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'IS-IS' ** Obsolete normative reference: RFC 3784 (Obsoleted by RFC 5305) ** Obsolete normative reference: RFC 3786 (Obsoleted by RFC 5311) ** Obsolete normative reference: RFC 4205 (Obsoleted by RFC 5307) == Outdated reference: A later version (-12) exists of draft-ietf-isis-wg-multi-topology-11 ** Obsolete normative reference: RFC 2434 (ref. 'BCP26') (Obsoleted by RFC 5226) ** Obsolete normative reference: RFC 3979 (ref. 'BCP79') (Obsoleted by RFC 8179) Summary: 8 errors (**), 0 flaws (~~), 9 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group L. Ginsberg 2 Internet Draft S. Previdi 3 Expiration Date: Dec 2006 M. Shand 4 Cisco Systems 5 June 2006 7 Simplified Extension of LSP Space for IS-IS 8 draft-ietf-isis-wg-extlsp-00.txt 10 Status of this Memo 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware 14 have been or will be disclosed, and any of which he or she becomes 15 aware will be disclosed, in accordance with Section 6 of BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six 23 months and may be updated, replaced, or obsoleted by other documents 24 at any time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/1id-abstracts.html 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html 33 Abstract 35 This draft describes a simplified method for extending the LSP space 36 beyond the 256 Link State PDU (LSP) limit defined in ISO 10589. This 37 method is intended as a preferred replacement for the method defined 38 in RFC 3786. 40 Table of Contents 41 1. Conventions used in this document..............................2 42 2. Overview.......................................................2 43 3. Definitions of Commonly Used Terms.............................3 44 4. Utilizing Additional System IDs................................4 45 4.1 Additional Information in Extended LSPs......................4 46 4.2 Extended LSP Restrictions....................................4 47 4.2.1 TLVs Which MUST NOT Appear................................4 48 4.2.2 Leaf Advertisements in Extended LSPs......................5 49 4.2.3 IS Neighbor Advertisement Restrictions....................5 50 4.2.4 Area Addresses............................................6 51 4.2.5 Overload, Attached, and Partition Repair Bits.............6 52 4.3 Originating LSP Requirements.................................6 53 4.4 IS Alias ID TLV (IS-Alias)...................................6 54 4.5 New TLVs in support of IS Neighbor Attributes................7 55 5. Comparison with the RFC 3786 Solution..........................8 56 6. Deployment Considerations......................................8 57 6.1 Advertising New TLVs in Extended LSPs........................8 58 6.2 Reachability and non-SPF TLV Staleness.......................9 59 6.3 Normal LSP OL State and the Use of Extended LSPs.............9 60 6.4 Moving Neighbor Attribute Information to Extended LSPs.......9 61 6.5 Advertising Leaf Information in Extended LSPs...............10 62 7. Security Considerations.......................................10 63 8. IANA Considerations...........................................10 64 9. Normative References..........................................10 65 10. Acknowledgments..............................................11 66 11. Authors' Addresses...........................................11 67 12. Full Copyright Statement.....................................12 69 1. Conventions used in this document 71 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 72 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 73 document are to be interpreted as described in RFC-2119 [BCP14]. 75 2. Overview 77 [IS-IS] defines the set of LSP fragments which may be originated by 78 a system at each level. This set is limited to 256 fragments. [IS- 79 IS] also defines a maximum value for an LSP fragment 80 (originatingLxLSPBufferSize) as 1492 bytes. The carrying capacity of 81 an LSP set, while bounded, has thus far been sufficient for 82 advertisements associated with an area/domain in existing deployment 83 scenarios. However, the definition of additional information to be 84 included in LSPs (e.g. multitopology support, traffic engineering 85 information, router capabilities, etc.) has the potential to exceed 86 the carrying capacity of an LSP set. 88 This issue first drew interest when traffic engineering extensions 89 were introduced. This interest resulted in the solution defined in 90 RFC 3786. However, that solution suffers from restrictions required 91 to maintain interoperability with systems which do not support the 92 extensions. 94 This document defines extensions which allow a system to exceed the 95 256 fragment limit and do so in a way which has no interoperability 96 issues with systems which do not support the extension. It is seen 97 as a simpler and therefore preferred solution to the problem. 99 3. Definitions of Commonly Used Terms 101 This section provides definitions for terms that are used throughout 102 the text. The terminology is consistent with that used in RFC 3786. 104 Originating System: A physical IS running the IS-IS protocol. As 105 this document describes a method which allows a single physical IS 106 to originate LSPs on behalf of multiple virtual ISs, the 107 Originating System represents the single physical IS. 109 Normal system-id: The system-id of an Originating System as defined 110 by [IS-IS]. 112 Additional system-id: A system-id other than the "Normal system-id" 113 that is assigned by the network administrator to an Originating 114 System in order to allow the generation of extended LSP fragments. 115 The Additional system-id, like the Normal system-id, must be 116 unique throughout the routing area (Level-1) or domain (Level-2). 118 Original LSP: An LSP using the Normal system-id in its LSP ID. 120 Extended LSP: An LSP using an Additional system-id in its LSP ID. 122 LSP set: Logical LSP. A group of LSP fragments (for a given level) 123 which have the same LSPID. This term is used to resolve the 124 ambiguity between a logical LSP and an LSP fragment, both of which 125 are sometimes termed "LSP". 127 Extended LSP set: An LSP set consisting of LSP fragments using an 128 Additional system-id. 130 Extension-capable IS: An IS implementing the mechanisms described in 131 this document. 133 4. Utilizing Additional System IDs 135 This extension allows an Originating System to be assigned 136 additional system-ids which may be used to generate additional LSP 137 sets. The additional system-ids are subject to the same restrictions 138 as normal system-ids i.e. when used at Level-1 the additional 139 system-id MUST be unique within the Level-1 area. When used at 140 Level-2 the additional system-id MUST be unique within the domain. 142 Extended LSPs are treated by the IS-IS Update Process in the same 143 manner as normal LSPs i.e. the same rules as to generation, 144 flooding, purging, etc. apply. In particular, if the Extended LSP 145 with LSP Number zero and remaining lifetime > 0 is not present for a 146 particular additional system-id then none of the extended LSPs in 147 that Extended LSP set shall be processed. 149 4.1 Additional Information in Extended LSPs 151 Fragment 0 of an Extended LSP Set MUST include the new IS alias ID 152 TLV defined in Section 4.4. This allows the Extended LSP set to be 153 associated with the Originating System which generated the LSP(s). 155 4.2 Extended LSP Restrictions 157 The following restrictions on the information which may appear in an 158 Extended LSP are defined in order to avoid interoperability issues 159 with systems which do not support the extensions defined in this 160 document. All TLV references are based on the current definitions in 161 the IANA IS-IS TLV Codepoints Registry. 163 4.2.1 TLVs Which MUST NOT Appear 165 The following TLVs MUST NOT appear in an Extended LSP: 167 TLV Name (#) 168 ----------- 169 ES Neighbors (3) 170 Part. DIS (4) 171 Prefix Neighbors (5) 173 If any of the TLVs listed above appear in an Extended LSP, an 174 Extension Capable IS MUST ignore those TLVs on receipt and SHOULD 175 report an error. Other TLVs in that extended LSP set MUST be 176 processed normally. 178 4.2.2 Leaf Advertisements in Extended LSPs 180 Advertisement of leaf information in Extended LSPs is allowed. 181 Inclusion of such information requires the advertisement of a 182 neighbor between the Originating System and the Virtual IS 183 associated with the extended LSP set in which the leaf 184 advertisements appear. See section 4.2.3. 186 When leaf advertisements for multiple topologies (see [M-IS-IS]) are 187 included in an Extended LSP set, the multi-topology TLV (229) MUST 188 include all topologies for which a leaf advertisement is included. 190 The following TLVs fall into this category: 192 TLV Name (#) 193 ----------- 194 IP Int. Reach (128) 195 IP Ext. Address (130) 196 The extended IP reachability TLV (135) 197 MT IP Reach (235) 198 IPv6 IP Reach (236) 199 MT IPv6 IP Reach (237) 201 4.2.3 IS Neighbor Advertisement Restrictions 203 Advertisement of IS Neighbor Reachability in an Extended LSP is 204 restricted to advertisement of neighbor reachability to the 205 Originating System. A neighbor to the Originating System MUST be 206 advertised in Extended LSPs. If multi-topology capability [M-IS-IS] 207 is supported, an MT IS Neighbor advertisement to the Originating 208 System IS MUST be included for every topology advertised in the 209 Extended LSP set. Neighbor advertisement(s) to the Originating 210 System in an Extended LSP MUST use a non-zero metric and SHOULD use 211 a metric of MaxLinkMetric-1. 213 The restrictions defined here apply to all TLVs used to advertise 214 neighbor reachability. These include the following TLVs: 216 TLV Name (#) 217 ----------- 218 IS Neighbors (2) 219 The extended IS reachability TLV (22) 220 MT-ISN (222) 222 4.2.4 Area Addresses 224 Fragment #0 of an Extended LSP set MUST include an Area Address TLV. 225 The set of area addresses advertised MUST be a subset of the set of 226 Area Addresses advertised in the normal LSP fragment #0 at the 227 corresponding level. Preferably the advertisement SHOULD be 228 syntactically identical to that included in the normal LSP fragment 229 #0 at the corresponding level. 231 4.2.5 Overload, Attached, and Partition Repair Bits 233 The Overload (OL), Attached (ATT), and Partition Repair (P) bits 234 MUST be set to 0 in all Extended LSP fragments. 236 Note that ISs NOT supporting these extensions will interpret these 237 bits normally in Extended LSPs they receive. If the ATT bit were set 238 in an Extended LSP this could indicate that the Virtual IS is 239 attached to other areas when the Originating System is not. This 240 might cause legacy systems to use the Virtual IS as a default exit 241 point from the area. 243 4.3 Originating LSP Requirements 245 The Original LSP set MUST include a neighbor to the Virtual IS 246 associated with each Extended LSP set generated. If multi-topology 247 capability [M-IS-IS] is supported, an MT IS Neighbor advertisement 248 to the Virtual IS MUST be included for every topology advertised in 249 the Extended LSP set. The neighbor advertisement(s) in the Original 250 LSP MUST specify a metric of zero. This guarantees that the two way 251 connectivity check between Originating System and Virtual IS will 252 succeed and that the cost of reaching the Virtual IS is the same as 253 the cost to reach the Originating System. 255 4.4 IS Alias ID TLV (IS-Alias) 257 The IS-Alias TLV allows extension-capable ISs to recognize the 258 Originating System of an Extended LSP set. It identifies the Normal 259 system-id of the Originating System. 261 Type 24 262 Length # of octets in the value field (7 to 255) 263 Value 265 No. of octets 266 +-----------------------+ 267 | Normal System-id | 6 268 +-----------------------+ 269 | Sub-TLV length | 1 270 +-----------------------+ 271 | Sub-TLVs (optional) | 0 to 248 272 +-----------------------+ 274 Normal system-id 276 The Normal system-id of the Originating System 278 Sub-TLVs length 280 Total length of all sub-TLVs. 282 Sub-TLVs 284 No subTLVs are defined in this document. Should future extensions 285 define subTLVs, the subTLVs MUST be formatted as described in RFC 286 3784. 288 4.5 New TLVs in support of IS Neighbor Attributes 290 One of the major sources of additional information in LSPs is the 291 subTLV information associated with the extended IS reachability TLV 292 (22) and MT IS Neighbor TLV (222). This includes (but is not limited 293 to) information required in support of Traffic Engineering (TE) as 294 defined in RFC 3784 and RFC 4205. The restrictions defined in this 295 document prohibit the presence of TLV 22 and/or TLV 222 in Extended 296 LSPs except to advertise the neighbor relationship to the 297 Originating System. In the event that there is a need to advertise 298 in Extended LSPs such information associated with neighbors of the 299 Originating System, it is necessary to define new TLVs to carry the 300 subTLV information. 302 Two new TLVs are therefore defined. 304 1)IS Neighbor Attribute TLV (23). It is identical in format to the 305 Extended IS Reachability TLV (22). 307 2)MT IS Neighbor Attribute TLV (223). It is identical in format to 308 the MT IS Neighbor TLV (222). 310 These new TLVs MAY be included in Original LSPs or Extended LSPs. 311 Regardless of the type of LSP in which the TLVs appear, the 312 information pertains to the neighbor relationship between the 313 Originating System and the IS identified in the TLV. 315 These TLVs MUST NOT be used to infer that a neighbor relationship 316 exists in the absence of TLV 22 or TLV 222 (whichever applies) in 317 the Originating LSP set for the specified neighbor. This restriction 318 is necessary in order to maintain compatibility with systems which 319 do not support these extensions. 321 5. Comparison with the RFC 3786 Solution 323 This document utilizes the same basic mechanism (additional system- 324 ids) as RFC 3786 to allow an originating system to generate more 325 than 256 LSP fragments. It differs from RFC 3786 in that it 326 restricts the content of Extended LSPs to information which does 327 NOT impact the building of a Shortest Path Tree (SPT). 329 Legacy IS-IS implementations which do not support the extensions 330 defined in this document see the extended LSPs as information 331 associated with a system which is reachable only via the Originating 332 System. As no other systems are reachable via the Virtual ISs, the 333 SPF calculation in legacy ISs is therefore consistent with that 334 performed by extension capable ISs. There is therefore no need for 335 the two different operating modes defined in RFC 3786. 337 There is also no need for the special handling of the original LSP 338 set and the extended LSP set(s) as a single Logical LSP during the 339 SPF as specified in Section 5 of RFC 3786. 341 6. Deployment Considerations 343 There are a number of deployment considerations which limit the 344 usefulness of extended LSPs unless all systems are extension-capable 345 ISs. 347 6.1 Advertising New TLVs in Extended LSPs 349 As extended LSPs MAY be utilized to advertise TLVs associated with 350 other protocol extensions (definition of which is outside the scope 351 of this document) and/or the extensions defined in Section 4.5 of 352 this document, it is obvious that the utilization of the information 353 in extended LSPs by legacy IS-IS implementations will be limited. 354 The implication of this is that as implementations are revised to 355 support the protocol extensions which define new TLVs/subTLVs that 356 MAY be advertised in extended LSPs, the implementation SHOULD also 357 be revised to support the extensions defined in this document so 358 that it is capable of processing the new information whether it 359 appears in normal or extended LSPs. 361 6.2 Reachability and non-SPF TLV Staleness 363 In cases where non-SPF information is advertised in LSPs, it is 364 necessary to determine whether the system which originated the 365 advertisement is reachable in order to guarantee that a receiving IS 366 does not use or leak stale information. So long as the OL bit is NOT 367 set by the Originating System in normal LSPs, reachability to the 368 Virtual IS will be consistent with reachability to the Originating 369 System. Therefore, no special rules are required in this case. 371 6.3 Normal LSP OL State and the Use of Extended LSPs 373 If the Originating System sets the OL bit in a normal LSP, legacy 374 systems will see the Virtual ISs associated with that Originating 375 System as unreachable and therefore will not use the information in 376 the corresponding Extended LSPs. Under these circumstances, 377 Extension capable ISs MUST also see the Virtual ISs as unreachable. 378 This avoids potential routing loops in cases where leaf information 379 is advertised in Extended LSPs. 381 6.4 Moving Neighbor Attribute Information to Extended LSPs 383 Section 4.5 defines new TLVs which MAY be used to advertise neighbor 384 attribute information in extended LSPs. In cases where neighbor 385 attribute information associated with the same context (e.g. the 386 same link) appears in both an Original LSP and in one or more 387 Extended LSP Sets, the following rules apply for each attribute: 389 o If the attribute information does not conflict, it MUST be 390 considered additive 392 o If the attribute information conflicts, then the information in 393 the Original LSP, if present, MUST be used. If no information is 394 in the Original LSP, then the information from the Extended LSP 395 with the lowest system-id SHALL be preferred. 397 Utilization of the new TLVs for neighbor attribute information would 398 provide additional benefits which include: 400 o Elimination of the need for redundant IS neighbor TLVs to be 401 processed as part of the SPF. 403 o Easier support for a set of TE information associated with a 404 single link which exceeds the 255 byte TLV limit by allowing the 405 interpretation of multiple TLVs to be considered additive rather 406 than mutually exclusive. 408 6.5 Advertising Leaf Information in Extended LSPs 410 The need to advertise leaf information in Extended LSPs may arise 411 because of extensive leaking of inter-level information or because 412 of the support of multiple topologies as described in [M-IS-IS]. 413 When leaf information is advertised in Extended LSPs, these LSPs now 414 contain information which MUST be processed in order to correctly 415 update the forwarding plane of an IS. This may increase the 416 frequency of SPF calculations by ISs in the network. It is therefore 417 recommended that, when possible, leaf information be restricted to 418 the normal LSP set. 420 7. Security Considerations 422 This document raises no new security issues for IS-IS. 424 8. IANA Considerations 426 This document defines the following new ISIS TLVs that need to be 427 reflected in the ISIS TLV code-point registry: 429 Type Description IIH LSP SNP 430 ---- ----------------------------------- --- --- --- 431 23 IS Neighbor Attribute n y n 432 24 IS Alias ID n y n 433 223 MT IS Neighbor Attribute n y n 435 9. Normative References 437 [IS-IS] ISO, "Intermediate system to Intermediate system routeing 438 information exchange protocol for use in conjunction with the 439 Protocol for providing the Connectionless-mode Network Service 440 (ISO 8473)," ISO/IEC 10589:2002, Second Edition. 442 [RFC 3784] Smit, H. and T. Li, "Intermediate System to 443 Intermediate System (IS-IS) Extensions for Traffic Engineering 444 (TE)", RFC 3784, June 2004. 446 [RFC 3786] Hermelin, A., Previdi, S. and Shand, M., "Extending the 447 Number of Intermediate to Intermediate (IS-IS) Link State PDU 448 (LSP) Fragments Beyond the 256 Limit," RFC 3786, May 2004. 450 [RFC 4205] Kompella, K. and Rehkter, Y., "Intermediate System to 451 Intermediate System (IS-IS) Extensions in Support of Generalized 452 Multi-Protocol Label Switching (GMPLS)", RFC 4205, October 2005. 454 [M-IS-IS] Pryzgienda, T., Shen, N., and Sheth, N., "Multi Topology 455 (MT) Routing in IS-IS", draft-ietf-isis-wg-multi-topology-11.txt 456 (work in progress), October 2005. 458 [BCP9] Bradner, S., "The Internet Standards Process -- Revision 459 3", BCP 9, RFC 2026, October 1996. 461 [BCP14] Bradner, S., "Key words for use in RFCs to Indicate 462 Requirement Levels", BCP 14, RFC 2119, March 1997 464 [BCP26] Narten, T. and Alvestrand, H., "Guidelines for Writing an 465 IANA Considerations Section in RFCs", BCP 26 , RFC 2434, October 466 1998 468 [BCP79] Bradner, S. Ed., "Intellectual Property Rights in IETF 469 Technology ", BCP 79 , RFC 3979, March 2005 471 10. Acknowledgments 473 11. Authors' Addresses 475 Les Ginsberg 476 Cisco Systems 477 510 McCarthy Blvd. 478 Milpitas, Ca. 95035 USA 479 Email: ginsberg@cisco.com 481 Stefano Previdi 482 CISCO Systems, Inc. 483 Via Del Serafico 200 484 00142 - Roma 485 ITALY 486 Email: sprevidi@cisco.com 488 Mike Shand 489 Cisco Systems 490 250 Longwater Avenue, 491 Reading, 492 Berkshire, 493 RG2 6GB 494 UK 495 Email: mshand@cisco.com 497 12. 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