idnits 2.17.1 draft-ietf-lsr-flex-algo-10.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 contains RFC2119-like boilerplate, but doesn't seem to mention RFC 2119. The boilerplate contains a reference [BCP14], but that reference does not seem to mention RFC 2119 either. -- The exact meaning of the all-uppercase expression 'MAY NOT' is not defined in RFC 2119. If it is intended as a requirements expression, it should be rewritten using one of the combinations defined in RFC 2119; otherwise it should not be all-uppercase. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: The RI LSA can be advertised at any of the defined opaque flooding scopes (link, area, or Autonomous System (AS)). For the purpose of OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The Autonomous System flooding scope SHOULD not be used by default unless local configuration policy on the originating router indicates domain wide flooding. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS FAESRLG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF FAEAG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF FAESRLG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. -- The document date (August 19, 2020) is 1345 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) == Unused Reference: 'I-D.ietf-lsr-ospf-reverse-metric' is defined on line 1504, but no explicit reference was found in the text -- Possible downref: Non-RFC (?) normative reference: ref. 'BCP14' == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-08 == Outdated reference: A later version (-13) exists of draft-ietf-lsr-ospf-reverse-metric-01 == Outdated reference: A later version (-15) exists of draft-ietf-lsr-ospfv3-srv6-extensions-01 -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10589' == Outdated reference: A later version (-13) exists of draft-ietf-rtgwg-segment-routing-ti-lfa-03 Summary: 1 error (**), 0 flaws (~~), 17 warnings (==), 4 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: February 20, 2021 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Individual 11 August 19, 2020 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-10.txt 16 Abstract 18 IGP protocols traditionally compute best paths over the network based 19 on the IGP metric assigned to the links. Many network deployments 20 use RSVP-TE based or Segment Routing based Traffic Engineering to 21 steer traffic over a path that is computed using different metrics or 22 constraints than the shortest IGP path. This document proposes a 23 solution that allows IGPs themselves to compute constraint-based 24 paths over the network. This document also specifies a way of using 25 Segment Routing (SR) Prefix-SIDs and SRv6 locators to steer packets 26 along the constraint-based paths. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on February 20, 2021. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 64 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 4. Flexible Algorithm . . . . . . . . . . . . . . . . . . . . . 5 66 5. Flexible Algorithm Definition Advertisement . . . . . . . . . 6 67 5.1. ISIS Flexible Algorithm Definition Sub-TLV . . . . . . . 6 68 5.2. OSPF Flexible Algorithm Definition TLV . . . . . . . . . 7 69 5.3. Common Handling of Flexible Algorithm Definition TLV . . 9 70 6. Sub-TLVs of ISIS FAD Sub-TLV . . . . . . . . . . . . . . . . 10 71 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV . . . 10 72 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV . 11 73 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV . 11 74 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV . . . . 12 75 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 13 76 7. Sub-TLVs of OSPF FAD TLV . . . . . . . . . . . . . . . . . . 13 77 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV . . . 13 78 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV . 14 79 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV . 14 80 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV . . . . 15 81 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 16 82 8. ISIS Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . . 16 83 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . . 17 84 10. Advertisement of Node Participation in a Flex-Algorithm . . . 18 85 10.1. Advertisement of Node Participation for Segment Routing 19 86 10.2. Advertisement of Node Participation for Other 87 Applications . . . . . . . . . . . . . . . . . . . . . . 19 88 11. Advertisement of Link Attributes for Flex-Algorithm . . . . . 19 89 12. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 20 90 12.1. Multi-area and Multi-domain Considerations . . . . . . . 21 91 13. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 23 92 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 23 93 13.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 23 94 13.3. Other Applications' Forwarding for Flex-Algorithm . . . 24 95 14. Operational considerations . . . . . . . . . . . . . . . . . 25 96 14.1. Inter-area Considerations . . . . . . . . . . . . . . . 25 97 14.2. Usage of SRLG Exclude Rule with Flex-Algorithm . . . . . 25 98 14.3. Max-metric consideration . . . . . . . . . . . . . . . . 26 99 15. Backward Compatibility . . . . . . . . . . . . . . . . . . . 26 100 16. Security Considerations . . . . . . . . . . . . . . . . . . . 26 101 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 102 17.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 27 103 17.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 27 104 17.1.2. IGP Metric-Type Registry . . . . . . . . . . . . . . 27 105 17.2. Flexible Algorithm Definition Flags Registry . . . . . . 28 106 17.3. ISIS IANA Considerations . . . . . . . . . . . . . . . . 28 107 17.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 28 108 17.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 28 109 17.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 110 TLV . . . . . . . . . . . . . . . . . . . . . . . . 29 111 17.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 29 112 17.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 30 113 17.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 30 114 17.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 30 115 17.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV 116 Registry . . . . . . . . . . . . . . . . . . . . . . 30 117 17.4.5. Link Attribute Applications Registry . . . . . . . . 31 118 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32 119 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 120 19.1. Normative References . . . . . . . . . . . . . . . . . . 32 121 19.2. Informative References . . . . . . . . . . . . . . . . . 34 122 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36 124 1. Introduction 126 An IGP-computed path based on the shortest IGP metric must often be 127 replaced by a traffic-engineered path due to the traffic requirements 128 which are not reflected by the IGP metric. Some networks engineer 129 the IGP metric assignments in a way that the IGP metric reflects the 130 link bandwidth or delay. If, for example, the IGP metric is 131 reflecting the bandwidth on the link and the application traffic is 132 delay sensitive, the best IGP path may not reflect the best path from 133 such an application's perspective. 135 To overcome this limitation, various sorts of traffic engineering 136 have been deployed, including RSVP-TE and SR-TE, in which case the TE 137 component is responsible for computing paths based on additional 138 metrics and/or constraints. Such paths need to be installed in the 139 forwarding tables in addition to, or as a replacement for, the 140 original paths computed by IGPs. Tunnels are often used to represent 141 the engineered paths and mechanisms like one described in [RFC3906] 142 are used to replace the native IGP paths with such tunnel paths. 144 This document specifies a set of extensions to ISIS, OSPFv2, and 145 OSPFv3 that enable a router to advertise TLVs that identify (a) 146 calculation-type, (b) specify a metric-type, and (c) describe a set 147 of constraints on the topology, that are to be used to compute the 148 best paths along the constrained topology. A given combination of 149 calculation-type, metric-type, and constraints is known as a 150 "Flexible Algorithm Definition". A router that sends such a set of 151 TLVs also assigns a Flex-Algorithm value to the specified combination 152 of calculation-type, metric-type, and constraints. 154 This document also specifies a way for a router to use IGPs to 155 associate one or more SR Prefix-SIDs or SRv6 locators with a 156 particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then 157 represents a path that is computed according to the identified Flex- 158 Algorithm. 160 2. Requirements notation 162 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 163 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 164 "OPTIONAL" in this document are to be interpreted as described in 165 [BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all 166 capitals, as shown here. 168 3. Terminology 170 This section defines terms that are often used in this document. 172 Flexible Algorithm Definition (FAD) - the set consisting of (a) 173 calculation-type, (b) metric-type, and (c) a set of constraints. 175 Flexible Algorithm - a numeric identifier in the range 128-255 that 176 is associated via configuration with the Flexible-Algorithm 177 Definition. 179 Local Flexible Algorithm Definition - Flexible Algorithm Definition 180 defined locally on the node. 182 Remote Flexible Algorithm Definition - Flexible Algorithm Definition 183 received from other nodes via IGP flooding. 185 Flexible Algorithm Participation - per application configuration 186 state that expresses whether the node is participating in a 187 particular Flexible Algorithm. 189 IGP Algorithm - value from the the "IGP Algorithm Types" registry 190 defined under "Interior Gateway Protocol (IGP) Parameters" IANA 191 registries. IGP Algorithms represents the triplet (Calculation Type, 192 Metric, Constraints), where the second and third elements of the 193 triple MAY not be specified. 195 ABR - Area Border Router. In ISIS terminology it is also known as 196 L1/L2 router. 198 ASBR - Autonomous System Border Router. 200 4. Flexible Algorithm 202 Many possible constraints may be used to compute a path over a 203 network. Some networks are deployed as multiple planes. A simple 204 form of constraint may be to use a particular plane. A more 205 sophisticated form of constraint can include some extended metric as 206 described in [RFC8570]. Constraints which restrict paths to links 207 with specific affinities or avoid links with specific affinities are 208 also possible. Combinations of these are also possible. 210 To provide maximum flexibility, we want to provide a mechanism that 211 allows a router to (a) identify a particular calculation-type, (b) 212 metric-type, (c) describe a particular set of constraints, and (d) 213 assign a numeric identifier, referred to as Flex-Algorithm, to the 214 combination of that calculation-type, metric-type, and those 215 constraints. We want the mapping between the Flex-Algorithm and its 216 meaning to be flexible and defined by the user. As long as all 217 routers in the domain have a common understanding as to what a 218 particular Flex-Algorithm represents, the resulting routing 219 computation is consistent and traffic is not subject to any looping. 221 The set consisting of (a) calculation-type, (b) metric-type, and (c) 222 a set of constraints is referred to as a Flexible-Algorithm 223 Definition. 225 Flexible-Algorithm is a numeric identifier in the range 128-255 that 226 is associated via configuratin with the Flexible-Algorithm 227 Definition. 229 IANA "IGP Algorithm Types" registry defines the set of values for IGP 230 Algorithms. We propose to allocate the following values for Flex- 231 Algorithms from this registry: 233 128-255 - Flex-Algorithms 235 5. Flexible Algorithm Definition Advertisement 237 To guarantee the loop-free forwarding for paths computed for a 238 particular Flex-Algorithm, all routers that (a) are configured to 239 participate in a particular Flex-Algorithm, and (b) are in the same 240 Flex-Algorithm definition advertisement scope MUST agree on the 241 definition of the Flex-Algorithm. 243 5.1. ISIS Flexible Algorithm Definition Sub-TLV 245 The ISIS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used 246 to advertise the definition of the Flex-Algorithm. 248 The ISIS FAD Sub-TLV is advertised as a Sub-TLV of the ISIS Router 249 Capability TLV-242 that is defined in [RFC7981]. 251 ISIS FAD Sub-TLV has the following format: 253 0 1 2 3 254 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 1 255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 256 | Type | Length |Flex-Algorithm | Metric-Type | 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 258 | Calc-Type | Priority | 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 | Sub-TLVs | 261 + + 262 | ... | 264 | | 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 267 where: 269 Type: 26 271 Length: variable, dependent on the included Sub-TLVs 273 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 275 Metric-Type: Type of metric to be used during the calculation. 276 Following values are defined: 278 0: IGP Metric 280 1: Min Unidirectional Link Delay as defined in [RFC8570], 281 section 4.2, encoded in the Application Specific Link 282 Attributes Sub-TLV [I-D.ietf-isis-te-app]. 284 2: Traffic Engineering Default Metric as defined in [RFC5305], 285 section 3.7, encoded in the Application Specific Link 286 Attributes Sub-TLV [I-D.ietf-isis-te-app]. 288 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 289 Types" registry defined under "Interior Gateway Protocol (IGP) 290 Parameters" IANA registries. IGP algorithms in the range of 0-127 291 have a defined triplet (Calculation Type, Metric, Constraints). 292 When used to specify the Calc-Type in the FAD Sub-TLV, only the 293 Calculation Type defined for the specified IGP Algorithm is used. 294 The Metric/Constraints MUST NOT be inherited. If the required 295 calculation type is Shortest Path First, the value 0 SHOULD appear 296 in this field. 298 Priority: Value between 0 and 255 inclusive that specifies the 299 priority of the advertisement. 301 Sub-TLVs - optional sub-TLVs. 303 The ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a 304 router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given 305 Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs 306 for a given Flexible-Algorithm from the same originator SHOULD select 307 the first advertisement in the lowest numbered LSP. 309 The ISIS FAD Sub-TLV has an area scope. The Router Capability TLV in 310 which the FAD Sub-TLV is present MUST have the S-bit clear. 312 ISIS L1/L2 router MAY be configured to re-generate the winning FAD 313 from level 2, without any modification to it, to level 1 area. The 314 re-generation of the FAD Sub-TLV from level 2 to level 1 is 315 determined by the L1/L2 router, not by the originator of the FAD 316 advertisement in the level 2. In such case, the re-generated FAD 317 Sub-TLV will be advertised in the level 1 Router Capability TLV 318 originated by the L1/L2 router. 320 L1/L2 router MUST NOT re-generate any FAD Sub-TLV from level 1 to 321 level 2. 323 5.2. OSPF Flexible Algorithm Definition TLV 325 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 326 defined in [RFC7770]. 328 OSPF FAD TLV has the following format: 330 0 1 2 3 331 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 1 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 | Type | Length | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 337 | Sub-TLVs | 338 + + 339 | ... | 341 | | 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 344 where: 346 Type: 16 348 Length: variable, dependent on the included Sub-TLVs 350 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 351 inclusive. 353 Metric-Type: Type of metric to be used during the calculation. 354 Following values are defined: 356 0: IGP Metric 358 1: Min Unidirectional Link Delay as defined in [RFC7471], 359 section 4.2, encoded in the Application Specific Link 360 Attributes Sub-TLV [I-D.ietf-ospf-te-link-attr-reuse]. 362 2: Traffic Engineering metric as defined in [RFC3630], section 363 2.5.5, encoded in the Application Specific Link Attributes Sub- 364 TLV [I-D.ietf-ospf-te-link-attr-reuse]. 366 Calc-Type: as described in Section 5.1 368 Priority: as described in Section 5.1 370 Sub-TLVs - optional sub-TLVs. 372 When multiple OSPF FAD TLVs, for the same Flexible-Algorithm, are 373 received from a given router, the receiver MUST use the first 374 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 375 TLV, for the same Flex-Algorithm, appears in multiple Router 376 Information LSAs that have different flooding scopes, the OSPF FAD 377 TLV in the Router Information LSA with the area-scoped flooding scope 378 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 379 in multiple Router Information LSAs that have the same flooding 380 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 381 numerically smallest Instance ID MUST be used and subsequent 382 instances of the OSPF FAD TLV MUST be ignored. 384 The RI LSA can be advertised at any of the defined opaque flooding 385 scopes (link, area, or Autonomous System (AS)). For the purpose of 386 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 387 Autonomous System flooding scope SHOULD not be used by default unless 388 local configuration policy on the originating router indicates domain 389 wide flooding. 391 5.3. Common Handling of Flexible Algorithm Definition TLV 393 This section describes the protocol-independent handling of the FAD 394 TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in 395 this section, even though in case of ISIS it is a Sub-TLV. 397 The value of the Flex-Algorithm MUST be between 128 and 255 398 inclusive. If it is not, the FAD TLV MUST be ignored. 400 Only a subset of the routers participating in the particular Flex- 401 Algorithm need to advertise the definition of the Flex-Algorithm. 403 Every router, that is configured to participate in a particular Flex- 404 Algorithm, MUST select the Flex-Algorithm definition based on the 405 following ordered rules. This allows for the consistent Flex- 406 Algorithm definition selection in cases where different routers 407 advertise different definitions for a given Flex-Algorithm: 409 1. From the advertisements of the FAD in the area (including both 410 locally generated advertisements and received advertisements) 411 select the one(s) with the highest priority value. 413 2. If there are multiple advertisements of the FAD with the same 414 highest priority, select the one that is originated from the 415 router with the highest System-ID, in the case of ISIS, or Router 416 ID, in the case of OSPFv2 and OSPFv3. For ISIS, the System-ID is 417 described in [ISO10589]. For OSPFv2 and OSPFv3, standard Router 418 ID is described in [RFC2328] and [RFC5340] respectively. 420 A router that is not configured to participate in a particular Flex- 421 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 422 Algorithm. 424 A router that is not participating in a particular Flex-Algorithm is 425 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 426 MUST consider FAD advertisement regardless of the Flex-Algorithm 427 participation of the FAD originator. 429 Any change in the Flex-Algorithm definition may result in temporary 430 disruption of traffic that is forwarded based on such Flex-Algorithm 431 paths. The impact is similar to any other event that requires 432 network-wide convergence. 434 If a node is configured to participate in a particular Flexible- 435 Algorithm, but the selected Flex-Algorithm definition includes 436 calculation-type, metric-type, constraint, flag, or Sub-TLV that is 437 not supported by the node, it MUST stop participating in such 438 Flexible-Algorithm. That implies that it MUST NOT announce 439 participation for such Flexible-Algorithm as specified in Section 10 440 and it MUST remove any forwarding state associated with it. 442 Flex-Algorithm definition is topology independent. It applies to all 443 topologies that a router participates in. 445 6. Sub-TLVs of ISIS FAD Sub-TLV 447 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV 449 The Flexible Algorithm definition can specify 'colors' that are used 450 by the operator to exclude links during the Flex-Algorithm path 451 computation. 453 The ISIS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 454 advertise the exclude rule that is used during the Flex-Algorithm 455 path calculation as specified in Section 12. 457 The ISIS Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub- 458 TLV) is a Sub-TLV of the ISIS FAD Sub-TLV. It has the following 459 format: 461 0 1 2 3 462 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 1 463 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 464 | Type | Length | 465 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 466 | Extended Admin Group | 467 +- -+ 468 | ... | 469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 470 where: 472 Type: 1 473 Length: variable, dependent on the size of the Extended Admin 474 Group. MUST be a multiple of 4 octets. 476 Extended Administrative Group: Extended Administrative Group as 477 defined in [RFC7308]. 479 The ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD 480 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 481 ignored by the receiver. 483 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV 485 The Flexible Algorithm definition can specify 'colors' that are used 486 by the operator to include links during the Flex-Algorithm path 487 computation. 489 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used 490 to advertise include-any rule that is used during the Flex-Algorithm 491 path calculation as specified in Section 12. 493 The format of the ISIS Flexible Algorithm Include-Any Admin Group 494 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 495 Section 6.1. 497 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 498 2. 500 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 501 appear more then once in an ISIS FAD Sub-TLV. If it appears more 502 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 504 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV 506 The Flexible Algorithm definition can specify 'colors' that are used 507 by the operator to include link during the Flex-Algorithm path 508 computation. 510 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used 511 to advertise include-all rule that is used during the Flex-Algorithm 512 path calculation as specified in Section 12. 514 The format of the ISIS Flexible Algorithm Include-All Admin Group 515 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 516 Section 6.1. 518 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 519 3. 521 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 522 appear more then once in an ISIS FAD Sub-TLV. If it appears more 523 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 525 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV 527 The ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 528 is a Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 530 0 1 2 3 531 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 1 532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 533 | Type | Length | 534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 535 | Flags | 536 +- -+ 537 | ... | 538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 539 where: 541 Type: 4 543 Length: variable, non-zero number of octets of the Flags field 545 Flags: 547 0 1 2 3 4 5 6 7... 548 +-+-+-+-+-+-+-+-+... 549 |M| | | ... 550 +-+-+-+-+-+-+-+-+... 552 M-flag: when set, the Flex-Algorithm specific prefix metric 553 MUST be used, if advertised with the prefix. This flag is not 554 applicable to prefixes advertised as SRv6 locators. 556 Bits are defined/sent starting with Bit 0 defined above. Additional 557 bit definitions that may be defined in the future SHOULD be assigned 558 in ascending bit order so as to minimize the number of bits that will 559 need to be transmitted. 561 Undefined bits MUST be transmitted as 0. 563 Bits that are NOT transmitted MUST be treated as if they are set to 0 564 on receipt. 566 The ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD 567 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 568 ignored by the receiver. 570 If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV, 571 all the bits are assumed to be set to 0. 573 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV 575 The Flexible Algorithm definition can specify Shared Risk Link Groups 576 (SRLGs) that the operator wants to exclude during the Flex-Algorithm 577 path computation. 579 The ISIS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used to 580 advertise the exclude rule that is used during the Flex-Algorithm 581 path calculation as specified in Section 12. 583 The ISIS FAESRLG Sub-TLV is a Sub-TLV of the ISIS FAD Sub-TLV. It 584 has the following format: 586 0 1 2 3 587 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 1 588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 589 | Type | Length | 590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 | Shared Risk Link Group Value | 592 +- -+ 593 | ... | 594 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 595 where: 597 Type: 5 599 Length: variable, dependent on number of SRLG values. MUST be a 600 multiple of 4 octets. 602 Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. 604 The ISIS FAESRLG Sub-TLV MAY NOT appear more then once in an ISIS FAD 605 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 606 ignored by the receiver. 608 7. Sub-TLVs of OSPF FAD TLV 610 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 612 The Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is 613 a Sub-TLV of the OSPF FAD TLV. It's usage is described in 614 Section 6.1. It has the following format: 616 0 1 2 3 617 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 1 618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 619 | Type | Length | 620 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 621 | Extended Admin Group | 622 +- -+ 623 | ... | 624 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 625 where: 627 Type: 1 629 Length: variable, dependent on the size of the Extended Admin 630 Group. MUST be a multiple of 4 octets. 632 Extended Administrative Group: Extended Administrative Group as 633 defined in [RFC7308]. 635 The OSPF FAEAG Sub-TLV MAY NOT appear more then once in an OSPF FAD 636 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 637 by the receiver. 639 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 641 The usage of this Sub-TLVs is described in Section 6.2. 643 The format of the OSPF Flexible Algorithm Include-Any Admin Group 644 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 645 Section 7.1. 647 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 648 2. 650 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 651 appear more then once in an OSPF FAD TLV. If it appears more then 652 once, the OSPF FAD TLV MUST be ignored by the receiver. 654 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 656 The usage of this Sub-TLVs is described in Section 6.3. 658 The format of the OSPF Flexible Algorithm Include-Any Admin Group 659 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 660 Section 7.1. 662 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 663 3. 665 The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 666 appear more then once in an OSPF FAD TLV. If it appears more then 667 once, the OSPF FAD TLV MUST be ignored by the receiver. 669 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 671 The OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 672 is a Sub-TLV of the OSPF FAD TLV. It has the following format: 674 0 1 2 3 675 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 1 676 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 677 | Type | Length | 678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 679 | Flags | 680 +- -+ 681 | ... | 682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 683 where: 685 Type: 4 687 Length: variable, dependent on the size of the Flags field. MUST 688 be a multiple of 4 octets. 690 Flags: 692 0 1 2 3 4 5 6 7... 693 +-+-+-+-+-+-+-+-+... 694 |M| | | ... 695 +-+-+-+-+-+-+-+-+... 697 M-flag: when set, the Flex-Algorithm specific prefix metric 698 MUST be used, if advertised with the prefix. This flag is not 699 applicable to prefixes advertised as SRv6 locators. 701 Bits are defined/sent starting with Bit 0 defined above. Additional 702 bit definitions that may be defined in the future SHOULD be assigned 703 in ascending bit order so as to minimize the number of bits that will 704 need to be transmitted. 706 Undefined bits MUST be transmitted as 0. 708 Bits that are NOT transmitted MUST be treated as if they are set to 0 709 on receipt. 711 The OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD 712 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 713 by the receiver. 715 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 716 the bits are assumed to be set to 0. 718 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV 720 The OSPF Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG Sub-TLV) is 721 a Sub-TLV of the OSPF FAD TLV. Its usage is described in 722 Section 6.5. It has the following format: 724 0 1 2 3 725 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 1 726 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 727 | Type | Length | 728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 729 | Shared Risk Link Group Value | 730 +- -+ 731 | ... | 732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 733 where: 735 Type: 5 737 Length: variable, dependent on the number of SRLGs. MUST be a 738 multiple of 4 octets. 740 Shared Risk Link Group Value: SRLG value as defined in [RFC4203]. 742 The OSPF FAESRLG Sub-TLV MAY NOT appear more then once in an OSPF FAD 743 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 744 by the receiver. 746 8. ISIS Flexible Algorithm Prefix Metric Sub-TLV 748 The ISIS Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the 749 advertisement of a Flex-Algorithm specific prefix metric associated 750 with a given prefix advertisement. 752 The ISIS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 and 753 has the following format: 755 0 1 2 3 756 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 1 757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 758 | Type | Length |Flex-Algorithm | 759 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 760 | Metric | 761 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 762 where: 764 Type: 6 766 Length: 5 octets 768 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 770 Metric: 4 octets of metric information 772 The ISIS FAPM Sub-TLV MAY appear multiple times in its parent TLV. 773 If it appears more then once with the same Flex-Algorithm value, the 774 first instance MUST be used and any subsequent instances MUST be 775 ignored. 777 If a prefix is advertised with a Flex-Algorithm prefix metric larger 778 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 779 considered during the Flexible-Algorithm computation. 781 The usage of the Flex-Algorithm prefix metric is described in 782 Section 12. 784 The ISIS FAPM Sub-TLV MUST NOT be advertised as a sub-TLV of the ISIS 785 SRv6 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. The ISIS SRv6 786 Locator TLV includes the Algorithm and Metric fields which MUST be 787 used instead. If the FAPM Sub-TLV is present as a sub-TLV of the 788 ISIS SRv6 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be 789 ignored. 791 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV 793 The OSPF Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the 794 advertisement of a Flex-Algorithm specific prefix metric associated 795 with a given prefix advertisement. 797 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLVis a Sub-TLV of 798 the: 800 - OSPFv2 Extended Prefix TLV [RFC7684] 802 - Following OSPFv3 TLVs as defined in [RFC8362]: 804 Intra-Area Prefix TLV 806 Inter-Area Prefix TLV 808 External Prefix TLV 810 OSPF FAPM Sub-TLV has the following format: 812 0 1 2 3 813 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 1 814 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 815 | Type | Length | 816 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 817 |Flex-Algorithm | Reserved | 818 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 819 | Metric | 820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 822 where: 824 Type: 3 for OSPFv2, 26 for OSPFv3 826 Length: 8 octets 828 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 830 Reserved: Must be set to 0, ignored at reception. 832 Metric: 4 octets of metric information 834 The OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. 835 If it appears more then once with the same Flex-Algorithm value, the 836 first instance MUST be used and any subsequent instances MUST be 837 ignored. 839 The usage of the Flex-Algorithm prefix metric is described in 840 Section 12. 842 10. Advertisement of Node Participation in a Flex-Algorithm 844 When a router is configured to support a particular Flex-Algorithm, 845 we say it is participating in that Flex-Algorithm. 847 Paths computed for a specific Flex-Algorithm MAY be used by various 848 applications, each potentially using its own specific data plane for 849 forwarding traffic over such paths. To guarantee the presence of the 850 application specific forwarding state associated with a particular 851 Flex-Algorithm, a router MUST advertise its participation for a 852 particular Flex-Algorithm for each application specifically. 854 10.1. Advertisement of Node Participation for Segment Routing 856 [RFC8667], [RFC8665], and [RFC8666] (IGP Segment Routing extensions) 857 describe how the SR-Algorithm is used to compute the IGP best path. 859 Routers advertise the support for the SR-Algorithm as a node 860 capability as described in the above mentioned IGP Segment Routing 861 extensions. To advertise participation for a particular Flex- 862 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 863 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 864 (OSPF) or sub-TLV (ISIS). 866 Segment Routing Flex-Algorithm participation advertisement is 867 topology independent. When a router advertises participation in an 868 SR-Algorithm, the participation applies to all topologies in which 869 the advertising node participates. 871 10.2. Advertisement of Node Participation for Other Applications 873 This section describes considerations related to how other 874 applications can advertise their participation in a specific Flex- 875 Algorithm. 877 Application-specific Flex-Algorithm participation advertisements MAY 878 be topology specific or MAY be topology independent, depending on the 879 application itself. 881 Application-specific advertisement for Flex-Algorithm participation 882 MUST be defined for each application and is outside of the scope of 883 this document. 885 11. Advertisement of Link Attributes for Flex-Algorithm 887 Various link attributes may be used during the Flex-Algorithm path 888 calculation. For example, include or exclude rules based on link 889 affinities can be part of the Flex-Algorithm definition as defined in 890 Section 6 and Section 7. 892 Link attribute advertisements that are to be used during Flex- 893 Algorithm calculation MUST use the Application-Specific Link 894 Attribute (ASLA) advertisements defined in [I-D.ietf-isis-te-app] or 895 [I-D.ietf-ospf-te-link-attr-reuse]. In particular, the Min 896 Unidirectional Link Delay, TE Default Metric, Administrative Group, 897 Extended Administrative Group and Shared Risk Link Group TLVs MUST be 898 encoded in the ASLA advertisements for use with FlexAlgo. 900 A new Application Identifier Bit is defined to indicate that the ASLA 901 advertisement is associated with the Flex-Algorithm application. 902 This bit is set in the Standard Application Bit Mask (SABM) defined 903 in [I-D.ietf-isis-te-app] or [I-D.ietf-ospf-te-link-attr-reuse]: 905 Bit-3: Flexible Algorithm (X-bit) 907 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 908 Application MAY use either the Administrative Group or Extended 909 Administrative Group encodings. If the Administrative Group encoding 910 is used, then the first 32 bits of the corresponding FAD sub-TLVs are 911 mapped to the link attribute advertisements as specified in RFC 7308. 913 12. Calculation of Flexible Algorithm Paths 915 A router MUST be configured to participate in a given Flex-Algorithm 916 K and MUST select the FAD based on the rules defined in Section 5.3 917 before it can compute any path for that Flex-Algorithm. 919 As described in Section 10, participation for any particular Flex- 920 Algorithm MUST be advertised on a per-application basis. Calculation 921 of the paths for any particular Flex-Algorithm MUST be application 922 specific. 924 The way applications handle nodes that do not participate in 925 Flexible-Algorithm is application specific. If the application only 926 wants to consider participating nodes during the Flex-Algorithm 927 calculation, then when computing paths for a given Flex-Algorithm, 928 all nodes that do not advertise participation for that Flex-Algorithm 929 in their application-specific advertisements MUST be pruned from the 930 topology. Segment Routing, including both SR MPLS and SRv6, are 931 applications that MUST use such pruning when computing Flex-Algorithm 932 paths. 934 When computing the path for a given Flex-Algorithm, the metric-type 935 that is part of the Flex-Algorithm definition (Section 5) MUST be 936 used. 938 When computing the path for a given Flex-Algorithm, the calculation- 939 type that is part of the Flex-Algorithm definition (Section 5) MUST 940 be used. 942 Various link include or exclude rules can be part of the Flex- 943 Algorithm definition. To refer to a particular bit within an AG or 944 EAG we uses term 'color'. 946 Rules, in the order as specified below, MUST be used to prune links 947 from the topology during the Flex-Algorithm computation. 949 For all links in the topology: 951 1. Check if any exclude rule is part of the Flex-Algorithm 952 definition. If such exclude rule exists, check if any color that 953 is part of the exclude rule is also set on the link. If such a 954 color is set, the link MUST be pruned from the computation. 956 2. Check if any exclude SRLG rule is part of the Flex-Algorithm 957 definition. If such exclude rule exists, check if the link is 958 part of any SRLG that is also part of the SRLG exclude rule. If 959 the link is part of such SRLG, the link MUST be pruned from the 960 computation. 962 3. Check if any include-any rule is part of the Flex-Algorithm 963 definition. If such include-any rule exists, check if any color 964 that is part of the include-any rule is also set on the link. If 965 no such color is set, the link MUST be pruned from the 966 computation. 968 4. Check if any include-all rule is part of the Flex-Algorithm 969 definition. If such include-all rule exists, check if all colors 970 that are part of the include-all rule are also set on the link. 971 If all such colors are not set on the link, the link MUST be 972 pruned from the computation. 974 5. If the Flex-Algorithm definition uses other than IGP metric 975 (Section 5), and such metric is not advertised for the particular 976 link in a topology for which the computation is done, such link 977 MUST be pruned from the computation. A metric of value 0 MUST NOT 978 be assumed in such case. 980 12.1. Multi-area and Multi-domain Considerations 982 Any IGP Shortest Path Tree calculation is limited to a single area. 983 This applies to Flex-Algorithm calculations as well. Given that the 984 computing router does not have visibility of the topology of the next 985 areas or domain, the Flex-Algorithm specific path to an inter-area or 986 inter-domain prefix will be computed for the local area only. The 987 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 988 will be selected based on the best path for the given Flex-Algorithm 989 in the local area and such egress ABR or ASBR router will be 990 responsible to compute the best Flex-Algorithm specific path over the 991 next area or domain. This may produce an end-to-end path, which is 992 sub-optimal based on Flex-Algorithm constraints. In cases where the 993 ABR or ASBR has no reachability to a prefix for a given Flex- 994 Algorithm in the next area or domain, the traffic may be dropped by 995 the ABR/ASBR. 997 To allow the optimal end-to-end path for an inter-area or inter- 998 domain prefix for any Flex-Algorithm to be computed, the FAPM has 999 been defined in Section 8 and Section 9. 1001 If the FAD selected based on the rules defined in Section 5.3 1002 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 1003 Section 9) when advertising the prefix between areas or domains. 1004 Such metric will be equal to the metric to reach the prefix for a 1005 given Flex-Algorithm in a source area or domain. This is similar in 1006 nature to how the metric is set when prefixes are advertised between 1007 areas or domains for the default algorithm. 1009 If the FAD selected based on the rules defined in Section 5.3 1010 includes the M-flag, the FAPM MUST be used during calculation of 1011 prefix reachability for the inter-area and external prefixes. If the 1012 FAPM for the Flex-Algorithm is not advertised with the inter-area or 1013 external prefix reachability advertisement, the prefix MUST be 1014 considered as unreachable for that Flex-Algorithm. 1016 Flex-Algorithm prefix metrics MUST NOT be used during the Flex- 1017 Algorithm computation unless the FAD selected based on the rules 1018 defined in Section 5.3 includes the M-Flag, as described in 1019 (Section 6.4 or Section 7.4). 1021 If the FAD selected based on the rules defined in Section 5.3 does 1022 not includes the M-flag, it is NOT RECOMMENDED to use the Flex- 1023 Algorithm for inter-area or inter-domain prefix reachability. The 1024 reason is that without the explicit Flex-Algorithm Prefix Metric 1025 advertisement, it is not possible to conclude whether the ABR or ASBR 1026 has reachability to the inter-area or inter-domain prefix for a given 1027 Flex-Algorithm in the next area or domain. Sending the Flex-Algoritm 1028 traffic for such prefix towards the ABR or ASBR may result in traffic 1029 looping or black-holing. 1031 The FAPM MUST NOT be advertised with ISIS L1 or L2 intra-area, OSPFv2 1032 intra-area, or OSPFv3 intra-area routes. If the FAPM is advertised 1033 for these route-types, it MUST be ignored during the prefix 1034 reachability calculation. 1036 The M-flag in FAD is not applicable to prefixes advertised as SRv6 1037 locators. The ISIS SRv6 Locator TLV includes the Algorithm and 1038 Metric fields [I-D.ietf-lsr-isis-srv6-extensions]. When the ISIS 1039 SRv6 Locator is advertised between areas or domains, the metric field 1040 in the Locator TLV MUST be used irrespective of the M-flag in the FAD 1041 advertisement. 1043 13. Flex-Algorithm and Forwarding Plane 1045 This section describes how Flex-Algorithm paths are used in 1046 forwarding. 1048 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm 1050 This section describes how Flex-Algorithm paths are used with SR MPLS 1051 forwarding. 1053 Prefix SID advertisements include an SR-Algorithm value and, as such, 1054 are associated with the specified SR-Algorithm. Prefix-SIDs are also 1055 associated with a specific topology which is inherited from the 1056 associated prefix reachability advertisement. When the algorithm 1057 value advertised is a Flex-Algorithm value, the Prefix SID is 1058 associated with paths calculated using that Flex-Algorithm in the 1059 associated topology. 1061 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 1062 using the MPLS label that corresponds to the Prefix-SID that was 1063 advertised for that Flex-algorithm. If the Prefix SID for a given 1064 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 1065 be installed in the MPLS forwarding plane. 1067 Traffic that is supposed to be routed via Flex-Algorithm specific 1068 paths, MUST be dropped when there are no such paths available. 1070 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 1071 computed using the same constraints as the calculation of the primary 1072 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 1073 advertised specifically for the given algorithm. LFA paths MUST NOT 1074 use an Adjacency-SID that belongs to a link that has been pruned from 1075 the Flex-Algorithm computation. 1077 If LFA protection is being used to protect a given Flex-Algorithm 1078 paths, all routers in the area participating in the given Flex- 1079 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 1080 SID. These Node-SIDs are used to steer traffic over the LFA computed 1081 backup path. 1083 13.2. SRv6 Forwarding for Flex-Algorithm 1085 This section describes how Flex-Algorithm paths are used with SRv6 1086 forwarding. 1088 In SRv6 a node is provisioned with topology/algorithm specific 1089 locators for each of the topology/algorithm pairs supported by that 1090 node. Each locator is an aggregate prefix for all SIDs provisioned 1091 on that node which have the matching topology/algorithm. 1093 The SRv6 locator advertisement in IGPs 1094 ([I-D.ietf-lsr-isis-srv6-extensions] 1095 [I-D.ietf-lsr-ospfv3-srv6-extensions]) includes the MTID value that 1096 associates the locator with a specific topology. SRv6 locator 1097 advertisements also includes an Algorithm value that explicitly 1098 associates the locator with a specific algorithm. When the algorithm 1099 value advertised with a locator represents a Flex-Algorithm, the 1100 paths to the locator prefix MUST be calculated using the specified 1101 Flex-Algorithm in the associated topology. 1103 Forwarding entries for the locator prefixes advertised in IGPs MUST 1104 be installed in the forwarding plane of the receiving SRv6 capable 1105 routers when the associated topology/algorithm is participating in 1106 them. Forwarding entries for locators associated with Flex- 1107 Algorithms in which the node is not participating MUST NOT be 1108 installed in the forwarding palne. 1110 When the locator is associated with a Flex-Algorithm, LFA paths to 1111 the locator prefix MUST be calculated using such Flex-Algorithm in 1112 the associated topology, to guarantee that they follow the same 1113 constraints as the calculation of the primary paths. LFA paths MUST 1114 only use SRv6 SIDs advertised specifically for the given Flex- 1115 Algorithm. 1117 If LFA protection is being used to protect locators associated with a 1118 given Flex-Algorithm, all routers in the area participating in the 1119 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1120 specific locator and END SID per node and one END.X SID for every 1121 link that has not been pruned from such Flex-Algorithm computation. 1122 These locators and SIDs are used to steer traffic over the LFA- 1123 computed backup path. 1125 13.3. Other Applications' Forwarding for Flex-Algorithm 1127 Any application that wants to use Flex-Algorithm specific forwarding 1128 needs to install some form of Flex-Algorithm specific forwarding 1129 entries. 1131 Application-specific forwarding for Flex-Algorithm MUST be defined 1132 for each application and is outside of the scope of this document. 1134 14. Operational considerations 1136 14.1. Inter-area Considerations 1138 The scope of the FA computation is an area, so is the scope of the 1139 FAD. In ISIS, the Router Capability TLV in which the FAD Sub-TLV is 1140 advertised MUST have the S-bit clear, which prevents it to be flooded 1141 outside of the level in which it was originated. Even though in OSPF 1142 the FAD Sub-TLV can be flooded in an RI LSA that has AS flooding 1143 scope, the FAD selection is performed for each individual area in 1144 which it is being used. 1146 There is no requirement for the FAD for a particular Flex-Algorithm 1147 to be identical in all areas in the network. For example, traffic 1148 for the same Flex-Algorithm may be optimized for minimal delay (e.g., 1149 using delay metric) in one area or level, while being optimized for 1150 available bandwidth (e.g., using IGP metric) in another area or 1151 level. 1153 As described in Section 5.1, ISIS allows the re-generation of the 1154 winning FAD from level 2, without any modification to it, into a 1155 level 1 area. This allows the operator to configure the FAD in one 1156 or multiple routers in the level 2, without the need to repeat the 1157 same task in each level 1 area, if the intent is to have the same FAD 1158 for the particular Flex-Algorithm across all levels. This can 1159 similarly be achieved in OSPF by using the AS flooding scope of the 1160 RI LSA in which the FAD Sub-TLV for the particular Flex-Algoritm is 1161 advertised. 1163 Re-generation of FAD from a level 1 area to the level 2 area is not 1164 supported in ISIS, so if the intent is to regenerate the FAD between 1165 ISIS levels, the FAD MUST be defined on router(s) that are in level 1166 2. In OSPF, the FAD definition can be done in any area and be 1167 propagated to all routers in the OSPF routing domain by using the AS 1168 flooding scope of the RI LSA. 1170 14.2. Usage of SRLG Exclude Rule with Flex-Algorithm 1172 There are two different ways in which SRLG information can be used 1173 with Flex-Algorithm: 1175 In a context of a single Flex-Algorithm, it can be used for 1176 computation of backup paths, as described in 1177 [I-D.ietf-rtgwg-segment-routing-ti-lfa]. This usage does not 1178 require association of any specific SRLG constraint with the given 1179 Flex-Algorithm definition. 1181 In the context of multiple Flex-Algorithms, it can be used for 1182 creating disjoint sets of paths by pruning the links belonging to 1183 a specific SRLG from the topology on which a specific Flex- 1184 Algorithm computes its paths. This usage: 1186 Facilitates the usage of already deployed SRLG configurations 1187 for setup of disjoint paths between two or more Flex- 1188 Algorithms. 1190 Requires explicit association of a given Flex-Algorithm with a 1191 specific set of SRLG constraints as defined in Section 6.5 and 1192 Section 7.5. 1194 The two usages mentioned above are orthogonal. 1196 14.3. Max-metric consideration 1198 Both ISIS and OSPF have a mechanism to set the IGP metric on a link 1199 to a value that would make the link either non-reachable or to serve 1200 as the link of last resort. Similar functionality would be needed 1201 for the Min Unidirectional Link Delay and TE metric, as these can be 1202 used to compute Flex-Algorithm paths. 1204 The link can be made un-reachable for all Flex-Algorithms that use 1205 Min Unidirectional Link Delay as metric, as described in Section 5.1, 1206 by removing the Flex-Algorithm ASLA Min Unidirectional Link Delay 1207 advertisement for the link. The link can be made the link of last 1208 resort by setting the delay value in the Flex-Algorithm ASLA delay 1209 advertisement for the link to the value of 16,777,215 (2^24 - 1). 1211 The link can be made un-reachable for all Flex-Algorithms that use TE 1212 metric, as described in Section 5.1, by removing the Flex-Algorithm 1213 ASLA TE metric advertisement for the link. The link can be made the 1214 link of last resort by setting the TE metric value in the Flex- 1215 Algorithm ASLA delay advertisement for the link to the value of (2^24 1216 - 1) in ISIS and (2^32 - 1) in OSPF. 1218 15. Backward Compatibility 1220 This extension brings no new backward compatibility issues. 1222 16. Security Considerations 1224 This draft adds two new ways to disrupt IGP networks: 1226 An attacker can hijack a particular Flex-Algorithm by advertising 1227 a FAD with a priority of 255 (or any priority higher than that of 1228 the legitimate nodes). 1230 An attacker could make it look like a router supports a particular 1231 Flex-Algorithm when it actually doesn't, or vice versa. 1233 Both of these attacks can be addressed by the existing security 1234 extensions as described in [RFC5304] and [RFC5310] for ISIS, in 1235 [RFC2328] and [RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] 1236 for OSPFv3. 1238 17. IANA Considerations 1240 17.1. IGP IANA Considerations 1242 17.1.1. IGP Algorithm Types Registry 1244 This document makes the following registrations in the "IGP Algorithm 1245 Types" registry: 1247 Type: 128-255. 1249 Description: Flexible Algorithms. 1251 Reference: This document (Section 4). 1253 17.1.2. IGP Metric-Type Registry 1255 IANA is requested to set up a registry called "IGP Metric-Type 1256 Registry" under a "Interior Gateway Protocol (IGP) Parameters" IANA 1257 registries. The registration policy for this registry is "Standards 1258 Action" ([RFC8126] and [RFC7120]). 1260 Values in this registry come from the range 0-255. 1262 This document registers following values in the "IGP Metric-Type 1263 Registry": 1265 Type: 0 1267 Description: IGP metric 1269 Reference: This document (Section 5.1) 1271 Type: 1 1273 Description: Min Unidirectional Link Delay as defined in 1274 [RFC8570], section 4.2, and [RFC7471], section 4.2. 1276 Reference: This document (Section 5.1) 1277 Type: 2 1279 Description: Traffic Engineering Default Metric as defined in 1280 [RFC5305], section 3.7, and Traffic engineering metric as defined 1281 in [RFC3630], section 2.5.5 1283 Reference: This document (Section 5.1) 1285 17.2. Flexible Algorithm Definition Flags Registry 1287 IANA is requested to set up a registry called "ISIS Flexible 1288 Algorithm Definition Flags Registry" under a "Interior Gateway 1289 Protocol (IGP) Parameters" IANA registries. The registration policy 1290 for this registry is "Standards Action" ([RFC8126] and [RFC7120]). 1292 This document defines the following single bit in Flexible Algorithm 1293 Definition Flags registry: 1295 Bit # Name 1296 ----- ------------------------------ 1297 0 Prefix Metric Flag (M-flag) 1299 Reference: This document (Section 6.4, Section 7.4). 1301 17.3. ISIS IANA Considerations 1303 17.3.1. Sub TLVs for Type 242 1305 This document makes the following registrations in the "sub-TLVs for 1306 TLV 242" registry. 1308 Type: 26. 1310 Description: Flexible Algorithm Definition. 1312 Reference: This document (Section 5.1). 1314 17.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1316 This document makes the following registrations in the "Sub-TLVs for 1317 for TLVs 135, 235, 236, and 237" registry. 1319 Type: 6 1321 Description: Flexible Algorithm Prefix Metric. 1323 Reference: This document (Section 8). 1325 17.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1327 This document creates the following Sub-Sub-TLV Registry: 1329 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1331 Registration Procedure: Expert review 1333 Reference: This document (Section 5.1) 1335 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1336 for Flexible Algorithm Definition Sub-TLV" registry: 1338 Type: 1 1340 Description: Flexible Algorithm Exclude Admin Group 1342 Reference: This document (Section 6.1). 1344 Type: 2 1346 Description: Flexible Algorithm Include-Any Admin Group 1348 Reference: This document (Section 6.2). 1350 Type: 3 1352 Description: Flexible Algorithm Include-All Admin Group 1354 Reference: This document (Section 6.3). 1356 Type: 4 1358 Description: Flexible Algorithm Definition Flags 1360 Reference: This document (Section 6.4). 1362 Type: 5 1364 Description: Flexible Algorithm Exclude SRLG 1366 Reference: This document (Section 6.5). 1368 17.4. OSPF IANA Considerations 1369 17.4.1. OSPF Router Information (RI) TLVs Registry 1371 This specification updates the OSPF Router Information (RI) TLVs 1372 Registry. 1374 Type: 16 1376 Description: Flexible Algorithm Definition TLV. 1378 Reference: This document (Section 5.2). 1380 17.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1382 This document makes the following registrations in the "OSPFv2 1383 Extended Prefix TLV Sub-TLVs" registry. 1385 Type: 3 1387 Description: Flexible Algorithm Prefix Metric. 1389 Reference: This document (Section 9). 1391 17.4.3. OSPFv3 Extended-LSA Sub-TLVs 1393 This document makes the following registrations in the "OSPFv3 1394 Extended-LSA Sub-TLVs" registry. 1396 Type: 26 1398 Description: Flexible Algorithm Prefix Metric. 1400 Reference: This document (Section 9). 1402 17.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1404 This document creates the following registry: 1406 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1408 Registration Procedure: Expert review 1410 Reference: This document (Section 5.2) 1412 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1413 define sub-TLVs at any level of nesting for the Flexible Algorithm 1414 TLV and should be added to the "Open Shortest Path First (OSPF) 1415 Parameters" registries group. New values can be allocated via IETF 1416 Review or IESG Approval. 1418 This document registers following Sub-TLVs in the "TLVs for Flexible 1419 Algorithm Definition TLV" registry: 1421 Type: 1 1423 Description: Flexible Algorithm Exclude Admin Group 1425 Reference: This document (Section 7.1). 1427 Type: 2 1429 Description: Flexible Algorithm Include-Any Admin Group 1431 Reference: This document (Section 7.2). 1433 Type: 3 1435 Description: Flexible Algorithm Include-All Admin Group 1437 Reference: This document (Section 7.3). 1439 Type: 4 1441 Description: Flexible Algorithm Definition Flags 1443 Reference: This document (Section 7.4). 1445 Type: 5 1447 Description: Flexible Algorithm Exclude SRLG 1449 Reference: This document (Section 7.5). 1451 Types in the range 32768-33023 are for experimental use; these will 1452 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1454 Types in the range 33024-65535 are not to be assigned at this time. 1455 Before any assignments can be made in the 33024-65535 range, there 1456 MUST be an IETF specification that specifies IANA Considerations that 1457 covers the range being assigned. 1459 17.4.5. Link Attribute Applications Registry 1461 This document registers following bit in the Link Attribute 1462 Applications Registry: 1464 Bit-3 1465 Description: Flexible Algorithm (X-bit) 1467 Reference: This document (Section 11). 1469 18. Acknowledgements 1471 This draft, among other things, is also addressing the problem that 1472 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1473 All authors of that draft agreed to join this draft. 1475 Thanks to Eric Rosen, Tony Przygienda for their detailed review and 1476 excellent comments. 1478 Thanks to Cengiz Halit for his review and feedback during initial 1479 phase of the solution definition. 1481 Thanks to Kenji Kumaki for his comments. 1483 Thanks to William Britto A J. for his suggestions. 1485 Thanks to Acee Lindem for editorial comments. 1487 19. References 1489 19.1. Normative References 1491 [BCP14] , . 1493 [I-D.ietf-isis-te-app] 1494 Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1495 J. Drake, "IS-IS Application-Specific Link Attributes", 1496 draft-ietf-isis-te-app-19 (work in progress), June 2020. 1498 [I-D.ietf-lsr-isis-srv6-extensions] 1499 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1500 Z. Hu, "IS-IS Extension to Support Segment Routing over 1501 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08 1502 (work in progress), April 2020. 1504 [I-D.ietf-lsr-ospf-reverse-metric] 1505 Talaulikar, K., Psenak, P., and H. Johnston, "OSPF Reverse 1506 Metric", draft-ietf-lsr-ospf-reverse-metric-01 (work in 1507 progress), June 2020. 1509 [I-D.ietf-lsr-ospfv3-srv6-extensions] 1510 Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, 1511 "OSPFv3 Extensions for SRv6", draft-ietf-lsr- 1512 ospfv3-srv6-extensions-01 (work in progress), August 2020. 1514 [I-D.ietf-ospf-te-link-attr-reuse] 1515 Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J., 1516 and J. Drake, "OSPF Application-Specific Link Attributes", 1517 draft-ietf-ospf-te-link-attr-reuse-16 (work in progress), 1518 June 2020. 1520 [ISO10589] 1521 International Organization for Standardization, 1522 "Intermediate system to Intermediate system intra-domain 1523 routeing information exchange protocol for use in 1524 conjunction with the protocol for providing the 1525 connectionless-mode Network Service (ISO 8473)", ISO/ 1526 IEC 10589:2002, Second Edition, Nov 2002. 1528 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1529 Requirement Levels", BCP 14, RFC 2119, 1530 DOI 10.17487/RFC2119, March 1997, 1531 . 1533 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 1534 Support of Generalized Multi-Protocol Label Switching 1535 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 1536 . 1538 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1539 in Support of Generalized Multi-Protocol Label Switching 1540 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1541 . 1543 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1544 Traffic Engineering (MPLS-TE)", RFC 7308, 1545 DOI 10.17487/RFC7308, July 2014, 1546 . 1548 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1549 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1550 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1551 2015, . 1553 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1554 S. Shaffer, "Extensions to OSPF for Advertising Optional 1555 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1556 February 2016, . 1558 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1559 for Advertising Router Information", RFC 7981, 1560 DOI 10.17487/RFC7981, October 2016, 1561 . 1563 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1564 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1565 May 2017, . 1567 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1568 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1569 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1570 2018, . 1572 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 1573 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1574 Extensions for Segment Routing", RFC 8665, 1575 DOI 10.17487/RFC8665, December 2019, 1576 . 1578 [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 1579 for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 1580 December 2019, . 1582 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 1583 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 1584 Extensions for Segment Routing", RFC 8667, 1585 DOI 10.17487/RFC8667, December 2019, 1586 . 1588 19.2. Informative References 1590 [I-D.gulkohegde-routing-planes-using-sr] 1591 Hegde, S. and a. arkadiy.gulko@thomsonreuters.com, 1592 "Separating Routing Planes using Segment Routing", draft- 1593 gulkohegde-routing-planes-using-sr-00 (work in progress), 1594 March 2017. 1596 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 1597 Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B., 1598 Francois, P., Voyer, D., Clad, F., and P. Camarillo, 1599 "Topology Independent Fast Reroute using Segment Routing", 1600 draft-ietf-rtgwg-segment-routing-ti-lfa-03 (work in 1601 progress), March 2020. 1603 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 1604 DOI 10.17487/RFC2328, April 1998, 1605 . 1607 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering 1608 (TE) Extensions to OSPF Version 2", RFC 3630, 1609 DOI 10.17487/RFC3630, September 2003, 1610 . 1612 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 1613 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 1614 RFC 3906, DOI 10.17487/RFC3906, October 2004, 1615 . 1617 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 1618 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 1619 . 1621 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1622 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1623 2008, . 1625 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 1626 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 1627 2008, . 1629 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 1630 and M. Fanto, "IS-IS Generic Cryptographic 1631 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 1632 2009, . 1634 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 1635 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 1636 . 1638 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 1639 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 1640 2014, . 1642 [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. 1643 Previdi, "OSPF Traffic Engineering (TE) Metric 1644 Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, 1645 . 1647 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 1648 "Security Extension for OSPFv2 When Using Manual Key 1649 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 1650 . 1652 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1653 Writing an IANA Considerations Section in RFCs", BCP 26, 1654 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1655 . 1657 [RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward, 1658 D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) 1659 Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March 1660 2019, . 1662 Authors' Addresses 1664 Peter Psenak (editor) 1665 Cisco Systems 1666 Apollo Business Center 1667 Mlynske nivy 43 1668 Bratislava, 82109 1669 Slovakia 1671 Email: ppsenak@cisco.com 1673 Shraddha Hegde 1674 Juniper Networks, Inc. 1675 Embassy Business Park 1676 Bangalore, KA, 560093 1677 India 1679 Email: shraddha@juniper.net 1681 Clarence Filsfils 1682 Cisco Systems, Inc. 1683 Brussels 1684 Belgium 1686 Email: cfilsfil@cisco.com 1688 Ketan Talaulikar 1689 Cisco Systems, Inc. 1690 S.No. 154/6, Phase I, Hinjawadi 1691 PUNE, MAHARASHTRA 411 057 1692 India 1694 Email: ketant@cisco.com 1696 Arkadiy Gulko 1697 Individual 1699 Email: arkadiy.gulko@gmail.com