1203 the link is part of such SRLG, the link MUST be pruned from the 1204 computation. 1206 3. Check if any include-any rule is part of the Flex-Algorithm 1207 definition. If such include-any rule exists, check if any color 1208 that is part of the include-any rule is also set on the link. If 1209 no such color is set, the link MUST be pruned from the 1210 computation. 1212 4. Check if any include-all rule is part of the Flex-Algorithm 1213 definition. If such include-all rule exists, check if all colors 1214 that are part of the include-all rule are also set on the link. 1215 If all such colors are not set on the link, the link MUST be 1216 pruned from the computation. 1218 5. If the Flex-Algorithm definition uses other than IGP metric 1219 (Section 5), and such metric is not advertised for the particular 1220 link in a topology for which the computation is done, such link 1221 MUST be pruned from the computation. A metric of value 0 MUST NOT 1222 be assumed in such case. 1224 13.1. Multi-area and Multi-domain Considerations 1226 Any IGP Shortest Path Tree calculation is limited to a single area. 1227 This applies to Flex-Algorithm calculations as well. Given that the 1228 computing router does not have visibility of the topology of the next 1229 areas or domain, the Flex-Algorithm specific path to an inter-area or 1230 inter-domain prefix will be computed for the local area only. The 1231 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 1232 will be selected based on the best path for the given Flex-Algorithm 1233 in the local area and such egress ABR or ASBR router will be 1234 responsible to compute the best Flex-Algorithm specific path over the 1235 next area or domain. This may produce an end-to-end path, which is 1236 sub-optimal based on Flex-Algorithm constraints. In cases where the 1237 ABR or ASBR has no reachability to a prefix for a given Flex- 1238 Algorithm in the next area or domain, the traffic may be dropped by 1239 the ABR/ASBR. 1241 To allow the optimal end-to-end path for an inter-area or inter- 1242 domain prefix for any Flex-Algorithm to be computed, the FAPM has 1243 been defined in Section 8 and Section 9. For external route 1244 calculation for prefixes originated by ASBRs in remote areas in OSPF, 1245 the FAAM has been defined in Section 10.2 for the ABR to indicate its 1246 ASBR reachability along with the metric for the specific Flex- 1247 Algorithm. 1249 If the FAD selected based on the rules defined in Section 5.3 1250 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 1251 Section 9) when advertising the prefix between areas or domains. 1252 Such metric will be equal to the metric to reach the prefix for a 1253 given Flex-Algorithm in a source area or domain. This is similar in 1254 nature to how the metric is set when prefixes are advertised between 1255 areas or domains for the default algorithm. 1257 In the case of OSPF, where the winning FAD includes the M-flag, an 1258 ABR MUST include the FAAM (Section 10.2) when advertising the ASBR 1259 reachability between areas. Such metric will be equal to the metric 1260 to reach the ASBR for a given Flex-Algorithm in a source area or the 1261 cumulative metric via ABR(s) when the ASBR is in a remote area. This 1262 is similar in nature to how the metric is set when ASBR reachability 1263 is advertised between areas for the default algorithm using the 1264 OSPFv2 Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. 1266 If the FAD selected based on the rules defined in Section 5.3 1267 includes the M-flag, the FAPM MUST be used during calculation of 1268 prefix reachability for the inter-area and external prefixes. If the 1269 FAPM for the Flex-Algorithm is not advertised with the inter-area or 1270 external prefix reachability advertisement, the prefix MUST be 1271 considered as unreachable for that Flex-Algorithm. This also applies 1272 to the FAAM for OSPF external prefix computation. 1274 Flex-Algorithm prefix metrics and the OSPF Flex-Algorithm ASBR 1275 metrics MUST NOT be used during the Flex-Algorithm computation unless 1276 the FAD selected based on the rules defined in Section 5.3 includes 1277 the M-Flag, as described in (Section 6.4 or Section 7.4). 1279 If the FAD selected based on the rules defined in Section 5.3 does 1280 not includes the M-flag, then the IGP metrics used by the base ISIS 1281 and OSPF protocol MUST be used for the Flex-Algorithm route 1282 computation. 1284 It is NOT RECOMMENDED to use the Flex-Algorithm for inter-area or 1285 inter-domain prefix reachability without the M-flag set. The reason 1286 is that without the explicit Flex-Algorithm Prefix Metric 1287 advertisement (and the Flex-Algorithm ASBR metric advertisement in 1288 the case of OSPF external route calculation), it is not possible to 1289 conclude whether the ABR or ASBR has reachability to the inter-area 1290 or inter-domain prefix for a given Flex-Algorithm in the next area or 1291 domain. Sending the Flex-Algoritm traffic for such prefix towards 1292 the ABR or ASBR may result in traffic looping or black-holing. 1294 During the route computation, it is possible for the Flex-Algorithm 1295 specific metric to exceed the maximum value that can be stored in an 1296 unsigned 32-bit variable. In such scenarios, the value MUST be 1297 considered to be of value 4,294,967,295 during the computation and 1298 advertised as such. 1300 The FAPM MUST NOT be advertised with ISIS L1 or L2 intra-area, OSPFv2 1301 intra-area, or OSPFv3 intra-area routes. If the FAPM is advertised 1302 for these route-types, it MUST be ignored during the prefix 1303 reachability calculation. 1305 The M-flag in FAD is not applicable to prefixes advertised as SRv6 1306 locators. The ISIS SRv6 Locator TLV 1307 [I-D.ietf-lsr-isis-srv6-extensions] and the OSPFv3 SRv6 Locator TLV 1308 [I-D.ietf-lsr-ospfv3-srv6-extensions] include the Algorithm and 1309 Metric fields. When the SRv6 Locator is advertised between areas or 1310 domains, the metric field in the respective Locator TLVs of ISIS and 1311 OSPFv3 MUST be used irrespective of the M-flag in the FAD 1312 advertisement. 1314 OSPF external and NSSA external prefix advertisements MAY include a 1315 non-zero forwarding address in the prefix advertisements in the base 1316 protocol. In such a scenario, the Flex-Algorithm specific 1317 reachability of the external prefix is determined by Flex-Algorithm 1318 specific reachability of the forwarding address. 1320 14. Flex-Algorithm and Forwarding Plane 1322 This section describes how Flex-Algorithm paths are used in 1323 forwarding. 1325 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm 1327 This section describes how Flex-Algorithm paths are used with SR MPLS 1328 forwarding. 1330 Prefix SID advertisements include an SR-Algorithm value and, as such, 1331 are associated with the specified SR-Algorithm. Prefix-SIDs are also 1332 associated with a specific topology which is inherited from the 1333 associated prefix reachability advertisement. When the algorithm 1334 value advertised is a Flex-Algorithm value, the Prefix SID is 1335 associated with paths calculated using that Flex-Algorithm in the 1336 associated topology. 1338 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 1339 using the MPLS label that corresponds to the Prefix-SID that was 1340 advertised for that Flex-algorithm. If the Prefix SID for a given 1341 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 1342 be installed in the MPLS forwarding plane. 1344 Traffic that is supposed to be routed via Flex-Algorithm specific 1345 paths, MUST be dropped when there are no such paths available. 1347 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 1348 computed using the same constraints as the calculation of the primary 1349 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 1350 advertised specifically for the given algorithm. LFA paths MUST NOT 1351 use an Adjacency-SID that belongs to a link that has been pruned from 1352 the Flex-Algorithm computation. 1354 If LFA protection is being used to protect a given Flex-Algorithm 1355 paths, all routers in the area participating in the given Flex- 1356 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 1357 SID. These Node-SIDs are used to steer traffic over the LFA computed 1358 backup path. 1360 14.2. SRv6 Forwarding for Flex-Algorithm 1362 This section describes how Flex-Algorithm paths are used with SRv6 1363 forwarding. 1365 In SRv6 a node is provisioned with topology/algorithm specific 1366 locators for each of the topology/algorithm pairs supported by that 1367 node. Each locator is an aggregate prefix for all SIDs provisioned 1368 on that node which have the matching topology/algorithm. 1370 The SRv6 locator advertisement in IGPs 1371 ([I-D.ietf-lsr-isis-srv6-extensions] 1372 [I-D.ietf-lsr-ospfv3-srv6-extensions]) includes the MTID value that 1373 associates the locator with a specific topology. SRv6 locator 1374 advertisements also includes an Algorithm value that explicitly 1375 associates the locator with a specific algorithm. When the algorithm 1376 value advertised with a locator represents a Flex-Algorithm, the 1377 paths to the locator prefix MUST be calculated using the specified 1378 Flex-Algorithm in the associated topology. 1380 Forwarding entries for the locator prefixes advertised in IGPs MUST 1381 be installed in the forwarding plane of the receiving SRv6 capable 1382 routers when the associated topology/algorithm is participating in 1383 them. Forwarding entries for locators associated with Flex- 1384 Algorithms in which the node is not participating MUST NOT be 1385 installed in the forwarding plane. 1387 When the locator is associated with a Flex-Algorithm, LFA paths to 1388 the locator prefix MUST be calculated using such Flex-Algorithm in 1389 the associated topology, to guarantee that they follow the same 1390 constraints as the calculation of the primary paths. LFA paths MUST 1391 only use SRv6 SIDs advertised specifically for the given Flex- 1392 Algorithm. 1394 If LFA protection is being used to protect locators associated with a 1395 given Flex-Algorithm, all routers in the area participating in the 1396 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1397 specific locator and END SID per node and one END.X SID for every 1398 link that has not been pruned from such Flex-Algorithm computation. 1399 These locators and SIDs are used to steer traffic over the LFA- 1400 computed backup path. 1402 14.3. Other Applications' Forwarding for Flex-Algorithm 1404 Any application that wants to use Flex-Algorithm specific forwarding 1405 needs to install some form of Flex-Algorithm specific forwarding 1406 entries. 1408 Application-specific forwarding for Flex-Algorithm MUST be defined 1409 for each application and is outside of the scope of this document. 1411 15. Operational Considerations 1413 15.1. Inter-area Considerations 1415 The scope of the FA computation is an area, so is the scope of the 1416 FAD. In ISIS, the Router Capability TLV in which the FAD Sub-TLV is 1417 advertised MUST have the S-bit clear, which prevents it to be flooded 1418 outside of the level in which it was originated. Even though in OSPF 1419 the FAD Sub-TLV can be flooded in an RI LSA that has AS flooding 1420 scope, the FAD selection is performed for each individual area in 1421 which it is being used. 1423 There is no requirement for the FAD for a particular Flex-Algorithm 1424 to be identical in all areas in the network. For example, traffic 1425 for the same Flex-Algorithm may be optimized for minimal delay (e.g., 1426 using delay metric) in one area or level, while being optimized for 1427 available bandwidth (e.g., using IGP metric) in another area or 1428 level. 1430 As described in Section 5.1, ISIS allows the re-generation of the 1431 winning FAD from level 2, without any modification to it, into a 1432 level 1 area. This allows the operator to configure the FAD in one 1433 or multiple routers in the level 2, without the need to repeat the 1434 same task in each level 1 area, if the intent is to have the same FAD 1435 for the particular Flex-Algorithm across all levels. This can 1436 similarly be achieved in OSPF by using the AS flooding scope of the 1437 RI LSA in which the FAD Sub-TLV for the particular Flex-Algoritm is 1438 advertised. 1440 Re-generation of FAD from a level 1 area to the level 2 area is not 1441 supported in ISIS, so if the intent is to regenerate the FAD between 1442 ISIS levels, the FAD MUST be defined on router(s) that are in level 1443 2. In OSPF, the FAD definition can be done in any area and be 1444 propagated to all routers in the OSPF routing domain by using the AS 1445 flooding scope of the RI LSA. 1447 15.2. Usage of SRLG Exclude Rule with Flex-Algorithm 1449 There are two different ways in which SRLG information can be used 1450 with Flex-Algorithm: 1452 In a context of a single Flex-Algorithm, it can be used for 1453 computation of backup paths, as described in 1454 [I-D.ietf-rtgwg-segment-routing-ti-lfa]. This usage does not 1455 require association of any specific SRLG constraint with the given 1456 Flex-Algorithm definition. 1458 In the context of multiple Flex-Algorithms, it can be used for 1459 creating disjoint sets of paths by pruning the links belonging to 1460 a specific SRLG from the topology on which a specific Flex- 1461 Algorithm computes its paths. This usage: 1463 Facilitates the usage of already deployed SRLG configurations 1464 for setup of disjoint paths between two or more Flex- 1465 Algorithms. 1467 Requires explicit association of a given Flex-Algorithm with a 1468 specific set of SRLG constraints as defined in Section 6.5 and 1469 Section 7.5. 1471 The two usages mentioned above are orthogonal. 1473 15.3. Max-metric consideration 1475 Both ISIS and OSPF have a mechanism to set the IGP metric on a link 1476 to a value that would make the link either non-reachable or to serve 1477 as the link of last resort. Similar functionality would be needed 1478 for the Min Unidirectional Link Delay and TE metric, as these can be 1479 used to compute Flex-Algorithm paths. 1481 The link can be made un-reachable for all Flex-Algorithms that use 1482 Min Unidirectional Link Delay as metric, as described in Section 5.1, 1483 by removing the Flex-Algorithm ASLA Min Unidirectional Link Delay 1484 advertisement for the link. The link can be made the link of last 1485 resort by setting the delay value in the Flex-Algorithm ASLA delay 1486 advertisement for the link to the value of 16,777,215 (2^24 - 1). 1488 The link can be made un-reachable for all Flex-Algorithms that use TE 1489 metric, as described in Section 5.1, by removing the Flex-Algorithm 1490 ASLA TE metric advertisement for the link. The link can be made the 1491 link of last resort by setting the TE metric value in the Flex- 1492 Algorithm ASLA delay advertisement for the link to the value of (2^24 1493 - 1) in ISIS and (2^32 - 1) in OSPF. 1495 16. Backward Compatibility 1497 This extension brings no new backward compatibility issues. ISIS, 1498 OSPFv2 and OSPFv3 all have well defined handling of unrecognized TLVs 1499 and sub-TLVs that allows the introduction of the new extensions, 1500 similar to those defined here, without introducing any 1501 interoperability issues. 1503 17. Security Considerations 1505 This draft adds two new ways to disrupt IGP networks: 1507 An attacker can hijack a particular Flex-Algorithm by advertising 1508 a FAD with a priority of 255 (or any priority higher than that of 1509 the legitimate nodes). 1511 An attacker could make it look like a router supports a particular 1512 Flex-Algorithm when it actually doesn't, or vice versa. 1514 Both of these attacks can be addressed by the existing security 1515 extensions as described in [RFC5304] and [RFC5310] for ISIS, in 1516 [RFC2328] and [RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] 1517 for OSPFv3. 1519 18. IANA Considerations 1521 18.1. IGP IANA Considerations 1523 18.1.1. IGP Algorithm Types Registry 1525 This document makes the following registrations in the "IGP Algorithm 1526 Types" registry: 1528 Type: 128-255. 1530 Description: Flexible Algorithms. 1532 Reference: This document (Section 4). 1534 18.1.2. IGP Metric-Type Registry 1536 IANA is requested to set up a registry called "IGP Metric-Type 1537 Registry" under an "Interior Gateway Protocol (IGP) Parameters" IANA 1538 registries. The registration policy for this registry is "Standards 1539 Action" ([RFC8126] and [RFC7120]). 1541 Values in this registry come from the range 0-255. 1543 This document registers following values in the "IGP Metric-Type 1544 Registry": 1546 Type: 0 1548 Description: IGP metric 1550 Reference: This document (Section 5.1) 1551 Type: 1 1553 Description: Min Unidirectional Link Delay as defined in 1554 [RFC8570], section 4.2, and [RFC7471], section 4.2. 1556 Reference: This document (Section 5.1) 1558 Type: 2 1560 Description: Traffic Engineering Default Metric as defined in 1561 [RFC5305], section 3.7, and Traffic engineering metric as defined 1562 in [RFC3630], section 2.5.5 1564 Reference: This document (Section 5.1) 1566 18.2. Flexible Algorithm Definition Flags Registry 1568 IANA is requested to set up a registry called "ISIS Flexible 1569 Algorithm Definition Flags Registry" under an "Interior Gateway 1570 Protocol (IGP) Parameters" IANA registries. The registration policy 1571 for this registry is "Standards Action" ([RFC8126] and [RFC7120]). 1573 This document defines the following single bit in Flexible Algorithm 1574 Definition Flags registry: 1576 Bit # Name 1577 ----- ------------------------------ 1578 0 Prefix Metric Flag (M-flag) 1580 Reference: This document (Section 6.4, Section 7.4). 1582 18.3. ISIS IANA Considerations 1584 18.3.1. Sub TLVs for Type 242 1586 This document makes the following registrations in the "sub-TLVs for 1587 TLV 242" registry. 1589 Type: 26. 1591 Description: Flexible Algorithm Definition. 1593 Reference: This document (Section 5.1). 1595 18.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1597 This document makes the following registrations in the "Sub-TLVs for 1598 for TLVs 135, 235, 236, and 237" registry. 1600 Type: 6 1602 Description: Flexible Algorithm Prefix Metric. 1604 Reference: This document (Section 8). 1606 18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1608 This document creates the following Sub-Sub-TLV Registry: 1610 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1612 Registration Procedure: Expert review 1614 Reference: This document (Section 5.1) 1616 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1617 for Flexible Algorithm Definition Sub-TLV" registry: 1619 Type: 1 1621 Description: Flexible Algorithm Exclude Admin Group 1623 Reference: This document (Section 6.1). 1625 Type: 2 1627 Description: Flexible Algorithm Include-Any Admin Group 1629 Reference: This document (Section 6.2). 1631 Type: 3 1633 Description: Flexible Algorithm Include-All Admin Group 1635 Reference: This document (Section 6.3). 1637 Type: 4 1639 Description: Flexible Algorithm Definition Flags 1641 Reference: This document (Section 6.4). 1643 Type: 5 1645 Description: Flexible Algorithm Exclude SRLG 1647 Reference: This document (Section 6.5). 1649 18.4. OSPF IANA Considerations 1651 18.4.1. OSPF Router Information (RI) TLVs Registry 1653 This specification updates the OSPF Router Information (RI) TLVs 1654 Registry. 1656 Type: 16 1658 Description: Flexible Algorithm Definition TLV. 1660 Reference: This document (Section 5.2). 1662 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1664 This document makes the following registrations in the "OSPFv2 1665 Extended Prefix TLV Sub-TLVs" registry. 1667 Type: 3 1669 Description: Flexible Algorithm Prefix Metric. 1671 Reference: This document (Section 9). 1673 18.4.3. OSPFv3 Extended-LSA Sub-TLVs 1675 This document makes the following registrations in the "OSPFv3 1676 Extended-LSA Sub-TLVs" registry. 1678 Type: 26 1680 Description: Flexible Algorithm Prefix Metric. 1682 Reference: This document (Section 9). 1684 Type: TBD (suggested value 28) 1686 Description: OSPF Flexible Algorithm ASBR Metric Sub-TLV 1688 Reference: This document (Section 10.2). 1690 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits 1692 This specification requests creation of "OSPF Flex-Algorithm Prefix 1693 Metric Bits" registry under the OSPF Parameters Registry with the 1694 following initial values. 1696 Bit Number: 0 1698 Description: E bit - External Type 1700 Reference: this document. 1702 The bits 1-7 are unassigned and the registration procedure to be 1703 followed for this registry is IETF Review. 1705 18.4.5. OSPF Opaque LSA Option Types 1707 This document makes the following registrations in the "OSPF Opaque 1708 LSA Option Types" registry. 1710 Value: TBD (suggested value 11) 1712 Description: OSPFv2 Extended Inter-Area ASBR LSA 1714 Reference: This document (Section 10.1). 1716 18.4.6. OSPFv2 Externded Inter-Area ASBR TLVs 1718 This specification requests creation of "OSPFv2 Extended Inter-Area 1719 ASBR TLVs" registry under the OSPFv2 Parameters Registry with the 1720 following initial values. 1722 Value: 1 1724 Description : Extended Inter-Area ASBR TLV 1726 Reference: this document 1728 The values 2 to 32767 are unassigned, values 32768 to 33023 are 1729 reserved for experimental use while the values 0 and 33024 to 65535 1730 are reserved. The registration procedure to be followed for this 1731 registry is IETF Review or IESG Approval. 1733 18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs 1735 This specification requests creation of "OSPFv2 Extended Inter-Area 1736 ASBR Sub-TLVs" registry under the OSPFv2 Parameters Registry with the 1737 following initial values. 1739 Value: 1 1741 Description : OSPF Flexible Algorithm ASBR Metric Sub-TLV 1743 Reference: this document 1745 The values 2 to 32767 are unassigned, values 32768 to 33023 are 1746 reserved for experimental use while the values 0 and 33024 to 65535 1747 are reserved. The registration procedure to be followed for this 1748 registry is IETF Review or IESG Approval. 1750 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1752 This document creates the following registry: 1754 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1756 Registration Procedure: Expert review 1758 Reference: This document (Section 5.2) 1760 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1761 define sub-TLVs at any level of nesting for the Flexible Algorithm 1762 TLV and should be added to the "Open Shortest Path First (OSPF) 1763 Parameters" registries group. New values can be allocated via IETF 1764 Review or IESG Approval. 1766 This document registers following Sub-TLVs in the "TLVs for Flexible 1767 Algorithm Definition TLV" registry: 1769 Type: 1 1771 Description: Flexible Algorithm Exclude Admin Group 1773 Reference: This document (Section 7.1). 1775 Type: 2 1777 Description: Flexible Algorithm Include-Any Admin Group 1779 Reference: This document (Section 7.2). 1781 Type: 3 1783 Description: Flexible Algorithm Include-All Admin Group 1785 Reference: This document (Section 7.3). 1787 Type: 4 1789 Description: Flexible Algorithm Definition Flags 1791 Reference: This document (Section 7.4). 1793 Type: 5 1795 Description: Flexible Algorithm Exclude SRLG 1797 Reference: This document (Section 7.5). 1799 Types in the range 32768-33023 are for experimental use; these will 1800 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1802 Types in the range 33024-65535 are not to be assigned at this time. 1803 Before any assignments can be made in the 33024-65535 range, there 1804 MUST be an IETF specification that specifies IANA Considerations that 1805 covers the range being assigned. 1807 18.4.9. Link Attribute Applications Registry 1809 This document registers following bit in the Link Attribute 1810 Applications Registry: 1812 Bit-3 1814 Description: Flexible Algorithm (X-bit) 1816 Reference: This document (Section 12). 1818 19. Acknowledgements 1820 This draft, among other things, is also addressing the problem that 1821 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1822 All authors of that draft agreed to join this draft. 1824 Thanks to Eric Rosen, Tony Przygienda for their detailed review and 1825 excellent comments. 1827 Thanks to Cengiz Halit for his review and feedback during initial 1828 phase of the solution definition. 1830 Thanks to Kenji Kumaki for his comments. 1832 Thanks to William Britto A J. for his suggestions. 1834 Thanks to Acee Lindem for editorial comments. 1836 20. References 1838 20.1. Normative References 1840 [BCP14] "Key words for use in RFCs to Indicate Requirement 1841 Levels", . 1843 [I-D.ietf-lsr-isis-srv6-extensions] 1844 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1845 Z. Hu, "IS-IS Extension to Support Segment Routing over 1846 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11 1847 (work in progress), October 2020. 1849 [I-D.ietf-lsr-ospfv3-srv6-extensions] 1850 Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, 1851 "OSPFv3 Extensions for SRv6", draft-ietf-lsr- 1852 ospfv3-srv6-extensions-01 (work in progress), August 2020. 1854 [ISO10589] 1855 International Organization for Standardization, 1856 "Intermediate system to Intermediate system intra-domain 1857 routeing information exchange protocol for use in 1858 conjunction with the protocol for providing the 1859 connectionless-mode Network Service (ISO 8473)", ISO/ 1860 IEC 10589:2002, Second Edition, Nov 2002. 1862 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1863 Requirement Levels", BCP 14, RFC 2119, 1864 DOI 10.17487/RFC2119, March 1997, 1865 . 1867 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 1868 Support of Generalized Multi-Protocol Label Switching 1869 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 1870 . 1872 [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The 1873 OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250, 1874 July 2008, . 1876 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1877 in Support of Generalized Multi-Protocol Label Switching 1878 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1879 . 1881 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1882 Traffic Engineering (MPLS-TE)", RFC 7308, 1883 DOI 10.17487/RFC7308, July 2014, 1884 . 1886 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1887 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1888 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1889 2015, . 1891 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1892 S. Shaffer, "Extensions to OSPF for Advertising Optional 1893 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1894 February 2016, . 1896 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1897 for Advertising Router Information", RFC 7981, 1898 DOI 10.17487/RFC7981, October 2016, 1899 . 1901 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1902 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1903 May 2017, . 1905 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1906 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1907 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1908 2018, . 1910 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 1911 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1912 Extensions for Segment Routing", RFC 8665, 1913 DOI 10.17487/RFC8665, December 2019, 1914 . 1916 [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 1917 for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 1918 December 2019, . 1920 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 1921 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 1922 Extensions for Segment Routing", RFC 8667, 1923 DOI 10.17487/RFC8667, December 2019, 1924 . 1926 [RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1927 J. Drake, "IS-IS Application-Specific Link Attributes", 1928 RFC 8919, DOI 10.17487/RFC8919, October 2020, 1929 . 1931 [RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura, 1932 J., and J. Drake, "OSPF Application-Specific Link 1933 Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020, 1934 . 1936 20.2. Informative References 1938 [I-D.gulkohegde-routing-planes-using-sr] 1939 Hegde, S. and a. arkadiy.gulko@thomsonreuters.com, 1940 "Separating Routing Planes using Segment Routing", draft- 1941 gulkohegde-routing-planes-using-sr-00 (work in progress), 1942 March 2017. 1944 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 1945 Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B., 1946 and D. Voyer, "Topology Independent Fast Reroute using 1947 Segment Routing", draft-ietf-rtgwg-segment-routing-ti- 1948 lfa-05 (work in progress), November 2020. 1950 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 1951 DOI 10.17487/RFC2328, April 1998, 1952 . 1954 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering 1955 (TE) Extensions to OSPF Version 2", RFC 3630, 1956 DOI 10.17487/RFC3630, September 2003, 1957 . 1959 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 1960 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 1961 RFC 3906, DOI 10.17487/RFC3906, October 2004, 1962 . 1964 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 1965 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 1966 . 1968 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1969 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1970 2008, . 1972 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 1973 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 1974 2008, . 1976 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 1977 and M. Fanto, "IS-IS Generic Cryptographic 1978 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 1979 2009, . 1981 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 1982 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 1983 . 1985 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 1986 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 1987 2014, . 1989 [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. 1990 Previdi, "OSPF Traffic Engineering (TE) Metric 1991 Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, 1992 . 1994 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 1995 "Security Extension for OSPFv2 When Using Manual Key 1996 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 1997 . 1999 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2000 Writing an IANA Considerations Section in RFCs", BCP 26, 2001 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2002 . 2004 [RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward, 2005 D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) 2006 Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March 2007 2019, . 2009 Authors' Addresses 2011 Peter Psenak (editor) 2012 Cisco Systems 2013 Apollo Business Center 2014 Mlynske nivy 43 2015 Bratislava, 82109 2016 Slovakia 2018 Email: ppsenak@cisco.com 2019 Shraddha Hegde 2020 Juniper Networks, Inc. 2021 Embassy Business Park 2022 Bangalore, KA, 560093 2023 India 2025 Email: shraddha@juniper.net 2027 Clarence Filsfils 2028 Cisco Systems, Inc. 2029 Brussels 2030 Belgium 2032 Email: cfilsfil@cisco.com 2034 Ketan Talaulikar 2035 Cisco Systems, Inc. 2036 S.No. 154/6, Phase I, Hinjawadi 2037 PUNE, MAHARASHTRA 411 057 2038 India 2040 Email: ketant@cisco.com 2042 Arkadiy Gulko 2043 Individual 2045 Email: arkadiy.gulko@gmail.com