Interdomain Routing Working Group C. Li Internet-Draft Z. Li Intended status: Standards Track Huawei Technologies Expires: February 12, 2021 H. Chen China Telecom W. Cheng China Mobile K. Talaulikar Cisco Systems August 11, 2020 SR Policy Extensions for Path Segment and Bidirectional Path draft-ietf-idr-sr-policy-path-segment-01 Abstract A Segment Routing (SR) policy is a set of candidate SR paths consisting of one or more segment lists with necessary path attributes. For each SR path, it may also have its own path attributes, and Path Segment is one of them. A Path Segment is defined to identify an SR path, which can be used for performance measurement, path correlation, and end-2-end path protection. Path Segment can be also used to correlate two unidirectional SR paths into a bidirectional SR path which is required in some scenarios, for example, mobile backhaul transport network. This document defines extensions to BGP to distribute SR policies carrying Path Segment and bidirectional path information. 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 Li, et al. Expires February 12, 2021 [Page 1] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 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 February 12, 2021. Copyright Notice Copyright (c) 2020 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 3. Path Segment in SR Policy . . . . . . . . . . . . . . . . . . 3 3.1. SR Path Segment Sub-TLV . . . . . . . . . . . . . . . . . 5 4. SR Policy for Bidirectional Path . . . . . . . . . . . . . . 6 4.1. Reverse Path Segment List Sub-TLV . . . . . . . . . . . . 7 5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6.1. Existing Registry: BGP Tunnel Encapsulation Attribute sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 10.1. Normative References . . . . . . . . . . . . . . . . . . 10 10.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 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 [I-D.ietf-spring-segment-routing-policy]. For distributing SR Li, et al. Expires February 12, 2021 [Page 2] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 policies to the headend, [I-D.ietf-idr-segment-routing-te-policy] specifies a mechanism by using BGP, and new sub-TLVs are defined for SR Policies in BGP UPDATE message. In many use cases such as performance measurement, the path to which the packets belong is required to be identified. Futhermore, in some scenarios, for example, mobile backhaul transport network, there are requirements to support bidirectional path. However, there is no path identification information for each Segment List in the SR Policies defined in [I-D.ietf-spring-segment-routing-policy]. Also, the SR Policies defined in [I-D.ietf-spring-segment-routing-policy] only supports unidirectional SR paths. Therefore, this document defines the extension to SR policies that carry Path Segment in the Segment List and support bidirectional path. The Path Segment can be a Path Segment in SR-MPLS [I-D.ietf-spring-mpls-path-segment] , or other IDs that can identify a path. Also, this document defines extensions to BGP to distribute SR policies carrying Path Segment and bidirectional path information. 2. Terminology This memo makes use of the terms defined in [RFC8402] and [I-D.ietf-idr-segment-routing-te-policy]. 2.1. Requirements Language 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. Path Segment in SR Policy As defined in [I-D.ietf-idr-segment-routing-te-policy] , the SR Policy encoding structure is as follows: Li, et al. Expires February 12, 2021 [Page 3] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 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 Segment Segment ... ... An SR path can be specified by an Segment List sub-TLV that contains a set of segment sub-TLVs and other sub-TLVs as shown above. As defined in [I-D.ietf-spring-segment-routing-policy], a candidate path includes multiple SR paths specified by SID list. The Path Segment can be used for identifying an SR path(specified by SID list) from the headend and the tailend. Also, it can be used for identifying an SR candidate path in some use cases if needed. This document defines a new Path Segment sub-TLV within Segment List sub-TLV, the details will be described at section 3.1. The new SR Policy encoding structure with Path Segmentg sub-TLV is expressed as below: Li, et al. Expires February 12, 2021 [Page 4] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 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 ... ... The Path Segment is used to identified an SR path, and it can be used in OAM or IOAM 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. Multiple Path Segment MAY be included in a Segment List for different use cases, all of them SHOULD be inserted into the SID List. 3.1. SR Path Segment Sub-TLV This section defines an SR Path Segment sub-TLV. An SR Path Segment sub-TLV is included in the segment list sub-TLV to identify an SID list. It 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 | Flags | ST | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Path Segment ID (Variable depends on ST) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. Path Segment sub-TLV Li, et al. Expires February 12, 2021 [Page 5] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 Where: Type: to be assigned by IANA. Length: the total length of the value field not including Type and Length fields. Flags: 8 bits of flags. Following flags are defined: 0 1 2 3 4 5 6 7 +--+--+--+--+--+--+--+--+ | Reserved |G | +--+--+--+--+--+--+--+--+ G-Flag: Global flag. Set when the Path Segment is global within an SR domain. The rest bits of Flag are reserved and MUST be set to 0 on transmission and MUST be ignored on receipt. ST: Segment type, specifies the type of the Path Segment, and it has following types: o 0: SR-MPLS Path Segment o 1-255:Reserved Path Segment ID: The Path Segment ID of an SR path. The Path Segment type is indicated by the Segment Type(ST) field. It can be a Path Segment in SR-MPLS [I-D.ietf-spring-mpls-path-segment], or other IDs that identifies a path. When ST is 0, the Path Segment ID is a SR- MPLS Path Segment, and format is shown below. 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 | ST=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Path Segment Label | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2. SR-MPLS Path Segment sub-TLV 4. SR Policy for Bidirectional Path In some scenarios, for example, 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. This document also defines a Reverse Segment List sub-TLV to describe the reverse path associated with the Li, et al. Expires February 12, 2021 [Page 6] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 forward path specified by the Segment List. An SR policy carrying SR bidirectional path information is expressed as below: 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 Path Segment Segment Segment ... 4.1. Reverse Path Segment List Sub-TLV A Reverse Path Segment List sub-TLV is defined to specify an SR reverse path associated with the path specified by the Segment List, and it 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (Variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3. SR Reverse Path Segment List Sub-TLV where: Type: TBA. Length: the total length of the sub-TLVs encoded within the Reverse Path Segment List Sub-TLV not including the Type and Length fields. Li, et al. Expires February 12, 2021 [Page 7] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 RESERVED: 1 octet of reserved bits. SHOULD be unset on transmission and MUST be ignored on receipt. sub-TLVs, reuse the sub-TLVs in Segment List defined in [I-D.ietf-idr-segment-routing-te-policy]. o One or more mandatory SR Path Segment sub-TLVs that contains the Path Segments of the reverse SR path. o One or more Segment sub-TLVs to specify the reverse SR path. The Segment sub-TLVs in the Reverse Path Segment List sub-TLV provides the information of the reverse SR path, which can be used for directing egress BFD peer to use specific path for the reverse direction of the BFD session [I-D.ietf-mpls-bfd-directed] or other applications. 5. 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 unidirectional or bidirectional SR policies carrying path identification infomation are configured by a controller. After configuration, the unidirectional or bidirectional SR policies carrying path identification infomation 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 reception. The consumer of the unidirectional or bidirectional SR policies is not the BGP process, it can be any applications, such as performance measurement [I-D.gandhi-spring-udp-pm]. The operation of sending information to consumers is out of scope of this document. 6. IANA Considerations This document defines new Sub-TLVs in following registries: Li, et al. Expires February 12, 2021 [Page 8] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 6.1. Existing Registry: BGP Tunnel Encapsulation Attribute sub-TLVs This document defines new sub-TLVs in the registry "SR Policy List Sub-TLVs" [I-D.ietf-idr-segment-routing-te-policy] to be assigned by IANA: Codepoint Description Reference ------------------------------------------------------------- TBA Path Segment sub-TLV This document TBA Reverse Segment List sub-TLV This document 7. Security Considerations TBA 8. 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 Li, et al. Expires February 12, 2021 [Page 9] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 9. Acknowledgements Many thanks to Shraddha Hedge for her detailed review and professional comments. 10. References 10.1. 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", draft-ietf-idr-segment-routing- te-policy-09 (work in progress), May 2020. [I-D.ietf-spring-mpls-path-segment] Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler, "Path Segment in MPLS Based Segment Routing Network", draft-ietf-spring-mpls-path-segment-02 (work in progress), February 2020. [I-D.ietf-spring-segment-routing-policy] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", draft- ietf-spring-segment-routing-policy-08 (work in progress), July 2020. [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, . 10.2. Informative References Li, et al. Expires February 12, 2021 [Page 10] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 [I-D.gandhi-spring-udp-pm] Gandhi, R., Filsfils, C., daniel.voyer@bell.ca, d., Salsano, S., Ventre, P., and M. Chen, "UDP Path for In- band Performance Measurement for Segment Routing Networks", draft-gandhi-spring-udp-pm-02 (work in progress), September 2018. [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)", draft-ietf- mpls-bfd-directed-15 (work in progress), August 2020. Authors' Addresses 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 Huanan Chen China Telecom 109 West Zhongshan Ave Guangzhou China Email: chenhn8.gd@chinatelecom.cn Weiqiang Cheng China Mobile Beijing China Email: chengweiqiang@chinamobile.com Li, et al. Expires February 12, 2021 [Page 11] Internet-Draft Path ID and Bi-directional Path in BGP August 2020 Ketan Talaulikar Cisco Systems Email: ketant@cisco.com Li, et al. Expires February 12, 2021 [Page 12]