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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-14 -- Possible downref: Non-RFC (?)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reference: RFC 8919 (Obsoleted by RFC 9479) ** Obsolete normative reference: RFC 8920 (Obsoleted by RFC 9492) == Outdated reference: A later version (-13) exists of draft-ietf-rtgwg-segment-routing-ti-lfa-06 Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--).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: November 27, 2021 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Edward Jones 11 May 26, 2021 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-16 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 November 27, 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 . . . . . . 22 88 11. Advertisement of Node Participation in a Flex-Algorithm . . . 24 89 11.1. Advertisement of Node Participation for Segment Routing 24 90 11.2. Advertisement of Node Participation for Other 91 Applications . . . . . . . . . . . . . . . . . . . . . . 24 92 12. Advertisement of Link Attributes for Flex-Algorithm . . . . . 24 93 13. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 25 94 13.1. Multi-area and Multi-domain Considerations . . . . . . . 27 95 14. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 29 96 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 30 97 14.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 30 98 14.3. Other Applications' Forwarding for Flex-Algorithm . . . 31 99 15. Operational Considerations . . . . . . . . . . . . . . . . . 31 100 15.1. Inter-area Considerations . . . . . . . . . . . . . . . 31 101 15.2. Usage of SRLG Exclude Rule with Flex-Algorithm . . . . . 32 102 15.3. Max-metric consideration . . . . . . . . . . . . . . . . 33 103 16. Backward Compatibility . . . . . . . . . . . . . . . . . . . 33 104 17. Security Considerations . . . . . . . . . . . . . . . . . . . 33 105 18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 106 18.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 34 107 18.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 34 108 18.1.2. IGP Metric-Type Registry . . . . . . . . . . . . . . 34 109 18.2. Flexible Algorithm Definition Flags Registry . . . . . . 35 110 18.3. ISIS IANA Considerations . . . . . . . . . . . . . . . . 35 111 18.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 35 112 18.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 35 113 18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 114 TLV . . . . . . . . . . . . . . . . . . . . . . . . 35 115 18.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 36 116 18.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 36 117 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 37 118 18.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 37 119 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits . . . . . . . 37 120 18.4.5. OSPF Opaque LSA Option Types . . . . . . . . . . . . 37 121 18.4.6. OSPFv2 Externded Inter-Area ASBR TLVs . . . . . . . 38 122 18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs . . . . . . . . . . 38 123 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV 124 Registry . . . . . . . . . . . . . . . . . . . . . . 38 125 18.4.9. Link Attribute Applications Registry . . . . . . . . 40 126 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 40 127 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 40 128 20.1. Normative References . . . . . . . . . . . . . . . . . . 40 129 20.2. Informative References . . . . . . . . . . . . . . . . . 42 130 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44 132 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 ISIS, OSPFv2, and 153 OSPFv3 that enable a router to advertise TLVs that identify (a) 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 ISIS 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. ISIS Flexible Algorithm Definition Sub-TLV 253 The ISIS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used 254 to advertise the definition of the Flex-Algorithm. 256 The ISIS FAD Sub-TLV is advertised as a Sub-TLV of the ISIS Router 257 Capability TLV-242 that is defined in [RFC7981]. 259 ISIS 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 ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a 311 router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given 312 Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs 313 for a given Flexible-Algorithm from the same originator SHOULD select 314 the first advertisement in the lowest numbered LSP. 316 The ISIS FAD Sub-TLV has an area scope. The Router Capability TLV in 317 which the FAD Sub-TLV is present MUST have the S-bit clear. 319 ISIS 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 (ISIS). We will refer to it as FAD TLV in 401 this section, even though in case of ISIS 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 ISIS, or Router 422 ID, in the case of OSPFv2 and OSPFv3. For ISIS, 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 ISIS FAD Sub-TLV 453 6.1. ISIS 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 ISIS 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 ISIS Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub- 464 TLV) is a Sub-TLV of the ISIS 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 ISIS FAEAG Sub-TLV MUST NOT appear more than once in an ISIS FAD 487 Sub-TLV. If it appears more than once, the ISIS FAD Sub-TLV MUST be 488 ignored by the receiver. 490 6.2. ISIS 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 ISIS 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 ISIS 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 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 505 2. 507 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 508 appear more than once in an ISIS FAD Sub-TLV. If it appears more 509 than once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 511 6.3. ISIS 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 ISIS 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 ISIS 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 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 526 3. 528 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 529 appear more than once in an ISIS FAD Sub-TLV. If it appears more 530 than once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 532 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV 534 The ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 535 is a Sub-TLV of the ISIS 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 ISIS FADF Sub-TLV MUST NOT appear more than once in an ISIS FAD 575 Sub-TLV. If it appears more than once, the ISIS FAD Sub-TLV MUST be 576 ignored by the receiver. 578 If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV, 579 all the bits are assumed to be set to 0. 581 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV 583 The Flexible Algorithm definition can specify Shared Risk Link Groups 584 (SRLGs) that the operator wants to exclude during the Flex-Algorithm 585 path computation. 587 The ISIS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used to 588 advertise the exclude rule that is used during the Flex-Algorithm 589 path calculation as specified in Section 13. 591 The ISIS FAESRLG Sub-TLV is a Sub-TLV of the ISIS FAD Sub-TLV. It 592 has the following format: 594 0 1 2 3 595 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 597 | Type | Length | 598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 599 | Shared Risk Link Group Value | 600 +- -+ 601 | ... | 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 603 where: 605 Type: 5 606 Length: variable, dependent on number of SRLG values. MUST be a 607 multiple of 4 octets. 609 Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. 611 The ISIS FAESRLG Sub-TLV MUST NOT appear more than once in an ISIS 612 FAD Sub-TLV. If it appears more than once, the ISIS FAD Sub-TLV MUST 613 be ignored by the receiver. 615 7. Sub-TLVs of OSPF FAD TLV 617 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 619 The Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is 620 a Sub-TLV of the OSPF FAD TLV. It's usage is described in 621 Section 6.1. It has the following format: 623 0 1 2 3 624 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 1 625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 626 | Type | Length | 627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 628 | Extended Admin Group | 629 +- -+ 630 | ... | 631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 632 where: 634 Type: 1 636 Length: variable, dependent on the size of the Extended Admin 637 Group. MUST be a multiple of 4 octets. 639 Extended Administrative Group: Extended Administrative Group as 640 defined in [RFC7308]. 642 The OSPF FAEAG Sub-TLV MUST NOT appear more than once in an OSPF FAD 643 TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored 644 by the receiver. 646 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 648 The usage of this Sub-TLVs is described in Section 6.2. 650 The format of the OSPF Flexible Algorithm Include-Any Admin Group 651 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 652 Section 7.1. 654 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 655 2. 657 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 658 appear more than once in an OSPF FAD TLV. If it appears more than 659 once, the OSPF FAD TLV MUST be ignored by the receiver. 661 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 663 The usage of this Sub-TLVs is described in Section 6.3. 665 The format of the OSPF Flexible Algorithm Include-Any Admin Group 666 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 667 Section 7.1. 669 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 670 3. 672 The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 673 appear more than once in an OSPF FAD TLV. If it appears more than 674 once, the OSPF FAD TLV MUST be ignored by the receiver. 676 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 678 The OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 679 is a Sub-TLV of the OSPF FAD TLV. It has the following format: 681 0 1 2 3 682 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 1 683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 684 | Type | Length | 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 686 | Flags | 687 +- -+ 688 | ... | 689 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 690 where: 692 Type: 4 694 Length: variable, dependent on the size of the Flags field. MUST 695 be a multiple of 4 octets. 697 Flags: 699 0 1 2 3 4 5 6 7... 700 +-+-+-+-+-+-+-+-+... 701 |M| | | ... 702 +-+-+-+-+-+-+-+-+... 704 M-flag: when set, the Flex-Algorithm specific prefix and ASBR 705 metric MUST be used for inter-area and external prefix 706 calculation. This flag is not applicable to prefixes 707 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 than once in an OSPF FAD 720 TLV. If it appears more than 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 than once in an OSPF 751 FAD TLV. If it appears more than 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 than 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 Inter-Area Prefix TLV 814 External Prefix TLV 816 OSPF FAPM Sub-TLV has the following format: 818 0 1 2 3 819 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 1 820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 821 | Type | Length | 822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 823 |Flex-Algorithm | Flags | Reserved | 824 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 825 | Metric | 826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 828 where: 830 Type: 3 for OSPFv2, 26 for OSPFv3 832 Length: 8 octets 834 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 836 Flags: single octet value 838 0 1 2 3 4 5 6 7 839 +-+-+-+-+-+-+-+-+ 840 |E| | 841 +-+-+-+-+-+-+-+-+ 843 E bit : position 0: The type of external metric. If bit is 844 set, the metric specified is a Type 2 external metric. This 845 bit is applicable only to OSPF External and NSSA external 846 prefixes. This is semantically the same as E bit in section 847 A.4.5 of [RFC2328] and section A.4.7 of [RFC5340] for OSPFv2 848 and OSPFv3 respectively. 850 Bits 1 through 7: MUST be cleared by sender and ignored by 851 receiver. 853 Reserved: Must be set to 0, ignored at reception. 855 Metric: 4 octets of metric information 857 The OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. 858 If it appears more than once with the same Flex-Algorithm value, the 859 first instance MUST be used and any subsequent instances MUST be 860 ignored. 862 The usage of the Flex-Algorithm prefix metric is described in 863 Section 13. 865 10. OSPF Flexible Algorithm ASBR Reachability Advertisement 867 An OSPF ABR advertises the reachability of ASBRs in its attached 868 areas to enable routers within those areas to perform route 869 calculations for external prefixes advertised by the ASBRs. OSPF 870 extensions for advertisement of Flex-Algorithm specific reachability 871 and metric for ASBRs is similarly required for Flex-Algorithm 872 external prefix computations as described further in Section 13.1. 874 10.1. OSPFv2 Extended Inter-Area ASBR LSA 876 The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) LSA is an OSPF Opaque 877 LSA [RFC5250] that is used to advertise additional attributes related 878 to the reachability of the OSPFv2 ASBR that is external to the area 879 yet internal to the OSPF domain. Semantically, the OSPFv2 EIA-ASBR 880 LSA is equivalent to the fixed format Type 4 Summary LSA [RFC2328]. 881 Unlike the Type 4 Summary LSA, the LSID of the EIA-ASBR LSA does not 882 carry the ASBR Router-ID - the ASBR Router-ID is carried in the body 883 of the LSA. OSPFv2 EIA-ASBR LSA is advertised by an OSPFv2 ABR and 884 its flooding is defined to be area-scoped only. 886 An OSPFv2 ABR generates the EIA-ASBR LSA for an ASBR when it is 887 advertising the Type-4 Summary LSA for it and has the need for 888 advertising additional attributes for that ASBR beyond what is 889 conveyed in the fixed format Type-4 Summary LSA. An OSPFv2 ABR MUST 890 NOT advertise the EIA-ASBR LSA for an ASBR for which it is not 891 advertising the Type 4 Summary LSA. This ensures that the ABR does 892 not generate the EIA-ASBR LSA for an ASBR to which it does not have 893 reachability in the base OSPFv2 topology calculation. The OSPFv2 ABR 894 SHOULD NOT advertise the EIA-ASBR LSA for an ASBR when it does not 895 have additional attributes to advertise for that ASBR. 897 The OSPFv2 EIA-ASBR LSA has the following format: 899 0 1 2 3 900 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 1 901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 902 | LS age | Options | LS Type | 903 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 904 | Opaque Type | Opaque ID | 905 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 906 | Advertising Router | 907 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 908 | LS sequence number | 909 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 910 | LS checksum | Length | 911 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 912 | | 913 +- TLVs -+ 914 | ... | 916 The Opaque Type used by the OSPFv2 EIA-ASBR LSA is TBD (suggested 917 value 11). The Opaque Type is used to differentiate the various 918 types of OSPFv2 Opaque LSAs and is described in Section 3 of 919 [RFC5250]. The LS Type MUST be 10, indicating that the Opaque LSA 920 flooding scope is area-local [RFC5250]. The LSA Length field 921 [RFC2328] represents the total length (in octets) of the Opaque LSA, 922 including the LSA header and all TLVs (including padding). 924 The Opaque ID field is an arbitrary value used to maintain multiple 925 OSPFv2 EIA-ASBR LSAs. For OSPFv2 EIA-ASBR LSAs, the Opaque ID has no 926 semantic significance other than to differentiate OSPFv2 EIA-ASBR 927 LSAs originated by the same OSPFv2 ABR. If multiple OSPFv2 EIA-ASBR 928 LSAs specify the same ASBR, the attributes from the Opaque LSA with 929 the lowest Opaque ID SHOULD be used. 931 The format of the TLVs within the body of the OSPFv2 EIA-ASBR LSA is 932 the same as the format used by the Traffic Engineering Extensions to 933 OSPFv2 [RFC3630]. The variable TLV section consists of one or more 934 nested TLV tuples. Nested TLVs are also referred to as sub- TLVs. 935 The Length field defines the length of the value portion in octets 936 (thus, a TLV with no value portion would have a length of 0). The 937 TLV is padded to 4-octet alignment; padding is not included in the 938 Length field (so a 3-octet value would have a length of 3, but the 939 total size of the TLV would be 8 octets). Nested TLVs are also 940 32-bit aligned. For example, a 1-byte value would have the Length 941 field set to 1, and 3 octets of padding would be added to the end of 942 the value portion of the TLV. The padding is composed of zeros. 944 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV 946 The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) TLV is a top-level TLV 947 of the OSPFv2 EIA-ASBR LSA and is used to advertise additional 948 attributes associated with the reachability of an ASBR. 950 The OSPFv2 EIA-ASBR TLV has the following format: 952 0 1 2 3 953 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 1 954 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 955 | Type | Length | 956 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 957 | ASBR Router ID | 958 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 959 . . 960 . Sub-TLVs . 961 . . 962 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 964 where: 966 Type: 1 968 Length: variable 970 ASBR Router ID: four octets carrying the OSPF Router ID of the 971 ASBR whose information is being carried. 973 Sub-TLVs : variable 975 Only a single OSPFv2 EIA-ASBR TLV MUST be advertised in each OSPFv2 976 EIA-ASBR LSA and the receiver MUST ignore all instances of this TLV 977 other than the first one in an LSA. 979 OSPFv2 EIA-ASBR TLV MUST be present inside an OSPFv2 EIA-ASBR LSA 980 with at least a single sub-TLV included, otherwise the OSPFv2 EIA- 981 ASBR LSA MUST be ignored by the receiver. 983 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV 985 The OSPF Flexible Algorithm ASBR Metric (FAAM) Sub-TLV supports the 986 advertisement of a Flex-Algorithm specific metric associated with a 987 given ASBR reachability advertisement by an ABR. 989 The OSPF Flex-Algorithm ASBR Metric (FAAM) Sub-TLV is a Sub-TLV of 990 the: 992 - OSPFv2 Extended Inter-Area ASBR TLV as defined in Section 10.1.1 994 - OSPFv3 Inter-Area-Router TLV defined in [RFC8362] 996 OSPF FAAM Sub-TLV has the following format: 998 0 1 2 3 999 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 1000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1001 | Type | Length | 1002 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1003 |Flex-Algorithm | Reserved | 1004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1005 | Metric | 1006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 where: 1010 Type: 1 for OSPFv2, TBD (suggested value 30) for OSPFv3 1012 Length: 8 octets 1014 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 1016 Reserved: Must be set to 0, ignored at reception. 1018 Metric: 4 octets of metric information 1020 The OSPF FAAM Sub-TLV MAY appear multiple times in its parent TLV. 1021 If it appears more than once with the same Flex-Algorithm value, the 1022 first instance MUST be used and any subsequent instances MUST be 1023 ignored. 1025 The advertisement of the ASBR reachability using the OSPF FAAM Sub- 1026 TLV inside the OSPFv2 EIA-ASBR LSA follows the section 12.4.3 of 1027 [RFC2328] and inside the OSPFv3 E-Inter-Area-Router LSA follows the 1028 section 4.8.5 of [RFC5340]. The reachability of the ASBR is 1029 evaluated in the context of the specific Flex-Algorithm. 1031 The FAAM computed by the ABR will be equal to the metric to reach the 1032 ASBR for a given Flex-Algorithm in a source area or the cumulative 1033 metric via other ABR(s) when the ASBR is in a remote area. This is 1034 similar in nature to how the metric is set when the ASBR reachability 1035 metric is computed in the default algorithm for the metric in the 1036 OSPFv2 Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. 1038 An OSPF ABR MUST NOT include the OSPF FAAM Sub-TLV with a specific 1039 Flex-Algorithm in its reachability advertisement for an ASBR between 1040 areas unless that ASBR is reachable for it in the context of that 1041 specific Flex-Algorithm. 1043 An OSPF ABR MUST include the OSPF FAAM Sub-TLVs as part of the ASBR 1044 reachability advertisement between areas for the Flex-Algorithm for 1045 which the winning FAD includes the M-flag and the ASBR is reachable 1046 in the context of that specific Flex-Algorithm. 1048 OSPF routers MUST use the OSPF FAAM Sub-TLV to calculate the 1049 reachability of the ASBRs if the winning FAD for the specific Flex- 1050 Algorithm includes the M-flag. OSPF routers MUST NOT use the OSPF 1051 FAAM Sub-TLV to calculate the reachability of the ASBRs for the 1052 specific Flex-Algorithm if the winning FAD for such Flex-Algorithm 1053 does not include the M-flag. Instead, the OSPFv2 Type 4 Summary LSAs 1054 or the OSPFv3 Inter-Area-Router-LSAs MUST be used instead as 1055 specified in section 16.2 of [RFC2328] and section 4.8.5 of [RFC5340] 1056 for OSPFv2 and OSPFv3 respectively. 1058 The processing of the new or changed OSPF FAAM Sub-TLV triggers the 1059 processing of the External routes similar to what is described in 1060 section 16.5 of the [RFC2328] for OSPFv2 and section 4.8.5 of 1061 [RFC5340] for OSPFv3 for the specific Flex-Algorithm. The External 1062 and NSSA External route calculation should be limited to Flex- 1063 Algorithm(s) for which the winning FAD(s) includes the M-flag. 1065 Processing of the OSPF FAAM Sub-TLV does not require the existence of 1066 the equivalent OSPFv2 Type 4 Summary LSA or the OSPFv3 Inter-Area- 1067 Router-LSA that is advertised by the same ABR inside the area. When 1068 the OSPFv2 EIA-ASBR LSA or the OSPFv3 E-Inter-Area-Router-LSA are 1069 advertised along with the OSPF FAAM Sub-TLV by the ABR for a specific 1070 ASBR, it is expected that the same ABR would advertise the 1071 reachability of the same ASBR in the equivalent base LSAs - i.e., the 1072 OSPFv2 Type 4 Summary LSA or the OSPFv3 Inter-Area-Router-LSA. The 1073 presence of the base LSA is not mandatory for the usage of the 1074 extended LSA with the OSPF FAAM Sub-TLV. This means that the order 1075 in which these LSAs are received is not significant. 1077 11. Advertisement of Node Participation in a Flex-Algorithm 1079 When a router is configured to support a particular Flex-Algorithm, 1080 we say it is participating in that Flex-Algorithm. 1082 Paths computed for a specific Flex-Algorithm MAY be used by various 1083 applications, each potentially using its own specific data plane for 1084 forwarding traffic over such paths. To guarantee the presence of the 1085 application specific forwarding state associated with a particular 1086 Flex-Algorithm, a router MUST advertise its participation for a 1087 particular Flex-Algorithm for each application specifically. 1089 11.1. Advertisement of Node Participation for Segment Routing 1091 [RFC8667], [RFC8665], and [RFC8666] (IGP Segment Routing extensions) 1092 describe how the SR-Algorithm is used to compute the IGP best path. 1094 Routers advertise the support for the SR-Algorithm as a node 1095 capability as described in the above mentioned IGP Segment Routing 1096 extensions. To advertise participation for a particular Flex- 1097 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 1098 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 1099 (OSPF) or sub-TLV (ISIS). 1101 Segment Routing Flex-Algorithm participation advertisement is 1102 topology independent. When a router advertises participation in an 1103 SR-Algorithm, the participation applies to all topologies in which 1104 the advertising node participates. 1106 11.2. Advertisement of Node Participation for Other Applications 1108 This section describes considerations related to how other 1109 applications can advertise their participation in a specific Flex- 1110 Algorithm. 1112 Application-specific Flex-Algorithm participation advertisements MAY 1113 be topology specific or MAY be topology independent, depending on the 1114 application itself. 1116 Application-specific advertisement for Flex-Algorithm participation 1117 MUST be defined for each application and is outside of the scope of 1118 this document. 1120 12. Advertisement of Link Attributes for Flex-Algorithm 1122 Various link attributes may be used during the Flex-Algorithm path 1123 calculation. For example, include or exclude rules based on link 1124 affinities can be part of the Flex-Algorithm definition as defined in 1125 Section 6 and Section 7. 1127 Link attribute advertisements that are to be used during Flex- 1128 Algorithm calculation MUST use the Application-Specific Link 1129 Attribute (ASLA) advertisements defined in [RFC8919] or [RFC8920], 1130 unless, in the case of IS-IS, the L-Flag is set in the ASLA 1131 advertisement. If the L-Flag is set, as defined in [RFC8919] 1132 Section 4.2 subject to the constraints discussed in Section 6 of the 1133 [[RFC8919], then legacy advertisements are to be used instead. 1135 The mandatory use of ASLA advertisements applies to link attributes 1136 specifically mentioned in this document (Min Unidirectional Link 1137 Delay, TE Default Metric, Administrative Group, Extended 1138 Administrative Group and Shared Risk Link Group) and any other link 1139 attributes that may be used in support of Flex-Algorithm in the 1140 future. 1142 A new Application Identifier Bit is defined to indicate that the ASLA 1143 advertisement is associated with the Flex-Algorithm application. 1144 This bit is set in the Standard Application Bit Mask (SABM) defined 1145 in [RFC8919] or [RFC8920]: 1147 Bit-3: Flexible Algorithm (X-bit) 1149 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 1150 Application MAY use either the Administrative Group or Extended 1151 Administrative Group encodings. If the Administrative Group encoding 1152 is used, then the first 32 bits of the corresponding FAD sub-TLVs are 1153 mapped to the link attribute advertisements as specified in RFC 7308. 1155 13. Calculation of Flexible Algorithm Paths 1157 A router MUST be configured to participate in a given Flex-Algorithm 1158 K and MUST select the FAD based on the rules defined in Section 5.3 1159 before it can compute any path for that Flex-Algorithm. 1161 As described in Section 11, participation for any particular Flex- 1162 Algorithm MUST be advertised on a per-application basis. Calculation 1163 of the paths for any particular Flex-Algorithm MUST be application 1164 specific. 1166 The way applications handle nodes that do not participate in 1167 Flexible-Algorithm is application specific. If the application only 1168 wants to consider participating nodes during the Flex-Algorithm 1169 calculation, then when computing paths for a given Flex-Algorithm, 1170 all nodes that do not advertise participation for that Flex-Algorithm 1171 in their application-specific advertisements MUST be pruned from the 1172 topology. Segment Routing, including both SR MPLS and SRv6, are 1173 applications that MUST use such pruning when computing Flex-Algorithm 1174 paths. 1176 When computing the path for a given Flex-Algorithm, the metric-type 1177 that is part of the Flex-Algorithm definition (Section 5) MUST be 1178 used. 1180 When computing the path for a given Flex-Algorithm, the calculation- 1181 type that is part of the Flex-Algorithm definition (Section 5) MUST 1182 be used. 1184 Various link include or exclude rules can be part of the Flex- 1185 Algorithm definition. To refer to a particular bit within an AG or 1186 EAG we use the term 'color'. 1188 Rules, in the order as specified below, MUST be used to prune links 1189 from the topology during the Flex-Algorithm computation. 1191 For all links in the topology: 1193 1. Check if any exclude AG rule is part of the Flex-Algorithm 1194 definition. If such exclude rule exists, check if any color that 1195 is part of the exclude rule is also set on the link. If such a 1196 color is set, the link MUST be pruned from the computation. 1198 2. Check if any exclude SRLG rule is part of the Flex-Algorithm 1199 definition. If such exclude rule exists, check if the link is 1200 part of any SRLG that is also part of the SRLG exclude rule. If 1201 the link is part of such SRLG, the link MUST be pruned from the 1202 computation. 1204 3. Check if any include-any AG rule is part of the Flex-Algorithm 1205 definition. If such include-any rule exists, check if any color 1206 that is part of the include-any rule is also set on the link. If 1207 no such color is set, the link MUST be pruned from the 1208 computation. 1210 4. Check if any include-all AG rule is part of the Flex-Algorithm 1211 definition. If such include-all rule exists, check if all colors 1212 that are part of the include-all rule are also set on the link. 1213 If all such colors are not set on the link, the link MUST be 1214 pruned from the computation. 1216 5. If the Flex-Algorithm definition uses other than IGP metric 1217 (Section 5), and such metric is not advertised for the particular 1218 link in a topology for which the computation is done, such link 1219 MUST be pruned from the computation. A metric of value 0 MUST NOT 1220 be assumed in such case. 1222 13.1. Multi-area and Multi-domain Considerations 1224 Any IGP Shortest Path Tree calculation is limited to a single area. 1225 This applies to Flex-Algorithm calculations as well. Given that the 1226 computing router does not have visibility of the topology of the next 1227 areas or domain, the Flex-Algorithm specific path to an inter-area or 1228 inter-domain prefix will be computed for the local area only. The 1229 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 1230 will be selected based on the best path for the given Flex-Algorithm 1231 in the local area and such egress ABR or ASBR router will be 1232 responsible to compute the best Flex-Algorithm specific path over the 1233 next area or domain. This may produce an end-to-end path, which is 1234 sub-optimal based on Flex-Algorithm constraints. In cases where the 1235 ABR or ASBR has no reachability to a prefix for a given Flex- 1236 Algorithm in the next area or domain, the traffic may be dropped by 1237 the ABR/ASBR. 1239 To allow the optimal end-to-end path for an inter-area or inter- 1240 domain prefix for any Flex-Algorithm to be computed, the FAPM has 1241 been defined in Section 8 and Section 9. For external route 1242 calculation for prefixes originated by ASBRs in remote areas in OSPF, 1243 the FAAM has been defined in Section 10.2 for the ABR to indicate its 1244 ASBR reachability along with the metric for the specific Flex- 1245 Algorithm. 1247 If the FAD selected based on the rules defined in Section 5.3 1248 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 1249 Section 9) when advertising the prefix, that is reachable in a given 1250 Flex-Algorithm, between areas or domains. Such metric will be equal 1251 to the metric to reach the prefix for that Flex-Algorithm in its 1252 source area or domain. This is similar in nature to how the metric 1253 is set when prefixes are advertised between areas or domains for the 1254 default algorithm. When a prefix is unreachable in its source area 1255 or domain in a specific Flex-Algorithm, then an ABR or ASBR MUST NOT 1256 include the FAPM for that Flex-Algorithm when advertising the prefix 1257 between areas or domains. 1259 If the FAD selected based on the rules defined in Section 5.3 1260 includes the M-flag, the FAPM MUST be used during the calculation of 1261 prefix reachability for the inter-area and external prefixes. If the 1262 FAPM for the Flex-Algorithm is not advertised with the inter-area or 1263 external prefix reachability advertisement, the prefix MUST be 1264 considered as unreachable for that Flex-Algorithm. Similarly in the 1265 case of OSPF, for ASBRs in remote areas, if the FAAM is not 1266 advertised by the local ABR(s), the ASBR MUST be considered as 1267 unreachable for that Flex-Algorithm and the external prefix 1268 advertisements from such an ASBR are not considered for that Flex- 1269 Algorithm. 1271 Flex-Algorithm prefix metrics and the OSPF Flex-Algorithm ASBR 1272 metrics MUST NOT be used during the Flex-Algorithm computation unless 1273 the FAD selected based on the rules defined in Section 5.3 includes 1274 the M-Flag, as described in (Section 6.4 or Section 7.4). 1276 In the case of OSPF, when calculating external routes in a Flex- 1277 Algorithm (with FAD selected includes the M-Flag) where the 1278 advertising ASBR is in a remote area, the metric will be the sum of 1279 the following: 1281 o the FAPM for that Flex-Algorithm advertised with the external 1282 route by the ASBR 1284 o the metric to reach the ASBR for that Flex-Algorithm from the 1285 local ABR i.e., the FAAM for that Flex-Algorithm advertised by the 1286 ABR in the local area for that ASBR 1288 o the Flex-Algorithm specific metric to reach the local ABR 1290 This is similar in nature to how the metric is calculated for routes 1291 learned from remote ASBRs in the default algorithm using the OSPFv2 1292 Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. 1294 If the FAD selected based on the rules defined in Section 5.3 does 1295 not includes the M-flag, then the IGP metrics associated with the 1296 prefix reachability advertisements used by the base ISIS and OSPF 1297 protocol MUST be used for the Flex-Algorithm route computation. 1298 Similarly, in the case of external route calculations in OSPF, the 1299 ASBR reachability is determined based on the base OSPFv2 Type 4 1300 Summary LSA and the OSFPv3 Inter-Area-Router LSA. 1302 It is NOT RECOMMENDED to use the Flex-Algorithm for inter-area or 1303 inter-domain prefix reachability without the M-flag set. The reason 1304 is that without the explicit Flex-Algorithm Prefix Metric 1305 advertisement (and the Flex-Algorithm ASBR metric advertisement in 1306 the case of OSPF external route calculation), it is not possible to 1307 conclude whether the ABR or ASBR has reachability to the inter-area 1308 or inter-domain prefix for a given Flex-Algorithm in the next area or 1309 domain. Sending the Flex-Algoritm traffic for such prefix towards 1310 the ABR or ASBR may result in traffic looping or black-holing. 1312 During the route computation, it is possible for the Flex-Algorithm 1313 specific metric to exceed the maximum value that can be stored in an 1314 unsigned 32-bit variable. In such scenarios, the value MUST be 1315 considered to be of value 4,294,967,295 during the computation and 1316 advertised as such. 1318 The FAPM MUST NOT be advertised with ISIS L1 or L2 intra-area, OSPFv2 1319 intra-area, or OSPFv3 intra-area routes. If the FAPM is advertised 1320 for these route-types, it MUST be ignored during the prefix 1321 reachability calculation. 1323 The M-flag in FAD is not applicable to prefixes advertised as SRv6 1324 locators. The ISIS SRv6 Locator TLV 1325 [I-D.ietf-lsr-isis-srv6-extensions] includes the Algorithm and Metric 1326 fields. When the SRv6 Locator is advertised between areas or 1327 domains, the metric field in the Locator TLV of ISIS MUST be used 1328 irrespective of the M-flag in the FAD advertisement. 1330 OSPF external and NSSA external prefix advertisements MAY include a 1331 non-zero forwarding address in the prefix advertisements in the base 1332 protocol. In such a scenario, the Flex-Algorithm specific 1333 reachability of the external prefix is determined by Flex-Algorithm 1334 specific reachability of the forwarding address. 1336 In OSPF, the procedures for translation of NSSA external prefix 1337 advertisements into external prefix advertisements performed by an 1338 NSSA ABR [RFC3101] remain unchanged for Flex-Algorithm. An NSSA 1339 translator MUST include the OSPF FAPM Sub-TLVs for all Flex- 1340 Algorithms that are in the original NSSA external prefix 1341 advertisement from the NSSA ASBR in the translated external prefix 1342 advertisement generated by it regardless of its participation in 1343 those Flex-Algorithms or its having reachability to the NSSA ASBR in 1344 those Flex-Algorithms. 1346 An area could become partitioned from the perspective of the Flex- 1347 Algorithm due to the constraints and/or metric being used for it, 1348 while maintaining the continuity in the algorithm 0. When that 1349 happens, some destinations inside that area could become unreachable 1350 in that Flex-Algorithm. These destinations will not be able to use 1351 an inter-area path. This is the consequence of the fact that the 1352 inter-area prefix reachability advertisement would not be available 1353 for these intra-area destinations within the area. It is RECOMMENDED 1354 to avoid such partitioning by providing enough redundancy inside the 1355 area for each Flex-Algorithm being used. 1357 14. Flex-Algorithm and Forwarding Plane 1359 This section describes how Flex-Algorithm paths are used in 1360 forwarding. 1362 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm 1364 This section describes how Flex-Algorithm paths are used with SR MPLS 1365 forwarding. 1367 Prefix SID advertisements include an SR-Algorithm value and, as such, 1368 are associated with the specified SR-Algorithm. Prefix-SIDs are also 1369 associated with a specific topology which is inherited from the 1370 associated prefix reachability advertisement. When the algorithm 1371 value advertised is a Flex-Algorithm value, the Prefix SID is 1372 associated with paths calculated using that Flex-Algorithm in the 1373 associated topology. 1375 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 1376 using the MPLS label that corresponds to the Prefix-SID that was 1377 advertised for that Flex-algorithm. If the Prefix SID for a given 1378 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 1379 be installed in the MPLS forwarding plane. 1381 Traffic that is supposed to be routed via Flex-Algorithm specific 1382 paths, MUST be dropped when there are no such paths available. 1384 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 1385 computed using the same constraints as the calculation of the primary 1386 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 1387 advertised specifically for the given algorithm. LFA paths MUST NOT 1388 use an Adjacency-SID that belongs to a link that has been pruned from 1389 the Flex-Algorithm computation. 1391 If LFA protection is being used to protect a given Flex-Algorithm 1392 paths, all routers in the area participating in the given Flex- 1393 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 1394 SID. These Node-SIDs are used to steer traffic over the LFA computed 1395 backup path. 1397 14.2. SRv6 Forwarding for Flex-Algorithm 1399 This section describes how Flex-Algorithm paths are used with SRv6 1400 forwarding. 1402 In SRv6 a node is provisioned with topology/algorithm specific 1403 locators for each of the topology/algorithm pairs supported by that 1404 node. Each locator is an aggregate prefix for all SIDs provisioned 1405 on that node which have the matching topology/algorithm. 1407 The SRv6 locator advertisement in ISIS 1408 [I-D.ietf-lsr-isis-srv6-extensions] includes the MTID value that 1409 associates the locator with a specific topology. SRv6 locator 1410 advertisements also includes an Algorithm value that explicitly 1411 associates the locator with a specific algorithm. When the algorithm 1412 value advertised with a locator represents a Flex-Algorithm, the 1413 paths to the locator prefix MUST be calculated using the specified 1414 Flex-Algorithm in the associated topology. 1416 Forwarding entries for the locator prefixes advertised in ISIS MUST 1417 be installed in the forwarding plane of the receiving SRv6 capable 1418 routers when the associated topology/algorithm is participating in 1419 them. Forwarding entries for locators associated with Flex- 1420 Algorithms in which the node is not participating MUST NOT be 1421 installed in the forwarding plane. 1423 When the locator is associated with a Flex-Algorithm, LFA paths to 1424 the locator prefix MUST be calculated using such Flex-Algorithm in 1425 the associated topology, to guarantee that they follow the same 1426 constraints as the calculation of the primary paths. LFA paths MUST 1427 only use SRv6 SIDs advertised specifically for the given Flex- 1428 Algorithm. 1430 If LFA protection is being used to protect locators associated with a 1431 given Flex-Algorithm, all routers in the area participating in the 1432 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1433 specific locator and END SID per node and one END.X SID for every 1434 link that has not been pruned from such Flex-Algorithm computation. 1435 These locators and SIDs are used to steer traffic over the LFA- 1436 computed backup path. 1438 14.3. Other Applications' Forwarding for Flex-Algorithm 1440 Any application that wants to use Flex-Algorithm specific forwarding 1441 needs to install some form of Flex-Algorithm specific forwarding 1442 entries. 1444 Application-specific forwarding for Flex-Algorithm MUST be defined 1445 for each application and is outside of the scope of this document. 1447 15. Operational Considerations 1449 15.1. Inter-area Considerations 1451 The scope of the FA computation is an area, so is the scope of the 1452 FAD. In ISIS, the Router Capability TLV in which the FAD Sub-TLV is 1453 advertised MUST have the S-bit clear, which prevents it to be flooded 1454 outside of the level in which it was originated. Even though in OSPF 1455 the FAD Sub-TLV can be flooded in an RI LSA that has AS flooding 1456 scope, the FAD selection is performed for each individual area in 1457 which it is being used. 1459 There is no requirement for the FAD for a particular Flex-Algorithm 1460 to be identical in all areas in the network. For example, traffic 1461 for the same Flex-Algorithm may be optimized for minimal delay (e.g., 1462 using delay metric) in one area or level, while being optimized for 1463 available bandwidth (e.g., using IGP metric) in another area or 1464 level. 1466 As described in Section 5.1, ISIS allows the re-generation of the 1467 winning FAD from level 2, without any modification to it, into a 1468 level 1 area. This allows the operator to configure the FAD in one 1469 or multiple routers in the level 2, without the need to repeat the 1470 same task in each level 1 area, if the intent is to have the same FAD 1471 for the particular Flex-Algorithm across all levels. This can 1472 similarly be achieved in OSPF by using the AS flooding scope of the 1473 RI LSA in which the FAD Sub-TLV for the particular Flex-Algoritm is 1474 advertised. 1476 Re-generation of FAD from a level 1 area to the level 2 area is not 1477 supported in ISIS, so if the intent is to regenerate the FAD between 1478 ISIS levels, the FAD MUST be defined on router(s) that are in level 1479 2. In OSPF, the FAD definition can be done in any area and be 1480 propagated to all routers in the OSPF routing domain by using the AS 1481 flooding scope of the RI LSA. 1483 15.2. Usage of SRLG Exclude Rule with Flex-Algorithm 1485 There are two different ways in which SRLG information can be used 1486 with Flex-Algorithm: 1488 In a context of a single Flex-Algorithm, it can be used for 1489 computation of backup paths, as described in 1490 [I-D.ietf-rtgwg-segment-routing-ti-lfa]. This usage does not 1491 require association of any specific SRLG constraint with the given 1492 Flex-Algorithm definition. 1494 In the context of multiple Flex-Algorithms, it can be used for 1495 creating disjoint sets of paths by pruning the links belonging to 1496 a specific SRLG from the topology on which a specific Flex- 1497 Algorithm computes its paths. This usage: 1499 Facilitates the usage of already deployed SRLG configurations 1500 for setup of disjoint paths between two or more Flex- 1501 Algorithms. 1503 Requires explicit association of a given Flex-Algorithm with a 1504 specific set of SRLG constraints as defined in Section 6.5 and 1505 Section 7.5. 1507 The two usages mentioned above are orthogonal. 1509 15.3. Max-metric consideration 1511 Both ISIS and OSPF have a mechanism to set the IGP metric on a link 1512 to a value that would make the link either non-reachable or to serve 1513 as the link of last resort. Similar functionality would be needed 1514 for the Min Unidirectional Link Delay and TE metric, as these can be 1515 used to compute Flex-Algorithm paths. 1517 The link can be made un-reachable for all Flex-Algorithms that use 1518 Min Unidirectional Link Delay as metric, as described in Section 5.1, 1519 by removing the Flex-Algorithm ASLA Min Unidirectional Link Delay 1520 advertisement for the link. The link can be made the link of last 1521 resort by setting the delay value in the Flex-Algorithm ASLA delay 1522 advertisement for the link to the value of 16,777,215 (2^24 - 1). 1524 The link can be made un-reachable for all Flex-Algorithms that use TE 1525 metric, as described in Section 5.1, by removing the Flex-Algorithm 1526 ASLA TE metric advertisement for the link. The link can be made the 1527 link of last resort by setting the TE metric value in the Flex- 1528 Algorithm ASLA delay advertisement for the link to the value of (2^24 1529 - 1) in ISIS and (2^32 - 1) in OSPF. 1531 16. Backward Compatibility 1533 This extension brings no new backward compatibility issues. ISIS, 1534 OSPFv2 and OSPFv3 all have well defined handling of unrecognized TLVs 1535 and sub-TLVs that allows the introduction of the new extensions, 1536 similar to those defined here, without introducing any 1537 interoperability issues. 1539 17. Security Considerations 1541 This draft adds two new ways to disrupt IGP networks: 1543 An attacker can hijack a particular Flex-Algorithm by advertising 1544 a FAD with a priority of 255 (or any priority higher than that of 1545 the legitimate nodes). 1547 An attacker could make it look like a router supports a particular 1548 Flex-Algorithm when it actually doesn't, or vice versa. 1550 Both of these attacks can be addressed by the existing security 1551 extensions as described in [RFC5304] and [RFC5310] for ISIS, in 1552 [RFC2328] and [RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] 1553 for OSPFv3. 1555 18. IANA Considerations 1557 18.1. IGP IANA Considerations 1559 18.1.1. IGP Algorithm Types Registry 1561 This document makes the following registrations in the "IGP Algorithm 1562 Types" registry: 1564 Type: 128-255. 1566 Description: Flexible Algorithms. 1568 Reference: This document (Section 4). 1570 18.1.2. IGP Metric-Type Registry 1572 IANA is requested to set up a registry called "IGP Metric-Type 1573 Registry" under an "Interior Gateway Protocol (IGP) Parameters" IANA 1574 registries. The registration policy for this registry is "Standards 1575 Action" ([RFC8126] and [RFC7120]). 1577 Values in this registry come from the range 0-255. 1579 This document registers following values in the "IGP Metric-Type 1580 Registry": 1582 Type: 0 1584 Description: IGP metric 1586 Reference: This document (Section 5.1) 1588 Type: 1 1590 Description: Min Unidirectional Link Delay as defined in 1591 [RFC8570], section 4.2, and [RFC7471], section 4.2. 1593 Reference: This document (Section 5.1) 1595 Type: 2 1597 Description: Traffic Engineering Default Metric as defined in 1598 [RFC5305], section 3.7, and Traffic engineering metric as defined 1599 in [RFC3630], section 2.5.5 1601 Reference: This document (Section 5.1) 1603 18.2. Flexible Algorithm Definition Flags Registry 1605 IANA is requested to set up a registry called "ISIS Flexible 1606 Algorithm Definition Flags Registry" under an "Interior Gateway 1607 Protocol (IGP) Parameters" IANA registries. The registration policy 1608 for this registry is "Standards Action" ([RFC8126] and [RFC7120]). 1610 This document defines the following single bit in Flexible Algorithm 1611 Definition Flags registry: 1613 Bit # Name 1614 ----- ------------------------------ 1615 0 Prefix Metric Flag (M-flag) 1617 Reference: This document (Section 6.4, Section 7.4). 1619 18.3. ISIS IANA Considerations 1621 18.3.1. Sub TLVs for Type 242 1623 This document makes the following registrations in the "sub-TLVs for 1624 TLV 242" registry. 1626 Type: 26. 1628 Description: Flexible Algorithm Definition. 1630 Reference: This document (Section 5.1). 1632 18.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1634 This document makes the following registrations in the "Sub-TLVs for 1635 for TLVs 135, 235, 236, and 237" registry. 1637 Type: 6 1639 Description: Flexible Algorithm Prefix Metric. 1641 Reference: This document (Section 8). 1643 18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1645 This document creates the following Sub-Sub-TLV Registry: 1647 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1649 Registration Procedure: Expert review 1650 Reference: This document (Section 5.1) 1652 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1653 for Flexible Algorithm Definition Sub-TLV" registry: 1655 Type: 1 1657 Description: Flexible Algorithm Exclude Admin Group 1659 Reference: This document (Section 6.1). 1661 Type: 2 1663 Description: Flexible Algorithm Include-Any Admin Group 1665 Reference: This document (Section 6.2). 1667 Type: 3 1669 Description: Flexible Algorithm Include-All Admin Group 1671 Reference: This document (Section 6.3). 1673 Type: 4 1675 Description: Flexible Algorithm Definition Flags 1677 Reference: This document (Section 6.4). 1679 Type: 5 1681 Description: Flexible Algorithm Exclude SRLG 1683 Reference: This document (Section 6.5). 1685 18.4. OSPF IANA Considerations 1687 18.4.1. OSPF Router Information (RI) TLVs Registry 1689 This specification updates the OSPF Router Information (RI) TLVs 1690 Registry. 1692 Type: 16 1694 Description: Flexible Algorithm Definition TLV. 1696 Reference: This document (Section 5.2). 1698 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1700 This document makes the following registrations in the "OSPFv2 1701 Extended Prefix TLV Sub-TLVs" registry. 1703 Type: 3 1705 Description: Flexible Algorithm Prefix Metric. 1707 Reference: This document (Section 9). 1709 18.4.3. OSPFv3 Extended-LSA Sub-TLVs 1711 This document makes the following registrations in the "OSPFv3 1712 Extended-LSA Sub-TLVs" registry. 1714 Type: 26 1716 Description: Flexible Algorithm Prefix Metric. 1718 Reference: This document (Section 9). 1720 Type: TBD (suggested value 30) 1722 Description: OSPF Flexible Algorithm ASBR Metric Sub-TLV 1724 Reference: This document (Section 10.2). 1726 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits 1728 This specification requests creation of "OSPF Flex-Algorithm Prefix 1729 Metric Bits" registry under the OSPF Parameters Registry with the 1730 following initial values. 1732 Bit Number: 0 1734 Description: E bit - External Type 1736 Reference: this document. 1738 The bits 1-7 are unassigned and the registration procedure to be 1739 followed for this registry is IETF Review. 1741 18.4.5. OSPF Opaque LSA Option Types 1743 This document makes the following registrations in the "OSPF Opaque 1744 LSA Option Types" registry. 1746 Value: TBD (suggested value 11) 1748 Description: OSPFv2 Extended Inter-Area ASBR LSA 1750 Reference: This document (Section 10.1). 1752 18.4.6. OSPFv2 Externded Inter-Area ASBR TLVs 1754 This specification requests creation of "OSPFv2 Extended Inter-Area 1755 ASBR TLVs" registry under the OSPFv2 Parameters Registry with the 1756 following initial values. 1758 Value: 1 1760 Description : Extended Inter-Area ASBR TLV 1762 Reference: this document 1764 The values 2 to 32767 are unassigned, values 32768 to 33023 are 1765 reserved for experimental use while the values 0 and 33024 to 65535 1766 are reserved. The registration procedure to be followed for this 1767 registry is IETF Review or IESG Approval. 1769 18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs 1771 This specification requests creation of "OSPFv2 Extended Inter-Area 1772 ASBR Sub-TLVs" registry under the OSPFv2 Parameters Registry with the 1773 following initial values. 1775 Value: 1 1777 Description : OSPF Flexible Algorithm ASBR Metric Sub-TLV 1779 Reference: this document 1781 The values 2 to 32767 are unassigned, values 32768 to 33023 are 1782 reserved for experimental use while the values 0 and 33024 to 65535 1783 are reserved. The registration procedure to be followed for this 1784 registry is IETF Review or IESG Approval. 1786 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1788 This document creates the following registry: 1790 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1792 Registration Procedure: Expert review 1793 Reference: This document (Section 5.2) 1795 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1796 define sub-TLVs at any level of nesting for the Flexible Algorithm 1797 TLV and should be added to the "Open Shortest Path First (OSPF) 1798 Parameters" registries group. New values can be allocated via IETF 1799 Review or IESG Approval. 1801 This document registers following Sub-TLVs in the "TLVs for Flexible 1802 Algorithm Definition TLV" registry: 1804 Type: 1 1806 Description: Flexible Algorithm Exclude Admin Group 1808 Reference: This document (Section 7.1). 1810 Type: 2 1812 Description: Flexible Algorithm Include-Any Admin Group 1814 Reference: This document (Section 7.2). 1816 Type: 3 1818 Description: Flexible Algorithm Include-All Admin Group 1820 Reference: This document (Section 7.3). 1822 Type: 4 1824 Description: Flexible Algorithm Definition Flags 1826 Reference: This document (Section 7.4). 1828 Type: 5 1830 Description: Flexible Algorithm Exclude SRLG 1832 Reference: This document (Section 7.5). 1834 Types in the range 32768-33023 are for experimental use; these will 1835 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1837 Types in the range 33024-65535 are not to be assigned at this time. 1838 Before any assignments can be made in the 33024-65535 range, there 1839 MUST be an IETF specification that specifies IANA Considerations that 1840 covers the range being assigned. 1842 18.4.9. Link Attribute Applications Registry 1844 This document registers following bit in the Link Attribute 1845 Applications Registry: 1847 Bit-3 1849 Description: Flexible Algorithm (X-bit) 1851 Reference: This document (Section 12). 1853 19. Acknowledgements 1855 This draft, among other things, is also addressing the problem that 1856 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1857 All authors of that draft agreed to join this draft. 1859 Thanks to Eric Rosen, Tony Przygienda, William Britto A J, Gunter Van 1860 De Velde, Dirk Goethals, Manju Sivaji and, Baalajee S for their 1861 detailed review and excellent comments. 1863 Thanks to Cengiz Halit for his review and feedback during initial 1864 phase of the solution definition. 1866 Thanks to Kenji Kumaki for his comments. 1868 Thanks to Acee Lindem for editorial comments. 1870 20. References 1872 20.1. Normative References 1874 [I-D.ietf-lsr-isis-srv6-extensions] 1875 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1876 Z. Hu, "IS-IS Extension to Support Segment Routing over 1877 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-14 1878 (work in progress), April 2021. 1880 [ISO10589] 1881 International Organization for Standardization, 1882 "Intermediate system to Intermediate system intra-domain 1883 routeing information exchange protocol for use in 1884 conjunction with the protocol for providing the 1885 connectionless-mode Network Service (ISO 8473)", ISO/ 1886 IEC 10589:2002, Second Edition, Nov 2002. 1888 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1889 Requirement Levels", BCP 14, RFC 2119, 1890 DOI 10.17487/RFC2119, March 1997, 1891 . 1893 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 1894 Support of Generalized Multi-Protocol Label Switching 1895 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 1896 . 1898 [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The 1899 OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250, 1900 July 2008, . 1902 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1903 in Support of Generalized Multi-Protocol Label Switching 1904 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1905 . 1907 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1908 Traffic Engineering (MPLS-TE)", RFC 7308, 1909 DOI 10.17487/RFC7308, July 2014, 1910 . 1912 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1913 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1914 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1915 2015, . 1917 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1918 S. Shaffer, "Extensions to OSPF for Advertising Optional 1919 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1920 February 2016, . 1922 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1923 for Advertising Router Information", RFC 7981, 1924 DOI 10.17487/RFC7981, October 2016, 1925 . 1927 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1928 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1929 May 2017, . 1931 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1932 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1933 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1934 2018, . 1936 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 1937 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1938 Extensions for Segment Routing", RFC 8665, 1939 DOI 10.17487/RFC8665, December 2019, 1940 . 1942 [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 1943 for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 1944 December 2019, . 1946 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 1947 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 1948 Extensions for Segment Routing", RFC 8667, 1949 DOI 10.17487/RFC8667, December 2019, 1950 . 1952 [RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1953 J. Drake, "IS-IS Application-Specific Link Attributes", 1954 RFC 8919, DOI 10.17487/RFC8919, October 2020, 1955 . 1957 [RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura, 1958 J., and J. Drake, "OSPF Application-Specific Link 1959 Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020, 1960 . 1962 20.2. Informative References 1964 [I-D.gulkohegde-routing-planes-using-sr] 1965 Hegde, S. and A. Gulko, "Separating Routing Planes using 1966 Segment Routing", draft-gulkohegde-routing-planes-using- 1967 sr-00 (work in progress), March 2017. 1969 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 1970 Litkowski, S., Bashandy, A., Filsfils, C., Francois, P., 1971 Decraene, B., and D. Voyer, "Topology Independent Fast 1972 Reroute using Segment Routing", draft-ietf-rtgwg-segment- 1973 routing-ti-lfa-06 (work in progress), February 2021. 1975 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 1976 DOI 10.17487/RFC2328, April 1998, 1977 . 1979 [RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", 1980 RFC 3101, DOI 10.17487/RFC3101, January 2003, 1981 . 1983 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering 1984 (TE) Extensions to OSPF Version 2", RFC 3630, 1985 DOI 10.17487/RFC3630, September 2003, 1986 . 1988 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 1989 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 1990 RFC 3906, DOI 10.17487/RFC3906, October 2004, 1991 . 1993 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 1994 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 1995 . 1997 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1998 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1999 2008, . 2001 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 2002 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2003 2008, . 2005 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 2006 and M. Fanto, "IS-IS Generic Cryptographic 2007 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2008 2009, . 2010 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 2011 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 2012 . 2014 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 2015 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 2016 2014, . 2018 [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. 2019 Previdi, "OSPF Traffic Engineering (TE) Metric 2020 Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, 2021 . 2023 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 2024 "Security Extension for OSPFv2 When Using Manual Key 2025 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 2026 . 2028 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2029 Writing an IANA Considerations Section in RFCs", BCP 26, 2030 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2031 . 2033 [RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward, 2034 D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) 2035 Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March 2036 2019, . 2038 Authors' Addresses 2040 Peter Psenak (editor) 2041 Cisco Systems 2042 Apollo Business Center 2043 Mlynske nivy 43 2044 Bratislava, 82109 2045 Slovakia 2047 Email: ppsenak@cisco.com 2049 Shraddha Hegde 2050 Juniper Networks, Inc. 2051 Embassy Business Park 2052 Bangalore, KA, 560093 2053 India 2055 Email: shraddha@juniper.net 2057 Clarence Filsfils 2058 Cisco Systems, Inc. 2059 Brussels 2060 Belgium 2062 Email: cfilsfil@cisco.com 2064 Ketan Talaulikar 2065 Cisco Systems, Inc. 2066 S.No. 154/6, Phase I, Hinjawadi 2067 PUNE, MAHARASHTRA 411 057 2068 India 2070 Email: ketant@cisco.com 2071 Arkadiy Gulko 2072 Edward Jones 2074 Email: arkadiy.gulko@edwardjones.com