**Session Date/Time:** 19 Mar 2026 01:00 # [RTGWG](../wg/rtgwg.html) ## Summary The Routing Working Group (RTGWG) met at IETF 125 in Shenzhen to discuss the status of active drafts and several new proposals focusing on AI/ML network fabrics, fast network notifications, and multicast requirements for large-scale data centers. Significant time was dedicated to the "Fast Network Notification" (FAN) initiative, which is progressing toward the potential formation of a new working group. Other major themes included hardware-accelerated IP Fast Reroute (FRR) and congestion control collaboration across Data Center Networks (DCN) and Wide Area Networks (WAN). ## Key Discussion Points ### WG Status and Administration [01-rtgwg-status](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-01-rtgwg-status-00) * **Draft Updates:** * `draft-ietf-rtgwg-multisegment-sdwan` has been submitted for publication. * `draft-ietf-rtgwg-srv6-egress-protection` finished its WGLC and will proceed to a joint last call with the LSR WG. * `draft-ietf-rtgwg-bgp-pic` has been updated with Yingzhen Qu as a co-author to improve readability and structure. * `draft-ietf-rtgwg-net-notif-ps` was recently adopted. * **FAN (Fast Network Notification):** Discussion continues regarding the charter for a potential new working group (formerly referred to as Fun-Tell). ### YANG Models for Quality of Service (QoS) [02-QoS_YANG](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-02-qos-yang-00) * Aseem Choudhary presented updates to `draft-ietf-rtgwg-qos-model` (v15). * **Technical Updates:** Addressed DSCP range violations by clarifying that gateway routers must respect RFC 8436. Clarified Per-Hop Behavior (PHP) selection at edge and core nodes. Data types for filters/actions were refined (e.g., using `leaf-list` for IP addresses and `leafref` for policy references). * **Next Steps:** The chairs noted that directorate reviews are complete and the document is nearing its Working Group Last Call (WGLC). ### Fast Network Notifications (FAN) [03-Fast Network Notifications Problem Statement](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-03-fast-network-notifications-problem-statement-00) * Jie Dong provided an update on `draft-ietf-rtgwg-net-notif-ps`. * **Scope:** The document focuses on the need for timely network operational status (congestion/failure) to support AI/ML training and cloud services. * **Discussion:** Jeff Tantsura noted that security mechanisms should not introduce latency, potentially leveraging the "limited domain" concept. A data model for these notifications is in development. ### IP Fast Reroute for AI/ML Fabrics [04-IP Fast Reroute for AI/ML Fabrics](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-07-ip-fast-reroute-for-aiml-fabrics-00) * Roy Yang presented a framework for sub-millisecond convergence in AI fabrics. * **Proposals:** Hardware-accelerated protection activation (bypassing the CPU), complete topology visibility in BGP-based networks (exchanging link-state via BGP), and quality-aware remote protection. * **Feedback:** Francois Clad questioned how 100-microsecond detection is guaranteed without hardware-level probing. Jeff Tantsura advised separating Data Center and WAN scenarios clearly, noting that existing technologies like TI-LFA are available for WAN but DCN requirements differ. ### Efficient Remote Protection [05-Efficient Remote Protection](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-05-efficient-remote-protection-00) * Francois Clad discussed limitations of local-only FRR, such as traffic "hair-pinning" and lack of load awareness. * **Solution:** A mechanism where a node detecting a failure or quality degradation (e.g., a partial link-bundle failure) notifies remote nodes to reroute traffic earlier. * **Discussion:** Jeff Tantsura cautioned against network-based "bypass" solutions in AI networks, as hair-pinning can be detrimental to collective performance. He emphasized the importance of ensuring network-level FRR does not conflict with host-level congestion control mechanisms. ### BGP-based Adaptive Routing for Scale-Up Networks [06-xu-fare-in-sun](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-06-xu-fare-in-sun-01) * Roy Yang presented `draft-xu-rtgwg-fare-in-sun`, proposing BGP on the host for scale-up (GPU) networks. * **Proposal:** Uses BGP to perform adaptive routing (WCMP) based on link capacity. * **Questions:** Jeff Tantsura asked about non-IP encapsulation in scale-up frameworks and the necessity of BGP in single-tier networks where no routing typically occurs. ### Flow Control Collaboration Across DCNs and WAN [07-Use cases and Requirement for Flow Control Collaboration Across DCNs and WAN](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-07-use-cases-and-requirement-for-flow-control-collaboration-across-dcns-and-wan-00) * Hanjunxin proposed Fine-Grained Flow Control (FGFC) to bridge PFC (DCN) and WAN congestion management. * **Mechanism:** Edge nodes coordinate protocol conversion and semantic mapping between PFC frames and FGFC packets (carried via ICMP/UDP). * **Feedback:** Jeff Tantsura requested the addition of a table detailing buffer memory requirements relative to WAN distances (e.g., 1MB per 20km). ### Multicast in AI Data Centers [08-Multicast Use Cases for Large Language Model Synchronization](https://datatracker.ietf.org/meeting/125/materials/slides-125-multicast-use-cases-for-large-language-model-synchronization-00) [09-Requirements and Gap Analysis of Multicast in AI Data Centers](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-09-requirements-and-gap-analysis-of-multicast-in-ai-data-centers-00) * Yisong Liu and Jian Zhang discussed multicast for LLM model distribution and collective communication (All-Reduce/MOE). * **Requirements:** Interactivity (MP2P feedback), reliability (lossless), and dynamics (microsecond membership changes). * **Gaps:** Existing technologies (PIM, SR-P2MP, BIER) were analyzed. Tony Przygienda noted that "U-BEER" (uncompressed BIER) might address sparse group concerns. ### Satellite Networking and SRv6 [10-SDAF for LEO Satellite Networks](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-symmetry-driven-asynchronous-forwarding-with-fast-reroute-for-leo-satellite-networks-sdaf-00) * Kemin Liang presented Symmetry-Driven Asynchronous Forwarding (STEP) for LEO satellites, leveraging Torus/Ring topology symmetry to prevent micro-loops. [11-Congestion Control Based on SRv6 Path](https://datatracker.ietf.org/meeting/125/materials/slides-125-rtgwg-congestion-control-based-on-srv6-path-00) * Yisong Liu proposed a hop-by-hop congestion notification for SRv6 paths to alleviate the processing load on the head-end node. ## Decisions and Action Items * **`draft-ietf-rtgwg-qos-model`**: Authors to incorporate final review comments and prepare for WGLC. * **`draft-ietf-rtgwg-srv6-egress-protection`**: Chair (Jeff Tantsura) to perform final review and progress to joint last call with LSR. * **`draft-ietf-rtgwg-bgp-pic`**: Chairs to shepherd the document following recent updates. ## Next Steps * **Interim Meeting:** The chairs indicated a potential interim meeting before IETF 126 to handle the high volume of AI Data Center-related submissions. * **FAN Working Group:** Continued refinement of the charter on the mailing list and GitHub. * **Data Model:** Jeff Tantsura and Yingzhen Qu plan to publish a data model draft related to fast network notifications.