A method for transmitting information effectively in a server/client network system is provided, the network system including a client placed behind a firewall and a server that provides the client with a predetermined service. The method includes the client generating a hole packet which is for making a hole in the firewall to allow a packet to pass through the firewall from the server, the hole being maintained for a certain period of time, and transmitting the hole packet to the firewall; and transmitting a packet from the server to the client through the hole made by the hole packet.