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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IS-IS Working Group J. Tantsura 3 Internet-Draft Individual 4 Intended status: Standards Track U. Chunduri 5 Expires: June 4, 2018 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 L. Ginsberg 9 Cisco Systems 10 December 01, 2017 12 Signaling MSD (Maximum SID Depth) using IS-IS 13 draft-ietf-isis-segment-routing-msd-06 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 IS-IS 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 impose the SID 22 stack of an appropriate depth. MSD is relevant to the head-end of a 23 SR tunnel or Binding-SID anchor node where Binding-SID expansions 24 might 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 June 4, 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 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 66 4. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 67 5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5 68 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 69 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 70 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6 71 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 72 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 73 10.1. Normative References . . . . . . . . . . . . . . . . . . 7 74 10.2. Informative References . . . . . . . . . . . . . . . . . 7 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 77 1. Introduction 79 When Segment Routing tunnels are computed by a centralized 80 controller, it is critical that the controller learns the MSD 81 "Maximum SID Depth" of the node or link SR tunnel exits over, so the 82 SID stack depth of a path computed doesn't exceed the number of SIDs 83 the node is capable of imposing. This document describes how to use 84 IS-IS to signal the MSD of a node or link to a centralized 85 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.ietf-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 IS-IS router in the 100 network. 102 [I-D.ietf-isis-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 impose SID's stack of a particular depth. 107 MSD of type 1 (IANA Registry), called Base MSD, is used to signal the 108 total number of SIDs a node is capable of imposing, to be used by a 109 path computation element/controller. In case, there are additional 110 SIDs (e.g. service) that are to be imposed to the stack - this would 111 be signaled with an another MSD type (TBD), no adjustment to the Base 112 MSD should be made. In the future, new MSD types could be defined to 113 signal additional capabilities: entropy labels, SIDs that can be 114 imposed thru recirculation, or another dataplane e.g IPv6. 116 1.1. Conventions used in this document 118 1.1.1. Terminology 120 BGP-LS: Distribution of Link-State and TE Information using Border 121 Gateway Protocol 123 IS-IS: Intermediate System to Intermediate System 125 MSD: Maximum SID Depth 127 PCC: Path Computation Client 129 PCE: Path Computation Element 131 PCEP: Path Computation Element Protocol 133 SID: Segment Identifier 135 SR: Segment Routing 137 1.2. Requirements Language 139 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 140 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 141 document are to be interpreted as described in RFC 2119 [RFC2119]. 143 2. Terminology 145 This memo makes use of the terms defined in [RFC7981]. 147 3. Node MSD Advertisement 149 A new sub-TLV within the body of IS-IS Router Capability TLV 150 [RFC7981], Node MSD sub-TLV is defined to carry the provisioned MSD 151 of the router originating the Router Capability TLV. Node MSD is the 152 lowest MSD supported by the node of any interface and can be 153 provisioned in IS-IS instance. 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 | Sub-Type and Value | 160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 Figure 1: Node MSD Sub-TLV 164 The Type (1 byte) of this sub-TLV has value of 23. 166 Length is variable (minimum of 2, multiple of 2 octets) and 167 represents the total length of value field. 169 Value field consists of a 1 octet sub-type (IANA Registry) and 1 170 octet value. 172 Sub-Type 1 (IANA Section), MSD and the Value field contains maximum 173 MSD of the router originating the Router Capability TLV. Node 174 Maximum MSD is a number in the range of 0-254. 0 represents lack of 175 the ability to impose MSD stack of any depth; any other value 176 represents that of the node. This value SHOULD represent the lowest 177 value supported by node. 179 Other Sub-types other than defined above are reserved for future 180 extensions. This sub-TLV is optional. The scope of the 181 advertisement is specific to the deployment. 183 4. Link MSD Advertisement 185 A new sub-TLV - Link MSD sub-TLV is defined for TLVs 22, 23, 141, 186 222, and 223 to carry the provisioned MSD of the interface associated 187 with the link. 189 0 1 2 3 190 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 1 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 193 | Type | Length | Sub-Type and Value | 194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 196 Figure 2: Link MSD Sub-TLV 198 The Type (1 byte) of this sub-TLV has value of 15. 200 Length is variable and similar to what is defined in Section 3. 202 Value field consists of a 1 octet sub-type (IANA Registry) and 1 203 octet value. 205 Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD 206 of the router originating the corresponding TLV's 22, 23, 141, 222, 207 and 223. Link MSD is a number in the range of 0-254. 0 represents 208 lack of the ability to impose MSD stack of any depth; any other value 209 represents that of the particular link MSD value. 211 5. Node MSD vs Link MSD conflict resolution 213 When both Node MSD and Link MSD are present, the value in the Link 214 MSD MUST be used. 216 6. IANA Considerations 218 This document includes a request to IANA to allocate sub-TLV type 219 codes for the new sub TLV proposed in Section 3 of this document from 220 IS-IS Router Capability TLV Registry as defined by [RFC7981]. 222 Following values have been allocated by IANA: 224 Value Description Reference 225 ----- --------------- ------------- 226 23 Node MSD This document 228 Figure 3: Node MSD 230 For the Link MSD, we request IANA to allocate new sub-TLV codes as 231 defined in Section 4 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223 232 registry. 234 Value Description Reference 235 ----- --------------- ------------- 236 15 Link MSD This document 238 Figure 4: Link MSD 240 Per TLV information where LINK MSD sub-TLV can be part of: 242 TLV 22 23 25 141 222 223 243 --- -------------------- 244 y y y y y y 246 Figure 5: TLVs where LINK MSD Sub-TLV can be present 248 This document requests the creation of a new IANA managed registry to 249 identify MSD types as proposed in Section 3, Section 4. The 250 registration procedure is "Expert Review" as defined in [RFC8126]. 251 Suggested registry name is "MSD Sub-types". Types are an unsigned 8 252 bit number. The following values are defined by this document 254 Value Name Reference 255 ----- --------------------- ------------- 256 0 Reserved This document 257 1 Base MSD This document 258 2-250 Unassigned This document 259 251-254 Experimental This document 260 255 Reserved This document 262 Figure 6: MSD Sub-type Codepoints Registry 264 7. Security Considerations 266 This document describes a mechanism to signal Segment Routing MSD 267 supported at node and/or link granularity through IS-IS LSPs and does 268 not introduce any new security issues. 270 8. Contributors 272 The following people contributed to this document: 274 Peter Psenak 276 Email: ppsenak@cisco.com 278 9. Acknowledgements 280 The authors would like to thank Stephane Litkowski and Bruno Decraene 281 for their reviews and valuable comments. 283 10. References 285 10.1. Normative References 287 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 288 Requirement Levels", BCP 14, RFC 2119, 289 DOI 10.17487/RFC2119, March 1997, 290 . 292 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 293 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 294 2008, . 296 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 297 for Advertising Router Information", RFC 7981, 298 DOI 10.17487/RFC7981, October 2016, 299 . 301 10.2. Informative References 303 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 304 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 305 "Signaling Maximum SID Depth using Border Gateway Protocol 306 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 307 (work in progress), October 2017. 309 [I-D.ietf-isis-mpls-elc] 310 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 311 Litkowski, "Signaling Entropy Label Capability Using IS- 312 IS", draft-ietf-isis-mpls-elc-02 (work in progress), 313 October 2016. 315 [I-D.ietf-pce-segment-routing] 316 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 317 and J. Hardwick, "PCEP Extensions for Segment Routing", 318 draft-ietf-pce-segment-routing-11 (work in progress), 319 November 2017. 321 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 322 dual environments", RFC 1195, DOI 10.17487/RFC1195, 323 December 1990, . 325 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 326 Topology (MT) Routing in Intermediate System to 327 Intermediate Systems (IS-ISs)", RFC 5120, 328 DOI 10.17487/RFC5120, February 2008, 329 . 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 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 338 Writing an IANA Considerations Section in RFCs", BCP 26, 339 RFC 8126, DOI 10.17487/RFC8126, June 2017, 340 . 342 Authors' Addresses 344 Jeff Tantsura 345 Individual 347 Email: jefftant.ietf@gmail.com 349 Uma Chunduri 350 Huawei Technologies 352 Email: uma.chunduri@huawei.com 354 Sam Aldrin 355 Google, Inc 357 Email: aldrin.ietf@gmail.com 359 Les Ginsberg 360 Cisco Systems 362 Email: ginsberg@cisco.com