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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: September 9, 2017 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 P. Psenak 9 Cisco Systems 10 March 8, 2017 12 Signaling MSD (Maximum SID Depth) using OSPF 13 draft-ietf-ospf-segment-routing-msd-02 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 push the SID stack 22 of an appropriate depth. MSD is relevant to the head-end of a SR 23 tunnel or Binding-SID anchor node where Binding-SID expansions might 24 result in creation of a new SID stack. Here the term OSPF means both 25 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 http://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 September 9, 2017. 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 (http://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.tantsura-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 push SID's stack of a particular depth. 107 MSD of type 1 (IANA Registry) is used to signal the number of SIDs a 108 node is capable of imposing, to be used by a path computation 109 element/controller and is only relevant to the part of the stack 110 created as the result of the computation. In case, there are 111 additional labels (e.g. service) that are to be pushed to the stack - 112 MSD SHOULD be adjusted to reflect that. In the future, new MSD types 113 could be defined to signal additional capabilities: entropy labels, 114 labels that can be pushed thru recirculation, or another dataplane 115 e.g IPv6. 117 1.1. Conventions used in this document 119 1.1.1. Terminology 121 BGP-LS: Distribution of Link-State and TE Information using Border 122 Gateway Protocol 124 OSPF: Open Shortest Path First 126 MSD: Maximum SID Depth 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", "MAY", and "OPTIONAL" in this 142 document are to be interpreted as described in RFC 2119 [RFC2119]. 144 2. Terminology 146 This memo makes use of the terms defined in [RFC4970]. 148 3. Node MSD TLV 150 A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD 151 TLV is defined to carry the provisioned SID depth of the router 152 originating the RI LSA. Node MSD is the lowest MSD supported by the 153 node. 155 0 1 2 3 156 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 1 158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 159 | Type | Length | 160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 161 | Sub-Type and Value ... 162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 164 Figure 1: Node MSD TLV 166 The Type (2 bytes) of this TLV is 12 (Suggested value - to be 167 assigned by IANA). 169 Length is variable (minimum of 2, multiple of 2 octets) and 170 represents the total length of value field. 172 Value field consists of a 1 octet sub-type (IANA Registry) and 1 173 octet 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 push MSD of any depth; any other value represents that of the node. 179 This value SHOULD represent the lowest value supported by node. 181 Other Sub-types other than defined above are reserved for future 182 extensions. 184 This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is 185 optional. The scope of the advertisement is specific to the 186 deployment. 188 4. LINK MSD sub-TLV 190 A new sub-TLV called Link MSD sub-TLV is defined to carry the 191 provisioned SID depth of the interface associated with the link. 193 0 1 2 3 194 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 1 196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 197 | Type | Length | 198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 199 | Sub-Type and Value ... 200 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 202 Figure 2: Link MSD Sub-TLV 204 The Type (2 bytes) of this TLV: 206 For OSPFv2, the Link level MSD value is advertised as an optional 207 Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684], and the 208 value is 5 (Suggested value - to be assigned by IANA) 210 For OSPFv3, the Link level MSD value is advertised as an optional 211 Sub-TLV of the Router-Link TLV as defined in 212 [I-D.ietf-ospf-ospfv3-lsa-extend], and the value is 3 (Suggested 213 value - to be assigned by IANA). 215 Length is variable and similar to what is defined in Section 3. 217 Value field consists of a 1 octet sub-type (IANA Registry) and 1 218 octet 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 push MSD of any depth; any other 224 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. Node MSD vs Link MSD conflict resolution 231 When both Node MSD and Link MSD are present, the value in the Link 232 MSD MUST be used. 234 6. IANA Considerations 236 This document includes a request to IANA to allocate TLV type codes 237 for the new TLV proposed in Section 3 of this document from OSPF 238 Router Information (RI) TLVs Registry as defined by [RFC4970]. Also 239 for link MSD, we request IANA to allocate new sub-TLV codes as 240 proposed in Section 4 from OSPFv2 Extended Link Opaque LSAs Extended 241 Link TLV registry and from Router-Link TLV defined in OSPFv3 Extend- 242 LSA Sub-TLV registry. 244 This document also request IANA to create a new Sub-type registry as 245 proposed in Section 3, Section 4. 247 Value Name Reference 248 ----- --------------------- ------------- 249 0 Reserved This document 250 1 MSD This document 251 2-250 Unassigned This document 252 251-254 Experimental This document 253 255 Reserved This document 255 Figure 3: MSD Sub-type Codepoints Registry 257 7. Security Considerations 259 This document describes a mechanism to signal Segment Routing MSD 260 supported at node and/or link granularity through OSPF LSA's and does 261 not introduce any new security issues. 263 8. Contributors 265 The following people contributed to this document: 267 Les Ginsberg 269 Email: ginsberg@cisco.com 271 9. Acknowledgements 273 The authors would like to thank Stephane Litkowski and Bruno Decraene 274 for their reviews and valuable comments. 276 10. References 277 10.1. Normative References 279 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 280 Requirement Levels", BCP 14, RFC 2119, 281 DOI 10.17487/RFC2119, March 1997, 282 . 284 [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 285 S. Shaffer, "Extensions to OSPF for Advertising Optional 286 Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 287 2007, . 289 10.2. Informative References 291 [I-D.ietf-ospf-mpls-elc] 292 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 293 Litkowski, "Signaling Entropy Label Capability Using 294 OSPF", draft-ietf-ospf-mpls-elc-04 (work in progress), 295 November 2016. 297 [I-D.ietf-ospf-ospfv3-lsa-extend] 298 Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 299 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-13 300 (work in progress), October 2016. 302 [I-D.ietf-pce-segment-routing] 303 Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., 304 Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and 305 J. Hardwick, "PCEP Extensions for Segment Routing", draft- 306 ietf-pce-segment-routing-08 (work in progress), October 307 2016. 309 [I-D.tantsura-idr-bgp-ls-segment-routing-msd] 310 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 311 "Signaling Maximum SID Depth using Border Gateway Protocol 312 Link-State", draft-tantsura-idr-bgp-ls-segment-routing- 313 msd-02 (work in progress), January 2017. 315 [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and 316 R. Aggarwal, "Support of Address Families in OSPFv3", 317 RFC 5838, DOI 10.17487/RFC5838, April 2010, 318 . 320 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 321 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 322 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 323 2015, . 325 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 326 S. Ray, "North-Bound Distribution of Link-State and 327 Traffic Engineering (TE) Information Using BGP", RFC 7752, 328 DOI 10.17487/RFC7752, March 2016, 329 . 331 Authors' Addresses 333 Jeff Tantsura 334 Individual 336 Email: jefftant.ietf@gmail.com 338 Uma Chunduri 339 Huawei Technologies 341 Email: uma.chunduri@huawei.com 343 Sam Aldrin 344 Google, Inc 346 Email: aldrin.ietf@gmail.com 348 Peter Psenak 349 Cisco Systems 351 Email: ppsenak@cisco.com