idnits 2.17.1 draft-ietf-lsr-flex-algo-04.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: 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: 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: 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: 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: 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: OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT appear more then once in an OPSF 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: OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT appear more then once in an OPSF 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: 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 document date (September 18, 2019) is 1675 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) -- Possible downref: Non-RFC (?) normative reference: ref. 'BCP14' == Outdated reference: A later version (-19) exists of draft-ietf-isis-te-app-06 == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-02 == Outdated reference: A later version (-16) exists of draft-ietf-ospf-te-link-attr-reuse-08 == Outdated reference: A later version (-07) exists of draft-li-ospf-ospfv3-srv6-extensions-05 -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10589' -- Obsolete informational reference (is this intentional?): RFC 7810 (Obsoleted by RFC 8570) Summary: 1 error (**), 0 flaws (~~), 14 warnings (==), 5 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: March 21, 2020 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Thomson Reuters 11 September 18, 2019 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-04.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 enforce traffic over a path that is computed using different metrics 22 or 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 March 21, 2020. 45 Copyright Notice 47 Copyright (c) 2019 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 . . . . . . . . . 5 67 5.1. ISIS Flexible Algorithm Definition Sub-TLV . . . . . . . 5 68 5.2. OSPF Flexible Algorithm Definition TLV . . . . . . . . . 7 69 5.3. Common Handling of Flexible Algorithm Definition TLV . . 8 70 6. Sub-TLVs of ISIS FAD Sub-TLV . . . . . . . . . . . . . . . . 9 71 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV . . . 9 72 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV . 10 73 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV . 10 74 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV . . . . 11 75 7. Sub-TLVs of OSPF FAD TLV . . . . . . . . . . . . . . . . . . 12 76 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV . . . 12 77 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV . 13 78 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV . 13 79 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV . . . . 13 80 8. ISIS Flex-Algorithm Prefix Metric Sub-TLV . . . . . . . . . . 14 81 9. OSPF Flex-Algorithm Prefix Metric Sub-TLV . . . . . . . . . . 15 82 10. Advertisement of Node Participation in a Flex-Algorithm . . . 16 83 10.1. Advertisement of Node Participation for Segment Routing 16 84 10.2. Advertisement of Node Participation for Other 85 Applications . . . . . . . . . . . . . . . . . . . . . . 17 86 11. Advertisement of Link Attributes for Flex-Algorithm . . . . . 17 87 12. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 18 88 12.1. Multi-area and Multi-domain Considerations . . . . . . . 19 89 13. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 20 90 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 20 91 13.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 21 92 13.3. Other Applications' Forwarding for Flex-Algorithm . . . 21 94 14. Backward Compatibility . . . . . . . . . . . . . . . . . . . 22 95 15. Security Considerations . . . . . . . . . . . . . . . . . . . 22 96 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 97 16.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 22 98 16.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 22 99 16.1.2. Flexible Algorithm Definition Metric-Type Registry . 22 100 16.2. Flex-Algorithm Definition Flags Registry . . . . . . . . 23 101 16.3. ISIS IANA Considerations . . . . . . . . . . . . . . . . 23 102 16.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 23 103 16.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 24 104 16.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 105 TLV . . . . . . . . . . . . . . . . . . . . . . . . 24 106 16.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 25 107 16.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 25 108 16.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 25 109 16.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 25 110 16.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV 111 Registry . . . . . . . . . . . . . . . . . . . . . . 25 112 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26 113 18. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 114 18.1. Normative References . . . . . . . . . . . . . . . . . . 27 115 18.2. Informative References . . . . . . . . . . . . . . . . . 28 116 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 118 1. Introduction 120 An IGP computed path based on the shortest IGP metric must often be 121 replaced by a traffic engineered path due to the traffic requirements 122 which are not reflected by the IGP metric. Some networks engineer 123 the IGP metric assignments in a way that the IGP Metric reflects the 124 link bandwidth or delay. If, for example, the IGP metric is 125 reflecting the bandwidth on the link and the application traffic is 126 delay sensitive, the best IGP path may not reflect the best path from 127 such an application's perspective. 129 To overcome this limitation, various sorts of traffic engineering 130 have been deployed, including RSVP-TE and SR-TE, in which case the TE 131 component is responsible for computing paths based on additional 132 metrics and/or constraints. Such paths need to be installed in the 133 forwarding tables in addition to, or as a replacement for, the 134 original paths computed by IGPs. Tunnels are often used to represent 135 the engineered paths and mechanisms like one described in [RFC3906] 136 are used to replace the native IGP paths with such tunnel paths. 138 This document specifies a set of extensions to ISIS, OSPFv2 and 139 OSPFv3 that enable a router to send TLVs that identify (a) 140 calculation-type, (b) specify a metric-type, and (c )describe a set 141 of constraints on the topology, that are to be used to compute the 142 best paths along the constrained topology. A given combination of 143 calculation-type, metric-type, and constraints is known as a 144 "Flexible Algorithm Definition". A router that sends such a set of 145 TLVs also assigns a Flex-Algorithm value, to the specified 146 combination of calculation-type, metric-type, and constraints. 148 This document also specifies a way for a router to use IGPs to 149 associate one or more SR Prefix-SIDs or SRv6 locators with a 150 particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then 151 represents a path that is computed according to the identified Flex- 152 Algorithm. 154 2. Requirements notation 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 158 "OPTIONAL" in this document are to be interpreted as described in 159 [BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all 160 capitals, as shown here. 162 3. Terminology 164 This section defines terms that are often used in this document. 166 Flexible Algorithm Definition - the set consisting of (a) 167 calculation-type, (b) metric-type, and (c) a set of constraints,. 169 Flexible Algorithm - a numeric identifier in the range 128-255 that 170 is associated via provisioning with the Flexible-Algorithm 171 Definition. 173 Local Flexible Algorithm Definition - Flexible Algorithm Definition 174 defined locally on the node. 176 Remote Flexible Algorithm Definition - Flexible Algorithm Definition 177 received from other nodes via IGP flooding. 179 Flexible Algorithm Participation - per application configuration 180 state that expresses whether the node is participating in a 181 particular Flexible Algorithm. 183 IGP Algorithm - value from the the "IGP Algorithm Types" registry 184 defined under "Interior Gateway Protocol (IGP) Parameters" IANA 185 registries. IGP Algorithms represents the triplet (Calculation Type, 186 Metric, Constraints), where the second and third elements of the 187 triple MAY not exist. 189 4. Flexible Algorithm 191 Many possible constraints may be used to compute a path over a 192 network. Some networks are deployed as multiple planes. A simple 193 form of constraint may be to use a particular plane. A more 194 sophisticated form of constraint can include some extended metric as 195 described in [RFC7810]. Constraints which restrict paths to links 196 with specific affinities or avoid links with specific affinities are 197 also possible. Combinations of these are also possible. 199 To provide maximum flexibility, we want to provide a mechanism that 200 allows a router to (a) identify a particular calculation-type, (b) 201 metric-type, (c) describe a particular set of constraints, and (d) 202 assign a numeric identifier, referred to as Flex-Algorithm, to the 203 combination of that calculation-type, metric-type and those 204 constraints. We want the mapping between the Flex-Algorithm and it's 205 meaning to be flexible and defined by the user. As long as all 206 routers in the domain have a common understanding as to what a 207 particular Flex-Algorithm represents, the resulting routing 208 computation is consistent and traffic is not subject to any looping. 210 The set consisting of (a) calculation-type, (b) metric-type and (c) a 211 set of constraints is referred to as a Flexible-Algorithm Definition. 213 Flexible-Algorithm is a numeric identifier in the range 128-255 that 214 is associated via provisioning with the Flexible-Algorithm 215 Definition. 217 IANA "IGP Algorithm Types" registry defines the set of values for IGP 218 Algorithms. We propose to allocate the following values for Flex- 219 Algorithms from this registry: 221 128-255 - Flex-Algorithms 223 5. Flexible Algorithm Definition Advertisement 225 To guarantee the loop free forwarding for paths computed for a 226 particular Flex-Algorithm, all routers that (a) are configured to 227 participate in a particular Flex-Algorithm, and (b) are in the same 228 Flex-Algorithm definition advertisement scope MUST agree on the 229 definition of the Flex-Algorithm. 231 5.1. ISIS Flexible Algorithm Definition Sub-TLV 233 ISIS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used to 234 advertise the definition of the Flex-Algorithm. 236 ISIS FAD Sub-TLV is advertised as a Sub-TLV of the ISIS Router 237 Capability TLV-242 that is defined in [RFC7981]. 239 ISIS FAD Sub-TLV has the following format: 241 0 1 2 3 242 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 1 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | Type | Length |Flex-Algorithm | Metric-Type | 245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 246 | Calc-Type | Priority | 247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 248 | Sub-TLVs | 249 + + 250 | ... | 252 | | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 where: 257 Type: TBD, suggested value 26 259 Length: variable, dependent on the included Sub-TLVs 261 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 263 Metric-Type: Type of metric to be used during the calculation. 264 Following values are defined: 266 0: IGP Metric 268 1: Min Unidirectional Link Delay as defined in [RFC7810]. 270 2: TE default metric as defined in [RFC5305]. 272 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 273 Types" registry defined under "Interior Gateway Protocol (IGP) 274 Parameters" IANA registries. IGP algorithms in the range of 0-127 275 have a defined triplet (Calculation Type, Metric, Constraints). 276 When used to specify the Calc-Type in the FAD Sub-TLV, only the 277 Calculation Type defined for the specified IGP Algorithm is used. 278 The Metric/Constraints MUST NOT be inherited. If the required 279 calculation type is Shortest Path First, the value 0 SHOULD appear 280 in this field. 282 Priority: Value between 0 and 255 inclusive that specifies the 283 priority of the advertisement. 285 Sub-TLVs - optional sub-TLVs. 287 The ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a 288 router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given 289 Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs 290 for a given Flexible-Algorithm from the same originator SHOULD select 291 the first advertisement in the lowest numbered LSP. 293 The ISIS FAD Sub-TLV MAY be flooded only in a given level or 294 throughout the domain. In the latter case the S-flag is set as 295 described in [RFC7981]. It is recommended that domain-wide flooding 296 NOT be the default behavior. 298 5.2. OSPF Flexible Algorithm Definition TLV 300 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 301 defined in [RFC7770]. 303 OSPF FAD TLV has the following format: 305 0 1 2 3 306 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 1 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | Type | Length | 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 | Sub-TLVs | 313 + + 314 | ... | 316 | | 317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 319 where: 321 Type: TBD, suggested value 16 323 Length: variable, dependent on the included Sub-TLVs 325 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 326 inclusive. 328 Metric-Type: as described in Section 5.1 330 Calc-Type: as described in Section 5.1 331 Priority: as described in Section 5.1 333 Sub-TLVs - optional sub-TLVs. 335 When multiple OPSF FAD TLVs, for the same Flexible-Algorithm, are 336 received from a given router, the receiver MUST use the first 337 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 338 TLV, for the same Flex-Algorithm, appears in multiple Router 339 Information LSAs that have different flooding scopes, the OSPF FAD 340 TLV in the Router Information LSA with the area-scoped flooding scope 341 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 342 in multiple Router Information LSAs that have the same flooding 343 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 344 numerically smallest Instance ID MUST be used and subsequent 345 instances of the OSPF FAD TLV MUST be ignored. 347 The RI LSA can be advertised at any of the defined opaque flooding 348 scopes (link, area, or Autonomous System (AS)). For the purpose of 349 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 350 Autonomous System flooding scope SHOULD not be used by default unless 351 local configuration policy on the originating router indicates domain 352 wide flooding. 354 5.3. Common Handling of Flexible Algorithm Definition TLV 356 This section describes the protocol independent handling of the FAD 357 TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in 358 this section, even though in case of ISIS it is a Sub-TLV. 360 The value of the Flex-Algorithm MUST be between 128 and 255 361 inclusive. If it is not, the FAD TLV MUST be ignored. 363 Only a subset of the routers participating in the particular Flex- 364 Algorithm need to advertise the definition of the Flex-Algorithm. 366 Every router, that is configured to participate in a particular Flex- 367 Algorithm, MUST select the Flex-Algorithm definition based on the 368 following ordered rules. This allows for the consistent Flex- 369 Algorithm definition selection in cases where different routers 370 advertise different definitions for a given Flex-Algorithm: 372 1. From the advertisements of the FAD in the area (including both 373 locally generated advertisements and received advertisements) 374 select the one(s) with the highest priority value. 376 2. If there are multiple advertisements of the FAD with the same 377 highest priority, select the one that is originated from the 378 router with the highest System-ID in case of ISIS or Router ID in 379 case of OSPFv2 and OSPFv3. For ISIS the System-ID is described in 380 [ISO10589]. For OSPFv2 and OSPFv3 standard Router ID is described 381 in [RFC2328] and [RFC5340] respectively. 383 A router that is not configured to participate in a particular Flex- 384 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 385 Algorithm. 387 A router that is not participating in a particular Flex-Algorithm is 388 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 389 MUST consider FAD advertisement regardless of the Flex-Algorithm 390 participation of the FAD originator. 392 Any change in the Flex-Algorithm definition may result in temporary 393 disruption of traffic that is forwarded based on such Flex-Algorithm 394 paths. The impact is similar to any other event that requires 395 network wide convergence. 397 If a node is configured to participate in a particular Flexible- 398 Algorithm, but the selected Flex-Algorithm definition includes 399 calculation-type, metric-type, constraint, flag or Sub-TLV that is 400 not supported by the node, it MUST stop participating in such 401 Flexible-Algorithm. That implies that it MUST NOT announce 402 participation for such Flexible-Algorithm as specified in Section 10 403 and it MUST remove any forwarding state associated with it. 405 Flex-Algorithm definition is topology independent. It applies to all 406 topologies that a router participates in. 408 6. Sub-TLVs of ISIS FAD Sub-TLV 410 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV 412 The Flexible-Algorithm definition can specify 'colors' that are used 413 by the operator to exclude links during the Flex-Algorithm path 414 computation. 416 ISIS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 417 advertise the exclude rule that is used during the Flex-Algorithm 418 path calculation as specified in Section 12. 420 Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a 421 Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 423 0 1 2 3 424 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 1 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 | Type | Length | 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 | Extended Admin Group | 429 +- -+ 430 | ... | 431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 432 where: 434 Type: 1 436 Length: variable, dependent on the size of the Extended Admin 437 Group. MUST be a multiple of 4 octets. 439 Extended Administrative Group: Extended Administrative Group as 440 defined in [RFC7308]. 442 ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- 443 TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 444 ignored by the receiver. 446 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV 448 The Flexible-Algorithm definition can specify 'colors' that are used 449 by the operator to include links during the Flex-Algorithm path 450 computation. 452 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used to 453 advertise include-any rule that is used during the Flex-Algorithm 454 path calculation as specified in Section 12. 456 The format of the ISIS Flexible Algorithm Include-Any Admin Group 457 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 458 Section 6.1. 460 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. 462 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 463 appear more then once in an ISIS FAD Sub-TLV. If it appears more 464 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 466 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV 468 The Flexible-Algorithm definition can specify 'colors' that are used 469 by the operator to include link during the Flex-Algorithm path 470 computation. 472 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used to 473 advertise include-all rule that is used during the Flex-Algorithm 474 path calculation as specified in Section 12. 476 The format of the ISIS Flexible Algorithm Include-All Admin Group 477 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 478 Section 6.1. 480 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 3. 482 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 483 appear more then once in an ISIS FAD Sub-TLV. If it appears more 484 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 486 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV 488 ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a 489 Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 491 0 1 2 3 492 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 1 493 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 494 | Type | Length | 495 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 496 | Flags | 497 +- -+ 498 | ... | 499 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 500 where: 502 Type: 4 504 Length: variable, non-zero number of octets of the Flags field 506 Flags: 508 0 1 2 3 4 5 6 7... 509 +-+-+-+-+-+-+-+-+... 510 |M| | | ... 511 +-+-+-+-+-+-+-+-+... 513 M-flag: when set, Flex-Algorithm specific prefix metric MUST be 514 used, if advertised with the prefix. This flag is not 515 applicable to prefixes advertised as SRv6 locators. 517 Bits are defined/sent starting with Bit 0 defined above. Additional 518 bit definitions that may be defined in the future SHOULD be assigned 519 in ascending bit order so as to minimize the number of bits that will 520 need to be transmitted. 522 Undefined bits MUST be transmitted as 0. 524 Bits that are NOT transmitted MUST be treated as if they are set to 0 525 on receipt. 527 ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- 528 TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 529 ignored by the receiver. 531 If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV, 532 all the bits are assumed to be set to 0. 534 7. Sub-TLVs of OSPF FAD TLV 536 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 538 Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a 539 Sub-TLV of the OSPF FAD TLV. It's usage is described in Section 6.1. 540 It has the following format: 542 0 1 2 3 543 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 1 544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 545 | Type | Length | 546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 547 | Extended Admin Group | 548 +- -+ 549 | ... | 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 where: 553 Type: 1 555 Length: variable, dependent on the size of the Extended Admin 556 Group. MUST be a multiple of 4 octets. 558 Extended Administrative Group: Extended Administrative Group as 559 defined in [RFC7308]. 561 OSPF FAEAG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. 562 If it appears more then once, the OSPF FAD TLV MUST be ignored by the 563 receiver. 565 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 567 The usage of this Sub-TLVs is described in Section 6.2. 569 The format of the OSPF Flexible Algorithm Include-Any Admin Group 570 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 571 Section 7.1. 573 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. 575 OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 576 appear more then once in an OPSF FAD TLV. If it appears more then 577 once, the OSPF FAD TLV MUST be ignored by the receiver. 579 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 581 The usage of this Sub-TLVs is described in Section 6.3. 583 The format of the OSPF Flexible Algorithm Include-Any Admin Group 584 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 585 Section 7.1. 587 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 3. 589 OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 590 appear more then once in an OPSF FAD TLV. If it appears more then 591 once, the OSPF FAD TLV MUST be ignored by the receiver. 593 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 595 OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a 596 Sub-TLV of the OSPF FAD TLV. It has the following format: 598 0 1 2 3 599 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 1 600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 | Type | Length | 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 603 | Flags | 604 +- -+ 605 | ... | 606 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 607 where: 609 Type: 4 611 Length: variable, dependent on the size of the Flags field. MUST 612 be a multiple of 4 octets. 614 Flags: 616 0 1 2 3 4 5 6 7... 617 +-+-+-+-+-+-+-+-+... 618 |M| | | ... 619 +-+-+-+-+-+-+-+-+... 621 M-flag: when set, Flex-Algorithm specific prefix metric MUST be 622 used, if advertised with the prefix. This flag is not 623 applicable to prefixes advertised as SRv6 locators. 625 Bits are defined/sent starting with Bit 0 defined above. Additional 626 bit definitions that may be defined in the future SHOULD be assigned 627 in ascending bit order so as to minimize the number of bits that will 628 need to be transmitted. 630 Undefined bits MUST be transmitted as 0. 632 Bits that are NOT transmitted MUST be treated as if they are set to 0 633 on receipt. 635 OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. 636 If it appears more then once, the OSPF FAD TLV MUST be ignored by the 637 receiver. 639 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 640 the bits are assumed to be set to 0. 642 8. ISIS Flex-Algorithm Prefix Metric Sub-TLV 644 ISIS Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the 645 advertisement of a Flex-Algorithm specific prefix metric associated 646 with a given prefix advertisement. 648 ISIS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 and has 649 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 |Flex-Algorithm | 655 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 656 | Metric | 657 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 658 where: 660 Type: TBD, suggested value 6 661 Length: 5 octets 663 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 665 Metric: 4 octets of metric information 667 ISIS FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it 668 appears more then once with the same Flex-Algorithm value, the first 669 appearance MUST be used and any subsequent ones MUST be ignored. 671 If a prefix is advertised with a Flex-Algorithm prefix metric larger 672 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 673 considered during the Flexible-Algorithm computation. 675 The usage of the Flex-Algorithm prefix metric is described in 676 Section 12. 678 ISIS FAPM Sub-TLV MUST NOT be advertised as sub-TLV of the ISIS SRv6 679 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. ISIS SRv6 Locator 680 TLV includes the Algorithm and Metric fields which MUST be used 681 instead. If FAPM Sub-TLV is present as sub-TLV of the ISIS SRv6 682 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be ignored. 684 9. OSPF Flex-Algorithm Prefix Metric Sub-TLV 686 OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the 687 advertisement of a Flex-Algorithm specific prefix metric associated 688 with a given prefix advertisement. 690 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLVis a Sub-TLV of 691 the: 693 - OSPFv2 Extended Prefix TLV [RFC7684] 695 - Following OSPFv3 TLVs as defined in [RFC8362]: 697 Intra-Area Prefix TLV 699 Inter-Area Prefix TLV 701 External Prefix TLV 703 OSPF FAPM Sub-TLV has the following format: 705 0 1 2 3 706 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 1 707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 708 | Type | Length | 709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 |Flex-Algorithm | Reserved | 711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 712 | Metric | 713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 715 where: 717 Type: TBD, suggested value for OSPFv2 is 3, for OSPFv3 is 26 719 Length: 8 octets 721 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 723 Reserved: Must be set to 0, ignored at reception. 725 Metric: 4 octets of metric information 727 OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it 728 appears more then once with the same Flex-Algorithm value, the first 729 appearance MUST be used and any subsequent ones MUST be ignored. 731 The usage of the Flex-Algorithm prefix metric is described in 732 Section 12. 734 10. Advertisement of Node Participation in a Flex-Algorithm 736 When a router is configured to support a particular Flex-Algorithm, 737 we say it is participating in that Flex-Algorithm. 739 Paths computed for a specific Flex-Algorithm MAY be used by various 740 applications, each potentially using its own specific data plane for 741 forwarding the data over such paths. To guarantee the presence of 742 the application specific forwarding state associated with a 743 particular Flex-Algorithm, a router MUST advertise its participation 744 for a particular Flex-Algorithm for each application specifically. 746 10.1. Advertisement of Node Participation for Segment Routing 748 [I-D.ietf-isis-segment-routing-extensions], 749 [I-D.ietf-ospf-segment-routing-extensions] and 750 [I-D.ietf-ospf-ospfv3-segment-routing-extensions] (IGP Segment 751 Routing extensions) describe how SR-Algorithm is used to define how 752 the best path is computed by the IGP. 754 Routers advertise the support for the SR-Algorithm as a node 755 capability as described in the above mentioned IGP Segment Routing 756 extensions. To advertise participation for a particular Flex- 757 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 758 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 759 (OSPF) or sub-TLV (ISIS). 761 Segment Routing Flex-Algorithm participation advertisement is 762 topology independent. When a router advertises participation in an 763 SR-Algorithm, the participation applies to all topologies in which 764 the advertising node participates. 766 10.2. Advertisement of Node Participation for Other Applications 768 This section describes considerations related to how other 769 applications can advertise its participation in a specific Flex- 770 Algorithm. 772 Application specific Flex-Algorithm participation advertisements MAY 773 be topology specific or MAY be topology independent, depending on the 774 application itself. 776 Application specific advertisement for Flex-Algorithm participation 777 MUST be defined for each application and is outside of the scope of 778 this document. 780 11. Advertisement of Link Attributes for Flex-Algorithm 782 Various link include or exclude rules can be part of the Flex- 783 Algorithm definition. These rules use Admin Groups (AG) as defined 784 in [RFC5305], or Extended Administrative Groups (EAG) as defined in 785 [RFC7308]. 787 To advertise a link affinity in a form of the AG or EAG that is used 788 during Flex-Algorithm calculation, an Application Specific Link 789 Attributes sub-TLV as described in [I-D.ietf-isis-te-app], or sub-TLV 790 of Extended Link TLV as described in 791 [I-D.ietf-ospf-te-link-attr-reuse] MUST be used. The advertisement 792 MUST indicate that it is usable by the Flex-Algorithm application. 794 If the link Flex-Algorithm application affinities are advertised in a 795 form of the AG inside the Application Specific Link Attributes sub- 796 TLV, these are mapped to the affinities specified in the FAD Sub-TLVs 797 as defined in [RFC7308]. 799 12. Calculation of Flexible Algorithm Paths 801 A router MUST be configured to participate in a given Flex-Algorithm 802 K and MUST use the FAD selected based on the rules defined in 803 Section 5.3 before it can compute any path for that Flex-Algorithm. 805 As described in Section 10, participation for any particular Flex- 806 Algorithm MUST be advertised on a per application basis. Calculation 807 of the paths for any particular Flex-Algorithm MUST be application 808 specific. 810 The way applications handle nodes that do not participate in 811 Flexible-Algorithm is application specific. If the application only 812 wants to consider participating nodes during the Flex-Algorithm 813 calculation, then when computing paths for a given Flex-Algorithm, 814 all nodes that do not advertise participation for that Flex-Algorithm 815 in the application specific advertisements MUST be pruned from the 816 topology. Segment Routing, including both SR MPLS and SRv6, are 817 applications that MUST use such pruning when computing Flex-Algorithm 818 paths. 820 When computing the path for a given Flex-Algorithm, the metric-type 821 that is part of the Flex-Algorithm definition (Section 5) MUST be 822 used. 824 When computing the path for a given Flex-Algorithm, the calculation- 825 type that is part of the Flex-Algorithm definition (Section 5) MUST 826 be used. 828 Various link include or exclude rules can be part of the Flex- 829 Algorithm definition. To refer to a particular bit within an AG or 830 EAG we uses term 'color'. 832 Rules, in the order as specified below, MUST be used to prune links 833 from the topology during the Flex-Algorithm computation. 835 For all links in the topology: 837 1. Check if any exclude rule is part of the Flex-Algorithm 838 definition. If such exclude rule exists, check if any color that 839 is part of the exclude rule is also set on the link. If such a 840 color is set, the link MUST be pruned from the computation. 842 2. Check if any include-any rule is part of the Flex-Algorithm 843 definition. If such include-any rule exists, check if any color 844 that is part of the include-any rule is also set on the link. If 845 no such color is set, the link MUST be pruned from the 846 computation. 848 3. Check if any include-all rule is part of the Flex-Algorithm 849 definition. If such include-all rule exists, check if all colors 850 that are part of the include-all rule are also set on the link. 851 If all such colors are not set on the link, the link MUST be 852 pruned from the computation. 854 4. If the Flex-Algorithm definition uses other than IGP metric 855 (Section 5), and such metric is not advertised for the particular 856 link in a topology for which the computation is done, such link 857 MUST be pruned from the computation. A metric of value 0 MUST NOT 858 be assumed in such case. 860 12.1. Multi-area and Multi-domain Considerations 862 Any IGP Shortest Path Tree calculation is limited to a single area. 863 Same applies to Flex-Algorithm calculations. Given that the 864 computing router may not have the visibility to the topology of 865 remote areas, the Flex-Algorithm specific path to an inter-area or 866 inter-domain prefix will be computed for the local area only. The 867 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 868 will be selected based on the best path for the given Flex-Algorithm 869 in the local area and such egress ABR or ASBR router will be 870 responsible to compute the best Flex-Algorithm specific path over the 871 next area or domain. This may produce an end-to-end path, which is 872 sub-optimal based on Flex-Algorithm constraints. 874 To allow the best end-to-end path for a prefix for a given Flex- 875 Algorithm to be computed, an ABR or ASBR MAY set the Flex-Algorithm 876 prefix metric (Section 8, Section 9) when advertising the prefix 877 between areas or domains. Such metric will be equal to the metric to 878 reach the prefix for a given Flex-Algorithm in a source area or 879 domain. This is similar in nature to how the metric is set when 880 prefixes are advertised between areas or domains for default 881 algorithm. 883 Flex-Algorithm prefix metrics MUST NOT be used during the Flex- 884 Algorithm computation unless the FAD selected based on the rules 885 defined in Section 5.3 includes the M-Flag, as described in 886 (Section 6.4 or Section 7.4). 888 If the FAD selected based on the rules defined in Section 5.3 889 includes the M-flag, Flex-Algorithm prefix metrics MUST be used 890 during calculation when advertised with the prefix. If the Flex- 891 Algorithm prefix metric is not advertised with the prefix, the 892 standard IGP metric advertised with the prefix MUST be used. 894 M-flag in FAD is not applicable to prefixes advertised as SRv6 895 locators. ISIS SRv6 Locator TLV includes the Algorithm and Metric 896 fields [I-D.ietf-lsr-isis-srv6-extensions]. When the ISIS SRv6 897 Locator is advertised between areas or domains, the metric field in 898 the Locator TLV MUST be used irrespective of the M flag in the FAD 899 advertisement. 901 13. Flex-Algorithm and Forwarding Plane 903 This section describes how Flex-Algorithm paths are used in 904 forwarding. 906 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm 908 This section describes how Flex-Algorithm paths are used with SR MPLS 909 forwarding. 911 Prefix SID advertisements include an SR-Algorithm value and as such 912 are associated with the specified SR-Algorithm. Prefix-SIDs are also 913 associated with a specific topology which is inherited from the 914 associated prefix reachability advertisement. When the algorithm 915 value advertised is a Flex-Algorithm value, the Prefix SID is 916 associated with paths calculated using that Flex-Algorithm in the 917 associated topology. 919 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 920 using the MPLS label that corresponds to the Prefix-SID that was 921 advertised for that Flex-algorithm. If the Prefix SID for a given 922 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 923 be installed in the MPLS forwarding plane. 925 Traffic that is supposed to be routed via Flex-Algorithm specific 926 paths, MUST be dropped where there are no such paths available. 928 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 929 computed using the same constraints as the calculation of the primary 930 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 931 advertised specifically for the given algorithm. LFA paths MUST NOT 932 use an Adjacency-SID that belongs to a link that has been pruned from 933 the Flex-Algorithm computation. 935 If LFA protection is being used to protect a given Flex-Algorithm 936 paths, all routers in the area participating in the given Flex- 937 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 938 SID. These Node-SIDs are used to enforce traffic over the LFA 939 computed backup path. 941 13.2. SRv6 Forwarding for Flex-Algorithm 943 This section describes how Flex-Algorithm paths are used with SRv6 944 forwarding. 946 In SRv6 a node is provisioned with topology/algorithm specific 947 locators for each of the topology/algorithm pairs supported by that 948 node. Each locator is a covering prefix for all SIDs provisioned on 949 that node which have the matching topology/algorithm. 951 SRv6 locator advertisement in IGPs 952 ([I-D.ietf-lsr-isis-srv6-extensions] 953 [I-D.li-ospf-ospfv3-srv6-extensions]) includes the MTID value that 954 associates the locator with a specific topology. SRv6 locator 955 advertisements also includes an Algorithm value that explicitly 956 associates the locator with a specific algorithm. When the algorithm 957 value advertised with a locator represents a Flex-Algorithm, the 958 paths to the locator prefix MUST be calculated using the specified 959 Flex-Algorithm in the associated topology. 961 Forwarding entries for the locator prefixes advertised in IGPs MUST 962 be installed in the forwarding plane of the receiving SRv6 capable 963 routers when the associated topology/algorithm is participating in 964 them. Forwarding entries for locators associated with Flex- 965 Algorithms in which the node is not participating MUST NOT be 966 installed in the forwarding. 968 When the locator is associated with the Flex-Algorithm, LFA paths to 969 the locator prefix MUST be calculated using such Flex-Algorithm in 970 the associated topology, to guarantee that they follow the same 971 constraints as the calculation of the primary paths. LFA paths MUST 972 only use SRv6 SIDs advertised specifically for the given Flex- 973 Algorithm. 975 If LFA protection is being used to protect locators associated with a 976 given Flex-Algorithm, all routers in the area participating in the 977 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 978 specific locator and END SID per node and one END.X SID for every 979 link that has not been pruned from such Flex-Algorithm computation. 980 These locators and SIDs are used to enforce traffic over the LFA 981 computed backup path. 983 13.3. Other Applications' Forwarding for Flex-Algorithm 985 Any application that wants to use Flex-Algorithm specific forwarding 986 needs to install some form of Flex-Algorithm specific forwarding 987 entries. 989 Application specific forwarding for Flex-Algorithm MUST be defined 990 for each application and is outside of the scope of this document. 992 14. Backward Compatibility 994 This extension brings no new backward compatibility issues. 996 15. Security Considerations 998 This draft adds two new ways to disrupt the IGP networks: 1000 An attacker can hijack a particular Flex-Algorithm by advertising 1001 a FAD with a priority of 255 (or any priority higher than that of 1002 the legitimate nodes). 1004 An attacker could make it look like a router supports a particular 1005 Flex-Algorithm when it actually doesn't, or vice versa. 1007 Both of these attacks can be addressed by the existing security 1008 extensions as described in [RFC5304] and [RFC5310] for ISIS, in 1009 [RFC2328] and [RFC7474] for OSPFv2 and in [RFC5340] and [RFC4552] for 1010 OSPFv3. 1012 16. IANA Considerations 1014 16.1. IGP IANA Considerations 1016 16.1.1. IGP Algorithm Types Registry 1018 This document makes the following registrations in the "IGP Algorithm 1019 Types" registry: 1021 Type: 128-255. 1023 Description: Flexible Algorithms. 1025 Reference: This document (Section 4). 1027 16.1.2. Flexible Algorithm Definition Metric-Type Registry 1029 IANA is requested to set up a registry called "Flexible Algorithm 1030 Definition Metric-Type Registry" under a "Interior Gateway Protocol 1031 (IGP) Parameters" IANA registries. The registration policy for this 1032 registry is "Standards Action" ([RFC8126] and [RFC7120]). 1034 Values in this registry come from the range 0-255. 1036 This document registers following values in the "Flexible Algorithm 1037 Definition Metric-Type Registry": 1039 Type: 0 1041 Description: IGP metric 1043 Reference: This document (Section 5.1) 1045 Type: 1 1047 Description: Min Unidirectional Link Delay [RFC7810] 1049 Reference: This document (Section 5.1) 1051 Type: 2 1053 Description: TE Default Metric [RFC5305] 1055 Reference: This document (Section 5.1) 1057 16.2. Flex-Algorithm Definition Flags Registry 1059 IANA is requested to set up a registry called "ISIS Flex-Algorithm 1060 Definition Flags Registry" under a "Interior Gateway Protocol (IGP) 1061 Parameters" IANA registries. The registration policy for this 1062 registry is "Standards Action" ([RFC8126] and [RFC7120]). 1064 This document defines the following single bit in Flex-Algorithm 1065 Definition Flags registry: 1067 Bit # Name 1068 ----- ------------------------------ 1069 0 Prefix Metric Flag (M-flag) 1071 Reference: This document (Section 6.4, Section 7.4). 1073 16.3. ISIS IANA Considerations 1075 16.3.1. Sub TLVs for Type 242 1077 This document makes the following registrations in the "sub-TLVs for 1078 TLV 242" registry. 1080 Type: TBD (suggested value 26). 1082 Description: Flexible Algorithm Definition. 1084 Reference: This document (Section 5.1). 1086 16.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1088 This document makes the following registrations in the "Sub-TLVs for 1089 for TLVs 135, 235, 236, and 237" registry. 1091 Type: TBD (suggested value 6). 1093 Description: Flex-Algorithm Prefix Metric. 1095 Reference: This document (Section 8). 1097 16.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1099 This document creates the following Sub-Sub-TLV Registry: 1101 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1103 Registration Procedure: Expert review 1105 Reference: This document (Section 5.1) 1107 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1108 for Flexible Algorithm Definition Sub-TLV" registry: 1110 Type: 1 1112 Description: Flexible Algorithm Exclude Admin Group 1114 Reference: This document (Section 6.1). 1116 Type: 2 1118 Description: Flexible Algorithm Include-Any Admin Group 1120 Reference: This document (Section 6.2). 1122 Type: 3 1124 Description: Flexible Algorithm Include-All Admin Group 1126 Reference: This document (Section 6.3). 1128 Type: 4 1130 Description: Flexible Algorithm Definition Flags 1131 Reference: This document (Section 6.4). 1133 16.4. OSPF IANA Considerations 1135 16.4.1. OSPF Router Information (RI) TLVs Registry 1137 This specification updates the OSPF Router Information (RI) TLVs 1138 Registry with the following value: 1140 o TBD (suggested value 16) - Flexible Algorithm Definition TLV 1142 16.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1144 This document makes the following registrations in the "OSPFv2 1145 Extended Prefix TLV Sub-TLVs" registry. 1147 Type: TBD (suggested value 3). 1149 Description: Flex-Algorithm Prefix Metric. 1151 Reference: This document (Section 9). 1153 16.4.3. OSPFv3 Extended-LSA Sub-TLVs 1155 This document makes the following registrations in the "OSPFv3 1156 Extended-LSA Sub-TLVs" registry. 1158 Type: TBD (suggested value 26). 1160 Description: Flex-Algorithm Prefix Metric. 1162 Reference: This document (Section 9). 1164 16.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1166 This document creates the following registry: 1168 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1170 Registration Procedure: Expert review 1172 Reference: This document (Section 5.2) 1174 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1175 define sub-TLVs at any level of nesting for Flexible Algorithm TLV 1176 and should be added to the "Open Shortest Path First (OSPF) 1177 Parameters" registries group. New values can be allocated via IETF 1178 Review or IESG Approval. 1180 This document registers following Sub-TLVs in the "TLVs for Flexible 1181 Algorithm Definition TLV" registry: 1183 Type: 1 1185 Description: Flexible Algorithm Exclude Admin Group 1187 Reference: This document (Section 7.1). 1189 Type: 2 1191 Description: Flexible Algorithm Include-Any Admin Group 1193 Reference: This document (Section 7.2). 1195 Type: 3 1197 Description: Flexible Algorithm Include-All Admin Group 1199 Reference: This document (Section 7.3). 1201 Type: 4 1203 Description: Flexible Algorithm Definition Flags 1205 Reference: This document (Section 7.4). 1207 Types in the range 32768-33023 are for experimental use; these will 1208 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1210 Types in the range 33024-65535 are not to be assigned at this time. 1211 Before any assignments can be made in the 33024-65535 range, there 1212 MUST be an IETF specification that specifies IANA Considerations that 1213 covers the range being assigned. 1215 17. Acknowledgements 1217 This draft, among other things, is also addressing the problem that 1218 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1219 All authors of that draft agreed to join this draft. 1221 Thanks to Eric Rosen, Tony Przygienda for their detailed review and 1222 excellent comments. 1224 Thanks to Cengiz Halit for his review and feedback during initial 1225 phase of the solution definition. 1227 Thanks to Kenji Kumaki for his comments. 1229 18. References 1231 18.1. Normative References 1233 [BCP14] , . 1235 [I-D.ietf-isis-segment-routing-extensions] 1236 Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., 1237 Gredler, H., and B. Decraene, "IS-IS Extensions for 1238 Segment Routing", draft-ietf-isis-segment-routing- 1239 extensions-25 (work in progress), May 2019. 1241 [I-D.ietf-isis-te-app] 1242 Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1243 J. Drake, "IS-IS TE Attributes per application", draft- 1244 ietf-isis-te-app-06 (work in progress), April 2019. 1246 [I-D.ietf-lsr-isis-srv6-extensions] 1247 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1248 Z. Hu, "IS-IS Extension to Support Segment Routing over 1249 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-02 1250 (work in progress), July 2019. 1252 [I-D.ietf-ospf-ospfv3-segment-routing-extensions] 1253 Psenak, P. and S. Previdi, "OSPFv3 Extensions for Segment 1254 Routing", draft-ietf-ospf-ospfv3-segment-routing- 1255 extensions-23 (work in progress), January 2019. 1257 [I-D.ietf-ospf-segment-routing-extensions] 1258 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 1259 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1260 Extensions for Segment Routing", draft-ietf-ospf-segment- 1261 routing-extensions-27 (work in progress), December 2018. 1263 [I-D.ietf-ospf-te-link-attr-reuse] 1264 Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J., 1265 and J. Drake, "OSPF Link Traffic Engineering (TE) 1266 Attribute Reuse", draft-ietf-ospf-te-link-attr-reuse-08 1267 (work in progress), August 2019. 1269 [I-D.li-ospf-ospfv3-srv6-extensions] 1270 Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, 1271 "OSPFv3 Extensions for SRv6", draft-li-ospf- 1272 ospfv3-srv6-extensions-05 (work in progress), August 2019. 1274 [ISO10589] 1275 International Organization for Standardization, 1276 "Intermediate system to Intermediate system intra-domain 1277 routeing information exchange protocol for use in 1278 conjunction with the protocol for providing the 1279 connectionless-mode Network Service (ISO 8473)", ISO/ 1280 IEC 10589:2002, Second Edition, Nov 2002. 1282 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1283 Requirement Levels", BCP 14, RFC 2119, 1284 DOI 10.17487/RFC2119, March 1997, 1285 . 1287 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1288 Traffic Engineering (MPLS-TE)", RFC 7308, 1289 DOI 10.17487/RFC7308, July 2014, 1290 . 1292 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1293 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1294 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1295 2015, . 1297 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1298 S. Shaffer, "Extensions to OSPF for Advertising Optional 1299 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1300 February 2016, . 1302 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1303 for Advertising Router Information", RFC 7981, 1304 DOI 10.17487/RFC7981, October 2016, 1305 . 1307 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1308 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1309 May 2017, . 1311 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1312 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1313 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1314 2018, . 1316 18.2. Informative References 1318 [I-D.gulkohegde-routing-planes-using-sr] 1319 Hegde, S. and a. arkadiy.gulko@thomsonreuters.com, 1320 "Separating Routing Planes using Segment Routing", draft- 1321 gulkohegde-routing-planes-using-sr-00 (work in progress), 1322 March 2017. 1324 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 1325 DOI 10.17487/RFC2328, April 1998, 1326 . 1328 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 1329 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 1330 RFC 3906, DOI 10.17487/RFC3906, October 2004, 1331 . 1333 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 1334 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 1335 . 1337 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1338 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1339 2008, . 1341 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 1342 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 1343 2008, . 1345 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 1346 and M. Fanto, "IS-IS Generic Cryptographic 1347 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 1348 2009, . 1350 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 1351 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 1352 . 1354 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 1355 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 1356 2014, . 1358 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 1359 "Security Extension for OSPFv2 When Using Manual Key 1360 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 1361 . 1363 [RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and 1364 Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", 1365 RFC 7810, DOI 10.17487/RFC7810, May 2016, 1366 . 1368 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1369 Writing an IANA Considerations Section in RFCs", BCP 26, 1370 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1371 . 1373 Authors' Addresses 1375 Peter Psenak (editor) 1376 Cisco Systems 1377 Apollo Business Center 1378 Mlynske nivy 43 1379 Bratislava, 82109 1380 Slovakia 1382 Email: ppsenak@cisco.com 1384 Shraddha Hegde 1385 Juniper Networks, Inc. 1386 Embassy Business Park 1387 Bangalore, KA, 560093 1388 India 1390 Email: shraddha@juniper.net 1392 Clarence Filsfils 1393 Cisco Systems, Inc. 1394 Brussels 1395 Belgium 1397 Email: cfilsfil@cisco.com 1399 Ketan Talaulikar 1400 Cisco Systems, Inc. 1401 S.No. 154/6, Phase I, Hinjawadi 1402 PUNE, MAHARASHTRA 411 057 1403 India 1405 Email: ketant@cisco.com 1406 Arkadiy Gulko 1407 Thomson Reuters 1409 Email: arkadiy.gulko@thomsonreuters.com