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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: September 29, 2017 Huawei Technologies 6 S. Aldrin 7 Google, Inc 8 L. Ginsberg 9 Cisco Systems 10 March 28, 2017 12 Signaling MSD (Maximum SID Depth) using IS-IS 13 draft-ietf-isis-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 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 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 29, 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 1.2. 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 . . . . . . . . . . . . . . . . . . . . . . 6 72 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 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.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 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 push 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 labels (e.g. service) that are to be pushed to the stack - this would 111 be signaled with an another MSD type (TBD), MSD SHOULD be adjusted to 112 reflect that. In the future, new MSD types could be defined to 113 signal additional capabilities: entropy labels, labels that can be 114 pushed 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 is 23 (Suggested value - to be 165 assigned by IANA). 167 Length is variable (minimum of 2, multiple of 2 octets) and 168 represents the total length of value field. 170 Value field consists of a 1 octet sub-type (IANA Registry) and 1 171 octet value. 173 Sub-Type 1 (IANA Section), MSD and the Value field contains maximum 174 MSD of the router originating the Router Capability TLV. Node 175 Maximum MSD is a number in the range of 0-254. 0 represents lack of 176 the ability to push MSD of any depth; any other value represents that 177 of the node. This value SHOULD represent the lowest value supported 178 by node. 180 Other Sub-types other than defined above are reserved for future 181 extensions. This sub-TLV is optional. The scope of the 182 advertisement is specific to the deployment. 184 4. LINK MSD Advertisement 186 A new sub-TLV - Link MSD sub-TLV is defined for TLVs 22, 23, 141, 187 222, and 223 to carry the provisioned MSD of the interface associated 188 with the link. 190 0 1 2 3 191 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 1 193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 194 | Type | Length | Sub-Type and Value | 195 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 197 Figure 2: Link MSD Sub-TLV 199 The Type (1 byte) of this sub-TLV is 15 (Suggested value - to be 200 assigned by IANA). 202 Length is variable and similar to what is defined in Section 3. 204 Value field consists of a 1 octet sub-type (IANA Registry) and 1 205 octet value. 207 Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD 208 of the router originating the corresponding TLV's 22, 23, 141, 222, 209 and 223. Link MSD is a number in the range of 0-254. 0 represents 210 lack of the ability to push MSD of any depth; any other value 211 represents that of the particular link MSD value. 213 5. Node MSD vs Link MSD conflict resolution 215 When both Node MSD and Link MSD are present, the value in the Link 216 MSD MUST be used. 218 6. IANA Considerations 220 This document includes a request to IANA to allocate sub-TLV type 221 codes for the new sub TLV proposed in Section 3 of this document from 222 IS-IS Router Capability TLV Registry as defined by [RFC7981]. 224 Type: 23 (suggested - to be assigned by IANA) 226 Description: Node MSD 228 Also for link MSD, we request IANA to allocate new sub-TLV codes as 229 defined in Section 4 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223 230 registry. 232 Type: 15 (suggested - to be assigned by IANA) 234 Description: Link MSD 236 Per TLV information where LINK MSD sub-TLV can be part of: 238 TLV 22 23 141 222 223 239 ---------------------- 240 y y y y y 242 Figure 3: TLVs where LINK MSD Sub-TLV can be present 244 This document requests the creation of a new IANA managed registry to 245 identify MSD types as proposed in Section 3, Section 4. The 246 registration procedure is "Expert Review" as defined in [RFC5226]. 247 Suggested registry name is "MSD Sub-types". Types are an unsigned 8 248 bit number. The following values are defined by this document 250 Value Name Reference 251 ----- --------------------- ------------- 252 0 Reserved This document 253 1 Base MSD This document 254 2-250 Unassigned This document 255 251-254 Experimental This document 256 255 Reserved This document 258 Figure 4: MSD Sub-type Codepoints Registry 260 7. Security Considerations 262 This document describes a mechanism to signal Segment Routing MSD 263 supported at node and/or link granularity through IS-IS LSPs and does 264 not introduce any new security issues. 266 8. Contributors 268 The following people contributed to this document: 270 Peter Psenak 272 Email: ppsenak@cisco.com 274 9. Acknowledgements 276 The authors would like to thank Stephane Litkowski and Bruno Decraene 277 for their reviews and valuable comments. 279 10. References 280 10.1. Normative References 282 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 283 Requirement Levels", BCP 14, RFC 2119, 284 DOI 10.17487/RFC2119, March 1997, 285 . 287 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 288 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 289 2008, . 291 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 292 for Advertising Router Information", RFC 7981, 293 DOI 10.17487/RFC7981, October 2016, 294 . 296 10.2. Informative References 298 [I-D.ietf-isis-mpls-elc] 299 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 300 Litkowski, "Signaling Entropy Label Capability Using IS- 301 IS", draft-ietf-isis-mpls-elc-02 (work in progress), 302 October 2016. 304 [I-D.ietf-pce-segment-routing] 305 Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., 306 Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and 307 J. Hardwick, "PCEP Extensions for Segment Routing", draft- 308 ietf-pce-segment-routing-08 (work in progress), October 309 2016. 311 [I-D.tantsura-idr-bgp-ls-segment-routing-msd] 312 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 313 "Signaling Maximum SID Depth using Border Gateway Protocol 314 Link-State", draft-tantsura-idr-bgp-ls-segment-routing- 315 msd-03 (work in progress), March 2017. 317 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 318 dual environments", RFC 1195, DOI 10.17487/RFC1195, 319 December 1990, . 321 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 322 Topology (MT) Routing in Intermediate System to 323 Intermediate Systems (IS-ISs)", RFC 5120, 324 DOI 10.17487/RFC5120, February 2008, 325 . 327 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 328 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 329 DOI 10.17487/RFC5226, May 2008, 330 . 332 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 333 S. Ray, "North-Bound Distribution of Link-State and 334 Traffic Engineering (TE) Information Using BGP", RFC 7752, 335 DOI 10.17487/RFC7752, March 2016, 336 . 338 Authors' Addresses 340 Jeff Tantsura 341 Individual 343 Email: jefftant.ietf@gmail.com 345 Uma Chunduri 346 Huawei Technologies 348 Email: uma.chunduri@huawei.com 350 Sam Aldrin 351 Google, Inc 353 Email: aldrin.ietf@gmail.com 355 Les Ginsberg 356 Cisco Systems 358 Email: ginsberg@cisco.com