idnits 2.17.1 draft-ietf-lsr-flex-algo-07.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: ISIS FAESRLG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: 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 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-All Admin Group Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: OSPF FAESRLG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. -- The document date (April 1, 2020) is 1483 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-12 == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-07 == Outdated reference: A later version (-15) exists of draft-ietf-lsr-ospfv3-srv6-extensions-00 == Outdated reference: A later version (-16) exists of draft-ietf-ospf-te-link-attr-reuse-10 -- 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 (~~), 16 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: October 3, 2020 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Thomson Reuters 11 April 1, 2020 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-07.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 October 3, 2020. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 64 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 4. Flexible Algorithm . . . . . . . . . . . . . . . . . . . . . 5 66 5. Flexible Algorithm Definition Advertisement . . . . . . . . . 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 . . 9 70 6. Sub-TLVs of ISIS FAD Sub-TLV . . . . . . . . . . . . . . . . 10 71 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV . . . 10 72 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV . 11 73 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV . 11 74 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV . . . . 11 75 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 12 76 7. Sub-TLVs of OSPF FAD TLV . . . . . . . . . . . . . . . . . . 13 77 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV . . . 13 78 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV . 14 79 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV . 14 80 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV . . . . 14 81 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . 16 82 8. ISIS Flex-Algorithm Prefix Metric Sub-TLV . . . . . . . . . . 16 83 9. OSPF Flex-Algorithm Prefix Metric Sub-TLV . . . . . . . . . . 17 84 10. Advertisement of Node Participation in a Flex-Algorithm . . . 18 85 10.1. Advertisement of Node Participation for Segment Routing 18 86 10.2. Advertisement of Node Participation for Other 87 Applications . . . . . . . . . . . . . . . . . . . . . . 19 88 11. Advertisement of Link Attributes for Flex-Algorithm . . . . . 19 89 12. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 20 90 12.1. Multi-area and Multi-domain Considerations . . . . . . . 21 91 13. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 22 92 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 22 93 13.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 23 94 13.3. Other Applications' Forwarding for Flex-Algorithm . . . 24 95 14. Backward Compatibility . . . . . . . . . . . . . . . . . . . 24 96 15. Security Considerations . . . . . . . . . . . . . . . . . . . 24 97 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 98 16.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 25 99 16.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 25 100 16.1.2. Flexible Algorithm Definition Metric-Type Registry . 25 101 16.2. Flex-Algorithm Definition Flags Registry . . . . . . . . 26 102 16.3. ISIS IANA Considerations . . . . . . . . . . . . . . . . 26 103 16.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 26 104 16.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 26 105 16.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 106 TLV . . . . . . . . . . . . . . . . . . . . . . . . 26 107 16.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 27 108 16.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 27 109 16.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 28 110 16.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 28 111 16.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV 112 Registry . . . . . . . . . . . . . . . . . . . . . . 28 113 16.4.5. Link Attribute Applications Registry . . . . . . . . 29 114 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 115 18. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 116 18.1. Normative References . . . . . . . . . . . . . . . . . . 30 117 18.2. Informative References . . . . . . . . . . . . . . . . . 32 118 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 120 1. Introduction 122 An IGP computed path based on the shortest IGP metric must often be 123 replaced by a traffic engineered path due to the traffic requirements 124 which are not reflected by the IGP metric. Some networks engineer 125 the IGP metric assignments in a way that the IGP Metric reflects the 126 link bandwidth or delay. If, for example, the IGP metric is 127 reflecting the bandwidth on the link and the application traffic is 128 delay sensitive, the best IGP path may not reflect the best path from 129 such an application's perspective. 131 To overcome this limitation, various sorts of traffic engineering 132 have been deployed, including RSVP-TE and SR-TE, in which case the TE 133 component is responsible for computing paths based on additional 134 metrics and/or constraints. Such paths need to be installed in the 135 forwarding tables in addition to, or as a replacement for, the 136 original paths computed by IGPs. Tunnels are often used to represent 137 the engineered paths and mechanisms like one described in [RFC3906] 138 are used to replace the native IGP paths with such tunnel paths. 140 This document specifies a set of extensions to ISIS, OSPFv2 and 141 OSPFv3 that enable a router to send TLVs that identify (a) 142 calculation-type, (b) specify a metric-type, and (c )describe a set 143 of constraints on the topology, that are to be used to compute the 144 best paths along the constrained topology. A given combination of 145 calculation-type, metric-type, and constraints is known as a 146 "Flexible Algorithm Definition". A router that sends such a set of 147 TLVs also assigns a Flex-Algorithm value, to the specified 148 combination of calculation-type, metric-type, and constraints. 150 This document also specifies a way for a router to use IGPs to 151 associate one or more SR Prefix-SIDs or SRv6 locators with a 152 particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then 153 represents a path that is computed according to the identified Flex- 154 Algorithm. 156 2. Requirements notation 158 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 159 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 160 "OPTIONAL" in this document are to be interpreted as described in 161 [BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all 162 capitals, as shown here. 164 3. Terminology 166 This section defines terms that are often used in this document. 168 Flexible Algorithm Definition - the set consisting of (a) 169 calculation-type, (b) metric-type, and (c) a set of constraints,. 171 Flexible Algorithm - a numeric identifier in the range 128-255 that 172 is associated via provisioning with the Flexible-Algorithm 173 Definition. 175 Local Flexible Algorithm Definition - Flexible Algorithm Definition 176 defined locally on the node. 178 Remote Flexible Algorithm Definition - Flexible Algorithm Definition 179 received from other nodes via IGP flooding. 181 Flexible Algorithm Participation - per application configuration 182 state that expresses whether the node is participating in a 183 particular Flexible Algorithm. 185 IGP Algorithm - value from the the "IGP Algorithm Types" registry 186 defined under "Interior Gateway Protocol (IGP) Parameters" IANA 187 registries. IGP Algorithms represents the triplet (Calculation Type, 188 Metric, Constraints), where the second and third elements of the 189 triple MAY not exist. 191 ABR - Area Border Router. In ISIS terminology it is also known as 192 L1/L2 router. 194 ASBR - Autonomous System Border Router. 196 4. Flexible Algorithm 198 Many possible constraints may be used to compute a path over a 199 network. Some networks are deployed as multiple planes. A simple 200 form of constraint may be to use a particular plane. A more 201 sophisticated form of constraint can include some extended metric as 202 described in [RFC7810]. Constraints which restrict paths to links 203 with specific affinities or avoid links with specific affinities are 204 also possible. Combinations of these are also possible. 206 To provide maximum flexibility, we want to provide a mechanism that 207 allows a router to (a) identify a particular calculation-type, (b) 208 metric-type, (c) describe a particular set of constraints, and (d) 209 assign a numeric identifier, referred to as Flex-Algorithm, to the 210 combination of that calculation-type, metric-type and those 211 constraints. We want the mapping between the Flex-Algorithm and it's 212 meaning to be flexible and defined by the user. As long as all 213 routers in the domain have a common understanding as to what a 214 particular Flex-Algorithm represents, the resulting routing 215 computation is consistent and traffic is not subject to any looping. 217 The set consisting of (a) calculation-type, (b) metric-type and (c) a 218 set of constraints is referred to as a Flexible-Algorithm Definition. 220 Flexible-Algorithm is a numeric identifier in the range 128-255 that 221 is associated via provisioning with the Flexible-Algorithm 222 Definition. 224 IANA "IGP Algorithm Types" registry defines the set of values for IGP 225 Algorithms. We propose to allocate the following values for Flex- 226 Algorithms from this registry: 228 128-255 - Flex-Algorithms 230 5. Flexible Algorithm Definition Advertisement 232 To guarantee the loop free forwarding for paths computed for a 233 particular Flex-Algorithm, all routers that (a) are configured to 234 participate in a particular Flex-Algorithm, and (b) are in the same 235 Flex-Algorithm definition advertisement scope MUST agree on the 236 definition of the Flex-Algorithm. 238 5.1. ISIS Flexible Algorithm Definition Sub-TLV 240 ISIS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used to 241 advertise the definition of the Flex-Algorithm. 243 ISIS FAD Sub-TLV is advertised as a Sub-TLV of the ISIS Router 244 Capability TLV-242 that is defined in [RFC7981]. 246 ISIS FAD Sub-TLV has the following format: 248 0 1 2 3 249 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 1 250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 251 | Type | Length |Flex-Algorithm | Metric-Type | 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 253 | Calc-Type | Priority | 254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 | Sub-TLVs | 256 + + 257 | ... | 259 | | 260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 262 where: 264 Type: 26 266 Length: variable, dependent on the included Sub-TLVs 268 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 270 Metric-Type: Type of metric to be used during the calculation. 271 Following values are defined: 273 0: IGP Metric 275 1: Min Unidirectional Link Delay as defined in [RFC7810]. 277 2: TE default metric as defined in [RFC5305]. 279 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 280 Types" registry defined under "Interior Gateway Protocol (IGP) 281 Parameters" IANA registries. IGP algorithms in the range of 0-127 282 have a defined triplet (Calculation Type, Metric, Constraints). 284 When used to specify the Calc-Type in the FAD Sub-TLV, only the 285 Calculation Type defined for the specified IGP Algorithm is used. 286 The Metric/Constraints MUST NOT be inherited. If the required 287 calculation type is Shortest Path First, the value 0 SHOULD appear 288 in this field. 290 Priority: Value between 0 and 255 inclusive that specifies the 291 priority of the advertisement. 293 Sub-TLVs - optional sub-TLVs. 295 The ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a 296 router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given 297 Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs 298 for a given Flexible-Algorithm from the same originator SHOULD select 299 the first advertisement in the lowest numbered LSP. 301 The ISIS FAD Sub-TLV has an area scope. The Router Capability TLV in 302 which the FAD Sub-TLV is present MUST have the S-bit clear. 304 ISIS L1/L2 router MAY be configured to re-generate the winning FAD 305 from level 2, without any modification to it, to level 1 area. The 306 re-generation of the FAD Sub-TLV from level 2 to level 1 is 307 determined by the L1/L2 router, not by the originator of the FAD 308 advertisement in the level 2. In such case, the re-generated FAD 309 Sub-TLV will be advertised in the level 1 Router Capability TLV 310 originated by the L1/L2 router. 312 L1/L2 router MUST NOT re-generate any FAD Sub-TLV from level 1 to 313 level 2. 315 5.2. OSPF Flexible Algorithm Definition TLV 317 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 318 defined in [RFC7770]. 320 OSPF FAD TLV has the following format: 322 0 1 2 3 323 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 1 324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 | Type | Length | 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | Sub-TLVs | 330 + + 331 | ... | 333 | | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 336 where: 338 Type: 16 340 Length: variable, dependent on the included Sub-TLVs 342 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 343 inclusive. 345 Metric-Type: as described in Section 5.1 347 Calc-Type: as described in Section 5.1 349 Priority: as described in Section 5.1 351 Sub-TLVs - optional sub-TLVs. 353 When multiple OSPF FAD TLVs, for the same Flexible-Algorithm, are 354 received from a given router, the receiver MUST use the first 355 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 356 TLV, for the same Flex-Algorithm, appears in multiple Router 357 Information LSAs that have different flooding scopes, the OSPF FAD 358 TLV in the Router Information LSA with the area-scoped flooding scope 359 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 360 in multiple Router Information LSAs that have the same flooding 361 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 362 numerically smallest Instance ID MUST be used and subsequent 363 instances of the OSPF FAD TLV MUST be ignored. 365 The RI LSA can be advertised at any of the defined opaque flooding 366 scopes (link, area, or Autonomous System (AS)). For the purpose of 367 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 368 Autonomous System flooding scope SHOULD not be used by default unless 369 local configuration policy on the originating router indicates domain 370 wide flooding. 372 5.3. Common Handling of Flexible Algorithm Definition TLV 374 This section describes the protocol independent handling of the FAD 375 TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in 376 this section, even though in case of ISIS it is a Sub-TLV. 378 The value of the Flex-Algorithm MUST be between 128 and 255 379 inclusive. If it is not, the FAD TLV MUST be ignored. 381 Only a subset of the routers participating in the particular Flex- 382 Algorithm need to advertise the definition of the Flex-Algorithm. 384 Every router, that is configured to participate in a particular Flex- 385 Algorithm, MUST select the Flex-Algorithm definition based on the 386 following ordered rules. This allows for the consistent Flex- 387 Algorithm definition selection in cases where different routers 388 advertise different definitions for a given Flex-Algorithm: 390 1. From the advertisements of the FAD in the area (including both 391 locally generated advertisements and received advertisements) 392 select the one(s) with the highest priority value. 394 2. If there are multiple advertisements of the FAD with the same 395 highest priority, select the one that is originated from the 396 router with the highest System-ID in case of ISIS or Router ID in 397 case of OSPFv2 and OSPFv3. For ISIS the System-ID is described in 398 [ISO10589]. For OSPFv2 and OSPFv3 standard Router ID is described 399 in [RFC2328] and [RFC5340] respectively. 401 A router that is not configured to participate in a particular Flex- 402 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 403 Algorithm. 405 A router that is not participating in a particular Flex-Algorithm is 406 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 407 MUST consider FAD advertisement regardless of the Flex-Algorithm 408 participation of the FAD originator. 410 Any change in the Flex-Algorithm definition may result in temporary 411 disruption of traffic that is forwarded based on such Flex-Algorithm 412 paths. The impact is similar to any other event that requires 413 network wide convergence. 415 If a node is configured to participate in a particular Flexible- 416 Algorithm, but the selected Flex-Algorithm definition includes 417 calculation-type, metric-type, constraint, flag or Sub-TLV that is 418 not supported by the node, it MUST stop participating in such 419 Flexible-Algorithm. That implies that it MUST NOT announce 420 participation for such Flexible-Algorithm as specified in Section 10 421 and it MUST remove any forwarding state associated with it. 423 Flex-Algorithm definition is topology independent. It applies to all 424 topologies that a router participates in. 426 6. Sub-TLVs of ISIS FAD Sub-TLV 428 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV 430 The Flexible-Algorithm definition can specify 'colors' that are used 431 by the operator to exclude links during the Flex-Algorithm path 432 computation. 434 ISIS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 435 advertise the exclude rule that is used during the Flex-Algorithm 436 path calculation as specified in Section 12. 438 Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a 439 Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 441 0 1 2 3 442 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 1 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 | Type | Length | 445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 446 | Extended Admin Group | 447 +- -+ 448 | ... | 449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 450 where: 452 Type: 1 454 Length: variable, dependent on the size of the Extended Admin 455 Group. MUST be a multiple of 4 octets. 457 Extended Administrative Group: Extended Administrative Group as 458 defined in [RFC7308]. 460 ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- 461 TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 462 ignored by the receiver. 464 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV 466 The Flexible-Algorithm definition can specify 'colors' that are used 467 by the operator to include links during the Flex-Algorithm path 468 computation. 470 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used to 471 advertise include-any rule that is used during the Flex-Algorithm 472 path calculation as specified in Section 12. 474 The format of the ISIS Flexible Algorithm Include-Any Admin Group 475 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 476 Section 6.1. 478 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. 480 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 481 appear more then once in an ISIS FAD Sub-TLV. If it appears more 482 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 484 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV 486 The Flexible-Algorithm definition can specify 'colors' that are used 487 by the operator to include link during the Flex-Algorithm path 488 computation. 490 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used to 491 advertise include-all rule that is used during the Flex-Algorithm 492 path calculation as specified in Section 12. 494 The format of the ISIS Flexible Algorithm Include-All Admin Group 495 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 496 Section 6.1. 498 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 3. 500 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 501 appear more then once in an ISIS FAD Sub-TLV. If it appears more 502 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 504 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV 506 ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a 507 Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 509 0 1 2 3 510 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 1 511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 512 | Type | Length | 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 514 | Flags | 515 +- -+ 516 | ... | 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 518 where: 520 Type: 4 522 Length: variable, non-zero number of octets of the Flags field 524 Flags: 526 0 1 2 3 4 5 6 7... 527 +-+-+-+-+-+-+-+-+... 528 |M| | | ... 529 +-+-+-+-+-+-+-+-+... 531 M-flag: when set, Flex-Algorithm specific prefix metric MUST be 532 used, if advertised with the prefix. This flag is not 533 applicable to prefixes advertised as SRv6 locators. 535 Bits are defined/sent starting with Bit 0 defined above. Additional 536 bit definitions that may be defined in the future SHOULD be assigned 537 in ascending bit order so as to minimize the number of bits that will 538 need to be transmitted. 540 Undefined bits MUST be transmitted as 0. 542 Bits that are NOT transmitted MUST be treated as if they are set to 0 543 on receipt. 545 ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- 546 TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 547 ignored by the receiver. 549 If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV, 550 all the bits are assumed to be set to 0. 552 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV 554 The Flexible-Algorithm definition can specify Shared Risk Link Groups 555 (SRLGs) that the operator wants to exclude during the Flex-Algorithm 556 path computation. 558 ISIS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used to 559 advertise the exclude rule that is used during the Flex-Algorithm 560 path calculation as specified in Section 12. 562 ISIS FAESRLG Sub-TLV is a Sub-TLV of the ISIS FAD Sub-TLV. It has 563 the following format: 565 0 1 2 3 566 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 1 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 | Type | Length | 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 570 | Shared Risk Link Group Value | 571 +- -+ 572 | ... | 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 where: 576 Type: 5 578 Length: variable, dependent on number of SRLG values. MUST be a 579 multiple of 4 octets. 581 Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. 583 ISIS FAESRLG Sub-TLV MAY NOT appear more then once in an ISIS FAD 584 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 585 ignored by the receiver. 587 7. Sub-TLVs of OSPF FAD TLV 589 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 591 Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a 592 Sub-TLV of the OSPF FAD TLV. It's usage is described in Section 6.1. 593 It has the following format: 595 0 1 2 3 596 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 1 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 | Type | Length | 599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 600 | Extended Admin Group | 601 +- -+ 602 | ... | 603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 where: 606 Type: 1 608 Length: variable, dependent on the size of the Extended Admin 609 Group. MUST be a multiple of 4 octets. 611 Extended Administrative Group: Extended Administrative Group as 612 defined in [RFC7308]. 614 OSPF FAEAG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. 615 If it appears more then once, the OSPF FAD TLV MUST be ignored by the 616 receiver. 618 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 620 The usage of this Sub-TLVs is described in Section 6.2. 622 The format of the OSPF Flexible Algorithm Include-Any Admin Group 623 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 624 Section 7.1. 626 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. 628 OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 629 appear more then once in an OSPF FAD TLV. If it appears more then 630 once, the OSPF FAD TLV MUST be ignored by the receiver. 632 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 634 The usage of this Sub-TLVs is described in Section 6.3. 636 The format of the OSPF Flexible Algorithm Include-Any Admin Group 637 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 638 Section 7.1. 640 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 3. 642 OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 643 appear more then once in an OSPF FAD TLV. If it appears more then 644 once, the OSPF FAD TLV MUST be ignored by the receiver. 646 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 648 OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a 649 Sub-TLV of the OSPF FAD TLV. It has the following format: 651 0 1 2 3 652 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 654 | Type | Length | 655 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 656 | Flags | 657 +- -+ 658 | ... | 659 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 660 where: 662 Type: 4 664 Length: variable, dependent on the size of the Flags field. MUST 665 be a multiple of 4 octets. 667 Flags: 669 0 1 2 3 4 5 6 7... 670 +-+-+-+-+-+-+-+-+... 671 |M| | | ... 672 +-+-+-+-+-+-+-+-+... 674 M-flag: when set, Flex-Algorithm specific prefix metric MUST be 675 used, if advertised with the prefix. This flag is not 676 applicable to prefixes advertised as SRv6 locators. 678 Bits are defined/sent starting with Bit 0 defined above. Additional 679 bit definitions that may be defined in the future SHOULD be assigned 680 in ascending bit order so as to minimize the number of bits that will 681 need to be transmitted. 683 Undefined bits MUST be transmitted as 0. 685 Bits that are NOT transmitted MUST be treated as if they are set to 0 686 on receipt. 688 OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. 689 If it appears more then once, the OSPF FAD TLV MUST be ignored by the 690 receiver. 692 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 693 the bits are assumed to be set to 0. 695 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV 697 OSPF Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG Sub-TLV) is a 698 Sub-TLV of the OSPF FAD TLV. It's usage is described in Section 6.5. 699 It has the following format: 701 0 1 2 3 702 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 1 703 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 704 | Type | Length | 705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 | Shared Risk Link Group Value | 707 +- -+ 708 | ... | 709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 where: 712 Type: 5 714 Length: variable, dependent on the number of SRLGs. MUST be a 715 multiple of 4 octets. 717 Shared Risk Link Group Value: SRLG value as defined in [RFC4203]. 719 OSPF FAESRLG Sub-TLV MAY NOT appear more then once in an OSPF FAD 720 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 721 by the receiver. 723 8. ISIS Flex-Algorithm Prefix Metric Sub-TLV 725 ISIS Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the 726 advertisement of a Flex-Algorithm specific prefix metric associated 727 with a given prefix advertisement. 729 ISIS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 and has 730 the following format: 732 0 1 2 3 733 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 735 | Type | Length |Flex-Algorithm | 736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 737 | Metric | 738 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 739 where: 741 Type: 6 742 Length: 5 octets 744 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 746 Metric: 4 octets of metric information 748 ISIS FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it 749 appears more then once with the same Flex-Algorithm value, the first 750 appearance MUST be used and any subsequent ones MUST be ignored. 752 If a prefix is advertised with a Flex-Algorithm prefix metric larger 753 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 754 considered during the Flexible-Algorithm computation. 756 The usage of the Flex-Algorithm prefix metric is described in 757 Section 12. 759 ISIS FAPM Sub-TLV MUST NOT be advertised as sub-TLV of the ISIS SRv6 760 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. ISIS SRv6 Locator 761 TLV includes the Algorithm and Metric fields which MUST be used 762 instead. If FAPM Sub-TLV is present as sub-TLV of the ISIS SRv6 763 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be ignored. 765 9. OSPF Flex-Algorithm Prefix Metric Sub-TLV 767 OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the 768 advertisement of a Flex-Algorithm specific prefix metric associated 769 with a given prefix advertisement. 771 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLVis a Sub-TLV of 772 the: 774 - OSPFv2 Extended Prefix TLV [RFC7684] 776 - Following OSPFv3 TLVs as defined in [RFC8362]: 778 Intra-Area Prefix TLV 780 Inter-Area Prefix TLV 782 External Prefix TLV 784 OSPF FAPM Sub-TLV has the following format: 786 0 1 2 3 787 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 1 788 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 789 | Type | Length | 790 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 791 |Flex-Algorithm | Reserved | 792 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 793 | Metric | 794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 796 where: 798 Type: 3 for OSPFv2, 26 for OSPFv3 800 Length: 8 octets 802 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 804 Reserved: Must be set to 0, ignored at reception. 806 Metric: 4 octets of metric information 808 OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it 809 appears more then once with the same Flex-Algorithm value, the first 810 appearance MUST be used and any subsequent ones MUST be ignored. 812 The usage of the Flex-Algorithm prefix metric is described in 813 Section 12. 815 10. Advertisement of Node Participation in a Flex-Algorithm 817 When a router is configured to support a particular Flex-Algorithm, 818 we say it is participating in that Flex-Algorithm. 820 Paths computed for a specific Flex-Algorithm MAY be used by various 821 applications, each potentially using its own specific data plane for 822 forwarding the data over such paths. To guarantee the presence of 823 the application specific forwarding state associated with a 824 particular Flex-Algorithm, a router MUST advertise its participation 825 for a particular Flex-Algorithm for each application specifically. 827 10.1. Advertisement of Node Participation for Segment Routing 829 [RFC8667], [RFC8665] and [RFC8666] (IGP Segment Routing extensions) 830 describe how SR-Algorithm is used to define how the best path is 831 computed by the IGP. 833 Routers advertise the support for the SR-Algorithm as a node 834 capability as described in the above mentioned IGP Segment Routing 835 extensions. To advertise participation for a particular Flex- 836 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 837 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 838 (OSPF) or sub-TLV (ISIS). 840 Segment Routing Flex-Algorithm participation advertisement is 841 topology independent. When a router advertises participation in an 842 SR-Algorithm, the participation applies to all topologies in which 843 the advertising node participates. 845 10.2. Advertisement of Node Participation for Other Applications 847 This section describes considerations related to how other 848 applications can advertise its participation in a specific Flex- 849 Algorithm. 851 Application specific Flex-Algorithm participation advertisements MAY 852 be topology specific or MAY be topology independent, depending on the 853 application itself. 855 Application specific advertisement for Flex-Algorithm participation 856 MUST be defined for each application and is outside of the scope of 857 this document. 859 11. Advertisement of Link Attributes for Flex-Algorithm 861 Various link attributes may be used during the Flex-Algorithm path 862 calculation. For example, include or exclude rules based on link 863 affinities can be part of the Flex-Algorithm definition as defined in 864 Section 6 and Section 7. 866 Link attribute advertisements that are to be used during Flex- 867 Algorithm calculation MUST use the Application Specific Link 868 Attribute (ASLA) advertisements defined in [I-D.ietf-isis-te-app] or 869 [I-D.ietf-ospf-te-link-attr-reuse]. 871 A new Application Identifier Bit is defined to indicate that the ASLA 872 advertisement is associated with the Flex-Algorithm application. 873 This bit is set in the Standard Application Bit Mask (SABM) defined 874 in [I-D.ietf-isis-te-app] or [I-D.ietf-ospf-te-link-attr-reuse]: 876 Bit-3: Flexible Algorithm (X-bit) 878 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 879 Application MAY use either the Administrative Group or Extended 880 Administrative Group encodings. If the Administrative Group encoding 881 is used then the first 32 bits of the corresponding FAD sub-TLVs are 882 mapped to the link attribute advertisements as specified in RFC 7308. 884 12. Calculation of Flexible Algorithm Paths 886 A router MUST be configured to participate in a given Flex-Algorithm 887 K and MUST use the FAD selected based on the rules defined in 888 Section 5.3 before it can compute any path for that Flex-Algorithm. 890 As described in Section 10, participation for any particular Flex- 891 Algorithm MUST be advertised on a per application basis. Calculation 892 of the paths for any particular Flex-Algorithm MUST be application 893 specific. 895 The way applications handle nodes that do not participate in 896 Flexible-Algorithm is application specific. If the application only 897 wants to consider participating nodes during the Flex-Algorithm 898 calculation, then when computing paths for a given Flex-Algorithm, 899 all nodes that do not advertise participation for that Flex-Algorithm 900 in the application specific advertisements MUST be pruned from the 901 topology. Segment Routing, including both SR MPLS and SRv6, are 902 applications that MUST use such pruning when computing Flex-Algorithm 903 paths. 905 When computing the path for a given Flex-Algorithm, the metric-type 906 that is part of the Flex-Algorithm definition (Section 5) MUST be 907 used. 909 When computing the path for a given Flex-Algorithm, the calculation- 910 type that is part of the Flex-Algorithm definition (Section 5) MUST 911 be used. 913 Various link include or exclude rules can be part of the Flex- 914 Algorithm definition. To refer to a particular bit within an AG or 915 EAG we uses term 'color'. 917 Rules, in the order as specified below, MUST be used to prune links 918 from the topology during the Flex-Algorithm computation. 920 For all links in the topology: 922 1. Check if any exclude rule is part of the Flex-Algorithm 923 definition. If such exclude rule exists, check if any color that 924 is part of the exclude rule is also set on the link. If such a 925 color is set, the link MUST be pruned from the computation. 927 2. Check if any exclude SRLG rule is part of the Flex-Algorithm 928 definition. If such exclude rule exists, check if the link is 929 part of any SRLG that is also part of the SRLG exclude rule. If 930 the link is part of such SRLG, the link MUST be pruned from the 931 computation. 933 4. Check if any include-any rule is part of the Flex-Algorithm 934 definition. If such include-any rule exists, check if any color 935 that is part of the include-any rule is also set on the link. If 936 no such color is set, the link MUST be pruned from the 937 computation. 939 4. Check if any include-all rule is part of the Flex-Algorithm 940 definition. If such include-all rule exists, check if all colors 941 that are part of the include-all rule are also set on the link. 942 If all such colors are not set on the link, the link MUST be 943 pruned from the computation. 945 5. If the Flex-Algorithm definition uses other than IGP metric 946 (Section 5), and such metric is not advertised for the particular 947 link in a topology for which the computation is done, such link 948 MUST be pruned from the computation. A metric of value 0 MUST NOT 949 be assumed in such case. 951 12.1. Multi-area and Multi-domain Considerations 953 Any IGP Shortest Path Tree calculation is limited to a single area. 954 This applies to Flex-Algorithm calculations as well. Given that the 955 computing router does not have the visibility of the topology of next 956 areas or domain, the Flex-Algorithm specific path to an inter-area or 957 inter-domain prefix will be computed for the local area only. The 958 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 959 will be selected based on the best path for the given Flex-Algorithm 960 in the local area and such egress ABR or ASBR router will be 961 responsible to compute the best Flex-Algorithm specific path over the 962 next area or domain. This may produce an end-to-end path, which is 963 sub-optimal based on Flex-Algorithm constraints. In cases where the 964 ABR or ASBR has no reachability to a prefix for a given Flex- 965 Algorithm in a next area or domain, the traffic may get dropped by 966 the ABR/ASBR. 968 To allow the optimal end-to-end path for a inter-area or inter-domain 969 prefixes for any Flex-Algorithm to be computed, the FAPM has been 970 defined in Section 8 and Section 9. 972 If the FAD selected based on the rules defined in Section 5.3 973 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 974 Section 9) when advertising the prefix between areas or domains. 975 Such metric will be equal to the metric to reach the prefix for a 976 given Flex-Algorithm in a source area or domain. This is similar in 977 nature to how the metric is set when prefixes are advertised between 978 areas or domains for default algorithm. 980 If the FAD selected based on the rules defined in Section 5.3 981 includes the M-flag, FAPM MUST be used during calculation of prefix 982 reachability for the inter-area and external prefixes. If the FAPM 983 for the Flex-Algorithm is not advertised with the inter-area or 984 external prefix reachability advertisement, the prefix MUST be 985 considered as unreachable for that Flex-Algorithm. 987 Flex-Algorithm prefix metrics MUST NOT be used during the Flex- 988 Algorithm computation unless the FAD selected based on the rules 989 defined in Section 5.3 includes the M-Flag, as described in 990 (Section 6.4 or Section 7.4). 992 If the FAD selected based on the rules defined in Section 5.3 does 993 not includes the M-flag, it is NOT RECOMMENDED to use the Flex- 994 Algoritm for inter-area or inter-domain prefix reachability. The 995 reason is that without the explicit Flex-Algorithm Prefix Metric 996 advertisement it is not possible to conclude whether the ABR or ASBR 997 has reachability to the inter-area or inter-domain prefix for a given 998 Flex-Algorithm in a next area or domain. Sending the Flex-Algoritm 999 traffic for such prefix towards the ABR or ASBR may result in traffic 1000 looping or black-holing. 1002 FAPM MUST NOT be advertised with ISIS L1 or L2 intra-area, OSPFv2 1003 intra-area or OSPFv3 intra area routes. If the FAPM is advertised 1004 for these route-types, it MUST be ignored during prefix reachability 1005 calculation. 1007 M-flag in FAD is not applicable to prefixes advertised as SRv6 1008 locators. ISIS SRv6 Locator TLV includes the Algorithm and Metric 1009 fields [I-D.ietf-lsr-isis-srv6-extensions]. When the ISIS SRv6 1010 Locator is advertised between areas or domains, the metric field in 1011 the Locator TLV MUST be used irrespective of the M flag in the FAD 1012 advertisement. 1014 13. Flex-Algorithm and Forwarding Plane 1016 This section describes how Flex-Algorithm paths are used in 1017 forwarding. 1019 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm 1021 This section describes how Flex-Algorithm paths are used with SR MPLS 1022 forwarding. 1024 Prefix SID advertisements include an SR-Algorithm value and as such 1025 are associated with the specified SR-Algorithm. Prefix-SIDs are also 1026 associated with a specific topology which is inherited from the 1027 associated prefix reachability advertisement. When the algorithm 1028 value advertised is a Flex-Algorithm value, the Prefix SID is 1029 associated with paths calculated using that Flex-Algorithm in the 1030 associated topology. 1032 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 1033 using the MPLS label that corresponds to the Prefix-SID that was 1034 advertised for that Flex-algorithm. If the Prefix SID for a given 1035 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 1036 be installed in the MPLS forwarding plane. 1038 Traffic that is supposed to be routed via Flex-Algorithm specific 1039 paths, MUST be dropped where there are no such paths available. 1041 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 1042 computed using the same constraints as the calculation of the primary 1043 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 1044 advertised specifically for the given algorithm. LFA paths MUST NOT 1045 use an Adjacency-SID that belongs to a link that has been pruned from 1046 the Flex-Algorithm computation. 1048 If LFA protection is being used to protect a given Flex-Algorithm 1049 paths, all routers in the area participating in the given Flex- 1050 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 1051 SID. These Node-SIDs are used to enforce traffic over the LFA 1052 computed backup path. 1054 13.2. SRv6 Forwarding for Flex-Algorithm 1056 This section describes how Flex-Algorithm paths are used with SRv6 1057 forwarding. 1059 In SRv6 a node is provisioned with topology/algorithm specific 1060 locators for each of the topology/algorithm pairs supported by that 1061 node. Each locator is a covering prefix for all SIDs provisioned on 1062 that node which have the matching topology/algorithm. 1064 SRv6 locator advertisement in IGPs 1065 ([I-D.ietf-lsr-isis-srv6-extensions] 1066 [I-D.ietf-lsr-ospfv3-srv6-extensions]) includes the MTID value that 1067 associates the locator with a specific topology. SRv6 locator 1068 advertisements also includes an Algorithm value that explicitly 1069 associates the locator with a specific algorithm. When the algorithm 1070 value advertised with a locator represents a Flex-Algorithm, the 1071 paths to the locator prefix MUST be calculated using the specified 1072 Flex-Algorithm in the associated topology. 1074 Forwarding entries for the locator prefixes advertised in IGPs MUST 1075 be installed in the forwarding plane of the receiving SRv6 capable 1076 routers when the associated topology/algorithm is participating in 1077 them. Forwarding entries for locators associated with Flex- 1078 Algorithms in which the node is not participating MUST NOT be 1079 installed in the forwarding. 1081 When the locator is associated with the Flex-Algorithm, LFA paths to 1082 the locator prefix MUST be calculated using such Flex-Algorithm in 1083 the associated topology, to guarantee that they follow the same 1084 constraints as the calculation of the primary paths. LFA paths MUST 1085 only use SRv6 SIDs advertised specifically for the given Flex- 1086 Algorithm. 1088 If LFA protection is being used to protect locators associated with a 1089 given Flex-Algorithm, all routers in the area participating in the 1090 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1091 specific locator and END SID per node and one END.X SID for every 1092 link that has not been pruned from such Flex-Algorithm computation. 1093 These locators and SIDs are used to enforce traffic over the LFA 1094 computed backup path. 1096 13.3. Other Applications' Forwarding for Flex-Algorithm 1098 Any application that wants to use Flex-Algorithm specific forwarding 1099 needs to install some form of Flex-Algorithm specific forwarding 1100 entries. 1102 Application specific forwarding for Flex-Algorithm MUST be defined 1103 for each application and is outside of the scope of this document. 1105 14. Backward Compatibility 1107 This extension brings no new backward compatibility issues. 1109 15. Security Considerations 1111 This draft adds two new ways to disrupt the IGP networks: 1113 An attacker can hijack a particular Flex-Algorithm by advertising 1114 a FAD with a priority of 255 (or any priority higher than that of 1115 the legitimate nodes). 1117 An attacker could make it look like a router supports a particular 1118 Flex-Algorithm when it actually doesn't, or vice versa. 1120 Both of these attacks can be addressed by the existing security 1121 extensions as described in [RFC5304] and [RFC5310] for ISIS, in 1122 [RFC2328] and [RFC7474] for OSPFv2 and in [RFC5340] and [RFC4552] for 1123 OSPFv3. 1125 16. IANA Considerations 1127 16.1. IGP IANA Considerations 1129 16.1.1. IGP Algorithm Types Registry 1131 This document makes the following registrations in the "IGP Algorithm 1132 Types" registry: 1134 Type: 128-255. 1136 Description: Flexible Algorithms. 1138 Reference: This document (Section 4). 1140 16.1.2. Flexible Algorithm Definition Metric-Type Registry 1142 IANA is requested to set up a registry called "Flexible Algorithm 1143 Definition Metric-Type Registry" under a "Interior Gateway Protocol 1144 (IGP) Parameters" IANA registries. The registration policy for this 1145 registry is "Standards Action" ([RFC8126] and [RFC7120]). 1147 Values in this registry come from the range 0-255. 1149 This document registers following values in the "Flexible Algorithm 1150 Definition Metric-Type Registry": 1152 Type: 0 1154 Description: IGP metric 1156 Reference: This document (Section 5.1) 1158 Type: 1 1160 Description: Min Unidirectional Link Delay [RFC7810] 1162 Reference: This document (Section 5.1) 1164 Type: 2 1166 Description: TE Default Metric [RFC5305] 1167 Reference: This document (Section 5.1) 1169 16.2. Flex-Algorithm Definition Flags Registry 1171 IANA is requested to set up a registry called "ISIS Flex-Algorithm 1172 Definition Flags Registry" under a "Interior Gateway Protocol (IGP) 1173 Parameters" IANA registries. The registration policy for this 1174 registry is "Standards Action" ([RFC8126] and [RFC7120]). 1176 This document defines the following single bit in Flex-Algorithm 1177 Definition Flags registry: 1179 Bit # Name 1180 ----- ------------------------------ 1181 0 Prefix Metric Flag (M-flag) 1183 Reference: This document (Section 6.4, Section 7.4). 1185 16.3. ISIS IANA Considerations 1187 16.3.1. Sub TLVs for Type 242 1189 This document makes the following registrations in the "sub-TLVs for 1190 TLV 242" registry. 1192 Type: 26. 1194 Description: Flexible Algorithm Definition. 1196 Reference: This document (Section 5.1). 1198 16.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1200 This document makes the following registrations in the "Sub-TLVs for 1201 for TLVs 135, 235, 236, and 237" registry. 1203 Type: 6 1205 Description: Flex-Algorithm Prefix Metric. 1207 Reference: This document (Section 8). 1209 16.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1211 This document creates the following Sub-Sub-TLV Registry: 1213 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1214 Registration Procedure: Expert review 1216 Reference: This document (Section 5.1) 1218 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1219 for Flexible Algorithm Definition Sub-TLV" registry: 1221 Type: 1 1223 Description: Flexible Algorithm Exclude Admin Group 1225 Reference: This document (Section 6.1). 1227 Type: 2 1229 Description: Flexible Algorithm Include-Any Admin Group 1231 Reference: This document (Section 6.2). 1233 Type: 3 1235 Description: Flexible Algorithm Include-All Admin Group 1237 Reference: This document (Section 6.3). 1239 Type: 4 1241 Description: Flexible Algorithm Definition Flags 1243 Reference: This document (Section 6.4). 1245 Type: 5 1247 Description: Flexible Algorithm Exclude SRLG 1249 Reference: This document (Section 6.5). 1251 16.4. OSPF IANA Considerations 1253 16.4.1. OSPF Router Information (RI) TLVs Registry 1255 This specification updates the OSPF Router Information (RI) TLVs 1256 Registry. 1258 Type: 16 1260 Description: Flexible Algorithm Definition TLV. 1262 Reference: This document (Section 5.2). 1264 16.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1266 This document makes the following registrations in the "OSPFv2 1267 Extended Prefix TLV Sub-TLVs" registry. 1269 Type: 3 1271 Description: Flex-Algorithm Prefix Metric. 1273 Reference: This document (Section 9). 1275 16.4.3. OSPFv3 Extended-LSA Sub-TLVs 1277 This document makes the following registrations in the "OSPFv3 1278 Extended-LSA Sub-TLVs" registry. 1280 Type: 26 1282 Description: Flex-Algorithm Prefix Metric. 1284 Reference: This document (Section 9). 1286 16.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1288 This document creates the following registry: 1290 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1292 Registration Procedure: Expert review 1294 Reference: This document (Section 5.2) 1296 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1297 define sub-TLVs at any level of nesting for Flexible Algorithm TLV 1298 and should be added to the "Open Shortest Path First (OSPF) 1299 Parameters" registries group. New values can be allocated via IETF 1300 Review or IESG Approval. 1302 This document registers following Sub-TLVs in the "TLVs for Flexible 1303 Algorithm Definition TLV" registry: 1305 Type: 1 1307 Description: Flexible Algorithm Exclude Admin Group 1309 Reference: This document (Section 7.1). 1311 Type: 2 1313 Description: Flexible Algorithm Include-Any Admin Group 1315 Reference: This document (Section 7.2). 1317 Type: 3 1319 Description: Flexible Algorithm Include-All Admin Group 1321 Reference: This document (Section 7.3). 1323 Type: 4 1325 Description: Flexible Algorithm Definition Flags 1327 Reference: This document (Section 7.4). 1329 Type: 5 1331 Description: Flexible Algorithm Exclude SRLG 1333 Reference: This document (Section 7.5). 1335 Types in the range 32768-33023 are for experimental use; these will 1336 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1338 Types in the range 33024-65535 are not to be assigned at this time. 1339 Before any assignments can be made in the 33024-65535 range, there 1340 MUST be an IETF specification that specifies IANA Considerations that 1341 covers the range being assigned. 1343 16.4.5. Link Attribute Applications Registry 1345 This document registers following bit in the Link Attribute 1346 Applications registry: 1348 Bit-3 1350 Description: Flexible Algorithm (X-bit) 1352 Reference: This document (Section 11). 1354 17. Acknowledgements 1356 This draft, among other things, is also addressing the problem that 1357 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1358 All authors of that draft agreed to join this draft. 1360 Thanks to Eric Rosen, Tony Przygienda for their detailed review and 1361 excellent comments. 1363 Thanks to Cengiz Halit for his review and feedback during initial 1364 phase of the solution definition. 1366 Thanks to Kenji Kumaki for his comments. 1368 Thanks to William Britto A J. for his suggestions. 1370 18. References 1372 18.1. Normative References 1374 [BCP14] , . 1376 [I-D.ietf-isis-te-app] 1377 Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1378 J. Drake, "IS-IS TE Attributes per application", draft- 1379 ietf-isis-te-app-12 (work in progress), March 2020. 1381 [I-D.ietf-lsr-isis-srv6-extensions] 1382 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1383 Z. Hu, "IS-IS Extension to Support Segment Routing over 1384 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-07 1385 (work in progress), March 2020. 1387 [I-D.ietf-lsr-ospfv3-srv6-extensions] 1388 Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, 1389 "OSPFv3 Extensions for SRv6", draft-ietf-lsr- 1390 ospfv3-srv6-extensions-00 (work in progress), February 1391 2020. 1393 [I-D.ietf-ospf-te-link-attr-reuse] 1394 Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J., 1395 and J. Drake, "OSPF Link Traffic Engineering Attribute 1396 Reuse", draft-ietf-ospf-te-link-attr-reuse-10 (work in 1397 progress), October 2019. 1399 [ISO10589] 1400 International Organization for Standardization, 1401 "Intermediate system to Intermediate system intra-domain 1402 routeing information exchange protocol for use in 1403 conjunction with the protocol for providing the 1404 connectionless-mode Network Service (ISO 8473)", ISO/ 1405 IEC 10589:2002, Second Edition, Nov 2002. 1407 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1408 Requirement Levels", BCP 14, RFC 2119, 1409 DOI 10.17487/RFC2119, March 1997, 1410 . 1412 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 1413 Support of Generalized Multi-Protocol Label Switching 1414 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 1415 . 1417 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1418 in Support of Generalized Multi-Protocol Label Switching 1419 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1420 . 1422 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1423 Traffic Engineering (MPLS-TE)", RFC 7308, 1424 DOI 10.17487/RFC7308, July 2014, 1425 . 1427 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1428 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1429 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1430 2015, . 1432 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1433 S. Shaffer, "Extensions to OSPF for Advertising Optional 1434 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1435 February 2016, . 1437 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1438 for Advertising Router Information", RFC 7981, 1439 DOI 10.17487/RFC7981, October 2016, 1440 . 1442 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1443 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1444 May 2017, . 1446 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1447 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1448 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1449 2018, . 1451 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 1452 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1453 Extensions for Segment Routing", RFC 8665, 1454 DOI 10.17487/RFC8665, December 2019, 1455 . 1457 [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 1458 for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 1459 December 2019, . 1461 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 1462 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 1463 Extensions for Segment Routing", RFC 8667, 1464 DOI 10.17487/RFC8667, December 2019, 1465 . 1467 18.2. Informative References 1469 [I-D.gulkohegde-routing-planes-using-sr] 1470 Hegde, S. and a. arkadiy.gulko@thomsonreuters.com, 1471 "Separating Routing Planes using Segment Routing", draft- 1472 gulkohegde-routing-planes-using-sr-00 (work in progress), 1473 March 2017. 1475 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 1476 DOI 10.17487/RFC2328, April 1998, 1477 . 1479 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 1480 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 1481 RFC 3906, DOI 10.17487/RFC3906, October 2004, 1482 . 1484 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 1485 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 1486 . 1488 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1489 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1490 2008, . 1492 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 1493 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 1494 2008, . 1496 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 1497 and M. Fanto, "IS-IS Generic Cryptographic 1498 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 1499 2009, . 1501 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 1502 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 1503 . 1505 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 1506 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 1507 2014, . 1509 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 1510 "Security Extension for OSPFv2 When Using Manual Key 1511 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 1512 . 1514 [RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and 1515 Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", 1516 RFC 7810, DOI 10.17487/RFC7810, May 2016, 1517 . 1519 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1520 Writing an IANA Considerations Section in RFCs", BCP 26, 1521 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1522 . 1524 Authors' Addresses 1526 Peter Psenak (editor) 1527 Cisco Systems 1528 Apollo Business Center 1529 Mlynske nivy 43 1530 Bratislava, 82109 1531 Slovakia 1533 Email: ppsenak@cisco.com 1535 Shraddha Hegde 1536 Juniper Networks, Inc. 1537 Embassy Business Park 1538 Bangalore, KA, 560093 1539 India 1541 Email: shraddha@juniper.net 1542 Clarence Filsfils 1543 Cisco Systems, Inc. 1544 Brussels 1545 Belgium 1547 Email: cfilsfil@cisco.com 1549 Ketan Talaulikar 1550 Cisco Systems, Inc. 1551 S.No. 154/6, Phase I, Hinjawadi 1552 PUNE, MAHARASHTRA 411 057 1553 India 1555 Email: ketant@cisco.com 1557 Arkadiy Gulko 1558 Thomson Reuters 1560 Email: arkadiy.gulko@thomsonreuters.com