idnits 2.17.1 draft-ietf-lsr-flex-algo-05.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 (November 4, 2019) is 1633 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-09 == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-03 == Outdated reference: A later version (-16) exists of draft-ietf-ospf-te-link-attr-reuse-10 == 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: May 7, 2020 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Thomson Reuters 11 November 4, 2019 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-05.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 May 7, 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 . . . . . . . 6 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 . 11 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 17 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 . . . 22 94 14. Backward Compatibility . . . . . . . . . . . . . . . . . . . 22 95 15. Security Considerations . . . . . . . . . . . . . . . . . . . 22 96 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 97 16.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 23 98 16.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 23 99 16.1.2. Flexible Algorithm Definition Metric-Type Registry . 23 100 16.2. Flex-Algorithm Definition Flags Registry . . . . . . . . 24 101 16.3. ISIS IANA Considerations . . . . . . . . . . . . . . . . 24 102 16.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 24 103 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 . . . . . . . . 26 109 16.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 26 110 16.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV 111 Registry . . . . . . . . . . . . . . . . . . . . . . 26 112 16.4.5. Link Attribute Applications Registry . . . . . . . . 27 113 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27 114 18. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 115 18.1. Normative References . . . . . . . . . . . . . . . . . . 28 116 18.2. Informative References . . . . . . . . . . . . . . . . . 29 117 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 119 1. Introduction 121 An IGP computed path based on the shortest IGP metric must often be 122 replaced by a traffic engineered path due to the traffic requirements 123 which are not reflected by the IGP metric. Some networks engineer 124 the IGP metric assignments in a way that the IGP Metric reflects the 125 link bandwidth or delay. If, for example, the IGP metric is 126 reflecting the bandwidth on the link and the application traffic is 127 delay sensitive, the best IGP path may not reflect the best path from 128 such an application's perspective. 130 To overcome this limitation, various sorts of traffic engineering 131 have been deployed, including RSVP-TE and SR-TE, in which case the TE 132 component is responsible for computing paths based on additional 133 metrics and/or constraints. Such paths need to be installed in the 134 forwarding tables in addition to, or as a replacement for, the 135 original paths computed by IGPs. Tunnels are often used to represent 136 the engineered paths and mechanisms like one described in [RFC3906] 137 are used to replace the native IGP paths with such tunnel paths. 139 This document specifies a set of extensions to ISIS, OSPFv2 and 140 OSPFv3 that enable a router to send TLVs that identify (a) 141 calculation-type, (b) specify a metric-type, and (c )describe a set 142 of constraints on the topology, that are to be used to compute the 143 best paths along the constrained topology. A given combination of 144 calculation-type, metric-type, and constraints is known as a 145 "Flexible Algorithm Definition". A router that sends such a set of 146 TLVs also assigns a Flex-Algorithm value, to the specified 147 combination of calculation-type, metric-type, and constraints. 149 This document also specifies a way for a router to use IGPs to 150 associate one or more SR Prefix-SIDs or SRv6 locators with a 151 particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then 152 represents a path that is computed according to the identified Flex- 153 Algorithm. 155 2. Requirements notation 157 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 158 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 159 "OPTIONAL" in this document are to be interpreted as described in 160 [BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all 161 capitals, as shown here. 163 3. Terminology 165 This section defines terms that are often used in this document. 167 Flexible Algorithm Definition - the set consisting of (a) 168 calculation-type, (b) metric-type, and (c) a set of constraints,. 170 Flexible Algorithm - a numeric identifier in the range 128-255 that 171 is associated via provisioning with the Flexible-Algorithm 172 Definition. 174 Local Flexible Algorithm Definition - Flexible Algorithm Definition 175 defined locally on the node. 177 Remote Flexible Algorithm Definition - Flexible Algorithm Definition 178 received from other nodes via IGP flooding. 180 Flexible Algorithm Participation - per application configuration 181 state that expresses whether the node is participating in a 182 particular Flexible Algorithm. 184 IGP Algorithm - value from the the "IGP Algorithm Types" registry 185 defined under "Interior Gateway Protocol (IGP) Parameters" IANA 186 registries. IGP Algorithms represents the triplet (Calculation Type, 187 Metric, Constraints), where the second and third elements of the 188 triple MAY not exist. 190 ABR - Area Border Router. In ISIS terminology it is also known as 191 L1/L2 router. 193 ASBR - Autonomous System Border Router. 195 4. Flexible Algorithm 197 Many possible constraints may be used to compute a path over a 198 network. Some networks are deployed as multiple planes. A simple 199 form of constraint may be to use a particular plane. A more 200 sophisticated form of constraint can include some extended metric as 201 described in [RFC7810]. Constraints which restrict paths to links 202 with specific affinities or avoid links with specific affinities are 203 also possible. Combinations of these are also possible. 205 To provide maximum flexibility, we want to provide a mechanism that 206 allows a router to (a) identify a particular calculation-type, (b) 207 metric-type, (c) describe a particular set of constraints, and (d) 208 assign a numeric identifier, referred to as Flex-Algorithm, to the 209 combination of that calculation-type, metric-type and those 210 constraints. We want the mapping between the Flex-Algorithm and it's 211 meaning to be flexible and defined by the user. As long as all 212 routers in the domain have a common understanding as to what a 213 particular Flex-Algorithm represents, the resulting routing 214 computation is consistent and traffic is not subject to any looping. 216 The set consisting of (a) calculation-type, (b) metric-type and (c) a 217 set of constraints is referred to as a Flexible-Algorithm Definition. 219 Flexible-Algorithm is a numeric identifier in the range 128-255 that 220 is associated via provisioning with the Flexible-Algorithm 221 Definition. 223 IANA "IGP Algorithm Types" registry defines the set of values for IGP 224 Algorithms. We propose to allocate the following values for Flex- 225 Algorithms from this registry: 227 128-255 - Flex-Algorithms 229 5. Flexible Algorithm Definition Advertisement 231 To guarantee the loop free forwarding for paths computed for a 232 particular Flex-Algorithm, all routers that (a) are configured to 233 participate in a particular Flex-Algorithm, and (b) are in the same 234 Flex-Algorithm definition advertisement scope MUST agree on the 235 definition of the Flex-Algorithm. 237 5.1. ISIS Flexible Algorithm Definition Sub-TLV 239 ISIS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used to 240 advertise the definition of the Flex-Algorithm. 242 ISIS FAD Sub-TLV is advertised as a Sub-TLV of the ISIS Router 243 Capability TLV-242 that is defined in [RFC7981]. 245 ISIS FAD Sub-TLV has the following format: 247 0 1 2 3 248 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 1 249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 250 | Type | Length |Flex-Algorithm | Metric-Type | 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 | Calc-Type | Priority | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 | Sub-TLVs | 255 + + 256 | ... | 258 | | 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 261 where: 263 Type: 26 265 Length: variable, dependent on the included Sub-TLVs 267 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 269 Metric-Type: Type of metric to be used during the calculation. 270 Following values are defined: 272 0: IGP Metric 274 1: Min Unidirectional Link Delay as defined in [RFC7810]. 276 2: TE default metric as defined in [RFC5305]. 278 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 279 Types" registry defined under "Interior Gateway Protocol (IGP) 280 Parameters" IANA registries. IGP algorithms in the range of 0-127 281 have a defined triplet (Calculation Type, Metric, Constraints). 282 When used to specify the Calc-Type in the FAD Sub-TLV, only the 283 Calculation Type defined for the specified IGP Algorithm is used. 284 The Metric/Constraints MUST NOT be inherited. If the required 285 calculation type is Shortest Path First, the value 0 SHOULD appear 286 in this field. 288 Priority: Value between 0 and 255 inclusive that specifies the 289 priority of the advertisement. 291 Sub-TLVs - optional sub-TLVs. 293 The ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a 294 router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given 295 Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs 296 for a given Flexible-Algorithm from the same originator SHOULD select 297 the first advertisement in the lowest numbered LSP. 299 The ISIS FAD Sub-TLV MAY be flooded only in a given level or 300 throughout the domain. In the latter case the S-flag is set as 301 described in [RFC7981]. It is recommended that domain-wide flooding 302 NOT be the default behavior. 304 5.2. OSPF Flexible Algorithm Definition TLV 306 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 307 defined in [RFC7770]. 309 OSPF FAD TLV has the following format: 311 0 1 2 3 312 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 1 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 314 | Type | Length | 315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 316 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 318 | Sub-TLVs | 319 + + 320 | ... | 322 | | 323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 where: 327 Type: 16 329 Length: variable, dependent on the included Sub-TLVs 330 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 331 inclusive. 333 Metric-Type: as described in Section 5.1 335 Calc-Type: as described in Section 5.1 337 Priority: as described in Section 5.1 339 Sub-TLVs - optional sub-TLVs. 341 When multiple OPSF FAD TLVs, for the same Flexible-Algorithm, are 342 received from a given router, the receiver MUST use the first 343 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 344 TLV, for the same Flex-Algorithm, appears in multiple Router 345 Information LSAs that have different flooding scopes, the OSPF FAD 346 TLV in the Router Information LSA with the area-scoped flooding scope 347 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 348 in multiple Router Information LSAs that have the same flooding 349 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 350 numerically smallest Instance ID MUST be used and subsequent 351 instances of the OSPF FAD TLV MUST be ignored. 353 The RI LSA can be advertised at any of the defined opaque flooding 354 scopes (link, area, or Autonomous System (AS)). For the purpose of 355 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 356 Autonomous System flooding scope SHOULD not be used by default unless 357 local configuration policy on the originating router indicates domain 358 wide flooding. 360 5.3. Common Handling of Flexible Algorithm Definition TLV 362 This section describes the protocol independent handling of the FAD 363 TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in 364 this section, even though in case of ISIS it is a Sub-TLV. 366 The value of the Flex-Algorithm MUST be between 128 and 255 367 inclusive. If it is not, the FAD TLV MUST be ignored. 369 Only a subset of the routers participating in the particular Flex- 370 Algorithm need to advertise the definition of the Flex-Algorithm. 372 Every router, that is configured to participate in a particular Flex- 373 Algorithm, MUST select the Flex-Algorithm definition based on the 374 following ordered rules. This allows for the consistent Flex- 375 Algorithm definition selection in cases where different routers 376 advertise different definitions for a given Flex-Algorithm: 378 1. From the advertisements of the FAD in the area (including both 379 locally generated advertisements and received advertisements) 380 select the one(s) with the highest priority value. 382 2. If there are multiple advertisements of the FAD with the same 383 highest priority, select the one that is originated from the 384 router with the highest System-ID in case of ISIS or Router ID in 385 case of OSPFv2 and OSPFv3. For ISIS the System-ID is described in 386 [ISO10589]. For OSPFv2 and OSPFv3 standard Router ID is described 387 in [RFC2328] and [RFC5340] respectively. 389 A router that is not configured to participate in a particular Flex- 390 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 391 Algorithm. 393 A router that is not participating in a particular Flex-Algorithm is 394 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 395 MUST consider FAD advertisement regardless of the Flex-Algorithm 396 participation of the FAD originator. 398 Any change in the Flex-Algorithm definition may result in temporary 399 disruption of traffic that is forwarded based on such Flex-Algorithm 400 paths. The impact is similar to any other event that requires 401 network wide convergence. 403 If a node is configured to participate in a particular Flexible- 404 Algorithm, but the selected Flex-Algorithm definition includes 405 calculation-type, metric-type, constraint, flag or Sub-TLV that is 406 not supported by the node, it MUST stop participating in such 407 Flexible-Algorithm. That implies that it MUST NOT announce 408 participation for such Flexible-Algorithm as specified in Section 10 409 and it MUST remove any forwarding state associated with it. 411 Flex-Algorithm definition is topology independent. It applies to all 412 topologies that a router participates in. 414 6. Sub-TLVs of ISIS FAD Sub-TLV 416 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV 418 The Flexible-Algorithm definition can specify 'colors' that are used 419 by the operator to exclude links during the Flex-Algorithm path 420 computation. 422 ISIS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 423 advertise the exclude rule that is used during the Flex-Algorithm 424 path calculation as specified in Section 12. 426 Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a 427 Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 429 0 1 2 3 430 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 1 431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 432 | Type | Length | 433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 434 | Extended Admin Group | 435 +- -+ 436 | ... | 437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 438 where: 440 Type: 1 442 Length: variable, dependent on the size of the Extended Admin 443 Group. MUST be a multiple of 4 octets. 445 Extended Administrative Group: Extended Administrative Group as 446 defined in [RFC7308]. 448 ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- 449 TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 450 ignored by the receiver. 452 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV 454 The Flexible-Algorithm definition can specify 'colors' that are used 455 by the operator to include links during the Flex-Algorithm path 456 computation. 458 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used to 459 advertise include-any rule that is used during the Flex-Algorithm 460 path calculation as specified in Section 12. 462 The format of the ISIS Flexible Algorithm Include-Any Admin Group 463 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 464 Section 6.1. 466 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. 468 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 469 appear more then once in an ISIS FAD Sub-TLV. If it appears more 470 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 472 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV 474 The Flexible-Algorithm definition can specify 'colors' that are used 475 by the operator to include link during the Flex-Algorithm path 476 computation. 478 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used to 479 advertise include-all rule that is used during the Flex-Algorithm 480 path calculation as specified in Section 12. 482 The format of the ISIS Flexible Algorithm Include-All Admin Group 483 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 484 Section 6.1. 486 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 3. 488 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 489 appear more then once in an ISIS FAD Sub-TLV. If it appears more 490 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 492 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV 494 ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a 495 Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 497 0 1 2 3 498 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 1 499 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 500 | Type | Length | 501 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 502 | Flags | 503 +- -+ 504 | ... | 505 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 506 where: 508 Type: 4 510 Length: variable, non-zero number of octets of the Flags field 512 Flags: 514 0 1 2 3 4 5 6 7... 515 +-+-+-+-+-+-+-+-+... 516 |M| | | ... 517 +-+-+-+-+-+-+-+-+... 519 M-flag: when set, Flex-Algorithm specific prefix metric MUST be 520 used, if advertised with the prefix. This flag is not 521 applicable to prefixes advertised as SRv6 locators. 523 Bits are defined/sent starting with Bit 0 defined above. Additional 524 bit definitions that may be defined in the future SHOULD be assigned 525 in ascending bit order so as to minimize the number of bits that will 526 need to be transmitted. 528 Undefined bits MUST be transmitted as 0. 530 Bits that are NOT transmitted MUST be treated as if they are set to 0 531 on receipt. 533 ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- 534 TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 535 ignored by the receiver. 537 If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV, 538 all the bits are assumed to be set to 0. 540 7. Sub-TLVs of OSPF FAD TLV 542 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 544 Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a 545 Sub-TLV of the OSPF FAD TLV. It's usage is described in Section 6.1. 546 It has the following format: 548 0 1 2 3 549 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 1 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 | Type | Length | 552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 | Extended Admin Group | 554 +- -+ 555 | ... | 556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 557 where: 559 Type: 1 561 Length: variable, dependent on the size of the Extended Admin 562 Group. MUST be a multiple of 4 octets. 564 Extended Administrative Group: Extended Administrative Group as 565 defined in [RFC7308]. 567 OSPF FAEAG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. 568 If it appears more then once, the OSPF FAD TLV MUST be ignored by the 569 receiver. 571 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 573 The usage of this Sub-TLVs is described in Section 6.2. 575 The format of the OSPF Flexible Algorithm Include-Any Admin Group 576 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 577 Section 7.1. 579 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. 581 OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 582 appear more then once in an OPSF FAD TLV. If it appears more then 583 once, the OSPF FAD TLV MUST be ignored by the receiver. 585 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 587 The usage of this Sub-TLVs is described in Section 6.3. 589 The format of the OSPF Flexible Algorithm Include-Any Admin Group 590 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 591 Section 7.1. 593 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 3. 595 OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 596 appear more then once in an OPSF FAD TLV. If it appears more then 597 once, the OSPF FAD TLV MUST be ignored by the receiver. 599 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 601 OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a 602 Sub-TLV of the OSPF FAD TLV. It has the following format: 604 0 1 2 3 605 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 1 606 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 607 | Type | Length | 608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 609 | Flags | 610 +- -+ 611 | ... | 612 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 613 where: 615 Type: 4 617 Length: variable, dependent on the size of the Flags field. MUST 618 be a multiple of 4 octets. 620 Flags: 622 0 1 2 3 4 5 6 7... 623 +-+-+-+-+-+-+-+-+... 624 |M| | | ... 625 +-+-+-+-+-+-+-+-+... 627 M-flag: when set, Flex-Algorithm specific prefix metric MUST be 628 used, if advertised with the prefix. This flag is not 629 applicable to prefixes advertised as SRv6 locators. 631 Bits are defined/sent starting with Bit 0 defined above. Additional 632 bit definitions that may be defined in the future SHOULD be assigned 633 in ascending bit order so as to minimize the number of bits that will 634 need to be transmitted. 636 Undefined bits MUST be transmitted as 0. 638 Bits that are NOT transmitted MUST be treated as if they are set to 0 639 on receipt. 641 OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. 642 If it appears more then once, the OSPF FAD TLV MUST be ignored by the 643 receiver. 645 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 646 the bits are assumed to be set to 0. 648 8. ISIS Flex-Algorithm Prefix Metric Sub-TLV 650 ISIS Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the 651 advertisement of a Flex-Algorithm specific prefix metric associated 652 with a given prefix advertisement. 654 ISIS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 and has 655 the following format: 657 0 1 2 3 658 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 1 659 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 660 | Type | Length |Flex-Algorithm | 661 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 662 | Metric | 663 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 664 where: 666 Type: 6 668 Length: 5 octets 670 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 672 Metric: 4 octets of metric information 674 ISIS FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it 675 appears more then once with the same Flex-Algorithm value, the first 676 appearance MUST be used and any subsequent ones MUST be ignored. 678 If a prefix is advertised with a Flex-Algorithm prefix metric larger 679 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 680 considered during the Flexible-Algorithm computation. 682 The usage of the Flex-Algorithm prefix metric is described in 683 Section 12. 685 ISIS FAPM Sub-TLV MUST NOT be advertised as sub-TLV of the ISIS SRv6 686 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. ISIS SRv6 Locator 687 TLV includes the Algorithm and Metric fields which MUST be used 688 instead. If FAPM Sub-TLV is present as sub-TLV of the ISIS SRv6 689 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be ignored. 691 9. OSPF Flex-Algorithm Prefix Metric Sub-TLV 693 OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the 694 advertisement of a Flex-Algorithm specific prefix metric associated 695 with a given prefix advertisement. 697 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLVis a Sub-TLV of 698 the: 700 - OSPFv2 Extended Prefix TLV [RFC7684] 702 - Following OSPFv3 TLVs as defined in [RFC8362]: 704 Intra-Area Prefix TLV 705 Inter-Area Prefix TLV 707 External Prefix TLV 709 OSPF FAPM Sub-TLV has the following format: 711 0 1 2 3 712 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 1 713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 714 | Type | Length | 715 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 716 |Flex-Algorithm | Reserved | 717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 718 | Metric | 719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 721 where: 723 Type: 3 for OSPFv2, 26 for OSPFv3 725 Length: 8 octets 727 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 729 Reserved: Must be set to 0, ignored at reception. 731 Metric: 4 octets of metric information 733 OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it 734 appears more then once with the same Flex-Algorithm value, the first 735 appearance MUST be used and any subsequent ones MUST be ignored. 737 The usage of the Flex-Algorithm prefix metric is described in 738 Section 12. 740 10. Advertisement of Node Participation in a Flex-Algorithm 742 When a router is configured to support a particular Flex-Algorithm, 743 we say it is participating in that Flex-Algorithm. 745 Paths computed for a specific Flex-Algorithm MAY be used by various 746 applications, each potentially using its own specific data plane for 747 forwarding the data over such paths. To guarantee the presence of 748 the application specific forwarding state associated with a 749 particular Flex-Algorithm, a router MUST advertise its participation 750 for a particular Flex-Algorithm for each application specifically. 752 10.1. Advertisement of Node Participation for Segment Routing 754 [I-D.ietf-isis-segment-routing-extensions], 755 [I-D.ietf-ospf-segment-routing-extensions] and 756 [I-D.ietf-ospf-ospfv3-segment-routing-extensions] (IGP Segment 757 Routing extensions) describe how SR-Algorithm is used to define how 758 the best path is computed by the IGP. 760 Routers advertise the support for the SR-Algorithm as a node 761 capability as described in the above mentioned IGP Segment Routing 762 extensions. To advertise participation for a particular Flex- 763 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 764 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 765 (OSPF) or sub-TLV (ISIS). 767 Segment Routing Flex-Algorithm participation advertisement is 768 topology independent. When a router advertises participation in an 769 SR-Algorithm, the participation applies to all topologies in which 770 the advertising node participates. 772 10.2. Advertisement of Node Participation for Other Applications 774 This section describes considerations related to how other 775 applications can advertise its participation in a specific Flex- 776 Algorithm. 778 Application specific Flex-Algorithm participation advertisements MAY 779 be topology specific or MAY be topology independent, depending on the 780 application itself. 782 Application specific advertisement for Flex-Algorithm participation 783 MUST be defined for each application and is outside of the scope of 784 this document. 786 11. Advertisement of Link Attributes for Flex-Algorithm 788 Various link attributes may be used during the Flex-Algorithm path 789 calculation. For example, include or exclude rules based on link 790 affinities can be part of the Flex-Algorithm definition as defined in 791 Section 6 and Section 7. 793 Link attribute advertisements that are to be used during Flex- 794 Algorithm calculation MUST use the Application Specific Link 795 Attribute (ASLA) advertisements defined in [I-D.ietf-isis-te-app] or 796 [I-D.ietf-ospf-te-link-attr-reuse]. 798 A new Application Identifier Bit is defined to indicate that the ASLA 799 advertisement is associated with the Flex-Algorithm application. 801 This bit is set in the Standard Application Bit Mask (SABM) defined 802 in [I-D.ietf-isis-te-app] or [I-D.ietf-ospf-te-link-attr-reuse]: 804 Bit-3: Flexible Algorithm (X-bit) 806 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 807 Application MAY use either the Administrative Group or Extended 808 Administrative Group encodings. If the Administrative Group encoding 809 is used then the first 32 bits of the corresponding FAD sub-TLVs are 810 mapped to the link attribute advertisements as specified in RFC 7308. 812 12. Calculation of Flexible Algorithm Paths 814 A router MUST be configured to participate in a given Flex-Algorithm 815 K and MUST use the FAD selected based on the rules defined in 816 Section 5.3 before it can compute any path for that Flex-Algorithm. 818 As described in Section 10, participation for any particular Flex- 819 Algorithm MUST be advertised on a per application basis. Calculation 820 of the paths for any particular Flex-Algorithm MUST be application 821 specific. 823 The way applications handle nodes that do not participate in 824 Flexible-Algorithm is application specific. If the application only 825 wants to consider participating nodes during the Flex-Algorithm 826 calculation, then when computing paths for a given Flex-Algorithm, 827 all nodes that do not advertise participation for that Flex-Algorithm 828 in the application specific advertisements MUST be pruned from the 829 topology. Segment Routing, including both SR MPLS and SRv6, are 830 applications that MUST use such pruning when computing Flex-Algorithm 831 paths. 833 When computing the path for a given Flex-Algorithm, the metric-type 834 that is part of the Flex-Algorithm definition (Section 5) MUST be 835 used. 837 When computing the path for a given Flex-Algorithm, the calculation- 838 type that is part of the Flex-Algorithm definition (Section 5) MUST 839 be used. 841 Various link include or exclude rules can be part of the Flex- 842 Algorithm definition. To refer to a particular bit within an AG or 843 EAG we uses term 'color'. 845 Rules, in the order as specified below, MUST be used to prune links 846 from the topology during the Flex-Algorithm computation. 848 For all links in the topology: 850 1. Check if any exclude rule is part of the Flex-Algorithm 851 definition. If such exclude rule exists, check if any color that 852 is part of the exclude rule is also set on the link. If such a 853 color is set, the link MUST be pruned from the computation. 855 2. Check if any include-any rule is part of the Flex-Algorithm 856 definition. If such include-any rule exists, check if any color 857 that is part of the include-any rule is also set on the link. If 858 no such color is set, the link MUST be pruned from the 859 computation. 861 3. Check if any include-all rule is part of the Flex-Algorithm 862 definition. If such include-all rule exists, check if all colors 863 that are part of the include-all rule are also set on the link. 864 If all such colors are not set on the link, the link MUST be 865 pruned from the computation. 867 4. If the Flex-Algorithm definition uses other than IGP metric 868 (Section 5), and such metric is not advertised for the particular 869 link in a topology for which the computation is done, such link 870 MUST be pruned from the computation. A metric of value 0 MUST NOT 871 be assumed in such case. 873 12.1. Multi-area and Multi-domain Considerations 875 Any IGP Shortest Path Tree calculation is limited to a single area. 876 This applies to Flex-Algorithm calculations as well. Given that the 877 computing router does not have the visibility of the topology of next 878 areas or domain, the Flex-Algorithm specific path to an inter-area or 879 inter-domain prefix will be computed for the local area only. The 880 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 881 will be selected based on the best path for the given Flex-Algorithm 882 in the local area and such egress ABR or ASBR router will be 883 responsible to compute the best Flex-Algorithm specific path over the 884 next area or domain. This may produce an end-to-end path, which is 885 sub-optimal based on Flex-Algorithm constraints. In cases where the 886 ABR or ASBR has no reachability to a prefix for a given Flex- 887 Algorithm in a next area or domain, the traffic may get dropped by 888 the ABR/ASBR. 890 To allow the optimal end-to-end path for a inter-area or inter-domain 891 prefixes for any Flex-Algorithm to be computed, the FAPM has been 892 defined in Section 8 and Section 9. 894 If the FAD selected based on the rules defined in Section 5.3 895 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 896 Section 9) when advertising the prefix between areas or domains. 897 Such metric will be equal to the metric to reach the prefix for a 898 given Flex-Algorithm in a source area or domain. This is similar in 899 nature to how the metric is set when prefixes are advertised between 900 areas or domains for default algorithm. 902 If the FAD selected based on the rules defined in Section 5.3 903 includes the M-flag, FAPM MUST be used during calculation of prefix 904 reachability for the inter-area and external prefixes. If the FAPM 905 for the Flex-Algorithm is not advertised with the inter-area or 906 external prefix reachability advertisement, the prefix MUST be 907 considered as unreachable for that Flex-Algorithm. 909 Flex-Algorithm prefix metrics MUST NOT be used during the Flex- 910 Algorithm computation unless the FAD selected based on the rules 911 defined in Section 5.3 includes the M-Flag, as described in 912 (Section 6.4 or Section 7.4). 914 If the FAD selected based on the rules defined in Section 5.3 does 915 not includes the M-flag, it is NOT RECOMMENDED to use the Flex- 916 Algoritm for inter-area or inter-domain prefix reachability. The 917 reason is that without the explicit Flex-Algorithm Prefix Metric 918 advertisement it is not possible to conclude whether the ABR or ASBR 919 has reachability to the inter-area or inter-domain prefix for a given 920 Flex-Algorithm in a next area or domain. Sending the Flex-Algoritm 921 traffic for such prefix towards the ABR or ASBR may result in traffic 922 looping or black-holing. 924 FAPM MUST NOT be advertised with ISIS L1 or L2 intra-area, OSPFv2 925 intra-area or OSPFv3 intra area routes. If the FAPM is advertised 926 for these route-types, it MUST be ignored during prefix reachability 927 calculation. 929 M-flag in FAD is not applicable to prefixes advertised as SRv6 930 locators. ISIS SRv6 Locator TLV includes the Algorithm and Metric 931 fields [I-D.ietf-lsr-isis-srv6-extensions]. When the ISIS SRv6 932 Locator is advertised between areas or domains, the metric field in 933 the Locator TLV MUST be used irrespective of the M flag in the FAD 934 advertisement. 936 13. Flex-Algorithm and Forwarding Plane 938 This section describes how Flex-Algorithm paths are used in 939 forwarding. 941 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm 943 This section describes how Flex-Algorithm paths are used with SR MPLS 944 forwarding. 946 Prefix SID advertisements include an SR-Algorithm value and as such 947 are associated with the specified SR-Algorithm. Prefix-SIDs are also 948 associated with a specific topology which is inherited from the 949 associated prefix reachability advertisement. When the algorithm 950 value advertised is a Flex-Algorithm value, the Prefix SID is 951 associated with paths calculated using that Flex-Algorithm in the 952 associated topology. 954 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 955 using the MPLS label that corresponds to the Prefix-SID that was 956 advertised for that Flex-algorithm. If the Prefix SID for a given 957 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 958 be installed in the MPLS forwarding plane. 960 Traffic that is supposed to be routed via Flex-Algorithm specific 961 paths, MUST be dropped where there are no such paths available. 963 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 964 computed using the same constraints as the calculation of the primary 965 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 966 advertised specifically for the given algorithm. LFA paths MUST NOT 967 use an Adjacency-SID that belongs to a link that has been pruned from 968 the Flex-Algorithm computation. 970 If LFA protection is being used to protect a given Flex-Algorithm 971 paths, all routers in the area participating in the given Flex- 972 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 973 SID. These Node-SIDs are used to enforce traffic over the LFA 974 computed backup path. 976 13.2. SRv6 Forwarding for Flex-Algorithm 978 This section describes how Flex-Algorithm paths are used with SRv6 979 forwarding. 981 In SRv6 a node is provisioned with topology/algorithm specific 982 locators for each of the topology/algorithm pairs supported by that 983 node. Each locator is a covering prefix for all SIDs provisioned on 984 that node which have the matching topology/algorithm. 986 SRv6 locator advertisement in IGPs 987 ([I-D.ietf-lsr-isis-srv6-extensions] 988 [I-D.li-ospf-ospfv3-srv6-extensions]) includes the MTID value that 989 associates the locator with a specific topology. SRv6 locator 990 advertisements also includes an Algorithm value that explicitly 991 associates the locator with a specific algorithm. When the algorithm 992 value advertised with a locator represents a Flex-Algorithm, the 993 paths to the locator prefix MUST be calculated using the specified 994 Flex-Algorithm in the associated topology. 996 Forwarding entries for the locator prefixes advertised in IGPs MUST 997 be installed in the forwarding plane of the receiving SRv6 capable 998 routers when the associated topology/algorithm is participating in 999 them. Forwarding entries for locators associated with Flex- 1000 Algorithms in which the node is not participating MUST NOT be 1001 installed in the forwarding. 1003 When the locator is associated with the Flex-Algorithm, LFA paths to 1004 the locator prefix MUST be calculated using such Flex-Algorithm in 1005 the associated topology, to guarantee that they follow the same 1006 constraints as the calculation of the primary paths. LFA paths MUST 1007 only use SRv6 SIDs advertised specifically for the given Flex- 1008 Algorithm. 1010 If LFA protection is being used to protect locators associated with a 1011 given Flex-Algorithm, all routers in the area participating in the 1012 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1013 specific locator and END SID per node and one END.X SID for every 1014 link that has not been pruned from such Flex-Algorithm computation. 1015 These locators and SIDs are used to enforce traffic over the LFA 1016 computed backup path. 1018 13.3. Other Applications' Forwarding for Flex-Algorithm 1020 Any application that wants to use Flex-Algorithm specific forwarding 1021 needs to install some form of Flex-Algorithm specific forwarding 1022 entries. 1024 Application specific forwarding for Flex-Algorithm MUST be defined 1025 for each application and is outside of the scope of this document. 1027 14. Backward Compatibility 1029 This extension brings no new backward compatibility issues. 1031 15. Security Considerations 1033 This draft adds two new ways to disrupt the IGP networks: 1035 An attacker can hijack a particular Flex-Algorithm by advertising 1036 a FAD with a priority of 255 (or any priority higher than that of 1037 the legitimate nodes). 1039 An attacker could make it look like a router supports a particular 1040 Flex-Algorithm when it actually doesn't, or vice versa. 1042 Both of these attacks can be addressed by the existing security 1043 extensions as described in [RFC5304] and [RFC5310] for ISIS, in 1044 [RFC2328] and [RFC7474] for OSPFv2 and in [RFC5340] and [RFC4552] for 1045 OSPFv3. 1047 16. IANA Considerations 1049 16.1. IGP IANA Considerations 1051 16.1.1. IGP Algorithm Types Registry 1053 This document makes the following registrations in the "IGP Algorithm 1054 Types" registry: 1056 Type: 128-255. 1058 Description: Flexible Algorithms. 1060 Reference: This document (Section 4). 1062 16.1.2. Flexible Algorithm Definition Metric-Type Registry 1064 IANA is requested to set up a registry called "Flexible Algorithm 1065 Definition Metric-Type Registry" under a "Interior Gateway Protocol 1066 (IGP) Parameters" IANA registries. The registration policy for this 1067 registry is "Standards Action" ([RFC8126] and [RFC7120]). 1069 Values in this registry come from the range 0-255. 1071 This document registers following values in the "Flexible Algorithm 1072 Definition Metric-Type Registry": 1074 Type: 0 1076 Description: IGP metric 1078 Reference: This document (Section 5.1) 1080 Type: 1 1082 Description: Min Unidirectional Link Delay [RFC7810] 1084 Reference: This document (Section 5.1) 1086 Type: 2 1088 Description: TE Default Metric [RFC5305] 1089 Reference: This document (Section 5.1) 1091 16.2. Flex-Algorithm Definition Flags Registry 1093 IANA is requested to set up a registry called "ISIS Flex-Algorithm 1094 Definition Flags Registry" under a "Interior Gateway Protocol (IGP) 1095 Parameters" IANA registries. The registration policy for this 1096 registry is "Standards Action" ([RFC8126] and [RFC7120]). 1098 This document defines the following single bit in Flex-Algorithm 1099 Definition Flags registry: 1101 Bit # Name 1102 ----- ------------------------------ 1103 0 Prefix Metric Flag (M-flag) 1105 Reference: This document (Section 6.4, Section 7.4). 1107 16.3. ISIS IANA Considerations 1109 16.3.1. Sub TLVs for Type 242 1111 This document makes the following registrations in the "sub-TLVs for 1112 TLV 242" registry. 1114 Type: 26. 1116 Description: Flexible Algorithm Definition. 1118 Reference: This document (Section 5.1). 1120 16.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1122 This document makes the following registrations in the "Sub-TLVs for 1123 for TLVs 135, 235, 236, and 237" registry. 1125 Type: 6 1127 Description: Flex-Algorithm Prefix Metric. 1129 Reference: This document (Section 8). 1131 16.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1133 This document creates the following Sub-Sub-TLV Registry: 1135 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1136 Registration Procedure: Expert review 1138 Reference: This document (Section 5.1) 1140 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1141 for Flexible Algorithm Definition Sub-TLV" registry: 1143 Type: 1 1145 Description: Flexible Algorithm Exclude Admin Group 1147 Reference: This document (Section 6.1). 1149 Type: 2 1151 Description: Flexible Algorithm Include-Any Admin Group 1153 Reference: This document (Section 6.2). 1155 Type: 3 1157 Description: Flexible Algorithm Include-All Admin Group 1159 Reference: This document (Section 6.3). 1161 Type: 4 1163 Description: Flexible Algorithm Definition Flags 1165 Reference: This document (Section 6.4). 1167 16.4. OSPF IANA Considerations 1169 16.4.1. OSPF Router Information (RI) TLVs Registry 1171 This specification updates the OSPF Router Information (RI) TLVs 1172 Registry. 1174 Type: 16 1176 Description: Flexible Algorithm Definition TLV. 1178 Reference: This document (Section 5.2). 1180 16.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1182 This document makes the following registrations in the "OSPFv2 1183 Extended Prefix TLV Sub-TLVs" registry. 1185 Type: 3 1187 Description: Flex-Algorithm Prefix Metric. 1189 Reference: This document (Section 9). 1191 16.4.3. OSPFv3 Extended-LSA Sub-TLVs 1193 This document makes the following registrations in the "OSPFv3 1194 Extended-LSA Sub-TLVs" registry. 1196 Type: 26 1198 Description: Flex-Algorithm Prefix Metric. 1200 Reference: This document (Section 9). 1202 16.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1204 This document creates the following registry: 1206 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1208 Registration Procedure: Expert review 1210 Reference: This document (Section 5.2) 1212 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1213 define sub-TLVs at any level of nesting for Flexible Algorithm TLV 1214 and should be added to the "Open Shortest Path First (OSPF) 1215 Parameters" registries group. New values can be allocated via IETF 1216 Review or IESG Approval. 1218 This document registers following Sub-TLVs in the "TLVs for Flexible 1219 Algorithm Definition TLV" registry: 1221 Type: 1 1223 Description: Flexible Algorithm Exclude Admin Group 1225 Reference: This document (Section 7.1). 1227 Type: 2 1228 Description: Flexible Algorithm Include-Any Admin Group 1230 Reference: This document (Section 7.2). 1232 Type: 3 1234 Description: Flexible Algorithm Include-All Admin Group 1236 Reference: This document (Section 7.3). 1238 Type: 4 1240 Description: Flexible Algorithm Definition Flags 1242 Reference: This document (Section 7.4). 1244 Types in the range 32768-33023 are for experimental use; these will 1245 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1247 Types in the range 33024-65535 are not to be assigned at this time. 1248 Before any assignments can be made in the 33024-65535 range, there 1249 MUST be an IETF specification that specifies IANA Considerations that 1250 covers the range being assigned. 1252 16.4.5. Link Attribute Applications Registry 1254 This document registers following bit in the Link Attribute 1255 Applications registry: 1257 Bit-3 1259 Description: Flexible Algorithm (X-bit) 1261 Reference: This document (Section 11). 1263 17. Acknowledgements 1265 This draft, among other things, is also addressing the problem that 1266 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1267 All authors of that draft agreed to join this draft. 1269 Thanks to Eric Rosen, Tony Przygienda for their detailed review and 1270 excellent comments. 1272 Thanks to Cengiz Halit for his review and feedback during initial 1273 phase of the solution definition. 1275 Thanks to Kenji Kumaki for his comments. 1277 18. References 1279 18.1. Normative References 1281 [BCP14] , . 1283 [I-D.ietf-isis-segment-routing-extensions] 1284 Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., 1285 Gredler, H., and B. Decraene, "IS-IS Extensions for 1286 Segment Routing", draft-ietf-isis-segment-routing- 1287 extensions-25 (work in progress), May 2019. 1289 [I-D.ietf-isis-te-app] 1290 Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1291 J. Drake, "IS-IS TE Attributes per application", draft- 1292 ietf-isis-te-app-09 (work in progress), October 2019. 1294 [I-D.ietf-lsr-isis-srv6-extensions] 1295 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1296 Z. Hu, "IS-IS Extension to Support Segment Routing over 1297 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-03 1298 (work in progress), October 2019. 1300 [I-D.ietf-ospf-ospfv3-segment-routing-extensions] 1301 Psenak, P. and S. Previdi, "OSPFv3 Extensions for Segment 1302 Routing", draft-ietf-ospf-ospfv3-segment-routing- 1303 extensions-23 (work in progress), January 2019. 1305 [I-D.ietf-ospf-segment-routing-extensions] 1306 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 1307 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1308 Extensions for Segment Routing", draft-ietf-ospf-segment- 1309 routing-extensions-27 (work in progress), December 2018. 1311 [I-D.ietf-ospf-te-link-attr-reuse] 1312 Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J., 1313 and J. Drake, "OSPF Link Traffic Engineering Attribute 1314 Reuse", draft-ietf-ospf-te-link-attr-reuse-10 (work in 1315 progress), October 2019. 1317 [I-D.li-ospf-ospfv3-srv6-extensions] 1318 Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, 1319 "OSPFv3 Extensions for SRv6", draft-li-ospf- 1320 ospfv3-srv6-extensions-05 (work in progress), August 2019. 1322 [ISO10589] 1323 International Organization for Standardization, 1324 "Intermediate system to Intermediate system intra-domain 1325 routeing information exchange protocol for use in 1326 conjunction with the protocol for providing the 1327 connectionless-mode Network Service (ISO 8473)", ISO/ 1328 IEC 10589:2002, Second Edition, Nov 2002. 1330 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1331 Requirement Levels", BCP 14, RFC 2119, 1332 DOI 10.17487/RFC2119, March 1997, 1333 . 1335 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1336 Traffic Engineering (MPLS-TE)", RFC 7308, 1337 DOI 10.17487/RFC7308, July 2014, 1338 . 1340 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1341 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1342 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1343 2015, . 1345 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1346 S. Shaffer, "Extensions to OSPF for Advertising Optional 1347 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1348 February 2016, . 1350 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1351 for Advertising Router Information", RFC 7981, 1352 DOI 10.17487/RFC7981, October 2016, 1353 . 1355 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1356 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1357 May 2017, . 1359 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1360 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1361 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1362 2018, . 1364 18.2. Informative References 1366 [I-D.gulkohegde-routing-planes-using-sr] 1367 Hegde, S. and a. arkadiy.gulko@thomsonreuters.com, 1368 "Separating Routing Planes using Segment Routing", draft- 1369 gulkohegde-routing-planes-using-sr-00 (work in progress), 1370 March 2017. 1372 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 1373 DOI 10.17487/RFC2328, April 1998, 1374 . 1376 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 1377 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 1378 RFC 3906, DOI 10.17487/RFC3906, October 2004, 1379 . 1381 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 1382 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 1383 . 1385 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1386 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1387 2008, . 1389 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 1390 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 1391 2008, . 1393 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 1394 and M. Fanto, "IS-IS Generic Cryptographic 1395 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 1396 2009, . 1398 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 1399 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 1400 . 1402 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 1403 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 1404 2014, . 1406 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 1407 "Security Extension for OSPFv2 When Using Manual Key 1408 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 1409 . 1411 [RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and 1412 Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", 1413 RFC 7810, DOI 10.17487/RFC7810, May 2016, 1414 . 1416 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1417 Writing an IANA Considerations Section in RFCs", BCP 26, 1418 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1419 . 1421 Authors' Addresses 1423 Peter Psenak (editor) 1424 Cisco Systems 1425 Apollo Business Center 1426 Mlynske nivy 43 1427 Bratislava, 82109 1428 Slovakia 1430 Email: ppsenak@cisco.com 1432 Shraddha Hegde 1433 Juniper Networks, Inc. 1434 Embassy Business Park 1435 Bangalore, KA, 560093 1436 India 1438 Email: shraddha@juniper.net 1440 Clarence Filsfils 1441 Cisco Systems, Inc. 1442 Brussels 1443 Belgium 1445 Email: cfilsfil@cisco.com 1447 Ketan Talaulikar 1448 Cisco Systems, Inc. 1449 S.No. 154/6, Phase I, Hinjawadi 1450 PUNE, MAHARASHTRA 411 057 1451 India 1453 Email: ketant@cisco.com 1454 Arkadiy Gulko 1455 Thomson Reuters 1457 Email: arkadiy.gulko@thomsonreuters.com