idnits 2.17.1 draft-ietf-lsr-flex-algo-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year ** The document contains RFC2119-like boilerplate, but doesn't seem to mention RFC 2119. The boilerplate contains a reference [BCP14], but that reference does not seem to mention RFC 2119 either. -- The exact meaning of the all-uppercase expression 'MAY NOT' is not defined in RFC 2119. If it is intended as a requirements expression, it should be rewritten using one of the combinations defined in RFC 2119; otherwise it should not be all-uppercase. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: The RI LSA can be advertised at any of the defined opaque flooding scopes (link, area, or Autonomous System (AS)). For the purpose of OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The Autonomous System flooding scope SHOULD not be used by default unless local configuration policy on the originating router indicates domain wide flooding. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The ISIS FAESRLG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF FAEAG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: The OSPF FAESRLG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored by the receiver. -- The document date (August 14, 2020) is 1350 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'I-D.ietf-lsr-ospf-reverse-metric' is defined on line 1489, but no explicit reference was found in the text -- Possible downref: Non-RFC (?) normative reference: ref. 'BCP14' == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-08 == Outdated reference: A later version (-13) exists of draft-ietf-lsr-ospf-reverse-metric-01 == Outdated reference: A later version (-15) exists of draft-ietf-lsr-ospfv3-srv6-extensions-00 -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10589' == Outdated reference: A later version (-13) exists of draft-ietf-rtgwg-segment-routing-ti-lfa-03 Summary: 1 error (**), 0 flaws (~~), 17 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Psenak, Ed. 3 Internet-Draft Cisco Systems 4 Intended status: Standards Track S. Hegde 5 Expires: February 15, 2021 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Refinitiv 11 August 14, 2020 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-09.txt 16 Abstract 18 IGP protocols traditionally compute best paths over the network based 19 on the IGP metric assigned to the links. Many network deployments 20 use RSVP-TE based or Segment Routing based Traffic Engineering to 21 steer traffic over a path that is computed using different metrics or 22 constraints than the shortest IGP path. This document proposes a 23 solution that allows IGPs themselves to compute constraint-based 24 paths over the network. This document also specifies a way of using 25 Segment Routing (SR) Prefix-SIDs and SRv6 locators to steer packets 26 along the constraint-based paths. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on February 15, 2021. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 64 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 4. Flexible Algorithm . . . . . . . . . . . . . . . . . . . . . 5 66 5. Flexible Algorithm Definition Advertisement . . . . . . . . . 6 67 5.1. ISIS Flexible Algorithm Definition Sub-TLV . . . . . . . 6 68 5.2. OSPF Flexible Algorithm Definition TLV . . . . . . . . . 7 69 5.3. Common Handling of Flexible Algorithm Definition TLV . . 9 70 6. Sub-TLVs of ISIS FAD Sub-TLV . . . . . . . . . . . . . . . . 10 71 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV . . . 10 72 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV . 11 73 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV . 11 74 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV . . . . 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 Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . . 16 83 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV . . . . . . . . 17 84 10. Advertisement of Node Participation in a Flex-Algorithm . . . 18 85 10.1. Advertisement of Node Participation for Segment Routing 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 . . . 23 93 13.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 23 94 13.3. Other Applications' Forwarding for Flex-Algorithm . . . 24 95 14. Operational considerations . . . . . . . . . . . . . . . . . 24 96 14.1. Inter-area Considerations . . . . . . . . . . . . . . . 24 97 14.2. Usage of SRLG Exclude Rule with Flex-Algorithm . . . . . 25 98 14.3. Max-metric consideration . . . . . . . . . . . . . . . . 26 99 15. Backward Compatibility . . . . . . . . . . . . . . . . . . . 26 100 16. Security Considerations . . . . . . . . . . . . . . . . . . . 26 101 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 102 17.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 27 103 17.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 27 104 17.1.2. IGP Metric-Type Registry . . . . . . . . . . . . . . 27 105 17.2. Flexible Algorithm Definition Flags Registry . . . . . . 28 106 17.3. ISIS IANA Considerations . . . . . . . . . . . . . . . . 28 107 17.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 28 108 17.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 28 109 17.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 110 TLV . . . . . . . . . . . . . . . . . . . . . . . . 28 111 17.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 29 112 17.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 29 113 17.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 30 114 17.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 30 115 17.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV 116 Registry . . . . . . . . . . . . . . . . . . . . . . 30 117 17.4.5. Link Attribute Applications Registry . . . . . . . . 31 118 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31 119 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 120 19.1. Normative References . . . . . . . . . . . . . . . . . . 32 121 19.2. Informative References . . . . . . . . . . . . . . . . . 34 122 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 124 1. Introduction 126 An IGP-computed path based on the shortest IGP metric must often be 127 replaced by a traffic-engineered path due to the traffic requirements 128 which are not reflected by the IGP metric. Some networks engineer 129 the IGP metric assignments in a way that the IGP metric reflects the 130 link bandwidth or delay. If, for example, the IGP metric is 131 reflecting the bandwidth on the link and the application traffic is 132 delay sensitive, the best IGP path may not reflect the best path from 133 such an application's perspective. 135 To overcome this limitation, various sorts of traffic engineering 136 have been deployed, including RSVP-TE and SR-TE, in which case the TE 137 component is responsible for computing paths based on additional 138 metrics and/or constraints. Such paths need to be installed in the 139 forwarding tables in addition to, or as a replacement for, the 140 original paths computed by IGPs. Tunnels are often used to represent 141 the engineered paths and mechanisms like one described in [RFC3906] 142 are used to replace the native IGP paths with such tunnel paths. 144 This document specifies a set of extensions to ISIS, OSPFv2, and 145 OSPFv3 that enable a router to advertise TLVs that identify (a) 146 calculation-type, (b) specify a metric-type, and (c) describe a set 147 of constraints on the topology, that are to be used to compute the 148 best paths along the constrained topology. A given combination of 149 calculation-type, metric-type, and constraints is known as a 150 "Flexible Algorithm Definition". A router that sends such a set of 151 TLVs also assigns a Flex-Algorithm value to the specified combination 152 of calculation-type, metric-type, and constraints. 154 This document also specifies a way for a router to use IGPs to 155 associate one or more SR Prefix-SIDs or SRv6 locators with a 156 particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then 157 represents a path that is computed according to the identified Flex- 158 Algorithm. 160 2. Requirements notation 162 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 163 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 164 "OPTIONAL" in this document are to be interpreted as described in 165 [BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all 166 capitals, as shown here. 168 3. Terminology 170 This section defines terms that are often used in this document. 172 Flexible Algorithm Definition (FAD) - the set consisting of (a) 173 calculation-type, (b) metric-type, and (c) a set of constraints. 175 Flexible Algorithm - a numeric identifier in the range 128-255 that 176 is associated via configuration with the Flexible-Algorithm 177 Definition. 179 Local Flexible Algorithm Definition - Flexible Algorithm Definition 180 defined locally on the node. 182 Remote Flexible Algorithm Definition - Flexible Algorithm Definition 183 received from other nodes via IGP flooding. 185 Flexible Algorithm Participation - per application configuration 186 state that expresses whether the node is participating in a 187 particular Flexible Algorithm. 189 IGP Algorithm - value from the the "IGP Algorithm Types" registry 190 defined under "Interior Gateway Protocol (IGP) Parameters" IANA 191 registries. IGP Algorithms represents the triplet (Calculation Type, 192 Metric, Constraints), where the second and third elements of the 193 triple MAY not be specified. 195 ABR - Area Border Router. In ISIS terminology it is also known as 196 L1/L2 router. 198 ASBR - Autonomous System Border Router. 200 4. Flexible Algorithm 202 Many possible constraints may be used to compute a path over a 203 network. Some networks are deployed as multiple planes. A simple 204 form of constraint may be to use a particular plane. A more 205 sophisticated form of constraint can include some extended metric as 206 described in [RFC8570]. Constraints which restrict paths to links 207 with specific affinities or avoid links with specific affinities are 208 also possible. Combinations of these are also possible. 210 To provide maximum flexibility, we want to provide a mechanism that 211 allows a router to (a) identify a particular calculation-type, (b) 212 metric-type, (c) describe a particular set of constraints, and (d) 213 assign a numeric identifier, referred to as Flex-Algorithm, to the 214 combination of that calculation-type, metric-type, and those 215 constraints. We want the mapping between the Flex-Algorithm and its 216 meaning to be flexible and defined by the user. As long as all 217 routers in the domain have a common understanding as to what a 218 particular Flex-Algorithm represents, the resulting routing 219 computation is consistent and traffic is not subject to any looping. 221 The set consisting of (a) calculation-type, (b) metric-type, and (c) 222 a set of constraints is referred to as a Flexible-Algorithm 223 Definition. 225 Flexible-Algorithm is a numeric identifier in the range 128-255 that 226 is associated via configuratin with the Flexible-Algorithm 227 Definition. 229 IANA "IGP Algorithm Types" registry defines the set of values for IGP 230 Algorithms. We propose to allocate the following values for Flex- 231 Algorithms from this registry: 233 128-255 - Flex-Algorithms 235 5. Flexible Algorithm Definition Advertisement 237 To guarantee the loop-free forwarding for paths computed for a 238 particular Flex-Algorithm, all routers that (a) are configured to 239 participate in a particular Flex-Algorithm, and (b) are in the same 240 Flex-Algorithm definition advertisement scope MUST agree on the 241 definition of the Flex-Algorithm. 243 5.1. ISIS Flexible Algorithm Definition Sub-TLV 245 The ISIS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used 246 to advertise the definition of the Flex-Algorithm. 248 The ISIS FAD Sub-TLV is advertised as a Sub-TLV of the ISIS Router 249 Capability TLV-242 that is defined in [RFC7981]. 251 ISIS FAD Sub-TLV has the following format: 253 0 1 2 3 254 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 256 | Type | Length |Flex-Algorithm | Metric-Type | 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 258 | Calc-Type | Priority | 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 | Sub-TLVs | 261 + + 262 | ... | 264 | | 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 267 where: 269 Type: 26 271 Length: variable, dependent on the included Sub-TLVs 273 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 275 Metric-Type: Type of metric to be used during the calculation. 276 Following values are defined: 278 0: IGP Metric 280 1: Min Unidirectional Link Delay as defined in 281 [I-D.ietf-isis-te-app]. 283 2: TE default metric as defined in [I-D.ietf-isis-te-app]. 285 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 286 Types" registry defined under "Interior Gateway Protocol (IGP) 287 Parameters" IANA registries. IGP algorithms in the range of 0-127 288 have a defined triplet (Calculation Type, Metric, Constraints). 289 When used to specify the Calc-Type in the FAD Sub-TLV, only the 290 Calculation Type defined for the specified IGP Algorithm is used. 291 The Metric/Constraints MUST NOT be inherited. If the required 292 calculation type is Shortest Path First, the value 0 SHOULD appear 293 in this field. 295 Priority: Value between 0 and 255 inclusive that specifies the 296 priority of the advertisement. 298 Sub-TLVs - optional sub-TLVs. 300 The ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a 301 router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given 302 Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs 303 for a given Flexible-Algorithm from the same originator SHOULD select 304 the first advertisement in the lowest numbered LSP. 306 The ISIS FAD Sub-TLV has an area scope. The Router Capability TLV in 307 which the FAD Sub-TLV is present MUST have the S-bit clear. 309 ISIS L1/L2 router MAY be configured to re-generate the winning FAD 310 from level 2, without any modification to it, to level 1 area. The 311 re-generation of the FAD Sub-TLV from level 2 to level 1 is 312 determined by the L1/L2 router, not by the originator of the FAD 313 advertisement in the level 2. In such case, the re-generated FAD 314 Sub-TLV will be advertised in the level 1 Router Capability TLV 315 originated by the L1/L2 router. 317 L1/L2 router MUST NOT re-generate any FAD Sub-TLV from level 1 to 318 level 2. 320 5.2. OSPF Flexible Algorithm Definition TLV 322 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 323 defined in [RFC7770]. 325 OSPF FAD TLV has the following format: 327 0 1 2 3 328 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 1 329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 330 | Type | Length | 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 | Sub-TLVs | 335 + + 336 | ... | 338 | | 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 341 where: 343 Type: 16 345 Length: variable, dependent on the included Sub-TLVs 347 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 348 inclusive. 350 Metric-Type: as described in Section 5.1 352 Calc-Type: as described in Section 5.1 354 Priority: as described in Section 5.1 356 Sub-TLVs - optional sub-TLVs. 358 When multiple OSPF FAD TLVs, for the same Flexible-Algorithm, are 359 received from a given router, the receiver MUST use the first 360 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 361 TLV, for the same Flex-Algorithm, appears in multiple Router 362 Information LSAs that have different flooding scopes, the OSPF FAD 363 TLV in the Router Information LSA with the area-scoped flooding scope 364 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 365 in multiple Router Information LSAs that have the same flooding 366 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 367 numerically smallest Instance ID MUST be used and subsequent 368 instances of the OSPF FAD TLV MUST be ignored. 370 The RI LSA can be advertised at any of the defined opaque flooding 371 scopes (link, area, or Autonomous System (AS)). For the purpose of 372 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 373 Autonomous System flooding scope SHOULD not be used by default unless 374 local configuration policy on the originating router indicates domain 375 wide flooding. 377 5.3. Common Handling of Flexible Algorithm Definition TLV 379 This section describes the protocol-independent handling of the FAD 380 TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in 381 this section, even though in case of ISIS it is a Sub-TLV. 383 The value of the Flex-Algorithm MUST be between 128 and 255 384 inclusive. If it is not, the FAD TLV MUST be ignored. 386 Only a subset of the routers participating in the particular Flex- 387 Algorithm need to advertise the definition of the Flex-Algorithm. 389 Every router, that is configured to participate in a particular Flex- 390 Algorithm, MUST select the Flex-Algorithm definition based on the 391 following ordered rules. This allows for the consistent Flex- 392 Algorithm definition selection in cases where different routers 393 advertise different definitions for a given Flex-Algorithm: 395 1. From the advertisements of the FAD in the area (including both 396 locally generated advertisements and received advertisements) 397 select the one(s) with the highest priority value. 399 2. If there are multiple advertisements of the FAD with the same 400 highest priority, select the one that is originated from the 401 router with the highest System-ID, in the case of ISIS, or Router 402 ID, in the case of OSPFv2 and OSPFv3. For ISIS, the System-ID is 403 described in [ISO10589]. For OSPFv2 and OSPFv3, standard Router 404 ID is described in [RFC2328] and [RFC5340] respectively. 406 A router that is not configured to participate in a particular Flex- 407 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 408 Algorithm. 410 A router that is not participating in a particular Flex-Algorithm is 411 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 412 MUST consider FAD advertisement regardless of the Flex-Algorithm 413 participation of the FAD originator. 415 Any change in the Flex-Algorithm definition may result in temporary 416 disruption of traffic that is forwarded based on such Flex-Algorithm 417 paths. The impact is similar to any other event that requires 418 network-wide convergence. 420 If a node is configured to participate in a particular Flexible- 421 Algorithm, but the selected Flex-Algorithm definition includes 422 calculation-type, metric-type, constraint, flag, or Sub-TLV that is 423 not supported by the node, it MUST stop participating in such 424 Flexible-Algorithm. That implies that it MUST NOT announce 425 participation for such Flexible-Algorithm as specified in Section 10 426 and it MUST remove any forwarding state associated with it. 428 Flex-Algorithm definition is topology independent. It applies to all 429 topologies that a router participates in. 431 6. Sub-TLVs of ISIS FAD Sub-TLV 433 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV 435 The Flexible Algorithm definition can specify 'colors' that are used 436 by the operator to exclude links during the Flex-Algorithm path 437 computation. 439 The ISIS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 440 advertise the exclude rule that is used during the Flex-Algorithm 441 path calculation as specified in Section 12. 443 The ISIS Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub- 444 TLV) is a Sub-TLV of the ISIS FAD Sub-TLV. It has the following 445 format: 447 0 1 2 3 448 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 1 449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 450 | Type | Length | 451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 452 | Extended Admin Group | 453 +- -+ 454 | ... | 455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 456 where: 458 Type: 1 460 Length: variable, dependent on the size of the Extended Admin 461 Group. MUST be a multiple of 4 octets. 463 Extended Administrative Group: Extended Administrative Group as 464 defined in [RFC7308]. 466 The ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD 467 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 468 ignored by the receiver. 470 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV 472 The Flexible Algorithm definition can specify 'colors' that are used 473 by the operator to include links during the Flex-Algorithm path 474 computation. 476 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used 477 to advertise include-any rule that is used during the Flex-Algorithm 478 path calculation as specified in Section 12. 480 The format of the ISIS Flexible Algorithm Include-Any Admin Group 481 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 482 Section 6.1. 484 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 485 2. 487 The ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 488 appear more then once in an ISIS FAD Sub-TLV. If it appears more 489 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 491 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV 493 The Flexible Algorithm definition can specify 'colors' that are used 494 by the operator to include link during the Flex-Algorithm path 495 computation. 497 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used 498 to advertise include-all rule that is used during the Flex-Algorithm 499 path calculation as specified in Section 12. 501 The format of the ISIS Flexible Algorithm Include-All Admin Group 502 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 503 Section 6.1. 505 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 506 3. 508 The ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 509 appear more then once in an ISIS FAD Sub-TLV. If it appears more 510 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 512 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV 514 The ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 515 is a Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 517 0 1 2 3 518 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 1 519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 520 | Type | Length | 521 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 522 | Flags | 523 +- -+ 524 | ... | 525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 526 where: 528 Type: 4 530 Length: variable, non-zero number of octets of the Flags field 532 Flags: 534 0 1 2 3 4 5 6 7... 535 +-+-+-+-+-+-+-+-+... 536 |M| | | ... 537 +-+-+-+-+-+-+-+-+... 539 M-flag: when set, the Flex-Algorithm specific prefix metric 540 MUST be used, if advertised with the prefix. This flag is not 541 applicable to prefixes advertised as SRv6 locators. 543 Bits are defined/sent starting with Bit 0 defined above. Additional 544 bit definitions that may be defined in the future SHOULD be assigned 545 in ascending bit order so as to minimize the number of bits that will 546 need to be transmitted. 548 Undefined bits MUST be transmitted as 0. 550 Bits that are NOT transmitted MUST be treated as if they are set to 0 551 on receipt. 553 The ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD 554 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 555 ignored by the receiver. 557 If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV, 558 all the bits are assumed to be set to 0. 560 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV 562 The Flexible Algorithm definition can specify Shared Risk Link Groups 563 (SRLGs) that the operator wants to exclude during the Flex-Algorithm 564 path computation. 566 The ISIS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used to 567 advertise the exclude rule that is used during the Flex-Algorithm 568 path calculation as specified in Section 12. 570 The ISIS FAESRLG Sub-TLV is a Sub-TLV of the ISIS FAD Sub-TLV. It 571 has the following format: 573 0 1 2 3 574 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 1 575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 576 | Type | Length | 577 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 578 | Shared Risk Link Group Value | 579 +- -+ 580 | ... | 581 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 582 where: 584 Type: 5 586 Length: variable, dependent on number of SRLG values. MUST be a 587 multiple of 4 octets. 589 Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. 591 The ISIS FAESRLG Sub-TLV MAY NOT appear more then once in an ISIS FAD 592 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 593 ignored by the receiver. 595 7. Sub-TLVs of OSPF FAD TLV 597 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 599 The Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is 600 a Sub-TLV of the OSPF FAD TLV. It's usage is described in 601 Section 6.1. It has the following format: 603 0 1 2 3 604 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 1 605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 | Type | Length | 607 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 608 | Extended Admin Group | 609 +- -+ 610 | ... | 611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 612 where: 614 Type: 1 616 Length: variable, dependent on the size of the Extended Admin 617 Group. MUST be a multiple of 4 octets. 619 Extended Administrative Group: Extended Administrative Group as 620 defined in [RFC7308]. 622 The OSPF FAEAG Sub-TLV MAY NOT appear more then once in an OSPF FAD 623 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 624 by the receiver. 626 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 628 The usage of this Sub-TLVs is described in Section 6.2. 630 The format of the OSPF Flexible Algorithm Include-Any Admin Group 631 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 632 Section 7.1. 634 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 635 2. 637 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 638 appear more then once in an OSPF FAD TLV. If it appears more then 639 once, the OSPF FAD TLV MUST be ignored by the receiver. 641 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 643 The usage of this Sub-TLVs is described in Section 6.3. 645 The format of the OSPF Flexible Algorithm Include-Any Admin Group 646 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 647 Section 7.1. 649 The OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 650 3. 652 The OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 653 appear more then once in an OSPF FAD TLV. If it appears more then 654 once, the OSPF FAD TLV MUST be ignored by the receiver. 656 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 658 The OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) 659 is a Sub-TLV of the OSPF FAD TLV. It has the following format: 661 0 1 2 3 662 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 1 663 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 664 | Type | Length | 665 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 666 | Flags | 667 +- -+ 668 | ... | 669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 670 where: 672 Type: 4 674 Length: variable, dependent on the size of the Flags field. MUST 675 be a multiple of 4 octets. 677 Flags: 679 0 1 2 3 4 5 6 7... 680 +-+-+-+-+-+-+-+-+... 681 |M| | | ... 682 +-+-+-+-+-+-+-+-+... 684 M-flag: when set, the Flex-Algorithm specific prefix metric 685 MUST be used, if advertised with the prefix. This flag is not 686 applicable to prefixes advertised as SRv6 locators. 688 Bits are defined/sent starting with Bit 0 defined above. Additional 689 bit definitions that may be defined in the future SHOULD be assigned 690 in ascending bit order so as to minimize the number of bits that will 691 need to be transmitted. 693 Undefined bits MUST be transmitted as 0. 695 Bits that are NOT transmitted MUST be treated as if they are set to 0 696 on receipt. 698 The OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD 699 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 700 by the receiver. 702 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 703 the bits are assumed to be set to 0. 705 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV 707 The OSPF Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG Sub-TLV) is 708 a Sub-TLV of the OSPF FAD TLV. Its usage is described in 709 Section 6.5. It 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 | Shared Risk Link Group Value | 717 +- -+ 718 | ... | 719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 720 where: 722 Type: 5 724 Length: variable, dependent on the number of SRLGs. MUST be a 725 multiple of 4 octets. 727 Shared Risk Link Group Value: SRLG value as defined in [RFC4203]. 729 The OSPF FAESRLG Sub-TLV MAY NOT appear more then once in an OSPF FAD 730 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 731 by the receiver. 733 8. ISIS Flexible Algorithm Prefix Metric Sub-TLV 735 The ISIS Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the 736 advertisement of a Flex-Algorithm specific prefix metric associated 737 with a given prefix advertisement. 739 The ISIS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 and 740 has the following format: 742 0 1 2 3 743 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 1 744 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 745 | Type | Length |Flex-Algorithm | 746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 747 | Metric | 748 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 749 where: 751 Type: 6 752 Length: 5 octets 754 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 756 Metric: 4 octets of metric information 758 The ISIS FAPM Sub-TLV MAY appear multiple times in its parent TLV. 759 If it appears more then once with the same Flex-Algorithm value, the 760 first instance MUST be used and any subsequent instances MUST be 761 ignored. 763 If a prefix is advertised with a Flex-Algorithm prefix metric larger 764 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 765 considered during the Flexible-Algorithm computation. 767 The usage of the Flex-Algorithm prefix metric is described in 768 Section 12. 770 The ISIS FAPM Sub-TLV MUST NOT be advertised as a sub-TLV of the ISIS 771 SRv6 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. The ISIS SRv6 772 Locator TLV includes the Algorithm and Metric fields which MUST be 773 used instead. If the FAPM Sub-TLV is present as a sub-TLV of the 774 ISIS SRv6 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be 775 ignored. 777 9. OSPF Flexible Algorithm Prefix Metric Sub-TLV 779 The OSPF Flexible Algorithm Prefix Metric (FAPM) Sub-TLV supports the 780 advertisement of a Flex-Algorithm specific prefix metric associated 781 with a given prefix advertisement. 783 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLVis a Sub-TLV of 784 the: 786 - OSPFv2 Extended Prefix TLV [RFC7684] 788 - Following OSPFv3 TLVs as defined in [RFC8362]: 790 Intra-Area Prefix TLV 792 Inter-Area Prefix TLV 794 External Prefix TLV 796 OSPF FAPM Sub-TLV has the following format: 798 0 1 2 3 799 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 1 800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 801 | Type | Length | 802 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 803 |Flex-Algorithm | Reserved | 804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 805 | Metric | 806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 808 where: 810 Type: 3 for OSPFv2, 26 for OSPFv3 812 Length: 8 octets 814 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 816 Reserved: Must be set to 0, ignored at reception. 818 Metric: 4 octets of metric information 820 The OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. 821 If it appears more then once with the same Flex-Algorithm value, the 822 first instance MUST be used and any subsequent instances MUST be 823 ignored. 825 The usage of the Flex-Algorithm prefix metric is described in 826 Section 12. 828 10. Advertisement of Node Participation in a Flex-Algorithm 830 When a router is configured to support a particular Flex-Algorithm, 831 we say it is participating in that Flex-Algorithm. 833 Paths computed for a specific Flex-Algorithm MAY be used by various 834 applications, each potentially using its own specific data plane for 835 forwarding traffic over such paths. To guarantee the presence of the 836 application specific forwarding state associated with a particular 837 Flex-Algorithm, a router MUST advertise its participation for a 838 particular Flex-Algorithm for each application specifically. 840 10.1. Advertisement of Node Participation for Segment Routing 842 [RFC8667], [RFC8665], and [RFC8666] (IGP Segment Routing extensions) 843 describe how the SR-Algorithm is used to compute the IGP best path. 845 Routers advertise the support for the SR-Algorithm as a node 846 capability as described in the above mentioned IGP Segment Routing 847 extensions. To advertise participation for a particular Flex- 848 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 849 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 850 (OSPF) or sub-TLV (ISIS). 852 Segment Routing Flex-Algorithm participation advertisement is 853 topology independent. When a router advertises participation in an 854 SR-Algorithm, the participation applies to all topologies in which 855 the advertising node participates. 857 10.2. Advertisement of Node Participation for Other Applications 859 This section describes considerations related to how other 860 applications can advertise their participation in a specific Flex- 861 Algorithm. 863 Application-specific Flex-Algorithm participation advertisements MAY 864 be topology specific or MAY be topology independent, depending on the 865 application itself. 867 Application-specific advertisement for Flex-Algorithm participation 868 MUST be defined for each application and is outside of the scope of 869 this document. 871 11. Advertisement of Link Attributes for Flex-Algorithm 873 Various link attributes may be used during the Flex-Algorithm path 874 calculation. For example, include or exclude rules based on link 875 affinities can be part of the Flex-Algorithm definition as defined in 876 Section 6 and Section 7. 878 Link attribute advertisements that are to be used during Flex- 879 Algorithm calculation MUST use the Application-Specific Link 880 Attribute (ASLA) advertisements defined in [I-D.ietf-isis-te-app] or 881 [I-D.ietf-ospf-te-link-attr-reuse]. In particular, the Min 882 Unidirectional Link Delay, TE Default Metric, Administrative Group, 883 Extended Administrative Group and Shared Risk Link Group TLVs MUST be 884 encoded in the ASLA advertisements for use with FlexAlgo. 886 A new Application Identifier Bit is defined to indicate that the ASLA 887 advertisement is associated with the Flex-Algorithm application. 888 This bit is set in the Standard Application Bit Mask (SABM) defined 889 in [I-D.ietf-isis-te-app] or [I-D.ietf-ospf-te-link-attr-reuse]: 891 Bit-3: Flexible Algorithm (X-bit) 893 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 894 Application MAY use either the Administrative Group or Extended 895 Administrative Group encodings. If the Administrative Group encoding 896 is used, then the first 32 bits of the corresponding FAD sub-TLVs are 897 mapped to the link attribute advertisements as specified in RFC 7308. 899 12. Calculation of Flexible Algorithm Paths 901 A router MUST be configured to participate in a given Flex-Algorithm 902 K and MUST select the FAD based on the rules defined in Section 5.3 903 before it can compute any path for that Flex-Algorithm. 905 As described in Section 10, participation for any particular Flex- 906 Algorithm MUST be advertised on a per-application basis. Calculation 907 of the paths for any particular Flex-Algorithm MUST be application 908 specific. 910 The way applications handle nodes that do not participate in 911 Flexible-Algorithm is application specific. If the application only 912 wants to consider participating nodes during the Flex-Algorithm 913 calculation, then when computing paths for a given Flex-Algorithm, 914 all nodes that do not advertise participation for that Flex-Algorithm 915 in their application-specific advertisements MUST be pruned from the 916 topology. Segment Routing, including both SR MPLS and SRv6, are 917 applications that MUST use such pruning when computing Flex-Algorithm 918 paths. 920 When computing the path for a given Flex-Algorithm, the metric-type 921 that is part of the Flex-Algorithm definition (Section 5) MUST be 922 used. 924 When computing the path for a given Flex-Algorithm, the calculation- 925 type that is part of the Flex-Algorithm definition (Section 5) MUST 926 be used. 928 Various link include or exclude rules can be part of the Flex- 929 Algorithm definition. To refer to a particular bit within an AG or 930 EAG we uses term 'color'. 932 Rules, in the order as specified below, MUST be used to prune links 933 from the topology during the Flex-Algorithm computation. 935 For all links in the topology: 937 1. Check if any exclude rule is part of the Flex-Algorithm 938 definition. If such exclude rule exists, check if any color that 939 is part of the exclude rule is also set on the link. If such a 940 color is set, the link MUST be pruned from the computation. 942 2. Check if any exclude SRLG rule is part of the Flex-Algorithm 943 definition. If such exclude rule exists, check if the link is 944 part of any SRLG that is also part of the SRLG exclude rule. If 945 the link is part of such SRLG, the link MUST be pruned from the 946 computation. 948 3. Check if any include-any rule is part of the Flex-Algorithm 949 definition. If such include-any rule exists, check if any color 950 that is part of the include-any rule is also set on the link. If 951 no such color is set, the link MUST be pruned from the 952 computation. 954 4. Check if any include-all rule is part of the Flex-Algorithm 955 definition. If such include-all rule exists, check if all colors 956 that are part of the include-all rule are also set on the link. 957 If all such colors are not set on the link, the link MUST be 958 pruned from the computation. 960 5. If the Flex-Algorithm definition uses other than IGP metric 961 (Section 5), and such metric is not advertised for the particular 962 link in a topology for which the computation is done, such link 963 MUST be pruned from the computation. A metric of value 0 MUST NOT 964 be assumed in such case. 966 12.1. Multi-area and Multi-domain Considerations 968 Any IGP Shortest Path Tree calculation is limited to a single area. 969 This applies to Flex-Algorithm calculations as well. Given that the 970 computing router does not have visibility of the topology of the next 971 areas or domain, the Flex-Algorithm specific path to an inter-area or 972 inter-domain prefix will be computed for the local area only. The 973 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 974 will be selected based on the best path for the given Flex-Algorithm 975 in the local area and such egress ABR or ASBR router will be 976 responsible to compute the best Flex-Algorithm specific path over the 977 next area or domain. This may produce an end-to-end path, which is 978 sub-optimal based on Flex-Algorithm constraints. In cases where the 979 ABR or ASBR has no reachability to a prefix for a given Flex- 980 Algorithm in the next area or domain, the traffic may be dropped by 981 the ABR/ASBR. 983 To allow the optimal end-to-end path for an inter-area or inter- 984 domain prefix for any Flex-Algorithm to be computed, the FAPM has 985 been defined in Section 8 and Section 9. 987 If the FAD selected based on the rules defined in Section 5.3 988 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 989 Section 9) when advertising the prefix between areas or domains. 991 Such metric will be equal to the metric to reach the prefix for a 992 given Flex-Algorithm in a source area or domain. This is similar in 993 nature to how the metric is set when prefixes are advertised between 994 areas or domains for the default algorithm. 996 If the FAD selected based on the rules defined in Section 5.3 997 includes the M-flag, the FAPM MUST be used during calculation of 998 prefix reachability for the inter-area and external prefixes. If the 999 FAPM for the Flex-Algorithm is not advertised with the inter-area or 1000 external prefix reachability advertisement, the prefix MUST be 1001 considered as unreachable for that Flex-Algorithm. 1003 Flex-Algorithm prefix metrics MUST NOT be used during the Flex- 1004 Algorithm computation unless the FAD selected based on the rules 1005 defined in Section 5.3 includes the M-Flag, as described in 1006 (Section 6.4 or Section 7.4). 1008 If the FAD selected based on the rules defined in Section 5.3 does 1009 not includes the M-flag, it is NOT RECOMMENDED to use the Flex- 1010 Algorithm for inter-area or inter-domain prefix reachability. The 1011 reason is that without the explicit Flex-Algorithm Prefix Metric 1012 advertisement, it is not possible to conclude whether the ABR or ASBR 1013 has reachability to the inter-area or inter-domain prefix for a given 1014 Flex-Algorithm in the next area or domain. Sending the Flex-Algoritm 1015 traffic for such prefix towards the ABR or ASBR may result in traffic 1016 looping or black-holing. 1018 The FAPM MUST NOT be advertised with ISIS L1 or L2 intra-area, OSPFv2 1019 intra-area, or OSPFv3 intra-area routes. If the FAPM is advertised 1020 for these route-types, it MUST be ignored during the prefix 1021 reachability calculation. 1023 The M-flag in FAD is not applicable to prefixes advertised as SRv6 1024 locators. The ISIS SRv6 Locator TLV includes the Algorithm and 1025 Metric fields [I-D.ietf-lsr-isis-srv6-extensions]. When the ISIS 1026 SRv6 Locator is advertised between areas or domains, the metric field 1027 in the Locator TLV MUST be used irrespective of the M-flag in the FAD 1028 advertisement. 1030 13. Flex-Algorithm and Forwarding Plane 1032 This section describes how Flex-Algorithm paths are used in 1033 forwarding. 1035 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm 1037 This section describes how Flex-Algorithm paths are used with SR MPLS 1038 forwarding. 1040 Prefix SID advertisements include an SR-Algorithm value and, as such, 1041 are associated with the specified SR-Algorithm. Prefix-SIDs are also 1042 associated with a specific topology which is inherited from the 1043 associated prefix reachability advertisement. When the algorithm 1044 value advertised is a Flex-Algorithm value, the Prefix SID is 1045 associated with paths calculated using that Flex-Algorithm in the 1046 associated topology. 1048 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 1049 using the MPLS label that corresponds to the Prefix-SID that was 1050 advertised for that Flex-algorithm. If the Prefix SID for a given 1051 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 1052 be installed in the MPLS forwarding plane. 1054 Traffic that is supposed to be routed via Flex-Algorithm specific 1055 paths, MUST be dropped when there are no such paths available. 1057 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 1058 computed using the same constraints as the calculation of the primary 1059 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 1060 advertised specifically for the given algorithm. LFA paths MUST NOT 1061 use an Adjacency-SID that belongs to a link that has been pruned from 1062 the Flex-Algorithm computation. 1064 If LFA protection is being used to protect a given Flex-Algorithm 1065 paths, all routers in the area participating in the given Flex- 1066 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 1067 SID. These Node-SIDs are used to steer traffic over the LFA computed 1068 backup path. 1070 13.2. SRv6 Forwarding for Flex-Algorithm 1072 This section describes how Flex-Algorithm paths are used with SRv6 1073 forwarding. 1075 In SRv6 a node is provisioned with topology/algorithm specific 1076 locators for each of the topology/algorithm pairs supported by that 1077 node. Each locator is an aggregate prefix for all SIDs provisioned 1078 on that node which have the matching topology/algorithm. 1080 The SRv6 locator advertisement in IGPs 1081 ([I-D.ietf-lsr-isis-srv6-extensions] 1082 [I-D.ietf-lsr-ospfv3-srv6-extensions]) includes the MTID value that 1083 associates the locator with a specific topology. SRv6 locator 1084 advertisements also includes an Algorithm value that explicitly 1085 associates the locator with a specific algorithm. When the algorithm 1086 value advertised with a locator represents a Flex-Algorithm, the 1087 paths to the locator prefix MUST be calculated using the specified 1088 Flex-Algorithm in the associated topology. 1090 Forwarding entries for the locator prefixes advertised in IGPs MUST 1091 be installed in the forwarding plane of the receiving SRv6 capable 1092 routers when the associated topology/algorithm is participating in 1093 them. Forwarding entries for locators associated with Flex- 1094 Algorithms in which the node is not participating MUST NOT be 1095 installed in the forwarding palne. 1097 When the locator is associated with a Flex-Algorithm, LFA paths to 1098 the locator prefix MUST be calculated using such Flex-Algorithm in 1099 the associated topology, to guarantee that they follow the same 1100 constraints as the calculation of the primary paths. LFA paths MUST 1101 only use SRv6 SIDs advertised specifically for the given Flex- 1102 Algorithm. 1104 If LFA protection is being used to protect locators associated with a 1105 given Flex-Algorithm, all routers in the area participating in the 1106 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1107 specific locator and END SID per node and one END.X SID for every 1108 link that has not been pruned from such Flex-Algorithm computation. 1109 These locators and SIDs are used to steer traffic over the LFA- 1110 computed backup path. 1112 13.3. Other Applications' Forwarding for Flex-Algorithm 1114 Any application that wants to use Flex-Algorithm specific forwarding 1115 needs to install some form of Flex-Algorithm specific forwarding 1116 entries. 1118 Application-specific forwarding for Flex-Algorithm MUST be defined 1119 for each application and is outside of the scope of this document. 1121 14. Operational considerations 1123 14.1. Inter-area Considerations 1125 The scope of the FA computation is an area, so is the scope of the 1126 FAD. In ISIS, the Router Capability TLV in which the FAD Sub-TLV is 1127 advertised MUST have the S-bit clear, which prevents it to be flooded 1128 outside of the level in which it was originated. Even though in OSPF 1129 the FAD Sub-TLV can be flooded in an RI LSA that has AS flooding 1130 scope, the FAD selection is performed for each individual area in 1131 which it is being used. 1133 There is no requirement for the FAD for a particular Flex-Algorithm 1134 to be identical in all areas in the network. For example, traffic 1135 for the same Flex-Algorithm may be optimized for minimal delay (e.g., 1136 using delay metric) in one area or level, while being optimized for 1137 available bandwidth (e.g., using IGP metric) in another area or 1138 level. 1140 As described in Section 5.1, ISIS allows the re-generation of the 1141 winning FAD from level 2, without any modification to it, into a 1142 level 1 area. This allows the operator to configure the FAD in one 1143 or multiple routers in the level 2, without the need to repeat the 1144 same task in each level 1 area, if the intent is to have the same FAD 1145 for the particular Flex-Algorithm across all levels. This can 1146 similarly be achieved in OSPF by using the AS flooding scope of the 1147 RI LSA in which the FAD Sub-TLV for the particular Flex-Algoritm is 1148 advertised. 1150 Re-generation of FAD from a level 1 area to the level 2 area is not 1151 supported in ISIS, so if the intent is to regenerate the FAD between 1152 ISIS levels, the FAD MUST be defined on router(s) that are in level 1153 2. In OSPF, the FAD definition can be done in any area and be 1154 propagated to all routers in the OSPF routing domain by using the AS 1155 flooding scope of the RI LSA. 1157 14.2. Usage of SRLG Exclude Rule with Flex-Algorithm 1159 There are two different ways in which SRLG information can be used 1160 with Flex-Algorithm: 1162 In a context of a single Flex-Algorithm, it can be used for 1163 computation of backup paths, as described in 1164 [I-D.ietf-rtgwg-segment-routing-ti-lfa]. This usage does not 1165 require association of any specific SRLG constraint with the given 1166 Flex-Algorithm definition. 1168 In the context of multiple Flex-Algorithms, it can be used for 1169 creating disjoint sets of paths by pruning the links belonging to 1170 a specific SRLG from the topology on which a specific Flex- 1171 Algorithm computes its paths. This usage: 1173 Facilitates the usage of already deployed SRLG configurations 1174 for setup of disjoint paths between two or more Flex- 1175 Algorithms. 1177 Requires explicit association of a given Flex-Algorithm with a 1178 specific set of SRLG constraints as defined in Section 6.5 and 1179 Section 7.5. 1181 The two usages mentioned above are orthogonal. 1183 14.3. Max-metric consideration 1185 Both ISIS and OSPF have a mechanism to set the IGP metric on a link 1186 to a value that would make the link either non-reachable or to serve 1187 as the link of last resort. Similar functionality would be needed 1188 for the Min Unidirectional Link Delay and TE metric, as these can be 1189 used to compute Flex-Algorithm paths. 1191 The link can be made un-reachable for all Flex-Algorithms that use 1192 Min Unidirectional Link Delay as metric, as described in Section 5.1, 1193 by removing the Flex-Algorithm ASLA Min Unidirectional Link Delay 1194 advertisement for the link. The link can be made the link of last 1195 resort by setting the delay value in the Flex-Algorithm ASLA delay 1196 advertisement for the link to the value of 16,777,215 (2^24 - 1). 1198 The link can be made un-reachable for all Flex-Algorithms that use TE 1199 metric, as described in Section 5.1, by removing the Flex-Algorithm 1200 ASLA TE metric advertisement for the link. The link can be made the 1201 link of last resort by setting the TE metric value in the Flex- 1202 Algorithm ASLA delay advertisement for the link to the value of (2^24 1203 - 1) in ISIS and (2^32 - 1) in OSPF. 1205 15. Backward Compatibility 1207 This extension brings no new backward compatibility issues. 1209 16. Security Considerations 1211 This draft adds two new ways to disrupt IGP networks: 1213 An attacker can hijack a particular Flex-Algorithm by advertising 1214 a FAD with a priority of 255 (or any priority higher than that of 1215 the legitimate nodes). 1217 An attacker could make it look like a router supports a particular 1218 Flex-Algorithm when it actually doesn't, or vice versa. 1220 Both of these attacks can be addressed by the existing security 1221 extensions as described in [RFC5304] and [RFC5310] for ISIS, in 1222 [RFC2328] and [RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] 1223 for OSPFv3. 1225 17. IANA Considerations 1227 17.1. IGP IANA Considerations 1229 17.1.1. IGP Algorithm Types Registry 1231 This document makes the following registrations in the "IGP Algorithm 1232 Types" registry: 1234 Type: 128-255. 1236 Description: Flexible Algorithms. 1238 Reference: This document (Section 4). 1240 17.1.2. IGP Metric-Type Registry 1242 IANA is requested to set up a registry called "IGP Metric-Type 1243 Registry" under a "Interior Gateway Protocol (IGP) Parameters" IANA 1244 registries. The registration policy for this registry is "Standards 1245 Action" ([RFC8126] and [RFC7120]). 1247 Values in this registry come from the range 0-255. 1249 This document registers following values in the "IGP Metric-Type 1250 Registry": 1252 Type: 0 1254 Description: IGP metric 1256 Reference: This document (Section 5.1) 1258 Type: 1 1260 Description: Min Unidirectional Link Delay [RFC8570] 1262 Reference: This document (Section 5.1) 1264 Type: 2 1266 Description: TE Default Metric [RFC5305] 1268 Reference: This document (Section 5.1) 1270 17.2. Flexible Algorithm Definition Flags Registry 1272 IANA is requested to set up a registry called "ISIS Flexible 1273 Algorithm Definition Flags Registry" under a "Interior Gateway 1274 Protocol (IGP) Parameters" IANA registries. The registration policy 1275 for this registry is "Standards Action" ([RFC8126] and [RFC7120]). 1277 This document defines the following single bit in Flexible Algorithm 1278 Definition Flags registry: 1280 Bit # Name 1281 ----- ------------------------------ 1282 0 Prefix Metric Flag (M-flag) 1284 Reference: This document (Section 6.4, Section 7.4). 1286 17.3. ISIS IANA Considerations 1288 17.3.1. Sub TLVs for Type 242 1290 This document makes the following registrations in the "sub-TLVs for 1291 TLV 242" registry. 1293 Type: 26. 1295 Description: Flexible Algorithm Definition. 1297 Reference: This document (Section 5.1). 1299 17.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1301 This document makes the following registrations in the "Sub-TLVs for 1302 for TLVs 135, 235, 236, and 237" registry. 1304 Type: 6 1306 Description: Flexible Algorithm Prefix Metric. 1308 Reference: This document (Section 8). 1310 17.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1312 This document creates the following Sub-Sub-TLV Registry: 1314 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1316 Registration Procedure: Expert review 1317 Reference: This document (Section 5.1) 1319 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1320 for Flexible Algorithm Definition Sub-TLV" registry: 1322 Type: 1 1324 Description: Flexible Algorithm Exclude Admin Group 1326 Reference: This document (Section 6.1). 1328 Type: 2 1330 Description: Flexible Algorithm Include-Any Admin Group 1332 Reference: This document (Section 6.2). 1334 Type: 3 1336 Description: Flexible Algorithm Include-All Admin Group 1338 Reference: This document (Section 6.3). 1340 Type: 4 1342 Description: Flexible Algorithm Definition Flags 1344 Reference: This document (Section 6.4). 1346 Type: 5 1348 Description: Flexible Algorithm Exclude SRLG 1350 Reference: This document (Section 6.5). 1352 17.4. OSPF IANA Considerations 1354 17.4.1. OSPF Router Information (RI) TLVs Registry 1356 This specification updates the OSPF Router Information (RI) TLVs 1357 Registry. 1359 Type: 16 1361 Description: Flexible Algorithm Definition TLV. 1363 Reference: This document (Section 5.2). 1365 17.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1367 This document makes the following registrations in the "OSPFv2 1368 Extended Prefix TLV Sub-TLVs" registry. 1370 Type: 3 1372 Description: Flexible Algorithm Prefix Metric. 1374 Reference: This document (Section 9). 1376 17.4.3. OSPFv3 Extended-LSA Sub-TLVs 1378 This document makes the following registrations in the "OSPFv3 1379 Extended-LSA Sub-TLVs" registry. 1381 Type: 26 1383 Description: Flexible Algorithm Prefix Metric. 1385 Reference: This document (Section 9). 1387 17.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1389 This document creates the following registry: 1391 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1393 Registration Procedure: Expert review 1395 Reference: This document (Section 5.2) 1397 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1398 define sub-TLVs at any level of nesting for the Flexible Algorithm 1399 TLV and should be added to the "Open Shortest Path First (OSPF) 1400 Parameters" registries group. New values can be allocated via IETF 1401 Review or IESG Approval. 1403 This document registers following Sub-TLVs in the "TLVs for Flexible 1404 Algorithm Definition TLV" registry: 1406 Type: 1 1408 Description: Flexible Algorithm Exclude Admin Group 1410 Reference: This document (Section 7.1). 1412 Type: 2 1413 Description: Flexible Algorithm Include-Any Admin Group 1415 Reference: This document (Section 7.2). 1417 Type: 3 1419 Description: Flexible Algorithm Include-All Admin Group 1421 Reference: This document (Section 7.3). 1423 Type: 4 1425 Description: Flexible Algorithm Definition Flags 1427 Reference: This document (Section 7.4). 1429 Type: 5 1431 Description: Flexible Algorithm Exclude SRLG 1433 Reference: This document (Section 7.5). 1435 Types in the range 32768-33023 are for experimental use; these will 1436 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1438 Types in the range 33024-65535 are not to be assigned at this time. 1439 Before any assignments can be made in the 33024-65535 range, there 1440 MUST be an IETF specification that specifies IANA Considerations that 1441 covers the range being assigned. 1443 17.4.5. Link Attribute Applications Registry 1445 This document registers following bit in the Link Attribute 1446 Applications Registry: 1448 Bit-3 1450 Description: Flexible Algorithm (X-bit) 1452 Reference: This document (Section 11). 1454 18. Acknowledgements 1456 This draft, among other things, is also addressing the problem that 1457 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1458 All authors of that draft agreed to join this draft. 1460 Thanks to Eric Rosen, Tony Przygienda for their detailed review and 1461 excellent comments. 1463 Thanks to Cengiz Halit for his review and feedback during initial 1464 phase of the solution definition. 1466 Thanks to Kenji Kumaki for his comments. 1468 Thanks to William Britto A J. for his suggestions. 1470 Thanks to Acee Lindem for editorial comments. 1472 19. References 1474 19.1. Normative References 1476 [BCP14] , . 1478 [I-D.ietf-isis-te-app] 1479 Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1480 J. Drake, "IS-IS Application-Specific Link Attributes", 1481 draft-ietf-isis-te-app-19 (work in progress), June 2020. 1483 [I-D.ietf-lsr-isis-srv6-extensions] 1484 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1485 Z. Hu, "IS-IS Extension to Support Segment Routing over 1486 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08 1487 (work in progress), April 2020. 1489 [I-D.ietf-lsr-ospf-reverse-metric] 1490 Talaulikar, K., Psenak, P., and H. Johnston, "OSPF Reverse 1491 Metric", draft-ietf-lsr-ospf-reverse-metric-01 (work in 1492 progress), June 2020. 1494 [I-D.ietf-lsr-ospfv3-srv6-extensions] 1495 Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, 1496 "OSPFv3 Extensions for SRv6", draft-ietf-lsr- 1497 ospfv3-srv6-extensions-00 (work in progress), February 1498 2020. 1500 [I-D.ietf-ospf-te-link-attr-reuse] 1501 Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J., 1502 and J. Drake, "OSPF Application-Specific Link Attributes", 1503 draft-ietf-ospf-te-link-attr-reuse-16 (work in progress), 1504 June 2020. 1506 [ISO10589] 1507 International Organization for Standardization, 1508 "Intermediate system to Intermediate system intra-domain 1509 routeing information exchange protocol for use in 1510 conjunction with the protocol for providing the 1511 connectionless-mode Network Service (ISO 8473)", ISO/ 1512 IEC 10589:2002, Second Edition, Nov 2002. 1514 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1515 Requirement Levels", BCP 14, RFC 2119, 1516 DOI 10.17487/RFC2119, March 1997, 1517 . 1519 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 1520 Support of Generalized Multi-Protocol Label Switching 1521 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 1522 . 1524 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1525 in Support of Generalized Multi-Protocol Label Switching 1526 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1527 . 1529 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1530 Traffic Engineering (MPLS-TE)", RFC 7308, 1531 DOI 10.17487/RFC7308, July 2014, 1532 . 1534 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1535 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1536 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1537 2015, . 1539 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1540 S. Shaffer, "Extensions to OSPF for Advertising Optional 1541 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1542 February 2016, . 1544 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1545 for Advertising Router Information", RFC 7981, 1546 DOI 10.17487/RFC7981, October 2016, 1547 . 1549 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1550 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1551 May 2017, . 1553 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1554 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1555 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1556 2018, . 1558 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 1559 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1560 Extensions for Segment Routing", RFC 8665, 1561 DOI 10.17487/RFC8665, December 2019, 1562 . 1564 [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 1565 for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 1566 December 2019, . 1568 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 1569 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 1570 Extensions for Segment Routing", RFC 8667, 1571 DOI 10.17487/RFC8667, December 2019, 1572 . 1574 19.2. Informative References 1576 [I-D.gulkohegde-routing-planes-using-sr] 1577 Hegde, S. and a. arkadiy.gulko@thomsonreuters.com, 1578 "Separating Routing Planes using Segment Routing", draft- 1579 gulkohegde-routing-planes-using-sr-00 (work in progress), 1580 March 2017. 1582 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 1583 Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B., 1584 Francois, P., Voyer, D., Clad, F., and P. Camarillo, 1585 "Topology Independent Fast Reroute using Segment Routing", 1586 draft-ietf-rtgwg-segment-routing-ti-lfa-03 (work in 1587 progress), March 2020. 1589 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 1590 DOI 10.17487/RFC2328, April 1998, 1591 . 1593 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 1594 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 1595 RFC 3906, DOI 10.17487/RFC3906, October 2004, 1596 . 1598 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 1599 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 1600 . 1602 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1603 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1604 2008, . 1606 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 1607 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 1608 2008, . 1610 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 1611 and M. Fanto, "IS-IS Generic Cryptographic 1612 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 1613 2009, . 1615 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 1616 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 1617 . 1619 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 1620 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 1621 2014, . 1623 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 1624 "Security Extension for OSPFv2 When Using Manual Key 1625 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 1626 . 1628 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1629 Writing an IANA Considerations Section in RFCs", BCP 26, 1630 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1631 . 1633 [RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward, 1634 D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) 1635 Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March 1636 2019, . 1638 Authors' Addresses 1640 Peter Psenak (editor) 1641 Cisco Systems 1642 Apollo Business Center 1643 Mlynske nivy 43 1644 Bratislava, 82109 1645 Slovakia 1647 Email: ppsenak@cisco.com 1648 Shraddha Hegde 1649 Juniper Networks, Inc. 1650 Embassy Business Park 1651 Bangalore, KA, 560093 1652 India 1654 Email: shraddha@juniper.net 1656 Clarence Filsfils 1657 Cisco Systems, Inc. 1658 Brussels 1659 Belgium 1661 Email: cfilsfil@cisco.com 1663 Ketan Talaulikar 1664 Cisco Systems, Inc. 1665 S.No. 154/6, Phase I, Hinjawadi 1666 PUNE, MAHARASHTRA 411 057 1667 India 1669 Email: ketant@cisco.com 1671 Arkadiy Gulko 1672 Refinitiv 1674 Email: arkadiy.gulko@refinitiv.com