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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-18 -- Possible downref: Non-RFC (?) normative reference: ref. '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reference: RFC 8919 (Obsoleted by RFC 9479) ** Obsolete normative reference: RFC 8920 (Obsoleted by RFC 9492) == Outdated reference: A later version (-13) exists of draft-ietf-rtgwg-segment-routing-ti-lfa-07 Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--).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: April 28, 2022 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Edward Jones 11 October 25, 2021 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-18 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 April 28, 2022. 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. IS-IS 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 IS-IS FAD Sub-TLV . . . . . . . . . . . . . . . . 10 71 6.1. IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV . . 10 72 6.2. IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV 11 73 6.3. IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV 12 74 6.4. IS-IS Flexible Algorithm Definition Flags Sub-TLV . . . . 12 75 6.5. IS-IS 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 . 15 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 . . . . . . 17 82 8. IS-IS 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 . . . 20 85 10.1. OSPFv2 Extended Inter-Area ASBR LSA . . . . . . . . . . 20 86 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV . . . . . . . . 22 87 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV . . . . . . 22 88 11. Advertisement of Node Participation in a Flex-Algorithm . . . 24 89 11.1. Advertisement of Node Participation for Segment Routing 25 90 11.2. Advertisement of Node Participation for Other 91 Applications . . . . . . . . . . . . . . . . . . . . . . 25 92 12. Advertisement of Link Attributes for Flex-Algorithm . . . . . 25 93 13. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 26 94 13.1. Multi-area and Multi-domain Considerations . . . . . . . 28 95 14. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 30 96 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 31 97 14.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 31 98 14.3. Other Applications' Forwarding for Flex-Algorithm . . . 32 99 15. Operational Considerations . . . . . . . . . . . . . . . . . 32 100 15.1. Inter-area Considerations . . . . . . . . . . . . . . . 32 101 15.2. Usage of SRLG Exclude Rule with Flex-Algorithm . . . . . 33 102 15.3. Max-metric consideration . . . . . . . . . . . . . . . . 34 103 16. Backward Compatibility . . . . . . . . . . . . . . . . . . . 34 104 17. Security Considerations . . . . . . . . . . . . . . . . . . . 34 105 18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 106 18.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 35 107 18.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 35 108 18.1.2. IGP Metric-Type Registry . . . . . . . . . . . . . . 35 109 18.2. Flexible Algorithm Definition Flags Registry . . . . . . 36 110 18.3. IS-IS IANA Considerations . . . . . . . . . . . . . . . 36 111 18.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 36 112 18.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 36 113 18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 114 TLV . . . . . . . . . . . . . . . . . . . . . . . . 36 115 18.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 37 116 18.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 37 117 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 38 118 18.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 38 119 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits . . . . . . . 38 120 18.4.5. OSPF Opaque LSA Option Types . . . . . . . . . . . . 38 121 18.4.6. OSPFv2 Externded Inter-Area ASBR TLVs . . . . . . . 39 122 18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs . . . . . . . . . . 39 123 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV 124 Registry . . . . . . . . . . . . . . . . . . . . . . 39 125 18.4.9. Link Attribute Applications Registry . . . . . . . . 41 126 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41 127 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 41 128 20.1. Normative References . . . . . . . . . . . . . . . . . . 41 129 20.2. Informative References . . . . . . . . . . . . . . . . . 43 130 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45 132 1. Introduction 134 An IGP-computed path based on the shortest IGP metric is often be 135 replaced by a traffic-engineered path due to the traffic requirements 136 which are not reflected by the IGP metric. Some networks engineer 137 the IGP metric assignments in a way that the IGP metric reflects the 138 link bandwidth or delay. If, for example, the IGP metric is 139 reflecting the bandwidth on the link and the application traffic is 140 delay sensitive, the best IGP path may not reflect the best path from 141 such an application's perspective. 143 To overcome this limitation, various sorts of traffic engineering 144 have been deployed, including RSVP-TE and SR-TE, in which case the TE 145 component is responsible for computing paths based on additional 146 metrics and/or constraints. Such paths need to be installed in the 147 forwarding tables in addition to, or as a replacement for, the 148 original paths computed by IGPs. Tunnels are often used to represent 149 the engineered paths and mechanisms like one described in [RFC3906] 150 are used to replace the native IGP paths with such tunnel paths. 152 This document specifies a set of extensions to IS-IS, OSPFv2, and 153 OSPFv3 that enable a router to advertise TLVs that (a) identify 154 calculation-type, (b) specify a metric-type, and (c) describe a set 155 of constraints on the topology, that are to be used to compute the 156 best paths along the constrained topology. A given combination of 157 calculation-type, metric-type, and constraints is known as a 158 "Flexible Algorithm Definition". A router that sends such a set of 159 TLVs also assigns a Flex-Algorithm value to the specified combination 160 of calculation-type, metric-type, and constraints. 162 This document also specifies a way for a router to use IGPs to 163 associate one or more SR Prefix-SIDs or SRv6 locators with a 164 particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then 165 represents a path that is computed according to the identified Flex- 166 Algorithm. 168 2. Requirements Language 170 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 171 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 172 "OPTIONAL" in this document are to be interpreted as described in BCP 173 14 [RFC2119] [RFC8174] when, and only when, they appear in all 174 capitals, as shown here. 176 3. Terminology 178 This section defines terms that are often used in this document. 180 Flexible Algorithm Definition (FAD) - the set consisting of (a) 181 calculation-type, (b) metric-type, and (c) a set of constraints. 183 Flexible Algorithm - a numeric identifier in the range 128-255 that 184 is associated via configuration with the Flexible-Algorithm 185 Definition. 187 Local Flexible Algorithm Definition - Flexible Algorithm Definition 188 defined locally on the node. 190 Remote Flexible Algorithm Definition - Flexible Algorithm Definition 191 received from other nodes via IGP flooding. 193 Flexible Algorithm Participation - per application configuration 194 state that expresses whether the node is participating in a 195 particular Flexible Algorithm. 197 IGP Algorithm - value from the the "IGP Algorithm Types" registry 198 defined under "Interior Gateway Protocol (IGP) Parameters" IANA 199 registries. IGP Algorithms represents the triplet (Calculation Type, 200 Metric, Constraints), where the second and third elements of the 201 triple MAY be unspecified. 203 ABR - Area Border Router. In IS-IS terminology it is also known as 204 L1/L2 router. 206 ASBR - Autonomous System Border Router. 208 4. Flexible Algorithm 210 Many possible constraints may be used to compute a path over a 211 network. Some networks are deployed as multiple planes. A simple 212 form of constraint may be to use a particular plane. A more 213 sophisticated form of constraint can include some extended metric as 214 described in [RFC8570]. Constraints which restrict paths to links 215 with specific affinities or avoid links with specific affinities are 216 also possible. Combinations of these are also possible. 218 To provide maximum flexibility, we want to provide a mechanism that 219 allows a router to (a) identify a particular calculation-type, (b) 220 metric-type, (c) describe a particular set of constraints, and (d) 221 assign a numeric identifier, referred to as Flex-Algorithm, to the 222 combination of that calculation-type, metric-type, and those 223 constraints. We want the mapping between the Flex-Algorithm and its 224 meaning to be flexible and defined by the user. As long as all 225 routers in the domain have a common understanding as to what a 226 particular Flex-Algorithm represents, the resulting routing 227 computation is consistent and traffic is not subject to any looping. 229 The set consisting of (a) calculation-type, (b) metric-type, and (c) 230 a set of constraints is referred to as a Flexible-Algorithm 231 Definition. 233 Flexible-Algorithm is a numeric identifier in the range 128-255 that 234 is associated via configuratin with the Flexible-Algorithm 235 Definition. 237 IANA "IGP Algorithm Types" registry defines the set of values for IGP 238 Algorithms. We propose to allocate the following values for Flex- 239 Algorithms from this registry: 241 128-255 - Flex-Algorithms 243 5. Flexible Algorithm Definition Advertisement 245 To guarantee the loop-free forwarding for paths computed for a 246 particular Flex-Algorithm, all routers that (a) are configured to 247 participate in a particular Flex-Algorithm, and (b) are in the same 248 Flex-Algorithm definition advertisement scope MUST agree on the 249 definition of the Flex-Algorithm. 251 5.1. IS-IS Flexible Algorithm Definition Sub-TLV 253 The IS-IS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used 254 to advertise the definition of the Flex-Algorithm. 256 The IS-IS FAD Sub-TLV is advertised as a Sub-TLV of the IS-IS Router 257 Capability TLV-242 that is defined in [RFC7981]. 259 IS-IS FAD Sub-TLV has the following format: 261 0 1 2 3 262 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 1 263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 264 | Type | Length |Flex-Algorithm | Metric-Type | 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 | Calc-Type | Priority | 267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 268 | Sub-TLVs | 269 + + 270 | ... | 272 | | 273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 275 where: 277 Type: 26 279 Length: variable, dependent on the included Sub-TLVs 280 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 282 Metric-Type: Type of metric to be used during the calculation. 283 Following values are defined: 285 0: IGP Metric 287 1: Min Unidirectional Link Delay as defined in [RFC8570], 288 section 4.2, encoded as application specific link attribute as 289 specified in [RFC8919] and Section 12 of this document. 291 2: Traffic Engineering Default Metric as defined in [RFC5305], 292 section 3.7, encoded as application specific link attribute as 293 specified in [RFC8919] and Section 12 of this document. 295 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 296 Types" registry defined under "Interior Gateway Protocol (IGP) 297 Parameters" IANA registries. IGP algorithms in the range of 0-127 298 have a defined triplet (Calculation Type, Metric, Constraints). 299 When used to specify the Calc-Type in the FAD Sub-TLV, only the 300 Calculation Type defined for the specified IGP Algorithm is used. 301 The Metric/Constraints MUST NOT be inherited. If the required 302 calculation type is Shortest Path First, the value 0 SHOULD appear 303 in this field. 305 Priority: Value between 0 and 255 inclusive that specifies the 306 priority of the advertisement. 308 Sub-TLVs - optional sub-TLVs. 310 The IS-IS FAD Sub-TLV MAY be advertised in an LSP of any number, but 311 a router MUST NOT advertise more than one IS-IS FAD Sub-TLV for a 312 given Flexible-Algorithm. A router receiving multiple IS-IS FAD Sub- 313 TLVs for a given Flexible-Algorithm from the same originator MUST 314 select the first advertisement in the lowest numbered LSP. 316 The IS-IS FAD Sub-TLV has an area scope. The Router Capability TLV 317 in which the FAD Sub-TLV is present MUST have the S-bit clear. 319 IS-IS L1/L2 router MAY be configured to re-generate the winning FAD 320 from level 2, without any modification to it, to level 1 area. The 321 re-generation of the FAD Sub-TLV from level 2 to level 1 is 322 determined by the L1/L2 router, not by the originator of the FAD 323 advertisement in the level 2. In such case, the re-generated FAD 324 Sub-TLV will be advertised in the level 1 Router Capability TLV 325 originated by the L1/L2 router. 327 L1/L2 router MUST NOT re-generate any FAD Sub-TLV from level 1 to 328 level 2. 330 5.2. OSPF Flexible Algorithm Definition TLV 332 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 333 defined in [RFC7770]. 335 OSPF FAD TLV has the following format: 337 0 1 2 3 338 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 1 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 340 | Type | Length | 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 342 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 344 | Sub-TLVs | 345 + + 346 | ... | 348 | | 349 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 351 where: 353 Type: 16 355 Length: variable, dependent on the included Sub-TLVs 357 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 358 inclusive. 360 Metric-Type: Type of metric to be used during the calculation. 361 Following values are defined: 363 0: IGP Metric 365 1: Min Unidirectional Link Delay as defined in [RFC7471], 366 section 4.2, encoded as application specific link attribute as 367 specified in [RFC8920] and Section 12 of this document. 369 2: Traffic Engineering metric as defined in [RFC3630], section 370 2.5.5, encoded as application specific link attribute as 371 specified in [RFC8920] and Section 12 of this document. 373 Calc-Type: as described in Section 5.1 374 Priority: as described in Section 5.1 376 Sub-TLVs - optional sub-TLVs. 378 When multiple OSPF FAD TLVs, for the same Flexible-Algorithm, are 379 received from a given router, the receiver MUST use the first 380 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 381 TLV, for the same Flex-Algorithm, appears in multiple Router 382 Information LSAs that have different flooding scopes, the OSPF FAD 383 TLV in the Router Information LSA with the area-scoped flooding scope 384 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 385 in multiple Router Information LSAs that have the same flooding 386 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 387 numerically smallest Instance ID MUST be used and subsequent 388 instances of the OSPF FAD TLV MUST be ignored. 390 The RI LSA can be advertised at any of the defined opaque flooding 391 scopes (link, area, or Autonomous System (AS)). For the purpose of 392 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 393 Autonomous System flooding scope SHOULD NOT be used by default unless 394 local configuration policy on the originating router indicates domain 395 wide flooding. 397 5.3. Common Handling of Flexible Algorithm Definition TLV 399 This section describes the protocol-independent handling of the FAD 400 TLV (OSPF) or FAD Sub-TLV (IS-IS). We will refer to it as FAD TLV in 401 this section, even though in the case of IS-IS it is a Sub-TLV. 403 The value of the Flex-Algorithm MUST be between 128 and 255 404 inclusive. If it is not, the FAD TLV MUST be ignored. 406 Only a subset of the routers participating in the particular Flex- 407 Algorithm need to advertise the definition of the Flex-Algorithm. 409 Every router, that is configured to participate in a particular Flex- 410 Algorithm, MUST select the Flex-Algorithm definition based on the 411 following ordered rules. This allows for the consistent Flex- 412 Algorithm definition selection in cases where different routers 413 advertise different definitions for a given Flex-Algorithm: 415 1. From the advertisements of the FAD in the area (including both 416 locally generated advertisements and received advertisements) 417 select the one(s) with the highest priority value. 419 2. If there are multiple advertisements of the FAD with the same 420 highest priority, select the one that is originated from the 421 router with the highest System-ID, in the case of IS-IS, or Router 422 ID, in the case of OSPFv2 and OSPFv3. For IS-IS, the System-ID is 423 described in [ISO10589]. For OSPFv2 and OSPFv3, standard Router 424 ID is described in [RFC2328] and [RFC5340] respectively. 426 A router that is not configured to participate in a particular Flex- 427 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 428 Algorithm. 430 A router that is not participating in a particular Flex-Algorithm is 431 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 432 MUST consider FAD advertisement regardless of the Flex-Algorithm 433 participation of the FAD originator. 435 Any change in the Flex-Algorithm definition may result in temporary 436 disruption of traffic that is forwarded based on such Flex-Algorithm 437 paths. The impact is similar to any other event that requires 438 network-wide convergence. 440 If a node is configured to participate in a particular Flexible- 441 Algorithm, but the selected Flex-Algorithm definition includes 442 calculation-type, metric-type, constraint, flag, or Sub-TLV that is 443 not supported by the node, it MUST stop participating in such 444 Flexible-Algorithm. That implies that it MUST NOT announce 445 participation for such Flexible-Algorithm as specified in Section 11 446 and it MUST remove any forwarding state associated with it. 448 Flex-Algorithm definition is topology independent. It applies to all 449 topologies that a router participates in. 451 6. Sub-TLVs of IS-IS FAD Sub-TLV 453 6.1. IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV 455 The Flexible Algorithm definition can specify 'colors' that are used 456 by the operator to exclude links during the Flex-Algorithm path 457 computation. 459 The IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 460 advertise the exclude rule that is used during the Flex-Algorithm 461 path calculation as specified in Section 13. 463 The IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub- 464 TLV) is a Sub-TLV of the IS-IS FAD Sub-TLV. It has the following 465 format: 467 0 1 2 3 468 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 1 469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 470 | Type | Length | 471 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 472 | Extended Admin Group | 473 +- -+ 474 | ... | 475 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 476 where: 478 Type: 1 480 Length: variable, dependent on the size of the Extended Admin 481 Group. MUST be a multiple of 4 octets. 483 Extended Administrative Group: Extended Administrative Group as 484 defined in [RFC7308]. 486 The IS-IS FAEAG Sub-TLV MUST NOT appear more than once in an IS-IS 487 FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLV 488 MUST be ignored by the receiver. 490 6.2. IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV 492 The Flexible Algorithm definition can specify 'colors' that are used 493 by the operator to include links during the Flex-Algorithm path 494 computation. 496 The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV is used 497 to advertise include-any rule that is used during the Flex-Algorithm 498 path calculation as specified in Section 13. 500 The format of the IS-IS Flexible Algorithm Include-Any Admin Group 501 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 502 Section 6.1. 504 The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 505 2. 507 The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 508 appear more than once in an IS-IS FAD Sub-TLV. If it appears more 509 than once, the IS-IS FAD Sub-TLV MUST be ignored by the receiver. 511 6.3. IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV 513 The Flexible Algorithm definition can specify 'colors' that are used 514 by the operator to include link during the Flex-Algorithm path 515 computation. 517 The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV is used 518 to advertise include-all rule that is used during the Flex-Algorithm 519 path calculation as specified in Section 13. 521 The format of the IS-IS Flexible Algorithm Include-All Admin Group 522 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 523 Section 6.1. 525 The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 526 3. 528 The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 529 appear more than once in an IS-IS FAD Sub-TLV. If it appears more 530 than once, the IS-IS FAD Sub-TLV MUST be ignored by the receiver. 532 6.4. IS-IS Flexible Algorithm Definition Flags Sub-TLV 534 The IS-IS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 535 is a Sub-TLV of the IS-IS FAD Sub-TLV. It has the following format: 537 0 1 2 3 538 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 1 539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 540 | Type | Length | 541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 542 | Flags | 543 +- -+ 544 | ... | 545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 546 where: 548 Type: 4 550 Length: variable, non-zero number of octets of the Flags field 552 Flags: 554 0 1 2 3 4 5 6 7... 555 +-+-+-+-+-+-+-+-+... 556 |M| | | ... 557 +-+-+-+-+-+-+-+-+... 559 M-flag: when set, the Flex-Algorithm specific prefix metric 560 MUST be used for inter-area and external prefix calculation. 561 This flag is not applicable to prefixes advertised as SRv6 562 locators. 564 Bits are defined/sent starting with Bit 0 defined above. Additional 565 bit definitions that may be defined in the future SHOULD be assigned 566 in ascending bit order so as to minimize the number of bits that will 567 need to be transmitted. 569 Undefined bits MUST be transmitted as 0. 571 Bits that are NOT transmitted MUST be treated as if they are set to 0 572 on receipt. 574 The IS-IS FADF Sub-TLV MUST NOT appear more than once in an IS-IS FAD 575 Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLV MUST be 576 ignored by the receiver. 578 If the IS-IS FADF Sub-TLV is not present inside the IS-IS FAD Sub- 579 TLV, all the bits are assumed to be set to 0. 581 If a node is configured to participate in a particular Flexible- 582 Algorithm, but the selected Flex-Algorithm definition includes a bit 583 in the IS-IS FADF Sub-TLV that is not supported by the node, it MUST 584 stop participating in such Flexible-Algorithm. 586 New flag bits may be defined in the future. Implementations MUST 587 check all advertised flag bits in the received IS-IS FADF Sub-TLV - 588 not just the subset currently defined. 590 6.5. IS-IS Flexible Algorithm Exclude SRLG Sub-TLV 592 The Flexible Algorithm definition can specify Shared Risk Link Groups 593 (SRLGs) that the operator wants to exclude during the Flex-Algorithm 594 path computation. 596 The IS-IS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used 597 to advertise the exclude rule that is used during the Flex-Algorithm 598 path calculation as specified in Section 13. 600 The IS-IS FAESRLG Sub-TLV is a Sub-TLV of the IS-IS FAD Sub-TLV. It 601 has the following format: 603 0 1 2 3 604 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 1 605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 | Type | Length | 607 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 608 | Shared Risk Link Group Value | 609 +- -+ 610 | ... | 611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 612 where: 614 Type: 5 616 Length: variable, dependent on number of SRLG values. MUST be a 617 multiple of 4 octets. 619 Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. 621 The IS-IS FAESRLG Sub-TLV MUST NOT appear more than once in an IS-IS 622 FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLV 623 MUST be ignored by the receiver. 625 7. Sub-TLVs of OSPF FAD TLV 627 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 629 The Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is 630 a Sub-TLV of the OSPF FAD TLV. It's usage is described in 631 Section 6.1. It has the following format: 633 0 1 2 3 634 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 1 635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 636 | Type | Length | 637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 638 | Extended Admin Group | 639 +- -+ 640 | ... | 641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 642 where: 644 Type: 1 646 Length: variable, dependent on the size of the Extended Admin 647 Group. MUST be a multiple of 4 octets. 649 Extended Administrative Group: Extended Administrative Group as 650 defined in [RFC7308]. 652 The OSPF FAEAG Sub-TLV MUST NOT appear more than once in an OSPF FAD 653 TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored 654 by the receiver. 656 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 658 The usage of this Sub-TLVs is described in Section 6.2. 660 The format of the OSPF Flexible Algorithm Include-Any Admin Group 661 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 662 Section 7.1. 664 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 665 2. 667 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 668 appear more than once in an OSPF FAD TLV. If it appears more than 669 once, the OSPF FAD TLV MUST be ignored by the receiver. 671 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 673 The usage of this Sub-TLVs is described in Section 6.3. 675 The format of the OSPF Flexible Algorithm Include-All Admin Group 676 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 677 Section 7.1. 679 The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV Type is 680 3. 682 The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 683 appear more than once in an OSPF FAD TLV. If it appears more than 684 once, the OSPF FAD TLV MUST be ignored by the receiver. 686 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 688 The OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 689 is a Sub-TLV of the OSPF FAD TLV. It has the following format: 691 0 1 2 3 692 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 1 693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 694 | Type | Length | 695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 696 | Flags | 697 +- -+ 698 | ... | 699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 700 where: 702 Type: 4 704 Length: variable, dependent on the size of the Flags field. MUST 705 be a multiple of 4 octets. 707 Flags: 709 0 1 2 3 4 5 6 7... 710 +-+-+-+-+-+-+-+-+... 711 |M| | | ... 712 +-+-+-+-+-+-+-+-+... 714 M-flag: when set, the Flex-Algorithm specific prefix and ASBR 715 metric MUST be used for inter-area and external prefix 716 calculation. This flag is not applicable to prefixes 717 advertised as SRv6 locators. 719 Bits are defined/sent starting with Bit 0 defined above. Additional 720 bit definitions that may be defined in the future SHOULD be assigned 721 in ascending bit order so as to minimize the number of bits that will 722 need to be transmitted. 724 Undefined bits MUST be transmitted as 0. 726 Bits that are NOT transmitted MUST be treated as if they are set to 0 727 on receipt. 729 The OSPF FADF Sub-TLV MUST NOT appear more than once in an OSPF FAD 730 TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored 731 by the receiver. 733 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 734 the bits are assumed to be set to 0. 736 If a node is configured to participate in a particular Flexible- 737 Algorithm, but the selected Flex-Algorithm definition includes a bit 738 in the OSPF FADF Sub-TLV that is not supported by the node, it MUST 739 stop participating in such Flexible-Algorithm. 741 New flag bits may be defined in the future. Implementations MUST 742 check all advertised flag bits in the received OSPF FADF Sub-TLV - 743 not just the subset currently defined. 745 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV 747 The OSPF Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG Sub-TLV) is 748 a Sub-TLV of the OSPF FAD TLV. Its usage is described in 749 Section 6.5. It has the following format: 751 0 1 2 3 752 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 1 753 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 754 | Type | Length | 755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 756 | Shared Risk Link Group Value | 757 +- -+ 758 | ... | 759 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 760 where: 762 Type: 5 764 Length: variable, dependent on the number of SRLGs. MUST be a 765 multiple of 4 octets. 767 Shared Risk Link Group Value: SRLG value as defined in [RFC4203]. 769 The OSPF FAESRLG Sub-TLV MUST NOT appear more than once in an OSPF 770 FAD TLV. If it appears more than once, the OSPF FAD TLV MUST be 771 ignored by the receiver. 773 8. IS-IS Flexible Algorithm Prefix Metric Sub-TLV 775 The IS-IS Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports 776 the advertisement of a Flex-Algorithm specific prefix metric 777 associated with a given prefix advertisement. 779 The IS-IS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 780 and has the following format: 782 0 1 2 3 783 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 1 784 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 785 | Type | Length |Flex-Algorithm | 786 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 787 | Metric | 788 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 789 where: 791 Type: 6 793 Length: 5 octets 795 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 797 Metric: 4 octets of metric information 799 The IS-IS FAPM Sub-TLV MAY appear multiple times in its parent TLV. 800 If it appears more than once with the same Flex-Algorithm value, the 801 first instance MUST be used and any subsequent instances MUST be 802 ignored. 804 If a prefix is advertised with a Flex-Algorithm prefix metric larger 805 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 806 considered during the Flexible-Algorithm computation. 808 The usage of the Flex-Algorithm prefix metric is described in 809 Section 13. 811 The IS-IS FAPM Sub-TLV MUST NOT be advertised as a sub-TLV of the IS- 812 IS SRv6 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. The IS-IS 813 SRv6 Locator TLV includes the Algorithm and Metric fields which MUST 814 be used instead. If the FAPM Sub-TLV is present as a sub-TLV of the 815 IS-IS SRv6 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be 816 ignored. 818 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV 820 The OSPF Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the 821 advertisement of a Flex-Algorithm specific prefix metric associated 822 with a given prefix advertisement. 824 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV is a Sub-TLV of 825 the: 827 - OSPFv2 Extended Prefix TLV [RFC7684] 829 - Following OSPFv3 TLVs as defined in [RFC8362]: 831 Inter-Area Prefix TLV 833 External Prefix TLV 835 OSPF FAPM Sub-TLV has the following format: 837 0 1 2 3 838 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 1 839 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 840 | Type | Length | 841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 842 |Flex-Algorithm | Flags | Reserved | 843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 844 | Metric | 845 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 847 where: 849 Type: 3 for OSPFv2, 26 for OSPFv3 851 Length: 8 octets 853 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 855 Flags: single octet value 857 0 1 2 3 4 5 6 7 858 +-+-+-+-+-+-+-+-+ 859 |E| | 860 +-+-+-+-+-+-+-+-+ 862 E bit : position 0: The type of external metric. If bit is 863 set, the metric specified is a Type 2 external metric. This 864 bit is applicable only to OSPF External and NSSA external 865 prefixes. This is semantically the same as E bit in section 866 A.4.5 of [RFC2328] and section A.4.7 of [RFC5340] for OSPFv2 867 and OSPFv3 respectively. 869 Bits 1 through 7: MUST be cleared by sender and ignored by 870 receiver. 872 Reserved: Must be set to 0, ignored at reception. 874 Metric: 4 octets of metric information 876 The OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. 877 If it appears more than once with the same Flex-Algorithm value, the 878 first instance MUST be used and any subsequent instances MUST be 879 ignored. 881 The usage of the Flex-Algorithm prefix metric is described in 882 Section 13. 884 10. OSPF Flexible Algorithm ASBR Reachability Advertisement 886 An OSPF ABR advertises the reachability of ASBRs in its attached 887 areas to enable routers within those areas to perform route 888 calculations for external prefixes advertised by the ASBRs. OSPF 889 extensions for advertisement of Flex-Algorithm specific reachability 890 and metric for ASBRs is similarly required for Flex-Algorithm 891 external prefix computations as described further in Section 13.1. 893 10.1. OSPFv2 Extended Inter-Area ASBR LSA 895 The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) LSA is an OSPF Opaque 896 LSA [RFC5250] that is used to advertise additional attributes related 897 to the reachability of the OSPFv2 ASBR that is external to the area 898 yet internal to the OSPF domain. Semantically, the OSPFv2 EIA-ASBR 899 LSA is equivalent to the fixed format Type 4 Summary LSA [RFC2328]. 900 Unlike the Type 4 Summary LSA, the LSID of the EIA-ASBR LSA does not 901 carry the ASBR Router-ID - the ASBR Router-ID is carried in the body 902 of the LSA. OSPFv2 EIA-ASBR LSA is advertised by an OSPFv2 ABR and 903 its flooding is defined to be area-scoped only. 905 An OSPFv2 ABR generates the EIA-ASBR LSA for an ASBR when it is 906 advertising the Type-4 Summary LSA for it and has the need for 907 advertising additional attributes for that ASBR beyond what is 908 conveyed in the fixed format Type-4 Summary LSA. An OSPFv2 ABR MUST 909 NOT advertise the EIA-ASBR LSA for an ASBR for which it is not 910 advertising the Type 4 Summary LSA. This ensures that the ABR does 911 not generate the EIA-ASBR LSA for an ASBR to which it does not have 912 reachability in the base OSPFv2 topology calculation. The OSPFv2 ABR 913 SHOULD NOT advertise the EIA-ASBR LSA for an ASBR when it does not 914 have additional attributes to advertise for that ASBR. 916 The OSPFv2 EIA-ASBR LSA has the following format: 918 0 1 2 3 919 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 1 920 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 921 | LS age | Options | LS Type | 922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 923 | Opaque Type | Opaque ID | 924 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 925 | Advertising Router | 926 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 927 | LS sequence number | 928 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 929 | LS checksum | Length | 930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 931 | | 932 +- TLVs -+ 933 | ... | 935 The Opaque Type used by the OSPFv2 EIA-ASBR LSA is TBD (suggested 936 value 11). The Opaque Type is used to differentiate the various 937 types of OSPFv2 Opaque LSAs and is described in Section 3 of 938 [RFC5250]. The LS Type MUST be 10, indicating that the Opaque LSA 939 flooding scope is area-local [RFC5250]. The LSA Length field 940 [RFC2328] represents the total length (in octets) of the Opaque LSA, 941 including the LSA header and all TLVs (including padding). 943 The Opaque ID field is an arbitrary value used to maintain multiple 944 OSPFv2 EIA-ASBR LSAs. For OSPFv2 EIA-ASBR LSAs, the Opaque ID has no 945 semantic significance other than to differentiate OSPFv2 EIA-ASBR 946 LSAs originated by the same OSPFv2 ABR. If multiple OSPFv2 EIA-ASBR 947 LSAs specify the same ASBR, the attributes from the Opaque LSA with 948 the lowest Opaque ID SHOULD be used. 950 The format of the TLVs within the body of the OSPFv2 EIA-ASBR LSA is 951 the same as the format used by the Traffic Engineering Extensions to 952 OSPFv2 [RFC3630]. The variable TLV section consists of one or more 953 nested TLV tuples. Nested TLVs are also referred to as sub- TLVs. 954 The Length field defines the length of the value portion in octets 955 (thus, a TLV with no value portion would have a length of 0). The 956 TLV is padded to 4-octet alignment; padding is not included in the 957 Length field (so a 3-octet value would have a length of 3, but the 958 total size of the TLV would be 8 octets). Nested TLVs are also 959 32-bit aligned. For example, a 1-byte value would have the Length 960 field set to 1, and 3 octets of padding would be added to the end of 961 the value portion of the TLV. The padding is composed of zeros. 963 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV 965 The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) TLV is a top-level TLV 966 of the OSPFv2 EIA-ASBR LSA and is used to advertise additional 967 attributes associated with the reachability of an ASBR. 969 The OSPFv2 EIA-ASBR TLV has the following format: 971 0 1 2 3 972 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 1 973 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 974 | Type | Length | 975 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 976 | ASBR Router ID | 977 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 978 . . 979 . Sub-TLVs . 980 . . 981 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 983 where: 985 Type: 1 987 Length: variable 989 ASBR Router ID: four octets carrying the OSPF Router ID of the 990 ASBR whose information is being carried. 992 Sub-TLVs : variable 994 Only a single OSPFv2 EIA-ASBR TLV MUST be advertised in each OSPFv2 995 EIA-ASBR LSA and the receiver MUST ignore all instances of this TLV 996 other than the first one in an LSA. 998 OSPFv2 EIA-ASBR TLV MUST be present inside an OSPFv2 EIA-ASBR LSA 999 with at least a single sub-TLV included, otherwise the OSPFv2 EIA- 1000 ASBR LSA MUST be ignored by the receiver. 1002 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV 1004 The OSPF Flexible Algorithm ASBR Metric (FAAM) Sub-TLV supports the 1005 advertisement of a Flex-Algorithm specific metric associated with a 1006 given ASBR reachability advertisement by an ABR. 1008 The OSPF Flex-Algorithm ASBR Metric (FAAM) Sub-TLV is a Sub-TLV of 1009 the: 1011 - OSPFv2 Extended Inter-Area ASBR TLV as defined in Section 10.1.1 1013 - OSPFv3 Inter-Area-Router TLV defined in [RFC8362] 1015 OSPF FAAM Sub-TLV has the following format: 1017 0 1 2 3 1018 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 1019 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1020 | Type | Length | 1021 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1022 |Flex-Algorithm | Reserved | 1023 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1024 | Metric | 1025 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1027 where: 1029 Type: 1 for OSPFv2, TBD (suggested value 30) for OSPFv3 1031 Length: 8 octets 1033 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 1035 Reserved: Must be set to 0, ignored at reception. 1037 Metric: 4 octets of metric information 1039 The OSPF FAAM Sub-TLV MAY appear multiple times in its parent TLV. 1040 If it appears more than once with the same Flex-Algorithm value, the 1041 first instance MUST be used and any subsequent instances MUST be 1042 ignored. 1044 The advertisement of the ASBR reachability using the OSPF FAAM Sub- 1045 TLV inside the OSPFv2 EIA-ASBR LSA follows the section 12.4.3 of 1046 [RFC2328] and inside the OSPFv3 E-Inter-Area-Router LSA follows the 1047 section 4.8.5 of [RFC5340]. The reachability of the ASBR is 1048 evaluated in the context of the specific Flex-Algorithm. 1050 The FAAM computed by the ABR will be equal to the metric to reach the 1051 ASBR for a given Flex-Algorithm in a source area or the cumulative 1052 metric via other ABR(s) when the ASBR is in a remote area. This is 1053 similar in nature to how the metric is set when the ASBR reachability 1054 metric is computed in the default algorithm for the metric in the 1055 OSPFv2 Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. 1057 An OSPF ABR MUST NOT include the OSPF FAAM Sub-TLV with a specific 1058 Flex-Algorithm in its reachability advertisement for an ASBR between 1059 areas unless that ASBR is reachable for it in the context of that 1060 specific Flex-Algorithm. 1062 An OSPF ABR MUST include the OSPF FAAM Sub-TLVs as part of the ASBR 1063 reachability advertisement between areas for the Flex-Algorithm for 1064 which the winning FAD includes the M-flag and the ASBR is reachable 1065 in the context of that specific Flex-Algorithm. 1067 OSPF routers MUST use the OSPF FAAM Sub-TLV to calculate the 1068 reachability of the ASBRs if the winning FAD for the specific Flex- 1069 Algorithm includes the M-flag. OSPF routers MUST NOT use the OSPF 1070 FAAM Sub-TLV to calculate the reachability of the ASBRs for the 1071 specific Flex-Algorithm if the winning FAD for such Flex-Algorithm 1072 does not include the M-flag. Instead, the OSPFv2 Type 4 Summary LSAs 1073 or the OSPFv3 Inter-Area-Router-LSAs MUST be used instead as 1074 specified in section 16.2 of [RFC2328] and section 4.8.5 of [RFC5340] 1075 for OSPFv2 and OSPFv3 respectively. 1077 The processing of the new or changed OSPF FAAM Sub-TLV triggers the 1078 processing of the External routes similar to what is described in 1079 section 16.5 of the [RFC2328] for OSPFv2 and section 4.8.5 of 1080 [RFC5340] for OSPFv3 for the specific Flex-Algorithm. The External 1081 and NSSA External route calculation should be limited to Flex- 1082 Algorithm(s) for which the winning FAD(s) includes the M-flag. 1084 Processing of the OSPF FAAM Sub-TLV does not require the existence of 1085 the equivalent OSPFv2 Type 4 Summary LSA or the OSPFv3 Inter-Area- 1086 Router-LSA that is advertised by the same ABR inside the area. When 1087 the OSPFv2 EIA-ASBR LSA or the OSPFv3 E-Inter-Area-Router-LSA are 1088 advertised along with the OSPF FAAM Sub-TLV by the ABR for a specific 1089 ASBR, it is expected that the same ABR would advertise the 1090 reachability of the same ASBR in the equivalent base LSAs - i.e., the 1091 OSPFv2 Type 4 Summary LSA or the OSPFv3 Inter-Area-Router-LSA. The 1092 presence of the base LSA is not mandatory for the usage of the 1093 extended LSA with the OSPF FAAM Sub-TLV. This means that the order 1094 in which these LSAs are received is not significant. 1096 11. Advertisement of Node Participation in a Flex-Algorithm 1098 When a router is configured to support a particular Flex-Algorithm, 1099 we say it is participating in that Flex-Algorithm. 1101 Paths computed for a specific Flex-Algorithm MAY be used by various 1102 applications, each potentially using its own specific data plane for 1103 forwarding traffic over such paths. To guarantee the presence of the 1104 application specific forwarding state associated with a particular 1105 Flex-Algorithm, a router MUST advertise its participation for a 1106 particular Flex-Algorithm for each application specifically. 1108 11.1. Advertisement of Node Participation for Segment Routing 1110 [RFC8667], [RFC8665], and [RFC8666] (IGP Segment Routing extensions) 1111 describe how the SR-Algorithm is used to compute the IGP best path. 1113 Routers advertise the support for the SR-Algorithm as a node 1114 capability as described in the above mentioned IGP Segment Routing 1115 extensions. To advertise participation for a particular Flex- 1116 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 1117 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 1118 (OSPF) or sub-TLV (IS-IS). 1120 Segment Routing Flex-Algorithm participation advertisement is 1121 topology independent. When a router advertises participation in an 1122 SR-Algorithm, the participation applies to all topologies in which 1123 the advertising node participates. 1125 11.2. Advertisement of Node Participation for Other Applications 1127 This section describes considerations related to how other 1128 applications can advertise their participation in a specific Flex- 1129 Algorithm. 1131 Application-specific Flex-Algorithm participation advertisements MAY 1132 be topology specific or MAY be topology independent, depending on the 1133 application itself. 1135 Application-specific advertisement for Flex-Algorithm participation 1136 MUST be defined for each application and is outside of the scope of 1137 this document. 1139 12. Advertisement of Link Attributes for Flex-Algorithm 1141 Various link attributes may be used during the Flex-Algorithm path 1142 calculation. For example, include or exclude rules based on link 1143 affinities can be part of the Flex-Algorithm definition as defined in 1144 Section 6 and Section 7. 1146 Application-specific link attributes, as specified in [RFC8919] or 1147 [RFC8920], that are to be used during Flex-Algorithm calculation MUST 1148 use the Application-Specific Link Attribute (ASLA) advertisements 1149 defined in [RFC8919] or [RFC8920], unless, in the case of IS-IS, the 1150 L-Flag is set in the ASLA advertisement. When the L-Flag is set, 1151 then legacy advertisements are to be used, subject to the procedures 1152 and constraints defined in [[RFC8919] Section 4.2 and Section 6. 1154 The mandatory use of ASLA advertisements applies to link attributes 1155 specifically mentioned in this document (Min Unidirectional Link 1156 Delay, TE Default Metric, Administrative Group, Extended 1157 Administrative Group and Shared Risk Link Group) and any other link 1158 attributes that may be used in support of Flex-Algorithm in the 1159 future. 1161 A new Application Identifier Bit is defined to indicate that the ASLA 1162 advertisement is associated with the Flex-Algorithm application. 1163 This bit is set in the Standard Application Bit Mask (SABM) defined 1164 in [RFC8919] or [RFC8920]: 1166 Bit-3: Flexible Algorithm (X-bit) 1168 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 1169 Application MAY use either the Administrative Group or Extended 1170 Administrative Group encodings. If the Administrative Group encoding 1171 is used, then the first 32 bits of the corresponding FAD sub-TLVs are 1172 mapped to the link attribute advertisements as specified in RFC 7308. 1174 A receiver supporting this specification MUST accept both ASLA 1175 Administrative Group and Extended Administrative Group TLVs as 1176 defined in [RFC8919] or [RFC8920]. In the case of ISIS, if the 1177 L-Flag is set in ASLA advertisement, as defined in [RFC8919] 1178 Section 4.2, then the receiver MUST be able to accept both 1179 Administrative Group TLV as defined in [RFC5305] and Extended 1180 Administrative Group TLV as defined in [RFC7308]. 1182 13. Calculation of Flexible Algorithm Paths 1184 A router MUST be configured to participate in a given Flex-Algorithm 1185 K and MUST select the FAD based on the rules defined in Section 5.3 1186 before it can compute any path for that Flex-Algorithm. 1188 No specific two way connectivity check is performed during the Flex- 1189 Algorithm path computation. The result of the existing, Flex- 1190 Algorithm agnostic, two way connectivity check is used during the 1191 Flex-Algorithm path computation. 1193 As described in Section 11, participation for any particular Flex- 1194 Algorithm MUST be advertised on a per-application basis. Calculation 1195 of the paths for any particular Flex-Algorithm MUST be application 1196 specific. 1198 The way applications handle nodes that do not participate in 1199 Flexible-Algorithm is application specific. If the application only 1200 wants to consider participating nodes during the Flex-Algorithm 1201 calculation, then when computing paths for a given Flex-Algorithm, 1202 all nodes that do not advertise participation for that Flex-Algorithm 1203 in their application-specific advertisements MUST be pruned from the 1204 topology. Segment Routing, including both SR MPLS and SRv6, are 1205 applications that MUST use such pruning when computing Flex-Algorithm 1206 paths. 1208 When computing the path for a given Flex-Algorithm, the metric-type 1209 that is part of the Flex-Algorithm definition (Section 5) MUST be 1210 used. 1212 When computing the path for a given Flex-Algorithm, the calculation- 1213 type that is part of the Flex-Algorithm definition (Section 5) MUST 1214 be used. 1216 Various link include or exclude rules can be part of the Flex- 1217 Algorithm definition. To refer to a particular bit within an AG or 1218 EAG we use the term 'color'. 1220 Rules, in the order as specified below, MUST be used to prune links 1221 from the topology during the Flex-Algorithm computation. 1223 For all links in the topology: 1225 1. Check if any exclude AG rule is part of the Flex-Algorithm 1226 definition. If such exclude rule exists, check if any color that 1227 is part of the exclude rule is also set on the link. If such a 1228 color is set, the link MUST be pruned from the computation. 1230 2. Check if any exclude SRLG rule is part of the Flex-Algorithm 1231 definition. If such exclude rule exists, check if the link is 1232 part of any SRLG that is also part of the SRLG exclude rule. If 1233 the link is part of such SRLG, the link MUST be pruned from the 1234 computation. 1236 3. Check if any include-any AG rule is part of the Flex-Algorithm 1237 definition. If such include-any rule exists, check if any color 1238 that is part of the include-any rule is also set on the link. If 1239 no such color is set, the link MUST be pruned from the 1240 computation. 1242 4. Check if any include-all AG rule is part of the Flex-Algorithm 1243 definition. If such include-all rule exists, check if all colors 1244 that are part of the include-all rule are also set on the link. 1245 If all such colors are not set on the link, the link MUST be 1246 pruned from the computation. 1248 5. If the Flex-Algorithm definition uses other than IGP metric 1249 (Section 5), and such metric is not advertised for the particular 1250 link in a topology for which the computation is done, such link 1251 MUST be pruned from the computation. A metric of value 0 MUST NOT 1252 be assumed in such case. 1254 13.1. Multi-area and Multi-domain Considerations 1256 Any IGP Shortest Path Tree calculation is limited to a single area. 1257 This applies to Flex-Algorithm calculations as well. Given that the 1258 computing router does not have visibility of the topology of the next 1259 areas or domain, the Flex-Algorithm specific path to an inter-area or 1260 inter-domain prefix will be computed for the local area only. The 1261 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 1262 will be selected based on the best path for the given Flex-Algorithm 1263 in the local area and such egress ABR or ASBR router will be 1264 responsible to compute the best Flex-Algorithm specific path over the 1265 next area or domain. This may produce an end-to-end path, which is 1266 sub-optimal based on Flex-Algorithm constraints. In cases where the 1267 ABR or ASBR has no reachability to a prefix for a given Flex- 1268 Algorithm in the next area or domain, the traffic may be dropped by 1269 the ABR/ASBR. 1271 To allow the optimal end-to-end path for an inter-area or inter- 1272 domain prefix for any Flex-Algorithm to be computed, the FAPM has 1273 been defined in Section 8 and Section 9. For external route 1274 calculation for prefixes originated by ASBRs in remote areas in OSPF, 1275 the FAAM has been defined in Section 10.2 for the ABR to indicate its 1276 ASBR reachability along with the metric for the specific Flex- 1277 Algorithm. 1279 If the FAD selected based on the rules defined in Section 5.3 1280 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 1281 Section 9) when advertising the prefix, that is reachable in a given 1282 Flex-Algorithm, between areas or domains. Such metric will be equal 1283 to the metric to reach the prefix for that Flex-Algorithm in its 1284 source area or domain. This is similar in nature to how the metric 1285 is set when prefixes are advertised between areas or domains for the 1286 default algorithm. When a prefix is unreachable in its source area 1287 or domain in a specific Flex-Algorithm, then an ABR or ASBR MUST NOT 1288 include the FAPM for that Flex-Algorithm when advertising the prefix 1289 between areas or domains. 1291 If the FAD selected based on the rules defined in Section 5.3 1292 includes the M-flag, the FAPM MUST be used during the calculation of 1293 prefix reachability for the inter-area and external prefixes. If the 1294 FAPM for the Flex-Algorithm is not advertised with the inter-area or 1295 external prefix reachability advertisement, the prefix MUST be 1296 considered as unreachable for that Flex-Algorithm. Similarly in the 1297 case of OSPF, for ASBRs in remote areas, if the FAAM is not 1298 advertised by the local ABR(s), the ASBR MUST be considered as 1299 unreachable for that Flex-Algorithm and the external prefix 1300 advertisements from such an ASBR are not considered for that Flex- 1301 Algorithm. 1303 Flex-Algorithm prefix metrics and the OSPF Flex-Algorithm ASBR 1304 metrics MUST NOT be used during the Flex-Algorithm computation unless 1305 the FAD selected based on the rules defined in Section 5.3 includes 1306 the M-Flag, as described in (Section 6.4 or Section 7.4). 1308 In the case of OSPF, when calculating external routes in a Flex- 1309 Algorithm (with FAD selected includes the M-Flag) where the 1310 advertising ASBR is in a remote area, the metric will be the sum of 1311 the following: 1313 o the FAPM for that Flex-Algorithm advertised with the external 1314 route by the ASBR 1316 o the metric to reach the ASBR for that Flex-Algorithm from the 1317 local ABR i.e., the FAAM for that Flex-Algorithm advertised by the 1318 ABR in the local area for that ASBR 1320 o the Flex-Algorithm specific metric to reach the local ABR 1322 This is similar in nature to how the metric is calculated for routes 1323 learned from remote ASBRs in the default algorithm using the OSPFv2 1324 Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. 1326 If the FAD selected based on the rules defined in Section 5.3 does 1327 not includes the M-flag, then the IGP metrics associated with the 1328 prefix reachability advertisements used by the base IS-IS and OSPF 1329 protocol MUST be used for the Flex-Algorithm route computation. 1330 Similarly, in the case of external route calculations in OSPF, the 1331 ASBR reachability is determined based on the base OSPFv2 Type 4 1332 Summary LSA and the OSFPv3 Inter-Area-Router LSA. 1334 It is NOT RECOMMENDED to use the Flex-Algorithm for inter-area or 1335 inter-domain prefix reachability without the M-flag set. The reason 1336 is that without the explicit Flex-Algorithm Prefix Metric 1337 advertisement (and the Flex-Algorithm ASBR metric advertisement in 1338 the case of OSPF external route calculation), it is not possible to 1339 conclude whether the ABR or ASBR has reachability to the inter-area 1340 or inter-domain prefix for a given Flex-Algorithm in the next area or 1341 domain. Sending the Flex-Algoritm traffic for such prefix towards 1342 the ABR or ASBR may result in traffic looping or black-holing. 1344 During the route computation, it is possible for the Flex-Algorithm 1345 specific metric to exceed the maximum value that can be stored in an 1346 unsigned 32-bit variable. In such scenarios, the value MUST be 1347 considered to be of value 4,294,967,295 during the computation and 1348 advertised as such. 1350 The FAPM MUST NOT be advertised with IS-IS L1 or L2 intra-area, 1351 OSPFv2 intra-area, or OSPFv3 intra-area routes. If the FAPM is 1352 advertised for these route-types, it MUST be ignored during the 1353 prefix reachability calculation. 1355 The M-flag in FAD is not applicable to prefixes advertised as SRv6 1356 locators. The IS-IS SRv6 Locator TLV 1357 [I-D.ietf-lsr-isis-srv6-extensions] includes the Algorithm and Metric 1358 fields. When the SRv6 Locator is advertised between areas or 1359 domains, the metric field in the Locator TLV of IS-IS MUST be used 1360 irrespective of the M-flag in the FAD advertisement. 1362 OSPF external and NSSA external prefix advertisements MAY include a 1363 non-zero forwarding address in the prefix advertisements in the base 1364 protocol. In such a scenario, the Flex-Algorithm specific 1365 reachability of the external prefix is determined by Flex-Algorithm 1366 specific reachability of the forwarding address. 1368 In OSPF, the procedures for translation of NSSA external prefix 1369 advertisements into external prefix advertisements performed by an 1370 NSSA ABR [RFC3101] remain unchanged for Flex-Algorithm. An NSSA 1371 translator MUST include the OSPF FAPM Sub-TLVs for all Flex- 1372 Algorithms that are in the original NSSA external prefix 1373 advertisement from the NSSA ASBR in the translated external prefix 1374 advertisement generated by it regardless of its participation in 1375 those Flex-Algorithms or its having reachability to the NSSA ASBR in 1376 those Flex-Algorithms. 1378 An area could become partitioned from the perspective of the Flex- 1379 Algorithm due to the constraints and/or metric being used for it, 1380 while maintaining the continuity in the algorithm 0. When that 1381 happens, some destinations inside that area could become unreachable 1382 in that Flex-Algorithm. These destinations will not be able to use 1383 an inter-area path. This is the consequence of the fact that the 1384 inter-area prefix reachability advertisement would not be available 1385 for these intra-area destinations within the area. It is RECOMMENDED 1386 to avoid such partitioning by providing enough redundancy inside the 1387 area for each Flex-Algorithm being used. 1389 14. Flex-Algorithm and Forwarding Plane 1391 This section describes how Flex-Algorithm paths are used in 1392 forwarding. 1394 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm 1396 This section describes how Flex-Algorithm paths are used with SR MPLS 1397 forwarding. 1399 Prefix SID advertisements include an SR-Algorithm value and, as such, 1400 are associated with the specified SR-Algorithm. Prefix-SIDs are also 1401 associated with a specific topology which is inherited from the 1402 associated prefix reachability advertisement. When the algorithm 1403 value advertised is a Flex-Algorithm value, the Prefix SID is 1404 associated with paths calculated using that Flex-Algorithm in the 1405 associated topology. 1407 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 1408 using the MPLS label that corresponds to the Prefix-SID that was 1409 advertised for that Flex-algorithm. If the Prefix SID for a given 1410 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 1411 be installed in the MPLS forwarding plane. 1413 Traffic that is supposed to be routed via Flex-Algorithm specific 1414 paths, MUST be dropped when there are no such paths available. 1416 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 1417 computed using the same constraints as the calculation of the primary 1418 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 1419 advertised specifically for the given algorithm. LFA paths MUST NOT 1420 use an Adjacency-SID that belongs to a link that has been pruned from 1421 the Flex-Algorithm computation. 1423 If LFA protection is being used to protect a given Flex-Algorithm 1424 paths, all routers in the area participating in the given Flex- 1425 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 1426 SID. These Node-SIDs are used to steer traffic over the LFA computed 1427 backup path. 1429 14.2. SRv6 Forwarding for Flex-Algorithm 1431 This section describes how Flex-Algorithm paths are used with SRv6 1432 forwarding. 1434 In SRv6 a node is provisioned with topology/algorithm specific 1435 locators for each of the topology/algorithm pairs supported by that 1436 node. Each locator is an aggregate prefix for all SIDs provisioned 1437 on that node which have the matching topology/algorithm. 1439 The SRv6 locator advertisement in IS-IS 1440 [I-D.ietf-lsr-isis-srv6-extensions] includes the MTID value that 1441 associates the locator with a specific topology. SRv6 locator 1442 advertisements also includes an Algorithm value that explicitly 1443 associates the locator with a specific algorithm. When the algorithm 1444 value advertised with a locator represents a Flex-Algorithm, the 1445 paths to the locator prefix MUST be calculated using the specified 1446 Flex-Algorithm in the associated topology. 1448 Forwarding entries for the locator prefixes advertised in IS-IS MUST 1449 be installed in the forwarding plane of the receiving SRv6 capable 1450 routers when the associated topology/algorithm is participating in 1451 them. Forwarding entries for locators associated with Flex- 1452 Algorithms in which the node is not participating MUST NOT be 1453 installed in the forwarding plane. 1455 When the locator is associated with a Flex-Algorithm, LFA paths to 1456 the locator prefix MUST be calculated using such Flex-Algorithm in 1457 the associated topology, to guarantee that they follow the same 1458 constraints as the calculation of the primary paths. LFA paths MUST 1459 only use SRv6 SIDs advertised specifically for the given Flex- 1460 Algorithm. 1462 If LFA protection is being used to protect locators associated with a 1463 given Flex-Algorithm, all routers in the area participating in the 1464 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1465 specific locator and END SID per node and one END.X SID for every 1466 link that has not been pruned from such Flex-Algorithm computation. 1467 These locators and SIDs are used to steer traffic over the LFA- 1468 computed backup path. 1470 14.3. Other Applications' Forwarding for Flex-Algorithm 1472 Any application that wants to use Flex-Algorithm specific forwarding 1473 needs to install some form of Flex-Algorithm specific forwarding 1474 entries. 1476 Application-specific forwarding for Flex-Algorithm MUST be defined 1477 for each application and is outside of the scope of this document. 1479 15. Operational Considerations 1481 15.1. Inter-area Considerations 1483 The scope of the Flex-Algorithm computation is an area, so is the 1484 scope of the FAD. In IS-IS, the Router Capability TLV in which the 1485 FAD Sub-TLV is advertised MUST have the S-bit clear, which prevents 1486 it to be flooded outside of the level in which it was originated. 1487 Even though in OSPF the FAD Sub-TLV can be flooded in an RI LSA that 1488 has AS flooding scope, the FAD selection is performed for each 1489 individual area in which it is being used. 1491 There is no requirement for the FAD for a particular Flex-Algorithm 1492 to be identical in all areas in the network. For example, traffic 1493 for the same Flex-Algorithm may be optimized for minimal delay (e.g., 1494 using delay metric) in one area or level, while being optimized for 1495 available bandwidth (e.g., using IGP metric) in another area or 1496 level. 1498 As described in Section 5.1, IS-IS allows the re-generation of the 1499 winning FAD from level 2, without any modification to it, into a 1500 level 1 area. This allows the operator to configure the FAD in one 1501 or multiple routers in the level 2, without the need to repeat the 1502 same task in each level 1 area, if the intent is to have the same FAD 1503 for the particular Flex-Algorithm across all levels. This can 1504 similarly be achieved in OSPF by using the AS flooding scope of the 1505 RI LSA in which the FAD Sub-TLV for the particular Flex-Algoritm is 1506 advertised. 1508 Re-generation of FAD from a level 1 area to the level 2 area is not 1509 supported in IS-IS, so if the intent is to regenerate the FAD between 1510 IS-IS levels, the FAD MUST be defined on router(s) that are in level 1511 2. In OSPF, the FAD definition can be done in any area and be 1512 propagated to all routers in the OSPF routing domain by using the AS 1513 flooding scope of the RI LSA. 1515 15.2. Usage of SRLG Exclude Rule with Flex-Algorithm 1517 There are two different ways in which SRLG information can be used 1518 with Flex-Algorithm: 1520 In a context of a single Flex-Algorithm, it can be used for 1521 computation of backup paths, as described in 1522 [I-D.ietf-rtgwg-segment-routing-ti-lfa]. This usage does not 1523 require association of any specific SRLG constraint with the given 1524 Flex-Algorithm definition. 1526 In the context of multiple Flex-Algorithms, it can be used for 1527 creating disjoint sets of paths by pruning the links belonging to 1528 a specific SRLG from the topology on which a specific Flex- 1529 Algorithm computes its paths. This usage: 1531 Facilitates the usage of already deployed SRLG configurations 1532 for setup of disjoint paths between two or more Flex- 1533 Algorithms. 1535 Requires explicit association of a given Flex-Algorithm with a 1536 specific set of SRLG constraints as defined in Section 6.5 and 1537 Section 7.5. 1539 The two usages mentioned above are orthogonal. 1541 15.3. Max-metric consideration 1543 Both IS-IS and OSPF have a mechanism to set the IGP metric on a link 1544 to a value that would make the link either non-reachable or to serve 1545 as the link of last resort. Similar functionality would be needed 1546 for the Min Unidirectional Link Delay and TE metric, as these can be 1547 used to compute Flex-Algorithm paths. 1549 The link can be made un-reachable for all Flex-Algorithms that use 1550 Min Unidirectional Link Delay as metric, as described in Section 5.1, 1551 by removing the Flex-Algorithm ASLA Min Unidirectional Link Delay 1552 advertisement for the link. The link can be made the link of last 1553 resort by setting the delay value in the Flex-Algorithm ASLA delay 1554 advertisement for the link to the value of 16,777,215 (2^24 - 1). 1556 The link can be made un-reachable for all Flex-Algorithms that use TE 1557 metric, as described in Section 5.1, by removing the Flex-Algorithm 1558 ASLA TE metric advertisement for the link. The link can be made the 1559 link of last resort by setting the TE metric value in the Flex- 1560 Algorithm ASLA delay advertisement for the link to the value of (2^24 1561 - 1) in IS-IS and (2^32 - 1) in OSPF. 1563 16. Backward Compatibility 1565 This extension brings no new backward compatibility issues. IS-IS, 1566 OSPFv2 and OSPFv3 all have well defined handling of unrecognized TLVs 1567 and sub-TLVs that allows the introduction of the new extensions, 1568 similar to those defined here, without introducing any 1569 interoperability issues. 1571 17. Security Considerations 1573 This draft adds two new ways to disrupt IGP networks: 1575 An attacker can hijack a particular Flex-Algorithm by advertising 1576 a FAD with a priority of 255 (or any priority higher than that of 1577 the legitimate nodes). 1579 An attacker could make it look like a router supports a particular 1580 Flex-Algorithm when it actually doesn't, or vice versa. 1582 Both of these attacks can be addressed by the existing security 1583 extensions as described in [RFC5304] and [RFC5310] for IS-IS, in 1584 [RFC2328] and [RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] 1585 for OSPFv3. 1587 18. IANA Considerations 1589 18.1. IGP IANA Considerations 1591 18.1.1. IGP Algorithm Types Registry 1593 This document makes the following registrations in the "IGP Algorithm 1594 Types" registry: 1596 Type: 128-255. 1598 Description: Flexible Algorithms. 1600 Reference: This document (Section 4). 1602 18.1.2. IGP Metric-Type Registry 1604 IANA is requested to set up a registry called "IGP Metric-Type 1605 Registry" under an "Interior Gateway Protocol (IGP) Parameters" IANA 1606 registries. The registration policy for this registry is "Standards 1607 Action" ([RFC8126] and [RFC7120]). 1609 Values in this registry come from the range 0-255. 1611 This document registers following values in the "IGP Metric-Type 1612 Registry": 1614 Type: 0 1616 Description: IGP metric 1618 Reference: This document (Section 5.1) 1620 Type: 1 1622 Description: Min Unidirectional Link Delay as defined in 1623 [RFC8570], section 4.2, and [RFC7471], section 4.2. 1625 Reference: This document (Section 5.1) 1627 Type: 2 1629 Description: Traffic Engineering Default Metric as defined in 1630 [RFC5305], section 3.7, and Traffic engineering metric as defined 1631 in [RFC3630], section 2.5.5 1633 Reference: This document (Section 5.1) 1635 18.2. Flexible Algorithm Definition Flags Registry 1637 IANA is requested to set up a registry called "IS-IS Flexible 1638 Algorithm Definition Flags Registry" under an "Interior Gateway 1639 Protocol (IGP) Parameters" IANA registries. The registration policy 1640 for this registry is "Standards Action" ([RFC8126] and [RFC7120]). 1642 This document defines the following single bit in Flexible Algorithm 1643 Definition Flags registry: 1645 Bit # Name 1646 ----- ------------------------------ 1647 0 Prefix Metric Flag (M-flag) 1649 Reference: This document (Section 6.4, Section 7.4). 1651 18.3. IS-IS IANA Considerations 1653 18.3.1. Sub TLVs for Type 242 1655 This document makes the following registrations in the "sub-TLVs for 1656 TLV 242" registry. 1658 Type: 26. 1660 Description: Flexible Algorithm Definition. 1662 Reference: This document (Section 5.1). 1664 18.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1666 This document makes the following registrations in the "Sub-TLVs for 1667 for TLVs 135, 235, 236, and 237" registry. 1669 Type: 6 1671 Description: Flexible Algorithm Prefix Metric. 1673 Reference: This document (Section 8). 1675 18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1677 This document creates the following Sub-Sub-TLV Registry: 1679 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1681 Registration Procedure: Expert review 1682 Reference: This document (Section 5.1) 1684 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1685 for Flexible Algorithm Definition Sub-TLV" registry: 1687 Type: 1 1689 Description: Flexible Algorithm Exclude Admin Group 1691 Reference: This document (Section 6.1). 1693 Type: 2 1695 Description: Flexible Algorithm Include-Any Admin Group 1697 Reference: This document (Section 6.2). 1699 Type: 3 1701 Description: Flexible Algorithm Include-All Admin Group 1703 Reference: This document (Section 6.3). 1705 Type: 4 1707 Description: Flexible Algorithm Definition Flags 1709 Reference: This document (Section 6.4). 1711 Type: 5 1713 Description: Flexible Algorithm Exclude SRLG 1715 Reference: This document (Section 6.5). 1717 18.4. OSPF IANA Considerations 1719 18.4.1. OSPF Router Information (RI) TLVs Registry 1721 This specification updates the OSPF Router Information (RI) TLVs 1722 Registry. 1724 Type: 16 1726 Description: Flexible Algorithm Definition TLV. 1728 Reference: This document (Section 5.2). 1730 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1732 This document makes the following registrations in the "OSPFv2 1733 Extended Prefix TLV Sub-TLVs" registry. 1735 Type: 3 1737 Description: Flexible Algorithm Prefix Metric. 1739 Reference: This document (Section 9). 1741 18.4.3. OSPFv3 Extended-LSA Sub-TLVs 1743 This document makes the following registrations in the "OSPFv3 1744 Extended-LSA Sub-TLVs" registry. 1746 Type: 26 1748 Description: Flexible Algorithm Prefix Metric. 1750 Reference: This document (Section 9). 1752 Type: TBD (suggested value 30) 1754 Description: OSPF Flexible Algorithm ASBR Metric Sub-TLV 1756 Reference: This document (Section 10.2). 1758 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits 1760 This specification requests creation of "OSPF Flex-Algorithm Prefix 1761 Metric Bits" registry under the OSPF Parameters Registry with the 1762 following initial values. 1764 Bit Number: 0 1766 Description: E bit - External Type 1768 Reference: this document. 1770 The bits 1-7 are unassigned and the registration procedure to be 1771 followed for this registry is IETF Review. 1773 18.4.5. OSPF Opaque LSA Option Types 1775 This document makes the following registrations in the "OSPF Opaque 1776 LSA Option Types" registry. 1778 Value: TBD (suggested value 11) 1780 Description: OSPFv2 Extended Inter-Area ASBR LSA 1782 Reference: This document (Section 10.1). 1784 18.4.6. OSPFv2 Externded Inter-Area ASBR TLVs 1786 This specification requests creation of "OSPFv2 Extended Inter-Area 1787 ASBR TLVs" registry under the OSPFv2 Parameters Registry with the 1788 following initial values. 1790 Value: 1 1792 Description : Extended Inter-Area ASBR TLV 1794 Reference: this document 1796 The values 2 to 32767 are unassigned, values 32768 to 33023 are 1797 reserved for experimental use while the values 0 and 33024 to 65535 1798 are reserved. The registration procedure to be followed for this 1799 registry is IETF Review or IESG Approval. 1801 18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs 1803 This specification requests creation of "OSPFv2 Extended Inter-Area 1804 ASBR Sub-TLVs" registry under the OSPFv2 Parameters Registry with the 1805 following initial values. 1807 Value: 1 1809 Description : OSPF Flexible Algorithm ASBR Metric Sub-TLV 1811 Reference: this document 1813 The values 2 to 32767 are unassigned, values 32768 to 33023 are 1814 reserved for experimental use while the values 0 and 33024 to 65535 1815 are reserved. The registration procedure to be followed for this 1816 registry is IETF Review or IESG Approval. 1818 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1820 This document creates the following registry: 1822 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1824 Registration Procedure: Expert review 1825 Reference: This document (Section 5.2) 1827 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1828 define sub-TLVs at any level of nesting for the Flexible Algorithm 1829 TLV and should be added to the "Open Shortest Path First (OSPF) 1830 Parameters" registries group. New values can be allocated via IETF 1831 Review or IESG Approval. 1833 This document registers following Sub-TLVs in the "TLVs for Flexible 1834 Algorithm Definition TLV" registry: 1836 Type: 1 1838 Description: Flexible Algorithm Exclude Admin Group 1840 Reference: This document (Section 7.1). 1842 Type: 2 1844 Description: Flexible Algorithm Include-Any Admin Group 1846 Reference: This document (Section 7.2). 1848 Type: 3 1850 Description: Flexible Algorithm Include-All Admin Group 1852 Reference: This document (Section 7.3). 1854 Type: 4 1856 Description: Flexible Algorithm Definition Flags 1858 Reference: This document (Section 7.4). 1860 Type: 5 1862 Description: Flexible Algorithm Exclude SRLG 1864 Reference: This document (Section 7.5). 1866 Types in the range 32768-33023 are for experimental use; these will 1867 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1869 Types in the range 33024-65535 are not to be assigned at this time. 1870 Before any assignments can be made in the 33024-65535 range, there 1871 MUST be an IETF specification that specifies IANA Considerations that 1872 covers the range being assigned. 1874 18.4.9. Link Attribute Applications Registry 1876 This document registers following bit in the Link Attribute 1877 Applications Registry: 1879 Bit-3 1881 Description: Flexible Algorithm (X-bit) 1883 Reference: This document (Section 12). 1885 19. Acknowledgements 1887 This draft, among other things, is also addressing the problem that 1888 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1889 All authors of that draft agreed to join this draft. 1891 Thanks to Eric Rosen, Tony Przygienda, William Britto A J, Gunter Van 1892 De Velde, Dirk Goethals, Manju Sivaji and, Baalajee S for their 1893 detailed review and excellent comments. 1895 Thanks to Cengiz Halit for his review and feedback during initial 1896 phase of the solution definition. 1898 Thanks to Kenji Kumaki for his comments. 1900 Thanks to Acee Lindem for editorial comments. 1902 20. References 1904 20.1. Normative References 1906 [I-D.ietf-lsr-isis-srv6-extensions] 1907 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1908 Z. Hu, "IS-IS Extensions to Support Segment Routing over 1909 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-18 1910 (work in progress), October 2021. 1912 [ISO10589] 1913 International Organization for Standardization, 1914 "Intermediate system to Intermediate system intra-domain 1915 routeing information exchange protocol for use in 1916 conjunction with the protocol for providing the 1917 connectionless-mode Network Service (ISO 8473)", ISO/ 1918 IEC 10589:2002, Second Edition, Nov 2002. 1920 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1921 Requirement Levels", BCP 14, RFC 2119, 1922 DOI 10.17487/RFC2119, March 1997, 1923 . 1925 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 1926 Support of Generalized Multi-Protocol Label Switching 1927 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 1928 . 1930 [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The 1931 OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250, 1932 July 2008, . 1934 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1935 in Support of Generalized Multi-Protocol Label Switching 1936 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1937 . 1939 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1940 Traffic Engineering (MPLS-TE)", RFC 7308, 1941 DOI 10.17487/RFC7308, July 2014, 1942 . 1944 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1945 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1946 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1947 2015, . 1949 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1950 S. Shaffer, "Extensions to OSPF for Advertising Optional 1951 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1952 February 2016, . 1954 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1955 for Advertising Router Information", RFC 7981, 1956 DOI 10.17487/RFC7981, October 2016, 1957 . 1959 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1960 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1961 May 2017, . 1963 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1964 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1965 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1966 2018, . 1968 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 1969 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1970 Extensions for Segment Routing", RFC 8665, 1971 DOI 10.17487/RFC8665, December 2019, 1972 . 1974 [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 1975 for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 1976 December 2019, . 1978 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 1979 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 1980 Extensions for Segment Routing", RFC 8667, 1981 DOI 10.17487/RFC8667, December 2019, 1982 . 1984 [RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1985 J. Drake, "IS-IS Application-Specific Link Attributes", 1986 RFC 8919, DOI 10.17487/RFC8919, October 2020, 1987 . 1989 [RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura, 1990 J., and J. Drake, "OSPF Application-Specific Link 1991 Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020, 1992 . 1994 20.2. Informative References 1996 [I-D.gulkohegde-routing-planes-using-sr] 1997 Hegde, S. and A. Gulko, "Separating Routing Planes using 1998 Segment Routing", draft-gulkohegde-routing-planes-using- 1999 sr-00 (work in progress), March 2017. 2001 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 2002 Litkowski, S., Bashandy, A., Filsfils, C., Francois, P., 2003 Decraene, B., and D. Voyer, "Topology Independent Fast 2004 Reroute using Segment Routing", draft-ietf-rtgwg-segment- 2005 routing-ti-lfa-07 (work in progress), June 2021. 2007 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 2008 DOI 10.17487/RFC2328, April 1998, 2009 . 2011 [RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", 2012 RFC 3101, DOI 10.17487/RFC3101, January 2003, 2013 . 2015 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering 2016 (TE) Extensions to OSPF Version 2", RFC 3630, 2017 DOI 10.17487/RFC3630, September 2003, 2018 . 2020 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 2021 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 2022 RFC 3906, DOI 10.17487/RFC3906, October 2004, 2023 . 2025 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 2026 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 2027 . 2029 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 2030 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2031 2008, . 2033 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 2034 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2035 2008, . 2037 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 2038 and M. Fanto, "IS-IS Generic Cryptographic 2039 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2040 2009, . 2042 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 2043 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 2044 . 2046 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 2047 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 2048 2014, . 2050 [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. 2051 Previdi, "OSPF Traffic Engineering (TE) Metric 2052 Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, 2053 . 2055 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 2056 "Security Extension for OSPFv2 When Using Manual Key 2057 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 2058 . 2060 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2061 Writing an IANA Considerations Section in RFCs", BCP 26, 2062 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2063 . 2065 [RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward, 2066 D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) 2067 Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March 2068 2019, . 2070 Authors' Addresses 2072 Peter Psenak (editor) 2073 Cisco Systems 2074 Apollo Business Center 2075 Mlynske nivy 43 2076 Bratislava, 82109 2077 Slovakia 2079 Email: ppsenak@cisco.com 2081 Shraddha Hegde 2082 Juniper Networks, Inc. 2083 Embassy Business Park 2084 Bangalore, KA, 560093 2085 India 2087 Email: shraddha@juniper.net 2089 Clarence Filsfils 2090 Cisco Systems, Inc. 2091 Brussels 2092 Belgium 2094 Email: cfilsfil@cisco.com 2096 Ketan Talaulikar 2097 Cisco Systems, Inc. 2098 S.No. 154/6, Phase I, Hinjawadi 2099 PUNE, MAHARASHTRA 411 057 2100 India 2102 Email: ketant@cisco.com 2103 Arkadiy Gulko 2104 Edward Jones 2106 Email: arkadiy.gulko@edwardjones.com