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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-19) exists of draft-ietf-isis-segment-routing-msd-16 == Outdated reference: A later version (-18) exists of draft-ietf-idr-bgp-ls-segment-routing-msd-02 == Outdated reference: A later version (-15) exists of draft-ietf-ospf-mpls-elc-07 == Outdated reference: A later version (-16) exists of draft-ietf-pce-segment-routing-12 -- Obsolete informational reference (is this intentional?): RFC 7752 (Obsoleted by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: March 29, 2019 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 P. Psenak 9 Cisco Systems 10 September 25, 2018 12 Signaling MSD (Maximum SID Depth) using OSPF 13 draft-ietf-ospf-segment-routing-msd-21 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 March 29, 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 . . . . . . . . . . . . . . . . . . . . . 7 67 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 68 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 69 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 70 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 71 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 72 9.2. Informative References . . . . . . . . . . . . . . . . . 9 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 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 where MSD is relevant, MSD capabilities should 97 be 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. In the future it 106 is expected, that new MSD types will be defined to signal additional 107 capabilities e.g., entropy labels, SIDs that can be imposed through 108 recirculation, or SIDs associated with another dataplane e.g., IPv6. 109 Although MSD advertisements are associated with Segment Routing, the 110 advertisements MAY be present even if Segment Routing itself is not 111 enabled. Note that in a non-SR MPLS network, label depth is what is 112 defined by the MSD advertisements. 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 OSPF: Open Shortest Path First 123 MSD: Maximum SID Depth - the number of SIDs a node or one of its 124 links can support 126 PCC: Path Computation Client 128 PCE: Path Computation Element 130 PCEP: Path Computation Element Protocol 132 SR: Segment Routing 134 SID: Segment Identifier 136 LSA: Link state advertisement 138 RI: OSPF Router Information LSA 140 1.2. Requirements Language 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 144 "OPTIONAL" in this document are to be interpreted as described in BCP 145 14 [RFC2119] [RFC8174] when, and only when, they appear in all 146 capitals, as shown here. 148 2. Node MSD Advertisement 150 The node MSD TLV within the body of the OSPF RI Opaque LSA [RFC7770] 151 is defined to carry the provisioned SID depth of the router 152 originating the RI LSA. Node MSD is the smallest MSD supported by 153 the node on the set of interfaces configured for use by the 154 advertising IGP instance. MSD values may be learned via a hardware 155 API or may be provisioned. 157 0 1 2 3 158 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 1 160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 161 | Type | Length | 162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 163 | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 166 Figure 1: Node MSD TLV 168 Type: TBD1 170 Length: variable (multiple of 2 octets) and represents the total 171 length of value field in octets. 173 Value: consists of one or more pairs of a 1 octet MSD-type and 1 174 octet MSD-Value. 176 MSD-Type: one of the values defined in the IGP MSD Types registry 177 defined in [I-D.ietf-isis-segment-routing-msd]. 179 MSD-Value: a number in the range of 0-255. For all MSD-Types, 0 180 represents lack of the ability to impose MSD stack of any depth; any 181 other value represents that of the node. This value MUST represent 182 the lowest value supported by any link configured for use by the 183 advertising OSPF instance. 185 This TLV is applicable to OSPFv2 and to OSPFv3 and is optional. The 186 scope of the advertisement is specific to the deployment. 188 When multiple Node MSD TLVs are received from a given router, the 189 receiver MUST use the first occurrence of the TLV in the Router 190 Information LSA. If the Node MSD TLV appears in multiple Router 191 Information LSAs that have different flooding scopes, the Node MSD 192 TLV in the Router Information LSA with the area-scoped flooding scope 193 MUST be used. If the Node MSD TLV appears in multiple Router 194 Information LSAs that have the same flooding scope, the Node MSD TLV 195 in the Router Information (RI) LSA with the numerically smallest 196 Instance ID MUST be used and subsequent instances of the Node MSD TLV 197 MUST be ignored. The RI LSA can be advertised at any of the defined 198 opaque flooding scopes (link, area, or Autonomous System (AS)). For 199 the purpose of Node MSD TLV advertisement, area-scoped flooding is 200 RECOMMENDED. 202 3. Link MSD sub-TLV 204 The link sub-TLV is defined to carry the MSD of the interface 205 associated with the link. MSD values may be learned via a hardware 206 API or may be provisioned. 208 0 1 2 3 209 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 1 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 | Type | Length | 213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 214 | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | 215 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 Figure 2: Link MSD Sub-TLV 219 Type: 221 For OSPFv2, the Link level MSD-Value is advertised as an optional 222 Sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], and 223 has a type of TBD2. 225 For OSPFv3, the Link level MSD-Value is advertised as an optional 226 Sub-TLV of the E-Router-LSA TLV as defined in [RFC8362], and has a 227 type of TBD3. 229 Length: variable and same as defined in Section 2. 231 Value: consists of one or more pairs of a 1 octet MSD-type and 1 232 octet MSD-Value. 234 MSD-Type: one of the values defined in the MSD Types registry defined 235 in [I-D.ietf-isis-segment-routing-msd]. 237 MSD-Value field contains Link MSD of the router originating the 238 corresponding LSA as specified for OSPFv2 and OSPFv3. Link MSD is a 239 number in the range of 0-255. For all MSD-Types, 0 represents lack 240 of the ability to impose MSD stack of any depth; any other value 241 represents that of the particular link when used as an outgoing 242 interface. 244 If this sub-TLV is advertised multiple times in the same OSPFv2 245 Extended Link Opaque LSA/E-Router-LSA, only the first instance of the 246 TLV MUST be used by receiving OSPF routers. This situation SHOULD be 247 logged as an error. 249 If this sub-TLV is advertised multiple times for the same link in 250 different OSPF Extended Link Opaque LSAs/E-Router-LSAs originated by 251 the same OSPF router, the OSPFv2 Extended Link TLV in the OSPFv2 252 Extended Link Opaque LSA with the smallest Opaque ID or in the OSPFv3 253 E-Router-LSA with the smallest Link State ID MUST be used by 254 receiving OSPF routers. This situation MAY be logged as a warning. 256 4. Using Node and Link MSD Advertisements 258 When Link MSD is present for a given MSD type, the value of the Link 259 MSD MUST take preference over the Node MSD. When a Link MSD type is 260 not signalled but the Node MSD type is, then the value of that Node 261 MSD type MUST be considered as the corresponding Link MSD type value. 262 In order to increase flooding efficiency, it is RECOMMENDED, that 263 routers with homogenous Link MSD values advertise just the Node MSD 264 value. 266 Information received in an MSD advertisements is to to ensure that 267 the controller learns the Maximum SID Depth (MSD) that can be imposed 268 at each node/link on a given SR path so that the SID stack depth of a 269 computed path doesn't exceed the number of SIDs the node is capable 270 of imposing 272 The meaning of the absence of both Node and Link MSD advertisements 273 for a given MSD type is specific to the MSD type. Generally it can 274 only be inferred that the advertising node does not support 275 advertisement of that MSD type. However, in some cases the lack of 276 advertisement might imply that the functionality associated with the 277 MSD type is not supported. The correct interpretation MUST be 278 specified when an MSD type is defined. 280 5. IANA Considerations 282 This document requests IANA to allocate TLV type (TBD1) from the OSPF 283 Router Information (RI) TLVs Registry as defined by [RFC7770]. IANA 284 has allocated the value 12 through the early assignment process. 286 Value Description Reference 287 ----- --------------- ------------- 288 12 Node MSD This document 290 Figure 3: RI Node MSD 292 Also, this document requests IANA to allocate a sub-TLV type (TBD2) 293 from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has 294 allocated the value 6 through the early assignment process. 296 Value Description Reference 297 ----- --------------- ------------- 298 6 OSPFv2 Link MSD This document 300 Figure 4: OSPFv2 Link MSD 302 Finally, this document requests IANA to allocate a sub-TLV type 303 (TBD3) from the OSPFv3 Extended-LSA Sub-TLV registry. 305 Value Description Reference 306 ----- --------------- ------------- 307 TBD3 OSPFv3 Link MSD This document 309 Figure 5: OSPFv3 Link MSD 311 6. Security Considerations 313 Security concerns for OSPF are addressed in [RFC7474], [RFC4552] and 314 [RFC7166]. Further security analysis for OSPF protocol is done in 315 [RFC6863]. Security considerations, as specified by [RFC7770], 316 [RFC7684] and [RFC8362] are applicable to this document. 318 Implementations MUST assure that malformed TLV and Sub-TLV defined in 319 this document are detected and do not provide a vulnerability for 320 attackers to crash the OSPF router or routing process. Reception of 321 malformed TLV or Sub-TLV SHOULD be counted and/or logged for further 322 analysis. Logging of malformed TLVs and Sub-TLVs SHOULD be rate- 323 limited to prevent a Denial of Service (DoS) attack (distributed or 324 otherwise) from overloading the OSPF control plane. 326 Advertisement of an incorrect MSD value may result: 328 If the value is smaller than supported - path computation failing to 329 compute a viable path. 331 If the value is larger than supported - instantiation of a path that 332 can't be supported by the head-end (the node performing the SID 333 imposition). 335 The MSD discloses capabilities of the nodes (how many SIDs it 336 supports), which could provide an indication of the abilities or even 337 types of the nodes being used. This information could be used to 338 gain intelligence about devices in the network. 340 There's no Denial of Service risk specific to this extension, and it 341 is not vulnerable to replay attacks. 343 7. Contributors 345 The following people contributed to this document: 347 Les Ginsberg 349 Email: ginsberg@cisco.com 351 8. Acknowledgments 353 The authors would like to thank Acee Lindem, Ketan Talaulikar, Tal 354 Mizrahi, Stephane Litkowski and Bruno Decraene for their reviews and 355 valuable comments. 357 9. References 359 9.1. Normative References 361 [I-D.ietf-isis-segment-routing-msd] 362 Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 363 "Signaling MSD (Maximum SID Depth) using IS-IS", draft- 364 ietf-isis-segment-routing-msd-16 (work in progress), 365 September 2018. 367 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 368 Requirement Levels", BCP 14, RFC 2119, 369 DOI 10.17487/RFC2119, March 1997, 370 . 372 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 373 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 374 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 375 2015, . 377 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 378 S. Shaffer, "Extensions to OSPF for Advertising Optional 379 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 380 February 2016, . 382 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 383 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 384 May 2017, . 386 [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and 387 F. Baker, "OSPFv3 Link State Advertisement (LSA) 388 Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 389 2018, . 391 9.2. Informative References 393 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 394 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 395 "Signaling MSD (Maximum SID Depth) using Border Gateway 396 Protocol Link-State", draft-ietf-idr-bgp-ls-segment- 397 routing-msd-02 (work in progress), August 2018. 399 [I-D.ietf-ospf-mpls-elc] 400 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 401 Litkowski, "Signaling Entropy Label Capability and Entropy 402 Readable Label-stack Depth Using OSPF", draft-ietf-ospf- 403 mpls-elc-07 (work in progress), September 2018. 405 [I-D.ietf-pce-segment-routing] 406 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 407 and J. Hardwick, "PCEP Extensions for Segment Routing", 408 draft-ietf-pce-segment-routing-12 (work in progress), June 409 2018. 411 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 412 for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, 413 . 415 [RFC6863] Hartman, S. and D. Zhang, "Analysis of OSPF Security 416 According to the Keying and Authentication for Routing 417 Protocols (KARP) Design Guide", RFC 6863, 418 DOI 10.17487/RFC6863, March 2013, 419 . 421 [RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting 422 Authentication Trailer for OSPFv3", RFC 7166, 423 DOI 10.17487/RFC7166, March 2014, 424 . 426 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 427 "Security Extension for OSPFv2 When Using Manual Key 428 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 429 . 431 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 432 S. Ray, "North-Bound Distribution of Link-State and 433 Traffic Engineering (TE) Information Using BGP", RFC 7752, 434 DOI 10.17487/RFC7752, March 2016, 435 . 437 Authors' Addresses 439 Jeff Tantsura 440 Nuage Networks 442 Email: jefftant.ietf@gmail.com 444 Uma Chunduri 445 Huawei Technologies 447 Email: uma.chunduri@huawei.com 449 Sam Aldrin 450 Google, Inc 452 Email: aldrin.ietf@gmail.com 454 Peter Psenak 455 Cisco Systems 457 Email: ppsenak@cisco.com