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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: draft-ietf-isis-mpls-elc has been published as RFC 9088 == Outdated reference: draft-ietf-ospf-mpls-elc has been published as RFC 9089 == Outdated reference: draft-ietf-pce-segment-routing has been published as RFC 8664 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR Working Group J. Tantsura 3 Internet-Draft Apstra, Inc. 4 Intended status: Standards Track U. Chunduri 5 Expires: December 3, 2019 Futurewei Technologies 6 K. Talaulikar 7 Cisco Systems 8 G. Mirsky 9 ZTE Corp. 10 N. Triantafillis 11 Apstra, Inc. 12 June 1, 2019 14 Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link- 15 State 16 draft-ietf-idr-bgp-ls-segment-routing-msd-05 18 Abstract 20 This document defines a way for a Border Gateway Protocol Link-State 21 (BGP-LS) speaker to advertise multiple types of supported Maximum SID 22 Depths (MSDs) at node and/or link granularity. 24 Such advertisements allow entities (e.g., centralized controllers) to 25 determine whether a particular Segment Identifier (SID) stack can be 26 supported in a given network. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on December 3, 2019. 45 Copyright Notice 47 Copyright (c) 2019 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 63 1.1. Conventions used in this document . . . . . . . . . . . . 3 64 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 65 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4 66 2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4 67 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 68 4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5 69 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 70 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 71 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6 72 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 73 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 74 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 75 9.2. Informative References . . . . . . . . . . . . . . . . . 7 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 78 1. Introduction 80 When Segment Routing (SR) [RFC8402] paths are computed by a 81 centralized controller, it is critical that the controller learns the 82 Maximum SID Depth (MSD) that can be imposed at each node/link on a 83 given SR path. This ensures that the Segment Identifier (SID) stack 84 depth of a computed path doesn't exceed the number of SIDs the node 85 is capable of imposing. 87 [I-D.ietf-pce-segment-routing] defines how to signal MSD in the Path 88 Computation Element Protocol (PCEP). The OSPF and IS-IS extensions 89 for signaling of MSD are defined in [RFC8476] and [RFC8491] 90 respectively. 92 However, if PCEP is not supported/configured on the head-end of a SR 93 tunnel or a Binding-SID anchor node, and controller does not 94 participate in IGP routing, it has no way of learning the MSD of 95 nodes and links. BGP-LS [RFC7752] defines a way to advertise 96 topology and associated attributes and capabilities of the nodes in 97 that topology to a centralized controller. This document defines 98 extensions to BGP-LS to advertise one or more types of MSDs at node 99 and/or link granularity. 101 Other types of MSD are known to be useful. For example, 102 [I-D.ietf-ospf-mpls-elc] and [I-D.ietf-isis-mpls-elc] define Readable 103 Label Depth Capability (RLDC) that is used by a head-end to insert an 104 Entropy Label (EL) at a depth that can be read by transit nodes. 106 In the future, it is expected that new MSD-Types will be defined to 107 signal additional capabilities, e.g., ELs, SIDs that can be imposed 108 through recirculation, or SIDs associated with another data plane 109 such as IPv6. MSD advertisements MAY be useful even if SR itself is 110 not enabled. For example, in a non-SR MPLS network, MSD defines the 111 maximum label depth. 113 1.1. Conventions used in this document 115 1.1.1. Terminology 117 BGP-LS: Distribution of Link-State and TE Information using Border 118 Gateway Protocol 120 MSD: Maximum SID Depth 122 PCC: Path Computation Client 124 PCE: Path Computation Element 126 PCEP: Path Computation Element Protocol 128 SID: Segment Identifier 130 SR: Segment routing 132 Label Imposition: Imposition is the act of modifying and/or adding 133 labels to the outgoing label stack associated with a packet. This 134 includes: 136 o replacing the label at the top of the label stack with a new 137 label. 139 o pushing one or more new labels onto the label stack The number of 140 labels imposed is then the sum of the number of labels that are 141 replaced and the number of labels that are pushed. See [RFC3031] 142 for further details. 144 1.1.2. Requirements Language 146 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 147 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 148 "OPTIONAL" in this document are to be interpreted as described in BCP 149 14 [RFC2119] [RFC8174] when, and only when, they appear in all 150 capitals, as shown here . 152 2. Advertisement of MSD via BGP-LS 154 This document describes extensions that enable BGP-LS speakers to 155 signal the MSD capabilities of nodes and their links in a network to 156 a BGP-LS consumer of network topology such as a centralized 157 controller. The centralized controller can leverage this information 158 in computation of SR paths and their instantiation on network nodes 159 based on their MSD capabilities. When a BGP-LS speaker is 160 originating the topology learnt via link-state routing protocols like 161 OSPF or IS-IS, the MSD information for the nodes and their links is 162 sourced from the underlying extensions as defined in [RFC8476] and 163 [RFC8491] respectively. The BGP-LS speaker may also advertise the 164 MSD information for the local node and its links when not running any 165 link-state IGP protocol e.g. when running BGP as the only routing 166 protocol. 168 The extensions introduced in this document allow for advertisement of 169 different MSD-Types. This document does not define these MSD-Types 170 but leverages the definition, guidelines and the code-point registry 171 specified in [RFC8491]. This enables sharing of MSD-Types that may 172 be defined in the future by the IGPs in BGP-LS. 174 3. Node MSD TLV 176 Node MSD is encoded in a new Node Attribute TLV [RFC7752] using the 177 following format: 179 0 1 2 3 180 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 1 181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 182 | Type | Length | 183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 184 | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | 185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 Figure 1: Node MSD TLV Format 189 Where: 191 o Type: 266 193 o Length: variable (multiple of 2); represents the total length of 194 the value field in octets. 196 o Value : consists of one or more pairs of a 1-octet MSD-Type and 197 1-octet MSD-Value. 199 * MSD-Type : one of the values defined in the IANA registry 200 titled "IGP MSD-Types" under the "Interior Gateway Protocol 201 (IGP) Parameters" registry created by [RFC8491]. 203 * MSD-Value : a number in the range of 0-255. For all MSD-Types, 204 0 represents the lack of ability to impose an MSD stack of any 205 depth; any other value represents that of the node. This value 206 MUST represent the lowest value supported by any link 207 configured for use by the advertising protocol instance. 209 4. Link MSD TLV 211 Link MSD is encoded in a new Link Attribute TLV [RFC7752] using the 212 following format: 214 0 1 2 3 215 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 1 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | Type | Length | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 Figure 2: Link MSD TLV Format 224 Where: 226 o Type: 267 227 o Length: variable (multiple of 2); represents the total length of 228 the value field in octets. 230 o Value : consists of one or more pairs of a 1-octet MSD-Type and 231 1-octet MSD-Value. 233 * MSD-Type : one of the values defined in the IANA registry 234 titled "IGP MSD-Types" under the "Interior Gateway Protocol 235 (IGP) Parameters" registry created by [RFC8491]. 237 * MSD-Value : a number in the range of 0-255. For all MSD-Types, 238 0 represents the lack of ability to impose an MSD stack of any 239 depth; any other value represents that of the link when used as 240 an outgoing interface. 242 5. IANA Considerations 244 This document requests assigning code-points from the registry "BGP- 245 LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute 246 TLVs" based on table below. Early allocation for these code-points 247 have been done by IANA. 249 +------------+-----------------+---------------------------+ 250 | Code Point | Description | IS-IS TLV/Sub-TLV | 251 +------------+-----------------+---------------------------+ 252 | 266 | Node MSD | 242/23 | 253 | 267 | Link MSD | (22,23,25,141,222,223)/15 | 254 +------------+-----------------+---------------------------+ 256 6. Security Considerations 258 The advertisement of an incorrect MSD value may have negative 259 consequences. If the value is smaller than supported, path 260 computation may fail to compute a viable path. If the value is 261 larger than supported, an attempt to instantiate a path that can't be 262 supported by the head-end (the node performing the SID imposition) 263 may occur. The presence of this information may also inform an 264 attacker of how to induce any of the aforementioned conditions. 266 This document does not introduce security issues beyond those 267 discussed in [RFC7752], [RFC8476] and [RFC8491] 269 7. Contributors 270 Siva Sivabalan 271 Cisco Systems Inc. 272 Canada 274 Email: msiva@cisco.com 276 8. Acknowledgements 278 We like to thank Acee Lindem, Stephane Litkowski and Bruno Decraene 279 for their reviews and valuable comments. 281 9. References 283 9.1. 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 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 291 S. Ray, "North-Bound Distribution of Link-State and 292 Traffic Engineering (TE) Information Using BGP", RFC 7752, 293 DOI 10.17487/RFC7752, March 2016, 294 . 296 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 297 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 298 May 2017, . 300 [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, 301 "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, 302 DOI 10.17487/RFC8476, December 2018, 303 . 305 [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 306 "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, 307 DOI 10.17487/RFC8491, November 2018, 308 . 310 9.2. Informative References 312 [I-D.ietf-isis-mpls-elc] 313 Xu, X., Kini, S., Psenak, P., Filsfils, C., and S. 314 Litkowski, "Signaling Entropy Label Capability and Entropy 315 Readable Label Depth Using IS-IS", draft-ietf-isis-mpls- 316 elc-07 (work in progress), May 2019. 318 [I-D.ietf-ospf-mpls-elc] 319 Xu, X., Kini, S., Psenak, P., Filsfils, C., and S. 320 Litkowski, "Signaling Entropy Label Capability and Entropy 321 Readable Label-stack Depth Using OSPF", draft-ietf-ospf- 322 mpls-elc-08 (work in progress), May 2019. 324 [I-D.ietf-pce-segment-routing] 325 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 326 and J. Hardwick, "PCEP Extensions for Segment Routing", 327 draft-ietf-pce-segment-routing-16 (work in progress), 328 March 2019. 330 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol 331 Label Switching Architecture", RFC 3031, 332 DOI 10.17487/RFC3031, January 2001, 333 . 335 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 336 Decraene, B., Litkowski, S., and R. Shakir, "Segment 337 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 338 July 2018, . 340 Authors' Addresses 342 Jeff Tantsura 343 Apstra, Inc. 345 Email: jefftant.ietf@gmail.com 347 Uma Chunduri 348 Futurewei Technologies 350 Email: umac.ietf@gmail.com 352 Ketan Talaulikar 353 Cisco Systems 355 Email: ketant@cisco.com 357 Greg Mirsky 358 ZTE Corp. 360 Email: gregimirsky@gmail.com 361 Nikos Triantafillis 362 Apstra, Inc. 364 Email: nikos@apstra.com