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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-01 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 . . . . . . . . . . . . . . . . . . 4 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 . . . . . . . . . . 6 69 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 70 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 71 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6 72 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 73 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 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 [I-D.ietf-ospf-mpls-elc] defines, RLDC which indicates how many 118 labels a node can read to take a decision to insert an Entropy Label 119 (EL) and is different than how many labels a node can push as defined 120 by MSD in this draft. 122 1.1. Conventions used in this document 124 1.1.1. Terminology 126 BGP-LS: Distribution of Link-State and TE Information using Border 127 Gateway Protocol 129 OSPF: Open Shortest Path First 131 MSD: Maximum SID Depth 133 PCC: Path Computation Client 135 PCE: Path Computation Element 137 PCEP: Path Computation Element Protocol 139 SID: Segment Identifier 141 SR: Segment routing 143 1.2. Requirements Language 145 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 146 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 147 document are to be interpreted as described in RFC 2119 [RFC2119]. 149 2. Terminology 151 This memo makes use of the terms defined in [RFC4970]. 153 3. Node MSD TLV 155 A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD 156 TLV is defined to carry the provisioned SID depth of the router 157 originating the RI LSA. Node MSD is the lowest MSD supported by the 158 node. 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 | Sub-Type and Value ... 167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 169 Figure 1: Node MSD TLV 171 The Type (2 bytes) of this TLV is 12 (Suggested value - to be 172 assigned by IANA). 174 Length is variable (minimum of 2, multiple of 2 octets) and 175 represents the total length of value field. 177 Value field consists of a 1 octet sub-type (IANA Registry) and 1 178 octet value. 180 Sub-Type 1 (IANA Section), MSD and the Value field contains maximum 181 MSD of the router originating the RI LSA. Node Maximum MSD is a 182 number in the range of 0-254. 0 represents lack of the ability to 183 push MSD of any depth; any other value represents that of the node. 184 This value SHOULD represent the lowest value supported by node. 186 Other Sub-types other than defined above are reserved for future 187 extensions. 189 This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is 190 optional. The scope of the advertisement is specific to the 191 deployment. 193 4. LINK MSD sub-TLV 195 A new sub-TLV called Link MSD sub-TLV is defined to carry the 196 provisioned SID depth of the interface associated with the link. 198 0 1 2 3 199 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 1 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 | Type | Length | 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | Sub-Type and Value ... 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 207 Figure 2: Link MSD Sub-TLV 209 The Type (2 bytes) of this TLV: 211 For OSPFv2, the Link level MSD value is advertised as an optional 212 Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684], and the 213 value is 5 (Suggested value - to be assigned by IANA) 215 For OSPFv3, the Link level MSD value is advertised as an optional 216 Sub-TLV of the Router-Link TLV as defined in 217 [I-D.ietf-ospf-ospfv3-lsa-extend], and the value is 3 (Suggested 218 value - to be assigned by IANA). 220 Length is variable and similar to what is defined in Section 3. 222 Value field consists of a 1 octet sub-type (IANA Registry) and 1 223 octet value. 225 Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD 226 of the router originating the corresponding LSA as specified for 227 OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0 228 represents lack of the ability to push MSD of any depth; any other 229 value represents that of the particular link MSD value. 231 Other Sub-types other than defined above are reserved for future 232 extensions. 234 5. Node MSD vs Link MSD conflict resolution 236 When both Node MSD and Link MSD are present, the value in the Link 237 MSD MUST be used. 239 6. IANA Considerations 241 This document includes a request to IANA to allocate TLV type codes 242 for the new TLV proposed in Section 3 of this document from OSPF 243 Router Information (RI) TLVs Registry as defined by [RFC4970]. Also 244 for link MSD, we request IANA to allocate new sub-TLV codes as 245 proposed in Section 4 from OSPFv2 Extended Link Opaque LSAs Extended 246 Link TLV registry and from Router-Link TLV defined in OSPFv3 Extend- 247 LSA Sub-TLV registry. 249 This document also request IANA to create a new Sub-type registry as 250 proposed in Section 3, Section 4. 252 Value Name Reference 253 ----- --------------------- ------------- 254 0 Reserved This document 255 1 MSD This document 256 2-250 Unassigned This document 257 251-254 Experimental This document 258 255 Reserved This document 260 Figure 3: MSD Sub-type Codepoints Registry 262 7. Security Considerations 264 This document describes a mechanism to signal Segment Routing MSD 265 supported at node and/or link granularity through OSPF LSA's and does 266 not introduce any new security issues. 268 8. Contributors 270 The following people contributed to this document: 272 Les Ginsberg 274 Email: ginsberg@cisco.com 276 9. Acknowledgements 278 The authors would like to thank Stephane Litkowski and Bruno Decraene 279 for their reviews and valuable comments. 281 10. References 283 10.1. Normative References 285 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 286 Requirement Levels", BCP 14, RFC 2119, 287 DOI 10.17487/RFC2119, March 1997, 288 . 290 [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 291 S. Shaffer, "Extensions to OSPF for Advertising Optional 292 Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 293 2007, . 295 10.2. Informative References 297 [I-D.ietf-ospf-mpls-elc] 298 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 299 Litkowski, "Signaling Entropy Label Capability Using 300 OSPF", draft-ietf-ospf-mpls-elc-04 (work in progress), 301 November 2016. 303 [I-D.ietf-ospf-ospfv3-lsa-extend] 304 Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 305 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-13 306 (work in progress), October 2016. 308 [I-D.ietf-pce-segment-routing] 309 Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., 310 Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and 311 J. Hardwick, "PCEP Extensions for Segment Routing", draft- 312 ietf-pce-segment-routing-08 (work in progress), October 313 2016. 315 [I-D.tantsura-idr-bgp-ls-segment-routing-msd] 316 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 317 "Signaling Maximum SID Depth using Border Gateway Protocol 318 Link-State", draft-tantsura-idr-bgp-ls-segment-routing- 319 msd-02 (work in progress), January 2017. 321 [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and 322 R. Aggarwal, "Support of Address Families in OSPFv3", 323 RFC 5838, DOI 10.17487/RFC5838, April 2010, 324 . 326 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 327 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 328 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 329 2015, . 331 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 332 S. Ray, "North-Bound Distribution of Link-State and 333 Traffic Engineering (TE) Information Using BGP", RFC 7752, 334 DOI 10.17487/RFC7752, March 2016, 335 . 337 Authors' Addresses 339 Jeff Tantsura 340 Individual 342 Email: jefftant.ietf@gmail.com 344 Uma Chunduri 345 Huawei Technologies 347 Email: uma.chunduri@huawei.com 349 Sam Aldrin 350 Google, Inc 352 Email: aldrin.ietf@gmail.com 354 Peter Psenak 355 Cisco Systems 357 Email: ppsenak@cisco.com