idnits 2.17.1 draft-ietf-lsr-flex-algo-19.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (April 7, 2022) is 743 days in the past. Is this intentional? 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-18 -- Possible downref: Non-RFC (?)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reference: RFC 8919 (Obsoleted by RFC 9479) ** Obsolete normative reference: RFC 8920 (Obsoleted by RFC 9492) == Outdated reference: A later version (-13) exists of draft-ietf-rtgwg-segment-routing-ti-lfa-08 Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--).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: October 9, 2022 Juniper Networks, Inc. 6 C. Filsfils 7 Cisco Systems, Inc. 8 K. Talaulikar 9 Arrcus, Inc 10 A. Gulko 11 Edward Jones 12 April 7, 2022 14 IGP Flexible Algorithm 15 draft-ietf-lsr-flex-algo-19 17 Abstract 19 IGP protocols traditionally compute best paths over the network based 20 on the IGP metric assigned to the links. Many network deployments 21 use RSVP-TE based or Segment Routing based Traffic Engineering to 22 steer traffic over a path that is computed using different metrics or 23 constraints than the shortest IGP path. This document proposes a 24 solution that allows IGPs themselves to compute constraint-based 25 paths over the network. This document also specifies a way of using 26 Segment Routing (SR) Prefix-SIDs and SRv6 locators to steer packets 27 along the constraint-based paths. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on October 9, 2022. 46 Copyright Notice 48 Copyright (c) 2022 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (https://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 65 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 4. Flexible Algorithm . . . . . . . . . . . . . . . . . . . . . 5 67 5. Flexible Algorithm Definition Advertisement . . . . . . . . . 6 68 5.1. IS-IS Flexible Algorithm Definition Sub-TLV . . . . . . . 6 69 5.2. OSPF Flexible Algorithm Definition TLV . . . . . . . . . 8 70 5.3. Common Handling of Flexible Algorithm Definition TLV . . 9 71 6. Sub-TLVs of IS-IS FAD Sub-TLV . . . . . . . . . . . . . . . . 10 72 6.1. IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV . . 11 73 6.2. IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV 12 74 6.3. IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV 12 75 6.4. IS-IS Flexible Algorithm Definition Flags Sub-TLV . . . . 13 76 6.5. IS-IS Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 14 77 7. Sub-TLVs of OSPF FAD TLV . . . . . . . . . . . . . . . . . . 15 78 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV . . . 15 79 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV . 16 80 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV . 16 81 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV . . . . 16 82 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 17 83 8. IS-IS Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . 18 84 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . . 19 85 10. OSPF Flexible Algorithm ASBR Reachability Advertisement . . . 21 86 10.1. OSPFv2 Extended Inter-Area ASBR LSA . . . . . . . . . . 21 87 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV . . . . . . . . 23 88 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV . . . . . . 23 89 11. Advertisement of Node Participation in a Flex-Algorithm . . . 25 90 11.1. Advertisement of Node Participation for Segment Routing 26 91 11.2. Advertisement of Node Participation for Other 92 Applications . . . . . . . . . . . . . . . . . . . . . . 26 93 12. Advertisement of Link Attributes for Flex-Algorithm . . . . . 26 94 13. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 27 95 13.1. Multi-area and Multi-domain Considerations . . . . . . . 29 96 14. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 31 97 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 32 98 14.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 32 99 14.3. Other Applications' Forwarding for Flex-Algorithm . . . 33 100 15. Operational Considerations . . . . . . . . . . . . . . . . . 33 101 15.1. Inter-area Considerations . . . . . . . . . . . . . . . 33 102 15.2. Usage of SRLG Exclude Rule with Flex-Algorithm . . . . . 34 103 15.3. Max-metric consideration . . . . . . . . . . . . . . . . 35 104 16. Backward Compatibility . . . . . . . . . . . . . . . . . . . 35 105 17. Security Considerations . . . . . . . . . . . . . . . . . . . 35 106 18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 107 18.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 36 108 18.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 36 109 18.1.2. IGP Metric-Type Registry . . . . . . . . . . . . . . 36 110 18.2. Flexible Algorithm Definition Flags Registry . . . . . . 37 111 18.3. IS-IS IANA Considerations . . . . . . . . . . . . . . . 37 112 18.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 37 113 18.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 37 114 18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 115 TLV . . . . . . . . . . . . . . . . . . . . . . . . 37 116 18.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 38 117 18.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 38 118 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 39 119 18.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 39 120 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits . . . . . . . 39 121 18.4.5. OSPF Opaque LSA Option Types . . . . . . . . . . . . 39 122 18.4.6. OSPFv2 Externded Inter-Area ASBR TLVs . . . . . . . 40 123 18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs . . . . . . . . . . 40 124 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV 125 Registry . . . . . . . . . . . . . . . . . . . . . . 40 126 18.4.9. Link Attribute Applications Registry . . . . . . . . 42 127 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 42 128 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 42 129 20.1. Normative References . . . . . . . . . . . . . . . . . . 42 130 20.2. Informative References . . . . . . . . . . . . . . . . . 44 131 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 133 1. Introduction 135 An IGP-computed path based on the shortest IGP metric is often be 136 replaced by a traffic-engineered path due to the traffic requirements 137 which are not reflected by the IGP metric. Some networks engineer 138 the IGP metric assignments in a way that the IGP metric reflects the 139 link bandwidth or delay. If, for example, the IGP metric is 140 reflecting the bandwidth on the link and the application traffic is 141 delay sensitive, the best IGP path may not reflect the best path from 142 such an application's perspective. 144 To overcome this limitation, various sorts of traffic engineering 145 have been deployed, including RSVP-TE and SR-TE, in which case the TE 146 component is responsible for computing paths based on additional 147 metrics and/or constraints. Such paths need to be installed in the 148 forwarding tables in addition to, or as a replacement for, the 149 original paths computed by IGPs. Tunnels are often used to represent 150 the engineered paths and mechanisms like one described in [RFC3906] 151 are used to replace the native IGP paths with such tunnel paths. 153 This document specifies a set of extensions to IS-IS, OSPFv2, and 154 OSPFv3 that enable a router to advertise TLVs that (a) identify 155 calculation-type, (b) specify a metric-type, and (c) describe a set 156 of constraints on the topology, that are to be used to compute the 157 best paths along the constrained topology. A given combination of 158 calculation-type, metric-type, and constraints is known as a 159 "Flexible Algorithm Definition". A router that sends such a set of 160 TLVs also assigns a Flex-Algorithm value to the specified combination 161 of calculation-type, metric-type, and constraints. 163 This document also specifies a way for a router to use IGPs to 164 associate one or more SR Prefix-SIDs or SRv6 locators with a 165 particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then 166 represents a path that is computed according to the identified Flex- 167 Algorithm. 169 2. Requirements Language 171 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 172 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 173 "OPTIONAL" in this document are to be interpreted as described in BCP 174 14 [RFC2119] [RFC8174] when, and only when, they appear in all 175 capitals, as shown here. 177 3. Terminology 179 This section defines terms that are often used in this document. 181 Flexible Algorithm Definition (FAD) - the set consisting of (a) 182 calculation-type, (b) metric-type, and (c) a set of constraints. 184 Flexible Algorithm - a numeric identifier in the range 128-255 that 185 is associated via configuration with the Flexible-Algorithm 186 Definition. 188 Local Flexible Algorithm Definition - Flexible Algorithm Definition 189 defined locally on the node. 191 Remote Flexible Algorithm Definition - Flexible Algorithm Definition 192 received from other nodes via IGP flooding. 194 Flexible Algorithm Participation - per application configuration 195 state that expresses whether the node is participating in a 196 particular Flexible Algorithm. 198 IGP Algorithm - value from the the "IGP Algorithm Types" registry 199 defined under "Interior Gateway Protocol (IGP) Parameters" IANA 200 registries. IGP Algorithms represents the triplet (Calculation Type, 201 Metric, Constraints), where the second and third elements of the 202 triple MAY be unspecified. 204 ABR - Area Border Router. In IS-IS terminology it is also known as 205 L1/L2 router. 207 ASBR - Autonomous System Border Router. 209 4. Flexible Algorithm 211 Many possible constraints may be used to compute a path over a 212 network. Some networks are deployed as multiple planes. A simple 213 form of constraint may be to use a particular plane. A more 214 sophisticated form of constraint can include some extended metric as 215 described in [RFC8570]. Constraints which restrict paths to links 216 with specific affinities or avoid links with specific affinities are 217 also possible. Combinations of these are also possible. 219 To provide maximum flexibility, we want to provide a mechanism that 220 allows a router to (a) identify a particular calculation-type, (b) 221 metric-type, (c) describe a particular set of constraints, and (d) 222 assign a numeric identifier, referred to as Flex-Algorithm, to the 223 combination of that calculation-type, metric-type, and those 224 constraints. We want the mapping between the Flex-Algorithm and its 225 meaning to be flexible and defined by the user. As long as all 226 routers in the domain have a common understanding as to what a 227 particular Flex-Algorithm represents, the resulting routing 228 computation is consistent and traffic is not subject to any looping. 230 The set consisting of (a) calculation-type, (b) metric-type, and (c) 231 a set of constraints is referred to as a Flexible-Algorithm 232 Definition. 234 Flexible-Algorithm is a numeric identifier in the range 128-255 that 235 is associated via configuratin with the Flexible-Algorithm 236 Definition. 238 IANA "IGP Algorithm Types" registry defines the set of values for IGP 239 Algorithms. We propose to allocate the following values for Flex- 240 Algorithms from this registry: 242 128-255 - Flex-Algorithms 244 5. Flexible Algorithm Definition Advertisement 246 To guarantee the loop-free forwarding for paths computed for a 247 particular Flex-Algorithm, all routers that (a) are configured to 248 participate in a particular Flex-Algorithm, and (b) are in the same 249 Flex-Algorithm definition advertisement scope MUST agree on the 250 definition of the Flex-Algorithm. 252 5.1. IS-IS Flexible Algorithm Definition Sub-TLV 254 The IS-IS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used 255 to advertise the definition of the Flex-Algorithm. 257 The IS-IS FAD Sub-TLV is advertised as a Sub-TLV of the IS-IS Router 258 Capability TLV-242 that is defined in [RFC7981]. 260 IS-IS FAD Sub-TLV has the following format: 262 0 1 2 3 263 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 1 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 265 | Type | Length |Flex-Algorithm | Metric-Type | 266 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 267 | Calc-Type | Priority | 268 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 269 | Sub-TLVs | 270 + + 271 | ... | 273 | | 274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 276 where: 278 Type: 26 280 Length: variable, dependent on the included Sub-TLVs 281 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 283 Metric-Type: Type of metric to be used during the calculation. 284 Following values are defined: 286 0: IGP Metric 288 1: Min Unidirectional Link Delay as defined in [RFC8570], 289 section 4.2, encoded as application specific link attribute as 290 specified in [RFC8919] and Section 12 of this document. 292 2: Traffic Engineering Default Metric as defined in [RFC5305], 293 section 3.7, encoded as application specific link attribute as 294 specified in [RFC8919] and Section 12 of this document. 296 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 297 Types" registry defined under "Interior Gateway Protocol (IGP) 298 Parameters" IANA registries. IGP algorithms in the range of 0-127 299 have a defined triplet (Calculation Type, Metric, Constraints). 300 When used to specify the Calc-Type in the FAD Sub-TLV, only the 301 Calculation Type defined for the specified IGP Algorithm is used. 302 The Metric/Constraints MUST NOT be inherited. If the required 303 calculation type is Shortest Path First, the value 0 SHOULD appear 304 in this field. 306 Priority: Value between 0 and 255 inclusive that specifies the 307 priority of the advertisement. 309 Sub-TLVs - optional sub-TLVs. 311 The IS-IS FAD Sub-TLV MAY be advertised in an LSP of any number. IS- 312 IS router MAY advertise more than one IS-IS FAD Sub-TLV for a given 313 Flexible-Algorithm (see Section 6). 315 The IS-IS FAD Sub-TLV has an area scope. The Router Capability TLV 316 in which the FAD Sub-TLV is present MUST have the S-bit clear. 318 IS-IS L1/L2 router MAY be configured to re-generate the winning FAD 319 from level 2, without any modification to it, to level 1 area. The 320 re-generation of the FAD Sub-TLV from level 2 to level 1 is 321 determined by the L1/L2 router, not by the originator of the FAD 322 advertisement in the level 2. In such case, the re-generated FAD 323 Sub-TLV will be advertised in the level 1 Router Capability TLV 324 originated by the L1/L2 router. 326 L1/L2 router MUST NOT re-generate any FAD Sub-TLV from level 1 to 327 level 2. 329 5.2. OSPF Flexible Algorithm Definition TLV 331 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 332 defined in [RFC7770]. 334 OSPF FAD TLV has the following format: 336 0 1 2 3 337 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 1 338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 339 | Type | Length | 340 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 341 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 343 | Sub-TLVs | 344 + + 345 | ... | 347 | | 348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 350 where: 352 Type: 16 354 Length: variable, dependent on the included Sub-TLVs 356 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 357 inclusive. 359 Metric-Type: Type of metric to be used during the calculation. 360 Following values are defined: 362 0: IGP Metric 364 1: Min Unidirectional Link Delay as defined in [RFC7471], 365 section 4.2, encoded as application specific link attribute as 366 specified in [RFC8920] and Section 12 of this document. 368 2: Traffic Engineering metric as defined in [RFC3630], section 369 2.5.5, encoded as application specific link attribute as 370 specified in [RFC8920] and Section 12 of this document. 372 Calc-Type: as described in Section 5.1 374 Priority: as described in Section 5.1 375 Sub-TLVs - optional sub-TLVs. 377 When multiple OSPF FAD TLVs, for the same Flexible-Algorithm, are 378 received from a given router, the receiver MUST use the first 379 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 380 TLV, for the same Flex-Algorithm, appears in multiple Router 381 Information LSAs that have different flooding scopes, the OSPF FAD 382 TLV in the Router Information LSA with the area-scoped flooding scope 383 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 384 in multiple Router Information LSAs that have the same flooding 385 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 386 numerically smallest Instance ID MUST be used and subsequent 387 instances of the OSPF FAD TLV MUST be ignored. 389 The RI LSA can be advertised at any of the defined opaque flooding 390 scopes (link, area, or Autonomous System (AS)). For the purpose of 391 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 392 Autonomous System flooding scope SHOULD NOT be used by default unless 393 local configuration policy on the originating router indicates domain 394 wide flooding. 396 5.3. Common Handling of Flexible Algorithm Definition TLV 398 This section describes the protocol-independent handling of the FAD 399 TLV (OSPF) or FAD Sub-TLV (IS-IS). We will refer to it as FAD TLV in 400 this section, even though in the case of IS-IS it is a Sub-TLV. 402 The value of the Flex-Algorithm MUST be between 128 and 255 403 inclusive. If it is not, the FAD TLV MUST be ignored. 405 Only a subset of the routers participating in the particular Flex- 406 Algorithm need to advertise the definition of the Flex-Algorithm. 408 Every router, that is configured to participate in a particular Flex- 409 Algorithm, MUST select the Flex-Algorithm definition based on the 410 following ordered rules. This allows for the consistent Flex- 411 Algorithm definition selection in cases where different routers 412 advertise different definitions for a given Flex-Algorithm: 414 1. From the advertisements of the FAD in the area (including both 415 locally generated advertisements and received advertisements) 416 select the one(s) with the highest priority value. 418 2. If there are multiple advertisements of the FAD with the same 419 highest priority, select the one that is originated from the 420 router with the highest System-ID, in the case of IS-IS, or Router 421 ID, in the case of OSPFv2 and OSPFv3. For IS-IS, the System-ID is 422 described in [ISO10589]. For OSPFv2 and OSPFv3, standard Router 423 ID is described in [RFC2328] and [RFC5340] respectively. 425 A router that is not configured to participate in a particular Flex- 426 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 427 Algorithm. 429 A router that is not participating in a particular Flex-Algorithm is 430 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 431 MUST consider FAD advertisement regardless of the Flex-Algorithm 432 participation of the FAD originator. 434 Any change in the Flex-Algorithm definition may result in temporary 435 disruption of traffic that is forwarded based on such Flex-Algorithm 436 paths. The impact is similar to any other event that requires 437 network-wide convergence. 439 If a node is configured to participate in a particular Flexible- 440 Algorithm, but there is no valid Flex-Algorithm definition available 441 for it, or 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 One of the limitations of IS-IS [ISO10589] is that the length of a 454 TLV/sub-TLV is limited to a maximum of 255 octets. For the FAD sub- 455 TLV, there are a number of sub-sub-TLVs (defined below) which are 456 supported. For a given Flex-Algorithm, it is possible that the total 457 number of octets required to completely define a FAD exceeds the 458 maximum length supported by a single FAD sub-TLV. In such cases, the 459 FAD may be split into multiple such sub-TLVs and the content of the 460 multiple FAD sub-TLVs combined to provide a complete FAD for the 461 Flex-Algorithm. In such case, the fixed portion of the FAD (see 462 Section 5.1) MUST be identical in all FAD sub-TLVs for a given Flex- 463 Algorithm from a given IS. In case the fixed portion of such FAD 464 Sub-TLVs differ, the values in the fixed portion in the FAD sub-TLV 465 in the first occurrence in the lowest numbered LSP from a given IS 466 MUST be used. 468 Any specification that introduces a new ISIS FAD sub-sub-TLV MUST 469 specify whether the FAD sub-TLV may appear multiple times in the set 470 of FAD sub-TLVs for a given Flex-Algorithm from a given IS and how to 471 handle them if multiple are allowed. 473 6.1. IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV 475 The Flexible Algorithm definition can specify 'colors' that are used 476 by the operator to exclude links during the Flex-Algorithm path 477 computation. 479 The IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 480 advertise the exclude rule that is used during the Flex-Algorithm 481 path calculation as specified in Section 13. 483 The IS-IS Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub- 484 TLV) is a Sub-TLV of the IS-IS FAD Sub-TLV. It has the following 485 format: 487 0 1 2 3 488 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 490 | Type | Length | 491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 492 | Extended Admin Group | 493 +- -+ 494 | ... | 495 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 496 where: 498 Type: 1 500 Length: variable, dependent on the size of the Extended Admin 501 Group. MUST be a multiple of 4 octets. 503 Extended Administrative Group: Extended Administrative Group as 504 defined in [RFC7308]. 506 The IS-IS FAEAG Sub-TLV MUST NOT appear more than once in a single 507 IS-IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub- 508 TLV MUST be ignored by the receiver. 510 The IS-IS FAEAG Sub-TLV MUST NOT appear more than once in the set of 511 FAD sub-TLVs for a given Flex-Algorithm from a given IS. If it 512 appears more than once in such set, the IS-IS FAEAG Sub-TLV in the 513 first occurrence in the lowest numbered LSP from a given IS MUST be 514 used and any other occurrences MUST be ignored. 516 6.2. IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV 518 The Flexible Algorithm definition can specify 'colors' that are used 519 by the operator to include links during the Flex-Algorithm path 520 computation. 522 The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV is used 523 to advertise include-any rule that is used during the Flex-Algorithm 524 path calculation as specified in Section 13. 526 The format of the IS-IS Flexible Algorithm Include-Any Admin Group 527 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 528 Section 6.1. 530 The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 531 2. 533 The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 534 appear more than once in a single IS-IS FAD Sub-TLV. If it appears 535 more than once, the IS-IS FAD Sub-TLV MUST be ignored by the 536 receiver. 538 The IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 539 appear more than once in the set of FAD sub-TLVs for a given Flex- 540 Algorithm from a given IS. If it appears more than once in such set, 541 the IS-IS Flexible Algorithm Include-Any Admin Group Sub-TLV in the 542 first occurrence in the lowest numbered LSP from a given IS MUST be 543 used and any other occurrences MUST be ignored. 545 6.3. IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV 547 The Flexible Algorithm definition can specify 'colors' that are used 548 by the operator to include link during the Flex-Algorithm path 549 computation. 551 The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV is used 552 to advertise include-all rule that is used during the Flex-Algorithm 553 path calculation as specified in Section 13. 555 The format of the IS-IS Flexible Algorithm Include-All Admin Group 556 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 557 Section 6.1. 559 The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 560 3. 562 The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 563 appear more than once in a single IS-IS FAD Sub-TLV. If it appears 564 more than once, the IS-IS FAD Sub-TLV MUST be ignored by the 565 receiver. 567 The IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 568 appear more than once in the set of FAD sub-TLVs for a given Flex- 569 Algorithm from a given IS. If it appears more than once in such set, 570 the IS-IS Flexible Algorithm Include-All Admin Group Sub-TLV in the 571 first occurrence in the lowest numbered LSP from a given IS MUST be 572 used and any other occurrences MUST be ignored. 574 6.4. IS-IS Flexible Algorithm Definition Flags Sub-TLV 576 The IS-IS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 577 is a Sub-TLV of the IS-IS FAD Sub-TLV. It has the following format: 579 0 1 2 3 580 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 1 581 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 582 | Type | Length | 583 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 584 | Flags | 585 +- -+ 586 | ... | 587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 588 where: 590 Type: 4 592 Length: variable, non-zero number of octets of the Flags field 594 Flags: 596 0 1 2 3 4 5 6 7... 597 +-+-+-+-+-+-+-+-+... 598 |M| | | ... 599 +-+-+-+-+-+-+-+-+... 601 M-flag: when set, the Flex-Algorithm specific prefix metric 602 MUST be used for inter-area and external prefix calculation. 603 This flag is not applicable to prefixes advertised as SRv6 604 locators. 606 Bits are defined/sent starting with Bit 0 defined above. Additional 607 bit definitions that may be defined in the future SHOULD be assigned 608 in ascending bit order so as to minimize the number of bits that will 609 need to be transmitted. 611 Undefined bits MUST be transmitted as 0. 613 Bits that are NOT transmitted MUST be treated as if they are set to 0 614 on receipt. 616 The IS-IS FADF Sub-TLV MUST NOT appear more than once in a single IS- 617 IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLV 618 MUST be ignored by the receiver. 620 The IS-IS FADF Sub-TLV MUST NOT appear more than once in the set of 621 FAD sub-TLVs for a given Flex-Algorithm from a given IS. If it 622 appears more than once in such set, the IS-IS FADF Sub-TLV in the 623 first occurrence in the lowest numbered LSP from a given IS MUST be 624 used and any other occurrences MUST be ignored. 626 If the IS-IS FADF Sub-TLV is not present inside the IS-IS FAD Sub- 627 TLV, all the bits are assumed to be set to 0. 629 If a node is configured to participate in a particular Flexible- 630 Algorithm, but the selected Flex-Algorithm definition includes a bit 631 in the IS-IS FADF Sub-TLV that is not supported by the node, it MUST 632 stop participating in such Flexible-Algorithm. 634 New flag bits may be defined in the future. Implementations MUST 635 check all advertised flag bits in the received IS-IS FADF Sub-TLV - 636 not just the subset currently defined. 638 6.5. IS-IS Flexible Algorithm Exclude SRLG Sub-TLV 640 The Flexible Algorithm definition can specify Shared Risk Link Groups 641 (SRLGs) that the operator wants to exclude during the Flex-Algorithm 642 path computation. 644 The IS-IS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used 645 to advertise the exclude rule that is used during the Flex-Algorithm 646 path calculation as specified in Section 13. 648 The IS-IS FAESRLG Sub-TLV is a Sub-TLV of the IS-IS FAD Sub-TLV. It 649 has the following format: 651 0 1 2 3 652 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 1 653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 654 | Type | Length | 655 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 656 | Shared Risk Link Group Value | 657 +- -+ 658 | ... | 659 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 660 where: 662 Type: 5 664 Length: variable, dependent on number of SRLG values. MUST be a 665 multiple of 4 octets. 667 Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. 669 The IS-IS FAESRLG Sub-TLV MUST NOT appear more than once in a single 670 IS-IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub- 671 TLV MUST be ignored by the receiver. 673 The IS-IS FAESRLG Sub-TLV MAY appear more than once in the set of FAD 674 sub-TLVs for a given Flex-Algorithm from a given IS. This may be 675 necessary in cases where the total number of SRLG values which are 676 specified cause the FAD sub-TLV to exceed the maximum length of a 677 single FAD sub-TLV. In such case the receiver MUST use the union of 678 all values across all IS-IS FAESRLG Sub-TLVs from such set. 680 7. Sub-TLVs of OSPF FAD TLV 682 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 684 The Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is 685 a Sub-TLV of the OSPF FAD TLV. It's usage is described in 686 Section 6.1. It has the following format: 688 0 1 2 3 689 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 1 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 691 | Type | Length | 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 | Extended Admin Group | 694 +- -+ 695 | ... | 696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 697 where: 699 Type: 1 701 Length: variable, dependent on the size of the Extended Admin 702 Group. MUST be a multiple of 4 octets. 704 Extended Administrative Group: Extended Administrative Group as 705 defined in [RFC7308]. 707 The OSPF FAEAG Sub-TLV MUST NOT appear more than once in an OSPF FAD 708 TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored 709 by the receiver. 711 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 713 The usage of this Sub-TLVs is described in Section 6.2. 715 The format of the OSPF Flexible Algorithm Include-Any Admin Group 716 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 717 Section 7.1. 719 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 720 2. 722 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MUST NOT 723 appear more than once in an OSPF FAD TLV. If it appears more than 724 once, the OSPF FAD TLV MUST be ignored by the receiver. 726 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 728 The usage of this Sub-TLVs is described in Section 6.3. 730 The format of the OSPF Flexible Algorithm Include-All Admin Group 731 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 732 Section 7.1. 734 The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV Type is 735 3. 737 The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MUST NOT 738 appear more than once in an OSPF FAD TLV. If it appears more than 739 once, the OSPF FAD TLV MUST be ignored by the receiver. 741 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 743 The OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 744 is a Sub-TLV of the OSPF FAD TLV. It has the following format: 746 0 1 2 3 747 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 1 748 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 749 | Type | Length | 750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 751 | Flags | 752 +- -+ 753 | ... | 754 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 755 where: 757 Type: 4 758 Length: variable, dependent on the size of the Flags field. MUST 759 be a multiple of 4 octets. 761 Flags: 763 0 1 2 3 4 5 6 7... 764 +-+-+-+-+-+-+-+-+... 765 |M| | | ... 766 +-+-+-+-+-+-+-+-+... 768 M-flag: when set, the Flex-Algorithm specific prefix and ASBR 769 metric MUST be used for inter-area and external prefix 770 calculation. This flag is not applicable to prefixes 771 advertised as SRv6 locators. 773 Bits are defined/sent starting with Bit 0 defined above. Additional 774 bit definitions that may be defined in the future SHOULD be assigned 775 in ascending bit order so as to minimize the number of bits that will 776 need to be transmitted. 778 Undefined bits MUST be transmitted as 0. 780 Bits that are NOT transmitted MUST be treated as if they are set to 0 781 on receipt. 783 The OSPF FADF Sub-TLV MUST NOT appear more than once in an OSPF FAD 784 TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored 785 by the receiver. 787 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 788 the bits are assumed to be set to 0. 790 If a node is configured to participate in a particular Flexible- 791 Algorithm, but the selected Flex-Algorithm definition includes a bit 792 in the OSPF FADF Sub-TLV that is not supported by the node, it MUST 793 stop participating in such Flexible-Algorithm. 795 New flag bits may be defined in the future. Implementations MUST 796 check all advertised flag bits in the received OSPF FADF Sub-TLV - 797 not just the subset currently defined. 799 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV 801 The OSPF Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG Sub-TLV) is 802 a Sub-TLV of the OSPF FAD TLV. Its usage is described in 803 Section 6.5. It has the following format: 805 0 1 2 3 806 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 1 807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 808 | Type | Length | 809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 810 | Shared Risk Link Group Value | 811 +- -+ 812 | ... | 813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 814 where: 816 Type: 5 818 Length: variable, dependent on the number of SRLGs. MUST be a 819 multiple of 4 octets. 821 Shared Risk Link Group Value: SRLG value as defined in [RFC4203]. 823 The OSPF FAESRLG Sub-TLV MUST NOT appear more than once in an OSPF 824 FAD TLV. If it appears more than once, the OSPF FAD TLV MUST be 825 ignored by the receiver. 827 8. IS-IS Flexible Algorithm Prefix Metric Sub-TLV 829 The IS-IS Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports 830 the advertisement of a Flex-Algorithm specific prefix metric 831 associated with a given prefix advertisement. 833 The IS-IS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 834 and has the following format: 836 0 1 2 3 837 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 1 838 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 839 | Type | Length |Flex-Algorithm | 840 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 841 | Metric | 842 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 843 where: 845 Type: 6 847 Length: 5 octets 849 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 851 Metric: 4 octets of metric information 853 The IS-IS FAPM Sub-TLV MAY appear multiple times in its parent TLV. 854 If it appears more than once with the same Flex-Algorithm value, the 855 first instance MUST be used and any subsequent instances MUST be 856 ignored. 858 If a prefix is advertised with a Flex-Algorithm prefix metric larger 859 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 860 considered during the Flexible-Algorithm computation. 862 The usage of the Flex-Algorithm prefix metric is described in 863 Section 13. 865 The IS-IS FAPM Sub-TLV MUST NOT be advertised as a sub-TLV of the IS- 866 IS SRv6 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. The IS-IS 867 SRv6 Locator TLV includes the Algorithm and Metric fields which MUST 868 be used instead. If the FAPM Sub-TLV is present as a sub-TLV of the 869 IS-IS SRv6 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be 870 ignored. 872 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV 874 The OSPF Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the 875 advertisement of a Flex-Algorithm specific prefix metric associated 876 with a given prefix advertisement. 878 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV is a Sub-TLV of 879 the: 881 - OSPFv2 Extended Prefix TLV [RFC7684] 883 - Following OSPFv3 TLVs as defined in [RFC8362]: 885 Inter-Area Prefix TLV 887 External Prefix TLV 889 OSPF FAPM Sub-TLV has the following format: 891 0 1 2 3 892 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 1 893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 894 | Type | Length | 895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 896 |Flex-Algorithm | Flags | Reserved | 897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 898 | Metric | 899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 901 where: 903 Type: 3 for OSPFv2, 26 for OSPFv3 905 Length: 8 octets 907 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 909 Flags: single octet value 911 0 1 2 3 4 5 6 7 912 +-+-+-+-+-+-+-+-+ 913 |E| | 914 +-+-+-+-+-+-+-+-+ 916 E bit : position 0: The type of external metric. If bit is 917 set, the metric specified is a Type 2 external metric. This 918 bit is applicable only to OSPF External and NSSA external 919 prefixes. This is semantically the same as E bit in section 920 A.4.5 of [RFC2328] and section A.4.7 of [RFC5340] for OSPFv2 921 and OSPFv3 respectively. 923 Bits 1 through 7: MUST be cleared by sender and ignored by 924 receiver. 926 Reserved: Must be set to 0, ignored at reception. 928 Metric: 4 octets of metric information 930 The OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. 931 If it appears more than once with the same Flex-Algorithm value, the 932 first instance MUST be used and any subsequent instances MUST be 933 ignored. 935 The usage of the Flex-Algorithm prefix metric is described in 936 Section 13. 938 10. OSPF Flexible Algorithm ASBR Reachability Advertisement 940 An OSPF ABR advertises the reachability of ASBRs in its attached 941 areas to enable routers within those areas to perform route 942 calculations for external prefixes advertised by the ASBRs. OSPF 943 extensions for advertisement of Flex-Algorithm specific reachability 944 and metric for ASBRs is similarly required for Flex-Algorithm 945 external prefix computations as described further in Section 13.1. 947 10.1. OSPFv2 Extended Inter-Area ASBR LSA 949 The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) LSA is an OSPF Opaque 950 LSA [RFC5250] that is used to advertise additional attributes related 951 to the reachability of the OSPFv2 ASBR that is external to the area 952 yet internal to the OSPF domain. Semantically, the OSPFv2 EIA-ASBR 953 LSA is equivalent to the fixed format Type 4 Summary LSA [RFC2328]. 954 Unlike the Type 4 Summary LSA, the LSID of the EIA-ASBR LSA does not 955 carry the ASBR Router-ID - the ASBR Router-ID is carried in the body 956 of the LSA. OSPFv2 EIA-ASBR LSA is advertised by an OSPFv2 ABR and 957 its flooding is defined to be area-scoped only. 959 An OSPFv2 ABR generates the EIA-ASBR LSA for an ASBR when it is 960 advertising the Type-4 Summary LSA for it and has the need for 961 advertising additional attributes for that ASBR beyond what is 962 conveyed in the fixed format Type-4 Summary LSA. An OSPFv2 ABR MUST 963 NOT advertise the EIA-ASBR LSA for an ASBR for which it is not 964 advertising the Type 4 Summary LSA. This ensures that the ABR does 965 not generate the EIA-ASBR LSA for an ASBR to which it does not have 966 reachability in the base OSPFv2 topology calculation. The OSPFv2 ABR 967 SHOULD NOT advertise the EIA-ASBR LSA for an ASBR when it does not 968 have additional attributes to advertise for that ASBR. 970 The OSPFv2 EIA-ASBR LSA has the following format: 972 0 1 2 3 973 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 1 974 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 975 | LS age | Options | LS Type | 976 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 977 | Opaque Type | Opaque ID | 978 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 979 | Advertising Router | 980 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 981 | LS sequence number | 982 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 983 | LS checksum | Length | 984 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 985 | | 986 +- TLVs -+ 987 | ... | 989 The Opaque Type used by the OSPFv2 EIA-ASBR LSA is TBD (suggested 990 value 11). The Opaque Type is used to differentiate the various 991 types of OSPFv2 Opaque LSAs and is described in Section 3 of 992 [RFC5250]. The LS Type MUST be 10, indicating that the Opaque LSA 993 flooding scope is area-local [RFC5250]. The LSA Length field 994 [RFC2328] represents the total length (in octets) of the Opaque LSA, 995 including the LSA header and all TLVs (including padding). 997 The Opaque ID field is an arbitrary value used to maintain multiple 998 OSPFv2 EIA-ASBR LSAs. For OSPFv2 EIA-ASBR LSAs, the Opaque ID has no 999 semantic significance other than to differentiate OSPFv2 EIA-ASBR 1000 LSAs originated by the same OSPFv2 ABR. If multiple OSPFv2 EIA-ASBR 1001 LSAs specify the same ASBR, the attributes from the Opaque LSA with 1002 the lowest Opaque ID SHOULD be used. 1004 The format of the TLVs within the body of the OSPFv2 EIA-ASBR LSA is 1005 the same as the format used by the Traffic Engineering Extensions to 1006 OSPFv2 [RFC3630]. The variable TLV section consists of one or more 1007 nested TLV tuples. Nested TLVs are also referred to as sub- TLVs. 1008 The Length field defines the length of the value portion in octets 1009 (thus, a TLV with no value portion would have a length of 0). The 1010 TLV is padded to 4-octet alignment; padding is not included in the 1011 Length field (so a 3-octet value would have a length of 3, but the 1012 total size of the TLV would be 8 octets). Nested TLVs are also 1013 32-bit aligned. For example, a 1-byte value would have the Length 1014 field set to 1, and 3 octets of padding would be added to the end of 1015 the value portion of the TLV. The padding is composed of zeros. 1017 10.1.1. OSPFv2 Extended Inter-Area ASBR TLV 1019 The OSPFv2 Extended Inter-Area ASBR (EIA-ASBR) TLV is a top-level TLV 1020 of the OSPFv2 EIA-ASBR LSA and is used to advertise additional 1021 attributes associated with the reachability of an ASBR. 1023 The OSPFv2 EIA-ASBR TLV has the following format: 1025 0 1 2 3 1026 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 1027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1028 | Type | Length | 1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1030 | ASBR Router ID | 1031 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1032 . . 1033 . Sub-TLVs . 1034 . . 1035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1037 where: 1039 Type: 1 1041 Length: variable 1043 ASBR Router ID: four octets carrying the OSPF Router ID of the 1044 ASBR whose information is being carried. 1046 Sub-TLVs : variable 1048 Only a single OSPFv2 EIA-ASBR TLV MUST be advertised in each OSPFv2 1049 EIA-ASBR LSA and the receiver MUST ignore all instances of this TLV 1050 other than the first one in an LSA. 1052 OSPFv2 EIA-ASBR TLV MUST be present inside an OSPFv2 EIA-ASBR LSA 1053 with at least a single sub-TLV included, otherwise the OSPFv2 EIA- 1054 ASBR LSA MUST be ignored by the receiver. 1056 10.2. OSPF Flexible Algorithm ASBR Metric Sub-TLV 1058 The OSPF Flexible Algorithm ASBR Metric (FAAM) Sub-TLV supports the 1059 advertisement of a Flex-Algorithm specific metric associated with a 1060 given ASBR reachability advertisement by an ABR. 1062 The OSPF Flex-Algorithm ASBR Metric (FAAM) Sub-TLV is a Sub-TLV of 1063 the: 1065 - OSPFv2 Extended Inter-Area ASBR TLV as defined in Section 10.1.1 1067 - OSPFv3 Inter-Area-Router TLV defined in [RFC8362] 1069 OSPF FAAM Sub-TLV has the following format: 1071 0 1 2 3 1072 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 1073 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1074 | Type | Length | 1075 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1076 |Flex-Algorithm | Reserved | 1077 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1078 | Metric | 1079 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1081 where: 1083 Type: 1 for OSPFv2, TBD (suggested value 30) for OSPFv3 1085 Length: 8 octets 1087 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 1089 Reserved: Must be set to 0, ignored at reception. 1091 Metric: 4 octets of metric information 1093 The OSPF FAAM Sub-TLV MAY appear multiple times in its parent TLV. 1094 If it appears more than once with the same Flex-Algorithm value, the 1095 first instance MUST be used and any subsequent instances MUST be 1096 ignored. 1098 The advertisement of the ASBR reachability using the OSPF FAAM Sub- 1099 TLV inside the OSPFv2 EIA-ASBR LSA follows the section 12.4.3 of 1100 [RFC2328] and inside the OSPFv3 E-Inter-Area-Router LSA follows the 1101 section 4.8.5 of [RFC5340]. The reachability of the ASBR is 1102 evaluated in the context of the specific Flex-Algorithm. 1104 The FAAM computed by the ABR will be equal to the metric to reach the 1105 ASBR for a given Flex-Algorithm in a source area or the cumulative 1106 metric via other ABR(s) when the ASBR is in a remote area. This is 1107 similar in nature to how the metric is set when the ASBR reachability 1108 metric is computed in the default algorithm for the metric in the 1109 OSPFv2 Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. 1111 An OSPF ABR MUST NOT include the OSPF FAAM Sub-TLV with a specific 1112 Flex-Algorithm in its reachability advertisement for an ASBR between 1113 areas unless that ASBR is reachable for it in the context of that 1114 specific Flex-Algorithm. 1116 An OSPF ABR MUST include the OSPF FAAM Sub-TLVs as part of the ASBR 1117 reachability advertisement between areas for the Flex-Algorithm for 1118 which the winning FAD includes the M-flag and the ASBR is reachable 1119 in the context of that specific Flex-Algorithm. 1121 OSPF routers MUST use the OSPF FAAM Sub-TLV to calculate the 1122 reachability of the ASBRs if the winning FAD for the specific Flex- 1123 Algorithm includes the M-flag. OSPF routers MUST NOT use the OSPF 1124 FAAM Sub-TLV to calculate the reachability of the ASBRs for the 1125 specific Flex-Algorithm if the winning FAD for such Flex-Algorithm 1126 does not include the M-flag. Instead, the OSPFv2 Type 4 Summary LSAs 1127 or the OSPFv3 Inter-Area-Router-LSAs MUST be used instead as 1128 specified in section 16.2 of [RFC2328] and section 4.8.5 of [RFC5340] 1129 for OSPFv2 and OSPFv3 respectively. 1131 The processing of the new or changed OSPF FAAM Sub-TLV triggers the 1132 processing of the External routes similar to what is described in 1133 section 16.5 of the [RFC2328] for OSPFv2 and section 4.8.5 of 1134 [RFC5340] for OSPFv3 for the specific Flex-Algorithm. The External 1135 and NSSA External route calculation should be limited to Flex- 1136 Algorithm(s) for which the winning FAD(s) includes the M-flag. 1138 Processing of the OSPF FAAM Sub-TLV does not require the existence of 1139 the equivalent OSPFv2 Type 4 Summary LSA or the OSPFv3 Inter-Area- 1140 Router-LSA that is advertised by the same ABR inside the area. When 1141 the OSPFv2 EIA-ASBR LSA or the OSPFv3 E-Inter-Area-Router-LSA are 1142 advertised along with the OSPF FAAM Sub-TLV by the ABR for a specific 1143 ASBR, it is expected that the same ABR would advertise the 1144 reachability of the same ASBR in the equivalent base LSAs - i.e., the 1145 OSPFv2 Type 4 Summary LSA or the OSPFv3 Inter-Area-Router-LSA. The 1146 presence of the base LSA is not mandatory for the usage of the 1147 extended LSA with the OSPF FAAM Sub-TLV. This means that the order 1148 in which these LSAs are received is not significant. 1150 11. Advertisement of Node Participation in a Flex-Algorithm 1152 When a router is configured to support a particular Flex-Algorithm, 1153 we say it is participating in that Flex-Algorithm. 1155 Paths computed for a specific Flex-Algorithm MAY be used by various 1156 applications, each potentially using its own specific data plane for 1157 forwarding traffic over such paths. To guarantee the presence of the 1158 application specific forwarding state associated with a particular 1159 Flex-Algorithm, a router MUST advertise its participation for a 1160 particular Flex-Algorithm for each application specifically. 1162 11.1. Advertisement of Node Participation for Segment Routing 1164 [RFC8667], [RFC8665], and [RFC8666] (IGP Segment Routing extensions) 1165 describe how the SR-Algorithm is used to compute the IGP best path. 1167 Routers advertise the support for the SR-Algorithm as a node 1168 capability as described in the above mentioned IGP Segment Routing 1169 extensions. To advertise participation for a particular Flex- 1170 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 1171 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 1172 (OSPF) or sub-TLV (IS-IS). 1174 Segment Routing Flex-Algorithm participation advertisement is 1175 topology independent. When a router advertises participation in an 1176 SR-Algorithm, the participation applies to all topologies in which 1177 the advertising node participates. 1179 11.2. Advertisement of Node Participation for Other Applications 1181 This section describes considerations related to how other 1182 applications can advertise their participation in a specific Flex- 1183 Algorithm. 1185 Application-specific Flex-Algorithm participation advertisements MAY 1186 be topology specific or MAY be topology independent, depending on the 1187 application itself. 1189 Application-specific advertisement for Flex-Algorithm participation 1190 MUST be defined for each application and is outside of the scope of 1191 this document. 1193 12. Advertisement of Link Attributes for Flex-Algorithm 1195 Various link attributes may be used during the Flex-Algorithm path 1196 calculation. For example, include or exclude rules based on link 1197 affinities can be part of the Flex-Algorithm definition as defined in 1198 Section 6 and Section 7. 1200 Application-specific link attributes, as specified in [RFC8919] or 1201 [RFC8920], that are to be used during Flex-Algorithm calculation MUST 1202 use the Application-Specific Link Attribute (ASLA) advertisements 1203 defined in [RFC8919] or [RFC8920], unless, in the case of IS-IS, the 1204 L-Flag is set in the ASLA advertisement. When the L-Flag is set, 1205 then legacy advertisements are to be used, subject to the procedures 1206 and constraints defined in [[RFC8919] Section 4.2 and Section 6. 1208 The mandatory use of ASLA advertisements applies to link attributes 1209 specifically mentioned in this document (Min Unidirectional Link 1210 Delay, TE Default Metric, Administrative Group, Extended 1211 Administrative Group and Shared Risk Link Group) and any other link 1212 attributes that may be used in support of Flex-Algorithm in the 1213 future. 1215 A new Application Identifier Bit is defined to indicate that the ASLA 1216 advertisement is associated with the Flex-Algorithm application. 1217 This bit is set in the Standard Application Bit Mask (SABM) defined 1218 in [RFC8919] or [RFC8920]: 1220 Bit-3: Flexible Algorithm (X-bit) 1222 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 1223 Application MAY use either the Administrative Group or Extended 1224 Administrative Group encodings. If the Administrative Group encoding 1225 is used, then the first 32 bits of the corresponding FAD sub-TLVs are 1226 mapped to the link attribute advertisements as specified in RFC 7308. 1228 A receiver supporting this specification MUST accept both ASLA 1229 Administrative Group and Extended Administrative Group TLVs as 1230 defined in [RFC8919] or [RFC8920]. In the case of ISIS, if the 1231 L-Flag is set in ASLA advertisement, as defined in [RFC8919] 1232 Section 4.2, then the receiver MUST be able to accept both 1233 Administrative Group TLV as defined in [RFC5305] and Extended 1234 Administrative Group TLV as defined in [RFC7308]. 1236 13. Calculation of Flexible Algorithm Paths 1238 A router MUST be configured to participate in a given Flex-Algorithm 1239 K and MUST select the FAD based on the rules defined in Section 5.3 1240 before it can compute any path for that Flex-Algorithm. 1242 No specific two way connectivity check is performed during the Flex- 1243 Algorithm path computation. The result of the existing, Flex- 1244 Algorithm agnostic, two way connectivity check is used during the 1245 Flex-Algorithm path computation. 1247 As described in Section 11, participation for any particular Flex- 1248 Algorithm MUST be advertised on a per-application basis. Calculation 1249 of the paths for any particular Flex-Algorithm MUST be application 1250 specific. 1252 The way applications handle nodes that do not participate in 1253 Flexible-Algorithm is application specific. If the application only 1254 wants to consider participating nodes during the Flex-Algorithm 1255 calculation, then when computing paths for a given Flex-Algorithm, 1256 all nodes that do not advertise participation for that Flex-Algorithm 1257 in their application-specific advertisements MUST be pruned from the 1258 topology. Segment Routing, including both SR MPLS and SRv6, are 1259 applications that MUST use such pruning when computing Flex-Algorithm 1260 paths. 1262 When computing the path for a given Flex-Algorithm, the metric-type 1263 that is part of the Flex-Algorithm definition (Section 5) MUST be 1264 used. 1266 When computing the path for a given Flex-Algorithm, the calculation- 1267 type that is part of the Flex-Algorithm definition (Section 5) MUST 1268 be used. 1270 Various link include or exclude rules can be part of the Flex- 1271 Algorithm definition. To refer to a particular bit within an AG or 1272 EAG we use the term 'color'. 1274 Rules, in the order as specified below, MUST be used to prune links 1275 from the topology during the Flex-Algorithm computation. 1277 For all links in the topology: 1279 1. Check if any exclude AG rule is part of the Flex-Algorithm 1280 definition. If such exclude rule exists, check if any color that 1281 is part of the exclude rule is also set on the link. If such a 1282 color is set, the link MUST be pruned from the computation. 1284 2. Check if any exclude SRLG rule is part of the Flex-Algorithm 1285 definition. If such exclude rule exists, check if the link is 1286 part of any SRLG that is also part of the SRLG exclude rule. If 1287 the link is part of such SRLG, the link MUST be pruned from the 1288 computation. 1290 3. Check if any include-any AG rule is part of the Flex-Algorithm 1291 definition. If such include-any rule exists, check if any color 1292 that is part of the include-any rule is also set on the link. If 1293 no such color is set, the link MUST be pruned from the 1294 computation. 1296 4. Check if any include-all AG rule is part of the Flex-Algorithm 1297 definition. If such include-all rule exists, check if all colors 1298 that are part of the include-all rule are also set on the link. 1299 If all such colors are not set on the link, the link MUST be 1300 pruned from the computation. 1302 5. If the Flex-Algorithm definition uses other than IGP metric 1303 (Section 5), and such metric is not advertised for the particular 1304 link in a topology for which the computation is done, such link 1305 MUST be pruned from the computation. A metric of value 0 MUST NOT 1306 be assumed in such case. 1308 13.1. Multi-area and Multi-domain Considerations 1310 Any IGP Shortest Path Tree calculation is limited to a single area. 1311 This applies to Flex-Algorithm calculations as well. Given that the 1312 computing router does not have visibility of the topology of the next 1313 areas or domain, the Flex-Algorithm specific path to an inter-area or 1314 inter-domain prefix will be computed for the local area only. The 1315 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 1316 will be selected based on the best path for the given Flex-Algorithm 1317 in the local area and such egress ABR or ASBR router will be 1318 responsible to compute the best Flex-Algorithm specific path over the 1319 next area or domain. This may produce an end-to-end path, which is 1320 sub-optimal based on Flex-Algorithm constraints. In cases where the 1321 ABR or ASBR has no reachability to a prefix for a given Flex- 1322 Algorithm in the next area or domain, the traffic may be dropped by 1323 the ABR/ASBR. 1325 To allow the optimal end-to-end path for an inter-area or inter- 1326 domain prefix for any Flex-Algorithm to be computed, the FAPM has 1327 been defined in Section 8 and Section 9. For external route 1328 calculation for prefixes originated by ASBRs in remote areas in OSPF, 1329 the FAAM has been defined in Section 10.2 for the ABR to indicate its 1330 ASBR reachability along with the metric for the specific Flex- 1331 Algorithm. 1333 If the FAD selected based on the rules defined in Section 5.3 1334 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 1335 Section 9) when advertising the prefix, that is reachable in a given 1336 Flex-Algorithm, between areas or domains. Such metric will be equal 1337 to the metric to reach the prefix for that Flex-Algorithm in its 1338 source area or domain. This is similar in nature to how the metric 1339 is set when prefixes are advertised between areas or domains for the 1340 default algorithm. When a prefix is unreachable in its source area 1341 or domain in a specific Flex-Algorithm, then an ABR or ASBR MUST NOT 1342 include the FAPM for that Flex-Algorithm when advertising the prefix 1343 between areas or domains. 1345 If the FAD selected based on the rules defined in Section 5.3 1346 includes the M-flag, the FAPM MUST be used during the calculation of 1347 prefix reachability for the inter-area and external prefixes. If the 1348 FAPM for the Flex-Algorithm is not advertised with the inter-area or 1349 external prefix reachability advertisement, the prefix MUST be 1350 considered as unreachable for that Flex-Algorithm. Similarly in the 1351 case of OSPF, for ASBRs in remote areas, if the FAAM is not 1352 advertised by the local ABR(s), the ASBR MUST be considered as 1353 unreachable for that Flex-Algorithm and the external prefix 1354 advertisements from such an ASBR are not considered for that Flex- 1355 Algorithm. 1357 Flex-Algorithm prefix metrics and the OSPF Flex-Algorithm ASBR 1358 metrics MUST NOT be used during the Flex-Algorithm computation unless 1359 the FAD selected based on the rules defined in Section 5.3 includes 1360 the M-Flag, as described in (Section 6.4 or Section 7.4). 1362 In the case of OSPF, when calculating external routes in a Flex- 1363 Algorithm (with FAD selected includes the M-Flag) where the 1364 advertising ASBR is in a remote area, the metric will be the sum of 1365 the following: 1367 o the FAPM for that Flex-Algorithm advertised with the external 1368 route by the ASBR 1370 o the metric to reach the ASBR for that Flex-Algorithm from the 1371 local ABR i.e., the FAAM for that Flex-Algorithm advertised by the 1372 ABR in the local area for that ASBR 1374 o the Flex-Algorithm specific metric to reach the local ABR 1376 This is similar in nature to how the metric is calculated for routes 1377 learned from remote ASBRs in the default algorithm using the OSPFv2 1378 Type 4 ASBR Summary LSA and the OSPFv3 Inter-Area-Router LSA. 1380 If the FAD selected based on the rules defined in Section 5.3 does 1381 not includes the M-flag, then the IGP metrics associated with the 1382 prefix reachability advertisements used by the base IS-IS and OSPF 1383 protocol MUST be used for the Flex-Algorithm route computation. 1384 Similarly, in the case of external route calculations in OSPF, the 1385 ASBR reachability is determined based on the base OSPFv2 Type 4 1386 Summary LSA and the OSFPv3 Inter-Area-Router LSA. 1388 It is NOT RECOMMENDED to use the Flex-Algorithm for inter-area or 1389 inter-domain prefix reachability without the M-flag set. The reason 1390 is that without the explicit Flex-Algorithm Prefix Metric 1391 advertisement (and the Flex-Algorithm ASBR metric advertisement in 1392 the case of OSPF external route calculation), it is not possible to 1393 conclude whether the ABR or ASBR has reachability to the inter-area 1394 or inter-domain prefix for a given Flex-Algorithm in the next area or 1395 domain. Sending the Flex-Algoritm traffic for such prefix towards 1396 the ABR or ASBR may result in traffic looping or black-holing. 1398 During the route computation, it is possible for the Flex-Algorithm 1399 specific metric to exceed the maximum value that can be stored in an 1400 unsigned 32-bit variable. In such scenarios, the value MUST be 1401 considered to be of value 4,294,967,295 during the computation and 1402 advertised as such. 1404 The FAPM MUST NOT be advertised with IS-IS L1 or L2 intra-area, 1405 OSPFv2 intra-area, or OSPFv3 intra-area routes. If the FAPM is 1406 advertised for these route-types, it MUST be ignored during the 1407 prefix reachability calculation. 1409 The M-flag in FAD is not applicable to prefixes advertised as SRv6 1410 locators. The IS-IS SRv6 Locator TLV 1411 [I-D.ietf-lsr-isis-srv6-extensions] includes the Algorithm and Metric 1412 fields. When the SRv6 Locator is advertised between areas or 1413 domains, the metric field in the Locator TLV of IS-IS MUST be used 1414 irrespective of the M-flag in the FAD advertisement. 1416 OSPF external and NSSA external prefix advertisements MAY include a 1417 non-zero forwarding address in the prefix advertisements in the base 1418 protocol. In such a scenario, the Flex-Algorithm specific 1419 reachability of the external prefix is determined by Flex-Algorithm 1420 specific reachability of the forwarding address. 1422 In OSPF, the procedures for translation of NSSA external prefix 1423 advertisements into external prefix advertisements performed by an 1424 NSSA ABR [RFC3101] remain unchanged for Flex-Algorithm. An NSSA 1425 translator MUST include the OSPF FAPM Sub-TLVs for all Flex- 1426 Algorithms that are in the original NSSA external prefix 1427 advertisement from the NSSA ASBR in the translated external prefix 1428 advertisement generated by it regardless of its participation in 1429 those Flex-Algorithms or its having reachability to the NSSA ASBR in 1430 those Flex-Algorithms. 1432 An area could become partitioned from the perspective of the Flex- 1433 Algorithm due to the constraints and/or metric being used for it, 1434 while maintaining the continuity in the algorithm 0. When that 1435 happens, some destinations inside that area could become unreachable 1436 in that Flex-Algorithm. These destinations will not be able to use 1437 an inter-area path. This is the consequence of the fact that the 1438 inter-area prefix reachability advertisement would not be available 1439 for these intra-area destinations within the area. It is RECOMMENDED 1440 to avoid such partitioning by providing enough redundancy inside the 1441 area for each Flex-Algorithm being used. 1443 14. Flex-Algorithm and Forwarding Plane 1445 This section describes how Flex-Algorithm paths are used in 1446 forwarding. 1448 14.1. Segment Routing MPLS Forwarding for Flex-Algorithm 1450 This section describes how Flex-Algorithm paths are used with SR MPLS 1451 forwarding. 1453 Prefix SID advertisements include an SR-Algorithm value and, as such, 1454 are associated with the specified SR-Algorithm. Prefix-SIDs are also 1455 associated with a specific topology which is inherited from the 1456 associated prefix reachability advertisement. When the algorithm 1457 value advertised is a Flex-Algorithm value, the Prefix SID is 1458 associated with paths calculated using that Flex-Algorithm in the 1459 associated topology. 1461 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 1462 using the MPLS label that corresponds to the Prefix-SID that was 1463 advertised for that Flex-algorithm. If the Prefix SID for a given 1464 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 1465 be installed in the MPLS forwarding plane. 1467 Traffic that is supposed to be routed via Flex-Algorithm specific 1468 paths, MUST be dropped when there are no such paths available. 1470 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 1471 computed using the same constraints as the calculation of the primary 1472 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 1473 advertised specifically for the given algorithm. LFA paths MUST NOT 1474 use an Adjacency-SID that belongs to a link that has been pruned from 1475 the Flex-Algorithm computation. 1477 If LFA protection is being used to protect a given Flex-Algorithm 1478 paths, all routers in the area participating in the given Flex- 1479 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 1480 SID. These Node-SIDs are used to steer traffic over the LFA computed 1481 backup path. 1483 14.2. SRv6 Forwarding for Flex-Algorithm 1485 This section describes how Flex-Algorithm paths are used with SRv6 1486 forwarding. 1488 In SRv6 a node is provisioned with topology/algorithm specific 1489 locators for each of the topology/algorithm pairs supported by that 1490 node. Each locator is an aggregate prefix for all SIDs provisioned 1491 on that node which have the matching topology/algorithm. 1493 The SRv6 locator advertisement in IS-IS 1494 [I-D.ietf-lsr-isis-srv6-extensions] includes the MTID value that 1495 associates the locator with a specific topology. SRv6 locator 1496 advertisements also includes an Algorithm value that explicitly 1497 associates the locator with a specific algorithm. When the algorithm 1498 value advertised with a locator represents a Flex-Algorithm, the 1499 paths to the locator prefix MUST be calculated using the specified 1500 Flex-Algorithm in the associated topology. 1502 Forwarding entries for the locator prefixes advertised in IS-IS MUST 1503 be installed in the forwarding plane of the receiving SRv6 capable 1504 routers when the associated topology/algorithm is participating in 1505 them. Forwarding entries for locators associated with Flex- 1506 Algorithms in which the node is not participating MUST NOT be 1507 installed in the forwarding plane. 1509 When the locator is associated with a Flex-Algorithm, LFA paths to 1510 the locator prefix MUST be calculated using such Flex-Algorithm in 1511 the associated topology, to guarantee that they follow the same 1512 constraints as the calculation of the primary paths. LFA paths MUST 1513 only use SRv6 SIDs advertised specifically for the given Flex- 1514 Algorithm. 1516 If LFA protection is being used to protect locators associated with a 1517 given Flex-Algorithm, all routers in the area participating in the 1518 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1519 specific locator and END SID per node and one END.X SID for every 1520 link that has not been pruned from such Flex-Algorithm computation. 1521 These locators and SIDs are used to steer traffic over the LFA- 1522 computed backup path. 1524 14.3. Other Applications' Forwarding for Flex-Algorithm 1526 Any application that wants to use Flex-Algorithm specific forwarding 1527 needs to install some form of Flex-Algorithm specific forwarding 1528 entries. 1530 Application-specific forwarding for Flex-Algorithm MUST be defined 1531 for each application and is outside of the scope of this document. 1533 15. Operational Considerations 1535 15.1. Inter-area Considerations 1537 The scope of the Flex-Algorithm computation is an area, so is the 1538 scope of the FAD. In IS-IS, the Router Capability TLV in which the 1539 FAD Sub-TLV is advertised MUST have the S-bit clear, which prevents 1540 it to be flooded outside of the level in which it was originated. 1541 Even though in OSPF the FAD Sub-TLV can be flooded in an RI LSA that 1542 has AS flooding scope, the FAD selection is performed for each 1543 individual area in which it is being used. 1545 There is no requirement for the FAD for a particular Flex-Algorithm 1546 to be identical in all areas in the network. For example, traffic 1547 for the same Flex-Algorithm may be optimized for minimal delay (e.g., 1548 using delay metric) in one area or level, while being optimized for 1549 available bandwidth (e.g., using IGP metric) in another area or 1550 level. 1552 As described in Section 5.1, IS-IS allows the re-generation of the 1553 winning FAD from level 2, without any modification to it, into a 1554 level 1 area. This allows the operator to configure the FAD in one 1555 or multiple routers in the level 2, without the need to repeat the 1556 same task in each level 1 area, if the intent is to have the same FAD 1557 for the particular Flex-Algorithm across all levels. This can 1558 similarly be achieved in OSPF by using the AS flooding scope of the 1559 RI LSA in which the FAD Sub-TLV for the particular Flex-Algoritm is 1560 advertised. 1562 Re-generation of FAD from a level 1 area to the level 2 area is not 1563 supported in IS-IS, so if the intent is to regenerate the FAD between 1564 IS-IS levels, the FAD MUST be defined on router(s) that are in level 1565 2. In OSPF, the FAD definition can be done in any area and be 1566 propagated to all routers in the OSPF routing domain by using the AS 1567 flooding scope of the RI LSA. 1569 15.2. Usage of SRLG Exclude Rule with Flex-Algorithm 1571 There are two different ways in which SRLG information can be used 1572 with Flex-Algorithm: 1574 In a context of a single Flex-Algorithm, it can be used for 1575 computation of backup paths, as described in 1576 [I-D.ietf-rtgwg-segment-routing-ti-lfa]. This usage does not 1577 require association of any specific SRLG constraint with the given 1578 Flex-Algorithm definition. 1580 In the context of multiple Flex-Algorithms, it can be used for 1581 creating disjoint sets of paths by pruning the links belonging to 1582 a specific SRLG from the topology on which a specific Flex- 1583 Algorithm computes its paths. This usage: 1585 Facilitates the usage of already deployed SRLG configurations 1586 for setup of disjoint paths between two or more Flex- 1587 Algorithms. 1589 Requires explicit association of a given Flex-Algorithm with a 1590 specific set of SRLG constraints as defined in Section 6.5 and 1591 Section 7.5. 1593 The two usages mentioned above are orthogonal. 1595 15.3. Max-metric consideration 1597 Both IS-IS and OSPF have a mechanism to set the IGP metric on a link 1598 to a value that would make the link either non-reachable or to serve 1599 as the link of last resort. Similar functionality would be needed 1600 for the Min Unidirectional Link Delay and TE metric, as these can be 1601 used to compute Flex-Algorithm paths. 1603 The link can be made un-reachable for all Flex-Algorithms that use 1604 Min Unidirectional Link Delay as metric, as described in Section 5.1, 1605 by removing the Flex-Algorithm ASLA Min Unidirectional Link Delay 1606 advertisement for the link. The link can be made the link of last 1607 resort by setting the delay value in the Flex-Algorithm ASLA delay 1608 advertisement for the link to the value of 16,777,215 (2^24 - 1). 1610 The link can be made un-reachable for all Flex-Algorithms that use TE 1611 metric, as described in Section 5.1, by removing the Flex-Algorithm 1612 ASLA TE metric advertisement for the link. The link can be made the 1613 link of last resort by setting the TE metric value in the Flex- 1614 Algorithm ASLA delay advertisement for the link to the value of (2^24 1615 - 1) in IS-IS and (2^32 - 1) in OSPF. 1617 16. Backward Compatibility 1619 This extension brings no new backward compatibility issues. IS-IS, 1620 OSPFv2 and OSPFv3 all have well defined handling of unrecognized TLVs 1621 and sub-TLVs that allows the introduction of the new extensions, 1622 similar to those defined here, without introducing any 1623 interoperability issues. 1625 17. Security Considerations 1627 This draft adds two new ways to disrupt IGP networks: 1629 An attacker can hijack a particular Flex-Algorithm by advertising 1630 a FAD with a priority of 255 (or any priority higher than that of 1631 the legitimate nodes). 1633 An attacker could make it look like a router supports a particular 1634 Flex-Algorithm when it actually doesn't, or vice versa. 1636 Both of these attacks can be addressed by the existing security 1637 extensions as described in [RFC5304] and [RFC5310] for IS-IS, in 1638 [RFC2328] and [RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] 1639 for OSPFv3. 1641 18. IANA Considerations 1643 18.1. IGP IANA Considerations 1645 18.1.1. IGP Algorithm Types Registry 1647 This document makes the following registrations in the "IGP Algorithm 1648 Types" registry: 1650 Type: 128-255. 1652 Description: Flexible Algorithms. 1654 Reference: This document (Section 4). 1656 18.1.2. IGP Metric-Type Registry 1658 IANA is requested to set up a registry called "IGP Metric-Type 1659 Registry" under an "Interior Gateway Protocol (IGP) Parameters" IANA 1660 registries. The registration policy for this registry is "Standards 1661 Action" ([RFC8126] and [RFC7120]). 1663 Values in this registry come from the range 0-255. 1665 This document registers following values in the "IGP Metric-Type 1666 Registry": 1668 Type: 0 1670 Description: IGP metric 1672 Reference: This document (Section 5.1) 1674 Type: 1 1676 Description: Min Unidirectional Link Delay as defined in 1677 [RFC8570], section 4.2, and [RFC7471], section 4.2. 1679 Reference: This document (Section 5.1) 1681 Type: 2 1683 Description: Traffic Engineering Default Metric as defined in 1684 [RFC5305], section 3.7, and Traffic engineering metric as defined 1685 in [RFC3630], section 2.5.5 1687 Reference: This document (Section 5.1) 1689 18.2. Flexible Algorithm Definition Flags Registry 1691 IANA is requested to set up a registry called "IS-IS Flexible 1692 Algorithm Definition Flags Registry" under an "Interior Gateway 1693 Protocol (IGP) Parameters" IANA registries. The registration policy 1694 for this registry is "Standards Action" ([RFC8126] and [RFC7120]). 1696 This document defines the following single bit in Flexible Algorithm 1697 Definition Flags registry: 1699 Bit # Name 1700 ----- ------------------------------ 1701 0 Prefix Metric Flag (M-flag) 1703 Reference: This document (Section 6.4, Section 7.4). 1705 18.3. IS-IS IANA Considerations 1707 18.3.1. Sub TLVs for Type 242 1709 This document makes the following registrations in the "sub-TLVs for 1710 TLV 242" registry. 1712 Type: 26. 1714 Description: Flexible Algorithm Definition. 1716 Reference: This document (Section 5.1). 1718 18.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1720 This document makes the following registrations in the "Sub-TLVs for 1721 for TLVs 135, 235, 236, and 237" registry. 1723 Type: 6 1725 Description: Flexible Algorithm Prefix Metric. 1727 Reference: This document (Section 8). 1729 18.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1731 This document creates the following Sub-Sub-TLV Registry: 1733 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1735 Registration Procedure: Expert review 1736 Reference: This document (Section 5.1) 1738 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1739 for Flexible Algorithm Definition Sub-TLV" registry: 1741 Type: 1 1743 Description: Flexible Algorithm Exclude Admin Group 1745 Reference: This document (Section 6.1). 1747 Type: 2 1749 Description: Flexible Algorithm Include-Any Admin Group 1751 Reference: This document (Section 6.2). 1753 Type: 3 1755 Description: Flexible Algorithm Include-All Admin Group 1757 Reference: This document (Section 6.3). 1759 Type: 4 1761 Description: Flexible Algorithm Definition Flags 1763 Reference: This document (Section 6.4). 1765 Type: 5 1767 Description: Flexible Algorithm Exclude SRLG 1769 Reference: This document (Section 6.5). 1771 18.4. OSPF IANA Considerations 1773 18.4.1. OSPF Router Information (RI) TLVs Registry 1775 This specification updates the OSPF Router Information (RI) TLVs 1776 Registry. 1778 Type: 16 1780 Description: Flexible Algorithm Definition TLV. 1782 Reference: This document (Section 5.2). 1784 18.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1786 This document makes the following registrations in the "OSPFv2 1787 Extended Prefix TLV Sub-TLVs" registry. 1789 Type: 3 1791 Description: Flexible Algorithm Prefix Metric. 1793 Reference: This document (Section 9). 1795 18.4.3. OSPFv3 Extended-LSA Sub-TLVs 1797 This document makes the following registrations in the "OSPFv3 1798 Extended-LSA Sub-TLVs" registry. 1800 Type: 26 1802 Description: Flexible Algorithm Prefix Metric. 1804 Reference: This document (Section 9). 1806 Type: TBD (suggested value 30) 1808 Description: OSPF Flexible Algorithm ASBR Metric Sub-TLV 1810 Reference: This document (Section 10.2). 1812 18.4.4. OSPF Flex-Algorithm Prefix Metric Bits 1814 This specification requests creation of "OSPF Flex-Algorithm Prefix 1815 Metric Bits" registry under the OSPF Parameters Registry with the 1816 following initial values. 1818 Bit Number: 0 1820 Description: E bit - External Type 1822 Reference: this document. 1824 The bits 1-7 are unassigned and the registration procedure to be 1825 followed for this registry is IETF Review. 1827 18.4.5. OSPF Opaque LSA Option Types 1829 This document makes the following registrations in the "OSPF Opaque 1830 LSA Option Types" registry. 1832 Value: TBD (suggested value 11) 1834 Description: OSPFv2 Extended Inter-Area ASBR LSA 1836 Reference: This document (Section 10.1). 1838 18.4.6. OSPFv2 Externded Inter-Area ASBR TLVs 1840 This specification requests creation of "OSPFv2 Extended Inter-Area 1841 ASBR TLVs" registry under the OSPFv2 Parameters Registry with the 1842 following initial values. 1844 Value: 1 1846 Description : Extended Inter-Area ASBR TLV 1848 Reference: this document 1850 The values 2 to 32767 are unassigned, values 32768 to 33023 are 1851 reserved for experimental use while the values 0 and 33024 to 65535 1852 are reserved. The registration procedure to be followed for this 1853 registry is IETF Review or IESG Approval. 1855 18.4.7. OSPFv2 Inter-Area ASBR Sub-TLVs 1857 This specification requests creation of "OSPFv2 Extended Inter-Area 1858 ASBR Sub-TLVs" registry under the OSPFv2 Parameters Registry with the 1859 following initial values. 1861 Value: 1 1863 Description : OSPF Flexible Algorithm ASBR Metric Sub-TLV 1865 Reference: this document 1867 The values 2 to 32767 are unassigned, values 32768 to 33023 are 1868 reserved for experimental use while the values 0 and 33024 to 65535 1869 are reserved. The registration procedure to be followed for this 1870 registry is IETF Review or IESG Approval. 1872 18.4.8. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1874 This document creates the following registry: 1876 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1878 Registration Procedure: Expert review 1879 Reference: This document (Section 5.2) 1881 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1882 define sub-TLVs at any level of nesting for the Flexible Algorithm 1883 TLV and should be added to the "Open Shortest Path First (OSPF) 1884 Parameters" registries group. New values can be allocated via IETF 1885 Review or IESG Approval. 1887 This document registers following Sub-TLVs in the "TLVs for Flexible 1888 Algorithm Definition TLV" registry: 1890 Type: 1 1892 Description: Flexible Algorithm Exclude Admin Group 1894 Reference: This document (Section 7.1). 1896 Type: 2 1898 Description: Flexible Algorithm Include-Any Admin Group 1900 Reference: This document (Section 7.2). 1902 Type: 3 1904 Description: Flexible Algorithm Include-All Admin Group 1906 Reference: This document (Section 7.3). 1908 Type: 4 1910 Description: Flexible Algorithm Definition Flags 1912 Reference: This document (Section 7.4). 1914 Type: 5 1916 Description: Flexible Algorithm Exclude SRLG 1918 Reference: This document (Section 7.5). 1920 Types in the range 32768-33023 are for experimental use; these will 1921 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1923 Types in the range 33024-65535 are not to be assigned at this time. 1924 Before any assignments can be made in the 33024-65535 range, there 1925 MUST be an IETF specification that specifies IANA Considerations that 1926 covers the range being assigned. 1928 18.4.9. Link Attribute Applications Registry 1930 This document registers following bit in the Link Attribute 1931 Applications Registry: 1933 Bit-3 1935 Description: Flexible Algorithm (X-bit) 1937 Reference: This document (Section 12). 1939 19. Acknowledgements 1941 This draft, among other things, is also addressing the problem that 1942 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1943 All authors of that draft agreed to join this draft. 1945 Thanks to Eric Rosen, Tony Przygienda, William Britto A J, Gunter Van 1946 De Velde, Dirk Goethals, Manju Sivaji and, Baalajee S for their 1947 detailed review and excellent comments. 1949 Thanks to Cengiz Halit for his review and feedback during initial 1950 phase of the solution definition. 1952 Thanks to Kenji Kumaki for his comments. 1954 Thanks to Acee Lindem for editorial comments. 1956 20. References 1958 20.1. Normative References 1960 [I-D.ietf-lsr-isis-srv6-extensions] 1961 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1962 Z. Hu, "IS-IS Extensions to Support Segment Routing over 1963 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-18 1964 (work in progress), October 2021. 1966 [ISO10589] 1967 International Organization for Standardization, 1968 "Intermediate system to Intermediate system intra-domain 1969 routeing information exchange protocol for use in 1970 conjunction with the protocol for providing the 1971 connectionless-mode Network Service (ISO 8473)", ISO/ 1972 IEC 10589:2002, Second Edition, Nov 2002. 1974 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1975 Requirement Levels", BCP 14, RFC 2119, 1976 DOI 10.17487/RFC2119, March 1997, 1977 . 1979 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 1980 Support of Generalized Multi-Protocol Label Switching 1981 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 1982 . 1984 [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The 1985 OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250, 1986 July 2008, . 1988 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1989 in Support of Generalized Multi-Protocol Label Switching 1990 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1991 . 1993 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1994 Traffic Engineering (MPLS-TE)", RFC 7308, 1995 DOI 10.17487/RFC7308, July 2014, 1996 . 1998 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1999 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 2000 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 2001 2015, . 2003 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 2004 S. Shaffer, "Extensions to OSPF for Advertising Optional 2005 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 2006 February 2016, . 2008 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 2009 for Advertising Router Information", RFC 7981, 2010 DOI 10.17487/RFC7981, October 2016, 2011 . 2013 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2014 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2015 May 2017, . 2017 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 2018 F. Baker, "OSPFv3 Link State Advertisement (LSA) 2019 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 2020 2018, . 2022 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 2023 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 2024 Extensions for Segment Routing", RFC 8665, 2025 DOI 10.17487/RFC8665, December 2019, 2026 . 2028 [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 2029 for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 2030 December 2019, . 2032 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 2033 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 2034 Extensions for Segment Routing", RFC 8667, 2035 DOI 10.17487/RFC8667, December 2019, 2036 . 2038 [RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 2039 J. Drake, "IS-IS Application-Specific Link Attributes", 2040 RFC 8919, DOI 10.17487/RFC8919, October 2020, 2041 . 2043 [RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura, 2044 J., and J. Drake, "OSPF Application-Specific Link 2045 Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020, 2046 . 2048 20.2. Informative References 2050 [I-D.gulkohegde-routing-planes-using-sr] 2051 Hegde, S. and A. Gulko, "Separating Routing Planes using 2052 Segment Routing", draft-gulkohegde-routing-planes-using- 2053 sr-00 (work in progress), March 2017. 2055 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 2056 Litkowski, S., Bashandy, A., Filsfils, C., Francois, P., 2057 Decraene, B., and D. Voyer, "Topology Independent Fast 2058 Reroute using Segment Routing", draft-ietf-rtgwg-segment- 2059 routing-ti-lfa-08 (work in progress), January 2022. 2061 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 2062 DOI 10.17487/RFC2328, April 1998, 2063 . 2065 [RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", 2066 RFC 3101, DOI 10.17487/RFC3101, January 2003, 2067 . 2069 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering 2070 (TE) Extensions to OSPF Version 2", RFC 3630, 2071 DOI 10.17487/RFC3630, September 2003, 2072 . 2074 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 2075 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 2076 RFC 3906, DOI 10.17487/RFC3906, October 2004, 2077 . 2079 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 2080 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 2081 . 2083 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 2084 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2085 2008, . 2087 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 2088 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2089 2008, . 2091 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 2092 and M. Fanto, "IS-IS Generic Cryptographic 2093 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2094 2009, . 2096 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 2097 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 2098 . 2100 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 2101 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 2102 2014, . 2104 [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. 2105 Previdi, "OSPF Traffic Engineering (TE) Metric 2106 Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, 2107 . 2109 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 2110 "Security Extension for OSPFv2 When Using Manual Key 2111 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 2112 . 2114 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2115 Writing an IANA Considerations Section in RFCs", BCP 26, 2116 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2117 . 2119 [RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward, 2120 D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) 2121 Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March 2122 2019, . 2124 Authors' Addresses 2126 Peter Psenak (editor) 2127 Cisco Systems 2128 Apollo Business Center 2129 Mlynske nivy 43 2130 Bratislava, 82109 2131 Slovakia 2133 Email: ppsenak@cisco.com 2135 Shraddha Hegde 2136 Juniper Networks, Inc. 2137 Embassy Business Park 2138 Bangalore, KA, 560093 2139 India 2141 Email: shraddha@juniper.net 2143 Clarence Filsfils 2144 Cisco Systems, Inc. 2145 Brussels 2146 Belgium 2148 Email: cfilsfil@cisco.com 2150 Ketan Talaulikar 2151 Arrcus, Inc 2152 India 2154 Email: ketant.ietf@gmail.com 2155 Arkadiy Gulko 2156 Edward Jones 2158 Email: arkadiy.gulko@edwardjones.com