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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10589' ** Downref: Normative reference to an Informational RFC: RFC 5309 Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force T. Li 3 Internet-Draft Arista Networks 4 Intended status: Standards Track L. Ginsberg 5 Expires: May 2, 2020 P. Wells 6 Cisco Systems 7 October 30, 2019 9 IS-IS Extended Hierarchy 10 draft-ietf-lsr-isis-extended-hierarchy-00 12 Abstract 14 The IS-IS routing protocol was originally defined with a two level 15 hierarchical structure. This was adequate for the networks at the 16 time. As we continue to expand the scale of our networks, it is 17 apparent that additional hierarchy would be a welcome degree of 18 flexibility in network design. 20 This document defines IS-IS Levels 3 through 8. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on May 2, 2020. 39 Copyright Notice 41 Copyright (c) 2019 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (https://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 58 2. PDU changes . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2.1. Circuit Type . . . . . . . . . . . . . . . . . . . . . . 3 60 2.2. PDU Type . . . . . . . . . . . . . . . . . . . . . . . . 4 61 3. Additional PDUs . . . . . . . . . . . . . . . . . . . . . . . 4 62 3.1. Level n LAN IS to IS hello PDU (Ln-LAN-HELLO-PDU) . . . . 4 63 3.2. Level n Point-to-point IS to IS hello PDU (Ln-P2P-HELLO- 64 PDU) . . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 4. Level Specific Area Identifiers . . . . . . . . . . . . . . . 5 66 4.1. IS-IS Area Identifier TLV . . . . . . . . . . . . . . . . 5 67 4.2. Adjacency Formation Rules . . . . . . . . . . . . . . . . 6 68 4.2.1. Level 3-8 Adjacency Formation Rules . . . . . . . . . 7 69 4.2.2. Special Level-2 Adjacency Formation Rules . . . . . . 7 70 5. New Flooding Scopes . . . . . . . . . . . . . . . . . . . . . 7 71 6. MAC Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 72 7. Inheritance of TLVs . . . . . . . . . . . . . . . . . . . . . 9 73 8. Behavior of Level n . . . . . . . . . . . . . . . . . . . . . 9 74 9. Relationship between levels . . . . . . . . . . . . . . . . . 9 75 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 76 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 77 11.1. PDU Type . . . . . . . . . . . . . . . . . . . . . . . . 9 78 11.2. New PDUs . . . . . . . . . . . . . . . . . . . . . . . . 10 79 11.3. New TLVs . . . . . . . . . . . . . . . . . . . . . . . . 10 80 11.4. New Flooding Scopes . . . . . . . . . . . . . . . . . . 10 81 11.5. New MAC Addresses . . . . . . . . . . . . . . . . . . . 11 82 12. Security Considerations . . . . . . . . . . . . . . . . . . . 12 83 13. Normative References . . . . . . . . . . . . . . . . . . . . 12 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 86 1. Introduction 88 The IS-IS routing protocol IS-IS [ISO10589] currently supports a two 89 level hierarchy of abstraction. The fundamental unit of abstraction 90 is the 'area', which is a (hopefully) connected set of systems 91 running IS-IS at the same level. Level 1, the lowest level, is 92 abstracted by routers that participate in both Level 1 and Level 2. 94 Practical considerations, such as the size of an area's link state 95 database, cause network designers to restrict the number of routers 96 in any given area. Concurrently, the dominance of scale-out 97 architectures based around small routers has created a situation 98 where the scalability limits of the protocol are going to become 99 critical in the foreseeable future. 101 The goal of this document is to enable additional hierarchy within 102 IS-IS. Each additional level of hierarchy has a multiplicative 103 effect on scale, so the addition of six levels should be a 104 significant improvement. While all six levels may not be needed in 105 the short term, it is apparent that the original designers of IS-IS 106 reserved enough space for these levels, and defining six additional 107 levels is only slightly harder than adding a single level, so it 108 makes sense to expand the design for the future. 110 The modifications described herein are designed to be fully backward 111 compatible and have no effect on existing networks. The 112 modifications are also designed to have no effect whatsoever on 113 networks that only use Level 1 and/or Level 2. 115 Section references in this document are references to sections of IS- 116 IS [ISO10589]. 118 1.1. Requirements Language 120 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 121 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 122 document are to be interpreted as described in RFC 2119 [RFC2119]. 124 2. PDU changes 126 In this section, we enumerate all of the redefinitions of protocol 127 header fields necessary to add additional levels. 129 2.1. Circuit Type 131 In the fixed header of some IS-IS PDUs, a field is named 'Reserved/ 132 Circuit Type' (Section 9.5). The high order six bits are reserved, 133 with the low order two bits indicating Level 1 (bit 1) and Level 2 134 (bit 2). 136 This field is renamed to be 'Circuit Type'. The bits are redefined 137 as follows: 139 1. Level 1 141 2. Level 2 143 3. Level 3 144 4. Level 4 146 5. Level 5 148 6. Level 6 150 7. Level 7 152 8. Level 8 154 The value of zero (no bits set) is reserved. PDUs with a Circuit 155 Type of zero SHALL be ignored. 157 The set bits of the Circuit Type MUST be contiguous. If bit n and 158 bit m are set in the Circuit Type, then all bits in the interval 159 [n:m] must be set. 161 2.2. PDU Type 163 The fixed header of IS-IS PDUs contains an octet with three reserved 164 bits and the 'PDU Type' field. The three reserved bits are 165 transmitted as zero and ignored on receipt. (Section 9.5) 167 To allow for additional PDU space, this entire octet is renamed the 168 'PDU Type' field. 170 3. Additional PDUs 172 3.1. Level n LAN IS to IS hello PDU (Ln-LAN-HELLO-PDU) 174 The 'Level n LAN IS to IS hello PDU' (Ln-LAN-HELLO-PDU) is identical 175 in format to the 'Level 2 LAN IS to IS hello PDU' (Section 9.6), 176 except that the PDU Types are defined as follows: 178 Level 3 (L3-LAN-HELLO-PDU): 33 (Suggested - to be assigned by 179 IANA) 181 Level 4 (L4-LAN-HELLO-PDU): 34 (Suggested - to be assigned by 182 IANA) 184 Level 5 (L5-LAN-HELLO-PDU): 35 (Suggested - to be assigned by 185 IANA) 187 Level 6 (L6-LAN-HELLO-PDU): 36 (Suggested - to be assigned by 188 IANA) 190 Level 7 (L7-LAN-HELLO-PDU): 37 (Suggested - to be assigned by 191 IANA) 192 Level 8 (L8-LAN-HELLO-PDU): 38 (Suggested - to be assigned by 193 IANA) 195 The Circuit Type field MUST be set to indicate all levels supported 196 on that circuit. 198 3.2. Level n Point-to-point IS to IS hello PDU (Ln-P2P-HELLO-PDU) 200 The 'Point-to-point IS to IS hello PDU' (Section 9.7) is used on 201 Level 1 and Level 2 circuits. Legacy systems will not expect the 202 circuit type field to indicate other levels, so a new PDU is used if 203 the circuit supports other levels. The additional PDU is the 'Level 204 n Point-to-point IS to IS hello PDU' (Ln-P2P-HELLO-PDU) and has PDU 205 Type 39 (Suggested - to be assigned by IANA). The format of this PDU 206 is identical to the existing Point-to-Point IS to IS hello PDU. Both 207 PDUs may be used on the same circuit. 209 4. Level Specific Area Identifiers 211 [ISO10589] defines an Area Address to uniquely identify a Level-1 212 area. A given area may have multiple synonymous area addresses - 213 which is useful in support of hitless merging or splitting of areas. 214 Area address matching is part of the adjacency formation rules 215 defined in Section 8 which determine whether a given adjacency 216 supports Level-1, Level-2, or both. Area addresses are advertised in 217 IIHs and LSPs using the Area Address TLV. 219 With the extensions defined in this document, there is a need to 220 define an equivalent identifier for Levels 2-8. This identifier is a 221 32 bit value and is advertised using the new Area Identifier TLV 222 defined in the following section. There is no relationship between 223 the Level-1 Area Addresses and the new Level Specific Area 224 Identifier. 226 Just as with Area Addresses, multiple synonomous Area Identifiers may 227 be assigned to a given level. This supports hitless merging or 228 splitting of the level specific area. Although it is legal to do so, 229 it is generally not useful to define more than two Area Identifiers 230 for a given level. 232 4.1. IS-IS Area Identifier TLV 234 The Area Identifier TLV is added to IS-IS to allow nodes to indicate 235 which areas they participate in for Levels 2-8. Area Identifiers are 236 locally administered 32 bit numbers. Each level may have multiple 237 Area Identifiers. The format of the TLV is: 239 0 1 2 3 240 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 1 241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 242 | TLV Type | TLV Length | Level | Count | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | Area Identifier | 245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 247 TLV Type: ZZZ 249 TLV Length: ( 2 * number of Levels) + ( 4 * each Count field ) 251 Level: The level number of the area. (1 octet) Legal values are 252 2-8 254 Count: The number of Area Identifier fields (1 octet) 256 Area Identifier: One or more identifiers associated with the area. 257 (4 * count octets) 259 The Level/Count/Area Identifier tuple MAY be repeated as necessary. 261 The Area Identifier TLV MAY appear in all types of IIHs except for 262 Level 1 LAN IS to IS hellos. 264 The Area Identifier TLV MAY appear in LSP #0 of non-pseudo-node Level 265 3-8 Flooding Scoped LSPs defined in Section 5. It MUST NOT be 266 present in any LSP with non-zero LSP number. If present in an LSP 267 with non-zero LSP number it MUST be ignored on receipt. 269 A system may participate in more than one level. At a given level, 270 an area may have a number of synonymous identifiers. A system MUST 271 advertise all of the levels it supports and the associated Area 272 Identifiers. 274 4.2. Adjacency Formation Rules 276 Adjacency formation rules for Levels 1 and 2 are defined in 277 [ISO10589] and are not altered by these extensions except where noted 278 below. 280 Adjacency Formation rules for Levels 3 and above are defined to 281 insure that adjacency support for a given level is only enabled when 282 there is a matching Area Identifier. Adjacency formation rules also 283 are defined so as to prevent interconnection of neighbors which will 284 connect to different areas at levels above any supported level. 286 4.2.1. Level 3-8 Adjacency Formation Rules 288 When the Area Identifier TLV appears in a Level N Point-to-point IS 289 to IS hello PDU or a Level N LAN IS to IS Hello PDU, the Circuit Type 290 field is inspected. For all levels with their corresponding bit set 291 in the Circuit Type in the range 3-8 the following checks are 292 performed: 294 o Check for a matching Area Identifier at the same level 296 o Check for a matching Area Identifier at all supported levels 297 greater than the level being checked 299 If both checks pass, then an adjacency can be formed supporting the 300 level. If any of the checks fail, then that level MUST NOT be 301 supported by an adjacency formed on that circuit. 303 On a Point-to-Point circuit, a single adjacency is formed which 304 supports all of the levels which pass the above checks. 306 On a LAN circuit, an adjacency is formed only for the level specified 307 by the PDU type. Nevertheless, the checks for all levels with the 308 corresponding bit set in the Circuit Type MUST be performed. 310 Note that (as previously specified) the set of levels supported MUST 311 be contiguous. 313 4.2.2. Special Level-2 Adjacency Formation Rules 315 The Area Identifier TLV MAY appear in a Point-to-point IS to IS hello 316 PDU or Level 2 LAN IS to IS Hello PDU (both specified in [ISO10589]). 317 In such a case, the neighbor may or may not support the Area 318 Identifier TLV. If the Area Identifier TLV is present and Level 2 is 319 indicated as being supported in the Circuit Type field, then in 320 addition to the checks specified in [ISO10589] the checks specified 321 in the previous section SHOULD be performed for Level 2. 323 5. New Flooding Scopes 325 For levels 3-8, all link state information, PSNPs, and CSNPs are 326 relayed in conformance with RFC 7356 [RFC7356]. Additional flooding 327 scopes are defined for each new level, for both circuit flooding 328 scope and level flooding scope. Level flooding scopes are defined 329 for both Standard and Extended TLV formats. The list of additional 330 flooding scopes is: 332 FS LSP ID Format/ 333 Value Description TLV Format 334 ----- ------------------------------ ----------------- 335 6 Level 3 Circuit Flooding Scope Extended/Standard 336 7 Level 4 Circuit Flooding Scope Extended/Standard 337 8 Level 5 Circuit Flooding Scope Extended/Standard 338 9 Level 6 Circuit Flooding Scope Extended/Standard 339 10 Level 7 Circuit Flooding Scope Extended/Standard 340 11 Level 8 Circuit Flooding Scope Extended/Standard 341 12 Level 3 Flooding Scope Extended/Standard 342 13 Level 4 Flooding Scope Extended/Standard 343 14 Level 5 Flooding Scope Extended/Standard 344 15 Level 6 Flooding Scope Extended/Standard 345 16 Level 7 Flooding Scope Extended/Standard 346 17 Level 8 Flooding Scope Extended/Standard 347 18 Level 3 Flooding Scope Standard/Standard 348 19 Level 4 Flooding Scope Standard/Standard 349 20 Level 5 Flooding Scope Standard/Standard 350 21 Level 6 Flooding Scope Standard/Standard 351 22 Level 7 Flooding Scope Standard/Standard 352 23 Level 8 Flooding Scope Standard/Standard 353 70 Level 3 Circuit Flooding Scope Extended/Extended 354 71 Level 4 Circuit Flooding Scope Extended/Extended 355 72 Level 5 Circuit Flooding Scope Extended/Extended 356 73 Level 6 Circuit Flooding Scope Extended/Extended 357 74 Level 7 Circuit Flooding Scope Extended/Extended 358 75 Level 8 Circuit Flooding Scope Extended/Extended 359 76 Level 3 Flooding Scope Extended/Extended 360 77 Level 4 Flooding Scope Extended/Extended 361 78 Level 5 Flooding Scope Extended/Extended 362 79 Level 6 Flooding Scope Extended/Extended 363 80 Level 7 Flooding Scope Extended/Extended 364 81 Level 8 Flooding Scope Extended/Extended 366 6. MAC Addresses 368 On a broadcast network, PDUs are currently sent to the AllL1Iss or 369 AllL2Iss MAC addresses. We will need additional MAC addresses for 370 Levels 3-8. 372 AllL3ISs: MAC3 374 AllL4ISs: MAC4 376 AllL5ISs: MAC5 378 AllL6ISs: MAC6 379 AllL7ISs: MAC7 381 AllL8ISs: MAC8 383 When operating in Point-to-Point mode on a broadcast network 384 [RFC5309], a Level N Point-to-Point Hello PDU will be sent. Any of 385 the above MAC addresses could be used in this case, but it is 386 recommended to use the AllL3ISs MAC address. 388 7. Inheritance of TLVs 390 All existing Level 2 TLVs may be used in the corresponding Level 3 391 through Level 8 PDUs. When used in a Level 3 through Level 8 PDU, 392 the semantics of these TLVs will be applied to the Level of the 393 containing PDU. If the original semantics of the PDU was carrying a 394 reference to Level 1 in a Level 2 TLV, then the semantics of the TLV 395 at level N will be a reference to level N-1. The intent is to retain 396 the original semantics of the TLV at the higher level. 398 8. Behavior of Level n 400 The behavior of Level n is analogous to the behavior of Level 2. 402 9. Relationship between levels 404 The relationship between Level n and Level n-1 is analogous to the 405 relationship between Level 2 and Level 1. 407 An area at Level n has at most one parent at Level n+1. 409 10. Acknowledgements 411 The authors would like to thank Dinesh Dutt for inspiring this 412 document and Huaimo Chen for his comments. 414 11. IANA Considerations 416 This document makes many requests to IANA, as follows: 418 11.1. PDU Type 420 The existing IS-IS PDU registry currently supports values 0-31. This 421 should be expanded to support the values 0-255. The existing value 422 assignments should be retained. Value 255 should be reserved. 424 11.2. New PDUs 426 IANA is requested to allocate values from the IS-IS PDU registry for 427 the following: 429 L3-LAN-HELLO-PDU: 33 (Suggested - to be assigned by IANA) 431 L4-LAN-HELLO-PDU: 34 (Suggested - to be assigned by IANA) 433 L5-LAN-HELLO-PDU: 35 (Suggested - to be assigned by IANA) 435 L6-LAN-HELLO-PDU: 36 (Suggested - to be assigned by IANA) 437 L7-LAN-HELLO-PDU: 37 (Suggested - to be assigned by IANA) 439 L8-LAN-HELLO-PDU: 38 (Suggested - to be assigned by IANA) 441 Ln-P2P-HELLO-PDU: 39 (Suggested - to be assigned by IANA) 443 11.3. New TLVs 445 IANA is requested to allocate values from the IS-IS TLV registry for 446 the following: 448 Area Identifier: ZZZ 450 11.4. New Flooding Scopes 452 IANA is requested to allocate the following values from the IS-IS 453 Flooding Scope Identifier Registry. 455 FS LSP ID Format/ IIH Announce 456 Value Description TLV Format Lx-P2P Lx-LAN 457 ----- ------------------------------ ----------------- ------ ------ 458 6 Level 3 Circuit Flooding Scope Extended/Standard Y Y 459 7 Level 4 Circuit Flooding Scope Extended/Standard Y Y 460 8 Level 5 Circuit Flooding Scope Extended/Standard Y Y 461 9 Level 6 Circuit Flooding Scope Extended/Standard Y Y 462 10 Level 7 Circuit Flooding Scope Extended/Standard Y Y 463 11 Level 8 Circuit Flooding Scope Extended/Standard Y Y 464 12 Level 3 Flooding Scope Extended/Standard Y Y 465 13 Level 4 Flooding Scope Extended/Standard Y Y 466 14 Level 5 Flooding Scope Extended/Standard Y Y 467 15 Level 6 Flooding Scope Extended/Standard Y Y 468 16 Level 7 Flooding Scope Extended/Standard Y Y 469 17 Level 8 Flooding Scope Extended/Standard Y Y 470 18 Level 3 Flooding Scope Standard/Standard Y Y 471 19 Level 4 Flooding Scope Standard/Standard Y Y 472 20 Level 5 Flooding Scope Standard/Standard Y Y 473 21 Level 6 Flooding Scope Standard/Standard Y Y 474 22 Level 7 Flooding Scope Standard/Standard Y Y 475 23 Level 8 Flooding Scope Standard/Standard Y Y 476 70 Level 3 Circuit Flooding Scope Extended/Extended Y Y 477 71 Level 4 Circuit Flooding Scope Extended/Extended Y Y 478 72 Level 5 Circuit Flooding Scope Extended/Extended Y Y 479 73 Level 6 Circuit Flooding Scope Extended/Extended Y Y 480 74 Level 7 Circuit Flooding Scope Extended/Extended Y Y 481 75 Level 8 Circuit Flooding Scope Extended/Extended Y Y 482 76 Level 3 Flooding Scope Extended/Extended Y Y 483 77 Level 4 Flooding Scope Extended/Extended Y Y 484 78 Level 5 Flooding Scope Extended/Extended Y Y 485 79 Level 6 Flooding Scope Extended/Extended Y Y 486 80 Level 7 Flooding Scope Extended/Extended Y Y 487 81 Level 8 Flooding Scope Extended/Extended Y Y 489 11.5. New MAC Addresses 491 IANA is requested to allocate values from the IANA Multicast 48-bit 492 MAC Addresses block for the following: 494 AllL3Iss: MAC3 496 AllL4Iss: MAC4 498 AllL5Iss: MAC5 500 AllL6Iss: MAC6 502 AllL7Iss: MAC7 503 AllL8Iss: MAC8 505 12. Security Considerations 507 This document introduces no new security issues. Security of routing 508 within a domain is already addressed as part of the routing protocols 509 themselves. This document proposes no changes to those security 510 architectures. 512 13. Normative References 514 [ISO10589] 515 International Organization for Standardization, 516 "Intermediate System to Intermediate System Intra-Domain 517 Routing Exchange Protocol for use in Conjunction with the 518 Protocol for Providing the Connectionless-mode Network 519 Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002. 521 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 522 Requirement Levels", BCP 14, RFC 2119, 523 DOI 10.17487/RFC2119, March 1997, 524 . 526 [RFC5309] Shen, N., Ed. and A. Zinin, Ed., "Point-to-Point Operation 527 over LAN in Link State Routing Protocols", RFC 5309, 528 DOI 10.17487/RFC5309, October 2008, 529 . 531 [RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding 532 Scope Link State PDUs (LSPs)", RFC 7356, 533 DOI 10.17487/RFC7356, September 2014, 534 . 536 Authors' Addresses 538 Tony Li 539 Arista Networks 540 5453 Great America Parkway 541 Santa Clara, California 95054 542 United States of America 544 Email: tony.li@tony.li 545 Les Ginsberg 546 Cisco Systems 547 United States of America 549 Email: ginsberg@cisco.com 551 Paul Wells 552 Cisco Systems 553 United States of America 555 Email: pauwells@cisco.com