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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: October 11, 2018 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 L. Ginsberg 9 Cisco Systems 10 April 09, 2018 12 Signaling MSD (Maximum SID Depth) using IS-IS 13 draft-ietf-isis-segment-routing-msd-10 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 October 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 65 4. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 5 66 5. Using Node and Link MSD Advertisements . . . . . . . . . . . 5 67 6. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6 68 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 69 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 70 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 71 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 72 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 73 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 74 11.2. Informative References . . . . . . . . . . . . . . . . . 8 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 77 1. Introduction 79 When Segment Routing(SR) paths are computed by a centralized 80 controller, it is critical that the controller learns the Maximum SID 81 Depth(MSD) that can be imposed at each node/link a given SR path to 82 insure that the SID stack depth of a computed path doesn't exceed the 83 number of SIDs the node is capable of imposing. 85 PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD 86 in SR PCE Capability TLV and METRIC Object. However, if PCEP is not 87 supported/configured on the head-end of a SR tunnel or a Binding-SID 88 anchor node and controller does not participate in IGP routing, it 89 has no way to learn the MSD of nodes and links which has been 90 configured. BGP-LS [RFC7752] defines a way to expose topology and 91 associated attributes and capabilities of the nodes in that topology 92 to a centralized controller. MSD signaling by BGP-LS has been 93 defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, 94 BGP-LS is configured on a small number of nodes that do not 95 necessarily act as head-ends. In order for BGP-LS to signal MSD for 96 all the nodes and links in the network MSD is relevant, MSD 97 capabilites should be advertised to every IS-IS router in the 98 network. 100 Other types of MSD are known to be useful. For example, 101 [I-D.ietf-isis-mpls-elc] defines Readable Label Depth Capability 102 (RLDC) that is used by a head-end to insert an Entropy Label (EL) at 103 a depth, that could be read by transit nodes. 105 This document defines an extension to IS-IS used to advertise one or 106 more types of MSD at node and/or link granularity. It also creates 107 an IANA registry for assigning MSD type identifiers. It also defines 108 the Base MPLS Imposition MSD type. In the future it is expected, 109 that new MSD types will be defined to signal additional capabilities 110 e.g., entropy labels, SIDs that can be imposed through recirculation, 111 or SIDs associated with another dataplane e.g., IPv6. 113 1.1. Conventions used in this document 115 1.1.1. Terminology 117 BGP-LS: Distribution of Link-State and TE Information using Border 118 Gateway Protocol 120 BMI: Base MPLS Imposition is the number of MPLS labels which can be 121 imposed inclusive of any service/transport labels 123 IS-IS: Intermediate System to Intermediate System 125 MSD: Maximum SID Depth - the number of SIDs a node or a link on a 126 node can support 128 PCC: Path Computation Client 130 PCE: Path Computation Element 132 PCEP: Path Computation Element Protocol 134 SID: Segment Identifier 136 SR: Segment Routing 138 1.2. Requirements Language 140 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 141 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 142 "OPTIONAL" in this document are to be interpreted as described in 143 BCP14 [RFC2119], [RFC8174] when, and only when they appear in all 144 capitals, as shown here . 146 2. Terminology 148 This memo makes use of the terms defined in [RFC4970]. 150 3. Node MSD Advertisement 152 The node MSD sub-TLV is defined within the body of the IS-IS Router 153 Capability TLV [RFC7981], to carry the provisioned SID depth of the 154 router originating the Router Capability TLV. Node MSD is the 155 minimum MSD supported by the node on any interface. MSD values may 156 be learned via a hardware API or may be provisioned. 158 0 1 159 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 | Type | Length | 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 164 | MSD-Type | MSD Value | 165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 166 // ................... // 167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 168 | MSD-Type | MSD Value | 169 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 171 Figure 1: Node MSD Sub-TLV 173 The Type: TBD1 175 Length: variable (minimum of 2, multiple of 2 octets) and represents 176 the total length of value field. 178 Value: field consists of one or more pairs of a 1 octet MSD-Type 179 (IANA Registry) and 1 octet Value. 181 Node MSD value is a number in the range of 0-255. 0 represents lack 182 of the ability to support SID stack of any depth; any other value 183 represents that of the node. This value MUST represent the lowest 184 value supported by any link associated with the node. 186 This sub-TLV is optional. The scope of the advertisement is specific 187 to the deployment. 189 4. Link MSD Advertisement 191 The link MSD sub-TLV is defined for TLVs 22, 23, 141, 222, and 223 to 192 carry the MSD of the interface associated with the link. MSD values 193 may be learned via a hardware API or may be provisioned. 195 0 1 196 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 199 | Type | Length | 200 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 201 | MSD-Type | MSD Value | 202 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 203 // ................... // 204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 205 | MSD-Type | MSD Value | 206 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 208 Figure 2: Link MSD Sub-TLV 210 The Type: TBD2 212 Length: variable (minimum of 2, multiple of 2 octets) and represents 213 the total length of value field. 215 Value: consists of one or more pairs of a 1 octet MSD-Type (IANA 216 Registry) and 1 octet Value. 218 Link MSD value is a number in the range of 0-255. 0 represents lack 219 of the ability to support SID stack of any depth; any other value 220 represents that of the link when used as an outgoing link. 222 This sub-TLV is optional. The scope of the advertisement is specific 223 to the deployment. 225 5. Using Node and Link MSD Advertisements 227 When Link MSD is present for a given MSD type, the value of the Link 228 MSD MUST take preference over the Node MSD. 230 The meaning of the absence of both Node and Link MSD advertisements 231 for a given MSD type is specific to the MSD type. Generally it can 232 only be inferred that the advertising node does not support 233 advertisement of that MSD type. However, in some cases the lack of 234 advertisement might imply that the functionality associated with the 235 MSD type is not supported. The correct interpretation MUST be 236 specified when an MSD type is defined. 238 6. Base MPLS Imposition MSD 240 Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS 241 labels a node is capable of imposing, including any service/transport 242 labels. 244 Absence of BMI-MSD advertisements indicates solely that the 245 advertising node does not support advertisement of this capability. 247 7. IANA Considerations 249 This document requests IANA to allocate a sub-TLV type (TBD1) for the 250 new sub TLV proposed in Section 3 of this document from IS-IS Router 251 Capability TLV Registry as defined by [RFC7981]. 253 IANA has allocated the following value through the early assignment 254 process: 256 Value Description Reference 257 ----- --------------- ------------- 258 23 Node MSD This document 260 Figure 3: Node MSD 262 This document requests IANA to allocate a sub-TLV type (TBD2) as 263 defined in Section 4 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223 264 registry. 266 IANA has allocated the following value through the early assignment 267 process: 269 Value Description Reference 270 ----- --------------- ------------- 271 15 Link MSD This document 273 Figure 4: Link MSD 275 Per TLV information where Link MSD sub-TLV can be part of: 277 TLV 22 23 25 141 222 223 278 --- -------------------- 279 y y y y y y 281 Figure 5: TLVs where LINK MSD Sub-TLV can be present 283 This document requests creation of an IANA managed registry under a 284 new category of "Interior Gateway Protocol (IGP) Parameters" IANA 285 registries to identify MSD types as proposed in Section 3 and 286 Section 4. The registration procedure is "Expert Review" as defined 287 in [RFC8126]. Suggested registry name is "MSD types". Types are an 288 unsigned 8 bit number. The following values are defined by this 289 document 291 Value Name Reference 292 ----- --------------------- ------------- 293 0 Reserved This document 294 1 Base MPLS Imposition MSD This document 295 2-250 Unassigned This document 296 251-254 Experimental This document 297 255 Reserved This document 299 Figure 6: MSD Types Codepoints Registry 301 8. Security Considerations 303 Security considerations, as specified by [RFC7981] are applicable to 304 this document 306 9. Contributors 308 The following people contributed to this document: 310 Peter Psenak 312 Email: ppsenak@cisco.com 314 10. Acknowledgements 316 The authors would like to thank Acee Lindem, Stephane Litkowski and 317 Bruno Decraene for their reviews and valuable comments. 319 11. References 320 11.1. Normative References 322 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 323 Requirement Levels", BCP 14, RFC 2119, 324 DOI 10.17487/RFC2119, March 1997, 325 . 327 [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 328 S. Shaffer, "Extensions to OSPF for Advertising Optional 329 Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 330 2007, . 332 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 333 for Advertising Router Information", RFC 7981, 334 DOI 10.17487/RFC7981, October 2016, 335 . 337 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 338 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 339 May 2017, . 341 11.2. Informative References 343 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 344 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 345 "Signaling Maximum SID Depth using Border Gateway Protocol 346 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 347 (work in progress), October 2017. 349 [I-D.ietf-isis-mpls-elc] 350 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 351 Litkowski, "Signaling Entropy Label Capability and 352 Readable Label-stack Depth Using IS-IS", draft-ietf-isis- 353 mpls-elc-03 (work in progress), January 2018. 355 [I-D.ietf-pce-segment-routing] 356 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 357 and J. Hardwick, "PCEP Extensions for Segment Routing", 358 draft-ietf-pce-segment-routing-11 (work in progress), 359 November 2017. 361 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 362 S. Ray, "North-Bound Distribution of Link-State and 363 Traffic Engineering (TE) Information Using BGP", RFC 7752, 364 DOI 10.17487/RFC7752, March 2016, 365 . 367 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 368 Writing an IANA Considerations Section in RFCs", BCP 26, 369 RFC 8126, DOI 10.17487/RFC8126, June 2017, 370 . 372 Authors' Addresses 374 Jeff Tantsura 375 Nuage Networks 377 Email: jefftant.ietf@gmail.com 379 Uma Chunduri 380 Huawei Technologies 382 Email: uma.chunduri@huawei.com 384 Sam Aldrin 385 Google, Inc 387 Email: aldrin.ietf@gmail.com 389 Les Ginsberg 390 Cisco Systems 392 Email: ginsberg@cisco.com