Abstract: A method of processing an external service request in a storage area network (SAN) is used for responding a service request in the SAN with multiple controllers, and the method includes the following steps. A first controller of the SAN receives a request packet of an external network. When the first controller determines that the request packet must be transmitted to a second controller actually providing service in an internal network, the request packet is transmitted to the second controller. The second controller receives the request packet, and parses a source address contained therein for recording. The second controller executes an operation instruction corresponding to the request packet, and then generates an acknowledge packet. The second controller takes the source address as a destination address of the acknowledge packet and directly transmits the acknowledge packet to an original request initiator.