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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: May 20, 2017 November 16, 2016 7 Signaling MSD (Maximum SID Depth) using IS-IS 8 draft-ietf-isis-segment-routing-msd-00 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 May 20, 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. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 4 61 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 62 7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 63 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 64 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 9.1. Normative References . . . . . . . . . . . . . . . . . . 4 66 9.2. Informative References . . . . . . . . . . . . . . . . . 5 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 69 1. Introduction 71 When Segment Routing tunnels are computed by a centralized 72 controller, it is crucial that the controller knows the MSD "Maximum 73 SID Depth" of the node or link SR tunnel exits over, so it doesn't 74 download a path with SID (label stack) of a depth more than the node 75 or link used is capable of imposing. This document describes how to 76 use IS-IS to expose the MSD of the node or link to a centralized 77 controller. 79 PCEP SR extensions [I-D.ietf-pce-segment-routing] has defined MSD, to 80 signal in SR PCE Capability TLV, METRIC Object. However, If PCEP is 81 not supported by a node (head-end of the SR tunnel) and controller 82 does not participate in IGP routing it has no way to learn the MSD of 83 the node or link configured. BGP-LS [RFC7752] defines a way to 84 expose topology and associated different attributes, capabilities of 85 the nodes in that topology to a centralized controller and MSD has 86 been defined in [I-D.tantsura-idr-bgp-ls-segment-routing-msd]. For 87 this information to be advertised by BGP for the all nodes and links 88 of the network, where this is provisioned, IS-IS module should have 89 this information in the LSDB. 91 [I-D.ietf-isis-mpls-elc] defines, RLSDC which indicates how many 92 labels a node can read to take a decision to insert an Entropy Label 93 (EL) and is different than how many labels a node can push as defined 94 by MSD in this draft. 96 1.1. Conventions used in this document 98 1.1.1. Terminology 100 BGP-LS: Distribution of Link-State and TE Information using Border 101 Gateway Protocol 103 ISIS: Intermediate System to Intermediate System 105 MSD: Maximum SID Depth 107 PCC: Path Computation Client 109 PCE: Path Computation Element 111 PCEP: Path Computation Element Protocol 113 SID: Segment Identifier 115 SR: Segment Routing 117 1.2. Requirements Language 119 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 120 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 121 document are to be interpreted as described in RFC 2119 [RFC2119]. 123 2. Terminology 125 This memo makes use of the terms defined in [RFC4971]. 127 3. Node MSD Advertisement 129 A new sub-TLV within the body of IS-IS Router Capability TLV 130 [RFC4971], called Node MSD sub-TLV is defined to carry the 131 provisioned SID depth of the router originating the Router Capability 132 TLV. Node MSD is the lowest MSD supported by the node and can be 133 provisioned in IS-IS instance. 135 The Type (1 byte) of this sub-TLV is TBD. 137 Length is 1 bytes, and 139 the Value field contains MSD of the router originating the Router 140 Capability TLV. Node MSD is a number in the range of 0-254. 0 141 represents lack of the ability to push MSD of any depth; any other 142 value represents that of the node. This value SHOULD represent the 143 lowest value supported by node. 145 This TLV is optional. The scope of the advertisement is specific to 146 the deployment. 148 4. LINK MSD Advertisement 150 A new sub-TLV called Link MSD sub-TLV is defined to carry the 151 provisioned SID depth of the interface associated with the link. 153 The Type (1 byte) of this sub- TLV is TBD. 155 Length is 1 byte, and 157 the Value field contains Link MSD of the router originating the 158 corresponding TLV's 22, 23, 141, 222, and 223. Link MSD is a number 159 in the range of 0-254. 0 represents lack of the ability to push MSD 160 of any depth; any other value represents that of the particular link 161 MSD value. 163 5. Node MSD vs Link MSD conflict resolution 165 When both Node MSD and Link MSD are present, the value in the Link 166 MSD MUST be used. 168 6. IANA Considerations 170 This document includes a request to IANA to allocate sub-TLV type 171 codes for the new TLV proposed in Section 3 of this document from IS- 172 IS Router Capability TLV Registry as defined by [RFC4971]. Also for 173 link MSD, we request IANA to allocate new sub-TLV codes as defined in 174 Section 4 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223 registry. 176 7. Security Considerations 178 This document describes a mechanism for advertising Segment Routing 179 SID depth supported at node and link level information through IS-IS 180 LSPs and does not introduce any new security issues. 182 8. Acknowledgements 184 TBD 186 9. References 188 9.1. Normative References 190 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 191 Requirement Levels", BCP 14, RFC 2119, 192 DOI 10.17487/RFC2119, March 1997, 193 . 195 [RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed., 196 "Intermediate System to Intermediate System (IS-IS) 197 Extensions for Advertising Router Information", RFC 4971, 198 DOI 10.17487/RFC4971, July 2007, 199 . 201 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 202 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 203 2008, . 205 9.2. Informative References 207 [I-D.ietf-isis-mpls-elc] 208 Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. 209 Litkowski, "Signaling Entropy Label Capability Using IS- 210 IS", draft-ietf-isis-mpls-elc-02 (work in progress), 211 October 2016. 213 [I-D.ietf-pce-segment-routing] 214 Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., 215 Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and 216 J. Hardwick, "PCEP Extensions for Segment Routing", draft- 217 ietf-pce-segment-routing-08 (work in progress), October 218 2016. 220 [I-D.tantsura-idr-bgp-ls-segment-routing-msd] 221 Tantsura, J., Mirsky, G., Sivabalan, S., and U. Chunduri, 222 "Signaling Maximum SID Depth using Border Gateway Protocol 223 Link-State", draft-tantsura-idr-bgp-ls-segment-routing- 224 msd-01 (work in progress), July 2016. 226 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 227 dual environments", RFC 1195, DOI 10.17487/RFC1195, 228 December 1990, . 230 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 231 Topology (MT) Routing in Intermediate System to 232 Intermediate Systems (IS-ISs)", RFC 5120, 233 DOI 10.17487/RFC5120, February 2008, 234 . 236 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 237 S. Ray, "North-Bound Distribution of Link-State and 238 Traffic Engineering (TE) Information Using BGP", RFC 7752, 239 DOI 10.17487/RFC7752, March 2016, 240 . 242 Authors' Addresses 244 Jeff Tantsura 245 Individual 247 Email: jefftant.ietf@gmail.com 249 Uma Chunduri 250 Individual 252 Email: uma.chunduri@gmail.com