When operation and management in the university network are performed, various problems occur. As one of those problems, user support problems in the network are often shown. As an example, coping with annoying communication to other users is described. The word of "annoying communication" means the communication which adversely affects processing performance and communication speed of other clients. In this case, under the management by DHCP Service, much time and effort are spent to specify where the client with annoying communication is. To simplify user supports such as this case, new form of user support by DACS (Destination Addressing Control System) Scheme, which is an efficient scheme for the network operation and management in university network, is proposed and examined. Without the virus infection client being specified by a system administrator, the communication port of the client is intercepted and the warning message is displayed on the screen of the client. The user who watches the warning message does an inquiry to the computer management section. Because the system administrator does not need to identify the virus infection client physically, network management is largely simplified.