Axon: A flexible substrate for source-routed Ethernet

This paper introduces the Axon, an Ethernet-compatible device for creating large-scale datacenter networks. Axons are inexpensive, practical devices that are demonstrated using prototype hardware. Functionally, Axons replace Ethernet switches and maintain full compatibility with existing Ethernet hosts. Between themselves, however, Axons transparently use source-routed Ethernet. This unlocks many benefits, such as improved network scalability, performance, and flexibility. In an Axon network, all state required to route a host's packets is placed in the local Axon-the Axon to which the host is directly connected. Therefore, regardless of the scale of the network, the route computation and storage needs of a single Axon device only need to scale with the demands of its locally-connected hosts. This is in stark contrast to conventional switched Ethernet, which requires routing resources proportional to the traffic that flows through the device. Scalability is also increased by eliminating the use of packet flooding for automatic location and address discovery. Further, source-routed Ethernet increases network flexibility by supporting different route selection strategies. For example, shortest-path routing could be employed, or longer paths selected to minimize congestion by balancing traffic across redundant links.