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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: September 9, 2017 Huawei Technologies 6 G. Mirsky 7 ZTE Corp. 8 S. Sivabalan 9 Cisco 10 March 8, 2017 12 Signaling Maximum SID Depth using Border Gateway Protocol Link-State 13 draft-tantsura-idr-bgp-ls-segment-routing-msd-03 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 http://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 September 9, 2017. 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 (http://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, as defined in Section 3 is used to signal the 95 number of SID's a node is capable of imposing, to be used by a path 96 computation element/controller and is only relevant to the part of 97 the stack created as the result of the computation. In case, there 98 are additional labels (e.g. service) that are to be pushed to the 99 stack - MSD SHOULD be adjusted to reflect that. In the future, new 100 MSD types could be defined to signal additional capabilities: entropy 101 labels, labels that can be pushed thru recirculation, or another 102 dataplane e.g IPv6. 104 1.1. Conventions used in this document 106 1.1.1. Terminology 108 BGP-LS: Distribution of Link-State and TE Information using Border 109 Gateway Protocol 111 MSD: Maximum SID Depth 113 PCC: Path Computation Client 115 PCE: Path Computation Element 117 PCEP: Path Computation Element Protocol 119 SID: Segment Identifier 121 SR: Segment routing 123 1.1.2. Requirements Language 125 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 126 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 127 "OPTIONAL" in this document are to be interpreted as described in 128 [RFC2119]. 130 2. Problem Statement 132 In existing technology only PCEP has extension to signal the MSD (SR 133 PCE Capability TLV/ METRIC Object as defined in 134 [I-D.ietf-pce-segment-routing],If PCEP is not supported by the node 135 (head-end of the SR tunnel) controller has no way to learn the MSD of 136 the node/link configured. OSPF and IS-IS extensions are defined in: 138 [I-D.ietf-ospf-segment-routing-msd] 140 [I-D.ietf-isis-segment-routing-msd] 142 3. MSD supported by a node 144 Node MSD is encoded in a new Node Attribute TLV, as defined in 145 [RFC7752] 147 0 1 2 3 148 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 1 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 | Type | Length | 151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 152 | Sub-Type and Value ... 153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 155 Figure 1: Node attribute format 157 Type : A 2-octet field specifiying code-point of the new TLV type. 158 Code-point: 1050 (Suggested value - to be assigned by IANA) from BGP- 159 LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute 160 TLVs registry 162 Length: A 2-octet field that indicates the length of the value 163 portion 165 Sub-Type and value fields are as defined in corresponding OSPF 166 [I-D.ietf-ospf-segment-routing-msd] and IS-IS 167 [I-D.ietf-isis-segment-routing-msd] extensions. 169 4. MSD supported on a link 171 Link MSD is encoded in a New Link Attribute TLV, as defined in 172 [RFC7752] 174 0 1 2 3 175 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 1 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 | Type | Length | 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 179 | Sub-Type and Value ... 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 182 Figure 2: Link attribute format 184 Type : A 2-octet field specifiying code-point of the new TLV type. 185 Code-point: 1110 (Suggested value - to be assigned by IANA) from BGP- 186 LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute 187 TLVs registry 188 Length: A 2-octet field that indicates the length of the value 189 portion 191 Sub-Type and value fields are as defined in corresponding OSPF 192 [I-D.ietf-ospf-segment-routing-msd] and IS-IS 193 [I-D.ietf-isis-segment-routing-msd] extensions. 195 5. IANA Considerations 197 This document requests IANA to assign 2 new code-points from the BGP- 198 LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute 199 TLVs registry as specified in sections 3 and 4. 201 6. Security Considerations 203 This document does not introduce security issues beyond those 204 discussed in [RFC7752] 206 7. Acknowledgements 208 We like to thank Nikos Triantafillis, Stephane Litkowski and Bruno 209 Decraene for their reviews and valuable comments. 211 8. References 213 8.1. Normative References 215 [I-D.ietf-isis-segment-routing-msd] 216 Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 217 "Signaling MSD (Maximum SID Depth) using IS-IS", draft- 218 ietf-isis-segment-routing-msd-02 (work in progress), March 219 2017. 221 [I-D.ietf-ospf-segment-routing-msd] 222 Tantsura, J. and U. Chunduri, "Signaling MSD (Maximum SID 223 Depth) using OSPF", draft-ietf-ospf-segment-routing-msd-00 224 (work in progress), November 2016. 226 [I-D.ietf-pce-segment-routing] 227 Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., 228 Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and 229 J. Hardwick, "PCEP Extensions for Segment Routing", draft- 230 ietf-pce-segment-routing-08 (work in progress), October 231 2016. 233 [I-D.ietf-spring-segment-routing-mpls] 234 Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 235 Litkowski, S., Horneffer, M., Shakir, R., 236 jefftant@gmail.com, j., and E. Crabbe, "Segment Routing 237 with MPLS data plane", draft-ietf-spring-segment-routing- 238 mpls-07 (work in progress), February 2017. 240 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 241 Requirement Levels", BCP 14, RFC 2119, 242 DOI 10.17487/RFC2119, March 1997, 243 . 245 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 246 S. Ray, "North-Bound Distribution of Link-State and 247 Traffic Engineering (TE) Information Using BGP", RFC 7752, 248 DOI 10.17487/RFC7752, March 2016, 249 . 251 8.2. Informative References 253 [I-D.ietf-isis-segment-routing-extensions] 254 Previdi, S., Filsfils, C., Bashandy, A., Gredler, H., 255 Litkowski, S., Decraene, B., and j. jefftant@gmail.com, 256 "IS-IS Extensions for Segment Routing", draft-ietf-isis- 257 segment-routing-extensions-10 (work in progress), February 258 2017. 260 [I-D.ietf-ospf-segment-routing-extensions] 261 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 262 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 263 Extensions for Segment Routing", draft-ietf-ospf-segment- 264 routing-extensions-11 (work in progress), February 2017. 266 Authors' Addresses 268 Jeff Tantsura 269 Individual 271 Email: jefftant.ietf@gmail.com 273 Uma Chunduri 274 Huawei Technologies 276 Email: uma.chunduri@huawei.com 277 Greg Mirsky 278 ZTE Corp. 280 Email: gregimirsky@gmail.com 282 Siva Sivabalan 283 Cisco 285 Email: msiva@cisco.com