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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 U. Chunduri 4 Intended status: Standards Track Individual 5 Expires: March 30, 2017 September 26, 2016 7 Signaling MSD (Maximum SID Depth) using IS-IS 8 draft-tantsura-isis-segment-routing-msd-02 10 Abstract 12 This document proposes a way to expose Maximum SID Depth (MSD) 13 supported by a node at node and/or link level by an ISIS Router. In 14 a Segment Routing (SR) enabled network a centralized controller that 15 programs SR tunnels at the head-end node needs to know the MSD 16 information at node level and/or link level to push the label stack 17 of an appropriate depth. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on March 30, 2017. 36 Copyright Notice 38 Copyright (c) 2016 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Conventions used in this document . . . . . . . . . . . . 3 55 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 56 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 3 59 4. LINK MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 60 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 61 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 62 7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 63 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 8.1. Normative References . . . . . . . . . . . . . . . . . . 4 65 8.2. Informative References . . . . . . . . . . . . . . . . . 5 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 68 1. Introduction 70 When Segment Routing tunnels are computed by a centralized 71 controller, it is crucial that the controller knows the MSD "Maximum 72 SID Depth" of the node or link SR tunnel exits over, so it doesn't 73 download a path with SID (label stack) of a depth more than the node 74 or link used is capable of imposing. This document describes how to 75 use IS-IS to expose the MSD of the node or link to a centralized 76 controller. 78 PCEP SR extensions [I-D.ietf-pce-segment-routing] has defined MSD, to 79 signal in SR PCE Capability TLV, METRIC Object. However, If PCEP is 80 not supported by a node (head-end of the SR tunnel) and controller 81 does not participate in IGP routing it has no way to learn the MSD of 82 the node or link configured. BGP-LS [RFC7752] defines a way to 83 expose topology and associated different attributes, capabilities of 84 the nodes in that topology to a centralized controller and MSD has 85 been defined in [I-D.tantsura-idr-bgp-ls-segment-routing-msd]. For 86 this information to be advertised by BGP for the all nodes and links 87 of the network, where this is provisioned, IS-IS module should have 88 this information in the LSDB. 90 [I-D.ietf-isis-mpls-elc] defines, RLSDC which indicates how many 91 labels a node can read to take a decision to insert an Entropy Label 92 (EL) and is different than how many labels a node can push as defined 93 by MSD in this draft. 95 1.1. Conventions used in this document 97 1.1.1. Terminology 99 BGP-LS: Distribution of Link-State and TE Information using Border 100 Gateway Protocol 102 ISIS: Intermediate System to Intermediate System 104 MSD: Maximum SID Depth 106 PCC: Path Computation Client 108 PCE: Path Computation Element 110 PCEP: Path Computation Element Protocol 112 SID: Segment Identifier 114 SR: Segment Routing 116 1.2. Requirements Language 118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 120 document are to be interpreted as described in RFC 2119 [RFC2119]. 122 2. Terminology 124 This memo makes use of the terms defined in [RFC4971]. 126 3. Node MSD Advertisement 128 A new sub-TLV within the body of IS-IS Router Capability TLV 129 [RFC4971], called Node MSD sub-TLV is defined to carry the 130 provisioned SID depth of the router originating the Router Capability 131 TLV. Node MSD is the lowest MSD supported by the node and can be 132 provisioned in IS-IS instance. 134 The Type (1 byte) of this sub-TLV is TBD. 136 Length is 1 bytes, and 138 the Value field contains MSD of the router originating the Router 139 Capability TLV. Node MSD is a number in the range of 0-254. 0 140 represents lack of the ability to push MSD of any depth; any other 141 value represents that of the node. This value SHOULD represent the 142 lowest value supported by node. 144 This TLV is optional. The scope of the advertisement is specific to 145 the deployment. 147 4. LINK MSD Advertisement 149 A new sub-TLV called Link MSD sub-TLV is defined to carry the 150 provisioned SID depth of the interface associated with the link. 152 The Type (1 byte) of this TLV is TBD. 154 Length is 1 byte, and 156 the Value field contains Link MSD of the router originating the 157 corresponding IS extended reachability TLV [RFC5305] or MT IS TLV 158 [RFC5120]. Link MSD is a number in the range of 0-254. 0 represents 159 lack of the ability to push MSD of any depth; any other value 160 represents that of the particular link MSD value. 162 5. Acknowledgements 164 TBD 166 6. IANA Considerations 168 This document includes a request to IANA to allocate sub-TLV type 169 codes for the new TLV proposed in Section 3 of this document from IS- 170 IS Router Capability TLV Registry as defined by [RFC4971]. Also for 171 link MSD, we request IANA to allocate new sub-TLV codes as defined in 172 Section 4 from IS extended reachability TLV (22) and MT IS TLV (222) 173 registry. 175 7. Security Considerations 177 This document describes a mechanism for advertising Segment Routing 178 SID depth supported at node and link level information through IS-IS 179 LSPs and does not introduce any new security issues. 181 8. References 183 8.1. Normative References 185 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 186 Requirement Levels", BCP 14, RFC 2119, 187 DOI 10.17487/RFC2119, March 1997, 188 . 190 [RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed., 191 "Intermediate System to Intermediate System (IS-IS) 192 Extensions for Advertising Router Information", RFC 4971, 193 DOI 10.17487/RFC4971, July 2007, 194 . 196 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 197 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 198 2008, . 200 8.2. Informative References 202 [I-D.ietf-isis-mpls-elc] 203 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 204 Litkowski, "Signaling Entropy Label Capability Using IS- 205 IS", draft-ietf-isis-mpls-elc-01 (work in progress), 206 November 2015. 208 [I-D.ietf-pce-segment-routing] 209 Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., 210 Lopez, V., Tantsura, J., Henderickx, W., and J. Hardwick, 211 "PCEP Extensions for Segment Routing", draft-ietf-pce- 212 segment-routing-07 (work in progress), March 2016. 214 [I-D.tantsura-idr-bgp-ls-segment-routing-msd] 215 Tantsura, J., Mirsky, G., Sivabalan, S., and U. Chunduri, 216 "Signaling Maximum SID Depth using Border Gateway Protocol 217 Link-State", draft-tantsura-idr-bgp-ls-segment-routing- 218 msd-01 (work in progress), July 2016. 220 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 221 dual environments", RFC 1195, DOI 10.17487/RFC1195, 222 December 1990, . 224 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 225 Topology (MT) Routing in Intermediate System to 226 Intermediate Systems (IS-ISs)", RFC 5120, 227 DOI 10.17487/RFC5120, February 2008, 228 . 230 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 231 S. Ray, "North-Bound Distribution of Link-State and 232 Traffic Engineering (TE) Information Using BGP", RFC 7752, 233 DOI 10.17487/RFC7752, March 2016, 234 . 236 Authors' Addresses 238 Jeff Tantsura 239 Individual 241 Email: jefftant.ietf@gmail.com 243 Uma Chunduri 244 Individual 246 Email: uma.chunduri@gmail.com