a switch fabric for routing a primary-protocol packet from an input port to a selected output port in response to a primary-protocol destination address of the primary-protocol packet, the primary-protocol destination address determining the selected output port in a plurality of output ports for the primary-protocol packet;

a plurality of external buses for connecting the dual-protocol switch to a plurality of hosts, each external bus in the plurality of external buses for connecting to a host in the plurality of hosts;

wherein the plurality of external buses carry secondary-protocol packets that encapsulate at least portions of primary-protocol packets;

wherein the secondary-protocol packets are formatted for a second protocol while the primary-protocol packets are formatted for a primary protocol, the second protocol and the primary protocol being different network protocols;

a plurality of input ports, each input port for receiving secondary-protocol packets from an external bus in the plurality of external buses, the secondary-protocol packets encapsulating the primary-protocol packets for transport over the external bus;

an input packet memory, for each input port, for storing primary-protocol packets encapsulated in the secondary-protocol packets sent over the external bus;

a secondary-protocol interface for each input port, the secondary-protocol interface transferring the secondary-protocol packets from a memory on the host, over the external bus to the input packet memory for the input port using secondary packets specified by the second protocol; and

a switch controller that receives the primary-protocol destination address extracted by an input port from the primary-protocol packet embedded inside the secondary-protocol packet, the switch controller determining a route through the switch fabric from the input port to the selected output port that is selected by the primary-protocol destination address;

wherein the secondary-protocol packets operate within a single host address space for a single host;

wherein the primary-protocol packets operate within multiple address spaces for a plurality of hosts;

wherein the primary protocol is Ethernet and the second protocol is Peripheral Component Interconnect (PCI), PCI-Express, (PCIE), or an extension of PCI or PCIE, and wherein the primary-protocol destination address is an Ethernet media-access controller (MAC) address,

whereby the second protocol is a single-address-domain protocol while the primary protocol is a multiple-address-domain protocol, and whereby the dual-protocol switch has PCI-Express ports but switches Ethernet packets using Ethernet MAC addresses, and whereby primary-protocol packets are routed through the switch fabric using the primary-protocol destination address, while input and output ports transfer over the plurality of external buses secondary-protocol packets that encapsulate the primary-protocol packets.