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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 OSPF Working Group J. Tantsura 3 Internet-Draft Nuage Networks 4 Intended status: Standards Track U. Chunduri 5 Expires: November 8, 2018 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 P. Psenak 9 Cisco Systems 10 May 07, 2018 12 Signaling MSD (Maximum SID Depth) using OSPF 13 draft-ietf-ospf-segment-routing-msd-11 15 Abstract 17 This document defines a way for an OSPF 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 defines only one type of 22 MSD, but defines an encoding that can support other MSD types. Here 23 the term OSPF means both OSPFv2 and OSPFv3. 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 8, 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 . . . . . . . . . . . . . . . . . . 4 63 2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 64 3. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . . . 7 70 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 71 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 72 10.1. Normative References . . . . . . . . . . . . . . . . . . 7 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 on a given SR path 81 to insure that the SID stack depth of a computed path doesn't exceed 82 the number of SIDs the node is capable of imposing. 84 The PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals 85 MSD in SR PCE Capability TLV and METRIC Object. However, if PCEP is 86 not supported/configured on the head-end of an SR tunnel or a 87 Binding-SID anchor node and controller does not participate in IGP 88 routing, it has no way to learn the MSD of nodes and links. BGP-LS 89 [RFC7752] defines a way to expose topology and associated attributes 90 and 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 OSPF router in the network. 98 Other types of MSD are known to be useful. For example, 99 [I-D.ietf-ospf-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 can be read by transit nodes. 103 This document defines an extension to OSPF 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 This memo makes use of the terms defined in [RFC7770] 120 BGP-LS: Distribution of Link-State and TE Information using Border 121 Gateway Protocol 123 BMI: Base MPLS Imposition is the number of MPLS labels that can be 124 imposed inclusive of all service/transport/special labels 126 OSPF: Open Shortest Path First 128 MSD: Maximum SID Depth - the number of SIDs a node or one of its 129 links can support 131 PCC: Path Computation Client 133 PCE: Path Computation Element 135 PCEP: Path Computation Element Protocol 137 SR: Segment Routing 139 SID: Segment Identifier 141 LSA: Link state advertisement 143 RI: Router Information LSA 145 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 150 BCP14 [RFC2119], [RFC8174] when, and only when they appear in all 151 capitals, as shown here . 153 2. Node MSD Advertisement 155 The node MSD TLV within the body of the OSPF RI Opaque LSA is defined 156 to carry the provisioned SID depth of the router originating the RI 157 LSA. Node MSD is the smallest MSD supported by the node on the set 158 of interfaces configured for use by the advertising IGP instance. 159 MSD values may be learned via a hardware API or may be provisioned.. 161 0 1 2 3 162 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 1 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 | Type | Length | 166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 | MSD Type and Value ... 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 170 Figure 1: Node MSD TLV 172 The Type: TBD1 174 Length: variable (minimum of 2, multiple of 2 octets) and represents 175 the total length of value field. 177 Value: consists of one or more pairs of a 1 octet sub-type (IANA 178 Registry) and 1 octet value. 180 MSD Type 1 (IANA Section), MSD and the Value field contains the MSD 181 of the originating router. Node MSD is a number in the range of 182 0-255. 0 represents lack of the ability to impose MSD stack of any 183 depth; any other value represents that of the node. This value 184 SHOULD represent the minimum value supported by a node. 186 Other MSD Types are reserved for future extensions. 188 This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is 189 optional. The scope of the advertisement is specific to the 190 deployment. 192 3. Link MSD sub-TLV 194 The link sub-TLV is defined to carry the MSD of the interface 195 associated with the link. MSD values may be learned via a hardware 196 API or may be provisioned. 198 0 1 2 3 199 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 1 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 | Type | Length | 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | MSD Type and Value ... 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 207 Figure 2: Link MSD Sub-TLV 209 Type: 211 For OSPFv2, the Link level MSD value is advertised as an optional 212 Sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], and 213 has value of TBD2. 215 For OSPFv3, the Link level MSD value is advertised as an optional 216 Sub-TLV of the E-Router-LSA TLV as defined in [RFC8362], and has 217 value of TBD3. 219 Length: variable and similar to that, defined in Section 2. 221 Value: consists of one or more pairs of a 1 octet MSD Type (IANA 222 Registry) and 1 octet value. 224 MSD Type 1 (IANA Section), MSD and the Value field contains Link MSD 225 of the router originating the corresponding LSA as specified for 226 OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-255. 0 227 represents lack of the ability to impose MSD stack of any depth; any 228 other value represents that of the particular link MSD value. 230 Other MSD Types are reserved for future extensions. 232 If these TLVs are advertised multiple times, only the first instance 233 of the TLV is used by receiving OSPF routers. This situation SHOULD 234 be logged as an error. 236 If these TLV is advertised multiple times for the same link in 237 different LSAs originated by the same OSPF router, the TLV with the 238 smallest Opaque ID/Link State ID is used by receiving OSPF routers. 239 This situation MAY be logged as a warning. 241 4. Using Node and Link MSD Advertisements 243 When Link MSD is present for a given MSD type, the value of the Link 244 MSD MUST take preference over the Node MSD. When a Link MSD type is 245 not signalled but the Node MSD type is, then the value of that Link 246 MSD type MUST be considered as the corresponding Node MSD type value. 247 In order to increase flooding efficiency, it is RECOMMENDED, that 248 routers with homogenous link MSD values advertise just the Node MSD 249 value. 251 The meaning of the absence of both Node and Link MSD advertisements 252 for a given MSD type is specific to the MSD type. Generally it can 253 only be inferred that the advertising node does not support 254 advertisement of that MSD type. However, in some cases the lack of 255 advertisement might imply that the functionality associated with the 256 MSD type is not supported. The correct interpretation MUST be 257 specified when an MSD type is defined. 259 5. Base MPLS Imposition MSD 261 The Base MPLS Imposition MSD (BMI-MSD) signals the total number of 262 MPLS labels a node is capable of imposing, including any service/ 263 transport labels. 265 Absence of BMI-MSD advertisements indicates solely that the 266 advertising node does not support advertisement of this capability. 268 6. IANA Considerations 270 This document requests IANA to allocate TLV type (TBD1) from the OSPF 271 Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA 272 has allocated the value 12 through the early assignment process. 273 Also, this document requests IANA to allocate a sub-TLV type (TBD2) 274 from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has 275 allocated the the value 6 through the early assignment process. 276 Finally, this document requests IANA to allocate a sub-TLV type 277 (TBD3) from the OSPFv3 Extended-LSA Sub-TLV registry. 279 This document requests creation of an IANA managed registry under a 280 new category of "Interior Gateway Protocol (IGP) Parameters" IANA 281 registries to identify MSD types as proposed in Section 2, Section 3. 282 The registration procedure is "Expert Review" as defined in 283 [RFC8126]. The suggested registry name is "MSD types". Types are an 284 unsigned 8 bit number. The following values are defined by this 285 document. 287 Value Name Reference 288 ----- --------------------- ------------- 289 0 Reserved This document 290 1 Base MPLS Imposition MSD This document 291 2-250 Unassigned This document 292 251-254 Experimental This document 293 255 Reserved This document 295 Figure 3: MSD Types Codepoints Registry 297 7. Security Considerations 299 Security concerns for OSPF are addressed in [RFC7474] and [RFC5310]. 300 Further security analysis for OSPF protocol is done in [RFC6853] 301 including analysis of both the above documents. Security 302 considerations, as specified by [RFC7770] are applicable to this 303 document. 305 Advertisement of the additional information defined in this document 306 that is false, e.g. MSD that is incorrect may result: in a path 307 computation failing and the service unavailable or instantiation of a 308 path that can't be supported by the head-end (the node performing the 309 imposition). 311 8. Contributors 313 The following people contributed to this document: 315 Les Ginsberg 317 Email: ginsberg@cisco.com 319 9. Acknowledgements 321 The authors would like to thank Acee Lindem, Stephane Litkowski and 322 Bruno Decraene for their reviews and valuable comments. 324 10. References 326 10.1. Normative References 328 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 329 Requirement Levels", BCP 14, RFC 2119, 330 DOI 10.17487/RFC2119, March 1997, 331 . 333 [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 334 S. Shaffer, "Extensions to OSPF for Advertising Optional 335 Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 336 2007, . 338 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 339 S. Shaffer, "Extensions to OSPF for Advertising Optional 340 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 341 February 2016, . 343 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 344 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 345 May 2017, . 347 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 348 F. Baker, "OSPFv3 Link State Advertisement (LSA) 349 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 350 2018, . 352 10.2. Informative References 354 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 355 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 356 "Signaling Maximum SID Depth using Border Gateway Protocol 357 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 358 (work in progress), October 2017. 360 [I-D.ietf-ospf-mpls-elc] 361 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 362 Litkowski, "Signaling Entropy Label Capability and 363 Readable Label-stack Depth Using OSPF", draft-ietf-ospf- 364 mpls-elc-05 (work in progress), January 2018. 366 [I-D.ietf-pce-segment-routing] 367 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 368 and J. Hardwick, "PCEP Extensions for Segment Routing", 369 draft-ietf-pce-segment-routing-11 (work in progress), 370 November 2017. 372 [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and 373 R. Aggarwal, "Support of Address Families in OSPFv3", 374 RFC 5838, DOI 10.17487/RFC5838, April 2010, 375 . 377 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 378 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 379 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 380 2015, . 382 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 383 S. Ray, "North-Bound Distribution of Link-State and 384 Traffic Engineering (TE) Information Using BGP", RFC 7752, 385 DOI 10.17487/RFC7752, March 2016, 386 . 388 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 389 Writing an IANA Considerations Section in RFCs", BCP 26, 390 RFC 8126, DOI 10.17487/RFC8126, June 2017, 391 . 393 Authors' Addresses 395 Jeff Tantsura 396 Nuage Networks 398 Email: jefftant.ietf@gmail.com 400 Uma Chunduri 401 Huawei Technologies 403 Email: uma.chunduri@huawei.com 405 Sam Aldrin 406 Google, Inc 408 Email: aldrin.ietf@gmail.com 410 Peter Psenak 411 Cisco Systems 413 Email: ppsenak@cisco.com