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SRv6 behavior extention for Flow Control in WAN#

IETF 126 (Vienna) digest Program Core pick Vienna · 18–24 July 2026

Draft Slides Session recording Materials

Zhengxin Han (China Unicom, presenter), Zheng Ruan, Yao Liu, MengYao Han, Ying Liu (China Unicom/ZTE).

  • Why: The SRv6-flavored answer to the same lossless-WAN problem — with two advantages over transparent PFC: backpressure can traverse legacy non-PFC devices, and it can be scoped to per-tenant/slice queues instead of coarse port-level pausing. The SPRING list already reached consensus (June–July 2025) that a new SRv6 behavior is the preferred approach.
  • What: A new End.X.PFC behavior that flags PFC-capable interfaces along an SRv6 path. PFC frames are encapsulated into reverse SRv6 tunnels whose final segment is the End.X.PFC SID of the target upstream interface, delivering backpressure precisely to the right node even across non-PFC legacy transit devices.
  • How: Capability flooded via IGP (OSPF/IS-IS) and BGP-LS to a controller, which provisions reverse tunnels (E→C, C→A) before congestion; the data-plane pseudocode strips the outer IPv6/SRH on Ethernet next-header (143) and applies flow control when the PFC multicast MAC is seen.
  • Where applicable: Inter-DC RDMA over L2VPN/L3VPN SRv6 policies in mixed PFC/legacy infrastructure; multi-tenant isolation via NRP/slice queues. Draft -03, actively seeking operator co-review.