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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 LSR Working Group Louis Chan 3 INTERNET-DRAFT Krzysztof Szarkowicz 4 Intended status: Standard Track Juniper Networks 5 Expires: Sep 6, 2022 Mar 6, 2022 7 IGP extensions for Advertising Offset for Flex-Algorithm 8 draft-chan-lsr-igp-adv-offset-00.txt 10 Abstract 12 This document describes the IGP extensions to provide predictable Adjacency-SIDs 13 per Flex-Algorithm [FLEXALGO] in segment routing. 15 We propose some methods to allow the advertisement of additional TLV in IGP so that 16 the Flex-Algorithm specific Adjacency-SIDs could be automatically derived. 18 With the proposed method, the size of advertisement on per node per link basis is 19 greatly reduced. Each participating router would derive the required labels 20 automatically. 22 Extensions for offset to derive Flex-Algorithm Prefix-SID is also included in the 23 document. 25 Status of this Memo 27 This Internet-Draft is submitted in full conformance with the provisions of BCP 78 28 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering Task Force 31 (IETF). Note that other groups may also distribute working documents as Internet- 32 Drafts. The list of current Internet-Drafts is at 33 http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months and may be 36 updated, replaced, or obsoleted by other documents at any time. It is 37 inappropriate to use Internet-Drafts as reference material or to cite them other 38 than as "work in progress." 40 This Internet-Draft will expire on Sep 6, 2022. 42 Copyright Notice 44 Copyright (c) 2017 IETF Trust and the persons identified as the document authors. 45 All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating 48 to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents carefully, as they 50 describe your rights and restrictions with respect to this document. Code 51 Components extracted from this document must include Simplified BSD License text as 52 described in Section 4.e of the Trust Legal Provisions and are provided without 53 warranty as described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction...................................................2 58 2. Conventions used in this document..............................2 59 3. ISIS extension.................................................2 60 3.1. Algorithm Offset for Adj-SID..............................3 61 3.2. Algorithm Offset for LAN based Adj-SID....................4 62 3.3. Algorithm Offset for Prefix SID...........................5 63 4. Compatibility..................................................6 64 5. OSPF extension.................................................6 65 6. Security Consideration.........................................6 66 7. References.....................................................7 67 7.1. Normative References......................................7 68 7.2. Informative References....................................7 69 8. Acknowledgments................................................7 71 1. Introduction 73 The draft proposes methods for routers to announce Flex-Algorithm specific 74 Adjacency-SID with minimal advertisement in IGP. When the other routers need a SR 75 policy (aka SR-TE) or TI-LFA path, the Flex-Algorithm specific Adjacency-SID would 76 be taken into the path label construction. 78 Hence, the top most label, either node or link related, in a SR policy stack would 79 be used to identify a certain Flex-Algo with full identification. 81 2. Conventions used in this document 83 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", 84 "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be 85 interpreted as described in RFC 2119 [RFC2119]. 87 In this document, these words will appear with that interpretation only when in ALL 88 CAPS. Lower case uses of these words are not to be interpreted as carrying 89 significance described in RFC 2119. 91 3. ISIS extension 93 With reference to RFC8667, the information could be advertised in SR-Capabilities 94 sub-TLV in Section 3. 96 3.1. Algorithm Offset for Adj-SID 98 0 1 2 3 99 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 1 100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 101 | Type | Length | Flags | Algorithm | 102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 103 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 104 | SID/Label | Base offset/Index offset (variable) ~ 105 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 108 ~ Flags/ Algo/ Base offset/ Index offset ~ 109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 111 where: 113 Type: TDB 115 Length: variable; multiple advertisements 117 Flags: 1 octet field of the following flags: 119 0 1 2 3 4 5 6 7 120 +-+-+-+-+-+-+-+-+ 121 | |B|V|L| | 122 +-+-+-+-+-+-+-+-+ 124 where: 126 B-Flag: Backup Flag. If set, the Adj-SID is eligible 127 for protection (e.g., using IP Fast Reroute 128 (IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as 129 described in [RFC8402]. 131 V-Flag: Value Flag. If set, then it carries 132 a label value. If not set, it is an index value. 134 L-Flag: Local Flag. Always set to 1 136 Algorithm: 1 octet 137 Flex-Algo value is between 128 and 255. 139 Base Offset: 3 octets 140 Local label base for Adjacency-SIDs for given Flex- 141 Algorithm. The derived Adjacency-SID is the sum of the base 142 offset and the Algo 0 label 144 Index Offset: 4 octets 145 If Adjacency-SID is advertised as index, this provides an 146 offset index value. The new label is sum of (SRGB base + 147 index + index offset) 149 The format of Base Offset and Index Offset is the same as RFC8667. The choice of 150 advertising Base Offset or Index Offset must match the advertisement of original 151 Adjacency-SID method from the same router. 153 3.2. Algorithm Offset for LAN based Adj-SID 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 1 157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 158 | Type | Length | Flags | Algorithm | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 161 | Neighbor System-ID (ID length octets) | 162 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 163 | | 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 166 | SID/Label Base Offset/Index Offset (variable) ~ 167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 ~ Flags/ Algo/NB Sys-ID/ SID/Label/Index Offset (variable) ~ 170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 172 where: 174 Type: TDB 176 Length: variable; multiple advertisements 178 Flags: 1 octet field of the following flags: 180 0 1 2 3 4 5 6 7 181 +-+-+-+-+-+-+-+-+ 182 | |B|V|L| | 183 +-+-+-+-+-+-+-+-+ 185 where: 187 B-Flag: Backup Flag. If set, the Adj-SID is eligible 188 for protection (e.g., using IP Fast Reroute 189 (IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as 190 described in [RFC8402]. 192 V-Flag: Value Flag. If set, then it carries 193 a label value. If not set, it is an index value. 195 L-Flag: Local Flag. Always set to 1 197 Algorithm: 1 octet. Same as Section 5.1 198 Neighbor System-ID: IS-IS System-ID of length "ID Length" as 199 defined in [ISO10589]. 201 Base Offset: 3 octets. Same as Section 5.1 203 Index Offset: 4 octets. Same as Section 5.1 205 3.3. Algorithm Offset for Prefix SID 207 Prefix-SID for Algorithm could also be generated by adding an index offset value or 208 a base offset for label. 210 This advertisement is an sub-TLV in RFC8667 Section 2. 212 0 1 2 3 213 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 1 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 | Type | Length | Flags | Algorithm | 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 218 | SID/Label Base offset/ Index offset ~ 219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 ~ Flags/ Algorithm/ Base Offset/ Index offset ~ 222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 224 Type: TDB 226 Length: variable 228 Flags: 1 octet field of the following flags: 230 0 1 2 3 4 5 6 7 231 +-+-+-+-+-+-+-+-+ 232 |R|N| |V|L| | 233 +-+-+-+-+-+-+-+-+ 235 where: 237 R-Flag: Re-advertisement Flag. If set, then the prefix 238 to which this Prefix-SID is attached has been 239 propagated by the router from either another 240 level (i.e., from Level-1 to Level-2 or the 241 opposite) or redistribution (e.g., from another 242 protocol). 244 N-Flag: Node-SID Flag. If set, then the Prefix-SID 245 refers to the router identified by the prefix. 246 Typically, the N-Flag is set on Prefix-SIDs that 247 are attached to a router loopback address. The 248 N-Flag is set when the Prefix-SID is a Node-SID 249 as described in [RFC8402]. 251 V-Flag: Value Flag. If set, then it carries 252 a label value. If not set, it is an index value. 254 L-Flag: Local Flag. Always set to 0 256 Algorithm: 1 octet 257 Flex-Algo value is between 128 and 255 259 Base offset: 3 octets 260 Label base for Prefix-SIDs for given Algorithm 261 The derived Prefix-SID is the sum of the base 262 Offset and the Algo 0 label 264 Index Offset: 4 octets 265 Index offset counting from Algo 0 266 The new label for Prefix is sum of (SRGB base + 267 index + index offset) 269 The format of Base offset and Index Offset is the same as RFC8667. The choice of 270 advertising Base Offset or Index Offset MUST match the advertisement of original 271 Prefix-SID method from the same router. 273 4. Compatibility 275 For nodes that do not support Algorithm Offset for Adj-SID extension, the label 276 stack could use normal Adj-SID, providing that the node still supports Flex-Algo 277 Prefix SID. 279 For TI-LFA, there would be two modes of operation - loose or strict. For strict 280 mode, all Adj-SID involved in TI-LFA candidate path must be derived with offset 281 method. 283 For loose mode, Adj-SID in the TI-LFA candidate path could be a mix of Adj-SID's 284 with and without offset. This allows backward compatibility with routers which only 285 support Flex-Algo. 287 5. OSPF extension 289 TBD 291 6. Security Consideration 293 TBD 295 7. References 297 7.1. Normative References 299 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", 300 BCP 14, RFC 2119, March 1997. 302 7.2. Informative References 304 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 305 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 306 Extensions for Segment Routing", RFC 8667, 307 DOI 10.17487/RFC8667, December 2019, 308 . 310 [TI-LFA] Litkowski, S., Bashandy, A., Filsfils, C., Francois, P., 311 Decraene, B., and D. Voyer, "Topology Independent Fast 312 Reroute using Segment Routing", 313 316 [FLEXAGLO] S. Hegde, P. Psenak and etc, IGP Flexible Algorithm 317 https://datatracker.ietf.org/doc/draft-ietf-lsr-flex-algo 319 [ISO10589] International Organization for Standardization, 320 "Information technology -- Telecommunications and 321 information exchange between systems -- Intermediate 322 system to Intermediate system intra-domain routeing 323 information exchange protocol for use in conjunction with 324 the protocol for providing the connectionless-mode network 325 service (ISO 8473)", ISO/IEC 10589:2002, Second Edition, 326 November 2002. 328 8. Acknowledgments 330 The following people have contributed to this document: 331 Shraddha Hegde, Juniper Networks 333 Author Address 335 Louis Chan 336 Juniper Networks 337 2604, Cityplaza One, 1111 King's Road 338 Taikoo Shing 339 Hong Kong 341 Phone: +852-25876659 342 Email: louisc@juniper.net 344 Krzysztof Grzegorz Szarkowicz 345 Juniper Networks 346 Parkring 10 347 A-1010 Wien 348 Austria 350 Phone: +49 89 203012127 351 Email: kszarkowicz@juniper.net