PIM H. Asaeda Internet-Draft NICT Intended status: Informational L. Contreras Expires: 24 April 2027 Telefonica 21 October 2026 Multipath Support for IGMP/MLD Proxy draft-ietf-pim-multipath-igmpmldproxy-05 Abstract This document specifies the framework to support multipath reception in Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD) proxy devices. The proposed mechanism allows IGMP/ MLD proxy devices to receive multicast sessions/channels through different upstream interfaces. It defines static configuration methods for associating upstream interfaces with channel identifiers and interface priority values. A mechanism for upstream interface takeover that enables switching from an inactive to active upstream interface is also described. 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 24 April 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 Asaeda & Contreras Expires 24 April 2027 [Page 1] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Static Upstream Interface Configuration and Selection Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Channel-Based Upstream Selection . . . . . . . . . . . . 5 3.2. Multiple Upstream Interface Selection for Robust Data Reception . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Upstream Interface Takeover . . . . . . . . . . . . . . . 6 4. Candidate Upstream Interface Configuration . . . . . . . . . 6 4.1. Multicast Channel Record . . . . . . . . . . . . . . . . 7 4.2. Interface Priority . . . . . . . . . . . . . . . . . . . 8 4.3. Default Upstream Interface . . . . . . . . . . . . . . . 8 5. Updating YANG Model . . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 10 9.2. Informative References . . . . . . . . . . . . . . . . . 10 Appendix A. Proof of Concept . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. Introduction The Internet Group Management Protocol (IGMP) [RFC3376][RFC5790] for IPv4 and the Multicast Listener Discovery Protocol (MLD) [RFC3810][RFC5790] for IPv6 are the standard protocols for hosts to initiate the joining or leaving of multicast sessions. A proxy device that performs IGMP/MLD-based forwarding (known as IGMP/MLD proxy) [RFC4605] maintains multicast membership information using IGMP/MLD protocols on downstream interfaces and sends IGMP/MLD membership report messages via the upstream interface to upstream multicast routers when the membership information changes (e.g., by receiving solicited/unsolicited report messages). The proxy device forwards the appropriate multicast packets received on its upstream interface to each downstream interface based on the subscription of the downstream receiver. According to the specification of [RFC4605], an IGMP/MLD proxy has _a single_ upstream interface and one or more downstream interfaces. Upstream and downstream interfaces on the IGMP/MLD proxy device must Asaeda & Contreras Expires 24 April 2027 [Page 2] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 be configured manually, and the upstream interface is expected to be connected to a wider multicast infrastructure. Therefore, IGMP/MLD proxy devices perform the router portion of the IGMP or MLD protocol on their downstream interfaces and the host portion of IGMP/MLD on their upstream interface. They must not perform the router portion of IGMP/MLD on the upstream interface. Conversely, there is a scenario in which IGMP/MLD proxy devices enable multiple upstream interfaces and receive multicast packets through these interfaces. For example, a proxy device with more than one interface may want to access different networks, such as the Internet and local-scope networks, or a proxy device with a wired link (e.g., Ethernet) and high-speed wireless link (e.g., 5G) may want to have the capability to connect to the Internet through both links. These proxy devices receive multicast packets from different upstream interfaces and forward them to the downstream interface(s). The applicability of IGMP/MLD proxies with multiple upstream interfaces in Proxy Mobile IPv6 (PMIPv6) [RFC5213] is described in [RFC6224]. This document specifies the framework to support multipath reception in IGMP/MLD proxy devices and defines the static upstream interface configuration mechanisms for IGMP/MLD proxies to select one or more upstream interfaces per multicast channel/session. Unlike the conventional approach [RFC4605], when a proxy device receives an IGMP/MLD report message on the downstream interface(s), it examines the source and multicast addresses in the records of the IGMP/MLD report message and selects the appropriate upstream interface(s). The upstream interfaces can be selected by static configurations based on channel identifiers and interface priority values. Note that the upstream interface selection by dynamic configurations is introduced in another document [I-D.contreras-pim-multiif-config] and out of scope of this document. In addition, this document defines the method for a proxy device to select one or more upstream interfaces from the candidate upstream interfaces per session/channel. In this case, it can receive duplicate (redundant) packets for the session/channel from different upstream interfaces simultaneously, resulting in "robust data reception." A mechanism for "upstream interface takeover" is also described in this document; when the selected upstream interface becomes unavailable or does not receive packets for the corresponding multicast channel during the configured active interval, one of the other available candidate upstream interfaces (i.e., backup upstream interface) takes over the upstream interface if configured. Asaeda & Contreras Expires 24 April 2027 [Page 3] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 2. Terminology 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. In addition, the following terms are used in this document. * Selected upstream interface (or simply, upstream interface): The interface of a proxy device in the direction of the root of the multicast forwarding tree. A proxy device performs the host portion of IGMP/MLD on its upstream interface. An upstream interface is selected from a list of candidate upstream interfaces. * Default upstream interface: An upstream interface for multicast sessions/channels for which a proxy device does not select other upstream interfaces. The default upstream interface is configurable. * Downstream interface: An interface that is not in the direction of the root of the multicast forwarding tree. A proxy device performs the router portion of IGMP/MLD on its downstream interfaces. * Active upstream interface: An upstream interface that has been receiving packets for specific multicast sessions/channels during a predefined active interval. * Inactive upstream interface: An interface that has not received packets for specific multicast sessions/channels during a predefined active interval. * Candidate upstream interface: An interface that potentially becomes an upstream interface of the proxy device. A list of candidate upstream interfaces is configured with channel/session identifiers and/or priority values on an IGMP/MLD proxy device. * Backup upstream interface: A candidate upstream interface that remains passive (i.e., not receiving traffic for the corresponding multicast channel until a failover event occurs). It may be used where operator policy prioritizes maintaining a backup path to ensure data transfer rather than active multipath forwarding. Asaeda & Contreras Expires 24 April 2027 [Page 4] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 * Channel/session identifier: A pair consisting of a source address prefix and a multicast address prefix. Either prefix can be "null". A null value acts as a wildcard for the corresponding field. For example, a null source address prefix matches any source for the specified multicast address prefix (i.e., (*,G)). For the default upstream interface, both values are set to null so that the entry matches any multicast session/channel. * Robust data reception: The behavior in which multiple upstream interfaces are used in parallel to receive the same multicast content from them concurrently. It is OPTIONAL for implementations to support this behavior. If this feature is disabled or not implemented, a single upstream interface is selected for each multicast channel. * Upstream interface takeover: The behavior in which a proxy device stops using an unavailable or inactive selected upstream interface for a session/channel and switches to a backup upstream interface. 3. Static Upstream Interface Configuration and Selection Mechanism 3.1. Channel-Based Upstream Selection An IGMP/MLD proxy device selects one or more upstream interfaces from the candidate upstream interfaces for each session/channel based on the configured channel/session identifier. This mechanism is referred to as "channel-based upstream selection." 3.2. Multiple Upstream Interface Selection for Robust Data Reception When more than one candidate upstream interface is configured with identical source and multicast addresses for the "channel/session identifiers" and with the same "interface priority value" (as described in Section 4.2), these candidate upstream interfaces act as upstream interfaces for the corresponding sessions/channels and receive the same multicast traffic simultaneously. Receiving the same multicast traffic through multiple upstream interfaces provides redundant packet reception and may improve the robustness of data reception. This behavior is similar to the redundant multicast reception used by Multicast-Only Fast Reroute (MoFRR) [RFC7431]. Duplicate multicast packets may therefore be received through the selected upstream interfaces. Duplicate packet detection and elimination are outside the scope of this document. Asaeda & Contreras Expires 24 April 2027 [Page 5] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 Robust data reception does not guarantee that packets are received over disjoint paths. The selected upstream interfaces are connected to different adjacent upstream routers, but the paths from these routers toward the multicast source may still overlap. 3.3. Upstream Interface Takeover "Upstream interface takeover" is a function for proxy devices to realize continuous multicast data reception. A proxy device can simultaneously use multiple upstream interfaces per session/ channel.　If a proxy device detects that a selected upstream interface is　unavailable or inactive, it stops using that interface for the　 session/channel and switches to a backup upstream interface.　To enable upstream interface takeover, the backup upstream interface MUST be configured. The backup upstream interface is selected from the candidate upstream　interfaces that match the same session/ channel.　If multiple backup upstream interfaces are configured, the interface priority value for each backup upstream interface MUST be configured. The condition of whether the upstream adjacent router is active or inactive can be determined by checking the link/interface conditions on the proxy device or by monitoring the IGMP/MLD Query or PIM [RFC7761] Hello message reception on the link. Note that there are cases where PIM is not running on the link or IGMP/MLD Query messages are not always transmitted by the upstream router (e.g., when the explicit tracking function [I-D.ietf-pim-explicit-tracking] is enabled). An active interval is a period in which the selected upstream interface on the proxy device remains active. The active interval of each candidate upstream interface can be configured. Active interval values vary depending on whether the network operators wish to trigger via IGMP/MLD or PIM messages. The default active interval for detecting an inactive upstream interface MAY be approximately twice the IGMP/MLD General Query interval and PIM Hello interval. However, defining the optimal timer value for switching from an inactive upstream interface to an active upstream interface from a list of candidate upstream interfaces is out of scope of this document. It SHOULD be possible for operators to change the timer value according to the network conditions or other factors. 4. Candidate Upstream Interface Configuration An IGMP/MLD proxy device selects one or more upstream interfaces from a set of candidate upstream interfaces. The upstream interface selection approach works with the configurations of "channel/session identifier" and "interface priority value." Asaeda & Contreras Expires 24 April 2027 [Page 6] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 4.1. Multicast Channel Record IGMP/MLD proxy devices can configure the "channel/session identifier" in the multicast channel record for each candidate upstream interface. A channel/session identifier consists of a source address prefix and a multicast address prefix. Source address prefixes MUST be valid unicast address prefixes, and multicast address prefixes MUST be valid multicast address prefixes. A proxy selects an upstream interface from its candidate upstream interfaces based on the channel/session identifier configuration. The default values of these address prefixes are "null." A null source address prefix represents a wildcard source address prefix, which indicates any host. A null multicast address prefix represents a wildcard multicast address prefix, which indicates the entire multicast address range (i.e., 224.0.0.0/4 for IPv4 or ff00::/8 for IPv6). The channel/session identifier configuration comprises the source and multicast address prefixes. A candidate upstream interface with a non-null source and multicast address configuration is prioritized for upstream interface selection. For example, if a proxy device has two candidate upstream interfaces for the same multicast address prefix G_p but one of them has a non-null source address prefix S_p configuration, that candidate upstream interface is selected for the source and multicast address pair (i.e., (S_p,G_p)). The other candidate upstream interface is selected for the configured multicast address prefix, excluding the source address prefix configured by the prior interface (i.e., (*-S_p,G_p)). The source address prefix configuration is prioritized over the multicast address prefix configuration. For example, consider the case where an IGMP/MLD proxy device has a configuration with the source address prefix S_p for candidate upstream interface A and the multicast address prefix G_p for candidate upstream interface B. When dealing with an IGMP/MLD record whose source address (S) is in the range of S_p and whose multicast address (G) is in the range of G_p, the proxy device selects candidate upstream interface A, which supports the source address prefix, as the upstream interface and transmits the (S,G) record via interface A. In summary, in environments where multiple static upstream interface configurations are defined, the proxy device determines the applicable upstream interface based on the following precedence order: Asaeda & Contreras Expires 24 April 2027 [Page 7] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 * (S,G) association: If a specific source and multicast group pair is configured, the corresponding upstream interface is used for delivering traffic matching that pair. * (S,*) association: If a source address is configured without a specific group, the corresponding upstream interface is used for traffic from that source, regardless of group. * (*,G) association: If a multicast group is configured without a specific source, the corresponding upstream interface is used for traffic to that group, regardless of source. When multiple upstream interfaces are configured with overlapping address prefixes, the interface with the highest priority value, as described in Section 4.2, is used. If multiple interfaces share the same highest priority value, they are used in parallel for redundant reception as described in Section 3.2. 4.2. Interface Priority An IGMP/MLD proxy device can configure an "interface priority" value for each candidate upstream interface. The priority is indicated by a non-negative integer value and is part　of the configuration. A lower value indicates a lower priority, and　the default value is zero. The interface priority value is used when no channel/session identifier is configured for a candidate upstream interface or when multiple candidate upstream interfaces are configured with the same channel/session identifier. In these cases, the candidate upstream interface with the highest priority is selected as the upstream interface. As stated in Section 3.2, if multiple candidate upstream interfaces have the same priority value, they act as upstream interfaces for the configured channel/session identifier in parallel and may receive duplicate packets. 4.3. Default Upstream Interface A proxy device MAY be configured with a default upstream interface. The default upstream interface is selected for a multicast session/ channel when no multicast channel record is configured for that session/channel. The source and multicast address prefixes of the default upstream interface are both set to null so that they match any session/channel. When a multicast channel record is configured for a session/channel, the proxy device selects an upstream interface from the candidate upstream interfaces specified in that record. If the selected Asaeda & Contreras Expires 24 April 2027 [Page 8] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 upstream interface becomes unavailable, another candidate upstream interface is selected according to the upstream interface takeover procedure described in Section 3.3. The default upstream interface is not used unless it is explicitly included as a candidate upstream interface in the record. If no candidate upstream interface can be selected, the proxy device does not send the corresponding IGMP/MLD Report through an upstream interface. An implementation SHOULD validate multicast channel records when the configuration is applied and reject invalid records. An invalid record MUST NOT be used for upstream interface selection. An invalid multicast channel record does not cause the default upstream interface to be selected. 5. Updating YANG Model Regarding the IGMP/MLD YANG model proposed in [RFC9166], there is a description of interfaces for IGMP (similarly for MLD). However, it is necessary to update the proposed YANG model to include all information about the upstream interfaces described in this document and to consider actions related to the dynamic upstream interface configuration. [I-D.zcl-pim-multiif-igmp-mld-proxy-yang] is a potential data model proposal used for this purpose. 6. Security Considerations This document neither provides new functions nor modifies the standard functions defined in [RFC3376][RFC3810][RFC5790]; therefore, no additional security considerations are provided for these protocols. Conversely, it is possible to encounter denial-of-service (DoS) attacks to stop upstream interface takeover if attackers illegally send IGMP/MLD Query or PIM Hello messages on a LAN within a shorter period (i.e., before the expiration of the active upstream interface interval). To bypass such threats, it is RECOMMENDED to capture the source addresses of the IGMP/MLD Query or PIM Hello message senders and examine whether these addresses correspond to the correct adjacent upstream routers. 7. IANA Considerations This document does not define any new IANA registries. 8. Acknowledgements TBD. 9. References Asaeda & Contreras Expires 24 April 2027 [Page 9] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 9.1. Normative References [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, . 9.2. Informative References [I-D.contreras-pim-multiif-config] Contreras, L. M. and H. Asaeda, "Signaling-based configuration for supporting multiple upstream interfaces in IGMP/MLD proxies", Work in Progress, Internet-Draft, draft-contreras-pim-multiif-config-03, 7 July 2025, . [I-D.ietf-pim-explicit-tracking] Asaeda, H., "IGMP/MLD-Based Explicit Membership Tracking Function for Multicast Routers", Work in Progress, Internet-Draft, draft-ietf-pim-explicit-tracking-13, 1 November 2015, . [I-D.zcl-pim-multiif-igmp-mld-proxy-yang] Zhao, H., Contreras, L. M., Liu, X., and H. Asaeda, "YANG Data Model for supporting multipath IGMP/MLD proxies", Work in Progress, Internet-Draft, draft-zcl-pim-multiif- igmp-mld-proxy-yang-04, 15 October 2026, . [ICIN.xml] Fernandez, D., Contreras, L. M., Moyano, R. F., Garcia, S., and IEEE, "NFV/SDN Based Multiple Upstream Interfaces Multicast Proxy Service", 2021 24th Conference on Innovation in Clouds, Internet and Networks and Workshops (ICIN), pp. 159-163, DOI 10.1109/icin51074.2021.9385529, 1 March 2021, . [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, DOI 10.17487/RFC3376, October 2002, . Asaeda & Contreras Expires 24 April 2027 [Page 10] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, DOI 10.17487/RFC3810, June 2004, . [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, August 2006, . [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", RFC 5213, DOI 10.17487/RFC5213, August 2008, . [RFC5790] Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet Group Management Protocol Version 3 (IGMPv3) and Multicast Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790, DOI 10.17487/RFC5790, February 2010, . [RFC6224] Schmidt, T., Waehlisch, M., and S. Krishnan, "Base Deployment for Multicast Listener Support in Proxy Mobile IPv6 (PMIPv6) Domains", RFC 6224, DOI 10.17487/RFC6224, April 2011, . [RFC7431] Karan, A., Filsfils, C., Wijnands, IJ., Ed., and B. Decraene, "Multicast-Only Fast Reroute", RFC 7431, DOI 10.17487/RFC7431, August 2015, . [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, . [RFC9166] Zhao, H., Liu, X., Liu, Y., Peter, A., and M. Sivakumar, "A YANG Data Model for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping", RFC 9166, DOI 10.17487/RFC9166, February 2022, . Asaeda & Contreras Expires 24 April 2027 [Page 11] Internet-Draft Multipath Support for IGMP/MLD Proxy October 2026 Appendix A. Proof of Concept The support of multiple upstream interfaces for IGMP/MLD proxies was experimentally implemented following a controller-based configuration approach. The implementation was based on Linux using a software- defined networking application running over a Ryu controller. This application uses OpenFlow from the controller to control an Open vSwitch, which relays downstream multicast data flows and upstream IGMP/MLD control traffic. The proof of concept is comprehensively described in [ICIN.xml]. Authors' Addresses Hitoshi Asaeda National Institute of Information and Communications Technology 4-2-1 Nukui-Kitamachi, Koganei, Tokyo 184-8795 Japan Email: asaeda@nict.go.jp Luis M. Contreras Telefonica Spain Email: luismiguel.contrerasmurillo@telefonica.com Asaeda & Contreras Expires 24 April 2027 [Page 12]