Interdomain Routing Working Group C. Li Internet-Draft Z. Li Intended status: Standards Track Huawei Technologies Expires: 17 February 2024 Y. Zhu China Telecom W. Cheng China Mobile K. Talaulikar Cisco Systems 16 August 2023 SR Policies Extensions for Path Segment and Bidirectional Path in BGP-LS draft-ietf-idr-bgp-ls-sr-policy-path-segment-05 Abstract This document specifies the way of collecting configuration and states of SR policies carrying Path Segment and bidirectional path information by using BPG-LS. Such information can be used by external conponents for many use cases such as performance measurement, path re-optimization and end-to-end protection. 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 RFC 2119 [RFC2119]. 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 17 February 2024. Li, et al. Expires 17 February 2024 [Page 1] Internet-Draft Path ID and Bi-directional Path in BGP-L August 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Carrying SR Path Sub-TLVs in BGP-LS . . . . . . . . . . . . . 3 3.1. SR Path Segment Sub-TLV . . . . . . . . . . . . . . . . . 5 3.2. Reverse Segment List Sub-TLV . . . . . . . . . . . . . . 7 4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 5.1. BGP-LS TLVs . . . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction Segment routing (SR) [RFC8402] is a source routing paradigm that allows the ingress node steers packets into a specific path according to the Segment Routing Policy [RFC9256]. However, the SR Policies defined in [RFC9256] only supports unidirectional SR paths and there is no path ID in a Segment List to identify an SR path. For identifying an SR path and supporting bidirectional path [I-D.ietf-spring-mpls-path-segment], new policies carrying Path Segment and bidirectional path information are defined in [I-D.ietf-idr-sr-policy-path-segment], as well as the extensions to BGP to distribute new SR policies. The Path Segment can be a Path Segment in SR-MPLS [I-D.ietf-spring-mpls-path-segment] and SRv6 [I-D.ietf-spring-srv6-path-segment], or other IDs that can identify a path. Li, et al. Expires 17 February 2024 [Page 2] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 In many network scenarios, the configuration and state of each TE Policy is required by a controller which allows the network operator to optimize several functions and operations through the use of a controller aware of both topology and state information [I-D.ietf-idr-te-lsp-distribution]. To collect the TE Policy information that is locally available in a router, [I-D.ietf-idr-te-lsp-distribution] describes a new mechanism by using BGP-LS update messages. Based on the mechanism defined in [I-D.ietf-idr-te-lsp-distribution], this document describes a mechanism to distribute configuration and states of the new SR policies defined in [I-D.ietf-idr-sr-policy-path-segment] to external components using BGP-LS. 2. Terminology This memo makes use of the terms defined in [RFC8402] and [I-D.ietf-idr-te-lsp-distribution]. 3. Carrying SR Path Sub-TLVs in BGP-LS A mechanism to collect states of SR Policies via BGP-LS is proposed by [I-D.ietf-idr-te-lsp-distribution]. The characteristics of an SR policy can be described by a TE Policy State TLV, which is carried in the optional non-transitive BGP Attribute "LINK_STATE Attribute" defined in [RFC7752]. The TE Policy State TLV contains several sub- TLVs such as SR TE Policy sub-TLVs. [I-D.ietf-idr-sr-policy-path-segment] defines the BGP extensions for Path Segment. The encoding is shown below. Li, et al. Expires 17 February 2024 [Page 3] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Priority Policy Name Explicit NULL Label Policy (ENLP) Segment List Weight Path Segment Segment Segment ... Segment List Weight Path Segment Segment Segment ... ... Figure 1. Path Segment in SR policy Also, [I-D.ietf-idr-sr-policy-path-segment] defines SR policy extensions for bidirectional SR path, the encoding is shown below: Li, et al. Expires 17 February 2024 [Page 4] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Priority Policy Name Explicit NULL Label Policy (ENLP) Segment List Weight Path Segment Segment Segment ... Reverse Segment List Weight Path Segment Segment Segment ... Figure 2. SR policy for Bidirectional path In order to collect configuration and states of unidirectional and bidirectional SR policies defined in [I-D.ietf-idr-sr-policy-path-segment], this document defines new sub- TLVs in SR TE Policy sub-TLVs. 3.1. SR Path Segment Sub-TLV This section defines the SR Path Segment sub-TLV to describe a Path Segment, and it can be included in the Segment List sub-TLV as defined in [I-D.ietf-idr-te-lsp-distribution] . An SR Path Segment sub-TLV can be associated with an SR path specified by a Segment List sub-TLV. Multiple Path Segment MAY be included in a Segment List for different use cases. When all the SID Lists within a candidate path share the same Path Segment ID, the Path Segment can be used to collect the aggregated information of the candidate path. The format of Path Segment TLV is shown below. Li, et al. Expires 17 February 2024 [Page 5] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flag | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Path Segment ID (4 or 16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Sub-TLVs (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3. Path Segment sub-TLV Where, * Type: to be assigned by IANA. * Length: the total length of the value field not including Type and Length fields. * Flags: 2 octet field that indicates attribute and status of the Path Segment. The following bit positions are defined. Other bits SHOULD be cleared by originator and MUST be ignored by receiver. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |D|B| |L| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: - D-Flag : Indicates the dataplane for the BSIDs, it is set when Path Segment ID is a 16-octet SRv6 SID unset when the Path Segment ID is a 4-octet SR/MPLS label value. - B-Flag: This flag, when set, indicates the presence of the SRv6 Endpoint Behavior and SID Structure encoding specified in [I-D.ietf-idr-bgpls-srv6-ext]. It MUST be ignored when D-flag is unset. They indicate the SRv6 Endpoint behavior and SID structure for the Path Segment ID value in the TLV. - L-Flag: Local flag. Set when the Path Segment has local significance on an SR node. * RESERVED: 2 octets. SHOULD be set to 0 by originator and MUST be ignored by receiver. Li, et al. Expires 17 February 2024 [Page 6] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 * Path Segment ID: It indicates the Path Segment ID value based on the status flags. The SRv6 Endpoint Behavior TLV (1250) and the SRv6 SID Structure TLV (1252) defined in [I-D.ietf-idr-bgpls-srv6-ext] are used as sub-TLVs of the SR Path Segment Sub-TLV to optionally indicate the SRv6 Endpoint behavior and SID structure for the Binding SID value in the TLV when the Path Segment is an SRv6 Path Segment. 3.2. Reverse Segment List Sub-TLV In some scenarios like mobile backhaul transport network, there are requirements to support bidirectional path. In SR, a bidirectional path can be represented as a binding of two unidirectional SR paths [I-D.ietf-spring-mpls-path-segment]. An SR policy carrying SR bidirectional path information is expressed in Figure 2. [I-D.ietf-idr-sr-policy-path-segment] defines a new sub-TLV to describe a reversed SR path of an SID list. This section defines a Reverse Segment List sub-TLV to specify a reverse SR path associated with the path specified by the Segment List, and it reuses the format of SR Segment List TLV defined in [I-D.ietf-idr-te-lsp-distribution]: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MTID | Algorithm | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Weight (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-TLVs (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5. Reverse Segment List Sub-TLV All fields, except the type are defined in [I-D.ietf-idr-te-lsp-distribution], and this TLV reuses it directly. The Type of this TLV is TBA. Li, et al. Expires 17 February 2024 [Page 7] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 The SR Segment sub-TLV [I-D.ietf-idr-te-lsp-distribution] MUST be included as an ordered set of sub-TLVs within the SR Segment List TLV when the SID-List is not empty. A SID-List may be empty in certain cases (e.g. for a dynamic path) where the headend has not yet performed the computation and hence not derived the segments required for the path; in such cases, the SR Segment List TLV SHOULD NOT include any SR Segment sub-TLVs [I-D.ietf-idr-te-lsp-distribution]. Note: currently, only one reverse SID list is supported, so the weight field CAN be ignored when processing. However, multiple reverse SID list MAY be supported in the future, and the use case of supporting this still need to be discussed. 4. Operations The operations procedures of [RFC7752] can apply to this document. Typically but not limited to, the uni/bidirectional SR policies carrying path identification information can be distributed by the ingress node. Generally, BGP-LS is used for collecting link states and synchronizing with the external component. The consumer of the uni/ bidirectional SR policies carrying path identification information is not BGP LS process by itself, and it can be any applications such as performance measurement [I-D.gandhi-spring-udp-pm] and path re- coputation or re-optimization, etc. The operation of sending information to other precesses is out of scope of this document. 5. IANA Considerations 5.1. BGP-LS TLVs IANA maintains a registry called "Border Gateway Protocol - Link State (BGP-LS) Parameters" with a sub-registry called "Node Anchor, Link Descriptor and Link Attribute TLVs". The following TLV codepoints are suggested (for early allocation by IANA): Codepoint Description Reference ------------------------------------------------------------- TBA Path Segment sub-TLV This document TBA Reverse Segment List sub-TLV This document Li, et al. Expires 17 February 2024 [Page 8] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 6. Security Considerations TBA 7. Contributors Mach(Guoyi) Chen Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: Mach.chen@huawei.com Jie Dong Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: jie.dong@huawei.com James N Guichard Futurewei Technologies 2330 Central Express Way Santa Clara USA Email: james.n.guichard@futurewei.com 8. Acknowledgements Many thanks to Shraddha Hedge for her detailed review and professional comments. 9. References 9.1. Normative References Li, et al. Expires 17 February 2024 [Page 9] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 [I-D.ietf-idr-bgpls-srv6-ext] Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., Bernier, D., and B. Decraene, "BGP Link State Extensions for SRv6", Work in Progress, Internet-Draft, draft-ietf- idr-bgpls-srv6-ext-14, 17 February 2023, . [I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and D. Jain, "Advertising Segment Routing Policies in BGP", Work in Progress, Internet-Draft, draft-ietf-idr-segment- routing-te-policy-23, 25 July 2023, . [I-D.ietf-idr-te-lsp-distribution] Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler, H., and J. Tantsura, "Distribution of Traffic Engineering (TE) Policies and State using BGP-LS", Work in Progress, Internet-Draft, draft-ietf-idr-te-lsp-distribution-19, 24 January 2023, . [I-D.ietf-spring-mpls-path-segment] Cheng, W., Li, H., Li, C., Gandhi, R., and R. Zigler, "Path Segment in MPLS Based Segment Routing Network", Work in Progress, Internet-Draft, draft-ietf-spring-mpls-path- segment-10, 31 July 2023, . [I-D.ietf-spring-srv6-path-segment] Li, C., Cheng, W., Chen, M., Dhody, D., and Y. Zhu, "Path Segment for SRv6 (Segment Routing in IPv6)", Work in Progress, Internet-Draft, draft-ietf-spring-srv6-path- segment-06, 4 May 2023, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Li, et al. Expires 17 February 2024 [Page 10] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, . [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, . [RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, July 2022, . 9.2. Informative References [I-D.gandhi-spring-udp-pm] Gandhi, R., Filsfils, C., Voyer, D., Salsano, S., Ventre, P. L., and M. Chen, "UDP Path for In-band Performance Measurement for Segment Routing Networks", Work in Progress, Internet-Draft, draft-gandhi-spring-udp-pm-02, 14 September 2018, . [I-D.ietf-idr-sr-policy-path-segment] Li, C., Li, Z., Yin, Y., Cheng, W., and K. Talaulikar, "SR Policy Extensions for Path Segment and Bidirectional Path", Work in Progress, Internet-Draft, draft-ietf-idr- sr-policy-path-segment-07, 9 February 2023, . [I-D.ietf-mpls-bfd-directed] Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen, "Bidirectional Forwarding Detection (BFD) Directed Return Path for MPLS Label Switched Paths (LSPs)", Work in Progress, Internet-Draft, draft-ietf-mpls-bfd-directed-24, 2 July 2023, . Authors' Addresses Li, et al. Expires 17 February 2024 [Page 11] Internet-Draft Path ID and Bi-directional Path in BGP-L August 2023 Cheng Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: c.l@huawei.com Zhenbin Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: lizhenbin@huawei.com Yongqing Zhu China Telecom 109 West Zhongshan Ave Guangzhou China Email: zhuyq8@chinatelecom.cn Weiqiang Cheng China Mobile Beijing China Email: chengweiqiang@chinamobile.com Ketan Talaulikar Cisco Systems Email: ketant.ietf@gmail.com Li, et al. Expires 17 February 2024 [Page 12]