PIM Working Group M. Mishra Internet-Draft Cisco Systems Intended status: Standards Track 20 July 2026 Expires: 21 January 2027 PIM Source Discovery for ASM Deployments draft-mankamana-pim-source-discovery-00 Abstract This document discusses the operational challenges of Any-Source Multicast deployments that use PIM Sparse Mode and explores whether PIM extensions can simplify source discovery and operational behavior while preserving the host-facing ASM service model. 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 21 January 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. Mishra Expires 21 January 2027 [Page 1] Internet-Draft PIM Source Discovery July 2026 Table of Contents 1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3 6. Capability Discovery . . . . . . . . . . . . . . . . . . . . 3 7. PIM Source Discovery Extensions . . . . . . . . . . . . . . . 3 8. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 3 9. Relationship to Existing ASM Mechanisms . . . . . . . . . . . 4 10. Security Considerations . . . . . . . . . . . . . . . . . . . 4 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 12. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 4 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 14.1. Normative References . . . . . . . . . . . . . . . . . . 4 14.2. Informative References . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Problem Statement [RFC7761] defines Protocol Independent Multicast - Sparse Mode (PIM- SM). PIM-SM supports the Any-Source Multicast (ASM) service model by building shared trees rooted at a Rendezvous Point (RP) for multicast groups, and by optionally switching to source trees after sources are discovered. ASM has been widely deployed in operational networks. In many deployments, especially IPTV deployments, the ASM service model is not only a network design choice but also part of the host and application behavior. A network operator cannot always remove ASM simply by changing the network. Moving away from ASM may require changes on receivers, applications, middleware, or customer premises devices. In IPTV networks, the number of set-top boxes can be in the millions, so requiring all end hosts to be upgraded or replaced is often not operationally practical. The PIM architecture defines the RP as the point where receivers and sources meet in the ASM model. Multiple mechanisms have been specified or deployed to configure or discover the RP, including static configuration and dynamic discovery mechanisms. In addition, MSDP [RFC3618] has been defined to support source discovery across PIM-SM domains, allowing RPs in different domains to advertise active sources to one another. These mechanisms solve important parts of the ASM problem space, but they also add operational dependencies around RP placement, RP discovery, inter-domain source discovery, filtering policy, scaling, and troubleshooting. Mishra Expires 21 January 2027 [Page 2] Internet-Draft PIM Source Discovery July 2026 As a result, the overall ASM deployment experience can become difficult for operators. The network may need to maintain RP state, source registration behavior, RP discovery behavior, MSDP peering and policy, and multicast forwarding state across many groups, sources, domains, and administrative boundaries. When service behavior is incorrect, the operator often has to reason across several control- plane mechanisms before determining whether the issue is host signaling, RP discovery, source registration, MSDP source advertisement, PIM Join/Prune state, or multicast forwarding. There is therefore a need to explore whether the ASM deployment experience can be simplified without requiring a disruptive migration of existing end hosts away from ASM. This document is intended to examine possible PIM extensions that can improve source discovery and operational behavior while preserving compatibility with deployed ASM host behavior. 2. Requirements Language To be added. 3. Terminology To be added. 4. Applicability To be added. 5. Protocol Overview To be added. 6. Capability Discovery To be added. 7. PIM Source Discovery Extensions To be added. 8. Router Behavior To be added. Mishra Expires 21 January 2027 [Page 3] Internet-Draft PIM Source Discovery July 2026 9. Relationship to Existing ASM Mechanisms To be added. 10. Security Considerations To be added. 11. IANA Considerations To be added. 12. Open Issues To be added. 13. Acknowledgements To be added. 14. References 14.1. Normative References [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 2016, . 14.2. Informative References [RFC3618] Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source Discovery Protocol (MSDP)", RFC 3618, DOI 10.17487/RFC3618, October 2003, . Author's Address Mankamana Mishra Cisco Systems 821 Alder Drive Milpitas, CA 95035 United States of America Email: mankamis@cisco.com Mishra Expires 21 January 2027 [Page 4]