idnits 2.17.1 draft-hegde-lsr-flex-algo-bw-con-01.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 : ---------------------------------------------------------------------------- ** There are 19 instances of too long lines in the document, the longest one being 20 characters in excess of 72. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 75 has weird spacing: '...m Delay sub-T...' -- The document date (March 8, 2021) is 1144 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) == Missing Reference: 'RFC8919' is mentioned on line 321, but not defined ** Obsolete undefined reference: RFC 8919 (Obsoleted by RFC 9479) == Missing Reference: 'RFC 8919' is mentioned on line 812, but not defined ** Obsolete undefined reference: RFC 8919 (Obsoleted by RFC 9479) == Missing Reference: 'RFC 5305' is mentioned on line 815, but not defined == Missing Reference: 'RFC 8570' is mentioned on line 321, but not defined == Missing Reference: 'RFC 8920' is mentioned on line 389, but not defined ** Obsolete undefined reference: RFC 8920 (Obsoleted by RFC 9492) == Outdated reference: A later version (-26) exists of draft-ietf-lsr-flex-algo-13 == Outdated reference: A later version (-16) exists of draft-bashandy-rtgwg-segment-routing-uloop-10 -- Obsolete informational reference (is this intentional?): RFC 5316 (Obsoleted by RFC 9346) Summary: 4 errors (**), 0 flaws (~~), 9 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SPRING S. Hegde 3 Internet-Draft W. Britto 4 Intended status: Standards Track R. Shetty 5 Expires: September 9, 2021 Juniper Networks Inc. 6 B. Decraene 7 Orange 8 P. Psenak 9 Cisco Systems 10 T. Li 11 Arista Networks 12 March 8, 2021 14 Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints 15 draft-hegde-lsr-flex-algo-bw-con-01 17 Abstract 19 Many networks configure the link metric relative to the link 20 capacity. High bandwidth traffic gets routed as per the link 21 capacity. Flexible algorithms provides mechanisms to create 22 constraint based paths in IGP. This draft documents a set of 23 bandwidth related constraints to be used in Flexible Algorithms. 25 Requirements Language 27 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 28 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 29 document are to be interpreted as described in RFC 2119 [RFC2119]. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on September 9, 2021. 48 Copyright Notice 50 Copyright (c) 2021 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (https://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Bandwidth Metric Advertisement . . . . . . . . . . . . . . . 3 67 2.1. ISIS Bandwidth Metric sub-TLV . . . . . . . . . . . . . . 4 68 2.2. OSPF Bandwidth Metric sub-TLV . . . . . . . . . . . . . . 5 69 3. FAD constraint sub-TLVs . . . . . . . . . . . . . . . . . . . 5 70 3.1. ISIS FAD constraint sub-TLVs . . . . . . . . . . . . . . 6 71 3.1.1. ISIS Exclude Minimum Bandwidth sub-TLV . . . . . . . 6 72 3.1.2. ISIS Exclude Maximum Delay sub-TLV . . . . . . . . . 7 73 3.2. OSPF FAD constraint sub-TLVs . . . . . . . . . . . . . . 7 74 3.2.1. OSPF Exclude Minimum Bandwidth sub-TLV . . . . . . . 8 75 3.2.2. OSPF Exclude Maximum Delay sub-TLV . . . . . . . . . 8 76 4. Automatic Metric Calculation . . . . . . . . . . . . . . . . 9 77 4.1. Automatic Metric Calculation Modes . . . . . . . . . . . 10 78 4.1.1. Simple Mode . . . . . . . . . . . . . . . . . . . . . 10 79 4.1.2. Interface Group Mode . . . . . . . . . . . . . . . . 10 80 4.2. Automatic Metric Calculation Methods . . . . . . . . . . 10 81 4.2.1. Reference Bandwidth method . . . . . . . . . . . . . 11 82 4.2.2. Bandwidth Thresholds method . . . . . . . . . . . . . 11 83 4.3. ISIS FAD constraint sub-TLVs for automatic metric 84 calculation . . . . . . . . . . . . . . . . . . . . . . . 11 85 4.3.1. Reference Bandwidth sub-TLV . . . . . . . . . . . . . 11 86 4.3.2. Bandwidth Thresholds sub-TLV . . . . . . . . . . . . 13 87 4.4. OSPF FAD constraint sub-TLVs for automatic metric 88 calculation . . . . . . . . . . . . . . . . . . . . . . . 15 89 4.4.1. Reference Bandwidth sub-TLV . . . . . . . . . . . . . 15 90 4.4.2. Bandwidth Threshold sub-TLV . . . . . . . . . . . . . 17 91 5. Bandwidth metric considerations . . . . . . . . . . . . . . . 19 92 6. Calculation of Flex-Algorithm paths . . . . . . . . . . . . . 19 93 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 20 94 8. Security Considerations . . . . . . . . . . . . . . . . . . . 20 95 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 96 9.1. IGP Metric-Type Registry . . . . . . . . . . . . . . . . 20 97 9.2. ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 98 TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 99 9.3. OSPF Sub-TLVs for Flexible Algorithm Definition Sub-TLV . 21 100 9.4. Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 . . . . . 21 101 9.5. Sub-sub-TLV Codepoints for Application-Specific Link 102 Attributes . . . . . . . . . . . . . . . . . . . . . . . 21 103 9.6. OSPFv2 Extended Link TLV Sub-TLVs . . . . . . . . . . . . 21 104 9.7. Types for sub-TLVs of TE Link TLV (Value 2) . . . . . . . 22 105 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 106 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22 107 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 108 12.1. Normative References . . . . . . . . . . . . . . . . . . 22 109 12.2. Informative References . . . . . . . . . . . . . . . . . 23 110 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 112 1. Introduction 114 High bandwidth traffic such as residential internet traffic and 115 machine to machine elephant flows benefit from using high capacity 116 links for the traffic. Many network operators define link metric 117 relative to the link capacity. It may be useful to exclude the high 118 bandwidth traffic from utilizing links below certain capacity. A 119 Flex-Algorithm [I-D.ietf-lsr-flex-algo] is defined as a set of 120 parameters consisting of calculation-type, metric-type and a set of 121 constraints. It is very convenient to define a Flex-Algorithm that 122 uses bandwidth based metric-type which can be used for carrying high 123 bandwidth traffic. In this regard, it's useful to define additional 124 metric-type and additional bandwidth related constraints to simplify 125 the operations. 127 This document specifies a new metric-type to be used in Flex- 128 Algorithm described in section Section 2. Additional Flexible 129 Algorithm Definition (FAD) constraints are defined in section 130 Section 3. Section 4 defines mechanisms to automatically calculate 131 metric based on parameters defined in a FAD constraint and the 132 advertised Maximum Link Bandwidth of the link. 134 2. Bandwidth Metric Advertisement 136 ISIS and OSPF advertise link metric in their respective link 137 information. Multiple types of metric are supported, IGP cost, te- 138 metric defined in [RFC5305] and [RFC3630] and delay metric defined in 139 [RFC8570] and [RFC7471]. A brownfield network might have deployed 140 legacy transport mechanisms using igp-cost and te-metric which 141 continue to run during migration period. In this brownfield network 142 if the operator wants to introduce two Flex-Algorithms, one for delay 143 metric and another for bandwidth metric, a new metric-type to carry 144 bandwidth related metric would be needed. The IGP cost and te-metric 145 may be already used by legacy applications and may not be available 146 to carry link bandwidth based metric. This document defines a new 147 metric called bandwidth metric. ISIS and OSPF will advertise this 148 new type of metric in their link information. This document also 149 defines a new metric-type called "Bandwidth Metric" in the FAD sub- 150 TLV. 152 2.1. ISIS Bandwidth Metric sub-TLV 154 The ISIS Bandwidth Metric sub-TLV specifies the link metric based on 155 link bandwidth. Typically, this metric is assigned by a network 156 administrator. The Bandwidth Metric sub-TLV is advertised in below 157 TLVs/sub-TLVs 159 TLV-22 (Extended IS reachability) [RFC5305] 161 TLV-222 (MT-ISN) [RFC5120] 163 TLV-23 (IS Neighbor Attribute) [RFC5311] 165 TLV-223 (MT IS Neighbor Attribute) [RFC5311] 167 TLV-141 (inter-AS reachability information) [RFC5316] 169 sub-TLV 16 (Application-Specific Link Attributes) of TLV 170 22/222/23/223/141 [RFC8919] 172 0 1 2 3 173 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 1 174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 175 | Type | Length | 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 | Value | 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 180 Type : TBD (To be assigned by IANA) 181 Length: 4 octets 182 Value : metric value range (1 - 4,261,412,864) 184 Figure 1: ISIS Bandwidth Metric sub-TLV 186 The Bandwidth Metric sub-TLV MUST be advertised only once. If there 187 are multiple Bandwidth Metric sub-TLVs advertised for a link in one 188 or more received LSPDUs, the first one MUST be used and the 189 subsequent ones MUST be ignored. 191 2.2. OSPF Bandwidth Metric sub-TLV 193 The Bandwidth Metric sub-TLV specifies the link metric based on link 194 bandwidth. Typically, this metric is assigned by a network 195 administrator. The Bandwidth Metric sub-TLV is advertised in below 196 TLVs 198 sub-TLV of the OSPF Link TLV of OSPF extended Link LSA [RFC7684]. 200 sub-TLV of TE Link TLV (2) of OSPF TE LSA [RFC3630]. 202 sub-sub-TLV of Application-Specific Link Attributes sub-TLV [RFC 203 8920] 205 The Bandwidth Metric sub-TLV is TLV type TBD (IANA), and is four 206 octets in length. 208 0 1 2 3 209 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 1 210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 211 | Type | Length | 212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 213 | Value | 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 216 Type : TBD (To be assigned by IANA) 217 Length: 4 octets 218 Value : metric value (1- 4,294,967,295) 220 Figure 2: OSPF Bandwidth Metric sub-TLV 222 The Bandwidth Metric sub-TLV MUST be advertised only once. If there 223 are multiple Bandwidth Metric sub-TLVs in a received Link TLV, the 224 first one MUST be used and the subsequent ones MUST be ignored. 226 3. FAD constraint sub-TLVs 228 It is useful to exclude Links having capacity lower than a minimum 229 value from the Flex-Algorithm topology that is designed to carry high 230 bandwidth traffic. This can be achieved by associating link affinity 231 to the lower capacity links and advertise exclude link constraint in 232 the FAD for that link affinity. This works well where the link 233 capacity is constant. When a Layer 3 link is collection of Layer 2 234 links (LAG/Layer 2 Bundle), the link bandwidth varies based on the 235 constituent link going up and down. The operator has to constantly 236 monitor the link capacity and assign appropriate link affinity if 237 link capacity changes beyond minimum value. In certain cases, the 238 minimum link bandwidth required may change based on the applications 239 that use the high bandwidth Flex-Algo. This document proposes a new 240 Exclude Minimum Bandwidth constraint. When this constraint is 241 advertised in a FAD, based on the advertised link bandwidth, the link 242 will be pruned from the Flex-Algorithm topology if the link's 243 advertised Maximum Link Bandwidth is below the FAD advertised Minimum 244 bandwidth value. 246 Similarly, exclude maximum link delay constraint is also defined in 247 this document. Links may have the link delay measured dynamically 248 and advertised in delay metric in IGP. For use cases that deploy 249 dynamic link delay measurement, A Flex-Algorithm may want to exclude 250 links that have link delay more than a defined threshold. 252 3.1. ISIS FAD constraint sub-TLVs 254 3.1.1. ISIS Exclude Minimum Bandwidth sub-TLV 256 ISIS Flex-Algorithm Exclude Minimum Bandwidth sub-TLV (FAEMB) is a 257 sub-TLV of the ISIS FAD sub-TLV. It has the following format. 259 0 1 2 3 260 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 1 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 262 | Type | Length | 263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 264 | Min bandwidth | 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 where: 268 Type: 1 270 Length: 4 octets. 272 Min Bandwidth: link bandwidth is encoded in 32 bits in IEEE 273 floating point format. The units are bytes per second. 275 Figure 3: ISIS FAEMB sub-TLV 277 The FAEMB sub-TLV MUST appear only once in the FAD sub-TLV. If it 278 appears more than once, the ISIS FAD Sub-TLV MUST be ignored by the 279 receiver. The Minimum bandwidth advertised in FAEMB sub-TLV MUST be 280 compared with Maximum Link Bandwidth advertised in sub-sub-TLV 9 of 281 ASLA sub-TLV [RFC 8919]. If L-Flag is set in the ASLA sub-TLV, the 282 Minimum bandwidth advertised in FAEMB sub-TLV MUST be compared with 283 Maximum Link Bandwidth as advertised by the sub-TLV 9 of the TLV 284 22/222/23/223/141 [RFC 5305] as defined in [RFC8919] Section 4.2. If 285 the Maximum Link Bandwidth is lower than the Minimum link bandwidth 286 advertised in FAEMB sub-TLV, the link MUST be excluded from the Flex- 287 Algorithm topology. If a link does not have the Maximum Link 288 Bandwidth advertised but the FAD contains this sub-TLV, then that 289 link MUST be included in the topology and proceed to apply further 290 pruning rules for the link. 292 3.1.2. ISIS Exclude Maximum Delay sub-TLV 294 ISIS Flex-Algorithm Exclude Maximum Delay sub-TLV (FAEMD) is a sub- 295 TLV of the ISIS FAD sub-TLV. It has the following format. 297 0 1 2 3 298 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 1 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 300 | Type | Length | 301 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 302 | max link delay | 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 304 where: 306 Type: TBD 308 Length: 3 octets 310 Max link delay: Maximum link delay in microseconds 312 Figure 4: ISIS FAEMD sub-TLV 314 The FAEMD sub-TLV MUST appear only once in the FAD sub-TLV. If it 315 appears more than once, the ISIS FAD Sub-TLV MUST be ignored by the 316 receiver. The Maximum link delay advertised in FAEMD sub-TLV MUST be 317 compared with Min Unidirectional Link Delay advertised in sub-sub-TLV 318 34 of ASLA sub-TLV [RFC 8919]. If L-Flag is set in the ASLA sub-TLV, 319 the Maximum link delay advertised in FAEMD sub-TLV MUST be compared 320 with Min Unidirectional Link Delay as advertised by the sub-TLV 34 of 321 the TLV 22/222/23/223/141 [RFC 8570] as defined in [RFC8919] 322 Section 4.2. If the Min Unidirectional Link Delay value is higher 323 than the Maximum link delay advertised in FAEMD sub-TLV, the link 324 MUST be excluded from the Flex-Algorithm topology. If a link does 325 not have the Min Unidirectional Link Delay advertised but the FAD 326 contains this sub-TLV, then that link MUST be included in the 327 topology and proceed to apply further pruning rules for the link. 329 3.2. OSPF FAD constraint sub-TLVs 330 3.2.1. OSPF Exclude Minimum Bandwidth sub-TLV 332 OSPF Flex-Algorithm Bandwidth Exclusion sub-TLV (FAEMB) is a sub-TLV 333 of the OSPF FAD TLV. It has the following format. 335 0 1 2 3 336 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 1 337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 338 | Type | Length | 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 340 | Min bandwidth | 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 342 where: 344 Type: TBD 346 Length: 4 octets. 348 Min Bandwidth: link bandwidth is encoded in 32 bits in IEEE 349 floating point format. The units are bytes per second. 351 Figure 5: OSPF FAEMB sub-TLV 353 The FAEMB sub-TLV MUST appear only once in the FAD sub-TLV. If it 354 appears more than once, the OSPF FAD TLV MUST be ignored by the 355 receiver. The Maximum Link Bandwidth as advertised by the sub-sub- 356 TLV 23 of ASLA [RFC 8920] MUST be compared against the Minimum 357 bandwidth advertised in FAEMB sub-TLV. If the link bandwidth is 358 lower than the Minimum bandwidth advertised in FAEMB sub-TLV, the 359 link MUST be excluded from the Flex-Algorithm topology. If a link 360 does not have the Maximum Link Bandwidth advertised but the FAD 361 contains this sub-TLV, then that link MUST be included in the 362 topology and proceed to apply further pruning rules for the link. 364 3.2.2. OSPF Exclude Maximum Delay sub-TLV 366 OSPF Flex-Algorithm Exclude Maximum Delay sub-TLV (FAEMD) is a sub- 367 TLV of the OSPF FAD TLV. It has the following format. 369 0 1 2 3 370 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 1 371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 372 | Type | Length | 373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 374 | max link delay | 375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 376 where: 378 Type: TBD 380 Length: 3 octets 382 Max link delay: Maximum link delay in microseconds 384 Figure 6: OSPF FAEMD sub-TLV 386 The FAEMD sub-TLV MUST appear only once in the OSPF FAD TLV. If it 387 appears more than once, the OSPF FAD TLV MUST be ignored by the 388 receiver. The Min Unidirectional Link Delay as advertised by sub- 389 sub-TLV 12 of ASLA sub-TLV [RFC 8920], MUST be compared against the 390 Maximum delay advertised in FAEMD sub-TLV. If the Min Unidirectional 391 Link Delay is higher than the Maximum delay advertised in FAEMD sub- 392 TLV, the link MUST be excluded from the Flex-Algorithm topology. If 393 a link does not have the Min Unidirectional Link Delay advertised but 394 the FAD contains this sub-TLV, then that link MUST be included in the 395 topology and proceed to apply further pruning rules for the link. 397 4. Automatic Metric Calculation 399 Networks which are designed to be highly regular and follow uniform 400 metric assignment may want to further simplify the operations by 401 automatically calculating the metric based on a reference bandwidth 402 or a staircase metric assignment based on bandwidth thresholds. When 403 a FAD advertises metric-type as Bandwidth Metric and the link does 404 not have the Bandwidth Metric advertised, automatic metric derivation 405 can be used with additional FAD constraint advertisements as 406 described in this section. Based on the advertised rules, every node 407 automatically calculates the link metric of all the links in the 408 Flex-Algorithm before running SPF algorithm for the Flex-Alogrithm. 410 Based on the delay in learning the link bandwidth changes on a remote 411 link, there may be possibility of micro-loops which is no different 412 from IGP susceptibility to micro-loops during metric change. The 413 micro-loop avoidance procedures described in 414 [I-D.bashandy-rtgwg-segment-routing-uloop] can be used to avoid 415 micro-loops when the automatic metric calculation is deployed. 417 4.1. Automatic Metric Calculation Modes 419 4.1.1. Simple Mode 421 In simple mode, the Maximum Link Bandwidth of a single Layer 3 link 422 is used to derive the metric. This mode is more suitable for 423 deployments that use Layer 2 bundles for parallel links between two 424 nodes. This layer 3 link may consist of Layer 2 bundles. In such 425 cases, the bandwidth of the link may vary based on Layer 2 links 426 going up/down. 428 4.1.2. Interface Group Mode 430 Simple mode of metric calculation may not work well when there are 431 multiple parallel layer 3 interfaces between two nodes. 433 A------B====C====F====D 434 | | 435 ------E------- 437 Figure 7: Parallel interfaces 439 In the above diagram, there are two parallel links between B->C, 440 C->F, F->D. Let us assume the link bandwidth is uniform 10Gbps on 441 all links. When Simple mode of metric derivation is used, the metric 442 is derived as 10 on all links. Traffic will be forwarded B->E->D. 443 Since the bandwidth is higher B->C->F->D path, the requirement is to 444 be able to assign smaller metric based on cumulative bandwidth of the 445 parallel links. Interface group mode is suitable for deployments 446 that do not use Layer 2 bundles. 448 In the interface group mode, every node MUST identify the set of 449 parallel links between a pair of nodes based on IGP link 450 advertisements and MUST consider cumulative bandwidth of the parallel 451 links while arriving at the metric of each link. 453 4.2. Automatic Metric Calculation Methods 455 In automatic metric calculation for simple and interface group mode, 456 Maximum Link Bandwidth of the links is used to derive the metric. 457 There are two types of automatic metric derivation methods. 459 1. Reference bandwidth method 461 2. Bandwidth thresholds method 463 4.2.1. Reference Bandwidth method 465 In many networks, the metric is assigned relative to the link 466 bandwidth. The metric is derived by dividing the reference bandwidth 467 by the advertised Maximum Link Bandwidth. It is useful to advertise 468 reference bandwidth in FAD constraints to simplify operations. When 469 there are changes to the reference bandwidth it can be easily changed 470 on FAD server rather than having to change it on every node. In 471 order to ensure that small bandwidth changes do not change the link 472 metric, it is useful to define a round-off value. The link bandwidth 473 will be rounded-off with this value before deriving the metric. For 474 example, 476 reference bandwidth = 1000G 478 round off value = 20G 480 The derived metric is 10 for link bandwidth in the range 100G to 481 119G 483 4.2.2. Bandwidth Thresholds method 485 The round-off bw along with reference bandwidth approach described 486 above provides a uniform metric value for a range of link bandwidth. 487 In certain cases there may be a need to define non-proportional 488 metric values for the varying ranges of link bandwidth. For Example, 489 10G to 30G metric value is 100, 30G to 70G metric value is 50, 490 greater than 70G metric is 10. In order to support this, a staircase 491 metric based on bandwidth threshold is supported in the FAD. This 492 advertisement contains a set of threshold values and their associated 493 metric. 495 4.3. ISIS FAD constraint sub-TLVs for automatic metric calculation 497 4.3.1. Reference Bandwidth sub-TLV 499 This section provides FAD constraint advertisement details for the 500 reference bandwidth method of metric calculation as described in 501 Section 4.2.1. The Flexible Algorithm Definition Reference Bandwidth 502 Sub-TLV (FADRB Sub-TLV) is a Sub-TLV of the ISIS FAD sub-TLV. It has 503 the following format: 505 0 1 2 3 506 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 1 507 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 508 | Type | Length |G| Flags | 509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 510 | Reference Bandwidth | 511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 512 | Round-Off Bandwidth | 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 515 where: 517 Type: TBD 519 Length: 14 octets. 520 Reference Bandwidth: Bandwidth encoded in 32 bits in IEEE floating point 521 format. The units are in bytes per second. 522 Round-Off Bandwidth: Bandwidth encoded in 32 bits in IEEE floating point 523 format. The units are in bytes per second. 525 Flags: 527 0 1 2 3 4 5 6 7 528 +-+-+-+-+-+-+-+-+ 529 |G| | | | 530 +-+-+-+-+-+-+-+-+ 532 G-flag: when set, interface group Mode MUST be used to derive total link bandwidth. 534 Metric calculation: (Reference_bandwidth) / 535 (Total_link_bandwidth - 536 (Modulus of(Total_link_bandwidth,Round_off_bw))) 538 Figure 8: ISIS FADRB sub-TLV 540 Round-off Bandwidth value is used to make sure the metric does not 541 change when there is smaller change in the link bandwidth. The ISIS 542 FADRB Sub-TLV MUST NOT appear more than once in an ISIS FAD sub-TLV. 543 If it appears more than once, the ISIS FAD sub-TLV MUST be ignored by 544 the receiver. If a Bandwidth Metric sub-TLV is advertised for a 545 link, the Flex-Algorithm calculation MUST use the Bandwidth Metric 546 advertised on the link, and MUST NOT use the automatically derived 547 metric for that link. 549 4.3.2. Bandwidth Thresholds sub-TLV 551 This section provides FAD constraint advertisement details for the 552 Bandwidth Thresholds method of metric calculation as described in 553 Section 4.2.2. The Flexible Algorithm Definition Bandwidth Threshold 554 Sub-TLV (FADBT Sub-TLV) is a Sub-TLV of the ISIS FAD sub-TLV. It has 555 the following format: 557 0 1 2 3 558 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 1 559 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 560 | Type | Length |G| Flags. | 561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 562 | Bandwidth Threshold 1 Min. | 563 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 564 | Threshold Metric 1 | 565 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 566 | Bandwidth Threshold 1 Max. | 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 | Threshold Metric 2 | 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 570 | Bandwidth Threshold 2 Max. | 571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 572 ..... 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 | Threshold Metric n-1 | 575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 576 | Bandwidth Threshold n-1 Max. | 577 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 578 | Threshold Metric n | 579 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 581 where: 583 Type: TBD 585 Length: 1 + n*7 octets. Here n is equal to number of Threshold Metrics specified. 586 n MUST be greater than or equal to 2. 588 Flags: 590 0 1 2 3 4 5 6 7 591 +-+-+-+-+-+-+-+-+ 592 |G| | | | 593 +-+-+-+-+-+-+-+-+ 595 G-flag: when set, interface group Mode MUST be used to derive total link bandwidth. 597 Staircase bandwidth threshold and associated metric values. 598 Bandwidth Threshold 1 Min.: Minimum Link Bandwidth is encoded in 32 bits in IEEE 599 floating point format. The units are bytes per second. 600 Bandwidth Threshold 1 Max.: Maximum Link Bandwidth is encoded in 32 bits in IEEE 601 floating point format. The units are bytes per second. 602 Threshold Metric 1 : metric value range (1 - 4,261,412,864) 604 Figure 9: ISIS FADBT sub-TLV 606 When G-flag is set, the cumulative bandwidth of the parallel links is 607 computed as described in section Section 4.1.2. If G-flag is not 608 set, the advertised Maximum Link Bandwidth is used. 610 When the computed link bandwidth is less than Bandwidth Threshold 1 611 Min, the MAX_METRIC value of 4,261,412,864 MUST be assigned as the 612 Bandwidth Metric on the link during Flex-Algorithm SPF calculation. 614 When the computed link bandwidth is greater than or equal to 615 Bandwidth Threshold 1 Min AND less than Bandwidth Threshold 1 Max, 616 Threshold Metric 1 MUST be assigned as the Bandwidth Metric on the 617 link during Flex-Algorithm SPF calculation. 619 Similarly, when the computed link bandwidth is greater than or equal 620 to Bandwidth Threshold 1 Max AND less than Bandwidth Threshold 2 Max, 621 Threshold Metric 2 MUST be assigned as the Bandwidth Metric on the 622 link during Flex-Algorithm SPF calculation. 624 Similarly, when the computed link bandwidth is greater than or equal 625 to Bandwidth Threshold n-1 Max, Threshold Metric n MUST be assigned 626 as the Bandwidth Metric on the link during Flex-Algorithm SPF 627 calculation. 629 The ISIS FADBT Sub-TLV MUST NOT appear more than once in an ISIS FAD 630 sub-TLV. If it appears more than once, the ISIS FAD sub-TLV MUST be 631 ignored by the receiver. 633 A FAD MUST NOT contain both FADBT sub-TLV and FADRB sub-TLV. If both 634 these sub-TLVs are advertised in the same FAD for a Flexible 635 Algorithm, the FAD must be ignored by the receiver. 637 If a Bandwidth Metric sub-TLV is advertised for a link, the Flex- 638 Algorithm calculation MUST use the Bandwidth Metric advertised on the 639 link, and MUST NOT use the automatically derived metric for that 640 link. 642 4.4. OSPF FAD constraint sub-TLVs for automatic metric calculation 644 4.4.1. Reference Bandwidth sub-TLV 646 The Flexible Algorithm Definition Reference Bandwidth Sub-TLV (FADRB 647 Sub-TLV) is a Sub-TLV of the OSPF FAD TLV. It has the following 648 format: 650 0 1 2 3 651 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 1 652 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 653 | Type | Length | 654 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 655 | Reserved |G| Flags | 656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 657 | Reference Bandwidth | 658 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 659 | Round-Off Bandwidth | 660 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 662 where: 664 Type: TBD 666 Length: 14 octets. 667 Reference Bandwidth: Bandwidth encoded in 32 bits in IEEE floating point 668 format. The units are in bytes per second. 669 Round-Off Bandwidth: Bandwidth encoded in 32 bits in IEEE floating point 670 format. The units are in bytes per second. 672 Flags: 674 0 1 2 3 4 5 6 7 675 +-+-+-+-+-+-+-+-+ 676 |G| | | | 677 +-+-+-+-+-+-+-+-+ 679 G-flag: when set, interface group Mode MUST be used 680 to derive total link bandwidth. 682 Metric calculation: (Reference_bandwidth) / 683 (Total_link_bandwidth - 684 (Modulus of(Total_link_bandwidth, Round_off_bw))) 686 Figure 10: OSPF FADRB sub-TLV 688 Round-off Bandwidth value is used to make sure the metric does not 689 change when there is smaller change in the link bandwidth. The OSPF 690 FADRB Sub-TLV MUST NOT appear more than once in an OSPF FAD TLV. If 691 it appears more than once, the OSPF FAD TLV MUST be ignored by the 692 receiver. If a Bandwidth Metric sub-TLV is advertised for a link, 693 the Flex-Algorithm calculation MUST use the Bandwidth Metric 694 advertised on the link, and MUST NOT use the automatically derived 695 metric for that link. 697 4.4.2. Bandwidth Threshold sub-TLV 699 The Flexible Algorithm Definition Bandwidth Thresholds Sub-TLV (FADBT 700 Sub-TLV) is a Sub-TLV of the OSPF FAD TLV. It has the following 701 format: 703 0 1 2 3 704 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 1 705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 | Type | Length | 707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 708 | Reserved |G| Flags | 709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 | Bandwidth Threshold 1 Min. | 711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 712 | Threshold Metric 1 | 713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 714 | Bandwidth Threshold 1 Max. | 715 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 716 | Threshold Metric 2 | 717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 718 | Bandwidth Threshold 2 Max. | 719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 720 ..... 721 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 722 | Threshold Metric n-1 | 723 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 724 | Bandwidth Threshold n-1 Max. | 725 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 726 | Threshold Metric n | 727 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 729 where: 731 Type: TBD 733 Length: 2 + n*8 octets. Here n is equal to number of Threshold Metrics specified. 734 n MUST be greater than or equal to 2. 736 Flags: 738 0 1 2 3 4 5 6 7 739 +-+-+-+-+-+-+-+-+ 740 |G| | | | 741 +-+-+-+-+-+-+-+-+ 743 G-flag: when set, interface group Mode MUST be used to derive total link bandwidth. 745 Staircase bandwidth threshold and associated metric values. 746 Bandwidth Threshold 1 Min.: Minimum Link Bandwidth is encoded in 32 bits in IEEE 747 floating point format. The units are bytes per second. 748 Bandwidth Threshold 1 Max.: Maximum Link Bandwidth is encoded in 32 bits in IEEE 749 floating point format. The units are bytes per second. 750 Threshold Metric 1 : metric value range (1 - 4,294,967,296) 752 Figure 11: OSPF FADBT sub-TLV 754 When G-flag is set, the cumulative bandwidth of the parallel links is 755 computed as described in section Section 4.1.2. If G-flag is not 756 set, the advertised Maximum Link Bandwidth is used. 758 When the computed link bandwidth is less than Bandwidth Threshold 1 759 Min, the MAX_METRIC value of 4,294,967,296 MUST be assigned as the 760 Bandwidth Metric on the link during Flex-Algorithm SPF calculation. 762 When the computed link bandwidth is greater than or equal to 763 Bandwidth Threshold 1 Min AND less than Bandwidth Threshold 1 Max, 764 Threshold Metric 1 MUST be assigned as the Bandwidth Metric on the 765 link during Flex-Algorithm SPF calculation. 767 Similarly, when the computed link bandwidth is greater than or equal 768 to Bandwidth Threshold 1 Max AND less than Bandwidth Threshold 2 Max, 769 Threshold Metric 2 MUST be assigned as the Bandwidth Metric on the 770 link during Flex-Algorithm SPF calculation. 772 Similarly, when the computed link bandwidth is greater than or equal 773 to Bandwidth Threshold n-1 Max, Threshold Metric n MUST be assigned 774 as the Bandwidth Metric on the link during Flex-Algorithm SPF 775 calculation. 777 The OSPF FADBT Sub-TLV MUST NOT appear more than once in an OSPF FAD 778 TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored 779 by the receiver. 781 A FAD MUST NOT contain both FADBT sub-TLV and FADRB sub-TLV. If both 782 these sub-TLVs are advertised in the same FAD (winner FAD) for a 783 Flexible Algorithm, the receiving nodes MUST stop participating in 784 such Flexible-Algorithm 785 If a Bandwidth Metric sub-TLV is advertised for a link, the Flex- 786 Algorithm calculation MUST use the Bandwidth Metric advertised on the 787 link, and MUST NOT use the automatically derived metric for that 788 link. 790 5. Bandwidth metric considerations 792 This section specifies the rules of deriving the Bandwidth Metric if 793 and only if the winning FAD for the Flex-Algorithm specifies the 794 metric-type as "Bandwidth Metric". 796 1. If the the Bandwidth Metric sub-TLV is advertised for the link 797 as described in Section 2, it MUST be used during the Flex- 798 Algorithm calculation. 800 2. If the Bandwidth Metric sub-TLV is not advertised for the link 801 and the winning FAD for the Flex-Algorithm does not specify the 802 automatic bandwidth metric calculation (as defined in Section 4 ), 803 the Bandwidth Metric is considered as not being advertised for the 804 link. 806 3. If the Bandwidth Metric sub-TLV is not advertised for the link 807 and the winning FAD for the Flex-Algorithm specifies the automatic 808 bandwidth metric calculation (as defined in Section 4), the 809 Bandwidth Metric metric MUST be automatically calculated as per 810 the procedures defined in Section 4. If the Bandwidth Metric can 811 not be calculated due to lack of Flex-Algorithm specific ASLA 812 advertisement of sub-sub-TLV 9 [RFC 8919], or in case of IS-IS, in 813 presence of the L-Flag in the Flex-Algorithm specific ASLA 814 advertisement the lack of sub-TLV 9 in the TLV 22/222/23/223/141 815 [RFC 5305], the Bandwidth Metric is considered as not being 816 advertised for the link. 818 6. Calculation of Flex-Algorithm paths 820 Two new additional rules are added to the existing rules in the Flex- 821 rules specified in sec 13 of [I-D.ietf-lsr-flex-algo]. 823 6. Check if any exclude FAEMB rule is part of the Flex-Algorithm 824 definition. If such exclude rule exists and the link has Maximum 825 Link Bandwidth advertised, check if the link bandwidth satisfies 826 the FAEMB rule. If the link does not satisfy the FAEMB rule, the 827 link MUST be pruned from the computation. 829 7. Check if any exclude FAEMD rule is part of the Flex-Algorithm 830 definition. If such exclude rule exists and the link has Min 831 Unidirectional link delay advertised, check if the link delay 832 satisfies the FAEMD rule. If the link does not satisfy the FAEMD 833 rule, the link MUST be pruned from the computation. 835 7. Backward Compatibility 837 8. Security Considerations 839 TBD 841 9. IANA Considerations 843 9.1. IGP Metric-Type Registry 845 Type: Suggested 3 (TBA) 847 Description: Bandwidth metric 849 Reference: This document 851 9.2. ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 853 Type: Suggested 6 (TBA) 855 Description: ISIS Exclude Minimum Bandwidth sub-TLV 857 Reference: This document Section 3.1.1 859 Type: Suggested 7 (TBA) 861 Description: ISIS Exclude Maximum Delay sub-TLV 863 Reference: This document Section 3.1.2 865 Type: Suggested 8 (TBA) 867 Description: ISIS Reference Bandwidth sub-TLV 869 Reference: This document Section 4.3.1 871 Type: Suggested 9 (TBA) 873 Description: ISIS Threshold Metric sub-TLV 875 Reference: This document Section 4.3.2 877 9.3. OSPF Sub-TLVs for Flexible Algorithm Definition Sub-TLV 879 Type: Suggested 6 (TBA) 881 Description: OSPF Exclude Minimum Bandwidth sub-TLV 883 Reference: This document Section 3.2.1 885 Type: Suggested 7 (TBA) 887 Description: OSPF Exclude Maximum Delay sub-TLV 889 Reference: This document Section 3.2.2 891 Type: Suggested 8 (TBA) 893 Description: OSPF Reference Bandwidth sub-TLV 895 Reference: This document Section 4.4.1 897 Type: Suggested 9 (TBA) 899 Description: OSPF Threshold Metric sub-TLV 901 Reference: This document Section 4.4.2 903 9.4. Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 905 Type: Suggested 45 (TBA) 907 Description: Bandwidth metric 909 Reference: This document Section 2.1 911 9.5. Sub-sub-TLV Codepoints for Application-Specific Link Attributes 913 Type: Suggested 45 (TBA) 915 Description: Bandwidth metric 917 Reference: This document Section 2.1 919 9.6. OSPFv2 Extended Link TLV Sub-TLVs 921 Type: Suggested 45 (TBA) 923 Description: Bandwidth metric 924 Reference: This document Section 2.2 926 9.7. Types for sub-TLVs of TE Link TLV (Value 2) 928 Type: Suggested 45 (TBA) 930 Description: Bandwidth metric 932 Reference: This document Section 2.2 934 10. Acknowledgements 936 Many thanks to Chris Bowers, Krzysztof Szarcowitz, Julian Lucek, Ram 937 Santhanakrishnan for discussions and inputs. 939 11. Contributors 941 1. Salih K A 943 Juniper Networks 945 salih@juniper.net 947 12. References 949 12.1. Normative References 951 [I-D.ietf-lsr-flex-algo] 952 Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and 953 A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex- 954 algo-13 (work in progress), October 2020. 956 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 957 Requirement Levels", BCP 14, RFC 2119, 958 DOI 10.17487/RFC2119, March 1997, 959 . 961 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering 962 (TE) Extensions to OSPF Version 2", RFC 3630, 963 DOI 10.17487/RFC3630, September 2003, 964 . 966 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 967 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 968 2008, . 970 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 971 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 972 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 973 2015, . 975 12.2. Informative References 977 [I-D.bashandy-rtgwg-segment-routing-uloop] 978 Bashandy, A., Filsfils, C., Litkowski, S., Decraene, B., 979 Francois, P., and P. Psenak, "Loop avoidance using Segment 980 Routing", draft-bashandy-rtgwg-segment-routing-uloop-10 981 (work in progress), December 2020. 983 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 984 Topology (MT) Routing in Intermediate System to 985 Intermediate Systems (IS-ISs)", RFC 5120, 986 DOI 10.17487/RFC5120, February 2008, 987 . 989 [RFC5311] McPherson, D., Ed., Ginsberg, L., Previdi, S., and M. 990 Shand, "Simplified Extension of Link State PDU (LSP) Space 991 for IS-IS", RFC 5311, DOI 10.17487/RFC5311, February 2009, 992 . 994 [RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in 995 Support of Inter-Autonomous System (AS) MPLS and GMPLS 996 Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316, 997 December 2008, . 999 [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. 1000 Previdi, "OSPF Traffic Engineering (TE) Metric 1001 Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, 1002 . 1004 [RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward, 1005 D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) 1006 Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March 1007 2019, . 1009 Authors' Addresses 1011 Shraddha Hegde 1012 Juniper Networks Inc. 1013 Exora Business Park 1014 Bangalore, KA 560103 1015 India 1017 Email: shraddha@juniper.net 1018 William Britto 1019 Juniper Networks Inc. 1021 Email: bwilliam@juniper.net 1023 Rajesh Shetty 1024 Juniper Networks Inc. 1026 Email: mrajesh@juniper.net 1028 Bruno Decraene 1029 Orange 1031 Email: bruno.decraene@orange.com 1033 Peter Psenak 1034 Cisco Systems 1036 Email: ppsenak@cisco.com 1038 Tony Li 1039 Arista Networks 1041 Email: tony.li@tony.li