RoCE
RDMA over Converged Ethernet — InfiniBand-like RDMA on Ethernet hardware. RoCEv1 is L2-only, RoCEv2 (2014) is L3-routable. Standard alternative to expensive InfiniBand.
Requires lossless Ethernet — DCB (Data Center Bridging) + PFC (Priority Flow Control) configured on all switches. Packet loss = RDMA performance catastrophically drops. Config-complex: mismatch on one switch in path → mystery hang. Modern hyperscaler DC moves toward RoCE (Microsoft Azure, Meta) over IB due to lower cost. Nvidia ConnectX NIC supports both RoCE + IB in same hardware. Open source alternative: Soft-RoCE (kernel implementation without dedicated NIC hardware) — good for dev/test, not production.