InfiniBand vs Ethernet for AI Fabrics

For most distributed-training collectives at scale, yes. Ethernet has a higher latency floor than InfiniBand by hundreds of nanoseconds, but that sits below the threshold that affects most workloads once RoCEv2 with PFC, DCQCN, and DLB is configured correctly.

Choose InfiniBand for tight HPC simulation where the absolute latency floor matters more than total cost of ownership, and for captive single-tenant clusters where single-vendor lock-in is acceptable.

Ethernet wins for multi-tenant GPU-as-a-Service, clusters that share one operational model and tooling with the rest of the data center, cost-sensitive multi-thousand-GPU builds, and fabrics that extend across data centers via coherent DCI and EVPN.

OcNOS-DC delivers RoCEv2 lossless transport, DLB adaptive routing, and the PFC deadlock watchdog today, GLB in 7.1 for end-to-end path scoring, and UEC support as NICs ship, all on validated open hardware from vendors such as Edgecore and UfiSpace.

Largely yes, though InfiniBand is not going away. According to Dell'Oro Group, Ethernet passed InfiniBand in AI back-end (scale-out) switching and reached about two-thirds of the market by early 2026, up from InfiniBand's roughly 80 percent share in late 2023. Dell'Oro also notes a strong InfiniBand rebound on the NVIDIA Blackwell Ultra 800G ramp, so it remains the specialist choice for tightly coupled HPC. Meta has described training its largest models over a RoCE Ethernet fabric on one of two 24,576-GPU clusters. The Ultra Ethernet Consortium, whose steering members include AMD, Arista, Broadcom, Cisco, Eviden, HPE, Intel, Meta, Microsoft and Oracle, standardizes this direction. The reasons are operational and economic: one network model shared with the rest of the data center, a multi-vendor supply chain, and lower cost per port at 400G and 800G.

Ethernet with RoCEv2 is the mainstream alternative. It carries RDMA losslessly using PFC, ECN and DCQCN, adds adaptive routing through DLB, and gains packet spray and multi-path RDMA through Ultra Ethernet as UEC NICs ship. On open hardware running OcNOS-DC, it delivers this on a multi-vendor stack rather than a single-vendor fabric.

Ultra Ethernet (UEC) brings the transport techniques that defined InfiniBand to standard Ethernet: packet spray across all paths, multi-path RDMA, out-of-order delivery, and selective retransmission. The UEC 1.0 specification, published in June 2025, defines this transport. The difference is the ecosystem: InfiniBand is effectively single-vendor for NIC and switch silicon, while Ultra Ethernet is an open, multi-vendor specification any vendor can build to.

The switching layer is a modest share of AI cluster total cost of ownership, usually a single-digit percentage over five years, though the figure rises once NICs, optics, and cabling are counted. For equivalent capacity, single-vendor InfiniBand generally carries a price premium over open-hardware Ethernet running OcNOS-DC. The more useful question is what the saved capital funds, whether that is more GPUs, a larger storage tier, or a second site for resilience.