Protocols Supported for DCBX

DCBX is primarily used to manage the following DCB protocols:

Priority-based Flow Control (PFC)

Priority-based Flow Control (PFC) (IEEE 802.1Qbb) is a link-level mechanism that enables the selective pausing of traffic based on priority levels to prevent packet loss, offering granular control over how various traffic classes are managed. While traditionally deployed in Layer 2 (Ethernet) environments, extending PFC to Layer 3 interfaces brings these benefits to routed networks, enhancing traffic handling across complex topologies. By providing flow control per class, PFC helps minimize packet loss, particularly in congestion-sensitive applications such as storage, AI/ML, and high-performance computing.

PFC is a Layer 2 mechanism — it only works between directly connected neighbors on an Ethernet link. PFC alone can not operate end-to-end on a typical IP-routed (L3) network. However, when the packet is routed hop-by-hop at L3, the actual transmission on each link is L2. Therefore, PFC can still apply at each hop, controlling traffic for a given priority (e.g., for CoS 3 used by RoCEv2). The result is that lossless behavior is preserved link-by-link, provided all hops agree on which priorities to pause, even though the overall path is routed.

Use Cases:

Large-scale model training such as deep learning models like GPT or ResNet involves high-volume east-west traffic between GPUs/TPUs and storage.

High throughput, low congestion, and lossless transport such as RoCEv2 with PFC.

Benefits

Ensures lossless delivery for storage and real-time traffic.

Enhances network convergence by supporting multiple traffic types on one fabric.

Reduces infrastructure cost by eliminating the need for separate SAN and Ethernet networks.