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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: September 11, 2021 S. Previdi 7 Huawei Technologies 8 D. Xiaodong 9 China Mobile 10 March 10, 2021 12 IS-IS Extensions in Support of Inter-Autonomous System (AS) MPLS and 13 GMPLS Traffic Engineering 14 draft-ietf-lsr-isis-rfc5316bis-02 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 September 11, 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 . . . . . . . . . . . . . . . . . . . . . . 10 80 3.3. Sub-TLVs for Inter-AS Reachability TLV . . . . . . . . . 11 81 3.3.1. Remote AS Number Sub-TLV . . . . . . . . . . . . . . 11 82 3.3.2. IPv4 Remote ASBR ID Sub-TLV . . . . . . . . . . . . . 11 83 3.3.3. IPv6 Remote ASBR ID Sub-TLV . . . . . . . . . . . . . 12 84 3.3.4. IPv6 Local ASBR ID sub-TLV . . . . . . . . . . . . . 13 85 3.4. Sub-TLVs for IS-IS Router Capability TLV . . . . . . . . 14 86 3.4.1. IPv4 TE Router ID sub-TLV . . . . . . . . . . . . . . 14 87 3.4.2. IPv6 TE Router ID sub-TLV . . . . . . . . . . . . . . 14 88 4. Procedure for Inter-AS TE Links . . . . . . . . . . . . . . . 15 89 4.1. Origin of Proxied TE Information . . . . . . . . . . . . 16 90 5. Security Considerations . . . . . . . . . . . . . . . . . . . 17 91 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 92 6.1. Inter-AS Reachability TLV . . . . . . . . . . . . . . . . 18 93 6.2. Sub-TLVs for the Inter-AS Reachability TLV . . . . . . . 18 94 6.3. Sub-TLVs for the IS-IS Router Capability TLV . . . . . . 18 95 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 96 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 97 8.1. Normative References . . . . . . . . . . . . . . . . . . 19 98 8.2. Informative References . . . . . . . . . . . . . . . . . 19 99 Appendix A. Changes to RFC 5316 . . . . . . . . . . . . . . . . 21 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 102 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 IS-IS 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 IS-IS. See Section 2.1 for 145 a 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 IS-IS 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 IS-IS 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 0 1 2 3 355 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 1 356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 357 | Router ID (4 octets) | 358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 359 | default metric | (3 octets) 360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 361 | Flags | (1 octet) 362 +-+-+-+-+-+-+-+-+ 363 |sub-TLVs length| (1 octet) 364 +-+-+-+-+-+-+-+-+-+-+-+- 365 | sub-TLVs ... (0-246 octets) 366 +-+-+-+-+-+-+-+-+-+-+-+- 368 Flags consists of the following: 369 0 1 2 3 4 5 6 7 370 +-+-+-+-+-+-+-+-+ 371 |S|D| Rsvd | 372 +-+-+-+-+-+-+-+-+ 374 where: 376 S bit: If the S bit is set(1), the Inter-AS Reachability TLV 377 MUST be flooded across the entire routing domain. If the S bit is 378 not set(0), the TLV MUST NOT be leaked between levels. This bit MUST 379 NOT be altered during the TLV leaking. 381 D bit: When the Inter-AS Reachability TLV is leaked from 382 Level 2 (L2) to Level 1 (L1), the D bit MUST be set. Otherwise, this 383 bit MUST be clear. Inter-AS Reachability TLVs with the D bit set 384 MUST NOT be leaked from Level 1 to Level 2. This is to prevent TLV 385 looping. 387 Rsvd bits MUST be zero when originated and ignored 388 when received. 390 Compared to the extended reachability TLV which is defined in 391 [RFC5305], the inter-AS reachability TLV replaces the "7 octets of 392 System ID and Pseudonode Number" field with a "4 octets of Router ID" 393 field and introduces an extra "control information" field, which 394 consists of a flooding-scope bit (S bit), an up/down bit (D bit), and 395 6 reserved bits. 397 The Router ID field of the inter-AS reachability TLV is 4 octets in 398 length, which contains the IPv4 Router ID of the router who generates 399 the inter-AS reachability TLV. The Router ID SHOULD be identical to 400 the value advertised in the Traffic Engineering Router ID TLV 402 [RFC5305]. If no Traffic Engineering Router ID is assigned, the 403 Router ID SHOULD be identical to an IP Interface Address [RFC1195] 404 advertised by the originating IS. If the originating node does not 405 support IPv4, then the reserved value 0.0.0.0 MUST be used in the 406 Router ID field and the IPv6 Router ID sub-TLV MUST be present in the 407 inter-AS reachability TLV. The Router ID could be used to indicate 408 the source of the inter-AS reachability TLV. 410 The flooding procedures for inter-AS reachability TLV are identical 411 to the flooding procedures for the GENINFO TLV, which are defined in 412 Section 4 of [RFC6823]. These procedures have been previously 413 discussed in [RFC7981]. The flooding-scope bit (S bit) SHOULD be set 414 to 0 if the flooding scope is to be limited to within the single IGP 415 area to which the ASBR belongs. It MAY be set to 1 if the 416 information is intended to reach all routers (including area border 417 routers, ASBRs, and PCEs) in the entire IS-IS routing domain. The 418 choice between the use of 0 or 1 is an AS-wide policy choice, and 419 configuration control SHOULD be provided in ASBR implementations that 420 support the advertisement of inter-AS TE links. 422 The sub-TLVs defined in [RFC5305], [RFC6119], and other documents for 423 describing the TE properties of a TE link are also applicable to the 424 inter-AS reachability TLV for describing the TE properties of an 425 Inter-AS TE link. Apart from these sub-TLVs, four new sub-TLVs are 426 defined for inclusion in the inter-AS reachability TLV defined in 427 this document: 429 Sub-TLV type Length Name 430 ------------ ------ --------------------------- 431 24 4 remote AS number 432 25 4 IPv4 remote ASBR identifier 433 26 16 IPv6 remote ASBR identifier 434 TBD1 16 IPv6 local ASBR identifier 436 Detailed definitions of the four new sub-TLVs are described in 437 Sections 3.3.1, 3.3.2, 3.3.3, and 3.3.4. 439 3.2. TE Router ID 441 The IPv4 TE Router ID TLV and IPv6 TE Router ID TLV, which are 442 defined in [RFC5305] and [RFC6119] respectively, only have area 443 flooding-scope. When performing inter-AS TE, the TE Router ID MAY be 444 needed to reach all routers within an entire IS-IS routing domain and 445 it MUST have the same flooding scope as the Inter-AS Reachability TLV 446 does. 448 [RFC7981] defines a generic advertisement mechanism for IS-IS which 449 allows a router to advertise its capabilities within an IS-IS area or 450 an entire IS-IS routing domain. [RFC7981] also points out that the 451 TE Router ID is a candidate to be carried in the IS-IS router 452 capability TLV when performing inter-area TE. 454 This document uses such mechanism for TE Router ID advertisement when 455 the TE Router ID is needed to reach all routers within an entire IS- 456 IS Routing domain. Two new sub-TLVs are defined for inclusion in the 457 IS-IS Router Capability TLV to carry the TE Router IDs. 459 Sub-TLV type Length Name 460 ------------ ------ ----------------- 461 11 4 IPv4 TE Router ID 462 12 16 IPv6 TE Router ID 464 Detailed definitions of the new sub-TLVs are described in 465 Section 3.4.1 and 3.4.2. 467 3.3. Sub-TLVs for Inter-AS Reachability TLV 469 3.3.1. Remote AS Number Sub-TLV 471 A new sub-TLV, the remote AS number sub-TLV, is defined for inclusion 472 in the inter-AS reachability TLV when advertising inter-AS links. 473 The remote AS number sub-TLV specifies the AS number of the 474 neighboring AS to which the advertised link connects. 476 The remote AS number sub-TLV is TLV type 24 (see Section 6.2) and is 477 4 octets in length. The format is as follows: 479 0 1 2 3 480 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 1 481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 482 | Type | Length | 483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 484 | Remote AS Number | 485 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 487 The remote AS number field has 4 octets. When only 2 octets are used 488 for the AS number, as in current deployments, the left (high-order) 2 489 octets MUST be set to 0. The remote AS number sub-TLV MUST be 490 included when a router advertises an inter-AS TE link. 492 3.3.2. IPv4 Remote ASBR ID Sub-TLV 494 A new sub-TLV, which is referred to as the IPv4 remote ASBR ID sub- 495 TLV, is defined for inclusion in the inter-AS reachability TLV when 496 advertising inter-AS links. The IPv4 remote ASBR ID sub-TLV 497 specifies the IPv4 identifier of the remote ASBR to which the 498 advertised inter-AS link connects. This could be any stable and 499 routable IPv4 address of the remote ASBR. Use of the TE Router ID as 500 specified in the Traffic Engineering router ID TLV [RFC5305] is 501 RECOMMENDED. 503 The IPv4 remote ASBR ID sub-TLV is TLV type 25 (see Section 6.2) and 504 is 4 octets in length. The format of the IPv4 remote ASBR ID sub-TLV 505 is as follows: 507 0 1 2 3 508 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 1 509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 510 | Type | Length | 511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 512 | Remote ASBR ID | 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 515 The IPv4 remote ASBR ID sub-TLV MUST be included if the neighboring 516 ASBR has an IPv4 address. If the neighboring ASBR does not have an 517 IPv4 address (not even an IPv4 TE Router ID), the IPv6 remote ASBR ID 518 sub-TLV MUST be included instead. An IPv4 remote ASBR ID sub-TLV and 519 IPv6 remote ASBR ID sub-TLV MAY both be present in an extended IS 520 reachability TLV. 522 3.3.3. IPv6 Remote ASBR ID Sub-TLV 524 A new sub-TLV, which is referred to as the IPv6 remote ASBR ID sub- 525 TLV, is defined for inclusion in the inter-AS reachability TLV when 526 advertising inter-AS links. The IPv6 remote ASBR ID sub-TLV 527 specifies the IPv6 identifier of the remote ASBR to which the 528 advertised inter-AS link connects. This could be any stable and 529 routable IPv6 address of the remote ASBR. Use of the TE Router ID as 530 specified in the IPv6 Traffic Engineering router ID TLV [RFC6119] is 531 RECOMMENDED. 533 The IPv6 remote ASBR ID sub-TLV is TLV type 26 (see Section 6.2) and 534 is 16 octets in length. The format of the IPv6 remote ASBR ID sub- 535 TLV is as follows: 537 0 1 2 3 538 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 1 539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 540 | Type | Length | 541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 542 | Remote ASBR ID | 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 544 | Remote ASBR ID (continued) | 545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 546 | Remote ASBR ID (continued) | 547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 548 | Remote ASBR ID (continued) | 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 The IPv6 remote ASBR ID sub-TLV MUST be included if the neighboring 552 ASBR has an IPv6 address. If the neighboring ASBR does not have an 553 IPv6 address, the IPv4 remote ASBR ID sub-TLV MUST be included 554 instead. An IPv4 remote ASBR ID sub-TLV and IPv6 remote ASBR ID sub- 555 TLV MAY both be present in an extended IS reachability TLV. 557 3.3.4. IPv6 Local ASBR ID sub-TLV 559 The IPv6 Local ASBR ID sub-TLV is TLV type TBD1 (see Section 6.3) and 560 is 16 octets in length. The format of the IPv6 Router ID sub-TLV is 561 as follows: 563 0 1 2 3 564 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 1 565 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 566 | Type | Length | 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 | Local ASBR ID | 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 570 | Local ASBR ID (continued) | 571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 572 | Local ASBR ID (continued) | 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 | Local ASBR ID (continued) | 575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 577 The IPv6 Local ASBR ID SHOULD be identical to the value advertised in 578 the IPv6 Traffic Engineering Router ID TLV [RFC6119]. 580 If the originating node does not support IPv4, the IPv6 Local ASBR ID 581 sub-TLV MUST be present in the inter-AS reachability TLV. Inter-AS 582 reachability TLVs which have a Router ID of 0.0.0.0 and do NOT have 583 the IPv6 Local ASBR ID sub-TLV present MUST be ignored. 585 3.4. Sub-TLVs for IS-IS Router Capability TLV 587 3.4.1. IPv4 TE Router ID sub-TLV 589 The IPv4 TE Router ID sub-TLV is TLV type 11 (see Section 6.3) and is 590 4 octets in length. The format of the IPv4 TE Router ID sub-TLV is 591 as follows: 593 0 1 2 3 594 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 1 595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 596 | Type | Length | 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 | TE Router ID | 599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 The IPv4 TE Router ID SHOULD be identical to the value advertised in 602 the IPv4 Traffic Engineering Router ID TLV [RFC5305]. 604 When the TE Router ID is needed to reach all routers within an entire 605 IS-IS routing domain, the IS-IS Router capability TLV MUST be 606 included in its LSP. If an ASBR supports Traffic Engineering for 607 IPv4 and if the ASBR has an IPv4 TE Router ID, the IPv4 TE Router ID 608 sub-TLV MUST be included. If the ASBR does not have an IPv4 TE 609 Router ID, the IPv6 TE Router sub-TLV MUST be included instead. An 610 IPv4 TE Router ID sub-TLV and IPv6 TE Router ID sub-TLV MAY both be 611 present in an IS-IS router capability TLV. 613 3.4.2. IPv6 TE Router ID sub-TLV 615 The IPv6 TE Router ID sub-TLV is TLV type 12 (see Section 6.3) and is 616 16 octets in length. The format of the IPv6 TE Router ID sub-TLV is 617 as follows: 619 0 1 2 3 620 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 1 621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 622 | Type | Length | 623 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 624 | TE Router ID | 625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 626 | TE Router ID (continued) | 627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 628 | TE Router ID (continued) | 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 630 | TE Router ID (continued) | 631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 633 The IPv6 TE Router ID SHOULD be identical to the value advertised in 634 the IPv6 Traffic Engineering Router ID TLV [RFC6119]. 636 When the TE Router ID is needed to reach all routers within an entire 637 IS-IS routing domain, the IS-IS router capability TLV MUST be 638 included in its LSP. If an ASBR supports Traffic Engineering for 639 IPv6 and if the ASBR has an IPv6 TE Router ID, the IPv6 TE Router ID 640 sub-TLV MUST be included. If the ASBR does not have an IPv6 TE 641 Router ID, the IPv4 TE Router sub-TLV MUST be included instead. An 642 IPv4 TE Router ID sub-TLV and IPv6 TE Router ID sub-TLV MAY both be 643 present in an IS-IS router capability TLV. 645 4. Procedure for Inter-AS TE Links 647 When TE is enabled on an inter-AS link and the link is up, the ASBR 648 SHOULD advertise this link using the normal procedures for [RFC5305]. 649 When either the link is down or TE is disabled on the link, the ASBR 650 SHOULD withdraw the advertisement. When there are changes to the TE 651 parameters for the link (for example, when the available bandwidth 652 changes), the ASBR SHOULD re-advertise the link but MUST take 653 precautions against excessive re-advertisements. 655 Hellos MUST NOT be exchanged over the inter-AS link, and 656 consequently, an IS-IS adjacency MUST NOT be formed. 658 The information advertised comes from the ASBR's knowledge of the TE 659 capabilities of the link, the ASBR's knowledge of the current status 660 and usage of the link, and configuration at the ASBR of the remote AS 661 number and remote ASBR TE Router ID. 663 Legacy routers receiving an advertisement for an inter-AS TE link are 664 able to ignore it because they do not know the new TLV and sub-TLVs 665 that are defined in Section 3 of this document. They will continue 666 to flood the LSP, but will not attempt to use the information 667 received. 669 In the current operation of ISIS-TE, the LSRs at each end of a TE 670 link emit LSPs describing the link. The databases in the LSRs then 671 have two entries (one locally generated, the other from the peer) 672 that describe the different 'directions' of the link. This enables 673 Constrained Shortest Path First (CSPF) to do a two-way check on the 674 link when performing path computation and eliminate it from 675 consideration unless both directions of the link satisfy the required 676 constraints. 678 In the case we are considering here (i.e., of a TE link to another 679 AS), there is, by definition, no IGP peering and hence no 680 bidirectional TE link information. In order for the CSPF route 681 computation entity to include the link as a candidate path, we have 682 to find a way to get LSPs describing its (bidirectional) TE 683 properties into the TE database. 685 This is achieved by the ASBR advertising, internally to its AS, 686 information about both directions of the TE link to the next AS. The 687 ASBR will normally generate a LSP describing its own side of a link; 688 here we have it 'proxy' for the ASBR at the edge of the other AS and 689 generate an additional LSP that describes that device's 'view' of the 690 link. 692 Only some essential TE information for the link needs to be 693 advertised; i.e., the Interface Address, the remote AS number, and 694 the remote ASBR ID of an inter-AS TE link. 696 Routers or PCEs that are capable of processing advertisements of 697 inter-AS TE links SHOULD NOT use such links to compute paths that 698 exit an AS to a remote ASBR and then immediately re-enter the AS 699 through another TE link. Such paths would constitute extremely rare 700 occurrences and SHOULD NOT be allowed except as the result of 701 specific policy configurations at the router or PCE computing the 702 path. 704 4.1. Origin of Proxied TE Information 706 Section 4 describes how an ASBR advertises TE link information as a 707 proxy for its neighbor ASBR, but does not describe where this 708 information comes from. 710 Although the source of this information is outside the scope of this 711 document, it is possible that it will be a configuration requirement 712 at the ASBR, as are other local properties of the TE link. Further, 713 where BGP is used to exchange IP routing information between the 714 ASBRs, a certain amount of additional local configuration about the 715 link and the remote ASBR is likely to be available. 717 We note further that it is possible, and may be operationally 718 advantageous, to obtain some of the required configuration 719 information from BGP. Whether and how to utilize these possibilities 720 is an implementation matter. 722 5. Security Considerations 724 The protocol extensions defined in this document are relatively minor 725 and can be secured within the AS in which they are used by the 726 existing IS-IS security mechanisms (e.g., using the cleartext 727 passwords or Hashed Message Authentication Codes - Message Digest 5 728 (HMAC-MD5) algorithm, which are defined in [RFC1195] and [RFC5304] 729 separately). 731 There is no exchange of information between ASes, and no change to 732 the IS-IS security relationship between the ASes. In particular, 733 since no IS-IS adjacency is formed on the inter-AS links, there is no 734 requirement for IS-IS security between the ASes. 736 Some of the information included in these new advertisements (e.g., 737 the remote AS number and the remote ASBR ID) is obtained manually 738 from a neighboring administration as part of a commercial 739 relationship. The source and content of this information should be 740 carefully checked before it is entered as configuration information 741 at the ASBR responsible for advertising the inter-AS TE links. 743 It is worth noting that in the scenario we are considering, a Border 744 Gateway Protocol (BGP) peering may exist between the two ASBRs and 745 that this could be used to detect inconsistencies in configuration 746 (e.g., the administration that originally supplied the information 747 may be lying, or some manual mis-configurations or mistakes may be 748 made by the operators). For example, if a different remote AS number 749 is received in a BGP OPEN [RFC4271] from that locally configured to 750 ISIS-TE, as we describe here, then local policy SHOULD be applied to 751 determine whether to alert the operator to a potential mis- 752 configuration or to suppress the IS-IS advertisement of the inter-AS 753 TE link. Note further that if BGP is used to exchange TE information 754 as described in Section 4.1, the inter-AS BGP session SHOULD be 755 secured using mechanisms as described in [RFC4271] to provide 756 authentication and integrity checks. 758 For a discussion of general security considerations for IS-IS, see 759 [RFC5304]. 761 6. IANA Considerations 763 IANA is requested to make the following allocations from registries 764 under its control. 766 6.1. Inter-AS Reachability TLV 768 This document defines the following new IS-IS TLV type, described in 769 Section 3.1, which has been registered in the IS-IS TLV codepoint 770 registry: 772 Type Description IIH LSP SNP Purge Reference 773 ---- ---------------------- --- --- --- ----- --------- 774 141 inter-AS reachability n y n n [This.I-D] 775 information 777 6.2. Sub-TLVs for the Inter-AS Reachability TLV 779 This document defines the following new sub-TLV types (described in 780 Sections 3.3.1, 3.3.2, 3.3.3, and, 3.3.4) of top-level TLV 141 (see 781 Section 6.1 above). Three of these sub-TLVs have been registered in 782 the IS-IS sub-TLV registry for TLVs 22, 23, 25, 141, 222, and 223 by 783 [RFC5316]. One additional sub-TLV (IPv6 local ASBR identifier) is 784 introduced by this document and needs to be added to the same 785 registry. 787 Type Description 22 23 25 141 222 223 Reference 788 ---- ----------------------------- --- --- --- --- --- --- --------- 789 24 remote AS number n n n y n n [This.I-D] 790 25 IPv4 remote ASBR identifier n n n y n n [This.I-D] 791 26 IPv6 remote ASBR identifier n n n y n n [This.I-D] 792 TBD1 IPv6 local ASBR identifier n n n y n n [This.I-D] 794 As described above in Section 3.1, the sub-TLVs which are defined in 795 [RFC5305], [RFC6119] and other documents for describing the TE 796 properties of a TE link are applicable to describe an inter-AS TE 797 link and MAY be included in the inter-AS reachability TLV when 798 adverting inter-AS TE links. 800 6.3. Sub-TLVs for the IS-IS Router Capability TLV 802 This document defines the following new sub-TLV types, described in 803 Sections 3.4.1 and 3.4.2, of top-level TLV 242 (which is defined in 804 [RFC7981]) that have been registered in the IS-IS sub-TLV registry 805 for TLV 242: 807 Type Description Reference 808 ---- ------------------------------ --------- 809 11 IPv4 TE Router ID [This.I-D] 810 12 IPv6 TE Router ID [This.I-D] 812 7. Acknowledgements 814 For the original version of [RFC5316] the authors would like to thank 815 Adrian Farrel, Jean-Louis Le Roux, Christian Hopps, Les Ginsberg, and 816 Hannes Gredler for their review and comments on this document. 818 8. References 820 8.1. Normative References 822 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 823 dual environments", RFC 1195, DOI 10.17487/RFC1195, 824 December 1990, . 826 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 827 Requirement Levels", BCP 14, RFC 2119, 828 DOI 10.17487/RFC2119, March 1997, 829 . 831 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 832 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 833 2008, . 835 [RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic 836 Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119, 837 February 2011, . 839 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 840 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 841 May 2017, . 843 8.2. Informative References 845 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 846 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 847 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 848 . 850 [RFC4216] Zhang, R., Ed. and J. Vasseur, Ed., "MPLS Inter-Autonomous 851 System (AS) Traffic Engineering (TE) Requirements", 852 RFC 4216, DOI 10.17487/RFC4216, November 2005, 853 . 855 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 856 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 857 DOI 10.17487/RFC4271, January 2006, 858 . 860 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 861 Element (PCE)-Based Architecture", RFC 4655, 862 DOI 10.17487/RFC4655, August 2006, 863 . 865 [RFC5152] Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A 866 Per-Domain Path Computation Method for Establishing Inter- 867 Domain Traffic Engineering (TE) Label Switched Paths 868 (LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008, 869 . 871 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 872 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 873 2008, . 875 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 876 in Support of Generalized Multi-Protocol Label Switching 877 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 878 . 880 [RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in 881 Support of Inter-Autonomous System (AS) MPLS and GMPLS 882 Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316, 883 December 2008, . 885 [RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux, 886 "A Backward-Recursive PCE-Based Computation (BRPC) 887 Procedure to Compute Shortest Constrained Inter-Domain 888 Traffic Engineering Label Switched Paths", RFC 5441, 889 DOI 10.17487/RFC5441, April 2009, 890 . 892 [RFC6823] Ginsberg, L., Previdi, S., and M. Shand, "Advertising 893 Generic Information in IS-IS", RFC 6823, 894 DOI 10.17487/RFC6823, December 2012, 895 . 897 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 898 for Advertising Router Information", RFC 7981, 899 DOI 10.17487/RFC7981, October 2016, 900 . 902 Appendix A. Changes to RFC 5316 904 The following is a summary of the substantive changes this document 905 makes to RFC 5316. Some editorial changes were also made. 907 RFC 5316 only allowed a 32 bit Router ID in the fixed header of TLV 908 141. This is problematic in an IPv6-only deployment where an IPv4 909 address may not be available. This document specifies: 911 1. The Router ID should be identical to the value advertised in the 912 Traffic Engineering Router ID TLV (134) if available. 914 2. If no Traffic Engineering Router ID is assigned the Router ID 915 should be identical to an IP Interface Address [RFC1195] advertised 916 by the originating IS. 918 3. If the originating node does not support IPv4, then the reserved 919 value 0.0.0.0 must be used in the Router ID field and the new IPv6 920 Local ASBR identifier sub-TLV must be present in the TLV. 922 Authors' Addresses 924 Mach(Guoyi) Chen 925 Huawei 927 Email: mach.chen@huawei.com 929 Les Ginsberg 930 Cisco Systems 932 Email: ginsberg@cisco.com 934 Stefano Previdi 935 Huawei Technologies 936 IT 938 Email: stefano@previdi.net 940 Xiaodong Duan 941 China Mobile 943 Email: duanxiaodong@chinamobile.com