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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-19) exists of draft-ietf-isis-segment-routing-msd-13 == Outdated reference: A later version (-18) exists of draft-ietf-idr-bgp-ls-segment-routing-msd-02 == Outdated reference: A later version (-15) exists of draft-ietf-ospf-mpls-elc-06 == Outdated reference: A later version (-16) exists of draft-ietf-pce-segment-routing-12 -- Obsolete informational reference (is this intentional?): RFC 7752 (Obsoleted by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 (~~), 5 warnings (==), 2 comments (--). 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: February 22, 2019 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 P. Psenak 9 Cisco Systems 10 August 21, 2018 12 Signaling MSD (Maximum SID Depth) using OSPF 13 draft-ietf-ospf-segment-routing-msd-17 15 Abstract 17 This document defines a way for an Open Shortest Path First (OSPF) 18 Router to advertise multiple types of supported Maximum SID Depths 19 (MSDs) at node and/or link granularity. Such advertisements allow 20 entities (e.g., centralized controllers) to determine whether a 21 particular SID stack can be supported in a given network. This 22 document defines only one type of MSD, but defines an encoding that 23 can support other MSD types. Here the term OSPF means both OSPFv2 24 and 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 February 22, 2019. 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. 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. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 67 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 68 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 69 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 70 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 71 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 72 9.2. Informative References . . . . . . . . . . . . . . . . . 8 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 75 1. Introduction 77 When Segment Routing (SR) paths are computed by a centralized 78 controller, it is critical that the controller learns the Maximum SID 79 Depth (MSD) that can be imposed at each node/link on a given SR path 80 to insure that the SID stack depth of a computed path doesn't exceed 81 the number of SIDs the node is capable of imposing. 83 Path Computation Element Protocol(PCEP) SR draft 84 [I-D.ietf-pce-segment-routing] signals MSD in SR Path Computation 85 Element 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 (Distribution 89 of Link-State and TE Information using Border Gateway Protocol) 90 [RFC7752] defines a way to expose topology and associated attributes 91 and capabilities of the nodes in that topology to a centralized 92 controller. MSD signaling by BGP-LS has been defined in 93 [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is 94 configured on a small number of nodes that do not necessarily act as 95 head-ends. In order for BGP-LS to signal MSD for all the nodes and 96 links in the network MSD is relevant, MSD capabilities should be 97 advertised by every OSPF router in the network. 99 Other types of MSD are known to be useful. For example, 100 [I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability 101 (RLDC) that is used by a head-end to insert an Entropy Label (EL) at 102 a depth that can be read by transit nodes. 104 This document defines an extension to OSPF used to advertise one or 105 more types of MSD at node and/or link granularity. 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. Terminology 116 This memo makes use of the terms defined in [RFC7770] 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 that can be 122 imposed inclusive of all service/transport/special labels 124 OSPF: Open Shortest Path First 126 MSD: Maximum SID Depth - the number of SIDs a node or one of its 127 links can support 129 PCC: Path Computation Client 131 PCE: Path Computation Element 133 PCEP: Path Computation Element Protocol 135 SR: Segment Routing 137 SID: Segment Identifier 139 LSA: Link state advertisement 141 RI: OSPF Router Information LSA 143 1.2. Requirements Language 145 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 146 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 147 "OPTIONAL" in this document are to be interpreted as described in BCP 148 14 [RFC2119] [RFC8174] when, and only when, they appear in all 149 capitals, as shown here. 151 2. Node MSD Advertisement 153 The node MSD TLV within the body of the OSPF RI Opaque LSA [RFC7770] 154 is defined to carry the provisioned SID depth of the router 155 originating the RI LSA. Node MSD is the smallest MSD supported by 156 the node on the set of interfaces configured for use by the 157 advertising IGP instance. MSD values may be learned via a hardware 158 API or may be provisioned. 160 0 1 2 3 161 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 1 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 164 | Type | Length | 165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 166 | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | 167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 Figure 1: Node MSD TLV 171 The Type: TBD1 173 Length: variable (multiple of 2 octets) and represents the total 174 length of value field in octets. 176 Value: consists of one or more pairs of a 1 octet MSD-type and 1 177 octet MSD-Value. 179 MSD-Type: one of the values defined in the IGP MSD Types registry 180 defined in [I-D.ietf-isis-segment-routing-msd]. 182 MSD-Value: a number in the range of 0-255. For all MSD-Types, 0 183 represents lack of the ability to impose MSD 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 OSPF instance. 188 This TLV is applicable to OSPFv2 and to OSPFv3 and is optional. The 189 scope of the advertisement is specific to the deployment. 191 When multiple Node MSD TLVs are received from a given router, the 192 receiver MUST use the first occurrence of the TLV in the Router 193 Information LSA. If the Node MSD TLV appears in multiple Router 194 Information LSAs that have different flooding scopes, the Node MSD 195 TLV in the Router Information LSA with the area-scoped flooding scope 196 MUST be used. If the Node MSD TLV appears in multiple Router 197 Information LSAs that have the same flooding scope, the Node MSD TLV 198 in the Router Information (RI) LSA with the numerically smallest 199 Instance ID MUST be used and subsequent instances of the Node MSD TLV 200 MUST be ignored. The RI LSA can be advertised at any of the defined 201 opaque flooding scopes (link, area, or Autonomous System (AS)). For 202 the purpose of Node MSD TLV advertisement, area-scoped flooding is 203 REQUIRED. 205 3. Link MSD sub-TLV 207 The link sub-TLV is defined to carry the MSD of the interface 208 associated with the link. MSD values may be learned via a hardware 209 API or may be provisioned. 211 0 1 2 3 212 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 1 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 | Type | Length | 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 Figure 2: Link MSD Sub-TLV 222 Type: 224 For OSPFv2, the Link level MSD value is advertised as an optional 225 Sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], and 226 has a type of TBD2. 228 For OSPFv3, the Link level MSD value is advertised as an optional 229 Sub-TLV of the E-Router-LSA TLV as defined in [RFC8362], and has a 230 type of TBD3. 232 Length: variable and same as defined in Section 2. 234 Value: consists of one or more pairs of a 1 octet MSD-type and 1 235 octet MSD-Value. 237 MSD-Type: one of the values defined in the MSD Types registry defined 238 in [I-D.ietf-isis-segment-routing-msd]. 240 MSD-Value field contains Link MSD of the router originating the 241 corresponding LSA as specified for OSPFv2 and OSPFv3. Link MSD is a 242 number in the range of 0-255. For all MSD-Types, 0 represents lack 243 of the ability to impose MSD stack of any depth; any other value 244 represents that of the particular link when used as an outgoing 245 interface. 247 If this sub-TLV is advertised multiple times in the same OSPFv2 248 Extended Link Opaque LSA/E-Router-LSA, only the first instance of the 249 TLV MUST be used by receiving OSPF routers. This situation SHOULD be 250 logged as an error. 252 If this sub-TLV is advertised multiple times for the same link in 253 different OSPF Extended Link Opaque LSAs/E-Router-LSAs originated by 254 the same OSPF router, the OSPFv2 Extended Link TLV in the OSPFv2 255 Extended Link Opaque LSA with the smallest Opaque ID or in the OSPFv3 256 E-Router-LSA with the smallest Link State ID is used by receiving 257 OSPF routers. This situation MAY be logged as a warning. 259 4. Using Node and Link MSD Advertisements 261 When Link MSD is present for a given MSD type, the value of the Link 262 MSD MUST take preference over the Node MSD. When a Link MSD type is 263 not signalled but the Node MSD type is, then the value of that Link 264 MSD type MUST be considered as the corresponding Node MSD type value. 265 In order to increase flooding efficiency, it is RECOMMENDED, that 266 routers with homogenous link MSD values advertise just the Node MSD 267 value. 269 The meaning of the absence of both Node and Link MSD advertisements 270 for a given MSD type is specific to the MSD type. Generally it can 271 only be inferred that the advertising node does not support 272 advertisement of that MSD type. However, in some cases the lack of 273 advertisement might imply that the functionality associated with the 274 MSD type is not supported. The correct interpretation MUST be 275 specified when an MSD type is defined. 277 5. IANA Considerations 279 This document requests IANA to allocate TLV type (TBD1) from the OSPF 280 Router Information (RI) TLVs Registry as defined by [RFC7770]. IANA 281 has allocated the value 12 through the early assignment process. 283 Also, this document requests IANA to allocate a sub-TLV type (TBD2) 284 from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has 285 allocated the value 6 through the early assignment process. Finally, 286 this document requests IANA to allocate a sub-TLV type (TBD3) from 287 the OSPFv3 Extended-LSA Sub-TLV registry. 289 6. Security Considerations 291 Security concerns for OSPF are addressed in [RFC7474]. Further 292 security analysis for OSPF protocol is done in [RFC6863] Security 293 considerations, as specified by [RFC7770], [RFC7684] and [RFC8362] 294 are applicable to this document. 296 Advertisement of an incorrect MSD value may result: in a path 297 computation failing and the service unavailable or instantiation of a 298 path that can't be supported by the head-end (the node performing the 299 imposition). 301 7. Contributors 303 The following people contributed to this document: 305 Les Ginsberg 307 Email: ginsberg@cisco.com 309 8. Acknowledgments 311 The authors would like to thank Acee Lindem, Ketan Talaulikar, Tal 312 Mizrahi, Stephane Litkowski and Bruno Decraene for their reviews and 313 valuable comments. 315 9. References 317 9.1. Normative References 319 [I-D.ietf-isis-segment-routing-msd] 320 Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 321 "Signaling MSD (Maximum SID Depth) using IS-IS", draft- 322 ietf-isis-segment-routing-msd-13 (work in progress), July 323 2018. 325 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 326 Requirement Levels", BCP 14, RFC 2119, 327 DOI 10.17487/RFC2119, March 1997, 328 . 330 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 331 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 332 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 333 2015, . 335 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 336 S. Shaffer, "Extensions to OSPF for Advertising Optional 337 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 338 February 2016, . 340 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 341 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 342 May 2017, . 344 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 345 F. Baker, "OSPFv3 Link State Advertisement (LSA) 346 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 347 2018, . 349 9.2. Informative References 351 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 352 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 353 "Signaling MSD (Maximum SID Depth) using Border Gateway 354 Protocol Link-State", draft-ietf-idr-bgp-ls-segment- 355 routing-msd-02 (work in progress), August 2018. 357 [I-D.ietf-ospf-mpls-elc] 358 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 359 Litkowski, "Signaling Entropy Label Capability and Entropy 360 Readable Label-stack Depth Using OSPF", draft-ietf-ospf- 361 mpls-elc-06 (work in progress), August 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-12 (work in progress), June 367 2018. 369 [RFC6863] Hartman, S. and D. Zhang, "Analysis of OSPF Security 370 According to the Keying and Authentication for Routing 371 Protocols (KARP) Design Guide", RFC 6863, 372 DOI 10.17487/RFC6863, March 2013, 373 . 375 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 376 "Security Extension for OSPFv2 When Using Manual Key 377 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 378 . 380 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 381 S. Ray, "North-Bound Distribution of Link-State and 382 Traffic Engineering (TE) Information Using BGP", RFC 7752, 383 DOI 10.17487/RFC7752, March 2016, 384 . 386 Authors' Addresses 388 Jeff Tantsura 389 Nuage Networks 391 Email: jefftant.ietf@gmail.com 393 Uma Chunduri 394 Huawei Technologies 396 Email: uma.chunduri@huawei.com 398 Sam Aldrin 399 Google, Inc 401 Email: aldrin.ietf@gmail.com 403 Peter Psenak 404 Cisco Systems 406 Email: ppsenak@cisco.com