methods for routing data units and pci express switches are disclosed . a plurality of devices may be coupled to a corresponding plurality of physical interfaces , each physical interface having a respective configurable status and a respective address domain , wherein in a first status the interface is transparent , and in a second status the interface is non - transparent . the status of each of the plurality of physical interfaces may be set as transparent or non - transparent . data units may be switched between the physical interfaces using mapped address input / output , switching data units including masking the address domain for the interfaces configured as non - transparent .