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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: October 7, 2018 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 P. Psenak 9 Cisco Systems 10 April 05, 2018 12 Signaling MSD (Maximum SID Depth) using OSPF 13 draft-ietf-ospf-segment-routing-msd-10 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 only defines one type of 22 MSD maximum label imposition, but defines an encoding which can 23 support other MSD types. Here the term OSPF means both OSPFv2 and 24 OSPFv3. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on October 7, 2018. 43 Copyright Notice 45 Copyright (c) 2018 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (https://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 1.1. Conventions used in this document . . . . . . . . . . . . 3 62 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 63 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 66 4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5 67 5. Using Node and Link MSD Advertisements . . . . . . . . . . . 5 68 6. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6 69 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 70 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 71 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 72 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 73 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 74 11.1. Normative References . . . . . . . . . . . . . . . . . . 7 75 11.2. Informative References . . . . . . . . . . . . . . . . . 7 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 78 1. Introduction 80 When Segment Routing(SR) paths are computed by a centralized 81 controller, it is critical that the controller learns the Maximum SID 82 Depth(MSD) that can be imposed at each node/link a given SR path to 83 insure that the SID stack depth of a computed path doesn't exceed the 84 number of SIDs the node is capable of imposing. 86 The PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals 87 MSD in SR PCE Capability TLV and METRIC Object. However, if PCEP is 88 not supported/configured on the head-end of an SR tunnel or a 89 Binding-SID anchor node and controller does not participate in IGP 90 routing, it has no way to learn the MSD of nodes and links which has 91 been configured. BGP-LS [RFC7752] defines a way to expose topology 92 and associated attributes and capabilities of the nodes in that 93 topology to a centralized controller. MSD signaling by BGP-LS has 94 been defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. 95 Typically, BGP-LS is configured on a small number of nodes that do 96 not necessarily act as head-ends. In order for BGP-LS to signal MSD 97 for all the nodes and links in the network MSD is relevant, MSD 98 capabilites should be advertised to every OSPF router in the network. 100 Other types of MSD are known to be useful. For example, 101 [I-D.ietf-ospf-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 can be read by transit nodes. 105 This document defines an extension to OSPF 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 laso 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 that can be 121 imposed inclusive of any service/transport labels 123 OSPF: Open Shortest Path First 125 MSD: Maximum SID Depth - the number of SIDs a node or one of its 126 links 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 TLV 152 The node MSD TLV within the body of the OSPF RI Opaque LSA is defined 153 to carry the provisioned SID depth of the router originating the RI 154 LSA. Node MSD is the minimum MSD supported by the node. 156 0 1 2 3 157 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 1 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 | Type | Length | 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 | Sub-Type and Value ... 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 165 Figure 1: Node MSD TLV 167 The Type: TBD1 169 Length: variable (minimum of 2, multiple of 2 octets) and represents 170 the total length of value field. 172 Value: consists of a 1 octet sub-type (IANA Registry) and 1 octet 173 value. 175 Sub-Type 1 (IANA Section), MSD and the Value field contains maximum 176 MSD of the router originating the RI LSA. Node Maximum MSD is a 177 number in the range of 0-254. 0 represents lack of the ability to 178 impose MSD stack of any depth; any other value represents that of the 179 node. This value SHOULD represent the minimum value supported by a 180 node. 182 Other Sub-types other than defined above are reserved for future 183 extensions. 185 This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is 186 optional. The scope of the advertisement is specific to the 187 deployment. 189 4. Link MSD sub-TLV 191 A new sub-TLV called Link MSD sub-TLV is defined to carry the 192 provisioned SID depth of the interface associated with the link. 194 0 1 2 3 195 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 1 197 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 198 | Type | Length | 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 | Sub-Type and Value ... 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 203 Figure 2: Link MSD Sub-TLV 205 Type: 207 For OSPFv2, the Link level MSD value is advertised as an optional 208 Sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], and 209 has value of TBD2. 211 For OSPFv3, the Link level MSD value is advertised as an optional 212 Sub-TLV of the Router-Link TLV as defined in 213 [I-D.ietf-ospf-ospfv3-lsa-extend], and has value of TBD3. 215 Length: variable and similar to what is defined in Section 3. 217 Value: consists of a 1 octet sub-type (IANA Registry) and 1 octet 218 value. 220 Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD 221 of the router originating the corresponding LSA as specified for 222 OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0 223 represents lack of the ability to impose MSD stack of any depth; any 224 other value represents that of the particular link MSD value. 226 Other Sub-types other than defined above are reserved for future 227 extensions. 229 5. Using Node and Link MSD Advertisements 231 When Link MSD is present for a given MSD type, the value of the Link 232 MSD MUST take preference over the Node MSD. 234 The meaning of the absence of both Node and Link MSD advertisements 235 for a given MSD type is specific to the MSD type. Generally it can 236 only be inferred that the advertising node does not support 237 advertisement of that MSD type. However, in some cases the lack of 238 advertisement might imply that the functionality associated with the 239 MSD type is not supported. The correct interpretation MUST be 240 specified when an MSD type is defined. 242 6. Base MPLS Imposition MSD 244 The Base MPLS Imposition MSD (BMI-MSD) signals the total number of 245 MPLS labels a node is capable of imposing, including any service/ 246 transport labels. 248 Absence of BMI-MSD advertisements indicates solely that the 249 advertising node does not support advertisement of this capability. 251 7. IANA Considerations 253 This document requests IANA to allocate TLV type (TBD1) from the OSPF 254 Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA 255 has allocated the value 12 through the early assignment process. 256 Also, this document requests IANA to allocate a sub-TLV type (TBD2) 257 from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has 258 allocated the the value 6 through the early assignment process. 259 Finally, this document requests IANA to allocate a sub-TLV type 260 (TBD3) from the OSPFv3 Extended-LSA Sub-TLV registry. 262 This document requests creation of an IANA managed registry under a 263 new category of "Interior Gateway Protocol (IGP) Parameters" IANA 264 registries to identify MSD types as proposed in Section 3, Section 4. 265 The registration procedure is "Expert Review" as defined in 266 [RFC8126]. The suggested registry name is "MSD types". Types are an 267 unsigned 8 bit number. The following values are defined by this 268 document. 270 Value Name Reference 271 ----- --------------------- ------------- 272 0 Reserved This document 273 1 Base MPLS Imposition MSD This document 274 2-250 Unassigned This document 275 251-254 Experimental This document 276 255 Reserved This document 278 Figure 3: MSD Types Codepoints Registry 280 8. Security Considerations 282 Security considerations, as specified by [RFC7770] are applicable to 283 this document 285 9. Contributors 287 The following people contributed to this document: 289 Les Ginsberg 291 Email: ginsberg@cisco.com 293 10. Acknowledgements 295 The authors would like to thank Acee Lindem, Stephane Litkowski and 296 Bruno Decraene for their reviews and valuable comments. 298 11. References 300 11.1. Normative References 302 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 303 Requirement Levels", BCP 14, RFC 2119, 304 DOI 10.17487/RFC2119, March 1997, 305 . 307 [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 308 S. Shaffer, "Extensions to OSPF for Advertising Optional 309 Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 310 2007, . 312 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 313 S. Shaffer, "Extensions to OSPF for Advertising Optional 314 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 315 February 2016, . 317 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 318 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 319 May 2017, . 321 11.2. Informative References 323 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 324 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 325 "Signaling Maximum SID Depth using Border Gateway Protocol 326 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 327 (work in progress), October 2017. 329 [I-D.ietf-ospf-mpls-elc] 330 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 331 Litkowski, "Signaling Entropy Label Capability and 332 Readable Label-stack Depth Using OSPF", draft-ietf-ospf- 333 mpls-elc-05 (work in progress), January 2018. 335 [I-D.ietf-ospf-ospfv3-lsa-extend] 336 Lindem, A., Roy, A., Goethals, D., Vallem, V., and F. 337 Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3- 338 lsa-extend-23 (work in progress), January 2018. 340 [I-D.ietf-pce-segment-routing] 341 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 342 and J. Hardwick, "PCEP Extensions for Segment Routing", 343 draft-ietf-pce-segment-routing-11 (work in progress), 344 November 2017. 346 [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and 347 R. Aggarwal, "Support of Address Families in OSPFv3", 348 RFC 5838, DOI 10.17487/RFC5838, April 2010, 349 . 351 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 352 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 353 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 354 2015, . 356 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 357 S. Ray, "North-Bound Distribution of Link-State and 358 Traffic Engineering (TE) Information Using BGP", RFC 7752, 359 DOI 10.17487/RFC7752, March 2016, 360 . 362 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 363 Writing an IANA Considerations Section in RFCs", BCP 26, 364 RFC 8126, DOI 10.17487/RFC8126, June 2017, 365 . 367 Authors' Addresses 369 Jeff Tantsura 370 Nuage Networks 372 Email: jefftant.ietf@gmail.com 373 Uma Chunduri 374 Huawei Technologies 376 Email: uma.chunduri@huawei.com 378 Sam Aldrin 379 Google, Inc 381 Email: aldrin.ietf@gmail.com 383 Peter Psenak 384 Cisco Systems 386 Email: ppsenak@cisco.com