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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-18) exists of draft-ietf-idr-bgp-ls-segment-routing-msd-01 == Outdated reference: A later version (-13) exists of draft-ietf-isis-mpls-elc-03 == Outdated reference: A later version (-16) exists of draft-ietf-pce-segment-routing-12 -- Obsolete informational reference (is this intentional?): RFC 7752 (Obsoleted by RFC 9552) Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IS-IS Working Group J. Tantsura 3 Internet-Draft Nuage Networks 4 Intended status: Standards Track U. Chunduri 5 Expires: January 25, 2019 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 L. Ginsberg 9 Cisco Systems 10 July 24, 2018 12 Signaling MSD (Maximum SID Depth) using IS-IS 13 draft-ietf-isis-segment-routing-msd-13 15 Abstract 17 This document defines a way for an IS-IS Router to advertise multiple 18 types of supported Maximum SID Depths (MSDs) at node and/or link 19 granularity. Such advertisements allow entities (e.g., centralized 20 controllers) to determine whether a particular SID stack can be 21 supported in a given network. This document only defines one type of 22 MSD maximum label imposition, but defines an encoding that can 23 support other MSD types. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on January 25, 2019. 42 Copyright Notice 44 Copyright (c) 2018 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 1.1. Conventions used in this document . . . . . . . . . . . . 3 61 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 62 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 63 2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 64 3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 5 65 4. Using Node and Link MSD Advertisements . . . . . . . . . . . 6 66 5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6 67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 68 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 69 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 70 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 71 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 72 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 73 10.2. Informative References . . . . . . . . . . . . . . . . . 8 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 76 1. Introduction 78 When Segment Routing(SR) paths are computed by a centralized 79 controller, it is critical that the controller learns the Maximum SID 80 Depth(MSD) that can be imposed at each node/link a given SR path to 81 insure that the SID stack depth of a computed path doesn't exceed the 82 number of SIDs the node is capable of imposing. 84 PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD 85 in SR PCE Capability TLV and METRIC Object. However, if PCEP is not 86 supported/configured on the head-end of an SR tunnel or a Binding-SID 87 anchor node and controller does not participate in IGP routing, it 88 has no way to learn the MSD of nodes and links. BGP-LS [RFC7752] 89 defines a way to expose topology and associated attributes and 90 capabilities of the nodes in that topology to a centralized 91 controller. MSD signaling by BGP-LS has been defined in 92 [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is 93 configured on a small number of nodes that do not necessarily act as 94 head-ends. In order for BGP-LS to signal MSD for all the nodes and 95 links in the network MSD is relevant, MSD capabilites should be 96 advertised by every IS-IS router in the network. 98 Other types of MSD are known to be useful. For example, 99 [I-D.ietf-isis-mpls-elc] defines Readable Label Depth Capability 100 (RLDC) that is used by a head-end to insert an Entropy Label (EL) at 101 a depth, that could be read by transit nodes. 103 This document defines an extension to IS-IS used to advertise one or 104 more types of MSD at node and/or link granularity. It also creates 105 an IANA registry for assigning MSD type identifiers. It also defines 106 the Base MPLS Imposition MSD type. In the future it is expected, 107 that new MSD types will be defined to signal additional capabilities 108 e.g., entropy labels, SIDs that can be imposed through recirculation, 109 or SIDs associated with another dataplane e.g., IPv6. Although MSD 110 advertisements are associated with Segment Routing, the 111 advertisements MAY be present even if Segment Routing itself is not 112 enabled. 114 1.1. Conventions used in this document 116 1.1.1. Terminology 118 BGP-LS: Distribution of Link-State and TE Information using Border 119 Gateway Protocol 121 BMI: Base MPLS Imposition is the number of MPLS labels which can be 122 imposed inclusive of all service/transport/special labels 124 IS-IS: Intermediate System to Intermediate System 126 MSD: Maximum SID Depth - the number of SIDs a node or a link on a 127 node can support 129 PCC: Path Computation Client 131 PCE: Path Computation Element 133 PCEP: Path Computation Element Protocol 135 SID: Segment Identifier 137 SR: Segment Routing 139 1.2. Requirements Language 141 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 142 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 143 "OPTIONAL" in this document are to be interpreted as described in BCP 144 14 [RFC2119] [RFC8174] when, and only when, they appear in all 145 capitals, as shown here . 147 2. Node MSD Advertisement 149 The node MSD sub-TLV is defined within the body of the IS-IS Router 150 Capability TLV [RFC7981], to carry the provisioned SID depth of the 151 router originating the Router Capability TLV. Node MSD is the 152 smallest MSD supported by the node on the set of interfaces 153 configured for use by the advertising IGP instance. MSD values may 154 be learned via a hardware API or may be provisioned. 156 0 1 157 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 | Type | Length | 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 | MSD-Type | MSD Value | 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 164 // ................... // 165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 166 | MSD-Type | MSD Value | 167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 Figure 1: Node MSD Sub-TLV 171 Type: 23 (allocated by IANA via the early assignment process) 173 Length: variable (minimum of 2, multiple of 2 octets) and represents 174 the total length of value field. 176 Value: field consists of one or more pairs of a 1 octet MSD-Type and 177 1 octet MSD-Value. 179 MSD-Type is one of the values defined in the IGP MSD Types registry 180 created by the IANA Section of this document. 182 MSD-Value is a number in the range of 0-255. For all MSD-Types, 0 183 represents lack of the ability to support SID stack of any depth; any 184 other value represents that of the node. This value MUST represent 185 the lowest value supported by any link configured for use by the 186 advertising IS-IS instance. 188 This sub-TLV is optional. The scope of the advertisement is specific 189 to the deployment. 191 If there exist multiple Node MSD advertisements for the same MSD-Type 192 originated by the same router, the procedures defined in [RFC7981] 193 apply. 195 3. Link MSD Advertisement 197 The link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and 198 223 to carry the MSD of the interface associated with the link. MSD 199 values may be learned via a hardware API or may be provisioned. 201 0 1 202 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 205 | Type | Length | 206 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 207 | MSD-Type | MSD Value | 208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 // ................... // 210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 211 | MSD-Type | MSD Value | 212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 214 Figure 2: Link MSD Sub-TLV 216 Type: 15 (allocated by IANA via the early assignment process) 218 Length: variable (minimum of 2, multiple of 2 octets) and represents 219 the total length of value field. 221 Value: consists of one or more pairs of a 1 octet MSD-Type and 1 222 octet Value. 224 MSD-Type is one of the values defined in the MSD Types registry 225 created by the IANA Section of this document. 227 MSD-Value is a number in the range of 0-255. For all MSD-Types, 0 228 represents lack of the ability to support SID stack of any depth; any 229 other value represents that of the link when used as an outgoing 230 link. 232 This sub-TLV is optional. The scope of the advertisement is specific 233 to the deployment. 235 If multiple Link MSD advertisements for the same MSD Type and the 236 same link are received, the procedure used to select which copy is 237 used is undefined. 239 4. Using Node and Link MSD Advertisements 241 When Link MSD is present for a given MSD type, the value of the Link 242 MSD MUST take preference over the Node MSD. When a Link MSD type is 243 not signalled but the Node MSD type is, then the Node MSD type value 244 MUST be considered as the MSD value for that link. 246 In order to increase flooding efficiency, it is RECOMMENDED that 247 routers with homogenous link MSD values advertise just the Node MSD 248 value. 250 The meaning of the absence of both Node and Link MSD advertisements 251 for a given MSD type is specific to the MSD type. Generally it can 252 only be inferred that the advertising node does not support 253 advertisement of that MSD type. However, in some cases the lack of 254 advertisement might imply that the functionality associated with the 255 MSD type is not supported. The correct interpretation MUST be 256 specified when an MSD type is defined. 258 5. Base MPLS Imposition MSD 260 Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS 261 labels a node is capable of imposing, including all 262 service/transport/special labels. 264 Absence of BMI-MSD advertisements indicates solely that the 265 advertising node does not support advertisement of this capability. 267 6. IANA Considerations 269 This document requests IANA to allocate a sub-TLV type for the new 270 sub TLV proposed in Section 2 of this document from IS-IS Router 271 Capability TLV Registry as defined by [RFC7981]. 273 IANA has allocated the following value through the early assignment 274 process: 276 Value Description Reference 277 ----- --------------- ------------- 278 23 Node MSD This document 280 Figure 3: Node MSD 282 This document requests IANA to allocate a sub-TLV type as defined in 283 Section 3 from Sub-TLVs for TLVs 22, 23, 25, 141, 222 and 223 284 registry. 286 IANA has allocated the following value through the early assignment 287 process: 289 Value Description Reference 290 ----- --------------- ------------- 291 15 Link MSD This document 293 Figure 4: Link MSD 295 Per TLV information where Link MSD sub-TLV can be part of: 297 TLV 22 23 25 141 222 223 298 --- -------------------- 299 y y y y y y 301 Figure 5: TLVs where LINK MSD Sub-TLV can be present 303 This document requests creation of an IANA managed registry under a 304 new category of "Interior Gateway Protocol (IGP) Parameters" IANA 305 registries to identify MSD types as proposed in Section 2 and 306 Section 3. The registration procedure is "Expert Review" as defined 307 in [RFC8126]. Suggested registry name is "IGP MSD Types". Types are 308 an unsigned 8 bit number. The following values are defined by this 309 document 311 Value Name Reference 312 ----- --------------------- ------------- 313 0 Reserved This document 314 1 Base MPLS Imposition MSD This document 315 2-250 Unassigned This document 316 251-254 Experimental This document 317 255 Reserved This document 319 Figure 6: MSD Types Codepoints Registry 321 7. Security Considerations 323 Security considerations as specified by [RFC7981] are applicable to 324 this document. 326 Advertisement of the additional information defined in this document 327 that is false, e.g., an MSD that is incorrect, may result in a path 328 computation failing, having a service unavailable, or instantiation 329 of a path that can't be supported by the head-end (the node 330 performing the imposition). 332 8. Contributors 334 The following people contributed to this document: 336 Peter Psenak 338 Email: ppsenak@cisco.com 340 9. Acknowledgements 342 The authors would like to thank Acee Lindem, Ketan Talaulikar, 343 Stephane Litkowski and Bruno Decraene for their reviews and valuable 344 comments. 346 10. References 348 10.1. Normative References 350 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 351 Requirement Levels", BCP 14, RFC 2119, 352 DOI 10.17487/RFC2119, March 1997, 353 . 355 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 356 for Advertising Router Information", RFC 7981, 357 DOI 10.17487/RFC7981, October 2016, 358 . 360 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 361 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 362 May 2017, . 364 10.2. Informative References 366 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 367 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 368 "Signaling Maximum SID Depth using Border Gateway Protocol 369 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 370 (work in progress), October 2017. 372 [I-D.ietf-isis-mpls-elc] 373 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 374 Litkowski, "Signaling Entropy Label Capability and 375 Readable Label-stack Depth Using IS-IS", draft-ietf-isis- 376 mpls-elc-03 (work in progress), January 2018. 378 [I-D.ietf-pce-segment-routing] 379 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 380 and J. Hardwick, "PCEP Extensions for Segment Routing", 381 draft-ietf-pce-segment-routing-12 (work in progress), June 382 2018. 384 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 385 S. Ray, "North-Bound Distribution of Link-State and 386 Traffic Engineering (TE) Information Using BGP", RFC 7752, 387 DOI 10.17487/RFC7752, March 2016, 388 . 390 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 391 Writing an IANA Considerations Section in RFCs", BCP 26, 392 RFC 8126, DOI 10.17487/RFC8126, June 2017, 393 . 395 Authors' Addresses 397 Jeff Tantsura 398 Nuage Networks 400 Email: jefftant.ietf@gmail.com 402 Uma Chunduri 403 Huawei Technologies 405 Email: uma.chunduri@huawei.com 407 Sam Aldrin 408 Google, Inc 410 Email: aldrin.ietf@gmail.com 412 Les Ginsberg 413 Cisco Systems 415 Email: ginsberg@cisco.com