RoCE vs InfiniBand: Why Ethernet Is Winning the AI Data Center Networking War

RoCEv2 (RDMA over Converged Ethernet version 2) has quietly become the dominant GPU interconnect for AI training clusters — and most network engineers haven't noticed yet. For deployments up to ~10K GPUs, properly tuned Ethernet with RoCEv2 delivers 85-95% of InfiniBand's training throughput at a fraction of the cost, using switches and skills you already have. InfiniBand still wins at the absolute largest scale, but the gap is closing fast. Here's the technical breakdown. Why RDMA Matters for AI Training RDMA (Remote Direct Memory Access) lets one server read/write another server's memory without touching either CPU . Traditional TCP/IP requires multiple CPU interrupts, kernel context switches, and memory copies. RDMA eliminates all of that, cutting latency from milliseconds to microseconds. Distributed AI training makes this essential. When training an LLM across thousands of GPUs, gradient updates (the math that makes the model learn) generate terabytes of east-west traffic that mus