Embodiments of the present invention provide an interface device and method for command processing for commands requiring data flow in both directions on a Fiber Channel or other data transport protocol exchange. The commands can include proprietary commands, SCSI linked commands or other commands known in the art. According to one embodiment, an interface device can assign a command a data flow direction indicator. When a reply to the command is received, the interface device can determine if the reply is expected or unexpected based on the data flow direction specified by the data flow direction indicator. If the reply is unexpected, the interface device can determine whether to process the reply. According to one embodiment, the data flow direction indicator can be the exchange identification.