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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 Individual 4 Intended status: Standards Track U. Chunduri 5 Expires: June 4, 2018 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 P. Psenak 9 Cisco Systems 10 December 01, 2017 12 Signaling MSD (Maximum SID Depth) using OSPF 13 draft-ietf-ospf-segment-routing-msd-06 15 Abstract 17 This document proposes a way to signal Maximum SID Depth (MSD) 18 supported by a node at node and/or link granularity by an OSPF 19 Router. In a Segment Routing (SR) enabled network a centralized 20 controller that programs SR tunnels needs to know the MSD supported 21 by the head-end at node and/or link granularity to impose the SID 22 stack of an appropriate depth. MSD is relevant to the head-end of a 23 SR tunnel or Binding-SID anchor node where Binding-SID expansions 24 might result in creation of a new SID stack. Here the term OSPF 25 means both OSPFv2 and OSPFv3. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on June 4, 2018. 44 Copyright Notice 46 Copyright (c) 2017 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (https://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 62 1.1. Conventions used in this document . . . . . . . . . . . . 3 63 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 64 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 67 4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5 68 5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5 69 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 70 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 71 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6 72 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 73 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 74 10.1. Normative References . . . . . . . . . . . . . . . . . . 7 75 10.2. Informative References . . . . . . . . . . . . . . . . . 7 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 78 1. Introduction 80 When Segment Routing tunnels are computed by a centralized 81 controller, it is critical that the controller learns the MSD 82 "Maximum SID Depth" of the node or link SR tunnel exits over, so the 83 SID stack depth of a path computed doesn't exceed the number of SIDs 84 the node is capable of imposing. This document describes how to use 85 OSPF to signal the MSD of a node or link to a centralized controller. 87 PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD 88 in SR PCE Capability TLV and METRIC Object. However, if PCEP is not 89 supported/configured on the head-end of a SR tunnel or a Binding-SID 90 anchor node and controller does not participate in IGP routing, it 91 has no way to learn the MSD of nodes and links which has been 92 configured. BGP-LS [RFC7752] defines a way to expose topology and 93 associated attributes and capabilities of the nodes in that topology 94 to a centralized controller. MSD signaling by BGP-LS has been 95 defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, 96 BGP-LS is configured on a small number of nodes, that do not 97 necessarily act as head-ends. In order, for BGP-LS to signal MSD for 98 the all nodes and links in the network MSD is relevant, MSD 99 capabilites SHOULD be distributed to every OSPF router in the 100 network. 102 [I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability 103 (RLDC) that is used by a head-end to insert Entropy Label (EL) at 104 appropriate depth, so it could be read by transit nodes. MSD in 105 contrary signals ability to impose SID's stack of a particular depth. 107 MSD of type 1 (IANA Registry), called Base MSD is used to signal the 108 total number of SIDs a node is capable of imposing, to be used by a 109 path computation element/controller. In case, there are additional 110 SIDs (e.g. service) that are to be imposed to the stack - this would 111 be signaled with an another MSD type (TBD), no adjustment to the Base 112 MSD should be made. In the future, new MSD types could be defined to 113 signal additional capabilities: entropy labels, SIDs that can be 114 imposed thru recirculation, or another dataplane e.g IPv6. 116 1.1. Conventions used in this document 118 1.1.1. Terminology 120 BGP-LS: Distribution of Link-State and TE Information using Border 121 Gateway Protocol 123 OSPF: Open Shortest Path First 125 MSD: Maximum SID Depth 127 PCC: Path Computation Client 129 PCE: Path Computation Element 131 PCEP: Path Computation Element Protocol 133 SID: Segment Identifier 135 SR: Segment routing 137 1.2. Requirements Language 139 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 140 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 141 document are to be interpreted as described in RFC 2119 [RFC2119]. 143 2. Terminology 145 This memo makes use of the terms defined in [RFC4970]. 147 3. Node MSD TLV 149 A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD 150 TLV is defined to carry the provisioned SID depth of the router 151 originating the RI LSA. Node MSD is the lowest MSD supported by the 152 node. 154 0 1 2 3 155 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 1 157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 158 | Type | Length | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 | Sub-Type and Value ... 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 163 Figure 1: Node MSD TLV 165 The Type (2 bytes) of this TLV has value of 12. 167 Length is variable (minimum of 2, multiple of 2 octets) and 168 represents the total length of value field. 170 Value field consists of a 1 octet sub-type (IANA Registry) and 1 171 octet value. 173 Sub-Type 1 (IANA Section), MSD and the Value field contains maximum 174 MSD of the router originating the RI LSA. Node Maximum MSD is a 175 number in the range of 0-254. 0 represents lack of the ability to 176 impose MSD stack of any depth; any other value represents that of the 177 node. This value SHOULD represent the lowest value supported by 178 node. 180 Other Sub-types other than defined above are reserved for future 181 extensions. 183 This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is 184 optional. The scope of the advertisement is specific to the 185 deployment. 187 4. Link MSD sub-TLV 189 A new sub-TLV called Link MSD sub-TLV is defined to carry the 190 provisioned SID depth of the interface associated with the link. 192 0 1 2 3 193 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 1 195 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 196 | Type | Length | 197 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 198 | Sub-Type and Value ... 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 201 Figure 2: Link MSD Sub-TLV 203 The Type (2 bytes) of this TLV: 205 For OSPFv2, the Link level MSD value is advertised as an optional 206 Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684], and has 207 value of 6. 209 For OSPFv3, the Link level MSD value is advertised as an optional 210 Sub-TLV of the Router-Link TLV as defined in 211 [I-D.ietf-ospf-ospfv3-lsa-extend], and has value of 3 (Suggested 212 value - to be assigned by IANA). 214 Length is variable and similar to what is defined in Section 3. 216 Value field consists of a 1 octet sub-type (IANA Registry) and 1 217 octet value. 219 Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD 220 of the router originating the corresponding LSA as specified for 221 OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0 222 represents lack of the ability to impose MSD stack of any depth; any 223 other value represents that of the particular link MSD value. 225 Other Sub-types other than defined above are reserved for future 226 extensions. 228 5. Node MSD vs Link MSD conflict resolution 230 When both Node MSD and Link MSD are present, the value in the Link 231 MSD MUST be used. 233 6. IANA Considerations 235 This document includes a request to IANA to allocate TLV type codes 236 for the new TLV proposed in Section 3 of this document from OSPF 237 Router Information (RI) TLVs Registry as defined by [RFC4970]. Also 238 for link MSD, we request IANA to allocate new sub-TLV codes as 239 proposed in Section 4 from OSPFv2 Extended Link Opaque LSAs Extended 240 Link TLV registry and from Router-Link TLV defined in OSPFv3 Extend- 241 LSA Sub-TLV registry. 243 This document also request IANA to create a new Sub-type registry as 244 proposed in Section 3, Section 4. 246 Value Name Reference 247 ----- --------------------- ------------- 248 0 Reserved This document 249 1 Base MSD This document 250 2-250 Unassigned This document 251 251-254 Experimental This document 252 255 Reserved This document 254 Figure 3: MSD Sub-type Codepoints Registry 256 7. Security Considerations 258 This document describes a mechanism to signal Segment Routing MSD 259 supported at node and/or link granularity through OSPF LSA's and does 260 not introduce any new security issues. 262 8. Contributors 264 The following people contributed to this document: 266 Les Ginsberg 268 Email: ginsberg@cisco.com 270 9. Acknowledgements 272 The authors would like to thank Stephane Litkowski and Bruno Decraene 273 for their reviews and valuable comments. 275 10. References 276 10.1. Normative References 278 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 279 Requirement Levels", BCP 14, RFC 2119, 280 DOI 10.17487/RFC2119, March 1997, 281 . 283 [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 284 S. Shaffer, "Extensions to OSPF for Advertising Optional 285 Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 286 2007, . 288 10.2. Informative References 290 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 291 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 292 "Signaling Maximum SID Depth using Border Gateway Protocol 293 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 294 (work in progress), October 2017. 296 [I-D.ietf-ospf-mpls-elc] 297 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 298 Litkowski, "Signaling Entropy Label Capability Using 299 OSPF", draft-ietf-ospf-mpls-elc-04 (work in progress), 300 November 2016. 302 [I-D.ietf-ospf-ospfv3-lsa-extend] 303 Lindem, A., Roy, A., Goethals, D., Vallem, V., and F. 304 Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3- 305 lsa-extend-18 (work in progress), November 2017. 307 [I-D.ietf-pce-segment-routing] 308 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 309 and J. Hardwick, "PCEP Extensions for Segment Routing", 310 draft-ietf-pce-segment-routing-11 (work in progress), 311 November 2017. 313 [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and 314 R. Aggarwal, "Support of Address Families in OSPFv3", 315 RFC 5838, DOI 10.17487/RFC5838, April 2010, 316 . 318 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 319 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 320 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 321 2015, . 323 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 324 S. Ray, "North-Bound Distribution of Link-State and 325 Traffic Engineering (TE) Information Using BGP", RFC 7752, 326 DOI 10.17487/RFC7752, March 2016, 327 . 329 Authors' Addresses 331 Jeff Tantsura 332 Individual 334 Email: jefftant.ietf@gmail.com 336 Uma Chunduri 337 Huawei Technologies 339 Email: uma.chunduri@huawei.com 341 Sam Aldrin 342 Google, Inc 344 Email: aldrin.ietf@gmail.com 346 Peter Psenak 347 Cisco Systems 349 Email: ppsenak@cisco.com