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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group K. Zhang 3 Internet-Draft J. Dong 4 Intended status: Informational Huawei 5 Expires: 6 September 2022 5 March 2022 7 BGP SR Policy Extensions for metric 8 draft-zhang-idr-sr-policy-metric-00 10 Abstract 12 SR Policy candidate paths can be represented in BGP UPDATE messages. 13 BGP can then be used to propagate the SR Policy candidate paths to 14 the headend nodes in the network. After SR Policy is installed on 15 the ingress node, the packets can be steered into SR Policy through 16 route selection. Therefore, route selection may be performed on the 17 ingress node of the SR Policy. If there are multiple routes to the 18 same destination, the route selection node can select routes based on 19 the local policy. The local policy may use the IGP metric of the 20 selected path, which is the IGP Metric of the SR Policy. Thus the 21 BGP UPDATE message need carry the metric of each segment list of the 22 SR Policy Candidate Path, which can be used in path selection of 23 routing. 25 Requirements Language 27 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 28 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 29 document are to be interpreted as described in BCP 14 [RFC2119] 30 [RFC8174] when, and only when, they appear in all capitals, as shown 31 here. 33 Status of This Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at https://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on 6 September 2022. 50 Copyright Notice 52 Copyright (c) 2022 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 57 license-info) in effect on the date of publication of this document. 58 Please review these documents carefully, as they describe your rights 59 and restrictions with respect to this document. Code Components 60 extracted from this document must include Revised BSD License text as 61 described in Section 4.e of the Trust Legal Provisions and are 62 provided without warranty as described in the Revised BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 68 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 69 4. SR Policy and Tunnel Encapsulation Attribute Update . . . . . 3 70 4.1. Metric sub-TLV . . . . . . . . . . . . . . . . . . . . . 4 71 5. Metric process of SR Policy segment list . . . . . . . . . . 5 72 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 73 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 74 8. Security Considerations . . . . . . . . . . . . . . . . . . . 5 75 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 78 1. Introduction 80 [I-D.ietf-idr-segment-routing-te-policy]defines SR Policy and Tunnel 81 Encapsulation Attributes. It defines the segment list of the SR 82 policies. Each segment list of an SR Policy is an segment routing 83 path, which may be calculated by path compuation element and 84 delivered to the head node of the device by BGP Update Message. On 85 the ingress node, when steer traffic to an SR Policy, the ingress 86 node may need to select between multiple SR Policy paths. And the 87 selection policy may need the path metric information. Therefore, 88 BGP needs to carry the metric of each path when delivering the 89 semgnet list of the SR Policy through Update messages to facilitate 90 route selection on the device. 92 2. Terminology 94 The following terminology is used in this document. 96 SR Policy: An ordered list of segments. 98 Candidate Path: the unit for signaling of an SR Policy to a headend 99 via protocol extensions like Path Computation Element (PCE) 100 Communication Protocol (PCEP) [RFC8664] 101 [I-D.ietf-pce-segment-routing-policy-cp] or BGP SR Policy 102 [I-D.ietf-idr-segment-routing-te-policy]. 104 SRPM: SR Policy Module. 106 3. Motivation 108 In route selection scenarios, the metric of the SR Policy segment 109 list may be required. 111 The specific scenarios are as follows: 113 +--+ +--+ +---+ 114 _ _ _ _ _|P1|_ _ _ _ _|P2|_ _ _ _ _|PE2|_ _ _ _ 115 | +--+ +--+ +---+ | 116 | | 117 +---+ +---+ +---+ 118 |CE1|_ _ _ _ |PE1| |CE1| 119 +---+ +---+ +---+ 120 | +--+ +--+ +---+ | 121 |_ _ _ _ _|P3|_ _ _ _ _|P4|_ _ _ _ _|PE3|_ _ _ _| 122 +--+ +--+ +---+ 124 On PE1, the route prefix to CE1 has two diffierent next hop, PE2 and 125 PE3. The next hop to PE1 uses an SR Policy1 on PE1, the endpoint of 126 SR Policy1 is PE2. The next hop to PE2 uses an SR Policy2 on PE1, 127 the endpoint of SR Policy2 is PE3. The prefix to CE1 want to choose 128 a next hop based on the IGP metric of the route PE1 to PE2 and PE1 129 and PE3, which uses SR Policy1 and SR Policy2. Thus need the IGP 130 metric of SR Policy semgent list on PE1. 132 4. SR Policy and Tunnel Encapsulation Attribute Update 134 As the metric is defined, the tunnel attribute encapsulation of the 135 BGP SR Policy needs to be updated. 137 The SR Policy Encoding structure is as follows: 139 SR Policy SAFI NLRI: 140 Attributes: 142 Tunnel Encaps Attribute (23) 144 Tunnel Type: SR Policy 146 Binding SID 148 Preference 150 Priority 152 Policy Name 154 Policy Candidate Path Name 156 Explicit NULL Label Policy (ENLP) 158 Segment List 160 Weight 162 Metric 164 Segment 166 Segment 168 .... 170 .... 172 Where metric indicates the metric for the segment list. 174 4.1. Metric sub-TLV 176 A new sub-TLV called Metric sub-TLV is defined. Metric sub-TLV 177 specifies the metric of an SR policy segment list. Each sub-TLV is 178 encoded as shown in Figure 1. 180 0 1 2 3 181 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 | Type | Length | Metric Type | Flags | 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 | Metric Vlaue(4 octets) | 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 Figure 1: Figure 1: Metric Sub-TLV 189 Type: Metric, 1 octet, TBD. 191 Length: 6. 193 Metric Type: 1 octet. The Type of metric, can be IGP metric, TE 194 metric, delay, ect. 196 Flags: 1 octet of flags. None are defined at this stage. Flags 197 SHOULD be set to zero on transmission and MUST be ignored on receipt. 199 Metric Value: a 4-octet value. 201 5. Metric process of SR Policy segment list 203 When SR Policy headend get the SR Policy segment list with metric, 204 how to process the metric is local policy. 206 The active candidate path of SR Policy may have several segment 207 lists, each segment list have different metric. It is recommended 208 that the segment lists in one candidate path have the same metric 209 type. If the metric value of segment lists in one candidate path is 210 different, the candidate path metric can use the minimum value as the 211 metric of candidate path. And the SR Policy metric use the metric 212 value of active candidate path. 214 6. Acknowledgements 216 TBD. 218 7. IANA Considerations 220 This document requests that IANA allocates a new sub-TLV type as 221 defined in Section 4.1 from the "Sub-TLVs for SR Policy" registry as 222 specified. 224 Value Description Reference 225 ---------------------- ---------------------------- -------------- 226 TBD Metric This document 228 Figure 2: Figure 2: Template ID sub-TLV 230 8. Security Considerations 232 These extensions to BGP SR Policy do not add any new security issues 233 to the existing protocol. 235 9. References 237 [I-D.ietf-idr-segment-routing-te-policy] 238 Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., 239 Jain, D., and S. Lin, "Advertising Segment Routing 240 Policies in BGP", Work in Progress, Internet-Draft, draft- 241 ietf-idr-segment-routing-te-policy-14, 10 November 2021, 242 . 245 [I-D.ietf-pce-segment-routing-policy-cp] 246 Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H. 247 Bidgoli, "PCEP extension to support Segment Routing Policy 248 Candidate Paths", Work in Progress, Internet-Draft, draft- 249 ietf-pce-segment-routing-policy-cp-06, 22 October 2021, 250 . 253 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 254 Requirement Levels", BCP 14, RFC 2119, 255 DOI 10.17487/RFC2119, March 1997, 256 . 258 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 259 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 260 May 2017, . 262 [RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 263 and J. Hardwick, "Path Computation Element Communication 264 Protocol (PCEP) Extensions for Segment Routing", RFC 8664, 265 DOI 10.17487/RFC8664, December 2019, 266 . 268 Authors' Addresses 270 Ka Zhang 271 Huawei 272 Huawei Bld., No.156 Beiqing Rd. 273 Beijing 274 100095 275 China 276 Email: zhangka@huawei.com 277 Jie Dong 278 Huawei 279 Huawei Bld., No.156 Beiqing Rd. 280 Beijing 281 100095 282 China 283 Email: dongjie@huawei.com