University of Cambridge University of Cambridge University of Cambridge Ethernet does not scale well to large networks. The flat MAC address space, whilst having obvious benefits for the user and administrator, is the primary cause of this poor scalability; other recent efforts to improve upon Ethernet's scalability have addressed symptoms, rather than this underlying cause. MOOSE, Multi-level Origin- Organised Scalable Ethernet, is an Ethernet switch architecture that performs in-place rewriting of MAC addresses in order to impose a hierarchy upon the address space without reconfiguration or modification of connected devices. This removes the need for switches to maintain large forwarding databases, is of direct use in implementing improved routing, and allows for a variety of other scalability and security innovations. MOOSE also includes a globally-scalable, distributed and resilient protocol for the automatic assignment of addresses to switches, and for detecting and cheaply resolving addressing conflicts.