idnits 2.17.1 draft-ietf-isis-ext-lsp-frags-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Looks like you're using RFC 2026 boilerplate. This must be updated to follow RFC 3978/3979, as updated by RFC 4748. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- == No 'Intended status' indicated for this document; assuming Proposed Standard Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) Miscellaneous warnings: ---------------------------------------------------------------------------- -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- Couldn't find a document date in the document -- date freshness check skipped. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '3' on line 444 -- Possible downref: Non-RFC (?) normative reference: ref. 'ISIS-ISO' -- Possible downref: Non-RFC (?) normative reference: ref. 'ISIS-TE' -- Obsolete informational reference (is this intentional?): RFC 2966 (ref. 'DOMAIN-WIDE') (Obsoleted by RFC 5302) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Amir Hermelin 3 Internet Draft Charlotte's Web Networks 4 Expiration Date: December 2002 5 Stefano Previdi 6 Mike Shand 7 Cisco Systems 9 Extending the Number of IS-IS LSP Fragments Beyond the 256 Limit 11 draft-ietf-isis-ext-lsp-frags-01.txt 13 Status 15 This document is an Internet-Draft and is in full conformance with 16 all provisions of Section 10 of RFC2026. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 Abstract 36 This document describes a mechanism that allows a system to originate 37 more than 256 LSP fragments, a limit set by the original Intermediate 38 System to Intermediate System (IS-IS) Routing protocol, as described 39 in ISO 10589. This mechanism can be used in IP-only, OSI-only, and 40 dual routers. 42 1. Introduction 44 In the IS-IS protocol, a system floods its link-state information in 45 Link State Protocol Data Units, or LSPs for short. These logical 46 LSPs can become quite large, therefore the protocol specifies a means 47 of fragmenting this information into multiple LSP fragments. The 48 number of fragments a system can generate is limited by ISO 10589 49 [ISIS-ISO] to 256 fragments, where each fragment's size is also 50 limited. Hence, there is a limit on the amount of link-state 51 information a system can generate. 53 A number of factors can contribute to exceeding this limit: 54 - Introduction of new TLVs and sub-TLVs to be included in LSPs. 55 - The use of LSPs to propagate various types of information (such 56 as traffic-engineering information). 57 - The increasing number of destinations and AS topologies. 58 - Finer granularity routing, and the ability to inject external 59 routes into areas [DOMAIN-WIDE]. 60 - Other emerging technologies, such as optical, IPv6, etc. 62 This document describes mechanisms to relax the limit on the number 63 of LSP fragments. 65 1.1 Keywords 67 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 68 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 69 document are to be interpreted as described in RFC 2119 [BCP14]. 71 1.2 Definitions of Commonly Used Terms 73 This section provides definitions for terms that are used throughout 74 the text. 76 Originating System 77 A router physically running the IS-IS protocol. As this 78 document describes methods allowing a single IS-IS process to 79 advertise its LSPs as multiple "virtual" routers, the 80 Originating System represents the single "physical" IS-IS 81 process. 83 Normal system-id 84 The system-id of an Originating System. 86 Additional system-id 87 An Additional system-id that is assigned by the network 88 administrator. Each Additional system-id allows generation of 89 256 additional, or extended, LSP fragments. The Additional 90 system-id, like the Normal system-id, must be unique throughout 91 the routing domain. 93 Virtual System 94 The system, identified by an Additional system-id, advertised as 95 originating the extended LSP fragments. These fragments specify 96 the Additional system-id in their LSP IDs. 98 Original LSP 99 An LSP using the Normal system-id in its LSP ID. 101 Extended LSP 102 An LSP using an Additional system-id in its LSP ID. 104 LSP set 105 Logical LSP. This term is used only to resolve the ambiguity 106 between a logical LSP and an LSP fragment, both of which are 107 sometimes termed "LSP". 109 Extended LSP set 110 A group of LSP fragments using an Additional system-id, and 111 originated by the Originating System. 113 Extension-capable IS 114 An IS implementing this extension. 116 1.3 Operation Modes 118 Two administrative operation modes are provided: 120 - Operation Mode 1 provides behavior that allows implementations 121 that don't support this extension, to correctly process the 122 extended fragment information, without any modifications. This 123 mode has some restrictions on what may be advertised in the 124 extended LSP fragments. Namely, only leaf information may be 125 advertised in the extended LSPs. 127 - Operation Mode 2 extends the previous mode and relaxes its 128 advertisement restrictions. Any link-state information may be 129 advertised in the extended LSPs. However, it mandates a change 130 to the way LSPs are considered during the SPF algorithm, in a way 131 that isn't compatible with previous implementations. 133 These modes are configured on a per-level and area basis. That is, 134 all LSPs considered in the same SPF instance MUST use the same Mode. 135 There is no restriction that an L1/L2 IS operates in the same mode, 136 for both its L1 and L2 instances. It can use Mode 1 for its L1 LSPs, 137 and Mode 2 for its L2 LSPs, or vice versa. 139 Routers MAY implement Operational Mode 2 without supporting running 140 in Operational Mode 1. They will still interoperate correctly with 141 routers that support both modes. 143 1.4 Overview 145 Using Additional system-ids assigned by the administrator, the 146 Originating System can advertise the excess link-state information in 147 extended LSPs under these Additional system-ids. It would do so as 148 if other routers, or "Virtual Systems", were advertising this 149 information. These extended LSPs will also have the specified limit 150 on their LSP fragments; however, the Originating System may generate 151 extended LSPs under numerous Virtual Systems. 153 For Operation Mode 1, 0-cost adjacencies are advertised from the 154 Originating System to its Virtual System(s). No adjacencies (other 155 than back to the Originating System) are advertised in the extended 156 LSPs. As a consequence, the Virtual Systems are 'stub', meaning they 157 can only be reached through their Originating System. Therefore, 158 older implementations do not need modifications in order to correctly 159 process these extended LSPs. 161 For both modes, each LSP (set) created by a node will contain on its 162 fragment-0 a new TLV (IS Alias ID TLV) that contains the Normal 163 system-id and PN Number of the (first) LSP created by the router. 164 Extension-capable ISs can then use this information and store the 165 original and extended LSPs as one logical LSP. 167 2.0 IS Alias ID TLV (IS-A) 169 The proposed IS-A TLV allows extension-capable ISs to recognize all 170 LSPs of an Originating System, and combine the original and extended 171 LSPs for the purpose of SPF computation. It identifies the Normal 172 system-id of the Originating System. 174 The proposed IS Alias ID TLV is type 24, and its format is as 175 follows: 177 x CODE - 24. 179 x LENGTH - total length of the value field. 181 x VALUE - 183 No. of Octets 184 +-------------------+ 185 | Normal system-id | 6 186 +-------------------+ 187 | Pseudonode number | 1 188 +-------------------+ 189 | Sub-TLVs length | 1 190 +-------------------+ 191 | | 0-247 192 : Sub-TLVs : 193 : : 194 | | 195 +-------------------+ 197 Normal system-id 198 The Normal system-id of the LSP set, as described in section 1.2 of 199 this document. 201 Pseudonode number 202 The Pseudonode number of the LSP set. LSPs with the same Normal 203 system-id and Pseudonode number are considered in SPF as one 204 logical LSP, as described in section 5 of this document. 206 Sub-Tlvs length 207 Total length of all sub-TLVs. 209 Sub-TLVs 210 A series of tuples with the following format: 212 No. of Octets 213 +-------------------+ 214 | Sub-type | 1 215 +-------------------+ 216 | Length | 1 217 +-------------------+ 218 | | 0-245 219 : Value : 220 : : 221 | | 222 +-------------------+ 224 Sub-type 225 Type of the sub-TLV 227 Length 228 Total length of the value field 230 Value 231 Type-specific TLV payload. 233 For an explanation on sub-TLV handling, see [ISIS-TE]. 235 Without sub-TLVs, this structure consumes 8 octets per LSP set. This 236 TLV MUST be included in fragment 0 of every LSP set belonging to an 237 Originating System. Currently, there are no sub-TLVs defined. 239 For a complete list of used IS-IS TLV numbers, see [ISIS-CODES]. 241 3.0 Generating LSPs 243 3.1 Both Operation Modes 245 Under both modes, the Originating System MUST include information 246 binding the Original LSP and the Extended ones. It can do this since 247 it is trivially an extension-capable IS. This is to ensure other 248 extension-capable routers correctly process the extra information in 249 their SPF calculation. This binding is advertised via a new IS Alias 250 ID TLV, which is advertised in all fragment 0, whether they belong to 251 the original LSP or to the extended ones. 253 +---------------------------------------------+ 254 | Originating System | 255 | system-id = S | 256 | is-alias-id = S | 257 +---------------------------------------------+ 259 +-------------------+ +-------------------+ 260 | Virtual System | | Virtual System | 261 | system-id = S' | | system-id = S''| 262 | is-alias-id = S | | is-alias-id = S | 263 +-------------------+ +-------------------+ 265 Figure 1. Advertising binding between all of a system's LSPs (both 266 modes). S' and S'' are configured as Additional system-ids. 268 When new extended LSP fragments are generated, these fragments should 269 be generated as specified in ISO 10589 [ISIS-ISO]. Furthermore, a 270 system SHOULD treat its extended LSPs the same as it treats its 271 original LSPs, with the exceptions noted in the following sections. 273 Specifically, creating, flooding, renewing, purging and all other 274 operations are similar for both original and extended LSPs, unless 275 stated otherwise. The extended LSPs will use one of the Additional 276 system-ids configured for the router, in their LSP ID. 278 Extended LSPs fragment zero should be regarded in the same special 279 manner as specified in 10589 for LSPs with number zero, and should 280 include the same type of extra information as specified in 10589 and 281 RFC 1195 [ISIS-IP]. So, for example, when a system reissues its LSP 282 fragemnt zero due to an area address change, it should reissue all 283 extended LSPs fragment zero as well. 285 An extended LSP fragment zero MUST be generated for every extended 286 LSP set, to allow a router's SPF calculation to consider those 287 fragments in that set. 289 3.1.1 The Attached Bits 291 The Attached (ATT) bits SHOULD be set to zero for all four metric 292 types, on all extended LSPs. This is due to the following: if a 293 Virtual System is reachable, so is its Originating System. It is 294 preferable, then, that an L1 IS chooses the Originating System and 295 not the Virtual System as its nearest L2 exit point, as connectivity 296 to the Virtual System has a higher probability of being lost (a 297 result of the extended LSP no longer being advertised). This could 298 cause unnecessary computations on some implementations. 300 3.1.2 The Partition Repair Bit 302 The Partition Repair (P) bit SHOULD be set to zero on all extended 303 LSPs. This is for the same reasons as for the Attached bits. 305 3.1.3 ES Neighbors TLV 307 ISO 10589 [ISIS-ISO] section 7.3.7 specifies inserting an ES Neighbor 308 TLV in L1 LSPs, with the system ID of the router. RFC 1195 [ISIS-IP] 309 relieves IP-only routers of this requirement. However, for routers 310 that do insert this ESN TLV in L1 LSPs (whether IP-only or OSI- 311 capable), then in an extended LSP, the ESN TLV should include the 312 relevant Additional system-id. Furthermore, OSI-capable routers 313 should accept packets destined for this Additional system-id. 315 3.1.4 Overload Bit 316 The overload bit should be set consistently across all LSPs, original 317 and extended, belonging to an originating system, and should reflect 318 the originating system's overload state. 320 3.1.5 Other Fields and TLVs 322 Other fields and TLVs not mentioned above remain the same, both for 323 original and extended LSPs. 325 3.2 Operation Mode 1 Additions 327 The following additions apply only to routers generating LSPs in Mode 328 1. Routers, which are configured to operate in Operation Mode 2, 329 SHOULD NOT apply these additions to their advertisements. 331 Under Operation Mode 1, adjacencies between the normal system and its 332 Virtual Systems are advertised using the standard neighbor TLVs. The 333 metric for these connections MUST be zero, since the cost of reaching 334 a Virtual System is the same as the cost of reaching its Originating 335 System. 337 To older implementations, Virtual Systems would appear reachable only 338 through their Originating System, hence loss of connectivity to the 339 Originating System means loss of connectivity to all of its 340 information, including that advertised in its extended LSPs. 341 Furthermore, the cost of reaching information advertised in non- 342 extended LSPs is the same as the cost of reaching information 343 advertised in the new extended LSPs, with an additional hop. 345 +---------------------------------------------+ 346 | Originating System | 347 | system-id = S | 348 | is-alias-id = S | 349 +---------------------------------------------+ 350 | /\ | /\ 351 cost=0 | |cost=max-1 cost=0 | |cost=max-1 352 | | | | 353 \/ | \/ | 354 +-------------------+ +-------------------+ 355 | Virtual System | | Virtual System | 356 | system-id = S' | | system-id = S''| 357 | is-alias-id = S | | is-alias-id = S | 358 +-------------------+ +-------------------+ 360 Figure 2. Advertising connections to Virtual Systems under Operation 361 Mode 1. S' and S'' are configured as Additional system-ids. 363 Under Operation Mode 1, only "leaf" information, i.e. information 364 that serves only as leaves in a shortest path tree, can be advertised 365 in extended LSPs. 367 When an extended LSP belonging to Additional system-id S' is first 368 created, the original LSP MUST specify S' as a neighbor, with metric 369 set to zero. This in order to consider the cost of reaching the 370 Virtual System S' the same as the cost of reaching its Originating 371 System. Furthermore, the extended LSP MUST specify the Normal 372 system-id as a neighbor, with metric set to (MaxLinkMetric - 1). 373 This in order to satisfy the two-way connectivity check on other 374 routers. Where relevant, this adjacency SHOULD be considered as 375 point-to-point. 377 Note, that the restriction specified in ISO 10589 section 7.2.5 378 holds: if an LSP Number zero of the Originating System is not 379 present, none of that system's neighbor entries would be processed 380 during SPF, hence none of its extended LSPs would be processed as 381 well. 383 3.2.1 IS Neighbors TLV 385 An Extended LSP must specify only the Originating System as a 386 neighbor, with the metric set to (MaxLinkMetric - 1). Where 387 relevant, this adjacency should be considered as point-to-point. 388 Other neighbors MUST NOT be specified in an Extended LSP, because 389 those other neighbors would only specify the Originating System and 390 not the additional system, and hence would not satisfy the bi- 391 directionality check in the SPF computation. 393 4. Purging Extended LSP Fragments 395 ISO 10589 [ISIS-ISO] section 7.3.4.4 note 21 suggests that an 396 implementation keeps the number of LSP fragments within a certain 397 limit based on the optimal (minimal) number of fragments needed. 398 Section 7.3.4.6 also recommends that an IS purge its empty LSPs to 399 conserve resources. These recommendations hold for the extended LSP 400 fragments as well. However, an extended LSP fragment zero should not 401 be purged until all of the fragments in its set (i.e. belonging to a 402 particular Additional system-id), are empty as well. This is to 403 ensure implementations consider the fragments in their SPF 404 computations, as specified in section 7.2.5. 406 In Operational Mode 1, when all the extended LSP fragments of a 407 particular Additional system-id S' have been purged, the Originating 408 System SHOULD remove the neighbor information to S' from its original 409 LSPs. 411 5. Modifications to LSP handling in SPF 413 This section describes modifications to the way extension-capable ISs 414 handle LSPs for the SPF computation. 416 When considering LSPs of an extension-capable IS (identified by the 417 inclusion of the IS Alias ID TLV), the original and extended LSPs are 418 combined to form one large logical LSP. If the LSP belongs to an IS 419 running Operational Mode 1, there might be adjacencies between the 420 original and extended LSPs. These are trivially ignored (since when 421 processing them the large logical LSP is already on PATHS), and 422 doesn't complicate the SPF. Furthermore, this check should already 423 be implemented (this scenario could occur on error, without this 424 extension). 426 If LSP fragment 0 of the original LSP set is missing or its 427 RemainingLifetime is zero, all of the LSPs generated by that 428 Originating System (extended as well) MUST NOT be considered in the 429 SPF. That is, the large logical LSP isn't considered in the SPF. 430 The original LSP fragments are identified when the is-alias-id value 431 is the same as the system-id of those LSPs. If an LSP fragment 0 of 432 an extended LSP set is missing or its RemainingLifetime is zero, only 433 that LSP set MUST NOT be considered in the SPF. These rules are 434 present to ensure consistent SPF results on Mode 1 and Mode 2 LSPs. 436 Note, that the above behavior is consistent with how previous 437 implementations will interpret Mode 1 LSPs. 439 6. Forming Adjacencies 441 It should be noted, that an IS MUST use the system-id of the LSP that 442 will include a neighbor, when forming an adjacency with that 443 neighbor. That is, if a neighbor is to be included in extended LSP 444 S', then S' should be used as the system-id in IS Hellos [3] and IS- 445 IS Hellos when forming an adjacency with that neighbor. This is 446 regardless of the Operational Mode. Of course, in Mode 1 this means 447 that only the Normal system-id will be used when sending hellos. 449 7. Interoperating between extension-capable and non-extension-capable 450 ISs. 452 In order to correctly advertise link-state information under 453 Operation Mode 2, all ISs in an area must be extension-capable. 454 However, it is possible to not upgrade every router in the network, 455 if the extended information is not routing information, but rather 456 data that is of use to only a subset of routers (e.g. optical 457 switches using ISIS could carry optical-specific information in 458 extended LSPs) 460 If a live network contains routers exceeding the 256 fragment limit, 461 and for some reason the upgrade has to be done incrementally, it is 462 possible to transition the network, using the following steps: 463 - Upgrade the routers, one-by-one, to run this extension in 464 Operation Mode 1. The other non-extension-capable routers will 465 interoperate correctly. 466 - When all routers are extension-capable, configure them one-by-one 467 to run in Operation Mode 2. All extension-capable routers 468 interoperate correctly, regardless of what mode they're run in. 470 Implementations SHOULD support a configuration parameter controlling 471 the LSP origination behavior. The default value of this parameter 472 SHOULD correspond to the behavior described in [ISIS-ISO], i.e. 473 neither of the two modes described in this document should be enabled 474 without explicit configuration when the router software is upgraded 475 with this extension. 477 8. Security Considerations 479 This document raises no new security issues for IS-IS. 481 9. Acknowledgments 483 The authors would like to thank Tony Li and Radia Perlman for helpful 484 comments and suggestions on the subject. 486 10. References 488 10.1 Normative References 490 [ISIS-ISO] ISO 10589, "Intermediate System to Intermediate System 491 Intra-Domain Routeing Exchange Protocol for use in Conjunction with 492 the Protocol for Providing the Connectionless-mode Network Service 493 (ISO 8473)" 495 [ISIS-IP] RFC 1195, "Use of OSI IS-IS for routing in TCP/IP and dual 496 environments", R.W. Callon, Dec. 1990 498 [ISIS-TE] Work in progress, "IS-IS extensions for Traffic 499 Engineering", T. Li, H. Smit 501 [BCP14] RFC 2119, "Key words for use in RFCs to Indicate Requirement 502 Levels", S. Bradner, March 1997 504 10.2 Informative References 506 [DOMAIN-WIDE] RFC 2966, "Domain-wide Prefix Distribution with Two- 507 Level IS-IS", T. Li, T. Przygienda, H. Smit, October 2000 509 [ISIS-CODES] Work in progress, "Reserved TLV Codepoints in ISIS", T. 510 Przygienda 512 11. Authors' Addresses 514 Amir Hermelin Email: amir@cwnt.com 515 Charlotte's Web Networks, Inc. Phone: +972 4 9592203 516 2 Ha'mada St. Fax: +972 4 9593325 517 POB 650 518 Yokneam, 20692 519 ISRAEL 521 Mike Shand, Email: mshand@cisco.com 522 Cisco Systems, Phone: +44 020 8824 8690 523 4, The Square, 524 Stockley Park, 525 UXBRIDGE, 526 Middlesex, 527 UB11 1BN, 528 UK 530 Stefano Previdi email: sprevidi@cisco.com 531 Cisco Systems, Inc. Phone: +32 2 7046590 532 De Kleetlaan 6A 533 1831 Diegem 534 Belgium