6man Working Group C. Li Internet-Draft Huawei Technologies Intended status: Standards Track W. Cheng Expires: November 9, 2021 China Mobile Y. Zhu China Telecom Z. Li D. Dhody Huawei Technologies May 8, 2021 Encapsulation of Path Segment in SRv6 draft-li-6man-srv6-path-segment-encap-06 Abstract Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding an ordered list of instructions, called "segments". The SR architecture can be implemented over an IPv6 data plane, called SRv6. In some use-cases such as end-to-end SR Path Protection and Performance Measurement (PM), an SRv6 path needs to be identified. An SRv6 Path Segment can be used for identifying an SRv6 path. This document defines a P-flag in the Segment Routing Header to indicate the appearence of SRv6 Path Segment. 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 November 9, 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. Li, et al. Expires November 9, 2021 [Page 1] Internet-Draft SRv6 P-bit May 2021 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 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Encoding of an SRv6 Path Segment . . . . . . . . . . . . . . 3 2.1. SRH.P-flag . . . . . . . . . . . . . . . . . . . . . . . 4 3. Processing of SRv6 Path Segment . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . 7 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 by inserting an ordered list of instructions, called segments. When segment routing is deployed on an IPv6 data plane, it is called SRv6, and it uses a new IPv6 [RFC8200] Routing Header (EH) called the IPv6 Segment Routing Header (SRH) [RFC8754] to construct an SRv6 path. As per [RFC8986], an SRv6 segment identifier is a 128-bit value. In several use cases, such as binding bidirectional path [I-D.ietf-pce-sr-bidir-path] and end-to-end performance measurement [I-D.gandhi-spring-twamp-srpm], the ability to implement path identification is a pre-requisite. An SRv6 path MAY be identified by the content of a segment list in the SRH. However, the segment list may not be a good key, since the length of a segment list is flexible according to the number of required SIDs. Also, the length of a segment list may be too long to be a key when it contains many SIDs. For instance, if packet A uses Li, et al. Expires November 9, 2021 [Page 2] Internet-Draft SRv6 P-bit May 2021 an SRH with 3 SIDs while Packet B uses an SRH with 10 SIDs, the key to identify these two paths will be a 384-bits value and a 1280-bits value, respectively. Furthermore, an SRv6 path cannot be identified by the information carried by the SRH in reduced mode [RFC8754] as the first SID is not present. Also, different SRv6 policies may use the same segment list for different candidate paths, so the traffic of different SRv6 policies are merged, resulting in the inability to measure the performance of the specific path. Therefore, [I-D.ietf-spring-srv6-path-segment] defines an SRv6 Path Segment to identify an SRv6 path. This document defines a P-bit in SRH to indicate the appearence of SRv6 Path Segment in SRH. 1.1. 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. 1.2. Terminology PM: Performance Measurement. SID: Segment ID. SL: Segment List. SR: Segment Routing. SRH: Segment Routing Header. PSID: Path Segment Identifier. PSP: Penultimate Segment Popping. Further, this document makes use of the terms defined in [RFC8402] and [RFC8986]. 2. Encoding of an SRv6 Path Segment This section describes the SRH encoding of an SRv6 Path Segment [I-D.ietf-spring-srv6-path-segment]. Li, et al. Expires November 9, 2021 [Page 3] Internet-Draft SRv6 P-bit May 2021 2.1. SRH.P-flag As per [I-D.ietf-spring-srv6-path-segment], an SRv6 Path Segment is a 128-bits value, and it MUST appear only once in a SID list, and it MUST appear as the last entry. To indicate the existence of a Path Segment in the SRH, this document defines a P-flag in the SRH flag field. The encapsulation of SRv6 Path Segment 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Last Entry | Flags |P| Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Segment List[0] (128 bits IPv6 address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | ... | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Segment List[n-1] (128 bits IPv6 address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | SRv6 Path Segment (Segment List[n],128 bits IPv6 value) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // // // Optional Type Length Value objects (variable) // // // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. SRv6 Path Segment in SID List o P-bit: set when SRv6 Path Segment is inserted. It MUST be ignored when a node does not support SRv6 Path Segment processing. Li, et al. Expires November 9, 2021 [Page 4] Internet-Draft SRv6 P-bit May 2021 SRH.P-bit processing can be enabled or disabled by configuration on devices, it can be done by CLI, NETCONF YANG or other ways, and this is out of the scope of this document. The pseudo code of SRH.P-bit processing is described as below. S01. if SRH.P-flag processing is enabled: S02. if SRH.P-flag is set: S03. SRv6 Path Segment processing ;;ref1 Ref1: The SRv6 Path Segment processing is accosiated with the specific application, such as SRv6 Path Segment based Performance measurement, and this is out of the scope of this document. In some use cases, only the egress need to process the SRv6 Path Segment, therefore, the P-bit processing can be done at the egress node only while the intermediate nodes do not need to process it. This feature can be enabled by configuration like CLI , NETCONF YANG or other ways. In this case, the pseudo code is described as below. S01. if SRH.P-flag processing is enabled: S02. if intermediate node processing is disabled: S03. if SRH.P-flag is set and SRH.SL == 0: S03. SRv6 Path Segment processing S04 else: S05. if SRH.P-flag is set: S06. SRv6 Path Segment processing 3. Processing of SRv6 Path Segment The processing of SRv6 path segment is out of the scope of this document and is defined in [I-D.ietf-spring-srv6-path-segment]. 4. IANA Considerations This document requests IANA to allocate bit position TBA within the "Segment Routing Header Flags" registry defined in [RFC8402]. 5. Security Considerations TBA Li, et al. Expires November 9, 2021 [Page 5] Internet-Draft SRv6 P-bit May 2021 6. Acknowledgements TBA 7. References 7.1. Normative References [I-D.ietf-spring-srv6-path-segment] Li, C., Cheng, W., Chen, M., Dhody, D., and R. Gandhi, "Path Segment for SRv6 (Segment Routing in IPv6)", draft- ietf-spring-srv6-path-segment-00 (work in progress), November 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, . [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 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, . [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, . [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 (SRv6) Network Programming", RFC 8986, DOI 10.17487/RFC8986, February 2021, . Li, et al. Expires November 9, 2021 [Page 6] Internet-Draft SRv6 P-bit May 2021 7.2. Informative References [I-D.gandhi-spring-twamp-srpm] Gandhi, R., Filsfils, C., Voyer, D., Chen, M., and B. Janssens, "Performance Measurement Using TWAMP Light for Segment Routing Networks", draft-gandhi-spring-twamp- srpm-11 (work in progress), October 2020. [I-D.ietf-idr-sr-policy-path-segment] Li, C., Li, Z., Chen, H., Cheng, W., and K. Talaulikar, "SR Policy Extensions for Path Segment and Bidirectional Path", draft-ietf-idr-sr-policy-path-segment-03 (work in progress), March 2021. [I-D.ietf-pce-sr-bidir-path] Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong, "Path Computation Element Communication Protocol (PCEP) Extensions for Associated Bidirectional Segment Routing (SR) Paths", draft-ietf-pce-sr-bidir-path-05 (work in progress), January 2021. [I-D.ietf-pce-sr-path-segment] Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong, "Path Computation Element Communication Protocol (PCEP) Extension for Path Segment in Segment Routing (SR)", draft-ietf-pce-sr-path-segment-03 (work in progress), February 2021. [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-11 (work in progress), April 2021. Authors' Addresses Cheng Li Huawei Technologies Email: c.l@huawei.com Weiqiang Cheng China Mobile Email: chengweiqiang@chinamobile.com Li, et al. Expires November 9, 2021 [Page 7] Internet-Draft SRv6 P-bit May 2021 Yongqing Zhu China Telecom Guangzhou Email: zhuyq8@chinatelecom.cn Zhenbin Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: lizhenbin@huawei.com Dhruv Dhody Huawei Technologies Divyashree Techno Park, Whitefield Bangalore 560066 India Email: dhruv.ietf@gmail.com Li, et al. Expires November 9, 2021 [Page 8]