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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-26) exists of draft-ietf-lsr-flex-algo-18 == Outdated reference: A later version (-17) exists of draft-ietf-lsr-ip-flexalgo-04 -- No information found for draft-cheng-lsr-flex-algo-metric - is the name correct? Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group L. Gong 2 Internet Draft W. Cheng 3 Intended status: Standards Track China Mobile 4 Expires: October 8, 2022 C. Lin 5 M. Chen 6 New H3C Technologies 7 R. Chen 8 ZTE Corporation 9 April 8, 2022 11 Advertising Exclusive Links for Flex-Algorithm in IGP 12 draft-gong-lsr-exclusive-link-for-flex-algo-00 14 Abstract 16 This document proposes a method to advertise exclusive links for 17 Flex-Algorithm in IGP. 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), its areas, and its working groups. Note that 26 other groups may also distribute working documents as Internet- 27 Drafts. 29 Internet-Drafts are draft documents valid for a maximum of six 30 months and may be updated, replaced, or obsoleted by other documents 31 at any time. It is inappropriate to use Internet-Drafts as 32 reference material or to cite them other than as "work in progress." 34 The list of current Internet-Drafts can be accessed at 35 http://www.ietf.org/ietf/1id-abstracts.txt 37 The list of Internet-Draft Shadow Directories can be accessed at 38 http://www.ietf.org/shadow.html 40 This Internet-Draft will expire on February 1, 2022. 42 Copyright Notice 44 Copyright (c) 2022 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 52 respect to this document. Code Components extracted from this 53 document must include Simplified BSD License text as described in 54 Section 4.e of the Trust Legal Provisions and are provided without 55 warranty as described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction ................................................ 2 60 1.1. Requirements Language .................................. 2 61 2. Problem Statement ........................................... 3 62 3. New Extension to Prune Links ................................ 3 63 4. Backward Compatibility Method in IS-IS ...................... 5 64 5. Security Considerations ..................................... 5 65 6. IANA Considerations ......................................... 5 66 7. References .................................................. 5 67 7.1. Normative References ................................... 5 68 7.2. Informative References ................................. 5 69 8. Acknowledgments ............................................. 6 70 Authors' Addresses ............................................. 7 72 1. Introduction 74 Flexible Algorithm (Flex-Algorithm) allows IGP to compute 75 constraint-based paths. [I-D.ietf-lsr-flex-algo] specifies the usage 76 of Flex-Algorithm in Segment Routing (SR) data planes - SR MPLS and 77 SRv6. [I-D.ietf-lsr-ip-flexalgo] extends the Flex-Algorithm for 78 native IPv4 and IPv6 data planes. 80 In some scenarios, exclusive links may be deployed for Flex- 81 Algorithm, but not for best-effort service. However, these links 82 cannot be pruned in normal SPF calculation, and unexpected flows may 83 be steered into these links. 85 This document proposes a method to advertise exclusive links for 86 Flex-Algorithm in IGP. 88 1.1. Requirements Language 90 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 91 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 92 "OPTIONAL" in this document are to be interpreted as described in 93 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 94 capitals, as shown here. 96 2. Problem Statement 98 Flex-Algorithm allows IGP to compute the best paths along the 99 constrained topology. 101 A network topology is shown in Figure 1. Node A, B, C and D have an 102 extra link between each other. These links have EAG attribute of 103 "red" color. 105 Flex-Algorithm 128 are enable on Node A, B, C and D, with metric- 106 type of IGP cost and EAG rule of including "red". The topology used 107 by Flex-Algorithm 128 is shown in Figure 2. 109 Flex-Algorithm 128 are used to transmit particular flows, such as 110 network slice. The links used by Flex-Algorithm 128 are sub- 111 interfaces with dedicated queues for bandwidth guarantee. So it is 112 expected that only the particular flows are transmitted on these 113 links using Flex-Algorithm 128. However, these links are also 114 contained in the default topology used by normal SPF calculation, 115 and unexpected flows of best-effort service may be steered into 116 these links. Therefore, it is a problem that exclusive links for 117 Flex-Algorithm cannot be pruned in normal SPF calculation. 119 A======C------E 120 || || | 121 || || | 122 || || | 123 B======D------F 125 Figure 1 127 A------C 128 | | 129 | | 130 | | 131 B------D 133 Figure 2 135 3. New Extension to Prune Links 137 A new Link Flags sub-TLV is defined in IS-IS. The format is as the 138 following: 140 0 1 2 3 141 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 1 142 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 143 | Type | Length | 144 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 145 | Flags ~ 146 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 148 o Type: TBD. 150 o Length: Variable, dependent on the size of the Flags field. MUST 151 be a multiple of 4 octets. 153 o Flags: Following flags are currently defined. 155 0 1 2 3 4 5 6 7 156 +-+-+-+-+-+-+-+-+ 157 |P| ~ 158 +-+-+-+-+-+-+-+-+ 160 o P-Flag: Pruning the link during SPF calculation. 162 The Link Flags sub-TLV is advertised in the TLVs/sub-TLVs below: 164 o TLV-22 (Extended IS reachability) [RFC5305] 166 o TLV-222 (MT-ISN) [RFC5120] 168 o TLV-23 (IS Neighbor Attribute) [RFC5311] 170 o TLV-223 (MT IS Neighbor Attribute) [RFC5311] 172 The Link Flags sub-TLV with P-Flag can be advertised for the 173 exclusive links used by Flex-Algorithm, so that these links will be 174 pruned during normal SPF calculation. 176 When using the Link Flags sub-TLV, all nodes in the same area or 177 level must support this sub-TLV. Otherwise routing loops may be 178 caused by topology inconsistences. 180 Relevant extensions for OSPF will be included in the future version 181 of this draft. 183 4. Backward Compatibility Method in IS-IS 185 As specified in [RFC5305], if a link is advertised with the maximum 186 link metric (2^24 - 1), this link MUST NOT be considered during the 187 normal SPF computation in IS-IS. 189 Instead of advertising the Link Flags sub-TLV in Section 3, the 190 metrics of exclusive links for Flex-Algorithm may be advertised by 191 the value of (2^24 - 1). It can also lead to the pruning of these 192 links in normal SPF computation. 194 If the associated Flex-Algorithm needs to use IGP-Cost as its 195 metric-type in path calculation, the Flex-Algorithm-associated 196 Generic Metric sub-TLV defined in [I-D.cheng-lsr-flex-algo-metric] 197 can be advertised to carry the actual value. 199 5. Security Considerations 201 TBD 203 6. IANA Considerations 205 Link Flags sub-TLV (TBD) 207 7. References 209 7.1. Normative References 211 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 212 Requirement Levels", BCP 14, RFC 2119, March 1997. 214 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 215 2119 Key Words", BCP 14, RFC 8174, May 2017 217 [I-D.ietf-lsr-flex-algo] Psenak, P., Hegde, S., Filsfils, C., 218 Talaulikar, K., and A. Gulko, "IGP Flexible Algorithm", 219 draft-ietf-lsr-flex-algo-18 (work in progress), October 220 2021. 222 7.2. Informative References 224 [I-D.ietf-lsr-ip-flexalgo] Britto, W., Hegde, S., Kaneriya, P., 225 Shetty, R., Bonica, R., and P. Psenak, "IGP Flexible 226 Algorithms (Flex- Algorithm) In IP Networks", draft-ietf- 227 lsr-ip-flexalgo-04 (work in progress), December 2021. 229 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 230 Topology (MT) Routing in Intermediate System to 231 Intermediate Systems (IS-ISs)", RFC 5120, DOI 232 10.17487/RFC5120, February 2008, . 235 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 236 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 237 2008, . 239 [RFC5311] McPherson, D., Ed., Ginsberg, L., Previdi, S., and M. 240 Shand, "Simplified Extension of Link State PDU (LSP) Space 241 for IS-IS", RFC 5311, DOI 10.17487/RFC5311, February 2009, 242 . 244 [I-D.cheng-lsr-flex-algo-metric] Cheng, W, "Advertisement of 245 Dedicated Metric for Flexible Algorithm in IGP", draft- 246 cheng-lsr-flex-algo-metric-00 (work in progress), February 247 2022. 249 8. Acknowledgments 251 The authors would like to thank the following for their valuable 252 contributions of this document: 254 TBD 256 Authors' Addresses 258 Liyan Gong 259 China Mobile 261 Email: gongliyan@chinamobile.com 263 Weiqiang Cheng 264 China Mobile 266 Email: chengweiqiang@chinamobile.com 268 Changwang Lin 269 New H3C Technologies 271 Email: linchangwang.04414@h3c.com 273 Mengxiao Chen 274 New H3C Technologies 276 Email: chen.mengxiao@h3c.com 278 Ran  Chen 279 ZTE Corporation  281 Email: chen.ran@zte.com.cn