**Session Date/Time:** 19 Mar 2026 08:30

# [BIER](../wg/bier.html)

## Summary
The BIER Working Group session at IETF 125 focused on the status of active drafts, recent multi-vendor interoperability testing results, and new proposals for monitoring, AI-driven use cases, and data plane optimizations. Key highlights included a report from EANTC testing, a new draft on IPFIX for BIER, a discussion on Large Language Model (LLM) synchronization requirements, and updates to the BIER-FRR framework.

## Key Discussion Points

### Working Group Status and Administrivia
*   **Presenters:** Sandy Zhang, Tony Przygienda
*   **Draft Status:** 
    *   Two documents are in the RFC Editor queue.
    *   `draft-ietf-bier-ping` is in the IESG; Gunter Van de Velde (Routing AD) noted that all DISCUSSions are resolved. However, a "probe" to the WG is needed to determine if the draft should be limited to the MPLS data plane or cover all data planes. Tony Przygienda agreed to review the thread.
    *   `draft-ietf-bier-ospfv3-extensions` is currently in Last Call in the LSR working group.
*   **LDP Signaling:** Hooman Bidgoli inquired about the status of LDP/MLDP signaling over BIER drafts. Sandy Zhang noted that these drafts need to be refreshed by the authors before moving forward.
*   **Charter Compliance:** Gunter Van de Velde reminded the group that the IESG is strictly enforcing charter compliance. Any new or progressing documents must clearly align with the current BIER charter.

### Interoperability Testing (EANTC 2026)
*   **Presentation:** [1-EANTC-2026](https://datatracker.ietf.org/meeting/125/materials/slides-125-bier-1-eantc-2026-00)
*   **Presenter:** Hooman Bidgoli
*   **Discussion:** 
    *   Testing showed successful interop between Huawei, Juniper, and Nokia for BIER forwarding and NG-MVPN (I-PMSI).
    *   A technical hurdle was identified regarding the "BIER Next Protocol" field for VC labels. Juniper used Protocol 1 (downstream/global), while Huawei/Nokia used Protocol 2 (upstream/context).
    *   Hooman reported that Nokia implemented a "knob" to allow Protocol 1 to enable interop but suggested the WG should simplify this field to avoid future "chaos."
    *   Tony Przygienda and Jeffrey Zhang cautioned against unification, noting that the distinction between global and context-specific lookups provides significant scalability benefits for certain implementations. 
    *   The group reached a consensus to clarify these behaviors in a forthcoming update/draft to ensure future implementations are aligned.

### Export of BIER Information in IPFIX
*   **Presentation:** [Export of BIER Information in IPFIX](https://datatracker.ietf.org/meeting/125/materials/slides-125-bier-export-of-bier-information-in-ipfix-00)
*   **Presenter:** Sandy Zhang
*   **Discussion:**
    *   This draft proposes 11 new IPFIX Information Elements (IEs) to monitor BIER flows (BIFT ID, BitString, BFER ID, etc.).
    *   Tony Przygienda raised a concern regarding how monitoring stations correlate BIFT IDs and labels to sub-domains and sets without extra context. He suggested adding a "Considerations" section to the draft explaining how to reconstruct the BIER context for collected data.

### Multicast for Large Language Model (LLM) Synchronization
*   **Presentation:** [Multicast Use Cases for Large Language Model Synchronization](https://datatracker.ietf.org/meeting/125/materials/slides-125-bier-multicast-use-cases-for-large-language-model-synchronization-00)
*   **Presenter:** Sandy Zhang
*   **Discussion:**
    *   The use case involves replicating models (70GB to 1TB+) across GPU clouds. BIER is identified as a potential solution due to its stateless nature.
    *   Hooman Bidgoli suggested exploring optimizations to remove IP/UDP headers and carry AI payloads directly over BIER.
    *   Tony Przygienda noted that BIER can already run directly over Ethernet, but the WG needs specific requirements from AI/HPC experts to determine if non-standard header optimizations are truly beneficial.

### Scalable Data Plane Architecture for BIER
*   **Presentation:** [4-Scalable Data Plane Architecture for BIER](https://datatracker.ietf.org/meeting/125/materials/slides-125-bier-scalable-data-plane-architecture-for-bier-00)
*   **Presenter:** Zhigiang Li
*   **Discussion:**
    *   The proposal shifts from a "bit-centric" to an "interface-centric" forwarding model using Replication Memory Tables (RMT) and Interface Bitmask Tables (IBMT).
    *   Jeffrey Zhang observed that the performance gain depends on whether the implementation is bottlenecked by the number of bits or the number of neighbors.
    *   Tony Przygienda noted the proposal is an implementation optimization (non-normative) and requested the authors include a section on ECMP equivalence and an analysis of ASIC update frequency during control plane changes.

### BIER-FRR Update
*   **Presentation:** [5-BIER-FRR update](https://datatracker.ietf.org/meeting/125/materials/slides-125-bier-bier-frr-update-00) (related to [draft-ietf-bier-frr](https://datatracker.ietf.org/id/draft-ietf-bier-frr))
*   **Presenter:** Tony Przygienda
*   **Discussion:**
    *   The presenter focused on simplifying the framework for Fast Reroute (FRR).
    *   A key point was that BIER provides "node protection" more effectively than stateful multicast (PIM).
    *   Tony proposed removing the "tunnel mode" from the draft as it is technically redundant to LFA-based approaches.
    *   The discussion touched on the "partitioned Q space" problem. Tony suggested using "protected adjacencies" to handle rerouting without requiring massive expansion of the BIFT.

## Decisions and Action Items
*   **`draft-ietf-bier-ping`:** Chairs/Authors to address the AD's question regarding data plane scope (MPLS vs. general).
*   **LDP/MLDP Signaling:** Authors (including Hooman Bidgoli) to refresh expired drafts.
*   **`draft-ietf-bier-frr`:** Tony Przygienda and co-authors to simplify the draft by removing "tunnel mode" and resolving pending reviews from the IESG.
*   **IPFIX Draft:** Sandy Zhang to add a section on metadata correlation considerations.
*   **Scalable Data Plane:** Zhigiang Li to add sections on ECMP and ASIC update metrics.

## Next Steps
*   Continue refining use cases for AI/LLM synchronization to identify potential technical gaps in the BIER architecture.
*   Prepare for the next meeting in Vienna with updated drafts and refined interop documentation.