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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 IS-IS Working Group J. Tantsura 2 Internet-Draft Individual 3 Intended status: Standards Track U. Chunduri 4 Expires: September 2, 2017 Huawei Technologies 5 S. Aldrin 6 Google, Inc 7 L. Ginsberg 8 Cisco Systems 9 March 1, 2017 11 Signaling MSD (Maximum SID Depth) using IS-IS 12 draft-ietf-isis-segment-routing-msd-02 14 Abstract 16 This document proposes a way to signal Maximum SID Depth (MSD) 17 supported by a node at node and/or link granularity by an ISIS 18 Router. In a Segment Routing (SR) enabled network a centralized 19 controller that programs SR tunnels needs to know the MSD supported 20 by the head-end at node and/or link granularity to push the SID stack 21 of an appropriate depth. MSD is relevant to the head-end of a SR 22 tunnel or Binding-SID anchor node where Binding-SID expansions might 23 result in creation of a new SID stack. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on September 2, 2017. 42 Copyright Notice 44 Copyright (c) 2017 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 1.1. Conventions used in this document . . . . . . . . . . . . 3 61 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 62 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 65 4. LINK MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 66 5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5 67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 68 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 69 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6 70 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 71 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 72 10.1. Normative References . . . . . . . . . . . . . . . . . . 7 73 10.2. Informative References . . . . . . . . . . . . . . . . . 7 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 76 1. Introduction 78 When Segment Routing tunnels are computed by a centralized 79 controller, it is critical that the controller learns the MSD 80 "Maximum SID Depth" of the node or link SR tunnel exits over, so the 81 SID stack depth of a path computed doesn't exceed the number of SIDs 82 the node is capable of imposing. This document describes how to use 83 IS-IS to signal the MSD of a node or link to a centralized 84 controller. 86 PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD 87 in SR PCE Capability TLV and METRIC Object. However, if PCEP is not 88 supported/configured on the head-end of a SR tunnel or a Binding-SID 89 anchor node and controller does not participate in IGP routing, it 90 has no way to learn the MSD of nodes and links which has been 91 configured. BGP-LS [RFC7752] defines a way to expose topology and 92 associated attributes and capabilities of the nodes in that topology 93 to a centralized controller. MSD signaling by BGP-LS has been 94 defined in [I-D.tantsura-idr-bgp-ls-segment-routing-msd]. Typically, 95 BGP-LS is configured on a small number of nodes, that do not 96 necessarily act as head-ends. In order, for BGP-LS to signal MSD for 97 the all nodes and links in the network MSD is relevant, MSD 98 capabilites SHOULD be distributed to every IS-IS router in the 99 network. 101 [I-D.ietf-isis-mpls-elc] defines Readable Label Depth Capability 102 (RLDC) that is used by a head-end to insert Entropy Label (EL) at 103 appropriate depth, so it could be read by transit nodes. MSD in 104 contrary signals ability to push SID's stack of a particular depth. 106 MSD of type 1 (IANA Registry) is used to signal the number of SIDs a 107 node is capable of imposing, to be used by a path computation 108 element/controller and is only relevant to the part of the stack 109 created as the result of the computation. In case, there are 110 additional labels (e.g. service) that are to be pushed to the stack - 111 MSD SHOULD be adjusted to reflect that. In the future, new MSD types 112 could be defined to signal additional capabilities: entropy labels, 113 labels that can be pushed thru recirculation, etc. 115 1.1. Conventions used in this document 117 1.1.1. Terminology 119 BGP-LS: Distribution of Link-State and TE Information using Border 120 Gateway Protocol 122 IS-IS: Intermediate System to Intermediate System 124 MSD: Maximum SID Depth 126 PCC: Path Computation Client 128 PCE: Path Computation Element 130 PCEP: Path Computation Element Protocol 132 SID: Segment Identifier 134 SR: Segment Routing 136 1.2. Requirements Language 138 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 139 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 140 document are to be interpreted as described in RFC 2119 [RFC2119]. 142 2. Terminology 144 This memo makes use of the terms defined in [RFC7981]. 146 3. Node MSD Advertisement 148 A new sub-TLV within the body of IS-IS Router Capability TLV 149 [RFC7981], Node MSD sub-TLV is defined to carry the provisioned MSD 150 of the router originating the Router Capability TLV. Node MSD is the 151 lowest MSD supported by the node of any interface and can be 152 provisioned in IS-IS instance. 154 0 1 2 3 155 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 1 157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 158 | Type | Length | Sub-Type and Value | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 161 Figure 1: Node MSD Sub-TLV 163 The Type (1 byte) of this sub-TLV is 23 (Suggested value - to be 164 assigned by IANA). 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 push MSD of any depth; any other value represents that 176 of the node. This value SHOULD represent the lowest value supported 177 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 is 15 (Suggested value - to be 199 assigned by IANA). 201 Length is variable and similar to what is defined in Section 3. 203 Value field consists of a 1 octet sub-type (IANA Registry) and 1 204 octet value. 206 Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD 207 of the router originating the corresponding TLV's 22, 23, 141, 222, 208 and 223. Link MSD is a number in the range of 0-254. 0 represents 209 lack of the ability to push MSD of any depth; any other value 210 represents that of the particular link MSD value. 212 5. Node MSD vs Link MSD conflict resolution 214 When both Node MSD and Link MSD are present, the value in the Link 215 MSD MUST be used. 217 6. IANA Considerations 219 This document includes a request to IANA to allocate sub-TLV type 220 codes for the new sub TLV proposed in Section 3 of this document from 221 IS-IS Router Capability TLV Registry as defined by [RFC7981]. 223 Type: 23 (suggested - to be assigned by IANA) 225 Description: Node MSD 227 Also for link MSD, we request IANA to allocate new sub-TLV codes as 228 defined in Section 4 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223 229 registry. 231 Type: 15 (suggested - to be assigned by IANA) 233 Description: Link MSD 235 Per TLV information where LINK MSD sub-TLV can be part of: 237 TLV 22 23 141 222 223 238 ---------------------- 239 y y y y y 241 Figure 3: TLVs where LINK MSD Sub-TLV can be present 243 This document requests the creation of a new IANA managed registry to 244 identify MSD types as proposed in Section 3, Section 4. The 245 registration procedure is "Expert Review" as defined in [RFC5226]. 246 Suggested registry name is "MSD Sub-types". Types are an unsigned 8 247 bit number. The following values are defined by this document 249 Value Name Reference 250 ----- --------------------- ------------- 251 0 Reserved This document 252 1 MSD This document 253 2-250 Unassigned This document 254 251-254 Experimental This document 255 255 Reserved This document 257 Figure 4: MSD Sub-type Codepoints Registry 259 7. Security Considerations 261 This document describes a mechanism to signal Segment Routing MSD 262 supported at node and/or link granularity through IS-IS LSPs and does 263 not introduce any new security issues. 265 8. Contributors 267 The following people contributed to this document: 269 Peter Psenak 271 Email: ppsenak@cisco.com 273 9. Acknowledgements 275 The authors would like to thank Stephane Litkowski and Bruno Decraene 276 for their reviews and valuable comments. 278 10. References 279 10.1. Normative References 281 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 282 Requirement Levels", BCP 14, RFC 2119, 283 DOI 10.17487/RFC2119, March 1997, 284 . 286 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 287 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 288 2008, . 290 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 291 for Advertising Router Information", RFC 7981, 292 DOI 10.17487/RFC7981, October 2016, 293 . 295 10.2. Informative References 297 [I-D.ietf-isis-mpls-elc] 298 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 299 Litkowski, "Signaling Entropy Label Capability Using IS- 300 IS", draft-ietf-isis-mpls-elc-02 (work in progress), 301 October 2016. 303 [I-D.ietf-pce-segment-routing] 304 Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., 305 Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and 306 J. Hardwick, "PCEP Extensions for Segment Routing", draft- 307 ietf-pce-segment-routing-08 (work in progress), October 308 2016. 310 [I-D.tantsura-idr-bgp-ls-segment-routing-msd] 311 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 312 "Signaling Maximum SID Depth using Border Gateway Protocol 313 Link-State", draft-tantsura-idr-bgp-ls-segment-routing- 314 msd-02 (work in progress), January 2017. 316 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 317 dual environments", RFC 1195, DOI 10.17487/RFC1195, 318 December 1990, . 320 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 321 Topology (MT) Routing in Intermediate System to 322 Intermediate Systems (IS-ISs)", RFC 5120, 323 DOI 10.17487/RFC5120, February 2008, 324 . 326 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 327 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 328 DOI 10.17487/RFC5226, May 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 Authors' Addresses 339 Jeff Tantsura 340 Individual 342 Email: jefftant.ietf@gmail.com 344 Uma Chunduri 345 Huawei Technologies 347 Email: uma.chunduri@huawei.com 349 Sam Aldrin 350 Google, Inc 352 Email: aldrin.ietf@gmail.com 354 Les Ginsberg 355 Cisco Systems 357 Email: ginsberg@cisco.com