idnits 2.17.1 draft-ietf-idr-bgp-ls-segment-routing-msd-15.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** There are 6 instances of too long lines in the document, the longest one being 8 characters in excess of 72. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 9, 2020) is 1480 days in the past. Is this intentional? 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references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) == Outdated reference: A later version (-17) exists of draft-ietf-idr-bgp-model-08 == Outdated reference: A later version (-13) exists of draft-ietf-isis-mpls-elc-10 == Outdated reference: A later version (-15) exists of draft-ietf-ospf-mpls-elc-12 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR Working Group J. Tantsura 3 Internet-Draft Apstra, Inc. 4 Intended status: Standards Track U. Chunduri 5 Expires: September 10, 2020 Futurewei Technologies 6 K. Talaulikar 7 Cisco Systems 8 G. Mirsky 9 ZTE Corp. 10 N. Triantafillis 11 Amazon Web Services 12 March 9, 2020 14 Signaling MSD (Maximum SID Depth) using Border Gateway Protocol - Link 15 State 16 draft-ietf-idr-bgp-ls-segment-routing-msd-15 18 Abstract 20 This document defines a way for a Border Gateway Protocol - Link 21 State (BGP-LS) speaker to advertise multiple types of supported 22 Maximum SID Depths (MSDs) at node and/or link granularity. 24 Such advertisements allow entities (e.g., centralized controllers) to 25 determine whether a particular Segment Identifier (SID) stack can be 26 supported in a given network. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on September 10, 2020. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 63 1.1. Conventions used in this document . . . . . . . . . . . . 3 64 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 65 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4 66 2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4 67 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 68 4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5 69 5. Procedures for Defining and Using Node and Link MSD 70 Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 72 7. Manageability Considerations . . . . . . . . . . . . . . . . 7 73 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 74 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 75 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 76 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 77 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 78 11.2. Informative References . . . . . . . . . . . . . . . . . 9 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 81 1. Introduction 83 When Segment Routing (SR) [RFC8402] paths are computed by a 84 centralized controller, it is critical that the controller learn the 85 Maximum SID Depth (MSD) that can be imposed at each node/link on a 86 given SR path. This ensures that the Segment Identifier (SID) stack 87 depth of a computed path doesn't exceed the number of SIDs the node 88 is capable of imposing. 90 [RFC8664] defines how to signal MSD in the Path Computation Element 91 Protocol (PCEP). The OSPF and IS-IS extensions for signaling of MSD 92 are defined in [RFC8476] and [RFC8491] respectively. 94 However, if PCEP is not supported/configured on the head-end of a SR 95 tunnel or a Binding-SID anchor node, and controller does not 96 participate in IGP routing, it has no way of learning the MSD of 97 nodes and links. BGP-LS [RFC7752] defines a way to expose topology 98 and associated attributes and capabilities of the nodes in that 99 topology to a centralized controller. 101 This document defines extensions to BGP-LS to advertise one or more 102 types of MSDs at node and/or link granularity. Other types of MSD 103 are known to be useful. For example, [I-D.ietf-ospf-mpls-elc] and 104 [I-D.ietf-isis-mpls-elc] define Readable Label Depth Capability 105 (RLDC) that is used by a head-end to insert an Entropy Label (EL) at 106 a depth that can be read by transit nodes. 108 In the future, it is expected that new MSD-Types will be defined to 109 signal additional capabilities, e.g., ELs, SIDs that can be imposed 110 through recirculation, or SIDs associated with another data plane 111 such as IPv6. MSD advertisements may be useful even if SR itself is 112 not enabled. For example, in a non-SR MPLS network, MSD defines the 113 maximum label depth. 115 1.1. Conventions used in this document 117 1.1.1. Terminology 119 MSD: Maximum SID Depth - the number of SIDs supported by a node or a 120 link on a node 122 PCC: Path Computation Client 124 PCE: Path Computation Element 126 PCEP: Path Computation Element Protocol 128 SID: Segment Identifier as defined in [RFC8402] 130 SR: Segment Routing 132 Label Imposition: Imposition is the act of modifying and/or adding 133 labels to the outgoing label stack associated with a packet. This 134 includes: 136 o replacing the label at the top of the label stack with a new 137 label. 139 o pushing one or more new labels onto the label stack. 141 o The number of labels imposed is then the sum of the number of 142 labels that are replaced and the number of labels that are pushed. 143 See [RFC3031] for further details. 145 1.1.2. Requirements Language 147 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 148 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 149 "OPTIONAL" in this document are to be interpreted as described in BCP 150 14 [RFC2119] [RFC8174] when, and only when, they appear in all 151 capitals, as shown here . 153 2. Advertisement of MSD via BGP-LS 155 This document describes extensions that enable BGP-LS speakers to 156 signal the MSD capabilities ([RFC8491] ) of nodes and their links in 157 a network to a BGP-LS consumer of network topology such as a 158 centralized controller. The centralized controller can leverage this 159 information in computation of SR paths based on their MSD 160 capabilities. When a BGP-LS speaker is originating the topology 161 learnt via link-state routing protocols like OSPF or IS-IS, the MSD 162 information for the nodes and their links is sourced from the 163 underlying extensions as defined in [RFC8476] and [RFC8491] 164 respectively. 166 The BGP-LS speaker may also advertise the MSD information for the 167 local node and its links when not running any link-state IGP protocol 168 e.g. when running BGP as the only routing protocol. The Protocol-ID 169 field should be set to BGP since the link and node attributes have 170 BGP based identifiers. Deployment model for such case would be: a 171 limited number (meeting resiliecy requirements) of BGP-LS speakers 172 exposing the topology to the controller, full-mesh/RouteReflectors 173 for iBGP(Internal Border Gateway Protocol) or regular eBGP(External 174 Border Gateway Protocol) connectivity between nodes in the topology. 176 The extensions introduced in this document allow for advertisement of 177 different MSD-Types, which are defined elsewhere and were introduced 178 in [RFC8491]. This enables sharing of MSD-Types that may be defined 179 in the future by the IGPs in BGP-LS. 181 3. Node MSD TLV 183 The Node MSD ([RFC8476] [RFC8491]) is encoded in a new Node Attribute 184 TLV [RFC7752] to carry the provisioned SID depth of the router 185 identified by the corresponding Router-ID. Node MSD is the smallest 186 MSD supported by the node on the set of interfaces configured for 187 use. MSD values may be learned via a hardware API or may be 188 provisioned. The following format is used: 190 0 1 2 3 191 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 1 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 193 | Type | Length | 194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 195 | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | 196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 198 Figure 1: Node MSD TLV Format 200 Where: 202 o Type: 266 204 o Length: variable (multiple of 2); represents the total length of 205 the value field in octets. 207 o Value : consists of one or more pairs of a 1-octet MSD-Type and 208 1-octet MSD-Value. 210 * MSD-Type : one of the values defined in the "IGP MSD-Types" 211 registry defined in [RFC8491]. 213 * MSD-Value : a number in the range of 0-255. For all MSD-Types, 214 0 represents the lack of ability to impose an MSD stack of any 215 depth; any other value represents that of the node. This value 216 MUST represent the lowest value supported by any link 217 configured for use by the advertising protocol instance. 219 4. Link MSD TLV 221 The Link MSD ([RFC8476] [RFC8491]) is defined to carry the MSD of the 222 interface associated with the link. It is encoded in a new Link 223 Attribute TLV [RFC7752] using the following format: 225 0 1 2 3 226 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 1 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 228 | Type | Length | 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | 231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 Figure 2: Link MSD TLV Format 235 Where: 237 o Type: 267 238 o Length: variable (multiple of 2); represents the total length of 239 the value field in octets. 241 o Value : consists of one or more pairs of a 1-octet MSD-Type and 242 1-octet MSD-Value. 244 * MSD-Type : MSD-Type : one of the values defined in the "IGP 245 MSD-Types" registry defined in [RFC8491]. 247 * MSD-Value : a number in the range of 0-255. For all MSD-Types, 248 0 represents the lack of ability to impose an MSD stack of any 249 depth; any other value represents that of the link when used as 250 an outgoing interface. 252 5. Procedures for Defining and Using Node and Link MSD Advertisements 254 When Link MSD is present for a given MSD-type, the value of the Link 255 MSD MUST take precedence over the Node MSD. When a Link MSD-type is 256 not signaled but the Node MSD-type is, then the Node MSD-type value 257 MUST be considered as the MSD value for that link. 259 In order to increase flooding efficiency, it is RECOMMENDED that 260 routers with homogenous link MSD values advertise just the Node MSD 261 value. 263 The meaning of the absence of both Node and Link MSD advertisements 264 for a given MSD-type is specific to the MSD-type. Generally it can 265 only be inferred that the advertising node does not support 266 advertisement of that MSD-type. However, in some cases the lack of 267 advertisement might imply that the functionality associated with the 268 MSD-type is not supported. The correct interpretation MUST be 269 specified when an MSD-type is defined in [RFC8491]. 271 6. IANA Considerations 273 This document requests assigning code-points from the registry "BGP- 274 LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute 275 TLVs" based on table below. Early allocation for these code-points 276 have been done by IANA. 278 +------------+-----------------+---------------------------+-------------------+ 279 | Code Point | Description | IS-IS TLV/Sub-TLV | Reference | 280 +------------+-----------------+---------------------------+-------------------+ 281 | 266 | Node MSD | 242/23 | This document | 282 | 267 | Link MSD | (22,23,25,141,222,223)/15 | This document | 283 +------------+-----------------+---------------------------+-------------------+ 284 7. Manageability Considerations 286 The new protocol extensions introduced in this document augment the 287 existing IGP topology information that is distributed via [RFC7752]. 288 Procedures and protocol extensions defined in this document do not 289 affect the BGP protocol operations and management other than as 290 discussed in the Manageability Considerations section of [RFC7752]. 291 Specifically, the malformed attribute tests for syntactic checks in 292 the Fault Management section of [RFC7752] now encompass the new BGP- 293 LS Attribute TLVs defined in this document. The semantic or content 294 checking for the TLVs specified in this document and their 295 association with the BGP-LS NLRI types or their BGP-LS Attribute is 296 left to the consumer of the BGP-LS information (e.g. an application 297 or a controller) and not the BGP protocol. 299 A consumer of the BGP-LS information retrieves this information over 300 a BGP-LS session (refer Section 1 and 2 of [RFC7752]). 302 This document only introduces new Attribute TLVs and any syntactic 303 error in them would result in the BGP-LS Attribute being discarded 304 [RFC7752]. The MSD information introduced in BGP-LS by this 305 specification, may be used by BGP-LS consumer applications like a SR 306 path computation engine (PCE) to learn the SR SID stack handling 307 capabilities of the nodes in the topology. This can enable the SR 308 PCE to perform path computations taking into consideration the size 309 of SID stack that the specific head-end node may be able to impose. 310 Errors in the encoding or decoding of the MSD information may result 311 in the unavailability of such information to the SR PCE or incorrect 312 information being made available to it. This may result in the head- 313 end node not being able to instantiate the desired SR path in its 314 forwarding and provide the SR based optimization functionality. The 315 handling of such errors by applications like SR PCE may be 316 implementation specific and out of scope of this document. 318 The extensions specified in this document, do not specify any new 319 configuration or monitoring aspects in BGP or BGP-LS. The 320 specification of BGP models is an ongoing work based on the 321 [I-D.ietf-idr-bgp-model]. 323 8. Security Considerations 325 The advertisement of an incorrect MSD value may have negative 326 consequences. If the value is smaller than supported, path 327 computation may fail to compute a viable path. If the value is 328 larger than supported, an attempt to instantiate a path that can't be 329 supported by the head-end (the node performing the SID imposition) 330 may occur. The presence of this information may also inform an 331 attacker of how to induce any of the aforementioned conditions. 333 The procedures and protocol extensions defined in this document do 334 not affect the BGP security model. See the "Security Considerations" 335 section of [RFC4271] for a discussion of BGP security. Also, refer 336 to [RFC4272] and [RFC6952] for analyses of security issues for BGP. 337 Security considerations for acquiring and distributing BGP-LS 338 information are discussed in [RFC7752]. The TLVs introduced in this 339 document are used to propagate the MSD IGP extensions defined in 340 [RFC8476] [RFC8491]. It is assumed that the IGP instances 341 originating these TLVs will support all the required security (as 342 described in [RFC8476] [RFC8491]) in order to prevent any security 343 issues when propagating the TLVs into BGP-LS. The advertisement of 344 the node and link attribute information defined in this document 345 presents no additional risk beyond that associated with the existing 346 node and link attribute information already supported in [RFC7752]. 348 9. Contributors 350 Siva Sivabalan 351 Cisco Systems Inc. 352 Canada 354 Email: msiva@cisco.com 356 10. Acknowledgements 358 We like to thank Acee Lindem, Stephane Litkowski, Bruno Decraene and 359 Alvaro Retana for their reviews and valuable comments. 361 11. References 363 11.1. Normative References 365 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 366 Requirement Levels", BCP 14, RFC 2119, 367 DOI 10.17487/RFC2119, March 1997, 368 . 370 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 371 S. Ray, "North-Bound Distribution of Link-State and 372 Traffic Engineering (TE) Information Using BGP", RFC 7752, 373 DOI 10.17487/RFC7752, March 2016, 374 . 376 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 377 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 378 May 2017, . 380 [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, 381 "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, 382 DOI 10.17487/RFC8476, December 2018, 383 . 385 [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 386 "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, 387 DOI 10.17487/RFC8491, November 2018, 388 . 390 11.2. Informative References 392 [I-D.ietf-idr-bgp-model] 393 Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP 394 YANG Model for Service Provider Networks", draft-ietf-idr- 395 bgp-model-08 (work in progress), February 2020. 397 [I-D.ietf-isis-mpls-elc] 398 Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S., 399 and M. Bocci, "Signaling Entropy Label Capability and 400 Entropy Readable Label Depth Using IS-IS", draft-ietf- 401 isis-mpls-elc-10 (work in progress), October 2019. 403 [I-D.ietf-ospf-mpls-elc] 404 Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S., 405 and M. Bocci, "Signaling Entropy Label Capability and 406 Entropy Readable Label-stack Depth Using OSPF", draft- 407 ietf-ospf-mpls-elc-12 (work in progress), October 2019. 409 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol 410 Label Switching Architecture", RFC 3031, 411 DOI 10.17487/RFC3031, January 2001, 412 . 414 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 415 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 416 DOI 10.17487/RFC4271, January 2006, 417 . 419 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", 420 RFC 4272, DOI 10.17487/RFC4272, January 2006, 421 . 423 [RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of 424 BGP, LDP, PCEP, and MSDP Issues According to the Keying 425 and Authentication for Routing Protocols (KARP) Design 426 Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013, 427 . 429 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 430 Decraene, B., Litkowski, S., and R. Shakir, "Segment 431 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 432 July 2018, . 434 [RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 435 and J. Hardwick, "Path Computation Element Communication 436 Protocol (PCEP) Extensions for Segment Routing", RFC 8664, 437 DOI 10.17487/RFC8664, December 2019, 438 . 440 Authors' Addresses 442 Jeff Tantsura 443 Apstra, Inc. 445 Email: jefftant.ietf@gmail.com 447 Uma Chunduri 448 Futurewei Technologies 450 Email: umac.ietf@gmail.com 452 Ketan Talaulikar 453 Cisco Systems 455 Email: ketant@cisco.com 457 Greg Mirsky 458 ZTE Corp. 460 Email: gregimirsky@gmail.com 462 Nikos Triantafillis 463 Amazon Web Services 465 Email: nikost@amazon.com