Network Working Group A. Farrel Internet-Draft Old Dog Consulting Intended status: Informational S. Krishnan Expires: 31 August 2025 Cisco Systems, Inc. 27 February 2025 Clarifying SRv6 SID List Processing draft-farrel-6man-sidlist-clarification-01 Abstract Segment Routing over IPv6 (SRv6) is the instantiation of Segment Routing (SR) on the IPv6 dataplane. Segments are indicated by Segment Identifiers (SIDs). SRv6 utilizes the Segment Routing Header (SRH), an IPv6 extension header, that includes a SID list indicating the sequence of segments and any additional processing to be performed. This document clarifies the processing of SID list entries. It does not change any elements of the SRv6 architecture and makes no technical changes to the mechanisms or procedures of SRv6. 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 31 August 2025. Copyright Notice Copyright (c) 2025 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. Farrel & Krishnan Expires 31 August 2025 [Page 1] Internet-Draft SID List Clarification February 2025 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. Clarification . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Security Considerations . . . . . . . . . . . . . . . . . . . 3 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 3 Normative References . . . . . . . . . . . . . . . . . . . . . . 3 Informative References . . . . . . . . . . . . . . . . . . . . . 3 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction The Segment Routing (SR) architecture is specified in [RFC8402]. SR forwards packets along a series of segments, and may perform additional segment-specific processing on packets. Segments are indicated by Segment Identifiers (SIDs). The mechanisms to achieve Segment Routing for IPv6 (SRv6) include the use of the Segment Routing Header (SRH) [RFC8754] an IPv6 extension header that includes a SID list indicating the sequence of segments and any additional processing to be performed. This document clarifies the processing of SID list entries. It does not change any elements of the SRv6 architecture and makes no technical changes to the mechanisms or procedures of SRv6. 2. Clarification At the end of a segment, the SRH is processed to determine the next segment on the packet's path per Section 4 of [RFC8754]. One objective is to determine the value to place in the Destination Address field of the IPv6 packet. To this end, the next entry in the SID list in the SRH is processed and mapped to the value to place in the Destination Address field. The value placed in the 128 bit Destination Address field of an IPv6 packet header needs to be a routable IPv6 address since that is required for forwarding the packet. Farrel & Krishnan Expires 31 August 2025 [Page 2] Internet-Draft SID List Clarification February 2025 Note that entries in the SID list do not need to be fully-formed IPv6 addresses that are copied direct to the Destination Address field of the IPv6 packet. The mapping from SID list entry could be a direct copy (the SID list contains a list of IPv6 addresses), or could involve a more complex function. Examples of such functions are shown in [I-D.ietf-spring-srv6-srh-compression] where a REPLACE-CSID compressed SID is expanded to be placed in the Destination Address field. 3. Security Considerations This document makes no changes to the security properties of SRv6. See [I-D.ietf-spring-srv6-security] for more discussion of SRv6 security. Note that the possibility of applying encryption functions to SID list members mentioned in Section 2 could offer additional security features. 4. IANA Considerations This document makes no requests for IANA action. Acknowledgments Thanks to Eric Vyncke and Erik Kline for inspiring the authors to write this document. Thanks to Bob Hinden and Mohamed Boucadair for their reviews and comments that improved this document. Normative References [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, . Informative References [I-D.ietf-spring-srv6-security] Buraglio, N., Mizrahi, T., tongtian124, Contreras, L. M., and F. Gont, "Segment Routing IPv6 Security Farrel & Krishnan Expires 31 August 2025 [Page 3] Internet-Draft SID List Clarification February 2025 Considerations", Work in Progress, Internet-Draft, draft- ietf-spring-srv6-security-02, 26 February 2025, . [I-D.ietf-spring-srv6-srh-compression] Cheng, W., Filsfils, C., Li, Z., Decraene, B., and F. Clad, "Compressed SRv6 Segment List Encoding (CSID)", Work in Progress, Internet-Draft, draft-ietf-spring-srv6-srh- compression-23, 6 February 2025, . Authors' Addresses Adrian Farrel Old Dog Consulting United Kingdom Email: adrian@olddog.co.uk Suresh Krishnan Cisco Systems, Inc. United States of America Email: suresh.krishnan@gmail.com Farrel & Krishnan Expires 31 August 2025 [Page 4]