Network Working Group K. Zhang Internet-Draft J. Dong Intended status: Standards Track Huawei Expires: 14 September 2023 K. Talaulikar Cisco Systems 13 March 2023 BGP SR Policy Extensions for metric draft-zhang-idr-sr-policy-metric-04 Abstract SR Policy candidate paths can be represented in BGP UPDATE messages. BGP can then be used to propagate the SR Policy candidate paths to the headend nodes in the network. After SR Policy is installed on the ingress node, the packets can be steered into SR Policy through route selection. Therefore, route selection may be performed on the ingress node of the SR Policy. If there are multiple routes to the same destination, the route selection node can select routes based on the local policy. The local policy may use the IGP metric of the selected path, which is the IGP Metric of the SR Policy. Thus the BGP UPDATE message need carry the metric of each segment list of the SR Policy Candidate Path, which can be used in path selection of routing. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." Zhang, et al. Expires 14 September 2023 [Page 1] Internet-Draft BGP SR Policy Extensions for metric March 2023 This Internet-Draft will expire on 14 September 2023. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. SR Policy and Tunnel Encapsulation Attribute Update . . . . . 3 4.1. Metric sub-TLV . . . . . . . . . . . . . . . . . . . . . 4 5. Metric process of SR Policy segment list . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction [I-D.ietf-idr-segment-routing-te-policy]defines SR Policy and Tunnel Encapsulation Attributes. It defines the segment list of the SR policies. Each segment list of an SR Policy is an segment routing path, which may be calculated by path compuation element and delivered to the head node of the device by BGP Update Message. On the ingress node, when steer traffic to an SR Policy, the ingress node may need to select between multiple SR Policy paths. And the selection policy may need the path metric information. Therefore, BGP needs to carry the metric of each path when delivering the semgnet list of the SR Policy through Update messages to facilitate route selection on the device. 2. Terminology The following terminology is used in this document. Zhang, et al. Expires 14 September 2023 [Page 2] Internet-Draft BGP SR Policy Extensions for metric March 2023 SR Policy: An ordered list of segments. Candidate Path: the unit for signaling of an SR Policy to a headend via protocol PCEP or BGP, which is defined in [I-D.ietf-pce-segment-routing-policy-cp] and [I-D.ietf-idr-segment-routing-te-policy]. SRPM: SR Policy Module. 3. Motivation In route selection scenarios, the metric of the SR Policy segment list may be required. The specific scenarios are as follows: +--+ +--+ +---+ _ _ _ _ _|P1|_ _ _ _ _|P2|_ _ _ _ _|PE2|_ _ _ _ | +--+ +--+ +---+ | | | +---+ +---+ +---+ |CE1|_ _ _ _ |PE1| |CE1| +---+ +---+ +---+ | +--+ +--+ +---+ | |_ _ _ _ _|P3|_ _ _ _ _|P4|_ _ _ _ _|PE3|_ _ _ _| +--+ +--+ +---+ On PE1, the route prefix to CE1 has two diffierent next hop, PE2 and PE3. The next hop to PE1 uses an SR Policy1 on PE1, the endpoint of SR Policy1 is PE2. The next hop to PE2 uses an SR Policy2 on PE1, the endpoint of SR Policy2 is PE3. The prefix to CE1 want to choose a next hop based on the IGP metric of the route PE1 to PE2 and PE1 and PE3, which uses SR Policy1 and SR Policy2. Thus need the IGP metric of SR Policy semgent list on PE1. 4. SR Policy and Tunnel Encapsulation Attribute Update As the metric is defined, the tunnel attribute encapsulation of the BGP SR Policy needs to be updated. The SR Policy Encoding structure is as follows: SR Policy SAFI NLRI: Zhang, et al. Expires 14 September 2023 [Page 3] Internet-Draft BGP SR Policy Extensions for metric March 2023 Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Priority Policy Name Policy Candidate Path Name Explicit NULL Label Policy (ENLP) Segment List Weight Metric Segment Segment .... .... Where metric indicates the metric for the segment list. 4.1. Metric sub-TLV A new sub-TLV called Metric sub-TLV is defined. Metric sub-TLV specifies the metric of an SR policy Segment List. Each sub-TLV is encoded as shown in Figure 1. More than one Metric Sub-TLVs may be present in one Segment List to refer to the metric values of different metric type. Zhang, et al. Expires 14 September 2023 [Page 4] Internet-Draft BGP SR Policy Extensions for metric March 2023 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Metric Type | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Metric Sub-TLV * Type: Metric, 1 octet, TBD. * Length: 6 octets. * Metric Type: 1-octet field which identifies the type of the metric being used. The metric type code points are listed as follows. The "Metric Type" code point is the same as the SR Segment List Metric Sub-TLV "Metric Type" defined in [I-D.ietf-idr-bgp-ls-sr-policy], and can re-use the IANA registry of it. +------------+------------------------------------------+ | Code Point | Metric Type | +------------+------------------------------------------+ | 0 | IGP Metric | | 1 | Min Unidirectional Link Delay [RFC7471] | | 2 | TE Metric [RFC3630] | | 3 | Hop Count (refer [RFC5440]) | | 4 | SID List Length | | 5-250 | Unassigned | | 251-255 | Private Use (not to be assigned by IANA) | +------------+------------------------------------------+ Figure 2: Metric Type Code Point * Flags: None are defined at this stage. Flags SHOULD be set to zero on transmission and MUST be ignored on receipt. * Metric Value: 4-octet value which indicates the metric of the computed path. 5. Metric process of SR Policy segment list When SR Policy headend get the SR Policy segment list with metric, how to process the metric is local policy. Zhang, et al. Expires 14 September 2023 [Page 5] Internet-Draft BGP SR Policy Extensions for metric March 2023 The active candidate path of SR Policy may have several segment lists, each segment list may have different metric type and value. The candidate path can choose one metric type to use. If the metric value of the Segment Lists in the candidate path is different, the candidate path can use the maximum value as the metric of candidate path. And the SR Policy can use the metric type and metric value of the active candidate path. 6. Acknowledgements TBD. 7. IANA Considerations This document defines a new Sub-TLV in requests registries "SR Policy List Sub- TLVs" [I-D.ietf-idr-segment-routing-te-policy]: Value Description Reference ---------------------- ---------------------------- -------------- TBD Metric This document Figure 3: Metric sub-TLV 8. Security Considerations These extensions to BGP SR Policy do not add any new security issues to the existing protocol. 9. References [I-D.ietf-idr-bgp-ls-sr-policy] Previdi, S., Talaulikar, K., Dong, J., Gredler, H., and J. Tantsura, "Advertisement of Segment Routing Policies using BGP Link-State", Work in Progress, Internet-Draft, draft- ietf-idr-bgp-ls-sr-policy-00, 9 March 2023, . [I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., Jain, D., and S. Lin, "Advertising Segment Routing Policies in BGP", Work in Progress, Internet-Draft, draft- ietf-idr-segment-routing-te-policy-20, 27 July 2022, . Zhang, et al. Expires 14 September 2023 [Page 6] Internet-Draft BGP SR Policy Extensions for metric March 2023 [I-D.ietf-pce-segment-routing-policy-cp] Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H. Bidgoli, "PCEP extension to support Segment Routing Policy Candidate Paths", Work in Progress, Internet-Draft, draft- ietf-pce-segment-routing-policy-cp-09, 7 March 2023, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Authors' Addresses Ka Zhang Huawei Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: zhangka@huawei.com Jie Dong Huawei Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: dongjie@huawei.com Ketan Talaulikar Cisco Systems India Email: ketant.ietf@gmail.com Zhang, et al. Expires 14 September 2023 [Page 7]