idnits 2.17.1 draft-ietf-lsr-flex-algo-08.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 (July 10, 2020) is 1385 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 1473, 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 -- Obsolete informational reference (is this intentional?): RFC 7810 (Obsoleted by RFC 8570) Summary: 1 error (**), 0 flaws (~~), 17 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: January 11, 2021 Juniper Networks, Inc. 6 C. Filsfils 7 K. Talaulikar 8 Cisco Systems, Inc. 9 A. Gulko 10 Refinitiv 11 July 10, 2020 13 IGP Flexible Algorithm 14 draft-ietf-lsr-flex-algo-08.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 January 11, 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 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. 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 . . . . . . . . . . . . . . . . . . . . . 26 102 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. Flex-Algorithm Definition Flags Registry . . . . . . . . 27 106 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 send 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 152 combination 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 - 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 provisioning 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 exist. 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 [RFC7810]. 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 it's 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) a 222 set of constraints is referred to as a Flexible-Algorithm Definition. 224 Flexible-Algorithm is a numeric identifier in the range 128-255 that 225 is associated via provisioning with the Flexible-Algorithm 226 Definition. 228 IANA "IGP Algorithm Types" registry defines the set of values for IGP 229 Algorithms. We propose to allocate the following values for Flex- 230 Algorithms from this registry: 232 128-255 - Flex-Algorithms 234 5. Flexible Algorithm Definition Advertisement 236 To guarantee the loop free forwarding for paths computed for a 237 particular Flex-Algorithm, all routers that (a) are configured to 238 participate in a particular Flex-Algorithm, and (b) are in the same 239 Flex-Algorithm definition advertisement scope MUST agree on the 240 definition of the Flex-Algorithm. 242 5.1. ISIS Flexible Algorithm Definition Sub-TLV 244 ISIS Flexible Algorithm Definition Sub-TLV (FAD Sub-TLV) is used to 245 advertise the definition of the Flex-Algorithm. 247 ISIS FAD Sub-TLV is advertised as a Sub-TLV of the ISIS Router 248 Capability TLV-242 that is defined in [RFC7981]. 250 ISIS FAD Sub-TLV has the following format: 252 0 1 2 3 253 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 1 254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 | Type | Length |Flex-Algorithm | Metric-Type | 256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 257 | Calc-Type | Priority | 258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 259 | Sub-TLVs | 260 + + 261 | ... | 263 | | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 where: 268 Type: 26 270 Length: variable, dependent on the included Sub-TLVs 272 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 274 Metric-Type: Type of metric to be used during the calculation. 275 Following values are defined: 277 0: IGP Metric 279 1: Min Unidirectional Link Delay as defined in [RFC7810]. 281 2: TE default metric as defined in [RFC5305]. 283 Calc-Type: value from 0 to 127 inclusive from the "IGP Algorithm 284 Types" registry defined under "Interior Gateway Protocol (IGP) 285 Parameters" IANA registries. IGP algorithms in the range of 0-127 286 have a defined triplet (Calculation Type, Metric, Constraints). 287 When used to specify the Calc-Type in the FAD Sub-TLV, only the 288 Calculation Type defined for the specified IGP Algorithm is used. 289 The Metric/Constraints MUST NOT be inherited. If the required 290 calculation type is Shortest Path First, the value 0 SHOULD appear 291 in this field. 293 Priority: Value between 0 and 255 inclusive that specifies the 294 priority of the advertisement. 296 Sub-TLVs - optional sub-TLVs. 298 The ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a 299 router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given 300 Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs 301 for a given Flexible-Algorithm from the same originator SHOULD select 302 the first advertisement in the lowest numbered LSP. 304 The ISIS FAD Sub-TLV has an area scope. The Router Capability TLV in 305 which the FAD Sub-TLV is present MUST have the S-bit clear. 307 ISIS L1/L2 router MAY be configured to re-generate the winning FAD 308 from level 2, without any modification to it, to level 1 area. The 309 re-generation of the FAD Sub-TLV from level 2 to level 1 is 310 determined by the L1/L2 router, not by the originator of the FAD 311 advertisement in the level 2. In such case, the re-generated FAD 312 Sub-TLV will be advertised in the level 1 Router Capability TLV 313 originated by the L1/L2 router. 315 L1/L2 router MUST NOT re-generate any FAD Sub-TLV from level 1 to 316 level 2. 318 5.2. OSPF Flexible Algorithm Definition TLV 320 OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is 321 defined in [RFC7770]. 323 OSPF FAD TLV has the following format: 325 0 1 2 3 326 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 1 327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 328 | Type | Length | 329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 330 |Flex-Algorithm | Metric-Type | Calc-Type | Priority | 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 | Sub-TLVs | 333 + + 334 | ... | 336 | | 337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 339 where: 341 Type: 16 343 Length: variable, dependent on the included Sub-TLVs 345 Flex-Algorithm:: Flex-Algorithm number. Value between 128 and 255 346 inclusive. 348 Metric-Type: as described in Section 5.1 350 Calc-Type: as described in Section 5.1 352 Priority: as described in Section 5.1 354 Sub-TLVs - optional sub-TLVs. 356 When multiple OSPF FAD TLVs, for the same Flexible-Algorithm, are 357 received from a given router, the receiver MUST use the first 358 occurrence of the TLV in the Router Information LSA. If the OSPF FAD 359 TLV, for the same Flex-Algorithm, appears in multiple Router 360 Information LSAs that have different flooding scopes, the OSPF FAD 361 TLV in the Router Information LSA with the area-scoped flooding scope 362 MUST be used. If the OSPF FAD TLV, for the same algorithm, appears 363 in multiple Router Information LSAs that have the same flooding 364 scope, the OSPF FAD TLV in the Router Information (RI) LSA with the 365 numerically smallest Instance ID MUST be used and subsequent 366 instances of the OSPF FAD TLV MUST be ignored. 368 The RI LSA can be advertised at any of the defined opaque flooding 369 scopes (link, area, or Autonomous System (AS)). For the purpose of 370 OSPF FAD TLV advertisement, area-scoped flooding is REQUIRED. The 371 Autonomous System flooding scope SHOULD not be used by default unless 372 local configuration policy on the originating router indicates domain 373 wide flooding. 375 5.3. Common Handling of Flexible Algorithm Definition TLV 377 This section describes the protocol independent handling of the FAD 378 TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in 379 this section, even though in case of ISIS it is a Sub-TLV. 381 The value of the Flex-Algorithm MUST be between 128 and 255 382 inclusive. If it is not, the FAD TLV MUST be ignored. 384 Only a subset of the routers participating in the particular Flex- 385 Algorithm need to advertise the definition of the Flex-Algorithm. 387 Every router, that is configured to participate in a particular Flex- 388 Algorithm, MUST select the Flex-Algorithm definition based on the 389 following ordered rules. This allows for the consistent Flex- 390 Algorithm definition selection in cases where different routers 391 advertise different definitions for a given Flex-Algorithm: 393 1. From the advertisements of the FAD in the area (including both 394 locally generated advertisements and received advertisements) 395 select the one(s) with the highest priority value. 397 2. If there are multiple advertisements of the FAD with the same 398 highest priority, select the one that is originated from the 399 router with the highest System-ID in case of ISIS or Router ID in 400 case of OSPFv2 and OSPFv3. For ISIS the System-ID is described in 401 [ISO10589]. For OSPFv2 and OSPFv3 standard Router ID is described 402 in [RFC2328] and [RFC5340] respectively. 404 A router that is not configured to participate in a particular Flex- 405 Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- 406 Algorithm. 408 A router that is not participating in a particular Flex-Algorithm is 409 allowed to advertise FAD for such Flex-Algorithm. Receiving routers 410 MUST consider FAD advertisement regardless of the Flex-Algorithm 411 participation of the FAD originator. 413 Any change in the Flex-Algorithm definition may result in temporary 414 disruption of traffic that is forwarded based on such Flex-Algorithm 415 paths. The impact is similar to any other event that requires 416 network wide convergence. 418 If a node is configured to participate in a particular Flexible- 419 Algorithm, but the selected Flex-Algorithm definition includes 420 calculation-type, metric-type, constraint, flag or Sub-TLV that is 421 not supported by the node, it MUST stop participating in such 422 Flexible-Algorithm. That implies that it MUST NOT announce 423 participation for such Flexible-Algorithm as specified in Section 10 424 and it MUST remove any forwarding state associated with it. 426 Flex-Algorithm definition is topology independent. It applies to all 427 topologies that a router participates in. 429 6. Sub-TLVs of ISIS FAD Sub-TLV 431 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV 433 The Flexible-Algorithm definition can specify 'colors' that are used 434 by the operator to exclude links during the Flex-Algorithm path 435 computation. 437 ISIS Flexible Algorithm Exclude Admin Group Sub-TLV is used to 438 advertise the exclude rule that is used during the Flex-Algorithm 439 path calculation as specified in Section 12. 441 Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a 442 Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 444 0 1 2 3 445 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 1 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 | Type | Length | 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 | Extended Admin Group | 450 +- -+ 451 | ... | 452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 453 where: 455 Type: 1 457 Length: variable, dependent on the size of the Extended Admin 458 Group. MUST be a multiple of 4 octets. 460 Extended Administrative Group: Extended Administrative Group as 461 defined in [RFC7308]. 463 ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- 464 TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 465 ignored by the receiver. 467 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV 469 The Flexible-Algorithm definition can specify 'colors' that are used 470 by the operator to include links during the Flex-Algorithm path 471 computation. 473 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used to 474 advertise include-any rule that is used during the Flex-Algorithm 475 path calculation as specified in Section 12. 477 The format of the ISIS Flexible Algorithm Include-Any Admin Group 478 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 479 Section 6.1. 481 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. 483 ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 484 appear more then once in an ISIS FAD Sub-TLV. If it appears more 485 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 487 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV 489 The Flexible-Algorithm definition can specify 'colors' that are used 490 by the operator to include link during the Flex-Algorithm path 491 computation. 493 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used to 494 advertise include-all rule that is used during the Flex-Algorithm 495 path calculation as specified in Section 12. 497 The format of the ISIS Flexible Algorithm Include-All Admin Group 498 Sub-TLV is identical to the format of the FAEAG Sub-TLV in 499 Section 6.1. 501 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 3. 503 ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 504 appear more then once in an ISIS FAD Sub-TLV. If it appears more 505 then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. 507 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV 509 ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a 510 Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: 512 0 1 2 3 513 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 1 514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 515 | Type | Length | 516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 517 | Flags | 518 +- -+ 519 | ... | 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 where: 523 Type: 4 525 Length: variable, non-zero number of octets of the Flags field 527 Flags: 529 0 1 2 3 4 5 6 7... 530 +-+-+-+-+-+-+-+-+... 531 |M| | | ... 532 +-+-+-+-+-+-+-+-+... 534 M-flag: when set, Flex-Algorithm specific prefix metric MUST be 535 used, if advertised with the prefix. This flag is not 536 applicable to prefixes advertised as SRv6 locators. 538 Bits are defined/sent starting with Bit 0 defined above. Additional 539 bit definitions that may be defined in the future SHOULD be assigned 540 in ascending bit order so as to minimize the number of bits that will 541 need to be transmitted. 543 Undefined bits MUST be transmitted as 0. 545 Bits that are NOT transmitted MUST be treated as if they are set to 0 546 on receipt. 548 ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- 549 TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 550 ignored by the receiver. 552 If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV, 553 all the bits are assumed to be set to 0. 555 6.5. ISIS Flexible Algorithm Exclude SRLG Sub-TLV 557 The Flexible-Algorithm definition can specify Shared Risk Link Groups 558 (SRLGs) that the operator wants to exclude during the Flex-Algorithm 559 path computation. 561 ISIS Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG) is used to 562 advertise the exclude rule that is used during the Flex-Algorithm 563 path calculation as specified in Section 12. 565 ISIS FAESRLG Sub-TLV is a Sub-TLV of the ISIS FAD Sub-TLV. It has 566 the following format: 568 0 1 2 3 569 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 1 570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 571 | Type | Length | 572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 573 | Shared Risk Link Group Value | 574 +- -+ 575 | ... | 576 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 577 where: 579 Type: 5 581 Length: variable, dependent on number of SRLG values. MUST be a 582 multiple of 4 octets. 584 Shared Risk Link Group Value: SRLG value as defined in [RFC5307]. 586 ISIS FAESRLG Sub-TLV MAY NOT appear more then once in an ISIS FAD 587 Sub-TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be 588 ignored by the receiver. 590 7. Sub-TLVs of OSPF FAD TLV 592 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 594 Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a 595 Sub-TLV of the OSPF FAD TLV. It's usage is described in Section 6.1. 596 It has the following format: 598 0 1 2 3 599 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 | Type | Length | 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 603 | Extended Admin Group | 604 +- -+ 605 | ... | 606 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 607 where: 609 Type: 1 611 Length: variable, dependent on the size of the Extended Admin 612 Group. MUST be a multiple of 4 octets. 614 Extended Administrative Group: Extended Administrative Group as 615 defined in [RFC7308]. 617 OSPF FAEAG Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. 618 If it appears more then once, the OSPF FAD TLV MUST be ignored by the 619 receiver. 621 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV 623 The usage of this Sub-TLVs is described in Section 6.2. 625 The format of the OSPF Flexible Algorithm Include-Any Admin Group 626 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 627 Section 7.1. 629 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. 631 OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT 632 appear more then once in an OSPF FAD TLV. If it appears more then 633 once, the OSPF FAD TLV MUST be ignored by the receiver. 635 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV 637 The usage of this Sub-TLVs is described in Section 6.3. 639 The format of the OSPF Flexible Algorithm Include-Any Admin Group 640 Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in 641 Section 7.1. 643 Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 3. 645 OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT 646 appear more then once in an OSPF FAD TLV. If it appears more then 647 once, the OSPF FAD TLV MUST be ignored by the receiver. 649 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV 651 OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a 652 Sub-TLV of the OSPF FAD TLV. It has the following format: 654 0 1 2 3 655 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 1 656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 657 | Type | Length | 658 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 659 | Flags | 660 +- -+ 661 | ... | 662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 663 where: 665 Type: 4 667 Length: variable, dependent on the size of the Flags field. MUST 668 be a multiple of 4 octets. 670 Flags: 672 0 1 2 3 4 5 6 7... 673 +-+-+-+-+-+-+-+-+... 674 |M| | | ... 675 +-+-+-+-+-+-+-+-+... 677 M-flag: when set, Flex-Algorithm specific prefix metric MUST be 678 used, if advertised with the prefix. This flag is not 679 applicable to prefixes advertised as SRv6 locators. 681 Bits are defined/sent starting with Bit 0 defined above. Additional 682 bit definitions that may be defined in the future SHOULD be assigned 683 in ascending bit order so as to minimize the number of bits that will 684 need to be transmitted. 686 Undefined bits MUST be transmitted as 0. 688 Bits that are NOT transmitted MUST be treated as if they are set to 0 689 on receipt. 691 OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV. 692 If it appears more then once, the OSPF FAD TLV MUST be ignored by the 693 receiver. 695 If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all 696 the bits are assumed to be set to 0. 698 7.5. OSPF Flexible Algorithm Exclude SRLG Sub-TLV 700 OSPF Flexible Algorithm Exclude SRLG Sub-TLV (FAESRLG Sub-TLV) is a 701 Sub-TLV of the OSPF FAD TLV. It's usage is described in Section 6.5. 702 It has the following format: 704 0 1 2 3 705 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 1 706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 707 | Type | Length | 708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 709 | Shared Risk Link Group Value | 710 +- -+ 711 | ... | 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 where: 715 Type: 5 717 Length: variable, dependent on the number of SRLGs. MUST be a 718 multiple of 4 octets. 720 Shared Risk Link Group Value: SRLG value as defined in [RFC4203]. 722 OSPF FAESRLG Sub-TLV MAY NOT appear more then once in an OSPF FAD 723 TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored 724 by the receiver. 726 8. ISIS Flex-Algorithm Prefix Metric Sub-TLV 728 ISIS Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the 729 advertisement of a Flex-Algorithm specific prefix metric associated 730 with a given prefix advertisement. 732 ISIS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 and has 733 the following format: 735 0 1 2 3 736 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 1 737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 738 | Type | Length |Flex-Algorithm | 739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 740 | Metric | 741 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 742 where: 744 Type: 6 745 Length: 5 octets 747 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 749 Metric: 4 octets of metric information 751 ISIS FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it 752 appears more then once with the same Flex-Algorithm value, the first 753 appearance MUST be used and any subsequent ones MUST be ignored. 755 If a prefix is advertised with a Flex-Algorithm prefix metric larger 756 then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be 757 considered during the Flexible-Algorithm computation. 759 The usage of the Flex-Algorithm prefix metric is described in 760 Section 12. 762 ISIS FAPM Sub-TLV MUST NOT be advertised as sub-TLV of the ISIS SRv6 763 Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. ISIS SRv6 Locator 764 TLV includes the Algorithm and Metric fields which MUST be used 765 instead. If FAPM Sub-TLV is present as sub-TLV of the ISIS SRv6 766 Locator TLV in the received LSP, such FAPM Sub-TLV MUST be ignored. 768 9. OSPF Flex-Algorithm Prefix Metric Sub-TLV 770 OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the 771 advertisement of a Flex-Algorithm specific prefix metric associated 772 with a given prefix advertisement. 774 The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLVis a Sub-TLV of 775 the: 777 - OSPFv2 Extended Prefix TLV [RFC7684] 779 - Following OSPFv3 TLVs as defined in [RFC8362]: 781 Intra-Area Prefix TLV 783 Inter-Area Prefix TLV 785 External Prefix TLV 787 OSPF FAPM Sub-TLV has the following format: 789 0 1 2 3 790 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 1 791 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 792 | Type | Length | 793 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 794 |Flex-Algorithm | Reserved | 795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 796 | Metric | 797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 799 where: 801 Type: 3 for OSPFv2, 26 for OSPFv3 803 Length: 8 octets 805 Flex-Algorithm: Single octet value between 128 and 255 inclusive. 807 Reserved: Must be set to 0, ignored at reception. 809 Metric: 4 octets of metric information 811 OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it 812 appears more then once with the same Flex-Algorithm value, the first 813 appearance MUST be used and any subsequent ones MUST be ignored. 815 The usage of the Flex-Algorithm prefix metric is described in 816 Section 12. 818 10. Advertisement of Node Participation in a Flex-Algorithm 820 When a router is configured to support a particular Flex-Algorithm, 821 we say it is participating in that Flex-Algorithm. 823 Paths computed for a specific Flex-Algorithm MAY be used by various 824 applications, each potentially using its own specific data plane for 825 forwarding the data over such paths. To guarantee the presence of 826 the application specific forwarding state associated with a 827 particular Flex-Algorithm, a router MUST advertise its participation 828 for a particular Flex-Algorithm for each application specifically. 830 10.1. Advertisement of Node Participation for Segment Routing 832 [RFC8667], [RFC8665] and [RFC8666] (IGP Segment Routing extensions) 833 describe how SR-Algorithm is used to define how the best path is 834 computed by the IGP. 836 Routers advertise the support for the SR-Algorithm as a node 837 capability as described in the above mentioned IGP Segment Routing 838 extensions. To advertise participation for a particular Flex- 839 Algorithm for Segment Routing, including both SR MPLS and SRv6, the 840 Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV 841 (OSPF) or sub-TLV (ISIS). 843 Segment Routing Flex-Algorithm participation advertisement is 844 topology independent. When a router advertises participation in an 845 SR-Algorithm, the participation applies to all topologies in which 846 the advertising node participates. 848 10.2. Advertisement of Node Participation for Other Applications 850 This section describes considerations related to how other 851 applications can advertise its participation in a specific Flex- 852 Algorithm. 854 Application specific Flex-Algorithm participation advertisements MAY 855 be topology specific or MAY be topology independent, depending on the 856 application itself. 858 Application specific advertisement for Flex-Algorithm participation 859 MUST be defined for each application and is outside of the scope of 860 this document. 862 11. Advertisement of Link Attributes for Flex-Algorithm 864 Various link attributes may be used during the Flex-Algorithm path 865 calculation. For example, include or exclude rules based on link 866 affinities can be part of the Flex-Algorithm definition as defined in 867 Section 6 and Section 7. 869 Link attribute advertisements that are to be used during Flex- 870 Algorithm calculation MUST use the Application Specific Link 871 Attribute (ASLA) advertisements defined in [I-D.ietf-isis-te-app] or 872 [I-D.ietf-ospf-te-link-attr-reuse]. 874 A new Application Identifier Bit is defined to indicate that the ASLA 875 advertisement is associated with the Flex-Algorithm application. 876 This bit is set in the Standard Application Bit Mask (SABM) defined 877 in [I-D.ietf-isis-te-app] or [I-D.ietf-ospf-te-link-attr-reuse]: 879 Bit-3: Flexible Algorithm (X-bit) 881 ASLA Admin Group Advertisements to be used by the Flexible Algorithm 882 Application MAY use either the Administrative Group or Extended 883 Administrative Group encodings. If the Administrative Group encoding 884 is used then the first 32 bits of the corresponding FAD sub-TLVs are 885 mapped to the link attribute advertisements as specified in RFC 7308. 887 12. Calculation of Flexible Algorithm Paths 889 A router MUST be configured to participate in a given Flex-Algorithm 890 K and MUST use the FAD selected based on the rules defined in 891 Section 5.3 before it can compute any path for that Flex-Algorithm. 893 As described in Section 10, participation for any particular Flex- 894 Algorithm MUST be advertised on a per application basis. Calculation 895 of the paths for any particular Flex-Algorithm MUST be application 896 specific. 898 The way applications handle nodes that do not participate in 899 Flexible-Algorithm is application specific. If the application only 900 wants to consider participating nodes during the Flex-Algorithm 901 calculation, then when computing paths for a given Flex-Algorithm, 902 all nodes that do not advertise participation for that Flex-Algorithm 903 in the application specific advertisements MUST be pruned from the 904 topology. Segment Routing, including both SR MPLS and SRv6, are 905 applications that MUST use such pruning when computing Flex-Algorithm 906 paths. 908 When computing the path for a given Flex-Algorithm, the metric-type 909 that is part of the Flex-Algorithm definition (Section 5) MUST be 910 used. 912 When computing the path for a given Flex-Algorithm, the calculation- 913 type that is part of the Flex-Algorithm definition (Section 5) MUST 914 be used. 916 Various link include or exclude rules can be part of the Flex- 917 Algorithm definition. To refer to a particular bit within an AG or 918 EAG we uses term 'color'. 920 Rules, in the order as specified below, MUST be used to prune links 921 from the topology during the Flex-Algorithm computation. 923 For all links in the topology: 925 1. Check if any exclude rule is part of the Flex-Algorithm 926 definition. If such exclude rule exists, check if any color that 927 is part of the exclude rule is also set on the link. If such a 928 color is set, the link MUST be pruned from the computation. 930 2. Check if any exclude SRLG rule is part of the Flex-Algorithm 931 definition. If such exclude rule exists, check if the link is 932 part of any SRLG that is also part of the SRLG exclude rule. If 933 the link is part of such SRLG, the link MUST be pruned from the 934 computation. 936 3. Check if any include-any rule is part of the Flex-Algorithm 937 definition. If such include-any rule exists, check if any color 938 that is part of the include-any rule is also set on the link. If 939 no such color is set, the link MUST be pruned from the 940 computation. 942 4. Check if any include-all rule is part of the Flex-Algorithm 943 definition. If such include-all rule exists, check if all colors 944 that are part of the include-all rule are also set on the link. 945 If all such colors are not set on the link, the link MUST be 946 pruned from the computation. 948 5. If the Flex-Algorithm definition uses other than IGP metric 949 (Section 5), and such metric is not advertised for the particular 950 link in a topology for which the computation is done, such link 951 MUST be pruned from the computation. A metric of value 0 MUST NOT 952 be assumed in such case. 954 12.1. Multi-area and Multi-domain Considerations 956 Any IGP Shortest Path Tree calculation is limited to a single area. 957 This applies to Flex-Algorithm calculations as well. Given that the 958 computing router does not have the visibility of the topology of next 959 areas or domain, the Flex-Algorithm specific path to an inter-area or 960 inter-domain prefix will be computed for the local area only. The 961 egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case, 962 will be selected based on the best path for the given Flex-Algorithm 963 in the local area and such egress ABR or ASBR router will be 964 responsible to compute the best Flex-Algorithm specific path over the 965 next area or domain. This may produce an end-to-end path, which is 966 sub-optimal based on Flex-Algorithm constraints. In cases where the 967 ABR or ASBR has no reachability to a prefix for a given Flex- 968 Algorithm in a next area or domain, the traffic may get dropped by 969 the ABR/ASBR. 971 To allow the optimal end-to-end path for a inter-area or inter-domain 972 prefixes for any Flex-Algorithm to be computed, the FAPM has been 973 defined in Section 8 and Section 9. 975 If the FAD selected based on the rules defined in Section 5.3 976 includes the M-flag, an ABR or ASBR MUST include the FAPM (Section 8, 977 Section 9) when advertising the prefix between areas or domains. 978 Such metric will be equal to the metric to reach the prefix for a 979 given Flex-Algorithm in a source area or domain. This is similar in 980 nature to how the metric is set when prefixes are advertised between 981 areas or domains for default algorithm. 983 If the FAD selected based on the rules defined in Section 5.3 984 includes the M-flag, FAPM MUST be used during calculation of prefix 985 reachability for the inter-area and external prefixes. If the FAPM 986 for the Flex-Algorithm is not advertised with the inter-area or 987 external prefix reachability advertisement, the prefix MUST be 988 considered as unreachable for that Flex-Algorithm. 990 Flex-Algorithm prefix metrics MUST NOT be used during the Flex- 991 Algorithm computation unless the FAD selected based on the rules 992 defined in Section 5.3 includes the M-Flag, as described in 993 (Section 6.4 or Section 7.4). 995 If the FAD selected based on the rules defined in Section 5.3 does 996 not includes the M-flag, it is NOT RECOMMENDED to use the Flex- 997 Algoritm for inter-area or inter-domain prefix reachability. The 998 reason is that without the explicit Flex-Algorithm Prefix Metric 999 advertisement it is not possible to conclude whether the ABR or ASBR 1000 has reachability to the inter-area or inter-domain prefix for a given 1001 Flex-Algorithm in a next area or domain. Sending the Flex-Algoritm 1002 traffic for such prefix towards the ABR or ASBR may result in traffic 1003 looping or black-holing. 1005 FAPM MUST NOT be advertised with ISIS L1 or L2 intra-area, OSPFv2 1006 intra-area or OSPFv3 intra area routes. If the FAPM is advertised 1007 for these route-types, it MUST be ignored during prefix reachability 1008 calculation. 1010 M-flag in FAD is not applicable to prefixes advertised as SRv6 1011 locators. ISIS SRv6 Locator TLV includes the Algorithm and Metric 1012 fields [I-D.ietf-lsr-isis-srv6-extensions]. When the ISIS SRv6 1013 Locator is advertised between areas or domains, the metric field in 1014 the Locator TLV MUST be used irrespective of the M flag in the FAD 1015 advertisement. 1017 13. Flex-Algorithm and Forwarding Plane 1019 This section describes how Flex-Algorithm paths are used in 1020 forwarding. 1022 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm 1024 This section describes how Flex-Algorithm paths are used with SR MPLS 1025 forwarding. 1027 Prefix SID advertisements include an SR-Algorithm value and as such 1028 are associated with the specified SR-Algorithm. Prefix-SIDs are also 1029 associated with a specific topology which is inherited from the 1030 associated prefix reachability advertisement. When the algorithm 1031 value advertised is a Flex-Algorithm value, the Prefix SID is 1032 associated with paths calculated using that Flex-Algorithm in the 1033 associated topology. 1035 A Flex-Algorithm path MUST be installed in the MPLS forwarding plane 1036 using the MPLS label that corresponds to the Prefix-SID that was 1037 advertised for that Flex-algorithm. If the Prefix SID for a given 1038 Flex-algorithm is not known, the Flex-Algorithm specific path cannot 1039 be installed in the MPLS forwarding plane. 1041 Traffic that is supposed to be routed via Flex-Algorithm specific 1042 paths, MUST be dropped where there are no such paths available. 1044 Loop Free Alternate (LFA) paths for a given Flex-Algorithm MUST be 1045 computed using the same constraints as the calculation of the primary 1046 paths for that Flex-Algorithm. LFA paths MUST only use Prefix-SIDs 1047 advertised specifically for the given algorithm. LFA paths MUST NOT 1048 use an Adjacency-SID that belongs to a link that has been pruned from 1049 the Flex-Algorithm computation. 1051 If LFA protection is being used to protect a given Flex-Algorithm 1052 paths, all routers in the area participating in the given Flex- 1053 Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- 1054 SID. These Node-SIDs are used to enforce traffic over the LFA 1055 computed backup path. 1057 13.2. SRv6 Forwarding for Flex-Algorithm 1059 This section describes how Flex-Algorithm paths are used with SRv6 1060 forwarding. 1062 In SRv6 a node is provisioned with topology/algorithm specific 1063 locators for each of the topology/algorithm pairs supported by that 1064 node. Each locator is a covering prefix for all SIDs provisioned on 1065 that node which have the matching topology/algorithm. 1067 SRv6 locator advertisement in IGPs 1068 ([I-D.ietf-lsr-isis-srv6-extensions] 1069 [I-D.ietf-lsr-ospfv3-srv6-extensions]) includes the MTID value that 1070 associates the locator with a specific topology. SRv6 locator 1071 advertisements also includes an Algorithm value that explicitly 1072 associates the locator with a specific algorithm. When the algorithm 1073 value advertised with a locator represents a Flex-Algorithm, the 1074 paths to the locator prefix MUST be calculated using the specified 1075 Flex-Algorithm in the associated topology. 1077 Forwarding entries for the locator prefixes advertised in IGPs MUST 1078 be installed in the forwarding plane of the receiving SRv6 capable 1079 routers when the associated topology/algorithm is participating in 1080 them. Forwarding entries for locators associated with Flex- 1081 Algorithms in which the node is not participating MUST NOT be 1082 installed in the forwarding. 1084 When the locator is associated with the Flex-Algorithm, LFA paths to 1085 the locator prefix MUST be calculated using such Flex-Algorithm in 1086 the associated topology, to guarantee that they follow the same 1087 constraints as the calculation of the primary paths. LFA paths MUST 1088 only use SRv6 SIDs advertised specifically for the given Flex- 1089 Algorithm. 1091 If LFA protection is being used to protect locators associated with a 1092 given Flex-Algorithm, all routers in the area participating in the 1093 given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm 1094 specific locator and END SID per node and one END.X SID for every 1095 link that has not been pruned from such Flex-Algorithm computation. 1096 These locators and SIDs are used to enforce traffic over the LFA 1097 computed backup path. 1099 13.3. Other Applications' Forwarding for Flex-Algorithm 1101 Any application that wants to use Flex-Algorithm specific forwarding 1102 needs to install some form of Flex-Algorithm specific forwarding 1103 entries. 1105 Application specific forwarding for Flex-Algorithm MUST be defined 1106 for each application and is outside of the scope of this document. 1108 14. Operational considerations 1110 14.1. Inter-area Considerations 1112 The scope of the FA computation is an area, so is the scope of the 1113 FAD. In ISIS the Router Capability TLV in which the FAD Sub-TLV is 1114 present MUST have the S-bit clear, which prevents it to be flooded 1115 outside of level in which it was originated. Even though in OSPF the 1116 FAD Sub-TLV can be flooded in the RI LSA that has AS flooding scope, 1117 the FAD selection is performed for individual area in which it is 1118 being used. 1120 There is no requirement for FAD for a particular Flex-Algorithm to be 1121 identical in all areas in the network. For example, traffic for the 1122 same Flex-Algorithm may be optimized for minimal delay (e.g., using 1123 delay metric) in one area or level, while being optimized for 1124 available bandwidth (e.g., using IGP metric) in the other area or 1125 level. 1127 As described in Section 5.1, ISIS allows the re-generation of the 1128 winning FAD from level 2, without any modification to it, into a 1129 level 1 area. This allows the operator to configure the FAD in one 1130 or multiple routers in the level 2, without the need to repeat the 1131 same task in each level 1 area, if the intent is to have the same FAD 1132 for the particular Flex-Algorithm across all levels. Similar can be 1133 achieved in OSPF by using the AS flooding scope of the RI LSA in 1134 which the FAD Sub-TLV for the particular Flex-Algoritm is advertised. 1136 Re-generation of FAD from level 1 area to level 2 area is not 1137 supported in ISIS, so if the intent is to regenerate the FAD between 1138 ISIS levels, the FAD MUST be defined on router(s) that are in level 1139 2. In OSPF the FAD definition can be done in any area and be 1140 propagated to all router in AS by the AS flooding scope of the RI 1141 LSA. 1143 14.2. Usage of SRLG Exclude Rule with Flex-Algorithm 1145 There are two different ways in which SRLG information can be used 1146 with Flex-Algorithm: 1148 In a context of a single Flex-Algorithm, it can be used for 1149 computation of backup paths, as described in 1150 [I-D.ietf-rtgwg-segment-routing-ti-lfa]. This usage does not 1151 require association of any specific SRLG constraint with the given 1152 Flex-Algorithm definition. 1154 In the context of multiple Flex-Algorithms, it can be used for 1155 creating disjoint sets of paths by pruning the links belonging to 1156 a specific SRLG from the topology on which a specific Flex- 1157 Algorithm computes its paths. This usage: 1159 Facilitates the usage of already deployed SRLG configurations 1160 for setup of disjoint paths between two or more Flex- 1161 Algorithms. 1163 Requires explicit association of a given Flex-Algorithm with a 1164 specific set of SRLG constraints as defined in Section 6.5 and 1165 Section 7.5. 1167 The two usages mentioned above are orthogonal. 1169 14.3. Max-metric consideration 1171 Both ISIS and OSPF have a mechanism to set the IGP metric on a link 1172 to a value that would make the link either non-reachable or to serve 1173 as the link of last resort. Similar functionality would be needed 1174 for the Min Unidirectional Link Delay and TE metric, as these can be 1175 used to compute Flex-Algorithm paths. 1177 The link can be made un-reachable for all Flex-Algorithms that use 1178 Min Unidirectional Link Delay as metric, as described in Section 5.1, 1179 by removing the Flex-Algorithm ASLA Min Unidirectional Link Delay 1180 advertisement for the link. The link can be made the link of last 1181 resort by setting the delay value in the Flex-Algorithm ASLA delay 1182 advertisement for the link to the value of 16,777,215 (2^24 - 1). 1184 The link can be made un-reachable for all Flex-Algorithms that use TE 1185 metric, as described in Section 5.1, by removing the Flex-Algorithm 1186 ASLA TE metric advertisement for the link. The link can be made the 1187 link of last resort by setting the TE metric value in the Flex- 1188 Algorithm ASLA delay advertisement for the link to the value of (2^24 1189 - 1) in ISIS and (2^32 - 1) in OSPF. 1191 15. Backward Compatibility 1193 This extension brings no new backward compatibility issues. 1195 16. Security Considerations 1197 This draft adds two new ways to disrupt the IGP networks: 1199 An attacker can hijack a particular Flex-Algorithm by advertising 1200 a FAD with a priority of 255 (or any priority higher than that of 1201 the legitimate nodes). 1203 An attacker could make it look like a router supports a particular 1204 Flex-Algorithm when it actually doesn't, or vice versa. 1206 Both of these attacks can be addressed by the existing security 1207 extensions as described in [RFC5304] and [RFC5310] for ISIS, in 1208 [RFC2328] and [RFC7474] for OSPFv2 and in [RFC5340] and [RFC4552] for 1209 OSPFv3. 1211 17. IANA Considerations 1212 17.1. IGP IANA Considerations 1214 17.1.1. IGP Algorithm Types Registry 1216 This document makes the following registrations in the "IGP Algorithm 1217 Types" registry: 1219 Type: 128-255. 1221 Description: Flexible Algorithms. 1223 Reference: This document (Section 4). 1225 17.1.2. IGP Metric-Type Registry 1227 IANA is requested to set up a registry called "IGP Metric-Type 1228 Registry" under a "Interior Gateway Protocol (IGP) Parameters" IANA 1229 registries. The registration policy for this registry is "Standards 1230 Action" ([RFC8126] and [RFC7120]). 1232 Values in this registry come from the range 0-255. 1234 This document registers following values in the "IGP Metric-Type 1235 Registry": 1237 Type: 0 1239 Description: IGP metric 1241 Reference: This document (Section 5.1) 1243 Type: 1 1245 Description: Min Unidirectional Link Delay [RFC7810] 1247 Reference: This document (Section 5.1) 1249 Type: 2 1251 Description: TE Default Metric [RFC5305] 1253 Reference: This document (Section 5.1) 1255 17.2. Flex-Algorithm Definition Flags Registry 1257 IANA is requested to set up a registry called "ISIS Flex-Algorithm 1258 Definition Flags Registry" under a "Interior Gateway Protocol (IGP) 1259 Parameters" IANA registries. The registration policy for this 1260 registry is "Standards Action" ([RFC8126] and [RFC7120]). 1262 This document defines the following single bit in Flex-Algorithm 1263 Definition Flags registry: 1265 Bit # Name 1266 ----- ------------------------------ 1267 0 Prefix Metric Flag (M-flag) 1269 Reference: This document (Section 6.4, Section 7.4). 1271 17.3. ISIS IANA Considerations 1273 17.3.1. Sub TLVs for Type 242 1275 This document makes the following registrations in the "sub-TLVs for 1276 TLV 242" registry. 1278 Type: 26. 1280 Description: Flexible Algorithm Definition. 1282 Reference: This document (Section 5.1). 1284 17.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 1286 This document makes the following registrations in the "Sub-TLVs for 1287 for TLVs 135, 235, 236, and 237" registry. 1289 Type: 6 1291 Description: Flex-Algorithm Prefix Metric. 1293 Reference: This document (Section 8). 1295 17.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1297 This document creates the following Sub-Sub-TLV Registry: 1299 Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 1301 Registration Procedure: Expert review 1303 Reference: This document (Section 5.1) 1305 This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs 1306 for Flexible Algorithm Definition Sub-TLV" registry: 1308 Type: 1 1310 Description: Flexible Algorithm Exclude Admin Group 1312 Reference: This document (Section 6.1). 1314 Type: 2 1316 Description: Flexible Algorithm Include-Any Admin Group 1318 Reference: This document (Section 6.2). 1320 Type: 3 1322 Description: Flexible Algorithm Include-All Admin Group 1324 Reference: This document (Section 6.3). 1326 Type: 4 1328 Description: Flexible Algorithm Definition Flags 1330 Reference: This document (Section 6.4). 1332 Type: 5 1334 Description: Flexible Algorithm Exclude SRLG 1336 Reference: This document (Section 6.5). 1338 17.4. OSPF IANA Considerations 1340 17.4.1. OSPF Router Information (RI) TLVs Registry 1342 This specification updates the OSPF Router Information (RI) TLVs 1343 Registry. 1345 Type: 16 1347 Description: Flexible Algorithm Definition TLV. 1349 Reference: This document (Section 5.2). 1351 17.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs 1353 This document makes the following registrations in the "OSPFv2 1354 Extended Prefix TLV Sub-TLVs" registry. 1356 Type: 3 1358 Description: Flex-Algorithm Prefix Metric. 1360 Reference: This document (Section 9). 1362 17.4.3. OSPFv3 Extended-LSA Sub-TLVs 1364 This document makes the following registrations in the "OSPFv3 1365 Extended-LSA Sub-TLVs" registry. 1367 Type: 26 1369 Description: Flex-Algorithm Prefix Metric. 1371 Reference: This document (Section 9). 1373 17.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 1375 This document creates the following registry: 1377 Registry: OSPF Flexible Algorithm Definition TLV sub-TLV 1379 Registration Procedure: Expert review 1381 Reference: This document (Section 5.2) 1383 The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will 1384 define sub-TLVs at any level of nesting for Flexible Algorithm TLV 1385 and should be added to the "Open Shortest Path First (OSPF) 1386 Parameters" registries group. New values can be allocated via IETF 1387 Review or IESG Approval. 1389 This document registers following Sub-TLVs in the "TLVs for Flexible 1390 Algorithm Definition TLV" registry: 1392 Type: 1 1394 Description: Flexible Algorithm Exclude Admin Group 1396 Reference: This document (Section 7.1). 1398 Type: 2 1399 Description: Flexible Algorithm Include-Any Admin Group 1401 Reference: This document (Section 7.2). 1403 Type: 3 1405 Description: Flexible Algorithm Include-All Admin Group 1407 Reference: This document (Section 7.3). 1409 Type: 4 1411 Description: Flexible Algorithm Definition Flags 1413 Reference: This document (Section 7.4). 1415 Type: 5 1417 Description: Flexible Algorithm Exclude SRLG 1419 Reference: This document (Section 7.5). 1421 Types in the range 32768-33023 are for experimental use; these will 1422 not be registered with IANA, and MUST NOT be mentioned by RFCs. 1424 Types in the range 33024-65535 are not to be assigned at this time. 1425 Before any assignments can be made in the 33024-65535 range, there 1426 MUST be an IETF specification that specifies IANA Considerations that 1427 covers the range being assigned. 1429 17.4.5. Link Attribute Applications Registry 1431 This document registers following bit in the Link Attribute 1432 Applications Registry: 1434 Bit-3 1436 Description: Flexible Algorithm (X-bit) 1438 Reference: This document (Section 11). 1440 18. Acknowledgements 1442 This draft, among other things, is also addressing the problem that 1443 the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. 1444 All authors of that draft agreed to join this draft. 1446 Thanks to Eric Rosen, Tony Przygienda for their detailed review and 1447 excellent comments. 1449 Thanks to Cengiz Halit for his review and feedback during initial 1450 phase of the solution definition. 1452 Thanks to Kenji Kumaki for his comments. 1454 Thanks to William Britto A J. for his suggestions. 1456 19. References 1458 19.1. Normative References 1460 [BCP14] , . 1462 [I-D.ietf-isis-te-app] 1463 Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and 1464 J. Drake, "IS-IS Application-Specific Link Attributes", 1465 draft-ietf-isis-te-app-19 (work in progress), June 2020. 1467 [I-D.ietf-lsr-isis-srv6-extensions] 1468 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 1469 Z. Hu, "IS-IS Extension to Support Segment Routing over 1470 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08 1471 (work in progress), April 2020. 1473 [I-D.ietf-lsr-ospf-reverse-metric] 1474 Talaulikar, K., Psenak, P., and H. Johnston, "OSPF Reverse 1475 Metric", draft-ietf-lsr-ospf-reverse-metric-01 (work in 1476 progress), June 2020. 1478 [I-D.ietf-lsr-ospfv3-srv6-extensions] 1479 Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, 1480 "OSPFv3 Extensions for SRv6", draft-ietf-lsr- 1481 ospfv3-srv6-extensions-00 (work in progress), February 1482 2020. 1484 [I-D.ietf-ospf-te-link-attr-reuse] 1485 Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J., 1486 and J. Drake, "OSPF Application-Specific Link Attributes", 1487 draft-ietf-ospf-te-link-attr-reuse-16 (work in progress), 1488 June 2020. 1490 [ISO10589] 1491 International Organization for Standardization, 1492 "Intermediate system to Intermediate system intra-domain 1493 routeing information exchange protocol for use in 1494 conjunction with the protocol for providing the 1495 connectionless-mode Network Service (ISO 8473)", ISO/ 1496 IEC 10589:2002, Second Edition, Nov 2002. 1498 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1499 Requirement Levels", BCP 14, RFC 2119, 1500 DOI 10.17487/RFC2119, March 1997, 1501 . 1503 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 1504 Support of Generalized Multi-Protocol Label Switching 1505 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 1506 . 1508 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1509 in Support of Generalized Multi-Protocol Label Switching 1510 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1511 . 1513 [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS 1514 Traffic Engineering (MPLS-TE)", RFC 7308, 1515 DOI 10.17487/RFC7308, July 2014, 1516 . 1518 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 1519 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 1520 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 1521 2015, . 1523 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 1524 S. Shaffer, "Extensions to OSPF for Advertising Optional 1525 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 1526 February 2016, . 1528 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 1529 for Advertising Router Information", RFC 7981, 1530 DOI 10.17487/RFC7981, October 2016, 1531 . 1533 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1534 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1535 May 2017, . 1537 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 1538 F. Baker, "OSPFv3 Link State Advertisement (LSA) 1539 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 1540 2018, . 1542 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 1543 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1544 Extensions for Segment Routing", RFC 8665, 1545 DOI 10.17487/RFC8665, December 2019, 1546 . 1548 [RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 1549 for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 1550 December 2019, . 1552 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 1553 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 1554 Extensions for Segment Routing", RFC 8667, 1555 DOI 10.17487/RFC8667, December 2019, 1556 . 1558 19.2. Informative References 1560 [I-D.gulkohegde-routing-planes-using-sr] 1561 Hegde, S. and a. arkadiy.gulko@thomsonreuters.com, 1562 "Separating Routing Planes using Segment Routing", draft- 1563 gulkohegde-routing-planes-using-sr-00 (work in progress), 1564 March 2017. 1566 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 1567 Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B., 1568 Francois, P., Voyer, D., Clad, F., and P. Camarillo, 1569 "Topology Independent Fast Reroute using Segment Routing", 1570 draft-ietf-rtgwg-segment-routing-ti-lfa-03 (work in 1571 progress), March 2020. 1573 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 1574 DOI 10.17487/RFC2328, April 1998, 1575 . 1577 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway 1578 Protocol (IGP) Routes Over Traffic Engineering Tunnels", 1579 RFC 3906, DOI 10.17487/RFC3906, October 2004, 1580 . 1582 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 1583 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 1584 . 1586 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1587 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1588 2008, . 1590 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 1591 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 1592 2008, . 1594 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 1595 and M. Fanto, "IS-IS Generic Cryptographic 1596 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 1597 2009, . 1599 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 1600 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 1601 . 1603 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 1604 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 1605 2014, . 1607 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 1608 "Security Extension for OSPFv2 When Using Manual Key 1609 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 1610 . 1612 [RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and 1613 Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", 1614 RFC 7810, DOI 10.17487/RFC7810, May 2016, 1615 . 1617 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1618 Writing an IANA Considerations Section in RFCs", BCP 26, 1619 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1620 . 1622 Authors' Addresses 1624 Peter Psenak (editor) 1625 Cisco Systems 1626 Apollo Business Center 1627 Mlynske nivy 43 1628 Bratislava, 82109 1629 Slovakia 1631 Email: ppsenak@cisco.com 1632 Shraddha Hegde 1633 Juniper Networks, Inc. 1634 Embassy Business Park 1635 Bangalore, KA, 560093 1636 India 1638 Email: shraddha@juniper.net 1640 Clarence Filsfils 1641 Cisco Systems, Inc. 1642 Brussels 1643 Belgium 1645 Email: cfilsfil@cisco.com 1647 Ketan Talaulikar 1648 Cisco Systems, Inc. 1649 S.No. 154/6, Phase I, Hinjawadi 1650 PUNE, MAHARASHTRA 411 057 1651 India 1653 Email: ketant@cisco.com 1655 Arkadiy Gulko 1656 Refinitiv 1658 Email: arkadiy.gulko@refinitiv.com