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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: draft-ietf-idr-bgp-ls-segment-routing-msd has been published as RFC 8814 == Outdated reference: draft-ietf-isis-mpls-elc has been published as RFC 9088 == Outdated reference: draft-ietf-pce-segment-routing has been published as RFC 8664 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). 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: November 11, 2018 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 L. Ginsberg 9 Cisco Systems 10 May 10, 2018 12 Signaling MSD (Maximum SID Depth) using IS-IS 13 draft-ietf-isis-segment-routing-msd-11 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 November 11, 2018. 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 . . . . . . . . . . . . . . . . . . . 4 65 4. Using Node and Link MSD Advertisements . . . . . . . . . . . 5 66 5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6 67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 68 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 69 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 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 177 (IANA Registry) and 1 octet Value. 179 Node MSD value is a number in the range of 0-255. 0 represents lack 180 of the ability to support SID stack of any depth; any other value 181 represents that of the node. This value MUST represent the lowest 182 value supported by any link configured for use by the advertising IS- 183 IS instance. 185 This sub-TLV is optional. The scope of the advertisement is specific 186 to the deployment. 188 3. Link MSD Advertisement 190 The link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and 191 223 to carry the MSD of the interface associated with the link. MSD 192 values may be learned via a hardware API or may be provisioned. 194 0 1 195 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 197 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 198 | Type | Length | 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 | MSD-Type | MSD Value | 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 // ................... // 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | MSD-Type | MSD Value | 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 207 Figure 2: Link MSD Sub-TLV 209 Type: 15 (allocated by IANA via the early assignment process) 211 Length: variable (minimum of 2, multiple of 2 octets) and represents 212 the total length of value field. 214 Value: consists of one or more pairs of a 1 octet MSD-Type (IANA 215 Registry) and 1 octet Value. 217 Link MSD value is a number in the range of 0-255. 0 represents lack 218 of the ability to support SID stack of any depth; any other value 219 represents that of the link when used as an outgoing link. 221 This sub-TLV is optional. The scope of the advertisement is specific 222 to the deployment. 224 4. Using Node and Link MSD Advertisements 226 When Link MSD is present for a given MSD type, the value of the Link 227 MSD MUST take preference over the Node MSD. When a Link MSD type is 228 not signalled but the Node MSD type is, then the Node MSD type value 229 MUST be considered as the MSD value for that link. 231 In order to increase flooding efficiency, it is RECOMMENDED that 232 routers with homogenous link MSD values advertise just the Node MSD 233 value. 235 The meaning of the absence of both Node and Link MSD advertisements 236 for a given MSD type is specific to the MSD type. Generally it can 237 only be inferred that the advertising node does not support 238 advertisement of that MSD type. However, in some cases the lack of 239 advertisement might imply that the functionality associated with the 240 MSD type is not supported. The correct interpretation MUST be 241 specified when an MSD type is defined. 243 5. Base MPLS Imposition MSD 245 Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS 246 labels a node is capable of imposing, including all 247 service/transport/special labels. 249 Absence of BMI-MSD advertisements indicates solely that the 250 advertising node does not support advertisement of this capability. 252 6. IANA Considerations 254 This document requests IANA to allocate a sub-TLV type for the new 255 sub TLV proposed in Section 2 of this document from IS-IS Router 256 Capability TLV Registry as defined by [RFC7981]. 258 IANA has allocated the following value through the early assignment 259 process: 261 Value Description Reference 262 ----- --------------- ------------- 263 23 Node MSD This document 265 Figure 3: Node MSD 267 This document requests IANA to allocate a sub-TLV type as defined in 268 Section 3 from Sub-TLVs for TLVs 22, 23, 25, 141, 222 and 223 269 registry. 271 IANA has allocated the following value through the early assignment 272 process: 274 Value Description Reference 275 ----- --------------- ------------- 276 15 Link MSD This document 278 Figure 4: Link MSD 280 Per TLV information where Link MSD sub-TLV can be part of: 282 TLV 22 23 25 141 222 223 283 --- -------------------- 284 y y y y y y 286 Figure 5: TLVs where LINK MSD Sub-TLV can be present 288 This document requests creation of an IANA managed registry under a 289 new category of "Interior Gateway Protocol (IGP) Parameters" IANA 290 registries to identify MSD types as proposed in Section 2 and 291 Section 3. The registration procedure is "Expert Review" as defined 292 in [RFC8126]. Suggested registry name is "MSD types". Types are an 293 unsigned 8 bit number. The following values are defined by this 294 document 296 Value Name Reference 297 ----- --------------------- ------------- 298 0 Reserved This document 299 1 Base MPLS Imposition MSD This document 300 2-250 Unassigned This document 301 251-254 Experimental This document 302 255 Reserved This document 304 Figure 6: MSD Types Codepoints Registry 306 7. Security Considerations 308 Security considerations as specified by [RFC7981] are applicable to 309 this document. 311 Advertisement of the additional information defined in this document 312 that is false, e.g., an MSD that is incorrect, may result in a path 313 computation failing, having a service unavailable, or instantiation 314 of a path that can't be supported by the head-end (the node 315 performing the imposition). 317 8. Contributors 319 The following people contributed to this document: 321 Peter Psenak 323 Email: ppsenak@cisco.com 325 9. Acknowledgements 327 The authors would like to thank Acee Lindem, Ketan Talaulikar, 328 Stephane Litkowski and Bruno Decraene for their reviews and valuable 329 comments. 331 10. References 333 10.1. Normative References 335 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 336 Requirement Levels", BCP 14, RFC 2119, 337 DOI 10.17487/RFC2119, March 1997, 338 . 340 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 341 for Advertising Router Information", RFC 7981, 342 DOI 10.17487/RFC7981, October 2016, 343 . 345 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 346 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 347 May 2017, . 349 10.2. Informative References 351 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 352 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 353 "Signaling Maximum SID Depth using Border Gateway Protocol 354 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 355 (work in progress), October 2017. 357 [I-D.ietf-isis-mpls-elc] 358 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 359 Litkowski, "Signaling Entropy Label Capability and 360 Readable Label-stack Depth Using IS-IS", draft-ietf-isis- 361 mpls-elc-03 (work in progress), January 2018. 363 [I-D.ietf-pce-segment-routing] 364 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 365 and J. Hardwick, "PCEP Extensions for Segment Routing", 366 draft-ietf-pce-segment-routing-11 (work in progress), 367 November 2017. 369 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 370 S. Ray, "North-Bound Distribution of Link-State and 371 Traffic Engineering (TE) Information Using BGP", RFC 7752, 372 DOI 10.17487/RFC7752, March 2016, 373 . 375 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 376 Writing an IANA Considerations Section in RFCs", BCP 26, 377 RFC 8126, DOI 10.17487/RFC8126, June 2017, 378 . 380 Authors' Addresses 382 Jeff Tantsura 383 Nuage Networks 385 Email: jefftant.ietf@gmail.com 387 Uma Chunduri 388 Huawei Technologies 390 Email: uma.chunduri@huawei.com 392 Sam Aldrin 393 Google, Inc 395 Email: aldrin.ietf@gmail.com 397 Les Ginsberg 398 Cisco Systems 400 Email: ginsberg@cisco.com