Net-P4ct: Enhanced WAN Bandwidth Fair Sharing Using P4 Programmable Switches

At growing internet companies like ByteDance, Wide Area Network (WAN) bandwidth sharing across diverse services with varying SLO requirements is a fundamental challenge. Conventional host-based enforcement systems, where agents identify and throttle traffic at the server end, face practical challenges such as "blind spot" traffic, kerneldependent operational complexity, and significant server resource overhead. To address these issues, we present Net-P4ct, an in-network bandwidth enforcement system using P4 programmable switches. Net-P4ct improves both bandwidth guarantees and fair sharing by shifting dynamic QoS control into the switch data plane. Specifically, it achieves broader traffic coverage by combining host-side traffic tagging with a P4-switch pipeline, where service classification and QoS class assignment are performed. Based on observed traffic metrics, a centralized control plane determines real-time policy updates according to the max-min fair bandwidth allocation. We demonstrate the system's benefits including improved bandwidth utilization, reduced operational complexity, and lower per-byte processing cost. Net-P4ct has been deployed in ByteDance's production WAN for nearly a year, and we hope to share our experience with the community.