PCEP Working Group J. Dong Internet-Draft Huawei Intended status: Standards Track C. Loibl Expires: 1 May 2027 Next Layer Communications G. Mishra Verizon Inc. Y. Zhu China Telecom S. Zhuang Huawei 28 October 2026 PCEP Extension for SRv6 Flow Specification draft-dong-pcep-flowspec-srv6-00 Abstract This document specifies extensions to the Path Computation Element Communication Protocol (PCEP) to support Flow Specification for Segment Routing over IPv6 (SRv6). Building upon the PCEP Flow Specification framework defined in RFC 9168, this specification introduces new PCEP Flow Specification TLVs to enable filtering and steering of IPv6 packets based on the structural components of standard SRv6 Segment Identifiers (SIDs) or SRv6 Compressed SID (CSID) containers present in IPv6 Destination Addresses or Segment Routing Headers (SRH). 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. 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/. Dong, et al. Expires 1 May 2027 [Page 1] Internet-Draft PCEP Flow Specification for SRv6 October 2026 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 May 2027. Copyright Notice Copyright (c) 2026 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 4 3. PCEP Capability Advertisement . . . . . . . . . . . . . . . . 5 4. PCEP Flow Specification Extensions for SRv6 . . . . . . . . . 5 4.1. SRv6 Standard SID Structure Match TLV (Type TBD1) . . . . 5 4.2. SRv6 CSID Dynamic Structure Match TLV (Type TBD2) . . . . 6 5. PCEP Operational Procedures . . . . . . . . . . . . . . . . . 7 5.1. Validation and Length Rules . . . . . . . . . . . . . . . 7 5.2. Error Handling . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 Dong, et al. Expires 1 May 2027 [Page 2] Internet-Draft PCEP Flow Specification for SRv6 October 2026 1. Introduction [RFC9168] defines extensions to the Path Computation Element Communication Protocol (PCEP) [RFC5440] to support the dissemination of Flow Specification rules using PCEP messages. A PCEP FLOWSPEC object carries match conditions and filtering actions managed by a Path Computation Element (PCE) and enforced by a Path Computation Client (PCC). Segment Routing over IPv6 (SRv6) [RFC8754] leverages the IPv6 data plane using a Segment Routing Header (SRH) to instantiate paths. The SRv6 Network Programming architecture [RFC8986] defines standard SID structures (LOC:FUNCT:ARG). Furthermore, [RFC9800] defines Compressed SRv6 SIDs (CSIDs), supporting NEXT-CSID and REPLACE-CSID flavors where multiple CSIDs are packed into a 128-bit IPv6 Destination Address (DA) container. While [RFC9168] supports basic IP and IPv6 Flow Specification matching, it lacks mechanisms to parse and filter traffic based on the internal structure of SRv6 SIDs or dynamic CSID containers. This document extends [RFC9168] by defining two new PCEP Flow Specification TLV types to be carried within the PCEP FLOWSPEC object: 1. SRv6 Standard SID Structure Match TLV [RFC8986]. 2. SRv6 CSID Dynamic Structure Match TLV [RFC9800]. The matching field is evaluated against the IPv6 Destination Address (or active SID within an SRH when present, as shown in Figure 1). Dong, et al. Expires 1 May 2027 [Page 3] Internet-Draft PCEP Flow Specification for SRv6 October 2026 +-----------------------------+ IPv6 Header| SA | DA |<-- Match Field +--------------------^--------+ | +--------------------|--------+ | +-------------+ | +-------------------+ | | Segment[0] +-------> Loc | Func | Arg | | +-------------+ | +-------------------+ | | Segment[1] | | | +-------------+ | | | ... | | SR Header| +-------------+ | (RFC 8754)| | Segment[n] | | | +-------------+ | | +-------------+ | | ~ Option TLV ~ | | +-------------+ | +-----------------------------+ Figure 1: Match Field 2. Definitions and Acronyms This document uses terminology defined in [RFC5440], [RFC9168], [RFC8754], [RFC8986], and [RFC9800]. * CSID: Compressed Segment Identifier [RFC9800] * FS: Flow Specification * NEXT-CSID: NEXT-CSID Flavor defined in [RFC9800] * PCEP FS: PCEP Flow Specification * REPLACE-CSID: REPLACE-CSID Flavor defined in [RFC9800] * SID: Segment Identifier * SR: Segment Routing * SRH: SR Header * SRv6: IPv6 Segment Routing, SRv6 is a method of forwarding IPv6 packets on the network based on the concept of source routing. In this document, the length parameters defining the constituent parts of a SID or CSID structure are defined as follows: Dong, et al. Expires 1 May 2027 [Page 4] Internet-Draft PCEP Flow Specification for SRv6 October 2026 * LOC-Len: Locator Length in bits for a standard 128-bit SRv6 SID (Component Type TBD1). * LB-Len: Locator-Block Length in bits for a CSID structure (Component Type TBD2). * LN-Len: Locator-Node Length in bits for a CSID structure. * F-Len: Function Length in bits for a SID or CSID structure. * ARG-Len: Argument Length in bits for a standard 128-bit SRv6 SID. In addition, the sum of LN-Len and F-Len (LN-Len + F-Len) represents the total length of a single CSID (also referred to as the "CSID length"). 3. PCEP Capability Advertisement A PCEP speaker (PCE or PCC) indicates its support for SRv6 Flow Specification extensions during the PCEP session establishment phase. [RFC9168] defines the FLOWSPEC-CAPABILITY TLV carried in the OPEN object. This document defines a new flag bit in the Flags field of the FLOWSPEC-CAPABILITY TLV: * Bit TBD (S-bit - SRv6 FlowSpec Support): Set to 1 by a PCEP speaker to indicate capability to process SRv6 Standard SID Structure and CSID Dynamic Structure Match TLVs. If both PCEP peers advertise the S-bit capability, SRv6 FlowSpec TLVs MAY be included in PCEP messages (e.g., PCUpd, PCInitiate, or PCRpt). 4. PCEP Flow Specification Extensions for SRv6 Flow Specification match conditions in PCEP are carried within the FLOWSPEC object [RFC9168]. This document defines two new TLVs for inclusion in the FLOWSPEC object. 4.1. SRv6 Standard SID Structure Match TLV (Type TBD1) The SRv6 Standard SID Structure Match TLV allows a PCE to instruct a PCC to match packets against individual or combined fields (Locator, Function, and Argument) of a standard SRv6 SID [RFC8986]. The format of the SRv6 Standard SID Structure Match TLV is as follows: Dong, et al. Expires 1 May 2027 [Page 5] Internet-Draft PCEP Flow Specification for SRv6 October 2026 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 (TBD1) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LOC-Len | FUNCT-Len | ARG-Len | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | [op, value] + | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding (0-3 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: * Type (16 bits): TBD1, assigned for SRv6 Standard SID Structure Match TLV. * Length (16 bits): Total length of the TLV in octets. * LOC-Len (8 bits): Length of the Locator field in bits. * FUNCT-Len (8 bits): Length of the Function field in bits. * ARG-Len (8 bits): Length of the Argument field in bits. * Reserved (8 bits): MUST be set to zero and ignored on receipt. * [op, value]+: A sequence of one or more {operator, value} pairs specifying the matching logic applied to the SID sub-fields, following the operator encoding rules in [RFC9168] and [I-D.ietf-idr-flowspec-srv6]. * Padding (variable): Padding octets (0-3) to align the TLV length to a 4-octet boundary. 4.2. SRv6 CSID Dynamic Structure Match TLV (Type TBD2) The SRv6 CSID Dynamic Structure Match TLV allows matching against dynamic Compressed SID containers (NEXT-CSID and REPLACE-CSID flavors) [RFC9800]. The format of the SRv6 CSID Dynamic Structure Match TLV is as follows: Dong, et al. Expires 1 May 2027 [Page 6] Internet-Draft PCEP Flow Specification for SRv6 October 2026 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 (TBD2) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LB-Len | LN-Len | F-Len | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | [op, value] + | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding (0-3 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: * Type (16 bits): TBD2, assigned for SRv6 CSID Dynamic Structure Match TLV. * Length (16 bits): Total length of the TLV in octets. * LB-Len (8 bits): Locator-Block Length in bits. * LN-Len (8 bits): Locator-Node Length in bits. * F-Len (8 bits): Function Length in bits. * Reserved (8 bits): MUST be set to zero and ignored on receipt. * [op, value]+: A sequence of {operator, value} pairs evaluating Locator-Block, Active CSID, and Next CSID fields as defined in [I-D.ietf-idr-flowspec-srv6]. * Padding (variable): Padding octets (0-3) to align the TLV length to a 4-octet boundary. 5. PCEP Operational Procedures 5.1. Validation and Length Rules Upon receiving an SRv6 FlowSpec TLV, the PCC MUST validate the structural lengths: 1. For Standard SID Structure (Type TBD1): The sum of LOC-Len, FUNCT-Len, and ARG-Len MUST NOT exceed 128 bits. Dong, et al. Expires 1 May 2027 [Page 7] Internet-Draft PCEP Flow Specification for SRv6 October 2026 2. For CSID Dynamic Structure (Type TBD2): The sum of LB-Len, LN- Len, and F-Len MUST NOT exceed 128 bits. If a structural validation fails, the TLV MUST be considered malformed. 5.2. Error Handling If a PCC receives an SRv6 FlowSpec TLV when the S-bit capability was not negotiated, or if the received TLV is malformed, the PCC MUST send a PCErr message with: * Error-Type = 30 (FlowSpec Error) [RFC9168] * Error-Value = TBD_EV (Unsupported or Malformed SRv6 FlowSpec Component) 6. Security Considerations The security considerations outlined in [RFC5440], [RFC9168], and [RFC8231] apply to the extensions defined in this document. Appropriate transport security (e.g., TLS or TCP-AO) MUST be employed to prevent unauthorized insertion or modification of SRv6 FlowSpec rules. 7. IANA Considerations IANA is requested to make the following allocations in the "PCEP Numbers" registry: 1. **FLOWSPEC-CAPABILITY TLV Flag Field**: * Bit TBD: S-bit (SRv6 FlowSpec Support) 2. **PCEP Flow Specification TLV Types**: * TBD1: SRv6 Standard SID Structure Match TLV * TBD2: SRv6 CSID Dynamic Structure Match TLV 8. Acknowledgments The authors would like to thank Joel Halpern, Jeffrey Haas, Ketan Talaulikar, Aijun Wang, Dhruv Dhody, Ming Shen and Rainsword Wang for their valuable suggestions and comments. 9. Contributors Dong, et al. Expires 1 May 2027 [Page 8] Internet-Draft PCEP Flow Specification for SRv6 October 2026 Lei Li Huawei Email: lily.lilei@huawei.com Zhenbin Li Huawei Email: robinli314@163.com Huaimo Chen Futurewei Email: hchen.ietf@gmail.com Yanhe Fan Casa Systems Email: yfan@casa-systems.com Lei Liu Fujitsu Email: liulei.kddi@gmail.com Xufeng Liu Volta Networks Email: xufeng.liu.ietf@gmail.com 10. References 10.1. Normative References [I-D.ietf-idr-flowspec-srv6] Li, Z., Dong, J., Loibl, C., Mishra, G. S., Zhu, Y., and S. Zhuang, "BGP Flow Specification for SRv6", Work in Progress, Internet-Draft, draft-ietf-idr-flowspec-srv6-11, 25 October 2026, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Dong, et al. Expires 1 May 2027 [Page 9] Internet-Draft PCEP Flow Specification for SRv6 October 2026 [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, . [RFC9168] Dhody, D., Farrel, A., and Z. Li, "Path Computation Element Communication Protocol (PCEP) Extension for Flow Specification", RFC 9168, DOI 10.17487/RFC9168, January 2022, . [RFC9800] Cheng, W., Ed., Filsfils, C., Li, Z., Decraene, B., and F. Clad, Ed., "Compressed SRv6 Segment List Encoding", RFC 9800, DOI 10.17487/RFC9800, June 2025, . 10.2. Informative References [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE", RFC 8231, DOI 10.17487/RFC8231, September 2017, . [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, . Authors' Addresses Jie Dong Huawei 156 Beiqing Road Beijing, 100095 P.R. China Email: jie.dong@huawei.com Christoph Loibl Next Layer Communications Mariahilfer Guertel 37/7 1150 Vienna Austria Email: cl@tix.at Dong, et al. Expires 1 May 2027 [Page 10] Internet-Draft PCEP Flow Specification for SRv6 October 2026 Gyan S. Mishra Verizon Inc. 13101 Columbia Pike Silver Spring, MD 20904 United States of America Phone: 301 502-1347 Email: gyan.s.mishra@verizon.com Yongqing Zhu China Telecom 109, West Zhongshan Road, Tianhe District Guangzhou 510000 China Email: zhuyq8@chinatelecom.cn Shunwan Zhuang Huawei 156 Beiqing Road Beijing 100095 P.R. China Email: zhuangshunwan@huawei.com Dong, et al. Expires 1 May 2027 [Page 11]