Network Working Group H. Li Internet-Draft M. Chen Intended status: Standards Track C. Lin Expires: 1 March 2024 New H3C Technologies W. Jiang W. Cheng China Mobile 29 August 2023 BGP Extensions of SR Policy for Composite Candidate Path draft-li-idr-sr-policy-composite-path-05 Abstract Segment Routing is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node. An SR Policy is associated with one or more candidate paths. A candidate path is either dynamic, explicit or composite. This document defines extensions to BGP to distribute SR policies carrying composite candidate path information. So that composite candidate paths can be installed when the SR policy is applied. 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." This Internet-Draft will expire on 1 March 2024. 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. Li, et al. Expires 1 March 2024 [Page 1] Internet-Draft BGP SR Policy Composite Candidate Path August 2023 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Constituent SR Policy Attributes in SR Policy . . . . . . . . 3 3.1. Constituent SR Policy Sub-TLV . . . . . . . . . . . . . . 4 4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction Segment routing (SR) [RFC8402] is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node. The ingress node steers packets into a specific path according to the Segment Routing Policy (SR Policy) as defined in [RFC9256]. In order to distribute SR policies to the headend, [I-D.ietf-idr-segment-routing-te-policy] specifies a mechanism by using BGP. An SR Policy is associated with one or more candidate paths. A composite candidate path acts as a container for grouping of SR Policies. As described in section 2.2 in [RFC9256], the composite candidate path construct enables combination of SR Policies, each with explicit candidate paths and/or dynamic candidate paths with potentially different optimization objectives and constraints, for a load-balanced steering of packet flows over its constituent SR Policies. [I-D.draft-jiang-spring-parent-sr-policy-use-cases] describes some use cases for SR policy group composite candidate path. This document defines extensions to Border Gateway Protocol (BGP) to distribute SR policies carrying composite candidate path information. So that composite candidate paths can be installed when the SR policy is applied. Li, et al. Expires 1 March 2024 [Page 2] Internet-Draft BGP SR Policy Composite Candidate Path August 2023 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "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. 3. Constituent SR Policy Attributes in SR Policy As defined in [I-D.ietf-idr-segment-routing-te-policy], the SR policy encoding structure is as follows: SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID SRv6 Binding SID Preference Priority Policy Name Policy Candidate Path Name Explicit NULL Label Policy (ENLP) Segment List Weight Segment Segment ... ... As described in section 2.2 in [RFC9256], the endpoints of the constituent SR Policies and the parent SR Policy MUST be identical, and the colors of each of the constituent SR Policies and the parent SR Policy MUST be different. Therefore a constituent SR Policy is referenced only by color in the composite candidate path since its headend and endpoint are identical to the parent SR policy. SR policy with composite candidate path information is expressed as below: Li, et al. Expires 1 March 2024 [Page 3] Internet-Draft BGP SR Policy Composite Candidate Path August 2023 SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID SRv6 Binding SID Preference Priority Policy Name Policy Candidate Path Name Explicit NULL Label Policy (ENLP) Segment List Weight Segment Segment ... Constituent SR Policy Weight ... 3.1. Constituent SR Policy Sub-TLV The Constituent SR Policy sub-TLV encodes a single composite path towards the endpoint. The Constituent SR Policy sub-TLV is an optional sub-TLV of BGP Tunnel Encapsulation Attribute, and MAY appear multiple times in the SR Policy encoding. The ordering of Constituent SR Policy sub-TLVs does not matter. The Constituent SR Policy sub-TLV MAY contain a Weight sub-TLV. Since a candidate path is either dynamic, explicit or composite, the Constituent SR Policy sub-TLV and the Segment List sub-TLV SHOULD NOT appear in the same candidate path. The Constituent SR Policy sub-TLV has the following format: 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Color | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-TLVs | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: * Type: to be assigned by IANA. Li, et al. Expires 1 March 2024 [Page 4] Internet-Draft BGP SR Policy Composite Candidate Path August 2023 * Length: the total length of the value field not including Type and Length fields. * RESERVED: 2 octet of reserved bits. SHOULD be set to zero on transmission and MUST be ignored on receipt. * Color: 4-octet value identifying the constituent SR policy. * sub-TLVs currently defined: - An optional single Weight sub-TLV which is defined in section 2.4.4.1 in [I-D.ietf-idr-segment-routing-te-policy]. According to [RFC9256], the fraction of flows steered into each constituent SR Policy is equal to the relative weight of each constituent SR Policy. 4. Operations The document does not bring new operation beyond the description of operations defined in [I-D.ietf-idr-segment-routing-te-policy]. The existing operations defined in [I-D.ietf-idr-segment-routing-te-policy] can apply to this document directly. Typically but not limit to, the SR policies carrying composite candidate path information are configured by a controller. After configuration, the SR policies carrying path composite candidate path information will be advertised by BGP update messages. The operation of advertisement is the same as defined in [I-D.ietf-idr-segment-routing-te-policy], as well as the receiption. 5. Security Considerations Procedures and protocol extensions defined in this document do not affect the security considerations discussed in [I-D.ietf-idr-segment-routing-te-policy]. 6. IANA Considerations This document defines a new Sub-TLV in registries "SR Policy List Sub-TLVs" [I-D.ietf-idr-segment-routing-te-policy]: Li, et al. Expires 1 March 2024 [Page 5] Internet-Draft BGP SR Policy Composite Candidate Path August 2023 +=======+===============================+===============+ | Value | Description | Reference | +=======+===============================+===============+ | TBA | Constituent SR Policy Sub-TLV | This document | +-------+-------------------------------+---------------+ Table 1 7. References 7.1. Normative References [I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., Rosen, E., Jain, D., and S. Lin, "Advertising Segment Routing Policies in BGP", Work in Progress, Internet- Draft, draft-ietf-idr-segment-routing-te-policy-23, 25 July 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, . [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, . 7.2. Informative References [I-D.draft-jiang-spring-parent-sr-policy-use-cases] Jiang, W., Cheng, W., Lin, C., and Y. Qiu, "Use Cases for Parent SR Policy", Work in Progress, Internet-Draft, draft-jiang-spring-parent-sr-policy-use-cases-02, 8 July 2023, . [RFC9256] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, July 2022, . Li, et al. Expires 1 March 2024 [Page 6] Internet-Draft BGP SR Policy Composite Candidate Path August 2023 Authors' Addresses Hao Li New H3C Technologies Email: lihao@h3c.com Mengxiao Chen New H3C Technologies Email: chen.mengxiao@h3c.com Changwang Lin New H3C Technologies Email: linchangwang.04414@h3c.com Wenying Jiang China Mobile Email: jiangwenying@chinamobile.com Weiqiang Cheng China Mobile Email: chengweiqiang@chinamobile.com Li, et al. Expires 1 March 2024 [Page 7]