Provided is a technology for increasing reliability of communication carried out by OSes and application programs operating on logical partitions set on a computer. The computer has multiple logical partitions constructed therein by a control program, the physical interfaces are shared by virtual interfaces respectively set for the multiple logical partitions, and the memory module stores management information indicating correspondences between the physical interface and the virtual interface. The control method comprising the steps of: obtaining, by the control module, communication data transferred to the external device and received by the virtual interface; obtaining, by the control module, correspondences between the physical interface and the virtual interface, selecting, by the control module, the physical interface used for the communication with the external device based on the correspondences between the physical interface and the virtual interface; and changing, by the control module, the correspondence between the physical interface and the virtual interface if a failure occurs in the communication path.