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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR Working Group J. Tantsura 3 Internet-Draft Individual 4 Intended status: Standards Track U. Chunduri 5 Expires: April 18, 2018 Huawei Technologies 6 G. Mirsky 7 ZTE Corp. 8 S. Sivabalan 9 Cisco 10 October 15, 2017 12 Signaling Maximum SID Depth using Border Gateway Protocol Link-State 13 draft-ietf-idr-bgp-ls-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 a BGP-LS 19 speaker. 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. 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 April 18, 2018. 43 Copyright Notice 45 Copyright (c) 2017 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. Conventions used in this document . . . . . . . . . . . . 3 62 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 63 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3 64 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 65 3. MSD supported by a node . . . . . . . . . . . . . . . . . . . 4 66 4. MSD supported on a link . . . . . . . . . . . . . . . . . . . 4 67 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 68 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 69 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 70 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 71 8.1. Normative References . . . . . . . . . . . . . . . . . . 5 72 8.2. Informative References . . . . . . . . . . . . . . . . . 6 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 75 1. Introduction 77 When Segment Routing tunnels are computed by a centralized 78 controller, it is critical that the controller learns the MSD 79 "Maximum SID Depth" of the node or link SR tunnel exits over, so the 80 SID stack depth of a path computed doesn't exceed the number of SIDs 81 the node is capable of imposing. This document describes how to use 82 BGP-LS to signal the MSD of a node or link to a centralized 83 controller. 85 PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD 86 in SR PCE Capability TLV and METRIC Object. However, if PCEP is not 87 supported/configured on the head-end of a SR tunnel or a Binding-SID 88 anchor node and controller does not participate in IGP routing, it 89 has no way to learn the MSD of nodes and links which has been 90 configured. BGP-LS [RFC7752] defines a way to expose topology and 91 associated attributes and capabilities of the nodes in that topology 92 to a centralized controller. 94 MSD of sub-type 1, called Base MSD as defined in Section 3 is used to 95 signal the number of SID's a node is capable of imposing, to be used 96 by a path computation element/controller. In case, there are 97 additional labels (e.g. service) that are to be pushed to the stack - 98 this would be signaled with an another MSD type (TBD), no adjustment 99 to the Base MSD should be made. In the future, new MSD types could 100 be defined to signal additional capabilities: entropy labels, labels 101 that can be pushed thru recirculation, or another dataplane e.g IPv6. 103 1.1. Conventions used in this document 105 1.1.1. Terminology 107 BGP-LS: Distribution of Link-State and TE Information using Border 108 Gateway Protocol 110 MSD: Maximum SID Depth 112 PCC: Path Computation Client 114 PCE: Path Computation Element 116 PCEP: Path Computation Element Protocol 118 SID: Segment Identifier 120 SR: Segment routing 122 1.1.2. Requirements Language 124 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 125 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 126 "OPTIONAL" in this document are to be interpreted as described in 127 [RFC2119]. 129 2. Problem Statement 131 In existing technology only PCEP has extension to signal the MSD (SR 132 PCE Capability TLV/ METRIC Object as defined in 133 [I-D.ietf-pce-segment-routing],If PCEP is not supported by the node 134 (head-end of the SR tunnel) controller has no way to learn the MSD of 135 the node/link configured. OSPF and IS-IS extensions are defined in: 137 [I-D.ietf-ospf-segment-routing-msd] 139 [I-D.ietf-isis-segment-routing-msd] 141 3. MSD supported by a node 143 Node MSD is encoded in a new Node Attribute TLV, as defined in 144 [RFC7752] 146 0 1 2 3 147 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 1 148 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 149 | Type | Length | 150 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 151 | Sub-Type and Value ... 152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 154 Figure 1: Node attribute format 156 Type : A 2-octet field specifiying code-point of the new TLV type. 157 Code-point:(TBD1) from BGP-LS Node Descriptor, Link Descriptor, 158 Prefix Descriptor, and Attribute TLVs registry 160 Length: A 2-octet field that indicates the length of the value 161 portion 163 Sub-Type and value fields are as defined in corresponding OSPF 164 [I-D.ietf-ospf-segment-routing-msd] and IS-IS 165 [I-D.ietf-isis-segment-routing-msd] extensions. 167 4. MSD supported on a link 169 Link MSD is encoded in a New Link Attribute TLV, as defined in 170 [RFC7752] 172 0 1 2 3 173 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 1 174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 175 | Type | Length | 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 | Sub-Type and Value ... 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 180 Figure 2: Link attribute format 182 Type : A 2-octet field specifiying code-point of the new TLV type. 183 Code-point:(TBD2) from BGP-LS Node Descriptor, Link Descriptor, 184 Prefix Descriptor, and Attribute TLVs registry 186 Length: A 2-octet field that indicates the length of the value 187 portion 188 Sub-Type and value fields are as defined in corresponding OSPF 189 [I-D.ietf-ospf-segment-routing-msd] and IS-IS 190 [I-D.ietf-isis-segment-routing-msd] extensions. 192 5. IANA Considerations 194 We request IANA assign code points from the registry BGP-LS Node 195 Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs, 196 as follows: TLV Code Point Description IS-IS TLV/Sub-TLV Reference 197 TBD1 Node MSD 242/23 (this document) TBD2 Link MSD 198 (22,23,25,141,222,223)/15 (this document) 200 6. Security Considerations 202 This document does not introduce security issues beyond those 203 discussed in [RFC7752] 205 7. Acknowledgements 207 We like to thank Nikos Triantafillis, Stephane Litkowski and Bruno 208 Decraene for their reviews and valuable comments. 210 8. References 212 8.1. Normative References 214 [I-D.ietf-isis-segment-routing-msd] 215 Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 216 "Signaling MSD (Maximum SID Depth) using IS-IS", draft- 217 ietf-isis-segment-routing-msd-04 (work in progress), June 218 2017. 220 [I-D.ietf-ospf-segment-routing-msd] 221 Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, 222 "Signaling MSD (Maximum SID Depth) using OSPF", draft- 223 ietf-ospf-segment-routing-msd-05 (work in progress), June 224 2017. 226 [I-D.ietf-pce-segment-routing] 227 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 228 and J. Hardwick, "PCEP Extensions for Segment Routing", 229 draft-ietf-pce-segment-routing-10 (work in progress), 230 October 2017. 232 [I-D.ietf-spring-segment-routing-mpls] 233 Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 234 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 235 data plane", draft-ietf-spring-segment-routing-mpls-10 236 (work in progress), June 2017. 238 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 239 Requirement Levels", BCP 14, RFC 2119, 240 DOI 10.17487/RFC2119, March 1997, 241 . 243 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 244 S. Ray, "North-Bound Distribution of Link-State and 245 Traffic Engineering (TE) Information Using BGP", RFC 7752, 246 DOI 10.17487/RFC7752, March 2016, 247 . 249 8.2. Informative References 251 [I-D.ietf-isis-segment-routing-extensions] 252 Previdi, S., Filsfils, C., Bashandy, A., Gredler, H., 253 Litkowski, S., Decraene, B., and j. jefftant@gmail.com, 254 "IS-IS Extensions for Segment Routing", draft-ietf-isis- 255 segment-routing-extensions-13 (work in progress), June 256 2017. 258 [I-D.ietf-ospf-segment-routing-extensions] 259 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 260 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 261 Extensions for Segment Routing", draft-ietf-ospf-segment- 262 routing-extensions-19 (work in progress), August 2017. 264 Authors' Addresses 266 Jeff Tantsura 267 Individual 269 Email: jefftant.ietf@gmail.com 271 Uma Chunduri 272 Huawei Technologies 274 Email: uma.chunduri@huawei.com 275 Greg Mirsky 276 ZTE Corp. 278 Email: gregimirsky@gmail.com 280 Siva Sivabalan 281 Cisco 283 Email: msiva@cisco.com