Data center networks rely on Ethernet. Over the decades, Ethernet has evolved as new types of architectures emerged. Today, data center networks carry traffic for a diverse set of applications including client/server, Web services, unified communications, virtual machines, and storage—each with different traffic patterns and network service requirements. For example, when Ethernet carries block storage traffic, it places stringent demands on the network including lossless packet delivery, deterministic latency and high bandwidth. Combined, these changes drive the next evolutionary step in Ethernet networks, the Ethernet fabric.