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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) -- Obsolete informational reference (is this intentional?): RFC 5316 (Obsoleted by RFC 9346) Summary: 0 errors (**), 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 M. Chen 3 Internet-Draft Huawei 4 Obsoletes: 5316 (if approved) L. Ginsberg 5 Intended status: Standards Track Cisco Systems 6 Expires: August 22, 2021 S. Previdi 7 Huawei Technologies 8 D. Xiaodong 9 China Mobile 10 February 18, 2021 12 ISIS Extensions in Support of Inter-Autonomous System (AS) MPLS and 13 GMPLS Traffic Engineering 14 draft-ietf-lsr-isis-rfc5316bis-01 16 Abstract 18 This document describes extensions to the Intermediate System to 19 Intermediate System (IS-IS) protocol to support Multiprotocol Label 20 Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering 21 (TE) for multiple Autonomous Systems (ASs). It defines IS-IS 22 extensions for the flooding of TE information about inter-AS links, 23 which can be used to perform inter-AS TE path computation. 25 No support for flooding information from within one AS to another AS 26 is proposed or defined in this document. 28 This document obsoletes RFC 5316. 30 Requirements Language 32 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 33 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 34 "OPTIONAL" in this document are to be interpreted as described in BCP 35 14 [RFC2119] [RFC8174] when, and only when, they appear in all 36 capitals, as shown here. 38 Status of This Memo 40 This Internet-Draft is submitted in full conformance with the 41 provisions of BCP 78 and BCP 79. 43 Internet-Drafts are working documents of the Internet Engineering 44 Task Force (IETF). Note that other groups may also distribute 45 working documents as Internet-Drafts. The list of current Internet- 46 Drafts is at https://datatracker.ietf.org/drafts/current/. 48 Internet-Drafts are draft documents valid for a maximum of six months 49 and may be updated, replaced, or obsoleted by other documents at any 50 time. It is inappropriate to use Internet-Drafts as reference 51 material or to cite them other than as "work in progress." 53 This Internet-Draft will expire on August 22, 2021. 55 Copyright Notice 57 Copyright (c) 2021 IETF Trust and the persons identified as the 58 document authors. All rights reserved. 60 This document is subject to BCP 78 and the IETF Trust's Legal 61 Provisions Relating to IETF Documents 62 (https://trustee.ietf.org/license-info) in effect on the date of 63 publication of this document. Please review these documents 64 carefully, as they describe your rights and restrictions with respect 65 to this document. Code Components extracted from this document must 66 include Simplified BSD License text as described in Section 4.e of 67 the Trust Legal Provisions and are provided without warranty as 68 described in the Simplified BSD License. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 73 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4 74 2.1. A Note on Non-Objectives . . . . . . . . . . . . . . . . 4 75 2.2. Per-Domain Path Determination . . . . . . . . . . . . . . 5 76 2.3. Backward Recursive Path Computation . . . . . . . . . . . 6 77 3. Extensions to ISIS-TE . . . . . . . . . . . . . . . . . . . . 7 78 3.1. Inter-AS Reachability TLV . . . . . . . . . . . . . . . . 8 79 3.2. TE Router ID . . . . . . . . . . . . . . . . . . . . . . 9 80 3.3. Sub-TLVs for Inter-AS Reachability TLV . . . . . . . . . 10 81 3.3.1. Remote AS Number Sub-TLV . . . . . . . . . . . . . . 10 82 3.3.2. IPv4 Remote ASBR ID Sub-TLV . . . . . . . . . . . . . 10 83 3.3.3. IPv6 Remote ASBR ID Sub-TLV . . . . . . . . . . . . . 11 84 3.3.4. IPv6 Local ASBR ID sub-TLV . . . . . . . . . . . . . 12 85 3.4. Sub-TLVs for IS-IS Router Capability TLV . . . . . . . . 13 86 3.4.1. IPv4 TE Router ID sub-TLV . . . . . . . . . . . . . . 13 87 3.4.2. IPv6 TE Router ID sub-TLV . . . . . . . . . . . . . . 13 88 4. Procedure for Inter-AS TE Links . . . . . . . . . . . . . . . 14 89 4.1. Origin of Proxied TE Information . . . . . . . . . . . . 15 90 5. Security Considerations . . . . . . . . . . . . . . . . . . . 16 91 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 92 6.1. Inter-AS Reachability TLV . . . . . . . . . . . . . . . . 17 93 6.2. Sub-TLVs for the Inter-AS Reachability TLV . . . . . . . 17 94 6.3. Sub-TLVs for the IS-IS Router Capability TLV . . . . . . 17 95 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 96 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 97 8.1. Normative References . . . . . . . . . . . . . . . . . . 18 98 8.2. Informative References . . . . . . . . . . . . . . . . . 18 99 Appendix A. Changes to RFC 5316 . . . . . . . . . . . . . . . . 20 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 102 1. Introduction 104 [RFC5305] defines extensions to the IS-IS protocol [RFC1195] to 105 support intra-area Traffic Engineering (TE). The extensions provide 106 a way of encoding the TE information for TE-enabled links within the 107 network (TE links) and flooding this information within an area. The 108 extended IS reachability TLV and traffic engineering router ID TLV, 109 which are defined in [RFC5305], are used to carry such TE 110 information. The extended IS reachability TLV has several nested 111 sub-TLVs that describe the TE attributes for a TE link. 113 [RFC6119] and [RFC5307] define similar extensions to IS-IS in support 114 of IPv6 and Generalized Multiprotocol Label Switching (GMPLS) TE 115 respectively. 117 Requirements for establishing Multiprotocol Label Switching (MPLS) TE 118 Label Switched Paths (LSPs) that cross multiple Autonomous Systems 119 (ASes) are described in [RFC4216]. As described in [RFC4216], a 120 method SHOULD provide the ability to compute a path spanning multiple 121 ASes. So a path computation entity that may be the head-end Label 122 Switching Router (LSR), an AS Border Router (ASBR), or a Path 123 Computation Element (PCE) [RFC4655] needs to know the TE information 124 not only of the links within an AS, but also of the links that 125 connect to other ASes. 127 In this document, a new TLV, which is referred to as the inter-AS 128 reachability TLV, is defined to advertise inter-AS TE information, 129 three new sub-TLVs are defined for inclusion in the inter-AS 130 reachability TLV to carry the information about the remote AS number 131 and remote ASBR ID. The sub-TLVs defined in [RFC5305][RFC6119] and 132 other documents for inclusion in the extended IS reachability TLV for 133 describing the TE properties of a TE link are applicable to be 134 included in the Inter-AS Reachability TLV for describing the TE 135 properties of an inter-AS TE link as well. Also, two more new sub- 136 TLVs are defined for inclusion in the IS-IS router capability TLV to 137 carry the TE Router ID when the TE Router ID needs to reach all 138 routers within an entire ISIS routing domain. The extensions are 139 equally applicable to IPv4 and IPv6 as identical extensions to 140 [RFC5305] and [RFC6119]. Detailed definitions and procedures are 141 discussed in the following sections. 143 This document does not propose or define any mechanisms to advertise 144 any other extra-AS TE information within ISIS. See Section 2.1 for a 145 full list of non-objectives for this work. 147 2. Problem Statement 149 As described in [RFC4216], in the case of establishing an inter-AS TE 150 LSP that traverses multiple ASes, the Path message [RFC3209] may 151 include the following elements in the Explicit Route Object (ERO) in 152 order to describe the path of the LSP: 154 o a set of AS numbers as loose hops; and/or 156 o a set of LSRs including ASBRs as loose hops. 158 Two methods for determining inter-AS paths are currently being 159 discussed. The per-domain method [RFC5152] determines the path one 160 domain at a time. The backward recursive method [RFC5441] uses 161 cooperation between PCEs to determine an optimum inter-domain path. 162 The sections that follow examine how inter-AS TE link information 163 could be useful in both cases. 165 2.1. A Note on Non-Objectives 167 It is important to note that this document does not make any change 168 to the confidentiality and scaling assumptions surrounding the use of 169 ASes in the Internet. In particular, this document is conformant to 170 the requirements set out in [RFC4216]. 172 The following features are explicitly excluded: 174 o There is no attempt to distribute TE information from within one 175 AS to another AS. 177 o There is no mechanism proposed to distribute any form of TE 178 reachability information for destinations outside the AS. 180 o There is no proposed change to the PCE architecture or usage. 182 o TE aggregation is not supported or recommended. 184 o There is no exchange of private information between ASes. 186 o No ISIS adjacencies are formed on the inter-AS link. 188 2.2. Per-Domain Path Determination 190 In the per-domain method of determining an inter-AS path for an MPLS- 191 TE LSP, when an LSR that is an entry-point to an AS receives a Path 192 message from an upstream AS with an ERO containing a next hop that is 193 an AS number, it needs to find which LSRs (ASBRs) within the local AS 194 are connected to the downstream AS. That way, it can compute a TE 195 LSP segment across the local AS to one of those LSRs and forward the 196 Path message to that LSR and hence into the next AS. See Figure 1 197 for an example. 199 R1------R3----R5-----R7------R9-----R11 200 | | \ | / | 201 | | \ | ---- | 202 | | \ | / | 203 R2------R4----R6 --R8------R10----R12 204 : : 205 <-- AS1 -->:<---- AS2 --->:<--- AS3 ---> 207 Figure 1: Inter-AS Reference Model 209 The figure shows three ASes (AS1, AS2, and AS3) and twelve LSRs (R1 210 through R12). R3 and R4 are ASBRs in AS1. R5, R6, R7, and R8 are 211 ASBRs in AS2. R9 and R10 are ASBRs in AS3. 213 If an inter-AS TE LSP is planned to be established from R1 to R12, 214 the AS sequence will be: AS1, AS2, AS3. 216 Suppose that the Path message enters AS2 from R3. The next hop in 217 the ERO shows AS3, and R5 must determine a path segment across AS2 to 218 reach AS3. It has a choice of three exit points from AS2 (R6, R7, 219 and R8), and it needs to know which of these provide TE connectivity 220 to AS3, and whether the TE connectivity (for example, available 221 bandwidth) is adequate for the requested LSP. 223 Alternatively, if the next hop in the ERO is the entry ASBR for AS3 224 (say R9), R5 needs to know which of its exit ASBRs has a TE link that 225 connects to R9. Since there may be multiple ASBRs that are connected 226 to R9 (both R7 and R8 in this example), R5 also needs to know the TE 227 properties of the inter-AS TE links so that it can select the correct 228 exit ASBR. 230 Once the Path message reaches the exit ASBR, any choice of inter-AS 231 TE link can be made by the ASBR if not already made by the entry ASBR 232 that computed the segment. 234 More details can be found in Section 4 of [RFC5152], which clearly 235 points out why advertising of inter-AS links is desired. 237 To enable R5 to make the correct choice of exit ASBR, the following 238 information is needed: 240 o List of all inter-AS TE links for the local AS. 242 o TE properties of each inter-AS TE link. 244 o AS number of the neighboring AS connected to by each inter-AS TE 245 link. 247 o Identity (TE Router ID) of the neighboring ASBR connected to by 248 each inter-AS TE link. 250 In GMPLS networks, further information may also be required to select 251 the correct TE links as defined in [RFC5307]. 253 The example above shows how this information is needed at the entry- 254 point ASBRs for each AS (or the PCEs that provide computation 255 services for the ASBRs). However, this information is also needed 256 throughout the local AS if path computation functionality is fully 257 distributed among LSRs in the local AS, for example to support LSPs 258 that have start points (ingress nodes) within the AS. 260 2.3. Backward Recursive Path Computation 262 Another scenario using PCE techniques has the same problem. 263 [RFC5441] defines a PCE-based TE LSP computation method (called 264 Backward Recursive Path Computation) to compute optimal inter-domain 265 constrained MPLS-TE or GMPLS LSPs. In this path computation method, 266 a specific set of traversed domains (ASes) are assumed to be selected 267 before computation starts. Each downstream PCE in domain(i) returns 268 to its upstream neighbor PCE in domain(i-1) a multipoint-to-point 269 tree of potential paths. Each tree consists of the set of paths from 270 all boundary nodes located in domain(i) to the destination where each 271 path satisfies the set of required constraints for the TE LSP 272 (bandwidth, affinities, etc.). 274 So a PCE needs to select boundary nodes (that is, ASBRs) that provide 275 connectivity from the upstream AS. In order for the tree of paths 276 provided by one PCE to its neighbor to be correlated, the identities 277 of the ASBRs for each path need to be referenced. Thus, the PCE must 278 know the identities of the ASBRs in the remote AS that are reached by 279 any inter-AS TE link, and, in order to provide only suitable paths in 280 the tree, the PCE must know the TE properties of the inter-AS TE 281 links. See the following figure as an example. 283 PCE1<------>PCE2<-------->PCE3 284 / : : 285 / : : 286 R1------R3----R5-----R7------R9-----R11 287 | | \ | / | 288 | | \ | ---- | 289 | | \ | / | 290 R2------R4----R6 --R8------R10----R12 291 : : 292 <-- AS1 -->:<---- AS2 --->:<--- AS3 ---> 294 Figure 2: BRPC for Inter-AS Reference Model 296 The figure shows three ASes (AS1, AS2, and AS3), three PCEs (PCE1, 297 PCE2, and PCE3), and twelve LSRs (R1 through R12). R3 and R4 are 298 ASBRs in AS1. R5, R6, R7, and R8 are ASBRs in AS2. R9 and R10 are 299 ASBRs in AS3. PCE1, PCE2, and PCE3 cooperate to perform inter-AS 300 path computation and are responsible for path segment computation 301 within their own domain(s). 303 If an inter-AS TE LSP is planned to be established from R1 to R12, 304 the traversed domains are assumed to be selected: AS1->AS2->AS3, and 305 the PCE chain is: PCE1->PCE2->PCE3. First, the path computation 306 request originated from the PCC (R1) is relayed by PCE1 and PCE2 307 along the PCE chain to PCE3. Then, PCE3 begins to compute the path 308 segments from the entry boundary nodes that provide connection from 309 AS2 to the destination (R12). But, to provide suitable path 310 segments, PCE3 must determine which entry boundary nodes provide 311 connectivity to its upstream neighbor AS (identified by its AS 312 number), and must know the TE properties of the inter-AS TE links. 313 In the same way, PCE2 also needs to determine the entry boundary 314 nodes according to its upstream neighbor AS and the inter-AS TE link 315 capabilities. 317 Thus, to support Backward Recursive Path Computation, the same 318 information listed in Section 2.2 is required. The AS number of the 319 neighboring AS connected to by each inter-AS TE link is particularly 320 important. 322 3. Extensions to ISIS-TE 324 Note that this document does not define mechanisms for distribution 325 of TE information from one AS to another, does not distribute any 326 form of TE reachability information for destinations outside the AS, 327 does not change the PCE architecture or usage, does not suggest or 328 recommend any form of TE aggregation, and does not feed private 329 information between ASes. See Section 2.1. 331 In this document, for the advertisement of inter-AS TE links, a new 332 TLV, which is referred to as the inter-AS reachability TLV, is 333 defined. Three new sub-TLVs are also defined for inclusion in the 334 inter-AS reachability TLV to carry the information about the 335 neighboring AS number and the remote ASBR ID of an inter-AS link. 336 The sub-TLVs defined in [RFC5305], [RFC6119], and other documents for 337 inclusion in the extended IS reachability TLV are applicable to be 338 included in the inter-AS reachability TLV for inter-AS TE links 339 advertisement. Also, two other new sub-TLVs are defined for 340 inclusion in the IS-IS router capability TLV to carry the TE Router 341 ID when the TE Router ID is needed to reach all routers within an 342 entire ISIS routing domain. 344 While some of the TE information of an inter-AS TE link may be 345 available within the AS from other protocols, in order to avoid any 346 dependency on where such protocols are processed, this mechanism 347 carries all the information needed for the required TE operations. 349 3.1. Inter-AS Reachability TLV 351 The inter-AS reachability TLV has type 141 (see Section 6.1) and 352 contains a data structure consisting of: 354 4 octets of Router ID 355 3 octets of default metric 356 1 octet of control information, consisting of: 357 1 bit of flooding-scope information (S bit) 358 1 bit of up/down information (D bit) 359 6 bits reserved 360 1 octet of length of sub-TLVs 361 0-246 octets of sub-TLVs, where each sub-TLV consists of a sequence 362 of: 363 1 octet of sub-type 364 1 octet of length of the value field of the sub-TLV 365 0-244 octets of value 367 Compared to the extended reachability TLV which is defined in 368 [RFC5305], the inter-AS reachability TLV replaces the "7 octets of 369 System ID and Pseudonode Number" field with a "4 octets of Router ID" 370 field and introduces an extra "control information" field, which 371 consists of a flooding-scope bit (S bit), an up/down bit (D bit), and 372 6 reserved bits. 374 The Router ID field of the inter-AS reachability TLV is 4 octets in 375 length, which contains the IPv4 Router ID of the router who generates 376 the inter-AS reachability TLV. The Router ID SHOULD be identical to 377 the value advertised in the Traffic Engineering Router ID TLV 378 [RFC5305]. If no Traffic Engineering Router ID is assigned, the 379 Router ID SHOULD be identical to an IP Interface Address [RFC1195] 380 advertised by the originating IS. If the originating node does not 381 support IPv4, then the reserved value 0.0.0.0 MUST be used in the 382 Router ID field and the IPv6 Router ID sub-TLV MUST be present in the 383 inter-AS reachability TLV. The Router ID could be used to indicate 384 the source of the inter-AS reachability TLV. 386 The flooding procedures for inter-AS reachability TLV are identical 387 to the flooding procedures for the GENINFO TLV, which are defined in 388 Section 4 of [RFC6823]. These procedures have been previously 389 discussed in [RFC7981]. The flooding-scope bit (S bit) SHOULD be set 390 to 0 if the flooding scope is to be limited to within the single IGP 391 area to which the ASBR belongs. It MAY be set to 1 if the 392 information is intended to reach all routers (including area border 393 routers, ASBRs, and PCEs) in the entire ISIS routing domain. The 394 choice between the use of 0 or 1 is an AS-wide policy choice, and 395 configuration control SHOULD be provided in ASBR implementations that 396 support the advertisement of inter-AS TE links. 398 The sub-TLVs defined in [RFC5305], [RFC6119], and other documents for 399 describing the TE properties of a TE link are also applicable to the 400 inter-AS reachability TLV for describing the TE properties of an 401 Inter-AS TE link. Apart from these sub-TLVs, four new sub-TLVs are 402 defined for inclusion in the inter-AS reachability TLV defined in 403 this document: 405 Sub-TLV type Length Name 406 ------------ ------ --------------------------- 407 24 4 remote AS number 408 25 4 IPv4 remote ASBR identifier 409 26 16 IPv6 remote ASBR identifier 410 TBD1 16 IPv6 Router ID 412 Detailed definitions of the four new sub-TLVs are described in 413 Sections 3.3.1, 3.3.2, 3.3.3, and 3.3.4. 415 3.2. TE Router ID 417 The IPv4 TE Router ID TLV and IPv6 TE Router ID TLV, which are 418 defined in [RFC5305] and [RFC6119] respectively, only have area 419 flooding-scope. When performing inter-AS TE, the TE Router ID MAY be 420 needed to reach all routers within an entire ISIS routing domain and 421 it MUST have the same flooding scope as the Inter-AS Reachability TLV 422 does. 424 [RFC7981] defines a generic advertisement mechanism for ISIS which 425 allows a router to advertise its capabilities within an ISIS area or 426 an entire ISIS routing domain. [RFC7981] also points out that the TE 427 Router ID is a candidate to be carried in the IS-IS router capability 428 TLV when performing inter-area TE. 430 This document uses such mechanism for TE Router ID advertisement when 431 the TE Router ID is needed to reach all routers within an entire ISIS 432 Routing domain. Two new sub-TLVs are defined for inclusion in the 433 IS-IS Router Capability TLV to carry the TE Router IDs. 435 Sub-TLV type Length Name 436 ------------ ------ ----------------- 437 11 4 IPv4 TE Router ID 438 12 16 IPv6 TE Router ID 440 Detailed definitions of the new sub-TLVs are described in 441 Section 3.4.1 and 3.4.2. 443 3.3. Sub-TLVs for Inter-AS Reachability TLV 445 3.3.1. Remote AS Number Sub-TLV 447 A new sub-TLV, the remote AS number sub-TLV, is defined for inclusion 448 in the inter-AS reachability TLV when advertising inter-AS links. 449 The remote AS number sub-TLV specifies the AS number of the 450 neighboring AS to which the advertised link connects. 452 The remote AS number sub-TLV is TLV type 24 (see Section 6.2) and is 453 4 octets in length. The format is as follows: 455 0 1 2 3 456 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 1 457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 458 | Type | Length | 459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 460 | Remote AS Number | 461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 The remote AS number field has 4 octets. When only 2 octets are used 464 for the AS number, as in current deployments, the left (high-order) 2 465 octets MUST be set to 0. The remote AS number sub-TLV MUST be 466 included when a router advertises an inter-AS TE link. 468 3.3.2. IPv4 Remote ASBR ID Sub-TLV 470 A new sub-TLV, which is referred to as the IPv4 remote ASBR ID sub- 471 TLV, is defined for inclusion in the inter-AS reachability TLV when 472 advertising inter-AS links. The IPv4 remote ASBR ID sub-TLV 473 specifies the IPv4 identifier of the remote ASBR to which the 474 advertised inter-AS link connects. This could be any stable and 475 routable IPv4 address of the remote ASBR. Use of the TE Router ID as 476 specified in the Traffic Engineering router ID TLV [RFC5305] is 477 RECOMMENDED. 479 The IPv4 remote ASBR ID sub-TLV is TLV type 25 (see Section 6.2) and 480 is 4 octets in length. The format of the IPv4 remote ASBR ID sub-TLV 481 is as follows: 483 0 1 2 3 484 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 1 485 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 486 | Type | Length | 487 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 488 | Remote ASBR ID | 489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 491 The IPv4 remote ASBR ID sub-TLV MUST be included if the neighboring 492 ASBR has an IPv4 address. If the neighboring ASBR does not have an 493 IPv4 address (not even an IPv4 TE Router ID), the IPv6 remote ASBR ID 494 sub-TLV MUST be included instead. An IPv4 remote ASBR ID sub-TLV and 495 IPv6 remote ASBR ID sub-TLV MAY both be present in an extended IS 496 reachability TLV. 498 3.3.3. IPv6 Remote ASBR ID Sub-TLV 500 A new sub-TLV, which is referred to as the IPv6 remote ASBR ID sub- 501 TLV, is defined for inclusion in the inter-AS reachability TLV when 502 advertising inter-AS links. The IPv6 remote ASBR ID sub-TLV 503 specifies the IPv6 identifier of the remote ASBR to which the 504 advertised inter-AS link connects. This could be any stable and 505 routable IPv6 address of the remote ASBR. Use of the TE Router ID as 506 specified in the IPv6 Traffic Engineering router ID TLV [RFC6119] is 507 RECOMMENDED. 509 The IPv6 remote ASBR ID sub-TLV is TLV type 26 (see Section 6.2) and 510 is 16 octets in length. The format of the IPv6 remote ASBR ID sub- 511 TLV is as follows: 513 0 1 2 3 514 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 1 515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 516 | Type | Length | 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 518 | Remote ASBR ID | 519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 520 | Remote ASBR ID (continued) | 521 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 522 | Remote ASBR ID (continued) | 523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 524 | Remote ASBR ID (continued) | 525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 527 The IPv6 remote ASBR ID sub-TLV MUST be included if the neighboring 528 ASBR has an IPv6 address. If the neighboring ASBR does not have an 529 IPv6 address, the IPv4 remote ASBR ID sub-TLV MUST be included 530 instead. An IPv4 remote ASBR ID sub-TLV and IPv6 remote ASBR ID sub- 531 TLV MAY both be present in an extended IS reachability TLV. 533 3.3.4. IPv6 Local ASBR ID sub-TLV 535 The IPv6 Local ASBR ID sub-TLV is TLV type TBD1 (see Section 6.3) and 536 is 16 octets in length. The format of the IPv6 Router ID sub-TLV is 537 as follows: 539 0 1 2 3 540 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 1 541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 542 | Type | Length | 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 544 | Local ASBR ID | 545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 546 | Local ASBR ID (continued) | 547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 548 | Local ASBR ID (continued) | 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 550 | Local ASBR ID (continued) | 551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 The IPv6 Local ASBR ID SHOULD be identical to the value advertised in 554 the IPv6 Traffic Engineering Router ID TLV [RFC6119]. 556 If the originating node does not support IPv4, the IPv6 Local ASBR ID 557 sub-TLV MUST be present in the inter-AS reachability TLV. Inter-AS 558 reachability TLVs which have a Router ID of 0.0.0.0 and do NOT have 559 the IPv6 Local ASBR ID sub-TLV present MUST be ignored. 561 3.4. Sub-TLVs for IS-IS Router Capability TLV 563 3.4.1. IPv4 TE Router ID sub-TLV 565 The IPv4 TE Router ID sub-TLV is TLV type 11 (see Section 6.3) and is 566 4 octets in length. The format of the IPv4 TE Router ID sub-TLV is 567 as follows: 569 0 1 2 3 570 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 1 571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 572 | Type | Length | 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 | TE Router ID | 575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 577 The IPv4 TE Router ID SHOULD be identical to the value advertised in 578 the IPv4 Traffic Engineering Router ID TLV [RFC5305]. 580 When the TE Router ID is needed to reach all routers within an entire 581 ISIS routing domain, the IS-IS Router capability TLV MUST be included 582 in its LSP. If an ASBR supports Traffic Engineering for IPv4 and if 583 the ASBR has an IPv4 TE Router ID, the IPv4 TE Router ID sub-TLV MUST 584 be included. If the ASBR does not have an IPv4 TE Router ID, the 585 IPv6 TE Router sub-TLV MUST be included instead. An IPv4 TE Router 586 ID sub-TLV and IPv6 TE Router ID sub-TLV MAY both be present in an 587 IS-IS router capability TLV. 589 3.4.2. IPv6 TE Router ID sub-TLV 591 The IPv6 TE Router ID sub-TLV is TLV type 12 (see Section 6.3) and is 592 16 octets in length. The format of the IPv6 TE Router ID sub-TLV is 593 as follows: 595 0 1 2 3 596 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 1 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 | Type | Length | 599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 600 | TE Router ID | 601 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 602 | TE Router ID (continued) | 603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 | TE Router ID (continued) | 605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 | TE Router ID (continued) | 607 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 609 The IPv6 TE Router ID SHOULD be identical to the value advertised in 610 the IPv6 Traffic Engineering Router ID TLV [RFC6119]. 612 When the TE Router ID is needed to reach all routers within an entire 613 ISIS routing domain, the IS-IS router capability TLV MUST be included 614 in its LSP. If an ASBR supports Traffic Engineering for IPv6 and if 615 the ASBR has an IPv6 TE Router ID, the IPv6 TE Router ID sub-TLV MUST 616 be included. If the ASBR does not have an IPv6 TE Router ID, the 617 IPv4 TE Router sub-TLV MUST be included instead. An IPv4 TE Router 618 ID sub-TLV and IPv6 TE Router ID sub-TLV MAY both be present in an 619 IS-IS router capability TLV. 621 4. Procedure for Inter-AS TE Links 623 When TE is enabled on an inter-AS link and the link is up, the ASBR 624 SHOULD advertise this link using the normal procedures for [RFC5305]. 625 When either the link is down or TE is disabled on the link, the ASBR 626 SHOULD withdraw the advertisement. When there are changes to the TE 627 parameters for the link (for example, when the available bandwidth 628 changes), the ASBR SHOULD re-advertise the link but MUST take 629 precautions against excessive re-advertisements. 631 Hellos MUST NOT be exchanged over the inter-AS link, and 632 consequently, an ISIS adjacency MUST NOT be formed. 634 The information advertised comes from the ASBR's knowledge of the TE 635 capabilities of the link, the ASBR's knowledge of the current status 636 and usage of the link, and configuration at the ASBR of the remote AS 637 number and remote ASBR TE Router ID. 639 Legacy routers receiving an advertisement for an inter-AS TE link are 640 able to ignore it because they do not know the new TLV and sub-TLVs 641 that are defined in Section 3 of this document. They will continue 642 to flood the LSP, but will not attempt to use the information 643 received. 645 In the current operation of ISIS TE, the LSRs at each end of a TE 646 link emit LSPs describing the link. The databases in the LSRs then 647 have two entries (one locally generated, the other from the peer) 648 that describe the different 'directions' of the link. This enables 649 Constrained Shortest Path First (CSPF) to do a two-way check on the 650 link when performing path computation and eliminate it from 651 consideration unless both directions of the link satisfy the required 652 constraints. 654 In the case we are considering here (i.e., of a TE link to another 655 AS), there is, by definition, no IGP peering and hence no 656 bidirectional TE link information. In order for the CSPF route 657 computation entity to include the link as a candidate path, we have 658 to find a way to get LSPs describing its (bidirectional) TE 659 properties into the TE database. 661 This is achieved by the ASBR advertising, internally to its AS, 662 information about both directions of the TE link to the next AS. The 663 ASBR will normally generate a LSP describing its own side of a link; 664 here we have it 'proxy' for the ASBR at the edge of the other AS and 665 generate an additional LSP that describes that device's 'view' of the 666 link. 668 Only some essential TE information for the link needs to be 669 advertised; i.e., the Interface Address, the remote AS number, and 670 the remote ASBR ID of an inter-AS TE link. 672 Routers or PCEs that are capable of processing advertisements of 673 inter-AS TE links SHOULD NOT use such links to compute paths that 674 exit an AS to a remote ASBR and then immediately re-enter the AS 675 through another TE link. Such paths would constitute extremely rare 676 occurrences and SHOULD NOT be allowed except as the result of 677 specific policy configurations at the router or PCE computing the 678 path. 680 4.1. Origin of Proxied TE Information 682 Section 4 describes how an ASBR advertises TE link information as a 683 proxy for its neighbor ASBR, but does not describe where this 684 information comes from. 686 Although the source of this information is outside the scope of this 687 document, it is possible that it will be a configuration requirement 688 at the ASBR, as are other local properties of the TE link. Further, 689 where BGP is used to exchange IP routing information between the 690 ASBRs, a certain amount of additional local configuration about the 691 link and the remote ASBR is likely to be available. 693 We note further that it is possible, and may be operationally 694 advantageous, to obtain some of the required configuration 695 information from BGP. Whether and how to utilize these possibilities 696 is an implementation matter. 698 5. Security Considerations 700 The protocol extensions defined in this document are relatively minor 701 and can be secured within the AS in which they are used by the 702 existing ISIS security mechanisms (e.g., using the cleartext 703 passwords or Hashed Message Authentication Codes - Message Digest 5 704 (HMAC-MD5) algorithm, which are defined in [RFC1195] and [RFC5304] 705 separately). 707 There is no exchange of information between ASes, and no change to 708 the ISIS security relationship between the ASes. In particular, 709 since no ISIS adjacency is formed on the inter-AS links, there is no 710 requirement for ISIS security between the ASes. 712 Some of the information included in these new advertisements (e.g., 713 the remote AS number and the remote ASBR ID) is obtained manually 714 from a neighboring administration as part of a commercial 715 relationship. The source and content of this information should be 716 carefully checked before it is entered as configuration information 717 at the ASBR responsible for advertising the inter-AS TE links. 719 It is worth noting that in the scenario we are considering, a Border 720 Gateway Protocol (BGP) peering may exist between the two ASBRs and 721 that this could be used to detect inconsistencies in configuration 722 (e.g., the administration that originally supplied the information 723 may be lying, or some manual mis-configurations or mistakes may be 724 made by the operators). For example, if a different remote AS number 725 is received in a BGP OPEN [RFC4271] from that locally configured to 726 ISIS-TE, as we describe here, then local policy SHOULD be applied to 727 determine whether to alert the operator to a potential mis- 728 configuration or to suppress the IS-IS advertisement of the inter-AS 729 TE link. Note further that if BGP is used to exchange TE information 730 as described in Section 4.1, the inter-AS BGP session SHOULD be 731 secured using mechanisms as described in [RFC4271] to provide 732 authentication and integrity checks. 734 For a discussion of general security considerations for IS-IS, see 735 [RFC5304]. 737 6. IANA Considerations 739 IANA is requested to make the following allocations from registries 740 under its control. 742 6.1. Inter-AS Reachability TLV 744 This document defines the following new IS-IS TLV type, described in 745 Section 3.1, which has been registered in the IS-IS TLV codepoint 746 registry: 748 Type Description IIH LSP SNP Purge 749 ---- ---------------------- --- --- --- ----- 750 141 inter-AS reachability n y n n 751 information 753 6.2. Sub-TLVs for the Inter-AS Reachability TLV 755 This document defines the following new sub-TLV types (described in 756 Sections 3.3.1, 3.3.2, 3.3.3, and, 3.3.4) of top-level TLV 141 (see 757 Section 6.1 above). Three of these sub-TLVs have been registered in 758 the IS-IS sub-TLV registry for TLVs 22, 23, 25, 141, 222, and 223 by 759 [RFC5316]. One additional sub-TLV (IPv6 local ASBR identifier) is 760 introduced by this document and needs to be added to the same 761 registry. Note that all four sub-TLVs SHOULD NOT appear in TLVs 22, 762 23, 25, 222, or 223 and MUST be ignored if they are included in any 763 of these TLVs. 765 Type Description 22 23 25 141 222 223 Reference 766 ---- ----------------------------- --- --- --- --- --- --- --------- 767 24 remote AS number n n n y n n [This.I-D] 768 25 IPv4 remote ASBR identifier n n n y n n [This.I-D] 769 26 IPv6 remote ASBR identifier n n n y n n [This.I-D] 770 TBD1 IPv6 local ASBR identifier n n n y n n [This.I-D] 772 As described above in Section 3.1, the sub-TLVs which are defined in 773 [RFC5305], [RFC6119] and other documents for describing the TE 774 properties of a TE link are applicable to describe an inter-AS TE 775 link and MAY be included in the inter-AS reachability TLV when 776 adverting inter-AS TE links. 778 6.3. Sub-TLVs for the IS-IS Router Capability TLV 780 This document defines the following new sub-TLV types, described in 781 Sections 3.4.1 and 3.4.2, of top-level TLV 242 (which is defined in 782 [RFC7981]) that have been registered in the IS-IS sub-TLV registry 783 for TLV 242: 785 Type Description Length 786 ---- ------------------------------ -------- 787 11 IPv4 TE Router ID 4 788 12 IPv6 TE Router ID 16 790 7. Acknowledgements 792 For the original version of [RFC5316] the authors would like to thank 793 Adrian Farrel, Jean-Louis Le Roux, Christian Hopps, Les Ginsberg, and 794 Hannes Gredler for their review and comments on this document. 796 8. References 798 8.1. Normative References 800 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 801 dual environments", RFC 1195, DOI 10.17487/RFC1195, 802 December 1990, . 804 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 805 Requirement Levels", BCP 14, RFC 2119, 806 DOI 10.17487/RFC2119, March 1997, 807 . 809 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 810 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 811 2008, . 813 [RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic 814 Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119, 815 February 2011, . 817 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 818 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 819 May 2017, . 821 8.2. Informative References 823 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 824 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 825 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 826 . 828 [RFC4216] Zhang, R., Ed. and J. Vasseur, Ed., "MPLS Inter-Autonomous 829 System (AS) Traffic Engineering (TE) Requirements", 830 RFC 4216, DOI 10.17487/RFC4216, November 2005, 831 . 833 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 834 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 835 DOI 10.17487/RFC4271, January 2006, 836 . 838 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 839 Element (PCE)-Based Architecture", RFC 4655, 840 DOI 10.17487/RFC4655, August 2006, 841 . 843 [RFC5152] Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A 844 Per-Domain Path Computation Method for Establishing Inter- 845 Domain Traffic Engineering (TE) Label Switched Paths 846 (LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008, 847 . 849 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 850 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 851 2008, . 853 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 854 in Support of Generalized Multi-Protocol Label Switching 855 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 856 . 858 [RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in 859 Support of Inter-Autonomous System (AS) MPLS and GMPLS 860 Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316, 861 December 2008, . 863 [RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux, 864 "A Backward-Recursive PCE-Based Computation (BRPC) 865 Procedure to Compute Shortest Constrained Inter-Domain 866 Traffic Engineering Label Switched Paths", RFC 5441, 867 DOI 10.17487/RFC5441, April 2009, 868 . 870 [RFC6823] Ginsberg, L., Previdi, S., and M. Shand, "Advertising 871 Generic Information in IS-IS", RFC 6823, 872 DOI 10.17487/RFC6823, December 2012, 873 . 875 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 876 for Advertising Router Information", RFC 7981, 877 DOI 10.17487/RFC7981, October 2016, 878 . 880 Appendix A. Changes to RFC 5316 882 This document makes the following changes to RFC 5316. 884 RFC 5316 only allowed a 32 bit Router ID in the fixed header of TLV 885 141. This is problematic in an IPv6-only deployment where an IPv4 886 address may not be available. This document specifies: 888 1. The Router ID SHOULD be identical to the value advertised in the 889 Traffic Engineering Router ID TLV (134) if available. 891 2. If no Traffic Engineering Router ID is assigned the Router ID 892 SHOULD be identical to an IP Interface Address [RFC1195] advertised 893 by the originating IS. 895 3. If the originating node does not support IPv4, then the reserved 896 value 0.0.0.0 MUST be used in the Router ID field and the new IPv6 897 Local ASBR identifier sub-TLV MUST be present in the TLV. 899 Authors' Addresses 901 Mach(Guoyi) Chen 902 Huawei 904 Email: mach.chen@huawei.com 906 Les Ginsberg 907 Cisco Systems 909 Email: ginsberg@cisco.com 911 Stefano Previdi 912 Huawei Technologies 913 IT 915 Email: stefano@previdi.net 917 Xiaodong Duan 918 China Mobile 920 Email: duanxiaodong@chinamobile.com